Acylation Process Research Articles

The crystal structure of ESBL TLA-1 in complex with clavulanic acid reveals a second acylation site

β-lactamases are the main molecules responsible for giving bacterial resistance against β-lactam antibiotics. The study of β-lactamases has allowed the development of antibiotics capable of inhibiting these enzymes. In this context, extended spectrum β-lactamase (ESBL) TLA-1 has spread in Escherichia coli and Enterobacter cloacae clinical isolates during the last 30 years in Mexico. In this research, the 3D structures of ESBL TLA-1 and TLA-1 S70G mutant, both ligand-free and in complex with clavulanic acid were determined by X-ray crystallography. Four clavulanic acid molecules were found in the structure of TLA-1, two of those were intermediaries of the acylation process and were localized covalently bound to two different amino acid residues, Ser70 and Ser237. The coordinates of TLA-1 in complex with clavulanic acid shows the existence of a second acylation site, additional to Ser70, which might be extendable to several members of the subclass A β-lactamases family. This is the first time that two serines involved in binding clavulanic acid has been reported and described to an atomic level.

O-Acylation of chitosan by l-arginine to remove the heavy metals and total organic carbon (TOC) from wastewater

Chitosan has acylated with l-arginine in the presence of H2SO4 as a catalyst to the aim of increasing the adsorption efficiency. Chitosan (CS) and chitosan-O-arginine (CS-Arg) were characterized and investigated by elemental analysis, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The results obtained from elemental analysis exhibited presence of sulfur content, indicate that sulfuric acid still a crosslinker between CS-Arg chains, also the degree of substitution (DS) of l arginine in CS backbone was 1.83, indicate the acylation process has took place in both C3-OH and C6-OH of CS. XRD results exhibited that CS-Arg is more crystalline than CS, due to the formation of intra and inter molecular hydrogen bonds between amino and hydroxyl groups. The removal of heavy metals (Mn2+, Pb2+and Al3+) and total organic carbon (TOC) from wastewater by CS and CS-Arg in batch mode has been studied at different adsorbent dosages, temperatures and contact times. The maximum removal efficiency for three metal ions using CS achieved 99.6%, 99.1% and 98.9%, respectively, while by using CS-Arg were 97.1%, 94.3% and 99%. However, the maximum adsorption capacity of TOC by CS achieved 50 mg/g and 40.35 mg/g by CS-Arg. The total maximum adsorption capacity of CS-Arg is lower than CS.

Non-covalent and covalent immobilization of Candida antarctica lipase B on chemically modified multiwalled carbon nanotubes for a green acylation process in supercritical CO2

• Efficient immobilization of Candida antarctica B lipase on modified MWCNTs. • Enzyme loading reaching as high as 21 wt.% for non-covalent immobilization. • Active O-acylation of geraniol into geranyl acetate by CAL-B in supercritical CO 2 . • Reaction regioselectivity unchanged through immobilization. • Development of a fully green enzymatic process. Candida antarctica B lipase (CAL-B) was immobilized on purified and functionalized multiwalled carbon nanotubes (MWCNTs). Both immobilization routes, physical adsorption and covalent bonding, were investigated. MWCNT functionalization by a non-aggressive oxidation by potassium permanganate led to an interesting balance between the hydrophilic and the hydrophobic areas of the MWCNT surface; the former being responsible of the good dispersion of MWCNTs in water and the latter having a favorable affinity with CAL-B. The enzyme loadings reached were significant: around 16 wt. % and 21 wt.% for non-covalent and covalent immobilization, respectively. The enzymatic activity was studied with the reaction of O-acylation of geraniol into geranyl acetate by CAL-B in supercritical CO 2 . Even if a decay in synthesis of geranyl acetate was observed over cycling for both CAL-B@MWCNT catalysts, it was demonstrated that the regioselectivity of CAL-B was unchanged through immobilization on the MWCNT surface for both routes. Interestingly, it was shown that a fully green enzymatic process can be achieved with these prepared CAL-B@MWCNT biocatalyst. Such approach could be transferred to other support/enzyme systems for developing new eco-friendly synthesis processes.

Quantum Mechanics/Molecular Mechanics (QM/MM) Calculations Support a Concerted Reaction Mechanism for the Zika Virus NS2B/NS3 Serine Protease with Its Substrate.

