Synthesis and spectroscopy of (14′‐¹³C)‐ and (15′‐¹³C)spheroidene

Abstract

Abstract The preparation of two 13 C‐labelled isotopomers of spheroidene, the carotenoid bound in the photosynthetic reaction center of Rhodobacter sphaeroides , is described. All‐E (14′‐ 13 C)‐spheroidene has been synthesized in high yield and purity and with more than 98% 13 C incorporation starting from (2‐ 13 C)acetonitrile; similarly, all‐ E (15′‐ 13 C)spheroidene has been obtained starting from (I‐ 13 C)acetonitrile. The spectroscopic properties of all‐ E spheroidene and its (14′‐ 13 C)‐ and (15′‐ 13 C)isotopomers are discussed. The mass spectra of the labelled compounds reveal that toluene is eliminated mainly from the central part of the molecule. Analysis of the ′H‐NMR spectrum of all‐ E (15′‐ 13 C)spheroidene gives a value of 14.0 Hz for the 1 H ‐ 1 H coupling constant of the 15‐15′ double bond.