Synthesis and evaluation of multisubstrate analogue inhibitors of purine nucleoside phosphorylases Original Research Article

1,1-Difluoro-2-(tetrahydro-3-furanyl)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 and tested as ‘multi-substrate analogue’ inhibitors for purine nucleoside phosphorylases. Radical cyclization of allylic α,α-difluorophosphonates 8a,b was applied to construct the α,α-difluorophosphonate-functionalized oxacycles 9a,b. The IC50 values of the nucleotide analogues (±)-cis-4a and (±)-cis-4b were 88 and 38 nM, respectively, for human erythrocyte PNP-catalyzed phosphorylation of inosine in the presence of 100 mM orthophosphate. The stereochemistry of the inhibitors was found to affect significantly the inhibitory potency. The trans-isomers (±)-trans-4a and (±)-trans-4b were ca. 4-fold less potent than the corresponding cis-isomers. At an intracellular concentration of orthophosphate (1 mM), (±)-cis-4b, the most potent compound of this series, was shown to have IC50 and Ki values of 8.7 and 3.5 nM, respectively.