The acylation of 3,4-dihydroxyphenylglycine (I) with 4-ethyl-2,3-dioxopiperazin-1-ylcarbonyl chloride (II) by means of N,N-diethyl-1,1,1-trimethylsilylamine (DTSA) gives the corresponding N-acyl derivative (III), which is acetylated with acetic anhydride and pyridine in THF yielding the corresponding diacetoxy compound (IV). The condensation of (IV) with benzyl 6B-amino-6a-formamidopenicillanate (V) [obtained from the trichloroethoxycarbonyl derivative (VI)] by means of dicyclohexyl carbodiimide (DCC) in dichloroethane affords the fully protected compound (VII), which is debenzylated by hydrogenolysis with H2 over Pd/C in THF - water giving the free acid (VIII). Finally, this compound is desacetylated with Subtilisin Calsberg.

The acylation of 3,4-dihydroxyphenylglycine (I) with 4-ethyl-2,3-dioxopiperazin-1-ylcarbonyl chloride (II) by means of N,N-diethyl-1,1,1-trimethylsilylamine (DTSA) gives the corresponding N-acyl derivative (III), which is acetylated with acetic anhydride and pyridine in THF yielding the corresponding diacetoxy compound (IV). The condensation of (IV) with benzyl 6B-amino-6a-formamidopenicillanate (V) [obtained from the trichloroethoxycarbonyl derivative (VI)] by means of dicyclohexyl carbodiimide (DCC) in dichloroethane affords the fully protected compound (VII), which is debenzylated by hydrogenolysis with H2 over Pd/C in THF - water giving the free acid (VIII). Finally, this compound is desacetylated with Subtilisin Calsberg.