Acyl Migration Research Articles

Impact of solvent and water activity on lipase selectivity and acyl migration of ARA-rich 2-monoacylglycerols in catalytic systems: Kinetic study by particle swarm optimization

The 2-arachidonoylglycerol enzymatic alcoholysis reaction model was established and kinetic parameters were calculated to explore the effects of solvent and water activity (aw) on the lipase positional selectivity and 2-monoacylglycerol acyl migration. Six rate constants (k1-k6) with the lowest mean square error were obtained using the particle swarm optimization algorithm, and the calculated molar concentration-time curves were well-fitted to the actual curves. As an indicator to characterize the positional selectivity of lipase, k5/k3 was significantly associated with log P of solvent, which first increased and then decreased with the increase of aw. The highest sn-1,3 selectivity of Lipozyme TL IM was found at the aw of 0.53. The changes of acyl migration with the solvent and aw in the enzymatic and non-catalytic systems showed a consistent law. This study provides theoretical support for the targeted synthesis of structural lipids and enzymatic production of diverse structural lipid products.

Applications of Baker-venkataraman Rearrangement in the Synthesis of Promising Organic Molecules

Abstract:: In organic synthesis, carbon-carbon bond formation is the fundamental transformation to create the carbon backbone of organic molecules and this key reaction is very popular in the improvement of organic chemistry, which exists at the bottom of the heart of the chemical sciences. The Baker- Venkataraman rearrangement has received great attention in the formation of 1,3-diketones through the regioselective construction of carboncarbon bonds. This rearrangement is an important type of chemical transformation in which the intramolecular migration of the ester acyl group takes place to provide 1,3-diketones in the presence of the base. Generally, 1,3-diketones or ortho-hydroxydibenzoylmethane derivatives undergo cyclization to provide the corresponding flavones in the presence of concentrated sulfuric acid. The Baker-Venkataraman rearrangement is frequently employed in the preparation of flavones and chromones. Besides, anthrapyran and anthracyclin antibiotics, benzopyrans, coumarins, xanthones, etc., are also synthesized with the help of these reactions. This review deals with the brilliant application of the Baker-Venkataraman rearrangement in the synthesis of promising organic compounds.

PLA2G15 is a Lysosomal BMP Hydrolase with Ester Position Specificity and its Targeting Ameliorates Lysosomal Disease.

Lysosomes catabolize lipids and other biological molecules, a function essential for cellular and organismal homeostasis. Key to lipid catabolism in the lysosome is bis(monoacylglycero)phosphate (BMP), a major lipid constituent of intralysosomal vesicles (ILVs) and a stimulator of lipid-degrading enzymes. BMP levels are altered in a broad spectrum of human conditions, including neurodegenerative diseases. Although BMP synthase was recently discovered, it has long been thought that BMP's unique stereochemistry confers resistance to acid phospholipases, a requirement for its role in the lysosome. Here, we demonstrate that PLA2G15, a major lysosomal phospholipase, efficiently hydrolyzes BMP with primary esters regardless of stereochemistry. Interestingly, we discover that BMP's unique esterification position is what confers resistance to hydrolysis. Purified PLA2G15 catabolizes most BMP species derived from cell and tissue lysosomes under acidic conditions. Furthermore, PLA2G15 catalytic activity against synthesized BMP stereoisomers with primary esters was comparable to its canonical substrates. Conversely, BMP with secondary esters is intrinsically stable in vitro and requires acyl migration for hydrolysis in lysosomes. Consistent with our biochemical data, PLA2G15-deficient tissues and cells accumulate multiple BMP species, a phenotype reversible by supplementing wildtype PLA2G15 but not its catalytically dead mutant. Increasing BMP levels by targeting PLA2G15 reverses the cholesterol accumulation phenotype in Niemann Pick Disease Type C (NPC1) patient fibroblasts and significantly ameliorate disease pathologies in NPC1-deficient mice leading to extended lifespan. Our findings establish the rules that govern the stability of BMP in the lysosome and identify PLA2G15 as a lysosomal BMP hydrolase and as a potential target for modulating BMP levels for therapeutic intervention.

