Leovigildo Quijano

Stimulation of witchweed germination by sesquiterpene lactones: a structure-activity study

Abstract Twenty-four natural and synthetic sesquiterpene lactones were tested as witchweed germination stimulants to determine the essential structural requirements for the stimulation of witchweed germination by dihydroparthenolide. All of the 10 germacranolides tested induced 40–65% germination of witchweed across a broad concentration range, from 10 −5 to 10 −9 M. The highest activity was observed with a mixture of the two eudesmanolides, santamarin and reynosin. These findings indicate that it is the spatial arrangement of the germacrane-eudesmane skeleton in conjunction with the five-membered lactone ring which is important in the promotion of witchweed germination, rather than the presence of any specific functional group on the molecule. The structure of these compounds is similar to portions of the active molecule (+)-strigol.

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.

Tetraludin A, B and C, three new melampolides from Tetragonotheca ludoviciana

Abstract The investigation of the roots of the four Tetragonotheca species, T. ludoviciana, T. repanda, T. texana and T. helianthoides , resulted in the isolation of the known heptadeca-2-( Z )-8,10-( E )-16-tetraene-4,6-diin-1-ol and its aldehyde derivative from all four species. Aerial parts of T. ludoviciana also contained the acetate of the latter compound as a minor constituent and provided three new melampolide-type sesquiterpene lactones, tetraludin A, B and C.

Sesquiterpene lactones and lignanes from Rudbeckia species

Abstract Rudbeckia grandiflora , R. subtomentosa , R. nitida var. texana , R. scabrifolia and R. maxima were investigated for their secondary constituents. Rudbeckia subtomentosa leaves afforded the known sesquiterpene lactones 4- O -desacetylligulatine C, and ligulatine C; the flowers provided costunolide, santamarine, reynosin, the flavonol eupatolin plus a mixture of β-sitosterol and stigmasterol; the roots gave costunolide, 11,13-dihydrocostunolide, gazaniolide, isogazaniolide, tamaulipin A angelate, caryophyllene, caryophyllene oxide and β-selinene. Rudbeckia nitida var. texana , R. scabrifolia and R. maxima gave the lignanes (+)-pinoresinol dimethyl ether and yangambin. The germacrolide tamaulipin A angelate, was the major constituent of root extracts of R. grandiflora . Structure and stereochemistry of the new lactones were elucidated by spectroscopic methods. The molecular structures of gazaniolide

Diterpenes from Chrysoma pauciflosculosa: Effects on Florida sandhill species

Abstract The aerial parts of Chrysoma pauciflosculosa (syn. Solidago pauciflosculosa ) gave the known diterpenes, 17-oxygrindelic acid, 17-oxogrindelic acid and 17-carboxygrindelic acid, as well as the new diterpene, 17-hydroxy-7α,8α-epoxygrindelic acid. 17-Oxogrindelic acid decomposes in the presence of air giving three products. The structural data of the diterpenes as well as those of degradation products and derivatives were elucidated by chemical and spectroscopic methods. 17-Oxygrindelic acid and 17-oxogrindelic acid were tested for their effect on the germination and radicle growth of three Florida sandhill species and Lactuca sativa . At concentrations of 12 to 48 ppm, 17-oxogrindelic acid reduced the germination and radicle growth of Schizachyrium scoparium and Leptochloa dubia , two native sandhill grasses, but had no significant effects on germination and only a slight stimulatory effect on radicle growth of Rudbeckia hirta and Lactuca sativa . Mixtures of 17-oxogrindelic acid with an equimolar mixture of three C. pauciflosculosa sesquiterpenes, (+)-curlone, (+)-sesquiphellandrene and (−)-α- trans -bergamontene, did not enhance activity. 17-Oxygrindelic acid was in general less active in reducing germination and growth than 17-oxogrindelic acid.

Guaianolides from Calea subcordata

Chemical analysis of Calea subcordata yielded three new guaianolides, 8-epi-isobutyrylrupicolin A, 8-epi-isobutyrylrupicolin B and subcordatolide A, which represent the first guaianolide-type sesquiterpene lactones reported in the genus Calea. The structures of the new compounds were established by chemical and spectroscopic methods.

Eudesmanolides, trichomatolides B–E, and A heliangolide from Calea trichomata

Abstract Calea trichomata gave in addition to four known 1β-hydroxy-8β-tigloyloxy-11(13)-eudesmen-6α, 12-olide derivatives a new heliangolide, 3-deoxy

Sesquiterpene and diterpene lactones from melampodium longipilum

Abstract the aerial parts of Melampodium longipilum afforded two new diterpene lactones, 17-hydroxy- and 17-acetoxyacanthoaustralide, and a new sesquiterpene lactone, repandin E, besides the known melampolides enhydrin and fluctuanin.

Eudesmanolides from Calea trichomata

Abstract Chemical analysis of Calea trichomata yielded, besides four known eudesmanolides, a new eudesmanolide, trichomatolide A. The structure of the new compound was established by chemical and spectral methods.