Chiral compounds with multiple stereogenic

In order to distinguish enantiomorphic structures, molecular chirality has conventionally been expressed in terms of center-, axis-, and plane-chirality. In the case of compounds involving several stereogenic centers, however, these terms seem to be insufficient to express their whole molecular chirality or anisotropy, although their local chirality is well confirmed in the conventional manner. Indeed, the steroidal molecules (Figure 26.13a), which have asymmetric, amphiphilic, facial structures with multiple stereogenic carbon atoms, are saddled with such a structural complexity. In order to solve this problem, we introduced a simple but unique concept, three-axial chirality , as shown in Figure 26.13b. Such three-axial chirality is based on the orthorhombic three axes applied in a molecular structure and is expressed by... 

Biochemical processes are catalyzed by enzymes that have multiple stereogenic centers and are therefore chiral. Enzymes provide a chiral environment in which to form stereogenic centers. As a consequence, only one enantiomer forms firom an enzyme-catalyzed reaction, even if the reactant is achiral. For example, fumaric acid reacts with water in an addition reaction catalyzed by the enzyme fumarase in the citric acid cycle to give only (i)-malic acid. We show the carboxyhc acids as their conjugate bases because they are ionized at pH 7. These ionic compounds are called fumarate and malate. This reaction converts fumarate to (i)-malate. 

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