Fexofenadine EP Impurity B, also known as meta-Fexofenadine and designated Fexofenadine USP Related Compound B, is the meta-positional isomer of the parent H1-antihistamine, chemically defined as 2-[3-[(1RS)-1-hydroxy-4-[4-(hydroxydiphenylmethyl)piperidin-1-yl]butyl]phenyl]-2-methylpropanoic acid, with molecular formula C₃₂H₃₉NO₄ and molecular weight 501.67 g/mol. This impurity arises from limited regioselectivity during the Friedel–Crafts acylation of the α,α-dimethylphenylacetic acid derivative used to build the Fexofenadine side chain; the minor meta-acylated isomer is carried through the subsequent steps, making it a key marker for monitoring synthetic-route selectivity. Because it has the same molecular weight as Fexofenadine, it must be separated chromatographically rather than distinguished by mass. Produced at Chemicea under precisely controlled synthetic and purification conditions, this reference standard is essential for impurity identification, positional-isomer resolution, method validation (AMV), and quality-control testing in compliance with EP, BP, and USP monograph requirements for Fexofenadine Hydrochloride. Each batch is supplied with a comprehensive Certificate of Analysis supported by HPLC, ¹H-NMR, and Mass Spectrometry characterization data, ensuring dependable analytical traceability for ANDA filings and pharmaceutical R&D. CAS No. 479035-75-1 | Explore complete technical documentation, Safety Data Sheet (SDS), and pricing.