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Photoaffinity labeling (PAL) technique using a fluorogenic cross-linker is used to monitor the nucleotide-binding pocket within a protein. A coumarin fluorophore formed in the binding domain due to ultraviolet (UV) irradiation has been shown to accelerate the sequencing of the labeled peptide as well as identification of the labeled site by liquid chromatography (LC)-tandem mass spectrometry (MS), in addition to providing information on the ligand binding state. Selective monitoring of the predefined fluorescence peaks among the numerous digests obtained from high performance liquid chromatography (HPLC) clearly indicates the binding capability of the ligand to the entire protein as well as to the corresponding binding domain under various conditions. In the current study, ligand-binding analysis confirmed by the structural information of the binding state has been demonstrated using fluorogenic ATP/ADP photoactivatable probes under allosteric regulation of multiple substrates in the enzyme glutamate dehydrogenase (GDH)., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Alternative one-pot synthesis of 3-(trifluoromethyl)-3-phenyldiazirine derivatives from corresponding tosyloximes is developed. The deprotonation of intermediate diaziridine by NH2(-) is a new approach for construction of diazirine. Moreover, a novel synthesis of optically pure (trifluoromethyl)diazirinylphenylalanine derivatives was attempted involving these methods.

Photoaffinity labeling has become increasingly important with the development of powerful specific probes that are synthesized by installing a photo-activatable functional group (photophore) on the framework of biological ligands. The present review summarizes the development of diazirine-based photoaffinity labeling by focusing on its application to the structural elucidation of ligand-accepting sites within proteins.

A photoaffinity labeling (PAL)-based method for the rapid identification of target proteins is presented in which a high-performance chemical tag, an isotope-coded fluorescent tag (IsoFT), can be attached to the interacting site by irradiation. Labeled peptides can be easily distinguished among numerous proteolytic digests by sequential detection with highly sensitive fluorescence spectroscopy and mass spectrometry. Subsequent MS/MS analysis provides amino acid sequence information with a higher depth of coverage. The combination of PAL and heterogeneous target-selecting techniques significantly reduces the amount of time and protein required for identification. An additional photocleavable moiety successfully accelerated proteomic analysis using cell lysate. This method is a widely applicable approach for the rapid and accurate identification of interacting proteins., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A photo-switchable fluorescent flagging approach has been developed to identify photoaffinity-labeled peptides in target protein. Upon photochemical release of the ligand, the protein was newly modified with a coumarin in place of the previously attached biotin. It allowed us to simplify complex identification processes for labeled sites.

5- and 6-trifluoromethyldiazirinyl indoles were synthesized from corresponding bromoindole derivatives for the first time. They acted as mother skeletons for the comprehensive synthesis of various bioactive indole metabolites. These can be used in biological functional analysis as diazirine-based photoaffinity labels.

Based on the application of our recent biotinyl photoprobe with a cleavable N-acylsulfonamide, an efficient process has been developed for profiling photoaffinity labeled peptides among a large excess of unlabeled concomitants. N-acylsulfonamide group was found to be stable under the usual S-pyridylethylation condition of cysteine residues whereas the group was easily cleaved by N-alkylation with iodoacetic acid in acidic condition. The selective nature between two common protein alkylation reactions was evaluated with L-glutamate dehydrogenase (GDH) using an acidic amino acid photoprobe with biotinylated acylsulfonamide function. The labeled GDH was successfully subjected to S-pyridylethylation keeping the biotin tag intact, and then was easily released from streptavidin matrix with high purity via iodoacetic acid-mediated alkylation under mild condition at pH 5.0., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Synthesis of diazirinyl organo-platinum complexes, which specifically interact with purine base, characterization of photoreactivity and interaction between guanosine 5'-monophosphate (GMP) were examined. The results indicated that the diazirinyl organo-platinum complex was useful for manipulations of photoaffinity labeled components.

Some D-amino acids such as d-tryptophan and D-phenylalanine are well known as naturally-occurring sweeteners. Photoreactive D-phenylalanine derivatives containing trifluoromethyldiazirinyl moiety at 3- or 4-position of phenylalanine, were designed as sweeteners for functional analysis with photoaffinity labeling. The trifluoromethyldiazirinyl D-phenylalanine derivatives were prepared effectively with chemo-enzymatic methods using L-amino acid oxidase and were found to have potent activity toward the human sweet taste receptor., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

A novel photoreactive ceramide analogue, which contains (3-trifluoromethyl)phenyldiazirinyl lipid and biotinylated sphingosine, was synthesized. The probe was recognized as an antigen by anti-ceramide antibody and as a substrate for sphingolipid ceramide N-deacylase. These results indicate that the probe may be useful as a photoaffinity-biotinylating agent in sphingolipid studies.

Selective hydrogenation of carbon-carbon double bond in the presence of nitrogen-nitrogen double bond in (3-trifluoromethyl) phenyldiazirine achieved with Wilkinson's catalyst.

