Design, synthesis, computational prediction, and biological evaluation of ester soft drugs as inhibitors of dihydrofolate reductase from Pneumocystiscarinii

A series of lipophilic soft drugs structurally related to the nonclassical dihydrofolate reductase (DHFR) inhibitors trimetrexate and piritrexim have been designed, synthesized, and evaluated in DHFR assays, with special emph asis on the inhibition of P. carinii DHFR. The best inhibitors, encompassin g an ester bond in the bridge connecting the two aromatic systems, were app roximately 10 times less potent than trimetrexate and piritrexim. The metab olites were designed to be poor inhibitors. Furthermore, molecular dynamics simulations of three ligands in complex with DHFR from Pneumocystis carini i and from the human enzyme were conducted in order to better understand th e factors determining the selectivity. A correct ranking of the relative in hibition of DHFR was achieved utilizing the linear interaction energy metho d. The soft drugs are intended for local administration. One representative ester was selected for a pharmacokinetic study in rats where it was found to undergo fast metabolic degradation to the predicted inactive metabolites .