A compound of formula (III), or a pharmaceutically acceptable derivative thereof for use in a method of combating and/or detecting a pathogen and/or tumour cells wherein X is selected from O, S and Se each of R2, R3 and R4 is independently selected from hydrogen or an optionally substituted alkyl, alkenyl, alkynyl or aryl group and R1 is selected from halogen, sulfo, acyl, sulfoxy, mercapto, nitro, amino, hydroxy or an optionally substituted alkyl, alkenyl, alkynyl, aryl, amine or alkoxy group wherein R1 is not methyl or hydrogen when each of R3 and R4 is methyl or hydrogen.
