Aspidospermidine-​3-​carboxylic acid, 4-​(acetyloxy)​-​6,​7-​didehydro-​15-​[(2R,​4R,​6S,​8S)​-​4-​(1,​1-​difluoroethyl)​-​1,​3,​4,​5,​6,​7,​8,​9-​octahydro-​8-​(methoxycarbonyl)​-​2,​6-​methano-​2H-​azecino[4,​3-​b]​indol-​8-​yl]​-​3-​hydroxy-​16-​methox