Rogelio Pereda-Miranda

Screening for antimicrobial activity of crude drug extracts and pure natural products from Mexican medicinal plants

Preliminary antimicrobial screening against Candida albicans and selected Gram-positive and Gram-negative bacteria of methanol extracts prepared from eight Mexican medicinal plants, noted for their antiseptic properties, was conducted. The significant activity exhibited for extracts of Ratibida latipalearis, Teloxys graveolens, Dodonaea viscosa, Hyptis albida, H. pectinata, H. Suaveolens and H. verticillata tends to support their traditional use as anti-infective agents. Only the extract of Hintonia latiflora was inactive. The antimicrobial activities of 44 pure natural compounds and two derivatives were determined. Of these, only 23 compounds were effective in inhibiting the growth of the tested organisms (MIC less than or equal to 100 micrograms/ml).

Application of molecular mechanics in the total stereochemical elucidation of spicigerolide, a cytotoxic 6-tetraacetyloxyheptenyl-5,6-dihydro-α-pyrone from Hyptis spicigera☆

Abstract Bioactivity-directed fractionation of the crude extract prepared from the medicinal Mexican plant Hyptis spicigera (Lamiaceae) tested on KB cells led to the isolation of spicigerolide (1). The structure for this novel cytotoxic compound was elucidated as 6R-[3S,4S,5S,6S-tetraacetyloxy-1Z-heptenyl]-5,6-dihydro-2H-pyran-2-one. The relative stereochemistry of this flexible molecule was determined by a combination of molecular mechanics calculations and 1H–1H coupling constant data, while the absolute configuration was established according to CD measurements. The MM/3JH–H calculations, as applied to 1, was validated with model linear compounds prepared from l -rhamnose: 2,3,4,5-tetra-O-acetyl-6-deoxy- l -mannose (5) and tetra-O-acetyl-1,6-dideoxy- l -mannitol (8). Both compounds possess the same stereochemistry predicted to be present in the acyclic moiety of spicigerolide (1) but lacking the stereochemical influence of the chiral pyrone.

Inhibitors of Bacterial Multidrug Efflux Pumps from the Resin Glycosides of Ipomoea murucoides

A reinvestigation of the CHCl 3-soluble extract from flowers of the Mexican medicinal arborescent morning glory, Ipomoea murucoides, through preparative-scale recycling HPLC, yielded six new pentasaccharides, murucoidins VI-XI (1- 6), as well as the known pescaprein III (7), stoloniferin I (8), and murucoidins I-V (9- 13). Their structures were characterized through the interpretation of their NMR spectroscopic and FABMS data. Compounds 1-6 were found to be macrolactones of three known glycosidic acids identified as simonic acids A and B, and operculinic acid A, with different fatty acids esterifying the same positions, C-2 on the second rhamnose unit and C-4 on the third rhamnose moiety. The lactonization site of the aglycone was placed at C-2 or C-3 of the second saccharide unit. The esterifying residues were composed of two short-chain fatty acids, 2-methylpropanoic and (2S)-methylbutyric acids, and two long-chain fatty acids, n-dodecanoic (lauric) acid and the new (8R)-(-)-8-hydroxydodecanoic acid. For the latter residue, its absolute configuration was determined by analysis of its Mosher ester derivatives. All members of the murucoidin series exerted a potentiation effect of norfloxacin against the NorA overexpressing Staphylococcus aureus strain SA-1199B by increasing the activity 4-fold (8 microg/mL from 32 microg/mL) at concentrations of 5-25 microg/mL. Stoloniferin I (8) enhanced norfloxacin activity 8-fold when incorporated at a concentration of 5 microg/mL. Therefore, this type of amphipathic oligosaccharide could be developed further to provide more potent inhibitors of this multidrug efflux pump.

