138 PRACTICAL ORGANIC AND BIO-CHEMISTRY 

 Tryptophan, or /3-indole-a-aminopropionic acid : 



C 8 H 6 N . CH 2 . CH(NH 2 ) . COOH. 

 Valine, or a-aminoisovalerianic acid : 



CH 3X 



)CH . CH(NH 2 ) . COOH. 

 CH 3 / 



Leucine, or a-aminoisocaproic acid : 



CH 3X 



)CH . CH 2 . CH(NH ) . COOH. 

 CH/ 



Isoleucine, or /3-methyl-/3-ethyl-a-aminopropionic acid : 



CH 3X 



/CH.CH(NH 2 ).COOH. 

 C 2 H 5 / 



B. Monoaminodicarboxylic Acids. 



Aspartic acid, or aminosuccinic acid : 



HOOC . CH 2 . CH(NH 2 ) . COOH. 

 Glutamic acid, or a-aminoglutaric acid : 



HOOC . CH 2 . CH 2 . CH(NH 2 ) . COOH. 



C. Diaminomonocarboxylic Acids. 



Ornithine, or a-, 8-diaminovalerianic acid, formed by the decom- 

 position of arginine (p. 165; : 



CH 2 (NH 2 ) . CH 2 . CH 2 . CH(NH 2 ) . COOH. 

 Lysine, or a-, e-diaminocaproic acid : 



CH 2 (NH 2 ) . CH 2 . CH 2 . CH 2 . CH(NH 2 ) . COOH. 



It should be noted that all these amino acids are a-amino deriva- 

 tives of acids, i.e. derivatives in which a hydrogen atom in the a-carbon 

 atom next to the COOH group has been substituted. 



In addition to these compounds the substances, proline and hydro xy- 

 proline are found as constituents of the protein molecule (pp. 304, 306). 



Preparation. 



The amino acids are prepared by two general methods : 



(i) By the action of ammonia upon the corresponding halogen 

 derivative : 



CH 2 C1 CH 2 .NH 2 



+ NH 3 = HC1 + | 

 COOH COOH 



Chloracetic acid. Aminoacetic acid. 



