Separation and detection of bis-maleimide-polyethylene glycol and mono-maleimide-polyethylene glycol by reversed-phase high pressure liquid chromatography

Click Chemistry-Enabled Conjugation Strategy for Producing Dibenzodiazepinone-Type Fluorescent Probes To Target M2 Acetylcholine Receptors

The development of fluorescently labeled receptor-targeting compounds represents a powerful pharmacological tool to study and characterize ligand-receptor interactions. Despite significant advances in developing sub-type-specific antagonists for muscarinic acetylcholine receptors (mAChRs), reports on antagonists feasible for click chemistry are less common. Here, we designed and synthesized an antagonist suitable for probe attachment through click chemistry, namely, dibenzodiazepinone (DIBA)-alkyne, based on a previously reported DIBA scaffold with a high binding affinity to type-2 mAChR (M2R). To demonstrate the versatility of DIBA-alkyne as a building block for bioconjugates, we assembled DIBA-alkyne with Cyanine5 fluorophores (Cy5) and polyethylene glycol (PEG) biomolecules to obtain fluorescent DIBA antagonist (DIBA-Cy5) and fluorescent DIBA PEG derivatives. Flow cytometric analysis showed that DIBA-Cy5 possessed a high binding affinity to M2R (Kd = 1.80 nM), a two-order magnitude higher binding affinity than M1R. Fluorescent DIBA PEG derivatives maintained a potent binding to the M2R (Kd ≤ 4 nM), confirmed by confocal microscopic imaging. Additionally, DIBA-Cy5 can serve as a fluorescent ligand in the receptor-ligand competitive binding assay for other mAChR ligands, an attractive alternative to the traditional radioligand-based assay. The competitive binding mode between DIBA-Cy5 and orthosteric antagonist atropine/allosteric modulator LY2119620 indicated a dualsteric binding mode of the DIBA-type antagonist to M2R. Lastly, we demonstrated the direct staining of DIBA-Cy5 to M2R receptors in the sinoatrial node of a mouse heart. The adaptability of the clickable DIBA antagonist to a wide range of fluorophores and biomolecules can facilitate its use in various biomedical applications such as binding assays that screen compounds for M2R as the receptor target.

Characterization of N-phenylmaleimide-terminated poly(ethylene glycol)s and their application to a tetra-arm poly(ethylene glycol) gel

Tetra-arm poly(ethylene glycol) (TetraPEG) gels are tough materials whose toughness originates from their uniform network structure. They can be formed by combining the termini of tetra-arm polymers via chemical reactions with high conversion efficiency, such as the Michael addition, condensations using an active ester group, and alkyne-azide cycloadditions. Herein, we report the synthesis of a tetra-PEG gel using a tetra-arm polymer with N-phenylmaleimide moieties at the polymer ends (tetra-N-aryl MA PEG) as a scaffold. Tetra-N-aryl MA PEG can be obtained via a simple maleimidation using the modification agent p-maleimidophenyl isocyanate (PMPI), which directly transforms the hydroxy groups at the polymer ends into reactive N-aryl maleimide groups in a one-pot reaction. The thus-obtained tetra-N-aryl MA PEG was fully characterized using high-performance liquid chromatography (HPLC), matrix-assisted laser desorption ionization time of flight mass spectrometry, and proton nuclear magnetic resonance spectroscopy. HPLC analysis not only demonstrated the high purity of tetra-N-aryl MA PEG and the full conversion of the hydroxy groups, but also provided an effective characterization method for N-aryl maleimide-based PEG using a simple protocol, which enables us quantitative analysis of functionalized polymers with different N-aryl maleimide numbers. Furthermore, we fabricated a TetraPEG gel via Michael addition of the obtained tetra-N-aryl MA and thiol-terminated TetraPEGs. Thus, this report presents the application of tetra-N-aryl MA PEG as an effective precursor to obtain a uniform network structure and a method for its characterization; these results should provide support for the development of functional molecules, soft materials, and further functional materials based on the uniform-network-structure concept.