Terpenoids and Steroids

Monoterpenoids occur seldom in ferns. Only two, the (3 5)-linalool glycosides (407, 408), have been reported, both from Arachniodes maxi-mowiczii (256), 

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D-Mevalonic acid is the fundamental intermediate in the biosynthesis of the terpenoids and steroids, together classed as poly-isoprenoids. The biogenetic isoprene unit is isopentenyl pyrophosphate which arises by enzymic decarboxylation-dehydration of mevalonic acid pyrophosphate. D-Mevalonic acid is almost quantitatively incorporated into cholesterol synthesized by rat liver homogenates. 

W. L. Duax and D. A. Norton, of Steroid Structure, lEI/Plenum Data, New York, 1975 Terpenoids and Steroids, Vol. 4, The Chemical Society,... 

W. Templeton, Introduction to the Chemistry of Terpenoids and Steroids, Butterworth Pubhshers Co. Ltd., Inc., London, 1969. 

Lipids are naturally occurring organic molecules that have limited solubility in water and can be isolated from organisms by extraction with nonpolar organic solvents. Fats, oils, waxes, many vitamins and hormones, and most nonprotein cell-meznbrane components are examples. Note that this definition differs from the sort used for carbohydrates and proteins in that lipids are defined by a physical property (solubility) rather than by structure. Of the many kinds of lipids, we ll be concerned in this chapter only with a few triacvlglycerols, eicosanoids, terpenoids, and steroids. 

Hydroxylation and Baeyer-Villiger reactions carried out by monooxygenation are important in the degradation of a range of terpenoids and steroids. The aerobic degradation of limonene can take place by a number of reactions several of which involve hydroxylation at allylic positions... 

E) coumarins, (F) quinones, (G) flavonoids, (H) tannins, (I) alkaloids, (J) terpenoids and steroids and (K) miscellaneous and unknowns. Although many of these compounds are secondary products of plant metabolism, several are also degradation products which occur in the presence of microbial enzymes. 

The recent work on the stereospecificity of hydroxymethylglutaryl-CoA reductase 71 76> is particularly interesting. The reaction catalyzed by this enzyme is an important early step in the synthesis of terpenoids and steroids. The yeast enzyme and the liver enzyme both have the same stereospecificities. The overall reaction catalyzed is the reduction of hydroxymethylglutaryl CoA to mevalonic acid, as shown in scheme 1. Two molecules of NADPH are used to reduce the Co-A-bound carboxyl... 

Terpenoids and Steroids. The Information given in Tables IV-VII and the blogenetlc relationships shown in Figures 2 and 3 speak for themselves. This class of compounds accounts for more than one-third of the known cotton plant secondary metabolites. The monoterpenoids listed in Table V, many of which have the para-menthane skeleton, are generally common compounds widely spread in the essential oils of plants. 

Geranyl diphosphate and farnesyl diphosphate are analogues of dimethylallyl diphosphate that contain two and three C5 subunits respectively they can undergo exactly the same SnI reactions as does dimethylallyl diphosphate. In all cases, a carbocation mechanism is favoured by the resonance stabilization of the allylic carbocation. Dimethylallyl diphosphate, geranyl diphosphate, and farnesyl diphosphate are precursors for natural terpenoids and steroids. 

Electrophilic additions to carbocations in terpenoid and steroid biosynthesis... 

BrasseU SC, Egfinton G, Maxwell JR, The geochemistry of terpenoids and steroids. Biochemical Society Transactions 11 575—586, 1983. 

Polyene cyclizations have been of substantial value in the synthesis of polycyclic natural products of the terpene type. These syntheses resemble the processes by which terpenoid and steroidal compounds are assembled in nature. The most dramatic example of biological synthesis of a polycyclic skeleton from a polyene intermediate is the conversion of squalene oxide to the steroid lanosterol. In the biological reaction, the enzyme presumably functions not only to induce the cationic cyclization but also to bind the substrate in a conformation corresponding to the stereochemistry of the polycyclic product.21... 

Templeton W (1969) An introduction to the chemistry of terpenoids and steroids. Butter-worth, London... 

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