Absolute Asymmetric Synthesis and Asymmetric Catalysts 



109 



The multiplet theory of catalysis of A. A. Balandin [42] designates those 

 atoms or groups of atoms in the reacting molecules, which form intermediate 

 adsorption complexes with the catalyst, as the multiplet. The multiplet theory 

 might be applied with advantage to the study of enzymic reactions, in that 

 enzymes are microheterogeneous while, in a number of cases, chemical models 

 of enzymes are also heterogeneous catalysts. Furthermore, it is easy to use the 

 multiplet theory for the classification of reactions catalysed both by enzymes 

 and by models of them. 



All reactions of enzymic asymmetric synthesis can be divided into two groups: 

 coupling at C zz: C and C zz O bonds [43]. 



Table i shows the enzymes, the starting material and the multiplet index of 

 the reaction. 



Table i 



Enzymes 



I. Oxynitrilase 



2. Carboligase 



3. Ketoaldomutase 



4. Reductase 



Starting material 



Aldehyde + HCN 



Aldehydes 



Aldehydes, Acids 



Oxo compounds 



Index of the reaction* 



= N 



* Points are active centres of catalysts. 



Optically active catalysts, even if of comparatively simple structure, exert an 

 asymmetrizing influence on reactions, similar to that of natural enzymes. 



At first, attempts were made to use optically active solvents as asymmetric 

 influences on reactions. 



It was discovered that the reaction between a-phenylethylamine and phenyl 

 isocyanate proceeded asymmetrically in a medium of (— )-a-pinene [44] as did 

 Grignard reactions in (+)-dimethoxybutane [45]. The extent of the asymmetry 

 was, however, small. Only by using optically active substances as catalysts in a 

 particular reaction, as, for example, in the decarboxylation of camphorcarboxylic 

 acid by the action of alkaloids, was any considerable (up to 17%) difference 

 found in the rate of decomposition of the antipodes, with the resultant produc- 

 tion of optically active camphor. 



