ethyl 2-{1-[(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]-1,4-dioxo-3-phenyl-5-aza-2-oxahex-6-yl}-3-acetyl-5,5-dimethyl-1,3-thiazolidine-4-carboxylate