Preparation of an Advanced Intermediate for the Synthesis of Stable Analogues of Guanofosfocin

The synthesis of C‐mannosyl‐guanosine 23 , an advanced intermediate for the preparation of stable analogues of guanofosfocin, is described. This convergent approach features an improved Traube‐type synthesis of a 8‐substituted guanine, followed by ribosylation. NMR Studies show that the C‐mannopyranosyl moiety of 23 adopts a distorted ¹C₄ conformation while the nucleoside is predominantly syn‐oriented.