Journal articles: 'Stereoisomeri'

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Costa, Maria L. M., Miguel Borges, Evaldo F. Vilela, Paulo de Marco Jr, and Eraldo R. Lima. "Effect of stereoisomers of the main component of the sex pheromone of Euschistus heros (F.) (Hemiptera: Pentatomidae) in the attractiveness of females." Anais da Sociedade Entomológica do Brasil 29, no. 3 (September 2000): 413–22. http://dx.doi.org/10.1590/s0301-80592000000300004.

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The attractiveness of Euschistus heros (F.) (Hemiptera: Pentatomidae) females to the eight stereoisomers of the methyl 2,6,10-trimethyltridecanoate, major component of the sex pheromone produced by the males of this species, was studied in a double choice olfactometer. Bioassays showed that the (2R, 6R, 10S) stereoisomer was necessary for the attractiveness of females, presenting better results in relation to the others. The stereoisomeric mixture was shown to present significative attractiveness to females, however, when compared to the (2R, 6R, 10S) stereoisomer, it showed lower attractiveness.

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Lapčík, Oldřich, Richard Hampl, Martin Hill, Luboslav Stárka, Alexander Kasal, Vladimír Pouzar, and Zdeněk Putz. "Radioimmunological and Chromatographic Properties of Tyrosine Methyl Ester Conjugates with Stereoisomeric Steroid Carboxy Derivatives." Collection of Czechoslovak Chemical Communications 61, no. 5 (1996): 799–807. http://dx.doi.org/10.1135/cccc19960799.

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Pure 3Z (syn) and 3E (anti) stereoisomers of testosterone 3-[O-(2-carboxyethyl)]oxime were synthesized, separated by HPLC or TLC, and used for preparation of tyrosine methyl ester (TME) conjugates by using mixed anhydride or carbodiimide-N-hydroxysuccinimide methods. While the latter method provided more than 96% of product with retained configuration, the mixed anhydride method yielded a mixture containing 26-40% of the opposite stereoisomer. The stereoisomers were used as model compounds, to which the other steroid TMEs and the corresponding radioiodinated products could be aligned according to their chromatographic properties. The TME conjugates of 3-(O-carboxymethyl)oximes of seven 4-en-3-oxo steroids were further prepared by carbodiimide-N-hydroxysuccinimide method. With exception of cortisol, the stereoisomeric (Z and E) radioiodinated TME conjugates could be separated by TLC. In addition, the conjugates with TME and consequently radioiodinated tracers were synthesized from hemisuccinates of cortisol and its 11α-isomer, via 11β- and 11α-hydroxy group. The radioiodinated conjugates were tested as radioligands with rabbit polyclonal antisera raised by using position-homologous conjugates of the respective steroid carboxy derivatives with bovine serum albumin as immunogens. With the exception of 11-deoxycorticosterone, the stereoisomeric Z and E radioiodinated TMEs did not differ in their binding properties. In the case of isomeric cortisol tracers conjugated through position 11 the antisera recognized only the sterically homologous radioligands, but the specificity of the system was poor.

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Kuchan, Matthew J., Søren K. Jensen, Elizabeth J. Johnson, and Jacqueline C. Lieblein-Boff. "The naturally occurring α-tocopherol stereoisomer RRR-α-tocopherol is predominant in the human infant brain." British Journal of Nutrition 116, no. 1 (May 16, 2016): 126–31. http://dx.doi.org/10.1017/s0007114516001719.

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Abstractα-Tocopherol is the principal source of vitamin E, an essential nutrient that plays a crucial role in maintaining healthy brain function. Infant formula is routinely supplemented with synthetic α-tocopherol, a racaemic mixture of eight stereoisomers with less bioactivity than the natural stereoisomer RRR-α-tocopherol. α-Tocopherol stereoisomer profiles have not been previously reported in the human brain. In the present study, we analysed total α-tocopherol and α-tocopherol stereoisomers in the frontal cortex (FC), hippocampus (HPC) and visual cortex (VC) of infants (n 36) who died of sudden infant death syndrome or other conditions. RRR-α-tocopherol was the predominant stereoisomer in all brain regions (P<0·0001) and samples, despite a large intra-decedent range in total α-tocopherol (5–17 μg/g). Mean RRR-α-tocopherol concentrations in FC, HPC and VC were 10·5, 6·8 and 5·5 μg/g, respectively. In contrast, mean levels of the synthetic stereoisomers were RRS, 1–1·5; RSR, 0·8–1·0; RSS, 0·7–0·9; and Σ2S 0·2–0·3 μg/g. Samples from all but two decedents contained measurable levels of the synthetic stereoisomers, but the intra-decedent variation was large. The ratio of RRR:the sum of the synthetic 2R stereoisomers (RRS+RSR+RSS) averaged 2·5, 2·3 and 2·4 in FC, HPC and VC, respectively, and ranged from 1 to at least 4·7, indicating that infant brain discriminates against synthetic 2R stereoisomers in favour of RRR. These findings reveal that RRR-α-tocopherol is the predominant stereoisomer in infant brain. These data also indicate that the infant brain discriminates against the synthetic 2R stereoisomers, but is unable to do so completely. On the basis of these findings, investigation into the impact of α-tocopherol stereoisomers on neurodevelopment is warranted.

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Sheikh, Ishfaq Ahmad, and Mohd Amin Beg. "Structural Aspects of Potential Endocrine-Disrupting Activity of Stereoisomers for a Common Pesticide Permethrin against Androgen Receptor." Biology 10, no. 2 (February 11, 2021): 143. http://dx.doi.org/10.3390/biology10020143.

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Endocrine-disrupting chemicals (EDCs) are a serious global public health and environmental concern. Pyrethroids are insecticide chemicals that are extensively used for crop protection and household purposes but have been identified as EDCs. On account of their ubiquitous environmental presence, human exposure occurs via food, dermal, or inhalation routes and is associated with health problems, including reproductive dysfunction. Permethrin is the most commonly used pyrethroid, and with two chiral centers in its structure, it has four stereoisomeric forms (two enantiomer pairs), i.e., permethrin (1R,3R)-cis, permethrin (1R,3S)-trans, permethrin (1S,3S)-cis, and permethrin (1S,3R)-trans. The current study was performed for predicting the potential endocrine-disrupting activity of the aforementioned four stereoisomers of permethrin against the androgen receptor (AR). The structural binding characterization and binding energy estimations in the AR binding pocket were done using induced fit docking. The structural binding data indicated that all stereoisomers were placed stably in the AR binding pocket and that the estimated binding energy values were comparable to the AR native ligand, except for permethrin (1S,3S)-cis. Furthermore, the commonality in the amino acid interactions to that of the AR native ligand and the binding energy values suggested the potential AR-disrupting activity of all the stereoisomers; however, stereoselective differences were not observed. Taken together, the results suggest that human exposure to permethrin, either as a racemate mixture or in individual stereoisomer form, could potentially interfere with AR function, which may lead to male reproductive dysfunction.

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DIEUAIDE-NOUBHANI, Martine, Stanny ASSELBERGHS, Guy P. MANNAERTS, and Paul P. VAN VELDHOVEN. "Evidence that multifunctional protein 2, and not multifunctional protein 1, is involved in the peroxisomal β-oxidation of pristanic acid." Biochemical Journal 325, no. 2 (July 15, 1997): 367–73. http://dx.doi.org/10.1042/bj3250367.

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The second (enoyl-CoA hydratase) and third (3-hydroxyacyl-CoA dehydrogenase) steps of peroxisomal β-oxidation are catalysed by two separate multifunctional proteins (MFPs), MFP-1 being involved in the degradation of straight-chain fatty acids and MFP-2 in the β-oxidation of the side chain of cholesterol (bile acid synthesis). In the present study we determined which of the two MFPs is involved in the peroxisomal degradation of pristanic acid by using the synthetic analogue 2-methylpalmitic acid. The four stereoisomers of 3-hydroxy-2-methylpalmitoyl-CoA were separated by gas chromatography after hydrolysis, methylation and derivatization of the hydroxy group with (S)-2-phenylpropionic acid, and the stereoisomers were designated I–IV according to their order of elution from the column. Purified MFP-1 dehydrated stereoisomer IV but dehydrogenated stereoisomer III, so by itself MFP-1 is not capable of converting a branched enoyl-CoA into a 3-ketoacyl-CoA. In contrast, MFP-2 dehydrated and dehydrogenated the same stereoisomer (II), so it is highly probable that MFP-2 is involved in the peroxisomal degradation of branched fatty acids and that stereoisomer II is the physiological intermediate in branched fatty acid oxidation. By analogy with the results obtained with the four stereoisomers of the bile acid intermediate varanoyl-CoA, stereoisomer II can be assigned the 3R-hydroxy, 2R-methyl configuration.

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Dersjant-Li, Jensen, Bos, and Peisker. "Bio-discrimination of α-tocopherol Stereoisomers in Rearing and Veal Calves Fed Milk Replacer Supplemented with All-rac-α-tocopheryl Acetate." International Journal for Vitamin and Nutrition Research 79, no. 4 (July 1, 2009): 199–211. http://dx.doi.org/10.1024/0300-9831.79.4.199.