Transacylation and hydrolysis of the acyl glucuronides of ibuprofen and its α-methyl-substituted analogues investigated by 1H NMR spectroscopy and computational chemistry: Implications for drug design

Drugs and drug metabolites containing a carboxylic-acid moiety can undergo in vivo conjugation to form 1-β-O-acyl-glucuronides (1-β-O-AGs). In addition to hydrolysis, these conjugates can undergo spontaneous acyl migration, and anomerisation reactions, resulting in a range of positional isomers. Facile transacylation has been suggested as a mechanism contributing to the toxicity of acyl glucuronides, with the kinetics of these processes thought to be a factor. Previous 1H NMR spectroscopic and HPLC-MS studies have been conducted to measure the degradation rates of the 1-β-O-AGs of three nonsteroidal anti-inflammatory drugs (ibufenac, R-ibuprofen, S-ibuprofen) and a dimethyl-analogue (termed here as “bibuprofen”). These studies have also determined the relative contributions of hydrolysis and acyl migration in both buffered aqueous solution, and human plasma. Here, a detailed kinetic analysis is reported, providing the individual rate constants for the acyl migration and hydrolysis reactions observed in buffer for each of the 4 AGs, together with the overall degradation rate constants of the parent 1-β-O-AGs. Computational modelling of the reactants and transition states of the transacylation reaction using density functional theory indicated differences in the activation energies that reflected the influence of both substitution and stereochemistry on the rate of transacylation/hydrolysis.

Lipase-Catalyzed Preparation and Optimization of Structured Phosphatidylcholine Containing Nervonic Acid.

This study investigated the incorporation of nervonic acid into the chemical structure of phosphatidylcholine via a lipase-catalyzed acidolysis reaction to obtain a functional phospholipid. Lipase immobilization was conducted, and Amberlite XAD7-HP was selected as a carrier to immobilize phospholipase A1 (PLA1) for subsequent experiments. The main acidolysis reaction parameters, including enzyme load, substrate ratio, temperature, and water content, were studied against the reaction time. The optimum reaction conditions obtained were enzyme load, 20%; reaction temperature, 55 °C; water content, 1%; and reaction time, 9 h. The maximum incorporation of nervonic acid into phosphatidylcholine was 48 mol%, with PC recovery at 61.6 mol%. The positional distribution of structured phosphatidylcholine shows that nervonic acid was found in the sn-1 position due to enzyme specificity and in the sn-2 position, possibly due to acyl migration.

Mechanism and origin of enantioselectivity for asymmetric Passerini reaction in the synthesis of ɑ-acyloxyamide catalyzed by chiral phosphoric acid

The enantioselective control of the three-component Passerini reaction was successfully achieved using chiral phosphoric acid as a catalyst with a wide range of substrates and high stereoselectivity. Quantum mechanical calculations reveals the detailed reaction mechanism and enantioselective origin of the reaction. The calculations revealed that the chiral phosphoric acid first forms a stable heterodimer with the carboxylic acid substrate, followed by C-C and C-O bond formations, the generation of a five-membered cyclic intermediate, and finally acyl migration to yield the product. Four reaction paths for the overall process were identified and compared to determine the optimal major and by-product paths. The enantioselective origin of the reaction has been elucidated systematically using distortion/interaction theory and truncated model system. QTAIM and IGMH analyses demonstrated the type and strength of interaction between catalyst and the substrates. The calculated e.e. value was 93 %, which was in good agreement with the experimental value. It is expected that the results of this study will offer new insights into the field of asymmetric Passerini reactions.

Gold Catalysis, Asymmetric Friedel-Crafts Alkylation Cascade for One-Pot Synthesis of Chiral Dihydrocarbazoles and Dihydrodibenzofurans.

A one-pot gold-catalyzed acyl migration followed by ytterbium-catalyzed asymmetric Friedel-Crafts alkylation is disclosed, leading to the rapid synthesis of chiral dihydrocarbazoles and dihydrodibenzofuran in generally moderate to good overall yields with good to excellent enantioselectivities. The gold-catalyzed acyl migration of propargyl acetates generates α-ylidene-β-diketones with high E/Z ratios, which are then subjected to the ytterbium-catalyzed asymmetric Friedel-Crafts alkylation without any purification. Importantly, this protocol provides a new type of substrate for asymmetric Friedel-Crafts alkylation.

