Academic literature on the topic 'Amidation reactions'

Owing to the inherent ability of amides to chelate transition-metal catalysts, amide-directed C–H activation reactions constitute a major tactic in directed C–H activation reactions. While the conventional procedures for these reactions usually involve prior preparation and purification of amide substrates before the C–H activation, the step economy is actually undermined by the operation of installing the directing group (DG) and related substrate purification. In this context, directed C–H activation via in situ amidation of the crude material provides a new protocol that can significantly enhance the step economy of amide-directed C–H activation. In this short review, the advances in C–H bond activation reactions mediated or initiated by in situ amidation are summarized and analyzed.1 Introduction2 In Situ Amidation in Aryl C–H Bond Activation3 In Situ Amidation in Alkyl C–H Bond Activation4 Annulation Reactions via Amidation-Mediated C–H Activation5 Remote C–H Activation Mediated by Amidation6 Conclusion

AbstractDetailed theoretical studies of azide/thioacid amidation are performed using density functional theory. The calculated results indicate that electronic properties of azide have significant effects on reaction pathways, which result in two distinct mechanisms for electron-rich and electron-poor azide coupling in the base-promoted amidation. For electron-rich azide amidation, after the concerted [3+2] cycloaddition of azide/thiocarboxylate, a new reaction channel is found challenging that recently mentioned, which follows two consecutive, unimolecular reactions with very low activation barriers (−1) to give an anionic amide and a nitrous sulfide (N2S). Distinct from electron-rich azide amidation, electron-poor azide first couples with thiocarboxylate to form a linear stable adduct, and then passes through the transition state of the rate-controlling step to afford the anionic amide, rather than the thiatrazoline. The free energy barrier of this step is 4.2 kcal mol−1 lower than that previously proposed. Comparatively, the azide/thioacid amidations undergo the concerted [3+2] cycloaddition and the subsequent retro-[3+2] cycloaddition process to give cis-enol form of the amide, which have higher activation barriers than those in the based-promoted amidation. Solvent effects investigated indicate that non-polar solvents, such as chloroform, are more preferable for the base-promoted thioacid/azide amidation.

Eight bis(amidato) rare-earth metal amides were successfully synthesized and well characterized, which exhibited high catalytic activities in both the direct amidation of aldehydes and the addition of amines with carbodiimine.

Reactions applying amidation- or esterification-type processes and diazonium salts chemistry constitute the most commonly applied synthetic approaches for the modification of graphene-family materials. This work presents a critical assessment of the amidation and esterification methodologies reported in the recent literature, as well as a discussion of the reactions that apply diazonium salts. Common misunderstandings from the reported covalent functionalization methods are discussed, and a direct link between the reaction mechanisms and the basic principles of organic chemistry is taken into special consideration.

Nickel catalysis has shown remarkable potential in amide C–N bond activation and functionalization. Particularly for the transformation between ester and amide, nickel catalysis has realized both the forward (ester to amide) and reverse (amide to ester) reactions, allowing a powerful approach for the ester and amide synthesis. Based on density functional theory (DFT) calculations, we explored the mechanism and thermodynamics of Ni/IPr-catalyzed amidation with both aromatic and aliphatic esters. The reaction follows the general cross-coupling mechanism, involving sequential oxidative addition, proton transfer, and reductive elimination. The calculations indicated the reversible nature of amidation, which highlights the importance of reaction thermodynamics in related reaction designs. To shed light on the control of thermodynamics, we also investigated the thermodynamic free energy changes of amidation with a series of esters and amides.

