A combined experimental and computational mechanistic study of amide formation from thio acids and azides is described. The data support two distinct mechanistic pathways dependent on the electronic character of the azide component. Relatively electron-rich azides undergo bimolecular coupling with thiocarboxylates via an anion-accelerated [3+2] cycloaddition to give a thiatriazoline. Highly electron-poor azides couple via bimolecular union of the terminal nitrogen of the azide with sulfur of the thiocarboxylate to give a linear adduct. Cyclization of this intermediate gives a thiatriazoline. Decomposition to amide is found to proceed via retro-[3+2] cycloaddition of the neutral thiatriazoline intermediates. Computational analysis (DFT, 6-31+G(d)) identified pathways by which both classes of azide undergo [3+2] cycloaddition with thio acid to give thiatriazoline intermediates, although these paths are higher in energy than the thiocarboxylate amidations. These studies also establish that the reaction profile of electron-poor azides is attributable to a prior capture mechanism followed by intramolecular acylation.
A strategy for the conjugation of alcohol-containing payloads to antibodies has been developed and involves the methylene alkoxy carbamate (MAC) self-immolative unit. A series of MAC β-glucuronide model constructs were prepared to evaluate stability and enzymatic release, and the results demonstrated high stability at physiological pH in a substitution-dependent manner. All the MAC model compounds efficiently released alcohol drug surrogates under the action of β-glucuronidase. To assess the MAC technology for ADCs, the potent microtubule-disrupting agent auristatin E (AE) was incorporated through the norephedrine alcohol. Conjugation of the MAC β-glucuronide AE drug linker to the anti-CD30 antibody cAC10, and an IgG control antibody, gave potent and immunologically specific activities in vitro and in vivo. These studies validate the MAC self-immolative unit for alcohol-containing payloads within ADCs, a class that has not been widely exploited.
A one-pot procedure for the conversion of carboxylic acids to N-acyl sulfonamides, via thio acid/azide amidation, is presented. The method is compatible with acid- and base-sensitive amino acid protection. N-Acyl sulfonamide synthesis on solid support, peptide thio acid/sulfonazide coupling, and N-alkyl amide synthesis via selective cleavage of sulfonyl from an N-alkyl-N-acyl sulfonamide are also reported.
A new method of allene synthesis is described. Suitably functionalized vinyl triflates undergo fragmentation to give allenes in high yield. Computational and experimental data provide a mechanistic framework for allene formation and the complementary formation of alkynes. The method is stereospecific.
Sulfonamides Q 0560Thio Acid/Azide Amidation: An Improved Route to N-Acyl Sulfonamides. -A novel method for the preparation of title compounds from active esters and sulfonamides is presented that is compatible with acid-and base-sensitive protecting groups and unprotected functionalities. Generation of the thio acid from the parent carboxylic acid followed by addition of sulfonyl azide gives the desired products in excellent yield. -(BARLETT, K. N.; KOLAKOWSKI, R. V.; KATUKOJVALA, S.; WILLIAMS*, L. J.; Org. Lett. 8 (2006) 5, 823-826; Dep. Chem. Chem. Biol., Rutgers State Univ. N. J., Piscataway, NJ 08854, USA; Eng.) -R. Steudel 28-084
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