Letters in Organic Chemistry - Volume 21, Issue 1, 2024

Natural products have been created by nature and are derived from organisms such as plants or microorganisms. The natural compounds are isolated from natural sources in very small quantities, making it difficult for the form to achieve the compounds' good yields. The last is relevant for doing biological essays and chemical structure elucidation. Besides, they have diverse chemical structures, which have inspired organic chemists to do their organic synthesis. It is important to construct a strategy based on a well-designed retrosynthesis. The reproducibility of the selected methodology, the yields of the compounds of each step and stereoselectivity or diastereoselectivity of the reactions that are being used are the main key points to guarantee the success of a natural compound synthesis. Modern technologies can be the solution. In this review, we try to compile in the form of a critic perspective the most modern techniques that organic chemists are applying for the synthesis of complex natural compounds.

The addition of camphor and oxone^¦reg; during the epoxidation led to the synthesis of seven novel epoxides. Since the tri-substituted double bond of -cyano-cinnamates has been epoxidized, the reaction is easier to carry out and cleaner, producing a high yield of epoxides. Several molecules with industrial applications will result from the selective ring opening of epoxides.

In this study, a new fluorous aza-crown ether derivative (1) conjugated with two Bfp (bisfluorous chain type propionyl) groups was prepared; then, the partition ratios of 1 in biphasic systems using FC 72 and several organic solvents were investigated. Next, the activities of 1 in an FC 72/acetonitrile biphasic system were assessed via the SN2-type acetoxylation reaction using 2- (bromomethyl)naphthalene and potassium acetate. Finally, the recyclability of 1 in a two-layer system based on its immobilization in an FC 72 solvent was examined during acetoxylation reactions.

Essential oils are widely used in cosmetic and personal care products. These essential oils such as menthol, limonene, rose oil, and jasmine oil are extracted from plants and also prepared in the laboratory. Menthol is the most common cyclic monoterpene alcohol, which has been produced due to its demand in various industries worldwide. In the literature, there were many protocols reported for the synthesis of menthols from natural or synthetic precursors. In this review, we summarized the synthesis of menthol from citral, citronellal, and pulegone using various heterogeneous catalysts under different conditions. Considering the world's demand for menthol in food preservatives and scents, the right optimization of citronella extraction and its conversion is highly important. It can be used in pharmaceutical industries due to the presence of active substances. The presence of flavored compounds has the potential to enhance the nutritional value of food. This review will be very helpful for researchers who are working on menthol synthesis in industry and institutions. The determination of direct conversion to menthol over indirect conversion can be proven to be effective for industrial use as it will be more economical and time-saving.

Chalcones are important scaffolds in the field of medicinal chemistry due to the presence of α,β-unsaturated ketone functionality. They are usually synthesized by reacting an aldehyde with acetophenone in the presence of acid or base using the Claisen-Schmidt condensation reaction. Numerous chalcone derivatives have been developed due to the simplicity of their synthesis, and they have intriguing biological activity that has clinical implications for a range of disorders. The review article discusses the advancements made since 2005 for the synthesis of chalcones derivatives using environmentally friendly methods such as the use of green catalysts and solvents, ultrasonic radiation, microwave energy, and methodologies involving grinding in the absence of solvents.

Green' methodologies have become the main route for producing selenium nanoparticles (SeNPs), as they do not involve toxic substances that can increase the reactivity of the synthesized nanoparticles and are practical and inexpensive. Extracts from plants, bacteria, fungi, yeasts, ascorbic acid, and polysaccharides are used to produce these nanoparticles. Plant extracts contain phytochemicals that act as reducing and stabilizing agents, while bacteria, fungi, and yeasts can synthesize SeNPs from metabolites secreted during their development or via intracellular mechanisms. Ascorbic acid is also an excellent agent for reducing precursor metal salts, and polysaccharides act as stabilizing agents for the synthesized nanoparticles. The SeNPs synthesized by these routes have desirable characteristics for clinical applications since they are safe, non-toxic, and stable, with high biocompatibility and bioavailability. In addition, they have antimicrobial, anti-cancer, anti-diabetic, anti-mosquito, antioxidant, and anti-inflammatory activities, as revealed by both in vitro and in vivo studies.

