The Course of N-Alkylation of 6-Methylmercaptopurines

Prodrugs of 6-thiopurines: enhanced delivery through the skin

Soft-alkylated derivatives of 6-mercaptopurine, its riboside, and 2-amino-6-mercaptopurine riboside have been prepared and evaluated to improve the delivery of the thiopurines through the skin. The soft-alkylated derivatives were prepared by the alkylation of the thiopurines with acylheteroalkyl halides under neutral or basic conditions. The penetration of the derivatives through hairless mouse skin was measured using diffusion cells. All of the derivatives underwent extensive degradation during their diffusion through skin so that the parent thiopurine, even in the case of the ribosides, was the major product observed in the receptor phase. The pivaloyloxymethyl derivatives showed the greatest potential for enhancing the penetration of the thiopurines through the skin. Among the 6-mercaptopurine derivatives, VII and XI were the most effective; they delivered 5 and 13 times, respectively, more 6-mercaptopurine than 6-mercaptopurine itself.

Oxidation of N-methyl substituted hypoxanthines, xanthines, purine-6,8-diones and the corresponding 6-thioxo derivatives by bovine milk xanthine oxidase

1. The oxidation of six series of purines (hypoxanthines, xanthines, purine-6,8-diones and the corresponding 6-thioxo derivatives) by a highly purified bovine milk xanthine oxidase (EC 1.2.3.2) has been studied, using a variety of N-methyl derivatives. 2. N-Methyl substituents can either enhance or reduce enzymic rates. Enhancement is ascribed to blockade of groups which mediate unfavorable modes of binding of substrate to enzyme. Introduction of N-methyl groups can also inhibit enzymic oxidation, either by occluding essential binding groups or by preventing spontaneous or enzyme-induced tautomerisation processes, which create suitable binding sites in the substrates. 3. In all purines which are rapidly attacked by xanthine oxidase, proper attachment to the active center is mediated by the groupings (3) NH, (9) N or (3) N, (9) NH. 4. Reduced rates usually express lowered substrate affinity, which finds its expression in weak competitive inhibition of xanthine oxidation.