Inverse Electron Demand Diels-Alder Chemistry Research Articles

Facile Fabrication of NIR-Responsive Alginate/CMC Hydrogels Derived through IEDDA Click Chemistry for Photothermal-Photodynamic Anti-Tumor Therapy.

Novel chemically cross-linked hydrogels derived from carboxymethyl cellulose (CMC) and alginate (Alg) were prepared through the utilization of the norbornene (Nb)-methyl tetrazine (mTz) click reaction. The hydrogels were designed to generate reactive oxygen species (ROS) from an NIR dye, indocyanine green (ICG), for combined photothermal and photodynamic therapy (PTT/PDT). The cross-linking reaction between Nb and mTz moieties occurred via an inverse electron-demand Diels-Alder chemistry under physiological conditions avoiding the need for a catalyst. The resulting hydrogels exhibited viscoelastic properties (G' ~ 492-270 Pa) and high porosity. The hydrogels were found to be injectable with tunable mechanical characteristics. The ROS production from the ICG-encapsulated hydrogels was confirmed by DPBF assays, indicating a photodynamic effect (with NIR irradiation at 1-2 W for 5-15 min). The temperature of the ICG-loaded hydrogels also increased upon the NIR irradiation to eradicate tumor cells photothermally. In vitro cytocompatibility assessments revealed the non-toxic nature of CMC-Nb and Alg-mTz towards HEK-293 cells. Furthermore, the ICG-loaded hydrogels effectively inhibited the metabolic activity of Hela cells after NIR exposure.

Abstract 2131: Immunoaffinity isolation of EpCAM expressing exosomes utilizing high throughput microfluidic chip with IEDDA chemistry (EpCAM-TCOOncoBean Chip)

Abstract The overall objective of this study is to investigate the microfluidic isolation of tumor derived exosome (TDEs) using the OncoBean Chip, functionalized with the unique inverse electron demand Diels-Alder (IEDDA) for downstream analysis of patient TDEs for therapeutic applications. This chemistry allows for capture and subsequent release of exosomes for immunomodulation and functional studies. We developed an approach for targeting TDEs in patient’s blood plasma by using the epithelial cell adhesion molecule (EpCAM) antibody, a highly expressed biomarker associated with non-small cell lung cancer.The OncoBean Chip is a high throughput radial-flow microfluidic device designed for the specific isolation of TDEs. The bean shaped micro-nodes allow for a varying shear profile to better capture nanosized particles by positioning them towards the middle curvature. We optimized the device using exosomes extracted from cell culture media by ultracentrifugation. First, the surface of the device was salinized with (3-Aminopropyl) triethoxysilane, as an anchor, following plasma activation of the surface. Then, bonded with 3,3'-dithiobis(sulfosuccinimidyl propionate) as a crosslinker, to facilitate the release. Finally, trans-cyclooctene (TCO) is attached as the exposed agent for capture of TDEs. The exosome sample is functionalized with an EpCAM antibody (Ab) conjugated to a tetrazine (Tz) molecule via incubation. The anti-EpCAM-Tz conjugate bonds to surface EpCAM on the TDEs creating a TDE-EpCAM-Tz complex for isolation. The TDEs are processed through the functionalized OncoBean Chip for Ab specific isolation. We tested and validated the EpCAM specific isolation and confirmed TDEs were forming complexes with the Ab-Tz conjugates and not arbitrarily sticking to the nodes. This was done by flowing a sample of TDE-Tz through a functionalized device where little to no capture was expected. Then we evaluated the isolation of EpCAM specific TDEs by using H1650 and A549 exosomes and comparing the capture with CD63, a common exosome marker. Limited capture is expected in the A549 group due to low EpCAM expression for the Ab-Tz conjugate to bind too.Additionally, EV isolation was confirmed and quantified by NTA which reveals capture efficiency up to 90% for the H1650 TDEs. Capture efficiency of the no Ab control was found to be at 30% and below while the A549 control, was found to be at about 20% and below. Hence, our OncoBean Chip with IEDDA chemistry has successfully demonstrated efficient and specific isolation of EpCAM and CD63 expressing TDEs from two different cell lines. Data from Western Blot analysis and scanning electron microscopy further confirm the physical characteristics and protein expression of the TDEs established by the International Society of Extracellular Vesicles (ISEV). Citation Format: Nna-Emeka Onukwugha, Sunitha Nagrath, Henry McEacheron. Immunoaffinity isolation of EpCAM expressing exosomes utilizing high throughput microfluidic chip with IEDDA chemistry (EpCAM-TCOOncoBean Chip) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2131.

Non-Chromatographic Purification of Synthetic RNA Using Bio-Orthogonal Chemistry.

