Bacterial Carotenoids. XV. On the Constitution of the Minor Carotenoids of Rhodopseudomonas. 5. The Structures of P518 (2,2'-Diketo-spirilloxanthin), OH-R (OH-Spheroidenone), and OH-Y (OH-Spheroidene).

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Abstract
Nuclear magnetic resonance data and further chemical evidence have allowed a revision of the previously suggested structure (I) for the carotenoid P518, which is now shown to be 2,2''-diketo-spirilloxanthin (VII). The nuclear magnetic resonance spectra of the pigments OH-R and OH-Y confirm that these carotenoids are l'',2''-dihydro-l''-hydroxy-spheroide-none (III) and l'',2''-dihydro-l''-hydroxy-spheroidene (V), respectively. The dehydration of OH-R (III) to spheroidenone (IV) and of OH-Y (V) to spheroidene (VI) is reported.