Synthesis of aldehydic peptides inhibiting renin

Concise Chemoenzymatic Total Synthesis and Identification of Cellular Targets of Cepafungin I

The natural product cepafungin I was recently reported to be one of the most potent covalent inhibitors of the 20S proteasome core particle through a series of in vitro activity assays. Here, we report a short chemoenzymatic total synthesis of cepafungin I featuring the use of a regioselective enzymatic oxidation to prepare a key hydroxylated amino acid building block in a scalable fashion. The strategy developed herein enabled access to a chemoproteomic probe, which in turn revealed the exceptional selectivity and potency of cepafungin I toward the β2 and β5 subunits of the proteasome. Further structure-activity relationship studies suggest the key role of the hydroxyl group in the macrocycle and the identity of the lipid tail in modulating the potency of this natural product family. This study lays the groundwork for further medicinal chemistry exploration to fully realize the anticancer potential of cepafungin I.

Design of peptidase-resistant peptide inhibitors of myosin light chain kinase

Myosin light chain kinase (MLCK) is a key regulator of various forms of cell motility including smooth muscle contraction, cell migration, cytokinesis, receptor capping, secretion, etc. Inhibition of MLCK activity in endothelial and epithelial monolayers using cell-permeant peptide Arg-Lys-Lys-Tyr-Lys-Tyr-Arg-Arg-Lys (PIK, Peptide Inhibitor of Kinase) allows protecting the barrier capacity, suggesting a potential medical use of PIK. However, low stability of L-PIK in a biological milieu prompts for development of more stable L-PIK analogues for use as experimental tools in basic and drug-oriented biomedical research. Previously, we designed PIK1, H-(N^α Me)Arg-Lys-Lys-Tyr-Lys-Tyr-Arg-Arg-Lys-NH₂ , that was 2.5-fold more resistant to peptidases in human plasma in vitro than L-PIK and equal to it as MLCK inhibitor. In order to further enhance proteolytic stability of PIK inhibitor, we designed the set of six site-protected peptides based on L-PIK and PIK1 degradation patterns in human plasma as revealed by ¹ H-NMR analysis. Implemented modifications increased half-live of the PIK-related peptides in plasma about 10-fold, and these compounds retained 25-100% of L-PIK inhibitory activity toward MLCK in vitro. Based on stability and functional activity ranking, PIK2, H-(N^α Me)Arg-Lys-Lys-Tyr-Lys-Tyr-Arg-D-Arg-Lys-NH₂ , was identified as the most stable and effective L-PIK analogue. PIK2 was able to decrease myosin light chain phosphorylation in endothelial cells stimulated with thrombin, and this effect correlated with the inhibition by PIK2 of thrombin-induced endothelial hyperpermeability in vitro. Therefore, PIK2 could be used as novel alternative to other cell-permeant inhibitors of MLCK in cell culture-based and in vivo studies where MLCK catalytic activity inhibition is required. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

The epimerization of peptide aldehydes—a systematic study

Peptide aldehydes are interesting targets as enzyme inhibitors, and can be used for pseudopeptide chemistry or ligation. However, they are known to be subjected to epimerization during synthesis or purification. By (1)H NMR, a model dipeptide aldehyde can be used to check the possible epimerization occurring during synthesis. Various purification methods were investigated, but none was free from epimerization.

Synthesis of peptide aldehydes

The functionalization of peptides and proteins by aldehyde groups has become the subject of intensive research since the discovery of the inhibition properties of peptide aldehydes towards various enzymes. Furthermore, peptide aldehydes are of great interest for peptide backbone modification or ligation reactions. This review focuses upon their synthesis, which has been developed following two main strategies. The first strategy consists of prior synthesis of the peptide, followed by the introduction of the aldehyde function. The second possible strategy uses alpha-amino aldehydes as starting materials. After protection of the aldehyde, peptide elongation occurs. At the end of the synthesis, the aldehyde function can be unmasked.

A C-terminal aldehyde insect kinin analog enhances inhibition of weight gain and induces significant mortality in Helicoverpa zea larvae

The first reported examples of C-terminal aldehyde analogs of an insect neuropeptide are described. They are hexapeptide insect kinin analogs Boc-VFFPWG-H and Fmoc-RFFPWG-H. Activity observed for these modified analogs in an in vitro insect diuretic assay confirms that the C-terminal aldehyde group is tolerated by an insect kinin receptor. The two analogs demonstrate greatly enhanced activity over standard C-terminal amide insect kinins in a larval weight gain inhibition assay in the corn earworm Helicoverpa zea. Treatment with Boc-VFFPWG-H led to significant increases in larval mortality at doses of 500pm (45%) and 5nm (67%). Boc-VFFPWG-H represents a lead analog in the development of novel, environmentally friendly pest insect management agents based on the insect kinin class of neuropeptides.

Post-synthesis incorporation of a lipidic side chain into a peptide on solid support

A new strategy for the synthesis of lipopeptides has been developed. Using Weinreb (N-methoxy, N-methyl) amide as an aldehyde function precursor on the side chains of Asp or Glu residues, this new strategy avoids the synthesis of a lipidic amino acid residue before its incorporation in the peptide sequence. The aldehyde generated on the solid support can react with ylides leading to unsaturated or saturated side chains or with various nucleophiles to yield non-coded amino acid residues incorporated into the sequence.

Functionalization of peptides and proteins by aldehyde or keto groups

The functionalization of peptides and proteins by aldehyde or keto groups has become the subject of intensive research since the discovery of the inhibition properties of peptide aldehydes and the advent of protein engineering. The first part of this review focuses upon the tremendous efforts devoted to the solid-phase synthesis of peptide aldehydes as protease inhibitors. The second part describes the utility of the aldehyde or keto functionalities for the site-specific modification of peptides or proteins.

