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Organics, Volume 4, Issue 4 (December 2023) – 5 articles

Cover Story (view full-size image): This Review is an attempt to summarize the contributions of researchers dedicated to the development of benzimidazole-based UV filters. It aims to chronologically trace advances in the area, from the first commercial benzimidazole UVB filter, to PBSAs, to recently discovered UV photoprotective agents with multifunctional characteristics that provide a shielding effect against ultraviolet radiation, antioxidant activity, and thus skin cancer. The modifications made to the substitution pattern of the lead compound and the structure–activity relationships are discussed, as well as the synthetic approaches employed for the preparation of 2-substituted benzimidazoles. These comprehensive data will pave the way for future developments in modern benzimidazole-based sunscreens. View this paper
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23 pages, 7756 KiB  
Review
4-Hydroxy-2-pyrones: Synthesis, Natural Products, and Application
by Vladislav V. Fedin, Dmitrii L. Obydennov, Sergei A. Usachev and Vyacheslav Y. Sosnovskikh
Organics 2023, 4(4), 539-561; https://doi.org/10.3390/org4040037 - 15 Dec 2023
Viewed by 1609
Abstract
4-Hydroxy-2-pyrones are of interest as potential biorenewable molecules for a sustainable transition from biomass feedstock to valuable chemical products. This review focuses on the methodologies for the synthesis of 4-hydroxy-2-pyrones published over the last 20 years. These pyrones as polyketides are widespread in [...] Read more.
4-Hydroxy-2-pyrones are of interest as potential biorenewable molecules for a sustainable transition from biomass feedstock to valuable chemical products. This review focuses on the methodologies for the synthesis of 4-hydroxy-2-pyrones published over the last 20 years. These pyrones as polyketides are widespread in Nature and possess versatile bioactivity that makes them an attractive target for synthesis and modification. Biosynthetic paths of the pyrones are actively developed and used as biotechnological approaches for the construction of natural and unnatural polysubstituted 4-hydroxy-2-pyrones. The major synthetical methods are biomimetic and are based on the cyclization of tricarbonyl compounds. Novel chemical methods of de novo synthesis based on alkyne cyclizations using transition metal complexes and ketene transformations allow for straightforward access to 4-hydroxy-2-pyrones and have been applied for the construction of natural products. Possible directions for further pyrone ring modification are discussed. Full article
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15 pages, 3217 KiB  
Review
Synthesis of 2-Substituted Benzimidazole Derivatives as a Platform for the Development of UV Filters and Radical Scavengers in Sunscreens
by Kameliya K. Anichina and Nikolai I. Georgiev
Organics 2023, 4(4), 524-538; https://doi.org/10.3390/org4040036 - 28 Nov 2023
Viewed by 1067
Abstract
The modern trend in sunscreen products is towards the development of UV filters with multi-functional properties, to provide a broad shielding against ultraviolet radiation, antioxidant activity, and the prevention of skin cancer. Additionally, they should also be safe for humans as well as [...] Read more.
The modern trend in sunscreen products is towards the development of UV filters with multi-functional properties, to provide a broad shielding against ultraviolet radiation, antioxidant activity, and the prevention of skin cancer. Additionally, they should also be safe for humans as well as the environment. The benzimidazole heterocycle is a suitable platform for the development of such multifunctional molecules with potential application in cosmetic formulations, due to their ability to act as both UV protectors and reactive pharmacophores. This review presents for the first time the progress in the synthesis and optimization of benzimidazole compounds as UV sunscreen filters. The modifications to the substitution pattern of the lead compound and structure–activity relationships are discussed, as well as the synthetic approaches for the preparation of 2-substituted benzimidazoles. These aggregated data will be useful in future in the development of modern benzimidazole-based sunscreen. Full article
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21 pages, 4556 KiB  
Review
Synthesis of Antifungal Heterocycle-Containing Mannich Bases: A Comprehensive Review
by Diego Quiroga and Ericsson Coy-Barrera
Organics 2023, 4(4), 503-523; https://doi.org/10.3390/org4040035 - 09 Nov 2023
Viewed by 1198
Abstract
Mannich bases are a class of organic compounds usually obtained by the condensation reaction between an amine, a compound with active hydrogens, and an aldehyde. They are versatile intermediates in organic synthesis, and those compounds containing this motif find applications in pharmaceutical, agrochemical, [...] Read more.
