Conjugated Alkenes in Biological Systems The Chemistry of Vision H O H H H H H trans Retinal O cis Retinal Nerve Impulse Terpene s Terpenes natural products whose carbon skeletons are built up largely from isoprene subunits Me Me Me OH Me Me Me H Me O H H Me S carvone caraway Me R carvone spearmint isoprene Me menthol Me Me O Me H H O nepetalactone oil of catnip OH chrysanthemic acid O an insecticide O H O O Me H2C Me H Me Me HO H Me Me H H nootkatone grapefruit flavor Me cholesterol steroid hormones Me Me periplanone sex attractant pheromone of the American cockroach Me Me Me Me Me O O Me O Me Me citronellal lemon oil H Isoprene Nature s C5 Building Block Me 2 methyl 1 3 butadiene isoprene t h OH OH t O OH h geraniol citronellol menthol camphor natural rubber carotene n Terpene Biosynthesis Me Me enzyme OPP Me dimethylallyl pyrophosphate DMAP isopentenyl pyrophosphate IPP O O O R O P O P OH O ROPP R O S O Me OPP DMAP SN1 Me CH2 ROTs tosylate chemist s leaving group Me Me OPP CH3 O pyrophosphate nature s leaving group Me OPP OPP Me Me Me Me HB H H OPP Me E1 OPP geranyl pyrophosphate Base H2O OH Me OH geraniol Me Me Me Steriod Biosynthesis Squalene Oxide Cyclization Me Me Me Me Me O Me squalene oxide Me H Me H Me O Me Me Me Me Me Me Me The enzyme folds the squalene oxide into the chair boat chair conformation HO Me Me H Me Me Me Me Me HO Me H Me Me Me Me Me Me Me Me Me HO Me Me Me H Me Me Me Me Me Me H Me Me HO Me Me H Me H H Me Steriod Biosynthesis Squalene Oxide Cyclization Me Me Me Me Me H Me Me Me Me Me H Me Me H HO HO Me H H Me Me H Me H elimination A series of 1 2 hydride and methyl shifts occur Me Me H Me Me Me Me H Higher Steriods Me H Me Me H HO Me HO Me Me Me lanosterol Me Intermolecular Diels Alder Reactions Takahiro Ichige Yusuke Okano Naoki Kanoh and Masaya Nakata Journal of Organic Chemistry Publication Date Web November 16 2008 Article Intramolecular Diels Alder Reactions CO2H H O O RO O O H Me H O O O O Me Me Me HO R3SiO CO2R H Me H OH Chlorothricolide O OH OH O t Bu O O OR Me H SiR3 OR OR O t Bu O toluene 120 C R3SiO 45 yield R3SiO Me Me O OR O O Me SiR3 O OMe O t Bu Me RO2C Roush Sciotti J Am Chem Soc 1998 120 7411 7419 SiR3 OR