Lipase-catalyzed kinetic resolution of beta-borylated carboxylic esters

The kinetic resolution of chiral beta-borylated carboxylic esters via lipase-catalyzed hydrolysis and transesterification reactions was studied. The enantioselective hydrolysis catalyzed by CAL-B furnished the beta-borylated carboxylic acid with reasonable enantiomeric excess (62% ee), while both methyl and ethyl beta-borylated carboxylic esters were recovered with excellent ee (>99%). Meanwhile, the transesterification reaction of beta-borylated carboxylic esters and several alcohols, catalyzed by CAL-B, only indicated a high selectivity when ethanol and methyl-(beta-pinacolylboronate)-butanoate were used as substrates, which gave ethyl-(beta-pinacolylboronate)-butanoate with >99% ee. (C) 2012 Elsevier Ltd. All rights reserved.

Further monoterpene chromane esters from Peperomia obtusifolia: VCD determination of the absolute configuration of a new diastereomeric mixture

A reinvestigation of the monoterpene chromane ester enriched fraction from Peperomia obtusifolia using chiral chromatography led to the identification of a minor peak, which was elucidated by NMR and HRMS as fenchyl-3,4-dihydro-5-hydroxy-2,7-dimethyl-8-(3 ''-methyl-2 ''-butenyl)-2-(4'-methyl-1',3'-pentadienyl)-2H-1-benzopyran-6-carboxylate, the same structure assigned to two other fenchyl esters described previously, pointing out a stereoisomeric relationship among them. Further NMR analysis revealed that it was actually a mixture of two compounds, whose absolute configurations were determined by VCD measurements. Although, almost no vibrational transitions could be assigned to the chiral chromane, the experimental VCD spectrum was largely opposite to that obtained for the average experimental VCD [(2S,1'''R,2'''R,4'''S + 2R,1'''R,2'''R,4'''S)/2] for fenchol derivatives. These results allowed us to assign the putative compounds as a racemic mixture of the chiral chromane esterified with the monoterpene (1S,2S,4R)fenchol, which had not been identified in our early work. (C) 2012 Elsevier Ltd. All rights reserved.

Ultrastructural changes in the ovary cells of engorged Rhipicephalus sanguineus female ticks treated with esters of ricinoleic acid from castor oil (Ricinus communis)

Rhipicephalus sanguineus is a widely distributed tick species that has adapted to the urban environment, and the dog is its main host. This species is also known as a vector and reservoir of diseases caused by bacteria, protozoa, and viruses. Currently, acaricides of synthetic chemical origin have been widely and indiscriminately used, leading to the development of resistance to these products by ticks and causing damage to the environment. Thus, these issues have made it necessary to seek other forms of controlling these ectoparasites. R. sanguineus was artificially infested in host New Zealand White rabbits, which were divided into four treatment groups: control (CG1 and CG2) and treatment (TG1 and TG2) groups. TG1 and TG2 hosts were provided with feed supplemented with esters of ricinoleic acid from castor oil at a concentration of 5 g/kg of feed for 7 and 15 days. Afterward, the ovaries of the female ticks were removed for analysis by transmission electron microscopy. The results showed ultrastructural changes in the somatic and germ cells of ovaries from TG1 and TG2 females, particularly with respect to chorion deposition, a protective membrane of the oocyte, as well as in the transport process of vitellogenic materials via the hemolymph and pedicel cells. Moreover, the mitochondria were less electron-dense and had cristae that were more disorganized than the mitochondria from CG1 and CG2 individuals. Thus, this study demonstrated the action of esters on the ovaries of R. sanguineus, signaling the prospect of a way to control this ectoparasite without affecting nontarget organisms or the environment. Microsc. Res. Tech., 2012. (c) 2011 Wiley Periodicals, Inc.

Ultrasound-assisted synthesis of aliphatic acid esters at room temperature

This work describes the ultrasound-assisted synthesis of saturated aliphatic esters from synthetic aliphatic acids and either methanol or ethanol. The products were isolated in good yields after short reaction times under mild conditions. (C) 2011 Elsevier BM. All rights reserved.

Effect of sorbitan-based surfactants on glass transition temperature of cellulose esters

Thermal behavior of mixtures composed of cellulose acetate butyrate (CAB), carboxymethylcellulose acetate butyrate (CMCAB), or cellulose acetate phthalate (CAPh), and sorbitan-based surfactants was investigated as a function of mixture composition by means of differential scanning calorimetry (DSC). Surfactants with three different alkyl chain lengths, namely, polyoxyethylenesorbitan monolaurate (Tween 20), polyoxyethylenesorbitan monopalmitate (Tween 40), and polyoxyethylene sorbitan monostearate (Tween 60) were chosen. DSC measurements revealed that Tween 20, 40, and 60 act as plasticizers for CAB, CMCAB, and CAPh (except for Tween 60), leading to a dramatic reduction of glass transition temperature (T-g). The dependence of experimental T-g values on the mixture composition was compared with theoretical predictions using the Fox equation. Plasticization was strongly dependent on mixture composition, surfactant hydrophobic chain length, and type of cellulose ester functional group.

