Research Of The Interaction Between Coumarins And Acetylcholinesterase

Alzheimer disease, has become the most common disease in middle-aged and old people with dementia. Acetylcholinesterase (AChE) inhibitors are considered to be the main drug treatment which has been widely recognized, The current clinical use of AChE inhibitors have low bioavailability, low activity, low selectivity with different degree of toxicity and side effects. Thus, seeking new AChE inhibitors with high-efficiency is one of the hot topics in the study of drug chemists. Studies have shown that natural products coumarins can inhibit cholinesterase activity. The nature of the drugs play efficacy is closely related to the interaction between molecules and molecular targets. And the study of interaction at molecular level can help to look for active group and research the inhibitory activity of new natural products on AChE. The biological activity of coumarins is related to the type and location of benzo pyran ring substituent closely. It is meaningful to study the relationship between the inhibitory activity and the interaction of small molecules with biological molecular targets in vitro. However, there is no related reports at present.For the above problem，different substituent structure of coumarins were selected and the impact of different structure factors of coumarins interact with AChE were discussed in this thesis by means of spectroscopic methods and molecular docking techniques. Ellman’s colorimetric method was employed to study the changing of AChE activity by different substituent structure of coumarins. The results in this thesis were meaningful to look for active group which can play efficacy and screen of new coumarins which have better inhibitory activity on AChE. The main contents of this thesis are as follows:Section1: Fluorescence, UV, synchronous fluorescence spectroscopy were employed to research the spectroscopy characteristics of the interaction between AChE and coumarins, the quenching mechanism, the numbers of binding sites, the binding constants, the binding distance and the conformational change of AChE were discussed. The results indicated that the fluorescence of AChE was quenched by coumarins via static quenching procedure with the formation of complexes. The binding distance between AChE and thirteen coumarins were all less than7nm. Hydrophobic interactions and van der Waals forces played the major role in stabilizing the complexes of coumarins with AChE. Hydrogen bonds forces and electrostatic interactions also existed. The results of the interaction between AChE and different substituent structure of coumarins showed that the hydroxyl substituents in4positions of benzo pyran ring and the methoxy or ethoxy substituent in7positions of benzo pyran ring could improve the interaction of coumarins with AChE.Section2: Molecular docking techniques was applied to investigate the binding mode include interaction energy, combining sites and reaction types in the interaction. The results showed that coumarins could interact with the activity sites of AChE.The amino acid residues which interacted with AChE were mainly hydrophobic or electriferous. Hydrophobic interactions and van der Waals forces played the major role in stabilizing the complexes of coumarins, Hydrogen bonds forces and electrostatic interactions also existed. The research in judgment about the type of interaction forces on molecular docking was basically identical with fluorescence methods. The π-π accumulation in the benzene ring of coumarins with the residues of AChE also could lead to the quenching of the intrinsic fluorescence of AChE. Different coumarins caused the number of hydrogen bonds in the complexes various，the hydroxyl substituents in4positions of benzo pyran ring had the biggest influence on the formation of hydrogen bonds.Section3: Ellman’s colorimetric method was employed to study the changing of AChE activity by different substituent structure of coumarins. The inhibitory activity was compared by means of calculating the half inhibitory concentration with the addition of coumarins. The results showed that the substituents in4or7positions of benzo pyran ring could improve the inhibitory activity on AChE, particularly when the hydroxyl substituents were in4or7positions or the hydroxyl substituents’ number increasing in benzo pyran ring.