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This study evaluated the biological discrimination of different α-tocopherol stereoisomers (i. e. RRR-, RRS-, RSR-, RSS- and the four 2S-α-tocopherols) from all-rac-α-tocopheryl acetate supplementation in milk replacer for rearing and veal calves respectively, in practical farming conditions. Two experiments were conducted. In experiment 1, six rearing calves were fed milk replacer supplemented with 80 mg/kg all-rac-α-tocopheryl acetate for a period of 9 weeks. The calves were supplied calf starter concentrate from 1 to 12 weeks. In experiment 2, six veal calves were fed milk replacer supplemented with 80 mg/kg all-rac-α-tocopheryl acetate for a period of 24 weeks. Blood samples were taken at the start and every 4 weeks until 12 weeks for rearing calves in experiment 1, and until slaughter (24 weeks) for veal calves in experiment 2. Liver, adipose, muscle, and brain samples were taken at slaughter of the six veal calves in experiment 2. The distribution of different α-tocopherol stereoisomers in feed, plasma, and tissues was analyzed. In both experiments, it was observed that RRR-α-tocopherol was the dominant stereoisomer in plasma and tissues. The average percentage of the RRR-α-tocopherol stereoisomer was 64 %, and 39 % of the total α-tocopherol in plasma for rearing and veal calves, respectively. The higher RRR-α-tocopherol stereoisomer proportion as percentage of the total α-tocopherol in rearing calves was related to higher dietary natural vitamin E intake. Other 2R-α-tocopherol stereoisomers had lower utilization efficiency than RRR-α-tocopherol stereoisomer. 2S-α-tocopherol stereoisomers were basically not utilized by calves.

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Tirri, Micaela, Paolo Frisoni, Sabrine Bilel, Raffaella Arfè, Claudio Trapella, Anna Fantinati, Giorgia Corli, et al. "Worsening of the Toxic Effects of (±)Cis-4,4′-DMAR Following Its Co-Administration with (±)Trans-4,4′-DMAR: Neuro-Behavioural, Physiological, Immunohistochemical and Metabolic Studies in Mice." International Journal of Molecular Sciences 22, no. 16 (August 16, 2021): 8771. http://dx.doi.org/10.3390/ijms22168771.

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4,4’-Dimethylaminorex (4,4’-DMAR) is a new synthetic stimulant, and only a little information has been made available so far regarding its pharmaco-toxicological effects. The aim of this study was to investigate the effects of the systemic administration of both the single (±)cis (0.1–60 mg/kg) and (±)trans (30 and 60 mg/kg) stereoisomers and their co-administration (e.g., (±)cis at 1, 10 or 60 mg/kg + (±)trans at 30 mg/kg) in mice. Moreover, we investigated the effect of 4,4′-DMAR on the expression of markers of oxidative/nitrosative stress (8-OHdG, iNOS, NT and NOX2), apoptosis (Smac/DIABLO and NF-κB), and heat shock proteins (HSP27, HSP70, HSP90) in the cerebral cortex. Our study demonstrated that the (±)cis stereoisomer dose-dependently induced psychomotor agitation, sweating, salivation, hyperthermia, stimulated aggression, convulsions and death. Conversely, the (±)trans stereoisomer was ineffective whilst the stereoisomers’ co-administration resulted in a worsening of the toxic (±)cis stereoisomer effects. This trend of responses was confirmed by immunohistochemical analysis on the cortex. Finally, we investigated the potentially toxic effects of stereoisomer co-administration by studying urinary excretion. The excretion study showed that the (±)trans stereoisomer reduced the metabolism of the (±)cis form and increased its amount in the urine, possibly reflecting its increased plasma levels and, therefore, the worsening of its toxicity.

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Cortinas, Lucia, Ana Barroeta, Jaume Galobart, and Søren K. Jensen. "Distribution of α-tocopherol stereoisomers in liver and thigh of chickens." British Journal of Nutrition 92, no. 2 (August 2004): 295–301. http://dx.doi.org/10.1079/bjn20041188.

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The effect of supplementation with different levels of all-rac-α-tocopheryl acetate and the inclusion of different dietary contents of PUFA on the deposition of α-tocopherol stereoisomers in liver and thigh of chickens was evaluated. Ninety-six 1-d-old Ross female broiler chickens were randomly distributed into eight experimental treatments (three replicates each) resulting from four levels of α-tocopheryl acetate without supplementation and supplemented with 100, 200 and 400 mg α-tocopheryl acetate/kg and two levels of dietary PUFA (15 and 61 g/kg). The feeds supplemented with α-tocopheryl acetate contained a similar proportion of each stereoisomer. The diets without α-tocopheryl acetate had the following α-tocopherol stereoisomers (%): RRR 35·1, RRS 24·5, RSR 25·3, RSS 13·9 and total 2S forms 1·3. Consumption of different levels of α-tocopheryl acetate did not lead to statistical differences in α-tocopherol stereoisomer proportion in the liver and thigh. In general, the stereoisomer profiles in the tissues studied were similar, responding to the stereoisomer profile of the diet. Both tissues preferentially accumulated 2R stereoisomer (69–100%). However, when α-tocopheryl acetate was used the discrimination was not specific for the RRR α-tocopherol form. Furthermore, the 2R:2S ratio had a tendency to increase as the polyunsaturation level of the diet increased.

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Hymøller, Lone, Saman Lashkari, Tove N. Clausen, and Søren K. Jensen. "Distribution of α-tocopherol stereoisomers in mink (Mustela vison) organs varies with the amount of all-rac-α-tocopheryl acetate in the diet." British Journal of Nutrition 120, no. 12 (October 17, 2018): 1332–37. http://dx.doi.org/10.1017/s0007114518002878.

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AbstractSynthetic α-tocopherol has eight isomeric configurations including four 2R (RSS, RRS, RSR, RRR) and four 2S (SRR, SSR, SRS, SSS). Only the RRR stereoisomer is naturally synthesised by plants. A ratio of 1·36:1 in biopotency of RRR-α-tocopheryl acetate to all-rac-α-tocopheryl acetate is generally accepted; however, studies indicate that neither biopotency of α-tocopherol stereoisomers nor bioavailability between them is constant, but depend on dose, time, animal species and organs. A total of forty growing young male mink were, after weaning, assigned one of the following treatments for 90 d: no α-tocopherol in diet (ALFA_0), 40 mg/kg RRR-α-tocopheryl acetate (NAT_40), 40 mg/kg all-rac-α-tocopheryl acetate (SYN_40) and 80 mg/kg feed all-rac-α-tocopheryl acetate (SYN_80). Mink were euthanised in CO2 and blood was collected by heart puncture. Mink were pelted and liver, heart, lungs, brain and abdominal fat were collected for α-tocopherol stereoisomer analysis. The proportion of RRR-α-tocopherol decreased in all organs and plasma with increasing amount of synthetic α-tocopherol stereoisomers in the diet (P≤0·05), whereas the proportion of all synthetic α-tocopherol stereoisomers increased with increasing amount of synthetic α-tocopherol stereoisomers in the diet (P≤0·05). The proportion of α-tocopherol stereoisomers in plasma, brain, heart, lungs and abdominal fat showed the following order: RRR>RRS, RSR, RSS>Σ2S, regardless of α-tocopherol supplement. The liver had the highest proportion of Σ2S stereoisomers, and lowest proportion of RRR-α-tocopherol. In conclusion, distribution of α-tocopherol stereoisomers differs with dose and form of α-tocopherol supplementation. The results did also reveal the liver’s role as the major organ for accumulation of Σ2S α-tocopherol stereoisomers.

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Brice-Tutt, Ariana C., Sanjeewa N. Senadheera, Michelle L. Ganno, Shainnel O. Eans, Tanvir Khaliq, Thomas F. Murray, Jay P. McLaughlin, and Jane V. Aldrich. "Phenylalanine Stereoisomers of CJ-15,208 and [d-Trp]CJ-15,208 Exhibit Distinctly Different Opioid Activity Profiles." Molecules 25, no. 17 (September 2, 2020): 3999. http://dx.doi.org/10.3390/molecules25173999.

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The macrocyclic tetrapeptide cyclo[Phe-d-Pro-Phe-Trp] (CJ-15,208) and its stereoisomer cyclo[Phe-d-Pro-Phe-d-Trp] exhibit different opioid activity profiles in vivo. The present study evaluated the influence of the Phe residues’ stereochemistry on the peptides’ opioid activity. Five stereoisomers were synthesized by a combination of solid-phase peptide synthesis and cyclization in solution. The analogs were evaluated in vitro for opioid receptor affinity in radioligand competition binding assays, and for opioid activity and selectivity in vivo in the mouse 55 °C warm-water tail-withdrawal assay. Potential liabilities of locomotor impairment, respiratory depression, acute tolerance development, and place conditioning were also assessed in vivo. All of the stereoisomers exhibited antinociception following either intracerebroventricular or oral administration differentially mediated by multiple opioid receptors, with kappa opioid receptor (KOR) activity contributing for all of the peptides. However, unlike the parent peptides, KOR antagonism was exhibited by only one stereoisomer, while another isomer produced DOR antagonism. The stereoisomers of CJ-15,208 lacked significant respiratory effects, while the [d-Trp]CJ-15,208 stereoisomers did not elicit antinociceptive tolerance. Two isomers, cyclo[d-Phe-d-Pro-d-Phe-Trp] (3) and cyclo[Phe-d-Pro-d-Phe-d-Trp] (5), did not elicit either preference or aversion in a conditioned place preference assay. Collectively, these stereoisomers represent new lead compounds for further investigation in the development of safer opioid analgesics.

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Licea Perez, Hermes, and Clara Andonian. "Chemical derivatization in combination with supercritical fluid chromatography to improve resolution of stereoisomers." Bioanalysis 13, no. 12 (June 2021): 985–99. http://dx.doi.org/10.4155/bio-2021-0053.

