Acyl Migration Research Articles

Diastereoselective Synthesis of oxa‐Bridged Tetracyclic Benzooxazines from the Reaction of 2‐Isocyanophenyloxyacrylates and Propargylic Esters

AbstractA cascade annulation of 2‐isocyanophenyloxyacrylate and propargylic ester under basic conditions has been disclosed. This methodology enables diastereoselective synthesis of oxa‐bridged tetracyclic benzooxazine. The annulation proceeds through isomerization, Michael addition, triple annulation and acyl migration processes.magnified image

Stereocontrolled Synthesis of Lyso‐phosphatidyl β‐D‐Glucoside

AbstractLyso‐phosphatidyl β‐D‐glucoside (lysoPtdGlc) is during embryonic development a neurite growth cone guidance cue associated with G‐protein coupled receptor 55, and has been found to be involved in a variety of physiological and pathological events, including inflammatory pain, and cancer. Hence, the ability to prepare large quantities of lysoPtdGlc is an important objective. Herein, we report the convergent chemical synthesis of lysoPtdGlc and its glyceryl epimer (S‐lysoPtdGlc). High stereocontrol during β‐glycosyl H‐phosphonate construction was achieved using a microfluidic approach, and common but undesirable regioisomerization due to acyl migration on the glyceryl subunit was successfully suppressed during deprotection. Purification of the final product was optimized to obtain sufficiently large amounts of lysoPtdGlc and S‐lysoPtdGlc for biological assaying purposes.

Cu‐Catalyzed Cascade Cyclization of Ketoxime Acetates and Alkynals Enabling Synthesis of Acylpyrroles

Main observation and conclusionA facile copper‐based catalytic system has been developed to enable efficient cyclization of methylketoximes and alkynals. This protocol provides a viable entry to synthetically and pharmaceutically useful 2‐acylpyrroles with a broad range of compatible functionalities. Mechanistically, a key acyl migration is probably involved that leads to the formation of N‐acyl pyrroles or otherwise NH pyrroles by further hydrolysis. More importantly, the present reaction system also gives an opportunity to realize three‐component pyrrole assembly by simple addition of carboxylic acid.

Exploring the Reactivity of Propargylic Ester: Acyloxy and Acyl Migratory Rearrangement Relay Enabled by Formal Double Isocyanide Insertion

AbstractA rearrangement of propargylic pivalate with isocyanide under transition metal‐free conditions is disclosed. Intermolecular 1,3‐acyloxy and acyl migration enables the rapid formation of a C(sp2)−C(sp3) bond from a C−O bond and the synthesis of polysubstituted 5‐iminopyrrolones.magnified image

Evaluation of 3-monochloropropanol esters and glycidyl esters during the production and concentration of diacylglycerol by two-stage short-path molecular distillation

Diacylglycerol (DAG) has been drawing increased global attention due to its health benefits; however, there is a biggest challenge raised by 3-monochloropropyl esters (3-MCPDEs) and glycidyl esters (GEs) during its preparation and concentration. Herein, a model firstly was clarified and evaluated for the preparation of 48.9% DAG achieved by enzymatic glycerolysis of soybean oil in a solvent-free system though Response Surface Methodology. Subsequently, the resulted DAG was concentrated to 79.7%, involving 75.1% 1,3-diacylglycerol and 24.9% 1,2-diacylglycerol due to the steric effect and/or acyl migration, thought two-stage short path molecular distillation (SPD), and 3-MCPDEs and GEs were concomitantly evaluated during the concentration. Comparative investigation of various SPD parameters (e.g., temperature, scraping speed and feed rate), temperature was dominant and dependency in both 3-MCPDEs and GEs formation during the primary molecular distillation. However, it has a less effect on the formation of 3-MCPDEs and more effect on levels of GEs during the secondary molecular distillation process. Nonetheless, the DAG and chloride increases the probability of formation of both 3-MCPDEs and GEs. The results may promote the engineering production of DAG with high purity and quality.

Catalytic, Regioselective Hydrocarbofunctionalization of Unactivated Alkenes Triggered by trans-Acetoxypalladation of Alkynes.