Alpha, Omega end group functionalization of RAFT polymers based on pentafluorophenyl esters and methane thiosulfonates

While polymers with different functional groups along the backbone have intensively been investigated, there is still a challenge in orthogonal functionalization of the end groups. Such well-defined systems are interesting for the preparation of multiblock (co) polymers or polymer networks, for bio-conjugation or as model systems for examining the end group separation of isolated polymer chains. rnHere, Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization was employed as method to investigate improved techniques for an a, w end group functionalization. RAFT produces polymers terminated in an R group and a dithioester-Z group, where R and Z stem from a suitable chain transfer agent (CTA). rnFor alpha end group functionalization, a CTA with an activated pentafluorophenyl (PFP) ester R group was designed and used for the polymerization of various methacrylate monomers, N-isopropylacrylamide and styrene yielding polymers with a PFP ester as a end group. This allowed the introduction of inert propyl amides, of light responsive diazo compounds, of the dyes NBD, Texas Red, or Oregon Green, of the hormone thyroxin and allowed the formation of multiblocks or peptide conjugates. rnFor w end group functionalization, problems of other techniques were overcome through an aminolysis of the dithioester in the presence of a functional methane thiosulfonate (MTS), yielding functional disulfides. These disulfides were stable under ambient conditions and could be cleaved on demand. Using MTS chemistry, terminal methyl disulfides (enabling self-assembly on planar gold surfaces and ligand substitution on gold and semiconductor nanoparticles), butynyl disulfide end groups (allowing the “clicking” of the polymers onto azide functionalized surfaces and the selective removal through reduction), the bio-target biotin, and the fluorescent dye Texas Red were introduced into polymers. rnThe alpha PFP amidation could be performed under mild conditions, without substantial loss of DTE. This way, a step-wise synthesis produced polymers with two functional end groups in very high yields. rnAs examples, polymers with an anchor group for both gold nanoparticles (AuNP) and CdSe / ZnS semi-conductor nanoparticles (QD) and with a fluorescent dye end group were synthesized. They allowed a NP decoration and enabled an energy transfer from QD to dye or from dye to AuNP. Water-soluble polymers were prepared with two different bio-target end groups, each capable of selectively recognizing and binding a certain protein. The immobilization of protein-polymer-protein layers on planar gold surfaces was monitored by surface plasmon resonance.Introducing two different fluorescent dye end groups enabled an energy transfer between the end groups of isolated polymer chains and created the possibility to monitor the behavior of single polymer chains during a chain collapse. rnThe versatility of the synthetic technique is very promising for applications beyond this work.

A Computationally Efficient Procedure for Modeling the First Step in the Alkaline Hydrolysis of Esters

A computationally efficient procedure for modeling the alkaline hydrolysis of esters is proposed based on calculations performed on methyl acetate and methyl benzoate systems. Extensive geometry and energy comparisons were performed on the simple ester methyl acetate. The effectiveness of performing high level single point ab initio energy calculations on the geometries obtained from semiempirical and ab initio methods was determined. The AM1 and PM3 semiempirical methods are evaluated for their ability to model the transition states and intermediates for ester hydrolysis. The Cramer/Truhlar SM3 solvation method was used to determine activation energies. The most computationally efficient way to model the transition states of large esters is to use the PM3 method. The PM3 transition structure can then be used as a template for the design of haptens capable of inducing catalytic antibodies.

Effect of exercise on the mobilization of retinol and retinyl esters in plasma of sled dogs

Fasting dogs do transport vitamin A (VA) in plasma not only as retinol but predominantly as retinyl esters. Contrary to retinol, nothing is known concerning the effects of athletic performance on plasma retinyl ester concentrations. The aim of this study was therefore to examine whether physical stress because of exercise and modification of the oxidative stress by supplementation of alpha-tocopherol influences the concentrations of retinol and retinyl esters in plasma of sled dogs. The study was carried out on 41 trained adult sled dogs, which were randomly assigned into two groups. One group (19 dogs) was daily substituted with 50 mg dl-alpha-tocopheryl acetate per kilogram body weight and the control group (22 dogs) was maintained on a basal diet during 3 months prior to exercise. The plasma concentrations of retinol, retinyl esters, alpha-tocopherol and triglycerides were measured immediately before, directly after and 24 h after exercise. The supplementation of alpha-tocopheryl acetate had no effect on plasma retinol and retinyl ester concentrations at any measurement time point. However, retinyl ester levels doubled in the non-supplemented group immediately after the race (p < 0.001), whereas in the supplemented group similar high levels were observed not until 24 h post-racing (p < 0.001). The high levels of retinyl esters were paralleled to some extent by an increase in plasma triglyceride concentrations, which were significantly higher 24 h post-racing than immediately before (p < 0.001) and after exercise (p < 0.001) in both groups. The increase in retinyl ester concentrations might be indicative of their mobilization from liver and adipose tissue. Whether plasma retinyl esters can be used as an indicator for the extent of nutrient mobilization during and post-exercise in sled dogs remains to be elucidated.

