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Updated: Aug 24, 2026

Application and Methodology of the Non-destructive 19F Time-domain NMR Technique to Measure the Content in Fluorine-containing Drug Products
Published on: August 22, 2017
Solution structure of rifaximin and its synthetic derivative rifaximin OR determined by experimental NMR and
Silvia Martini1, Claudia Bonechi, Gianfranco Corbini
1Department of Chemical and Biosystem Sciences, University of Siena, Via Aldo Moro, 2-53100 Siena, Italy. martinis@unisi.it
Abstract:
The solution structure of rifaximin and its derivative rifaximin OR (open ring) was determined by combining NMR experimental results, theoretical simulation of two-dimensional NMR spectra by complete relaxation matrix analysis (corma), and molecular dynamics calculations. In this study the structural rearrangements due to the opening of the aliphatic chain of rifaximin after the reduction process to form rifaximin OR were investigated. Close spatial proximity of CH(3)(14) and H28b protons detected by 2D-ROESY spectrum of rifaximin OR, which was not present in rifaximin and the down-field shift of CH(3)(34) protons in rifaximin OR (1)H spectrum were crucial to understand the structural modifications, which occurred within the system. The aliphatic chain of rifaximin OR was found to be no longer symmetrical with respect to the aromatic moiety. Although no dramatic structural rearrangements were detected, the aliphatic chain moved toward CH(3)(14), causing a reduction of the aromatic shielding contribution in particular on CH(3)(34).
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