New apocarotenoids and β-carotene cleavage in Blakeslea trispora

Abstract

Mixed cultures of strains of opposite sex (“mated” cultures) of Blakeslea trispora contain trisporic acids and other apocarotenoids, some of which mediate the sexual responses of this fungus and other Mucorales. In mated cultures of the wild-type strains F986 and F921 we identified eleven apocarotenoids: two C₁₈ trisporoids, three C₁₅ compounds with a monocyclofarnesane skeleton, a C₁₃ compound, and five C₇ compounds with a 2-methylhexane skeleton. Six of them are new natural products and two others are new for Blakeslea. Their structures were established by NMR and mass spectra and those of the C₇ and C₁₃ compounds were confirmed by chemical synthesis. The finding of these compounds and the presence of approximately equimolecular amounts of the C₁₈, C₁₅, and C₇ families led to the conclusion that β-carotene is initially split in three fragments by cleavage of its 13,14 and 11′,12′ double bonds.