Reactions of hydroxyamino acids during hydrochloric acid hydrolysis

Chlorosubstitution reactions occur readily during HCl hydrolysis of δ- and ϵ-hydroxynorleucines (Hnle), the products of deamination of poly- l-lysine by nitrite at low pH. During amino acid analysis, chloronorleucines elute as new peaks after δ- and ϵ-Hnle. To determine if other hydroxyamino acids undergo similar changes during hydrolysis, they were subjected individually to HCl hydrolysis conditions with and without added phenol. Amino acid analyses indicated that terminal hydroxy groups on linear side chains undergo reactions during HCl hydrolysis; the products appear as new peaks which may be chloroderivatives. In contrast, no new peaks are observed in HCl hydrolysates of δ-hydroxylysine or amino acids with β-hydroxy groups (β-hydroxynorvaline, serine, and threonine). Phenol did not protect linear amino acids from reactions during HCl hydrolysis but did prevent loss of the cyclic amino acids tyrosine, hydroxyproline, and 3,4-dihydroxyphenylalanine. Although the γ-hydroxy group of homoserine would be expected to undergo reaction, HCl catalyzes its cyclization to form homoserine lactone instead.