Determining the Predominant Conformations of Mortiamides A-D in Solution Using NMR Data and Molecular Modeling Tools.

Macrocyclic peptidomimetics have been seriously contributing to our arsenal of drugs to combat diseases. The search for nature's discoveries led us to mortiamides A-D (found in a novel fungus from Northern Canada), which is a family of cyclic peptides that clearly have demonstrated impressive pharmaceutical potential. This prompted us to learn more about their solution-state properties as these are central for binding to target molecules. Here, we secured and isolated mortiamide D, and then acquired high-resolution nuclear magnetic resonance (NMR) data to learn more about its structure and dynamics attributes. Sets of two-dimensional NMR experiments provided atomic-level (through-bond and through-space) data to confirm the primary structure, and NMR-driven molecular dynamics (MD) simulations suggested that more than one predominant three-dimensional (3D) structure exist in solution. Further steps of MD simulations are consistent with the finding that the backbones of mortiamides A-C also have at least two prominent macrocyclic shapes, but the side-chain structures and dynamics differed significantly. Knowledge of these solution properties can be exploited for drug design and discovery.

Chemical Composition and Antiplasmodial Activity of the Essential Oil of Rhododendron subarcticum Leaves from Nunavik, Québec, Canada.

Dwarf Labrador tea, Rhododendron subarcticum Harmaja, is a popular medicinal plant in use by First Nations of Northern Canada, but its phytochemistry has remained largely unexplored. We have isolated and characterized the essential oil from a population of this species harvested near the treeline in Nunavik, Québec. Analyses by gas chromatography-mass spectrometry (GC-MS) and gas chromatography/flame-ionization detection (GC/FID) led to the identification of 53 compounds; the main secondary metabolites were ascaridole (64.7% of the total FID area) and p-cymene (21.1%). Such a composition resembles a chemotype observed for R. tomentosum, a close relative found mainly in Europe and Asia, but has never been attributed to R. subarcticum. Growth inhibition assays against different strains of Plasmodium falciparum (3D7, Dd2), the parasite responsible for the most severe form of malaria, were conducted with either the R. subarcticum's essential oil or the isolated ascaridole. Our results show that the essential oil's biological activity can be attributed to ascaridole as its IC50 is more than twice that of ascaridole [ascaridole's IC50 values are 147.3 nM (3D7) and 104.9 nM (Dd2)].

Squaramide Tethered Clindamycin, Chloroquine, and Mortiamide Hybrids: Design, Synthesis, and Antimalarial Activity.

Malaria remains one of the major health problems in the world. In this work, a series of squaramide tethered chloroquine, clindamycin, and mortiamide D hybrids have been synthesized to assess their in vitro antiplasmodial activity against 3D7 (chloroquine-sensitive) and Dd2 strains of Plasmodium falciparum. The most active compound, a simple chloroquine analogue, displayed low nanomolar IC50 value against both strains (3 nM for 3D7 strain and 18 nM for Dd2 strain). Moreover, all molecular hybrids incorporating the hydroxychloroquine scaffold showed the most potent activities, exemplified with a chloroquine dimer, IC50 = 31 nM and 81 nM against 3D7 and Dd2 strains, respectively. These results highlight the first time use of clindamycin and mortiamide D as antimalarial molecular hybrids and establish these valuable hits for future optimization.

Characterization of the Volatilome of Tuber canaliculatum Harvested in Quebec, Canada.

The first detailed characterization of volatile compounds from Tuber canaliculatum, a truffle newly grown in Quebec, Canada, was performed with headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC/MS). A total of 30 compounds were identified, making up more than 98% of the volatile extract. The volatilome of T. canaliculatum is dominated by (E)-1-methylthio-1-propene, (Z)-1-methylthio-1-propene, dimethyl disulfide, and 1-octen-3-ol. It also includes six compounds identified for the first time in truffles, namely, 4-hydroxy-4-methyl-2-pentanone, pentyl propanoate, (Z)-1-methyl-2-(prop-1-en-1-yl)disulfide, (E)-1-methyl-2-(prop-1-en-1-yl)disulfide, (Z)-1-methyl-3-(prop-1-en-1-yl)trisulfide, and (E)-1-methyl-3-(prop-1-en-1-yl)trisulfide. With the growing interest in gastronomy in truffles in North America, it is becoming important to gather knowledge for identification purposes and to delineate the key volatile compounds responsible for the aroma of North American truffles, especially the newly harvested T. canaliculatum.

Antipsoriatic Potential of Quebecol and Its Derivatives.

