Cysteine derivatives with reactive groups as potential antitumor agents

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Abstract
Cysteine derivatives having diazo ketone and chloro ketone functions were prepared. In order to effect adequate protection for modifying the carboxyl group, cysteine was converted to a thiazolidine derivative I, which was then converted to the N-acetyl derivative VII. The active ester method or activation with DCC [dicyclohexylcarbodiimide] yielded the diazo ketone derivative VIII. Similar treatment of the parent compound I with DCC led to a self-condensation reaction giving a diketopiperazine VI. The diazo keton derivative VIII was used in preparing .alpha.-chloro ketone derivative X and a homologue of cysteine. Deblocking N-acetylated thiazolidine derivatives with various reagents did not proceed satisfactorily. Interaction of the N-acetylated blocked ester XII with trifluoroacetic acid opened the thiazolidine ring to give the N-acetylated blocked diester XIII and other products. The chloro ketone derivative X had a moderate inhibitory activity against mouse mammary adenocarcinoma in cell culture. S-(1-Adamantyl)-L-cyteine was prepared and was inactive.