Zika virus (ZIKV) is mainly transmitted to humans by Aedes species mosquitoes and is associated with serious pathological disorders including microcephaly in newborns and Guillain-Barré syndrome in adults. Currently, there is no vaccine or anti-ZIKV drug available for preventing or controlling ZIKV infection. An attractive drug target for ZIKV treatment is a two-compartment (NS2B/NS3) serine protease that processes viral polyprotein during infection. Here, conventional molecular dynamics simulations of the ZIKV protease in complex with peptide substrate (TGKRS) sequence at the C-terminus of NS2B show that the substrate is in the active conformation for the cleavage reaction by ZIKV protease. Hybrid quantum mechanics/molecular mechanics (QM/MM) umbrella sampling simulations (PM6/ff14SB) of acylation results reveal that proton transfer from S135 to H51 and nucleophilic attack on the substrate by S135 are concerted. The rate-limiting step involves the formation of a tetrahedral intermediate. In addition, the single-point energy QM/MM calculations, precisely at the level of coupled cluster theory (LCCSD(T)/(aug)-cc-pVTZ), were performed to correct the potential energy profiles for the first step of the acylation process. The average computed activation barrier at this level of theory is 16.3 kcal mol-1. Therefore, the computational approaches presented here are helpful for further designing of NS2B/NS3 inhibitors based on transition-state analogues.

Computational insight into the mechanism and origins of high selectivities in the acylation of polyamines with 5-benzoyl-5-phenyl-1,5-dihydro-4H-pyrazol-4-one.

Amide bonds have gained much attention from numerous scientists and acyl transfer is a good way to form amide bonds. The acylation mechanism of polyamines and their high selectivity in dichloromethane were investigated by the use of the density functional theory (DFT), M06-2X/6-311+G (d, p)//M06-2X/6-31G (d, p) method combined with the solvation SMD model. The calculated results suggest that the reaction process involved two steps: an acylation step and a proton-transfer step, with the former being the rate-limiting step. Meanwhile, with the substituent group effects of amines and 5-acyl-5-phenyl-1,5-dihydro-4H-pyrazol-4-one (BCPP) on the acylation step, different substituent groups of amines have little influence on the kinetic properties of the acylation step, and the para-substituent groups of the phenyl group in BCPP lead to a linear relationship according to the electronegativity of the substituents. Furthermore, regarding the rate-selectivity of amines, the rate-selectivity of primary amines is higher than that of secondary amines, and polyamines very easily take part in acylation owing to the intramolecular hydrogen bond interaction. Moreover, it is harder for the amine group which has an α-position substituent group in polyamines to take part in an acylation reaction compared to the one without an α-position substituent group. The site-selectivity of the acylation process in polyamines is determined by steric hindrance. What's more, the auxiliary analysis of the distortion/interaction analysis and the frontier molecular orbital (FMO) analysis is used to investigate the origins of the rate- and site-selectivities.

Stereocontrolled Synthesis of 1,4-Dicarbonyl Compounds by Photochemical Organocatalytic Acyl Radical Addition to Enals.

We report a visible‐light‐mediated organocatalytic strategy for the enantioselective acyl radical conjugate addition to enals, leading to valuable 1,4‐dicarbonyl compounds. The process capitalizes upon the excited‐state reactivity of 4‐acyl‐1,4‐dihydropyridines that, upon visible‐light absorption, can trigger the generation of acyl radicals. By means of a chiral amine catalyst, iminium ion activation of enals ensures a stereoselective radical trap. We also demonstrate how the combination of this acylation process with a second catalyst‐controlled bond‐forming event allows to selectively access the full matrix of all possible stereoisomers of the resulting 2,3‐substituted 1,4‐dicarbonyl products.

Stereocontrolled Synthesis of 1,4‐Dicarbonyl Compounds by Photochemical Organocatalytic Acyl Radical Addition to Enals

AbstractWe report a visible‐light‐mediated organocatalytic strategy for the enantioselective acyl radical conjugate addition to enals, leading to valuable 1,4‐dicarbonyl compounds. The process capitalizes upon the excited‐state reactivity of 4‐acyl‐1,4‐dihydropyridines that, upon visible‐light absorption, can trigger the generation of acyl radicals. By means of a chiral amine catalyst, iminium ion activation of enals ensures a stereoselective radical trap. We also demonstrate how the combination of this acylation process with a second catalyst‐controlled bond‐forming event allows to selectively access the full matrix of all possible stereoisomers of the resulting 2,3‐substituted 1,4‐dicarbonyl products.

Requirement of Two Acyltransferases for 4- O-Acylation during Biosynthesis of Harzianum A, an Antifungal Trichothecene Produced by Trichoderma arundinaceum.

