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A number of novel amides were synthesized by coupling of 6-[(9H-purin-6-yl)amino]hexanoic acid to heterocyclic amines. The antiviral activity of the obtained compounds, as well as of purine conjugates in which 7,8-difluoro-3-methyl-3,4-dihydro-2H-1,4-benzoxazine is linked to position 6 of purine through a fragment of ω-amino acids with varying lengths of polymethylene chains against influenza A and B viruses was studied in vitro. Purine derivatives have been shown to have moderate activity against influenza A (H1N1) virus. The antiinfluenza activity and cytotoxicity of conjugates with 7,8-difluoro-3-methyl-3,4-dihydro-2H-1,4-benzoxazine depend on the length of the linker fragment.

The deboronation of enantiomers of planar-chiral benzyl (3-formamido-1,2-dicarba-closo-dodecaboran-1-yl)acetate gave the individual (RP)- and (SP)-enantiomers (ee > 98%) of a new amino acid containing a nido-carborane fragment, (3-ammonio-7,8-dicarba-nido-undecaboran-7-yl)acetic acid. Chiral HPLC methods for the analysis of enantiomeric purity of this compound was developed.

A comparative study of the kinetic resolution of racemic 3-tert-butyl-3,4-dihydro-2H-[1,4]-benzoxazine through the acylation by various chiral acyl chlorides was carried out. A preparative method for obtaining enantiomerically pure (S)-3-tert-butyl-3,4-dihydro-2H-[1,4]benzoxazine can be based on the acylation with N-phthaloyl-(S)-phenylalanyl or (R)-2-phenoxypropionyl chlorides, followed by the acid hydrolysis of the corresponding diastereomerically pure amides.

The enantiomerically pure N- and C-protected derivatives of planar-chiral (3-amino-1,2-dicarba-closo-dodecaboran-1-yl)acetic acid (>99% ee) have first been obtained in good yields via a combination of HPLC separation and synthetic procedures. Assignment of absolute configuration of the carborane fragments has been made based on the X-ray diffraction data of diastereoisomeric derivatives of (S)-amino acids.

New (S)-homocysteine derivatives containing a meta-carborane fragment were synthesized. m-Carboranyl-(S)-homocysteine sulfoxide was obtained as a mixture of diastereoisomers. The reduction of the side-chain carboxy group of N-tert-butoxycarbonyl-(S)-aspartic acid α-tert-butyl ester with sodium tetrahydridoborate was not accompanied by racemization.

Reversed-phase HPLC on chiral stationary phases was used to study the influence of the structure of purine and 2-aminopurine conjugates with chiral heterocyclic amines on the retention times. The optimum conditions for separation of enantiomers were found. The best parameters of separation of stereoisomers of all the compounds examined were achieved on a (S,S)-Whelk-O1 column in weakly alkaline aqueous methanol systems.

The review summarizes the data published over the last 10 – 15 years concerning the key groups of purine derivatives with antituberculosis activity. The structures of purines containing heteroatoms (S, O, N), fragments of heterocycles, amino acids and peptides, in the 6-position, as well as of purine nucleosides are presented. The possible targets for the action of such compounds and structure – activity relationship are discussed. Particular attention is paid to the most active compounds, which are of considerable interest as a basis for the development of efficient antituberculosis drugs. The bibliography includes 99 references.

Stereoselective acylation of racemic 3-methyl-3,4-dihydro-2Н-1,4-benzoxazine and its 7,8-difluoro-substituted analog with racemic 2-alkoxyacyl chlorides was stidied. The reactions of 3-methyl-3,4-dihydro-2H-1,4-benzoxazines with 2-methoxyisopentanoyl chloride were found to be more selective (selectivity factor s 31–32) compared to the acylation with other studied propanoyl chlorides (s 18–21). This fact was probably caused by the significant steric hindrance due to the isopropyl substituent in acyl chloride compared to the methyl group in reagents derived from propanoic acid.

4-Hydroxy-(2S)-prolines bearing 3,4-dihydro-2H-1,4-benzoxazine or 1,2,3,4-tetrahydroquinoline fragments were synthesized and studied as chiral catalysts in the Biginelli reaction. The target product ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate was obtained with 54% enantiomeric excess (ee). An increase in ee values of the reaction product up to 76% was observed in the presence of nanosized oxides SiO2–ZrO2 as heterogeneous promoters.

Novel purin-6-yl, 2-aminopurin-6-yl and N-(purin-6-yl)glycyl derivatives of (S)-lysine and (S)-ornithine with free α-functional groups, as well as compounds containing N9-(2-hydroxy-ethoxy)methyl substituent in the purine core have been synthesized and tested for their inhibitory effect against Mycobacterium tuberculosis strains. Among the synthesized conjugates, one compound exhibiting a significant level of antimycobacterial activity has been found.

