(2,4'-Bi-1H-indole)-3,3'-dipropanoic acid, alpha,alpha'-diamino-6',7'-dihydro-6',7'-dioxo- 134645-25-3 4-(2'-Tryptophyl)tryptophan-6,7-dione Tryptophan-tryptophan quinone tryptophan tryptophylquinone