Trichothecenes are sesquiterpenoid toxins produced by multiple fungi, including plant pathogens, entomopathogens, and saprotrophs. Most of these fungi have the acyltransferase-encoding gene tri18. Even though its function has not been determined, tri18 is predicted to be involved in trichothecene biosynthesis because of its pattern of expression and its location near other trichothecene biosynthetic genes. Here, molecular genetic, precursor feeding, and analytical chemistry experiments indicate that in the saprotroph Trichoderma arundinaceum the tri18-encoded acyltransferase (TRI18) and a previously characterized acyltransferase (TRI3) are required for conversion of the trichothecene biosynthetic intermediate trichodermol to harzianum A, an antifungal trichothecene analog with an octa-2,4,6-trienedioyl acyl group. On the basis of the results, we propose that TRI3 catalyzes trichothecene 4- O-acetylation, and subsequently, TRI18 catalyzes replacement of the resulting acetyl group with octa-2,4,6-trienedioyl to form harzianum A. Thus, the findings provide evidence for a previously unrecognized two-step acylation process during trichothecene biosynthesis in T. arundinaceum and possibly other fungi.

Catalytic Reaction Mechanism for Drug Metabolism in Human Carboxylesterase-1: Cocaine Hydrolysis Pathway.

Carboxylesterase-1 (CE-1) is a crucial enzyme responsible for metabolism/activation/inactivation of xenobiotics (therapeutic agents, prodrugs, abused drugs, and organophosphorus nerve agents etc.) and also involved in many other biological processes. In this study, we performed extensive computational modeling and simulations to understand the fundamental reaction mechanism of cocaine hydrolysis catalyzed by CE-1, revealing that CE-1-catalyzed cocaine hydrolysis follows a novel reaction pathway with only two reaction steps: a single-step acylation process and a single-step deacylation process. In the transition states of both single-step processes, the cocaine NH group joins the oxyanion hole to form an additional hydrogen bond with the negatively charged carbonyl oxygen atom of the cocaine. Thus, the transition states are stabilized by both intermolecular and intramolecular hydrogen bonds with the methyl ester of cocaine, specifically the carbonyl oxygen atom. The rate-limiting transition state is associated with the acylation process, and the activation free energy barrier was predicted to be 20.1 kcal/mol. Further, in vitro experimental kinetic analysis was performed for human CE-1-catalyzed cocaine hydrolysis. For CE-1-catalyzed cocaine hydrolysis, the computationally predicted free energy barrier (20.1 kcal/mol) is reasonably close to the experimentally derived turnover number ( kcat = 0.058 min-1), indicating the reasonability of the computational results. The obtained novel mechanistic insights are expected to benefit not only CE-1 related rational drug discovery but also future research on the catalytic mechanism of other esterases.

Modular photoinduced grafting onto approach by ketene chemistry

ABSTRACTA modular approach for the synthesis of graft copolymers by the combination of reversible addition–fragmentation chain‐transfer (RAFT) polymerization and photoinduced acylation processes is described. In the two‐step approach, first the copolymers of benzodioxinone containing monomer, namely, 4‐oxo‐2,2‐diphenyl‐4H‐benzo[d][1,3]dioxin‐7‐yl methacrylate (BDMA) and methyl methacrylate (MMA) in different feed ratios were prepared by RAFT polymerization. In the subsequent step, dichloromethane solutions of these copolymers (PMMA‐co‐PBDMA) were irradiated at λ = 300 nm in the presence of independently prepared hydroxyl functional polymers such as poly(ethylene glycol) (MeO‐PEG‐OH) and poly(ɛ‐caprolactone) (PCL‐OH). Side‐chain esterification reaction between photochemically generated ketene groups and hydroxyl functionalities resulted in the formation graft copolymers. The intermediates and final graft copolymers were characterized by 1H NMR, UV, IR, fluorescence, and GPC measurements. The success of the process was also confirmed by a model reaction using pyrene methanol. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 274–280

Enantioselective Synthesis of Aminodiols by Sequential Rhodium-Catalysed Oxyamination/Kinetic Resolution: Expanding the Substrate Scope of Amidine-Based Catalysis.

Regio- and stereoselective oxyamination of dienes through a tandem rhodium-catalysed aziridination-nucleophilic opening affords racemic oxazolidinone derivatives, which undergo a kinetic resolution acylation process with amidine-based catalysts (ABCs) to achieve s values of up to 117. This protocol was applied to the enantioselective synthesis of sphingosine.

