6 M. WINITZ 
mediates in the metabolic processes, as components of antibiotics and as bacterial 
decomposition products. Reports in the chemical literature allude to well over a 
hundred different amino acids of non-protein derivation that have been isolated from 
such sources”. That they may be possessed of a most diverse composition and structure 
is indicated by the few examples shown in Fig. 1. Although some of these amino acids 
have been unequivocally established as occurring in nature by a strong body of ex- 
perimental data, somewhat more have been supported by data that would, at best, 

CO2H Cook Po oak oon 
| 
NH2-C-H MaeGeh NH2—C-H H-C-NH-C-H 
| 
CHo ° CH (CHa), CH3 (CHa), 
H-C-OH CH H-C-NH2 NH 
CO2H NH» COH HaN—C=NH 
y—Hydroxyglutamic y—Aminobutyrine a,e—Diaminopimelic Octopine 
Acid Acid 
CO>H CO2H H CO2H 
C-H NH2-C-H HO H Neca 
ae CH» CH 
| 
HN eae A H CO>H coe 
CH2 LN | l 
H 
Hee G=6Hp iu CH3 
Azetidine—2—carboxylic Hypoglycin 5—Hydroxypipecolic 5—Methylcysteine 
Acid Acid Sulfoxide 
Fig. r. Some naturally occurring amino acids of non-protein derivation. 
provide only strong presumptive evidence for their natural occurrence. With most 
of the amino ecids, however, sufficient evidence has not yet been amassed to demon- 
strate their existence in nature with even a modicum of assurance. These considerations, 
in addition to the appearance of a continually increasing number of reports of new 
amino acids of both the p- and L-varieties in nature, point out the urgent need for 
criteria which, if met, would reliably establish the natural occurrence of these amino 
acids. Proposals for such criteria are offered below: 
1) The new amino acid should be physically isolated in sufficient quantity, and 
purified by several crystallizations from water, water—alcohol, or some other suitable 
solvent system, in order to obtain accurate and meaningful carbon, hydrogen, nitro- 
gen and other possible elemental analyses. 
2) Chromatographic procedures, whether two-dimensional techniques on paper 
employing different solvent systems, or elution techniques with columns employing 
various solvent mixtures, should show it to possess a single spot or peak, respectively, 
in order to assure the possibility of molecular homogeneity. 
3) The molecule should be degraded by chemical organic procedures or unequivocal 
enzymatic procedures to identifiable products or fragments in order to obtain a 
knowledge of its structure. 
4) Verification of the structure ultimately assigned to the molecule should be 
achieved through synthesis of the material employing unequivocal chemical procedures. 
5) The synthetic material should be resolved into its optical antipodes and the 
References p. 22/24 
