Prolyl Oligopeptidase Inhibition by N-Acyl-pro-pyrrolidine-type Molecules

Study of the Conformational Dynamics of Prolyl Oligopeptidase by Mass Spectrometry: Lessons Learned

Ion mobility mass spectrometry (IM-MS) can be used to analyze native proteins according to their size and shape. By sampling individual molecules, it allows us to study mixtures of conformations, as long as they have different collision cross sections and maintain their native conformation after dehydration and vaporization in the mass spectrometer. Even though conformational heterogeneity of prolyl oligopeptidase has been demonstrated in solution, it is not detectable in IM-MS. Factors that affect the conformation in solution, binding of an active site ligand, the stabilizing Ser554Ala mutation, and acidification do not qualitatively affect the collision-induced unfolding pattern. However, measuring the protection of accessible cysteines upon ligand binding provides a principle for the development of MS-based ligand screening methods.

Highly Diastereoselective [3 + 2] Cycloaddition of Aziridines with Difluorinated Silyl Enol Ethers: Divergent Synthesis of 4,4-Difluoropyrrolidines and 4-Fluoropyrroles

A highly diastereoselective [3 + 2] cycloaddition of aziridines with difluorinated silyl enol ethers has been developed. This approach provides a facile methodology for highly functionalized gem-difluorinated pyrrolidines in good to excellent yields with good functional group tolerance. A one-pot, two-step approach for synthesis of structurally interesting fluorinated pyrroles has also been developed through a cycloaddition/aromatization/desulfonation sequence. Moreover, readily available substrates, mild reaction conditions, and easy scale-up synthesis show practical advantages.

Construction of benzoheterocycles by the reaction of α-arylglyoxylic acids and ortho-functionalized aniline under mild and minimal conditions

This work describes an environmentally friendly method for the synthesis of benzoxazinones, quinoxalinones and benzothiazoles by the reaction of α-arylglyoxylic acids and ortho-functionalized aniline. In this reaction, no other reagents are needed except for reactants and solvents. The reaction was carried out at a mild temperature of 50 °C with only water and/or carbon dioxide as the by-product. Therefore, the reaction has high practical atom economy. In addition, this strategy could be scaled up to the gram level, and the natural product Cephamandole A could be synthesized on a mass scale.

Visible Light Photoredox-Catalyzed Direct C-H Arylation of Quinoxalin-2(1H)-ones with Diaryliodonium Salts

A photoredox-catalyzed direct arylation of quinoxalin-2-(1H)-ones using diaryliodonium triflates as the convenient, stable, and cheap aryl source is described. A broad variety of quinoxalin-2-(1H)-ones are shown to react with structurally and electronically diverse diaryliodonium triflates, allowing efficient access to a wide variety of pharmaceutically important 3-arylquinoxalin-2-(1H)-ones. The presented method is attractive with regard to operational simplicity, mild conditions, broad scope, scalability, and high functional group tolerance.

A HCl-Mediated, Metal- and Oxidant-Free Photocatalytic Strategy for C3 Arylation of Quinoxalin(on)es with Arylhydrazine

A novel and simple HCl-mediated, photocatalytic method for quinoxaline(on)es C3-H arylation with arylhydrazine under transition metal catalyst- and oxidant-free conditions is presented. Various quinoxaline(on)es underwent this transformation smoothly, demonstrating a broad substrate tolerance and providing the corresponding aryl products in moderate to excellent yields. Mechanistic studies indicated that a radical pathway may be involved in this transformation.

Electrochemical Oxidative C-H Arylation of Quinoxalin(on)es with Arylhydrazine Hydrochlorides under Mild Conditions

A practical and scalable protocol for electrochemical arylation of quinoxalin(on)es with arylhydrazine hydrochlorides under mild conditions has been developed. This method exhibits high efficiency, easy scalability, and broad functional group tolerance. Various quinoxalin(on)es and arylhydrazines underwent this transformation smoothly in an undivided cell, providing the corresponding aryl-substituted quinoxalin(on)es in moderate to good yields. A radical mechanism is involved in this arylation reaction.

