methyl N-((2S,3R,3aR,5aR,7S,9aS,9bR)-3-((R)-1-hydroxyethyl)-7,9b-dimethyl-1-oxo-2,3,3a,5a,6,7,8,9,9a,9b-decahydro-1H-cyclopenta[a]naphthalene-2-carbonyl)-N-methyl-D-serinate