Synthesis of 9-halogenated 9-deazaguanine N-7-(2 `-deoxyribonucleosides)

Abstract

The syntheses of N-7-glycosylated 9-deazaguanine 1a as well as of its 9-bromo and 9-iodo derivatives 1b,c are described. The regioselective 9-halogenation with N-bromosuccinimide (NBS) and N-iodosuccinimide (NIS) was accomplished at the protected nucleobase 4a (2-{[(dimethylamino)methylidene]amino}-3,5-dihydro-3-[(pivaloyloxy )methyl]-4H-pyrrolo[3,2-d]pyrimidin-4-one). Nucleobase-anion glycosylation of 4a-c with 2-deoxy-3,5-di-O-(p-toluoyl)-alpha-D-erythro-pentofuranosyl chloride (5) furnished the fully protected intermediates 6a-c (Scheme 2). They were deprotected with 0.01M NaOMe yielding the sugar-deprotected derivatives 8a-c (Scheme 3). At higher concentrations (0.1M NaOMe), also the pivaloyloxymethyl group was removed to give 7a-c, while conc. aq. NH3 solution furnished the nucleosides 1a-c. In D2O, the sugar conformation was always biased towards S (67-61%).