MECHANISM OF ANTIBODY FORMATION 127 



influence the combination of benzaldehyde and hydrogen cyanide so 

 that the reaction took place one-sidedly, the mandelonitrile formed 

 being dextrorotatory. The extent of the asymmetric synthesis must 

 have been considerable for the dextrorotatory nitrile was formed in 

 large excess over its antipode since 1-mandelic acid obtained on hydrol- 

 ysis of the nitrile was optically pure after two crystallizations from 

 benzene. 



Emulsin 



CeHgCHO+HCN >C6H5CHCOH)CN 



d-Mandelonitrile 



Hydrolysis 

 C6H5CHCOH)CN >C6H5CHCOH)COOH 



d-Mandelonitrile 1-Mandelic acid 



This was the first definite example of an asymmetric synthesis 

 carried out in the laboratory by an enzyme. Rosenthaler (1913) 

 found in the leaves of Taraktogenos Bluenci HSSK also an enzyme, 

 called l-oxynitriluse, which brought about the formation of 1-man- 

 delonitrile from benzaldehyde and hydrogen cyanide, as distinct from 

 the common d-oxynitrilase which forms d-nitrile. The emulsin from 

 cherries was found by Krieble (1913) to yield sometimes a d- and 

 sometimes an 1-nitrile. 



Working with bacteria as an enzyme source Mayer (1926) was able 

 to obtain from phenylglyoxylic acid and hydrocyanic acid 1-mandelic 

 acid by Bacterium ascendens, and d-mandelic acid by lactic acid 

 bacteria. 



Bredig and Fiske (1912) made similar observations using optically 

 active organic catalysts. They dissolved 50 ml. of benzaldehyde (0.5 

 mole) in 170 ml. of chloroform (as solvent) and treated the solution 

 with anhydrous hydrocyanic gas (0.5 mole). After one hour at 25°C., 



nitrile can thereupon be racemized according to the requirements of true catalysis; 

 that is, the d-nitrile originating from excess free 1-nitrile is again transformed into 

 ig-gentiobioside and the process continues until all the 1-nitrile is converted into the 

 less soluble glucoside or d-mandelonitrile. 



The preponderance of optical purity in an enzymatic sjmthetic process is observed 

 also: (a) when widely different velocities in the formation of the two optical isomers 

 determine the degree of preponderance of the d- or 1-isomer in the substance syn- 

 thesized; (b) an increase of optical purity can be observed when the reaction is in- 

 terrupted before the optical activity disappears as the result of gradual racemization 

 (Langenbeck and Triem, 1936); (c) by the elimination from the living system 

 without utilization (Abderhalden and Samuely, 1906), or by more rapid metabolism 

 of the unnatural optical isomer CKrebs, 1933). 



