FSBA, 85, Fig. 30a) acts as a non-selective covalent kinase inhibitor typically
modifying the catalytic lysine. While investigating the reactivity of sulfur
(VI) fluorides, Mukherjee and colleagues from AstraZeneca tested meta-substituted
FSBA analogs (m-FSBAs, general structure 86) with a variety of additional substituents in the 4-position of the phenyl ring (ÀR, ortho to the sulfonyl fluoride
warhead) as inhibitors of the kinases FGFR1 and SYK. Covalent binding of the two
analogs 86a and 86b to Lys514 in FGFR1 was shown by X-ray crystallography
(PDB: 5O49A and 5O4A) and only a single product was observed in MS. The rate of
covalent complex formation correlated reasonably with the σ p
À parameter of the
substituent ÀR and also with the reactivity data previously determined using model
amino acids. In contrast, negligible covalent modification was observed for two
analogous aryl fluorosulfates derived from m- and p-FSBA, respectively, which is in
line with the very low intrinsic reactivity described for this electrophile.
An interesting application for sulfonyl fluoride-based probes was recently
reported by Zhao et al. [141]. Pyrimidinyl 3-aminopyrazole XO44 (87, Fig. 30b)
was designed as a clickable broad-spectrum kinase ligand enabling chemoproteomic
selectivity profiling. As predicted, the compound specifically labeled the catalytic
lysine (Lys295; see Fig. 31b) in the model kinase c-SRC. A similar binding mode
was observed in the EGFR kinase domain (PDB: 5U8L). At a concentration of 1 μM,
XO44 inhibited 219 of 375 protein kinases in a panel (!50%) and captured
133 kinases in Jurkat T-cells. Although many non-kinase off-targets were also
modified, kinases accounted for most of the signal intensity in MS experiments.
Using the poorly selective reversible kinase inhibitor dasatinib as a competitor,
compound 87 was validated as a probe enabling cellular selectivity profiling.
A very recent example of a tyrosine-targeted covalent kinase inhibitor was
provided by Hatcher et al. [142]. After discovering that the approved reversible
anaplastic lymphoma kinase (ALK) inhibitor alectinib (88a, Fig. 30c) strongly
Fig. 31 (a) Inhibitor 83b covalently bound to Lys779 of PI3Kδ (PDB: 6EYZ). (b) Probe XO44
covalently bound to chicken c-SRC-Lys295 (PDB: 5K9I)
Covalent Kinase Inhibitors: An Overview
81
modifying the catalytic lysine. While investigating the reactivity of sulfur
(VI) fluorides, Mukherjee and colleagues from AstraZeneca tested meta-substituted
FSBA analogs (m-FSBAs, general structure 86) with a variety of additional substituents in the 4-position of the phenyl ring (ÀR, ortho to the sulfonyl fluoride
warhead) as inhibitors of the kinases FGFR1 and SYK. Covalent binding of the two
analogs 86a and 86b to Lys514 in FGFR1 was shown by X-ray crystallography
(PDB: 5O49A and 5O4A) and only a single product was observed in MS. The rate of
covalent complex formation correlated reasonably with the σ p
À parameter of the
substituent ÀR and also with the reactivity data previously determined using model
amino acids. In contrast, negligible covalent modification was observed for two
analogous aryl fluorosulfates derived from m- and p-FSBA, respectively, which is in
line with the very low intrinsic reactivity described for this electrophile.
An interesting application for sulfonyl fluoride-based probes was recently
reported by Zhao et al. [141]. Pyrimidinyl 3-aminopyrazole XO44 (87, Fig. 30b)
was designed as a clickable broad-spectrum kinase ligand enabling chemoproteomic
selectivity profiling. As predicted, the compound specifically labeled the catalytic
lysine (Lys295; see Fig. 31b) in the model kinase c-SRC. A similar binding mode
was observed in the EGFR kinase domain (PDB: 5U8L). At a concentration of 1 μM,
XO44 inhibited 219 of 375 protein kinases in a panel (!50%) and captured
133 kinases in Jurkat T-cells. Although many non-kinase off-targets were also
modified, kinases accounted for most of the signal intensity in MS experiments.
Using the poorly selective reversible kinase inhibitor dasatinib as a competitor,
compound 87 was validated as a probe enabling cellular selectivity profiling.
A very recent example of a tyrosine-targeted covalent kinase inhibitor was
provided by Hatcher et al. [142]. After discovering that the approved reversible
anaplastic lymphoma kinase (ALK) inhibitor alectinib (88a, Fig. 30c) strongly
Fig. 31 (a) Inhibitor 83b covalently bound to Lys779 of PI3Kδ (PDB: 6EYZ). (b) Probe XO44
covalently bound to chicken c-SRC-Lys295 (PDB: 5K9I)
Covalent Kinase Inhibitors: An Overview
81