1147103-42-1

1053232-60-2

1147103-42-1

Compound A of the present invention can be prepared by a conventional aminoprotection method to obtain the known telaprevir intermediate A. In this method, when the aminoprotecting group P is a tert-butoxycarbonyl group, the procedure is as follows: under argon protection, compound I is slowly added to an ethyl acetate solution (69.9 g) containing 11 wt% hydrogen chloride cooled to 0°C. The reaction is carried out by stirring for 4 hours. After the addition was completed, the reaction system was warmed to 30-35°C and stirred continuously at this temperature for 4 hours to ensure complete reaction. Upon completion of the reaction, the reaction solution was concentrated to dryness by distillation under reduced pressure. Subsequently, methyl tert-butyl ether (80 mL) was added to the residue at room temperature, stirred for 1 hour and then filtered. The filter cake was dried under vacuum to constant weight to give a white to off-white solid, timosartan intermediate A, in a yield of 15.4 g with 99.5% HPLC purity. The overall four-step molar yield from compound II to intermediate A was 70%.