Cady, SG; Sono, M (1991). "1-Methyl-DL-tryptophan, beta-(3-benzofuranyl)-DL-alanine (the oxygen analog of tryptophan), and beta-3-benzo[b]thienyl-DL-alanine (the sulfur analog of tryptophan) are competitive inhibitors for indoleamine 2,3-dioxygenase". Archives of Biochemistry and Biophysics. 291 (2): 326–33. doi:10.1016/0003-9861(91)90142-6. PMID1952947.
Cady, SG; Sono, M (1991). "1-Methyl-DL-tryptophan, beta-(3-benzofuranyl)-DL-alanine (the oxygen analog of tryptophan), and beta-3-benzo[b]thienyl-DL-alanine (the sulfur analog of tryptophan) are competitive inhibitors for indoleamine 2,3-dioxygenase". Archives of Biochemistry and Biophysics. 291 (2): 326–33. doi:10.1016/0003-9861(91)90142-6. PMID1952947.