4-Amino-3- butyric acid isomers

The circulins—As early as 1949, Peterson and Reineke characterized circulin as its sulphate. Total hydrolysis yielded D-leucine, L-threonine and L-K,y-diaminobutyric acid together with an optically active isomer of pelargonic acid. The existence of two components, found by Peterson and Reineke was later confirmed by the chromatographic separation of crude circulin into two major components, named circulin A and circulin B. In addition there was evidence for at least three other ninhydrin-positive, biologically active entities. In the hydrolysate of circulin A, L-isoleucine was found besides the amino acids previously reported . Quantitative amino acid analysis showed circulin A and B to be composed of L-a,y-diamino-butyric acid, L-threonine, D-leucine, L-isoleucine and ( + )-6-methyloctanoic acid in the molar ratio 6 2 1 1 1. After partial acid hydrolysis, fractionation and structure determination of the resulting peptides, circulin A and circulin B were formulated as cyclodecapeptides . Very recently, however, Japanese workers have revised the structure of circulin A. According to them, circulin A differs from colistin A only by a replacement of L-leucine in the latter by L-isoleucine Figure 1.7). 

The isomers of 4-amino-3-(4-chlorophenyl)butyric acid were separated on a preparative scale using a silica column (A = 260nm) and 80/20 ethyl acetate/ hexane mobile phase [882], Up to 375 mg of sample was injected and baseline resolution was achieved in 6 min. 

Lipase-catalyzed acylation of one isomer of iV-hydroxymethyl /3-lactam 121 by vinyl butyrate in acetone yielded the ester 122, which afforded 123 after acidic hydrolysis and ion-exchange chromatography (Scheme 7). The unesterified alcohol 124 gave the /3-amino acid 125. Similar reactions yielded 2-aminocyclohex-3-en-l-carboxylic acid and 2-aminocyclohex-4-ene-l-carboxylic acid from l-azabicyclo[4.2.0]oct-3-en-8-one and l-azabicyclo[4.2.0]oct-... 

---