Synthesis of 7-alkynylated 8-aza-7-deaza-2 `-deoxyadenosines via the Pd-catalysed cross-coupling reaction

Abstract

The synthesis of 7-alkynylated 8-aza-7-deazaadenine (pyrazolo[3,4-d]pyrimidine) 2'-deoxyribonucleosides is described. Nucleobase anion-glycosylation of 8-aza-7-deaza-7-iodo-6-methoxypurine (15) with 2-deoxy-3,5-di-O-(p-toluoyl)-alpha-D-erythro-pentofuranosyl chloride (16) furnishes the 8-aza-7-deaza-7-iodo-6-methoxypurine N-1-beta-D-2'-deoxyribonucleoside 17a as the main product (38% yield). After detoluoylation of products 17a and 17b(27) (--> 19a,b) and amination the 7-bromo and the 7-iodo derivatives of 8-aza-7-deaza-2'-deoxyadenosine (compounds 2b,c) were obtained. Compound 2b served as the starting material for a series of 7-alkynyl- or 7-alkenyl-8-aza-7-deazaadenine 2'-deoxynucleosides 3-13 by employing the Pd-0/Cu-1-catalysed. cross-coupling reaction. The 7-halogenated or 7-alkynylated nucleosides show a more stable glycosylic bond than does 8-aza-7-deaza-2'-deoxyadenosine (2a).