Anupam Bhattacharya

Rebeccamycin and Staurosporine Biosynthesis: Insight into the Mechanisms of the Flavin-Dependent Monooxygenases RebC and StaC

nistically distinct bioactivities that can be achieved with the indolocarbazole scaffold, the former as a DNA topoisomerase I poison, the latter as a protein kinase inhibitor. Identification of the bacterial biosynthetic genes for 1 and 2, along with in vitro studies on individual enzymes’ activities, has delineated a four-enzyme pathway to assemble the corresponding indolocarbazoles arcyriaflavin A (6) and K252c (7). As summarized in Scheme 1, these enzymes are RebODPC and StaODPC for 6 and 7, respectively. The first three reactions catalyzed by RebODP or StaODP are essentially identical. The flavin-dependent enzyme RebO oxidizes l-tryptophan to indole-3-pyruvate. RebD, a heme-dependent oxidase, subsequently oxidatively couples two equivalents of the imine form of indole-3-pyruvate to form chromopyrrolic acid (3). 7, 9] Compound 3 is moderately stable and slowly oxidizes to form 6, 7, and 7-hydroxyK252c (8) in low yields. A cytochrome P450 enzyme, RebP, is thought to accelerate this spontaneous reaction by oxidatively coupling the 5 and 5’ indole carbons of 3 to generate a labile intermediate 4, 11] which can likewise undergo spontaneous oxidative decarboxylation to form 6–8 in greater yields, with 8 being the major product. 12] In what is an interesting example of biosynthetic evolution, addition of the flavin-dependent monooxygenase RebC to the pathway specifies the formation of dioxygenated 6. 12] By contrast, addition of the homologous enzyme StaC directs forma-

New class of antitubercular compounds: synthesis and anti-tubercular activity of 4-substituted pyrrolo[2,3- c ]quinolines

Modified synthesis and antitubercular activity of 4-substituted pyrrolo[2,3-c]quinolines are reported. Some of the compounds showed significant antitubercular activity, when compared to some of the existing antitubercular drugs. A compound with an imidazole moiety at position 4 shows the highest activity and least toxicity.Graphical abstract

Selective Zn2+ sensing using a modified bipyridine complex

A novel fluorescent Zn2+ sensor, 4-(pyridin-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ), has been designed, synthesized and characterized by various spectroscopic and analytical techniques. PPQ exhibits superior detection of Zn2+ in the presence of various cations tested, including Cd2+ and Hg2+, via shifting its emission maxima and fluorescence intensity enhancement. An emission wavelength at 500 nm, ensures probable non-interference from cellular components while performing biological applications.

Selective detection of fluoride using fused quinoline systems: effect of pyrrole

Selective detection of fluoride by 2-(3H-pyrrolo[2,3-c]quinolin-4-yl)phenol is reported using a turn-on fluorescence method. The presence of a pyrrole ring along with substituted o-phenol is essential as their absence results in either loss of selectivity or decrease in fluorescence intensity.

Synthesis and anti-tubercular activity of fused thieno-/furo-quinoline compounds

A simple route for preparation of 4-substituted thieno/furo[2,3-c]quinoline compounds is reported in this paper. These compounds were synthesized by using Suzuki coupling between appropriate boronic acid and 2-iodoaniline, followed by reaction with diverse aldehydes in the presence of a catalytic amount of FeCl3. Naphthyridine analogues were also prepared in order to demonstrate the efficacy of the developed method. Further anti-tubercular activity screening of the molecules was undertaken, wherein compounds bearing a fused furo[2,3-c][1,8]naphthyridine skeleton displayed highest activity. The best MIC (minimum inhibitory concentration) value of 5.6 μmol was obtained for 4-(4-methoxyphenyl)furo[2,3-c][1,8]naphthyridine, which is found to be superior to the existing first line anti-tubercular drug ethambutol (7.6 μmol).

Immobilized lipase from Lactobacillus plantarum in meat degradation and synthesis of flavor esters

Microbial lipases owing to their broad substrate specificity are widely used in various industrial applications like food processing, organic synthesis, detergent formulation and oil manufacturing. In the current study the immobilized lipase from Lactobacillus plantarum was found novel in degrading meat which can be applied in medical field and also in synthesizing different short chain fatty acid esters like 2,3,4-hydroxybenzyl acetates and triazole ester which makes a great impingement in natural flavor industry. The 4-hydroxybenzyl acetate obtained can also be used in cosmetics.

Correction: Selective detection of fluoride using fused quinoline systems: effect of pyrrole

Correction for ‘Selective detection of fluoride using fused quinoline systems: effect of pyrrole’ by Mahesh Akula et al., RSC Adv., 2015, 5, 57231–57234.

Gold nanoparticle induced enhancement of molecular fluorescence for Zn^2+ detection in aqueous niosome solution

Modified bipyridine-based construct 4-(pyridine-2-yl)-3H-pyrrolo [2,3-c] quinoline (PPQ), and its assemblies with niosomes and gold nanoparticles (GNP) to function as turn-on fluorescent sensors for biologically important Zn2+ in aqueous solution are evaluated. Earlier, we have shown fluorescence-based selective ratiometric detection of Zn2+ by PPQ in DMF [RSC Adv. 2014, 4, 25605]. This work attempts to overcome the water solubility problem of the hydrophobic PPQ, by using non-ionic surfactant led niosomes. The interest in niosome resides in the fact that they can mimic biological systems. Metals like Ag, Au are known to quench fluorescence, but using metal nanoparticles molecular fluorescence can be enhanced by increasing rate of excitation with concentrating electric field around the fluorophore and also by increasing the rate of radiative decay. This is known as Metal enhanced Fluorescence (MEF). When, PPQ binds with Zn2+ and forms the complex in presence of GNP, MEF is evident; whereas no significant fluorescence intensity enhancement is observed for PPQ in absence of either gold nanoparticles or Zn2+. The optimum size for the gold nanoparticles used in our study is ~40 nm, which shows the enhancement. The MEF is evident in niosomes, as there is an optimal distance between PPQ-Zn2+-PPQ complex (residing in the hydrophobic bilayer) and the nanoparticles (in the water pool). The enhancement in fluorescence intensity is accompanied by decrease in fluorescence lifetimes. The described sensing systems, are capable of detecting Zn2+ in HeLa cells at physiological conditions, as shown by bioimaging studies.