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Aim: Quantification of stereoisomers in biological matrices is of pivotal importance for drug development. Supercritical fluid chromatography paired with chiral stationary phases is the gold standard for resolution of enantiomers. However, this technique often proves inadequate for resolution of polar stereoisomers. Materials & methods: A combination of achiral chemical derivatization with supercritical fluid chromatography using chiral stationary columns to improve enantiomeric resolution is described. Results: Separation of four possible stereoisomers of linerixibat was achieved after derivatization with 3N HCl in n-butanol within 12 min (case1). Derivatization with acetic, propionic, butyric, isobutyric, valeric and isovaleric anhydrides significantly improved the separation of stereoisomers (case 2 and 3) within 10 min. The best stereoisomeric resolution was achieved using valeric and isovaleric anhydrides.

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Perlikowska, Wiesława, Remigiusz Żurawiński, and Marian Mikołajczyk. "A new and expeditious synthesis of all enantiomerically pure stereoisomers of rosaprostol, an antiulcer drug." Beilstein Journal of Organic Chemistry 12 (October 21, 2016): 2234–39. http://dx.doi.org/10.3762/bjoc.12.215.

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Four enantiomerically pure stereoisomers of rosaprostol (1), an antiulcer drug, were efficiently synthesized from the enantiomers of 2-(dimethoxyphosphoryl)-3-hexylcyclopentanone (3) as chiral substrates. The latter were obtained by resolution of racemic 3 with (+)-(R)-1-(1-naphthyl)ethylamine. The conversion of (+)-3 into rosaprostol stereoisomer (−)-1a was accomplished in four steps in 56% overall yield. According to the same protocol, the second stereoisomer (+)-1c was obtained from (−)-3 in 55% overall yield. A slightly improved procedure of the last two steps of the transformation of (+)-3 into (−)-1a allowed an increase in the overall yield to 64%. The remaining two stereoisomers, (−)-1b and (+)-1d, were obtained from (−)-1a and (+)-1c in 71 and 68% yield, respectively, by a two-reaction sequence, in which a Mitsunobu inversion of configuration at C-5 was the key step.

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Presini, Francesco, Graziano Di Carmine, Pier Paolo Giovannini, Virginia Cristofori, Lindomar Alberto Lerin, Olga Bortolini, Claudio Trapella, and Anna Fantinati. "Chemoenzymatic Stereodivergent Synthesis of All the Possible Stereoisomers of the 2,3-Dimethylglyceric Acid Ethyl Ester." Catalysts 11, no. 12 (November 26, 2021): 1440. http://dx.doi.org/10.3390/catal11121440.

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2,3-dihydroxy-2-methylbutyric acid, also known as 2,3-dimethylglyceric acid, constitutes the acyl and/or the alcoholic moiety of many bioactive natural esters. Herein, we describe a chemoenzymatic methodology which gives access to all the four possible stereoisomers of the 2,3-dimethylglyceric acid ethyl ester. The racemic ethyl α-acetolactate, produced by the N-heterocycle carbene (NHC)-catalyzed coupling of ethyl pyruvate and methylacetoin was employed as the starting material. The racemic mixture was resolved through (S)-selective reductions, promoted by the acetylacetoin reductase (AAR) affording the resulting ethyl (2R,3S)-2,3-dimethylglycerate; the isolated remaining (S)-ethyl α-acetolactate was successively treated with baker’s yeast to obtain the corresponding (2S,3S) stereoisomer. syn-2,3-Dimethylgliceric acid ethyl ester afforded by reducing the rac-α-acetolactate with NaBH4 in the presence of ZnCl2 was kinetically resolved through selective acetylation with lipase B from Candida antarctica (CAL-B) and vinyl acetate to access to (2S,3R) stereoisomer. Finally, the (2R,3R) stereoisomer, was prepared by C3 epimerization of the (2R,3S) stereoisomer recovered from the above kinetic resolution, achieved through the TEMPO-mediated oxidation, followed by the reduction of the produced ketone with NaBH4. The resulting 2,3-dimethylglycertate enriched in the (2R,3R) stereoisomer was submitted to stereospecicific acetylation with vinyl acetate and CAL-B in order to separate the major stereoisomer. The entire procedure enabled conversion of the racemic α-acetolactate into the four enantiopure stereoisomers of the ethyl 2,3-dihydroxy-2-methylbutyrate with the following overall yields: 42% for the (2R,3S), 40% for the (2S,3S), 42% for the (2S,3R) and 20% for the (2R,3R).

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Jia, Qi, Nana Xu, Pengqian Mu, Bo Wang, Shuming Yang, and Jing Qiu. "Stereoselective Separation and Acute Toxicity of Tau-Fluvalinate to Zebrafish." Journal of Chemistry 2015 (2015): 1–5. http://dx.doi.org/10.1155/2015/931908.

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Tau-fluvalinate (TFLV) is one of the most potent chiral synthetic pyrethroids to control a wide range of pests in agricultural fields, especially in apiary. In this study, two stereoisomers of TFLV were fully separated by high-performance liquid chromatography (HPLC) with a semipreparative chiral column using cellulose-tris(3,5-dimethylphenylcarbamate) as chiral stationary phase andn-hexane and 2-propanol (96/4, v/v) as mobile phase at a flow rate of 2.5 mL min−1. The (+)-stereoisomer was first eluted by detecting with an optical rotation detector. After obtaining pure single stereoisomer of TFLV, acute toxicities of each isomer and TFLV standard to zebrafish were evaluated. The results showed that the (+)-stereoisomer exhibited 273.4 times higher toxicity than the (−)-stereoisomer and 6.7 times higher than TFLV standard, according to their LC50values at 96 h after exposure. This indicates that the toxicity of TFLV mainly originates from (+)-stereoisomer. These results are very helpful to prepare single stereoisomer of chiral pesticides and evaluate their different toxicological effects to aquatic organisms.

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McIntosh, John M., and Ivy E. E. Hayes. "Stereochemistry of 3-carboxylated 2,5-dihydrothiophene formation." Canadian Journal of Chemistry 65, no. 1 (January 1, 1987): 110–13. http://dx.doi.org/10.1139/v87-018.

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The preparation of 2-carboxylated-1,3-dienes from carbomethoxy vinylphosphonates and 2-mercaptocarbonyl compounds has been shown to give stereoisomeric mixtures. This may be due to the formation of stereoisomers of the intermediate 2,5-dihydrothiophenes and (or) to the occurrence of both modes of disrotatory sulfur dioxide elimination.

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Duong-Thi, Minh-Dao, Maria Bergström, Tomas Fex, Susanne Svensson, Sten Ohlson, and Roland Isaksson. "Weak Affinity Chromatography for Evaluation of Stereoisomers in Early Drug Discovery." Journal of Biomolecular Screening 18, no. 6 (March 11, 2013): 748–55. http://dx.doi.org/10.1177/1087057113480391.

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In early drug discovery (e.g., in fragment screening), recognition of stereoisomeric structures is valuable and guides medicinal chemists to focus only on useful configurations. In this work, we concurrently screened mixtures of stereoisomers and estimated their affinities to a protein target (thrombin) using weak affinity chromatography–mass spectrometry (WAC-MS). Affinity determinations by WAC showed that minor changes in stereoisomeric configuration could have a major impact on affinity. The ability of WAC-MS to provide instant information about stereoselectivity and binding affinities directly from analyte mixtures is a great advantage in fragment library screening and drug lead development.

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Pham, Hoai, Madelyn Hunsley, Chou-Hsun Yang, Haobin Wang, and Scott M. Reed. "Demonstration of a Stereospecific Photochemical Meta Effect." Photochem 2, no. 1 (January 12, 2022): 69–76. http://dx.doi.org/10.3390/photochem2010006.

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A fundamental goal of photochemistry is to understand how structural features of a chromophore can make specific bonds within a molecule prone to cleavage by light, or photolabile. The meta effect is an example of a regiochemical explanation for photolability, in which electron donating groups on an aromatic ring cause photolability selectively at the meta position. Here, we show, using a chromophore containing one ring with a meta-methoxy group and one ring with a para-methoxy group, that two stereoisomers of the same compounds can react with light differently, based simply on the three-dimensional positioning of a meta anisyl ring. The result is that the stereoisomers of the compound with the same configuration at both stereogenic centers are photolabile while the stereoisomers with opposite configuration do not react with light. Furthermore, time-dependent density functional theory (TD-DFT) calculations show distinct excitation pathways for each stereoisomer.

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Castillo-Aguirre, Alver A., Zuly Jenny Rivera Monroy, and Mauricio Maldonado. "Analysis by RP-HPLC and Purification by RP-SPE of the C-Tetra(p-hydroxyphenyl)resorcinolarene Crown and Chair Stereoisomers." Journal of Analytical Methods in Chemistry 2019 (April 16, 2019): 1–6. http://dx.doi.org/10.1155/2019/2051282.

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A method for the separation of stereoisomer mixture of the octol C-tetra(p-hydroxyphenyl)calix[4]resorcinarene that was obtained by an acid cyclocondensation reaction between resorcinol and benzaldehyde is reported in this paper. A crude product from octol formation reaction was analyzed by reverse-phase high-performance liquid chromatography (RP-HPLC), and two well-resolved signals corresponding to the crown and chair isomers were found. A reverse phase in solid-phase extraction (RP-SPE) protocol allowed the separation of the two stereoisomers with high purity of each isomer. Finally, the crude and purified stereoisomers were characterized by using FT-IR, 1H-NMR, and 13C-NMR techniques, confirming the chemical identity of the two isomers and the efficiency in the separation process.

