Hydrocarbon stapled temporin-L analogue as potential antibacterial and antiendotoxin agents with enhanced protease stability

Antimicrobial resistance (AMR) is a serious global concern and a huge burden on the healthcare system. Antimicrobial peptides (AMPs) are considered as a solution of AMR due to their membrane-lytic and intracellular mode of action and therefore resistance development against AMPs is less frequent. One such AMPs, temporin-L (TL) is a 13-mer peptide reported as a potent and broad-spectrum antibacterial agent with significant immunomodulatory activity. However, TL is toxic to human erythrocytes at their antibacterial concentrations and therefore various analogues were synthesized with potent antimicrobial activity and lower hemolytic activity. In this work, we have selected a non-toxic engineered analogue of TL (eTL) and performed hydrocarbon stapling of amino acid residues at i to i + 4 positions at different part of sequence. The synthesized peptides were investigated against both the gram-positive and gram-negative bacteria as well as methicillin resistant S. aureus, its MIC was measured in the concentrations range of 0.9-15.2 µM. All analogues were found equal or better antibacterial as compared to parent peptide. Interestingly one analogue eTL [5-9] was found to be non-cytotoxic and stable in presence of the human serum. Mode of action studies revealed membrane depolarizing and disruptive mode of action with live MRSA. Further in vivo studies of antimicrobial against MRSA infection and anti-endotoxin activities in mice model revealed potential activity of the stapled peptide analogue. Overall, this reports on stapled analogue of the AMPs highlights an important strategy for the development of new antibacterial therapeutics against AMR.

Stereoconvergent Synthesis of Z-1,3-Disubstituted-1,3-Dienes by Uphill Photocatalysis

A variety of 1-aryl-1,3-dienes were isomerized from E to Z isomers by photocatalysis using Ru(bpy)₃ [PF₆ ]₂ and blue LED light. Enrichment of the Z-isomer is thought to occur by selective triplet energy transfer from the photocatalyst to the stereoisomeric mixture. The 1,3-diene starting materials are easily made by catalytic ene-yne metathesis (EYM). To access 1,3-diene Z-stereoisomers directly, a one pot procedure was developed. Additional 1,3-dienes were investigated for both isomerization and Z-enrichment. The combination of cross EYM with photocatalysis allows for the stereoconvergent synthesis of Z-1,3-dienes.

Modular synthesis of non-conjugated N-(quinolin-8-yl) alkenyl amides via cross-metathesis

We report a direct and modular method to access non-conjugated alkenyl amides containing the 8-aminoquinoline (AQ) directing auxiliary and related groups via cross-metathesis. In this way, readily available, AQ-containing, terminal β,γ-unsaturated amides can be coupled with various terminal alkenes to furnish internal alkene products that are otherwise difficult to prepare. The value of this family of products stems from their ability to participate in a number of directed alkene functionalization reactions.

Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes

An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.

Discovery of highly potent and selective antiparasitic new oxadiazole and hydroxy-oxindole small molecule hybrids

A series of highly active hybrids were discovered as novel antiparasitic agents. Two heterocyclic scaffolds (1,2,4-oxadiazole and 3-hydroxy-2-oxindole) were linked, and the resulting compounds showed in vitro activities against intracellular amastigotes of two protozoan parasites, Trypanosoma cruzi and Leishmania infantum. Their cytotoxicity was assessed using HFF-1 fibroblasts and HepG2 hepatocytes. Compounds 5b, 5d, 8h and 8o showed selectivity against L. infantum (IC₅₀ values of 3.89, 2.38, 2.50 and 2.85 μM, respectively). Compounds 4c, 4q, 8a and 8k were the most potent against T. cruzi, exhibiting IC₅₀ values of 6.20, 2.20, 2.30 and 2.20 μM, respectively. Additionally, the most potent anti-T. cruzi compounds showed in vitro efficacies comparable or superior to that of benznidazole. These easy-to-synthesize molecules represent novel chemotypes for the design of potent and selective lead compounds for Chagas disease and leishmaniasis drug discovery.

