7‐Nitro‐7‐deaza‐2′‐deoxyadenosine and 8‐Methyl‐7‐deaza‐2′‐deoxyguanosine: Pyrrolo[2,3‐ d ]pyrimidine Nucleosides with Different Sugar Conformations

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 ( 3′ T 2′ ) whereas compound 5 shows 2′ E 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 1 H NMR spectroscopy, is consistent with those in the solid state.