Isolation , Synthesis and Characterization of Rosiglitazone Maleate Impurities

Three unknown impurities in rosiglitazone maleate 1 bulk drug at level below 0.1% (ranging from 0.05 to 0.1%) were detected by simple reverse phase high performance liquid chromatography. These impurities were preliminarily identified with LC-MS and characterized by the mass number of the impurities. Different experiments were conducted and finally synthesized and characterized the unknown impurities.


Introduction
Rosiglitazone maleate 1, is an anti diabetic drug, which is a choice of non insulin dependent diabetes mellitus (NIDDM) [1][2][3][4][5] , during the process development of rosiglitazone maleate 1, three unknown impurities were identified in the analysis of different batches whose percentage area ranged from 0.05 to 0.1% by HPLC.A comprehensive study has been carried out to isolate or to prepare and characterize those impurities, due to the importance of the stringent requirement of regulatory authorities and all the impurities should be at the levels of >0.1% must identified and characterized.The present paper aims to isolate or prepare impurities and characterization.

Samples
The investigated samples of Rosiglitazone maleate bulk drug material were prepared in Dr. Reddy's Laboratories Ltd., Active Pharmaceutical Ingredient, Hyderabad, India.

High performance liquid chromatography (HPLC)
An in-house LC isocratic method was developed for the analysis of rosiglitazone maleate and its impurities, where a column (Inertsil ODS 3V, 250 x 4.6 mm, 5 µ) with a mobile phase consisting of buffer (4.14 g of sodium dihydrogen phosphate in 1000 mL of water, adjusted the pH to 6.2 with diluted sodium hydroxide), and acetonitrile in the ratio of 50:50 (v/v) with a flow rate of 1.0 mL/min, UV detection at 245 nm was used.This LC method was able to detect all these impurities.

Liquid chromatography-Mass spectrometry (LC-MS)
LC-MS/MS compatible method was developed for the analysis of Rosiglitazone maleate and its impurities, where a column (Inertsil ODS 3V 250 X 4.6 X 5.0 µ) with a mobile phase consisting of 0.01M ammonium acetate (pH=6.0)adjusted with dilute acetic acid and acetonitrile in the ratio of 65:35, with a flow rate of 1.0 mL/min, UV detection at 280 nm was used.This LC method was able to detect all the impurities.The mass spectrum of impurities was recorded on AB-4000 Q-trap LC-MS/MS mass spectrometer.

Mass spectrometry
The electro spray ionization and MS-MS studies were performed on AB-4000 LC-MS/MS mass spectrometer.The positive and negative electro spray MS data was obtained by switching the capillary voltage between n+5000 and -4500V respectively.

NMR spectroscopy
The 1 H NMR experiments of rosiglitazone maleate were done at 400 MHz and 100 MHz on Varian Mercury plus 400 MHz FT NMR Spectrometer and similar experiments for impurities 1, 2 and 3 were performed on Gemini-2000 (200 MHz) in DMSO-d 6.The 1 H chemical shift values were reported on the δ scale in ppm relative to TMS (δ=0.00ppm) and the chemical shift values were reported relative to CDCl 3 (δ=77.00ppm)and DMSO-d 6 (δ=39.50ppm)as internal standards respectively.DEPT spectra revealed the presence of methyl and methane groups as positive peaks and methylenes as negative peaks.

FT IR spectroscopy
The IR spectra were recorded in the solid state as KBr dispersion medium using Perkin Elmer Spectrum One FT IR spectrophotometer.

Results and Discussion
In our approach based on the mass information from LC-MS we have proposed structures and synthetic schemes (1-3) for the impurities.We have also designed different experiment and synthesized these compounds and characterized.The isolated compounds RRT's are matching with of unknown impurities.The same impurities were enriched from the filtrates of the isolated compounds, by keeping compound stability at variable temperatures.

Conclusion
The results from various physio-chemical techniques confirm the structures of three impurities of Rosiglitazone maleate 1.Based on the through analytical and the sequence of preparations, the structures of three impurities were established with well characterization.