Bioactive isoquinoline alkaloids from Cissampelos pareira†

The phytochemical and biological investigation of Cissampelos pareira leads to the isolation of one new isoquinoline alkaloid (7) along with six known isoquinoline alkaloids, namely, magnoflorine (1), magnocurarine (2), cissamine (3), curine (4), hayatinine (5) and cycleanine (6). Magnoflorine (1) and magnocurarine (2) were isolated for the first time from C. pareira. A new, rapid, simple and sensitive UPLC method was developed for simultaneous quantification of five pure compounds (1–5). Seasonal variation study revealed higher content of these compounds during the rainy season. The chloroform (CPCF) and n-butanol (CPBF) fractions showed cytotoxic efficacy against KB cells. Among pure compounds, hayatinine (5) was found to be most active against KB and A549, while, cycleanine (6) against KB cells.     

Coupled in-tube and on-fibre solid-phase microextractions for cleanup and preconcentration of organic micropollutants from aqueous samples and analysis by gas chromatography-mass spectrometry

Matrix interference removal is an important step when large volumes of aqueous samples are required to be processed to detect trace levels of analytes. A combination of two sample extraction methods has been used in this work with the aim of cleanup and preconcentration of analytes. For first objective, mild but preferential sorption of a range of analytes has been performed with in-tube solid-phase microextraction (SPME) using polytetrafluoroethylene (PTFE) tubing, and for the second, the eluate from in-tube SPME was subjected to on-fibre SPME using DVB/Caboxen/PDMS (30/50 μm) fibre. Knitting of PTFE tubing created secondary flow pattern that enhanced radial diffusion and retention of organic analytes. Up to 2 mg L⁻¹ of a broad range of substances that are not extracted by PTFE include nitrogen containing aromatic heterocyclic compounds, anilines, phenols and certain organophosphorus pesticides, thus providing a clean extract using this method of sample preparation. The proposed combination of in-tube and on-fibre SPME produced a rectilinear calibration graph over 0.03-150 μg L⁻¹ of a range of analytes using 60 mL of aqueous sample. The overall recovery of analytes was in the range 27-78%. The detection limits were between 6.1 and 21.8 ng L⁻¹. The R.S.D. was in range 5.4-8.2% and 4.2-6.5% in the analysis of respectively 2 and 20 μg L⁻¹ of analytes.     

A new diastereoselective intramolecular electroreductive coupling of unsaturated β-ketoesters and β-ketoamides in ionic liquids at a tin cathode

The diastereoselective intramolecular electroreductive coupling of several β-ketoesters and β-ketoamides has been accomplished at a tin cathode in ionic liquids and isopropanol (9:1). The ionic liquids used are 1-butyl-3-methylimidazolium bromide [BMIM]Br, 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM]BF₄, 1-methoxyethyl-3-methylimidazolium trifluoroacetate [MOEMIM]CF₃COO and 1-methoxyethyl-3-methylimidazolium mesylate [MOEMIM]Ms. This methodology offers a clean and green process for the synthesis of functionalized carbocycles in good yields with excellent stereochemical control at three stereogenic centres.     

Busy period analysis of queue: Lattice path approach

In this paper, we find the busy period density of queues in explicit computational form, through lattice path (LP) approach. Both the arrival and service time distributions are approximated by 2-phase Cox distribution C₂, which has a Markovian property enabling us to use LP combinatorics. Since any distribution with rational Laplace–Stieltjes transform (LST) and square coefficient of variation (CV²) lying in [1/2,∞) can be approximated by a C₂([M. Agarwal, K. Sen, B. Borkakaty, Busy period density of queueing system C₃/M/1, Journal of Combinatorics, Information and Systems Sciences 31 (1–4) (2006) 127–161]), the results obtained would be applicable to a very wide class of distributions occurring in real life.     

Conformational mapping and energetics of saccharide-aromatic residue interactions: implications for the discrimination of anomers and epimers and in protein engineering

Aromatic residues play a key role in saccharide-binding sites. Experimental studies have given an estimate of the energetics of saccharide-aromatic residue interactions. In this study, dependence of the energetics on the mutual position-orientation (PO) of saccharide and aromatic residue has been investigated by geometry optimization of a very large number (164) of complexes at MP2/6-31G(d,p) level of theory. The complexes are of Tyr and Phe analogs with α/β-D-Glc, β-D-Gal, α-D-Man and α/β-L-Fuc. A number of iso-energy POs are found for the complexes of all six saccharides. Stacking and non-stacking modes of binding are found to be of comparable strengths. In general, complexes of p-OHTol are stronger than those of Tol, and those dominated by OH···O interactions are more stable than ones dominated by CH···π interactions. The strengths of OH···O/π interactions, but not those of CH···π, show large variations. Even though an aromatic residue has a large variety of POs to interact with a saccharide, distinct preferences are found due to anomeric and epimeric differences. An aromatic residue can interact from either the a- or b-face of Glc, but only through the b-face with Gal, its C4-epimer. In contrast, stacking interaction with Man (C2-epimer of Glc) requires the participation of the -CH(2)OH group and free rotation of this group, as is observed in solution, precludes all modes of stacking interactions. It is also found that an aromatic residue can be strategically placed either to discriminate or to accommodate (i) anomers of Glc and of Fuc and (ii) Gal/Fuc. Thus, analysis of the optimized geometries of by far the largest number of complexes, and with six different saccharides, at this level of theory has given insights into how Nature cleverly uses aromatic residues to fine tune saccharide specificities of proteins. These are of immense utility for protein engineering and protein design studies.     

