HIV protease inhibitors

Compounds of the formula

• and pharmaceutically acceptable salts thereof
• wherein R1 is H, hydroxy or NHR2
• wherein R2 is H, alkyl, alkenyl, alkynyl, arylalkyl, heterocyclylalkyl, cycloalkyl, alkyl carbonyl, cycloalkyl carbonyl, aryl carbonyl, heterocyclyl carbonyl, aryl alkyl carbonyl, heterocyclyl alkyl carbonyl, alkyl oxy carbonyl, aryl alkyl oxy carbonyl, heterocyclyl alkyl oxy carbonyl, aryl, heterocyclyl, sulfonyl, alkyl sulfonyl, aryl sulfonyl, heterocyclyl sulfonyl or a group of the formula
• wherein X is O or S and
• R7 and R8 independently are H, alkyl, aryl, heterocyclyl, aryl alkyl, heterocyclyl alkyl or R7 and R8 together with the nitrogen atom to which they are attached form a saturated ring optionally containing a further hetero atom or a group
• wherein when n=0, Y represents O or S
• and R10 is H, alkyl, aryl alkyl, heterocyclyl alkyl, aryl, heterocyclyl or when n=1, Y represents N, R9 is H or alkyl and R10 is H, alkyl, aryl alkyl, heterocyclyl alkyl, aryl, heterocyclyl
• or R9 and R10 taken together with the hetero atom to which they are attached form a heterocycle, R11 and R12 independently are H or alkyl
• or R11 and R12 taken together with the carbon atom to which they are attached form a cycle,
• R3, R4 independently are alkyl or taken together with the carbon atom to which they are attached form a carbocycle,
• R5 is alkyl, aryl alkyl, heterocyclyl alkyl or R4 and R5 taken together with the carbon and sulfur atom to which they are attached form a heterocycle and
• R6 is alkyl, aryl alkyl, heterocyclyl alkyl, alkyl oxy alkyl, hydroxy alkyl, amino alkyl, fluoro alkyl and
• R13 is H or the residue of an inorganic or an organic ester and
• R15 is aryl,
• with the proviso that, if R3, R4 and R5 are methyl, R6 is tert-butyl, R13 is H and R15 is phenyl, R2 is not benzyl oxycarbonyl and not 2-quinoline carbonyl.