Use Of Amides Research Articles

Ionizable Lipids with Optimized Linkers Enable Lung-Specific, Lipid Nanoparticle-Mediated mRNA Delivery for Treatment of Metastatic Lung Tumors.

Lipid nanoparticles (LNPs) have emerged as a groundbreaking delivery system for vaccines and therapeutic mRNAs. Ionizable lipids are the most pivotal component of LNPs due to their ability to electrostatically interact with mRNA, allowing its encapsulation while concurrently enabling its endosomal escape following cellular internalization. Thus, extensive research has been performed to optimize the ionizable lipid structure and to develop formulations that are well tolerated and allow efficient targeting of different organs that result in a high and sustained mRNA expression. However, one facet of the ionizable lipids' structure has been mostly overlooked: the linker segment between the ionizable headgroup and their tails. Here, we screened a rationally designed library of ionizable lipids with different biodegradable linkers. We extensively characterized LNPs formulated using these ionizable lipids and elucidated how these minor structural changes in the ionizable lipids structure radically influenced the LNPs' biodistribution in vivo. We showed how the use of amide and urea linkers can modulate the LNPs' pKa, resulting in an improved specificity for lung transfection. Finally, we demonstrated how one of these lipids (lipid 35) that form LNPs entrapping a bacterial toxin [pseudomonas exotoxin A (mmPE)] in the form of an mRNA reduced tumor burden and significantly increased the survival of mice with lung metastasis.

Synthesis of non-equivalent diamides and amido-esters via Pd-catalysed carbonylation

Given the widespread use of amides in chemistry and biology, the development of methods for their synthesis remains important. Although the construction of amide bonds has in principle been known since Wöhler’s urea synthesis, the direct and atom-efficient preparation of amides, especially with multiple amido groups, continues to be difficult. To address this challenge, we developed an efficient access to heterobifunctional compounds through linking amines as well as alcohols with specific molecular pincers in the presence of advanced carbonylation catalysts. In detail, we describe the synthesis of non-symmetrical diamides and amido-esters from available propargylic acetates using selective palladium-catalysed diamino- and amino-alkoxy carbonylations. Mechanistic studies and control experiments reveal a cascade process with allenoic amides, allylic amine and dienamide as crucial intermediates. The generality of this protocol is showcased by the highly selective synthesis of >100 heterobifunctional molecules including many pharmaceutically relevant products.

Efficient Base‐Catalyzed Hydrosilylation of Tertiary Amides to Aldehydes

AbstractA chemoselective catalytic reduction of tertiary amides to aldehydes is reported. The catalytic system KOtBu/(EtO)2MeSiH has been found to be highly active in the conversion of tertiary amides to silylated hemiaminals, which after acidic work‐up yields the respective aldehydes under mild conditions. The use of amides containing α‐protons in this catalytic reaction resulted in elimination to furnish enamines characterized by 1H‐NMR. This mild and selective process is compatible with nitriles, ethers, amines, and heterocyclic functionalities. However, competition experiments revealed poor tolerance for easily reducible functional groups, such as esters, ketones, and aldehydes. This transition metal‐free strategy presents a cheap and readily available process for the efficient reduction of tertiary amides to the corresponding aldehydes.

Water-Based Dynamic Depsipeptide Chemistry: Building Block Recycling and Oligomer Distribution Control Using Hydration-Dehydration Cycles.

The high kinetic barrier to amide bond formation has historically placed narrow constraints on its utility in reversible chemistry applications. Slow kinetics has limited the use of amides for the generation of diverse combinatorial libraries and selection of target molecules. Current strategies for peptide-based dynamic chemistries require the use of nonpolar co-solvents or catalysts or the incorporation of functional groups that facilitate dynamic chemistry between peptides. In light of these limitations, we explored the use of depsipeptides: biorelevant copolymers of amino and hydroxy acids that would circumvent the challenges associated with dynamic peptide chemistry. Here, we describe a model system of N-(α-hydroxyacyl)-amino acid building blocks that reversibly polymerize to form depsipeptides when subjected to two-step evaporation–rehydration cycling under moderate conditions. The hydroxyl groups of these units allow for dynamic ester chemistry between short peptide segments through unmodified carboxyl termini. Selective recycling of building blocks is achieved by exploiting the differential hydrolytic lifetimes of depsipeptide amide and ester bonds, which we show are controllable by adjusting the solution pH, temperature, and time as well as the building blocks’ side chains. We demonstrate that the polymerization and breakdown of the depsipeptides are facilitated by cyclic morpholinedione intermediates, and further show how structural properties dictate half-lives and product oligomer distributions using multifunctional building blocks. These results establish a cyclic mode of ester-based reversible depsipeptide formation that temporally separates the polymerization and depolymerization steps for the building blocks and may have implications for prebiotic polymer chemical evolution.

