Several 4-Substituted Glutamic Acid Derivatives and Small Peptides in Some Liliaceae Plants

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Abstract
Acidic non-protein amino acids and peptides in five species belonging to the family Liliaceae —Smilax china, Lilium maximowiczii, Tulipa gesneriana, Allium cepa and A. sativum— were surveyed. Two new amino acids —4-hydroxymethyl- and 4-ethyl-4-hydroxyglutamic acid— were isolated from bulbs of T. gesneriana. The first unequivocal identification of 4-ethylglutamic acid was performed from the same plant tissue. A new dipeptide —S-(2-carboxy-n-propyl)cysteinyl glycine— was isolated from A. cepa. Besides the compounds described above, 4-methylene-, 4-methyl- and 4-hydroxy-4-methylglutamic acid were isolated from S. china, L. maximowiczii, and T. gesneriana, but 4-ethylideneglutamic acid was isolated only from T. gesneriana. 4-Methyleneglutamic acid showed no appreciable biological activity, although this aminoacid has an α,β-unsaturated carboxyl group and reacts easily with cysteine in vitro. The most abundant free amino acid in the plant tissues examined in this study is arginine; nevertheless, acidic Nα-acylarginine derivatives which have been found in S. china and L. maximowiczii and published elsewhere could not be detected in bulbs of T. gesneriana, A. cepa, and A. sativum.