1H-Pyrano[3',4':6,7]indolizino[1,2-b]quinoline,tryptophan deriv. NSC681640 Tryptophan, [(4-ethyl-3,4,12,14-tetrahydro-4-hydroxy- 3,14-dioxo-1H-pyrano[3',4':6,7]indolizino[1,2-b]quinolin-11-yl)methylene]hydrazide, monohydrochloride