Acyl Transfer Reactions Research Articles

Supramolecular Catalysis of Acyl Transfer within Zinc Porphyrin-Based Metal-Organic Cages.

To illustrate the supramolecular catalysis process in molecular containers, two porphyrinatozinc(II)-faced cubic cages with different sizes were synthesized and used to catalyze acyl-transfer reactions between N-acetylimidazole (NAI) and various pyridylcarbinol (PC) regioisomers (2-PC, 3-PC, and 4-PC). A systemic investigation of the supramolecular catalysis occurring within these two hosts was performed, in combination with a host-guest binding study and density functional theory calculations. Compared to the reaction in a bulk solvent, the results that the reaction of 2-PC was found to be highly efficient with high rate enhancements (kcat/kuncat = 283 for Zn-1 and 442 for Zn-2), as well as the different efficiencies of the reactions with various ortho-substituted 2-PC substrates and NAI derivates should be attributed to the cages having preconcentrated and preoriented substrates. The same cage displayed different catalytic activities toward different PC regioisomers, which should be mainly attributed to different binding affinities between the respective reactant and product with the cages. Furthermore, control experiments were carried out to learn the effect of varying reactant concentrations and product inhibition. The results all suggested that, besides the confinement effect caused by the inner microenvironment, substrate transfer, including the encapsulation of the reactant and the release of products, should be considered to be a quite important factor in supramolecular catalysis within a molecular container.

Energy Decomposition Analysis Reveals the Nature of Lone Pair-π Interactions with Cationic π Systems in Catalytic Acyl Transfer Reactions.

Lone pair-π (LP-π) interactions between Lewis basic heteroatoms, such as oxygen and sulfur, and electron-deficient π systems are important noncovalent interactions. However, they have seldom been used to control catalyst-substrate interactions in catalysis. We performed density functional theory calculations to investigate the strengths of LP-π interactions between different lone pair donors and cationic π systems, and in different complexation geometries. Energy decomposition analysis calculations indicated that the dominant stabilizing force in LP-π complexes is electrostatic interaction and the electrostatic potential surface of the π system predicts the most favorable site for forming LP-π complexes. Benzotetramisole (BTM) is revealed as a privileged acyl transfer catalyst that promotes LP-π interactions because the positive charge of the acylated BTM is delocalized onto the dihydroimidazole ring, which binds strongly with a variety of oxygen and sulfur lone pair donors.

Reactions of 4‐Nitrophenyl 5‐substituted Furan‐2‐carboxylates with R2NH/R2NH2+ in 20 mol% DMSO(aq): Effect of Aryl Group on the Acyl‐Transfer Reaction

Reactions of 4‐nitrophenyl 2‐furoates (1a–e) with R2NH/R2NH2+ in 20 mol% DMSO(aq) have been studied. The reactions produced aminolysis products and exhibited second‐order kinetics. The Brönsted plots were linear with βnuc values of 0.75–0.89, which remained nearly the same for all 5‐furyl substituents. The rate data showed excellent correlations on the Yukawa‐Tsuno plots with ρ(x) = 0.72–1.1, and r = 0.55–0.95, respectively. The ρ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the CO bond and a decrease in the resonance contribution. The results have been interpreted with the addition–elimination mechanism in which the second step is the rds. By comparing with the data for ArC(O)OC6H4‐4‐NO2 (Ar = Ph, thienyl), the effect of the aryl group on the acyl transfer reaction was assessed.

Enzyme Catalyzed Hydrogel as Versatile Bioadhesive for Tissue Wound Hemostasis, Bonding, and Continuous Repair.

Developing a versatile bioadhesive which is biocompatible, adhesive, hemostatic, and therapeutic is of great significance to promote wound sealing and healing. Herein, an adhesive (GTT-3 hydrogel) is fabricated by catalysis of tannic acid modified gelatin (Gel-TA) with transglutaminase (TG). The hydrogen bonding, imine linking, and acyl-transfer reaction between GTT-3 hydrogel and tissue enable efficient hydrogel integration and adhesion to tissue instantly, so as to seal the wound and stop bleeding. Moreover, the intrinsic wound healing ability of gelatin and the antibacterial properties of TA provide favorable conditions for wound healing after adhesion. In vitro mechanical property testing and cell experimental results determine the elasticity, adhesion, and biocompatibility of the GTT-3 hydrogel. The wound operation in mouse models and pathological sectioning results indicate that GTT-3 adhesive obviously accelerates hemostasis, wound bonding, and healing. With the special property of instant adhesion and excellent hemostatic and therapeutic repair effects, GTT-3 hydrogel may provide a new option for surgical operation.

