Related Concept Videos
01:24Intracellular Signaling Cascades
Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. The continuation of a signal in this manner is called signal transduction. Signal transduction only occurs with cell-surface receptors, which cannot interact with most components of the cell, such as DNA. Only internal receptors can interact directly with DNA in the nucleus to initiate protein synthesis. When a ligand binds to its receptor, conformational changes occur that affect the...
01:24Intracellular Signaling Cascades
Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. The continuation of a signal in this manner is called signal transduction. Signal transduction only occurs with cell-surface receptors, which cannot interact with most components of the cell, such as DNA. Only internal receptors can interact directly with DNA in the nucleus to initiate protein synthesis. When a ligand binds to its receptor, conformational changes occur that affect the...
01:22Amplifying Signals via Enzymatic Cascade
When a ligand binds to a cell-surface receptor, the receptor's intracellular domain changes shape, which may either activate its enzyme function or allow its binding to other molecules. The initial signal is amplified by most signal transduction pathways. This means that a single ligand molecule can activate multiple molecules of a downstream target. Proteins that relay a signal are most commonly phosphorylated at one or more sites, activating or inactivating the protein. Kinases catalyze the...
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:33Radical Reactivity: Intramolecular vs Intermolecular
Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
01:16Cycloaddition Reactions: MO Requirements for Thermal Activation
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
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Supramolecular activation in triggered cascade inversion.
Hai Dong1, Zhichao Pei, Olof Ramström
1Royal Institute of Technology (KTH), Stockholm, Sweden.
Chemical Communications (Cambridge, England)
|April 5, 2008
Summary
Combinations of anionic reagents and amine bases unexpectedly accelerated carbohydrate cascade inversions. This discovery offers a novel approach for efficient carbohydrate chemistry.
Area of Science:
- Carbohydrate Chemistry
- Organic Synthesis
Background:
- Carbohydrate inversion reactions are crucial for synthesizing various carbohydrate derivatives.
- Developing efficient and selective methods for carbohydrate inversion remains a significant challenge in organic chemistry.
Purpose of the Study:
- To investigate the effect of anionic reagents and amine bases on carbohydrate cascade inversion reactions.
- To identify novel catalytic systems that enhance the rate and efficiency of these transformations.
Main Methods:
- Screening of various anionic reagents and amine bases in combination.
- Monitoring reaction progress using techniques such as Nuclear Magnetic Resonance (NMR) spectroscopy.
- Analysis of reaction kinetics to determine rate enhancements.
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Main Results:
- An unexpected synergistic activation effect was observed with specific combinations of anionic reagents and amine bases.
- Dramatic rate enhancements were achieved in multiple carbohydrate cascade inversion reactions.
- The optimized conditions led to significantly improved yields and reduced reaction times.
Conclusions:
- The combination of anionic reagents and amine bases provides a powerful strategy for accelerating carbohydrate cascade inversions.
- This finding opens new avenues for the efficient synthesis of complex carbohydrates.
- Further exploration of this activation mode could lead to broader applications in carbohydrate chemistry.