Novel amidino-substituted benzimidazoles: Synthesis of compounds and inhibition of dipeptidyl peptidase III

Design and synthesis of efficient fluororethylene-peptidomimetic inhibitors of dipeptidyl peptidase III (DPP3)

Dipeptidyl peptidase III (DPP3) is a ubiquitously expressed zinc-dependent peptide cutting enzyme and selectively hydrolyses amide bonds to cleave N-terminal dipeptide fragments off of physiologically important oligopeptides. DPP3 has been found in a multitude of different types of cells and appears to be involved in various physiological processes (e.g. nociception, blood pressure control, protein turnover). Using the slowly converted peptide substrate tynorphin (VVYPW) as starting point, we have replaced the scissile bond with a fluoroethylene bioisostere to design ground state inhibitors, which led to the so far most effective peptide-based inhibitor of DPP3.

Survey of Dipeptidyl Peptidase III Inhibitors: From Small Molecules of Microbial or Synthetic Origin to Aprotinin

Dipeptidyl peptidase III (DPP III) was originally thought to be a housekeeping enzyme that contributes to intracellular peptide catabolism. More specific roles for this cytosolic metallopeptidase, in the renin-angiotensin system and oxidative stress regulation, were confirmed, or recognized, only recently. To prove indicated (patho)physiological functions of DPP III in cancer progression, cataract formation and endogenous pain modulation, or to reveal new ones, selective and potent inhibitors are needed. This review encompasses natural and synthetic compounds with experimentally proven inhibitory activity toward mammalian DPP III. Except for the polypeptide aprotinin, all others are small molecules and include flavonoids, coumarin and benzimidazole derivatives. Presented are current strategies for the discovery or development of DPP III inhibitors, and mechanisms of inhibitory actions. The most potent inhibitors yet reported (propioxatin A and B, Tyr-Phe- and Phe-Phe-NHOH, and JMV-390) are active in low nanomolar range and contain hydroxamic acid moiety. High inhibitory potential possesses oligopeptides from the hemorphin group, valorphin and tynorphin, which are poor substrates of DPP III. The crystal structure of human DPP III-tynorphin complex enabled the design of the transition-state peptidomimetics inhibitors, effective in low micromolar concentrations. A new direction in the field is the development of fluorescent inhibitor for monitoring DPP III activity.

The emerging role of dipeptidyl peptidase 3 in pathophysiology

Dipeptidyl peptidase 3 (DPP3), a zinc-dependent aminopeptidase, is a highly conserved enzyme among higher animals. The enzyme cleaves dipeptides from the N-terminus of tetra- to decapeptides, thereby taking part in activation as well as degradation of signalling peptides critical in physiological and pathological processes such as blood pressure regulation, nociception, inflammation and cancer. Besides its catalytic activity, DPP3 moonlights as a regulator of the cellular oxidative stress response pathway, e.g., the Keap1-Nrf2 mediated antioxidative response. The enzyme is also recognized as a key modulator of the renin-angiotensin system. Recently, DPP3 has been attracting growing attention within the scientific community, which has significantly augmented our knowledge of its physiological relevance. Herein, we review recent advances in our understanding of the structure and catalytic activity of DPP3, with a focus on attributing its molecular architecture and catalytic mechanism to its wide-ranging biological functions. We further highlight recent intriguing reports that implicate a broader role for DPP3 as a valuable biomarker in cardiovascular and renal pathologies and furthermore discuss its potential as a promising drug target.

Efficient Entropy-Driven Inhibition of Dipeptidyl Peptidase III by Hydroxyethylene Transition-State Peptidomimetics

Dipeptidyl peptidase III (DPP3) is a ubiquitously expressed Zn‐dependent protease, which plays an important role in regulating endogenous peptide hormones, such as enkephalins or angiotensins. In previous biophysical studies, it could be shown that substrate binding is driven by a large entropic contribution due to the release of water molecules from the closing binding cleft. Here, the design, synthesis and biophysical characterization of peptidomimetic inhibitors is reported, using for the first time an hydroxyethylene transition‐state mimetic for a metalloprotease. Efficient routes for the synthesis of both stereoisomers of the pseudopeptide core were developed, which allowed the synthesis of peptidomimetic inhibitors mimicking the VVYPW‐motif of tynorphin. The best inhibitors inhibit DPP3 in the low μM range. Biophysical characterization by means of ITC measurement and X‐ray crystallography confirm the unusual entropy‐driven mode of binding. Stability assays demonstrated the desired stability of these inhibitors, which efficiently inhibited DPP3 in mouse brain homogenate.

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4 , whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

Novel dipeptidyl hydroxamic acids that inhibit human and bacterial dipeptidyl peptidase III

Human dipeptidyl peptidase III (hDPP III), a zinc-metallopeptidase of the family M49, is an activator of the Keap1-Nrf2 cytoprotective pathway involved in defense against oxidative stress. Pathophysiological roles of DPP III have not been elucidated yet, partly due to the lack of specific inhibitors. We showed that substrate analog H-Tyr-Phe-NHOH is a strong competitive inhibitor of hDPP III, while H-Tyr-Gly-NHOH expresses much weaker inhibition. To investigate the effects of amino acid substitutions in inhibitor P1 position, we synthesized three new dipeptidyl hydroxamates and examined their influence on the activity of hDPP III and DPP III from the human gut symbiont Bacteroides thetaiotaomicron. The extent of inhibition of hDPP III, but not of bacterial enzyme, was dependent on the amino acid in P1. H-Phe-Phe-NHOH is recognized as one of the strongest inhibitors of hDPP III (K_i = 0.028 μM), and H-Phe-Leu-NHOH discriminated between human and bacterial ortholog of the M49 family.