Structures of LnmK, a Bifunctional Acyltransferase/Decarboxylase, with Substrate Analogues Reveal the Basis for Selectivity and Stereospecificity

LnmK stereospecifically accepts (2R)-methylmalonyl-CoA, generating propionyl-S-acyl carrier protein to support polyketide biosynthesis. LnmK and its homologues are the only known enzymes that carry out a decarboxylation (DC) and acyl transfer (AT) reaction in the same active site as revealed by structure-function studies. Substrate-assisted catalysis powers LnmK, as decarboxylation of (2R)-methylmalonyl-CoA generates an enolate capable of deprotonating active site Tyr62, and the Tyr62 phenolate subsequently attacks propionyl-CoA leading to a propionyl-O-LnmK acyl-enzyme intermediate. Due to the inherent reactivity of LnmK and methylmalonyl-CoA, a substrate-bound structure could not be obtained. To gain insight into substrate specificity, stereospecificity, and catalytic mechanism, we determined the structures of LnmK with bound substrate analogues that bear malonyl-thioester isosteres where the carboxylate is represented by a nitro or sulfonate group. The nitro-bearing malonyl-thioester isosteres bind in the nitronate form, with specific hydrogen bonds that allow modeling of the (2R)-methylmalonyl-CoA substrate and rationalization of stereospecificity. The sulfonate isosteres bind in multiple conformations, suggesting the large active site of LnmK allows multiple binding modes. Considering the smaller malonyl group has more conformational freedom than the methylmalonyl group, we hypothesized the active site can entropically screen against catalysis with the smaller malonyl-CoA substrate. Indeed, our kinetic analysis reveals malonyl-CoA is accepted at 1% of the rate of methylmalonyl-CoA. This study represents another example of how our nitro- and sulfonate-bearing methylmalonyl-thioester isosteres are of use for elucidating enzyme-substrate binding interactions and revealing insights into catalytic mechanism. Synthesis of a larger panel of analogues presents an opportunity to study enzymes with complicated structure-function relationships such as acyl-CoA carboxylases, trans-carboxytransferases, malonyltransferases, and β-ketoacylsynthases.

Phosphine-Mediated MBH-Type/Acyl Transfer/Wittig Sequence for Construction of Functionalized Furo[3,2-c]coumarins.

A new method for the construction of functionalized furo[3,2-c]coumarins via MBH-type/acyl-transfer/Wittig reaction is reported. The current approach would open a new route for the simultaneous formation of two rings in a one-pot reaction which is accompanied by incorporation of a keto functionality on the furan ring by activating the terminal alkynoates with phosphine. Furthermore, this protocol could also be applicable to the internal alkynoates/propiolamides to generate the 2,3-disubstituted furo[3,2-c]coumarins/furo[3,2-c]quinolinones by excluding the acyl-transfer reaction.

Investigating students’ reasoning over time for case comparisons of acyl transfer reaction mechanisms

Reasoning about organic chemistry reaction mechanisms requires engagement with multiple concepts and necessitates balancing the relative influence of different chemical properties. A goal of organic chemistry instruction is to support students with engaging in this type of reasoning. In this study, we describe our use of case comparison problems to elicit students’ reasoning about acyl transfer reaction mechanisms across a semester. Using an instrumental case study methodology, we analysed three students’ reasoning across three time points: in a pre-interview at the beginning of the semester, on their written responses to one implementation of an in-class scaffold activity, and in a post-interview near the middle of the semester. Through the theoretical lens of Hammer's resources framework, we analysed the resources that students activated when approaching the case comparison problems. We characterized how students used each resource to support their reasoning, alongside characterizing how students weighed the different resources they activated. Our findings indicate that the case comparison problems activated a number of resources for each student across the time points by encouraging students to relate the surface-feature differences between reactions with the associated underlying properties. Students generally used resources, such as resonance and steric effects, in similar ways to support their reasoning across the time points. The study also illustrates the range in students’ abilities to weigh multiple conceptual influences and how this ability might change across the semester. This case study has implications for future research exploring how students reason with multiple concepts and for instructors seeking to implement activities that support students’ reasoning with case comparison problems.

