18 M. WINITZ 
Application of this rule in our laboratory to over 70 different L-amino acids revealed 
no exceptions as long as the measurements were confined only to amino acids which 
possessed a single asymmetric center. Certain exceptions to the rule were found, 
however, in the case of diasymmetric amino acids” 7, 
In any event, from what has already been said, it is clear that a number of relatively 
simple biological and optical methods are available for determining the optical con- 
figuration of an amino acid which require, in many instances, only a few mg of material. 
It is therefore puzzling that many papers reporting the occurrence of a new amino 
acid still appear in which no attempt at all has been made to ascertain the configuration 
of the material. 
IDENTIFICATION OF NATURAL y-HYDROXYGLUTAMIC ACID 
In conclusion, I should like to discuss the identification and characterization of natural 
y-hydroxyglutamic acid, firstly, because its natural occurrence may be considered as 
established according to the criteria presented earlier; and secondly, because it 
covers the somewhat more complex case of an amino acid with two asymmetric centers. 
The natural occurrence of y-hydroxyglutamic acid was first observed by VIRTANEN 
AND HIETALA” in 1955 when two-dimensional paper chromatograms, with butanol— 
acetic acid and phenol-ammonia, of a 70°, ethanolic extract of the green parts of the 
plant, Phlox decussata, revealed a hitherto unknown ninhydrin-reactive spot just 
above that of aspartic acid. Approx.124 mg of the material was isolated from 3.5 kg 
of the fresh plant by column chromatography. Elemental analytical data, together 
with the fact that reduction of the material with hydriodic acid and red phosphorus 
at 140° led to the formation of glutamic acid, indicated that the new compound was 
a hydroxyglutamic acid. Oxidation of the material with potassium permanganate in 
sulfuric acid solution at 140° proceeded with the formation of aspartic acid, while 
comparison of the Rk; value of the new compound in butanol-acetic acid with that 
of authentic 6-hydroxyglutamic acid indicated that these compounds were not iden- 
tical. It therefore appeared probable that the new acidic compound was a y-hydroxy- 
glutamic acid. No optical rotation data were presented for the new compound, nor 
was its optical configuration ascertained. 
During the same year that y-hydroxyglutamic acid was isolated from natural 
sources, its synthesis was described by BENOITON AND BOUTHILLIER in Canada” (cf. 
ref. 49). The reaction sequence employed is given in Fig. 5. Since this amino acid 
CN PASSA ce oe O2CCHs 
GASCONHCH + CICH2CHCO2Et On Sresed Sensis Oe _— 
CO2Et CO2Et 
| II Wl 
CO2H CO2H CO2H CO2H CO pone 
NH)—C-H H-C-NHa NHg-C-H H-C-NHo uc, | CHNHgHCI CHNH2HC! 
CHa CH CH CH aoe CH + CH 
ner peal Baas ose O5CH eet 
CO2H CO2H CO2H CO2H CO7H CO 2H 
Epimeric Mixture of y—Hydroxyglutamic Acid A-—Racemate B-—Racemate 
(insoluble) (soluble) 
Fig. 5. Synthetic route to y-hydroxyglutamic acid. 
References p. 22/24 
