遥远的碳酸盐保护基对拉姆诺基化中的β选择性的影响
Asger Munk Koue1, Christian Marcus Pedersen1
1Department of Chemistry, University of Copenhagen, Universitetsparken 6, DK-2100 Copenhagen O, Denmark. cmp@chem.ku.dk.
Organic & biomolecular chemistry
|June 3, 2024
概括
在L-thiorhamnosyl供体上保护组显著影响糖化选择性. 一个C-4碳酸基团增强了rhamnosylations中的β选择性,较少的取电子的基团产生了更好的结果.
科学领域:
- 碳水化合物化学 碳水化合物化学
- 有机合成 有机合成
- 糖基化反应 糖基化反应
背景情况:
- 复杂碳水化合物的选择性合成对于理解生物过程至关重要.
- L-拉姆诺斯衍生物是葡萄糖生物学中的重要组成部分.
- 控制糖化反应中的立体选择性仍然是一个挑战.
研究的目的:
- 为了合成L-thiorhamnosyl捐赠者与O-carbamate保护组.
- 调查保护群体位置和自然对rhamnosylation选择性的影响.
- 开发有效的合成路径,用于受保护的兰氏体.
主要方法:
- 合成L-thiorhamnosyl捐赠体,其中包括各种O-碳酸盐保护基.
- 使用这些捐赠体在不同的催化条件下进行的糖化反应.
- 对反应产物的分析以确定立体选择性 (α/β比).
- 探索用于选择性化的相转移催化.
主要成果:
- 与C-2或C-3位置相比,在Rhamnosylations中C-4位置的碳酸盐保护组显著增强了β选择性.
- 降低C-4碳酸的电子吸收特性增加了β选择性.
- 三叶酸催化剂降低了β-选择性.
- 通过相转移催化实现了2,4-O-基化拉姆诺化的高效单步合成.
结论:
- O-酸盐保护基的位置和电子特性是L-基化中的立体选择性的关键决定因素.
- 保护组的战略性放置可以将糖化转向所需的异构体.
- 阶段转移催化为碳水化合物合成中选择性保护策略提供了一种可行的方法.
相关概念视频
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
14.1K
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
14.1K
02:35Regioselectivity of Electrophilic Additions-Peroxide Effect
8.5K
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
8.5K
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
8.4K
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
8.4K
02:36Regioselectivity and Stereochemistry of Hydroboration
8.1K
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn...
8.1K
01:24Acetals and Thioacetals as Protecting Groups for Aldehydes and Ketones
4.1K
Acetals are formed by reacting two equivalents of alcohol with carbonyl compounds like aldehydes or ketones. Acetals are unaffected by bases, nucleophiles, oxidizing agents, and reducing agents. They serve as protecting groups for aldehydes and ketones. Acetals can be easily formed and also easily removed via mild acid hydrolysis.
In the presence of multiple functional groups, when selective reduction of one group over the other is desired, groups like aldehydes and ketones that form acetals...
In the presence of multiple functional groups, when selective reduction of one group over the other is desired, groups like aldehydes and ketones that form acetals...
4.1K
01:23Protecting Groups for Aldehydes and Ketones: Introduction
6.9K
Protecting groups are compounds that can bind to a specific functional group in the presence of other functional groups to protect them from undesired chemical reactions. These compounds can selectively bind to particular functional groups and advance chemoselective reactions in polyfunctional systems (Figure 1). After the functional group has served its purpose, it is removed by reacting it with specific compounds.
6.9K