Stereoselective synthesis of 2‐azapurine 2′‐deoxy‐β‐D‐ribonucleosides by nucleobase‐anion glycosylation

Abstract
Nucleobase‐anion glycosylation of 6‐(methylthio)‐2‐azapurine (1) with 2‐deoxy‐3,5‐di‐O‐(p‐toluoyl)‐α‐D‐erythro‐pentofuranosyl chloride (2) yields the 2′‐deoxy‐β‐D‐ribofuranosides 3–5 stereoselectively. The distribution of regioisomers is as follows: N‐9 (32%); N‐2 (30%), and N‐7 (7%) together with a minor amount of an unidentified labile glycosylation product. The anomeric configuration and the site of glycosylation have been assigned on the basis of the 1H‐NOE difference spectral data in combination with gated‐decoupled 13C‐NMR and selective INEPT spectroscopy. The regioisomeric 6‐methylthio nucleosides have been converted into 6‐substituted derivatives of biological interest including 2′‐deoxy‐2‐azaadenosine (8). Compound 8 is a substrate of adenosine deaminase.

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