Psoriasis is a chronic inflammatory skin disease mainly characterized by the hyperproliferation and abnormal differentiation of the epidermal keratinocytes. An interesting phenolic compound, namely quebecol (2,3,3-tri-(3-methoxy-4-hydroxyphenyl)-1-propanol) (compound 1, CPD1), was isolated from maple syrup in 2011 and was recently synthesized. Quebecol and its derivatives ethyl 2,3,3-tris(3-hydroxy-4-methoxyphenyl)propenoate (compound 2, CPD2) and bis(4-hydroxy-3-methoxyphenyl)methane (compound 3, CPD3) have shown antiproliferative and anti-inflammatory potential, making them promising candidates for the treatment of psoriasis. This study aimed to evaluate the antipsoriatic potential of quebecol and its derivatives on psoriatic skin substitutes produced according to the self-assembly method. A sulforhodamine B (SRB) assay determining the concentration that inhibits 20% of cell growth (IC20) was performed for CPD1, CPD2 and CPD3, and their IC20 values were 400, 150 and 350 µM, respectively. At these concentrations, cell viability was 97%, 94% and 97%, respectively. The comparative control methotrexate (MTX) had a cell viability of 85% at a concentration of 734 µM. Histological analyses of psoriatic skin substitutes treated with CPD1, CPD2 and CPD3 exhibited significantly reduced epidermal thickness compared with untreated psoriatic substitutes, which agreed with a decrease in keratinocyte proliferation as shown by Ki67 immunofluorescence staining. The immunofluorescence staining of differentiation markers (keratin 14, involucrin and loricrin) showed improved epidermal differentiation. Taken together, these results highlight the promising potential of quebecol and its derivatives for the treatment of psoriasis.

Chemical Composition of the Unexplored Volatile Fraction of Betula glandulosa, a Prevalent Shrub in Nunavik, Québec.

The volatile fraction of the leaves of Betula glandulosa Michx. has been investigated for its secondary metabolite composition by GC/MS and GC/FID. The rapid expansion of this shrub species in subarctic landscapes, like the ones found in Nunavik (Northern Québec, Canada), highly impacts ecosystem dynamics. Yet, despite its abundance, few phytochemical investigations have yet been conducted on this species. In this study, we present the first phytochemical investigation of the volatile metabolites of B. glandulosa leaves. Although no essential oil was isolated, volatile compounds were extracted from the hydrosol by steam distillation. The main metabolites observed were linalool (14.6-19.0 %), C6 oxylipins (known as green leaf volatiles, GLV; total of 18.2-40.2 %), eugenol (1.6-8.6 %) and α-terpineol (3.3-4.8 %). Dwarf birch is an important food source for insects and herbivores, so knowledge of its metabolite composition could help understand parts of its functional role in subarctic ecosystems. The composition of the volatile fraction could serve as marker for differentiating B. glandulosa from other dwarf birch species like Betula nana L.

Membrane binding properties of the C-terminal segment of retinol dehydrogenase 8.

Light absorption by rhodopsin leads to the release of all-trans retinal (ATRal) in the lipid phase of photoreceptor disc membranes. Retinol dehydrogenase 8 (RDH8) then reduces ATRal into all-trans retinol, which is the first step of the visual cycle. The membrane binding of RDH8 has been postulated to be mediated by one or more palmitoylated cysteines located in its C-terminus. Different peptide variants of the C-terminus of RDH8 were thus used to obtain information on the mechanism of membrane binding of this enzyme. Steady-state and time-resolved fluorescence measurements were performed using short and long C-terminal segments of bovine RDH8, comprising one or two tryptophan residues. The data demonstrate that the amphipathic alpha helical structure of the first portion of the C-terminus of RDH8 strongly contributes to its membrane binding, which is also favored by palmitoylation of at least one of the cysteines located in the last portion of the C-terminus.

Development of sulfahydantoin derivatives as ß-lactamase inhibitors.

Sulfahydantoin-based molecules may provide a means to counteract antibiotic resistance, which is on the rise. These molecules may act as inhibitors of ß-lactamase enzymes, which are key in some resistance mechanisms. In this paper, we report on the synthesis of 6 novel sulfahydantoin derivatives by the key reaction of chlorosulfonyl isocyanate to form α-amino acid derived sulfamides, and their cyclization into sulfahydantoins. The synthesis is rapid and provides the target compounds in 8 steps. We investigated their potential as ß-lactamase inhibitors using two common Class A ß-lactamases, TEM-1 and the prevalent extended-spectrum TEM-15. Two compounds, 3 and 6, show substantial inhibition of the ß-lactamases with IC50 values between 130 and 510 µM and inferred Ki values between 32 and 55 µM.

Preventing Candida albicans biofilm formation using aromatic-rich piperazines.

The global increase in microbial resistance is an imminent threat to public health. Effective treatment of infectious diseases now requires new antimicrobial therapies. We report herein the discovery of aromatic-rich piperazines that inhibit biofilm formation by C. albicans. 22 piperazines, including 16 novel ones, were prepared efficiently using a combination of solid- and solution phase synthesis. The most potent compound prevents morphological switching under several hypha-inducing conditions and reduces C. albicans' ability to adhere to epithelial cells. These processes are essential to the development of Candida biofilms, which are associated with its increased resistance to immune defenses and antifungal agents.

