This indicates that the impurity is Metoprolol-lactose adduct as proposed. The high resolution mass proposed
the probable molecular formula C27H45NO13.
The 1H NMR spectrum of this impurity displayed signals at δ = 1.27–1.30(6H), δ = 2.73–2.76 (2H), δ = 2.95–2.98 (1H), δ = 3.12–3.18(1H), δ = 3.23 (3H), δ = 3.44–3.68(11H), δ = 3.73–3.77(2H), δ = 3.83–3.84(2H), δ = 4.15–4.17(3H), δ = 4.41–4.43(1H), δ = 4.64–4.67 (1H), δ = 6.68–6.90 (2H), δ = 7.15–7.17(2H)
corresponding to 37 protons, indicating the Metoprolol adduct impurity possibility as it contains total 45 protons out of which 8 protons are of hydroxyl groups of lactose.
The 1H and 13C NMR spectra of Metoprolol adduct impurity and Metoprolol tartrate was compared and significant changes were observed. In 1H NMR spectrum of impurity additional 13 protons in aliphatic region were observed. While in 13C NMR, additional 12 carbon signals can be seen. Methylene carbons C21 and C16 were observed at 60.5 and 61.8 ppm respectively and 10 carbon signals were observed between 68.5 ppm to 103 ppm. These signals
confirmed the presence of both lactose as well as Metoprolol moieties in the impurity.
Further to confirm the exact structure of Metoprolol adduct impurity, the 2D NMR HSQC has also been reviewed (see
Supplementary Fig. S-5). It was observed that the proton in aliphatic region showing doublet at (4.41–4.43) ppm corresponds to C22 which appeared at 103 ppm. This confirms the presence of anomeric carbon of pyranose ring. Also C17 appeared at 95.4 ppm found to be quaternary carbon which confirms the presence of furanose anomeric carbon. Proton corresponding to C20 found to shown multiplet in the region of (4.15–4.17) ppm which confirms that C20 is from furanose ring. Apart from these interactions, carbon signals appeared at 70.7, 72.2, 74.5, 61.8 ppm confirming the arabinosyl moiety.
Based on the above observations it has been confirmed that the impurity is Metoprolol lactose adduct and the ‘glucose moiety’ of lactose present in adduct exists in furanose form
The 1H Metoprolol tartrate
The 13C NMR spectra Metoprolol tartrate
The 1H spectra of Metoprolol adduct impurity
The13C NMR spectra of Metoprolol adduct impurity
HSQC spectra of Metoprolol adduct impurity
Identification, synthesis, isolation and characterization of new impurity in metoprolol tartrate tablets
- Ipca Laboratories Ltd., Chemical Research Division, Kandivali Industrial Estate, Kandivali (W). Mumbai 400067, India
Dr. Leena Gupta