The 1,2,5-oxadiazole framework has garnered a lot of interest among many nitrogen heterocycles because of its capacity to give off NO under physiological circumstances. Because of this, major efforts by chemical scientists have been made to create novel drug possibilities in medicinal, material, and agriculture science that include the NO-donor 1,2,5-oxadiazole N-oxide subunit coupled to a known drug or a possible pharmacophore by C-C/C-N links or by using a suitable spacer. In the last few years, 1,2,5-oxadiazole and its derivatives have been reported as good pharmacophores as carbonic anhydrase inhibitors, antibacterial, vasodilating agents, antimalarial, anticancer, etc. In the presented manuscript, we reviewed granted patents (last 10 years), different synthetic strategies (last 27 years) of 1,2,5- oxadiazoles and their N-oxide derivatives synthesis such as cycloaddition, dimerization, cyclodehydration, condensation, thermolysis, nitration, oxidation, ring-conversion, etc. These synthetic methods have also been analyzed for their merits and demerits. The manuscript also highlighted various applications of 1,2,5-oxadiazole and its derivatives. We hope that researchers across the scientific streams will benefit from the presented review articles for designing their work related to 1,2,5-oxadiazoles.

This research work presents the use of base-modified Tunisian Smectite as catalysts for the condensation of Knoevenagel. The prepared clay-catalysts were characterized via FTIR and XRD studies. A series of condensation reactions based on ultrasonic irradiation of various types of active methylene compounds and a variety of aryl aldehydes have shown the high efficacy of prepared catalysts. The stability and catalytic performance of the clay-catalysts were excellent since they could be reused four times without considerable loss in catalytic activity.

With multi-drug-resistant tumours continuously evolving, developing new drugs with enhanced efficacy is essential. This study aims to synthesise flavonoid Mannich bases and evaluate their cytotoxic activity. The flavonoids isolated from the leaves of Muntingia calabura were used as reactants for the synthesis. Twenty flavonoid Mannich bases were synthesised via the Mannich reaction. Cytotoxic activity of the parent compounds and synthesised compounds were evaluated against two breast cancer cell lines, i.e., MCF-7, MDA-MB-231, and one normal breast cell line, MCF-10A, via MTT assay. Cytotoxic activity against the MDA-MB-231 cancer cell line showed that flavonoid Mannich bases exhibited greater activity than their parent compounds. 5,7-dihydroxy-8-(4- methoxybenzylamine)-2-phenyl-4H-chromen-4-one (4f) showed the highest cytotoxic activity against MDA-MB-231 cell with IC50 of 5.75±0.82 μM. For the MCF-7 cell line, the parent compounds and Mannich bases showed moderate activity with the IC50 range of 9.17-68.5 μM. For cytotoxic activity against the MCF-10A cell line, the parent compound, 5,7-dihydroxyflavone (4), showed the highest toxicity against MCF-10A with IC50 of 10.55±1.05 μM. The results suggest synthetic modifications have produced compounds with improved anticancer activity and selectivity against breast cancer cells.

In this research, poly (4-vinyl pyridine)-supported nickel oxide nanoparticles (P4VP-NiO nanocatalyst) as an efficient recyclable catalyst have been prepared and used for the regioselective synthesis of triazole derivatives. The nanocatalyst we characterized by Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), thermogravimetric analysis (TGA), inductively coupled plasma (ICP), and brunauer-emmett-teller (BET) surface area analysis. The most important advantages of using poly (4-vinylpyridine)-nickel oxide nanocatalysts in these reactions are the short reaction time, cost-effectiveness, easy recycling of the catalyst, and high yield of the product. Also, the antimicrobial properties of the new triazole derivatives have been studied.

An improved synthesis of the monoterpene cyclic ketone karahanaenone, an ingredient in cosmetics, perfumery, and pest-control agents, is reported. The synthesis uses linalyl acetate as the starting material, which is converted to the epoxide with m-CPBA and submitted to an anhydrous lithium perchlorate catalyzed rearrangement to the corresponding ketone. Hydrolysis and thermolysis of the ketone afford karahanaenone in good yield. The catalyst can be recycled by simple dehydration and reused without affecting the yield for the rearrangement.