Kinetic resolution of racemic secondary aliphatic allylic alcohols in lipase-catalyzed transesterification

Biocatalytic asymmetric synthesis of secondary allylic alcohols using Burkholderia cepacia lipase immobilized on multiwalled carbon nanotubes

The lipase from Burkholderia cepacia (BCL) was immobilized through physical adsorption on pristine and functionalized multiwalled carbon nanotubes (MWCNTs) with carboxyl or amine groups and used in the stereoselective acylation of (R,S)-1-octen-3-ol (1) and (R,S)-(E)-4-phenyl-3-buten-2-ol (4) with vinyl acetate. All immobilized preparations produced better results than free BCL. For (R,S)-4, 50% conversion and E > 200 were obtained in n-hexane or in solvent-free medium. For (R,S)-1, in solvent-free medium, the conversion was 38% with a slight increase in the E-value (E = 10).

Understanding FAHFAs: From structure to metabolic regulation

The discovery of branched fatty acid esters of hydroxy fatty acids (FAHFAs) in humans draw attention of many researches to their biological effects. Although FAHFAs were originally discovered in insects and plants, their introduction into the mammalian realm opened new horizons in bioactive lipid research. Hundreds of isomers from different families have been identified so far and their role in (patho) physiological processes is currently being explored. The family of palmitic acid esters of hydroxy stearic acids (PAHSAs), especially 5-PAHSA and 9-PAHSA regioisomers, stands out in the crowd of other FAHFAs for their anti-inflammatory and anti-diabetic effects. Beneficial effects of PAHSAs have been linked to metabolic disorders such as type 1 and type 2 diabetes, colitis, and chronic inflammation. Besides PAHSAs, a growing family of polyunsaturated FAHFAs exerts mainly immunomodulatory effects and biological roles of many other FAHFAs remain currently unknown. Therefore, FAHFAs represent unique lipid messengers capable of affecting many immunometabolic processes. The objective of this review is to summarize the knowledge concerning the diversity of FAHFAs, nomenclature, and their analysis and detection. Special attention is paid to the total syntheses of FAHFAs, optimal strategies, and to the formation of the stereocenter required for optically active molecules. Biosynthetic pathways of saturated and polyunsaturated FAHFAs in mammals and plants are reviewed together with their metabolism and degradation. Moreover, an overview of biological effects of branched FAHFAs is provided and many unanswered questions regarding FAHFAs are discussed.

Enantioselective Transesterification of Allyl Alcohols with (E)-4-Arylbut-3-en-2-ol Motif by Immobilized Lecitase™ Ultra

Lecitase™ Ultra was immobilized on four different supports and tested for the first time as the biocatalyst in the kinetic resolution of racemic allyl alcohols with the (E)-4-arylbut-3-en-2-ol system in the process of transesterification. The most effective biocatalyst turned out to be the enzyme immobilized on agarose activated with cyanogen bromide (LU-CNBr). The best results (E > 200, ees and eep = 95–99%) were obtained for (E)-4-phenylbut-3-en-2-ol and its analog with a 2,5-dimethylphenyl ring whereas the lowest ee of kinetic resolution products (90%) was achieved for the substrate with a 4-methoxyphenyl substituent. For all substrates, (R)-enantiomers were esterified faster than their (S)-antipodes. The results showed that LU-CNBr is a versatile biocatalyst, showing high activity and enantioselectivity in a wide range of organic solvents in the presence of commonly used acyl donors. High operational stability of LU-CNBr allows it to be reused in three subsequent reaction cycles without negative effects on the efficiency and enantioselectivity of transesterification. This biocatalyst can become attractive to the commercial lipases in the process of the kinetic resolution of allyl alcohols.

