NAD-analogues as potential anticancer agents: Conformational restrictions as basis for selectivity

Cofactor type inhibitors (NAD-analogues) of IMP-dehydrogenase (IMPDH) were synthesized and their application as potential anticancer agents are discussed. C-nucleoside isosteres of NAD, C-NAD and C-PAD, showed an effective competitive inhibition of IMPDH. C-NAD but not C-PAD caused extremely potent inhibition of alcohol dehydrogenase. We also synthesized compounds in which nicotinamide riboside was replaced with tiazofurin (TAD-analogues) and the 2′ and 3′-positions of adenosine part were fluorinated. The ribose ring of 2′-deoxy-2′-fluoroadenosine is in the C3′-endo conformation whereas 3′-deoxy-3′-fluoroadenosine favors the C2′-endo sugar pucker. These derivatives are good inhibitors of IMPDH type II, the isoenzyme dominant in neoplastic cells. In contrast, all these analogues showed rather week inhibitory activity against alcohol dehydrogenase. Nicotinamide riboside derivatives in which the base and the sugar are linked through an oxygen or a methylene bridge were synthesized. NAD-analogues containing such conformationally restricted nicotinamide nucleoside moiety (syn or anti) are expected to be selective inhibitors of B-specific (IMPDH) or A-specific dehydrogenases, respectively.