3,4,5a,5b,8,13,15a,15b-Octahydro-5b,15a-dimethyl-1,14:5,7-dimethano-2H-[1,4]diazepino[2,3:3,4]cyclobuta[1,2-d][2,7]benzodiazecine-6,15,16,17-tetrone