AbstractSialic acids occur ubiquitously throughout vertebrate glycomes and often endcap glycans in either α2,3- or α2,6-linkage with diverse biological roles. Linkage-specific sialic acid characterization is increasingly performed by mass spectrometry, aided by differential sialic acid derivatization to discriminate between linkage isomers. Typically, during the first step of such derivatization reactions, in the presence of a carboxyl group activator and a catalyst, α2,3-linked sialic acids condense with the subterminal monosaccharides to form lactones, while α2,6-linked sialic acids form amide or ester derivatives. In a second step, the lactones are converted into amide derivatives. Notably, the structure and role of the lactone intermediates in the reported reactions remained ambiguous, leaving it unclear to which extent the amidation of α2,3-linked sialic acids depended on direct aminolysis of the lactone, rather than lactone hydrolysis and subsequent amidation. In this report, we used mass spectrometry to unravel the role of the lactone intermediate in the amidation of α2,3-linked sialic acids by applying controlled reaction conditions on simple and complex glycan standards. The results unambiguously show that in common sialic acid derivatization protocols prior lactone formation is a prerequisite for the efficient, linkage-specific amidation of α2,3-linked sialic acids, which proceeds predominantly via direct aminolysis. Furthermore, nuclear magnetic resonance spectroscopy confirmed that exclusively the C2 lactone intermediate is formed on a sialyllactose standard. These insights allow a more rationalized method development for linkage-specific sialic derivatization in the future.

There is still no exact mathematical model or control system for sodium sulphacyl production, so not all available control systems are accurate and not all possible disturbances of the system during operation have been identified. An urgent problem is to create an optimal mathematical model and use it as the basis for the synthesis of an amidator control system using a controller. In creating a mathematical model for the synthesis of the control system for the amidation process, it is necessary to understand the component of its mechanism. The amidation reaction takes place with a significant heat release, as well as through the available catalyst in the amidator, and side reactions occur. Using static and dynamic characteristics, a mathematical model was created, from which a control system was developed using a PID controller. After a mathematical model has been developed, it becomes clear that the amidator must be cooled constantly for its correct operation, because the lower the temperature of the amide at the outlet, the better the product. The temperature must be maintained at a level of 324K to 327K with water supply for cooling at 19-20 kg/s. The implemented automatic process control allows the production capacity to be managed at minimal cost. The PID controller, which is configured according to the formula of the transfer function of the amidator and the transport delay link, was selected as the main controller. The controller used includes two components: integral and differential. The synthesis of the control system based on the PID controller made it possible to fully investigate the process taking into account the disturbances, which were still uncertain, increased the rate of reaching a steady level, and reduced production costs.

This thesis describes the further development of a borate ester, B(OCH2CF3)3, as a reagent for amidation with a focus on carboxylic acids, including N-protected amino acids, and on the amidation of unprotected amino acids. In addition, a novel methodology for the determination of enantiomeric ratio in chiral amines is reported. The B(OCH2CF3)3-mediated direct amidation of carboxylic acids furnishes the amide product in generally excellent yield (A). A formylation method using DMF as the formyl donor was also developed (B). The B(OCH2CF3)3-mediated amidation method allows the amidation of α-chiral acids (for example, N-protected amino acids) in good yield with excellent retention of enantiopurity (C). Importantly, a solid-phase work-up procedure was developed which enables the purification of all of these amide products without the need for column chromatography or aqueous work-up. The application of B(OCH2CF3)3 to the amidation of unprotected amino acids is described (D). This covers an optimisation study and an investigation into the scope of the reaction. As a result of this study a new method for the determination of enantiomeric purity of chiral amines was developed. Using an aldehyde derived from lactic acid the enantiopurity of chiral amines can be determined by NMR, circumventing the need for chiral HPLC. Additionally, a mechanistic study of the direct amidation reaction is discussed. A reaction intermediate as well as a tentative mechanism are proposed based on the results of this mechanistic study and preliminary experimental evidence.

