Glycosylation of Pyrrolo[2,3-d]pyrimidines with 1-O-Acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose: Substituents and Protecting Groups Effecting the Synthesis of 7-Deazapurine Ribonucleosides

Abstract

Glycosylation of nonfunctionalized 6-chloro-7-deazapurine with commercially available 1-0-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose (45%) followed by amination and deprotection gave tubercidin in only two steps. Similar conditions applied for the synthesis of 7-deazaguanosine employing pivaloylated 2-amino-6-chloro-7-deazapurine gave 18% glycosylation yield. The less bulky isobutyryl or acetyl protected amino group directed the glycosylation toward the exocyclic amino substituent. 7-Halogenated intermediates were glycosylated followed by dehalogenation to overcome the low glycosylation yield in the synthesis of 7-deazaguanosine.