Fexofenadine EP Impurity E, chemically defined as Diphenyl(piperidin-4-yl)methanol (α,α-Diphenyl-4-piperidinemethanol) and widely known as Azacyclonol, is a diphenylmethanol-piperidine impurity of Fexofenadine, with molecular formula C₁₈H₂₁NO and molecular weight 267.37 g/mol. This compound is the key piperidine building block of Fexofenadine synthesis, in which its secondary amine is N-alkylated with the 4-halobutyrophenone side chain; it is equally a building block of Terfenadine, the prodrug from which Fexofenadine was developed. Its presence in the API therefore reflects unreacted starting-material carryover, and it is also a known metabolite of Terfenadine. Owing to this structural relationship, the compound serves as a critical reference marker for impurity profiling, starting-material control, and process-related purity control during Fexofenadine Hydrochloride API manufacturing. Manufactured at Chemicea under precisely controlled synthetic and purification protocols, this reference standard supports impurity identification, method validation (AMV), and quality-control testing in accordance with EP and BP monograph requirements. 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 regulatory submissions and pharmaceutical R&D. CAS No. 115-46-8 | Explore complete technical documentation, Safety Data Sheet (SDS), and pricing.