This thesis discusses the study and further developments of boron-mediated amidation reactions. Chapter I introduces the conventional and recent methods and developments for the direct amidation of carboxylic acids and their derivatives. An overview of boron-mediated transformations is also given with the focus on stoichiometric methods and boronic acid catalysts. Chapter II describes the utilisation of B(OCH2CF3)3 in the synthesis of medicinally-relevant amides, selective monoacylation of symmetrical diamines, and amidation of unprotected amino acids. Design of Experiments (DoE) is applied as the optimisation method for the improvement of efficiency of the amidation reaction and therefore the yield of one of the medicinally relevant amides. Furthermore, a convenient derivatisation method of amino amide products is applied to determine enantiopurity of the products. Chapter III discusses investigations performed with the aim of understanding boron-mediated amidation reactions. A spectroscopic study is provided along with the proposed tentative mechanism. Chapter IV describes the design and synthesis of a potential boronic acid amidation catalyst, which incorporates a borate moiety. Conclusions and future developments as well as an outlook of the applications of borates in organic synthesis are described in Chapter V. Chapter VI provides experimental details of this work and full characterisation of compounds synthesised throughout this project. Chapter VII contains an appendix that includes chiral HPLC and spectroscopic data from Marfey’s reagent derivatisation of chiral amino acid amide products. Moreover, spectra from 11B NMR study of boron-mediated amidations and the DoE study for the optimisation of decarboxylation of amino acids are included.

This thesis describes the investigation of various amino acids derivatives as reagents for copper-catalyzed, silver-catalyzed and iron-catalyzed reactions and the investigation of an enantioselective cobalt-catalyzed aldehyde-alkyne-amine (A3) coupling reaction. The first part focuses on the large-scale optimization of the oxidative amidation of aldehydes in the presence of amine hydrochloride salts as well as our effort to enhance the reaction scope by the use of amino acids derivatives and short peptides. This is then followed by the development of an enantioselective cobalt-catalyzed A3-coupling using binaphthol ligands as a source of chirality. Finally, the last part involves silver-catalyzed alkyne addition to iminoesters as well as silver-catalyzed A3-coupling.
La présente thèse a pour but de présenter l'utilisation de divers dérivés d'acides aminés comme substrats pour plusieurs réactions catalysées par des sels de cuivre, d'argent et de fer, de même que du développement d'une réaction de couplage énantiosélective entre aldéhyde, alcyne et amine (A3) catalysée par des sels de cobalt. La première partie met l'emphase sur l'optimisation à grande échelle d'un procédé d'amidation oxydative d'aldéhydes en présence de sels d'amine ainsi que nos efforts pour adapter cette méthode à des substrats tels que courts peptides et dérivés d'acides aminés. Cela est suivi par le développement d'une réaction de couplage énantiosélective entre aldehyde, alcyne et amine (A3) catalysée par des sels de cobalt misant sur l'utilisation de binaphtols comme ligands chiraux. La dernière partie porte sur l'addition d'alcyne à des iminoesters catalysés par des sels d'argent ainsi que sur des réactions de couplage A3, elles aussi catalysées par des sels d'argent.

Les amides perfluores et mixtes (a doubles chaines hydrogenee et perfluoree) sont des precurseurs de tensioactifs susceptibles d'ameliorer les proprietes des mousses extinctrices, par diminution de la tension interfaciale entre l'eau et l'huile par un meilleur etalement de la mousse. Ces amides sont synthetises par photoamidation d'olefines : r::(f)-ch=ch::(2), r::(f)-ch=ch-r::(h), r::(f)-ch::(2)-ch=ch-r::(h) dans le t-butanol et dans des microemulsions de formamide

