Design,Synthesis And Evaluation Of Near-infrared Fluorescent Probes For Detecting β-amyloid Aggregates

Alzheimer’s disease(AD)is a degenerative disease of the central nervous system characterized by progressive cognitive dysfunction and behavioral impairment.The main clinical manifestations are memory disorders,aphasia,and agnosia,which can lead to the gradual loss of self-care ability and bring a huge economic burden to the patient’s family and society.The onset of AD is insidious,the incubation period is long,and the course of disease is irreversible.The design and development of diagnostic tools for imaging detection of early pathological markers of AD is of great significance for early intervention and control of the development of AD.The etiology of AD is complex and the pathogenesis is unknown.The early pathological features are amyloid-β(Aβ)deposition,neurofibrillary tangles,and neuronal damage in the brain.To realize the early and accurate diagnosis of AD,researchers have developed a large number of imaging probes targeting Aβ protein for the advantages of near-infrared fluorescent probe imaging,such as safety,high efficiency,and low cost.However,the currently reported probes are still limited by shortcomings such as short emission wavelength and poor bloodbrain barrier permeability,and it is difficult to enter subsequent clinical trials.In this paper,four novel near-infrared fluorescent probes for the detection of Aβ1-42 aggregates were designed and synthesized.The main contents of this paper are as follows:(1)Twelve pyrazinedicarbonitrile near-infrared fluorescent probes were designed and synthesized,and their optical properties and biological activities were evaluated.The maximum emission wavelengths(λem)of probes 2c,3c,and 4c can enter the near-infrared region and combine with Aβ1-42 aggregates to produce significant fluorescence enhancement,and to a certain extent,the fluorescence interference of bovine serum albumin(BSA)can be avoided.Probes 2c,3c,and 4c showed high binding affinity to Aβ1-42 aggregates and a certain ability to monitor concentration changes;in the MTT experiment,probes 2c,3c,and 4c showed low cytotoxicity.The experimental results show that this series of probes have the potential for safe and efficient imaging(2)Three quinoxalinedicarbonitrile near-infrared fluorescent probes were designed and synthesized,and the optical properties and preliminary activity evaluation were completed.Among them,probe 6c showed good optical properties(λem=714 nm),significant fluorescence response to Aβ1-42 aggregates,good selectivity,high affinity(Kd=8.92±0.62 nM),and certain concentration change monitoring ability.In addition,it showed high biosafety in the MTT experiment,indicating that this series of probes have potential application value for early diagnosis and early pathological study of AD.(3)Five benzylidenemalononitrile near-infrared fluorescent probes were designed and synthesized.Through the study of optical activity,it was found that the λem of this series of probes did not achieve the expected effect,but the probes showed a strong fluorescence response to Aβ1-42 aggregates.Good selectivity and a certain range of concentration change monitoring capabilities prove that this series of probes are worthy of subsequent optimization and transformation as a structural skeleton,providing new ideas for the research and development of D-A probes.(4)Four D-A-D near-infrared fluorescent probes were designed and synthesized.The λem of such probes is close to the near-infrared region.Biological experiments show that probes has significant fluorescence response,good selectivity,and certain concentration change monitoring ability after binding to Aβ1-42 aggregates,which proves that this series of probes are expected to meet the imaging requirements of near-infrared fluorescent probes through further design optimization.