- Absolute configuration of helminthogermacrene
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The absolute configuration of the sesquiterpene hydrocarbon helminthogermacrene is established. Helminthogermacrene is an (E,Z)-configurational isomer of germacrene A and thus undergoes similar transformations forming elemenes via Cope rearrangement and yielding bicyclic systems via acid catalyzed reactions. The reaction products are investigated using enantioselective GC and extensive NMR measurements (1H-; 1H1H-COSY; HSQC; HMBC and NOE-experiments). In addition, NMR data of related compounds isolated during the course of this investigation not yet reported in literature are given.
- Adio, Adewale Martins,Paul, Claudia,Tesso, Hailemichael,Kloth, Petra,Koenig, Wilfried A.
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p. 1631 - 1635
(2007/10/03)
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- Germacrenes from fresh costus roots
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Four germacrenes, previously shown to be intermediates in sesquiterpene lactone biosynthesis, were isolated from fresh costus roots (Saussurea lappa). The structures of (+)-germacrene A, germacra-1(10),4,11(13)-trien-12-ol, germacra-1(10),4,11(13)-trien-12-al, and germacra-1(10),4,11(13)-trien-12-oic acid were deduced by a combination of spectral data and chemical transformations. Heating of these compounds yields (-)-β-elemene, (-)-elema-1,3,11(13)-trien-12-ol, (-)-elema-1,3,11(13)-trien-12-al, and elema-1,3,11(13)-trien12-oic acid respectively, in addition to small amounts of their diastereomers. Acid induced cyclisation of the germacrenes yields selinene, costol, costal, and costic acid respectively. It is highly probable that the elemenes reported in literature for costus root oil are artefacts.
- De Kraker, Jan-Willem,Franssen, Maurice C.R,De Groot, Aede,Shibata, Toshiro,Bouwmeester, Harro J
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p. 481 - 487
(2007/10/03)
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- Sesquiterpenes from the essential oil of the liverwort Conocephalum conicum
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Three new brasilane type sesquiterpenes related to the known alcohol conocephalenol and the sesquiterpene alcohol presilphiperfolan-1-ol were isolated from a chemotype of the liverwort Conocephalum conicum collected in southern Germany and identified by NMR investigations, enantioselective gas chromatography and chemical correlations. In addition ent-(-)-dactylol, the enantiomer of a compound so far only found as a constituent of the Caribbean sea hare Aplysia dactylomela, was identified.
- Melching, Stephanie,Koenig, Wilfried A.
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p. 517 - 523
(2007/10/03)
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