Search results for "yield"
showing 10 items of 1338 documents
Green conditions for the Suzuki reaction using microwave irradiation and a new HNT-supported ionic liquid-like phase (HNT-SILLP) catalyst
2014
A new catalytic system based on modified halloysite nanotubes was employed in the Suzuki reaction under microwave irradiation. A set of solvents, times and bases was screened and the best experimental conditions were obtained when the reactions were carried out for 10 min in water–ethanol at 120 °C in presence of K2CO3 as base. Good recyclability was observed. The new catalytic system was employed using either 1 mol% or 0.1 mol%. The palladium catalyst displayed good activity, allowing the synthesis of several biphenyl compounds in high yield working with only 0.1 mol% palladium loading. The application of microwave irradiation decreased the reaction time and also improved conversion with r…
Effects of foal presence at milking and dietary extra virgin olive oil on jennet milk fatty acids profile
2009
TwelveRagusanajennetswerestudiedtoinvestigatetheeffectsof dietaryextra Twelve Ragusana jennets were studiedtoinvestigatetheeffectsof dietaryextra studied to investigatetheeffectsof dietaryextra the effects of dietaryextra dietary extra virgin olive oil and thepresenceofthefoal duringmilkingonmilkfattyacids(FA)profile.At20, 50 thepresenceofthefoal duringmilkingonmilkfattyacids(FA)profile.At20, 50 he presence of the foal during milking on milk fatty acids (FA) profile. At 20, 50 and 90 days post-foaling, each jennet was milked 4 times per day. The feeding system and the milking procedures are given by Alabiso et al. (2009). FA profiles of the composites from milkings without foals (1MNF+3MNF)…
Convenient Synthesis of Biologically Important Retinoids
1995
The toxic and teratogenic effects caused by the highly biologically active (all-E)-retinoic acid and its derivatives prompted us to synthesize a number of retinoids. We developed synthetic approaches to (all-E)-retinyl β-D-glucuronide 3, methyl (retinoyl β-D-glucopyranoside)uronate 5, (all-E)-retinoic acid β-D-glucopyranosyl ester 8 and (all-E)-retinoyl β-D-glucuronide 6 in high purity and yield. Compound 3 was synthesized under Koenigs-Knorr conditions from (all-E)-retinol and an α-halogenose. Compounds 5 and 8 were prepared by esterification of a silver salt of (all-E)-retinoic acid with an α-glycosyl halide in pyridine. (all-E)-Retinoyl β-D-glucuronide 6 was prepared by reaction of (all-…
Synthesis of C1-[18F]fluoroethylamnino asparagine for imaging cancer
2001
C1-[18F]fluoroethylamino asparagine was synthesised from N1-t-boc C1-p-nitrophenol asparagine and the radiolabelled precursor [18F]flouroethylamine in a one-pot-synthesis. The yield of this synthesis was 22% referring to [18F]fluoride, including the removal of the protection groups. The in vivo tests are in progress.
Lewis Acid-Catalyzed Stereoselection on Carbohydrate Templates
1989
The chirality and the complexing abilities of carbohydrates are utilized for chemical stereoselection in different reactions. In this sense, the carbohydrates are investigated as the chiral auxiliaries in alkylation reactions and in Michael additions of ester enolates. Furthermore, carbohydrates are demonstrated to be efficient chiral matrices in Lewis acid-catalyzed Diels-Alder reactions. They also effect stereoselection in a new synthesis of β-branched carboxylic acid derivatives. O-Acylated glycosylamines are shown to be potent chiral templates in the Strecker synthesis and in the Ugi four-component condensation to give α-amino acid derivatives in high yield and diastereoselectivity. In …
High-Yield Formation of Arbutin from Hydroquinone by Cell-Suspension Cultures ofRauwolfia serpentina
1992
High-density cell-suspension cultures of Rauwolfia serpentina cultivated in a nutrition medium optimized for the production of the glucoalkaloid raucaffricine synthesize hydroquinone glycosides from continuously added hydroquinone with a total yield of 23.87 g/1 (18 g/1 of arbutin and 5.87 g/1 of a hydroquinone diglycoside) in 7 days. This arbutin production is by far the highest formation of a natural product by plant-cell-culture systems reported to date.
Direct acid-catalysed mechanical depolymerisation of fibre sludge to reducing sugars using planetary milling
2016
Abstract This study performed a direct solvent-free acid-catalysed mechanical depolymerisation of fibre sludge to reducing sugars which involves one step of acid milling in a planetary mill. The common reported ‘solvent-free’ mechanocatalytic depolymerisation of lignocellulose which includes 1) acid impregnation, 2) vacuum evaporation and 3) mechanocatalytic depolymerisation was also performed as a reference. The major converted monosaccharides were determined by capillary electrophoresis and the results of total reducing sugar (TRS) yields were carried out based on the 3,5-dinitrosalicylic acid (DNS) method. The results showed that the TRS conversion of direct acid-catalysed mechanical dep…
Capping α-Cyclodextrin with Cyclotriveratrylene by Triple Disulfide-Bridge Formation
2013
Disulfide-bond formation is an expeditious coupling reaction to make macropolycyclic symmetrical receptors. It is used here for the preparation of unsymmetrical cavitands based on α-cyclodextrin (α-CDX) and cyclotriveratrylene (CTV) analogues. Accordingly, diastereomeric hemicryptophanes 2a and 2b were obtained in 11 % isolated yield by the iodine oxidation of a 1:1 mixture of racemic cyclotrithiophenolene (3) and the C3-symmetric trithiol derivative of permethylated α-cyclodextrin (PM α-CDX) 4. Remarkably, the target hemicryptophanes were obtained in a 5:3 diastereomeric ratio. The reaction produced mainly (34 %) a singly disulfide-bridged PM α-CDX dimer 7, however no traces of triply disu…
Pauson–Khand reaction of fluorinated compounds
2020
The Pauson–Khand reaction (PKR) is one of the key methods for the construction of cyclopentenone derivatives, which can in turn undergo diverse chemical transformations to yield more complex biologically active molecules. Despite the increasing availability of fluorinated building blocks and methodologies to incorporate fluorine in compounds with biological interest, there have been few significant advances focused on the fluoro-Pauson–Khand reaction, both in the inter- and intramolecular versions. Furthermore, the use of vinyl fluorides as olefinic counterparts had been completely overlooked. In this review, we collect the advances both on the stoichiometric and catalytic intermolecular an…
Synthesis of γ-Amino Acid Esters by 1,4-Addition of Deprotonated α-Aminonitriles and α-(Alkylideneamino)nitriles to α,β-Unsaturated Esters.
2007
α-Aminonitriles and α-(alkylideneamino)nitriles can serve as readily available α-aminocarbanion equivalents. Their conjugate addition to α,β-unsaturated esters followed by reduction furnishes polysubstituted γ-amino acid esters in moderate to high yield.