1,721,023 research outputs found
Organocatalytic Formation of Quaternary Stereocenters
No full textThis work reviews the authors' choice of recently published papers where at least one asymmetric quaternary stereocenter has been formed via organocatalysis. The scope and limitations of the reactions are highlighted
90% ee and >10 : 1 dr
The Suzuki Reaction Applied to the Synthesis of Novel Pyrrolyl and Thiophenyl Indazoles
No full textThe paper describes the Suzuki cross-coupling of a variety of N and C-3 substituted 5-bromoindazoles with N-Boc-2-pyrrole and 2-thiopheneboronic acids. The reactions, performed in the presence of K2CO3, dimethoxyethane and Pd(dppf)Cl2 as catalyst, gave the corresponding adducts in good yields. The methodology allows the facile production of indazole-based heteroaryl compounds, a unique architectural motif that is ubiquitous in biologically active molecules
Synergic asymmetric organocatalysis (SAOc) of Cinchona alkaloids and secondary amines in the synthesis of bicyclo[2.2.2]octan-2-ones
No full textA synergistic effect between chiral secondary and tertiary amines gives access to bicyclo[2.2.2]octan-2-ones with up to 90% ee and >10: 1 dr. © The Royal Society of Chemistry
Alcossicarbonil Allilsilani per la Sintesi di Ammino Esteri
No full text(Comunicazione orale Tecla Gasperi))
Rapid, high performance method for the determination of vitamin K-1, menaquinone-4 and vitamin K-1 2,3-epoxide in human serum and plasma using liquid chromatography-hybrid quadrupole linear ion trap mass spectrometry
No full textUnlike the other fat-soluble vitamins, vitamin K circulates in the human bloodstream at very low levels because of a low intake in the diet. Mammals have developed an efficient recycling system, known as vitamin K-epoxide cycle, which involve quinone, hydroquinone and epoxide forms of the vitamin. Phylloquinone (K-1) is the main homologue, while menaquinone-4 (MK-4) is both a member of the vitamin 1(2 family and metabolite of K1 in extra-hepatic tissues. Notwithstanding the recent advances, many aspects of the complex vitamin K physiology still remain to be investigated. Therefore, there is a critical need to develop more reliable analytical methods for determining the vitamin K and its metabolites in biological fluids and tissues. Nevertheless, relatively low concentrations, unavailability of some authentic standards and occurrence of interfering lipids make this a challenging task. The method proposed in the present paper can directly and accurately estimate K-1, K-1 2,3-epoxide (K1O), and MK-4 in human serum and plasma at concentrations in the ng/L-mu g/L range, using labelled internal standards and a quadrupole linear ion trap instrument operated in multiple reaction monitoring (MRM) mode. High sensitivity was achieved by removing signal "endogenous suppressors" and making the composition of the non-aqueous mobile phase suitable to support the positive atmospheric pressure chemical ionization of the analytes. An excellent selectivity resulted from the combination of some factors: the MRM acquisition, the adoption of an identification point system, an extraction optimized to remove most of the lipids and a tandem-C18 column-system necessary to separate isobaric interferences from analytes. The method was validated according to the Food and Drug Administration (FDA) guidelines and its accuracy was assessed by analysing 9 samples from the Vitamin K External Quality Assessment Scheme (KEQAS). Its feasibility in evaluating vitamin K status in human serum was also tested by monitoring a group of six healthy subjects and a group of six patients under oral anticoagulant therapy (OAT). Warfarinised patients did not show deficiency of K1 but levels comparable with those of healthy people and an accumulation of 1(10 up to 3.760 mu g/L. MK-4 was not detected in either of the two groups. (C) 2014 Elsevier B.V. All rights reserved
Silylating Reagents: A Powerful Tool for the Construction of Isosteric Analogs of Highly Branched Odorants
No full textWe have discovered that alpha-dimethyl(thexyl)silyl]acetaldehyde (= [dimethyl(1,1,2-trimethylpropyl)silyl]acetaldchyde; 31) has a strong, woody odor. Structural analysis has shown resemblance to known odorants with similar organoleptic properties. On the basis of structure-odor relationships, new and more-powerful woody and ambery sila odorants were prepared. Further derivatization led to a set of compounds with very interesting organoleptic properties. Selected chiral compounds were also prepared stereoselectively. The influence of the absolute configuration on the olfactory properties was in agreement with theoretical assumptions. We also designed other groups of organosilicon odorants. The compounds discovered can be obtained in a few simple steps from commercially available reagents, and may find application in the fragrance and flavor industry. Their structures provide interesting data for further research on structure-odor relationships
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