Method for making intermediates useful in synthesis of retroviral protease inhibitors

A method for preparing an aminoepoxide of the formula (I):

• wherein P1 and P2 independently or taken together comprise amino protecting groups;
• wherein R1 is selected from alkyl, aryl, cycloalkyl, cycloalkylalkyl and aralkyl, which are optionally substituted with a group selected form the group consisting of alkyl, halo, NO2, OR9, and SR9, wherein R9 is selected from the group consisting of hydrogen and alkyl;
• and wherein any of the foregoing groups P1, P2, and R1 may be substituted at one or more substitutable positions with one or more radicals independently selected from the group consisting of halo, alkyl of C1-C8, alkoxy, hydroxy, nitro, alkenyl, amino, alkylamino, acylamino and acyl;
• or a pharmaceutically acceptable salt thereof;
• said method comprising the steps of forming a protected aminoalcohol of formula (II):
• then oxidizing said protected aminoalcohol to a chiral protected aminoaldehyde and diastereoselectively forming the aminoepoxide by reacting said aminoaldehyde with chloromethyllithium or bromomethyllithium.