Product recovery of an enzymatically synthesized (-)-menthol ester in a deep eutectic solvent

Deep eutectic solvents (DESs) have gained increased attention as alternative reaction media for biocatalysis in recent years. There are many investigations on biotransformations in a variety of DESs, but the purification of bioproducts from DES reaction mixtures has not yet been sufficiently addressed. The present study demonstrates a product recovery strategy from a DES reaction medium composed of (-)-menthol and dodecanoic acid. Since the DES is not formed by equimolar amounts of the substrates, but the eutectic point occurs at a 3:1 molar ratio, product isolation is an important task for effective biocatalytic process development, even if the limiting substrate is converted completely. Both DES compounds acted as substrates and reaction solvent in the lipase-catalyzed esterification to synthesize (-)-menthyl dodecanoate. The product (-)-menthyl dodecanoate ester was separated from the DES reaction mixture by a vacuum distillation step and a second esterification reaction can be performed with the recovered (-)-menthol.

Optimization of solvent-free enzymatic esterification in eutectic substrate reaction mixture

The Candida rugosa lipase catalyzed esterification of (-)-menthol and lauric acid (LA) was studied in a eutectic mixture formed by both substrates((-)-menthol:LA 3:1, mol/mol). No additional reaction solvent was necessary, since the (-)-menthol:LA deep eutectic solvent (DES) acts as combined reaction medium and substrate pool. Therefore, the esterification is conducted under solvent-free conditions. The thermodynamic water activity (a_w) was identified as a key parameter affecting the esterification performance in the (-)-menthol:LA DES. A response surface methodology was applied to optimize the esterification conditions in terms a_w, amount of C. rugosa lipase (m_CRL) and reaction temperature. Under the optimized reaction conditions (a_w = 0.55; m_CRL =60 mg; T =45 °C), a conversion of 95 ± 1% LA was achieved (one day), the final (-)-menthyl lauric acid ester concentration reached 1.36 ± 0.04 M (2.25 days). The experimental product formation rate agreed very well with the model prediction.

Reaction engineering of biocatalytic (S)-naproxen synthesis integrating in-line process monitoring by Raman spectroscopy

Biocatalytic (S)-naproxen synthesis using an (S)-selective arylmalonate decarboxylase mutant (AMDase G74C/M159L/C188G/V43I/A125P/V156L, AMDase-CLGIPL) exposes a promising environmentally friendly alternative to conventional chemical synthesis strategies.

Fish consumption, insulin sensitivity and beta-cell function in the Insulin Resistance Atherosclerosis Study (IRAS)

BACKGROUND AND AIMS

Previous research on the association between fish consumption and incident type 2 diabetes has been inconclusive. In addition, few studies have investigated how fish consumption may be related to the metabolic abnormalities underlying diabetes. Therefore, we examined the association of fish consumption with measures of insulin sensitivity and beta-cell function in a multi-ethnic population.

METHODS AND RESULTS

We examined the cross-sectional association between fish consumption and measures of insulin sensitivity and secretion in 951 non-diabetic participants in the Insulin Resistance Atherosclerosis Study (IRAS). Fish consumption, categorized as <2 vs. ≥2 portions/week, was measured using a validated food frequency questionnaire. Insulin sensitivity (S(I)) and acute insulin response (AIR) were determined from frequently sampled intravenous glucose tolerance tests. Higher fish consumption was independently associated with lower S(I)-adjusted AIR (β = -0.13 [-0.25, -0.016], p = 0.03, comparing ≥2 vs. <2 portions/week). Fish consumption was positively associated with intact and split proinsulin/C-peptide ratios, however, these associations were confounded by ethnicity (multivariable-adjusted β = 0.073 [-0.014, 0.16] for intact proinsulin/C-peptide ratio, β = 0.031 [-0.065, 0.13] for split proinsulin/C-peptide ratio). We also observed a significant positive association between fish consumption and fasting blood glucose (multivariable-adjusted β = 2.27 [0.68, 3.86], p = 0.005). We found no association between fish consumption and S(I) (multivariable-adjusted β = -0.015 [-0.083, 0.053]) or fasting insulin (multivariable-adjusted β = 0.016 [-0.066, 0.10]).

CONCLUSIONS

Fish consumption was not associated with measures of insulin sensitivity in the multi-ethnic IRAS cohort. However, higher fish consumption may be associated with pancreatic beta-cell dysfunction.

Process development for the electroenzymatic synthesis of (R)-methylphenylsulfoxide by use of a 3-dimensional electrode

The electrogeneration of hydrogen peroxide via reduction of dissolved oxygen was carried out in a three-dimensional electrochemical cell using graphite grains as cathode material and combined with the enantioselective oxidation of thioanisole to (R)-methylphenylsulfoxide catalyzed by Chloroperoxidase from Caldariomyces fumago. The relevant parameters for process development (e.g., conductivity of the biotransformation medium) were identified and optimized, leading to an efficient electroenzymatic process with a space-time yield of 104 g x L(-1) x d(-1). The isolated product was produced on gram scale (1.2 g, purity >98%, ee > 98.5%).

Synthesis of enantiopure (5R)-hydroxyhexane-2-one with immobilised whole cells of Lactobacillus kefiri

Whole-cell reduction of (2,5)-hexanedione to yield highly enantiopure (5R)-hydroxyhexane-2-one (enantiomeric excess >99%) with Lactobacillus kefiri DSM 20587 was investigated. Cell immobilisation with sodium cellulose sulphate was chosen as the most suitable encapsulation matrix, giving an immobilisation yield of 40%. Despite the lowered biocatalytic activity from cell immobilisation, the bioreduction process was vastly improved with the help of reaction engineering techniques (batch to a plug flow reactor set-up). High selectivity (95%) and space-time yield (87 g L(-1) day(-1)) were achieved in the plug flow reactor. The biocatalyst remained active (68% residual activity) after 6 days of operation.