attached at position 4 6 or 7 of the benzimidazole ring structure it was surprisingly found by the present invention that the novel 4 6 or 7 positions of the n lost moiety in the iso bendamustine derivatives of compound of formula ix provide for a beneficial alteration of both electronic as well as steric effects compared to conventional bendamustine in which the n lost moiety is in 5 position of the benzimidazole ring structure without wishing to be bound to theory it is believed that these altered electronic and or steric effects provide for a good or even an improved antiproliferative potency of compound of formula ix compared to conventional bendamustine hcl furthermore antiproliferative potency and further useful properties may be additionally fine tuned and eventually improved by suitable selections for substituents r 1 r 2 y 1 and y 2 according to another aspect of the invention compounds of formula vii or viii wherein r 1 and r 3 are independently from each other selected from alkyl aryl or alkylaryl r 2 represents alkanediyl arylene alkylarylene or arylalkanediyl y 1 and y 2 independently from each other represent oxygen or sulphur wherein the bis 2 chloroethyl amino group or the bis 2 hydroxyethyl amino group is attached at position 4 6 or 7 of the benzimidazole ring structure optionally r 3 is substituted with an amine moiety u2014 nr 5 r 6 in which r 5 and r 6 independently from each other represent substituted or unsubstituted alkyl or r 5 and r 6 together represent a c3 c7 alkyl chain forming a 4 to 8 membered ring structure together with the nitrogen located between r 5 and r 6 wherein.