T4 M. WINITZ 
is capable of acting asymmetrically only on the L-isomers of DL-amino acid amides?” 43, 
as follows: 
L-RCONHCHR’CO,H 
acylase L-NH,CHR’CO,H (organic solvent—insoluble) 
SSS 
carboxy- + RCO,H + 
peptidase b-RCONHCHR’CO,H (organic solvent—soluble) 
D-RCONHCHR’CO,H - 
t-NH,CHR’CONH, L-NH,CHR’CO,H (organic solvent—insoluble) 
amidase 
eat Sears + NH, + 
p-NH,CHR’CONH, b-NH,CHR’CONH, (organic solvent—soluble) 
The renal acylase and amidase systems have proven effective in the resolution of 
nearly all a-amino acids studied. Because of the optical specificity of the enzymes 
involved, the method of resolution is extremely simple. The racemic amino acids 
are N-acylated, generally by reaction with acetic anhydride or chloroacetyl chloride, 
the purified compound dissolved at pi 7.0 and at 0.1 M concentration in water, and 
the solution treated with the appropriate amount of purified enzyme. Hydrolysis at 
37° proceeds to exactly 50% of the racemate, which may be readily checked by mano- 
metric ninhydrin measurements on aliquots, and goes no further irrespective of how 
long the digest stands. The enzyme is removed, the solution condensed, and the free 
L-amino acid separated from the N-acyl-p-amino acid either by precipitation with 
ethanol or passage over an lon-exchange resin. A similar procedure applies for the 
amino acid amides, which also reach a 50°, hydrolysis end point. 
Table II lists some of the amino acids resolved in our laboratory *; by the enzymatic 
procedures just described. The power of this general approach as a tool in the identi- 
fication of naturally occurring amino acids is revealed by the fact that it permitted 
the configurational elucidation of natural a-aminoadipic acid, which was resolved*# 
prior to its discovery in nature, that is has been employed in our laboratory by Dr. 
E. Work®*: 46 for the purpose of establishing the configuration of a,e-diaminopimelic 
acid and by Dr. Fones to determine the configuration both of natural hydroxylysine*’ 
and of a-methylserine (cf. ref. 48), that it has been recently employed’ to establish 
the configurationalidentity of the y-hydroxyglutamic acid of VIRTANEN AND HIETALA™, 
and finally, that it will ultimately serve to establish the configuration of the a~amino- 
pimelic acid of VIRTANEN AND BERG?®! after a sufficient amount of the natural material 
has been isolated to permit a comparison of its optical-rotation value with that of the 
synthetically obtained antipodes®®. 
It is an unfortunate occurrence that all too many of the reports concerned with 
the isolation and structural elucidation of new naturally occurring amino acids 
neglect to include optical-rotation data, presumably because of a scarcity of material. 
Yet, from the standpoint of identification, the optical behavior of the new amino 
acid is probably its most important characteristic, not only because it may ultimately 
prove of utility in assigning an optical configuration to the material, but primarily 
because it represents a means for providing unequivocal evidence for or against the 
assigned structure after synthesis and subsequent resolution of the synthetic material. 
References p. 22!24 
