CXCR4 antagonist 5 (compound 23) is a highly potent CXCR4 antagonist with an IC 50 value of 8.8 nM. CXCR4 antagonist 5 can inhibit CXCL12-induced cytosolic calcium increase (IC 50 = 0.02 nM) and inhibits CXCR4/CXLC12-mediated chemotaxis. CXCR4 antagonist 5 has good physicochemical properties and in vitro safety profiles, inhibiting CYP isozymes and hERG marginally or moderately.