Chemically, pantothenic acid is considered to be a ¡-alanine derivative of the asymmetric pantoic acid and thus shows asymmetry (Fig. 28.31). Only the naturally occurring d(+)-stereoisomer (with R configuration) is biologically active and the L(-)-stereoisomer (with S configuration) is inactive. When its carboxylate functional group is attached through an amide linkage with ¡-mercaptoethylamine, it is known as pantetheine (also spelled pantotheine). The biologically active form of pantothenic acid, CoA, is formed when the terminal alcoholic function of pantetheine is attached to ADP 3'-phosphate as shown in Figure 28.32.
H3C CH3O O
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