8: Reactions at the α-Carbon, Part II
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- 8.1: Prelude to Reactions at the α-Carbon, Part II
- To begin this chapter, we will first learn about 'carboxylation' and 'decarboxylation' reactions, in which organic molecules gain or lose a bond to carbon dioxide, respectively, in a mechanism that is really just an extension of the aldol/retro-aldol reactions we learned about in the previous chapter.
- 8.2: Decarboxylation
- Many carbon-carbon bond-forming and bond-breaking processes in biological chemistry involve the gain or loss, by an organic molecule, of a single carbon atom in the form of CO2 . You undoubtedly have seen this chemical equation before in an introductory biology or chemistry class.
- 8.3: An Overview of Fatty Acid Metabolism
- Fatty acid metabolism is a two-carbon process: in the synthetic directions, two carbons are added at a time to a growing fatty acid chain, and in the degradative direction, two carbons are removed at a time. In each case, there is a four-step reaction cycle that gets repeated over and over.
- 8.4: Claisen Condensation
- The major points to recall are that a nucleophile attacks a carboxylic acid derivative, leading to a tetrahedral intermediate, which then collapses to expel the leaving group (X). The whole process results in the formation of a different carboxylic acid derivative. A typical nucleophilic acyl substitution reaction might have an alcohol nucleophile attacking a thioester, driving off a thiol and producing an ester.
- 8.5: Conjugate Addition and Elimination
- In this section, we will look at two more common biochemical reactions that proceed through enolate intermediates. In a typical conjugate addition, a nucleophile and a proton are 'added' to the two carbons of an alkene which is conjugated to a carbonyl (i.e. in the α−β position). an β -elimination step, the reverse process occurs.
- 8.6: Carboxylation
- You can think of a carboxylation reaction as essentially a special kind of aldol reaction, except that the carbonyl electrophile being attacked by the enolate is CO2 rather than a ketone or aldehyde.
