Dissertations / Theses on the topic 'Amino-carboxylic'

The coenzyme B12-dependent enzyme, glutamate mutase (E. C. 5.4.99.1), catalyses the reversible carbon-skeleton rearrangement of (2S)-glutamic acid to (25.35)-3-methylaspartic acid. Glutamate mutase is the first enzyme on the mesaconate pathway. A variety of glutamate and 3-methylaspartate analogues (which also include isotopically labelled molecules), were synthesised as molecular probes of the enzyme. Synthesis of stereospecifically labelled 3-ethylaspartic acid: (2S,3S)-[3'-C2H3], and (2S,3S)-[C2H2C2H3]-ethylaspartic acids were constructed using appropriately labelled iodoethane. (2S,3S)-2-Bromo-3-methylsuccinic acid was synthesised via the diazotization of (2S,3S)-3-methylaspartic acid, in the presence of bromide ion. (2S)-Methylsuccinic acid was synthesised by the catalytic hydrogenation of (2S,3S)-2-bromo-3-methylsucdnic acid. Biological studies of the synthesised compounds (including the labelled isotopomers) displayed no activity against glutamate mutase. 3-Methylaspartate ammonia-lyase, the second enzyme in the mesaconate pathway, catalyses the deamination of (2S,3S)-3-methylaspartic acid to mesaconic acid. A range of 1-substituted cyclopropane 1,2-dicarboxylic acids were synthesised using short efficient routes and were found to be good to potent inhibitors of 3-methylaspartase. X-ray crystallographic studies have determined the absolute stereochemistry. The mode of action of the most potent inhibitor, (1S,2S)-1-methylcyclopropane 1,2-dicarboxylic acid (20 mumol dm-3), is consistent with it acting as a transition state analogue for the central substrate deamination reaction catalysed by the enzyme. beta-Amino acids are constituents of many biologically active peptides. A general procedure for the synthesis of alpha-substituted-beta-amino acids has been developed. The synthesis involves a Baylis-Hillman amine catalysed conversion of methyl acrylate, with an appropriate aldehyde, to give the alpha-(hydroxyalkyl) acrylate. Bromination and subsequent azide displacement furnishes the azido alkene, which is catalytically hydrogenated, to furnish the beta-amino ester.

This thesis describes investigations into the synthesis and secondary structural properties of novel carbohydrate-derived peptidomimetics. The syntheses from diacetone-D-glucose of five diastereomeric 3-azido-tetrahydrofuran carboxylates are described. These highly functionalised β-amino acid equivalents are accessed via the diacetone-3-azido-3-deoxy sugars and 3-azido-3-deoxy-1,4-lactones. An acid-catalysed rearrangement results in the formation of the tetrahydrofuran ring with the protected amine functionality already in place in a position β- to the carboxylate group. Attempts to synthesise "carbopeptoids" via various oligomerisation strategies, including three novel approaches to oligomerisation, are delineated. The first approach attempted involves an iterative addition of a bicyclic lactone, which acts as the activated acid component, to the substrate containing an amine functionality. A new solid-phase oligomerisation strategy, whereby the coupling reagent is tethered to the polystyrene support and the substrates remain in solution, is described. The third attempted novel oligomerisation strategy involves activation by microwave irradiation, in the absence of coupling reagents. The conventional coupling using a carbodiimide coupling reagent proves to be a highly efficient means to access oligomers up to six residues in length, and is utilised for the synthesis of the homooligomers of four diastereomeric carbohydrate-derived β-amino acids. The prospect that the carbopeptoids may emulate the helical conformations reported for closely related 2-aminocyclopentanecarboxylic acid oligomers is investigated. Different methods of spectroscopic analysis of the tetrameric and hexameric oligomers are discussed. Circular dichroism spectroscopy provides a rapid diagnostic tool for the investigation of peptide bond orientations and forms the basis for a postulation on a possible stabilised hydrogen-bonding secondary structural conformation in two tetrameric species. Several nuclear magnetic resonance spectroscopic experiments are performed, enabling the assignment of each signal in the proton spectrum for a hexameric oligomer. However the resulting data does not provide sufficient evidence for a well-defined secondary structural motif, and so the potential conformational preference postulated on the basis of circular dichroism spectroscopy is not confirmed.

