[Highlights from 43 years of chemistry of naturally occurring nitrogen-containing heterocycles. (2). Syntheses and reactions of purines and of their nucleosides].

The studies on the syntheses and reactions of purines and their nucleosides, carried out by the present author's group for these 34 years, are reviewed with particular emphasis on the employed synthetic strategies and tactics. Among the studies included in this review are as follows: ring-opening and recyclization of the adenine ring utilizing an N(1)-alkoxy group; kinetic studies of the Dimroth rearrangement and related reactions in the adenine series; syntheses and reactions of new Nx,Ny-disubstituted adenines and of new Nx-substituted adenosines; syntheses, structure determinations, and structure-activity relationships of new natural cytokinins; syntheses and reactions of new marine 8-oxopurines; syntheses, reactions, and biological activities of the N(7)-oxides of guanine, hypoxanthine, adenine, 6-mercaptopurine, and 6-methylthiopurine.