Hairpins with optimized chemical modifications are single-digit nM A3A inhibitors. (A) Hairpin sequence, structure, and chemical modification patterns targeting A3A (* denotes PS linkage, black is DNA sugar, and red is LNA sugar). (B) Table of sugar and phosphate modified hairpin inhibitors targeting A3A. Relative binding affinities to A3A measured by MST, data shown as fold change relative to full PO control H1_A. Kinetic parameters versus A3A measured by ¹H NMR deamination assay, percentage inhibition is relative to substrate only velocity. (C) Inverse velocity versus inhibitor plot (Dixon plot) used to determine inhibition constants (K_i) from the slope (see SI). Steeper line indicates a stronger inhibitor (datapoints triplicate, error bars SD).