A compound of formula I: and isomers, salts, solvates, chemically protected forms, and prodrugs thereof, wherein: R1 and R2 are independently selected from hydrogen, an optionally substituted C1-7 alkyl group, C3-20 heterocyclyl group, or C5-20 aryl group, or may together form, along with the nitrogen atom to which they are attached, an optionally substituted heterocyclic ring having from 4 to 8 ring atoms; Q is —NH—C(═O)— or —O—; Y is an optionally substituted C1-5 alkylene group; X is selected from SR3 or NR4R5, wherein, R3, or R4 and R5 are independently selected from hydrogen, optionally substituted C1-7 alkyl, C5-20 aryl, or C3-20 heterocyclyl groups, or R4 and R5 may together form, along with the nitrogen atom to which they are attached, an optionally substituted heterocyclic ring having from 4 to 8 ring atoms; if Q is —O—, X is additionally selected from —C(═O)—NR6R7, wherein R6 and R7 are independently selected from hydrogen, optionally substituted C1-7 alkyl, C5-20 aryl, or C3-20 heterocyclyl groups, or R6 and R7 may together form, along with the nitrogen atom to which they are attached, an optionally substituted heterocyclic ring having from 4 to 8 ring atoms; and if Q is —NH—C(═O)—, —Y—X may additionally be selected from C1-7 alkyl.