Enantioselective resolution of 2-(1-hydroxy-3-butenyl)-5-methylfuran by immobilized lipase

Enzymatic Synthesis and Molecular Modelling Studies of Rhamnose Esters Using Lipase from Pseudomonas stutzeri

Rhamnolipids are becoming an important class of glycolipid biosurfactants. Herein, we describe for the first time the enzymatic synthesis of rhamnose fatty acid esters by the transesterification of rhamnose with fatty acid vinyl esters, using lipase from Pseudomonas stutzeri as a biocatalyst. The use of this lipase allows excellent catalytic activity in the synthesis of 4-O-acylrhamnose (99% conversion and full regioselectivity) after 3 h of reaction using tetrahydrofuran (THF) as the reaction media and an excess of vinyl laurate as the acyl donor. The role of reaction conditions, such as temperature, the substrates molar ratio, organic reaction medium and acyl donor chain-length, was studied. Optimum conditions were found using 35 °C, a molar ratio of 1:3 (rhamnose:acyldonor), solvents with a low logP value, and fatty acids with chain lengths from C4 to C18 as acyl donors. In hydrophilic solvents such as THF and acetone, conversions of up to 99–92% were achieved after 3 h of reaction. In a more sustainable solvent such as 2-methyl-THF (2-MeTHF), high conversions were also obtained (86%). Short and medium chain acyl donors (C4–C10) allowed maximum conversions after 3 h, and long chain acyl donors (C12–C18) required longer reactions (5 h) to get 99% conversions. Furthermore, scaled up reactions are feasible without losing catalytic action and regioselectivity. In order to explain enzyme regioselectivity and its ability to accommodate ester chains of different lengths, homology modelling, docking studies and molecular dynamic simulations were performed to explain the behaviour observed.

Efficient Biocatalytic Synthesis of Chiral Intermediate of Pregabalin Using Immobilized Talaromyces thermophilus Lipase

A mutant L206F/P207F/L259F of Talaromyces thermophilus lipase (TTL) exhibited high hydrolytic activity towards 2-carboxyethyl-3-cyano-5-methylhexanoic acid ethyl ester (CNDE) for synthesis of (S)-2-carboxyethyl-3-cyano-5-methylhexanoic acid (S-CCMA), a key chiral intermediate of pregabalin. However, low conversion at high CNDE concentration and unreusability of the free TTL mutant restricted its industrial applications. In this study, the TTL mutant was immobilized onto epoxy resin and its catalytic properties for kinetic resolution of CNDE were investigated. Under the optimized conditions, the immobilized lipase exhibited an increased catalytic efficiency even at a CNDE concentration of 3 M with 49.7% conversion and 95% ee _p. The conversion retained higher than 46.3% even after 10 times repeated use of the immobilized lipase in n-heptane-water biphasic system. These results demonstrated great potential of the immobilized TTL mutant for industrial production of the chiral intermediate of pregabalin.

Additives enhancing the catalytic properties of lipase from Burkholderia cepacia immobilized on mixed-function-grafted mesoporous silica gel

Effects of various additives on the lipase from Burkholderia cepacia (BcL) immobilized on mixed-function-grafted mesoporous silica gel support by hydrophobic adsorption and covalent attachment were investigated. Catalytic properties of the immobilized biocatalysts were characterized in kinetic resolution of racemic 1-phenylethanol (rac-1a) and 1-(thiophen-2-yl)ethan-1-ol (rac-1b). Screening of more than 40 additives showed significantly enhanced productivity of immobilized BcL with several additives such as PEGs, oleic acid and polyvinyl alcohol. Effects of substrate concentration and temperature between 0–100 °C on kinetic resolution of rac-1a were studied with the best adsorbed BcLs containing PEG 20 k or PVA 18–88 additives in continuous-flow packed-bed reactor. The optimum temperature of lipase activity for BcL co-immobilized with PEG 20k found at around 30 °C determined in the continuous-flow system increased remarkably to around 80 °C for BcL co-immobilized with PVA 18–88.

Enantioselective total syntheses of FR901464 and spliceostatin A and evaluation of splicing activity of key derivatives

FR901464 (1) and spliceostatin A (2) are potent inhibitors of spliceosomes. These compounds have shown remarkable anticancer activity against multiple human cancer cell lines. Herein, we describe efficient, enantioselective syntheses of FR901464, spliceostatin A, six corresponding diastereomers and an evaluation of their splicing activity. Syntheses of spliceostatin A and FR901464 were carried out in the longest linear sequence of 9 and 10 steps, respectively. To construct the highly functionalized tetrahydropyran A-ring, we utilized CBS reduction, Achmatowicz rearrangement, Michael addition, and reductive amination as key steps. The remarkable diastereoselectivity of the Michael addition was specifically demonstrated with different substrates under various reaction conditions. The side chain B was prepared from an optically active alcohol, followed by acetylation and hydrogenation over Lindlar’s catalyst. The other densely functionalized tetrahydropyran C-ring was derived from readily available (R)-isopropylidene glyceraldehyde through a route featuring 1,2-addition, cyclic ketalization, and regioselective epoxidation. These fragments were coupled together at a late stage through amidation and cross-metathesis in a convergent manner. Six key diastereomers were then synthesized to probe the importance of specific stereochemical features of FR901464 and spliceostatin A, with respect to their in vitro splicing activity.

Effects of additives on lipase immobilization in microemulsion-based organogels

An inexpensive, facile, and environmentally benign method was developed to improve the activity and stability of Candida rugosa lipase (triacylglycerol acylhydrolase) immobilized on microemulsion-based organogels (CRL MBGs) via the addition of additives during immobilization. The additives used were polyethylene glycol (PEG) or polysaccharides. This study is the first report on the effect of additives in CRL MBGs. Among the tested additives, PEG produced the most improvement in the immobilized CRL, enhancing its stability in organic solvents (specifically polar solvents). The results of circular dichroism and fluorescence spectra experiments indicated that exposure of the acidic CRL to electronegative additives in the buffer, such as polyethylenimine and the electropositive surfactant cetyltrimethylammonium bromide, may change the lipase secondary structure, ultimately causing enzyme inactivation. However, sodium bis(2-ethylhexyl)sulfosuccinate and PEG 2000 had minimal effects on the secondary structure of CRL. The CRL MBGs containing PEG 2000 demonstrated remarkable retention of their catalytic activity during the recycling test. No significant changes in enzymatic activity were observed, even after nine runs, and 90% of the original yield was maintained after 15 cycles.