The combined use of amide I bands in polarized Raman, IR, and vibrational dichroism spectra for the structure analysis of peptide fibrils and disordered peptides and proteins

AbstractRaman spectroscopy is generally a versatile tool to explore the structure of proteins and peptides in solution. However, in spite of the development of ultraviolet (UV) resonance Raman spectroscopy as a tool that allows for the investigation of samples with lower concentrations, Raman has not played the same role as infrared (IR) spectroscopy with regard to secondary structure analysis. Reported UV Raman studies have recently focused on the ψ‐dependence of amide III as a useful tool for the structural analysis even of disordered peptides. Amide I based structural analysis generally uses visible excitation. Rather than describing the traditional secondary structure analysis of proteins, this review focusses on work that used Raman in conjunction with other vibrational spectroscopies such as IR and vibrational circular dichroism to probe the conformational distribution of amino acid residues in unfolded peptides and the self‐assembling of peptides into fibrils. We argue against the use of spectral decomposition into Gaussian bands particularly if this type of analysis is exclusively applied to either IR or Raman band profiles. The article emphasizes the delocalized excitonic character of amide I wavefunctions which has to be accounted for in any attempt to use the respective bands for structure analysis.

Cytotoxic and apoptosis-inducing effects of novel 8-amido isocoumarin derivatives against breast cancer cells.

Isocoumarin is a lactone, a type of natural organic compound that is used as synthetic intermediates of several natural products and pharmaceutical compounds explored for their potential therapeutic applications like antifungal, antimicrobial, anti-inflammatory, and anticancer activities. In our previous work, we were the first group to report the use of amide C-N bond of isatins as the oxidizing directing group for the synthesis of 8-amido isocoumarin derivatives. Whereas in our present work, we have screened the cytotoxic effects of novel 8-amido isocoumarin derivatives (S1-S10) in human breast cancer MCF-7 and MDA-MB-231 cells. Our novel results revealed that N-(3-(4-methoxyphenyl)-1-oxo-4-(4-propylphenyl)-1H-isochromen-8yl)acetamide (S1) and N-(4-(3,5-difluorophenyl)-1-oxo-3-(p-tolyl)-1H-isochromen-8-yl) acetamide (S2) are the two potent compounds among the rest synthesized isocoumarin derivatives that are cytotoxic against MCF-7 and MDA-MB-231 cells, whereas less toxic to the non-tumorigenic IOSE-364 cells. Flow cytometry studies have confirmed the induction of apoptotic effects of compounds by Annexin V/PI double staining. We also observed the cytotoxic effects of S1 and S2, as evaluated by DAPI-PI immunostaining and H&E staining. The morphological alterations consistent with apoptotic blebs were observed in both cancer cells treated with compounds assessed by scanning electron microscopy. Overall, this present study strongly demonstrates that 8-amido isocoumarin derivatives have potent cytotoxic and apoptotic effects in breast cancer cells.

