Trans-Geranylgeranyl pyrophosphate

The condensation of geranylgeranyl pyrophosphate (66) may lead to the formation of 15-cis-phytoene (88a) or all-trans-phytoene (88b), depending on the stereochemistry of... 

The chemical structure of naturally occurring ais polyisoprenes was determined by 13C NMR spectroscopy using acyclic terpenes and polyprenols as model compounds. The arrangement of the isoprene units along the polymer chain was estimated to be in the order dimethylallyl terminal unit, three trans units, a long block of ais units, and ais isoprenyl terminal unit. This result demonstrates that the biosynthesis of cis-polyisoprenes in higher plants starts from trans,trans,trarcs-geranylgeranyl pyrophosphate. ... 

This alignment of the trans and cis units clearly indicates that these polyprenols are synthesized in vivo by the cis addition of isopentenyl pyrophosphate to trans,trans,trems-geranylgeranyl pyrophosphate (10). 

The polyprenols composed of trans and cis isoprene units isolated so far have been classified into two types the ficaprenoltype and the betulaprenol-type, containing three and two internal trans units, respectively (12). The findings described above suggest that trans,trans,tra s-geranylgeranyl pyrophosphate or trans,trans-farnesyl pyrophosphate acts as an initiator of the biosynthesis of polyprenols. 

Isoprenoids may possess cis- or frans-configuration with respect to the double bonds. Most are derived from key products (prenyl pyrophosphates) with trans-configuration (geranyl, farnesyl, geranylgeranyl pyrophosphates, etc.). There are, however, also compounds with all-cis configuration such as rubber, or with mixed configuration such as... 

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... 

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