Morteza M. Vaghefi

An improved method for the synthesis and deprotection of methylphosphonate oligonucleotides.

The methylphosphonate oligonucleotide synthesis methods described here give the desired products in good yield. Superior amounts of product are achieved by modifying both the DNA synthesis program and the reagent to compensate for the unstable methylphosphonite intermediate. Deprotection conditions have also been altered to maximize the recovery of oligonucleotide from DNA synthesis supports and to minimize the amount of base modification. Mass-spectrometry analysis of our oligonucleotides has verified their purity and confirmed the absence of modified bases. When compared to standard DNA synthesis methods, this procedure uses only about one-third the usual amount of monomer. Using these procedures, it should be possible to synthesize reliably methylphosphonate oligonucleotides at 1- and 15-mumol scales.

Introduction of Fluorine Into the C8 Position of Purine Nucleosides

Abstract We have synthesized 2-amino-6,8-difluoro-9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purine (3) from 2-amino-6,8-dichloro-9-(2,3,5-tri-O-acetyl-s-D-ribofuranosyl)purine (1) in a two-step procedure. The reaction of 3 with anhydrous ammonia in dry 1,2-dimethoxyethane gave 2,8-diamino-6-fluoro-9-(2,3,5-tri-O-acetyl-s-D-ribofuranosyl)purine (4) in 64.1% yield. Compound 4 was deaminated with t-butylnitrite in tetrahydrofuran to give 2-amino-6-fluoro-9-(2,3,5-tri-O-acetyl-s-D-ribofuranosyl)purine (6). The 1H, 19F, and 13C NMR spectral data were determined and evaluated for each of the compounds.

A convenient high yield synthesis of N4-isobutyryl-2'-O-methylcytidine and its monomer units for incorporation into oligonucleotides

Abstract We designed an efficient three step procedure for the synthesis of N4-isobutyryl-2′-O-methylcytidine. This protected nucleoside was then used to prepare a methylphosphonamidite monomer for incorporation into oligonucleotides. Transamination at the C4 position of cytidine using ethylenediamine, which has been reported for the N4-benzoyl cytidine, was not observed with N4-isobutyryl protected 2′-O-methylcytidine.

Improved and reliable synthesis of 3'-azido-2',3'-dideoxyguanosine derivatives.

An improved synthesis of N2‐protected‐3′‐azido‐2′,3′‐dideoxyguanosine 20 and 23 is described. Deoxygenation of 2′‐O‐alkyl (and/or aryl) sulfonyl‐5′‐dimethoxytritylguanosine coupled with [1,2]‐hydride shift rearrangement gave protected 9‐(2‐deoxy‐threo‐pentofuranosyl)guanines ( 10 , 12 and 16 ). This rearrangement was accomplished in high yield with a high degree of stereoselectivity using lithium triisobutylborohydride (l‐Selectride®). Compounds 10 , 12 and 16 were transformed into 3′‐O‐mesylates ( 18 and 21 ), which can be used for 3′‐substitution. The 3′‐azido nucleosides were obtained by treatment of 18 and 21 with lithium azide. This procedure is reproducible with a good overall yield. †In honor and celebration of the 70th birthday of Professor Leroy B. Townsend.

8-Diazoguanosine, 2,8-Diaminoadenosine and Other Purine Nucleosides Derived from Guanosine

Abstract Diazotization of 8-aminoguanosine gave 8-diazoguanosine (2) which is stable in neutral and basic media, but decomposes to D-ribose and 8-diazoguanine in acidic conditions. 2-Amino-6,8-dichloro-9-(2,3,5-tri-0-acetyl-β-D-ribo-furanosyl)purine (5) was employed to synthesize 9-β-D-ribofuranosyl-2,6,8-triaminopurine (8) and a number of N6-alkyl-2-amino-8-chloro-9-β-D-ribofuranosylpurines.

Stereocontrolled synthesis of nucleoside-methylphosphonate-methyl ester diastereomers from mixed anhydride

Abstract Nucleoside-3′-methylphosphonate was converted to a diastereomeic mixture of di-n-butylphosphiothioic anhydride and the stereoisomers were separated. Activation of each isomer with silver nitrate and coupling with methanol resulted in the formation of a methyl ester with inversion of configuration.

An efficient regioselective synthesis of substituted purine analogues of guanosine and inosine

Condensation of 2-bromo-6-(4-nitrophenylethoxy)purine as the trimethylsilyl derivative (5a) with 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose, 1-O-acetyl-2,3-di-O-benzoyl-5-diethoxy-phosphinyl-β-D-ribofuranose, and (2-acetoxythoxy)methyl bromide resulted in N9-regioselective alkylation to give (6a–c), which were then converted to guanine and hypoxanthine nucleosides, nucleotides, and Acyclovir analogues, respectively.