Herein we demonstrate a Pd(II)-catalyzed regioselective hydrocarbofunctionalization of unactivated alkenes. The σ-vinyl-palladium(II) intermediate generated by the trans-acetoxypalladation of alkynes was added across carbon-carbon double bond to realize an efficient hydroalkenylation protocol. Bidentate auxiliary 8-aminoquinoline controls the regioselectivity of the carbopalladation step and thereby controls the regioselectivity of the hydroalkenylation. Additionally, when alkynes containing a hydroxy group at the three- or four-position were employed, the cascade sequence led to 1,6-dicarbonyl compounds via hydroalkenylation followed by intramolecular acyl migration.

Acyl migration occurrence of palm olein during interesterification catalyzed by sn-1,3 specific lipase

Palm olein was enzymatically interesterified (EIE) using sn-1,3 specific lipase and the effect of different reaction conditions on the degree of acyl migration (AMD) was investigated. The AMD increased with the amount of lipase loaded, recording the highest AMD of 63.41% when 11% of lipase was added at 80 °C for 2 h. When the reaction time and temperature was further increased, the AMD remained constant at 100%, reaching a completely randomized interesterification. Post EIE, the triacylglycerol (TAG) molecular structures were modified and this contributed to the modification of the crystallization behaviour, solid fat content, and thermal properties of the interesterified products. Higher AMD promoted a random rearrangement of the TAG to obtain tri-saturated TAG and achieved a fast crystallization. Hence, the crystal microstructures were observed to be more uniform and was dominated with β′ crystals. The findings that were acquired in this study are meaningful for the establishment of a theoretical framework that can be used to monitor and control the AMD during an sn-1,3 specific lipase-catalyzed EIE.

Study on the stability of intermediates in the process of enzymatic hydrolysis of phosphatidic acid by phospholipase A1

In the degumming process of crude soybean oil by phospholipase A1 (PLA1), the content of free fatty acids (FFA) in the product increases excessively. In this study, PLA1 was used to hydrolyse simulated crude soybean oil. It was found that the acyl group at the sn-2 position migrated to the sn-1 position, the content of FFA in the oil was as high as 1.26 ± 0.03 g/100 g, and the acyl migration rate was up to 38.9 ± 0.10% after 2.8 h. Under the conditions of H3BO3 addition of 2 g/100 g, pH of 5, enzymatic hydrolysis temperature of 50 °C and enzymatic hydrolysis time of 2 h, the acyl migration rate of sn-2-HPA was 16.8 ± 0.50%, the content of FFA was 1.14 ± 0.02 g/100 g, and the enzymatic hydrolysis efficiency was increased by 28.57 ± 0.07%.

Competition between cyclization and unusual Norrish type I and type II nitro-acyl migration pathways in the photouncaging of 1-acyl-7-nitroindoline revealed by computations

The 7-nitroindolinyl family of caging chromophores has received much attention in the past two decades. However, its uncaging mechanism is still not clearly understood. In this study, we performed state-of-the-art density functional theory calculations to unravel the photo-uncaging mechanism in its entirety, and we compared the probabilities of all plausible pathways. We found competition between a classical cyclization and an acyl migration pathway, and here we explain the electronic and steric reasons behind such competition. The migration mechanism possesses the characteristics of a combined Norrish type I and a 1,6-nitro-acyl variation of a Norrish type II mechanism, which is reported here for the first time. We also found negligible energetic differences in the uncaging mechanisms of the 4-methoxy-5,7-dinitroindolinyl (MDNI) cages and their mononitro analogues (MNI). We traced the experimentally observed improved quantum yields of MDNI to a higher population of the reactants in the triplet surface. This fact is supported by a more favorable intersystem crossing due to the availability of a higher number of triplet excited states with the correct symmetry in MDNI than in MNI. Our findings may pave the way for improved cage designs that possess higher quantum yields and a more efficient agonist release.

Enzymatic Interesterification of Palm Stearin and Palm Olein Blend Catalyzed by sn-1,3-Specific Lipase: Interesterification Degree, Acyl Migration, and Physical Properties

