Inhibition of dipeptidyl peptidase IV by fluoroolefin-containing N-peptidyl-O-hydroxylamine peptidomimetics

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.

gem-Heteroatom-Substituted Fluoroalkenes as Mimics of Amide Derivatives or Phosphates: A Comprehensive Review

gem-Heteroatom-substituted fluoroalkenes have received little attention despite their great potential in medicinal chemistry or in fine chemistry. Indeed, due to the electronic and steric similarity between the fluoroalkene moiety and the amide bond as well as the high strength of the carbon-fluorine bond, these gem-heteroatom-substituted fluoroalkenes could be envisioned as stable mimics of various important organic functions, such as phosphates, carbamates, S-thiocarbamates and ureas. We present herein an overview describing the syntheses over the last decade of heteroatom-substituted fluoroalkenes in geminal position. This review will be divided into several sections covering each the common following heteroatom: oxygen-, nitrogen-, sulfur-, phosphorus-, boron- and silicon-substituted fluoroalkenes.

Palladium-catalyzed selective defluorinative sulfenylation for the synthesis of fluorovinylthioethers

An efficient transformation of trifluoromethylated benzyl bromides to monofluoroalkenes through Pd-catalyzed selective defluorinative sulfenylation is described.

Nickel-Catalyzed Defluorinative Reductive Cross-Coupling Reaction of gem-Difluoroalkenes with Thiosulfonate or Selenium Sulfonate

A nickel-catalyzed defluorinative reductive cross-coupling of gem-difluoroalkenes with thiosulfonate or selenosulfonates is described. The reaction involves the formation of thiolated or selenylated monofluoroolefins via regioselective C-F bond cleavage and C-S or C-Se bond formation and features easily available substrates, mild reaction conditions, and high E-selectivity. One of the derivatives by further cross coupling with PhMgBr exhibited an aggregation-induced emission enhancement effect.

Applications of amide isosteres in medicinal chemistry

Isosteric replacement of amide groups is a classic practice in medicinal chemistry. This digest highlights the applications of most commonly employed amide isosteres in drug design aiming at improving potency and selectivity, optimizing physicochemical and pharmacokinetic properties, eliminating or modifying toxicophores, as well as providing novel intellectual property of lead compounds.

Organic photoredox catalytic decarboxylative cross-coupling of gem-difluoroalkenes with unactivated carboxylic acids

The first redox neutral decarboxylative alkylation of gem-difluoroalkenes via C–F bond activation enabled by organic photoredox catalysis has been developed.

Visible-light-mediated defluorinative cross-coupling of gem-difluoroalkenes with thiols

Here we report a visible-light-mediated monofluoroalkenylation through defluorinative cross-coupling of gem-difluoroalkenes with aryl, benzyl, and alkyl thiols.

Synthesis of N-(α-fluorovinyl)azoles by the reaction of difluoroalkenes with azoles

A mild and versatile method for the construction of C-N bonds by the reaction of (2,2-difluorovinyl)arenes with various N-H-containing heterocycles in the presence of K3PO4 has been developed. The reaction proceeded efficiently at room temperature (25 °C) affording the (E)-N-α-fluorovinyl derivatives of azoles 3 in good to excellent yields with relatively high stereoselectivity.

Recent approaches to medicinal chemistry and therapeutic potential of dipeptidyl peptidase-4 (DPP-4) inhibitors

Dipeptidyl peptidase-4 (DPP-4) is one of the widely explored novel targets for Type 2 diabetes mellitus (T2DM) currently. Research has been focused on the strategy to preserve the endogenous glucagon like peptide (GLP)-1 activity by inhibiting the DPP-4 action. The DPP-4 inhibitors are weight neutral, well tolerated and give better glycaemic control over a longer duration of time compared to existing conventional therapies. The journey of DPP-4 inhibitors in the market started from the launch of sitagliptin in 2006 to latest drug teneligliptin in 2012. This review is mainly focusing on the recent medicinal aspects and advancements in the designing of DPP-4 inhibitors with the therapeutic potential of DPP-4 as a target to convey more clarity in the diffused data.

Fluorinated pseudopeptide analogues of the neuropeptide 26RFa: synthesis, biological, and structural studies

A series of four fluorinated dipeptide analogues each containing a fluoro-olefin moiety as peptide bond surrogate has been designed and synthesized. These motifs have been successfully introduced into the bioactive C-terminal heptapeptide of the neuropeptide 26RFa by conventional SPPS. We then evaluated the ability of the generated pseudopeptides to increase [Ca²⁺](i) in GPR103-transfected cells. For these fluorinated analogues, greater stability in human serum was observed. Their conformations were also investigated, leading to the valuable identification of differences depending on the position of the fluoro-olefin moiety in the sequence.