The amide unit constitutes the backbone of proteins, and it is present in a large number of pharmaceutically active molecules, polymeric materials such as nylon and Kevlar, as well as in food additives like aspartame. Amides are produced in enormous amounts every year, thus, environmentally friendly and selective methods for their formation are of great importance. This thesis deals with the direct formation of amides from non-activated carboxylic acids and amines with the aid of group (IV) metal complexes. Water is the only by-product of this environmentally benign process. This fact stands in contrast to the most common methods for amide formation to date, which involve the use of waste-intensive, expensive and often toxic coupling reagents. The catalytic protocols presented herein use titanium, zirconium and hafnium complexes under mild reaction conditions to produce amides in good to excellent yields. Furthermore, carbamates are demonstrated to be suitable sources of gaseous amines for the formation of primary and tertiary amides under catalytic conditions. In addition, preliminary results from on-going mechanistic investigations of the zirconium- and hafnium-catalyzed processes are presented.
Amidbindningen är en kemisk enhet som utgör ryggraden i proteiner, och som även återfinns i en stor mängd läkemedelsmolekyler, polymera material som nylon och Kevlar, samt i tillsatser i livsmedelsindustrin, exempelvis aspartam. Amider produceras i enorma mängder varje år, och det är av stor vikt att utveckla miljövänliga och selektiva metoder för deras framställning. Denna avhandling behandlar direkt amidering av icke-aktiverade karboxylsyror och aminer med hjälp av katalytiska mängder metallkomplex, baserade på titan, zirkonium och hafnium. Den enda biprodukten från denna amideringsreaktion är vatten. Jämfört med de metoder som generellt används idag för amidsyntes, så är de presenterade metoderna avsevärt mer miljövänliga med avseende på toxicitet hos reagensen såväl som på mängden avfall som genereras. Dessutom redovisas här en katalytisk metod för syntes av primära och tertiära amider genom att använda olika karbamat som källa till gasformiga aminer, vilka annars kan vara praktiskt svåra att arbeta med. Preliminära resultat från en pågående mekanistisk studie av de zirkonium- och hafnium-katalyserade processerna är också inkluderade.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Accepted.

We have described herein a convenient one-pot synthesis of lisulfides/diselenides from a-amino acids mediated by ammonium etrathiomolybdate in water. (Figure 1) (Figure) Figure 1 Transformation of α-amino acids into the corresponding tiiocyanates/selenocyanates/disulfides/diselenides Halo-de-amination of a-amino acids using HBr/NaNCte followed by treatment with ammonium tetrathiomolybdate (NH4)2]VloS4 jLb provided a general route for the the one-pot synthesis of chiral a,a' bis (dithio) carboxylic acids (Figure 1, 2b). The yields were moderate, limited mainly the moderate conversion of a-amino acids into the corresponding chiral a-bromides. It was possible to synthesize the 2-thiocyanto carboxylic acids from the corresponding a-amino acids by a similar strategy. Thus diazotization in the presence of KSCN yielded in the chiral 2-thiocyanto carboxylic acids in moderate yields (Figure 1, 3). Thiocyanato-de-amination thus afforded the thiocyanates which when treated with JJD provided the chiral disulfides (Figure 1, 4a). We could thus synthesize both enantiomers of the disulfide from a single enantiomer of the starting a-amino acid. (Figure 1, 4a,4b) Using a similar strategy we have also demonstrated an efficient method for the synthesis of chiral selenocyanates starting from a-amino acids, using selenocyanate anion as the nucleophile (Figure 1, 5). It is possible to demonstrate a one-pot synthesis of chiral diselenides by reductive coupling of selenocyanates using JJb. (Figure 1, 6) (for figure see the pdf file)

Chemistry
Ph.D.
