MrgprX2 antagonist-4 and compound B-51 E117, is a potent MrgprX2 antagonist. It specifically targets and inhibits the MrgprX2 receptor, making it suitable for investigating various inflammatory skin disorders.

MRGPRX2, a member of the Mas-related gene family, was found to be expressed in sensory neurons, mast cells and, most recently, in keratinocytes. MRGPRX2 mRNA is present in adipose tissue, esophagus, urinary bladder, lungs with the highest levels found in skin. Activation of MRGPRX2 leads to mast cell degranulation with subsequent pseudo-allergic reactions[2].