Bacterial Carotenoids. XXIV. The Carotenoids of Thiorhodaceae 7. Cross-conjugated Carotenals.

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Abstract
The structures of the carotenoids warmingol, anhydro-warmingone, warmingone and P500 isolated from Thiorhodaceae spp. were investigated by spectroscopic (electronic-, infrared, mass, and proton magnetic resonance spectra) and chemical methods. The last 3 carotenoids represent a class of cross-conjugated carotenals in which one of the lateral methyl groups of the polyene chain is formally oxidized to an aldehyde group. Anhydro-warmingone is considered to be a lycopenal, 13-cis-lycopen 20-al (2a) or 9-cis-lycopen-19-al (2b); warmingone a rhodopinal, 13- or 13''-cis-rhodopin-20- or 20''-al (4a) or 9- or 9''-cis-rhodopin 19- or 19''-al (4b); and P500 a tetrahydro-spirilloxanthinal, 13-cis 3,43'',4''-tetrahydro-spirilloxanthin-20-al (17a) or 9-cis-3,4,3'',4'' tetrahydro-spirilloxanthin-19-al (17b). Warmingol is the rhodopinol (5a or b) corresponding to rhodopinal (4a or b). Their previous trivial names should be abandoned. Twenty-one derivatives prepared from the new carotenals, appear to have stable cis-configuration and exhibit peculiar electronic spectra.