A SHORT SYNTHESIS OF A NOVEL RING-EXPANDED PURINE AND ITS NUCLEOSIDE ANALOG CONTAINING THE IMIDAZO[4,5-E][1,3]DIAZEPINE RING SKELETON WITH MULTIPLE AMINO SUBSTITUENTS ATTACHED TO THE 7-MEMBERED RING

The synthesis of 4,6,8-triaminoimidazo[4,5-e][1,3]diazepine (1) and it s nucleoside analogue (6) are reported. The heterocycle was prepared i n a single step by condensation of 4,5-dicyanoimidazole with guanidine . The 5,7-fused ring structure of 1 was distinguished from the other p ossible 5:5-fused isomer 2 by preparing the N-15-labeled heterocycle ( 1) and exploring its N-15-H-1 coupling patterns in both H-1 and N-15 NMR spectra. These spectral patterns also enabled establishment of the triamino tautomeric form of 1 as assigned. Compound 1, a novel ring-e xpanded (''fat'') analogue of purine, is anticipated to be planar and aromatic as predicted by molecular modeling. The 1-benzyl analogue (4) , a protocol for the ribosyl analogue 6, was similarly prepared from 1 -benzyl-4,5-dicyanoimidazole. The nucleoside 6 was prepared by the mod ified Vorbruggen ribosylation of 1. The position of ribosylation was u nequivocally established by an unambiguous synthesis of 6 from condens ation of 1-(2',3',5'-tri-O-benzoyl-beta-($) under bar D-ribofuranosyl) -4,5-dicyanoimidazole (7) with guanidine in a solution of sodium metho xide in methanol. The nucleoside 7 was prepared by the Vorbruggen ribo sylation of 4,5-dicyanoimidazole.