Structure-based drug design studies of the interactions of ent-kaurane diterpenes derived from Wedelia paludosa with the Plasmodium falciparum sarco/endoplasmic reticulum Ca²âº-ATPase PfATP6.

Malaria is responsible for more deaths around the world than any other parasitic disease. Due to the emergence of strains that are resistant to the current chemotherapeutic antimalarial arsenal, the search for new antimalarial drugs remains urgent though hampered by a lack of knowledge regarding the molecular mechanisms of artemisinin resistance. Semisynthetic compounds derived from diterpenes from the medicinal plant Wedelia paludosa were tested in silico against the Plasmodium falciparum Ca2+-ATPase, PfATP6. This protein was constructed by comparative modelling using the three-dimensional structure of a homologous protein, 1IWO, as a scaffold. Compound 21 showed the best docking scores, indicating a better interaction with PfATP6 than that of thapsigargin, the natural inhibitor. Inhibition of PfATP6 by diterpene compounds could promote a change in calcium homeostasis, leading to parasite death. These data suggest PfATP6 as a potential target for the antimalarial ent-kaurane diterpenes.

Synthesis, cytotoxicity and antiplasmodial activity of novel ent-kaurane derivatives.

This paper reports on the syntheses and spectrometric characterisation of eleven novel ent-kaurane diterpenoids, including a complete set of (1)H, (13)C NMR and crystallographic data for two novel ent-kaurane diepoxides. Moreover, the antineoplastic cytotoxicity for kaurenoic acid and the majority of ent-kaurane derivatives were assessed in vitro against a panel of fourteen cancer cell lines, of which allylic alcohols were shown to be the most active compounds. The good in vitro antimalarial activity and the higher selectivity index values observed for some ent-kaurane epoxides against the chloroquine-resistant W2 clone of Plasmodium falciparum indicate that this class of natural products may provide new hits for the development of antimalarial drugs.

The semi-synthetic kaurane ent-16α-methoxykauran-19-oic acid induces vascular relaxation and hypotension in rats.

The present work investigates the mechanisms involved in the vasorelaxant effect of ent-16α-methoxykauran-19-oic acid (KA-OCH3), a semi-synthetic derivative obtained from the kaurane-type diterpene ent-kaur-16-en-19-oic acid (kaurenoic acid). Vascular reactivity experiments were performed in aortic rings isolated from male Wistar rats using standard muscle bath procedures. The cytosolic calcium concentration ([Ca2+]c) was measured by confocal microscopy using the fluorescent probe Fluo-3 AM. Blood pressure measurements were performed in conscious rats. KA-OCH3 (10, 50 and 100 µmol/l) inhibited phenylephrine-induced contraction in either endothelium-intact or endothelium-denuded rat aortic rings. KA-OCH3 also reduced CaCl2-induced contraction in a Ca2+-free solution containing KCl (30 mmol/l) or phenylephrine (0.1 µmol/l). KA-OCH3 (0.1-300 µmol/l) concentration-dependently relaxed endothelium-intact and endothelium-denuded aortas pre-contracted with either phenylephrine or KCl, to a greater extent than kaurenoic acid. Moreover, a Ca2+ mobilisation study showed that KA-OCH3 (100 µmol/l) inhibited the increase in Ca2+ concentration in smooth muscle and endothelial cells induced by phenylephrine or KCl. Pre-incubation of intact or denuded aortic rings with NG-nitro-L-arginine methyl ester (L-NAME, 100 µmol/l), 7-nitroindazole (100 µmol/l), wortmannin (0.5 µmol/l) and 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 µmol/l) produced a rightward displacement of the KA-OCH3 concentration-response curve. Intravenous administration of KA-OCH3 (1-10 mg/kg) reduced mean arterial blood pressure in normotensive rats. Collectively, our results show that KA-OCH3 induces vascular relaxation and hypotension. The mechanisms underlying the cardiovascular actions of KA-OCH3 involve blockade of Ca2+ influx and activation of the NO-cGMP pathway.

Preparation and phytotoxicity of novel kaurane diterpene amides with potential use as herbicides.

Novel kaurane ditepene monoamides were synthesized in good yields directly from kaurenoic ( 1) and grandiflorenic ( 2) acids and unprotected symmetrical diamines, using a modified protocol for monoacylation. Amides from 1 and 2 and monoamines were also obtained and tested against seed germination and growth of radicle and shoot of Lactuca sativa (lettuce), at 10 (-3), 10 (-5), and 10 (-7) M. Amides from symmetrical diamines showed significant inhibitory activity at higher concentrations.

Synthesis and trypanocidal activity of ent-kaurane glycosides.

Novel ent-kaurane glucosides were synthezised by a Koenigs-Knorr reaction between C17 and C19 alcohols derived from kaurenoic acid and 2,3,4,6-tetra-O-acetyl-glucopyranosyl bromide, followed by the hydrolysis of the acetates. Main products were assayed in vitro and in vivo against blood trypomastigote forms of Trypanosoma cruzi, the aetiological agent of Chagas' disease (American trypanosomiasis). The results allowed to establish structure-activity relationships among these derivatives, as well as pointed out the C19-methylester-C17-O-glucoside as a potential trypanocidal agent, whose trypanocidal profile was shown to be comparable to those of gentian violet and benznidazole.