Studies of the antimycobacterial activity of 2-amino-6-chloropurine and its N-acyl derivatives against laboratory (Mycobacterium tuberculosis H37Rv, M. avium, M. terrae) and clinical Mycobacterium tuberculosis strains (MDR-TB) identified compounds with high tuberculostatic activity (MIC from 0.35 – 1.5 μg/ml). The cytotoxic activities of the compounds with antimycobacterial activity against human embryo fibroblasts were studied in the MTT test, which showed that the study compounds were essentially nontoxic (IC50 > 50 μM). Further chemical modification may yield compounds with potential for creating drugs for the treatment of tuberculosis. With the aim of identifying the possible mechanism of the tuberculostatic activity, the ability of the study compounds to inhibit mycobacterial serine-threonine protein kinases (STPK) was assessed. The tuberculostatic activity of 2-amino-6-chloropurine derivatives was not linked with their inhibition of STPK.

The acylative kinetic resolution of racemic heterocyclic amines such as 3,4-dihydro-3-methyl-2H-[1,4]benzoxazines, 3,4-dihydro-3-methyl-2H-[1,4]benzothiazine, 2-methyl-1,2,3,4-tetrahydro-quinolines and 2-methylindoline with enantiopure (R)-2-phenoxypropionyl chloride has been studied. It has been found that acylation of 3,4-dihydro-3-methyl-2H-[1,4]benzothiazine proceeds with the best stereoselectively when compared with other racemic amines. An efficient method for the preparation of (S)-3,4-dihydro-3-methyl-2H-[1,4]benzothiazine (99.4% ee) via a kinetic resolution protocol was developed. The possibility of recycling (R)-2-phenoxypropionic acid has been demonstrated.

peer-reviewed The difference in the crystal structure and growth kinetics of microtubes formed from l- and d-enantiomers of diphenylalanine dipeptide is investigated both experimentally and theoretically by computer simulation. The microtubes of l- and d-enantiomers grown simultaneously and under identical experimental conditions possess different crystallographic space groups, have essential difference in sizes, and demonstrate different growth kinetics. Computer simulation by molecular mechanics methods revealed a fundamental difference in the interaction between structural units of microtubes of different chiralities. A model describing chirality-dependent growth of microtubes is proposed. Accepted peer-reviewed

Derivatives of dicarba-closo-dodecaboranes and dicarba-nido-undecaboranes (carboranes) are of increasing interest for modern medicinal chemistry and materials science. The combination of carborane residues and amino acid fragments in one structure can serve as a basis for obtaining promising medicinal agents (primarily, for boron neutron capture therapy), as well as for design the materials with unique properties. For the first time, this review summarizes and analyzes information on the methods of preparation and possible applications of compounds combining in their structure amino acid and peptide residues and carborane clusters, their biological and physicochemical properties. Special attention is paid to the preparation of enantiopure conjugates, the chirality of which is due to both the presence of an asymmetric carbon atom in amino acid fragments and the planar chirality of the carborane cluster. We believe that this review provides comprehensive information about carborane-containing amino acids and peptides and will give a new impetus to the in-depth fundamental research in this field.

Novel purine and 2-aminopurine conjugates containing fragments of (S)-aspartic and (S)-glutamic acids with free α-functional groups attached via a 1,2-ethylenediamine linker at 6-position of the purine core, as well as their analogues with N9-(2-hydroxyethoxy)methyl substituent have been synthesized. Among the conjugates obtained, compounds exhibiting a significant antimycobacterial activity have been found.

A series of ribo- and deoxyribonucleosides bearing 2-aminopurine as a nucleobase with 7,8-difluoro- 3,4-dihydro-3-methyl-2H-[1,4]benzoxazine (conjugated directly or through an aminohexanoyl spacer) was synthesized using an enzymatic transglycosylation reaction. Nucleosides 3-6 were resistant to deamination under action of adenosine deaminase (ADA) Escherichia coli and ADA from calf intestine. The antiviral activity of the modified nucleosides was evaluated against herpes simplex virus type 1 (HSV-1, strain L2). It has been shown that at sub-toxic concentrations, nucleoside (S)-4-[2-amino-9-(β-D-ribofuranosyl)-purin-6-yl]-7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine exhibit significant antiviral activity (SI > 32) on the model of HSV-1 in vitro, including an acyclovir-resistant virus strain (HSV-1, strain L2/R).

Chemoenzymatic transglycosylation of 2-aminopurine conjugates with enantiomerically pure 7,8-difluoro-3-methyl-3,4-dihydro-2H-[1,4]benzoxazines under the action of recombinant E. coli purine nucleoside phosphorylase afforded the corresponding arabinofuranosides, yields of the target compounds being dependent on both the structure and configuration of the fragment of heterocyclic amine attached at C-6 position of purine moiety.

Synthetic routes to novel N-(purin-6-yl)- and N-(2-aminopurin-6-yl) conjugates with amino acids and glycine-containing dipeptides were developed. In vitro testing of 42 new and known compounds made it possible to reveal a series of N-(purin-6-yl)- and N-(2-aminopurin-6-yl) conjugates exhibiting significant antimycobacterial activity against Mycobacterium tuberculosis H37Rv, Mycobacterium avium, Mycobacterium terrae, and multidrug-resistant M. tuberculosis strain isolated from tuberculosis patients in the Ural region (Russia). N-(2-Aminopurin-6-yl)- and N-(purin-6-yl)-glycyl-(S)-glutamic acids were the most active compounds.