SYNTHESIS AND BIOLOGICAL EVALUATION OF THIOSEMICARBAZONE ANALOGUES OF ORNIDAZOLE AS ANTIFUNGAL AGENTS

To synthesize a series of ornidazole thiosemicarbazone analogues on the basis of literature reviews of 2-Methyl-5-nitroimidazoles and thiosemicarbazones and to evaluate all the analogues in vitro for their activity against Aspergillus niger and fumigatus. Thiosemicarbazone analogues were synthesized from oxidising ornidazole with potassium dichromate and refluxing the oxidised product with substituted thiosemicarbazide using ethanol as solvent in the acidic medium overnight. All the synthesized analogues of ornidazole showed good antifungal action against fumigatus and niger except compound C-4. Unsubstituted amine analogue C-2 has shown highest percentage inhibition (96.6%, 500 μg/ml) against fumigatus while aromatic amine with or without electronegative atom analogues C-3 and C-5 has shown highest activity against Aspergillus niger which is two times than standard drug ornidazole (100%, 1000 μg/ml).

H-bonds and DNA

Hydrogen bonds or ‘H-bonds’ are polar, non-covalent bonds or interactions between a hydrogen atom (H) attached to a more electronegative atom, such as oxygen (O) or nitrogen (N), which partially pulls the electron cloud away from the H, leaving it electropositive—with another electronegative atom, such as O or N from a different molecule or from a different part of the same molecule. H-bond interactions play a huge role in the biochemistry of living processes, and in the structures and interactions of biological molecules, with each other and with different molecules including water. Nature's natural solvent, water, is itself a dynamic H-bonded polar structure, which strongly affects solubility and, as (dynamic) water of hydration, interactions between molecules. Compared with covalent and ionic bonds, H-bonds are individually much weaker (<20 kJ/mol), which make them ideal for molecular recognition phenomena. When many H-bonds come together they can form strong insoluble structures such as cellulose and the impermeable derivative of cellulose known as chitin, or helical structures with intra-chain stabilizing H-bonds such as the α-helix. Perhaps the most important H-bonded structure of them all is DNA.

Caenorhabditis elegans Infrared-Based Motility Assay Identified New Hits for Nematicide Drug Development

Nematode parasites have a profound impact on humankind, infecting nearly one-quarter of the world’s population, as well as livestock. There is a pressing need for discovering nematicides due to the spread of resistance to currently used drugs. The free-living nematode Caenorhabditis elegans is a formidable experimentally tractable model organism that offers key advantages in accelerating nematicide discovery. We report the screening of drug-like libraries using an overnight high-throughput C. elegans assay, based on an automated infrared motility reader. As a proof of concept, we screened the “Pathogen Box” library, and identical results to a previous screen using Haemonchus contortus were obtained. We then screened an in-house library containing a diversity of compound families. Most active compounds had a conjugation of an unsaturation with an electronegative atom (N, O, or S) and an aromatic ring. Importantly, we identified symmetric arylidene ketones and aryl hydrazine derivatives as novel nematicides. Furthermore, one of these compounds, (1E,2E)-1,2-bis(thiophen-3-ylmethylene)hydrazine, was active as a nematicide at 25 µm, but innocuous to the vertebrate model zebrafish at 50 µm. Our results identified novel nematicidal scaffolds and illustrate the value of C. elegans in accelerating nematicide discovery using a nonlabor-intensive automated assay that provides a simple overnight readout.

Synthesis and Investigations on Antioxidant Behaviour of Chromone Based Semicarbazones

Chromone derived carbazones provide an important antioxidant activity by exhibiting radical scavenging action, Semicarbazones are synthesized in good yield and these act as a good radical scavenger, where the presence of various substituent at C-6 of chromone nucleus tend to alter the activity behaviour, presence of electronegative atom such as fluoro/ chloro enhances the radical scavenging activity in comparison to electron donating group.

Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide. However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically. In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen) reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen.

Heteroatom Substitution at Amide Nitrogen — Resonance Reduction and HERON Reactions of Anomeric Amides

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. &nbsp;Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide.&nbsp;&nbsp;However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically.&nbsp;&nbsp;In certain configurations,&nbsp;reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen)&dagger; reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. &nbsp;In other cases the anomeric effect facilitates S&shy;N1 and SN2 reactivity at the amide nitrogen.

The role of substituents in the HERON reaction of anomeric amides

Anomeric amides, RCON(X)(Y), have two electronegative atoms at the amide nitrogen, a configuration that results in greatly reduced amide resonance and strongly pyramidal nitrogen atoms. This, combined with facilitation of anomeric interactions, can result in the HERON reaction, an intramolecular migration of the more electronegative atom, X, from nitrogen to the carbonyl with production of a Y-stabilised nitrene. We have modelled, at the B3LYP/6-31G(d) level, a variety of anomeric amides that undergo the HERON reaction to determine factors that underpin the process. The overriding driving force is anomeric destabilisation of the bond to the migrating group. Rotated transition states show loss of residual resonance and this is a component of the overall activation energies. However, the reduced resonance in these systems plays only a minor role. We have determined the resonance energies (RE) and HERON activation barriers (EA) of five anomeric systems. REs for the amides have been calculated isodesmically using our calibrated trans amidation method and COSNAR calculations. Reduction of their overall EAs by the corresponding RE gives rearrangement energies (Erearr.), a measure of relative impact on rearrangement of substituents on nitrogen. In CH3CON(OMe)(Y) systems producing (CH3CO2Me + NY), a loosely bound electron pair on the donor atom, Y, in nY–σ*NOMe anomeric interactions drives the reaction. Erearr. increases in the sequence Y = N(nitrene) < O−(oxide) ≪ NMe2 < SMe ≪ OMe. For the same systems, RE increases in the order Y = N < O− ≪ OMe ≪ NMe2 ∼ SMe. Other effects such as molecular conformation, nature of the migrating group, X, and acyl substituents at the carbonyl carbon are discussed.