Development of an efficient stability-indicating LC-MS/MS method for the analysis of selexipag and characterization of its degradation products.

A new RP-HPLC method with a quick, sensitive and stable indication for the quantitative measurement of selexipag and its associated substances was developed and validated in the present study. In this new method, using the impurity-spiked solution, the chromatographic approach was optimized. Similarly, using the X-bridge phenyl column with isocratic elution of mobile phase containing acetonitrile and formic acid, selexipag and its impurities were separated. Recovery experiments obtained were satisfactory, and also the calibration graphs plotted for selexipag and its five impurities were found to be linear. The system validation parameters such as specificity, linearity, precision, accuracy and robustness were determined successfully. The obtained results indicated that the developed method was found to be useful for analyzing selexipag from its impurities. Further, using stress tests against acid, alkali, peroxide, reduction, thermal, hydrolysis and UV conditions, the present established method of HPLC was assessed and validated as per ICH Q2(R1) guidelines.

Chumacin-1 and Chumacin-2 from Pseudomonas aeruginosa strain CGK-KS-1 as novel quorum sensing signaling inhibitors for biocontrol of bacterial blight of rice.

The in vitro inhibition of quorum sensing signal, xanthan gum secretion, biofilm formation in different Xanthomonas pathovars and biological control of bacterial blight of rice by the two bioactive extrolites produced by Pseudomonas aeruginosa strain CGK-KS-1 were explored. These extrolites were extracted from Diaion HP-20 resin with methanol and purified by preparative-thin layer chromatography. Further, spectroscopic structural elucidation revealed the tentative identity of these extrolites to be (R,3E,5E,9Z,11E)-13-((3S,5R)-5-acetyl-2,6-dimethylheptan-3-yl)-10-hydroxy-4-methyl-1,8-diazabicyclo[9.3.1]pentadeca-3,5,9,11(15),13-pentaen-2-one and (R,3E,5E,8E,11E)-13-((3S,5R)-5-acetyl-2,6-dimethylheptan-3-yl)-4-methyl-1,8-diazabicyclo[9.3.1]pentadeca-3,5,8,11(15),13-pentaene-2,10-dione, named as Chumacin-1 and Chumacin-2, respectively. Antimicrobial assay showed Chumacin-1 and Chumacin-2 exhibited a strong in vitro growth inhibition against various Xanthomonas pathovars. Quorum sensing overlay assay using a reporter strain Chromobacterium violaceum strain CV026 showed that Chumacin-1 and Chumacin-2 inhibited quorum sensing signaling. The mechanistic studies revealed that these extrolites inhibited the production of quorum sensing signaling factor, cis-11-methyl-2-dodecenoic acid; suppressed the xanthan gum secretion and also inhibited the biofilms formed by various Xanthomonas pathovars. Both Chumacin-1 and Chumacin-2 showed ROS generation in the test Xanthomonas strains, resulting in in vitro cell membrane damage was revealed through CSLM and FE-SEM micrographs. Further, greenhouse experiments using Samba Mashuri (BPT-5204) revealed that seed treatment with Chumacin-1 and Chumacin-2 along with foliar spray groups showed up to ˜80% reduction in bacterial blight disease in rice. To the best of our knowledge, this is the first report on new quorum sensing inhibitors, Chumacin-1 and Chumacin-2 produced by Pseudomonas aeruginosa strain CGK-KS-1 exhibiting DSF inhibition activity in Xanthomonas oryzae pv. oryzae.