(2R,4S)-3-{[(3S,6aR,6R)-6-{[(2R)-2-{[(4-ethyl-2,3-dioxopiperazin-1-yl)carbonyl]amino}-2-phenylacetyl]amino}-2,2-dimethyl-5-oxo-3,5,6,6a-tetrahydro-2H-azeto[2,1-b][1,3]thiazol-3-yl]carbonyl}-2-[(1R,4R)-1-carboxy-6-(4-ethyl-2,3-dioxopiperazin-1-yl)-3,6-dioxo-4-phenyl-2,5-diazahex-1-yl]-5,5-dimethyl-1,3-thiazolidine-4-carboxylic acid