(S)-7-(tert-butoxycarbonyl)-1,4-dithia-7-azaspiro[4.4]nonane-8-carboxylic acid

(S)-7-tert-butyl 8-(2-(trimethylsilyl)ethyl) 1,4-dithia-7-azaspiro[4.4]nonane-7,8-dicarboxylate

(8S)-1,4-dithia-7-azaspiro[4.4]nonane-8-carboxylic acid

(S)-2-[(R)-1-(2,5-Dioxo-pyrrolidin-1-yloxycarbonyl)-ethylamino]-4-phenyl-butyric acid ethyl ester