Novel derivatives of the highly potent and selective histamineH3-receptorantagonist ciproxifan (3) with different chain lengths as well as with structural variants of the cyclopropyl ketone moiety have been prepared and screened for their antagonistH3-receptor potencies in vitro and in vivo. Some derivatives (2, 6-8, 12) containing other functionalities were effective in vitro in the same (sub)nanomolar