Base-Catalyzed Enediol Rearrangement

Mechanism 23-2 Base-Catalyzed Epimerization of Glucose 1115 Mechanism 23-3 Base-Catalyzed Enediol Rearrangement 1115 23-9 Reduction of Monosaccharides 1116... [Pg.22]

Epimerization and the Enediol Rearrangement One of the most important aspects of sugar chemistry is the inability, in most cases, to use basic reagents because they cause unwanted side reactions. Two common base-catalyzed side reactions are epimerization and enediol rearrangement. [Pg.1115]

Another base-catalyzed side reaction is the enediol rearrangement, which moves the carbonyl group up and down the chain, as shown in Mechanism 23-3. If the enolate ion (formed by removal of a proton on C2) reprotonates on the Cl oxygen, an enediol intermediate results. Removal of a proton from the C2 oxygen and reprotonation on Cl gives fructose, a ketose. [Pg.1115]

Base-Catalyzed Epimerization of Glucose 1115 Base-Catalyzed Enediol Rearrangement 1115... [Pg.1294]

In the proton-transfer mechanism, the alcohol is presumed to form a hemiacetal at the C(5) carbonyl group. Then an acid-base pair in the active site performs an elimination reaction, producing the aldehyde product and the reduced cofactor, PQQH2. The hydride-transfer mechanism envisions the approximation of the scis-sile C-H bond of the alcohol to C(5) of the cofactor, followed by an acid-base catalyzed delivery of hydride ion to C(5), resulting in formation of the aldehyde product and the ketol form of PQQH2, which can readily rearrange to the enediol form. [Pg.1070]

MECHANISM FOR THE BASE-CATALYZED ENEDIOL REARRANGEMENT OF A MONOSACCHARIDE... [Pg.1023]

We have already encountered several base-catalyzed reactions, such as the interconversion of keto and enol tautomers (Section 18.3), the Claisen condensation (Section 18.13), and the enediol rearrangement (Section 21.5). A base catalyst increases the rate of a reaction by removing a proton from the reactant. For example, the dehydration of a hydrate in the presence of hydroxide ion is a base-catalyzed reaction. Hydroxide ion (the base) increases the rate of the reaction by removing a proton from the neutral hydrate. [Pg.1105]

The Mechanism for an Enzyme-Catalyzed Reaction That Is Reminiscent of the Base-Catalyzed Enediol Rearrangement 1125... [Pg.1125]

THE MECHANISM FOR AN ENZYME-CATALYZED REACTION THAT IS REMINISCENT OF THE BASE-CATALYZED ENEDIOL REARRANGEMENT... [Pg.1125]

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