Patent ID: 7951943

Claim:
A method for purifying a 3-hydroxyamidinophenylalanine compound having the formula (I): in which R 1 is a group of the formula in which R 4 is (i) an unsubstituted C 1 -C 6 -alkyl residue, or a C 1 -C 6 -alkyl-, C 1 -C 3 -alkoxy-, hydroxyl-, carboxyl-, nitro-, cyano-, or/and halogen-substituted C 1 -C 6 -alkyl residue; (ii) a saturated or unsaturated branched or unbranched C 1 -C 6 -alkoxy residue; (iii) an unsubstituted phenoxy or benzyloxycarbonyl residue, a C 1 -C 6 -alkyl-, C 1 -C 3 -alkoxy-, hydroxyl-, carboxyl-, nitro-, cyano-, or/and halogen-substituted phenoxy or benzyloxycarbonyl residue; (iv) phenyl, p-halophenyl, or naphthyl, or (v) ethoxycarbonyl, R 2 is an unsubstituted phenyl residue, or a C 1 -C 6 -alkyl-, C 1 -C 3 -alkoxy-, hydroxyl-, carboxyl-, nitro-, cyano-, or/and halogen-substituted phenyl residue, R 3 is H or branched or unbranched C 1 -C 4 -alkyl, n is 0 or 1, and Z is CR 9 where R 9 is H, comprising the steps of: (a) forming a salt precipitate by adding an aromatic sulfonic acid to a solution of a contaminated 3-hydroxyamidinophenylalanine compound, (b) separating said precipitate formed in step (a), and (c) recovering a purified 3-hydroxyamidinophenylalanine compound from the precipitate.