Method of preparing retroviral protease inhibitor intermediates

A method for purifying a diastereomer, said method comprising

• (a) preparing an organic acid salt or an inorganic acid salt of an amino compound having the formula
• wherein
• R1 represents alkyl, aryl, cycloalkyl, cycloalkylalkyl or aralkyl radicals, which are optionally substituted with alkyl, halogen, NO2, OR9 or SR9 radicals, where R9 represents hydrogen, alkyl, aryl or aralkyl radicals;
• R3 represents hydrogen, alkyl, alkenyl, alkynyl, hydroxyalkyl, alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heteroaryl, heterocycloalkylalkyl, aryl, aralkyl, heteroaralkyl, aminoalkyl or N-mono- or N,N-disubstituted aminoalkyl radicals, wherein said N-mono- or N,N-disubstituted aminoalkyl radicals are substituted with alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, or heterocycloalkylalkyl radicals, or wherein said N,N-disubstituted aminoalkyl radical is substituted with substituents that, together with the nitrogen atom to which they are bonded, form heterocycloalkyl or heteroaryl radicals;
• and
• P1 and P2 are each independently hydrogen, acyl, aralkyl, silyl, aralkoxycarbonyl, alkoxycarbonyl, alkylcarbonyl, aralkylcarbonyl, arylcarbonyl or cycloalkenylalkyl radicals;
• or P1 and P2 together with the nitrogen atom to which they are bonded form a heterocyclic ring system;
• and
• (b) precipitating or crystallizing said organic acid salt or said inorganic acid salt from a solution.