Syn/anti isomerization of cefuroxime by ultraviolet light

Cefuroxime, like all the oximino cephalosporins on the market, has the methoxyimino group in the syn (Z) configuration. By U.V. light irradiation of cefuroxime, a syn/anti isomerization occurs until equilibration of the two isomers is reached. Measurement of the 1H-N.M.R. chemical shift differences of the two isomers allows the assignment of methoxyimine stereochemistry.