The thesis entitled “Design and Development of Synthetic Methods using Metal-mediated and Metal-free Redox Reactions: Novel C-H Activations, Reductions and Oxidative Transformations” is presented in 4 chapters Chapter 1; Iodine catalyzed amination of benzoxazoles: efficient metal free route to 2-aminobenzoxazoles under mild conditions. The Chapter 1 of this thesis describes iodine catalyzed C-H activation of benzoxazole with primary and secondary amines to form oxidative aminated products. Selective C-H oxidation is a frontline area of modern chemical research as it offers the opportunities to new avenues and more direct synthetic strategies for the synthesis of complex organic molecules.1 In this context, transition metals such as palladium copper, nickel etc, are used extensively for the functional group directed C-H activation, and thus provides new, rapid, low-cost, and environmentally benign protocols for the construction of new chemical bonds.2 During the past two decades iodine and hypervalent iodine have been focus of great attention as they provide mild, chemoselective and environmentally benign strategies in contrast to toxic metal oxidants.3 In this chapter, a facile metal-free route of oxidative amination of benzoxazole with secondary or primary amines in the presence of catalytic amount of iodine (5 mol%) in aq tert-butyl hydroperoxide (1equiv) and AcOH (1.1 equiv) at ambient temperature, under the solvent-free reaction condition is presented. This user-friendly method to form C-N bonds produces tert-butanol and water as the by-products, which are environmentally benign. A wide range of benzoxazole derivatives containing electron-donating and electron-withdrawing groups were coupled with both primary and secondary amines (Scheme 1). Application of this methodology is demonstrated by synthesizing therapeutically active benzoxazoles by reacting 5-chloro-7-methylbenzoxazole with N-methylpiperazine and N-ethylhomopiperazine to obtain corresponding N-aminatedbenzaxozoles, which exhibit antidiarrhetic activity (Scheme 2).4 Scheme 2 Chapter 2: NIS catalyzed reactions. amidation of acetophenones and oxidative amination of propiophenones Chapter 2 is divided in to 2 parts. Part 1 describes the synthesis of α-ketoamides by using acetophenone and secondary amine in the presence of N-iodosuccinamide and TBHP in acetonitrile at room temperature, whereas Part 2 reveals the synthesis of 2-aminoketones by reacting aryl alkyl ketones and suitable secondary amine in the presence of NIS and TBHP. Part 1: Oxidative amidation, synthesis of α-ketoamide: Alpha α-ketoamides are important intermediates in organic synthesis that are present in a variety of natural products, and pharmaceutically active compounds. Herein, a mild and efficient conversion of acetophenones to α-ketoamide is documented by using aq.TBHP and N-iodosuccinamide (NIS) as a catalyst, at ambient temperature. This amidation reaction was found to be versatile as several aetophenone derivitives containing electron-withdrawing and electron-donating substituents underwent a facile amidation. It was also found that acetyl derivatives of heterocylic compounds could be easily converted to their corresponding ketoamides (few examples are shown in Scheme 3).5 Scheme3 Part 2 of Chapter 2 narrates a novel amination of propiophenone and its derivatives catalysed by NIS in the presence of TBHP to furnish their corresponding 2-aminoketone derivatives (Scheme 4). These derivatives are ubiquitous scaffolds that are present in a wide variety of therapeutic agents. Some of these compounds are used in the treatment of depression, smoking cessation, as monoamine uptake inhibitors, rugs for cancer. They are photoinitiators, precursors to β-aminoalcohols, such as pseudoephedrine analogues. 2-Aminoacetophenone analogues are also important intermediates for the formation of several heterocyclic compounds and are active moieties in several important drugs such as ifenprodil, Scheme 4. Chapter 3: Efficient oxidation of primary azides to nitriles This Chapter is divided in to 2 parts, which presents the oxidation of primary azides to their corresponding nitriles. Part 1: An Efficient oxidation of primary azides catalyzed by copper iodide: a convenient method for the synthesis of nitriles In Part 1, an efficient oxidation of primary azides catalyzed by copper iodide to their corresponding nitriles is reported. Herein, the oxidation of primary azide to nitrile is performed using catalytic amount of copper iodide, and aq TBHP in water at 100 ° C. This methodology is compatible with a wide range of primary benzylic azides that contain electron-donating and electron-withdrawing functional groups. The oxidation was found to be selective and a number of oxidizable functional groups were well-tolerated during the reaction conditions (few examples are shown in Scheme 5).6 Scheme 6 Furthermore, oxidation of secondary azides furnished the corresponding ketones in excellent yields (Scheme 6).6 In the Part 2 of Chapter 3, a non-metal catalysed oxidation of primary azides to nitriles at ambient temperature is reported. This part reveals the oxidation of primary azides to nitriles by employing catalytic amounts of KI (25 mol%), DABCO (25 mol%) and aq. TBHP (3 equiv., 70% solution in water). This reaction provides a good selectivity, as double and triple bonds were not oxidized under the reaction conditions. Additionally, chemoselective oxidation of benzylicazides against aliphatic azides increases the potential application of the present method (Scheme 7).7 Chapter 4: Chemoeselective reduction of olefins Part 1: Iron chloride catalysed aerobic reduction of olefins using aqueous hydrazine at ambient temperature Chapter 4 describes the reduction olefins and acetylenes, which is presented in two Parts. Part 1 documents utility of hydrazine (1.5 equiv) for the chemoselective reduction of nonpolarised carbon-carbon bond using iron catalysts. In this part, a chemoselective reduction of alkenes and alkynes in the presence of a variety of reducible functional groups is demonstrated (Scheme 8). The highlight of the present method is that the reduction proceeds well at room temperature and requires only 1.5 equiv of hydrazine hydrate. The olefin reduction by hydrazine depends upon the controlled release of diimide during the reduction. Generally, metal catalyzed reduction of olefins employ a large excess of hydrazine (10-20 equiv), which might be attributed to uncontrolled release of diimide during the reduction.8 Scheme 8 Part 2: Guanidine catalyzed aerobic reduction: a selective aerobic hydrogenation of olefins using aqueous hydrazine In Chapter 4, part 2, organocatalytic generation of diimide and its utility to reduce the double bonds is presented. Generation of diimide in situ by using organo catalysts and its use for the reduction of carbon-carbon double bond is one of the interesting topics in organic chemistry. It has been shown in this part of the thesis that the reduction of olefin at room temperature can be efficiently performed by using 10 mol% of guanidine nitrate, 2 equiv of aqueous hydrazine in oxygen atmosphere. This method tolerates a variety of reducible functional groups such as nitro, azido, and bromo and protective groups such as methyl ethers, benzyl ethers, and Cbz groups. It is also shown that terminal olefin can be selectively reduced in the presence of internal olefin (Scheme 9). Unlike other methods that employ diimide strategy, the present method is shown to be efficient in reducing substrates those contain internal double bonds such as cinnamyl alcohol and its derivatives

