1.0 g (2.94 mmol) of 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutarate ammonium salt was dissolved in 10 ml of water, to which 1 ml of a Raney-nickel catalyst (manufactured by Kawaken Fine Chemicals Co., Ltd.; developed nickel catalyst NDHT-90) was added with a syringe, and the mixture stirred at a hydrogen pressure of 20 atmospheres for 10 hours. The catalyst was filtered off, and the resulting solution was concentrated to obtain the residue. The residue was analyzed by NMR. It was shown that 0.29 g (0.89 mmol; yield, 30%) of (2S,4S)/(2R,4R)-4-hydroxy-4-(3-indolylmethyl)-2-aminoglutaric acid (monatin) and 0.29 g (0.89 mmol; yield, 30%) of (2S,4R)/(2R,4S)-4-hydroxy-4-(3-indolylmethyl)-2-aminoglutaric acid were generated.
