ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The novel briarane diterpenoids verecynarmin B(=(-)-(1R*, 10S*, 11R*, 4E, 12Z)-briara-4,7,12,17,-tetraen-14-one; (-)-4); verecynarmin C (=(-)-(1R*, 10R*, 11S*, 4E, 12Z)-11-hydroxybriara-4,7,12,17-tetraen-14-one; (-)-5); and verecynarmin D (=(-)-(1R*, 10R*, 11R*, 4E, 12E)-13-chloro-11-hydroxybriara-4,7,12,17,-tetraen-14-one; (-)-6) are reported here as constituents of both the Mediterranean nudibranch mollusc Armina maculata (Rafinesque) and its prey, the pennatulacean octocoral Veretillum cynomorium (PALLAS). The structural assignments rest mainly on (i) establishing that these briaranes occur in solution as two stable conformers which interconvert slowly (ca. 10 time per second at r.t. according to dynamic NMR) by 180° flipping of the C(4)=C(5) group in the ten-membered ring (Scheme 1), (ii) deriving, for both conformers, 1H, 1H coupling constants from 1D spectra, as well as 1H, 1H, 13C, 1H, and 13C, 1H, and 13C, 13C, correlations from 2D experiments; (iii) subjecting the briaranes to SeO2 oxidation at the C(16) methyl group with isomerization at the C(4)=C(5) bond to give, in each case, only one observable molecular species as shown by NMR spectroscopy (Scheme 2).
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19880710221
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