Reported herein is a brief summary of the history, properties, and applications of amine-boranes. The past methods devised for their preparation are described and the routes used to produce the compounds used in the work presented here are detailed. Building on prior synthetic approaches to amine-boranes, a new carbon dioxide mediated synthesis is presented. Proceeding through a monoacyloxyborane intermediate, the borane complexes of ammonia, primary, secondary, tertiary, and heteroaromatic amine are provided in 53-99% yields. Utilizing the amine-boranes obtained from the methods described, two divergent methods for direct amidation are introduced. The first uses amine-boranes as dual-purpose reagents, where the carboxylic acid is first activated by the borane moiety to form a triacyloxyborane-amine complex. This allows the delivery of the coordinated amine to form the amide products. A series of primary, secondary, and tertiary amides were prepared in 55-99% yields using this protocol, which displays a broad functional group tolerance. Extended from this dual-purpose methodology, a catalytic amidation is described. Utilizing ammonia-borane as a substoichiometric (10%) catalyst, a series of secondary and tertiary amide are prepared directly from carboxylic acids and amines in 59-99% yields, including amines containing typically borane reactive functionalities including alcohols, thiols, and alkenes. Amine-boranes are additionally used in two borylation methodologies. By reaction with n-butyl lithium, the amine-boranes are converted to the corresponding lithium aminoborohydrides, which upon reaction with a terminal alkyne provides the alkynyl borane-amine complexes in 65-98% yields. This process is compatible with both alkenes and internal alkynes, as well as a range of aprotic functionalities. A new strategy for aminoborane synthesis is also described and applied to the borylation of haloarenes. Activation of a series of amine-boranes with iodine produces the iodinated amine-borane, which undergoes dehydrohalogenation with an appropriate base to produce either monomeric or dimeric aminoboranes. Several aminoboranes were synthesized exclusively as the monomeric species, which due to their greater reactivity, were used directly in the synthesis of a series of aryl boronates in 65-99% yields.

