Organic Chemistry MCAT Practice Exam

What is the first step in the Strecker amino acid synthesis?

1. Nucleophilic addition by KCN

2. Imine formation from aldehyde and NH4Cl

3. Conversion to carboxylic acid with acid

4. Deprotonation with KOH

The correct answer is: Imine formation from aldehyde and NH4Cl

In the Strecker amino acid synthesis, the first step involves the formation of an imine from an aldehyde and ammonia (or an ammonium salt, such as NH4Cl). This step is crucial because it establishes the necessary carbon-nitrogen bond that is characteristic of amino acids. In the presence of an aldehyde and ammonia, the carbonyl group of the aldehyde can undergo a nucleophilic attack by the nitrogen atom in ammonia, leading to the formation of an intermediate imine. This imine serves as a critical intermediate that can subsequently undergo further reactions in the synthesis pathway, ultimately leading to the formation of an α-amino acid. Specifically, after the imine is formed, it can be hydrolyzed and undergo further reactions in the presence of cyanide ions (KCN) to yield the final amino acid structure. The other options represent subsequent steps or irrelevant pathways in the overall synthesis process. The first step directly leads to the formation of a key intermediate that enables the continuation of the synthesis, making the establishment of the imine an essential initial reaction in the Strecker synthesis.