Novel isochroman-triazoles and thiadiazole hybrids: Design, synthesis and antimicrobial activity

Enantioselective Synthesis of α-Quaternary Isochromanes by Oxidative Aminocatalysis and Gold Catalysis

A novel strategy that combines oxidative aminocatalysis and gold catalysis allows the preparation of chiral α-quaternary isochromanes, a motif that is prevalent in natural products and synthetic bioactive compounds. In the first step, α-branched aldehydes and propargylic alcohols are transformed into α-quaternary ethers with excellent optical purities (>90 % ee) via oxidative umpolung with DDQ and an amino acid-derived primary amine catalyst. Subsequent gold(I)-catalyzed intramolecular hydroarylation affords the isochromane products with retention of the quaternary stereocenter. A second approach explores the use of allylic alcohols as reaction partners for the oxidative coupling to furnish α-quaternary ethers with generally lower enantiopurities. Stereoretentive cyclization to isochromane products is achieved via intramolecular Friedel-Crafts type alkylation with allylic acetates as a reactive handle. A number of synthetic elaborations and a biological study on these α-quaternary isochromanes highlight the potential applicability of the presented method.

Efficient Synthesis of Novel N-[4-Methyl-3-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)thiazol-2(3H)-ylidene]benzamide Hybrid Ring System as Potential Antibacterial Agents

BACKGROUND

Heterocyclic compounds display versatile biological applications, so the aim of this paper was to prepare biologically important heterocycles with enhanced bacterial resistance and to evaluate for their various structural features that are responsible for their biological properties.

OBJECTIVE

The objective was to synthesize bacterial resistance compounds with enhanced antibacterial properties.

METHOD

Ester moiety containing thiazole ring was converted into its hydrazide derivatives. These heterocyclic derivatives were cyclized into another ring oxadiazole; hence a hybrid ring system of two biologically active rings was prepared.

RESULT

All the synthesized compounds were characterized by spectroscopic techniques and were screened for their antibacterial potential; they possess significant antibacterial activities.

CONCLUSION

New hybrid heterocyclic ring systems were synthesized by cyclization of hydrazide derivatives by adopting two step strategy in good yields. All the synthesized compounds were evaluated for their antioxidant activities; they showed moderate to significant activities. QSAR and Molecular docking studies were performed to determine the mode of interaction. Experimental and computational data is in accordance with the determined antibacterial activities.

Tautomers of homophthalic anhydride in the ground and excited electronic states: analysis through energy, hardness and vibrational signatures

The keto-enol tautomerisation in homophthalic anhydride (HA) is investigated in the ground (S₀) and excited (S₁) electronic states. The keto form with a dicarbonyl structure is found to be the most stable form in S₀ and enol form with a monocarbonyl structure in S₁ indicating an excited state intramolecular proton transfer (ESIPT) process. The computed results show consistency with the change in basis sets and methods of calculations. Apart from the two tautomers, transition states are also identified. The barrier to interconversion is found to reduce substantially in S₁. Internal reaction coordinate (IRC) calculations confirm the pathway of interconversion between the two forms in S₀ and S₁. The observed FT-IR spectra corroborate well with our computed spectra. The appearance of two strong lines around 1800 cm^-1 confirms the lowest energy structure to be the keto tautomer with a dicarbonyl form in S₀. Our computations corroborate well with the crystal structure data for an analogous molecule. Electron distribution in HOMO and LUMO indicate the excitation process as π → π^* in nature. The qualitative chemical concepts like hardness and electrophilicity are calculated to estimate the stability of the tautomers. The energy and hardness profiles with the variation of IRC are opposite to each other, verifying the principle of maximum hardness.

Heterocycle Compounds with Antimicrobial Activity

Background:

Bacterial infections are a growing problem worldwide causing morbidity and mortality mainly in developing countries. Moreover, the increased number of microorganisms, developing multiple resistances to known drugs, due to abuse of antibiotics, is another serious problem. This problem becomes more serious for immunocompromised patients and those who are often disposed to opportunistic fungal infections.

Objective:

The objective of this manuscript is to give an overview of new findings in the field of antimicrobial agents among five-membered heterocyclic compounds. These heterocyclic compounds especially five-membered attracted the interest of the scientific community not only for their occurrence in nature but also due to their wide range of biological activities.

Method:

To reach our goal, a literature survey that covers the last decade was performed.

Results:

As a result, recent data on the biological activity of thiazole, thiazolidinone, benzothiazole and thiadiazole derivatives are mentioned.

Conclusion:

It should be mentioned that despite the progress in the development of new antimicrobial agents, there is still room for new findings. Thus, research still continues.