Structural Basis of Specificity for Carboxyl-Terminated Acyl Donors in a Bacterial Acyltransferase.

Macrolactins (MLNs) are a class of important antimacular degeneration and antitumor agents. Malonylated/succinylated MLNs are even more important due to their efficacy in overcoming multi-drug-resistant bacteria. However, which enzyme catalyzes this reaction remains enigmatic. Herein, we deciphered a β-lactamase homologue BmmI to be responsible for this step. BmmI could specifically attach C3-C5 alkyl acid thioesters onto 7-OH of MLN A and also exhibits substrate promiscuity toward acyl acceptors with different scaffolds. The crystal structure of BmmI covalently linked to the succinyl group and systematic mutagenesis highlighted the role of oxyanion holelike geometry in the recognition of carboxyl-terminated acyl donors. The engineering of this geometry expanded its substrate scope, with the R166A/G/Q variants recognizing up to C12 alkyl acid thioester. The structure of BmmI with acyl acceptor MLN A revealed the importance of Arg292 in the recognition of macrolide substrates. Moreover, the mechanism of the BmmI-catalyzed acyltransfer reaction was established, unmasking the deft role of Lys76 in governing acyl donors as well as catalysis. Our studies uncover the delicate mechanism underlying the substrate selectivity of acyltransferases, which would guide rational enzyme engineering for drug development.

Environment-friendly treatment to reduce photoyellowing and improve UV-blocking of wool

Wool products are widely used in people's daily life due to their various excellent properties. However, long-term exposure to solar radiation containing ultraviolet light (UV) can cause severe photoyellowing issues. Also, when used to fabricate apparel, fabrics are expected to own an outstanding UV-blocking feature to protect the skin underneath. In this study, we have developed an eco-friendly treatment to reduce the photoyellowing as well as improve UV-blocking capacity of wool fabrics by introducing para-aminobenzoic acid (PABA) through a microbial transglutaminase (mTGase) mediated acyl transfer reaction in a tris(hydroxymethyl)aminomethane-hydrochloric acid (Tris-HCl) buffer at mild condition. Fluorescent and UV–Vis reflectance spectra proved the successful attachment of PABA on wool fabrics. In addition, relative properties measured after laundering demonstrated the existence of strong covalent bonds, which ensure the stable performance of corresponding fabrics. Moreover, we found that wool fabrics processed by an appropriate concentration of PABA in the enzyme-tris reaction system could effectively resist photoyellowing and exhibit dramatic improvement of UV protection factor (UPF) values. Tensile test results indicated some improvement in the mechanical performance of the treated fabrics after long-term accelerated irradiation. The feasible and effective method developed in current research has great potential to improve the durability and performance of wool products.

Quinolin-8-yl Formate: A New Option for Small-Scale Carbonylation Reactions in Microwave Reactors

A convenient procedure for conducting small-scale carbonylations of aryl or benzyl halides in a microwave reactor by using quinolin-8-yl formate is described. The resulting 8-acyloxyquinolines were shown to be more reactive than phenyl esters in acyl-transfer reactions, and their utility for the production of esters and amides was demonstrated.

Fast and Stable N-Terminal Cysteine Modification through Thiazolidino Boronate Mediated Acyl Transfer.

We report a novel conjugation of N-terminal cysteines (NCys) that proceeds with fast kinetics and exquisite selectivity, thereby enabling facile modification of NCys-bearing proteins in complex biological milieu. This new NCys conjugation proceeds via a thiazolidine boronate (TzB) intermediate that results from fast (k2 : ≈5000 m-1 s-1 ) and reversible conjugation of NCys with 2-formylphenylboronic acid (FPBA). We designed a FPBA derivative that upon TzB formation elicits intramolecular acyl transfer to give N-acyl thiazolidines. In contrast to the quick hydrolysis of TzB, the N-acylated thiazolidines exhibit robust stability under physiologic conditions. The utility of the TzB-mediated NCys conjugation is demonstrated by rapid and non-disruptive labeling of two enzymes. Furthermore, applying this chemistry to bacteriophage allows facile chemical modification of phage libraries, which greatly expands the chemical space amenable to phage display.

