5-Hydroxytryptamine 6 receptors (5-HT6R) are being perceived as the possible target for treatment of cognitive disorders as well as obesity. The present article deals with the design, synthesis, in vitro binding and structure–activity relationship of a novel series of tetracyclic tryptamines with the rigidized N-arylsulphonyl, N-arylcarbonyl and N-benzyl substituents as 5-HT6 receptor ligands. The chiral sulphonyl derivatives 15a and 17a showed high affinity ...