High-Temperature Batch and Continuous-Flow Transesterification of Alkyl and Enol Esters with Glycerol and Its Acetal Derivatives

A new procedure for the transesterification of alkyl acetates and formates with model glycerol acetals (GAs: Solketal and glycerol formal) was explored in the absence of any catalysts at 180–275 °C. Highly selective transformations occurred in both batch and continuous-flow (CF) modes; particularly, the enol derivative isopropenyl acetate (iPAc) was the best performing reactant by which quantitative acetylation reactions were achieved with yields on GAs acetates >95%. An excess acylating agent was necessary (2–20 molar equivs), but the unconverted ester was fully recovered and could be reused. The reaction plausibly involved multiple mechanisms where either the electrophilic and the nucleophilic activation of reagents took place through both traces of acetic acid (formed in situ by the hydrolysis of esters) and the autoprotolysis of GAs. iPAc confirmed a superior performance than other esters also for the high-temperature conversion of glycerol; in this case, although acylation and acetalization processes...

Hydrogen bond donor solvents enabled metal and halogen-free Friedel–Crafts acylations with virtually no waste stream

We have developed a metal and halogen-free Friedel–Crafts acylation protocol with virtually no waste stream generation. We propose a hydrogen bonding donor solvent will form a hydrogen bonding network and may provide significant rate enhancement for Friedel–Crafts reactions. Trifluoroacetic acid is one of the strongest H-bond donor solvents, which is also volatile and can be easily recovered by distillation without need for reaction workup. Our protocol is a ‘green’ Friedel–Crafts acylation process: 1) the catalyst can be recovered and reused; 2) using halogen free starting material (carboxylic acids anhydride or carboxylic acids); 3) no need for aqueous reaction work-up; 4) minimum or no waste steam generation.

Improvement of the self-consistent-charge density-functional-tight-binding theory by a modified Mulliken charge

Although extensive efforts had been carried out to improve the accuracy of the self-consistent-charge density-functional-tight-binding (SCC-DFTB), the application of SCC-DFTB on biological systems (e.g., enzymes) is still limited. Our benchmark calculations show that the original SCC-DFTB/MM is not able to properly descript the human carboxylesterase 1 (CES1) catalyzed hydrolysis of d-threo-methylphenidate (dMD). In contrast to the ab initio QM/MM results, SCC-DFTB/MM underestimates the activation free energy barrier and renders the acylation process as a single-step reaction without a tetrahedral intermediate. It seems like that SCC-DFTB/MM misestimates the developing negative QM Mulliken charge of the substrate oxygen atom in the oxyanion hole. To improve the SCC-DFTB energy and the electrostatic interaction between QM (SCC-DFTB) and MM atoms, we adopt an optimization strategy for QM Mulliken charge, in which an empirical parameter is trained to fit the SCC-DFTB Mulliken charge to high-level DFT method along the reaction coordinate. Herein, the optimized Mulliken charge-based SCC-DFTB method is denoted as SCC-DFTBMR. Finally, benchmark and free energy calculations were performed to prove the applicability of SCC-DFTBMR to CES1-catalyzed reaction.

An efficient and green pathway for continuous Friedel-Crafts acylation over α-Fe2O3 and CaCO3 nanoparticles prepared in the microreactors

α-Fe2O3 nanoparticles were prepared by using a continuous precipitation method with a valve assisted micromixer in the presence of iron (III) sulfate and ammonia water. The resulting nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). Meanwhile, CaCO3 nanoparticles were synthesized in a tube-in-tube flow reactor AF-2400. The acylation process catalyzed by modified lipophilic α-Fe2O3 and CaCO3 nanoparticles in the flow reactor were systematically investigated. Under the optimal conditions, a yield of 97.8% was obtained. Addition of CaCO3 nanoparticles resulted in higher catalytic efficiency compared with pure modified α-Fe2O3 nanoparticles. Moreover, this novel acylation also worked well for other substrates.

Preparation of the HIV Attachment Inhibitor BMS-663068. Part 6. Friedel–Crafts Acylation/Hydrolysis and Amidation

The development of a process for appending the oxalyl amide side chain to the azaindole core of the HIV-attachment inhibitor BMS-663068 is described. A Friedel–Crafts acylation installed the oxalyl ester, which was subsequently hydrolyzed and amidated with a benzoyl piperazine. The development of the commercial route necessitated several key changes to the initial synthesis. For instance, in the original acylation process, nitromethane, a commonly used, but highly energetic cosolvent, was employed which was eventually replaced by catalytic tetra-n-butylammonium bisulfate to overcome gelling issues encountered during the reaction when nitromethane was omitted. It was further demonstrated that the amidation sequence could be relegated to a single-pot, homogeneous transformation through the use of the cost-effective coupling reagent diphenylphosphinic chloride. The above modifications have been utilized in multiple campaigns and reproducibly demonstrated on scales of up to 200 kg input.