Rapid and Visual Detection and Quantitation of Ethylene Released from Ripening Fruits: The New Use of Grubbs Catalyst

Herein, we report on fluorophore-tagged Grubbs catalysts as turn-on fluorescent probes for the sensitive detection and quantitation of ethylene, a plant hormone that plays a critical role in many phases of plant growth and fruit ripening. The ruthenium-based weak fluorescent probes were prepared handily through the metathesis reaction between the first-generation Grubbs catalyst and selected fluorophores that have high quantum yields and contain terminal vinyl groups. Upon exposure to ethylene, fluorescence enhancement was observed via the release of fluorophore from the probe. Our probe shows an excellent limit of detection for ethylene at 0.9 ppm in air and was successfully applied for monitoring ethylene released during the fruit-ripening process. Our work opens up a new avenue of application of Grubbs catalysts for bioanalytical chemistry of ethylene, which is critically important in plant biology, agriculture, and food industry.

Synthesis of side-chain oxysterols and their enantiomers through cross-metathesis reactions of Δ22 steroids

A synthetic route that utilizes a cross-metathesis reaction with Δ²² steroids has been developed to prepare sterols with varying C-27 side-chains. Natural sterols containing hydroxyl groups at the 25 and (25R)-26 positions were prepared. Enantiomers of cholesterol and (3β,25R)-26-hydroxycholesterol (27-hydroxycholesterol) trideuterated at C-19 were prepared for future biological studies.

Synthesis, Characterization and Thermal Properties of Poly(ethylene oxide), PEO, Polymacromonomers via Anionic and Ring Opening Metathesis Polymerization

Branched polymers are a valuable class of polymeric materials. In the present study, anionic polymerization techniques were employed for the synthesis of low molecular weight poly(ethylene oxide) (PEO) macromonomers bearing norbornenyl end groups. The macromonomers were characterized by SEC, MALDI-TOF and NMR spectroscopy. Subsequent ring opening metathesis polymerization (ROMP) of the macromonomers using ruthenium catalysts (Grubbs catalysts of the 1st, 2nd and 3rd generations) afforded the corresponding polymacromonomers. The effects of the macromonomer molecular weight, the type of the catalyst, the nature of the solvent, the monomer concentration and the polymerization temperature on the molecular characteristics of the branched polymers were examined in detail. The crystallization behavior of the macromonomers and the corresponding polymacromonomers were studied by Differential Scanning Calorimetry (DSC). The thermal stability and the kinetics of the thermal decomposition of the samples were also studied by Thermogravimetric Analysis (TGA). The activation energies of the thermal decomposition were analyzed using the Ozawa–Flynn–Wall and Kissinger methodologies.

Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots

Core-shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original trioctylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48-53 nm.

Spontaneously Healable Thermoplastic Elastomers Achieved through One-Pot Living Ring-Opening Metathesis Copolymerization of Well-Designed Bulky Monomers

We report here a series of novel spontaneously healable thermoplastic elastomers (TPEs) with a combination of improved mechanical and good autonomic self-healing performances. Hard-soft diblock and hard-soft-hard triblock copolymers with poly[exo-1,4,4a,9,9a,10-hexahydro-9,10(1',2')-benzeno-l,4-methanoanthracene] (PHBM) as the hard block and secondary amide group containing norbornene derivative polymer as the soft block were synthesized via living ring-opening metathesis copolymerization by use of Grubbs third-generation catalyst through sequential monomer addition. The microstructure, mechanical, self-healing, and surface morphologies of the block copolymers were thoroughly studied. Both excellent mechanical performance and self-healing capability were achieved for the block copolymers because of the interplayed physical cross-link of hard block and dynamic interaction formed by soft block in the self-assembled network. Under an optimized hard block (PHBM) weight ratio of 5%, a significant recovery of tensile strength (up to 100%) and strain at break (ca. 85%) was achieved at ambient temperature without any treatment even after complete rupture. Moreover, the simple reaction operations and well-designed monomers offer versatility in tuning the architectures and properties of the resulting block copolymers.

