(1S,3aS,3bS,9aR,9bS,11aS)-1-Dibenzylcarbamoyl-9a,11a-dimethyl-7-oxo-1,2,3,3a,3b,4,7,8,9,9a,9b,10,11,11a-tetradecahydro-cyclopenta[i]phenanthridine-5-carboxylic acid tert-butyl ester