Batch and continuous enzymatic interesterification of beef tallow: Interesterification degree, reaction relationship, and physicochemical properties

The relationship between batch and continuous enzymatic interesterification was studied through enzymatic interesterification of beef tallow. The interesterification degree (ID) during the batch reaction was monitored based on triacylglycerol composition, sn-2 fatty acid composition, solid fat content, and melting profile and was described by an exponential model. A relationship equation featuring reaction parameters of the two reations was established to predict the ID and physicochemical characteristics in continuous interesterification. The prediction of the ID based on triacylglycerol composition was reliable, with an R2 value greater than 0.85. Interesterification produced more high-melting-point components for both reactions, but the acyl migration in the batch-stirring reactor was much greater, resulting in faster crystallization, a more delicate crystal network, and lower hardness. The relationship equation can be employed to predict the ID, but the prediction of physicochemical properties was constrained by the difference in acyl migration degree between the two reactions.

Synthesis of lipids with sn-2 palmitic acid and sn-1,3 oleic acid from hard palm stearin and oleic acid

Human milk fat substitute (HMFS) is a fat that contains 1,3-dioleoyl-2-palmitoyl-glycerol (OPO) as the main triacylglycerol. Hard palm stearin (HPS) is a palm oil fraction containing high palmitic acid (PA), which can be used as a raw material in OPO synthesis. The challenge in OPO synthesis using HPS is to maintain sn-2 PA and increase sn-1,3 oleic acid (OA). This research was conducted to synthesize OPO through enzymatic acidolysis of the HPS-solid fraction and OA (1:6, mole ratio) using Lipozyme TL IM 10% of the substrate weight at 60 °C for 2 – 24 h. The results showed that acidolysis caused increased partial acylglycerol, decreased TAG, and decreased sn-2 PA while increased sn-2 OA and sn-1,3 OA. The presence of acyl migration caused the incorporation of OA using Lipozyme TL IM at the sn-1,3 positions after 2 h was not significantly different. The product obtained at 2 h contained TAG with 74% sn-2 PA and 17% sn-2 OA, 78% sn-1,3 PA, and 11% sn-1,3 OA.

Regiospecificity of Immobilized Candida antarctica Lipase B (CAL-B) towards 2,3-Diacyl-1-O-alkyl Glyceryl Ether in Ethanol.

Highly pure 2,3-dioleoyl-1-O-alkyl glyceryl ether (DOGE), whose 1-position is a lipase-tolerant ether bond, was chemically synthesized and its detailed regioselectivity and acyl transfer were confirmed. During ethanolysis using immobilized Candida antarctica lipase B (CAL-B) with DOGE as the substrate, monooleoyl-1-O-alkyl glyceryl ethers (MOGEs) and a few 1-alkyl glyceryl ethers were formed upon consumption of the substrate. The structure of MOGE was confirmed using nuclear magnetic resonance spectroscopy and only the isomer of 2-MOGE was formed, indicating that CAL-B has complete α- regiospecificity. During ethanolysis, 3-MOGE was formed via acyl migration. These results indicate that the formation of 1-alkyl glyceryl ethers is not due to the imperfect regiospecificity of CAL-B, but rather due to ethanolysis of the formed 3-MOGE. The ethanolysis rate at the 3-α-position of DOGE was faster and the rate of acyl transfer was slightly slower for chain lengths greater than 14. These results show for the first time that both deacylation at the 3-position and acyl migration from the 2- to 3-position are affected by the structure of 1-position.

Reaction of unsymmetrical α-bromo-1,3-diketones with N-substituted thioureas: regioselective access to 2-(N-arylamino)-5-acyl-4-methylthiazoles and/or rearranged 2-(N-acylimino)-3-N-aryl-4-methylthiazoles.

The present study reports some fascinating results of Hantzsch's [3 + 2] cyclic condensation of α-bromo-1,3-diketones, a tri-electrophilic synthon generated in situ by bromination of 1,3-diketones using the mild brominating reagent NBS with trinucleophilic N-substituted thioureas. Interestingly, out of a total of 20 combinations, 10 resulted in the exclusive formation of the desired 2-(N-arylamino)-5-acyl-4-methylthiazoles regioselectively, seven led to the formation of unexpected 2-(N-acylimino)-3-N-aryl-4-methylthiazoles through an interesting C-N acyl migration, and three furnished a mixture consisting of both products. The regioselectivity pattern of the two products may be attributed to a greater electrophilicity of the carbonyl carbon of the acetyl group than that of the acyl group towards both nitrogens of thiourea. The structures of the thiazole derivatives were unambiguously assigned using 1H-NMR, 13C-NMR, and rigorous heteronuclear 2D-NMR [(1H-13C) HMQC and (1H-13C) HMBC] spectroscopic techniques. The outcomes of the spectroscopic experiments were further concurred through X-ray crystallographic studies, and a plausible mechanism for acyl migration was proposed for the formation of the unexpected rearranged product.

