| Alzheimer's Disease, discovered by Dr. Alois Alzheimer in 1907, is described as a degenerative of the central nervous system (CNS). AD patients exhibit marked decline in cognitive ability and severe behavioral abnormalities such as irritability, anxiety, depression, disorientation and restlessness. AD is a progressive disease, i.e. the onset of the disease may show mild symptoms but these symptoms will sooner or later become more and more severe until the patient loses his or her capacity to handle normal daily activities.Acetylcholinesterase is an enzyme projecting into the synapse. It promotes the hydrolysis of the neurotransmitter acetylcholine at the cholinergic synapses with liberation of choline. Because of its central role in the neurotransmission system, the AChE has been an attractive target for the rational design of mechanism-based inhibitors. Presently, in the frame of the so-called "cholinergic hypothesis", a great deal of research is being devoted to the discovery of the potent and selective AChE inhibitors able to maintain high levels of acetylcholine at the muscarinic and nicotinic receptors in the central nervous system. In the search for original AChE inhibitors with potential central bioavailability, men concentrated on research on an aminopyridazine, minaprine, which possesses favorable characteristics. Effectively, minaprine, in addition to its original antidepressive properties, exhibits cholinomimetive activities. Thus, an invo administration of minaprine (30mg/kg) to rats significantly increases acetylcholine levels in the hippocampus (38%) and striatum (60%). In vitro, minaprine presents a weak, competitive and reversible AChE inhibitory activity on homogenized rat striatum (IC50=85uM) and a very weak activity on electric eel AChE (IC50=600uM) . On the other hand, minaprine exhibits a weak but highly selective affinity for muscarinic Ml receptor (IC50=17uM). These promoted us to investigated further around this lead compound.We have done much for this reason. The related results are summarized in the following article:1 .On the basis of pyridazine and benzidine, we synthesized four novel 3-benzidinopyridazine derivatives: 3-benzidino-6-phenylpyridazine (a), 3-benzidino-5-methyl-6-phenylpyridazine (b), 3-benzidino-6(4-chlorophenyl)pyridazine (c) and 3-benzidino-6(4-methoxyphenyl)pyridazine (d). And we have characterized them with elemental analysis, nuclear magnetic resonance spectra and infra-red spectra. From the obtained data, we reached that the front three chemical compoundswere identical with the designed compounds. But the fourth was different: perhaps it has decomposed because of being laid up for long. All of the happiest is that we got the single crystal of 3-benzidino-6 (4-chlorophenyl) pyridazine, which gave a credible evidence to the main structure of this kind of the derivatives.2.Simultaneously, we wanted to use 4-(2-aminoethyl)-l-benzylpiperidine as primary amine to substitute in the 3-position of the pyridazine ring and obtain the other kind of novel AChE inhibitors. In the course of the synthesis, we failed perhaps because of the complicated step. But we got the single crystal of (1-benzylpiperidin-4-ylidene) acetonitrile, which gave us a credible evidence to the structure and more base for the future work.3.We used acetylthiocholine idodide as the substrate of the enzymatic reaction and 5,5'-dithio-bis(2-nitrobenzoic acid) for the measurement of cholinesterase activity by the conventional spectrophotometric method of Ellman et al. and studied the influential factors on the enzyme activity. In the procedure, we studied the different pH values of the buffer solution and the different concentrations of the enzyme how to influence the enzyme activity. As a result, we reached that the enzyme activity was increasing with the addition of the pH value and the concentration of the enzyme. Finally, we determined the reaction condition was that the temperature was 37C, the pH value of the buffer solution was 7.20 and the total of the enzyme didn't exceed... |
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