Scheme 5 Reagents and conditions: (i) [2-(4-(pyridin-2-yl)piperazin-1-yl)ethyl]amine, [3-(4-(pyridin-2-yl)piperazin-1-yl)propyl]amine, Et₂O/EtOH (3:1), rt; (ii) K₂CO₃, dry DMF, 80°C; (iii) 1-(1,3-benzothiazol-2-yl)piperazine, K₂CO₃, dry DMF, 80°C; (iv) H₂, Raney Ni, DMF rt; (v) 4% NaOH, reflux.