Modeling Disorder in the Crystal Structure of the α Polymorph of Alq<Subscript>3</Subscript>

Abstract  

Alq₃, tris(quinolin-8-olato)aluminum(III) is used in the electron transport and/or electron-injecting layer in multilayer organic light-emitting diode device structures. In recent years, five crystalline phases (α, β, γ, δ, and ε) of Alq₃ have been identified. A structure of the α form, containing the meridional isomer, has been reported in literature based on powder XRD data. Single crystals of α Alq₃ have been found to have essentially the same unit cell parameters [triclinic, space group P [`1]P \bar {1}, a = 6.2455(10) ?, b = 12.8710(18) ?, c = 14.739(3) ?, α = 69.890(6)°, β = 89.464(5)°, and γ = 82.520(13)°] as reported previously from powder XRD: triclinic, space group P [`1]P \bar {1}, a = 6.2586(8) ?, b = 12.914(2) ?, c = 14.743(2) ?, α = 109.66(1)°, β = 89.66(1)°, and γ = 97.68(1)°. The single-crystal XRD structure for α Alq₃, however, appeared to be present mostly as the facial isomer, with a high degree of disorder. Although the structure obtained by single-crystal XRD appears to be predominantly or entirely facial, various spectroscopy results (particularly NMR) are more consistent with a meridional composition. To resolve the α Alq₃ isomerism contradiction, we have reconsidered the structural conclusions that were drawn from the single crystal XRD. Based on modeling results, the hypothesis is that α Alq₃ could be a disordered analog of ε Alq_3, with meridional conformation.     

Conformational specificity of non-canonical base pairs and higher order structures in nucleic acids: crystal structure database analysis

Non-canonical base pairs contribute immensely to the structural and functional variability of RNA, which calls for a detailed characterization of their spatial conformation. Intra-base pair parameters, namely propeller, buckle, open-angle, stagger, shear and stretch describe structure of base pairs indicating planarity and proximity of association between the two bases. In order to study the conformational specificities of non-canonical base pairs occurring in RNA crystal structures, we have upgraded NUPARM software to calculate these intra-base pair parameters using a new base pairing edge specific axis system. Analysis of base pairs and base triples with the new edge specific axis system indicate the presence of specific structural signatures for different classes of non-canonical pairs and triples. Differentiating features could be identified for pairs in cis or trans orientation, as well as those involving sugar edges or C-H-mediated hydrogen bonds. It was seen that propeller for all types of base pairs in cis orientation are generally negative, while those for trans base pairs do not have any preference. Formation of a base triple is seen to reduce propeller of the associated base pair along with reduction of overall flexibility of the pairs. We noticed that base pairs involving sugar edge are generally more non-planar, with large propeller or buckle values, presumably to avoid steric clash between the bulky sugar moieties. These specific conformational signatures often provide an insight into their role in the structural and functional context of RNA.     

Synthesis of 25-oxygenated D:A-friedooleananes from D:A-friedoolean-7β -ol

D:A-Friedoolean-25-ol ( ) and 25-al ( ) have been synthesised from D:A-friedoolean-7β -ol ( ). Substituted tetrahydrofuran rings are opened up on treatment with lithium in ethylene-diamine to yield the corresponding saturated alcohols.     

Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-²H₂]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.     

Salt-assisted liquid-liquid microextraction with water-miscible organic solvents for the determination of carbonyl compounds by high-performance liquid chromatography

A simple and rapid method has been reported for the determination of carbonyl compounds involving reaction with 2,4-dinitrophenylhydrazine and extraction of hydrazones with water-miscible organic solvent acetonitrile when the phase separation occurs by addition of ammonium sulphate, a process called salt-assisted liquid-liquid microextraction. The extract was analyzed by high-performance liquid chromatography with UV detection at 360 nm. The procedure has been optimized with respect to solvent suitable for extraction, salt for phase separation between water and organic solvent, reaction temperature and reaction time. The method has been validated when a linear dynamic range was obtained between the amount of analyte and peak area of hydrazones in the range 7 μg-15 mg L⁻¹, the correlation coefficient over 0.9964-0.9991, and the limit of detection in the range 0.58-3.2 μg L⁻¹. Spiked water samples have been analyzed with adequate accuracy, and application of the method has been demonstrated in the analysis of benzaldehyde formed as oxidation product in pharmaceutical preparation where benzyl alcohol is used as preservative, and for a keto drug dexketoprofen.