Studies On Bioorthogonal Reaction Of Sydnone Derivatives

Bioorthogonal chemistry has emerged as a kind of new important tool for studying the process of biomolecules in complex environments,which is inert to biological systems and will not interfer with life processes.Due to the fast kinetics and high selectivity of bioorthogonal chemistry,they have been used for tracking and imaging biomolecules in living systems,and for targeted activation at specific sites.Up to now,more and more investigations have been developing various of bioorthogonal reagents and reactions,in order to realize the visualization of biomolecules and "smart" delivery of drugs in physiological environment.The bioorthogonal reactions mainly include polar reactions,Staudinger reactions and cycloaddition reactions.Especially,cycloaddition reactions play a predominant role in bioorthogonal chemistry.Here,we focused on the 1,3-dipole cycloaddition of sydnone derivatives for the studying of the targeted drug-release and fluorescent imaging in the living systems.The main studies are summarized as follows:Section 1,we developed a new bioorthogonal reaction of N6-sulfonyl sydnonimines and dibenzoazacyclooctyne(DIBAC)to liberate sulfonamides efficiently.The second-order rate constant of the cycloaddition reaction can be up to 0.62 M-1·s-1,and the reactants are highly stable under physiological conditions.Most significantly,we also discovered the mutual orthogonality between the sydnonimine-DIBAC and benzonorbornadiene-tetrazine cycloaddition pairs,which can be used for selective and simultaneous liberation of sulfonamide and primary amine drugs.Section 2,we designed and synthesized a clickable OFF-ON type fluorescent probe based on sydnonimine skeleton.Due to the fluorescence resonance energy transfer(FRET)effect,the whole molecule comtaining fluorophore and quencher exhibited non-fluorescence character.After reacting with dibenzoazacyclooctyne(DIBAC),the quencher was released accompanying with strong red florescence signal(enhanced 600-fold).The second-order rate constant of the cycloaddition reaction can be up to 0.71 M-1·s-1.Section 3,we developed a 1,8-naphthalimide-based fluorescent OFF-ON type bioorthogonal probe for imaging application in cellular environment.Sydnone unit effectively inhibited the native fluorescence of 1,8-naphthalimide,which can be restored with the enhancement of about 300-fold,after reacting with strained cyclooctynes to form pyrazole products.The second-order rate constant of this bioorthogonal cycloaddition can be up to 2.5 M-1·s-1,which benefits imaging of biomolecules at low concentrations in cellular environment.