addition products of a mono - substituted keto - aldehyde compound with a secondary amine . the compounds have the formula ## str1 ## wherein r 1 stands for various organic radicals as defined in the body of the specification and x is a 4 -, 5 - or 6 - member ring or fused double ring which includes a nitrogen atom in the ring attached to the keto - aldehyde group and wherein the latter ring is substituted by = o in the two positions ortho to said nitrogen atom . the compounds are anti - bacterial , anti - viral and anti - neoplastic agents and are valuable in connection with combatting the rejection mechanism in transplantations . they are furthermore useful as radiosensitizers in connection with radiation treatments for various purposes .