(3s,8s)-8-{(s)-1-Carboxy-2-[4-(2,3-dimethyl-pyridin-4-yl)-phenyl]-ethyl-carbamoyl}-3-(4-hydroxy-phenyl)-2,3,8,9-tetrahydro-6h-[1,4]dioxino[2,3-g]isoquinoline-7-carboxylic acid tert-butyl ester