Unprecedented single-electron-transfer reduction-based N → C acyl migration reactions of imides enabled by redox-neutral photocatalysis

N → C acyl migration: in the absence of a base, redox-neutral photocatalyzed acyl migration reactions have been realized via the reaction of N-vinylimides with alkyl radicals derived from alkyl silicates.

Simple pyrazoles as efficient organocatalysts for alkyne–CO2 carboxylation and one-pot construction of heterocycles

Simple pyrazoles are highly active bifunctional organocatalysts for alkyne–CO2 carboxylation and are applicable to orthogonal tandem catalysis for the one-pot construction of various heterocycles, during which unexpected acyl migration is observed.

Intramolecular Carboxyamidation of Alkyne-Tethered O-Acylhydroxamates through Formation of Fe(III)-Nitrenoids.

We developed intramolecular carboxyamidations of alkyne-tethered O-acylhydroxamates followed by either thermally induced spontaneous or 4-(dimethylamino)pyridine-catalyzed O→O or O→N acyl group migration. Under iron-catalyzed conditions, the carboxyamidation products were generated in high yield from both Z-alkene and arene-tethered substrates. DFT calculations indicate that the iron-catalyzed carboxyamidation proceeds via a stepwise mechanism involving iron-imidyl radical cyclization followed by intramolecular acyloxy transfer from the iron center to the alkenyl radical center to furnish the cis-carboxyamidation product. Upon treatment with 4-(dimethylamino)pyridine, the Z-alkene-tethered carboxyamidation products underwent selective O→O acyl migration to generate 2-acyloxy-5-acyl pyrroles. Thermal O→N acyl migration occurs during carboxyamidation if the Z-alkene linker contains an alkyl or an aryl substituent at the β-position of the carbonyl group. On the other hand, the arene linker-containing compounds selectively undergo O→N acyl migration to generate N-acyl-3-acylisoindolinones, and the corresponding O→O acyl migration forming isoindole derivatives was not observed.

Preparation of vacuum-assisted conjugated linoleic acid phospholipids under nitrogen: Mechanism of acyl migration of lysophospholipids

Sn-Glycerol-3-phosphatidylcholine (GPC) was prepared by hydrolysis of phosphatidylcholine (PC) catalyzed by phospholipase A1 (PLA1). Nitrogen flow assisted the esterification of conjugated linoleic acid (CLA) and GPC to produce conjugated linoleic acid lysophosphatidylcholine (LPC − CLA). The effects of different reaction conditions on the PC conversion and acyl migration rates were investigated, and the acyl migration mechanism under acidic and alkaline conditions was studied. In addition, the optimum conditions for the esterification of CLA and GPC were selected. The optimal condition for the hydrolysis of PC was an enzyme loading of 5 %, pH of 5, reaction temperature of 50 ℃, and reaction time of 3 h. The results also showed that the maximum esterification rate reached 82.37 % at an enzyme loading of 15 %, CLA/GPC molar ratio of 50:1, and vacuum pressure of 13.3 kPa. This study not only improved the bioavailability of PC but also effectively increased the content of LPC − CLA.

Base-Promoted Tandem Synthesis of 2-Substituted Indoles and N-Fused Polycyclic Indoles.

Herein is developed a base-promoted approach for the synthesis of C2-substituted indoles and N-fused polycyclic indoles via 5-endo-dig cyclization of 2-alkynyl anilines, followed by a 1,3'-acyl migration or a dearomatizing Michael addition process. A range of N-H free indoles and 8,9-dihydropyrido[1,2-a]indol-6(7H)-one scaffolds were synthesized in good to excellent yields with broad scope.