Acyl migration of fatty acid at sn-2 is often observed alongside enzymatic interesterification (EIE), causing the loss of lipase selectivity toward the acyl group at sn-1,3. In this study, an oil blend consisting of palm stearin (PST) and palm olein (POL) was interesterified via a chemical interesterification (CIE) and enzymatic method using a packed bed reactor. Characterization in terms of the triacylglycerol (TAG) compositions, sn-2 fatty acid distributions, and solid fat content profiles was performed. In comparison to that of CIE fats, EIE fats showed different modification effects on the solid fat content. Under similar reaction conditions, different interesterification degrees (IDs) were obtained according to the various blend ratios. Using the same mass ratio of substrates (POL/PST of 9:1), the EIE reaction time and temperature affected the ID and the change in the fatty acyl group at the sn-2 position. Under the reaction time of 46 min, an ID of 94.41% was acquired, while at 80 °C, the degree of acyl migration at sn-2 was 92.87%. EIE with high acyl migration exhibited a lower crystallization rate than that of EIE with low acyl migration. However, the effect of acyl migration on crystal polymorphism and oxidative stability was insignificant. Outcomes from this study are meaningful for the establishment of a theoretical basis for a controlled positional-specific EIE that is catalyzed by sn-1,3-specific lipase.

Integral Stereoselectivity of Lipase Based on the Chromatographic Resolution of Enantiomeric/Regioisomeric Diacylglycerols.

Stereoselectivity, a distinctive characteristic of lipase (EC 3.1.1.3), refers to the ability to differentiate between enantiomeric positions (sn-1 and sn-3) in triacylglycerol (TAG). This property has been determined based on the time course of enantiomeric excess of diacylglycerol (DAG) considering several consecutive steps of lipase-catalyzed hydrolysis of TAG; however, this concept is insufficient to represent the true nature of lipases which are capable of hydrolyzing the sn-2 position of TAG under the condition acyl migration occurs. Here, we suggest "integral stereoselectivity" to capture the preference of lipases for all ester groups of both TAG and DAG, as a novel index of the stereochemistry of lipase. To determine integral stereoselectivity, we established an analytical system based on the chromatographic resolution of dioleoylglycerol (DO) enantiomers and regioisomers. DO enantiomers were derivatized with 4-nitrophenyl isocyanate, and subsequently, resolved by chiral-phase high-performance liquid chromatography-ultraviolet. Regioisomers of monooleoylglycerol and DO were analyzed by HPLC with an evaporative light-scattering detector. Time-course analysis of three model lipases involved in the hydrolysis of trioleoylglycerol validated the analytical system designed to determine the integral stereoselectivity. As an accurate indicator of lipase stereochemistry reflecting all hydrolysis steps, integral stereoselectivity can expedite the development of lipases with unique stereochemistry from agricultural sources and their application to the food industry.

Integrated Green and Enzymatic Process to Produce Omega‐3 Acylglycerols from Echium plantagineum Using Immobilized Lipases

AbstractThis work presents an original approach to develop an integrated process to improve the nutritional characteristics of natural oils, starting with the extraction from raw material by ecofriendly methods, followed by the production of novel acylglycerols using immobilized lipases. Specifically, 2‐monoacylglycerols (2‐MAG) enriched in omega‐3 stearidonic acid (SDA) were synthesized by selective ethanolysis of extracted Echium plantagineum oil using the lipase from Thermomyces lanuginosus (TLL). Different reaction conditions were investigated to minimize acyl migration and to ensure the purity of final products. The biocatalyst produced in our laboratory by the immobilization of TLL on Sepabeads C‐18 reached the maximum theoretical amount of 2‐MAG (33%) in only 2 hour at mild reaction conditions (25 °C), achieving a product enriched in omega‐3 SDA (up to 25%). Moreover, the produced biocatalyst exhibited higher stability than commercial lipases. The average activity after five cycles was 71%, allowing several reutilization cycles and developing a feasible enzymatic process. Finally, 2‐MAG were used as starting material to synthesize structured triacyclglycerols (STAG) through transesterification with caprylic acid ethyl esters using the lipase from Rhizomucor miehei (RML) in solvent‐free systems. The use of molecular sieves in combination with RML immobilized on Sepabeads C‐18 was demonstrated to be an extraordinarily fast strategy to produce pure STAG (100% in 1 hour), four times higher than the activity showed by commercial biocatalyst. Thus, the enzymatic processes developed in this study open a range of possibilities to synthesize omega‐3 acylglycerols with improved characteristics, proving the usefulness of immobilized lipases to produce novel lipids.

Effect of Solvent on Acyl Migration of 2-Monoacylglycerols in Enzymatic Ethanolysis.

