Novel rearranged acetophenone derivatives possessing diverse architectures from the leaves of Melicope ptelefolia

Natural-derived acetophenones: chemistry and pharmacological activities

Acetophenones are naturally occurring phenolic compounds which have found in over 24 plant families and also fungi strains. They are exist in both free or glycosides form in nature. The biological activities of these compounds have been assayed and reported including cytotoxicity, antimicrobial, antimalarial, antioxidant and antityrosinase activities. Herein, we review the chemistry and biological activity of natural acetophenone derivatives that have been isolated and identified until January 2024. Taken together, it was reported 252 acetophenone derivatives in which the genera Melicope (69) and Acronychia (44) were the principal species as producers of acetophenones.

A Review of the Ethnomedicinal, Phytochemical, and Anticancer Properties of Melicope Species

The genus Melicope, which consists of 230 species, stands out as the largest genus within the Rutaceae family. Melicope species are characterized by their evergreen nature and can range from shrubs to predominantly dioecious trees. The Melicope species have been utilized in traditional medicine to address a wide range of ailments, including fever, colds, cramps, and inflammation. These plants have gained significant attention due to their noteworthy ethnopharmacological and ethnomedicinal significance. Researchers have isolated numerous biologically active secondary metabolites from different Melicope species, which include polymethoxylated flavonoids, furanocoumarins, acetophenones, benzenoids, and quinolone alkaloids. These compounds exhibit diverse biological activities, such as antibacterial, antidiabetic, antifungal, and antiproliferative properties against human cancer cell lines. This review provides an update on the chemical constituents of the selected species of Melicope. The study also highlights the anticancer and cytotoxicity properties of the plant extracts and phytochemical constituents from Melicope species. Furthermore, the molecular mechanisms underlying the anticancer effects are elucidated. Overall, this review contributes to understanding the significant pharmacological potential of Melicope species and unlocking their chemical composition, emphasizing their relevance in the development of therapeutic agents, particularly in the field of cancer research.

Molecular networking-based discovery of anti-inflammatory chromene dimers from Melicope pteleifolia

With the aid of a feature-based molecular networking strategy, five undescribed C₂ and C₁ symmetric chromene dimers, namely, melptelchromenes A-E, were isolated from the leaves of Melicope pteleifolia. Four asymmetric dimers were found to be racemates and were resolved by chiral phase HPLC analyses. Their structures, including absolute configurations, were elucidated by HRMS, NMR spectroscopy, and quantum mechanical calculations of ECD spectra and NMR chemical shifts. Melptelchromenes A-D possess a unique ethylidene linkage via two 2H-chromene cores, while melptelchromene E represents the first example of a dimeric chromene featuring a 1,3-diarylbutan-1-ol moiety. Of these compounds, 6,6'-linked dimeric chromenes showed nitric oxide inhibitory activities on lipopolysaccharide-induced RAW 264 cells, and (-)- and (+)-melptelchromene E were the two most potent compounds (IC₅₀, 3.0 and 5.1 μM, respectively).

The complete chloroplast genome of Melicope pteleifolia (Champ. ex Benth.) T. G. Hartley (Rutaceae)

Melicope pteleifolia, an important medicinal and horticultural plant, has antipyretic, anti-inflammatory, and analgesic effects. Here, the complete chloroplast genome of M. pteleifolia was sequenced and its phylogenetic relationship was investigated. The complete chloroplast genome of M. pteleifolia was 159,014 bp in size, including a pair of inverted repeat regions (IR, 27,640 bp), a large single copy region (LSC, 85,124 bp), and a small single copy region (SSC, 18,610 bp). The GC content of the chloroplast genome was 38.3%. A total of 133 genes were annotated, including 88 protein-coding genes, 8 rRNA genes, and 37 tRNA genes. Phylogenetic analysis revealed that M. pteleifolia clusters together with species of Toddalia, Zanthoxylum, Tetradium, Phellodendron, and Casimiroa.

New Acetophenones and Chromenes from the Leaves of Melicope barbigera A. Gray

The dichloromethane extract from leaves of Melicope barbigera (Rutaceae), endemic to the Hawaiian island of Kaua'i, yielded four new and three previously known acetophenones and 2H-chromenes, all found for the first time in M. barbigera. The structures of the new compounds obtained from the dichloromethane extract after purification by chromatographic methods were unambiguously elucidated by spectroscopic analyses including 1D/2D NMR spectroscopy and HRESIMS. The absolute configuration was determined by modified Mosher's method. Compounds 2, 4 and the mixture of 6 and 7 exhibited moderate cytotoxic activities against the human ovarian cancer cell line A2780 with IC₅₀ values of 30.0 and 75.7 µM for 2 and 4, respectively, in a nuclear shrinkage cytotoxicity assay.

Total Syntheses of (±)-Melicolones A and B

The first total syntheses of (±)-melicolones A and B, which have a unique and densely functionalized framework derived from a rearranged prenylated acetophenone, were accomplished in 12.3% combined overall yield. The concise and divergent synthesis of these two natural products, which were isolated in racemic form, was achieved in a longest linear sequence requiring only 9 steps (11 total steps) and 8 isolated intermediates using commercially available starting materials. This approach, which might enable access to all tetracyclic melicolones, features the highly regioselective (16:1) and diastereoselective (15:1) dipolar cycloaddition of a carbonyl ylide generated by the unusual cyclization of a rhodium carbene with the carbonyl oxygen atom of an aliphatic aldehyde. This cycloaddition proceeds with dominant steric control to give a highly functionalized oxabicycloheptane core. Stereoselective enolate alkylation led to a prenylated intermediate that underwent an intramolecular aldol reaction to give the penultimate tricyclic intermediate. Tandem epoxidation of the pendant prenyl group followed by a regioselective, acid-catalyzed cyclization delivered (±)-melicolones A and B.

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