Abstract: There are described compounds of formula I, ##STR1## in which X represents a C2 to 8 alkylene chain optionally interrupted by a double bond or by S(O).sub.n, wherein n is 0, 1 or 2;Y represents O or NH,l and m each independently represent 2, 3 or 4,R.sub.10 represents phenyl substituted by one or more substituents R.sub.23, which may be the same or different; or R.sub.10 represents pyridyl, a saturated carbocyclic group, alkyl C 1 to 6 or hydrogen,R.sub.15 represents hydrogen or together with R.sub.23 forms a (CH.sub.2).sub.p chain, wherein p represents 0, 1 or 2;R.sub.20, R.sub.21, R.sub.22 and R.sub.23, which may be the same or different, independently represent hydrogen, alkyl C 1 to 6, NHR.sub.25, SH, NO.sub.2, halogen, CF.sub.3, SO.sub.2 R.sub.30, CH.sub.2 OH or OH, wherein R.sub.25 represents hydrogen, alkyl C 1 to 6, alkanoyl C 1 to 6 or SO.sub.2 alkyl C 1 to 6, and R.sub.30 represents alkyl C 1 to 6 or NH.sub.