(E)-(S)-4-{(2R,4S,5S)-4-(tert-Butyl-dimethyl-silanyloxy)-6-methyl-2-(3-methyl-but-2-enyl)-5-[(5-methyl-isoxazole-3-carbonyl)-amino]-heptanoylamino}-5-((S)-2-oxo-pyrrolidin-3-yl)-pent-2-enoic acid ethyl ester

(2S,4S)-5-Oxo-4-((E)-pent-3-enyl)-pyrrolidine-1,2-dicarboxylic acid 1-tert-butyl ester 2-methyl ester

(2S,4S)-5-Oxo-4-((E)-pent-3-enyl)-pyrrolidine-2-carboxylic acid methyl ester

dimethyl (2S,4S)-N,N-bis(tert-butoxycarbonyl)-4-methylglutamate