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Landge, Shashikant B., Sanjay A. Jadhav, Sunil B. Dahale, Navanath C. Niphade, Ch Lakshmi Narayana, Vishwas B. Gaikwad, and Vijayavitthal T. Mathad. "Development and Validation of New Chromatographic Method for the Determination of Enantiomeric and Diastereomeric Purity of Solifenacin Succinate: An Antimuscarinic Agent." Chromatography Research International 2011 (October 21, 2011): 1–7. http://dx.doi.org/10.4061/2011/243491.

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A new, simple, and rapid stereoselective normal phase-liquid chromatographic (NP-LC) method was developed to separate and quantify the solifenacin succinate and its three stereoisomers. The stereoisomeric separation was achieved on Chiralpak IC ( mm ID) column. The mobile phase was consisting of n-hexane, ethanol, isopropyl alcohol, and diethylamine in the ratio (60 : 15 : 25 : 0.1, v/v/v/v), and the flow rate was maintained at 1.0 mL min−1. UV detection was carried out at 220 nm. In addition, chiroptical detection was carried out using laser polarimeter to understand the elution orders. Resolution between all the stereoisomers was not less than 3. Effect of column temperature on resolution between the stereoisomers was studied. The method was validated as per ICH guideline and found to be robust. The proposed NP-LC method was successfully applied to the analysis of commercial formulation. The method could be of use not only for routine evaluation of the quality of solifenacin succinate in bulk drug manufacturing unit but also for detection of impurities in pharmaceutical formulations.

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Tonoi, Takayuki, Takehiko Inohana, Teruyuki Sato, Yuuki Noda, Miyuki Ikeda, Miku Akutsu, Takatsugu Murata, et al. "Total Synthesis and Antimicrobial Evaluation of 23-Demethyleushearilide and Extensive Antimicrobial Evaluation of All Synthetic Stereoisomers of (16Z,20E)-Eushearilide and (16E,20E)-Eushearilide." Molecules 24, no. 19 (September 22, 2019): 3437. http://dx.doi.org/10.3390/molecules24193437.

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A novel stereoisomer of eushearilide, 23-demethyleushearilide, was synthesized, and the structure–activity relationships of this compound along with known eushearilide stereoisomers were investigated in order to design novel lead compounds for the treatment of fungal infections. It was discovered that all of these congeners, together with the natural product, exhibited a wide range of antimicrobial activity against not only fungi but also against bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE).

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Rousselin, Yoann, Hugo Laureano, and Alexandre Clavel. "Crystal structure of (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman." Acta Crystallographica Section E Crystallographic Communications 71, no. 8 (July 8, 2015): o552—o553. http://dx.doi.org/10.1107/s205698901501261x.

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The title compound, C11H11FO2, is a building block in the synthesis of the active pharmaceutical ingredient DL-nebivolol. The synthesis starting from the enantiomerically pure (R)-6-fluoro-4-oxo-3,4-dihydro-2H-chromene-2-carboxylic acid resulted in a mixture of two stereoisomers, namely (R)-6-fluoro-2-[(S)-oxiran-2-yl]chroman and (R)-6-fluoro-2-[(R)-oxiran-2-yl]chroman. The mixture was separated by column chromatography but only one stereoisomer crystallized. The X-ray structure analysis revealed that the solid consisted of theR,Sisomer. A similar procedure was repeated for (S)-6-fluoro-4-oxo-3,4-dihydro-2H-chromene-2-carboxylic acid and, in this case, theS,Risomer was produced as a crystalline solid. Thus, all four stereoisomers of the title epoxide were obtained and their absolute configuration was assigned. The crystal studied was refined as an inversion twin.

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22

Kuchan, Matthew J., Katherine M. Ranard, Priyankar Dey, Sookyoung Jeon, Geoff Y. Sasaki, Karen J. Schimpf, Richard S. Bruno, Martha Neuringer, and John W. Erdman. "Infant Rhesus Macaque Brain α-Tocopherol Stereoisomer Profile Is Differentially Impacted by the Source of α-Tocopherol in Infant Formula." Journal of Nutrition 150, no. 9 (July 2, 2020): 2305–13. http://dx.doi.org/10.1093/jn/nxaa174.

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ABSTRACT Background α-Tocopherol (αT) in its natural form [2′R, 4′R, 8′R αT (RRR-αT)] is more bioactive than synthetic α-tocopherol (all rac-αT). All rac-αT is widely used in infant formulas, but its accretion in formula-fed infant brain is unknown. Objective We sought to compare αT and stereoisomer status in infant rhesus macaques (Macaca mulatta) fed infant formula (RRR-αT or all rac-αT) with a reference group fed a mixed diet of breast milk and maternal diet. Methods From 1 d after birth until 6 mo of age, infants (n = 23) were either nursery reared and exclusively fed 1 of 2 formulas by staff personnel or were community housed with their mothers and consumed a mixed reference diet of breast milk (69 mL/d at 6 mo) transitioning to monkey diet at ∼2 mo (MF; n = 8). Formulas contained either 21 μmol RRR-αT/L (NAT-F; n = 8) or 30 μmol all rac-αT/L (SYN-F; n = 7). Total αT and αT stereoisomers were analyzed in breast milk at 2, 4, and 6 mo and in monkey plasma and liver and 6 brain regions at 6 mo of age. α-Tocopherol transfer protein (α-TTP), lipoprotein αT, and urinary α-carboxyethyl-hydroxychroman (α-CEHC) were measured. One-way ANOVA with Tukey's post-hoc test was used for analysis. Results At study termination, plasma, liver, lipoprotein, and brain total αT did not differ between groups. However, the NAT-F–fed group had higher RRR-αT than the SYN-F–fed group (P < 0.01) and the MF group (P < 0.0001) in plasma (1.7- and 2.7-fold) and brain (1.5- and 2.5-fold). Synthetic αT 2R stereoisomers (SYNTH-2R) were generally 3- and 7-fold lower in brain regions of the NAT-F group compared with those of the SYN-F and MF groups (P < 0.05). SYNTH-2R stereoisomers were 2-fold higher in MF than SYN-F (P < 0.0001). The plasma percentage of SYNTH-2R was negatively correlated with the brain percentage of RRR-αT (r = −0.99, P < 0.0001). Brain αT profiles were not explained by α-TTP mRNA or protein expression. Urine α-CEHC was 3 times higher in the NAT-F than in the MF group (P < 0.01). Conclusions Consumption of infant formulas with natural (NAT-F) compared with synthetic (SYN-F) αT differentially impacted brain αT stereoisomer profiles in infant rhesus macaques. Future studies should assess the functional implications of αT stereoisomer profiles on brain health.

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FUJITA, Shinsaku. "RS-Stereoisomeric Groups and Enumeration of Quadruplets of RS-Stereoisomers." Journal of Computer Chemistry, Japan 13, no. 3 (2014): 155–56. http://dx.doi.org/10.2477/jccj.2014-0014.

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Il`in, E. G., A. S. Parshakov, V. G. Yarzhemsky, E. A. Ugolkova, L. V. Goyeva, and V. I. Privalov. "Physical chemistry CeF4 complexes in organic solvents." Доклады Академии наук 488, no. 1 (September 24, 2019): 47–51. http://dx.doi.org/10.31857/s0869-5652488147-51.

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The first complexes of cerium tetrafluoride in solutions were investigated by 19F NMR and IR spectroscopy. The temperature dependence of the 19F NMR spectra was, studied and it was concluded that mobile equilibrium exists between the molecular adduct and singly charged ionic forms, including geometric isomers. The static probability of stereoisomer formation [CeF4(dmso)4] was calculated using the square antiprism configuration and, based on the relative intensity of the 19F NMR resonance signals, they were assigned to possible stereoisomers. Quantum-chemical calculations of the structure of the isomer [CeF4(dmso)4], the isomer [CeF3(dmso)5]+ and [CeF5(dmso)3]-, showing their thermodynamic stability, were performed.

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Bencke, Carlos, Mário Marangoni, Adriano Camargo, Cassio Fantinel, Helio Bonacorso, Marcos Martins, and Nilo Zanatta. "Synthesis of Penta-2,4-dienenitriles by the Horner–Wadsworth–Emmons Olefination of Enones." Synthesis 49, no. 23 (August 24, 2017): 5131–42. http://dx.doi.org/10.1055/s-0036-1590871.

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Three new series of compounds, 5-alkoxy-3-(trifluoromethyl)penta-2,4-dienenitriles, 5-(phenylthio)-3-(trifluoromethyl)penta-2,4-dienenitriles, and ethyl 4-alkoxy-2-(cyanomethylene)but-3-enoates, obtained from the olefination reaction of the respective enones with diethyl cyanomethylphosphonate via the Horner–Wadsworth–Emmons olefination are reported. All products were obtained as single regioisomers; however, the composition of the stereoisomers changed according to the enone substituents. A study based on 1H and 13C NMR chemical shifts, 1H–19F and 13C–19F NMR coupling constants, 1H NMR signal integrals, and HSQC, HMBC, and NOESY experiments was performed in order to assign the structure and percentage of each stereoisomer obtained.

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KIDANE, A., I. L. NESHEIM, H. J. S. LARSEN, E. THUEN, S. K. JENSEN, and H. STEINSHAMN. "Effects of supplementing mid-lactation dairy cows with seaweed and vitamin E on plasma and milk α-tocopherol and antibody response to immunization." Journal of Agricultural Science 153, no. 5 (March 18, 2015): 929–42. http://dx.doi.org/10.1017/s0021859615000052.