Microbial Hydrolysis of Racemic β-Aryl-γ-ethylidene-γ-lactones and Antifeedant Activity of the Products against Alphitobius diaperinus Panzer

Hydrolysis of (±)-β-aryl-γ-ethylidene-γ-lactones by fungal strain Aspergillus ochraceus AM370 afforded (−)-(S)-γ-ethylidene-γ-lactones 2a–d and (+)-(R)-γ-ketoacids 3a–d. Enantiomeric purity of the unreacted lactones was strictly related to a size of an aryl substituent at C-4 of γ-lactone ring, with the highest ee (77%) obtained for the (−)-(S)-γ-ethylidene-γ-lactone possessing unsubstituted benzene ring (2a) and the lowest one (15%) determined for the (−)-(S)-γ-ethylidene-γ-lactone with bulky 1,3-benzodioxole system (2d). Lactones 2a–d, both racemic and enantiomerically enriched, as well as products of their hydrolysis showed varying degrees of feeding deterrent activity against lesser mealworm, Alphitobius diaperinus Panzer, which depended on the structure of the compound and the developmental stage of the lesser mealworm. In the case of adults, more active were γ-lactones 2a–d, compared with ketoacids 3a–d. Only in the case of lactone 2a was the effect of configuration of stereogenic center on the activity found. Particularly strong deterrents against this stage (T > 180) were racemic and (−)-(S)-γ-ethylidene-γ-lactone with p-methoxysubstituted phenyl ring (2c).

Chemoenzymatic Synthesis of trans-β-Aryl-δ-hydroxy-γ-lactones and Enzymatic Kinetic Resolution of Their Racemic Mixtures

Two novel and convenient routes to obtain enantiomerically enriched trans-β-aryl-δ-hydroxy-γ-lactones 5a–d with potential antifeedant and anticancer activity were developed. In the first method starting from corresponding enantiomers of γ,δ-unsaturated esters 4a–d derived from enzymatically resolved allyl alcohols 1a–d, both enantiomers of hydroxylactones 5a–d were synthesized with high enantiomeric excesses (73%–97%). Configurations of the stereogenic centers of the synthesized compounds were assigned based on the mechanism of acidic lactonization of esters 4a–d in the presence of m-chloroperbenzoic acid (m-CPBA). An alternative method for the production of optically active trans-β-aryl-δ-hydroxy-γ-lactones 5a–d was lipase-catalyzed kinetic resolution of their racemic mixtures by transesterification with vinyl propionate as the acyl donor. The most efficient enzyme in the screening procedure was lipase B from Candida antarctica. Its application on a preparative scale after 6 h afforded unreacted (+)-(4S,5R,6S)-hydroxylactones 5a–d and (+)-(4R,5S,6R)-propionates 6a–d, most of them with high enantiomeric excesses (92%–98%). Resolution of lactone 5d with bulky 1,3-benzodioxol ring provided products with significantly lower optical purity (ee = 89% and 84% for hydroxylactone 5d and propionate 6d, respectively). The elaborated methods give access to both enantiomers of trans-β-aryl-δ-hydroxy-γ-lactones 5a–d with the defined absolute configurations of stereogenic centers, which is crucial requirement for the investigations of relationship: spatial structure–biological activity.

Sugar based amphiphiles: easily accessible and efficient crude oil spill thickening agents

In this work, we demonstrate the use of biomass for the catalytic production of phase-selective gelators (PSGs) as a cost-effective, environmentally benign and ideal method for crude oil spill remediation, as well as execute the study exclusively in crude oil. The use of PSGs has recently provided great promise relative to that of their traditional counterparts. However, the use of PSGs with crude oil is much more complicated due to its complex composition. All of the current PSG methods are demonstrated with refined oils or do not employ eco-friendly methods like enzymatic synthesis. Our current project entails studying sugar alcohol-derived amphiphiles for their phase-selective gelation in crude oil; the PSGs are derived from renewable, benign materials and synthesized via a simple, single-step, enzymatic catalysis that required no purification. The results showed that, after a rigorous and systematic testing, the mannitol-derived amphiphile using 8-carbon alkyl chain length (M-8) turned out to be the best crude oil PSG among the studied amphiphiles. M-8 demonstrated a versatility towards thickening of different crude oil types, an efficient ability towards selective gelation of the oil (forming crude oil gel that is over sixty-one-times its mass and stable up to 109.7 °C) in a crude oil/water mixture, and an ability to form gel under practical situations such as seawater conditions. These qualities, in addition to the use of a simple and environmentally benign method to synthesize the structuring agents, make this amphiphile very practical in real life application.

