Design, Synthesis and Evaluation of Donepezil-Rasagiline Based Compounds as Multipotent Inhibitors for the Treatment of Alzheimer’s Disease

Abstract

Alzheimer’s disease (AD) is multifactorial in nature and different enzymes including MAO, AChE, and amyloid beta are implicated in its pathogenesis. The pathomechanism of AD is complex in nature and single target drugs proved to be ineffective for the treatment of the disease. With an aim of developing dual/multipotent inhibitors, 4,6- diphenylpyrimidines were optionally substituted with propargyl group and an ethyl chain containing a cyclic or acyclic tertiary nitrogen atom (piperidine/morpholine/pyrrolidine/N,N-dimethyl) as potential pharmacophores for MAO and AChE enzymes. Compound VB1 was found to be the most potent MAO-A (IC50 value of 18.34 ± 0.38 nM) inhibitor and VB8 was found to be the most potent AChE (IC50 value of 9.54 ± 0.07 nM) inhibitor. Compound VB3 was another promising compound in series-I with IC50 values of 28.33 ± 3.22 nM and 18.92 ± 0.29 nM against MAO-A and AChE, respectively and displayed very high selectivity index (103) for AChE over BuChE. These compounds were found to be reversible inhibitors of MAO and AChE enzymes and non-toxic to the human neuroblastoma SH-SY5Y cells. Based on structure-activity relationship analysis of the first series of compounds, second series of the compounds were designed by fixing the position of piperidine/morpholine ethyl chain at the para position of one of the phenyl rings. In the second series, compound VP15 v was found to be a multi-potent inhibitor of MAO-B and AChE with IC50 values of 0.37 ± 0.03 μM and 0.04 ± 0.003 μM, respectively. VP15 was found to be selective for MAOB with selectivity index of 270 over MAO-A. It also displayed SI of 625 for AChE over BuChE. VP15 was found to be irreversible inhibitor of MAO-B. In the third series of target compounds, both the phenyl rings of diphenylpyrimidines were substituted with O-propargyl groups. Different derivatives have been synthesized with O-propargyl groups substituted at ortho, meta and para positions of the phenyl rings. In the third series of compounds, AVB1 and AVB4 were found to be the most potent inhibitors of AChE and MAO-B with IC50 values of 1.35 ±0.03 μM and 1.49 ± 0.09 μM, respectively. In the reversible inhibition studies, the lead compounds were found to be reversible inhibitors of MAO-B and AChE enzymes. In the ROS protection inhibition studies, AVB1 and AVB4 displayed good activity in SH-SY5Y cells and AVB1 reduced the ROS levels up to 30% at 5 μM. This series of compounds were also found to be non-toxic to the SH-SY5Y cells in the cytotoxicity studies. Thus, from the present study it can be concluded that 4,6-diphenylpyrimidine derivatives can act as potential lead for the development of effective drug candidates for the treatment of AD. Compound VB3 and VP15 were found to be the most potent dual inhibitors of MAO and AChE.