Abstract: Compounds of formula (I): wherein X is selected from CRX and N; RN1 is selected from H and C1-4 alkyl, which may be substituted by SH or halo; RG1 is selected from H and SH; RC2 is selected from H and optionally substituted C1-7 alkyl; RC3 is selected from H and optionally substituted C1-7 alkyl; Rx is selected from H, OH and NH2; RC4 is selected from: (i) an optionally substituted C3-12 N-containing heterocyclyl; (ii) C(?O)NRN5RN6, where RN5 and RN6 are independently selected from H, optionally substituted C1-7 alkyl, optionally substituted C3-20 heterocyclyl and optionally substituted C5-20 aryl or RN5 and RN6 and the nitrogen atom to which they are attached form an optionally substituted N-containing C5-7 heterocyclyl group; (iii) C(?O)ORO1, where RO1 is selected from H, optionally substituted C1-7 alkyl, optionally substituted C3-20 heterocyclyl and optionally substituted C5-20 aryl; (iv) C(?O)NHNHSO2RS1, where RS1 is selected from H, optionally substituted C1-7 alkyl, optionally substituted C3-20 heteroc