Preparation method of delta3 isomer of cefoselis

The invention provides a preparation method of a delta3 isomer of cefoselis in the field of compound preparation. The method comprises the following steps: (1) carrying out reaction on cefoselis or pharmaceutically acceptable salt thereof in the presence of aqueous alkali to obtain a reaction liquid; (2) adjusting the pH value of the reaction liquid obtained in the step (1) to 3-8 by dilute acid; (3) concentrating the reaction liquid obtained in the step (2), and carrying out reversed-phase high-performance liquid chromatography separation on the concentrated liquid to obtain a delta3 isomer fraction of cefoselis; (4) drying the delta3 isomer fraction of cefoselis, obtained in the step (3), to obtain a delta3 isomer of cefoselis. The cefoselis or pharmaceutically acceptable salt thereof is selected from one or more of cefoselis, cefoselis sulfate and cefoselis hydrochloride. The preparation method provided by the invention is easy to get raw materials, simple to operate, mild in reaction condition, few in reaction steps, high in product purity and short in reaction time, instruments and equipment used in the preparation method are widely applied, and the whole preparation and separation processes are stable and good in reproducibility.