Metabolic Profiling of the Mexican Anxiolytic and Sedative Plant Galphimia glauca Using Nuclear Magnetic Resonance Spectroscopy and Multivariate Data Analysis

Galphimia glauca is popularly employed in Mexico for the treatment of central nervous system disorders. Pharmacological and phytochemical studies have resulted in the identification of the anxiolytic and sedative principle consisting of a mixture of nor-secofriedelanes, named the galphimine series (1 - 9). These active constituents were found in plants collected in the vicinity of a restricted region in Central Mexico, where this species is abundant. A metabolic profiling carried out by means of 1H-NMR spectroscopy and multivariate data analysis was applied to crude extracts from wild plant populations, collected from six different locations as a quality control assessment, in order to differentiate their chemical profile. Principal component analysis (PCA) of the 1H-NMR spectra revealed clear variations among the populations, with two populations out of the six studied manifesting differences, when the principal components PC-1 and PC-2 were analyzed. These two PCs permitted the differentiation of the various sample populations, depending on the presence of galphimines. This information consistently correlated with the corresponding HPLC analysis. The neuropharmacological effects of the crude extracts were evaluated by using ICR mice in the elevated plus maze, as well as the sodium pentobarbital-induced hypnosis models. Both assays demonstrated anxiolytic and sedative responses only among those sample populations which had previously been differentiated by PC-1. Partial least square regression-discriminant analysis (PLS-DA) also confirmed a strong correlation between the observed effects and the metabolic profiles of the plants. The overall results of this study confirm the benefits of using metabolic profiling for the in silico analysis of active principles in medicinal plants.

Biodynamic constituents in the Mexican morning glories: purgative remedies transcending boundaries.

Jalap, a pre-Hispanic herbal remedy still considered a useful laxative, is an ingredient in some over-the-counter products sold by herbalists in contemporary Mexico. The purgative crude drugs are prepared from the roots of several morning glories species which all have been identified as members of the Ipomoea genus (Convolvulaceae). Their incorporation as therapeutical agents into Europe is an outstanding example of the assimilation of botanical drugs from the Americas as substitutes for traditional Old World remedies. Phytochemical investigations on the resin glycosides, main constituents of these drugs, were initiated during the second half of the XIX century; however, the structures of their active ingredients had remained poorly known, and still are for some members of these purgative root species. Modern analytical techniques with higher resolution capabilities (HPLC) for the isolation of the active principles of these crude drugs used in conjunction with powerful spectroscopic methods (high field NMR) have facilitated the investigation of these relevant, to the herbal product market, convolvulaceous species during the last decade. The advantages and limitations of theses techniques will be discussed. This review will also describe the ethnobotanical information associated with the Mexican morning glory species and how the traditional usages of these plants have played an important role in the selection of these materials for chemical studies. Little is as yet known about either the mechanism of purge action caused by the resin glycosides or the ecological significance of these same compounds for the producing plants. Over the five centuries of Mexican herbal medicine, one hundred years of phytochemistry has only partially elucidated the active ingredients of the jalap roots but has exemplified how to further contemporary drug discoveries through the investigation of those plants traditionally held to be economically and medicinally important in developing countries.

Hepatotoxic pyrrolizidine alkaloids in the Mexican medicinal plant Packera candidissima (Asteraceae: Senecioneae)

A study of the hepatotoxic pyrrolizidine alkaloids (PAs) contained in Packera candidissima (Greene) Weber & Löve (Senecio candidissimus Greene), a Mexican medicinal plant used for the treatment of kidney ailments and noted for its antiseptic properties, is reported. Analysis by TLC and GC-MS have shown the presence in high levels of both PAs and their N-oxides in the root (0.76% dry weight) and the aerial parts (0.36% dry weight) of the plant material. GC-MS analysis showed the presence of senecionine, integerrimine, retrorsine, and usaramine in the aerial parts. The root was found to contain senkirkine as the major component. These results indicate that users of this herb are at high risk of poisoning, especially members of certain cultural groups in Northern Mexico and the Hispanic population in the southwestern United States. In addition, two sesquiterpenes, neoadenostylone and epineoadenostylone were identified from the neutral extracts of this plant material. The 6 alpha-angeloyloxy-9-oxo-delta 10(1)-furanoeremophilane is reported for the first time as a natural product.

