Chemoselective deprotection of cyclic N,O-aminals using catalytic bismuth(III) bromide in acetonitrile

Cyclic N,O-aminals can be chemoselectively and efficiently deprotected using a catalytic amount of bismuth(III) bromide in acetonitrile at room temperature. This selectivity was also achieved in the presence of terminal O,O-acetal functionality. The susceptibility of various other groups to cleavage was also investigated. This method has advantages of ease of operation and use of nontoxic and inexpensive reagents in catalytic amounts.     

Synthesis studies toward chloroazaphilone and vinylogous gamma-pyridones: two common natural product core structures

Chloroazaphilone is a common structure found in a number of natural products. Reported herein is a practical synthesis of a model chloroazaphilone that utilizes Pb(OAc)4 oxidation of HClO4/HOAc pyrinium salt in a key one-pot operation. Reaction of this chloroazaphilone with various primary amines to afford the corresponding vinylogous gamma-pyridones was also fully investigated. The isolation of stable enamine intermediates provided direct evidence of reaction mechanisms.     

Enantioselective synthesis of (2S,3R)-3-hydroxy-3-methylproline, a novel amino acid found in polyoxypeptins

The enantioselective synthesis of (2S,3R)-3-hydroxy-3-methylproline (3) was achieved by the Sharpless AD, regioselective opening of cyclic sulfate by NaN(3) and intramolecular ring-closing reaction. The reported route has the advantage of a high overall yield and good enantiomeric purity, as well as starting from readily available chemical substrates and inexpensive reagents.     

Studies on mimicry of naturally occurring annonaceous acetogenins: non-THF analogues leading to remarkable selective cytotoxicity against human tumor cells

A class of structurally simplified analogues of the naturally occurring annonaceous acetogenins were developed, amongst which some non-THF analogues showed remarkable cytotoxicities against tumor cell lines, as well as good selectivity between human tumor cells and normal cells. The synthetic routes were significantly shortened because of the removal of the chiral centers bearing the THF rings on the natural templates. This simplification also provides access to the parallel synthesis of these mimics by a combinatorial strategy. The remaining stereogenic centers at the positions alpha to the ethereal links were introduced by the Chiron approach from the easily accessible chiral building blocks 6a and/or 6b, made in turn from L-ascorbic acid or D-mannitol, while the one in the butenolide segment was taken from L-lactate. All four diastereomeric non-THF analogues 2a-2d showed remarkable activity against the HCT-8 cell line, and better differentiation was found when testing against the HT-29 cell line. It was also discovered that both the butenolide and ethylene glycol subunits play essential roles in the cytotoxicities against tumor cell lines, while the 10-substituted hydroxy group and the absolute configuration of methyl group at the butenolide moiety are less important for their activity.     

指数二分性与退化情形下的异宿分支

利用指数型二分性理论,研究了较高退化程度下的异宿分支理论;给出了一个能确定系统在退化情形下横截同、异宿轨道存在性的Melnikov向量;提供了一个处理高维退化情形下横截同、异宿轨道存在性的泛函分析方法.     

犬尿氨酸羟化酶选择性抑制剂L-3-(邻甲氧基苯甲酰基)丙氨酸的简捷合成

从Boc-保护氨基的天冬氨酸苄酯出发, 通过5步反应简捷地合成了犬尿氨酸羟化酶的选择性抑制剂L-3-(邻甲氧基苯甲酰基)丙氨酸(o-MBA). 其中关键反应为锂试剂对Weinreb酰胺的亲核取代反应.     

Studies on the synthesis of (2S,3R)-3-hydroxy-3-methylproline via C2-N bond formation

A new efficient synthesis of (2S,3R)-3-hydroxy-3-methylproline (3) is reported. During the course of a recent study on the Lewis acid promoted intramolecular opening of an epoxide by a carbamate NH, a highly concerted rearrangement was unexpectedly observed. Further investigations of substrate generality show that delta-carbamate-alpha,beta-epoxide esters commonly underwent similar rearrangements with the aid of Lewis acids. Retrosynthetic analysis of such a C(2)-N disconnection can lead to an efficient synthesis of (2S,3R)-3-hydroxy-3-methylproline (3) in high enantio purity. Stereochemistries were established by a Sharpless asymmetric dihydroxylation and a diastereoselective reductive amination.     

ce(ⅳ)-rhodamine b-噻枯唑体系化学发光法测定噻枯唑

在酸性介质中,Ce(Ⅳ)可以氧化噻枯唑产生较弱的化学发光,罗丹明B可以显著增强此发光,且增加的发光强度与噻枯唑的质量浓度在一定范围内呈良好的线性关系,由此建立了测定噻枯唑的流动注射化学发光新方法。该法的检出限为12μg/L(3σ),线性范围为30～1 000μg/L,对500μg/L的噻枯唑连续平行测定11次,其相对标准偏差(RSD)为2.4%。用于测定环境水样中和大米中噻枯唑含量,回收率为96.4%～104.1%。     

Synthesis of 4-azido-4-deoxy-Neu5,7,8,9Ac42en1Me. A key intermediate for the synthesis of GG167 from D-glucono-delta-lactone

[reaction: see text] Stereoselective synthesis of 5-acetamido-7,8,9-tri-O-acetyl-2,6-anhydro-4-azido-3,4,5-trideoxy-D-glycero-D-galacto-non-2-enonic acid methyl ester, an advanced key intermediate for the synthesis of neuraminidase inhibitor GG167 (Zanamivir, Relenza), was accomplished using D-glucono-delta-lactone as starting material. A highly diastereoselective allyllation of an imine intermediate, a regioselective azide-opening of an aziridine, and chemoselective oxidations of vicinal diols served successfully as key steps.     

A novel capillary microliter droplet sample injection-chemiluminescence detector and its application to the determination of benzoyl peroxide in wheat flour

A novel capillary microliter order droplet injection-chemiluminescence (CL) system is proposed. In this system, the liquid sample microdrops, automatically formed at the end of a capillary tip by the effect of the gravity and the gas pressure, repeatedly drop into the miniature reaction cell and reacts with CL reagent to generate CL signal. The phenomena of sample zone dilution and spreading are eliminated as the capillary is used as the sample channel and gas pressure is used as driving force without the liquid carrier stream. Therefore, a high sensitivity is obtained. To evaluate the applicability of the proposed method, a determination of benzoyl peroxide (BP) is examined. The system shows that the benzoyl peroxide is detected linearly in the concentration range from 5×10⁻¹⁰ to 1×10⁻⁶ g ml⁻¹. The detection limit (signal-to-noise ratio=3) is 1.4×10⁻¹⁰ g ml⁻¹ for benzoyl peroxide (mass concentration is 1.1 pg, i.e., 4.5 fmol), which is the best result reported so far. The relative standard deviation (n=11) is 1.5% for 2.0×10⁻⁸ g ml⁻¹ BP. The proposed detector for the detection of benzoyl peroxide offers the advantages of sensitivity, simplicity, rapidity, automation and miniaturization. The proposed method has been applied satisfactorily to the determination of benzoyl peroxide in wheat flour.