Structure based design, stability study and synthesis of the dinitrophenylhydrazone derivative of the oxidation product of lanosterol as a potential P. falciparum transketolase inhibitor and in-vivo antimalarial study

The growing resistance to the current antimalarial drugs in the absence of a vaccine can be effectively tackled by identifying new metabolic pathways that are essential to the survival of the malaria parasite and developing new drugs against them. Triterpenes and steroids are the most abundant group of natural products with a great variety of biological activities. However, lanosterol is not known to possess any significant biological activity. In this study the binding and interactions of a dinitrophenyl hydrazine (DNP) derivative of lanosterol, LAN (a derivative that incorporates a substantially polar moiety into the steroid) with P. falciparum transketolase was studied by molecular docking and MD simulation with the view to exploit the DNP derivative as a lead in antimalarial chemotherapy development considering that the P. falciparum transketolase (PfTk) is a novel target in antimalarial chemotherapy. The enzyme catalyses the production of ribose sugars needed for nucleic acid synthesis; it lacks a three-dimensional (3D) structure necessary for docking because it is difficult to obtain a crystalline form. A homology model of PfTk was constructed using Saccharomyces cerevisiae transketolase (protein data bank ID of 1TRK) as the template. The compound was observed to have Free Energy of Binding higher than that of the cofactor of the protein (Thiamine Pyrophosphate, TPP) and a synthetic analog (SUBTPP) used as reference compounds after MD Simulation. The compound was synthesized in a two-step, one-pot reaction, utilizing a non-acidic and mild oxidant to oxidize the lanosterol in order to avoid the rearrangement that accompanies the oxidation of sterols using acidic oxidants. The LAN was characterized using IR spectroscopy and NMR experiments and tested in-vivo for its antimalarial chemo suppression using a murine model with Chloroquine as a standard. The LAN at a concentration of 25 mg/kg was found to have a comparable activity with Chloroquine at 10 mg/kg and no mortality was observed among the test animals 24 days post drug administration showing that the compound indeed has potential as an antimalarial agent and a likely inhibitor of PfTk considering that there is a strong agreement between the in-silico results and biological study.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40203-021-00097-8.

Anti-inflammatory and analgesic activity of a cucurbitacin isolated from Lagenaria breviflora Roberty fruit

BACKGROUND

In this study, the bioactive compound in Lagenaria breviflora Roberty responsible for its anti-inflammatory and analgesic activities was isolated and chemically characterized.

METHOD

Compounds in the whole fruit, bark, pulp and seed of L. breviflora were partitioned utilizing their various polarity in n-hexane, ethyl acetate, chloroform and ethanol. The fractions of the extract obtained were tested for their bioactivities. The fraction with the most consistent anti-inflammatory and analgesic activities was further purified using accelerated gradient chromatography (AGC) and open column chromatography. Elution of compounds in this fraction was monitored through the different chromatography methods using thin layer chromatography (TLC). The pure compound isolated from the chromatography methods was taken for chemical characterization and elucidation of the structure.

RESULTS

Ethyl acetate fraction of the whole fruit exhibited the most consistent anti-inflammatory and analgesic activities out of the 16 fractions obtained. Purification of this fraction with AGC yielded 7 subfractions composing of eluents with similar Rf values on the TLC plate. One of the sub-fractions yielded a compound which was further purified using the open column chromatography method. Eluent obtained from this sub-fraction was renamed YO1.

CONCLUSION

From the result of mass spectroscopy and nuclear magnetic resonance spectroscopy of the compound, the structure of YO1 was determined as a cucurbitacin with 10á-cucurbit-5-ene skeleton (9â-methyl-19-norlanosta 5-ene) backbone structure, with six carbon atoms attached to double bonds and one hydroxyl group.

Methanolic extract of Tetracera potatoria, an antiulcer agent increases gastric mucus secretion and endogenous antioxidants

In this study, the possible mechanism(s) underlying the antiulcer activity of the methanolic extract of the root of Tetracera potatoria (MeTp) was studied in albino rats. Misoprostol and omeprazole were used as reference drugs. The animals had MeTp administered to them at varying doses of 100, 400 and 800 mg/kg for 15 days. MeTp significantly (P < 0.05) increased gastric mucus secretion and gastric mucus cell counts when compared to control. MeTp treated animals also showed significant (P < 0.05) increase in the activity of SOD with concurrent decrease in the level of MDA with respect to control. These findings suggest that part of the gastroprotective property of MeTp is associated with the ability of the extract to cause stimulation of gastric mucus secretion through increased number of gastric mucus cells. Increased SOD-activity and decreased MDA-levels further lend support to its gastroprotective effect.

Antiulcerogenic effects of Tylophora conspicua in male rats

Studies were undertaken on the effect of a crude (TC) and an alkaloid fraction (TA) of the leaf extracts of Tylophora conspicua on indomethacin-induced gastric ulceration and gastric acid secretion in male albino rats. Both the TC and TA produced a dose-dependent inhibition of gastric ulceration. At a dose level of 40 mg/kg TC and TA were more effective (TA being more potent) than propranolol in inhibiting gastric ulceration. The highest dose of the extracts used (80 mg/kg) completely inhibited gastric ulceration. Intravenous administration of the TC and TA significantly decreased acid output at low dose (20 mg/kg), medium dose (40 mg/kg) and high dose (80 mg/kg) from the peak basal of 0.54 +/- 0.02 mEq/L/min to 0. 49 +/- 0.02 mEq/L/min, 0.35 +/- 0.01 mEq/L/min and 0.21 +/- 0.02 Meq/L/min respectively. 80 mg/kg of TC and TA significantly reduced the histamine (1 mg/kg) induced gastric acid secretion. The results suggest that the antiulcer activity of Tylophora conspicua might be produced by gastric acid inhibition.

Methyl angolensate: the antiulcer agent of the stem bark of Entandrophragma angolense

Methyl angolensate (1), the major compound isolated from the methanol extract of the stem bark of Entandrophragma angolense produced a dose-related inhibition of gastric ulceration, 40 mg/kg body weight (B.W.) being more effective than 40 mg/kg B.W. of propranolol. The highest dose used (80 mg/kg B.W.) completely inhibited gastric ulceration and significantly reduced gastric acidity (P < 0.05). Furthermore, 1 (40 mg/kg B.W.) significantly reduced gastric acid secretion induced by histamine (1.0 mg/kg B.W.) and carbachol (1.0 mg/kg B.W.). These results suggest that 1 produces its antiulcer activity by inhibition of gastric acid secretion.