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SUMMARYThe objective of the current experiment was to compare the effects of supplementing mid-lactation dairy cows with all-rac-α-tocopheryl acetate (SyntvE), RRR-α-tocopheryl acetate (NatvE) or seaweed meal (Seaweed) in the presence of a Control group (no supplemental vitamin E or seaweed) on the concentration of α-tocopherol in plasma and milk, and antibody response following immunization. The hypothesis was that supplementation of dairy cows with vitamin E, regardless of its form, would increase plasma and milk α-tocopherol compared to the control diet and this incremental response would be bigger with NatvE than SyntvE. Furthermore, it was hypothesized that vitamin E, regardless of its form, will provide an improved adaptive immune response to immunization than the Control diet, and cows supplemented with Seaweed meal would produce better adaptive immune response following immunization than cows in the Control group. Twenty-four Norwegian Red (NR) dairy cows in their mid-lactation were allocated randomly to the four treatments in a replicated Latin square design. The cows were fed on a basal diet of silage and concentrate on top of which the experimental supplements were provided. Plasma and milk α-tocopherol concentrations were higher in NatvE and SyntvE groups than in the other two groups. The RRR-α-tocopherol stereoisomer was the predominant form (>0·86), in both plasma and milk, whereas the remaining part was largely made up of the other three 2R stereoisomers (RRS, RSR and RSS). In cows fed the Control, Seaweed and NatvE, the proportion of the RRR-α-tocopherol stereoisomer in plasma and milk constituted >0·97 of the total α-tocopherol. Mid-lactation NR dairy cows had higher than adequate levels of plasma α-tocopherol (9·99 mg/l) even when not supplemented with external source of vitamin E, suggesting that with a good quality silage these cows may not be at risk of vitamin E deficiency. Furthermore, the present study shows that dairy cows in mid to late lactation have preferential uptake of RRR stereoisomer of α-tocopherol compared with other stereoisomers. All cows responded well to immunization with different antigens, but there were no significant group effects of the diet on the immune response measured.

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27

Anderbrant, Olle, D. Barry Lyons, Joakim Bång, Erik Hedenström, and Hans-Erik Högberg. "Sex Pheromone of the Introduced Pine Sawfly, Diprion similis, Revisited to Define a Useful Monitoring Lure: Deviating Chiral Composition and Behavioural Responses Compared to Earlier Reports." Insects 12, no. 10 (September 29, 2021): 886. http://dx.doi.org/10.3390/insects12100886.

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Extracts of Diprion similis females contained about 15 ng of the sex pheromone precursor 3,7-dimethylpentadecan-2-ol per female. After derivatisation with (S)-2-acetoxypropanoyl chloride, we found that the major stereoisomer in the extract was (2S,3R,7R)-3,7-dimethylpentadecan-2-ol. Small amounts of other stereoisomers of 3,7-dimethylpentadecan-2-ol were also identified in the extract, namely 1% of (2R,3S,7S), 0.3% (2R,3R,7R) and 0.4% of (2R,3R,7S). An unknown fifth substance showed a very similar spectrum to 3,7-dimethylpentadecan-2-ol, both in SIM and full scan mode. None of the earlier suggested behavioural synergistic isomers ((2S,3S,7S), (2S,3S,7R) and (2S,3R,7S)) were detected in the extracts. In field tests in Ontario, Canada, the earlier identified main pheromone component, viz. the propanoate of (2S,3R,7R)-3,7-dimethylpentadecan-2-ol, was tested alone and in combination with other stereoisomers, earlier reported to be synergistic. No synergistic effects were detected and the threo four-isomer blend was as attractive as the pure main compound. Thus, one of the few examples of a diprionid sawfly using more than one substance in its sex pheromone could not be confirmed. The results also suggest that monitoring programs can use the more easily synthesized threo-blend without losing efficiency. Furthermore, the study suggests that other diprionid pheromones may benefit from a reinvestigation, to clarify possible synergistic effects of stereoisomers.

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Fujita, Shinsaku. "Klein Four-Group as the Factor Group for Elucidating RS-Stereoisomerism of Cubane Derivatives. The Factor-Group Method for Type-Itemized Enumeration of Stereoisograms." MATCH Communications in Mathematical and in Computer Chemistry 88, no. 2 (2022): 239–318. http://dx.doi.org/10.46793/match.88-2.239f.

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Van't Hoff's way (asymmetry, stereogenicity) and Le Bel's way (dissymmetry, chirality) are compared from the viewpoint of two ways for investigating organic stereochemistry, where cubane derivatives of the point group are selected as probes. For emphasizing Le Bel's way, combinatorial enumerations of 3D structures under point groups are first discussed to develop Fujita's proligand method and Fujita's USCI approach. The foundations of these enumerations are applied to support synthetic studies of stereoisomers for emphasizing van't Hoff's way after the proposal of Fujita's stereoisogram approach based on RS-stereoisomeric groups, e.g., . Importance of the proligand-promolecule model is emphasized in enumerations under point groups (Fujita's proligand method and Fujita's USCI approach) as well as in enumerations of RS-stereoisomeric groups (Fujita's stereoisogram approach). After the five types (type I to type V) of stereoisograms are classified into three categories (i.e., Category 1 (types I/IV), Category 2 (types II/III/V), and the co-existence case), the half-size-subgroup method and the factor-group method have been developed for type-itemized enumerations of stereoisograms. Type-V stereoisograms for characterizing "extended pseudoasymmetry" are discussed by assigning their configuration numbers and CA-descriptors.

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Xu, Yangrong, Hangjun Tang, Yijie Xu, Jialin Guo, Xu Zhao, Qingguo Meng, and Junhai Xiao. "Design, Synthesis, Bioactivity Evaluation, Crystal Structures, and In Silico Studies of New α-Amino Amide Derivatives as Potential Histone Deacetylase 6 Inhibitors." Molecules 27, no. 10 (May 22, 2022): 3335. http://dx.doi.org/10.3390/molecules27103335.

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Hydroxamate, as a zinc-binding group (ZBG), prevails in the design of histone deacetylase 6(HDAC6) inhibitors due to its remarkable zinc-chelating capability. However, hydroxamate-associated genotoxicity and mutagenicity have limited the widespread application of corresponding HDAC6 inhibitors in the treatment of human diseases. To avoid such side effects, researchers are searching for novel ZBGs that may be used for the synthesis of HDAC6 inhibitors. In this study, a series of stereoisomeric compounds were designed and synthesized to discover non-hydroxamate HDAC6 inhibitors using α-amino amide as zinc-ion-chelating groups, along with a pair of enantiomeric isomers with inverted L-shaped vertical structure as cap structures. The anti-proliferative activities were determined against HL-60, Hela, and RPMI 8226 cells, and 7a and its stereoisomer 13a exhibited excellent activities against Hela cells with IC50 = 0.31 µM and IC50 = 5.19 µM, respectively. Interestingly, there is a significant difference between the two stereoisomers. Moreover, an evaluation of cytotoxicity toward human normal liver cells HL-7702 indicated its safety for normal cells. X-ray single crystal diffraction was employed to increase insights into molecule structure and activities. It was found that the carbonyl of the amide bond is on the different side from the amino and pyridine nitrogen atoms. To identify possible protein targets to clarify the mechanism of action and biological activity of 7a, a small-scale virtual screen using reverse docking for HDAC isoforms (1–10) was performed and the results showed that HDAC6 was the best receptor for 7a, suggesting that HDAC6 may be a potential target for 7a. The interaction pattern analysis showed that the α-amino amide moiety of 7a coordinated with the zinc ion of HDAC6 in a bidentate chelate manner, which is similar to the chelation pattern of hydroxamic acid. Finally, the molecular dynamics simulation approaches were used to assess the docked complex’s conformational stability. In this work, we identified 7a as a potential HDAC6 inhibitor and provide some references for the discovery of non-hydroxamic acid HDAC6 inhibitors.

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Leitgeb, Balázs. "Spatial relationships between the pharmacophores of endomorphin-2: a comparative study of stereoisomers." Open Chemistry 10, no. 6 (December 1, 2012): 1791–98. http://dx.doi.org/10.2478/s11532-012-0105-3.

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AbstractThe spatial relationships between the pharmacophore elements were investigated in the case of four different stereoisomeric forms of opioid tetrapeptide, endomorphin-2, taking into account the L-D and cis-trans isomerisms. On the basis of distances and angles measured between the pharmacophoric points, a comparative analysis of conformational distributions was performed, applying a variety of distance-angle maps. The results obtained by this theoretical study indicated that the stereoisomers of endomorphin-2 could be distinguished from one another, based on the comparative analysis of distance-angle maps. Nevertheless, it could be concluded that this method proved to be suitable to examine the effects of L-D and cis-trans isomerisms on the spatial relationships of the pharmacophores of tetrapeptide.

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Bernát, Juraj, Ladislav Kniežo, Gabriela Birošová, Miloš Buděšínský, Jaroslav Podlaha, Jana Podlahová, and Jiří Novotný. "Reactions of PO(NCS)3 with 4-Hydroxy-1,3-dioxanes. Crystal Structure of rel-(2S,4R,5S,6S)-2,6-Diethyl-5-methyl-4-(N'-benzylthioureido)-1,3-dioxane." Collection of Czechoslovak Chemical Communications 57, no. 6 (1992): 1299–313. http://dx.doi.org/10.1135/cccc19921299.

