Experimental methods have been devised for the permethylation of both adenosine (la-lb) and guanosine (2a-2b+ 3ar) employing trimethylanilinium methoxide (TMAM). Reaction of the TMAM reagent with inosine (5a) and xanthosine (11) was found to promote imidazole ring and/or riboside cleavage (eg, 5a-7a and 10). While methylation of inosine resulted in a variety of such reaction pathways, xanthosine followed essentially a single direction, ...