ISSN:
1572-8854
Keywords:
Sesquiterpene lactone
;
melampolide
;
montahibisciolide
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract The structures of a new skeletal type of sesquiterpene lactone, containing a seven, five, fivering system, and of its putative precursor, a 9-oxo-melampolide, have been confirmed by single crystal X-ray structure determination. The central 5-membered ring of the new skeleton istrans-fused to the cycloheptene ring andcis-fused to the lactone ring. Transannular interactions and the geometry of thetrans carbon-carbon double bond of the oxo-melampolide and the keto-group at C9, suggest that the new seven, five, five tricyclic skeleton-type of montahibisciolide can easily be reached by a transannular cyclization process. The isobutyrloxy group of the oxo-melampolide is disordered into two partially populated conformations. 8α-(2′-Methylbutyryloxy)-9α-hydroxymontahibisciolide,3, C20H28O5, crystallizes in orthorhombic space groupP212121 witha=8.294(2),b=9.740(2),c=22.675(1) Å,V=1832(1)Å3,Z=4. The structure was refined toR=0.043 andR w=0.048 for 2898 observed reflections with CuKα radiation. 8α-isobutyryloxy-9-oxo-germacra-4E, 1(10)Z-dien-6β, 12-olide,4, C19H24O5, crystallizes in monoclinic space groupC2 witha=32.879(7),b=5.793(2),c=9.884(4)Å, β=99.01(3)°,V=1859.5(9)å3,Z=4. The structure was refined toR=0.054 andR w=0.064 for 1010 observed reflections with MoKα radiation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01664652
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