1.17 g of 3,4-diacetoxy-benzenesulphonyl chloride were added to a solution of 6.0 g of 2-(tritylamino)-4-thiazoleglyoxylic acid ethyl ester (Z)-O-(2-aminoethyl) oxime and 0.49 g of 4-dimethylamino-pyridine in 50 ml of N,N-dimethylformamide. The reaction solution was stirred at 20° C. for 3 hours, 10 ml of 2N sodium hydroxide solution were then added, and the solution was stirred at 20° C. for an additional hour. Then, 20 ml of water were added and the pH of the reaction mixture was lowered to 3 by the addition of 3N hydrochloric acid. The resulting precipitate was filtered off under suction, washed with a small amount of water and then heated to 50° C. for 40 minutes in 60 ml of 80% aqueous acetic acid. The mixture was cooled to 20° C. and evaporated completely in a vacuum. The residue was dissolved in 30 ml of methanol and treated in an ice bath with a total of 180 ml of diethyl ether. The precipitate was filtered off under suction, suspended in a small amount of water and brought into solution by the dropwise addition of 2N sodium hydroxide solution. The solution of pH 7.5 was applied to a MCI gel column (CHP2OP) conditioned with 1% aqueous acetic acid and chromatographed according to the procedure described in the first paragraph of this Example. The product was eluted with a 9:1 (v/v) water/acetonitrile mixture. The pure fractions were concentrated completely in a vacuum and the solid residue was crystallized from methanol/diethyl ether. There was obtained 2-amino-4-thiazoleglyoxylic acid (Z)-O-[2-[(3,4-dihydroxyphenyl)sulphonamido]ethyl] oxime as white crystals of melting point 92°-94° C. (decomposition).
