Isolation and characterisation of degradant impurities in dipyridamole formulation.

Dipyridamole is an antithrombotic drug. In the stability study of drug product of Dipyridamole, two unknown impurities (referred as DP-I and DP-II) were detected at levels of 0.25% and 0.54% by gradient reverse phase HPLC method. The drug product was subjected to stress to enhance the level of these impurities. An elegant isocratic preparative method was employed using a Reprosil CN column with a short run time of 14 min to isolate these impurities. The DP-I and DP-II were isolated with purities of 99.1% and 99.8% respectively. Structural studies of these impurities were undertaken using spectroscopic techniques such as IR, NMR and Mass. Based on the spectral data, the structures of DP-I and DP-II have been characterised to be 2,2',2″,2'″-(4-hydroxy-8-(piperidin-1-yl) pyrimido [5,4-d]pyrimidine-2,6 diyl) bis(azanetriyl) tetraethanol, 4-(2-((6-(bis (2-hydroxyethyl) amino)-4, 8-di (piperidin-1-yl) pyrimido [5,4-d] pyrimidin-2-yl) (2-hydroxyethyl) amino) ethoxy)-2, 3-dihydroxy-4-oxobutanoic acid, respectively. A detailed elucidation of the structure is presented in this article.

Identification of degradation products in stressed tablets of Rabeprazole sodium by HPLC-hyphenated techniques.

Three unknown impurities of Rabeprazole, a proton pump inhibitor, were formed in the formulated drug under the stress conditions, [40 degrees C/75% relative humidity (RH) for 6 months] with relative retention times (RRTs) 0.17, 0.22 and 0.28. The Impurity-I (0.17 RRT) was isolated using preparative HPLC and characterized by NMR and MS. The other two impurities, Impurity-II (RRT 0.22) and Impurity-III (RRT 0.28) could not be isolated, hence they are characterized by HPLC-hyphenated techniques, LC-NMR and high-resolution LC-MS. On the basis of the spectral data, the Impurity-I, Impurity-II and Impurity-III were characterized as 1-(1H-benzo[d]imidazol-2-yl)-3-methyl-4-oxo-1,4-dihydropyridine-2-carboxylic acid, 1H-benzo [d] imidazole-2-sulfonic acid and 4-(3-methoxy propoxy)-3-methyl-2-pyridine carboxylic acid, respectively.

Isolation and characterization of impurities in docetaxel.

During the process development of docetaxel, two polar impurities (Impurities I and II) and two non-polar impurities (Impurities III and IV) were detected by high performance liquid chromatography (HPLC). All the impurities were isolated by Medium Pressure Liquid Chromatography (MPLC). The Impurities I, II, III and IV were identified as 13-[(4S,5R)-2-oxo-4-phenyl-oxazolidine-5-carboxy]-10-deacetyl baccatin III ester, 2'-epi docetaxel, 7-epi docetaxel and 13-[(4S,5R)-2-oxo-4-phenyl-oxazolidine-3,5-dicarboxyl-3-tert-butyl)]-10-deacetyl baccatin III ester, respectively, based on one- (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy data. The Impurity IV was crystallized and the structure was solved by single crystal X-ray diffraction (XRD). Two impurities (Impurities II and III) were found to be process related, while the remaining two impurities (Impurities I and IV) turned out to be isomers. The formation of these impurities was discussed.