Question

Question: Devise a stepwise mechanism for the following reaction, a key step in the synthesis of the antibiotic abyssomicin C. Abyssomicin C was isolated from sediment collected from almost 1000 ft below the surface in the Sea of Japan. (Hint: The mechanism begins with a Dieckmann reaction.)

Short answer

Answer

Mechanism of the reaction

Step-by-step solution

Abyssomicin C

Abyssomicin-C is a polycyclic compound used as an antibiotic drug. It is isolated from Verrucosispora species which is a marine anitibacterium.

The antibiotic inhibits the biosynthesis of p-aminobenzoic acid and folic acid.

The atropisomer of this drug is called atrop-Abyssomicin and is found as the major product in the biosynthesis of Abyssomicin.

Dieckmann reaction

A condensation reaction taking place between two esters to beta ketoesters is called a Claisen condensation.

In some bifunctional compounds with an ester and carbonyl group in the same molecule, Claisen condensation can occur within the molecule.

This is called Dieckmann condensation which forms cyclic compounds.

This reaction is favored when the product ring is five-membered or six-membered.

Mechanism of the given reaction

The reaction is initiated by a proton abstraction and the subsequent formation of an enol.

The enol attacks the carbonyl carbon and a five-membered ring is formed. The compound is stabilized by the removal of the alkoxide ion.

An attack by water molecules causes another intramolecular cyclization to form a bridged compound which is the final product.

Mechanism of the reaction