SOME AMINO ACIDS FROM PLANTS 49 
Elementary analysis indicated the formula C,H,NO,, which contains four hydrogen 
atoms less than a saturated, open-chain C, amino acid such as leucine. The presence 
of a terminal =CH, was inferred from its infrared spectrum which showed strong 
absorptions at 5.9 and 11.0 w (see Fig. 1, curve B). ETTLINGER AND KENNEDY" have 
demonstrated that the exocyclic methylene group as it occurs in Feist’s acid (1- 
methylenecyclopropane-trans-2,3-dicarboxylic acid) is characterized by strong infra- 
red-absorption bands at 5.9, 7.1 and 11.0 w. The 7.1 uw band cannot be used as a cri- 
terion for recognition of a =CH, group in an amino acid for the symmetrical stretching 
frequency of the —COO- group gives a superimposed peak at this wavelength. This 


AM 
A 
B B 
Cc 
S 
po 1 i 1 rt 1 Js Me r ic 

rt 
3 4 5 6 10 11 12 as) 14 
7. 8 
Wavelength uU 
Fig. t. Shows the infrared spectra determined with liquid-paraffin mulls of (A) hypoglycin A, 
(B) a-(methylenecyclopropyl)glycine, and (C) a-(methylcyclopropyl)glycine (major isomer, XV). 
spectral evidence for the presence of the —=CH, group was supported by the infrared 
spectrum of the primary product of hydrogenation, a-(methylcyclopropyl)glycine 
(major isomer, XV; see Fig. 1, curve C), which no longer possesses absorption peaks 
at 5.9 and 11.0“. In the infrared spectrum of hypoglycin A (Fig. 1, curve A), the 
absorptions associated with the —CH, group are apparently shifted slightly; the 
11.0 w band of XIV is seen at 11.2 w for XIII (compare ANDERSON et al.*°) and the 
absorption band at 5.9 wu presumably is shifted to slightly longer wavelength at 6.2— 
6.3 « where it is overlapped by the band attributed to antisymmetrical stretching of 
the —COO- group. 
The acid was decomposed completely when treated with 5 N HCl at roo° for 24h. 
The main products included three ninhydrin-reacting compounds but these were not 
identical with any commonly-encountered amino acids. 
The clue to the structure of the acid came from a study of the products obtained 
during catalytic hydrogenation in the presence of PtO, catalyst. The course of the 
reduction was followed by paper chromatography using a fert.-amyl alcohol—-water— 
acetic acid mixture (10 : 10 : I, v/v; upper phase used). A diagrammatic represen- 
tation of the results is shown in Fig. 2. The final products included isoleucine (XVIT), 
leucine (XVIII), and norleucine (XIX); isoleucine was formed in greater amount 
References p. 53 