A highly efficient acyl-transfer approach to urea-functionalized silanes and their immobilization onto silica gel as stationary phases for liquid chromatography.

An alternative method for efficient synthesis of urea-functionalized silanes was proposed on the basis of an N, N'-carbonyldiimidazole-mediated acyl-transfer reaction between various amino-containing building blocks. The employment of different parent aminosilanes and alkylamines afforded an array of urea-containing silanes, which were subsequently immobilized onto silica gel to form corresponding urea-embedded alkyl stationary phases for high-performance liquid chromatography. The different substituents on the silicon core of the derivatized silane were found to significantly influence the final chromatographic behaviors. The comparative chromatographic characterization of thus-prepared silica packings with conventional octadecyl (C18) stationary phases revealed that the urea group was beneficial to suppress silanol activity towards basic probes, as well as to increase the water-compatibility of the alkyl stationary phases. The combination of a polar urea moiety and a non-polar long alkyl chain was favorable for an enhanced steric selectivity towards shape-constrained isomers. The polarizability-sensitive feature of such stationary phases made them good candidates for efficient separation of nitro-containing polar substances.

Protein Engineering for Enhanced Acyltransferase Activity, Substrate Scope, and Selectivity of the Mycobacterium smegmatis Acyltransferase MsAcT

The highly efficient and versatile acyltransferase MsAcT from Mycobacterium smegmatis catalyzes aqueous acyl transfer reactions, enabling applications in environmentally friendly processes and enzy...

Substrate Recognition and Catalytic Mechanism of the Phosphate Acyltransferase PlsX from Bacillus subtilis.

Phosphate: acyl-acyl carrier protein (ACP) acyltransferase PlsX is a peripheral enzyme catalysing acyl transfer to orthophosphate in phospholipid synthesis. Little is known about how it recognises substrates and catalyses the acyl transfer. Here we show that its active site includes many residues lining a long, narrow gorge at the dimeric interface, two positive residues forming a positive ACP docking pad next to the interfacial gorge, and a number of strictly conserved residues significantly contributing to the catalytic activity. These findings suggest a substrate recognition mode and a catalytic mechanism that are different from those of phosphotransacetylases catalysing a similar acyl transfer reaction. The catalytic mechanism involves substrate activation and transition-state stabilization by two strictly conserved residues, Lys184 and Asn229. Another noticeable feature of the catalysis is the release of the acyl phosphate product near the membrane, which might facilitate its membrane insertion.

One‐pot peptide cleavage and macrocyclization through direct amidation using triazabicyclodecene

AbstractWe have developed a novel protocol for a one‐pot cleavage from solid support and subsequent cyclization to form small macrocyclic peptides. Synthesized on a 4‐hydroxymethyl benzamide (HMBA) resin, the peptides are cleaved from the solid support through a 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) assisted acyl transfer reaction. The resulting linear peptides then undergo an intramolecular cyclization, presumably upon in situ attack of the N‐terminal amine on the TBD‐activated ester. This protocol requires catalytic quantities of TBD and eliminates the need for orthogonal side chain deprotection strategies and ether trituration/work‐up steps, streamlining the synthesis of head‐to‐tail macrocyclic peptides.

Theoretical study on reaction mechanism of phosphate-catalysed N-S acyl transfer of N-sulfanylethylanilide (SEAlide).

C-Terminally thioesterificated peptides are essential building blocks for chemical protein synthesis. To date, many acyl transfer auxiliaries have been developed to enable facile preparation of peptide thioesters. We previously developed an N-sulfanylethylanilide (SEAlide) auxiliary, which causes an N-S acyl transfer reaction upon addition of phosphate salt to convert a C-terminal amide to a thioester. The mechanism of how phosphate triggers the reaction is speculative, and the details are unknown. In this study, the mechanism by which phosphate promotes acyl transfer is discussed based on density functional theory (DFT) calculations and non-covalent interaction (NCI) analysis. As a result, although the notion that phosphate acts as an acid-base catalyst, as speculated in our previous study, was correct, it became clear that two competing reaction pathways exist: a previously proposed stepwise pathway and a concerted one. Furthermore, calculation was performed in the presence of various additives other than phosphate to uncover the effect of the additives on the stability of transition states.

