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.