Figure 2: Structures of reported tacrine-donepezil hybrids with AChE inhibitory activity. Molecular weights (MW) and polar surface areas (PSA, Å2) were estimated (ACD /Labs, Version 12.5, 2010). Clog P values were obtained from ChemDraw, Version 12, Cambridgesoft. IC50 for AChE were from human (63, 51) [24],rat (61) [25] and bovine (62) [26] sources. IC50 for BChE were obtained from human (62, 63) [ 26,24], rat (61) [ 25] and equine (51) sources.