Methyl 5-Deoxy-α and β-D-Xylofuranosides

Wayanin and guaijaverin, two active metabolites found in a Psidium acutangulum Mart. ex DC (syn. P. persoonii McVaugh) (Myrtaceae) antimalarial decoction from the Wayana Amerindians

ETHNOPHARMACOLOGICAL RELEVANCE

Psidium acutangulum Mart. ex DC is a small tree used by the Wayana Amerindians from the Upper-Maroni in French Guiana for the treatment of malaria.

AIM OF THE STUDY

In a previous study, we highlighted the in vitro antiplasmodial, antioxidant and anti-inflammatory potential of the traditional decoction of P. acutangulum aerial parts. Our goal was then to investigate on the origin of the biological activity of the traditional remedy, and eventually characterize active constituents.

MATERIALS AND METHODS

Liquid-liquid extractions were performed on the decoction, and the antiplasmodial activity evaluated against chloroquine-resistant FcB1 ([(3)H]-hypoxanthine bioassay) and 7G8 (pLDH bioassay) P. falciparum strains, and on a chloroquine sensitive NF54 ([(3)H]-hypoxanthine bioassay) P. falciparum strain. The ethyl acetate fraction (D) was active and underwent bioguided fractionation. All the isolated compounds were tested on P. falciparum FcB1 strain. In vitro anti-inflammatory activity (IL-1β, IL-6, IL-8, TNFα) of the ethyl acetate fraction and of an anti-Plasmodium active compound, was concurrently assessed on LPS-stimulated human PBMC and NO secretion inhibition was measured on LPS stimulated RAW murine macrophages. Cytotoxicity of the fractions and pure compounds was measured on VERO cells, L6 mammalian cells, PBMCs, and RAW cells.

RESULTS

Fractionation of the ethyl acetate soluble fraction (IC50 ranging from 3.4 to <1µg/mL depending on the parasite strain) led to the isolation of six pure compounds: catechin and five glycosylated quercetin derivatives. These compounds have never been isolated from this plant species. Two of these compounds (wayanin and guaijaverin) were found to be moderately active against P. falciparum FcB1 in vitro (IC50 5.5 and 6.9µM respectively). We proposed the name wayanin during public meetings organized in June 2015 in the Upper-Maroni villages, in homage to the medicinal knowledge of the Wayana population. At 50µg/mL, the ethyl acetate fraction (D) significantly inhibited IL-1β secretion (-46%) and NO production (-21%), as previously observed for the decoction. The effects of D and guiajaverin (4) on the secretion of other cytokines or NO production were not significant.

CONCLUSIONS

The confirmed antiplasmodial activity of the ethyl acetate soluble fraction of the decoction and of the isolated compounds support the previous results obtained on the P. acutangulum decoction. The antiplasmodial activity might be due to a mixture of moderately active non-toxic flavonoids. The anti-inflammatory activities were less marked for ethyl acetate fraction (D) than for the decoction.

Diapolycopenedioic acid xylosyl esters A, B, and C, novel antioxidative glyco-C30-carotenoic acids produced by a new marine bacterium Rubritalea squalenifaciens

Novel acyl glyco-carotenoic acids, diapolycopenedioic acid xylosyl esters A, B, and C, were isolated as red pigments by using chromatographic methods from a marine bacterium, Rubritalea squalenifaciens, belonging to subdivision 1 of Verrucomicrobia. The structures of these diapolycopenedioic acid xylosyl esters were determined to be 4-[2-O-acyl-beta-D-xylopyranosyl] hydrogen 4,4'-diapo-Psi,Psi-carotene-4,4'-dioate by spectroscopic analysis. Diapolycopenedioic acid xylosyl ester A showed potent antioxidative activity in a (1)O(2) suppression model.

A Cyclic Enamine Derived from 1,2-O-Isopropylidene-α-d-xylofuranose As a Novel Carbohydrate Intermediate To Achieve Skeletal Diversity

The commercially available carbohydrate 1,2-O-isopropylidene-alpha-D-xylofuranose was efficiently transformed into the high-added-value synthetic scaffold 8. The transformation requires the synthesis of the 5-O-tosyl derivative 7 and its subsequent intramolecular cyclization under basic conditions to give the cyclic enamine 8. Reaction of 8 with O-, N-, S-, and C-nucleophiles and amino acids allowed its efficient transformation (one-step, high yields, and easy purifications) into fused cyclic sugar derivatives with rather unusual molecular skeletons in a completely regio- and stereoselective manner. The characteristics of the sugar derivative 8 established here, high reactivity, synthetic accessibility, and the potential for conversion into a vast collection of products by the action of different nucleophiles, indicate that it will prove to be a useful chiral intermediate for achieving skeletal diversity. The constrained structures and dense functionalization of the polycyclic sugar derivatives generated from 8 make these compounds promising candidates for use as starting agents for the production of new analogues and as drugs.

Conformational studies of methyl 3-O-methyl-alpha-D-arabinofuranoside: an approach for studying the conformation of furanose rings

A computational method for probing furanose conformation has been developed using a methylated monosaccharide derivative 1. First, a large library of conformers was generated by a systematic pseudo Monte Carlo search followed by optimization with the AMBER molecular mechanics force field. A subset of these conformers was then subjected to ab initio and density functional theory calculations in both the gas and aqueous phases. These calculations indicate that entropic contributions to the Gibbs free energy are important determinants of the Boltzmann distribution for the conformational preferences of 1 in the gas phase. The results obtained at each level of theory are discussed and compared with the experimentally determined conformer distribution from NMR studies in aqueous solution. In addition, the ability of each level of theory to reproduce the experimentally measured 1H-1H coupling constants in 1 is discussed. Empirical Karplus equations and density functional theory methods were used to determine average 3J(H1,H2), 3J(H2,H3), and 3J(H3,H4) for each level of theory. On the basis of this comparison, consideration of solvation with the MN-GSM model provided good agreement with the experimental data.