Heterocyclecarbonyl amino acid hydroxyethylamino sulfonamide retroviral protease inhibitors

A compound represented by the formula:

• or a pharmaceutically acceptable salt, or ester thereof, wherein
• R1 represents alkyl of 3-4 carbon atoms, alkenyl of 2-5 carbon atoms, alkynyl of 2-3 carbon atoms, imidazolylmethyl, —CH2CONH2, —CH2S(O)2NH2, —CH2SCH3, —CH2S(O)2CH3, —C(CH3)2SCH3, —C(CH3)2S(O)CH3 or —C(CH3)2S(O)2CH3 radicals,
• and Z is either S or NH, and R9 represents a radical formula
• wherein Y is either O or NH;
• X represents a bond, O or NH;
• R20 represents hydrogen, methyl, ethyl, propyl, isopropyl, isobutyl, benzyl, 2-(1-pyrrolidinyl)ethyl, 2-(piperidinyl)ethyl, 2-(1-piperazinyl)ethyl, 2-(4-methylpiperazin-1-yl)ethyl, 2-(1-morpholinyl)ethyl, 2-(1-thiamorpholinyl)ethyl or 2-(N,N-dimethylamino)ethyl radicals.