In the study of structurally restricted cyclic β-amino acids and peptides, methanopyrrolidine-5-carboxylic acids (MetPyr-5-acids), or 5-syn-carboxy-2-azabicyclo[2.1.1] hexanes, and derivatives were investigated. MetPyr-5-acids are a series of highly conformationally constrained β-proline derivatives, which belong to a novel category of β-amino acids utilized as building blocks for the synthesis of β-peptides. These β-peptides lack the backbone hydrogen bonds necessary for folding in the usual manner. Substituents and functional groups in this ring system were envisioned to impact the folding properties and functionalities of the corresponding β-peptides. In the present study, the analogues of MetPyr-5-acids with C6- substitutions were prepared, and the folding properties of their peptides were explored. To introduce different functionalities at C6 in MetPyr-5-acids, 6-syn-hydroxymethyl substituted derivatives were synthesized and were used as key intermediates. In the synthesis of this core structure, the major steps in their preparation included the Michael addition of benzyloxymethyl allyl amine to 3-butynone, followed by UV light irradiation of the diene to afford 5-acetyl-6-benzyloxymethyl-2-azabicyclo[2.1.1]hexane. Haloform (Br2/NaOH) oxidation of the acetyl group leads to the 6-substituted MetPyr-5-acid. Resolution of the racemate was achieved either by resolving (±)-6-syn-benzyloxymethyl-MetPyr-5-acid via a classical crystallization resolution method using (S)-(-)-α-methylbenzylamine, or by chiral preparative HPLC separation of (±)-6-syn-benzyloxymethyl-MetPyr-5-acid methyl ester. The absolute stereochemistry was confirmed by X-ray crystallography of a derivative. Novel analogs with a range of functionalities incorporated at the C6 position in MetPyr-5-acid were synthesized from 6-syn-hydroxymethyl-MetPyr-5-acid methyl ester, and include hydrophilic groups such as hydroxyl, amino, methyl ether, and hydrophobic groups, such as substituted phenyl groups and triazole. From the protected C6-substituted analogs of MetPyr-5-acids, peptide oligomers of C6-benzyloxymethyl-2,4-methanopyrrolidine-b-amino acid were prepared up to the length of octomer in high yields. This series of oligomers were characterized by circular dichroism (CD) and indicated enhanced order of folding uniformity for the tetramer and up, with increasing ordered folding for longer oligomers. The octomer exhibited minimal solvent effects, and was stable with increasing temperature up to 80 °C. Analysis by NMR of the iso-butyric amide capped monomer indicated a mixture of cis/trans conformation favoring the cis conformation. This was slightly different from the C6 unsubstituted iso-butyric amide derivative, which favored the trans conformation. For the dipeptide, the C6-benzyloxymethyl substitution increased the percentage of cis conformation of the dipeptide amide bond, but the major peptide had the trans conformation. This demonstrated that C6 substitutions could shift the cis/trans equilibrium towards the cis conformation. Longer oligomers showed ordered secondary folding structure as demonstrated by the increase in ellipticity per amino acid unit, but was too complicated to be determined by NMR analysis. Both the CD patterns and molecular model calculation predicted that the longer oligomers (tetramer and above) favor the trans conformation. This preference was driven by the backbone dipole effect. II. SYNTHESIS OF 2,2-DISUBSTITUTED PYRROLIDINE-3-CARBOXYLIC ACIDS Due to the perceived steric influence of 2,2-disubstitution in the pyrrolidine-3-carboxylic acid, it is believed that the adjacent amide/peptide bonds should result in a trans amide bond conformation. Because of the difficulty in introducing disubstitution at the hindered C2 position, the synthesis of such derivatives has not been successful. For this reason a new method was introduced to prepare novel derivatives, at the N- and C- termini of protected 2,2-dimethyl pyrrolidine-3-carboxylic acid, i.e., benzyloxycarbonyl protected 2,2-dimethylpyrrolidine-3-carboxylate. This procedure included the Michael addition of 2-nitropropane to dimethyl fumarate, followed by ring closure of the amino ester derived from reduction of the nitro ester providing the pyrrolidinone. Reduction of the pyrrolidinone to the pyrrolidine with borane finished 2,2-dimethylpyrrolidine-3-carboxylate in moderate overall yield. A preliminary set of two amides, iso-butyric amide and 3,5-dichlorobenzamide of this 2,2-dimethylpyrrolidine-3-carboxylate, were also prepared. NMR analysis of this pyrrolidine derivative suggested the amide bonds adopted the trans conformation. It was concluded that steric bulk of the 2,2-disubstitution favorably influenced the trans amide conformation. This demonstrated that trans amide conformation control of a β-proline amide was possible.
