SAR studies indicated that
the central aromatic ring is crucial for high CXCR4 affinity, and that a one - carbon separation between the central aromatic phenyl ring and the nitrogen of the acyclic linker is strictly required for potency.
The lack of ROEs between HN22 and either HC17 or HC25 indicates that the
central methyl - containing
aromatic ring is roughly perpendicular to the amide plane of HN22, as would be expected based on steric considerations.