Nucleosides XII.¹ Synthesis of 5‐Modified Isoguanosines and Reinvestigation of 5′‐Deoxy‐N³,5′‐cycloisoguanosine

Abstract

Isoguanosine (3) underwent a coupling reaction with diaryl disulfides in the presence of tri-n-butylphosphine when its 6-amino group was protected by N,N-dimethylaminomethylidene. The synthesis of 5¢-deoxy-N 3 ,5¢-cycloisoguanosine (6) and its 2¢,3¢-O-isopropylidene derivative (11) were accomplished in excellent yields from isoguanosines (3 & 10) in the presence of triphenylphospine and carbon tetrachloride in pyridine. Chlorination at the 5¢-position of isoguanosine (3) with thionyl chloride followed by the aqueous basepromoted cyclization afforded the same product 6. The structures were elucidated by spectroscopic analysis including IR, UV, 1-D and 2-D NMR.