Temple University--Theses

Trypanosoma cruzi é dependente de prolina para diversos processos tal como metabolismo energético, invasão celular, diferenciação e resistência a estresse osmótico, metabólico e oxidativo. O ácido L-tiazolidina-4-carboxílico (T4C), um análogo estrutural da prolina, inibe competitivamente o transporte deste aminoácido em T. cruzi, e interage sinergicamente com fatores de estresse que ocorrem ao longo do seu ciclo de vida. Aqui nós avaliamos o efeito de T4C na infecção de camundongos pelo T. cruzi. Foi observada uma redução de 49% do pico parasitêmico de animais infectados e tratados com dose única de T4C (100 mg/Kg). A análise histológica e por PCR quantitativa de diferentes tecidos revelou uma redução significativa da carga parasitária apenas no intestino de animais tratados com T4C (100 ou 150 mg/Kg). Por outro lado, a dose única de 200 mg/Kg diminuiu o peso corporal e sobrevida de animais não infectados. O tratamento prolongado (10 mg/Kg dia) não reduziu a parasitemia, mas aumentou a sobrevida e diminuiu a carga parasitária no intestino. T4C não afetou a expressão gênica de IFN-g e IL-10 em qualquer um dos tecidos analisados (coração, baço, intestino). Em conclusão, T4C contribui em reduzir a virulência da infecção, mas é tóxico em doses que superem 150 mg/kg.
Trypanosoma cruzi is dependent on proline for a variety of processes such as energy metabolism, host cell invasion, differentiation and resistance to osmotic, metabolic and oxidative stress. L-thiazolidine-4-carboxylic acid (T4C), a proline structural analogue, inhibits the proline uptake and interacts with several stress factors that the parasite undergoes throughout its life cycle. Herein, we evaluated the T4C effects on mice infection by T. cruzi. It was observed a reduction of 49% of the parasitemia peak in infected mice that were treated with a unique dose of T4C (100 mg/Kg). Histological and quantitative PCR analysis of several tissues revealed a significant reduction of parasite load in the intestine (100 or 150 mg/kg). In the other hand, the unique dose of 200 mg/Kg reduced the body weight and survival of non-infected mice. A T4C prolonged treatment (10 mg/Kg day), did not diminish the parasitemia, but increased survival and reduced the parasite load in the intestine. T4C did not affect the gene expression of g-IFN and IL-10 in any of the organs analyzed (heart, spleen, intestine). In conclusion, T4C-treatment contributes to reduce the virulence of T. cruzi infection, but it was toxic in doses over 150 mg/kg.