Total Synthesis and Antimalarial Activity of Dominicin, a Cyclic Octapeptide from a Marine Sponge.

Dominicin, a macrocyclic peptide isolated from the marine sponge Eurypon laughlini, has been synthesized for the first time by solid-phase peptide synthesis. The strategy uses oxime resin and takes advantage of the nucleophile susceptibility of the oxime ester bond. The synthesis relies on the preparation of a linear precursor followed by on-resin head-to-tail concomitant cyclization-cleavage. This is the first report of the use of a Boc/OtBu biorthogonal protection strategy on oxime resin to facilitate concomitant N-terminal and side-chain tert-butyl ether deprotection cyclization of unprotected peptides. Also, we report the first antimalarial investigation of dominicin. Interestingly, the natural macrocyclic peptide demonstrates effective low micromolar activity (1.8 µM) against the chloroquine-mefloquine-pyrimethamine-resistant Dd2 strain of Plasmodium falciparum.

Structure of a Parkinson's Disease-Involved α-Synuclein Peptide Is Modulated by Membrane Composition and Physical State.

α-Synuclein (AS), the protein responsible for Parkinson's disease, contains a 12-residue-long sequence, AS71-82, that is thought to play a crucial role in the α-synuclein aggregation process. Neuronal membranes are direct interacting partners of α-synuclein and play a role in fibrillogenesis by providing a charged catalytic surface, notably from anionic phospholipids. However, details are lacking regarding the impact of membrane composition and the driving forces leading to membrane anchorage and peptide structure conversion. To decipher the interplay of α-synuclein with neuronal membranes, the structure of AS71-82 was investigated in the presence of anionic model membranes. Infrared (IR) spectroscopy and solid-state nuclear magnetic resonance data show that AS71-82 adopts a perfectly in-register parallel ß-sheet structure with fibrillar morphology upon interactions with anionic model membranes. IR thermotropism experiments conducted with several membrane compositions revealed that the phospholipids' phase transition induces a rearrangement of the AS71-82 ß-sheet structure. In contrast, membranes are not significantly affected by the presence of AS71-82, which advocates for the amyloid fibrils to lie loosely on the membrane surface. The results bring new arguments for the lipid-sensing capabilities of AS71-82 and revealed its protofibrillar structure. The striking similarities between AS71-82 and α-synuclein make it a potential good aggregation inhibitor upon chemical modifications.

Crown ether modified peptides: Length and crown ring size impact on membrane interactions.

Antimicrobial peptides are widely studied as an alternative to traditional antibiotics. However, they are difficult to develop, as multiple factors influence their potency and selectivity toward bacterial cells. In this paper, we investigate three simplified model peptides that bear crown ethers, and the effects of simple structural modifications (peptide length and crown ether ring size) on their secondary structures and their permeabilizing activity on living cells and model membranes made with egg yolk phosphatidylcholine or 1-palmitoyl-2-oleoylphosphatidylglycerol. Circular dichroism studies show that the peptide length and the crown ether ring size do influence the conformation, but no trend could be determined from the results. Permeabilization studies with model membranes and with red blood cells demonstrated that from 13 residues to 16 residues, there is a gradual increase in activity as the peptides get longer. However, the shortest tested analogs, with 12 residues, also exhibited an increase in activity caused by the removal of one amino acid that was bearing a crown ether. Permeabilization assays showed that larger ring size analogs showed higher hemolytic activities. Altogether, the results reported help design new and more selective antimicrobial peptides.

Synthesis of C-terminal glycopeptides via oxime resin aminolysis.

Natural glycopeptides have been shown to possess interesting biological activities. In this work, we have developed a general solid-phase approach to C-terminal glycopeptides. Taking advantage of oxime resin ester bond nucleophile susceptibility, we optimised the nucleophilic cleavage step with glycosylamines and demonstrated the generality and scope of this method. In addition, this reaction has high functional group tolerance and can be used for the preparation of longer C-terminal glycopeptides, demonstrated with the synthesis of a glycododecapeptide in one single step. The results pave the way to access efficiently novel medically relevant compounds.

Total synthesis and antimalarial activity of mortiamides A-D.

Mortiamides A-D (1-4) are head-to-tail cyclic heptapeptides that were identified from a novel Mortierella sp. isolate obtained from marine sediments from Northern Canada. Herein we report the first total synthesis of mortiamides A-D (1-4) on a solid support by concomitant cyclization/cleavage without any oligomerization side reactions, and overall yields up to 48%. We also report on the antiplasmodial activity of mortiamides A-D (1-4). We show that three out of the four tested mortiamides (A, B and D) have moderate antiplasmodial activity, while mortiamide D (4) exhibits low micromolar activity.

