The (R-Acy-R) 4 -PMO conjugate (compound 7 with a C8 linker) did not follow the ranking observed for other conjugates in this series since it had lower heparin-binding affinity but corrected splicing less efficiently than (R-Ahx-R) 4 -PMO. This might be explained by the higher hydrophobicity of its longer spacer as evidenced by an increased retention on a C18-affinity column ( Figure 2B ).