7-DEAZAPURINE 2'-DEOXYRIBOFURANOSIDES ARE NONCLEAVABLE COMPETITIVE INHIBITORS OF ESCHERICHIA-COLI PURINE NUCLEOSIDE PHOSPHORYLASE (PNP)

A series of 7-deazapurine 2'-deoxyribofuranosides were synthesized acc ording to already known procedures and their substrate and inhibitor p roperties with purified E. coli purine nucleoside phosphorylase were e xamined. In agreement with previous findings, substrate activity was n ot detected for any of the compounds tested. Most of the nucleosides s howed weak inhibition in the preliminary screening, i.e. at a concentr ation of about 100 mu M. However some combinations of 6-chloro, 6-amin o or 6-methoxy substituents with bulky hydrophobic groups at position 7 of the base and/or chloro, amino, methoxy or methylthio group at pos ition 2 markedly enhanced affinity of such modified nucleosides for th e E. coli enzyme. The most potent inhibition was observed for two nucl eosides: 6-chloro- and 2-amino-6-chloro-7-deazapurine 2'-deoxyribofura nosides that show inhibition constants K-i = 2.4 and 2.3 mu M, respect ively. Several other compounds were also found to be good inhibitors, with inhibition constants in the range 5-50 mu M. In all instances the inhibition was competitive us. the nucleoside substrate 7-methylguano sine, Inhibition constants for 7-deazapurine nucleosides are in genera l several-fold lower than those observed for their purine counterparts . Therefore 7-deaza modification together with substitutions at positi ons 2, 6 and 7 of the base is a very promising approach to obtain comp etitive noncleavable inhibitors of E. coli PNP that may bind to the en zyme with inhibition constants in the mu M range.