对β-L-rhamnopyranosides的立体选择性合成
Yong Joo Lee1, Akihiro Ishiwata, Yukishige Ito
1RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Journal of the American Chemical Society
|April 25, 2008
概括
这项研究介绍了复杂碳水化合物的立体选择性合成方法,使用纳非甲基乙介导的分子内亚格利康输送 (NAP-IAD). 这种多功能技术成功地产生了一种特定的细菌多糖,证明了它的有效性.
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
- 葡萄糖科学 (Glycoscience) 是一种科学.
背景情况:
- 复杂碳水化合物的立体选择合成对于理解生物功能至关重要.
- 在碳水化合物化学中,开发高效的甘氨酸键形成方法仍然是碳水化合物化学的一个关键挑战.
研究的目的:
- 为了实现1,2-cis-beta-L-rhamnopyranosides的立体选择性合成.
- 为了证明纳甲基 (NAP) 乙介导的分子内甘氨输送 (IAD) 方法的多功能性.
- 为了完成特定细菌细胞外多糖的完整立体选择合成.
主要方法:
- 使用的纳甲基 (NAP) 以太介导的分子内甘氨酸输送 (IAD).
- 应用了NAP-IAD方法论,用于刻板选择性地构建糖链接.
- 合成了来自Sphaerotilus natans的α-L-Rhap-(1-->3)-β-L-Rhap-(1-->4) Glcp多糖体.
主要成果:
- 获得了1,2-cis-beta-L-rhamnopyranoside的高度立体选择性构造.
- 成功完成了目标细菌多糖的立体选择性合成.
- 证明了NAP-IAD战略的广泛适用性和多功能性.
结论:
- 该NAP-IAD方法提供了复杂碳水化合物的立体选择性合成的有效途径.
- 这种方法非常通用,适用于生物相关多糖的合成.
- 在Sphaerotilus natans多糖的成功合成验证了NAP-IAD技术的实用性.
相关概念视频
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
02:05Prochirality
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
02:36Regioselectivity and Stereochemistry of Hydroboration
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 stereochemistry.
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 stereochemistry.
02:21Naming Enantiomers
The naming of enantiomers employs the Cahn–Ingold–Prelog rules that involve assigning priorities to different substituent groups at a chiral center. Each enantiomer, being a distinct molecule, is assigned a unique name by the Cahn–Ingold–Prelog (CIP) rules, also called the R–S system. The prefix R- or S- attached to the chiral centers in an enantiomer is dependent on the spatial arrangement of the four substituents on the chiral center. The R–S system essentially comprises three steps:...
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This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
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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...