Exploring the Chemical Properties and Medicinal Applications of Tetramethylthiocycloheptyne Sulfoximine Used in Strain-Promoted Azide–Alkyne Cycloaddition Reactions

Abstract

The recently developed compound, tetramethylthiocycloheptyne sulfoximine (TMTHSI), has shown to be a promising strained alkyne for strain-promoted azide–alkyne cycloaddition (SPAAC), metal-free click chemistry. This research explores the properties of TMTHSI-based compounds via three aspects: (1) large-scale production, (2) unique stability in acidic conditions and its subsequent use in peptide synthesis, and (3) the functionalization of antibodies. Here, it is shown that (1) scale-up is achieved on a scale of up to 100 g. (2) TMTHSI is remarkably stable against TFA allowing for the site-specific functionalization of peptides on resin. Finally, (3) the functionalization of an antibody with a model payload is very efficient, with antibody conjugation demonstrating more beneficial features such as a high yield and limited hydrophobicity as compared to other alkyne reagent conjugates. These results illustrate the high potential of TMTHSI for diverse bioconjugation applications, with production already being GMP-compatible and a highly efficient conversion resulting in attractive costs of goods.

Versatile Click Linker Enabling Native Peptide Release from Nanocarriers upon Redox Trigger

“…26 A recently developed seven-membered ringstrained alkyne, 3,3,6,6-tetramethylthiacycloheptyne sulfoximine (TMTHSI), was demonstrated a more reactive and more hydrophilic click handle as compared to DBCO and BCN and, importantly, stable during TFA deprotection reactions. 27,28 Furthermore, the higher hydrophilicity of the TMTHSI click handle allows for linker/conjugate applications in aqueous solutions, which is particularly beneficial for conjugation of peptides to nanoparticles dispersed in water.…”

“…Current readily available ring-strained alkynes such as dibenzocyclooctyne (DBCO, which is rather bulky and hydrophobic) and the later improved bicyclo[6.1.0]­non-4-yn-9-ylmethanol (BCN, which is less bulky but still hydrophobic) have limited applications in SPPS since they do not endure the typical TFA deprotection conditions, requiring multistep procedures . A recently developed seven-membered ring-strained alkyne, 3,3,6,6-tetramethylthiacycloheptyne sulfoximine (TMTHSI), was demonstrated a more reactive and more hydrophilic click handle as compared to DBCO and BCN and, importantly, stable during TFA deprotection reactions. , Furthermore, the higher hydrophilicity of the TMTHSI click handle allows for linker/conjugate applications in aqueous solutions, which is particularly beneficial for conjugation of peptides to nanoparticles dispersed in water.…”

“…Linker-LTX on Resin Conjugation. The stability of the TMTHSI click handle toward TFA deprotection conditions 27,28 allows for on-the-resin conjugation of the linker and subsequent selective N-terminal modification of peptides (Fmoc deprotected N-terminus, protected side chains while on the resin). Particularly, a peptide such as LTX-315 (containing five lysine residues) benefits from this site-specific approach to obtain a well-defined and characterizable conjugate (Scheme 3).…”