Conformation about the glycosidic bond and susceptibility to 5'-nucleotidase of 8-substituted analogues of 5'-GMP.

Susceptibilities to snake venom 5'-nucleotidase (EC 3.1.3.5) have been evaluated for several 8-substituted analogues of 5'-GMP with varying populations of syn/anti conformations about the glycosidic bond. Improved syntheses of some of these are described, including direct chlorination of 5'-GMP to give 8-chloro-5'-GMP, a procedure which should be applicable to other purine nucleotides. The conformations of the various analogues were determined by means of 1H NMR spectroscopy, with particular emphasis on the glycosidic bond conformations. All the 8-substituted derivatives of 5'-GMP were relatively poor substrates of 5'-nucleotidase. This was shown to result largely from steric effects and the nature of the 8-substituent, and consistent with a requirement for the anti conformation. Although ribose-5-phosphate was not a substrate, it was a weak inhibitor, and its inhibitory properties account in part for the weak inhibitory properties of the 8-substituted 5'-GMP, and other, analogues. Attention is drawn to the hitherto largely neglected differences in properties of 5'-nucleotidases from different sources and their relevance to the present findings.