Levels of retinol and retinyl esters in plasma and urine of dogs with urolithiasis

Vitamin A (VA) deficiency and Tamm-Horsfall glycoprotein (THP), a protein that binds retinol and retinyl esters in canine urine, might be involved in the pathogenesis of urolithiasis in dogs. In the present study, we assessed levels of retinol, retinyl esters, retinol-binding protein (RBP) and THP in plasma and urine of dogs with a history of urolithiasis (n = 25) compared with clinically healthy controls (n = 18). Plasma retinol concentrations were higher in dogs with uroliths of struvit (P < 0.01), calcium oxalate (P < 0.05), urate (P < 0.01) and cysteine, but there were no differences in the concentrations of plasma RBP and retinyl esters. Excretion of urinary retinol and retinyl esters were tentatively, but not significantly higher in the stone-forming groups, which was accompanied by increased levels of urinary RBP (P < 0.01) and lower excretions in THP (P < 0.01). The results show that VA deficiency may be excluded as a potential cause for canine urolithiasis. However, the occurrence of RBP and a concomitant reduction of THP in urine indicates a disturbed kidney function as cause or consequence of stone formation in dogs.

Determination of fatty acid ethyl esters in dried blood spots by LC-MS/MS as markers for ethanol intake: application in a drinking study.

The forensic utility of fatty acid ethyl esters (FAEEs) in dried blood spots (DBS) as short-term confirmatory markers for ethanol intake was examined. An LC-MS/MS method for the determination of FAEEs in DBS was developed and validated to investigate FAEE formation and elimination in a drinking study, whereby eight subjects ingested 0.66-0.84 g/kg alcohol to reach blood alcohol concentrations (BAC) of 0.8 g/kg. Blood was taken every 1.5-2 h, BAC was determined, and dried blood spots were prepared, with 50 μL of blood, for the determination of FAEEs. Lower limits of quantitation (LLOQ) were between 15 and 37 ng/mL for the four major FAEEs. Validation data are presented in detail. In the drinking study, ethyl palmitate and ethyl oleate proved to be the two most suitable markers for FAEE determination. Maximum FAEE concentrations were reached in samples taken 2 or 4 h after the start of drinking. The following mean peak concentrations (c̅ max) were reached: ethyl myristate 14 ± 4 ng/mL, ethyl palmitate 144 ± 35 ng/mL, ethyl oleate 125 ± 55 ng/mL, ethyl stearate 71 ± 21 ng/mL, total FAEEs 344 ± 91 ng/mL. Detectability of FAEEs was found to be on the same time scale as BAC. In liquid blood samples containing ethanol, FAEE concentrations increase post-sampling. This study shows that the use of DBS fixation prevents additional FAEE formation in blood samples containing ethanol. Positive FAEE results obtained by DBS analysis can be used as evidence for the presence of ethanol in the original blood sample. Graphical Abstract Time courses for fatty acid ethyl ester (FAEE) concentrations in DBS and ethanol concentrations for subject 1 over a period of 7 h. Ethanol ingestion occured during the first hour of the time course.

Density of alkyl esters and its mixtures

Biodiesel density is a key parameter in biodiesel simulations and process development. In this work we selected, evaluated and improved two density models, one theoretical (Rackett-Soave) and one empirical (Lapuerta's method) for methanol based biodiesels (FAME) and ethanol based biodiesel (FAEE). For this purpose, biodiesel was produced from vegetable oils (sunflower, rapeseed, soybean, olive, safflower and other two commercial mixtures of vegetable oils) and animal fats (edible and crude pork fat and beef tallow) using both methanol and ethanol for the transesterification reactions, and blended to get 21 FAME and 21 FAEE, reporting their density and detailed composition. Bibliographic data have also been used. The Rackett-Soave method has been improved by the use of a new acentric factor correlation, whereas the parameters of the empirical one are improved by considering a bigger density data bank. Results show that the evaluated models could be used to estimate the biodiesel density with a good grade of accuracy but the performed modifications improve the accuracy of the models: ARD (%) for FAME; 0.33, and FAEE; 0.26, both calculated with the modification of Rackett-Soave method and ARD (%) for FAME; 0.40 calculated with the modification of the Lapuerta's method).