Dendrimers are highly branched macromolecules with unique structural properties. They may be thought of as core–shell type macromolecules wherein they amplify their mass and terminal groups as a function of growth stages. These growth stages are referred to as generations (i.e. G= 0, 1, 2, . . .). They possess three key architectural features: (i) a core region; (ii) interior shell zones containing cascading tiers of branch cells (generations) with radial connectivity to the initiator core; and (iii) an exterior or surface region of terminal moieties attached to the outermost generation. With this architecture, a careful choice of building blocks and functional groups can provide control over shape, dimensions, density, polarity, reactivity, and solubility. One of the earlier dendrimers made, using a divergent strategy, is the Starburst® poly(amidoamine) (PAMAM) dendrimer family (Scheme 1). This method involved assembling repeat units to introduce branch cells around the initiator core through successive chemical reactions at the periphery of the growing macromolecule. The first step of PAMAM synthesis involves Michael addition of four moles of methyl acrylate to the nucleophilic ethylenediamine core. This leads to an electrophilic carbomethoxy surface, which is then allowed to react with an excess of 1,2-diaminoethane to give a nucleophilic surface at generation zero. Reiteration of these two steps now involves addition of 8 mol of methyl acrylate to give G = 0.5 (electrophilic, carbomethoxy surface). This is followed by amidation to return to a nucleophilic surface at G = 1.0. As a result of this reiterative branch cell assembly, it is apparent that these constructions follow systematic dendritic branching rules, with radial symmetry giving a well-defined three-dimensional geometry to the final dendritic product. In general, the placement of reactive functionalities on the exterior surface of the dendrimers allows introduction of a wide variety of terminal moieties. In alternate synthetic approaches, spacer groups have been deliberately introduced to relieve the steric hindrance in order to facilitate construction of the next generation. This may provide the possibility of enhancing interior cargo spaces for ‘guest–host’ type chemistry.

Glenn M. Samm is at the University of British Columbia reported (Angew. Chem. Int. Ed. 2012, 51, 10804) the photofluorodecarboxylation of aryloxyacids such as 1 using Selectfluor 2. Jean-François Paquin at the Université Laval found (Org. Lett. 2012, 14, 5428) that the halogenation of alcohols (e.g., 4 to 5) could be achieved with [Et2NSF2]BF4 (XtalFluor-E) in the presence of the appropriate tetraethylammonium halide. A method for the reductive bromination of carboxylic acid 6 to bromide 7 was developed (Org. Lett. 2012, 14, 4842) by Norio Sakai at the Tokyo University of Science. Professor Sakai also reported (Org. Lett. 2012, 14, 4366) a related method for the reductive coupling of acid 8 with octanethiol to produce thioether 9. The esterification of primary alcohols in water-containing solvent was achieved (Org. Lett. 2012, 14, 4910) by Michio Kurosu at the University of Tennessee Health Science Center using the reagent 11, such as in the conversion of alcohol 10 to produce 12 in high yield. Hosahudya N. Gopi discovered (Chem. Commun. 2012, 48, 7085) that the conversion of thioacid 13 to amide 14 was rapidly promoted by CuSO4. A ruthenium-catalyzed dehydrative amidation procedure using azides and alcohols, such as the reaction of 15 with phenylethanol to produce 16, was reported (Org. Lett. 2012, 14, 6028) by Soon Hyeok Hong at Seoul National University. An alternative oxidative amidation was developed (Tetrahedron Lett. 2012, 53, 6479) by Chengjian Zhu at Nanjing University and the Shanghai Institute of Organic Chemistry who utilized catalytic tetrabutylammonium iodide and disubstituted formamides to convert alcohols such as 17 to amides 18. A redox catalysis strategy was developed (Angew. Chem. Int. Ed. 2012, 51, 12036) by Brandon L. Ashfeld at Notre Dame for the triphenylphosphine-catalyzed Staudinger ligation of carboxylic acid 19 to furnish amide 20. For direct catalytic amidation of carboxylic acids and amines such as in the conversion of 21 to 23, Dennis G. Hall at the University of Alberta reported (J. Org. Chem. 2012, 77, 8386) that the boronic acid 22 was a highly effective catalyst that operated at room temperature.

