Synthesis of purines and azapurines

The synthesis of a series of C-(8) unsubstituted (11a-h), C-(8), substitute d (12a-e), 8-mercapto (13a-e) 1,3-diaryl-2-thioxanthines, as well as, 8-aza -1,3-diaryl-2-thioxanthines 14a-g, through precursors, 5,6-diamino-1,3-diar yl-2-thiouracils 10 has been reported. Recently, the synthesis of a navel s eries of 6-amino-1,3-diaryl-2-thiouracils 8 under the influence of dry HCl gas has been reported.(14,15). These compounds are converted to the requisi te 5,6-diamino-1,3-diaryl-2-thiouracils 10 via reduction of an intermediate 5-nitroso-6-amino-1,3-diaryl-2-thiouracil 9. Cyclocondensation of 5,6-diam ino-2-thiouracils 10 with appropriate one carbon donors afford the desired purines 11-13.