Captopril EP Impurity B (SQ-14534) is a thiol-containing, orally active ACE inhibitor degradation product with potent antihypertensive activity, exhibiting an IC50 of 0.025 μM. It serves as a key reference standard in pharmaceutical research for studying Captopril stability, metabolism, and the biochemical mechanisms of ACE inhibition in both in vitro and in vivo models.