Ajay K. Sah

Selective oxidation of organic sulfides to sulfoxides using sugar derived cis-dioxo molybdenum(VI) complexes: kinetic and mechanistic studies

Six Mo(VI) complexes of 4,6-O-ethylidene-β-D-glucopyranosylamine derived ligands have been used for the selective oxidation of five organic sulfides to corresponding sulfoxides. The structure of a new sulfide [(((2-(phenylthio)phenyl)imino)methyl)naphthalen-2-ol] (S5) and its corresponding sulfoxide (SO5) has been established using single crystal X-ray diffraction studies along with other routine analytical techniques. The yields of sulfoxides were calculated using HPLC and one of the catalysts was recycled five times without any appreciable loss in its activity. Kinetic studies on sulfoxide formation was performed on compound S5 using UV-visible spectroscopy, which suggested overall first order kinetics. A plausible mechanism for sulfide oxidation has been proposed based on our findings and previous literature reports.

Selective Synthesis of Bis(indolyl)methanes Under Solvent Free Condition Using Glucopyranosylamine Derived cis-Dioxo Mo(VI) Complex as an Efficient Catalyst

Abstractcis-Dioxomolybdenum(VI) complex of 4,6-O-ethylidene-β-d-glucopyranosylamine derived ligand has been used as an efficient catalyst in the selective synthesis of a series of bis(indolyl)methanes (BIMs) by condensing indole derivatives with carbonyl compounds. The adopted synthetic procedure is green in nature as solvent free reactions have been carried out using naturally occurring d-glucose derived ligands. Total 15 BIMs have been synthesised including four new ones, which have been characterized by mp, FTIR, NMR and mass spectroscopy. The catalyst has afforded good to excellent yield of BIMs in short reaction time and the former has been recycled five times without any significant loss in it’s catalytic efficiency.Graphical Abstract

Selective Retention of Methanol over Ethanol by a Cyclen-Based Cryptand/Copper(II) Complex

A cyclen-based cryptand (2) was prepared in a two-step synthesis from dioxocyclen. When a Cu(CF3SO3)2 complex with 2 was prepared in methanol, the 2/Cu(CF3SO3)2 complex incorporated one methanol in the cavity formed by the diethyleneoxy unit and the NH group of the cyclen. When prepared in ethanol, the 2/Cu(CF3SO3)2 complex similarly incorporated one ethanol. Cold electrospray ionization mass spectrometry (CSI-MS) of the 2/Cu(CF3SO3)2/alcohol complexes selectively retains methanol over ethanol under CSI-MS conditions.

Synthesis and Characterization of Glucose Derived Dioxo-molybdenum (VI) Complexes and Their Application in Sulphide Oxidation

Three new molybdenum (VI) complexes of 4,6-O-ethylidene-β-d-glucopyranosylamine derived ligands has been synthesized and the same has been used in the oxidation of thioanisole along with an earlier reported analogous complex. A selective oxidation of thioanisole to methyl phenyl sulphoxide in high yield is achieved using 1:1 mixture of thioanisole and urea hydrogen peroxide (UHP) in ethanol. A longer reaction time or excess of UHP, leads to the formation of corresponding sulphone, which was confirmed using HPLC and NMR measurements.Graphical AbstractThe oxidation of thioanisole into corresponding sulphoxide and sulphone has been explored using dioxo-molybdenum (VI) complexes of 4,6-O-ethylidene-β-d-glucopyranosylamine derived Schiff base ligands.

Synthesis, evaluation and molecular docking studies of amino acid derived N-glycoconjugates as antibacterial agents.

Six amino acid derived N-glycoconjugates of d-glucose were synthesized, characterized and tested for antibacterial activity against G(+)ve (Bacillus cereus) as well as G(-)ve (Escherichia coli and Klebsiella pneumoniae) bacterial strains. All the tested compounds exhibited moderate to good antibacterial activity against these bacterial strains. The results were compared with the antibacterial activity of standard drug Chloramphenicol, where results of A5 (Tryptophan derived glycoconjugates) against E. coli and A4 (Isoleucine derived glycoconjugates) against K. pneumoniae bacterial strains are comparable with the standard drug molecule. In silico docking studies were also performed in order to understand the mode of action and binding interactions of these molecules. The docking studies revealed that, occupation of compound A5 at the ATP binding site of subunit GyrB (DNA gyrase, PDB ID: 3TTZ) via hydrophobic and hydrogen bonding interactions may be the reason for its significant in vitro antibacterial activity.

The synthesis of amino acid derived glycoconjugates and the investigation of their anti-inflammatory and analgesic properties

A series of 4,6-O-ethylidene-β-D-glucopyranosylamine derived glycoconjugates containing amino- and aromatic acids have been synthesized. All these molecules have been tested for their anti-inflammatory and analgesic activity on Wistar rat and Swiss Albino mice respectively. The anti-inflammatory studies were explored using a carrageenan induced paw oedema model while an acetic acid induced writhing model was adapted for the analgesic studies. All of the compounds exhibited anti-inflammatory and analgesic activity in the range of 63–84% and 86–94% respectively.

Alanyl glycoconjugate: a selective receptor for free and protein-bound tryptophan

The free and protein-bound tryptophan (Trp) sensing ability of an alanyl-(4,6-O-ethylidene-β-D-glucopyranosylamine) derived chiral receptor (L-N2O2) has been explored using UV-vis absorption, fluorescence and mass spectroscopy. L-N2O2 decreases the intrinsic emission intensity of Trp at 360 nm via a static quenching mechanism, revealing the interactions between the two.

Double-armed and tetra-armed cyclen-based cryptands

Abstract Double-armed and tetra-armed cyclen-based cryptands (1a–1d and 2) that bridge two aromatic rings by diethyleneoxy and triethyleneoxy units were prepared. The CSI-MS of 1:1 mixtures ([Ag+]/[ligand]) indicated that these new cryptands form 1:1 complexes with Ag+. The log K values for the interaction between Ag+ and 2 was greater than those of 1a–1d, double-armed cyclens (3a–3c and 4), and tetra-armed cyclen (5). The Ag+-ion-induced 1H NMR spectral changes suggest that the Ag+–π interactions of the Ag+ complexes with the cryptands (1a–1d and 2) are stronger than those in Ag+/double-armed and tetra-armed cyclens. To visualise the Ag+−π interactions, the isosurfaces of the LUMO and HOMOs of the Ag+ complexes were calculated at the B3LYP/3–21G(*) theoretical level. The LUMO of the Ag+ ion is distorted by interaction with the HOMOs of the aromatic side arms. The calculations reveal Ag+−π interactions between the Ag+ ion and the aromatic side arms, and these are shown graphically.

Metal-Free Synthesis of Aminomethylated Imidazoheterocycles: Dual Role of tert-Butyl Hydroperoxide both as an Oxidant and Methylene Source

A novel and efficient aminomethylation approach has been developed for the regioselective functionalization of imidazoheterocycles under metal-free conditions. A wide range of imidazoheterocycles and 2/4-aminoazaheterocycles successfully provided corresponding aminomethylated imidazoheterocycles in moderate to excellent (33-80%) yields. The isotopic labelling study suggested that TBHP played a dual role as both an oxidant and a methylene source in this transformation. The developed protocol follows a radical pathway which is supported by radical trapping experiments.