Developing a Dissociative Nanocontainer for Peptide Drug Delivery

The potency, selectivity, and decreased side effects of bioactive peptides have propelled these agents to the forefront of pharmacological research. Peptides are especially promising for the treatment of neurological disorders and pain. However, delivery of peptide therapeutics often requires invasive techniques, which is a major obstacle to their widespread application. We have developed a tailored peptide drug delivery system in which the viral capsid of P22 bacteriophage is modified to serve as a tunable nanocontainer for the packaging and controlled release of bioactive peptides. Recent efforts have demonstrated that P22 nanocontainers can effectively encapsulate analgesic peptides and translocate them across blood-brain-barrier (BBB) models. However, release of encapsulated peptides at their target site remains a challenge. Here a Ring Opening Metathesis Polymerization (ROMP) reaction is applied to trigger P22 nanocontainer disassembly under physiological conditions. Specifically, the ROMP substrate norbornene (5-Norbornene-2-carboxylic acid) is conjugated to the exterior of a loaded P22 nanocontainer and Grubbs II Catalyst is used to trigger the polymerization reaction leading to nanocontainer disassembly. Our results demonstrate initial attempts to characterize the ROMP-triggered release of cargo peptides from P22 nanocontainers. This work provides proof-of-concept for the construction of a triggerable peptide drug delivery system using viral nanocontainers.

Concise Synthesis of Broussonone A

A concise and expeditious approach to the total synthesis of broussonone A, a p-quinol natural compound, has been developed. The key features of the synthesis include the Grubbs II catalyst mediated cross metathesis of two aromatic subunits, and a chemoselective oxidative dearomatizationin the presence of two phenol moieties. Especially, optimization associated with the CM reaction of ortho-alkoxystyrenes was also studied, which are known to be ineffective for Ru-catalyzed metathesis reactions under conventional reaction conditions because ortho-alkoxy group could coordinate to the ruthenium center, resulting in the potential complication of catalyst inhibition.

A comparison of low and high activity precatalysts: do the calculated energy barriers during the self-metathesis reaction of 1-octene correlate with the precatalyst metathesis activity?

The self-metathesis reaction of 1-octene with several well-known Grubbs-type precatalysts and the new Z-selective Grubbs precatalyst were studied with molecular modeling. The obtained Gibbs-free energy values for all the steps during the productive metathesis of 1-octene were compared to the values obtained for some low catalytic activity precatalysts. Determining how the Gibbs-free energy values of highly active precatalysts compare to that of low catalytic activity precatalysts gave a deeper insight into the mechanism. The questionable correlation of the theoretically observed trends with those obtained experimentally does point to the need to be very cautious when making assumptions from theoretical results without a sufficiently large dataset.

A molecular modeling study of the changes of some steric properties of the precatalysts during the olefin metathesis reaction

The productive self-metathesis of 1-octene with a series of new phosphine ligated Grubbs-type precatalysts was studied. The resulting structures were used to compare some steric properties of the new precatalysts with those of well-known precatalysts. The possibility of α-CC agnostic stabilization as well as the ability of the ligands to shield the metal was studied. A comparison of the obtained data, pointed to the unlikelihood that α-CC agostic stabilization is a major contribution to the stabilization of the various metallacyclobutane rings. The similarity in the ability of the ligands to shield the metal also raised questions about the comparison of experimentally observed trends with those obtained theoretically.

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium-arene complexes

The tandem catalysis of ring-closing metathesis/atom transfer radical reactions was investigated with the homobimetallic ruthenium-indenylidene complex [(p-cymene)Ru(μ-Cl)₃RuCl(3-phenyl-1-indenylidene)(PCy₃)] (1) to generate active species in situ. The two catalytic processes were first carried out independently in a case study before the whole sequence was optimized and applied to the synthesis of several polyhalogenated bicyclic γ-lactams and lactones from α,ω-diene substrates bearing trihaloacetamide or trichloroacetate functionalities. The individual steps were carefully monitored by ¹H and ³¹P NMR spectroscopies in order to understand the intimate details of the catalytic cycles. Polyhalogenated substrates and the ethylene released upon metathesis induced the clean transformation of catalyst precursor 1 into the Ru(II)-Ru(III) mixed-valence compound [(p-cymene)Ru(μ-Cl)₃RuCl(2)(PCy₃)], which was found to be an efficient promoter for atom transfer radical reactions under the adopted experimental conditions.