Fluorescent pigment and phenol glucosides from the heartwood of Pterocarpus marsupium.

The fluorescence shown by extracts of the heartwood of Pterocarpus marsupium is attributed to salts of the new compound 1, whose structure was elaborated using detailed spectroscopic/spectrometric studies. The plant material also contains the nonfluorescent compounds 2 and 3. The absolute configuration of 1 was determined by experimental and theoretically calculated electronic CD spectra, while that of 3 was deduced from ECD comparison with reported results in the α-hydroxydihydrochalcone series.

A novel galacto-glycerolipid from Oxalis corniculata kills Entamoeba histolytica and Giardia lamblia.

Oxalis corniculata is a naturally occurring weed that has been used in traditional medicine for the cure of dysentery and diarrhea in India. One of the common causes of dysentery is due to infection by the protist pathogen Entamoeba histolytica. Bioactivity profiling of extracts from O. corniculata identified several compounds that showed antiamoebic activity in axenic cultures of E. histolytica. These were characterized by nuclear magnetic resonance, infrared, and mass spectrometry as (i) Oc-1, a mixture of saturated fatty acids C24 to C28; (ii) Oc-2, a mixture of long-chain alcohols C18 to C28; and (iii) Oc-3, a single compound that was a galacto-glycerolipid (GGL). Of the different compounds that were obtained, the strongest antiamoebic activity was found in GGL. The addition of GGL to E. histolytica xenic cultures containing other microbial flora from the large intestine did not affect its antiamoebic activity. Amoebicidal concentrations of GGL had no effect on intestinal microbial flora or on the mammalian cell line HEK-293. GGL was also found to be equally effective in killing another protist pathogen, Giardia lamblia, that causes diarrhea in humans. The importance of this study is based on the identification of novel natural products and the possibility of developing these compounds as active agents to treat at least two pathogenic parasitic intestinal infections endemic to tropical regions.

Effect of fatty acids and cholesterol present in bile on expression of virulence factors and motility of Vibrio cholerae.

Bile induces pleiotropic responses that affect production of virulence factors, motility, and other phenotypes in the enteric pathogen Vibrio cholerae. Since bile is a heterogeneous mixture, crude bile was fractionated, and the components that mediate virulence gene repression and enhancement of motility were identified by nuclear magnetic resonance, gas chromatography (GC), and GC-mass spectrometry analyses. The unsaturated fatty acids detected in bile, arachidonic, linoleic, and oleic acids, drastically repressed expression of the ctxAB and tcpA genes, which encode cholera toxin and the major subunit of the toxin-coregulated pilus, respectively. The unsaturated fatty acid-dependent repression was due to silencing of ctxAB and tcpA expression by the histone-like nucleoid-structuring protein H-NS, even in the presence of the transcriptional activator ToxT. Unsaturated fatty acids also enhanced motility of V. cholerae due to increased expression of flrA, the first gene of a regulatory cascade that controls motility. H-NS had no role in the fatty acid-mediated enhancement of motility. It is likely that the ToxR/ToxT system that negatively regulates motility is rendered nonfunctional in the presence of unsaturated fatty acids, leading to an increase in motility. Motility and flrA expression were also increased in the presence of cholesterol, another component of bile, in an H-NS- and ToxR/ToxT-independent manner.

Intramolecular nitrone cycloaddition reaction on carbohydrate-based precursors: application in the synthesis of spironucleosides and spirobisnucleosides.

A simple synthesis of chiral spironucleosides and spirobisnucleosides is described. Intramolecular 1,3-dipolar nitrone cycloaddition reaction of d-glucose-derived precursors having olefin at C-3 and nitrone at C-5, C-1, or C-2 (in nor-series) furnished bisisoxazolidinospirocycles 4-7, 11, and 12 in good yields. Reductive ring opening of the isoxazolidine moieties in 4-6 followed by construction of a nucleoside base upon the generated amino groups smoothly yielded spirobisnucleosides 17 and 18 and spironucleosides 20 and 21.