To a solution of O-methoxymethyl-N-methyl-β-hydroxytyrosine (15.1 g) and bis(trimethylsilyl)acetamide (25 ml) in dichloromethane (150 ml) was added a solution of 2-nitrophenylsulfenyl chloride (11.2 g) in dichloromethane (50 ml). After stirring for 2 hours at 0° C., bis(trimethylsilyl)acetamide (10 ml) and 2-nitrophenylsulfenyl chloride (5.6 g) was added to the solution. The mixture was stirred for 3 hours at room temperature and added to 1N-sodium hydroxide (200 ml). The organic layer was washed with water (300 ml) and the aqueous solutions were combined. After the aqueous solution was acidified with diluted hydrochloric acid, the product was extracted with ethyl acetate (300 ml) and the extract was washed with water (100 ml×3). After the solution was dried over magnesium sulfate, the solvent was removed in vacuo to give O-methoxymethyl-N-methyl-N-(2-nitrophenylthio)-β-hydroxytyrosine (20.5 g).