Novel diazirinyl photoaffinity ligand, which contains (3-trifluoromethyl) phenyldiazirine and penta(epsilon-Boc-Lys) as a photoreactive code, allows the introduction of a positive cascade to alter the pI value of labeled components, facilitating the isolation of photolabeled biocomponents with isoelectric focusing techniques.

Photoaffinity labeling enables the direct probing of a target protein through a covalent bond between a ligand and its binding protein, and even a complex formed by weak interactions can be isolated by the method. The photochemical fishing approach accelerates the throughput, isolating crosslinked complexes and analyzing the structure of the ligand binding site within the protein. We used carbene-generating phenyldiazirine for this approach because practical examinations had shown that the phenyldiazirine functioned as the powerful barb on the hook. Improving the synthetic pathways of the photoprobes and using chemoselective-integrated photoreactive units makes possible the easy and rapid preparation of carbene-generating photoreactive probes including the derivatives in peptides, proteins, DNAs, and carbohydrates. This review also shows several recent impacts of photoaffinity labeling, including the in vivo preparation of photoreactive proteins in living cells.

An efficient method of photoaffinity labeling has been developed based on rationally designed multifunctional photoprobes. Photoaffinity techniques have been used to elucidate the protein structure at the interface of biomolecules by the photochemical labeling of interacting sites. However, the identification of labeled sites within target proteins is often difficult. Novel biotinyl bioprobes bearing a diazirine photophore have contributed significantly to the rapid elucidation of ligand binding sites within proteins, thereby extending conventional photoaffinity methods. This article discusses the synthesis and applications of various photoprobes bearing a biotin, including strategies using cleavable linkages between photophores. The combination of photoaffinity methods with chip technology is also described as a novel entry to rapid affinity-based screening of inhibitors. This review focuses on a rapid and reliable photoaffinity method utilizing diazirine-based multifunctional photoprobes with numerous potential applications in functional proteomics of biomolecular interactions., (2005 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.)

Summary A convenient procedure for the synthesis of (E)- and (Z)-beta-bromostyrene containing trifluoromethyldiazirine is described, which involves the stereoselective reduction of the corresponding trifluoromethyldiazirinyl beta,beta-dibromostyrene without damaging the photophor. The synthetic route easily introduced deuterium, which can be utilized for the detection of a photolabeled component by MS spectrometry, after construction of a trifluoromethyldiazirinyl skeleton.

The efficient synthesis of an enzyme cleavable biotinylated diazirinyl photoaffinity ligand is described to allow the effective manipulation of the photolabeled biocomponents. The compound contains a glutamic acid gamma-methyl ester, which is a precursor of the substrate for V8 protease, between the diazirinyl photophor and biotin moiety. After alkaline hydrolysis of the ester, the compound can be proteolyzed at the Glu moiety by V8 protease. The photophore was introduced to L-Phe p-nitroanilide and the ligand was applied to photolabel of chymotrypsin to manipulate the application of the concept.

A novel application of the photoaffinity technique has been developed for the efficient discovery of small ligand and macromolecule interaction. The approach, photoaffinity capture, uses a photoreactive protein together with immobilized ligand for the rapid screening of competitive inhibitors. The set of photoreactive glyceraldehyde-3-phosphate dehydrogenase (photo-GAPDH) and immobilized dye ligand was prepared and examined as a model system. The photo-GAPDH was shown to efficiently capture the immobilized ligand. When nonimmobilized competitive ligands were included in the system, the capture was prevented in accordance with the affinity of the ligands. The present approach would provide an efficient tool for affinity-based screening of ligand libraries.

One of the major events occurring at biological interfaces is the specific recognition of bioactive ligands by their receptor proteins. The elucidation of interacting partners is an immediate entrance into the discovery of medicinal leads. The method of photoaffinity labeling enables the direct probing of target protein through a covalent bond introduced between a ligand and its specific receptor. Thus, the photoaffinity labeling is applied in two stages of drug discovery and development processes. First, the method is useful for the screening of early leads. If the binding site analysis of target protein is important for defining a particular pharmacophore, the photoaffinity labeling will give the structural information at the contact point of drugs with receptors. Second, emerging new technologies, combinatorial chemistry, recombinant DNA techniques, and high-throughput analysis, are extending the potential of photoaffinity labeling to become a rapid and more sensitive means for the identification of drug-receptor pairs as well as the elucidation of molecular recognition mechanism at drug-receptor interfaces. This review focuses on several recent impacts of photoaffinity labeling as a useful tool for drug discovery and developments.

A versatile synthesis of diazirine-based photoreactive fatty acid analogues is reported. The key step is phenoxy alkylation of diazirine with halo alkyl acid esters. The conditions described will be acceptable for the synthesis of various alkyl-length derivatives. The fatty acid derivatives are acceptors for reverse reactions of sphingolipid ceramide N-deacylase (SCDase), which catalyzes the condensation of psychosine and fatty acids to form photoreactive galactosylceramide. The photoreactive galactosylceramide can also be prepared with chemical synthesis, condensation of psychosine and fatty acid succinimidyl ester, and is recognized with anti-GarCer antibody both before and after irradiation.