Amides as surrogates of aldehydes for C-C bond formation: amide-based direct Knoevenagel-type condensation reaction and related reactions

Aldehydes are perhaps the most versatile compounds that enable many C–C bond forming reactions, which are not amenable for other subclasses of carbonyl compounds. We report the first use of amides as surrogates of aldehydes for C–C bond formation, namely, the direct Knoevenagel-type condensation based on amides. The one-pot method consists of controlled reduction of an amide with LDBIPA [LiAlH( i Bu)2(O i Pr)], Lewis acid-mediated release of a reactive iminium ion intermediate, nucleophilic addition, and in situ elimination of amine. The reaction shows good functional group tolerance. We also demonstrated that the Schwartz reagent could be used as an alternative of LDBIPA. The employment of nitromethane and a silyl enol ether as the nucleophiles opens an avenue for the unprecedented amide-based nitro-aldol condensation reaction and aldol condensation reaction, respectively.

N-Boc-Amides in Cross-Coupling Reactions.

Since 2015, the use of amides as electrophilic partners in cross-coupling reactions has experienced exponential growth. Diverse amide derivatives have been studied and among them N-Boc-amides have shown good activities towards various cross-coupling reactions and presents, in our view, an important synthetic usefulness. This review describes the recent developments of these chemical transformations involving N-Boc-amides.

Breaking Amides using Nickel Catalysis.

Amides have been widely studied for decades, but their synthetic utility has remained limited in reactions that proceed with rupture of the amide C-N bond. Using Ni catalysis, we have found that amides can now be strategically employed in several important transformations: esterification, transamidation, Suzuki-Miyaura couplings, and Negishi couplings. These methodologies provide exciting new tools to build C-heteroatom and C-C bonds using an unconventional reactant (i.e., the amide), which is ideally suited for use in multi-step synthesis. It is expected that the area of amide C-N bond activation using nonprecious metals will continue to flourish and, in turn, will promote the growing use of amides as synthons in organic synthesis.

Nickel‐Catalyzed Esterification of Aliphatic Amides

AbstractRecent studies have demonstrated that amides can be used in nickel‐catalyzed reactions that lead to cleavage of the amide C−N bond, with formation of a C−C or C−heteroatom bond. However, the general scope of these methodologies has been restricted to amides where the carbonyl is directly attached to an arene or heteroarene. We now report the nickel‐catalyzed esterification of amides derived from aliphatic carboxylic acids. The transformation requires only a slight excess of the alcohol nucleophile and is tolerant of heterocycles, substrates with epimerizable stereocenters, and sterically congested coupling partners. Moreover, a series of amide competition experiments establish selectivity principles that will aid future synthetic design. These studies overcome a critical limitation of current Ni‐catalyzed amide couplings and are expected to further stimulate the use of amides as synthetic building blocks in C−N bond cleavage processes.

Nickel-Catalyzed Esterification of Aliphatic Amides.

Recent studies have demonstrated that amides can be used in nickel-catalyzed reactions that lead to cleavage of the amide C-N bond, with formation of a C-C or C-heteroatom bond. However, the general scope of these methodologies has been restricted to amides where the carbonyl is directly attached to an arene or heteroarene. We now report the nickel-catalyzed esterification of amides derived from aliphatic carboxylic acids. The transformation requires only a slight excess of the alcohol nucleophile and is tolerant of heterocycles, substrates with epimerizable stereocenters, and sterically congested coupling partners. Moreover, a series of amide competition experiments establish selectivity principles that will aid future synthetic design. These studies overcome a critical limitation of current Ni-catalyzed amide couplings and are expected to further stimulate the use of amides as synthetic building blocks in C-N bond cleavage processes.

Different Behaviors of a Cu Catalyst in Amine Solvents: Controlling N and O Reactivities of Amide

Controlling the reactivity of the nitrogen or oxygen nucleophile of an amide group to form C–N or C–O bonds by tuning reaction conditions is one of the most challenging issues in the use of amides in organic synthesis. Both nucleophiles in the amide group can individually participate in reactions, and most reactions employ a substrate-controlled methodology to achieve selectivity. However, in the reaction of α-bromoamides and acrylates, we successfully controlled the reactivity of the nitrogen or oxygen nucleophile of the amide group to afford a lactam via carboamidation or an iminolactone via carbooxygenation, using a copper catalyst system with an appropriate base.

Nickel-Catalyzed Alkylation of Amide Derivatives.

