Masupirdine free base (SUVN-502 free base) shows high selectivity over 5-HT2A receptor and other 100 target sites, and has potential for treatment of Alzheimer's disease. Masupirdine free base (SUVN-502 free base) is a potent, selective, orally bioavailable, and brain penetrant 5-HT6 receptor antagonist (Ki of 2.04 nM for human 5-HT6 receptor).