Cis/trans ISOMERIZATION OF CAROTENOIDS BY THE TRIPLET CARBONYL SOURCE 3‐HYDROXYMETHYL‐3,4,4‐TRIMETHYL‐1,2‐DIOXETANE*

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Abstract
Abstract— The interaction of biological carotenoids with 3‐hydroxymethyl‐3,4,4‐trimethyl‐1,2‐dioxetane (HTMD), a thermodissociable source of electronically excited ketones, was investigated using reversed‐phase high‐performance liquid chromatography. Incubation of the all‐trans isomers of β‐carotene, lycopene and canthaxanthin with HTMD led to significant trans‐to‐cis isomerization, with cis isomers accounting for 20–50% of products formed (the balance assigned as oxidation products). The isomers forming from all‐trans‐β‐carotene were identified as 9‐cis‐, 13‐cis‐ and 15‐cis‐β‐carotene by cochromatography of cis isomer standards and by on‐line diode array absorbance spectroscopy. An HTMD‐dependent cis‐to‐trans isomerization was observed in incubations started with 15‐cis‐β‐carotene, and it occurred more rapidly and to a greater extent than the isomerization of all‐trans‐β‐carotene. The isomer patterns generated from lycopene and β‐carotene are generally similar to those reported recently for various human tissues (Stahl et al, 1992, Arch. Biochem. Biophys.294, 173–177).