(R)-Tamsulosin ((R)-(-)-YM12617 free base, LY253351 free base) is the enantiomerically pure, pharmacologically active form of tamsulosin, a selective α₁A-adrenergic receptor antagonist used in the treatment of benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). This form is synthesized using chiral N-(1-phenylethyl)aziridine-2-carboxylate derivatives, which allow for highly stereoselective processes in its production.