We report the catalytic alkylation of amide derivatives, which relies on the use of nonprecious metal catalysis. Amide derivatives are treated with organozinc reagents, utilizing nickel catalysis, to yield ketone products. The methodology is performed at ambient temperature and is tolerant of variation in both coupling partners. A precursor to a nanomolar glucagon receptor modulator was synthesized using the methodology, underscoring the mild nature of this chemistry and its potential utility in pharmaceutical synthesis. These studies are expected to further promote the use of amides as synthetic building blocks.

Conversion of amides to esters by the nickel-catalysed activation of amide C-N bonds.

Amides are common functional groups that have been well studied for more than a century.1 They serve as the key building blocks of proteins and are present in an broad range of other natural and synthetic compounds. Amides are known to be poor electrophiles, which is typically attributed to resonance stability of the amide bond.1,2 Whereas Nature can easily cleave amides through the action of enzymes, such as proteases,3 the ability to selectively break the C–N bond of an amide using synthetic chemistry is quite difficult. In this manuscript, we demonstrate that amide C–N bonds can be activated and cleaved using nickel catalysts. We have used this methodology to convert amides to esters, which is a challenging and underdeveloped transformation. The reaction methodology proceeds under exceptionally mild reaction conditions, and avoids the use of a large excess of an alcohol nucleophile. Density functional theory (DFT) calculations provide insight into the thermodynamics and catalytic cycle of this unusual transformation. Our results provide a new strategy to harness amide functional groups as synthons and are expected fuel the further use of amides for the construction of carbon–heteroatom or carbon–carbon bonds using non-precious metal catalysis.

Conformational dynamics of human FXR-LBD ligand interactions studied by hydrogen/deuterium exchange mass spectrometry: Insights into the antagonism of the hypolipidemic agent Z-guggulsterone

Farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily of transcription factors that plays a key role in the regulation of bile acids, lipid and glucose metabolisms. The regulative function of FXR is governed by conformational changes of the ligand binding domain (LBD) upon ligand binding. Although FXR is a highly researched potential therapeutic target, only a limited number of FXR-agonist complexes have been successfully crystallized and subsequently yielded high resolution structures. There is currently no structural information of any FXR-antagonist complexes publically available. We therefore explored the use of amide hydrogen/deuterium exchange (HDX) coupled with mass spectrometry for characterizing conformational changes in the FXR-LBD upon ligand binding. Ligand-specific deuterium incorporation profiles were obtained for three FXR ligand chemotypes: GW4064, a synthetic non-steroidal high affinity agonist; the bile acid chenodeoxycholic acid (CDCA), the endogenous low affinity agonist of FXR; and Z-guggulsterone (GG), an in vitro antagonist of the steroid chemotype. A comparison of the HDX profiles of their ligand-bound FXR-LBD complexes revealed a unique mode of interaction for GG. The conformational features of the FXR-LBD–antagonist interaction are discussed.

ChemInform Abstract: Diastereoselective 1,3‐Dipolar Cycloaddition of Pyrylium Ylides with Chiral Enamides.

AbstractThe first example of the use of amides as alkene in the title reaction is demonstrated.

Use of amides as cryoprotectants in extenders for frozen sperm of tambaqui, Colossoma macropomum

