Palladium-unleashed proteins: gentle aldehyde decaging for site-selective protein modification.

Protein bioconjugation frequently makes use of aldehydes as reactive handles, with methods for their installation being highly valued. Here a new, powerful strategy to unmask a reactive protein aldehyde is presented. A genetically encoded caged glyoxyl aldehyde, situated in solvent-accessible locations, can be rapidly decaged through treatment with just one equivalent of allylpalladium(ii) chloride dimer at physiological pH. The protein aldehyde can undergo subsequent oxime ligation for site-selective protein modification. Quick yet mild conditions, orthogonality and powerful exposed reactivity make this strategy of great potential in protein modification.