Abstract: The disclosure relates to a compound of formula I, or a pharmaceutically acceptable salt or ester thereof, wherein: R1 is selected from a group consisting of alkyl, cycloalkyl, alkenyl, cycloalkenyl and alkynyl; R2 is selected from a group consisting of H, halo, OR11, NHR11, alkyl, alkenyl and alkynyl; R3 is selected from a group consisting of alkyl, alkenyl, alkynyl, aryl, halo, aryloxy, NHCO2R4, NHCONR5R6, NHCOR7, NH-alkyl, NH-alkenyl, NH(CH2)n-aryl, (CH2)p-heteroaryl, (CH2)qCO2R8, (CH2)qCOR9 and NHSO2R10, wherein each alkyl, alkenyl, aryl or heteroaryl moiety in the aforementioned list is optionally further substituted by one or more groups selected from alkyl, halo, OH, NH2, alkoxy, aryloxy, alkylamino, arylamino, carboxyl and carboxamide; R4 to R11 are each independently selected from a group consisting of alkyl, alkenyl and aryl; and n is selected from a group consisting of 0, 1, 2, 3, 4, 5 and 6, p is selected from a group consisting of 0, 1, 2, 3, 4, 5 and 6, q is selected from a group consisting of 0