Modulation of Antimalarial Activity at a Putative Bisquinoline Receptor in vivo Using Fluorinated Bisquinolines

Antimalarials can interact with heme covalently, by - interactions or hydrogen bonding. Consequently, the prototropy of 4-aminoquinolines and quinoline methanols was investigated using quantum mechanics. Calculations showed mefloquine protonated preferentially at the piperidine and was impeded at the endocyclic nitrogen due to electronic rather than steric factors. In gas phase calculations, 7-substituted mono- and bis-4-aminoquinolines were preferentially protonated at the endocyclic quinoline nitrogen. By contrast, compounds with a trifluoromethyl substituent on both the 2- and 8-positions, reversed the order of protonation which now favored the exocyclic secondary amine nitrogen at the 4-position. Loss of antimalarial efficacy by CF3 groups simultaneously occupying the 2- and 8-positions was recovered if the CF3 group occupied the 7-position. Hence, trifluromethyl groups buttressing quinolinyl nitrogen shifted binding of antimalarials to hematin, enabling switching from endocyclic to the exocyclic N. Both theoretical calculations (DFT calculations: B3LYP/6- 31+G*) and crystal structure of (±)-trans-N1,N2-bis-(2,8-ditrifluoromethylquinolin-4- yl)cyclohexane-1,2-diamine were used to reveal preferred mode(s) of interaction with hematin. The order of antimalarial activity in vivo followed the capacity for a redox change of the iron(III)state which has important implications for the future rational design of 4- aminoquinoline antimalarials

Synthesis, Structural Determination, and Pharmacology of Putative Dinitroaniline Antimalarials

A series of novel, homologous compounds possessing the general formula N1‐Nn‐bis(2,6‐dinitro‐4‐trifluormethylphenyl)‐1,n‐diamino alkanes (where n=4, 6, 10 or 12), were designed to probe inter‐ and intra‐ binding site dimensions in malarial parasite (Plasmodium) tubulin. Various crystal structures, including chloralin and trifluralin, an isopropyl dimer, and 2,6‐dinitro‐4‐trifluoromethyl‐phenylamine, were determined. Dinitroanilines, when soluble, were evaluated both in culture and in vivo. Trifluralin was up to 2‐fold more active than chloralin against cultured parasites. The isopropyl dimer was water soluble (>5 mM) and revealed activity superior to that of chloralin in culture. The effects of selected dinitroanilines upon the mitotic microtubular structures of Plasmodium, the putative target of these dinitroanilines, were also determined. Electronic properties of the molecules were calculated using DFT (B3LYP/6‐31+G* level) to ascertain whether incorporation of such a pharmacophore could allow both QSAR and rational development of more selectively toxic antiparasitic agents

Purpurogallin-A heme binding component of oak galls

Recently, it has been shown that Purpurogallin (PPG), an orange benztropolone constituent of oak galls and its derivative, CU-CPT22, can compete with the binding of the specific lipoprotein ligand to toll-like receptors (TLRs), which are type I transmembrane proteins. These recognize pathogen-derived macromolecules that play a key role in the innate immune system. This system provides an attractive target for the treatment of various immune disorders. Notably, PPG also interacts with various metals and its mode of action against HIV in vitro may involve inhibition of metal containing integrases. In the current study, an optimised synthesis of PPG is presented together with its gas phase behaviour (probed by mass spectrometry) as well as its redox behaviour with porphyrins such as heme. This interaction may also explain its effects at metal containing integrases within HIV in vitro as well as its action during processing of iron complexes within Plasmodia. This compound could serve as a novel prototype for the synthesis of novel redox active antimalarials