Diastereoselective preparation of azetidines and pyrrolidines

Iodine-mediated cyclization of homoallyl amines at room temperature delivered cis-2,4-azetidine through a 4-exo trig cyclization. Isomerization of iodo-azetidines to cis-pyrrolidines could be achieved by heating, with complete stereocontrol. The relative stereochemistry of the iodo-azetidines and pyrrolidines was confirmed by NMR spectroscopy and X-ray crystallography. Further functionalization was achieved through nucleophilic displacement of iodine to deliver substituted azetidines and pyrrolidines. 1,2,3-Triazole-appended azetidines and pyrrolidines were also prepared.     

近红外光谱法测定5-羟基色氨酸的含量

本文利用近红外光谱法建立了5-羟基色氨酸的偏最小二乘(PLS)定量模型。采用相关数法选择波段以及二阶导数、Norris derivative平滑滤波进行数据预处理,所建校正模型的R为0.99907,RMSEC为0.0638,RMSEP为0.0675。经验证模型的预测性能良好,为5-HTP的快速测定提供了一种方法。     

Study of acetylated EGCG synthesis by enzymatic transesterification in organic media

(-)-Epigallocatechin-3-O-gallate (EGCG), the most abundant polyphenolic compound in catechins, exerts excellent physiological effects including antioxidant. However, with its high hydrophilicity and poor lipophilicity, the application of EGCG in oil products is limited. In this study, EGCG acetylated derivatives were prepared by transesterification of EGCG with vinyl ester in acetonitrile/isopropanol (1:1 v/v). Lipase Lipozyme RM IM was found to be the optimum catalyst at concentration of 12 U/g EGCG, with a molar ratio of 1:5 of EGCG to vinyl acetate as the substrates. And 83.2% conversion was obtained after 10 h reaction at 50 °C. Based on the ping-pong model, the kinetic equation was constructed to determine the reaction kinetic parameters. The analysis of the initial rate and progress curve indicated that the transesterification of EGCG and vinyl acetate was kinetically regulated. Two major acetylated derivatives were identified as 5″-O-acetyl-EGCG and 3″, 5″-di-O-acetyl-EGCG by LC-MS/MS and NMR. Their enhanced lipophilicity was confirmed by transmittance test and octanol–water partition coefficient. The antioxidant activity of di-acetylated EGCG was superior to mono-acetylated EGCG and EGCG, but slightly lower than tert-butyl hydroquinone (TBHQ) as determined by peroxide values (POV) and Rancimat test. Acetylated EGCG might be used as a potent antioxidant for controlling oxidation of oil.     

Convenient preparation of 5-ethynyl-octaethylporphyrin free base and zinc complex

A method leading to the preparation of the free base or zinc meso-ethynyl functionalized octaethylporphyrin has been developed, which will open the access to various meso-ethynyl metalloporphyrins.     

Diastereoselective synthesis of 5-benzylthio- and 5-mercaptohexahydropyrimidin-2-ones

A three-stage diastereoselective synthesis of (4R^∗,5R^∗,6S^∗)-5-mercapto-4-methyl-6-phenylhexahydropyrimidin-2-one has been developed. The first stage involves the formation of 4-hydroxy-5-(4-methoxybenzylthio)-4-methyl-6-phenylhexahydropyrimidin-2-one by the reaction of N-[(phenyl)(tosyl)methyl]urea with the sodium enolate of 1-(4-methoxybenzylthio)propan-2-one. Reduction of the obtained compound by NaBH₄-CF₃COOH and removal of the p-methoxybenzyl protecting group results in the target compound.     

Diastereoselective alkynylation of chiral phosphinoylimines: preparation of optically active propargylamines

Chiral phosphinoylimines were prepared from methylphenylphosphonamides and tested as new chiral and activated imines. The addition of aluminum acetylides was proved to be highly diastereoselective while lithium or magnesium acetylides gave poor results. The cleavage of the chiral auxiliary was done under mild conditions and allows the recovery of the starting phosphonamide without loss of optical purity.     

Diastereoselective Ti-mediated preparation of bicyclic aminocyclopropanes from N-alkenyl amides

Intramolecular Ti-mediated alkene-amide couplings of a range of N-alk-3-enyl amides fitted with a substituent at the homoallylic position are described. CF₃-substituted compounds are suitable substrates and bicyclic aminocyclopropanes bearing a CF₃ group can be prepared in this way. Good diastereoselectivities can be observed depending on the substitution pattern, and best results are obtained in diethyl ether rather than in THF.     