Solid-phase synthesis of RNA oligonucleotides over 100 nt in length remains challenging due to the complexity of purification of the target strands from the failure sequences. This article describes a non-chromatographic procedure that will enable routine solid-phase synthesis and purification of long RNA strands. The optimized five-step process is based on bio-orthogonal inverse electron demand Diels-Alder chemistry between trans-cyclooctene (TCO) and tetrazine (Tz), and entails solid-phase synthesis of RNA on a photo-labile support. The target oligonucleotide strands are selectively tagged with Tz while on-support. After photocleavage from the solid support, the target oligonucleotide strands can be captured and purified from the failure sequences using immobilized TCO. The approach can be applied for purification of 76-nt long tRNA and 101-nt long sgRNA for CRISPR experiments. Purity of the isolated oligonucleotides should be evaluated using gel electrophoresis, while functional fidelity of the sgRNA should be confirmed using CRISPR-Cas9 experiments. © 2021 Wiley Periodicals LLC. Basic Protocol: Five-step non-chromatographic purification of synthetic RNA oligonucleotides Support Protocol 1: Synthesis of the components that are required for the non-chromatographic purification of long RNA oligonucleotides. Support Protocol 2: Solid-phase RNA synthesis.

Radiolabelling an 18F biologic via facile IEDDA "click" chemistry on the GE FASTLab™ platform.

The use of biologics in positron emission tomography (PET) imaging is an important area of radiopharmaceutical development and new automated methods are required to facilitate their production. We report an automated radiosynthesis method to produce a radiolabelled biologic via facile inverse electron demand Diels–Alder (IEDDA) “click” chemistry on a single GE FASTLab™ cassette. We exemplified the method by producing a fluorine-18 radiolabelled interleukin-2 (IL2) radioconjugate from a trans-cyclooctene (TCO) modified IL2 precursor. The radioconjugate was produced using a fully automated radiosynthesis on a single FASTLab™ cassette in a decay-corrected radiochemical yield (RCY, d.c.) of 19.8 ± 2.6% in 110 min (from start of synthesis); the molar activity was 132.3 ± 14.6 GBq μmol−1. The in vitro uptake of [18F]TTCO-IL2 correlated with the differential receptor expression (CD25, CD122, CD132) in PC3, NK-92 and activated human PBMCs. The automated method may be adapted for the radiosynthesis of any TCO-modified protein via IEDDA chemistry.

Expanding the Scope of RNA Metabolic Labeling with Vinyl Nucleosides and Inverse Electron-Demand Diels-Alder Chemistry.

Optimized and stringent chemical methods to profile nascent RNA expression are still in demand. Herein, we expand the toolkit for metabolic labeling of RNA through application of inverse electron demand Diels-Alder (IEDDA) chemistry. Structural examination of metabolic enzymes guided the design and synthesis of vinyl-modified nucleosides, which we systematically tested for their ability to be installed through cellular machinery. Further, we tested these nucleosides against a panel of tetrazines to identify those which are able to react with a terminal alkene, but are stable enough for selective conjugation. The selected pairings then facilitated RNA functionalization with biotin and fluorophores. We found that this chemistry not only is amenable to preserving RNA integrity but also endows the ability to both tag and image RNA in cells. These key findings represent a significant advancement in methods to profile the nascent transcriptome using chemical approaches.

PP#67 - Drug formulation and its impact on the distribution of [99mTc] Tc-tetrazines for pretargeting applications via inverse-electron demand Diels-Alder chemistry

PP#67 - Drug formulation and its impact on the distribution of [99mTc] Tc-tetrazines for pretargeting applications via inverse-electron demand Diels-Alder chemistry

Bio-Orthogonal Chemistry and Reloadable Biomaterial Enable Local Activation of Antibiotic Prodrugs and Enhance Treatments against Staphylococcus aureus Infections.

Systemic administration of antibiotics can cause severe side-effects such as liver and kidney toxicity, destruction of healthy gut bacteria, as well as multidrug resistance. Here, we present a bio-orthogonal chemistry-based strategy toward local prodrug concentration and activation. The strategy is based on the inverse electron-demand Diels–Alder chemistry between trans-cyclooctene and tetrazine and involves a biomaterial that can concentrate and activate multiple doses of systemic antibiotic therapy prodrugs at a local site. We demonstrate that a biomaterial, consisting of alginate hydrogel modified with tetrazine, is efficient at activating multiple doses of prodrugs of vancomycin and daptomycin in vitro as well as in vivo. These results support a drug delivery process that is independent of endogenous environmental markers. This approach is expected to improve therapeutic efficacy with decreased side-effects of antibiotics against bacterial infections. The platform has a wide scope of possible applications such as wound healing, and cancer and immunotherapy.

Preparation of tetrazine-containing [2 + 1] complexes of 99mTc and in vivo targeting using bioorthogonal inverse electron demand Diels-Alder chemistry.