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Substituted 4-hydroxy-1,3-dioxanes II react rapidly with PO(NCS)3 to give 4-isothiocyanato-1,3-dioxanes III. The 1H NMR spectra showed that in the isothiocyanate IIIa the predominant stereoisomer has its NCS group in axial position. The addition of benzylamine to the isothiocyanates IIIa and IIIb gave uniform thioureas IVa and IVb with equatorial alkyl groups at 2 and 6 positions and axial thioureido group at 4 position. On the other hand, the isothiocyanate IIIc reacts with benzylamine to give a mixture of three stereoisomeric thioureas V,VI, and VIII. The structure of VI was proved by means of X-ray diffraction analysis; in crystalline form the molecules of VI are present as H-bonded dimers (N-H...O).

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Brine, G. A., F. I. Carroll, T. M. Richardson-Leibert, H. Xu, and R. B. Rothman. "Ohmefentanyl and Its Stereoisomers: Chemistry and Pharmacology." Current Medicinal Chemistry 4, no. 4 (August 1997): 247–70. http://dx.doi.org/10.2174/0929867304666220313115017.

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Ohmefentanyl., or β-hydroxy-3-methylfentanyl, is an unique member of the 4-anilidopiperidine class of opiates. This review summarizes both the initial studies on mixtures of ohmefentanyl stereoisomers and some more recent studies on the eight individual stereoisomers, in particular those in which the 3- methyl and 4-propionanilide substituents on the piperidine ring have a cis relationship to each other. Analog studies, also on stereoisomer mixtures, have revealed that structural changes in the β-hydroxy- ·phenethyl portion of the molecule have considerable impact on the biological activity in the cis series while changes in the 4-propionanilide portion have smaller effects. The analog data are consistent with the idea that the cis-3-methyl group, the β -hydroxyl group and the β-phenethyl group play key roles in cis-ohmefentanyl's unique activity. Biological studies on the four cis-stereoisomers [( S,3R,4S)-4a, ( R,3R,4S)-4b, ( R,3S,4R)-4c, ( S,3S,4R)-4d] have shown that they differ considerably in their in vitro and in vivo biological properties. Since these stereoisomers differ from each other in their absolute stereochemistries, which focuses the analysis on asymmetric structural factors and avoids confounding changes in physiochemical characteristics, they constitute a unique set of molecular probes for investigation of 11 receptor mediated phenomena. We summarize in this review data showing that these four cis stereoisomers are characterized by different parameter profiles for ligand-receptor interaction: binding affinity (Ki value), potency (ED50 for receptor activation), efficacy (maximal response) and intrinsic efficacy (relationship between receptor occupation and response). We speculate that the different profiles result from binding to different domains of the 11 opioid receptor. Moreover, we expect that continued studies with these stereoisomers, as well as the corresponding stereoisomers of selected cis-ohmefentanyl analogs, will help to elucidate the molecular basis of these parameters and to develop more refined pharmacophores for the opioid 11 receptor. This review traces the evolution of ohmefentanyl,or β-hydroxy-3-methylfentanyl, from the initial papers on the identification of an unexpectedly potent congener of cis-3-methylfentanyl to some of the more recent work involving the four pure cis-stereoisomers and ligands derived from cis-A-ohmefentanyl. While an effort is made to place the discovery of ohmefentanyl into the context of earlier work on 4-anilidopiperidines and then to follow a chronological sequence of events, the review has been organized so that related work from different groups is covered in the same section. Some of the initial biological data on ohmefentanyl from the Shanghai Institute of Materia Medica was summarized previously in a short review [1].

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Ozenil, Marius, Jonas Aronow, Daniela Piljak, Chrysoula Vraka, Wolfgang Holzer, Helmut Spreitzer, Wolfgang Wadsak, Marcus Hacker, and Verena Pichler. "Synthesis, Biological, and Computational Evaluation of Antagonistic, Chiral Hydrobenzoin Esters of Arecaidine Targeting mAChR M1." Pharmaceuticals 13, no. 12 (November 30, 2020): 437. http://dx.doi.org/10.3390/ph13120437.

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Muscarinic acetylcholine receptors (mAChRs) are a pivotal constituent of the central and peripheral nervous system. Yet, therapeutic and diagnostic applications thereof are hampered by the lack of subtype selective ligands. Within this work, we synthesized and chemically characterized three different stereoisomers of hydrobenzoin esters of arecaidine by NMR, HR-MS, chiral chromatography, and HPLC-logP. All compounds are structurally eligible for carbon-11 labeling and show appropriate stability in Dulbecco’s phosphate-buffered saline (DPBS) and F12 cell culture medium. A competitive radioligand binding assay on Chinese hamster ovary cell membranes comprising the human mAChR subtypes M1-M5 showed the highest orthosteric binding affinity for subtype M1 and a strong influence of stereochemistry on binding affinity, which corresponds to in silico molecular docking experiments. Ki values toward M1 were determined as 99 ± 19 nM, 800 ± 200 nM, and 380 ± 90 nM for the (R,R)-, (S,S)-, and racemic (R,S)-stereoisomer, respectively, highlighting the importance of stereochemical variations in mAChR ligand development. All three stereoisomers were shown to act as antagonists toward mAChR M1 using a Fluo-4 calcium efflux assay. With respect to future positron emission tomography (PET) tracer development, the (R,R)-isomer appears especially promising as a lead structure due to its highest subtype selectivity and lowest Ki value.

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Ježek, Rudolf, Miroslava Žertová, Jiřina Slaninová, Pavel Majer, and Zdenko Procházka. "Antagonistic Analogs of Oxytocin with Substituted Phenylalanine or Tyrosine in Position 2." Collection of Czechoslovak Chemical Communications 59, no. 6 (1994): 1430–38. http://dx.doi.org/10.1135/cccc19941430.

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Solid phase method on p-methylbenzhydrylamine resin was used for the synthesis of seven analogs of oxytocin with non-coded amino acids in position 2. [L-Phe(4-Me)2]oxytocin (I), [D-Phe(4-Me)2]oxytocin (II), [L-Phe(2-Me,4-Et)2]oxytocin (III), [D-Phe(2-Me,4-Et)2]oxytocin (IV), [D-Tyr(Me)2]oxytocin (V), [D-Tyr(Et)2]oxytocin (VI) and [L-Tyr(2-Me)2]oxytocin (VII) were synthesized. All analogs with D-stereoisomer of alkyl or alkoxy substituted phenylalanine possess uterus in vitro inhibiting activity. In the case of L-stereoisomers the structure activity relationship is more complicated. As far as the pressor activity is concerned, the analogs have either very low agonistic activity or low degree of antagonism.

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Polívka, Zdeněk, Jiří Holubek, Emil Svátek, Jan Metyš, and Miroslav Protiva. "Synthesis of the semi-rigid analogues of prothiadene and dithiadene as potential antidepressant and antihistamine agents: 11-[2-(Dimethylaminomethyl)cyclohexylidene]-6,11-dihydrodibenzo[b,e]thiepins and 4-[2-(dimethylaminomethyl)cyclohexylidene]-4,9-dihydrothieno-[2,3-c]-2-benzothiepins." Collection of Czechoslovak Chemical Communications 50, no. 5 (1985): 1078–88. http://dx.doi.org/10.1135/cccc19851078.

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Reaction of dibenzo[b,e]thiepin-11(6H)-one with 2-(dimethylaminomethyl)cyclohexylmagnesium chloride gave a mixture of stereoisomeric amino alcohols IX from which four homogeneous bases (IXa to IXd) were separated by chromatography. Dehydration of these compounds with boiling dilute hydrochloric acid afforded mixtures of racemic geometric isomers of the title compound VII, which were separated by crystallization. To the prevailing less polar base VIIa (E)-configuration was assigned on the basis of the IR spectrum. Using a similar procedure, thieno[2,3-c]-2-benzothiepin-4(9H)-one gave mixture of amino alcohols X from which three homogeneous stereoisomers X-A to X-C were isolated. Their dehydration resulted in both expected racemic geometric isomers VIII-A and VIII-B. Pharmacological testing proved the character of an antidepressant for the semi-rigid analogue of dithiadene VIII.

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Gill, Brendon D., Jackie E. Wood, and Harvey E. Indyk. "Analysis of α-Tocopherol Stereoisomers in Fortified Infant Formula by Chiral Chromatography." Journal of AOAC INTERNATIONAL 104, no. 3 (January 23, 2021): 725–31. http://dx.doi.org/10.1093/jaoacint/qsab012.

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Abstract Background Direct measurement of the bioavailable α-tocopherol content presents a significant analytical challenge and requires chiral separation of the α-tocopherol stereoisomers. Objective The objective of the study was to validate an analytical method for the analysis of α-tocopherol stereoisomers in infant formulas and dairy products. Method Samples were saponified at elevated temperature and lipophilic components were extracted into an organic solvent, with subsequent chromatographic separation of the α-tocopherol stereoisomers achieved by HPLC with a chiral column and fluorescence detection. Results The method was shown to be accurate, with spike recoveries of 91.9–108.8% for RRR-α-tocopherol and 90.1–104.7% for α-tocopherol, with no statistical bias against NIST 1849a certified reference material (P-value = 0.54) and an HPLC-UV analytical method (P-value = 0.48). Acceptable precision was confirmed, with repeatabilities estimated at 3.5% RSDr (HorRat = 0.6) for RRR-α-tocopherol and 4.6% RSDr (HorRat = 0.4) for α-tocopherol. Conclusions A straightforward chiral chromatographic method for the analysis of stereoisomeric forms of α-tocopherol is described. In a single analytical run, the method can quantify: (i) the total α-tocopherol content; (ii) the nutritionally important RRR-α-tocopherol and/or 2 R, 4′-ambo, 8′-ambo-α-tocopherol contents; (iii) the amount of all-rac-α-tocopherol, all-rac-α-tocopheryl acetate, or all-rac-α-tocopheryl succinate fortified into the product. Highlights An accurate and precise chiral chromatographic method for the analysis of isomeric forms of α-tocopherol is described. The method is able to distinguish between natural and synthetic tocopherol sources. The method is accurate and precise and is suitable either for routine product compliance testing during product manufacture or as a possible reference method.

