Which of the following is the 1st product of tryptophan catabolism?

Tryptophan is degraded to amphibolic intermediates the kynurenine-anthranilate pathway. Tryptophan oxygenase conves tryptophan to N formyl kynurenine by opening the indole ring and by incorporating molecular oxygen. This inturn is catalysed by kynurenine formylase to produce kynurenine. Hanup's disease result from impaired intestinal and renal transpo of tryptophan and other neutral amino acids. This defect accounts for deficient niacin biosynthesis resulting in pellagra like signs and symptoms. Ref: Harper's Illustrated Biochemistry, 29e, Chapter 29