Using AMD070 as a starting point for structural modification, a novel series of isoquinoline CXCR4 antagonists was developed. A structure–activity scan of alternate lower heterocycles led to the 3-isoquinolinyl moiety as an attractive replacement for benzimidazole. Side chain optimization in the isoquinoline series led to a number of compounds with low nanomolar anti-HIV activities and promising rat PK properties.