Chapter 24, Problem 10PP

Interpretation Introduction

Interpretation:

The chemical changes involved in treating oxytocin with reducing agents (namely sodium in the presence of liquid ammonia), which can be reverted by air oxidation are to be represented.

Concept introduction:

舧 Electrophiles are electron-deficient species, which has positive or partially positive charge. Lewis acids are electrophiles, which accept electron pair.

舧 Nucleophiles are electron-rich species, which has negative or partially negative charge. Lewis bases are nucleophiles, which donate electron pair.

舧 Amino acids are organic compounds containing amine ($-{\text{NH}}_2$) and carboxyl ($-\text{COOH}$) functional group along with a side chain (R group) specific to each amino acid.

舧 Sodium in liquid ammonia can be used to carry out the reductive cleavage of C-S, S-S, C-Cl, and N-N bonds. Moreover, it can also be used for the reduction of alkenes and alkynes, proton –abstraction, nucleophilic substitution of the aryl halides, and aminolysis of trichlorosilanes.  In polypeptide or proteins, under oxidizing conditions, two amino acid residues can dimerize through the formation of a  disulfide bond, which can be broken down by the utilization of reducing agents.

舧 The structure of oxytocin is composed of a single disulfide bond between two cysteine residues.

舧 The introduction of reducing agents results in the breakdown of disulfide brides. In this reaction, the reducing agent acts as an electron donor and initiates a nucleophilic attack on the disulfide linkage. This results in the reductive cleavage of the disulfide bond to produce thiol groups.

舧 These thiol groups on exposure to oxidizing environment (air) reestablish the disulfide linkages.