Amides were tested as cryoprotectants in comparison with glycerol and DMSO (more traditional cryoprotectants) for recovery of Colossoma macropomum (tambaqui fish) sperm. Milt was extended in Beltsville Thawing Solution, then frozen with the addition of 2%, 5%, 8%, or 11% of: (1) dimethylacetamide (DMA), (2) dimethylformamide (DMF), (3) methylformamide (MF), or with 5% glycerol or 10% dimethylsulfoxide. Fertilization rates were greatest (P < 0.001) with amides; 8% DMF (91.6 ± 1.3%), 5% DMF (88.9 ± 1.6%), and 8% MF (83.0 ± 1.6%), which did not significantly differ among themselves, when compared with glycerol (51.6 ± 2.4%) and DMSO (61.9 ± 3.1%). The best hatching rates (P < 0.001) also occurred for 5% or 8% DMF and 8% MF (79.1 ± 3.1, 87.6 ± 1.5, and 74.8 ± 3.0, respectively) and were also similar (P > 0.05). For such treatments, both fertilization and hatching rates were similar (P > 0.05) to those with fresh sperm (91.7 ± 1.4 and 87.4 ± 1.4, respectively). The best sperm motility across extenders (at least 55.7%) was with 5%, 8%, and 11% DMF (P < 0.001). Those same treatments, along with 11% MF, provided the longest (P < 0.001) period of motility (at least 1 min). The greatest sperm integrity (more than 54%) was with 5% and 11% MF and with DMA and DMF at all tested concentrations (P < 0.001). The greatest (P < 0.001) sperm viability (at least 31%) was for 5%, 8%, and 11% DMA, and with 8% and 11% MF, and also for DMF at all tested concentrations. Sperm DNA integrity was best (more than 50%) for 2%, 5%, and 8% MF and for DMA and DMF at all concentrations (P < 0.001), whereas 2% DMA, 11% MF, 11% DMF, and the three amides at both 5% and 8% yielded the highest mitochondrial functionality (at least 44%; P < 0.001); thus, 8% MF and both 5% and 8% DMF were the cryoprotectants with the best postthaw quality for C. macropomum sperm.

A simple synthesis of aminopyridines: use of amides as amine source

A transition metal/microwave irradiation (or base) free synthesis of aminopyridines has been accomplished via C-N bond forming reaction between chloropyridine and a variety of simple amides under refluxing conditions.

Evaluation of amides and centrifugation temperature in boar semen cryopreservation

Two experiments were conducted to evaluate the use of amides as cryoprotectants and two centrifugation temperatures (15 or 24 degrees C) in boar semen cryopreservation protocols. Semen was diluted in BTS, cooled centrifuged, added to cooling extenders, followed by the addition of various cryoprotectants. In experiment 1, mean (+/-S.E.M.) sperm motility for 5% dimethylformamide (DMF; 50.6+/-1.9%) and 5% dimethylacetamide (DMA; 53.8+/-1.7%) were superior (P<0.05) to 5% methylformamide (MF; 43.2+/-2.4%) and 3% glycerol (GLY; 38.1+/-2.3%), with no significant difference between MF and GLY. Sperm membrane integrity was higher (P<0.05) for DMA than for MF or GLY (50.9+/-1.9, 43.3+/-2.5, and 34.5+/-2.8%, respectively). Sperm membrane integrity was higher in DMF (47.9+/-2.1%) than in glycerol (34.5+/-2.8%, P<0.05), but was similar to other treatments (P>0.05). In experiment 2, we tested MF, DMF, and DMA at 3, 5, and 7%. Sperm motility and membrane integrity were higher for 5% DMA (53.8+/-1.7 and 50.9+/-1.9%) and 5% DMF (50.6+/-1.9 and 47.9+/-2.1%), in comparison with 7% DMF and all MF concentrations (P<0.05). For sperm motility and membrane integrity, 5% DMA exceeded (P<0.05) 3% DM, with greater membrane integrity than 3% DMF (P<0.05). In both experiments, sperm motility and membrane integrity were superior at 15 degrees C versus 24 degrees C (P<0.05), with no interaction between centrifugation temperature and treatments (P>0.05). In conclusion, boar semen was successfully cryopreserved by replacement of glycerol with amides (especially 5% DMA) and centrifugation at 15 degrees C, with benefits for post-thaw sperm motility and membrane integrity.

Amides as cryoprotectants for freezing stallion semen: A review

Stallion semen cryopreservation, despite its impact on the horse industry, is not an established technology. During the last years, a number of modifications have been proposed to the freezing process, however, a large population of stallions still have poor semen quality and fertility after frozen-thawed. Glycerol toxicity could be a reason for the variation on stallion sperm freezability. There are limited publications concerning the use of alternative cryoprotectants for equine sperm. Glycerol is contraceptive for some species and other cryoprotectors, such as amides, have been show to be a good option for freezing semen of these species. Recent reports have shown encouraging data respecting the use of amides as cryoprotectants for stallions, with more remarkable improvements for semen from stallions that freeze poorly when glycerol is used.