Acyl migration occurs in many reactions and is the main obstacle for structured lipid synthesis. In this study, 2-monoacylglycerol (2-MAG) was prepared by enzymatic ethanolysis in three different media to evaluate the effect of environment on product composition. The contents of 2-MAG obtained in ethanol, hexane + ethanol, and t-butanol + ethanol systems were 30.6, 15.7, and 32.4%, respectively, after 3 h reaction. Afterward, the acyl migration kinetics of 2-MAG were studied in solvent and solventless systems without the use of lipase. Results indicate that 2-MAG in the solventless system had the highest acyl migration rate. The isomerization was efficiently prevented by the use of polar solvents, especially t-butanol. The rate constants were shown to be the highest and activation energy values were the lowest in solventless systems. The novel finding in this study was that solvent had inhibitory effect on 2-MAG isomerization, but the nonpolar hexane had the lowest inhibition of acyl migration compared to other solvents.

LC–MS/MS Quantification of Ataluren and Ataluren Acyl Glucuronide in Human Plasma/Urine: Application in Clinical Studies

Background: This paper describes for the first-time analytical procedures established to resolve the challenges associated with simultaneous and direct quantification of ataluren and ataluren-O-1β-acyl glucuronide (AAG) by LC-MS/MS in human plasma and urine matrices. Methodology/results: The plasma quantification method was validated for calibration rangeof 12.5-12500ng/ml for ataluren and 6.25-2500ng/ml for AAG. The urine quantification method was validated for calibration range of 0.01-10and 1-1000μg/ml for ataluren and AAG, respectively. Plasma and urine samples were stabilized upon collection and through storage to prevent hydrolysis and acyl migration of AAG. Conclusion: Methods described in this paper enabled successful completion of ataluren clinical pharmacology studies for simultaneous pharmacokinetic assessment of ataluren and AAG.

Characteristics and emulsifying properties of structured phospholipids from palm pressed fiber and omega-3 fatty acid concentrates from by-products of fish processing by enzymatic acidolysis.

The synthesis of structured phospholipids (SPLs) containing ω-3 fatty acids was carried out through enzymatic acidolysis reactions using lipase from Rhizomucor miehei between palm pressed fiber phospholipids (PPF PL) with four ω-3 fatty acid concentrates as different acyl sources. The purity of SPLs increased compared to original PPF PLs. The degree of ω-3 fatty acid incorporation to the SPLs was different that depended on the sources of acyl. The highest degree of incorporation was in PE (phosphatidylethanolamine). The phenomenon of acyl migration of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) was found from the sn-1 to the sn-2 position of the PE. This acyl migration occurred at all four SPLs. Modification of PLs made better emulsifying properties for oil in water emulsion system, compared to PPF PL. The increase in the HLB (hydrophilic-lipophilic balance) value, EAI (emulsifying activity index), and ESI (emulsion stability index) of SPLs compared to PPF PL was supposed to relate to an increase in polarity. The composition of more polar PLs (PC/phosphatidylcholine, PE, PG/phosphatidylglycerol, and PA/phosphatidic acid) in the four SPLs is higher than that of PPF PL. The sources of acyl also affected the emulsifying properties of four SPLs.

Anomeric configuration-dependence of the Lattrell-Dax epimerization from D-glucose to synthetically useful D-allose derivatives.

D-Allose and its derivatives play important roles in the field of health care and food nutrition. Pure and well-defined D-allose derivatives can facilitate the elucidation of their structure-activity relationship as an essential step for drug design. The Lattrell-Dax epimerization, refers to the triflate inversion using nitrite reagent, is known as valuable method for the synthesis of rare D-allose derivatives. Here, the influence of protecting group patterns on the transformation efficiency of D-glucose derivatives into synthetically useful D-alloses and D-allosamines via the Lattrell-Dax epimerization was studied. For C3 epimerization of D-glucose derivatives bearing O2-acyl group, an anomeric configuration-dependent acyl migration from O2 to O3 was found. In addition, a neighbouring group participation effect-mediated SN1 nucleophilic substitution of the D-glucosamine bearing C2 trichloroacetamido (TCA) group in the Lattrell-Dax epimerization was dependent upon anomeric configuration. Thus, the effect of anomeric configuration on the Lattrell-Dax epimerization of D-glucose suggests that β-D-glucosides with low steric hindrance at C2 should be better substrates for the synthesis of D-allose derivatives. Significantly, the efficient synthesis of the orthogonally protected D-allose 13 and D-allosamine 18 will serve well for further assembly of complex glycans.

Kinetics and Mechanism of Solvent Influence on the Lipase-Catalyzed 1,3-Diolein Synthesis.

