A compound of formula (I) wherein X is O, C═O or S; Y is N or CH; R2 and R4 are each independently H, —(CH2)pCOOH, —(CH2)pCON(R5)2 or —(CH2)pCOOC1-6alkyl; or R2 and R4 together form a 6-membered phenyl ring fused to the five membered ring; each R1 is independently selected from H, halo (e.g. fluoro or chloro), C6-10aryl, C7-12arylalkyl, C2-12 alkenyl; OC1-12 alkyl, OC2-12 alkenyl or a C1-12 alkyl group; each R5 is H or C1-6 alkyl; each p is 0 to 3; n is 1 to 4; or a salt, ester, solvate, N-oxide, or prodrug thereof, e.g. a salt thereof.