the)bioorthogonal)clickreac:on)of)cyclobutenes)and)tetrazines) · synthesis...
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Synthesis The rela(vely new field of bioorthogonal or copper-‐free “click” chemistry has flourished in recent years because of the poten(al to conduct rapid and selec(ve liga(ons under condi(ons compa(ble with living cells (Bertozzi, 2003). This research seeks to expand on the narrow set of cycloalkene and tetrazine pairings of bioorthogonal chemistry that are suitable for inverse electron-‐demand Diels-‐Alder 4+2 cycloaddi(on (the “click” mechanism) with the introduc(on and characteriza(on of 3-‐subs(tuted cyclobutene as a viable alterna(ve.
Conclusions Through a nine step synthe(c pathway of our cyclobutene (ini(ally established by Wantanee SiOwong), as well as a unique tetrazine synthe(c method, we have developed a model system with which to explore the use of cyclobutene in inverse electron-‐demand Diels-‐Alder 4+2 reac(ons. As a result of this research, we hope that cyclobutene garners acceptance as a new and effec(ve bioorthogonal molecule.
Materials & Methods
Background Why choose click chemistry?
• Wide in scope • Rapid liga(on rate • Selec(ve: No undesired byproducts • Stable and irreversible • Effec(ve means of immobilizing or linking molecules
A recent innova(on • Azide-‐alkyne Huisgen 1,3-‐dipolar cycloaddi(on (2001) • Sharpless-‐Fokin Copper(I)-‐catalyzed Azide-‐alkyne cycloaddi(on or
CuAAC (2002) • Bertozzi Bioorthogonal cycloaddi(on (2003)
The popular copper catalyzed click reac:on
The Bioorthogonal Click Reac:on of Cyclobutenes and Tetrazines William Lambert1, Wantanee SiOwong1 & Patrick Dussault1,2
Department of Chemistry1 and The Center for Nanohybrid Func(onal Materials2, University of Nebraska–Lincoln 68588
Purpose
Work on the synthesis of amphiphilic cyclobutenes developed by SiOwong, et. al.*
Four step pathway established for conversion of carboxylic acid func(onalized tail (SiOwong) to thiol
Future Work • SAM forma(on • Click reac(on kine(cs in collabora(on with Prof. Rebecca Lai:
Stability, Selec(vity, Liga(on Rates • Improving synthe(c yields and/or shortening pathways • Other cyclobutene func(onaliza(on or cons(tuents • Possible biochemical applica(ons
I. Chemical sensors II. Imaging proper(es III. Bioconjuga(ons
Cyclobutene Synthe:c Pathway
Tetrazine Synthe:c Pathway q Amphiphilic cyclobutene (hydrophobic + hydrophilic ends) for coordinated forma(on of self-‐assembled monolayer (SAM)
q Thiol (-‐SH) func(onalized tail to
take advantage of strong gold-‐sulfur affinity
q Forma(on of SAM
q 1,2,4,5-‐tetrazine partner
q Incorporated redox indicator for quan(ta(ve measurement
q The bioorthogonal click reac(on on monolayer surface
1,2,4,5-‐tetrazine with incorporated redox indicator synthesized in two part pathway followed by a coupling step
Redox Indicator Synthesis
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Bioorthogonal Chemistry Bioorthogonal strain-‐promoted cycloaddi(ons encompass a wider variety of molecules and reac(on condi(ons than azide-‐alkyne cycloaddi(ons. Strained cycloalkenes are paired with a tetrazine in this spontaneous (uncatalyzed) reac(on. Three types are typically employed: Cyclooctenes Cyclopropenes Norbornenes 1,2,4,5-‐Tetrazine
The tetrazine and these cycloalkenes are also discrete as func(onal groups in a biological system and do not perturb regular func(ons. It is for this reason the bioorthogonal click reac(on has been useful in biochemical imaging (fluorescent and PET).
Synthesis
Acknowledgements
Funding for this research was provided by The Center for Nanohybrid Func(onal Materials (CNFM) NSF Grant EPS-‐1004094.
*ChemMedChem 2014, E-‐pub. ahead of print June 5, DOI:10.1002/cmdc.201402067