4-nitrobenzyl(5R)-6-[(acetyloxy)([1,3]thiazolo[3,2-a]benzimidazol-6-yl)methyl]-6-bromo-7-oxo-4-thia-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate → (5R,6Z)-7-oxo-6-([1,3]thiazolo[3,2-a]benzimidazol-6-ylmethylene)-4-thia-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid

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4-nitrobenzyl (5R)-6-[(acetyloxy)([1,3]thiazolo[3,2-a]benzimidazol-6-yl)methyl]-6-bromo-7-oxo-4-thia-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate (630 mg, 1 mmol) was suspended in 20 ml THF and 20 ml pH=6.5 aqueous phosphate buffer. The mixture was then subjected to 45 psi hydrogen for two hours. Then it was filtered through a pad of celite and concentrated in vacuo to remove most of the THF. The solution was then cooled to zero degree and basified to pH=8 with 1 N sodium hydroxide. Then it was purified via reverse phase HPLC using 1 liter of water followed by 5%˜25% acetonitrile and water. Water was then removed through concentrate in vacuo and 33 mg of product (Yield 8%) was collected. MP: >250° C.;

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