Abstract: There is provided a compound of formula R1—CO—X—Y—Z—R2 wherein X and Z are each optional groups that are, independently, saturated or unsaturated carbon chains having a length of 1 to 3 carbons; Y is SO, S, SO2, CH?CH, CH2CH2 or O; R1 is wherein denotes the point of attachment; R2 is a heteroaryl group comprising an optionally substituted 5 or 6 membered ring, which ring contains only carbon and at least one nitrogen, or contains only carbon, and at least two nitrogens and at least one sulfur; and wherein (i) when R1 is and —CO—X—Y—Z— is CO—CH2—SO, CO—CH2—S, or CO—CH2—SO2, R2 is other than and; (ii) when R1 is and —CO—X—Y—Z— is —CO—CH2—O—, R2 is other than