There are described compounds of general formula (I) and isomeric forms thereof wherein n is 0, 1, 2 or 3, saturated or unsaturated; most preferably at least one of R.sub.1 to R.sub.5 represents halogen; at least one of R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 is selected from --S--R or --COOR, or two or more Of R.sub.1-R.sub.5 comprise a linking group such as --S--(CH2).sub.mS--, where m is 1, 2 or 3 and R is selected from alkyl having 1 to 5 carbon atoms, cycloalkyl having 3-6 carbon atoms, hydroxy, and aryl having 6 to 10 carbon atoms, such groups being optionally substituted, and when R.sub.1 is selected from --S--R, then at least one of R.sub.2, R.sub.3 and R.sub.5 is most preferably selected from halogen; and R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are otherwise the same or different and are selected from hydrogen, halogen, alkyl having 1 to 5 carbon atoms, electron donor groups such as alkoxy having 1-5 carbon atoms or hydroxy, electron acceptor groups selected from cyano, nitro, trifluoroalkyl or amide; alkylamino, benzoyloxy, nitroxy, phenyl or sulpho; and pharmacologically acceptable salts thereof. Compounds described have activity on the melanocortin receptors and have application in the treatment of a wide range of inflammatory, arthritic or central nerve regeneration conditions. ##STR00001##