rac-methyl (4R,6aR,8aS,9S,12aR,12bR)-4-hydroxy-5,9,12a-trimethyl-4,5,6,6a,7,8,8a,9,10,11,12,12a-dodecahydro-4,12b-methanonaphtho[1,2-d]oxocine-9-carboxylate