Noemí Waksman

Stereochemical Analysis of Leubethanol, an Anti-TB-Active Serrulatane, from Leucophyllum frutescens

Bioactivity-guided fractionation of the methanolic root bark extract of Leucophyllum frutescens led to the identification of leubethanol (1), a new serrulatane-type diterpene with activity against both multi-drug-resistant and drug-sensitive strains of virulent Mycobacterium tuberculosis. Leubethanol (1) was identified by 1D/2D NMR data, as a serrulatane closely related to erogorgiane (2), and exhibited anti-TB activity with minimum inhibitory concentrations in the range 6.25-12.50 μg/mL. Stereochemical evidence for 1 was gleaned from 1D and 2D NOE experiments, from 1H NMR full spin analysis, and by comparison of the experimental vibrational circular dichroism (VCD) spectrum to density functional theory calculated VCD spectra of two diastereomers.

Determination of the Antioxidant Activity of Plants from Northeast Mexico

Abstract Six methanol extracts from different parts of plants used in northeast Mexico as general health supplements were examined for their potential as antioxidants. The plants evaluated were: Turnera diffusa. Wild. (Turneraceae), Cucurbita. foetidissima Kunth (Cucurbitaceae), Flourensia cernua. D.C. (Asteraceae), Selaginella pilifera. A. Braun (Selaginellaceae), Juglans mollis. Engelm. (Juglandaceae) and Centaurea americana. Nutt. (Asteraceae alt. Compositae). Antioxidant properties of these extracts were evaluated by means of different assays, including the l,l-diphenyl-2-picrylhydrazyl radical test by TLC and spectrophotometry, inhibition of xanthine oxidase (XO) activity, and total phenolics content. Five plants showed high scavenging potential; their total phenolics content was also high. The extracts from four plants inhibited the activity of XO. Two of the most promising plants, T. diffusa. and J. mollis., did not show cytotoxicity. Considering that antioxidants prevent lipid peroxidation in foods and help in the treatment and prevention of degenerative illness, these two species are good candidates to be considered and further evaluated as natural additives in foods to provide protection against oxidative degradation.

Host defenses in subcutaneous mycoses.

Subcutaneous mycoses include diverse clinical syndromes, characterized by invasion of the skin and subcutaneous tissue by saprobic fungi. Individuals living in rural areas constantly suffer lesions or trauma; however, only a few of them develop disease. In this contribution, we describe recent advances in the understanding of the virulence of these organisms, focusing on the most prevalent infections, sporotrichosis, chromoblastomycosis, and mycetoma. Although these infectious diseases are considered neglected tropical diseases, modern molecular techniques have been able to identify the etiologic agents and observe variations in the former monolithic concept of the species, which was based mostly on morphologic characteristics. The complete genetic characterization of the causative agents, along with that of their host, will help in the understanding of the factors on which the development of these infections depends.

Biologically active anthracenones from roots of Karwinskia parvifolia

Tullidinol, a neurotoxin isolated from fruits and roots of several Karwinskia species, was resolved for the first time into two stereoisomers. This was achieved by means of preparative HPLC from roots of Karwinskia parvifolia. Structural assignments were made on the basis of spectroscopic data, including long range correlations as well as geometry optimization by means of semi-empirical methods.

Dioxins in beef samples from Mexico using a low resolution GC/MS screening method

Dioxins in beef were quantified by high resolution gas chromatography coupled to low-resolution mass spectrometry (GC/LRMS). The analyses were performed according to the minimum requirements described in the USEPA 1613 method with some minor modifications. Levels found in the samples were in the range 1.02–8.04 pg WHO-TEQ PCDDs/PCDFs g−1 fat. For comparison purposes, the maximum level allowed by the European Union is 3 pg WHO-TEQ PCDDs/PCDFs g−1 fat, and some of these samples surpassed the above-mentioned limit and can be considered as contaminated food. The results confirm that a preliminary screening of dioxins in beef can be performed by GC/LRMS. As far as we know, this is the first report of dioxins in beef in Mexico. After the appropriated tests, the applied methodology could be considered as an alternative screening method for the analysis of PCDD/Fs in other food products.

Centrosymmetric Binuclear Boron Compounds Derived from Dithiooxamides: Synthesis, Characterization, and Their Photophysical Properties

In this paper, we report the synthesis and characterization of new boron compounds derived from dithiooxamides. The compounds were characterized by NMR (1H and 13C), UV-vis, fluorescence spectroscopy, and high resolution mass spectrometry. The crystal structure of the mononuclear boron compound was determined by single-crystal X-ray diffraction analysis. The photophysical properties of the boron compounds were investigated, and we found moderate fluorescence emission (compound 2 ΦF: 4.07% and compound 4 ΦF: 2.89%). We also observed that the mononuclear complex presented greater stability. Compound 4 showed interesting luminescent properties; in solid state, it exhibited an increase in fluorescence by mechanostimuli by changing to a bright red color, and also in solution, it showed a decrease in fluorescence intensity when oxygen and air were supplied to the solution.

4-[(E)-(4-Fluoro-benzyl-idene)amino]-benzoic acid.

In the title compound, C14H10FNO2, the benzene rings make a dihedral angle of 57.50 (13)°, and the molecule has an E configuration about the C=N bond. In the crystal, molecules are linked via pairs of O—H⋯O hydrogen bonds, forming inversion dimers.