Zunsemetinib M-atropisomer is the inactive isomer of Zunsemetinib. Zunsemetinib, also known as ATI-450 and CDD450, is the P-atropisomer and is a potent MK2 Inhibitor. ATI-450 binds with high affinity to the interface of the p38MAPK-MK2 complex and selectively inhibits p38MAPK-catalysed phosphorylation of MK2 which stabilises the inactive conformation of MK2, and subsequently reduces inflammatory cytokine levels. ATI-450 specifically blocks the downstream MK2-mediated inflammatory drive on the p38 pathway and may therefore avoid the tachyphylaxis associated with p38 inhibitors. Note CAS#1640282-42-3 is the active P-atropisomer. CAS# 1640282-44-5 is the inactive M-astropisomer.