J. Moses Babu

Novel D-ring analogues of podophyllotoxin as potent anti-cancer agents ☆

Several D-ring modified analogues of podophyllotoxin were prepared viz semi-synthesis starting from naturally occurring podophyllotoxin and determined their in vitro anti-cancer activity. Most of the analogues have shown good activity towards human cancer cell lines.

Isolation and characterization of process-related impurities in linezolid.

Two unknown impurities in linezolid bulk drug at levels below 0.1% (ranging from 0.05 to 0.1%) were detected by a simple isocratic reverse phase high performance liquid chromatography (HPLC). These impurities were isolated from crude sample of linezolid using reverse phase preparative HPLC. Based on the spectroscopic data (IR, NMR and MS) the structures of the impurities were characterized as (S)-N-[[-(3-(3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl] acetate(I) and (S)-N-[[-(3-(3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl] chloride(II). The synthesis from an unambiguous route and the formation of impurities was discussed.

Identification, synthesis, isolation and spectral characterization of potential impurities of montelukast sodium

During the process development of montelukast sodium, three polar impurities and one non-polar impurity with respect to montelukast sodium were detected by simple reverse phase high-performance liquid chromatography (HPLC). Initially, all the four impurities were identified by the liquid chromatography-mass spectrometry (LC-MS) data and out of four impurities, three have been prepared by the synthetic method and remaining one is isolated by preparative HPLC. Based on the spectral data (IR, (1)H NMR, (13)C NMR and MS), the structure of these impurities 1-4 were characterised as 1-[[[(1R)-1-[3-[(1E)-2-(7-chloro-2-quinolinyl)ethenyl]phenyl-3-[2-(1-hydroxy-1-methylethyl)phenyl]propyl]thio]methyl]cyclopropane acetamide (impurity-1), {1-[1-{3-[2-(7-chloro-quinolin-2-yl)-vinyl]-phenyl}-3-(2-isopropenyl-phenyl)-propylsulfanylmethyl]-cyclopropyl}-acetic acid (impurity-2), 1-[[[(1R)-1-[3-[(1E)-2-(7-chloro-2-quinolinyl)ethyl]phenyl-3-[2-(1-hydroxy-1-methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (impurity-3) and 1-[[[(1R)-1-[3-[(1E)-2-(2-quinolinyl)ethenyl]phenyl-3-[2-(1-hydroxy-1-methylethyl)phenyl]propyl]thio]methyl]cyclopropaneacetic acid (impurity-4).

A validated chiral HPLC method for the enantiomeric separation of Linezolid on amylose based stationary phase

Two chiral HPLC methods namely method A and method B were developed for the separation of enantiomers of Linezolid. The mobile phases containing hexane, 2-propanol and trifluoro acetic acid (TFA) in the ratio (80:20:0.1, v/v/ v); hexane, ethanol and TFA in the ratio (65:35:0.1, v/v/v) were used in method A and method B, respectively. The assay results of the two methods were checked in terms of F-test variance ratio and found to be less than the table value, confirming their good precision. The enantiomeric separation of Linezolid on different chiral stationary phases was investigated. The two enantiomers of Linezoild were well resolved on a Chiralpak AD, an amylose based stationary phase. Preparative chiral HPLC was carried out to obtain pure (+) enantiomer of Linezolid from its racemate. The method A was extensively validated and found to be robust. The chiral assay of Linezolid in bulk and pharmaceutical formulations (tablet) were found to be 100.4 +/- 0.4 and 101.2 +/- 1.4%, respectively at 95% confidence interval. The percentage recovery of (+) enantiomer (chiral impurity) was found to be 99.2 +/- 1.9 at 95% confidence interval. The limit of detection and limit of quantification of (+) enantiomer were found to be 123 and 374 ng/ml, respectively for 10 microl injection volume.

Impurity profile study of repaglinide.

