Some time ago! we described certain cystathionine** derivatives suitable for the synthesis of the so-called carba analogs of biologically active peptides, ie of such ana- logs in which cystine is replaced by cystathionine. The synthesis of additional com- pounds of this type4 required that the series of derivatives lIb through lIe (ref. l ... The tert-butyloxycarbonyl derivative of cystathionine IIj was prepared by reduction of cystine by sodium in liquid ammonia and alkylativn of ...
