7-nitro-7-deaza-2 `-deoxyadenosine and 8-methyl-7-deaza-2 `-deoxyguanosine: Pyrrolo[2,3-d]pyrimidine nucleosides with different sugar conformations

Abstract

The crystal structures of 7-nitro-7-deaza-2'-deoxyadenosine (3) and 8-methyl-7-deaza-2'-deoxyguanosine (5) have been determined and were compared with those of the parent 7-deaza-2'-deoxyadenosine (2) and other 7-substituted 7-deazapurine 2'-deoxynucleosides 4 and 6. The sugar pucker of compound 3 is N (T-3'(2')) whereas compound 5 shows E-2' conformation (S-type). Despite the methyl group, compound 5 exhibits anti conformation about the N-glycosylic bond as in all other cases. The predominant conformations of 3 and 5 in aqueous solution, determined by H-1 NMR spectroscopy, is consistent with those in the solid state.