1H-[1,2,4]Diazaphospholo[1,2-a]pyridazine-5,8-dione,2,2'-(1,2-ethanediyl)bis[tetrahydro-6,7-dimethoxy-1,3-diphenyl-,(1R,1'R,3R,3'R,6R,6'R,7R,7'R)-