other indoles that are structurally related to serotonin ( d- and l-tryptophan , 5-hydroxy-l-tryptophan , n-acetyl-5-hydroxytryptamine , melatonin , 5-hydroxyindoleacetic acid , and 5-hydroxytryptophol ) and quipazine were inactive .
C0041249
l-tryptophan
C0000578
5-hydroxy-l-tryptophan