<i>N</i><sup>1</sup>‑Fluoroalkyltryptophan Analogues: Synthesis and <i>in vitro</i> Study as Potential Substrates for Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase (hIDO) is an enzyme that catalyzes the oxidative cleavage of the indole ring of l-tryptophan through the kynurenine pathway, thereby exerting immunosuppressive properties in inflammatory and tumoral tissues. The syntheses of 1-(2-fluoroethyl)-tryptophan (1-FETrp) and 1-((1-(2-fluoroethyl)-1<i>H</i>-1,2,3-triazol-4-yl)­methyl)-tryptophan, two <i>N</i><sup>1</sup>-fluoroalkylated tryptophan derivatives, are described here. <i>In vitro</i> enzymatic assays with these two new potential substrates of hIDO show that 1-FETrp is a good and specific substrate of hIDO. Therefore, its radioactive isotopomer, 1-[<sup>18</sup>F]­FETrp, should be a molecule of choice to visualize tumoral and inflammatory tissues and/or to validate new potential inhibitors.