Copper-catalyzed multi-component synthesis of acrylamidines and benzoimidazoles

Acrylamidines were synthesized via the copper-catalyzed three-component reaction of propargyl acetates, sulfonyl azides and amines, which are readily accessible materials.

(18)F Labeled benzimidazole derivatives as potential radiotracer for positron emission tomography (PET) tumor imaging

This article reported the synthesis and bioevaluation of two [(18)F] labeled benzimidazole derivatives, 4-(5-(2-[(18)F] fluoro-4-nitrobenzamido)-1-methyl-1H-benzimidazol-2-yl) butanoic acid ([(18)F] FNBMBBA, [(18)F]a1) and 3-(2-fluoroethyl)-7-methyl-2-propyl-3H-benzimidazole-5-carboxylic acid ([(18)F] FEMPBBA, [(18)F]b1) for PET tumor imaging. The preparation [(18)F] FEMPBBA was completed in 1h with overall radiochemical yield of 50-60% (without decay corrected). Biodistribution assay in S180 tumor bearing mice of both compounds were carried out, and the results are both meaningful. [(18)F] FEMPBBA which can be taken as a revision of [(18)F] FNBMBBA got an excellent result, and has significant advantages in some aspects compared with L-[(18)F] FET and [(18)F]-FDG in the same animal model, especially in tumor/brain uptake ratio. The tumor/brain uptake ratio of [(18)F] FEMPBBA gets to 4.81, 7.15, and 9.8 at 30min, 60min and 120min, and is much higher than that of L-[(18)F] FET (2.54, 2.92 and 2.95) and [(18)F]-FDG (0.61, 1.02, 1.33) at the same time point. The tumor/muscle and tumor/blood uptake ratio of [(18)F] FEMPBBA is also higher than that of L-[(18)F] FET at 30min and 60min. This result indicates compound [(18)F] FEMPBBA is a promising radiotracer for PET tumor imaging.

The first structure of dipeptidyl-peptidase III provides insight into the catalytic mechanism and mode of substrate binding

Dipeptidyl-peptidases III (DPP III) are zinc-dependent enzymes that specifically cleave the first two amino acids from the N terminus of different length peptides. In mammals, DPP III is associated with important physiological functions and is a potential biomarker for certain types of cancer. Here, we present the 1.95-A crystal structure of yeast DPP III representing the prototype for the M49 family of metallopeptidases. It shows a novel fold with two domains forming a wide cleft containing the catalytic metal ion. DPP III exhibits no overall similarity to other metallopeptidases, such as thermolysin and neprilysin, but zinc coordination and catalytically important residues are structurally conserved. Substrate recognition is accomplished by a binding site for the N terminus of the peptide at an appropriate distance from the metal center and by a series of conserved arginine residues anchoring the C termini of different length substrates.

Proteomic biomarkers for prenatal bisphenol A-exposure in mouse immune organs

Many investigators have encountered difficulty in clarifying the risks of exposure to bisphenol A (BPA), an endocrine disrupting chemical in epidemiological studies or animal experiments. In the present study, we developed biomarkers of BPA-induced proteomic alterations in immune organs of mouse offspring that were prenatally exposed to BPA (15 and 300 mg/L of drinking water; they were exposed to 8.9 +/- 1.8 mg of BPA/kg/day and 171.1 +/- 16.8 mg of BPA/kg/day, respectively) that were evaluated in terms of sex, age, and BPA-exposure levels. We performed 2D-gel analyses of samples from various tissues (thymus and spleen), exposure levels, sex, and ages (3- and 7-week-old) (N = 48), and found seven proteins that were altered in a BPA dose-dependent manner. Among them, we further studiedapo-AI, DPPIII, and VAT1, which are suspected to be associated with endocrine disorders. By performing Western blots, we confirmed BPA upregulation of all three proteins. Moreover, the apo-AI mRNA levels were increased in a BPA dose-dependent manner in 3- and 7-week-old female mice. Females and young offspring were somewhat more sensitive to protein alterations than others. Our study, which is based on proteome analyses, suggests that apo-AI, DPPIII, and VAT represent protein biomarkers for BPA and provide useful mechanistic clues for BPA-induced endocrine disruption.

Synthesis, antiviral and antitumor activity of 2-substituted-5-amidino-benzimidazoles

We have prepared a set of heterocyclic benzimidazole derivatives bearing amidino substituents at C-5 of benzimidazole ring, by introducing various heterocyclic nuclei (pyridine, N-methyl-pyrrole or imidazole) at C-2, and evaluated their antitumor and antiviral activities. The most pronounced antiproliferative activity was shown with compounds 6 and 9, having imidazolinylamidino-substituent. Interestingly, all compounds show noticeable selectivity toward breast cancer cell line MCF-7. The most distinct and selective antiviral activity toward coxsackieviruses and echoviruses was observed with compounds having pyridine ring at C-2. Especially interesting was fairly strong activity of 4 and 8 toward adenoviruses, which could be considered as leads against adenoviral replication.