David Vargas

Diterpenes from Solidago rugosa

Investigation of the roots and aerial parts of Solidago rugosa afforded the known diterpenes kolavenol, hardwickiic acid, (-)-kaur-16-en-19-oic acid, (+)-manool, (+)-3 beta-hydroxymanool, manoyl oxide and ent-abietic acid. In addition, the new labdane diterpene (+)-18-tigloyloxymanool and four new ent-abietanes were obtained. The structures of all known and new compounds were elucidated by spectroscopic methods, especially high-field 1H and 13C NMR, and inverse 1H-13C-correlation techniques, as well as chemical transformations. Six diterpenes were tested against Mycobacterium tuberculosis and M. avium, but showed no significant activities with minimum inhibitory concentrations of > 100 micrograms ml-1.

Polyacetylenes and diterpenes from Solidago canadensis

Abstract Investigation of the roots of Solidago canadensis resulted in the isolation of seven clerodane-type diterpenes related to kolavenic acid, one of wh

Sesquiterpenes and thiarubrines from Ambrosia trifida and its transformed roots

Abstract The roots of giant ragweed ( Ambrosia trifida ) afforded β-farnesene, β-bisabolene and squalene. In addition, thiarubrine B and its related thiop

Studies on the biosynthesis of thiarubrine A in hairy root cultures of Ambrosia artemisiifolia using 13C-labelled acetates

Abstract The 13C NMR spectra of thiarubrine A and B have been completely assigned. In a biosynthetic study using hairy root cultures of Ambrosia artemisiifolia, the 13C NMR spectra of thiarubrine A labelled by incorporation of [1-13C]-, [2-13C]- and [1,2-13C2]-acetate showed patterns of enrichment consistent with a biosynthetic pathway in which the 13-carbon 1,2-dithiin arises from a longer-chain precursor, most likely a 14-carbon homologue, by carbon-carbon scission.

Sesquiterpenes from southern Magnolia virginiana

Abstract A chemical study of the leaves of the southern evergreen Magnolia virginiana provided, besides the known sesquiterpene lactones costunolide, parthenolide and trifloculoside, two new sesquiterpenes, costunolact-12β-ol and its acetal dimer. The molecular structure of the acetal dimer of costunolact-12β-ol was determined by single crystal X-ray diffraction. An annual study of the relative ratios of the major sesquiterpenes in leaves of M. virginiana showed 90% of parthenolide in July/August and a minimum of M. virginiana could be detected in the annual study of the southern variety of this taxon.

Sesquiterpenes from Brintonia discoidea

Abstract Investigation of the roots of Brintonia discoidea resulted in the isolation of 10 eudesmane-type sesquiterpene cinnamates, two of which are new. In

Biosynthetic Studies of Bithiophenes in Hairy Root Cultures of Tagetes Patula Using 13C-labeled Acetates

Abstract Biosynthetic studies of two bithiophenes, [5-(3-buten-1-ynyl)-2,2′-bithiophene (BBT) and 5-(4-acetoxy-1-butynyl)-2,2′-bithiophene (BBTOAc)], were performed in hairy root cultures of Tagetes patula using [1-13C]-, [2-13C]- and [1,2-13C2]-labeled sodium acetate as precursors. The data support previous biogenetic proposals and demonstrate that hairy root cultures provide a highly suitable medium for biosynthetic studies of root constituents.

Sesquiterpene lactones from Squamopappus skutchii

Abstract Chemical analysis of Squamopappus skutchii afforded a new eudesmanolide, chapinolin, and two new guaianolides, skutchinolide A and B. Their structures were elucidated by 1H NMR and mass spectral methods.

Assignments of the 13C NMR Spectra of Enhydrin and 2′,3′-Dehydromelnerin A and the Molecular Structure of Enhydrin

Abstract Two melampolide-type sesquiterpene lactones, enhydrin and 2,′ 3′-dehydromelnerin A, were isolated from a Louisiana population of Polymnia uvedalia. Their 13C NMR spectra were assigned using 13C-1H correlation, DEPT and COLOC experiments. The molecular structure of enhydrin was established by single crystal X-ray diffraction.

Terpenes from Liatris ohlingerae

Abstract Investigation of the aerial parts of Liatris ohlingerae resulted in the isolation of seven heliangolide-type sesquiterpene lactones, two of which are new. In addition, four known triterpenes, taraxasterol, pseudo-taraxasterol and their acetates, were found. The structures of all compounds were elucidated by spectroscopic methods and spectral comparison with related compounds. The 13C NMR spectra of five sesquiterpenes were assigned by combined applications of COSY, inverse 1H, 13C-correlation and DEPT methods. The molecular structure of liscunditrin was determined by single crystal X-ray diffraction.