Anti-biofilm and anti-adherence properties of novel cyclic dipeptides against oral pathogens.

Microorganisms embedded in a biofilm are significantly more resistant to antimicrobial agents and the defences of the human immune system, than their planktonic counterpart. Consequently, compounds that can inhibit biofilm formation are of great interest for novel therapeutics. In this study, a screening approach was used to identify novel cyclic dipeptides that have anti-biofilm activity against oral pathogens. Five new active compounds were identified that prevent biofilm formation by the cariogenic bacterium Streptococcus mutans and the pathogenic fungus Candida albicans. These compounds also inhibit the adherence of microorganisms to a hydroxylapatite surface. Further investigations were conducted on these compounds to establish the structure-activity relationship, and it was deduced that the common cleft pattern is required for these molecules to act effectively against biofilms.

Lobaric acid and pseudodepsidones inhibit NF-κB signaling pathway by activation of PPAR-γ.

Herein we report the anti-inflammatory activity of lobaric acid and pseudodepsidones isolated from the nordic lichen Stereocaulon paschale. Lobaric acid (1) and three compounds (2, 7 and 9) were found to inhibit the NF-κB activation and the secretion of pro-inflammatory cytokines (IL-1ß and TNF-α) in LPS-stimulated macrophages. Inhibition and docking simulation experiments provided evidence that lobaric acid and pseudodepsidones bind to PPAR-γ between helix H3 and the beta sheet, similarly to partial PPAR-γ agonists. These findings suggest that lobaric acid and pseudodepsidones reduce the expression of pro-inflammatory cytokines by blocking the NF-κB pathway via the activation of PPAR-γ.

A novel route towards cycle-tail peptides using oxime resin: teaching an old dog a new trick.

Two anabaenopeptins, Schizopeptin 791 and anabaenopeptin NZ825, have similar structural features and have been synthesized via a novel acid-catalyzed head-to-side-chain concomitant cyclization/cleavage reaction on oxime resin. The methodology gave rapid access to the anabaenopeptin scaffold by taking advantage of a combined solid-phase/solution-phase synthetic strategy. Also, as side-products of the synthesis, large C2-symmetric 38-member cyclic peptides ring bearing two endocyclic lysine side-chains were isolated, constituting a novel cyclic peptide scaffold.

Direct Phosphorylation of SRC Homology 3 Domains by Tyrosine Kinase Receptors Disassembles Ligand-Induced Signaling Networks.

Phosphotyrosine (pTyr) signaling has evolved into a key cell-to-cell communication system. Activated receptor tyrosine kinases (RTKs) initiate several pTyr-dependent signaling networks by creating the docking sites required for the assembly of protein complexes. However, the mechanisms leading to network disassembly and its consequence on signal transduction remain essentially unknown. We show that activated RTKs terminate downstream signaling via the direct phosphorylation of an evolutionarily conserved Tyr present in most SRC homology (SH) 3 domains, which are often part of key hub proteins for RTK-dependent signaling. We demonstrate that the direct EPHA4 RTK phosphorylation of adaptor protein NCK SH3s at these sites results in the collapse of signaling networks and abrogates their function. We also reveal that this negative regulation mechanism is shared by other RTKs. Our findings uncover a conserved mechanism through which RTKs rapidly and reversibly terminate downstream signaling while remaining in a catalytically active state on the plasma membrane.

Revisiting the Juliá-Colonna enantioselective epoxidation: supramolecular catalysis in water.

We describe an efficient epoxidation process leading to chiral epoxyketones using the reusable homo-oligopeptide poly-l-leucine (PLL) in pure water, without any organic co-solvent. A range of substituted epoxyketones can be accessed with good conversions and high enantioselectivities. Based on the experimental results and computational studies, we propose a mechanism that demonstrates the importance of both the α-helical structure and the presence of a hydrophobic groove of the homo-oligopeptide catalyst for reactivity and selectivity.

Synthesis and anti-inflammatory activity of isoquebecol.

We report here the synthesis of isoquebecol, an unprecedented constitutional isomer of quebecol, a polyphenolic compound discovered in maple syrup. The methodology used to prepare isoquebecol involves, as key steps, the formation of a dibromoalkene from an α-ketoester precursor, followed by a double Suzuki-Miyaura reaction. The anti-inflammatory activity of isoquebecol was studied on macrophage cells by monitoring its ability to inhibit LPS-induced IL-6 secretion. Results show that this new compound has an improved bioactivity over that of its natural isomer. Precursors and derivatives of quebecol, isoquebecol and model analog 2,3,3-triphenylpropanol were also prepared and tested in this study. Comparison between the three series of compounds led to establishing new SARs concerning the aryl ring substitution pattern on the triarylpropanol scaffold and substructure functionalization.