Bisoprolol fumarate impurity and preparation method thereof

The invention discloses a bisoprolol fumarate impurity and a preparation method thereof, according to the method, bisoprolol is taken as a raw material, and the impurity is synthesized through a three-step reaction. The method comprises the following steps: 1) reacting a compound I with dimethyl butynedioate to obtain an intermediate II; 2) reacting the intermediate II with sodium cyanoborohydride to obtain an intermediate III; and 3) carrying out hydrolysis reaction on the intermediate III and potassium trimethylsilanolate to obtain an impurity IV. The synthetic route is reasonable in design, post-treatment is simple, reaction conditions are mild, and operability is high. The bisoprolol fumarate impurity IV prepared by the invention can be used as an impurity standard substance for detection and analysis of a bisoprolol fumarate finished product, so that accurate positioning and qualification of the impurity IV in the detection and analysis of the bisoprolol fumarate finished product are improved, control on