Evaluation of Novel Chalcone-Thiosemicarbazones Derivatives as Potential Anti-Leishmania amazonensis Agents and Its HSA Binding Studies.

A series of seven chalcone-thiosemicarbazones (5a-5g) were synthesized and evaluated as potential new drugs (anti-leishmanial effect). Although four of the chalcone-thiosemicarbazones are already known, none of them or any compound in this class has been previously investigated for their effects on parasites of the Leishmania genus. The compounds were prepared in satisfactory yields (40-75%) and these compounds were evaluated against promastigotes, axenic amastigotes and intracellular amastigotes of L. amazonensis after 48 h of culture. The half maximal inhibitory concentration (IC50) values of the intracellular amastigotes were determined to be in the range of 3.40 to 5.95 µM for all compounds assayed. The selectivity index showed value of 15.05 for 5a, whereas pentamidine (reference drug) was more toxic in our model (SI = 2.32). Furthermore, to understand the preliminary relationship between the anti-leishmanial activity of the chalcone-thiosemicarbazones, their electronic (σ), steric (MR) and lipophilicity (π) properties were correlated, and the results indicated that moieties with electronic withdrawing effects increase the anti-leishmanial activity. The preliminary pharmacokinetic evaluation of one of the most active compound (5e) was studied via interaction to human serum albumin (HSA) using multiple spectroscopic techniques combined with molecular docking. The results of antiparasitic effects against L. amazonensis revealed the chalcone-thiosemicarbazone class to be novel prototypes for drug development against leishmaniasis.

Antileishmanial activity and trypanothione reductase effects of terpenes from the Amazonian species Croton cajucara Benth (Euphorbiaceae).

BACKGROUND: Leishmaniasis comprises several infectious diseases caused by protozoa parasites of Leishmania genus. In recent years, there has been a growing interest in the therapeutic use of natural products to treat parasitic diseases. Among them Croton cajucara Benth. (Euphorbiaceae) is a plant found in the Amazonian region with a history of safe use in folk medicine. PURPOSE: The purpose of this study was to investigate the effects of clerodane diterpenes, trans-dehydrocrotonin (DCTN), trans-crotonin (CTN) and acetylaleuritolic acid (AAA) obtained from powdered bark of C. cajucara against promastigotes, axenic and intracellular amastigotes of Leishmania amazonensis. Furthermore, the effects of DCTN and CTN on the trypanotiona reductase enzyme were also investigated. The extraction of the terpenes was carried out as previously reported (Maciel et al., 1998; 2003). METHODS: The effect of the isolated compounds (DCTN, CTN and AAA) from the bark of C. cajucara was assessed in vitro against promastigotes, axenic amastigotes and intracellular amastigotes of L. amazonensis by counting of remaining parasites in a Neubauer chamber in comparison to pentamidine used as standard drug. The action of natural products on trypanothione reductase was assessed using soluble protein fraction of promastigotes. The assays were performed by incubation with HEPES, EDTA, NADPH and trypanothione disulfide to quantify the NAPH consumption by TryR. RESULTS: The results showed very high efficacy, especially of the diterpene DCTN, against promastigotes (IC50 = 6.30 ± 0.06 µg/ml) and axenic amastigotes (IC50 = 19.98 ± 0.05 µg/ml) of L. amazonenesis. The cytotoxic effect of the best active natural product was evaluated on mouse peritoneal infected macrophages (IC50 = 0.47 ± 0.03 µg/ml in 24 h of culture), and the treatment revealed that DCTN never reaches toxic concentrations while reducing the infection and, most importantly, with no toxicity (>100 µg/ml with 0% of macrophage kill) when compared to pentamidine (37.5 µg/ml with 100% of macrophage kill). Furthermore, all of the natural products assayed on the trypanothione reductase enzyme inhibited the enzyme activity compared to the control. CONCLUSION: Clerodane diterpenes from C. cajucara showed promising in vitro antileishmanial effects against L. amazonensis, specially the DCTN with no macrophage toxicity up to the assayed concentration. In addition, the action on trypanothione reductase enzyme revealed a possible mechanism of action.

Synthesis, antileishmanial activity and structure-activity relationship of 1-N-X-phenyl-3-N'-Y-phenyl-benzamidines.

Two series of N,N'-diphenyl-benzamidines were synthesized as part of a study to search potential new drugs with antileishmanial activity. These compounds were obtained by anilides in PCl5 halogenation reaction with generation in situ of the corresponding benzimidoyl chlorides, and subsequently treatment with adequate anilines. The series I showed expressive results of antileishmanial activity, highlighted the compounds 9a with IC50 = 81.28 µM (log IC50 = 1.91 µM) against Leishmania chagasi, 8e with IC50 = 26.30 (log IC50 = 1.52 µM) against Leishmania braziliensis. From the results obtained from SAR study (series I), the series II was planned from Craig 2-dimensional map, in which was possible the discovery of the potent compounds, 9v and 9j with IC50 = 12.60 µM (log IC50 = 1.10 µM) and 13.00 µM (log IC50 = 1.11 µM), respectively, against Leishmania amazonensis. The results obtained from the SAR and QSAR studies indicated the best results when electron-donor groups in the ring attached to amidinic carbon, unlike when electron-withdrawing groups at the phenyl-N ring showing inhibitory activity increased. Furthermore, the QSAR model obtained indicated the hydrophobicity as a fundamental property for antileishmanial activity presented by these series.