Tetraterpenes

Tetraterpenes are constructed in a manner similar to squalene, by head-to-head condensation of two molecules of geranylgeranyl pyrophosphate, also through a cyclopropane intermediate. The initial product is phytoene (Figure 7.16). It is desaturated to carotenes, which have long conjugated systems of double bonds, usually all trans, and are strongly coloured. Tetraterpenes appear now to be synthesized in the plastids of plants via the methylerythritol phosphate process (Figure 6.6). They were

2 x geranylgeranyl pyrophosphate

2 x geranylgeranyl pyrophosphate

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