title: Mechanistic insight into benzenethiol catalyzed amide bond formations from thioesters and primary amines.
abstract: The influence of arylthiols on cysteine-free ligation, i.e. the reaction between an alkyl thioester and a primary amine forming an amide bond, was studied in a polar aprotic solvent. We reacted the ethylthioester of hippuric acid with cyclohexylamine in the absence or presence of various quantities of thiophenol (PhSH) in a slurry of disodium hydrogen phosphate in dry DMF. Quantitative conversions into the resulting amide were observed within a few hours in the presence of equimolar amounts of thiophenol. Ab initio calculations showed that the reaction mechanism in DMF is similar to the well-known aqueous reaction mechanism. The energy barrier of the catalyzed amidation reaction is approximately 40 kJ mol(-1) lower than the non-catalyzed amidation reaction. At least partially this can be explained by a hydrogen bond from the amine to the π-electrons of the thiophenol, stabilizing the transition state in the aromatic thioester amidation reaction. Under similar conditions, cysteine-free ligation was achieved by coupling a fully side-chain protected 15 amino acid phosphopeptide thioester to the free N-terminal of a side-chain protected 9 amino acid peptide producing the corresponding 24 amino acid phosphopeptide.
authors: Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors: Nicolai
authors: N
authors: Stuhr-Hansen
authors: Nicolai
authors: N
authors: Bork
authors: Kristian
authors: K
authors: Strømgaard
mesh_terms: D000577:Amides / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D000595:Amino Acid Sequence; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000737:chemistry; D004952:Esters / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D007700:Kinetics; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010636:Phenols / Q000737:chemistry*; D010748:Phosphopeptides / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D000577:Amides; D000588:Amines; D004952:Esters; D010636:Phenols; D010748:Phosphopeptides; D013438:Sulfhydryl Compounds; C042983:thiophenol; D003545:Cysteine