Lycopadiene L Race

Hydrogenation in the presence of Rh/C furnished a C40H82 hydrocarbon exhibiting the same mass spectrum and GC retention time as lycopane, the entirely reduced derivative of the acyclic C40 carotenoids. 

Ozonolysis of lycopadiene followed by oxidative cleavage of the ozonide afforded 6,10,14-trimethylpentadecan-2-one thus establishing the C(14)-C(15) and C(18)-C(19) location of the unsaturations. Moreover, the optical rotation of this ketone was identical with that observed for the 6(R),10(R), 14-trimethylpentadecan-2-one obtained from ozonolysis of natural phytol this result allowed assignment of stereochemistry to the asymmetric centers. Therefore, lycopadiene (45) was identified as 

On the basis of the configuration of the four chiral centers, a biosynthetic pathway can be proposed with phytol as precursor. In this mechanism, two phytyl chains would condense, probably as pyrophosphate derivatives, to produce the prelycopadiene pyrophosphate (46), which would be converted to lycopadiene (45) by addition of a hydride ion to a rearranged cyclopropylcation. An intermediate analogous to (46) is known to occur in the synthesis of phytoene, the precursor of the carotenoids in this latter case two geranylgeranyl pyrophosphates are condensed (45). In another possible pathway, lycopadiene (45) would merely result from reduction of phytoene. 

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