Novel Benzimidazole and Quinazolinone Inhibitors of the DNA Repair Enzyme Poly(ADP‐ribose)polymerase*

Abstract

Two novel series of inhibitors of the DNA repair enzyme poly(ADP-ribose)polymerase (PARP) were synthesized and evaluated for biological activity. In the benzimidazole-4-carboxamide series, the carbamoyl function was restricted into the putative biologically active conformation via an intramolecular hydrogen bond, while for quinazolin-4-[3H]-ones this was achieved by incorporation of the group into a heterocyclic ring. For both series of compounds, syntheses involved acylation of substituted anthranilic acid derivatives, followed by acid- or base-catalysed cyclization. 8-Hydroxyquinazolin-4-[3H]-ones were prepared from the corresponding 8-methoxy compounds by dealkylation with boron tribromide. PARP inhibitory activity was determined in permeabilized L1210 murine leukaemia cells, in comparison with the established inhibitor 3-hydroxybenzamide (IC50 = 8-3 um). For both series, inhibitory activity varied with the nature of the 2-substituent, with benzimidazole-4-carboxamides proving approximately tenfold more potent than the previously prepared benzoxazole-4-carboxamides. 2-Arylbenzimidazoles were especially active, and 2-(4-methoxyphenyl)benzimidazole-4-carboxamide (IC50 = 60 nM) is the most potent PARP inhibitor reported to date. In the quinazolinone series, a 2-(4-nitrophenyl) substituent, and either an 8-methyl or 8-hydroxy group conferred potent inhibitory activity, with IC50 values of 0–13 and 0–23 μM, respectively, being observed.