Les nuages représentent un milieu multiphasique complexe et réactif. Une grande partie de composés chimiques atmosphériques de la phase particulaire ou gazeuse se dissout dans les gouttelettes de nuage où peuvent subir des transformations chimiques, photochimiques et microbiologiques. L'eau de nuage a été échantillonnée à la station du puy de Dôme et caractérisée par des mesures physico-chimiques. La première partie de mon travail de thèse est focalisée sur la réactivité de l’eau du nuage. La formation d’espèces réactives, le radical hydroxyle, est étudiée par photolyse directe de sources inorganiques et photolyses nano-pulsée et sa vitesse de formation a été corrélée à la concentration de sources. Les propriétés spectroscopiques et la dégradation d'un composé modèle, l'acide tartronique, ont été étudiés. Les expériences faite par irradiation continue (photolyse directe et induite par le radical hydroxyle) et par photolyse pulsée ont permis de comprendre la réactivité de ce composé dans le milieu nuageux. La deuxième partie de mon travail est focalisée sur la caractérisation et la réactivité de la matière organique dans la phase aqueuse des nuages. La détection et la quantification de tryptophane par spectroscopie de fluorescence et l'étude de sa réactivité ainsi que la détection et quantification d‘acides aminés représente une partie importante de ce travail. Les acides aminés ont été détectés pour la première fois dans l'eau de nuage grâce à l'utilisation d'une méthode chromatographique de dérivation et détection par fluorescence. Ce travail à démontré que les acides aminés peuvent représenter entre 4 et 21 % de la concentration en carbone de la matière organique dissoute dans le nuage. La réactivité des acides aminés avec le radical hydroxyle a été comparée avec celle des acides carboxyliques et de la matière organique dissoute. Ce résultat montre clairement que le rôle des acides aminés comme piège de radicaux hydroxyles ne peut plus être négligé
Clouds represent a multiphase complex and reactive medium in which gases, liquid particles and aerosols are in continuous interaction. A large fraction of atmospheric chemical compounds present in the particulate and gaseous phases can be transferred to the cloud droplets where can undergo chemical, photochemical and microbiological transformations. Cloud waters were sampled at the puy de Dôme station. The first part of my PhD work is focused on the photoreactivity of cloud water. Formation of a reactive species such as hydroxyl radical, by direct photolysis of inorganic sources was investigated, as well as the correlation between the concentration of sources and the hydroxyl radical formation rate. The spectroscopic proprieties and fate of tartronic acid, were investigated under cloud water conditions. Moreover, photochemical experiments were performed using continuous irradiation (direct and hydroxyl radical mediated photolysis) and nanosecond flash photolysis in order to assess the reactivity of this compound in cloud aqueous phase. The second part of my work is centered on the characterization of organic matter in clouds. Two studies are presented: i) Detection and quantification of tryptophan by fluorescence spectroscopy and the assessment of its reactivity; ii) detection and quantification of amino acids. Amino acids are detected for the first time in cloud water using a derivatization method and this work show that they represent the 9% of the dissolved organic matter in cloud. Their reactivity with hydroxyl radical was compared to the reactivity of carboxylic acids and dissolved organic matter. These results clearly demonstrate that amino acids represent a major sink of hydroxyl radicals in cloud water

碩士
國立清華大學
化學系
102
A series of chiral oxidovanadium (V) methoxides were derived from 3,5-disubstituted-N-salicylidene α-amino carboxylic acids and tetrazoles. These complexes serve as enantioselective catalysts for asymmetric reduction and aldol reaction. We are the first group that used chiral vanadyl (V) complexes to study the asymmetric reduction. In this study, α-keto amides served as the best substrate class and methanol-modified pinacolborane served as the best reducing agent among five different reducing agents examined. With catalysts 1a (C3 = tBu, C5 = Br) and 1a’ (C3 = tBu, C5 = Br), up to 62% yield and 85% ee (R form) of the α-hydroxyamides were afforded at -20 oC in toluene. In the past five years, we have already found that chiral vanadyl (V) complexes derived from N-salicylidene α-amino carboxylic acids 1a and tetrazoles 11a (C3 = 2,5-dimethoxyphenyl, C5 = NO2) could achieve complementary asymmetric catalytic aldol processes in addition of silyl ketene acetals (SKA) to isatins at -40 oC in dichloromethane. Herein we further optimized these reactions in the case of 5-nitro-isatin by adding trichloroethanol to facilitate turnover, leading to the corresponding aldol product in moderate yield (61%) and good enantioselectivity (88% ee, S form) with catalyst 1a. Without any additives, using catalyst 11a could furnish a series of R form isatin adducts with up to 97% yield and 90% ee in a complementary manner. Molecular simulations of the adducts between these two catalysts and N-benzylisatin indicated that the preferred coordination mode involve in a facile π-π interaction between the N-benzyl moiety and N-salicylidene template of catalyst 1a to avoid concomitantly the steric hindrance of the C3 tert-butyl. On the other hand, another π-π interaction between the C3 2,5-dimethoxylphenyl group of catalyst 11a and the N-benzyl group of the isatin to avoid concomitantly the el-el repulsion with the tetrazole moiety is involved, leading to a complementary, enantiofacial exposure of the carbonyl moiety in the N-benzylisatin.

