Crossing the Solubility Rubicon: 15-Crown‑5 Facilitates the Preparation of Water-Soluble Sulfo-NHS Esters in Organic Solvents

• Published in: Bioconjugate chemistry Vol. 35; no. 1; pp. 22 - 27
• Main Authors: Yates, Nicholas D. J., Miles, Connor G., Spicer, Christopher D., Fascione, Martin A., Parkin, Alison
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.01.2024
• Subjects: Amines; Carboxylic acids; Crown Ethers; Esterification; Esters; Hydrophobicity; Incompatibility; N-Hydroxysulfosuccinimide; Organic solvents; Proteins; Reagents; Salts; Sodium; Sodium salts; Solubility; Solvation; Solvents; Solvents - chemistry; Succinimides; Water; Water chemistry
• ISSN: 1043-1802; 1520-4812
• DOI: 10.1021/acs.bioconjchem.3c00396

The Sulfo-NHS ester is a mainstay reagent for facilitating amide bond formation between carboxylic acids and amine functionalities in water. However, the preparation of Sulfo-NHS esters currently requires hydrophobic carboxylic acids, which are poorly water-soluble, to first be reacted with the N-hydroxysulfosuccinimide sodium salt, which is insoluble in organic solvents. The mutually incompatible solvation requirements thus complicate the synthesis of Sulfo-NHS esters. As a simple, rapid, and cost-effective solution to this problem, we report that the use of 15-crown-5 to complex the sodium cation of N-hydroxysulfosuccinimide sodium salt circumnavigates these solvation incompatibility issues by rendering the N-hydroxysulfosuccinimide salt soluble in organic solvents, resulting in a cleaner esterification reaction and thus improved yields of activated ester product. We also demonstrate that the resultant “crowned” Sulfo-NHS-ester remains water-soluble and is no less reactive than its classic “uncrowned” Sulfo-NHS counterpart when used in bioconjugation reactions between protein amine-functionalities and hydrophobic carboxylic acids.