A synthesis of 2‐β‐D‐ribofuranosyl‐4‐selenazolecarboxamide (selenazofurin) and certain N ‐substituted amide derivatives suitable for large scale syntheses

A new process suitable for large scale synthesis of the antitumor‐antiviral agent, 2‐β‐D‐ribofuranosyl‐4‐selenazolecarboxamide (selenazofurin, 1 ), has been developed. Thus, 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐β‐D‐ribofuranose ( 3 ) was converted with cyanotrimethylsilane and stannic chloride to the crystalline 2,5‐anhydro‐3,4,6‐tri‐ O ‐benzoyl‐β‐D‐allononitrile ( 4 ) without chromatography. Cyanosugar 4 in ethanol was treated with hydrogen selenide gas to afford stereospecifically the unstable 2,5‐anhydro‐3,4,6‐tri‐ O ‐benzoyl‐β‐D‐allonoselenoamide ( 5 ) which was converted in situ by ethyl bromopyruvate to the stable ethyl 2‐(2,3,5‐tri‐ O ‐benzoyl‐β‐D‐ribofuranosyl)‐4‐selenazolecarboxylate ( 6). Selenazole ethyl ester 6 was deprotected with sodium methoxide affording methyl 2‐β‐D‐ribofuranosyl‐4‐selenazolecarboxylate ( 7 ) which was aminated with ammonia to provide selenazofurin ( 1 ) or with other amines to provide N ‐substituted selenazofurin amides.