Fluorine-Containing Prolines: Synthetic Strategies, Applications, and Opportunities

Fluorinated prolines play an important role in peptide studies, protein engineering, medicinal chemistry, drug discovery, and agrochemistry. Since the first synthesis of 4-fluoroprolines by Gottlieb and Witkop in 1965, their popularity started to grow exponentially. For example, during the past two decades, all isomeric trifluoromethyl-substituted prolines have been synthesized. In this Perspective, chemical properties and applications of fluorinated prolines are discussed. Synthetic approaches to all known fluorine-containing prolines are also discussed and analyzed. This analysis unexpectedly revealed an unsolved problem: in strict contrast to fluoro- and trifluoromethyl-substituted prolines, the corresponding analogues with fluoromethyl and difluoromethyl groups are mostly unknown. At the end of the paper, structures of several interesting, yet unknown, fluorinated prolines are disclosed─a good opportunity for chemists to make them.

Sustainable C–H activation approach for palladium-catalyzed, regioselective functionalization of 1-methyl-3-phenyl quinoxaline-2(1H)-ones in water

An environment-friendly approach for regioselective acylation of 1-methyl-3-phenyl quinoxaline-2(1H)-ones was developed using water as a solvent. The protocol exhibits a wide substrate scope and employs commercially available, non-toxic acyl surrogates.

Discovery of novel berberine derivatives with balanced cholinesterase and prolyl oligopeptidase inhibition profile

Berberine, a naturally occurring compound, possesses an interesting multipotent pharmacological profile potentially applicable for Alzheimer's disease (AD) treatment. In this study, a series of novel 22 berberine derivatives was developed and tested in vitro. Berberine core was substituted at position 9-O of its aromatic ring region. All the hybrids under the study revealed multi-targeted profile inhibiting prolyl oligopeptidase, acetylcholinesterase and butyrylcholinesterase highlighting 4a, 4g, 4j, 4l and 4s possessing balanced activities in the micromolar range. The top-ranked candidates in terms of the most pronounced potency against POP, AChE and BChE can be classified as 4d, 4u and 4v, bearing 4-methylbenzyl, (naphthalen-2-yl)methylene and 1-phenoxyethyl moieties, respectively. In vitro data were corroborated by detailed kinetic analysis of the selected lead molecules. 4d, 4u and 4v were also inspected for their potential to inhibit aggregation of two abberant proteins in AD, namely amyloid beta and tau, indicating their potential disease-modifying properties. To explain the results of our study, we carried out docking simulation to the active sites of the respective enzyme with the best berberine derivatives, along with QSAR study. We also investigated compounds' potential permeability through blood-brain barrier by applying parallel artificial membrane permeation assay and addressed their cytotoxicity profile.

K2S2O8 mediated C-3 arylation of quinoxalin-2(1H)-ones under metal-, photocatalyst- and light-free conditions

Two facile and effective C-3 arylation protocols of quinoxalin-2(1H)-ones with arylhydrazines and aryl boronic acids respectively via free radical cross-coupling reactions under metal-, photocatalyst- and light-free conditions have been unveiled. K₂S₂O₈ has been used as an efficient oxidant to generate aryl radicals from arylhydrazines and aryl boronic acids under two different reaction conditions. The generated aryl radicals undergo a free radical coupling reaction at the C-3 position of quinoxalin-2(1H)-ones producing 3-arylquinoxalin-2(1H)-ones in good to excellent yields. The involvement of radicals in the course of the reaction has been demonstrated by radical trapping experiments with 2,2,6,6-tetramethylpiperidine-1-oxyl.

C-3 arylation protocols of quinoxalin-2(1H)-ones with arylhydrazines and aryl boronic acids under metal-, photocatalyst- and light-free conditions using non-toxic K₂S₂O₈.

ACE inhibitory peptides in standard and fermented deer velvet: an in silico and in vitro investigation

BACKGROUND

The use of deer velvet antler (DVA) as a potent traditional medicine ingredient goes back for over 2000 years in Asia. Increasingly, though, DVA is being included as a high protein functional food ingredient in convenient, ready to consume products in Korea and China. As such, it is a potential source of endogenous bioactive peptides and of 'cryptides', i.e. bioactive peptides enzymatically released by endogenous proteases, by processing and/or by gastrointestinal digestion. Fermentation is an example of a processing step known to release bioactive peptides from food proteins. In this study, we aimed to identify in silico bioactive peptides and cryptides in DVA, before and after fermentation, and subsequently to validate the major predicted bioactivity by in vitro analysis.

