Section 26.8 Biosynthesis of Terpenes 021PROBLEM 16Propose a mechanism for the conversion of the Eisomer of geranyl pyrophosphate to the Z
isomer.PROBLEM 17Propose mechanisms for the formation of and limonene from geranyl
pyrophosphate.Geranyl pyrophosphate can react with another molecule of isopentenyl pyrophos-
phate to form farnesyl pyrophosphate, a 15-carbon compound.
Two molecules of farnesyl pyrophosphate form squalene, a 30-carbon compound.
The reaction is catalyzed by the enzyme squalene synthase, which joins the two mole-
cules in a tail-to-tail linkage. Squalene is the precursor of cholesterol, and cholesterol
is the precursor of all other steroids.
geranyl pyrophosphate isopentenyl pyrophosphatefarnesyl pyrophosphateOOOPO−OO−PO−OOOPO−OO−PO−−OOOPO−OO−PO−H++OOOPO−OO−PO−OOOPO−OO−PO−+++a-terpineolE isomer
Z isomerOOOO−PPOO− O−OOOO−PPOO− O−