3-(Trifluoromethyl)-3-(m-isothiocyanophenyl)diazirine: synthesis and chemical characterization of a heterobifunctional carbene-generating crosslinking reagent

Fishing for Drug Targets: A Focus on Diazirine Photoaffinity Probe Synthesis

Target identification is a high-priority, albeit challenging, aspect of drug discovery. Diazirine-based photoaffinity probes (PAPs) can facilitate the process by covalently capturing transient molecular interactions. This can help identify target proteins and map the ligand's interactome. Diazirine probes have even been incorporated by cellular machinery into proteins. Embarking on the synthesis of customized PAPs, containing either an aliphatic or trifluoromethyl phenyl diazirine, can be a considerable endeavor, particularly for medicinal chemists and chemical biologists new to the field. This review takes a synthetic focus, aiming to summarize available routes, propose new avenues, and illuminate recent advances in diazirine synthesis. Select examples of diazirine photoaffinity labeling applications have been included throughout to provide instructive definition of the advantages and limitations of the technology while simultaneously highlighting how these reagents can be applied in a practical sense.

Development and application of diazirines in biological and synthetic macromolecular systems

Many different reagents and methodologies have been utilised for the modification of synthetic and biological macromolecular systems. In addition, an area of intense research at present is the construction of hybrid biosynthetic polymers, comprised of biologically active species immobilised or complexed with synthetic polymers. One of the most useful and widely applicable techniques available for functionalisation of macromolecular systems involves indiscriminate carbene insertion processes. The highly reactive and non-specific nature of carbenes has enabled a multitude of macromolecular structures to be functionalised without the need for specialised reagents or additives. The use of diazirines as stable carbene precursors has increased dramatically over the past twenty years and these reagents are fast becoming the most popular photophors for photoaffinity labelling and biological applications in which covalent modification of macromolecular structures is the basis to understanding structure-activity relationships. This review reports the synthesis and application of a diverse range of diazirines in macromolecular systems.

Covalent bound sensing layers on surface acoustic wave (SAW) biosensors

This paper reports on the development of immunosensors based on commercially available surface acoustic wave (SAW) devices working at 380 MHz. Approaches for coating the sensor surface with a sensing layer of receptive biomolecules are presented and discussed. It was found that the sensitivity strongly relates to the immobilization method. Additionally, the sensitivity can be influenced by the density of accessible biomolecules on the active sensing area. Usually, by most of the standard immobilization procedures, two-dimensional layers of receptive biomolecules are obtained. We present a three-dimensional layer, which provides a higher absolute amount of recognition molecules. A dextran layer is photoimmobilized to the sensor surface and the recognition molecules are covalently embedded into the dextran matrix. The feasibility of specific immunosensing is investigated using SAW sensors connected to a fluid handling system.

Covalent photolinker-mediated immobilization of an intermediate dextran layer to polymer-coated surfaces for biosensing applications

A new method is presented for the covalent binding of dextran as an intermediate layer on surface acoustic wave (SAW) devices. For biosensing applications in aqueous media commercially available SAW devices require surface passivation to prevent corrosion of the aluminum device structures in electrolytes. Thin films of polyimide and parylene revealed exceptional passivation properties. They were used as a base for dextran immobilization. Covalent binding of dextran to polymer-coated surfaces was achieved by photoimmobilization. Aryldiazirine-functionalized bovine serum albumin served as the multifunctional light-activable linking agent (photolinker polymer). Dextran and photolinker polymer were mixed and photobonded to sensor surfaces. Essential photoimmobilization parameters were optimized. The binding of proteins to dextran applying carbodiimide chemistries was exemplified with antiurease antibodies and the feasibility of specific immunosensing was investigated on SAW sensors connected to a fluid handling system.

Photochemical linkage of antibodies to silicon chips

Antibodies and antigen binding fragments thereof were photochemically immobilized on surface-modified silicon chips of 5 x 5 mm size. Silicon surface-grafted diazirines and benzophenones formed covalent bonds with the immunoreagents on light activation. Photolithographic immobilization of monoclonal antibodies in aqueous media was achieved on silicon chips by activating surface-grafted benzophenones. The presence of bovine serum albumin during irradiation reduced nonspecific adsorption of the immunoreagents and retained the immunoactivity of the photoimmobilized molecules.

A novel biotinylated heterobifunctional cross-linking reagent bearing an aromatic diazirine

The synthesis of a p-[(3-trifluoromethyl)diazirine-3-yl]benzoic acid derivative is described as a new carbene generating heterobifunctional cross-linking reagent. The cross-linker carries a biotin moiety in order to make use of avidin-biotin technology for specific manipulation of cross-linked components. To evaluate the ability of this reagent, the inter-subunit cross-linking of egg-white avidin tetramer was investigated. As a typical application of avidin-biotin technology for cross-linking experiments, a chemiluminescent detection method was examined to identify photobiotinylated components. A cross-linked dimeric product with an apparent molecular mass of 38 kDa was clearly visualized by the combined use of a horseradish peroxidase-streptavidin conjugate and a luminol-based chemiluminescent system.

Light–Dependent, Covalent Immobilization of Biomolecules on ‘Inert’ Surfaces

We describe a novel, versatile procedure for the light-dependent immobilization of ligands to 'inert' material surfaces. Covalent immobilization of ligands differing in chemical nature and complexity is accomplished under mild and non-destructive conditions. Topical interaction of ligands with organic or inorganic surfaces is mediated by photoactivable polymers with carbene generating trifluoromethyl-aryl-diazirines which serve as linker molecules. Light activation of aryl-diazirino functions at 350 nm yields highly reactive carbenes, and covalent coupling is achieved by simultaneous carbene insertion into both the ligand and inert surface. Thus, reactive functional groups are not required on either the ligand or the supporting material. These procedures are applicable whenever ligands, from molecules to cells--synthetically or genetically produced, or isolated from biological sources--need to be immobilized for improved performance.

Planar bilayer membranes from photoactivable phospholipids

Planar bilayer membranes formed from photoactivable phospholipids have been characterized by low frequency voltametry. Cyclic voltametric measurements were applied for simultaneous registration of planar membrane conductivity and capacitance. The procedure has been utilized to characterize the formation and stability of planar bilayer membranes. Bilayer membranes were formed from N'-(1,2-dimyristoyl-sn-glycero-3-phosphoethyl)-N-((m-3- trifluoromethyldiazirine)phenyl)thiourea (C14-PED), a head-group photosensitive phospholipid. In situ photoactivation of C14-PED at wavelengths greater than or equal to 320 nm altered neither the mean conductivity nor the capacitance of the bilayer. Ionophore (valinomycin) and ion channel (gramicidin) activities were not impaired upon photoactivation. In contrast, bilayer membranes formed from 1,2-bis(hexadeca-2,4-dienoyl)-sn- glycero-3-phosphocholine (C16-DENPC) revealed short life times. In situ photopolymerization of the diene fatty acids significantly increased the membrane conductivity or led to membrane rupture.