Identification of l-Tryptophan by down-field ¹ H MRS: A precursor for brain NAD⁺ and serotonin syntheses.

Based on the chemical shift, this new peak was identified as the indole (-NH) proton of l-tryptophan (l-TRP) and was further confirmed from phantom experiments on l-TRP. These promising preliminary results potentially pave the way to investigate the role of cerebral metabolism of l-TRP in healthy and disease conditions.