The bromination of 3,4-diacetoxyphenylacetic acid with N-bromosuccinimide (NBS) and SOCl2 gives the corresponding bromoacetic acid (II), which is esterified with diphenyldiazomethane (III) in acetone affording the diphenylmethyl ester (IV). The reaction of (IV) with N-hydroxyphthalimide (V) by means of triethylamine in acetonitrile yields diphenylmethyl-2-phthalimidooxy-2-(3,4-diacetoxy phenyl)acetate (VI), which is treated witb methyl hydrazine in dichloromethane to give diphenylmethyl-2-aminooxy-2-(3,4-diacetoxyphenyl)acetate (VII). The condensation of (VII) with (2-triphenylmethylamino-4-thiazolyl)glyoxylic acid (VIII) in methanol affords 2-(2-triphenylmethylamino-4-thiazolyl)-2-[(Z)-(diphenyl)methoxyimino]acetic acid (IX), which is condensed with 7beta-amino-3-[2-(diphenylmethoxycarbonyl)-5-methyl-s-triazolo[1,5-a]pyrimidin-7-ylthiomethyl]-3-cephem-4-carboxylic acid diphenylmethyl ester (X) by means of dicyclohexylcarbodiimide (DCC) in dichloromethane giving the protected final product (XI). Finally, this compound is deprotected by treatment first with trifluoroacetic acid and then with NaHCO3 in water.
2-[1(S)-(3,4-dihydroxyphenyl)-1-(diphenylmethoxycarbonyl)methoxyimino]-2-[2-(triphenylmethylamino)thiazol-4-yl]-acetic acid (IX) is condensed with 7beta-amino-3-[2-(diphenylmethoxycarbonyl)-5-methyl-s-triazolo[1,5-a]pyrimidin-7-ylthiomethyl]-3-cephem-4-carboxylic acid diphenylmethyl ester (X) by means of dicyclohexylcarbodiimide (DCC) in dichloromethane giving the protected final product (XI). Finally, this compound is deprotected by treatment first with trifluoroacetic acid and then with NaHCO3 in water.