Reaktionen mit L‐Cystinderivaten, I. Chlorierende Spaltung

Conversion of β-chloro-L-alanine to α-carbobenzoxy-DL-diaminopropionic acid

“…A stream of chlorine was passed into a suspension of ester (1) (40 g) in purified chloroform (700 ml) for 1 h at 0" while the mixture was being stirred (13). The solution was clear after h. The flask was stoppered and kept at 0" for 48 h. The mixture was then allowed to warm to 20°, ether (500 ml) was added, and air was bubbled through for 1 h. The precipitate was filtered off and washed four times with ether; yield, 27.5 g (68%).…”

“…The ethyl ester (2) (5.64 g) was converted to the free P-chloro-L-alanine hydrochloride (3) by refluxing 1 h in 2 N HCI (60 ml) (13). The mixture was repeatedly evaporated to dryness with the addition of water and finally ethanol, and the residue was crystallized from methanolether; yield, 4.0 g (go%), [a], -10.8" (3.2, water containing one equivalent of NaOH), corresponding to [a], -14.0" (2.5, water) for the free acid, lit.…”

“…P-Chloroalanine ester was prepared by bubbling chlorine through a suspension of cystine dimethyl ester dihydrochloride in chloroform (13). This appeared to us as a possible simple route to mono-N-substituted DAPr derivatives and eventually mixed peptides, as well as a quick source for P-chloroalanine derivatives, so this was investigated.…”

“…Both cystine esters were initially prepared by the classical hydrogen chloride method (14), however, because of the limited solubility of the ethyl ester in the reaction medium, the thionyl chloride procedure (1 5) was adopted. The chlorination was carried out essentially as described in the original paper (13). The yield of P-chloroalanine methyl ester was higher, but the ethyl ester was preferred for subsequent reactions.…”