Design,Synthesis And Preliminary Activity Evaluations Of Multitargeted GSK-3? Inhibitors

Alzheimer's disease(AD)is a common degenerative disease of central nervous system.Its main pathological features include the deposition of amyloid-?(A?),the formation neurofibrillary tangles(NFTs)due to the over-phosphorylation of tau protein,and the loss of synapses.The pathological mechanisms of AD are rather complex and still unclear.At present,the clinical anti-AD drugs can only alleviate the symptoms of patients,but can not reverse the progression of the disease.Therefore,the multi-target directed agents,especially drugs targeting the multi-facets of AD,has become focus in the development of anti-AD drugs.Glycogen synthase kinase 3?(GSK-3?)is involved in glycogen synthesis,protein transcription activation,cell growth and proliferation,cell differentiation,apoptosis control,inflammation,among many others.In AD patients,the overexpression of GSK-3? is closely related to tau hyperphosphorylation,A? production,inflammation and neuronal apoptosis.Therefore,GSK-3? is a key mediator molecule linking the A?,tau,inflammation,synapses and neurons.Because the existing GSK-3? inhibitors fails to target the metal dyshomeostasis and oxidative stress related to AD,in our previous research,we designed a series of novel pyrrolopyridine GSK-3? inhibitors by incorporating a quinolin-8-ol moiety that has the metal-chelating ability and antioxidant activity,and discovered for the first time a unique and high potent and multi-targeted GSK-3?inhibitor B10,that not target metal dyshomeostasis and oxidative stress,but also has a direct effect on A?.At the cellular level,B10 can significantly inhibit tau protein phosphorylation,enhance the mRNA expression of GAP43,N-myc and MAP-2,and significantly promote the neuronal neurite outgrowth through the GSK-3? and the?-catenin signal pathways.At present,there are not so many small molecules that can directly act on A?,so the structural information about them is rather limited.In order to further study the structure-activity relationships of the pyrrolopyridine-based GSK-3? inhibitors and to investigate the rules about interactions between small molecules and A?,we designed a series of pyrrolopyridine derivatives based on the structure features of B10 by keeping the pyrrolopyridine moiety to interact with the hinge region,and the quinolin-8-ol scaffold to interact with zone I and target the metal dyshomeostasis as well as the oxidative stress,and making variation at the pyrrolopyrrole 5-position through introducing a phenyl,or monosubstituted phenyl with fluorine,methyl,methoxy or trifluoromethyl,disubstituted phenyl,and trisubstituted phenyl,or a phenyl bridged by an amide at the meta-position to a phenyl,benzyl,4-F-benzyl or pyridine-4-methyl group.For the synthesis these novel pyrrolopyridine derivatives,the 8-methoxy-6-bromoquinoline was firstly prepared via the typical Skraup reaction and further converted into the pinacol borate.The 8-methoxyquinoline moiety was next incorporated into the pyrrolopyridine 3-position by Suzuki coupling reaction.After removing the benzenesulfonyl group at the pyrrole nitrogen and the methyl protecting group in 8-methoxyquinoline,the hydroxyl group was protected by TBS ether formation.Different substituted phenyl groups were introduced into the pyrrolopyridine 5-position by Suzuki coupling reactions.After the removal of the TBS protective group,a series of pyrrolopyridine derivatives A1-A16 containing the 8-hydroxyquinoline scaffold were finally synthesized,and their structures were characterized by 1H NMR,13C NMR and MS spectra.The biological activity of these pyrrolopyridine derivatives were preliminarily evaluated.Compounds Al-A16 showed no or weak GSK-3? inhibitory activity with IC50 greater than 1 ?M.Compounds A1-A12 with simply substituted phenyl at the pyrrolopyridine 5-position had no direct effect on A?,while the compounds A13-A16 with the phenyl,benzyl,4-F-benzyl and pyridine-4-methyl linking to the meta-position of the phenyl at the pyrrolopyridine 5-position via the amide bond had direct effects on A?.A13-A16 can significantly inhibit A?1-42 aggregation.,while A14-A16 can also promote the disaggregation of A?1-42 oligomers.These results provided very useful structural information for the further study of the interaction between small molecules and A?.Vitro metal ion chelation experiments were carried out on The typical compounds A2,A5,A7,A9,A10 and A13-A16 were evaluated in vitro metal chelating assay.The results showed that these compounds can selectively chelate with the AD metal dyshomeostasis related Cu2+,Fe2+,Zn2+and Al3+ions without affecting the normal Mg2+,Na+,Ca2+and K+ions.Compounds A13-A16 can inhibit Cu2+-nduced A?1-42 aggregation and promote the disaggregation of Cu2+-A?1-42 oligomers,indicating that these compounds have the potential to target the metal dyshomeostasis of AD.