Antidepressant agent 6 (S-3a) is a lead compound with potent and sustained antidepressant effects. Antidepressant agent 6 (S-3a) displays high cognitive safety margin.Antidepressant agent 6 (S-3a) antagonizes M1 receptors and elevates BDNF levels, suggesting its potential as an antidepressant for further exploration.