QUINAZOLINE ANTIFOLATES THYMIDYLATE SYNTHASE INHIBITORS - LIPOPHILIC ANALOGS WITH MODIFICATION TO THE C2-METHYL SUBSTITUENT

Modification of the potent thymidylate synthase (TS) inhibitor 1-[[N-[ 4-[N-[(3,4-dihydro-2-methyl-4-ore-6- methyl]-N-prop-2-ynylamino]benzoy l]amino]methyl]-3 -nitrobenzene (4a) has led to the synthesis of quina zolinone antifolates bearing functionalized alkyl substituents at C2. A general synthetic route was developed which involved coupling the ap propriate lamino)benzoyl)aminol]methyl]-3-nitrobenzene-20-22 with a yl )-2-(acetoxymethyl)-3,4-dihydro-4-oxoquinazoline 9 or 10. Replacement of the 2-acetoxy group by a chlorine atom followed by the displacement of the halogen of 25a-c by various nucleophiles led to compounds 26-4 0. Good TS (IC50 <1 mu M)and growth inhibition (IC50 0.1-1 mu M) were found with most of these new antifolates. TS inhibitors in this series do not apparently require the reduced folate carrier (RFC) for cell e ntry (they most likely penetrate the cell membrane by passive diffusio n) and are not polyglutamated. N, O, S, Cl, and CN as well as large am ino and mercapto substituents were tolerated by the enzyme. The simult aneous incorporation of 7-methyl and 2'-F substituents gave a series o f highly potent agents inhibiting cell growth at concentrations <1 mu M (24, 27bc; 30-32b, 35b). The incorporation of suitable C2 substituen ts has overcome the decrease in aqueous solubility observed with lipop hilic quinazoline antifolates. This is best illustrated by compound 31 a, where up to a 54-fold increase in solubility has been achieved by t he incorporation of an N-methylpiperazine nucleus into the C2-methyl g roup of 4a.