Vinyl sulfonamide synthesis for irreversible tethering via a novel α-selenoether protection strategy

Abstract

Vinyl sulfonamides are valuable electrophiles for targeted protein modification and inhibition. We describe a novel approach to the synthesis of terminal vinyl sulfonamides which uses mild oxidative conditions to induce elimination of an α-selenoether masking group. The method complements traditional synthetic approaches and typically yields vinyl sulfonamides in high purity after aqueous work-up without requiring column chromatography of the final electrophilic product. The methodology is applied to the synthesis of covalent fragments for use in irreversible protein tethering and crucially enables the attachment of diverse fragments to the vinyl sulfonamide warhead via a chemical linker. Using thymidylate synthase as a model system, ethylene glycol is identified as an effective linker for irreversible protein tethering.

Fig. 1. Structures of terminal vinyl sulfonamide containing protein inhibitors.

Scheme 1. Strategies for the preparation of terminal vinyl sulfonamides.

Scheme 2. Proposed sulfonylation reagent 1 is inaccessible via chlorination of sulfonate salt 2 due to rapid SO₂ elimination.

Scheme 3. Synthesis of terminal vinyl sulfonamides. (a) General scheme and reaction conditions; (b) proof-of-concept study using 4-aminopiperidine 4a and (c) substrate scope.

Scheme 4. Attempted selenide displacement resulted in proto-debrominated product.

Fig. 2. Chemical linker approach for irreversible tethering.

Scheme 5. Preparation of carboxylic acid functionalised PEG linkers.

Scheme 6. Two step synthesis of PEG-linked vinyl sulfonamides. *Amide coupling by method A or B.

Fig. 3. Testing PEG-linked vinyl sulfonamides against TS. TS (10 μM) was incubated with a mixture of positive control and negative control ligands (each at 100 μM) and analyzed by intact protein mass spectrometry after 30 minutes. (a) Testing PEG(n = 1) ligands 15a and 15a (b) testing PEG(n = 2) ligands 16a and 16b.

Scheme 7. (a) NMR rate study. Vinyl sulfonamides (10 mM) were reacted with N-acetyl cysteine methyl ester (78 mM) and the rate of reaction monitored by ¹H NMR spectroscopy. (b) Comparison of unlinked and linker thiadiazole fragments for irreversible tethering.