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Henthorn, Thomas K., Tom C. Krejcie, Claus U. Niemann, Cheri Enders-Klein, Colin A. Shanks, and Michael J. Avram. "Ketamine Distribution Described by a Recirculatory Pharmacokinetic Model Is Not Stereoselective." Anesthesiology 91, no. 6 (December 1, 1999): 1733. http://dx.doi.org/10.1097/00000542-199912000-00027.

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Background Differences in the pharmacokinetics of the enantiomers of ketamine have been reported. The authors sought to determine whether these differences extend to pulmonary uptake and peripheral tissue distribution and to test the hypothesis that tissue distribution of the stereoisomers differs because of carrier-mediated drug transport. Methods The dispositions of markers of intravascular space and blood flow (indocyanine green, ICG) and total body water and tissue perfusion (antipyrine) were determined along with S-(+)- and R-(-)-ketamine in five mongrel dogs. The dogs were studied while anesthetized with 2.0% halothane. Marker and drug dispositions were described by recirculatory pharmacokinetic models based on frequent early and less-frequent later arterial blood samples. These models characterize pulmonary uptake and the distribution of cardiac output into parallel peripheral circuits. Results Plasma elimination clearance of the S-(+)-ketamine enantiomer, 29.9 ml x min(-1) x kg(-1), was higher than that of the R-(-)-enantiomer, 22.2 ml x min(-1) x kg(-1). The apparent pulmonary tissue volumes of the ketamine S-(+) and R-(-)-enantiomers (0.31 l) did not differ and was approximately twice that of antipyrine (0.16 l). The peripheral tissue distribution volumes and clearances and the total volume of distribution (2.1 l/kg) were the same for both stereoisomers when elimination clearances were modeled from the rapidly equilibrating peripheral compartment. Conclusions Although the elimination clearance of S-(+)-ketamine is 35% greater than that of the R-(-)-enantiomer, there is no difference in the apparent pulmonary tissue volume or peripheral tissue distribution between the stereoisomers, suggesting that physicochemical properties of ketamine other than stereoisomerism determine its perfusion-limited tissue distribution.

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38

Reichert, Sylvia, Matthias Wüst, Thomas Beck, and Armin Mosandl. "Stereoisomeric Flavor Compounds LXXXI: Dill Ether and Itscis-Stereoisomers: Synthesis and Enantioselective Analysis." Journal of High Resolution Chromatography 21, no. 3 (March 1, 1998): 185–88. http://dx.doi.org/10.1002/(sici)1521-4168(19980301)21:3<185::aid-jhrc185>3.0.co;2-j.

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Reichert, Sylvia, and Armin Mosandl. "Stereoisomeric Flavor Compounds LXXXII Dill Ether and Its Stereoisomers: Synthesis and Enantioselective Analysis." Journal of High Resolution Chromatography 22, no. 11 (November 1, 1999): 631–34. http://dx.doi.org/10.1002/(sici)1521-4168(19991101)22:11<631::aid-jhrc631>3.0.co;2-o.

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40

Kobayashi, Yuichi, Yuji Nakayama, and Shinya Yoshida. "Determination of the stereoisomer of korormicin from eight possible stereoisomers by total synthesis." Tetrahedron Letters 41, no. 9 (February 2000): 1465–68. http://dx.doi.org/10.1016/s0040-4039(99)02319-9.

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Timperley, Christopher M., Jonathan E. Forman, Mohammad Abdollahi, Abdullah Saeed Al-Amri, Isel Pascual Alonso, Augustin Baulig, Veronica Borrett, et al. "Advice from the Scientific Advisory Board of the Organisation for the Prohibition of Chemical Weapons on isotopically labelled chemicals and stereoisomers in relation to the Chemical Weapons Convention." Pure and Applied Chemistry 90, no. 10 (October 25, 2018): 1647–70. http://dx.doi.org/10.1515/pac-2018-0803.

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AbstractThe Chemical Weapons Convention (CWC) is an international disarmament treaty that prohibits the development, stockpiling and use of chemical weapons. This treaty has 193 States Parties (nations for which the treaty is binding) and entered into force in 1997. The CWC contains schedules of chemicals that have been associated with chemical warfare programmes. These scheduled chemicals must be declared by the States that possess them and are subject to verification by the Organisation for the Prohibition of Chemical Weapons (OPCW, the implementing body of the CWC). Isotopically labelled and stereoisomeric variants of the scheduled chemicals have presented ambiguities for interpretation of the requirements of treaty implementation, and advice was sought from the OPCW’s Scientific Advisory Board (SAB) in 2016. The SAB recommended that isotopically labelled compounds or stereoisomers related to the parent compound specified in a schedule should be interpreted as belonging to the same schedule. This advice should benefit scientists and diplomats from the CWC’s State Parties to help ensure a consistent approach to their declarations of scheduled chemicals (which in turn supports both the correctness and completeness of declarations under the CWC). Herein, isotopically labelled and stereoisomeric variants of CWC-scheduled chemicals are reviewed, and the impact of the SAB advice in influencing a change to national licensing in one of the State Parties is discussed. This outcome, an update to national licensing governing compliance to an international treaty, serves as an example of the effectiveness of science diplomacy within an international disarmament treaty.

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Yakovleva, M. P., V. A. Vydrina, N. M. Ishmuratova, and G. Yu Ishmuratov. "CONTRIBUTION OF UFA SCIENTISTS TO THE CHEMISTRY OF OPTICALLY ACTIVE SEX PHEROMONE OF PINE SAWFLIES." ÈKOBIOTEH 3, no. 4 (2020): 634–42. http://dx.doi.org/10.31163/2618-964x-2020-3-4-634-642.

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Pine sawflies of the genera Neodiprion, Diprion and Gilpinia (Diprionidae) are malignant and economically important pests of coniferous trees. The most effective and environmentally safe method of controlling and regulating the number of pine sawflies is the use in traps of synthetically obtained sex feromone, identified for its different species as acetates and propionates of 3,7-dimethyl-2-pentadecan-2-ol (diprionol) in the form of various stereoisomeric forms due to the presence of three asymmetric carbon atoms. At the same time, it was noted that the 2S configuration of the optical centre of the erythro-isomerium is crucial for the stereochemistry of the sex pheromone of pine sawflies. The article presents the results of research of the laboratory of insect bioregulators of the Ufa Institute of chemistry of the UFIC RAS in the field of synthesis of optically active pine Sawfly pheromone, its stereoisomers and analogues based on (S)-(+)-dihydromircene and (-)-mentolactone obtained from available natural monoterpenes – (+)-α-pinene and l-menthol, respectively.

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Zaikin, Vladimir G., and Roman S. Borisov. "Stereospecific Ion—molecule Reactions in the Trans-Decahydro-4-Hydroxyquinoline Series upon Chemical Ionization." European Journal of Mass Spectrometry 8, no. 2 (April 2002): 139–45. http://dx.doi.org/10.1255/ejms.482.

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A series of C-2- and C-4-stereoisomeric 2-methyl-, 1,2-dimethyl- and 1-butyl-2-methyl- trans-decahydro-4-hydroxyquinolines, having a conformationally stable bicyclic system and an additional 4-substituent (chosen from ethyl, ethynyl, ethenyl, butyl and vinylethynyl), was investigated by isobutane and methane chemical ionisation (CI). It was shown that, independently of the nature of the reagent gas, the spectra of stereoisomers at C-4 differed in the intensity ratios of the [MH]+ and [MH–H2O]+ ion peaks; the latter peaks are always less intense in the case of compounds containing an axial 4-OH group. The same regularity was observed for isobutane CI followed by collision-induced dissociation and for methane CI, although the intensity ratios differ. “Approach control” was suggested to explain the observed stereospecificity of the protonation of the alcohols at the hydroxyl group. The results obtained provide a useful tool for the determination of the configuration of hydroxyl-carrying centers in other trans-decahydro-4-hydroxyquinolines and related compounds.

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Morikawa, Atsushi, Masa-Aki Kakimoto, and Yoshio Imai. "Preparation of aromatic polyamides from newly separated optically pure phenylindanedicarboxylic acid and their application to enantioseparation." High Performance Polymers 6, no. 4 (August 1994): 415–21. http://dx.doi.org/10.1088/0954-0083/6/4/009.

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An optically pure isomer of 1,l,3.-trimethyl-3-phenylindane-4',5-dicarboxylic acid (PIDA) was obtained by introduction of racemric PIDA to a diester of the optically pure alcohol. D-(-)-pantolactone, followed by hydrolysis of the separated stereoisomer of the diester. Optically active aromatic polyamides (aramids) were synthesized by the reaction of the optically pure PIDA with various aromatic diamines. The specific rotations of these aramids ranged from + 284 to +4416. The aramids were soluble in organic solvents such as N,N-dimethylacetamide, pyridine and m-cresol. These materials had glass transition temperatures over 290 'C, and did not decompose below 380 C. The solubility and thermal behaviour were almost the same as those of the racemic aramids. The optically active aramids were examined as a stationary phase for chromatographic enantioseparation. When the aramid derived from p-phenylenediamine was used for this purpose, the stereoisomers of l-phenylethylamine could be easily separated.

