Alfredo Usubillaga

University of the Andes

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Luís B. Rojas

University of the Coast

Rosa Aparicio

University of the Andes

Judith Velasco

University of the Andes

Nancy Khouri

University of the Andes

Alexis Peña

Universidad de Los Andes

Libia Alarcón

Rafael Urdaneta University

Alida Pérez Colmenares

University of the Andes

Gina Meccia

University of the Andes

Bernardo Chataing

Universidad de Los Andes

Juan Carmona Arzola

Universidad de Los Andes

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University of the Andes

127

Universidad de Los Andes

Centre National de la Recherche Scientifique

Central University of Venezuela

Universidad Nacional Experimental del Táchira

Universidad de La Laguna

Laboratoire de Chimie

Laboratoire de Chimie Organique

Instituto Venezolano de Investigaciones Científicas

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Steroidal saponins from the fruits of Solanum torvum

Phytochemistry (2012)

Alida Pérez Colmenares Luís B. Rojas Anne‐Claire Mitaine‐Offer Laurent Pouységu Stéphane Quideau

10.1016/j.phytochem.2012.10.010

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Citations (11)

Synthesis and antimicrobial activity of new ent-kaurene-type diterpenoid derivatives

European Journal of Chemistry (2023)

Andrés Márquez Alida Pérez Colmenares Luís B. Rojas Rosa Aparicio Freddy A. Ramos

This research consists in the synthesis of ent-kaurene-type diterpenoid derivatives from the new natural product ent-kaur-3-acetoxy-15-ene, to carry out structural modifications on the C3 carbon of the ent-kaurene core by introducing different oxygenated groups, especially esters, in order to probe the structure-activity relationship (SAR) against microorganisms. The structure of the compounds was confirmed by FT-IR, 1H NMR, 13C NMR, and GC-MS. The antimicrobial activity of the synthesized derivatives was evaluated, ent-kaur-3-O-(6’,7’-bibenzyl-oxy-caffeoyl)-15-ene (4) exhibited activity against all tested microorganisms: Staphylococcus aureus (16 mm), Enterococcus faecalis (12 mm), Escherichia coli (13 mm), Klebsiella pneumoniae (10 mm), Pseudomonas aeruginosa (8 mm) and Candida krusei (10 mm). These results reveal a remarkable structure-activity relationship over the C3 carbon of the ent-kaurene core, where the presence of oxygenated groups such as hydroxyl or alkyl esters enhances activity.

Enterococcus faecalis

Candida krusei

Natural product

Proton NMR

10.5155/eurjchem.14.4.478-485.2478

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Analysis of Chemical Constituents of the Volatile Oil from Leaves of Solanum bicolor

Natural Product Communications (2010)

Alida Pérez Colmenares Luís B. Rojas E.M. Pérez-Laorga Arias Juan Carmona Arzola Alfredo Usubillaga

The volatile components from the leaves of Solanum bicolor Roemer & Schultes, was obtained by hydrodistillation and was analizad by GC/MS. A total of 20 compounds, representing 96.3 % of the oil, were identified. The dominant compounds were trans-caryophyllene (23.2%), trans-2-pentadecene (22.6%), germacrene D (12.2%), biciclogermecrene (8.0%) and caryophyllene oxide (4.7%).

Germacrene D

Germacrene

Caryophyllene

10.1177/1934578x1000500424

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Optimization of HPLC Conditions to Analyze Widely Distributed Ethoxylated Alkylphenol Surfactants

Journal of Liquid Chromatography &amp Related Technologies (1994)

N. Márquez Raquel Antón Alfredo Usubillaga Jean‐Louis Salager

Abstract Commercial ethoxylated alkylphenol surfactants are always a mixture of oligomers with different ethylene oxide number (EON). The different oligomers can be separated by various HPLC techniques. Isocratic mode with mixed solvent on silica column allows to separate oligomers up to EON = 10; gradient programming moves the limit up to EON = 15. For higher EON values (up to 25) a NH2 column has to be used, either with isocratic or gradient mode. Applications to the analysis of microemulsion systems and to the separation of tributyl phenol ethoxylates are discussed. Extreme separation of wide range EON distribution is attained with two columns (Si and NH2) in series, and a solvent programming.

