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