Bacterial Carotenoids. 52. C50-Carotenoids 22. Naturally Occurring Geometrical Isomers of Bacterioruberin.

Abstract

Bacterioruberin has been submitted to iodine-catalyzed stereomutation. The quantitative composition of the quasi-equilibrium mixture was established by separation of the geometrical isomers by a published HPLC procedure and identification by VIS and H-1 NMR spectroscopy: all-E (54% of total), 5Z (17%), 9Z (15%), 13Z (9%) and 5Z,9'Z (5 %). The di-Z isomer has not previously been characterized. These geometrical isomers served as HPLC and VIS spectral standards. A fast and gentle procedure has been developed for the isolation of bacteriorubering from Haloferax volcanii, based on extraction at 3-degrees-C and HPLC analysis within 10 min, showing the presence of all-E (57% of total), 5Z (19%), 9Z (11%), 13Z (10%) and 5Z,9'Z (3%). Extrapolation to zero time gave slightly modified values. Isomerization after 10 min in solution at 3-degrees-C and 20-degrees-C was monitored by HPLC. The composition of the equilibrium mixtures at these temperatures are given. This is the first report on the natural occurrence of a carotenoid as an equilibrium mixture of geometrical isomers.