METHODS

Peptides that were either free or located within proteins were identified in the DVA samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) followed by database searching. Bioactive peptides and cryptides were identified in silico by sequence matching against a database of known bioactive peptides. Angiotensin-converting enzyme (ACE) inhibitory activity was measured by a colorimetric method.

RESULTS

Three free bioactive peptides (LVVYPW, LVVYPWTQ and VVYPWTQ) were solely found in fermented DVA, the latter two of which are known ACE inhibitors. However matches to multiple ACE inhibitor cryptides were obtained within protein and peptide sequences of both unfermented and fermented DVA. In vitro analysis showed that the ACE inhibitory activity of DVA was more pronounced in the fermented sample, but both unfermented and fermented DVA had similar activity following release of cryptides by simulated gastrointestinal digestion.

CONCLUSIONS

DVA contains multiple ACE inhibitory peptide sequences that may be released by fermentation or following oral consumption, and which may provide a health benefit through positive effects on the cardiovascular system. The study illustrates the power of in silico combined with in vitro methods for analysis of the effects of processing on bioactive peptides in complex functional ingredients like DVA.

Covalent Organic Frameworks: A Sustainable Photocatalyst toward Visible-Light-Accelerated C3 Arylation and Alkylation of Quinoxalin-2(1H)-ones

A practical and scalable protocol for visible-light-accelerated arylation and alkylation of quinoxalin-2(1H)-ones with hydrazines is reported. In this protocol, a hydrazone-based two-dimensional covalent organic frameworks (2D-COF-1) was employed as the heterogeneous photocatalyst (PC). Due to its excellent photocatalytic properties, good chemical stability and heterogeneous nature, the present method exhibits high efficiency, good functional group tolerance, easy scalability and remarkable catalyst reusability. More importantly, it provides an alternative way that allows rapid access to various C3 arylated or alkylated quinoxalin-2(1H)-ones in a greener and sustainable manner.

Prolyl oligopeptidase and its role in the organism: attention to the most promising and clinically relevant inhibitors

Prolyl oligopeptidase (POP), also called prolyl endopeptidase, is a cytosolic enzyme investigated by several research groups. It has been proposed to play an important role in physiological processes such as modulation of the levels of several neuronal peptides and hormones containing a proline residue. Due to its proteolytic activity and physiological role in cell signaling pathways, inhibition of POP offers an emerging approach for the treatment of Alzheimer's and Parkinson's diseases as well as other diseases related to cognitive impairment. Furthermore, it may also represent an interesting target for treatment of neuropsychiatric disorders, and as an antiangiogenesis or antineoplastic agent. In this review paper, we summarized naturally occurring POP inhibitors together with peptide-like inhibitors and their biological effects. Some of them have shown promising results and interesting pharmacological profiles. However, to date, there is no POP inhibitor available on the market although several clinical trials have been undertaken.

Transition-Metal-Free Direct C-H Arylation of Quinoxalin-2(1H)-ones with Diaryliodonium Salts at Room Temperature

A method of synthesizing 3-arylquinoxalin-2(1H)-ones using diaryliodonium tetrafluoroborates under mild conditions is described. This protocol has a wide substrate scope and enables direct C-H functionalization. The synthetic potential of this coupling was explored using a range of readily accessible diaryliodonium salts and quinoxalin-2(1H)-ones.

