Enzyme inhibitors

A compound, or a pharmaceutically acceptable ester or salt thereof, of formula:

• wherein R5 is selected from the following substituent groups:
• (1) an alkyl group having 1 to 12 carbon atoms, substituted by —CN and optionally interrupted by a group selected from —O—, —S—, —NR3—, —C(═O)—, —CO2—, —OCO—, —CONR3—, —NR3CONR3—, —SO2—, —NR3SO2—, and —SO2NR3—;
• where each R3 independently is H or lower alkyl of 1 to 6 carbon atoms;
• (2) —OR4 where R4 is an aralkyl group having 3 to 16 carbon atoms optionally substituted with any one or more of groups:
• (a) —OH;
• (b) —SH;
• (c) -halogen,
• (d) —CO2H;
• (e) —CN;
• (f) —NO2;
• (g) —NR1R2 wherein each of R1 and R2 is selected from H and lower alkyl groups having 1 to 6 carbon atoms;
• (h) —SO2NR1R2 where R1 and R2 are as defined above;
• (i) —CONR1R2, —NR1CO2H, or —NR1COCOOH where R1 and R2 are as defined above;
• (j) an alkyl (or alkenyl or alkynyl group) group having 1 to 12 carbon atoms, optionally substituted by any one or more of the groups (a)–(i) above and/or optionally interrupted by a group selected from —O—, —S—, —NR3—, —C(═O)—, —CO2—, —OCO—, —CONR3—, —NR3CONR3—, —SO2—, —NR3SO2—, and —SO2NR3—;
• where each R3 independently is as defined above;
• and
• (3) —NHSO2R4* or —SO2NHR4*, where R4* is an aryl group having 2 to 10 carbon atoms optionally substituted with any one or more of groups (a) to (j) above;
• and
• wherein R6 is independently selected from hydrogen and the substituent groups (a) to (j) as defined above.