Nucleobase-involved native chemical ligation: a novel reaction between an oxanine nucleobase and N-terminal cysteine for oligonucleotide–peptide conjugation

In bioconjugation chemistry, achieving a target-specific reaction for a non-modified amino acid is challenging. Here, we report a novel nucleobase-involved native chemical ligation (NbCL) that allows a site-specific oligonucleotide-peptide conjugation via a new S-N acyl transfer reaction between an oxanine nucleobase and N-terminal cysteine.

Adipostatins E-J, new potent antimicrobials identified as inhibitors of coenzyme-A biosynthesis

Phosphopantetheine is a key structural element in biological acyl transfer reactions found embedded within coenzyme A (CoA). Phosphopantothenoylcysteine synthetase (PPCS) is responsible for installing a cysteamine group within phosphopantetheine. Therefore, it holds considerable potential as a drug target for developing new antimicrobials. In this study, we adapted a biochemical assay specific for bacterial PPCS to screen for inhibitors of CoA biosynthesis against a library of marine microbial derived natural product extracts (NPEs). Analysis of the NPE derived from Streptomyces blancoensis led to the isolation of novel antibiotics (10–12, and 14) from the adipostatin class of molecules. The most potent molecule (10) displayed in vitro activity with IC50 = 0.93 µM, against S. pneumoniae PPCS. The whole cell antimicrobial assay against isolated molecules demonstrated their ability to penetrate bacterial cells and inhibit clinically relevant pathogenic strains. This establishes the validity of PPCS as a pertinent drug target, and the value of NPEs to provide new antibiotics.

Thermal Metamorphosis in (Meth)acrylate Photopolymers: Stress Relaxation, Reshaping, and Second-Stage Reaction

Thermally transformable/responsive (meth)acrylate photopolymer networks were constructed from commercial (meth)acrylate esters and synthetic di- and mono(meth)acylate monomers bearing thioester functionalities. The thermal responsiveness, here self-limited exchange, relied on the catalytic metamorphosis of thioesters into esters with the concomitant depletion of hydroxyls and subsequent generation of free thiols. The thioester–hydroxyl cross-exchange was demonstrated in network systems with interchain thioesters as well as in networks with side-chain pendant thioacetyls. The interchain metamorphosis resulted in close to 80% conversion of thioesters into esters when 2 equiv of hydroxyl groups was initially present. In practical terms, such an outcome enabled efficient stress relaxation (60%) and good shape adaptation (90% shape fixity) in 1 h at 105 °C. On the other hand, side-chain S → O acyl transfer reactions were found to vary in efficiency depending on the vicinity of thioesters and hydroxyls. When in close vicinity, efficient noncatalytic exchange was observed in materials with 1-to-1 thioester-to-hydroxyl ratios nearing 60%. The benefits of generating free thiols postpolymerization were further explored in enhanced two-stage curing systems where a subsequent thiol–ene photopolymerization was demonstrated at ambient as well as at elevated temperatures.

Origins of Enantiopreference of Mycobacterium smegmatis Acyl Transferase: A Computational Analysis.

Acyl transferase from Mycobacterium smegmatis (MsAcT) is a promising biocatalyst because it catalyzes an acyl transfer reaction in aqueous solution, thereby accepting many primary and secondary alcohols as substrates. MsAcT also exhibits high enantioselectivity for a selected number of secondary alcohols. To increase the applicability of this enzyme for the production of optically active compounds, a detailed understanding of the reaction mechanism and the factors that affect enantioselectivity is essential. Herein, quantum chemical calculations are employed to study the reactions of two secondary alcohols, 1-isopropyl propargyl alcohol and 2-hydroxy propanenitrile, for which the enzyme displays opposite enantiopreference, favoring the S enantiomer in the former case and R enantiomer in the latter. A model of the active site has been designed and for both substrates various binding modes are evaluated and the intermediates and transition states along the reaction path are then located. The calculated energy profiles agree with the experimental observations, and reproduce the selectivity outcome. Through a detailed analysis of the geometries of key transition states, insights into the origins of the enantiopreference are obtained.