The present invention relates to a method of treatment and/or prophylaxis of a microbial infection, comprising the step of administering an effective amount of a compound of formula (I), in which X and Y are either the same or different and selected from a heteroatom; is a double or single bond depending on the heteroatoms X and Y; R1 to R5 are either the same or different and selected from hydrogen or a non-deleterious substituent; and R6 and R7 are either the same or different and selected from hydrogen and a non-deleterious substituent or one of R6 and R7 are absent when there is a double bond present, pharmaceutically acceptable salts or derivatives, pro-drugs, tautomers and/or isomers thereof. The present invention also relates to a method for protecting a subject from radiation damage, a method of cancer radiotherapy and use as an antimicrobial or radioprotective agent of the compound of formula (I) defined above. Some of the compounds of formula (I) are novel and are also described in the present invention, together with pharmaceutical or veterinary compositions containing them.