1,3-Diacylglycerol preparation has roused increasing attention in recent years as the 1,3-diacylglycerol-rich oils can suppress the deposition of visceral fat and prevent the body weight increasing. Lipozyme TL IM-mediated esterification of oleic acid with monoolein was effective for 1,3-diacylglycerol production. During the esterification process, the solvent shows obvious influence on the diolein synthesis as well as the 1,3-diolein production. This work investigated the related kinetics and mechanism of the solvent effect on the esterification and Lipozyme TL IM performance. The results indicated that both the esterification rate constant and the acyl migration rate constant positively correlated with the logP of the solvent, while the site specificity of lipase has negative correlation with solvent logP. The acylation toward the 2-position of 1-monoolein was more sensitive to the solvent logP compared to the 1-position of glycerides. Molecular dynamics simulation revealed that solvents with different logP influenced the structure of Lipozyme TL IM including RMSD, hydrogen bond, and radial distribution function to a large extent, which subsequently led to the catalytic activity and selectivity variation of the lipase.

Identification and Determination of Betacyanins in Fruit Extracts of Melocactus Species

Betacyanin pigments were studied in edible fruits of four Melocactus species, M. violaceus Pfeiff., M. bahiensis (Britton & Rose) Luetzelb, M. amoenus (Hoffm.) Pfeiff., and M. curvispinus Pfeiff., by means of chromatographic and mass spectrometric techniques. The main pigment constituent, melocactin, endogenously present in the Melocactus species, was identified as betanidin 5-O-β-sophoroside betacyanin, previously known as “bougainvillein-r-I”. The highest total concentration of betacyanins was found in fruits of M. amoenus (∼0.08 mg/g). Except for melocactin being the most abundant betacyanin (34.8–38.8%) in the analyzed species, a presence of its malonylated derivative, mammillarinin (15.2–19.9%), as well as more hydrophobic feruloyled and sinapoyled melocactins was confirmed by additional co-chromatographic experiments with authentic reference betacyanins. The acyl migration isomers of the malonylated betacyanins as well as a presence of 5′′-O-E-sinapoyl-2′-O-apiosyl-betanin (2.3–3.0%) found frequently in light-stressed cacti was also acknowledged.

Enzymatic Synthesis of Poly(glycerol sebacate): Kinetics, Chain Growth, and Branching Behavior.

Immobilized Candida antarctica lipase B (CALB)-catalyzed polycondensation of glycerol and sebacic acid at mild reaction conditions resulted in branched poly(glycerol sebacate) (PGS). To understand how PGS chains grow and branch, the kinetics of the CALB-catalyzed polycondensation were studied. The influence of the reaction temperature, solvent, CALB amount, and sebacic acid/glycerol feed ratio on the poly(glycerol sebacate) (PGS) molecular weight, degree of branching, and glyceridic repetitive unit distribution was also investigated. PGS architecture changes from linear to branched with the progression of the reaction, and the branching results from the simultaneous CALB-catalyzed esterification and acyl migration. For reactions performed in acetone at the temperature range from 30 to 50 °C, the apparent rate constant increases from 0.7 to 1.5 h–1, and the apparent energy of activation of 32 kJ mol–1 was estimated. The higher mass average molecular weight (16 kDa) and degree of branching (41%) were achieved using the equimolar sebacic acid/glycerol feed ratio in acetone at 40 °C with a CALB amount of 13.6 wt % and in the presence of the molecular sieves.

Highly efficient preparation of 1-lysophosphatidylcholine via high proportion of Novozym® 435 (lipase B from Candida antarctica)-catalyzed ethanolysis

Efficient preparation methods for 1-lysophosphatidylcholine (1-LPC), a physiologically important compound, are lacking. Here, we established a method for 1-LPC preparation via Novozym® 435 (a lipase B from Candida antarctica)-catalyzed ethanolysis. Novozym® 435 showed sn-1 regiospecificity to phosphatidylcholine, although it does not exhibit regiospecificity to triacylglycerol. In particular, quantitative 1-LPC yields (96.5 ± 0.2 mol%) were reliably obtained in the presence of Novozym® 435 (100 wt% of PC), 97 % ethanol, in 72 h at 40 °C. During the reaction, acyl migration from 1-LPC to 2-LPC was rare. This novel synthetic method is expected to expand the practical applications of 1-LPC.