Abstract: A compound comprising a cyclopentanone, cyclopentenone, cyclohexanone or cyclohexenone group, wherein a first ring carbon atom carries an —SR substituent, R is a substituted or unsubstituted alkyl, alkenyl, alkynyl, aryl, aralkyl, aralkenyl, or aralkynyl group that, optionally, includes at least one heteroatom in its carbon skeleton, the remaining available ring carbon atoms are optionally substituted, and said compound either:—(a) is more soluble in water at a temperature of 20-40° C.; (b) is less lipophilic; and/or, (c) has a greater therapeutic index; or; (d) is less soluble in water at a temperature of 20-40° C.; (e) is more lipophilic; and/or, (f) has a greater therapeutic index; than an equivalent cyclohex-2-en-1-one or cyclopent-2-en-1-one derivative in which a hydrogen atom replaces said —SR group.