The aim of this work was to synthesize and evaluate [2 + 1] 99mTc(i) polypyridine complexes containing tetrazines, which along with the corresponding Re(i) complexes, represent a new class of isostructural nuclear and turn-on luminescent probes that can be derivatized and targeted using bioorthogonal chemistry. To this end, [2 + 1] complexes of 99mTc(i) of the type [99mTc(CO)3(N^N)(L)] (N^N = bathophenanthroline disulfonate (BPS) or 2,2'-bipyridine (bipy)), where the monodentate ligand (L) was a tetrazine linked to the metal through an imidazole derivative, were prepared. The desired products were obtained in nearly quantitative radiochemical yield by adding [99mTc(CO)3(N^N)(OH2)]n to the imidazole-tetrazine ligand and heating at 60 °C for 30 min. Measurement of the reaction kinetics between the tetrazine and (E)-cyclooct-4-enol revealed a second-order rate constant of 8.6 × 103 M-1 s-1 at 37 °C, which is suitable for in vivo applications that require rapid coupling. Stability studies showed that the metal complexes were resistant to ligand challenge and exhibited reasonable protein binding in vitro. Biodistribution studies of the more water-soluble BPS derivative in normal mice, one hour after administration of a bisphosphonate derivative of trans-cyclooctene (TCO-BP), revealed high activity concentrations in the knee (9.3 ± 0.3 %ID g-1) and shoulder (5.3 ± 0.7 %ID g-1). Using the same pretargeting approach, SPECT/CT imaging showed that the [2 + 1] tetrazine complex localized to implanted skeletal tumors. This is the first report of the preparation of 99mTc complexes of BPS and demonstration that their tetrazine derivatives can be used to prepare targeted imaging probes by employing bioorthogonal chemistry.

Reprint of: Synthesis, characterization and radiolabeling of carborane-functionalized tetrazines for use in inverse electron demand Diels–Alder ligation reactions

Carborane-tetrazine derivatives were developed that can be used to enable boron clusters to bind specific targets in vivo using pretargeting strategies and bioorthogonal inverse electron demand Diels–Alder chemistry. Specifically, 1,12-dicarba-closo-dodecaborate-1-(4-(1,2,4,5-tetrazin-3-yl)phenyl)methanamide and 1,2-dicarba-closo-dodecaborate-1-(4-(1,2,4,5-tetrazin-3-yl)phenyl)methanamide were synthesized in 49% and 78% yield respectively, and X-ray structures of both compounds determined. The ortho-carborane derivative was converted to the corresponding nido-cluster under mild conditions, and the product successfully radiolabelled with 125I and 123I. The carborane-tetrazines react rapidly and in quantitative yields with (E)-cyclooct-4-enol (TCO) via a [4 + 2] inverse-electron demand Diels–Alder type reaction, where the second order rate constant in acetonitrile for the iodinated cluster was 199 ± 26 M−1s−1. The labelled tetrazines were stable in solution for extended periods and they were shown to bind in vitro to H520 cells, labelled with a TCO-modified antibody. Imaging studies on the 123I-labeled carborane-tetrazine were performed in healthy mice, and demonstrated minimal loss of iodine in vivo and high uptake in the liver and gall bladder. The reported compounds offer an alternative means of developing targeted boron neutron capture therapy (BNCT) and boron-based molecular imaging agents.

Synthesis, characterization and radiolabeling of carborane-functionalized tetrazines for use in inverse electron demand Diels–Alder ligation reactions

Carborane-tetrazine derivatives were developed that can be used to enable boron clusters to bind specific targets in vivo using pretargeting strategies and bioorthogonal inverse electron demand Diels–Alder chemistry. Specifically, 1,12-dicarba-closo-dodecaborate-1-(4-(1,2,4,5-tetrazin-3-yl)phenyl)methanamide and 1,2-dicarba-closo-dodecaborate-1-(4-(1,2,4,5-tetrazin-3-yl)phenyl)methanamide were synthesized in 49% and 78% yield respectively, and X-ray structures of both compounds determined. The ortho-carborane derivative was converted to the corresponding nido-cluster under mild conditions, and the product successfully radiolabelled with 125I and 123I. The carborane-tetrazines react rapidly and in quantitative yields with (E)-cyclooct-4-enol (TCO) via a [4 + 2] inverse-electron demand Diels–Alder type reaction, where the second order rate constant in acetonitrile for the iodinated cluster was 199 ± 26 M−1s−1. The labelled tetrazines were stable in solution for extended periods and they were shown to bind in vitro to H520 cells, labelled with a TCO-modified antibody. Imaging studies on the 123I-labeled carborane-tetrazine were performed in healthy mice, and demonstrated minimal loss of iodine in vivo and high uptake in the liver and gall bladder. The reported compounds offer an alternative means of developing targeted boron neutron capture therapy (BNCT) and boron-based molecular imaging agents.

Inverse electron-demand Diels–Alder chemistry in the synthesis of a regioselectively protected analogue of the staurosporine aglycone

Regioselective Weinreb amidation of the C1 ester of dimethyl pyridazino[4,5- b]indole-1,4-dicarboxylate followed by an intramolecular inverse electron-demand Diels–Alder reaction and palladium-catalyzed coupling produced regioselectively protected N 6-methylindolo[2,3- a]pyrrolo[3,4- c]carbazole ( N 6-methylstaurosporinone).