Mannich bases are a class of organic compounds usually obtained by the condensation reaction between an amine, a compound with active hydrogens, and an aldehyde. They are versatile intermediates in organic synthesis, and those compounds containing this motif find applications in pharmaceutical, agrochemical, and even material fields since they are widely known for their wide range of biological activities, including antimicrobial properties. Thus, as part of our interest in antifungal agents, this narrative review aimed to gather information from the literature on the synthesis of various representative Mannich-base-containing compounds, particularly centered on those exhibiting antifungal properties. In this context, the compilation indicated that Mannich bases could be considered as a relevant toxophore/pharmacophore by incorporating heterocyclic moieties to be implemented for the design of new antifungal agents, given its proven efficacy against phytopathogens, other opportunistic human pathogens, and some dermatophytic fungal species, which can be further exploited as agrochemical agents or in medicinal applications to treat fungal infections. The antifungal effect exhibited by Mannich bases conjugated with oxa and/or aza-heterocycles suggests that compounds that have a heterocyclic system attached to the β-amino core are attractive alternatives oriented to the synthesis of novel and helpful antifungal agents. Full article
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13 pages, 2363 KiB  
Article
Absorption Spectra of Protonated Corroles: Two Distinct Patterns Due to Peripheral Substitution Architecture
by Lev L. Gladkov, Dmitry V. Klenitsky and Mikalai M. Kruk
Organics 2023, 4(4), 490-502; https://doi.org/10.3390/org4040034 - 09 Oct 2023
Viewed by 933
Abstract
The origin of individual features in the ground state absorption spectra of two protonated corroles differing in the architecture of peripheral substitution (either Cm-aryl or Cb-alkyl) have been studied in detail with the ground state absorption spectroscopy and density [...] Read more.
The origin of individual features in the ground state absorption spectra of two protonated corroles differing in the architecture of peripheral substitution (either Cm-aryl or Cb-alkyl) have been studied in detail with the ground state absorption spectroscopy and density functional theory calculations. The geometry optimization, molecular orbitals and absorption spectra calculation have been carried out. It was found that protonation leads to the saddle type macrocycle conformation in contrast with the wave type conformation known for the parent-free base corroles. The mean plane deviation parameter Δ23 for the macrocycle, pyrrole tilting angles and the degree of pyramidalization λ2 of all four pyrrole nitrogens was found to depend on the peripheral substitution architecture. Macrocycle conformation of the protonated forms has distinct asymmetrical features which are reflected by the sets of values of the tilting angles and values of pyramidalization degree. The pair of pyrroles B and C has smaller tilting angles and higher pyramidalization degree values, whereas the opposite trend was found for the pair of pyrroles A and D. Electronic effects and structural differences induced by substitution lead to the pronounced shifts of the molecular orbitals. In the Cb-alkylated corrole, almost-degenerated HOMO and HOMO-1 molecular orbitals lead to enhancement of the configuration interaction. As a result, the Qx transition oscillator strength goes down, becoming comparable to that of the Qy one. A large HOMO-HUMO-1gap in the Cm-aryl corrole minimizes the configuration interaction, giving rise to Qx band domination in the visible range spectrum. Full article
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31 pages, 13206 KiB  
Review
Recent Advances in Application of Alkoxy Radical in Organic Synthesis
by Munsaf Ali, Shi Sewell, Juncheng Li and Ting Wang
Organics 2023, 4(4), 459-489; https://doi.org/10.3390/org4040033 - 28 Sep 2023
Viewed by 1563
Abstract
Alkoxy radicals have been identified as versatile intermediates in synthetic chemistry in the last few decades. Over the last decade, various catalytic processes for the in situ generation of alkoxy radicals have been explored, leading to the development of new synthetic methodologies based [...] Read more.
Alkoxy radicals have been identified as versatile intermediates in synthetic chemistry in the last few decades. Over the last decade, various catalytic processes for the in situ generation of alkoxy radicals have been explored, leading to the development of new synthetic methodologies based on alkoxy radicals. In this review, we provided a comprehensive review of recent developments in the utilization of alkoxy radicals in diverse organic transformations, natural product synthesis, and the late-stage modification of bioactive molecules through the implementation of the photoredox methodology. Full article
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Scheme 1

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