α-单取代环十二酮肟及缩氨基硫脲的合成及晶体结构

单晶X射线衍射分析表明, α-单取代环十二酮与氨衍生物羟胺和氨基硫脲发生缩合反应得到两种母体构象均为[3333], 而取代基为边外向或角反向的α-单取代环十二酮肟或缩氨基硫脲. 利用底物的“角位羰基参与反应”原理, “记忆效应”及进攻试剂与底物是否形成氢键解释了这一实验结果. 通常情况下, 试剂从空间障碍小的一面进攻羰基而生成α-角反取代环十二酮肟或缩氨基硫脲. 当试剂与底物的取代基之间能够形成分子间氢键时, 则生成α-边外取代环十二酮肟或缩氨基硫脲.     

Polyhydroxy pregnanes from Dregea volubilis

Three new polyhydroxy pregnanes named dregealol (1), volubilogenone (2) and volubilol (3) were isolated from the flowers of Dregea volubilis, and their structures elucidated from extensive 2D NMR analysis. The structure of volubilol (3) was confirmed by X-ray crystallographic studies. The known pregnane derivatives drevogenin D, iso-drevogenin P and 17α-marsdenin were also isolated.     

Synthetic applications of the carbanion generated from 4,4,4-trifluorobutan-2-one

Synthetic routes for α-trifluoromethylated carbonyl compounds based on the aldol reaction of silylenol ether and the palladium(0) catalyzed reaction using by 4,4,4-trifluorobutan-2-one are described.     

Catalytic, asymmetric synthesis of α,α-disubstituted amino acids

Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented.     

Site-specific detection of S-nitrosylated PKB alpha/Akt1 from rat soleus muscle using CapLC-Q-TOF(micro) mass spectrometry

Protein Kinase Balpha(PKBalpha, or Akt1) is believed to play a crucial role in programmed cell death, cancer progression and the insulin-signaling cascade. The protein is activated by phosphorylation at multiple sites and subsequently phosphorylates and activates eNOS. Free cysteine residues of the protein may capture reactive, endogenously produced nitric oxide (NO) as S-nitrosothiols. Site-specific detection of S-nitrosylated cysteine residues, usually at low stoichiometry, has been a major challenge in proteomic research largely due to the lack of mass marker for S-nitrosothiols that are very labile under physiologic conditions. In this report we describe a sensitive and specific MS method for detection of S-nitrosothiols in PKB alpha/Akt1 in rat soleus muscle. PKB alpha/Akt1 was isolated by immunoprecipitation and 2D-gel electrophoresis, subjected to in-gel tryptic digestion, and cysteinyl nitrosothiols were reacted with iodoacetic acids [2-C(12)/C(13) = 50/50] under ascorbate reduction conditions. This resulted in the production of relatively stable carboxymethylcysteine (CMC) immonium ions (m/z 134.019 and m/z 135.019) within a narrow argon collision energy (CE = 30 +/- 5 V) in the high MS noise region. In addition, free and disulfide-linked cysteine residues were converted to carboxyamidomethylcysteines (CAM). Tryptic S-nitrosylated parent ion was detected with a mass accuracy of 50 mDa for the two CMC immonium ions at the triggered elution time during capillary liquid chromatography (LC) separation. A peptide containing Cys(296) was discriminated from four co-eluting tryptic peptides under lock mass conditions (m/z 785.8426). S-nitrosothiol in the tryptic peptide, ITDFGLBKEGIK (B: CAM, [M + 2H](2+) = 690.86, Found: 690.83), is believed to be present at a very low level, since the threshold for the CMC immonium trigger ions was set at 3 counts/s in the MS survey. The high levels of NO that are produced under stress conditions may result in increased S-nitrosylation of Cys(296) which blocks disulfide bond formation between Cys(296) and Cys(310) and suppresses the biological effects of PKB alpha/Akt1. With the procedures developed here, this process can be studied under physiological and pathological conditions.     

Convenient syntheses of isomaltose derivatives from amygdalin

The isomaltose trichloroacetimidate 7 was synthesized in five steps from d-amygdalin. The key step in this series of reactions was the acid catalyzed rearrangement of the inter-glycosydic bond to give the thermodynamically more stable α-anomer. The reaction was also applied to different di-, tri-, and tetrasaccharide derivatives of amygdalin giving the corresponding rearrangement products.     

α-硝基环烷酮的制备及其合成应用

介绍了α-硝基环烷酮的制备方法, 以及它们的特殊反应性和合成应用, 参考文献40多篇.     

LiBF4: a mild and novel reagent for the OH insertion reactions of α-diazoketones

Lithium tetrafluoroborate (10 mol%) is found to catalyze efficiently the OH insertion reactions of α-diazoketones with various alcohols including benzylic, allylic, propargylic and cyclopropyl carbinols to produce the corresponding α-alkoxy ketones in excellent yields with high selectivity. A solution of 10 mol% of LiBF₄ in acetonitrile provides a convenient reaction medium to carry out the OH insertion reactions under mild and neutral conditions.     

A novel deacylation during the amination of trifluoromethyl β-dicarbonyl compounds

Starting from trifluoromethyl β-dicarbonyl compounds, a rare loss of CF₃CO was observed in the amination reactions performed under heterogeneous conditions using NsONHCO₂Et as the aminating agent and CaO or NaH as the base, while corresponding nonfluorinated β-dicarbonyl compounds under analogous conditions give non deacylated aminated compounds. This reaction can facilitate a direct synthesis of N-substituted α-amino esters or α-amino ketones.     

A study of the thermal decarboxylation of three perfluoropolyether salts

The thermal decarboxylation of three dicarboxylic perfluoropolyether potassium salts of relatively short chain length has been investigated and the products and kinetics of the main reactions have been defined. From the rate constants and Arrhenius parameters data, the second decarboxylation appears to be quantitatively rather close to the first.