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Chapter 27: Problem 52

The BOC-protecting group may be added by treatment of an amino acid with di- tert-butyl dicarbonate as shown in the following reaction sequence. Propose a mechanism to account for formation of these products.

Short Answer

Expert verified
Question: Describe the mechanism for the formation of a BOC-protected amino acid when an amino acid is treated with di-tert-butyl dicarbonate. Answer: The mechanism involves a nucleophilic attack of the amine group of the amino acid on the electrophilic carbonyl group of di-tert-butyl dicarbonate. This forms a tetrahedral intermediate which then rearranges, releasing tert-butanol as a leaving group and reforming the carbonyl group, resulting in the formation of the BOC-protected amino acid through a carbamate linkage.

Step by step solution

01

Identify the reaction components

In this reaction, an amino acid is treated with di-tert-butyl dicarbonate (BOC-protecting group) to form a BOC-protected amino acid. The first thing to do is identify the key functional groups involved in the reaction: the amine group of the amino acid and the carbonate group of the di-tert-butyl dicarbonate.
02

Identify the nucleophile and electrophile

For proposing a mechanism, it is important to determine which reactant is the nucleophile and which one is the electrophile. In this case, the amine group of the amino acid acts as a nucleophile due to the presence of a lone pair on the nitrogen atom, and the di-tert-butyl dicarbonate group acts as an electrophile due to the presence of an electrophilic carbonyl group.
03

Nucleophilic attack

The reaction mechanism begins with a nucleophilic attack by the amine nitrogen (N) of the amino acid on the carbonyl carbon (C) of the di-tert-butyl dicarbonate. This results in the formation of a tetrahedral intermediate and the migration of a negative charge to the carbonyl oxygen (O).
04

Rearrangement

Once the tetrahedral intermediate is formed, the negatively charged oxygen atom reclaims the electron pair, breaking the C-O bond, and simultaneously releasing one equivalent of tert-butanol (t-BuOH) as a leaving group.
05

Formation of the BOC-protected amino acid

Following the release of tert-butanol, the carbonyl group reforms, resulting in the formation of the BOC-protected amino acid. The BOC-protecting group is now bonded to the nitrogen atom of the amino acid through a carbamate linkage. In summary, the proposed mechanism for the formation of the BOC-protected amino acid involves a nucleophilic attack of the amine group of the amino acid on the electrophilic carbonyl group of di-tert-butyl dicarbonate, followed by a rearrangement to release tert-butanol and form the BOC-protected amino acid.

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Most popular questions from this chapter

The configuration of the chiral center in \(\alpha\)-amino acids is most commonly specified using the D,L convention. It can also be identified using the \(R, S\) convention (Section 3.3). Does the chiral center in L-serine have the \(R\) or the \(S\) configuration?

Several \(\beta\)-amino acids exist. There is a unit of \(\beta\)-alanine, for example, contained within the structure of coenzyme A (Problem 25.35). Write the structural formula of \(\beta\)-alanine.

Enzyme-catalyzed decarboxylation of glutamic acid gives 4-aminobutanoic acid (Section 27.1D). Estimate the pI of 4-aminobutanoic acid.

Account for the fact that the isoelectric point of glutamine (pI 5.65) is higher than the isoelectric point of glutamic acid (pI 3.08).

Assign an \(R\) or \(S\) configuration to the chiral center in each amino acid. (a) L-Phenylalanine (b) L-Glutamic acid (c) L-Methionine
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