macrolactonizationmacrolactamization

Macrolactonization and macrolactamization are organic chemistry reactions that form large cyclic esters (macrolactones) and cyclic amides (macrolactams), respectively. These reactions involve the intramolecular cyclization of a linear precursor containing both a carboxylic acid or ester group and an alcohol or amine group. The size of the resulting ring is a key characteristic, with "macro" generally referring to rings containing twelve or more atoms.

Macrolactonization typically proceeds by esterification, where the hydroxyl group of an alcohol attacks the carbonyl carbon of a carboxylic acid or ester. This reaction often requires activating agents to facilitate the formation of the ester bond. Common methods include using coupling reagents like DCC (dicyclohexylcarbodiimide) or Mukaiyama's reagent, or employing reactions like the Yamaguchi esterification or Shiina macrolactonization. The choice of method depends on the specific substrate and desired yield, as side reactions such as intermolecular polymerization can compete with the desired intramolecular cyclization.

Macrolactamization, the formation of cyclic amides, follows a similar principle but involves the attack of an amine nitrogen on a carboxylic acid or ester carbonyl. This amide bond formation can be achieved using peptide coupling reagents, activating the carboxylic acid, or through reactions like the Mitsunobu reaction with an amine and an alcohol. Like macrolactonization, macrolactamization can be challenging due to competing intermolecular reactions, and high dilution conditions are often employed to favor the intramolecular pathway. Both macrolactones and macrolactams are important structural motifs found in many natural products with diverse biological activities.