Inhibition of hepatitis C virus NS5A by fluoro-olefin based γ-turn mimetics

The HCV non-structural protein NS5A has been established as a viable target for the development of direct acting antiviral therapy. From computational modeling studies strong intra-molecular hydrogen bonds were found to be a common structural moiety within known NS5A inhibitors that have low pico-molar replicon potency. Efforts to reproduce these γ-turn-like substructures provided a novel NS5A inhibitor based on a fluoro-olefin isostere. This fluoro-olefin containing inhibitor exhibited picomolar activity (EC(50)=79 pM) against HCV genotype 1b replicon without measurable cytotoxicity. This level of activity is comparable to the natural peptide-based inhibitors currently under clinic evaluation, and demonstrates that a peptidomimetic approach can serve as a useful strategy to produce potent and structurally unique inhibitors of HCV NS5A.

Chitosan-based therapeutic nanoparticles for combination gene therapy and gene silencing of in vitro cell lines relevant to type 2 diabetes

Glucagon like peptide 1 (GLP-1), a blood glucose homeostasis modulating incretin, has been proposed for the treatment of type 2 diabetes mellitus (T2DM). However, native GLP-1 pharmacokinetics reveals low bioavailability due to degradation by the ubiquitous dipeptydil peptidase IV (DPP-IV) endoprotease. In this study, the glucosamine-based polymer chitosan was used as a cationic polymer-based in vitro delivery system for GLP-1, DPP-IV resistant GLP-1 analogues and siRNA targeting DPP-IV mRNA. We found chitosans to form spherical nanocomplexes with these nucleic acids, generating two distinct non-overlapping size ranges of 141-283 nm and 68-129 nm for plasmid and siRNA, respectively. The low molecular weight high DDA chitosan 92-10-5 (degree of deacetylation, molecular weight and N:P ratio (DDA-Mn-N:P)) showed the highest plasmid DNA transfection efficiency in HepG2 and Caco-2 cell lines when compared to 80-10-10 and 80-80-5 chitosans. Recombinant native GLP-1 protein levels in media of transfected cells reached 23 ng/L while our DPP-IV resistant analogues resulted in a fivefold increase of GLP-1 protein levels (115 ng/L) relative to native GLP-1, and equivalent to the Lipofectamine positive control. We also found that all chitosan-DPP-IV siRNA nanocomplexes were capable of DPP-IV silencing, with 92-10-5 being significantly more effective in abrogating enzymatic activity of DPP-IV in media of silenced cells, and with no apparent cytotoxicity. These results indicate that specific chitosan formulations may be effectively used for the delivery of plasmid DNA and siRNA in a combination therapy of type 2 diabetes.

Amino acid-based synthesis of trifluoromethylalkene dipeptide isosteres by alcohol-assisted nucleophilic trifluoromethylation and organozinc-copper-mediated S(N)2' alkylation

A novel synthetic approach to Xaa-Yaa-type (Z)-trifluoromethylalkene dipeptide isostere (CF(3)-ADI) has been developed. Starting from readily available l-phenylalanine and l-alanine, several CF(3)-ADIs were obtained through nucleophilic trifluoromethylation of gamma-keto esters and S(N)2' alkylation of trifluoromethylated mesylates. The influence of a trifluoromethyl group on the diastereoselectivity of the S(N)2' reaction is also discussed.

Fluoroolefins as peptide mimetics: a computational study of structure, charge distribution, hydration, and hydrogen bonding

The design of peptide mimetic compounds is greatly facilitated by the identification of functionalities that can act as peptide replacements. The fluoroalkene moiety has recently been employed for that purpose. The purpose of this work is to characterize prototypical fluoroalkenes (fluoroethylene and 2-fluoro-2-butene) with respect to key properties of peptides (amides) including structure, charge distribution, hydration, and hydrogen bonding. The results are compared to those obtained for model peptides (formamide, N-methylacetamide). Calculations have been carried out at the MP2 and B3LYP levels of theory with the 6-311++G(2d,p) and 6-311++G(2d,2p) basis sets. The results suggest that the fluoroalkene is similar in steric requirements to a peptide bond but that there is less charge separation. Calculations of the hydration free energies with the PCM bulk continuum solvent model indicate that the fluoroalkene has much smaller hydration free energies than an amide but that the difference in solvation free energy for cis and trans isomers is comparable. In studies of complexes with water molecules, the fluoroalkene is found to engage in interactions that are analogous to backbone hydrogen-bonding interactions that govern many properties of natural peptides and proteins but with smaller interaction energies. In addition, key structural differences are noted when the fluoroalkene is playing the role of hydrogen-bond acceptor which may have implications in binding, aggregation, and conformational preferences in fluoroalkene peptidomimetics. The issue of cooperativity in hydrogen-bonding interactions in complexes with multiple waters has also been investigated. The fluoroalkene is found to exhibit cooperative effects that mirror those of the peptide but are smaller in magnitude. Thus, pairwise addivitity of interactions appears to more adequately describe the fluoroalkenes than the peptides they are intended to mimic.