Chaozhong Li of the Shanghai Institute of Organic Chemistry reported (J. Am. Chem. Soc. 2012, 134, 10401) the silver nitrate catalyzed decarboxylative fluorination of carboxylic acids, which shows interesting chemoselectivity in substrates such as 1. A related decarboxylative chlorination was also reported by Li (J. Am. Chem. Soc. 2012, 134, 4258). Masahito Ochiai at the University of Tokushima has developed (Chem. Commun. 2012, 48, 982) an iodobenzene-catalyzed Hofmann rearrangement (e.g., 3 to 4) that proceeds via hypervalent iodine intermediates. The dehydrating agent T3P (propylphosphonic anhydride), an increasingly popular reagent for acylation chemistry, has been used (Tetrahedron Lett. 2012, 53, 1406) by Vommina Sureshbabu at Bangalore University to convert amino or peptide acids such as 5 to the corresponding thioacids with sodium sulfide. Jianqing Li and co-workers at Bristol-Myers Squibb have shown (Org. Lett. 2012, 14, 214) that trimethylaluminum, which has long been known to effect the direct amidation of esters, can also achieve the direct coupling of acids and amines, such as in the preparation of amide 8. The propensity of severely hindered 2,2,6,6-tetramethylpiperidine (TMP) amides such as 9 to undergo solvolysis at room temperature has been shown (Angew. Chem. Int. Ed. 2012, 51, 548) by Guy Lloyd-Jones and Kevin Booker-Milburn at the University of Bristol. The reaction proceeds by way of the ketene and is enabled by sterically induced destabilization of the usual conformation that allows conjugation of the nitrogen lone pair with the carbonyl. Matthias Beller at Universität Rostock has found (Angew. Chem. Int. Ed. 2012, 51, 3905) that primary amides may be transamidated via copper(II) catalysis. The conditions are mild enough that an epimerization-prone amide such as 11 undergoes no observable racemization during conversion to amide 13. A photochemical transamidation has been achieved (Chem. Sci. 2012, 3, 405) by Christian Bochet at the University of Fribourg that utilizes 385-nm light to activate a dinitroindoline amide in the presence of amines such as 15, which produces the amide 16. Notably, photochemical cleavage of the Ddz protecting group occurs at a shorter wavelength of 300 nm.

The inhibitory reaction between plasmin and α2-plasmin inhibitor (α2-PI) proceeds with two steps, a very fast reversible reaction followed by a slower irreversible transition. The first step is dependent on the interaction between lysine binding site (LBS) of plasmin and the corresponding complementary site of α2-PI (kringle binding site(KBS)). It has been reported that KBS is located in a C-terminal tryptic fragment (T-11; J. Biochem. 99, 1699 (1986)).In order to investigate which amino acid residues of T-ll play important roles in binding of plasmin kringle, we tested inhibitory activity of synthesized peptides on the apparent rate constant in the reaction between α2-PI and plasmin. 50% inhibition concentrations of T-ll, peptide I, II, III and IV were 7, 18, 13, 35 and 250pM respectively, indicating that Leu9-Lysl0 is an important part for binding of T-ll to LBS. Peptide III lost its activity by depletion or amidation of the C-terminal lysine residue.In the system consisted of α2-PI and miniplasmin which lacked kringle 1-4, peptide I did not inhibit the interaction between them. Furthermore, peptide II competitively inhibited the binding of tranexamic acid to kringle 1-3 (Ki 0.85μM).These findings suggest that the C-terminal part is involved in the high affinity binding of α2-PI to plasmin kringle and that LyslO in T-ll and C-terminal carboxyl residue play crucial roles in binding to LBS of kringle.

