Lecithin: cholesterol acyltransferase (LCAT) activity in patients with liver disease has been found to be either normal or lower than normal, but no information on LCAT mass in these patients is available. In this study, LCAT mass concentration together with LCAT activity and cholesterol esterification rate were measured in the plasma of 19 patients with cholestatic liver disease and 21 patients with non-cholestatic liver disease. The LCAT mass in plasma correlated positively with serum albumin (r=0.69, p<0.001) and pre-albumin (r=0.77, p<0.001) and negatively with serum bilirubin (r=-0.42, p<0.01) and bile salts (r=-0.43, p<0.01), thus reflecting the severity of liver disease and liver protein synthesizing capacity. In plasma, LCAT mass concentration also correlated well with LCAT activity (r=0.88, p<0.001) and cholesterol esterification rate (r=0.73, p<0.001), thereby indicating that the decrease of LCAT activity and cholesterol esterification rate in liver disease is primarily a function of decreased LCAT mass.
Palladium-catalyzed reactions of unsaturated hydrocarbons are important processes in organic chemistry especially for the generation of ring systems. This thesis describes the development and mecha ...
Palladium(0)-catalyzed reaction of allene-substituted allylic carboxylates 3-8 employing 2-5 mol % of Pd(dba)(2) in refluxing toluene leads to the carbocyclization and elimination of carboxylic acid to give bicyclo[4.3.0]nonadiene and bicyclo[5.3.0]decadiene derivatives (12-17). The carbon-carbon bond formation is stereospecific, occurring syn with respect to the leaving group. Addition of maleic anhydride as a ligand to the above-mentioned procedures changed the outcome of the reaction, and under these conditions 3-5 afforded cycloisomerized products 21-23. The experimental results are consistent with a mechanism involving oxidative addition of the allylic carboxylate to Pd(0) to give an electron-deficient (pi-allyl)palladium intermediate, followed by nucleophilic attack by the allene on the face of the pi-allyl opposite to that of the palladium atom. Furthermore, it was found that the Pd(dba)(2)-catalyzed cyclization of the trans-cycloheptene derivative (trans-8) can be directed to give either the trans-fused (trans-17) or the cis-fused (cis-17) ring system by altering the solvent. The former reaction proceeds via a nucleophilic trans-allene attack on the (pi-allyl)palladium intermediate, whereas the latter involves a syn-allene insertion into the allyl-Pd bond of the same intermediate. The products from the carbocylization undergo stereoselective Diels-Alder reactions to give stereodefined polycyclic systems in high yields.
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In addition: The scope of the title reaction is demonstrated by the synthesis of chiral lactones and lactams. The latter class of compounds is very important for the preparation of the pharmaceutical compounds such as (−)-paroxetine and (+)-femoxetine. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z601025_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Abstract The versatility of the trityl cation (TrBF 4 ) as a highly efficient Lewis acid organocatalyst is demonstrated in a light induced benzylic brominaion of alkyl‐arenes under mild conditions. The reaction was conducted at ambient temperature under common hood light (55 W fluorescent light) with catalyst loadings down to 2.0 mol% using N‐bromosuccinimide (NBS) as the brominating agent. The protocol is applicable to an extensive number of substrates to give benzyl bromides in good to excellent yields. In contrast to most previously reported strategies, this protocol does not require any radical initiator or extensive heating. For electron‐rich alkyl‐arenes, the trityl ion catalyzed bromination could be easily switched between benzylic sp 3 C−H functionalization and arene sp 2 C−H functionalization by simply alternating the solvent. This chemoselective switch allows for high substrate control and easy preparation of benzyl bromides and bromoarenes, respectively. The chemoselective switch was also applied in a one‐pot reaction of 1‐methylnaphthalene for direct introduction of both sp 3 C−Br and sp 2 C−Br functionality. magnified image
An organocatalytic asymmetric multicomponent domino and a conjugated addition reaction to alpha,beta-unsaturated aldehydes are presented. The development is based, first, on an organocatalyzed highly enantioselective nucleophilic thiol addition to the beta-carbon atom in the iminium ion intermediate, followed by an electrophilic amination of the alpha-carbon atom to the enamine intermediate. The multicomponent reactions proceed to give enantiopure amino-thiols in moderate to good yields. Furthermore, the organocatalyzed thiol addition to alpha,beta-unsaturated aldehydes takes place in good yields and excellent enantioselectivities.
Abstract One class of potential Lewis acids that has received negligible attention as a catalyst is the carbocation. Here we show the potential of triarylmethylium ions as highly powerful Lewis acid catalysts for organic reactions. The Lewis acidity of the triarylmethylium ion can be easily tuned by variation of the electronic properties of the aromatic rings and the catalytic activity of the carbocation is shown to correlate directly to the level of stabilization of the empty p C ‐orbital at the cationic carbon. The versatility of triarylmethylium ions as efficient Lewis acid catalysts for organic reactions is demonstrated in Diels–Alder, aza‐Diels–Alder, conjugate addition, halogenation, epoxide rearrangement and intramolecular hetro‐ene reactions. magnified image
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