HTR6 and Alzheimer disease: Apart from the structures of quinoline-2,4-diones (6) [34] and asenapine (7) [35] described in 2008–2009, the last five years have also provided non-indole and non-sulfonic derivatives of triazine (8, 9) [36,37,38,39], hydantoin (10) [40,41], imidazopyridine (11) [42], as well as non-basic 5-HT6R ligands (12, 13) [43,44], which also showed procognitive activity in animal models (8–10), promising for potential AD therapies (Figure 1b).