Role of IkappaBalpha ubiquitination in signal-induced activation of NFkappaB in vivo

In unstimulated cells, the transcription factor NF-kappaB is held in the cytoplasm in an inactive state by the inhibitor protein IkappaBalpha. Stimulation of cells results in rapid phosphorylation and degradation of IkappaBalpha, thus releasing NF-kappaB, which translocates to the nucleus and activates transcription of responsive genes. Here we demonstrate that in cells where proteasomal degradation is inhibited, signal induction by tumor necrosis factor alpha results in the rapid accumulation of higher molecular weight forms of IkappaBalpha that dissociate from NF-kappaB and are consistent with ubiquitin conjugation. Removal of the high molecular weight forms of IkappaBalpha by a recombinant ubiquitin carboxyl-terminal hydrolase and reactivity of the immunopurified material with a monoclonal antibody specific for ubiquitin indicated that IkappaBalpha was conjugated to multiple copies of ubiquitin. Western blot analysis of immunopurified IkappaBalpha from cells expressing epitope-tagged versions of IkappaBalpha and ubiquitin revealed the presence of multiple copies of covalently bound tagged ubiquitin. An S32A/S36A mutant of IkappaBalpha that is neither phosphorylated nor degraded in response to signal induction fails to undergo inducible ubiquitination in vivo. Thus signal-induced activation of NF-kappaB involves phosphorylation-dependent ubiquitination of IkappaBalpha, which targets the protein for rapid degradation by the proteasome and releases NF-kappaB for translocation to the nucleus.

14-membered cyclic opioids related to dermorphin and their partially retro-inverso modified analogues. I. Synthesis and biological activity

As a continuation of our program to study structure-activity relationships of opiate peptides, we report the syntheses and biological activities of a series of 14-membered cyclic dermorphin analogues closely related to enkephalin analogue Tyr-c[D-A2bu-Gly-Phe-Leu] incorporating a phenylalanine at the third position in place of glycine. In addition to two parent dermorphin analogues Tyr-c[D-A2bu-Phe-Phe-(L and D)-Leu], four stereoisomeric retro-inverso modified analogues Tyr-c[D-A2bu-Phe-gPhe-(S and R)-mLeu] with a reversed amide bond between residues four and five, and Tyr-c[D-Glu-Phe-gPhe-(L and D)-rLeu] with two reversed amide bonds between residues four and five, and between residue five and the side chain of residue two have been synthesized. The results from the guinea pig ileum (GPI) and mouse vas deferens (MVD) assays show that all analogues are superactive at either one or both opiate receptors and in general display higher activities as compared to the corresponding enkephalin analogues with a glycine at the third position. Results from the in vitro biological assays and conformational analysis using 1H-NMR spectroscopy (adjoining paper) will provide useful information to understand the role of the Phe3 aromatic side chain in dermorphin, and that of the Phe4 aromatic side chain in enkephalin, on opiate activity since these cyclic dermorphin analogues contain two Phe residues at both the third and fourth positions.

Proteinases and their inhibitors in cells and tissues

A large body of evidence has been assembled to indicate the substantial importance of proteolytic processes in various physiological functions. It has recently become clear too that endo-acting peptide bond hydrolases provisionally characterized and classified at present as serine, cysteine, aspartic and metallo together with unknown catalytic mechanism proteinases sometimes act in cascades. They are controlled by natural proteinase inhibitors present in cells and body fluids. In the first part of the present monograph the author was concerned to present an overview on the morphological and physiological approach to localization, surveying reaction principles and methods suitable for visualization of proteolytic enzymes and their natural and synthetic inhibitors. In the second part the roles played by proteinases have been summarized from the point of view of cell biology. The selection of earlier and recent data reviewed on the involvement of proteolysis in the behavior of individual cells reveals that enzymes, whether they be exogeneous or intrinsic, can be effective and sensitive modulators of cellular growth and morphology. There exists a close correlation between malignant growth and degradation of cells. It appears likely that as yet unknown or at least so far inadequately characterized factors that influence the survival or the death of cells may turn out to be proteinases. The causal role of extracellular proteolysis in cancer cell metastases, in stopping cancer cell growth and in cytolysis remains for further investigated. Ovulation, fertilization and implantation are basic biological functions in which proteolytic enzymes play a key role. The emergence of new approaches in reproductive biology and a growing factual basis will inevitably necessitate a reevaluation of present knowledge of proteolytic processes involved. The molecular aspects of intracellular protein catabolism have been discussed in terms of the inhibition of lysosomal and/or non-lysosomal protein breakdown. Peptide and protein hormone biosynthesis and inactivation are still at the centre of interest in cell biology, and a number of proteinases have been implicated in both processes. A number of conjectures partly based on the author's own work have been discussed which suggest the possibility of the involvement of proteolysis in exocytosis and endocytosis. The author's optimistic conclusion is that through the common action of biochemists, cell biologists, cytochemists, and pharmacologists the mystery of cellular proteolysis is beginning to be solved.

Inhibition of cathepsin B by peptidyl aldehydes and ketones: slow-binding behavior of a trifluoromethyl ketone

Inhibition of the cysteine proteinase cathepsin B by a series of N-benzyloxycarbonyl-L-phenylalanyl-L-alanine ketones and the analogous aldehyde has been investigated. Surprisingly, whereas the aldehyde was found to be almost as potent a competitive reversible inhibitor as the natural peptidyl aldehyde, leupeptin, the corresponding trifluoromethyl ketone showed comparatively weak (and slow-binding) reversible inhibition. Evaluation of competitive hydration and hemithioketal formation in a model system led to a structure-activity correlation spanning several orders of magnitude in both cathepsin B inhibition constants (Ki) and model system equilibrium data (KRSH,apparent).