The invention concerns compounds of formula (I): R-A-R' wherein: A is as defined in the description; R represents a group (V), (VI), (VII) or (VIII), where E, Q, R.sup.1, R.sup.2, R.sup.3, v and R.sup.4 are as defined in the description; R' represents a --(CH.sub.2)t-R.sup.5 group wherein t and R.sup.5 are as defined in the description ##STR00001##