Trinucleotide phosphoramidites that correspond to the codons of all 20 amino acids were synthesized in high yield in 5g scale. Precursors of those amidites--trinucleotide phosphotriesters--have been prepared using the phosphotriester approach without protection of the 3'-hydroxyl function. The structures of trinucleotide phosphotriesters and intermediates were confirmed by 1H- and 31P-NMR spectra, mass-spectra and by analysis of SPDE-hydrolysates of deprotected preparations. Purity of the target products has been confirmed by test reactions. The synthons have been used for automated synthesis of oligonucleotides and corresponding libraries by a phosphite-triester approach. A 54mer, containing 12 randomized internal bases, and a 72mer with 24 internal randomized bases have been synthesized.

A new method to produce a set of 20 high quality trinucleotide phosphoramidites on a 5-10 g scale each was developed. The procedure starts with condensation reactions of P-components with N-acyl nucleosides, bearing the 3 '-hydroxyl function protected with 2-azidomethylbenzoyl, to give fully protected dinucleoside phosphates 13. Upon cleavage of dimethoxytrityl group from 13, dinucleoside phosphates 16 are initially transformed into trinucleoside diphosphates 19 and then the 2-azidomethylbenzoyl is selectively removed under neutral conditions to generate trinucleoside diphosphates 5 in excellent yield. Subsequent 3 '-phosphitylation affords target trinucleotide phosphoramidites 7. When mutagenic oligonucleotides are synthesized employing mixtures of building blocks 7 as well as following the new synthetic protocol, representative oligonucleotide libraries are generated in good yields.

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).

A series of 5,6-disubstituted benzimidazole nucleosides, obtained earlier, did not show any significant antiviral activity at relatively low cytotoxicity in vitro. In the course of our research we have succeeded in introducing an additional fluorine atom into the benzimidazole ring system. A new series of 4,6-difluorobenzimidazoles, bearing various groups (fluoro-, methoxy-, ethoxy-, morpholino-, and pyrrolidino-) in the 5-position of the benzene ring, have been synthesized. All these compounds proved to be substrates for recombinant E. coli purine nucleoside phosphorylase (PNP) in the transglycosylation reaction. Effective methods for the synthesis of ribo-and 2′-deoxyribonucleosides with high yields (60-90%) have been described, and the formation of regioisomeric N3-nucleosides of benzimidazoles have been detected. The biological activity of the nucleosides obtained against herpes simplex virus type 1 (HSV-1) has been elucidated. All compounds show a low cytotoxicity in the cell culture Vero E6. 4,5,6-Trifluoro-1-(β-D-ribofuranosyl)benzimidazole and 5-methoxy-4,6-difluoro-1-(β-D-2′-deoxyribofuranosyl)benzimidazole proved to inhibit completely the progression of the virus cytopathic effect (CPE) at a multiplicity of infection (MOI) of 0.01 PFU/cell.

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