A water-assisted nucleophilic mechanism utilized by BphD, the meta-cleavage product hydrolase in biphenyl degradation

As members of the α/β-hydrolase superfamily, Meta-cleavage product (MCP) hydrolases generally utilize a Ser-His-Asp catalytic triad to hydrolyze the cleavage of CC bond during the aerobic catabolism of aromatic compounds by bacteria. BphD is one kind of MCP hydrolase that catalyzes the hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) to 2-hydroxypenta-2,4-dienoic acid (HPD) and benzoate. In this article, a combined quantum mechanics and molecule mechanics (QM/MM) approach has been employed to explore the reaction mechanism of BphD from Burkholderia xenovorans LB400. On the basis of the recently resolved crystal structures, three computational models have been constructed. Our calculation results reveal that BphD utilizes a water-assisted nucleophilic mechanism, which contains acylation and deacylation stages. In acylation reaction, an active site water molecule assists the proton transfer from Ser112 to the carbanion intermediate (substrate) by forming hydrogen bonds with Ser112 and His265, and this proton transfer is in concert with the nucleophilic attack of deprotonated Ser112 on the C6-carbonyl of substrate to form the acylated intermediate. In deacylation, the Asp237-His265 dyad acts as a general base to activate the hydrolytic water, whose nucleophilic attack leads to the collapses of acyl-enzyme intermediate. The acylation and deacylation process correspond to the highest energy barriers of 21.0 and 23.9kcal/mol, respectively. During the catalytic reaction, the active site water and Asp237-His265 dyad play an important role for each elementary steps.

Enzyme catalysis: the case of the prostate-specific antigen

Proteases are a class of enzymes that lower the activation energy for the cleavage of the peptide bonds by polarizing the carbonyl group. The catalytic mechanism of proteases is characterized by the formation and the dissociation of a tetrahedral acyl-intermediate. The rate-limiting step in catalysis is either the acylation process (leading to the release of the newly formed $$ {-}{\text{NH}}_{3}^{ + } $$ terminal) or the subsequent deacylation step (leading to the release of the newly formed –COO− terminal). As a case, the detailed kinetic analysis for the hydrolysis of the chromogenic substrate Mu-His-Ser-Ser-Lys-Leu-Gln-AMC (wherein Mu is the morpholinocarbonyl protecting group and AMC is the 7-amino-4-methylcoumarin chromophoric group) by the prostate-specific antigen (PSA) is reported here. The pH dependence of the catalytic parameters clearly indicates the existence of protonation/deprotonation processes involving (at least) two ionizing groups in the proximity of the active site. In view of the physio-pathological relevance of PSA in prostate diseases (including cancer), the detailed analysis of the catalytic parameters opens new scenarios for the design of selective inhibitors, which might influence the “in vivo” activity of this protease.

Direct synthesis of 2-/3-(trifluoromethyl)thiochroman-4-ones: Superacid-induced tandem alkylation-cyclic acylation of benzenethiols using 2-/3-(trifluoromethyl)acrylic acid

Incorporation of fluorinated heterocyclic framework into organic molecules results in profound changes in their physical, chemical and biological properties. Realizing that the fluorinated thiochroman-4-ones are important scaffolds in medicinal chemistry and are rare in the chemical literature, one-pot synthesis of 2-/3-(trifluoromethyl)thiochroman-4-ones was attempted. Direct access to 2-/3-(trifluoromethyl)thiochroman-4-ones was achieved by a tandem alkylation-cyclic acylation process promoted by superelectrophilic activation of 2-/3-(trifluoromethyl)acrylic acid in superacidic trifluoromethanesulfonic acid under microwave-assisted Friedel-Crafts alkylation of benzenethiols followed by cyclization (via intramolecular acylation). Synthesis of a series of 2-/3-(trifluoromethyl)thiochroman-4-ones from protosolvated 2-/3-(trifluoromethyl)acrylic acid intermediates and benzenethiols is described.

Acylperoxycoumarins asortho-CH Acylating Agentviaa Palladium(II)-Catalyzed Redox-Neutral Process

An unprecedented palladium(II)-catalyzed biomimetic aliphatic acyl (-COR) group transfer was observed from acyl-α-peroxycoumarins to the ortho CH sites of directing arenes. Here, the CH activation is associated with a concomitant acyl group transfer via a Pd(II)-catalyzed, redox-neutral process. While methods for ortho aroylation (-COAr) are well documented ortho acylation (-COR) processes are scarce, hence the present redox-neutral method is most ideal for o-acylation of directing substrates.