20 M. WINITZ 
have amply demonstrated that such conversion of an a-amino acid to the correspond- 
ing a-hydroxy acid proceeds in the absence of inversion of configuration. Hence, the 
a-configuration of each of the isomers of the dihydroxy acid could be considered as 
identical with that of the a-amino acid from which it was derived. The two dihydroxy- 
glutaric acid isomers corresponding to the D- and L-antipodes of y-hydroxyglutamic 
acid A revealed molecular rotation values of +31° and —31°, respectively, as solutions 
of their barium salts in water, whereas the two isomers whose parent amino acids 
COOH COOH COOH COOH 
we NH, ote H NH> 
CH CHo 
+4 4. of H OH 
COOH COOH COOH COOH 
fl D 
a Se ae eee eee 
y-HYDROXYGLUTAMIC ACID A y-HYDROXYGLUTAMIC ACID B 
COOH COOH COOH COOH 
“ a ma aa fe 
CH CH, Che a CH 
! 
H OH HO H HO H H OH 
COOH COOH COOH COOH 
E D meso meso 
ey ——— ed 
a, a!-DIHYDROXYGLUTARIC ACID a a'-DIHYDROXYGLUTARIC ACID 
Fig. 7. Projections of the four stereomers of y-hydroxyglutamic acid and the corresponding a, a’- 
dihydroxyglutaric acids derived therefrom. 
» 
represented the antipodes of the B form were completely devoid of optical activity. 
This data now sufficed to establish the y-configuration of each of the four antipodes 
of the amino acid. 
Assignments of configuration based on these results become readily explicable 
through examination of the Fischer projections of the four isomers of y-hydroxygluta- 
mic acid and the dihydroxy acids corresponding thereto. Thus, although the dihydroxy 
acid molecule embodies two centers of optical asymmetry, it also possesses symmetry 
such that, of the four theoretically possible isomers, only two constitute an externally 
compensated optically active pair, whereas the other two constitute the identical 
optically inactive meso form by virtue of internal compensation. Inasmuch as deami- 
nation of the antipodes of the A form of the amino acid results in two optically active 
enantiomorphic forms of the dihydroxy acid, it follows that the a-amino and y-hydroxy] 
groups of the parent amino acid must assume a ¢tvans representation in the Fischer 
formulation. On the other hand, the functional groups of the enantiomorphic B forms 
must occupy a cis position by virtue of the fact that deamination of the amino acid 
leads to meso-dihydroxyglutaric acid. 
References p. 22/24 
