Chapter 19.6, Problem 16ATS

(a)

Interpretation Introduction

Interpretation: Without charge separation, the neutral form of $\text{pinnatoxin}\text{A}$ has to be drawn.

Concept Introduction:

Zwitterion and neutral compound:

A Zwitterion species has charge neutrality with the separation of equal magnitude of positive and negative charges whereas the neutral compound has charge neutrality without the separation of charges.

Amino acid serves as a best example for zwitterion and neutral forms:

  

(b)

Interpretation Introduction

Interpretation: The amino ketone precursor that would afford $\text{pinnatoxin}\text{A}$ via intramolecular imine formation has to be drawn.

Concept Introduction:

Precursor means the starting material of the given compound that is analysed by retro analysis of that compound.

Retro synthetic analysis:

It is the analysis of the synthetic starting materials for a given compound through its precursors or fragments which are known as synthons. The synthons can be obtained by logical cleavage of the chemical bonds in the compounds. The resulted synthons will be therefore known as logical synthons.

Retro analysis for cyclic imine formation:

The analysis for cyclic imine formation will reveal that the imine formation is intramolecular because both the amine group as well as the carbonyl group will be present within the same starting material or precursor of the retro analysis.

Example

  

(c)

Interpretation Introduction

Interpretation: The mechanism for the imine formation in $\text{pinnatoxin}\text{A}$ has to be drawn.

Concept Introduction:

Imine formation:

Aldehyde or ketone reacts with a primary amine and forms imine in mildly acidic conditions.

Example for the formation of imine is shown here:

  

• Imines contain $C=N$ .
• Imines are also called as Schiff bases, named after Hugo Schiff who described their formation.