122 mg of 4-[[(aminooxy)methyl]sulphonyl]pyrocatechol were reacted with 236 mg of (6R,7R)-7-(2-amino-4-thiazoleglyoxylamido)-3-[[[2-(methoxycarbonyl)-5-methyl-s-triazolo[1,5-a]pyrimidin-7-yl)thio]methyl]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid according to the procedure described in Example 7. The crude product obtained was suspended in 10 ml of water and brought into solution by the slow addition of 0.1N sodium hydroxide solution, with care being taken that the pH of the solution did not exceed 7. By chromatography on MCI gel CHP 2OP using water as the elution agent as well as water/methanol mixtures with increasing amounts of methanol and lyophilization of the concentrated product fractions, there was obtained (6R,7R)-7-[(Z)-2-(2-amino-4-thiazolyl)-2-[[[(3,4-dihydroxyphenyl)sulphonyl]methoxy]imino]acetamido]-3-[[(2-(methoxycarbonyl)-5-methyl-s-triazolo[1,5-a]pyrimidin-7-yl]thio]methyl]-8-oxo-5-thia-1 azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid monosodium salt as a white powder.