碩士
國立清華大學
化學系
104
We have developed a catalytic protocol for complementary enantioselective reduction of α-ketobenzylamide with pinacolborane and catecholborane catalyzed by chiral oxidovanadium (V) methoxides complexes derived from 3,5-disubstituted-N-salicylidene α-tert-leucinate. The catalysts 1a and its reduce form 1a' (C3 = t-Bu, C5 = Br) with pinacholborane afforded upto 62% yield and 84% (R-form) enantioselectivity, at −20 °C in toluene under Argon. However, asymmetric reduction with catecholborane provides complementary enantioselectivity upto 64% (S-form) and 99% yield. A series of α-ketobenzylamide substrates were examined, the substrates with small and planar α-keto functional groups can get better enantioselectivity. With pinacolborane, α-cinnamyl substituted system shows better enantioselectivity 93% (R-form) and 45% yield. While in the case of catecholborane, 2-thiophenyl case show better enantioselectivity 76% (S-form) and 89% yield. The complementary enantioselectivity can be explained by a plausible mechanism, in which the step is the chelation of carbonyl group of amide with vanadyl(V) center axially anti to vanadyl oxygen . In the next step, the methoxide chelates with bulky pinacholborane lead to a s-trans conformation of the α-ketoamide and directs the hydride transfer from Si-face. This results in the formation of R-isomer. Conversely, the π-π interaction between the catecholborane and substrate coordinates in an s-cis conformation instigate the hydride transfer from Re-face. This results in the formation of S-isomer.

碩士
朝陽科技大學
應用化學系碩士班
91
Abstract Due to dissimilarity of steric structure, the optically active medicines often result in the significant difference of pharmacology. This situation is gradually changing as number of companies have now stared to move towards producing enatiomerically pure forms. This proposal plans to develop one type of quinidine-derived chiral stationary phases (3,5-dinitrobenzoyl quinidine thiopropylsilanized silica ) which simultaneously possess the functions of aromatic π acid, aromatic π base and anion-exchanger. With this type of CSP, we plan to do enantioseparations of non-steroidal anti-inflammatory drugs and N-derivatized amino acids by high performance liquid chromatography. This CSP is used in HPLC with normal-phase mode and reversed-phase mode. In normal-phase mode, DNB-, DNP-derivatized amino acids and ascorbic acid are well separated. An example of 3,5-dintrobenzoyl leucine, the mobile phase was 100% methanol at a flow-rate of 1 ml/min and 240 nm wavelength of detection. The resolution(Rs) is 1.3. In reversed-phase mode, DNB-, DNP-derivatized amino acids and non-steroidal anti- inflammatory drugs are well separated. An example of 3,5-dintrobenzoyl leucine, the mobile phase is consisted of 2% 10 mM ammonium acetate (the mixture is adjusted with trifluoracetic acid to the pH = 4.5) and 98% methanol at a flow-rate of 1 ml/min and 240 nm wavelength of detection. This resolution is 2.5. This chiral column can enantioseparate several kinds of compound induding aromatic π acid, aromatic π base and ascorbic acid.

