Privileged structures have been widely used as an effective template in medicinal chemistry for drug discovery. Chalcone is a common simple scaffold found in many naturally occurring compounds. Many chalcone derivatives have also been prepared due to their convenient synthesis. These natural products and synthetic compounds have shown numerous interesting biological activities with clinical potentials against various diseases. This review aims to highlight the recent evidence of chalcone as a privileged scaffold in medicinal chemistry. Multiple aspects of chalcone will be summarized herein, including the isolation of novel chalcone derivatives, the development of new synthetic methodologies, the evaluation of their biological properties, and the exploration of the mechanisms of action as well as target identification. This review is expected to be a comprehensive, authoritative, and critical review of the chalcone template to the chemistry community.

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Chalcone: A Privileged Structure in Medicinal Chemistry.

The borrowing hydrogen (BH) principle, also called hydrogen auto-transfer, is a powerful approach which combines transfer hydrogenation (avoiding the direct use of molecular hydrogen) with one or more intermediate reactions to synthesize more complex molecules without the need for tedious separation or isolation processes. The strategy which usually relies on three steps, (i) dehydrogenation, (ii) intermediate reaction, and (iii) hydrogenation, is an excellent and well-recognized process from the synthetic, economic, and environmental point of view. In this context, the objective of the present review is to give a global overview on the topic starting from those contributions published prior to the emergence of the BH concept to the most recent and current research under the term of BH catalysis. Two main subareas of the topic (homogeneous and heterogeneous catalysis) have been identified, from which three subheadings based on the source of the electrophile (alkanes, alcohols, and amines) have been consid...

/pdf/advances-in-one-pot-synthesis-through-borrowing-hydrogen-5955xy1911.pdf

Advances in One-Pot Synthesis through Borrowing Hydrogen Catalysis

In order for catalytic biomass pyrolysis to be economically sustainable, low cost and highly efficient catalysts are needed. In a previous work, Magnesium oxide (MgO) basic catalysts produced from natural magnesite (MgCO3) were found to be highly efficient alternatives to zeolitic catalysts which apart from their relatively high cost, they are easily deactivated due to biomass alkali deposition. In order to validate these findings in pilot scale, these natural MgO catalysts were investigated in a circulating fluidized bed pilot scale unit and were compared to a commercially available ZSM-5 catalyst. This is to the best of our knowledge the first attempt to evaluate a basic catalyst in biomass fast pyrolysis in a pilot unit employing commercially relevant process technology. The basic sites of the MgO catalysts enhanced ketonization and aldol condensation reactions, as it was verified by 2DGC-TOFMS analyses of the produced bio-oils. Deoxygenation was achieved mainly via formation of CO2, while H2O yield was substantially reduced in comparison to the ZSM-5 catalyst. As a result, bio-oils richer in hydrogen were obtained by the use of MgOs. However, the MgO catalysts led to a significant increase of the catalytically produced coke compared to ZSM-5. The effect of MgO properties, such as surface area and basicity on product yields and bio-oil composition was elaborated. In contrast to the acidic ZSM-5, no alkali metals were found to deposit on MgO, indicating different deactivation mechanisms between acidic and basic catalysts in biomass fast pyrolysis.

First pilot scale study of basic vs acidic catalysts in biomass pyrolysis: Deoxygenation mechanisms and catalyst deactivation

The synthesis of diesel or jet fuels intermediates from furfural or 5-hydroxymethylfurfural (HMF) via aqueous aldol-condensation with cyclopentanone was studied. Cyclopentanone is the product of furfural rearrangement in an aqueous system. Since the aldol-condensation reaction is conducted in an aqueous solution all these biomass-derived reactants can be applied as water solutions formed in the processes of their preparation. The aldol condensation of furfural with cyclopentanone is at low concentration of base and molar ratio of reactants 2:1 highly selective and after 40–80 min of reaction at a temperature of 40–100 °C more than 95 mol% yield of 2,5-bis (2-furylmethylidene) cyclopentan-1-one (F2C) was obtained. When instead of furfural as a reactant HMF was used higher than 98 mol% yield of 2,5-bis (5-hydroxymethyl-2-furylmethylidene) cyclopentan-1-one was achieved. The final products of aldol condensation of furfural and HMF are exclusively corresponding dimers, what enables to obtain after subsequent hydrogenation/hydrodeoxygenation step dialkylcyclopentane type of diesel or jet fuels having C15 or C17 molecules.

Cyclopentanone: A raw material for production of C15 and C17 fuel precursors

Two types of regioisomeric chromene-based chalcones namely, 1-(6-methoxy-2H-chromen-3-yl)-3-phenylpropen-1-ones and 3-(6-methoxy-2H-chromen-3-yl)-1-phenylpropen-1-ones were prepared and investigated for their antileishmanial activity against promastigotes form of Leishmania major. The obtained results from in vitro biological assays indicated that chloro-substituted 1-(6-methoxy-2H-chromen-3-yl)-3-phenylpropen-1-ones exhibited excellent activity against Leishmania major at non-cytotoxic concentrations.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1747-0285.2010.00959.x

Chromene-based synthetic chalcones as potent antileishmanial agents: synthesis and biological activity.

The aldol condensation takes its name from aldol (3-hydroxybutanal) a name introduced by Wurtz who first prepared the beta-hydroxy aldehyde from acetaldehdye in 1872. The aldol condensation includes reactions producing beta-hydroxy aldehydes or beta-hydroxy ketones by self condensations or mixed condensations of aldehydes and ketones as well as reactions leading to alpha, beta-unsaturated aldehydes or alpha,beta-unsaturated ketones formed by dehydration of intermediate beta-aldols or beta-ketals. The Claisen-Schmidt condensation is most often taken to be the condensation of an aromatic aldehyde or ketone usually in the presence of a basic catalyst. The term aldol condensation has also been applied to many other condensations involving the reaction of an aldehyde or ketone. These condenations are discussed. The present review includes examples that are solely condensation reactions of aldehydes and ketones.


Keywords:

aldol condensation;
catalysis;
condensation;
aldehydes;
ketones;
intramolecular condensations;
stereochemistry;
amines;
acids;
bases;
self-condensation;
mixed condensation;
acyclic ketones;
alicyclic ketones;
alkyl aryl ketones;
dialdehydes;
diketones;
keto aldehydes

William J. Houlihan

Papers

The Aldol Condensation