Three unknown impurities and a byproduct in repaglinide bulk drug at levels below 0.1% (ranging from 0.05 to 0.1%) were detected by a simple isocratic reversed-phase high performance liquid chromatography (HPLC) method. These impurities were isolated from crude sample of repaglinide using reversed-phase preparative high performance liquid chromatography. Based on the spectroscopic data (IR, NMR and MS) the structures of these impurities (I, II and IV) and byproduct (III) were characterised as 4-carboxymethyl-2-ethoxy-benzoic acid (I), 4-cyclohexylaminocarbamoylmethyl-2-ethoxy-benzoic acid (II), 1-cyclohexyl-3-[3-methyl-1-(2-piperidin-1-yl-phenyl)-butyl]-urea (IV) and 1,3-dicyclohexyl urea (III), respectively. Their synthesis and formation is discussed.

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 °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. Copyright

Solid state structural studies of saccharin salts with some heterocyclic bases

Five saccharin salts with heterocyclic bases 1,2-bis(4-pyridyl)ethane, 1; trans-1,2-bis(4-pyridyl)ethylene, 2; piperazine, 3; 1,4-dimethylpiperazine, 4 and 2,2′-dipyridylamine, 5 have been synthesized and characterized by single crystal X-ray diffraction. The crystal structures reveal that in all the salts, the hydrogen atom has been transferred from saccharin nitrogen to the base nitrogen and sustained through charge-assisted hydrogen bonds. In salts 1–3, N+–H donor forms N+–H⋯O hydrogen bonds with the carbonyl oxygen of saccharinate, whereas it forms N+–H⋯N− in 4 and intramolecular N+–H⋯N in 5. Salts 2 and 3 also form weak N+–H⋯N−hydrogen bonds. Only in salt3, the SO2 moiety is involved in conventional hydrogen bonding.

A direct entry to the 1-methoxyindole skeleton and to the corresponding indoles by a novel rearrangement: general syntheses of substituted 1-methoxyindoles

A short and efficient route to 1-methoxyindoles via a novel rearrangement is disclosed. This route involves only three steps from commercially available nitro compounds. The methodology is also generalized with a variety of examples to afford a series of 2-substituted-1-methoxyindoles possessing an electron-withdrawing group at position 3. In addition, a 1-methoxyindole compound 10 was converted to the corresponding indole 11 under mild conditions thereby constituting a new synthesis of substituted indoles.

Impurity profile study of loratadine

Three unknown impurities in loratadine bulk drug at levels below 0.1% (ranging from 0.05 to 0.1%) were detected by a simple isocratic reversed-phase high performance liquid chromatography (HPLC). These impurities were isolated from mother liquor sample of loratadine using reversed-phase preparative HPLC. Based on the spectral data (IR, NMR and MS) the structures of these impurities were characterized as 11-(N-carboethoxy-4-piperidylidene)-6,11-dihydro-5H-benzo(5,6) cyclopenta(1,2-b)-pyridine (I), 8-bromo-11-(N-carboethoxy-4-piperidylidene)-6,11-dihydro-5H-benzo(5,6) cyclopenta (1,2-b)-pyridine (II) and 8-chloro-11-(N-carboethoxy-4-piperidylidene)-5H-benzo(5,6) cyclopenta (1,2-b)-pyridine (III). The synthesis of these impurities was discussed.

Application of LC–MS/MS for the identification of a polar impurity in mosapride, a gastroprokinetic drug

In the impurity profile of mosapride a polar impurity (0.1%) was detected in HPLC with respect to mosapride. Based on the mass spectral data obtained by LC-MS/MS analysis this impurity structure was characterised as 4-amino-5-chloro-2-ethoxy-N-[[(4-benzyl)-2-morphinyl] methyl] benzamide. It is interesting to note that this impurity is potent analogue of mosapride, which will have much higher gastroprokinetic activity than metoclopramide. This impurity was synthesised from an unambiguous route and confirmed the structure by collecting various spectral data and the formation is discussed. To our knowledge this compound was not reported as process impurity elsewhere.