Experiments on the synthesis of pyrazine nucleosides

Abstract

Pyrazine nucleosides were prepared by condensation of acylglycosyl halides with trimethylsilyloxypyrazines in benzene in the presence of silver perchlorate. Reaction of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (1) with 2,3-bis(trimethylsilyloxy)pyrazine (2) gave 1,4-dihydro-1,4-bis-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl) pyrazine-2,3-dione (3). Similar reactions of 2,3,5-tri-O-benzoyl-D-ribofuranosyl chloride (4) with the pyrazine (2) and 1-benzyl-3-trimethylsilyloxypyrazine-2(1H)-one (14) afforded 1,4-dihydro-1,4-bis-(β-D-ribofuranosyl)pyrazine-2,3-dione (6) and 1-benzyl-1,4-dihydro-4-(β-D-ribofuranosyl)pyrazine-2,3-dione (16), respectively, via their 2′,3′,5′-tri-O-benzoates [(5) and (15)]. 1-Benzyl-1,4-dihydropyrazine-2,3-dione (12) was prepared by acid-catalysed cyclization of N-benzyl-N′-(2,2-dimethoxyethyl)oxamide (9), which was obtained by condensation of ethyl N-(2,2-dimethoxyethyl)oxamate (7) with benzylamine.