This invention concerns compounds of generic formula: ##STR1## or a pharmaceutically acceptable salt thereof, where the dotted line represents an optional bond, one of R.sup.1 and R.sup.5 represents hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.7 -C.sub.16 aralkyl, --(CHR.sup.6).sub.n CHR.sup.7 CN, --(CHR.sup.6).sub.n CHR.sup.7 CONH.sub.2, --(CHR.sup.6).sub.n CHR.sup.7 COOR.sup.8, --(CHR.sup.6).sub.n CHR.sup.7 CH.sub.2 OH wherein n is 0 or 1, R.sup.6 and R.sup.7 independently represent hydrogen, C.sub.1 -C.sub.6 alkyl- or C.sub.7 -C.sub.16 aralkyl-, and R.sup.7 also represents hydroxy(C.sub.1 -C.sub.6)alkyl-, (C.sub.2 -C.sub.7)alkanoyloxy(C.sub.1 -C.sub.6)alkyl-, (C.sub.1 -C.sub.6 alkoxy)carbonyl- and R.sup.8 is hydrogen or C.sub.1 -C.sub.6 alkyl; the other of R.sup.1 and R.sup.5 is hydrogen, C.sub.1 -C.sub.6 alkyl or C.sub.7 -C.sub.16 aralkyl; R.sup.3 is C.sub.6 -C.sub.10 aryl or heteroaryl group optionally substituted by one or more substituents the same or differnet, R.sup.2 and R.sup.4 independently represent hydrogen, or a group of formula --CR.sup.a R.sup.b R.sup.c where R.sup.a, R.sup.b and R.sup.c are independently selected from hydrogen, C.sub.1 -C.sub.6 alkyl, optionally substituted C.sub.6 -C.sub.10 aryl, optionally substituted heteroaryl, C.sub.1 -C.sub.6 alkyl substituted by optionally substituted C.sub.6 -C.sub.10 aryl or heteroaryl or R.sup.2 also represents COR.sup.11 where R.sup.11 is C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy or an optionally substituted (C.sub.6 -C.sub.10 aryl)alkyl or a heteroaryl alkyl radical; one of Y and Y.sub.1 is ##STR2## where R.sup.13 represents hydrogen, C.sub.1 -C.sub.6 alkyl or C.sub.7 -C.sub.16 aralkyl; the other of Y and Y.sub.1 is --CHR.sup.12 -- where R.sup.12 is hydrogen, C.sub.1 -C.sub.6 alkyl or C.sub.7 -C.sub.16 aralkyl,which compounds have pharmaceutical uses conferred by their ability to block voltage gated potassium channels.