Patent ID: 8236985

Claim:
A compound of formula I, wherein R 1a represents C 1-4 alkyl (which latter group is optionally substituted by one or more substituents selected from halogeno and aryl), aryl, (CH 2 ) 2 -L 1 or the structural fragment wherein R x represents H or N(R 1b )R 2b ; R 1b and R 2b independently represent C 1-4 alkyl (which latter group is optionally substituted by one or more substituents selected from halogeno and aryl), aryl or (CH 2 ) 2 -L 2 ; R y represents halogeno or C 1-4 alkyl; R 2a represents H, C 1-4 alkyl (which latter group is optionally substituted by one or more substituents selected from halogeno and aryl), aryl or (CH 2 ) 2 -L 3 ; L 1 , L 2 and L 3 each represents, independently at each occurrence, a leaving group; R 3 represents halogeno or C 1-4 alkyl; a represents, independently at each occurrence, an integer from 0 to 4; X 1 —X 2 represents C(O)—CH(Y 1 ), C(H)═C(Y 1 ), CH 2 —CH(Y 1 ), NH—CH(Y 1 ), CH 2 —C(O), NH—C(O) or CH(Y 1 ); b represents 0 or 1; X 3 —X 4 represents CH═C(Y 2 ), O—CH(Y 2 ), NH—CH(Y 2 ), O—C(O) or NH—C(O); c represents an integer from 0 to 10; X 5 —X 6 represents CH 2 —CH 2 , CH═CH or O—CH 2 ; and Y 1 and Y 2 independently represent, at each occurrence, H or C 1-4 alkyl; or a pharmaceutically acceptable derivative thereof, provided that at least one of the following is the case: (a) R 1a represents (CH 2 ) 2 -L 1 ; (b) R 1b and/or R 2b represents (CH 2 ) 2 -L 2 ; (c) R 2 represents (CH 2 ) 2 -L 3 .