(2S,7aR,8R,8aS,11S,11aS,11bR,11cR)-8-Ethyl-11-methyl-2-[(2S,4S)-4-methyl-5-oxotetrahydro-2-furanyl]dodecahydroazepino[3,2,1-hi]furo[3,2-e]indol-10(2H)-one