Natural organic matter (NOM) plays an important role in the environment and its chemical properties and molecular composition reflect balance between mineralization and sequestration of organic carbon. Ultrahigh resolution mass spectrometry (e.g., FTICR MS) provides essential molecular information about NOM. However, NOM molecular heterogeneity prevents application of tandem MS experiments and direct structural information is ultimately missing leaving opportunities to only ambiguous formula-based annotation. The main aim of this work was to develop a chemical workflow to reliably examine the accuracy of several FTICR MS-derived structural indices with the focus on aromaticity and O-functional groups, which greatly impact compound properties. Four NOM samples of different origin (coal, oxidized lignin, river, and permafrost thaw) were brominated by NBS in acetonitrile for 24 hrs at RT. Carboxylic groups in all samples were determined by selective deuteromethylation using CD 3OD/SOCl2 reaction and by HATU amidation with 15N labeled glycine. Carbonyl groups were reduced by NaBD4. All parent and labeled mixtures were analyzed by ESI FTCR MS. Custom python scripts were developed to treat spectra and enumerate specific structural moieties in individual components. Obtained data was used to assess reliability of exact aromaticity indices (AI)1 and aromaticity equivalents (Xc) 2. Lignin- and coal-derived samples turned out to be the most sensitive to bromination which corroborated with the model phenolic structures. On contrary, permafrost thaw, which is enriched with labile species, was mostly resistant to bromination - 22% of molecular ions were brominated. Moreover, unlike oxidized riverine sample, coal NOM included polybrominated species, which implies that reaction efficiency depends on reactivity (i.e. substituents) of aromatic fragments. Samples were characterized by drastically different bromine distributions on van Krevelen diagrams, which correlated with the distribution of non-carboxylic oxygen atoms. Further, we compared AI and Xc aromaticity indices in terms of the proportion of correctly assigned aromatics. The data on brominated molecules were in good agreement with the AI values; however, apparently AI tends to overestimate the number of non-aromatics in the sample since it describe averaged aromaticity rather than the factual presence of aromatic ring. On the other hand, Xc perfectly recognized non-aromatics. In general, a higher proportion of correctly attributed aromatics was observed for the aromaticity equivalent Xc (up to 68%), which tends to find aromatic moieties in non-aromatic molecules assigned by AI. Still, we observed a number of aromatic- and condensed aromatic-assigned compounds, which were resistant to bromination or included lesser Br-atoms than the evaluated number of aromatic rings. Reaction with NaBD4 and enumeration of labeling series revealed the presence of carbonyl groups in these species, which in case of multiple reducing could be reliably assigned to quinone – condensed non-aromatic compounds. The approach may be of great importance in biogeochemical and medicinal studies of NOM. Acknowledgements. This work was supported by the Russian Science Foundation gran No 21-47-04405. References 1. Zherebker, A., Lechtenfeld, O. J., Sarycheva, A., Kostyukevich, Y., Kharybin, O., Fedoros, E. I. and Nikolaev, E. N. Anal. Chem., 2020, 92 (13), 9032-9038; 2. Yassine, M.M., Harir, M., Dabek-Zlotorzynska, E. and Schmitt-Kopplin, P. Rapid Commun. Mass Spectrom., 2014, 28, 2445-2454.