P2-substituted N-acylprolylpyrrolidine inhibitors of prolyl oligopeptidase: biochemical evaluation, binding mode determination, and assessment in a cellular model of synucleinopathy

We have investigated the effect of regiospecifically introducing substituents in the P2 part of the typical dipeptide derived basic structure of PREP inhibitors. This hitherto unexplored modification type can be used to improve target affinity, selectivity, and physicochemical parameters in drug discovery programs focusing on PREP inhibitors. Biochemical evaluation of the produced inhibitors identified several substituent types that significantly increase target affinity, thereby reducing the need for an electrophilic "warhead" functionality. Pronounced PREP specificity within the group of Clan SC proteases was generally observed. Omission of the P1 electrophilic function did not affect the overall binding mode of three representative compounds, as studied by X-ray crystallography, while the P2 substituents were demonstrated to be accommodated in a cavity of PREP that, to date, has not been probed by inhibitors. Finally, we report on results of selected inhibitors in a SH-SY5Y cellular model of synucleinopathy and demonstrate a significant antiaggregation effect on α-synuclein.

Low molecular weight inhibitors of Prolyl Oligopeptidase: a review of compounds patented from 2003 to 2010

INTRODUCTION

Prolyl Oligopeptidase (POP) is a serine peptidase that cleaves post-proline bonds in short peptides. Besides the direct hydrolytic regulation function over peptides, neuropeptides and peptide hormones, POP is probably involved in the regulation of the inositol pathway and participates in protein-protein interactions. Experimental data show that POP inhibitors have neuroprotective, anti-amnesic and cognition-enhancing properties. These compounds are considered therapeutic agents of interest for the treatment of cognitive deficits related to neuropsychiatric and neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Recent findings pointed to the involvement of POP in angiogenesis, although the exact mechanism is still under study.

AREAS COVERED

This review comprises patents and patent applications involving POP inhibitors patented between 2003 and 2010, classified as peptidomimetics, heteroaryl ketones and alkaloids. The binding processes and the mechanisms of inhibition of these inhibitors are also discussed, together with their in vivo effects.

EXPERT OPINION

The major part of the repertory of POP inhibitors derived from systematical modification of the canonical compound benzyloxycarbonyl-prolyl-prolinal (ZPP). Nevertheless, only two of them have progressed into the clinical trials. One possible reason for this failure is the lack of studies concerning pharmacodynamics, pharmacokinetics and toxicity, together with the absence of suitable animal models. Moreover, POP is still not a well-defined therapeutic target. Further studies are required for the elucidation of the biological role of POP and to validate the therapeutic action of inhibitors in cognitive processes. In contrast, the involvement of POP in protein-protein interactions together with the recent evidences in angiogenesis opens alternative approaches to the traditional active site-directed inhibitors, as well as new therapeutic applications.

Design and synthesis of prolylcarboxypeptidase (PrCP) inhibitors to validate PrCP as a potential target for obesity

Prolylcarboxypeptidase (PrCP) is a serine protease that may have a role in metabolism regulation. A class of reversible, potent, and selective PrCP inhibitors was developed starting from a mechanism based design for inhibiting this serine protease. Compound 8o inhibits human and mouse PrCP at IC(50) values of 1 and 2 nM and is not active (IC(50) > 25 μM) against a panel of closely related proteases. It has lower serum binding than its close analogues and is bioavailable in mouse. Subchronic dosing of 8o in PrCP(-/-) and WT mice at 100 mg/kg for 5 days resulted in a 5% reduction in body weight in WT mice and a 1% reduction in PrCP KO mice.

Molecular dynamics study of prolyl oligopeptidase with inhibitor in binding cavity

We used the crystal structure of prolyl oligopeptidase (POP) with bound Z-pro-prolinal (ZPP) inhibitor (Protein Data Bank (PDB) structure 1QFS) to perform an intensive molecular dynamics study of the POP-ZPP complex. We performed 100 ns of simulation with the hemiacetal bond, through which the ZPP is bound to the POP, removed in order to better investigate the binding cavity environment. From basic analysis, measuring the radius of gyration, root mean square deviation, solvent accessible surface area and definition of the secondary structure of protein, we determined that the protein structure is highly stable and maintains its structure over the entire simulation time. This demonstrates that such long time simulations can be performed without the protein structure losing stability. We found that water bridges and hydrogen bonds play a negligible role in binding the ZPP thus indicating the importance of the hemiacetal bond. The two domains of the protein are bound by a set of approximately 12 hydrogen bonds, specific to the particular POP protein.