Question 1

Which reagent is commonly used to protect the amino group of an amino acid during peptide synthesis, and what is the structure of the resulting protected group?

Accepted Answer

Boc$$_2O$$; the resulting group is $$-NHBoc$$

Question 2

What is the main function of DCC (dicyclohexylcarbodiimide) in peptide synthesis?

Accepted Answer

To activate the carboxyl group for amide bond formation

Question 3

Given the following sequence: $$	ext{EtO}_2CCH_2NH_2 \xrightarrow{1.\ Br_2$,\ $$PBr_3$$} \xrightarrow{2.\ xs\ NH_3$} \xrightarrow{3.\ H_2O}$$, what is the final product?

Accepted Answer

A free amino acid (glycine)

Question 4

Which of the following sequences correctly describes the Gabriel synthesis of an amino acid?

Accepted Answer

Alkyl halide $$\rightarrow$$ phthalimide $$\rightarrow$$ hydrolysis

Question 5

In the synthesis of a dipeptide from two amino acids, why is it important to protect the amino group of one amino acid?

Accepted Answer

To ensure that only one amide bond forms between the correct amino and carboxyl groups

Question 6

Which of the following best describes the mechanism of peptide bond formation using DCC?

Accepted Answer

DCC reacts with the carboxyl group to form an O-acylisourea intermediate, which is then attacked by the amino group of another amino acid.

Question 7

A chemist wants to synthesize the dipeptide Ala-Val. Which sequence of steps is most appropriate?

Accepted Answer

Protect Ala's amino group with Boc, activate Val's carboxyl group with DCC, couple, then deprotect.

Question 8

Which of the following is a correct order of reagents for converting an $$	ext{EtO}_2CCH_2Br ($$ethyl bromoacetate) to glycine?

Accepted Answer

NH$$_3$$, then H$$_3O$^+$$, heat

Question 9

Which of the following statements about Boc deprotection is correct?

Accepted Answer

Boc groups are removed under acidic conditions, such as with HCl.

Question 10

A student attempts to synthesize the tripeptide Ile-Phe-Gly. Which of the following strategies is most likely to succeed?

Accepted Answer

Sequential coupling using protected amino acids and DCC, followed by deprotection.

Question 11

Which of the following is a plausible intermediate in the Strecker synthesis of an amino acid?

Accepted Answer

An $$	ext{R-CH(NH_2$)CN} ($$amino nitrile)

Question 12

Which of the following best explains why DCC is used in peptide synthesis instead of direct coupling of amino acids?

Accepted Answer

DCC activates the carboxyl group, making it more reactive toward nucleophilic attack by the amino group.

Question 13

Which of the following is the correct structure for a Boc-protected leucine?

Accepted Answer

$$\mathrm{BocNHCH(C_4H_9)COOH}$$

Question 14

A chemist wants to synthesize Val-Ala from the individual amino acids. Which of the following is the correct order of steps?

Accepted Answer

Protect Ala's amino group, activate Val's carboxyl group, couple, then deprotect.

Question 15

Which of the following is a correct statement about the use of protecting groups in peptide synthesis?

Accepted Answer

Protecting groups are used to prevent unwanted side reactions during peptide bond formation.

Question 16

Which of the following best describes the outcome when Boc-protected alanine is treated with DCC and leucine?

Accepted Answer

Ala-Leu dipeptide with Boc still on the N-terminus

Question 17

Which of the following is the correct order of steps for the Strecker synthesis of alanine?

Accepted Answer

Aldehyde $$\rightarrow NH$_4Cl$$, NaCN $$\rightarrow H$_3O$^+$$, heat

Question 18

Which of the following is a reason why direct coupling of two amino acids without protecting groups is not efficient for peptide synthesis?

Accepted Answer

Both amino and carboxyl groups can react, leading to a mixture of products.

Question 19

Which of the following is the correct product when Boc-protected glycine is coupled with leucine using DCC?

Accepted Answer

Boc-Gly-Leu

Question 20

Which of the following best describes the role of H$$_3O$^+$$ and heat in the Strecker synthesis?

Accepted Answer

Hydrolyzes the nitrile to a carboxylic acid, forming the amino acid

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