The absolute configuration of antiinflammatory marine sesterterpenes belonging to the manoalide and cacospongionolide structural type has been determined by comparison of the CD spectra of the natural compounds with those of analogues that have been stereoselectively synthesized. In the derived acetates the relative stereochemistry of the stereogenic centres in the pyranofuranone moiety is assigned from 1H‐NMR data and the absolute configuration from CD spectra. The absolute configuration of the naturally occurring marine sesterterpenes thorectolide monoacetate, manoalide monoacetate, petrosaspongiolide M and cavernosolide has been determined.
The degraded C-21 sesterterpenoid (+)-3, enantiomeric
with (−)-untenospongin B, has been
isolated from the Mediterranean sponge Spongia virgultosa.
The absolute stereochemistry of
3 was assigned by applying Mosher's method. On the
basis of this work, the absolute
stereochemistry at C-11 of nitenin (1) and dihydronitenin
(2) has been reanalyzed by applying
Mosher's method, whereas the R chirality at C-8 of
2 was determined by recording NOE
spectra.The structures of two known C-21 furanoterpenes,
tetradehydrofurospongin-1 (8) and
7, have been revised as (+)-3 (named “revised
tetradehydrofurospongin-1”) and its acetyl
derivative 5, respectively. Finally, a comparison
between the Mosher and Horeau methods
was carried out, paying attention to the reliability of the
stereochemical predictions obtained
by the two approaches applied to compounds (+)-3, nitenin
(1), and dihydronitenin (2),
containing aliphatic-type alcohols.
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