Alkylphenol

Oligomer

Microemulsion

10.1080/10826079408013392

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Citations (44)

ESTUDIO POR DIFRACCIÓN DE RAYOS-X DE PRODUCTOS NATURALES AISLADOS DE PLANTAS DE LOS ANDES VENEZOLANOS

Revista cubana de química (2007)

Julia Bruno-Colmenárez Graciela Dı́az de Delgado Alfredo Usubillaga Nancy Khouri Juan M. Amaro‐Luis

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Composición química de los aceites esenciales de Piper dilatatum L.C. Rich. y Piper tuberculatum Jacq. de Mérida, Venezuela

Flor Mora Jhon Peña Luís B. Rojas Alfredo Usubillaga Pablo Meléndez

La composicion quimica del aceite esencial de las especies Piper dilatatum L.C. Rich. y Piper tuberculatum Jacq., provenientes de dos localidades del estado Merida, Venezuela, fue determinada. Los aceites esenciales fueron obtenidos por hidrodestilacion de las hojas frescas de la planta y analizados por espectrometria de gases-masa. En el aceite de P. dilatatum se identificaron 23 componentes que constituyen el 86,9% del aceite, de los cuales se encuentran en mayor proporcion el _-Pineno (17,2 %), el _-Pineno (10,8%) y el cis-Ocimeno (10,3%). En el aceite esencial P. tuberculatum se identificaron un total de 11 compuestos que conforman el 96,6% de la muestra, siendo el fenil propanoide dilapiol el componente mayoritario (72,4%). Esta especie representa una variedad quimiotaxonomica diferente a las reportadas en la literatura

Piperaceae

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Studies on Rearrangements in Derivatives of Grandiflorenic Acid, Part 2. Synthesis of Methyl (-)-20-Norkaur-9α-Methyl-5(10), 16-Dien-19-Oate, A New Tetracyclic Rosane-Type Diterpene

Journal of Natural Products (1986)

Tatsuhiko Nakano A. MARTIN Alfredo Usubillaga

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudies on Rearrangements in Derivatives of Grandiflorenic Acid, Part 2. Synthesis of Methyl (-)-20-Norkaur-9α-Methyl-5(10), 16-Dien-19-Oate, A New Tetracyclic Rosane-Type DiterpeneTatsuhiko Nakano, Alfonso Martín, and Alfredo UsubillagaCite this: J. Nat. Prod. 1986, 49, 1, 62–66Publication Date (Print):January 1, 1986Publication History Published online1 July 2004Published inissue 1 January 1986https://pubs.acs.org/doi/10.1021/np50043a006https://doi.org/10.1021/np50043a006research-articleACS PublicationsRequest reuse permissionsArticle Views81Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

10.1021/np50043a006

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Citations (5)

Comparación de los componentes volátiles mayoritarios endiferentes épocas del año de la Coespeletia timotensis Cuatrec

Revista de la Facultad de Farmacia de la Universidad de Los Andes (1999)

Luís B. Rojas Alfredo Usubillaga

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Estudio clínico de la efectividad de extractos alcaloideos obtenidos de los frutos del solanun americanum Miller sobre el herpes simplex herpes zoster y herpes genitalis

Bernardo Chataing Juan Luís Concepción Nersa Buitrago de Cristancho Alfredo Usubillaga

Herpes Genitalis

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On the Isomerization of ent-Kaurenic Acid

Natural Product Communications (2011)

Julio Otoniel Rojas Rosa Aparicio Thayded Villasmil Alexis Peña Alfredo Usubillaga

Kaurenic acid (1a) is a tetracyclic diterpene that has an exocyclic double bond at delta16. Isokaurenic acid (2a) has an endocyclic delta15double bond. This compound has been isolated from Espeletia tenore (Espeletinae), a resinous plant from the Venezuelan Andes, but its occurrence is rare. In order to obtain a larger amount of 2a, the isomerization of la, which is easily obtained from other Espeletinae, was tried. Kaurenic acid methyl ester (1b) was treated with dil. HCl in CH3Cl/EtOH, after 6 h under reflux a yield of 41.5% isokaurenic acid methyl ester (2b) was obtained but 35.7% 16alpha-ethoxy-kauran-19-oic acid methyl ester (3b) had formed as a byproduct. Treating 1b with CF3COOH in refluxing CH2Cl2 permitted to obtain a yield of 66.6% of 2b in 4 h and only traces of 16alpha-hydroxy-kauran-19-oic acid methyl ester (3a) as a byproduct. Both isomers were separated on a silica gel column impregnated with 20% AgNO3. Treating 2b with KOH in refluxing DMSO yielded pure isokaurenic acid, no back isomerization was observed.

10.1177/1934578x1100600703

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Citations (4)