Absolute configurational assignment of 3-hydroxycarotenoids
Attempts were made to develop an exciton chirality method applicable to the unique cases represented by 3-hydroxycarotenoids. However, this approach has so far not been successful. The 3-hydroxy configurations were therefore determined by the extended Mosher 1H-NMR method. Nine carotenoids with seven different end groups and of known 3-hydroxy configurations were derivatized with (R)- and (S)-methoxyphenylacetic acid (MPA); they all gave the expected shift differences. Three other auxiliary reagents with naphthalene and anthracene nuclei gave larger and consistent NMR shift differences, but they are not yet commercially available.