The thiol–maleimide reaction has served as a cornerstone of antibody–drug conjugate (ADC) construction for years—valued for its efficiency, chemoselectivity, and reliability. However, one persistent issue remains: maleimide–cysteine linkages can be unstable over time.

Under physiological conditions, these linkages may undergo a retro-Michael reaction, reversing the conjugation and risking premature payload release. This not only reduces therapeutic efficacy but also increases the chance of off-target toxicity.

How to Improve Maleimide Stability

A proven strategy to overcome this limitation is to promote post-conjugation hydrolysis of the maleimide ring. Once hydrolyzed, the maleimide becomes resistant to retro-Michael cleavage, producing a significantly more stable ADC.

Beyond this, rational modifications to the maleimide scaffold can greatly accelerate hydrolysis:

• N-aryl substitutions
  Electron-withdrawing groups (e.g., N-phenyl, N-fluorophenyl) drive faster hydrolysis and enhance conjugate stability.

• PEGylated or dioxolane motifs
  Nearby oxygen atoms coordinate water molecules, boosting hydrolysis rates.

• Basic amino groups
  Strategically positioned basic sites act as intramolecular catalysts, enabling rapid hydrolysis at physiological pH.

The Outcome: Faster Hydrolysis, Stronger ADCs

By encouraging controlled hydrolysis, maleimide-based ADCs can achieve long-lasting stability, improved potency, and a better therapeutic index.

Our Work at SigutLabs

At SigutLabs, we design and synthesize custom linker–payload systems, frequently incorporating engineered maleimide derivatives that deliver superior stability and performance. If your next-generation ADC program requires more resilient conjugation chemistry, we’d be excited to collaborate.