Diastereoselective ruthenium-catalysed cycloisomerisation of diallyllactones: preparation of exo-methylene spirolactones

Diallyllactones (obtained from cyclic anhydrides via a double allylation reaction promoted by titanium tetrachloride) were cycloisomerised using 5 mol% of cyclooctadienyl ruthenium dichloride in ethanol providing the corresponding exomethylene spirolactones in good yields, with moderated to good diastereomeric excess.     

Diastereoselective generation of triple-stranded helicates induced by gem-dimethyl groups on a linker

The diastereoselectivity of the self-assembly of bis(dipyrromethene) ligands with trivalent metals was improved by introducing gem-dimethyl groups to the linker.     

Diastereoselective mukaiyama and free radical processes for the synthesis of polypropionate units

[reaction: see text] Reported herein is the synthesis of 8 out of 16 polypropionates derived from our propionate units. A new strategy involving a stereoselective Mukaiyama aldol reaction followed by a stereoselective free-radical-based hydrogen transfer, both under Lewis acid control, is used. Of particular interest is the remarkable reactivity of (i-PrO)TiCl(3) in this context to give only the 3,4-anti bromoesters.     

Diastereoselective ortho-lithiation of [5]ferrocenophanes

Planarly chiral ferrocene derivatives with bridged cyclopentadienyl rings are interesting ligands in asymmetric catalysis. A planar stereogenic unit is conveniently introduced by diastereoselective ortho-lithiation. The directed lithiation of several [5]ferrocenophane derivatives followed by quenching with chlorodiphenylphosphane led to planarly chiral ligands. The sense of diastereoselection was studied by computational methods. Absolute configuration of methoxy phosphane was determined by single crystal X-ray diffraction study.     

Diastereoselective preparation and characterization of ruthenium bis(bipyridine) sulfoxide complexes

A new concept in the synthesis of optically active octahedral ruthenium complexes was realized for the first time when cis- or trans-Ru(bpy)2Cl, (cis- or trans-1) was reacted with either (R)-(+)- or (S)-(-)-methyl p-tolyl sulfoxide (2 or 3); this novel asymmetric synthesis leads to the diastereoselective formation of the ruthenium bis(bipyridine) complex cis-delta-[Ru(bpy)2(2)Cl]Cl (4) (49.6% de) or cis-lambda-[Ru(bpy)2(3)Cl]Cl (5) (48.4% de), respectively. cis- or trans-Ru(dmbpy)2Cl2 (cis- or trans-6) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine) also reacts with 2 or 3, leading to the diastereoselective formation of cis-delta-[Ru(dmbpy)2(2)Cl]Cl (7) (59.5% de) or cis-lambda-[Ru(dmbpy)2(3)Cl]Cl (8) (57.2% de), respectively. The diastereoselectivity of these reactions is governed solely by the chirality of the sulfoxide nucleophile. This represents the first process by which a sigma-bonded ligand occupying only a single coordination site has had such an important influence on the stereochemical outcome of a ruthenium bis(bipyridine) complex formation. These novel complexes were fully characterized by elemental analysis and IR, UV/vis, and 1H, 13C, and 2D NMR spectroscopy. An investigation into the chiroptical properties of these novel ruthenium bis(bipyridine) sulfoxide complexes has been carried out, and circular dichroism spectra are used to assign absolute stereochemistry.     

Luminescence properties of PPV derivatives carrying anthracene pendent groups

Photo- (PL) and electroluminescence (EL) properties of three different PPV derivatives carrying the 9,10-diphenylanthracene units are compared. One (polymer 1 ) of the polymers contains the 9,10-diphenylanthracene structure as an integral part of the main chain, but the other two have it as the pendent group attached to the main chain through either oxyethyleneoxy (polymer 2 ) or oxyhexamethyleneoxy (polymer 3 ) spacer. Polymers 1 and 2 exhibit very similar PL and EL spectra that are more or less of superimposed feature of the spectra from the backbones and the anthracene pendents. In contrast, polymer 3 shows an EL spectrum that is completely different from its PL spectrum. Whereas the PL spectrum of polymer 3 appears to be a combination of the spectra from the main chain and the pendents, as for polymer 1 and 2 , the EL spectrum of polymer 3 , however, looks as if the lights were emitted only from the backbone. This difference is explained in terms of excited state electronic interactions between the main chain and the pendents.     