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Brem, Jürgen, Sander S. van Berkel, David Zollman, Sook Y. Lee, Opher Gileadi, Peter J. McHugh, Timothy R. Walsh, Michael A. McDonough, and Christopher J. Schofield. "Structural Basis of Metallo-β-Lactamase Inhibition by Captopril Stereoisomers." Antimicrobial Agents and Chemotherapy 60, no. 1 (October 19, 2015): 142–50. http://dx.doi.org/10.1128/aac.01335-15.

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ABSTRACTβ-Lactams are the most successful antibacterials, but their effectiveness is threatened by resistance, most importantly by production of serine- and metallo-β-lactamases (MBLs). MBLs are of increasing concern because they catalyze the hydrolysis of almost all β-lactam antibiotics, including recent-generation carbapenems. Clinically useful serine-β-lactamase inhibitors have been developed, but such inhibitors are not available for MBLs.l-Captopril, which is used to treat hypertension via angiotensin-converting enzyme inhibition, has been reported to inhibit MBLs by chelating the active site zinc ions via its thiol(ate). We report systematic studies on B1 MBL inhibition by all four captopril stereoisomers. High-resolution crystal structures of three MBLs (IMP-1, BcII, and VIM-2) in complex with either thel- ord-captopril stereoisomer reveal correlations between the binding mode and inhibition potency. The results will be useful in the design of MBL inhibitors with the breadth of selectivity required for clinical application against carbapenem-resistantEnterobacteriaceaeand other organisms causing MBL-mediated resistant infections.

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Meglia, Guillermo E., Søren K. Jensen, Charlotte Lauridsen, and Karin Persson Waller. "α-Tocopherol concentration and stereoisomer composition in plasma and milk from dairy cows fed natural or synthetic vitamin E around calving." Journal of Dairy Research 73, no. 2 (March 30, 2006): 227–34. http://dx.doi.org/10.1017/s0022029906001701.

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The aim of this study was to compare the effects of supplementing dairy cows with 1000 IU/day of all-rac-α-tocopheryl acetate (SynAc), RRR-α-tocopheryl acetate (NatAc), or RRR-α-tocopherol (NatAlc), from approximately 3 weeks before estimated calving until 2 weeks after calving, on the concentration of α-tocopherol and its stereoisomers (RRR-, RSS-, RRS-, RSR- and the four 2S-forms of α-tocopherol) in blood and milk. An unsupplemented group was included as control. Blood samples were collected at 3, 2 and 1 weeks before estimated calving, at calving, and 3, 7 and 14 days after calving, while milk samples were taken twice within 24 h after calving and at 7 and 14 days in milk. Overall, time and treatment had significant effects on plasma α-tocopherol with higher concentrations in NatAc than in the other groups. In addition, SynAc had higher concentrations than Control, and NatAlc tended to be higher than Control. The lowest plasma concentrations were observed at calving and 3 days after calving. Independent of treatment, the concentration was higher in colostrum than in milk day 7 and 14 after calving. Analyses of the stereoisomer distribution in plasma and milk showed that, irrespective of dietary treatment, RRR-α-tocopherol was the most predominant form, constituting more than 86%, whereas the remaining part of α-tocopherol was made up by the three synthetic 2R isomers, while the 2S isomers only contributed less than 1% of the total α-tocopherol. In control cows and cows supplemented with natural vitamin E, the proportion of RRR-α-tocopherol in plasma and milk constituted more than 98% of the total α-tocopherol. In conclusion, the results indicate that daily oral supplementation of dairy cows with RRR-α-tocopheryl acetate gives the highest blood concentrations of α-tocopherol in the periparturient period. Analyses of the distribution of the individual stereoisomers of α-tocopherol further indicate that the bioavailability of RRR-α-tocopherol relative to synthetic stereoisomers in cattle is considerably higher than officially accepted until now.

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47

Luong, Thanh-Truc, Guylain Boulay, and Gaétan Guillemette. "Study on the stereoselectivity of Inositol 1,4,5-trisphosphate recognition sites of bovine adrenal cortex." Canadian Journal of Physiology and Pharmacology 70, no. 4 (April 1, 1992): 434–41. http://dx.doi.org/10.1139/y92-055.

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Inositol 1,4,5-trisphosphate (InsP3) is an intracellular messenger generated from the hydrolysis of phosphatidylinositol 4,5-bisphosphate by phospholipase C in response to Ca2+-mobilizing stimuli. InsP3 interacts with a specific receptor responsible for the release of sequestered Ca2+ from an intracellular store. The purpose of the present study was to evaluate the relative affinities of the naturally occurring D-isomer of InsP3 and that of its L-stereoisomer for the InsP3 receptor and the InsP3 metabolizing enzymes from bovine adrenal cortex. The InsP3 receptor recognized D- and L-isomers with respective affinities of 4.8 nM and 7.3 μM. This high degree of selectivity was also reflected in the capacity of both isomers to mobilize Ca2+ from the microsomal preparation. The partially purified InsP3 kinase preparation was also able to discriminate between the two stereoisomers. The activity of the kinase was half-maximally inhibited in the presence of 11 μM L-InsP3, a value much higher than the Km of the kinase for D-InsP3 (0.4 μM). Both stereoisomers exhibited equipotent affinities (around 17 μM) for the particulate preparation of InsP3 phosphatase. The enzyme, however, appeared to hydrolyze L-InsP3 at a much slower rate. These results demonstrated that the different recognition sites for InsP3 were expressing distinct levels of stereoselectivity. This property, which is an important aspect of ligand – receptor interaction, could be exploited for the design of new selective drugs interfering with InsP3 action and metabolism.Key words: inositol 1,4,5-trisphosphate (InsP3), InsP3 kinase, InsP3 phosphatase, InsP3 receptor, stereoselectivity, Ca2+ mobilization, adrenal cortex.

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48

Mosandl, Armin, Uwe Hener, and Heinz-Dieter Fenske. "Stereoisomere Aromastoffe, XXXI Tetrahydro-2-methylthiophen-3-ol - Struktur und Eigenschaften der Stereoisomeren." Liebigs Annalen der Chemie 1989, no. 9 (September 13, 1989): 859–62. http://dx.doi.org/10.1002/jlac.198919890237.

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Diukendjieva, Antonia, Merilin Al Sharif, Petko Alov, Tania Pencheva, Ivanka Tsakovska, and Ilza Pajeva. "ADME/Tox Properties and Biochemical Interactions of Silybin Congeners: In silico Study." Natural Product Communications 12, no. 2 (February 2017): 1934578X1701200. http://dx.doi.org/10.1177/1934578x1701200208.

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Silymarin, the active constituent of Silybum marianum (milk thistle), and its main component, silybin, are products with well-known hepatoprotective, cytoprotective, antioxidant, and chemopreventative properties. Despite substantial in vitro and in vivo investigations of these flavonolignans, their mechanisms of action and potential toxic effects are not fully defined. In this study we explored important ADME/Tox properties and biochemical interactions of selected flavonolignans using in silico methods. A quantitative structure–activity relationship (QSAR) model based on data from a parallel artificial membrane permeability assay (PAMPA) was used to estimate bioavailability after oral administration. Toxic effects and metabolic transformations were predicted using the knowledge-based expert systems Derek Nexus and Meteor Nexus (Lhasa Ltd). Potential estrogenic activity of the studied silybin congeners was outlined. To address further the stereospecificity of this effect the stereoisomeric forms of silybin were docked into the ligand-binding domain of the human estrogen receptor alpha (ERα) (MOE software, CCG). According to our results both stereoisomers can be accommodated into the ERα active site, but different poses and interactions were observed for silybin A and silybin B.

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Janeba, Zlatko, Antonín Holý, Hana Votavová, and Milena Masojídková. "Intramolecular Cyclization of Some Acyclic Nucleoside Analogs." Collection of Czechoslovak Chemical Communications 61, no. 3 (1996): 442–57. http://dx.doi.org/10.1135/cccc19960442.

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Reaction of stereoisomeric 8-bromo-9-(2,3-O-isopropylidene-2,3,4-trihydroxybutyl)adenines (8) with concentrated aqueous ammonia, sodium hydride, potassium tert-butoxide, or 1,8-diazabicyclo[5,4,0]undec-7-ene afforded 4e-O,8-anhydro-9-(2,3-O-isopropylidene-2,3,4-trihydroxybutyl)adenines 9 (derivatives of 1,3-oxazepino[2,3-e]adenine). The CD spectra of optically active stereoisomers of 9 have been studied and it was found that for threo isomers 9a and 9b their character corresponds to 5'-O,8-cycloadenosine. The compounds 9 were also prepared by oxidative cyclization of 9-(2,3-O-isopropylidene-2,3,4-trihydroxybutyl)adenines (7) with lead(IV) acetate in benzene. Reaction of 9-(4-hydroxybutyl)adenine (14) with lead(IV) acetate smoothly afforded the seven-membered ring derivative, 4'-O,8-anhydro-9-(4-hydroxybutyl)adenine (15); no anhydro products with five-, six-, and eight-membered ring were found. 2',3'-O-Isopropylideneinosine (16) reacted with lead(IV) acetate to give 5'-O,8-cyclo-2',3'-O-isopropylideneinosine (17) whereas 9-(4-hydroxybutyl)hypoxanthine (18) afforded no cyclic products.

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Journal articles on the topic 'Stereoisomeri'

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