Fmoc-based solid-phase synthesis of GPR54-agonistic pentapeptide derivatives containing alkene- and fluoroalkene-dipeptide isosteres

Fmoc-protected Phe-Gly-type (Z)-alkene dipeptide isostere (ADI) and (E)-fluoroalkene dipeptide isostere (FADI) were synthesized and applied to Fmoc-based solid-phase peptide synthesis (SPPS). These cis-peptide bond mimetics were introduced into a bioactive pentapeptide [H-Amb-Phe-Gly-Leu-Arg-Trp-NH(2); Amb = 4-(aminomethyl) benzoic acid], which has potent GPR54 agonistic activity. The resulting pentapeptide derivatives showed low GPR54 agonistic activity, as compared with the parent peptide and (E)-ADI-containing derivative. This suggests that the trans-amide conformer of Phe-Gly peptide bond of the parent peptide would be significantly important for bioactivity. Contrary to our expectations, a (Z)-FADI-containing derivative exhibited essentially no activity, revealing the necessity of critical validation of FADI-bioisosterism.

Chiral dipeptide mimics possessing a fluoroolefin moiety: a relevant tool for conformational and medicinal studies

The replacement of the amide bond in a peptide backbone is a promising strategy in peptidomimetic drug research. Over the various amide bond surrogates, the fluoroolefin moiety has been successfully developed as an effective mimic. Today, fluorine-containing compounds account for a large proportion of new active molecules in life sciences. The synthesis of fluoroolefin peptide mimics is not a trivial task and innovative approaches often need to be addressed, in particular for the stereocontrol of the double bond configuration and the chiral centres adjacent to the fluoroalkene. These fluorinated peptidomimetics have been synthesised and evaluated as metabolically stable and/or conformationally constrained analogs of enzyme inhibitors, and as tools for probing the function, structure, and binding process of receptors.

Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Dipeptidyl-peptidase IV/CD26 (DPP IV) is a cell-surface protease belonging to the prolyloligopeptidase family. It selectively removes the N-terminal dipeptide from peptides with proline or alanine in the second position. Apart from its catalytic activity, it interacts with several proteins, for instance, adenosine deaminase, the HIV gp120 protein, fibronectin, collagen, the chemokine receptor CXCR4, and the tyrosine phosphatase CD45. DPP IV is expressed on a specific set of T lymphocytes, where it is up-regulated after activation. It is also expressed in a variety of tissues, primarily on endothelial and epithelial cells. A soluble form is present in plasma and other body fluids. DPP IV has been proposed as a diagnostic or prognostic marker for various tumors, hematological malignancies, immunological, inflammatory, psychoneuroendocrine disorders, and viral infections. DPP IV truncates many bioactive peptides of medical importance. It plays a role in glucose homeostasis through proteolytic inactivation of the incretins. DPP IV inhibitors improve glucose tolerance and pancreatic islet cell function in animal models of type 2 diabetes and in diabetic patients. The role of DPP IV/ CD26 within the immune system is a combination of its exopeptidase activity and its interactions with different molecules. This enables DPP IV/CD26 to serve as a co-stimulatory molecule to influence T cell activity and to modulate chemotaxis. DPP IV is also implicated in HIV-1 entry, malignant transformation, and tumor invasion.

The crystal structure of dipeptidyl peptidase IV (CD26) reveals its functional regulation and enzymatic mechanism

The membrane-bound glycoprotein dipeptidyl peptidase IV (DP IV, CD26) is a unique multifunctional protein, acting as receptor, binding and proteolytic molecule. We have determined the sequence and 1.8 A crystal structure of native DP IV prepared from porcine kidney. The crystal structure reveals a 2-2-2 symmetric tetrameric assembly which depends on the natively glycosylated beta-propeller blade IV. The crystal structure indicates that tetramerization of DP IV is a key mechanism to regulate its interaction with other components. Each subunit comprises two structural domains, the N-terminal eight-bladed beta-propeller with open Velcro topology and the C-terminal alpha/beta-hydrolase domain. Analogy with the structurally related POP and tricorn protease suggests that substrates access the buried active site through the beta-propeller tunnel while products leave the active site through a separate side exit. A dipeptide mimicking inhibitor complexed to the active site discloses key determinants for substrate recognition, including a Glu-Glu motif that distinguishes DP IV as an aminopeptidase and an oxyanion trap that binds and activates the P(2)-carbonyl oxygen necessary for efficient postproline cleavage. We discuss active and nonactive site-directed inhibition strategies of this pharmaceutical target protein.

Inhibition of dipeptidyl peptidase IV (DPP IV) by 2-(2-amino-1-fluoro-propylidene)-cyclopentanecarbonitrile, a fluoroolefin containing peptidomimetic

Novel, potent inhibitors of dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5, CD26), containing the fluoroolefin peptide isostere psi [CFz.dbnd6;C], have been prepared via the intermediacy of the Peterson fluoroolefination reaction. The nitrile containing inhibitors were found to inhibit dipeptidyl peptidase IV competitively with K(i) values for the l-3 and u-3 inhibitors of 7.69 and 6.03 microM, respectively. In contrast to earlier reported fluoroolefin containing inhibitors, the nitriles underwent no detectable degradation at pH 7.6 under buffered conditions.