OI'T. A(TI\ .. H Eh'HniTY WD i:S \ I ROX M EXT 73 



/. V o 11 t r () 1 of the I * r o d u c t i o n o t' U p - 

 t i c a 1 isomers by an Inversion of 

 t li e W a 1 d e n Type. "Walden (1905) has shown 

 that some optically active substances, when subjected to 

 a series of substitution reactions, come out inverted. For 

 example, dextrorotatory alanine treated w^ith bromides 

 forms l-bromopropionic acid and, upon reaction with am- 

 monia, alanine is again obtained, but laevorotatory alan- 

 ine. Such a process is known as the ''Walden inver- 

 sion" and, according to Eniil Fischer, it is "the most 

 remarkable finding in the field of optical activity since the 

 fundamental investigations of Pasteur". 



The mechanism of this inversion is far from clear. 

 In reactions of a certain type the asymmetric carbon 

 atom must be acted upon in such a manner that the con- 

 figuration of the molecule is inverted. In the example 

 given above one cannot even say if this is accomplished in 

 the transformation of alanine into bromopropionic acid 

 or in the transformation of bromopropionic acid into 

 alanine. 



Mills (1932) had attempted to explain the Walden in- 

 version on the basis of some peculiarities of substitution 

 reactions. According to Levene, Rotheii and Kuna (1937), 

 there does not seem to be any general agreement on this 

 point. 



Some have assumed that in biochemical reactions the 

 presence of a special enzyme, the waldenase, would be 

 responsible for the Walden inversion of some amino- 

 acids. This assumption, however, does not seem to stand 

 a critical stud3\ 



Walden inversion might perhaps play a role in some 

 biochemical processes, such as in the formation by some 

 bacteria of laevorotatory lactic acid from dextrorota- 

 tory glucose (see Freudenberg, Brauns and Siegel, 1923), 

 while other bacteria form dextrorotatory lactic acid. This 

 assumption, however, is not in the trend of current bio- 

 chemical theories. It is generally .supposed that, in the 