Stereoselective yeast-mediated reduction of trans-5-(1'-oxo-3'-methylbutyl)-3-methyldihydrofuran-2-one: production of chiral intermediates for the synthesis of β-secretase inhibitors

OBJECTIVE

To investigate the usefulness of yeast strains to the production of chiral hydroxylactones, important synthons in the synthesis of β-secretase inhibitors.

RESULTS

Strains Rhodotorula glutinis KCh 242, Rhodotorula rubra KCh 82, Rhodotorula marina KCh 77 and Saccharomyces cerevisiae KCh 464 reduced racemic trans-5-(1'-oxo-3'-methylbutyl)-3-methyldihydrofuran-2-one (4) according to the Prelog's rule to afford preferentially the stereoisomers with S configurations at C-1'. R. marina KCh 77 and R. glutinis KCh 242 exhibited selectivity towards 3S, 5R enantiomer of the substrate, whereas R. rubra KCh 82 and S. cerevisiae KCh 464 preferred the reduction of its antipode. The highest yield of 3R,5S,1'S-hydroxylactone 3c (78 %) was obtained with R. rubra KCh 82.

CONCLUSIONS

Different stereoisomers of trans-5-(1'-hydroxy-3'-methylbutyl)-3-methyldihydrofuran-2-one and its 5-substituted analogues are produced as important intermediates in the synthesis of drugs for the therapy of Alzheimer's disease.

A convergent synthesis of carbocyclic sinefungin and its C5 epimer

A convergent synthesis of carbocyclic sinefungin 2 and its C5 epimer 3 is described. The key features in our synthesis include the use of commercial available L-methionine and readily available (1R, 4S)-4-hydroxy-2-cyclopentenyl acetate as starting materials, cross-metathesis coupling, enzymatic kinetic resolution and Staudinger reduction. The current synthesis is flexible and therefore provides convenient access to the synthesis of various carbocyclic SIN analogues for biological evaluation.

Enantioselective synthesis of isotopically labeled homocitric acid lactone

A concise synthesis of homocitric acid lactone was developed to accommodate systematic placement of carbon isotopes (specifically (13)C) for detailed studies of this cofactor. This new route uses a chiral allylic alcohol, available in multigram quantities from enzymatic resolution, as a starting material, which transposes asymmetry through an Ireland-Claisen rearrangement.

Syntheses of enantiopure aliphatic secondary alcohols and acetates by bioresolution with lipase B from Candida antarctica

The lipase B from Candida antarctica (Novozym 435^®, CALB) efficiently catalyzed the kinetic resolution of some aliphatic secondary alcohols: (±)-4-methylpentan-2-ol (1), (±)-5-methylhexan-2-ol (3), (±)-octan-2-ol (4), (±)-heptan-3-ol (5) and (±)-oct-1-en-3-ol (6). The lipase showed excellent enantioselectivities in the transesterifications of racemic aliphatic secondary alcohols producing the enantiopure alcohols (>99% ee) and acetates (>99% ee) with good yields. Kinetic resolution of rac-alcohols was successfully achieved with CALB lipase using simple conditions, vinyl acetate as acylating agent, and hexane as non-polar solvent.

Small-scale production of Burkholderia cepacia ATCC21808 lipase adapted to high-throughput screening

The screening of variant libraries of recombinant Burkholderia cepacia ATCC21808 lipase generated in Escherichia coli is limited by expression difficulties that are mainly due to the formation of inclusion bodies. To circumvent these difficulties and provide an efficient small-scale screening protocol, the gene encoding the lipase from B. cepacia was expressed in various expression vectors. With the pFLAG-ATS-Lip-Hp construct, expression of up to 6807 U/L of culture was possible in Erlenmeyer flasks. The production protocol was miniaturized in 96 deep-well plates, yielding 1300 U/L of lipase in fusion with the FLAG tag. With this protocol, the activity was determined in less than 10 min for a full plate, with a coefficient of variance of about 25%. For validation, 18 mutants constructed by site-directed mutagenesis on position Valine 266 were screened. Nice variations of activity were detected and found to be in agreement with those obtained in Erlenmeyer flask cultures. The protocol enabled the identification of 5 mutants showing enhanced activity toward para-nitrophenyl butyrate.