Preparation, acyl migration and applications of the acylglycerols and their isomers: A review

Acylglycerols in natural oils includes monoacylglycerols (MAG), diacylglycerols (DAG) and triacylglycerols (TAG). Each acylglycerol possesses different isomers, which results in variation in physicochemical and nutritional properties that can be used in various applications. Acyl migration is a spontaneous reaction involving the transition of acylglycerols into more stable isomers. Inhibition of acyl migration is beneficial for the application of different acylglycerol isomers. Whilst, the promotion of acyl migration positively impacts the synthesis of acylglycerols, altering the properties and improving the stability of the lipid system. Few studies have been performed recently on the synthesis of various acylglycerol isomers and the approach to control the acyl migration of acylglycerols. This paper discusses the preparation of acylglycerols isomers, the factors influencing acyl migration and the application of the isomers of acylglycerols, which is important for expanding the use of different isomeric acylglycerols as functional foods.

Purification of mono-saturated acid sn-1,3 diacylglycerols: Effects of acyl migration on the crystallization behaviors and physical properties

Sn-1,3 diacylglycerol (Sn-1,3 DAG) is widely applied as a functional lipid. Recently there has been escalating interest in understanding the acyl migration of sn-1,3 DAG that could bring about various physicochemical properties of the functional oils. In this study, 97.8% of sn-1,3 lauryl diacylglycerol (Sn-1,3 LDAG) and 98.3% of sn-1,3 palmityl diacylglycerol (Sn-1,3 PDAG) were synthesized by esterification and purified via crystallization using mixed solvent n-hexane: ethyl acetate = 92:8 (V/V) and n-hexane: ethyl acetate = 98:2 (V/V), respectively. Increasing temperature and system dispersion, enhanced the acyl migration rate (Km) of sn-1,3 DAGs and reduced its half-life (T1/2). As the acyl migration degrees (AMDs) of DAG increased, DAGs crystallization and melting were completed at a shorter temperature range and time while the crystal aggregation mode of DAGs shifted from disordered needle crystals to more organized Maltese cross-shape. Acyl-migrated LDAG forms β+β′ crystals, while acyl-migrated PDAG forms β+α crystals in 25 °C. The dynamics of acyl migration and crystallization of sn-1,3 DAGs can be applied to prepare high content sn-1,3 DAG products. The crystal morphology and polymorphism properties of sn-1,3 LDAG and sn-1,3 PDAG with different AMDs are beneficial to obtain functional sn-1,3 DAG customized products with desirable characteristics.

Mechanism of Acyl Group Migration in Carbohydrates.

Acyl group migration has been the subject of several studies. Such migration processes may cause problems during synthesis, isolation, and purification of different acyl-bearing compounds, and have biological relevance, for example, in the metabolism of pharmaceuticals. Considering the recent evidence of acyl group migration being possible even over glycosidic bonds, it could be hypothesized to be involved also in the regulation of biological activity of natural polysaccharides in the host cells. Migrations are mostly observed in carbohydrates, typically having several hydroxyl groups near each other. Several studies have investigated the migration in a single or only a few different carbohydrate molecules, providing different suggestions for the mechanisms of migration, seldom supported by comprehensive computational investigations. In this concept article we discuss the recent progress on the mechanistic aspects of acyl group migration, with carbohydrates in particular focus.

Cyclic di-peptide in situ inhibited protein-aggregation

An increasing number of neurodegenerative diseases seem to be associated with protein misfolding that often leads to misfolded protein aggregates with a β-sheet conformation and accumulation in the brain which directly contributes to or modulates the associated pathology. Protein aggregation diseases like Huntington’s disease results from the deposition of aggregated huntingtin proteins within the nucleus, transmissible prion encephalopathies occur due to extracellular deposition of pathogenic prion proteins whereas Alzheimer’s disease from the accumulation of both extracellular β-amyloid and intracellular hyperphosphorylated tau protein aggregates. In the generalized purpose, we have taken the core sequence of amyloid-β (responsible for its aggregation) as the aggregating peptide (AP). Among the various emerging therapeutic approaches against aggregation-related degenerative diseases such as diminishing the monomeric precursor protein, inhibiting aggregation, or blocking aggregation-induced cellular toxicity pathways, we focussed on the strategy based on the inhibition of protein aggregation using rationally designed peptide inhibitors comprising both the recognition and β-breaking component in the sequence. The “O → N acyl migration” concept was used to form cyclic peptide in situ for the generation of a bent unit which may act as disruption moiety for the inhibition process. The kinetics of aggregation was characterized by various biophysical tools (ThT-assay, TEM, CD, and FTIR). Results implied that the designed inhibitor peptides (IP) might be valuable to inhibit all the related aggregated peptides.