Synthetic studies of 3-(3-fluorooxindol-3-yl)-l-alanine

Oxidative fluorination of several protected tryptophans 8b–g with Selectfluor™ proceeded smoothly in aqueous media to give a diastereomeric mixture of the corresponding 3-fluorooxindoles 9b–g. Attempted deprotection of the 3-fluorooxindoles 9b–g under various conditions did not afford 3-(3-fluorooxindol-3-yl)-l-alanine (6). Reaction of the suitably protected tryptophan derivative 16 with Selectfluor™ produced the fluorinated product 17. Simultaneous cleavage of all protective groups of 17 under acidic conditions successfully gave the target compound 6 in excellent yield.