HPLC Isolation and structural elucidation of diastereomeric niloyl ester tetrasaccharides from Mexican scammony root

Abstract The application of preparative-scale recycling HPLC is illustrated by describing the complete resolution of diastereomeric mixtures of niloyl esters involving both of the (2R,3R) and (2S,3S) enantiomers of 3-hydroxy-2-methylbutanoic acid bonded to a macrocyclic tetrasaccharide from the resin of the Mexican scammony root (Ipomoea orizabensis). The characterization of 13 new diastereomeric niloyl ester glycosides, orizabins IX–XXI, based on the same structure of scammonic acid A was performed by high field NMR spectroscopy. The absolute configuration of the stereogenic carbinol center in the saponification-liberated nilic acid residues esterifying each of the individual pure glycolipids has been determined by careful 1H NMR analysis of (S)- and (R)-Moshers ester derivatives.

Reversal of multidrug resistance by morning glory resin glycosides in human breast cancer cells.

Reversal of multidrug resistance (MDR) by thirty resin glycosides from the morning glory family (Convolvulaceae) was evaluated in vinblastine-resistant human breast carcinoma cells (MCF-7/Vin). The effects of these amphipathic compounds on the cytotoxicity and P-glycoprotein (P-gp)-mediated MDR were estimated with the sulforhodamine B colorimetric assay. Active noncytotoxic compounds exerted a potentiation effect of vinblastine susceptibility by 1- to over 1906-fold at tested concentrations of 5 and 25 μg/mL. Murucoidin V (1) enhanced vinblastine activity 255-fold when incorporated at 25 μg/mL and also, based on flow cytometry, significantly increased the intracellular accumulation of rhodamine 123 with the use of reserpine as a positive control for a MDR reversal agent. Incubation of MCF-7/Vin cells with 1 caused an increase in uptake and notably lowered the efflux rate of rhodamine 123. Decreased expression of P-glycoprotein by compound 1 was detected by immunofluorescence flow cytometry after incubation with an anti-P-gp monoclonal antibody. These results suggest that resin glycosides represent potential efflux pump inhibitors for overcoming MDR in cancer therapy.

Antimycobacterial agents from selected Mexican medicinal plants

As part of the ICBG program Bioactive Agents from Dryland Biodiversity of Latin America, the present investigation was undertaken to explore the possible antimycobacterial potential of compounds derived from selected Mexican medicinal plants. Bioassay‐guided fractionation of the crude extracts of Rumex hymenosepalus (Polygonaceae), Larrea divaricata (Zygophyllaceae), Phoradendron robinsonii (Loranthaceae) and Amphipteryngium adstringens (Julianiaceae) led to the isolation of several antimycobacterial compounds. Four stilbenoids, two flavan‐3‐ols and three anthraquinones were isolated from R. hymenosepalus. Two flavonols and nordihydroguaiaretic acid were obtained from L. divaricata. Sakuranetin was the antimycobacterial agent isolated from P. robinsonii. Two known triterpenoids and the novel natural product 3‐dodecyl‐1,8‐dihydroxy‐2‐naphthoic acid were obtained from A. adstringens. In general, the isolates were identified by spectral means. The antimycobacterial activity of the secondary compounds isolated from the analysed species, as well as that of nine pure compounds previously isolated in our laboratories, was investigated; the MIC values ranged from 16 to 128μ mL−1. Among the tested compounds, the glycolipids, sesquiterpenoids and triterpenoids showed the best antimycobacterial activity. The antimycobacterial property of the glycolipids is reported for the first time. Although the tested compounds showed moderate antimycobacterial activity, their presence in the analysed species provides the rationale for their traditional use in the treatment of tuberculosis.

Flavonoids and terpenoids of Chenopodium graveolens

Abstract Three flavonoids, four terpenoids and three steroids were isolated from Chenopodium graveolens. These included pinostrobin, stigmasterol, stigmast-22-en-3-ol, 3α-sitosteryl-glucoside, geranyl acetate, pinocembrin, chrysin, cryptomeridiol, and two new sesquiterpenes which were characterized by spectral means as (+)-8α-hydroxyelemol and (+)-8α-acetoxycryptomeridiol.