Germacranolides from Schkuhria anthemoidea

The isolation of eucannabinolide and three new sesquiterpene lactones from Schkuhria anthemoidea is reported. The structures and stereochemistries of the new compounds were established by chemical and spectroscopic means. The structure of santhemoidin B was confirmed by X-ray crystallography.     

Germacranolides from Piptolepis leptospermoides

Piptolepis leptospermoides afforded, in addition to known compounds, a new eremanthanolide and a germacranolide closely related to piptolepolide.     

Germacranolides from Mikania grazielae

Mikania grazielae afforded two new germacranolides which were identified as 2α-acetoxyeupatolide and 2α-acetoxylaurenobiolide.     

Germacranolides from Stilpnopappus species

The investigation of four Stilpnopappus species afforded in addition to known compounds seven new germacranolides, all related to glaucolides. The structures were elucidated by spectroscopic methods. The chemotaxonomy of the genus is discussed briefly.     

Germacranolides from Mikania guaco

Fourteen novel sesquiterpene lactones of the germacranolide type have been isolated from the aerial parts of Mikania guaco: six costunolide, two melampolide and six germacra-4-trans,10(14),11(13)-trien-12.6alpha-olide derivatives. Except for one compound all the others possess a carbonyl function at C-9. Eight were obtained in the form of four isomer pairs which were difficult to separate. Structure elucidation was based on mass and ID and 2D NMR measurements. Low energy conformations were obtained by quantum mechanical calculations. Pyrrolizidine alkaloids could not be detected.     

Germacranolides from Lychnophora species

The investigation of three further Lychnophora species and the re-investigation of one species afforded, in addition to known compounds, seven new sesquiterpene lactones all being closely related to those isolated before from the subtribe Lychnophorinae. Furthermore, a new bisabolene diketone was present in one species. The structures were elucidated by spectroscopic methods. The chemotaxonomic situation of the genus is briefly discussed.     

Germacranolides from Proteopsis Argentea

Proteopsis argentea (tribe Vernonieae) afforded in addition to known compounds three new sesquiterpene lactones, closely related to those isolated from Eremanthus species, indicating a close relationship between these genera.     

Germacranolides from Calea urticifolia

Four germacranolides, named calealactones A-C and calealactone B [corrected] were isolated from the leaves of Calea urticifolia (Compositae) in addition to three known germacranolides. Their structures were established on the basis of spectroscopic analysis including by 2D NMR spectroscopy. Calealactone C and 2,3-epoxyjuanisulamin displayed potent toxicity to U937 cells.     

Germacranolides from Dicoma tomentosa

An investigation of the aerial parts of Dicoma tomentosa afforded four new germacranolides and four melampolides together with urospermal A and its 11β,13-dihydroderivative. The structures were elucidated by spectroscopic methods. The chemotaxonomic situation is discussed briefly.     

Germacranolides from Inula cappa

Authentic Inula cappa DC afforded a known and four unknown germacranolides related to the ineupatorolides as well as a new 2,3-dihydroxy-9-angeloxygermacra-4-en-6,12-olide. A collection previously described as Inula cappa which yielded only flavones was identified as Blumea balsamifera DC.     

Germacranolides and diterpenes from Viguiera species

The investigation of six Viguiera species afforded in addition to known compounds two new diterpenes, the 9,11-dehydro derivatives of trachylobanic and stachenic acid, two new heliangolides closely related to viguiestenin, and the acetate of falcarinol. The chemotaxonomic situation is discussed briefly.     

Germacranolides from Gochnatia vernonioides

The aerial parts of Gochnatia vernonioides afforded, in addition to dehydrocostus lactone, zaluzanin C and desacetyllaurenobiolide angelate, 14 further sesquiterpene lactones, ten 8, 12-and three 6,12-germacranolides as well as one eudesmanolide and three bisabolene derivatives. The structures were elucidated by spectroscopic methods and by comparing the data with those of closely related compounds. 8α-Angeloyloxytaraxic acid underwent an unusual autocatalysed cyclisation while the usual Cope rearrangement was not observed.     

Germacranolides from Eupatoriastrum nelsonii

The aerial parts of Eupatoriastrum nelsonii afforded, in addition to known sesquiterpene lactones, four new lactones all closely related to the germacranolides isolated previously from other genera of the tribe Eupatorieae. The structures were elucidated by spectroscopic methods. Chemotaxonomic aspects are discussed briefly.     

Germacranolides from Helianthus californicus

Five germacranolide sesquiterpene lactones and a trachylobane diterpene were isolated from the hexaploid species Helianthus californicus. Four of the sesquiterpene lactones are new, including a 1-oxo-3,10-diol without any carbon-carbon double bonds in the main ring whose structure was confirmed by X-ray crystallography. These results require revision of the structures of several previously published compounds. Two of the germacranolides have alkyl ether functions at a position β to a ketone and are believed to be artifacts of the isolation process. Based on terpenoid chemistry, there are no obvious progenitors of H. californicus among the diploid species of Helianthus examined to date.     

Germacranolides from Viguiera microphylla

Three new germacranolides, including two heliangolides (niveusin C-2′,3′-epoxide and 1,2-dehydroniveusin C-2′,3′-epoxide) and a germacrolide (3β-hydroxy-8β-epoxyangeloyloxycostunolide-1β,10α-epoxide) were isolated from Viguiera microphylla. Their structures were established by spectroscopic analyses, including extensive ¹H NMR and ¹³C NMR decoupling experiments and chemical transformations. X-ray diffraction analysis confirmed the structure of niveusin C-2′,3′-epoxide.     

Germacranolides from Piptolepis Ericoides and Vanillosmopsis species

The aerial parts of Piptolepis ericoides afforded in addition to known compounds two new germacranolides, a zexbrevanolide and piptolepolide, tentatively characterized as a germacranolide with a trans-disubstituted double bond. From the aerial parts of two Vanillosmopis species in addition to goyazensolide, a new isomer with an exocyclic double bond was isolated.     

Germacranolides from Artemisia myriantha and their conformation

The CH(2)Cl(2) extract of the aerial parts of Artemisia myriantha afforded three germacranolides derived from 13-acetoxy-3beta-hydroxy-germacra-1(10)E,4E,7(11)-trien-12,6alpha-olide, whose structures were elucidated by 2D-NMR spectroscopic analyses. Some conclusions are drawn about the possible conformations of the ten-membered germacranolide ring system from the exchange peaks seen in the NOESY spectra, and an estimate is made of the energy barrier to ring-flipping from variable-temperature NOESY experiments. The conclusions reached were supported by molecular modeling studies and an NMR spectroscopic investigation of the commercially available germacranolide, parthenolide.     

Germacranolides and an alkyl glucoside from Tanacetum vulgare

The aerial parts of Tanacetum vulgare afforded two new germacranolides and an n-decyl glucoside. The structures have been elucidated by spectroscopic methods and chemical transformations.