Synthesis and evaluation of multisubstrate analogue inhibitors of purine nucleoside phosphorylases

1,1-Difluoro-2-(tetrahydro-3-furanly)ethylphosphonic acids (+/-)-cis-4a and (+/-)-trans-4a possessing a (purine-9-yl)methyl functionality at the ring as well as their homologues (+)-cis-4b and (+)-trans-4b were synthesized an d tested as 'multi-substrate analogue' inhibitors for purine nucleoside pho sphorylases. Radical cyclization of allylic alpha,alpha -difluorophosphonat es 8a,b was applied to construct the alpha,alpha -difluorophosphonate-funct ionalized oxacycles 9a,b. The IC50 values of the nucleo tide analogues (+/- )-cis-4a and (+/-)-cis-4b were 88 and 38 nM, respectively, for human erythr ocyte PNP-catalyzed phosphorylation of inosine in the presence of 100 mM or thophosphate. The stereochemistry of the inhibitors was found to affect sig nificantly the inhibitory potency. The transisomers (+/-)-trans-4a and (+/- )-trans4b were ca. 4-fold less potent than the corresponding cis-isomers. A t an intracellular concentration of orthophosphate (1 mM), (+/-)-cis-4b, th e most potent compound of this series, was shown to have IC50 and K-i value s of 8.7 and 3.5 nM, respectively. (C) 2000 Elsevier Science Ltd. All right s reserved.