Encouraged by these results, we prepared a first series of 2aminopyridine analogues to explore the relevance of the difluorophenol to the thermal stabilization of the two VRKs (Table ). For both proteins, simultaneously replacing the difluorophenol moiety with phenol groups in R1 and R2 (6) resulted in a drop of the observed ΔTm, suggesting that increasing the phenol acidic character or altering the electronic properties of the aromatic ring is important for binding. VRK1-FL seemed to tolerate the substitution of a difluorophenol by a phenol on either R1 or R2 position equally well, whereas maintaining a difluorophenol group in R1 proved to be more important for VRK2-KD (8 and 7). Nevertheless, removal of the HB (hydrogen bond) capacity in R2, whilst maintaining the difluorophenol group in R1, still resulted in a ΔTm drop for both VRKs (9). We attempted to improve compound binding by replacing the difluorophenol in R1 with a variety of groups of distinct sizes, polarities and electronic proprieties (Supplementary Table ), but none of these changes resulted in an improved ΔTm over the difluorophenol moiety.