SOME AMINO ACIDS FROM PLANTS 45 
(C,H,yO2N,), which is probably a heterocyclic amino acid whose ring opens upon 
hydrogenation to give an amino guanidino or a substituted amino guanidino acid, 
is present in seeds of Lathyrus tingitanus (BELL), whilst 4-aminopipecolic acid (XI) 
has been isolated from Strophanthus scandens (SCHENK AND SCHUTTE}’). 
NH, 
CH, (NH,):CH,-CH,-CH,-CH-COOH “abs 
| Lae x 
NH ie ie 
| CH, | 1@H-COOH 
CH,:CH:-COOH eges 
x H XI 
Table I lists some of the properties of these newly isolated compounds. 
Amino Acids of the Cucurbitaceae 
The family of plants has been a source from which several non-protein amino acids 
have been isolated. 
Citrulline was isolated many years ago from the juice of water melons, Crtrullus 
vulgaris (WADA?*). More recently it has been isolated from members of other plant 
families, e.g. nodules of alder, Alnus (MIETTINEN AND VIRTANEN”), and from red 
algae (KURIYAMA, TAKAGI AND Murata?!). During the course of our work on the 
substituted asparagines of Bryonia, we have isolated approx. 3 g of citrulline from 
20 kg of fresh shoots. 
b-Pyrazol-1-ylalanine (XII) was isolated more recently from seeds of water melon 
(NOE AND FOWDEN”: 23), and shown to be present in the seeds of the following addi- 
tional members of the Cucurbitaceae: Cucurbita pepo (vegetable marrow), Cucurbita 
ficifolia, Cucumis melo (melon), Cucumis sativa (cucumber), Ecballium elaterium, 
Bryonia dioica, and Echinocystis lobata. This compound provided the first instance 
of a naturally occurring pyrazole derivative and its structure suggests that it may 
act as an antimetabolite of histidine. Perhaps this possibility stimulated attempts at 
chemical synthesis for several methods are now available (FINAR AND UTTING™4; NOE 
AND FOWDEN??; SUGIMOTO, WATANABE AND IDE”*; TAKESHITA, KIMURA, YABUUCHI, 
NISHIZUKA AND HAYAISHI”®; also private communications from Professor A. E. BRAUN- 
STEIN, Moscow, and Dr. G. TALBot, Saskatoon). 
CH N 
| | 
CH N—CH,-CH(NH,)-COOH 
SCH ~ 
XII 
No definite biosynthetic pathway is yet known but experiments in which pyrazole 
was supplied to germinating seeds of Cucumis melo suggested that the heterocyclic 
base may be utilized directly (NOE AND FowpEN**). Biosynthesis may be found 
ultimately to resemble that of another heterocyclic derivative of alanine, namely 
tryptophan from indole. One pathway for the bio-degradation of /-pyrazol-1-ylalanine, 
References p. 53 
