A convenient synthesis of novel nucleosides of 2-thioxo-5h-3,4-dihydropyrimido[5,4-b]indol-4-one

Reaction of 3-amino-2-ethoxycarbonylindole ( 1 ) with per- O -acetyl-sugar isothiocyanates 2a-c gave the corresponding glycopyranosyl thioureas 3a-c . The N -nucleosides analogues 3-(per- O -acetyl- β -D-glycopyranosyl)-2-thioxo-5H-3, 4-dihydropyrimido [5,4-b] indol- 4 -one 4a-c were obtained by cyclization of 3a-c in the presence of ZnCl2. Deacetylation of 4a-c with sodium methoxide in methanol yielded the free nucleoside derivatives 5a-c . Alkylation of 5a,b with methyl iodide and benzyl bromide gave good yields of the corresponding 2-methylthio 6a,b and the 2-benzylthio 6c,d analogues. The 2-methylsulfonyl compounds 7a,b were obtained from the corresponding 2-methylthio compounds 6a,b by oxidation with m -chloroperoxybenzoic acid.