This thesis reports diverse synthetic and mechanistic studies in six chapters, as summarized below. Chapter 1. Revised mechanism and improved methodology for the perkin condensation.1 The generally accepted mechanism for the well-known Perkin condensation is unviable for at least two reasons: (1) the normally employed base, acetate ion, is too weak to deprotonate acetic anhydride (Ac2O, the substrate); and (2) even were Ac2O to be derprotonated , its anion would rapidly fragment to ketene and acetate ion at the high temperatures employed for the reaction. It has proved in this study that the Perkin condensation occurs most likely via the initial formation of a fem-diacetate (3, Scheme 1) from benzaldehyde (2) and acetic anhydride (1).1 The key nucleophile appears to be the enolate of 3 (and not of 1), which adds t the C=O group of the aldehyde 2 (present in equilibrium with 3). Thus cinnamic acid (4a) was formed in -75% yield with 3 as the substrate under the normal conditions of the Perkin reaction. The deprotonation of the diacetate appears to be electrophilically assisted by the neighbouring acetate group, the resulting enolate being also thermodynamically stabilized in form of an orthoester (I). The possibility that the diacetate 3 is the actual substrate in the Perkin reaction indicates that the reaction can be effected under far milder conditions, with a base much stronger than acetate ion. This was indeed realized with potassium t-butoxide in dioxane, which converted the gem-diacetates derived from a variety of aromatic aldehydes to the corresponding cinnamic acids (4), rapidly and in good yields at room temperature (Scheme 2). This represents a vast improvement in the synthetic protocol for the classical Perkin reaction, which remains an important carbon-carbon bond forming reaction to this day. Chapter 2. Aromaticity in azlactone anions and its sifnificance for the Erlenmeyer synthesis.2 The classical Erlenmeyer azlactone synthesis of amino acids occur via the formation of an intermediate azlactone, and its subsequent deprotonation by a relatively weak base(acetate ion),. The resulting azlactone anion (cf. II, Scheme 3) functions as a glycine enolate equilvalent, and is considered in situ with an aromatic aldehyde, subsequent dehydration leading to the 4-alkylidene oxazolone(analogously to the Perkin reaction). Interestingly, azlactone anions are possibly aromatic, as they possess 6π electrons in cyclic conjugation; this would explain their facile formation as also the overall success of the Erlenmeyer synthesis. The following studies evidence this possibility. The strategy involved studying the rates of base-catalyzed deprotonation in 2-phenyl-5(4H)-oxazolone (azlactone, 5) and its amide and ketone analogs, 3-methyl-2-phenyl-4(5H)-imidazolone (6), and 3,3-dimethyl-2-phenyl-493H)-pyrrolone (7) respectively.2 Two processes were studied, deuterium exchange and condensation with hexadeuteroacetone (Scheme3): both are presumably mediated by the anions II-IV, so their stabilities would govern the overall rates. These were followed by 1H NMR spectroscopy by monitoroing the disappearance of the resonance of the proton α to the carbonyl group. The order of deprotonation was found to be 6 > 5 > 7. However, the expected order based on pKa values would be ketone > ester > amide, i.e. 7 > 5 > 6. The inverted order observed strongly indicates the incursion of aromaticity, which would be enhanced by the electron-donor capabilities of the heteroatoms is 5 and 6. This is further substantiated by the greater reactivity in the case of the nitrogen analog 6 relative to the oxygen 5, which parallel the electronegativity order. (The aromaticity order would thus be: III > II > IV. The imidazole nucleus is indeed to be considerably more aromatic than the oxazole.) The synthesis of the analogs 6 and 7 was accomplished via an interesting intramolecular aza-Wittig reaction (Schemes 4 & 5) Chapter 3. Umpolung approach to the Erlenmeyer process in the synthesis of dehydro amino acids. These studies are based on the general observation that most of the strategies for the synthesis of α-amino acids introduce the side chain (or part was inverted in an umpolung