Folate-synthesizing enzyme system as target for development of inhibitors and inhibitor combinations against Candida albicans-synthesis and biological activity of new 2,4-diaminopyrimidines and 4'-substituted 4-aminodiphenyl sulfones.

The paper describes the design, synthesis, and testing of inhibitors of folate-synthesizing enzymes and of whole cell cultures of Candida albicans. The target enzymes used were dihydropteroic acid synthase (SYN) and dihydrofolate reductase (DHFR). Several series of new 2,4-diaminopyrimidines were synthesized and tested as inhibitors of DHFR and compared with their activity against DHFR derived from mycobacteria and Escherichia coli. To test for selectivity, also rat DHFR was used. A series of substituted 4-aminodiphenyl sulfones was tested for inhibitory activity against SYN and the I(50) values compared to those obtained previously against Plasmodium berghei- and E. coli-derived SYN. Surprisingly, QSAR equations show very similar structural dependencies. To find an explanation for the large difference in the I(50) values observed for enzyme inhibition (SYN, DHFR) and for inhibition of cell cultures of Candida, mutant strains with overexpressed efflux pumps and strains in which such pumps are deleted were included in the study and the MICs compared. Efflux pumps were responsible for the low activity of some of the tested derivatives, others showed no increase in activity after pumps were knocked out. In this case it may be speculated that these derivatives are not able to enter the cells.

Studies on the toxicity and efficacy of some ester analogues of dapsone in vitro using rat and human tissues.

The toxicity and efficacy of a series of 13 anti-tubercular sulphone esters has been evaluated using human and rat tissues. The toxicity studies involved comparison of the esters' ability to generate rat microsomally mediated NADPH-dependent methaemoglobin with that of dapsone. All the compounds formed significantly less methaemoglobin in the 1 compartment studies compared with dapsone itself. The ethyl, propyl, 3-methyl-butyl cyclopentyl esters and the carboxy parent derivative all yielded less than 5% of the methaemoglobin generated by dapsone. The 3-nitro benzoic acid ethyl and propyl esters generated 30 and 25% of dapsone's methaemoglobin formation. A similar effect was seen in the 2 compartment system, except for the butyl ester, which yielded similar haemoglobin oxidation to dapsone. The low toxicity ethyl and propyl esters, were also low in toxicity using human liver microsomes, producing less than 30% of the dapsone mediated methaemoglobin. All the compounds except the benzoic acid parent were superior to dapsone in terms of suppression of human neutrophil respiratory burst using a lucigenin-based chemiluminescence assay. The most potent derivatives were the phenyl, propyl and 3-nitro benzoic acid ethyl esters, which were between two- and threefold more potent compared with dapsone in arresting the respiratory burst. Overall, the ethyl ester showed the best combination of low toxicity in the rat and human microsomal systems and its IC(50) was approximately 40% lower than that of dapsone in neutrophil respiratory burst inhibition. These compounds indicate some promise for future development in their superior anti-inflammatory capability and lower toxicity compared with the parent sulphone, dapsone.