Development of a lead inhibitor for the A16V+S108T mutant of dihydrofolatereductase from the cycloguanil-resistant strain (T9/94) of Plasmodium falciparum

The Ala16Val+Ser108Thr (A16V+S108T) mutant of the Plasmodium falciparum dih ydrofolate reductase (DHFR) is a key mutant responsible for cycloguanil-res istant malaria due to steric interaction between Val-16 and one of the C-2 methyl groups of cycloguanil. 4,6-Diamino-1,2-dihydrotriazines have been pr epared, in which both methyl groups of cycloguanil are replaced by H or by H and an alkyl or phenyl group, and their inhibition constants against wild -type and mutant DHFR determined. The S108T mutation is considered to decre ase cycloguanil binding further through the effect on the orientation of th e p-chlorophenyl group. By moving the p-chloro-substituent to the m-positio n in the chlorophenyl group, the activity against the A16V+S108T mutant enz yme is improved, and this effect is reinforced by the p-chloro substituent in the 3,4-dichlorophenyl group. A lead compound has been found with inhibi tory activity similar to that of cycloguanil against the wild-type DHFR and about 120-fold more effective than cycloguanil against the A16V+S108T muta nt enzyme. The activity of this compound against P. falciparum clone (T9/94 RC17) which harbors the A16V+S108T DHFR is about 85-fold greater than cycl oguanil.