Diastereoselective synthesis of propargylic fluorides and its application in preparation of monofluorinated sugar

An effective method to diastereoselectively synthesize enantioenriched propargylic fluorides was developed via S_N1 type reaction of DAST participated dehydroxy-fluorination of diastereomeric propargylic alcohol cobalt–carbonyl complexes. A serious of propargylic fluorides can be prepared by this approach in good yields with moderate to high diastereoselectivities. To demonstrate the application of this approach in synthesis, monofluorinated sugar 12, an important and versatile building block, was prepared in an efficient manner.     

Diastereoselective free radical halogenation,azidation, and rearrangement of beta-silyl Barton esters

[reaction: see text] Barton esters of beta-silylcarboxylic acids were decomposed by photolysis alone in organic solvents or in the presence of ethanesulfonyl azide or bromotrichloromethane. Products of the reaction, beta-silylthiopyridyl ethers, beta-silyl azides, or alkenes, were formed with significant control of stereochemistry.     

含咔唑和偶氮苯的乙炔衍生物的合成

采用Sonagashira偶联反应和N-烷基化反应合成了含有咔唑和偶氮苯的乙炔衍生物:3-乙炔基-9-(4-[4-(硝基)苯基偶氮苯]氧)亚丁基咔唑3.其结构通过IR,1H NMR,13C NMR,元素分析和X-射线单晶衍射法测定.标题化合物属单斜晶系,P21/c空间群;a=9.238(3),b=28.240(8),c...     

Diastereoselective enzymatic synthesis of highly substituted 3,4-dihydropyridin-2-ones via domino Knoevenagel condensation-Michael addition-intramolecular cyclization

A direct method to construct 3,4-dihydropyridin-2-ones by enzymatic condensation of aldehyde with cyanoacetamide and 1,3-dicarbonyl compounds was developed. One ring and four new bonds (two C-C, one C-N, one CC) were formed in one pot. And reaction conditions involving hydrolases, solvents, substrate molar ratios, and hydrolase loading were optimized. A series of new compounds based on the 3,4-dihydropyridin-2-one core were synthesized by the unprecedented three-component domino reaction.     

固定化脲酶的制备及酶学性质研究

固定化酶是束缚在一定空间内仍能进行其特有反应的生物催化剂,近年来对于固定化酶的研究非常活跃[1-2].目前酶的固定化方法主要有吸附法,交联法,包埋法以及化学共价法,这些方法各有特点[3-5],应用领域多为食品工业、制药、医学治疗等方面.     

An efficient enzymatic preparation of rhinovirus protease inhibitor intermediates

The development of an efficient route for the preparation of (2S)-2-[3-{[(5-methylisoxazol-3-yl)carbonyl]amino}-2-oxopyridin-1(2H)-yl]pent-4-ynoic acid (4), a key intermediate in the synthesis of a human rhinovirus (HRV) protease inhibitor, is presented. In the presence of 40% acetonitrile, the alkaline protease from Bacillus lentus can catalyze the kinetic resolution of racemic ester 7 to afford (S)-acid 4 in 49% chemical yield/per cycle with 98% ee and >98% HPLC purity. The (R)-ester can then be readily recycled via a DBU catalyzed epimerization. The enzymatic preparation described here is superior to the existing chemical resolution route, exhibiting lower costs as well as higher yields, enantioselectivity, and substrate loads. In addition, this protease displays broad substrate specificity toward this class of compounds and can be easily extended to the preparation of other tripeptide mimetics of rhinovirus protease inhibitors.     

Solvent free preparation of amidophosphonates from isocyanides

New amidophosphonates are prepared via a two-step Mannich/Ugi one-pot procedure from isocyanides. Aminophosphonates are readily prepared from primary amines, dialkyl phosphites and carbonyl compounds under LiClO₄ catalysis without any solvent. After completion, addition of an isocyanide, an aldehyde and acetic acid give access to phosphono Ugi-type adducts in good to moderate yields.