sense. The key reaction studied was that of 2-phenyl-4-ethoxymethylne-5(4H)-oxazolone (11) with Grignard reagents: this resulted in the opening to yield a protected dehydro amino acid (12), in good to excellent yields (65-87%)(Scheme ^). As the azlactone reactant 11 is the ekectrophilic partner, this may be viewed as a partial umpolung version of the classical Erlenmeyer process. The readily available reactants, simple procedure and mild reaction conditions make this a very attractive method for the synthesis of a variety of α-dehydro amino acids. Chapter 4. The Erlenmeyer azlactone synthesis with aliphatic aldehydes under solvent-free microwave conditions. 3 A serious limitation to the classical Erlenmeyer reaction is that it generally fails in the case of aliphatic aldehydes. This chapter describes a convenient approach to this problem that extends the scope of the Erlenmeyer synthesis, via a novel microwave-induced, solvent-free process. This, it was observed that azlactones (5) react with aliphatic aldehydes (13) upon adsorption on neutral alumina and irradiation with microwaves (< 2 min), forming the corresponding Erlenmeyer products (14) in good yields (62-78%, Scheme 7). (The possible mechanistic basis of the procedure, which is presumably mediated by V , is discussed).3 Chapter 5. 2,4, 10-Trioxaadamantane as a carboxyl protecting group: application to the asymmetric synthesis of α-amino acids (umpolung approach).It is known that the 2,4,10-trioxaadamantane moiety is not only remarkably stable to nucleophilic attack, but can also be easily hydrolyzed to the corresponding carboxylic acid.4 It was of interest to apply this carboxyl protection strategy for designing a synthesis of α-amino acids, essentially by starting with a protected glyoxylic acid. The corresponding aldimine was expected to (nucleophilically) add organometallic reagents at the C=N moiety (cf. Shceme 8), the side chain of the amino acid being thus introduced in umpolung fashion. Also, a chiral aldimine would define an asymmetric synthesis of amino acids. Indeed, the chiral aldimine 17, derived from 2,4,10-troxaadamantane-3-carbaldehyde 15 and [(S)-(-)-1-phenylethylamine] 16, reacted with a variety of Grignard reagents to furnish the corresponding protected α-amino acids (18) in good yields, with moderate diastereometric excess (Scheme 8). Better yields and ‘de’ values were obtained with organolithium reagents. Chapter 6: possible one-pot oligopeptide synthesis with azlactones or amino acid N-carboxyanhydrides (NCAs). This chapter describes a novel approach to oligopeptide synthesis employing azlactones or NCA’s as amino acid equivalents which are simultaneously protected and activated (Scheme 9). Thus, the addition of the 4-substituted 2-benzyloxyazlactone (19) to an N-protected amino acid under basic conditions, was initially explored. The reaction was expected to yield a dipeptide (21) via the rearrangement of the mixed anhydride intermediate (VI) (Scheme 9). The subsequent addition of a different azlactone to the dipeptide (21) would analogously lead to the formation of a tripeptide (22). This may be performed repetitively to define a strategy for C-terminal extension of an oligopeptide chain, noting that no intervening deprotecting and activating steps are necessary. (In toto deprotection may be effected finally via the hydrogenolyis of the bvenzyloxy groups, to obtain 23.) A closely analogous strategy may also be envisaged by employing N.carboxyanhydrides (NCA’S, 24) instead of azlactones, as shown in Scheme 10 (forming dipeptide 26 and tripeptide 27). The main difference n this case is that the carbamic acid moiety of the intermediate mixed anhydride (VII) is expected to undergo decarboxylation to VIII (thus obviating the need for a deprotection step). However, this putative advantage is offset by the instability of NCA’s and their tendency toward polymerization. However, only partial success could be achieved in these attempts, although a variety of conditions were explored. The strategy and the experimental results have been analyzed in detail, as this interesting approach appears to be promising, and worth further study. (For structural formula pl refer the pdf file)