The D-and La-amino-ybutyrolactone hydrobromides were then converted to the corresponding optically active 3, 6-bis-(j% hydroxyethyl)-2, 5-diketopiperazines which, after chlorination, yielded D-and~-3, 6-bis-(j3-chloroethyl)-2, 5-diketopiperazines. By a suitable choice of the isomers of cysteine or homocysteine, or their S-benzyl derivative, and of the isomers of the dichlorodiketopiperazines, L-cystathionine, L-allocystathionine and the L, D ...
