The present invention provides aprocess for the preparation of lopinavir intermediate (2S,3S,5S)-2-Amino-3-hydroxy-5-[2S-(l-tetrahydro-pyrimid-2- onyl)-3-methyl butanoyl]amino-l,6-diphenylhexane (S)-Pyroglutamic acid salt(II) comprising: (a) N-debenzylation of (2S,3S,5S)-2-N,N-dibenzylamino-3-hydroxy- 5-[2S-(l-tetrahydro-pyrimid-2-onyl)-3-methyl butanoyl]amino-1,6- diphenylhexane (III) to get (2S,3S,5S)-2-amino-3-hydroxy-5-[2S-(l-tetrahydro-pyrimid-2-onyl)-3-methyl butanoyI]amino-l,6-diphenylhexane (IV) in the presence of transition metal catalyst on activated carbonand formic acid salt in alcoholic solvent, (b) treatment of the reaction mixture with aqueous inorganic base and (c) reaction with L-pyroglutamic acid.
