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Slowly Interconverting Conformers of The Briarane Diterpenoids Verecynarmin B, C, and D, Isolated from the nudibranch mollusc Armina maculata and the pennatulacean octocoral Veretillum cynomorium of East Pyrenean waters
Author(s) -
Guerriero Antonio,
D'Ambrosio Michele,
Pietra Francesco
Publication year - 1988
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19880710221
Subject(s) - chemistry , conformational isomerism , stereochemistry , nudibranch , isomerization , crystallography , molecule , gastropoda , paleontology , organic chemistry , biology , catalysis , biochemistry
The novel briarane diterpenoids verecynarmin B(=(−)‐(1 R *, 10 S *, 11 R *, 4 E , 12 Z )‐briara‐4,7,12,17,‐tetraen‐14‐one; (−)‐ 4 ); verecynarmin C (=(−)‐(1 R *, 10 R *, 11 S *, 4 E , 12 Z )−11‐hydroxybriara‐4,7,12,17‐tetraen‐14‐one; (−)‐ 5 ); and verecynarmin D (=(−)‐(1 R *, 10 R *, 11 R *, 4 E , 12 E )‐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 (P ALLAS ). 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, 1 H, 1 H coupling constants from 1D spectra, as well as 1 H, 1 H, 13 C, 1 H, and 13 C, 1 H, and 13 C, 13 C, correlations from 2D experiments; ( iii ) subjecting the briaranes to SeO 2 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 ).