Chalcones are secondary metabolites belonging to the flavonoid (C 6 -C 3 -C 6 system) family that are ubiquitous in edible and medicinal plants, and they are bioprecursors of plant flavonoids. Chalcones and their natural derivatives are important intermediates of the flavonoid biosynthetic pathway. Plants containing chalcones have been used in traditional medicines since antiquity. Chalcones are basically α,β-unsaturated ketones that exert great diversity in pharmacological activities such as antioxidant, anticancer, antimicrobial, antiviral, antitubercular, antiplasmodial, antileishmanial, immunosuppressive, anti-inflammatory, and so on. This review provides an insight into the chemistry, biosynthesis, and occurrence of chalcones from natural sources, particularly dietary and medicinal plants. Furthermore, the pharmacological, pharmacokinetics, and toxicological aspects of naturally occurring chalcone derivatives are also discussed herein. In view of having tremendous pharmacological potential, chalcone scaffolds/chalcone derivatives and bioflavonoids after subtle chemical modification could serve as a reliable platform for natural products-based drug discovery toward promising drug lead molecules/drug candidates.

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Over the years, Friedel-Crafts (FC) reactions have been acknowledged as the most useful and powerful synthetic tools for the construction of a special kind of carbon-carbon bond involving an aromatic moiety. Its stoichiometric and, more recently, its catalytic procedures have extensively been studied. This reaction in recent years has frequently been used as a key step (steps) in the total synthesis of natural products and targeted complex bioactive molecules. In this review, we try to underscore the applications of intermolecular and intramolecular FC reactions in the total syntheses of natural products and complex molecules, exhibiting diverse biological properties.

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Gaps between molecular ages and fossils undermine the validity of time-calibrated molecular phylogenies. An example of the time gap surrounds the age of angiosperm's origin. We calculate molecular ages of the earliest flowering plant lineages using 22 fossil calibrations (101 genera, 40 families). Our results reveal the origin of angiosperms at the late Permian, ~275 million years ago. Different prior probability curves of molecular age calculations on dense calibration point distributions had little effect on overall age estimates compared to the effects of altered calibration points. The same is true for reasonable root age constraints. We conclude that our age estimates based on multiple datasets, priors, and calibration points are robust and the true ages are likely between our extremes. Our results, when integrated with the ecophysiological evolution of early angiosperms, imply that the ecology of the earliest angiosperms is critical to understand the pre-Cretaceous evolution of flowering plants.

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The fragmentations of hydroxylated flavanones, chalcones and dihydrochalcones were investigated by direct loop injection using an ion trap mass spectrometry equipped with atmospheric pressure chemical ionization (APCI) probe. Some of them have been isolated from the leaves of Piper hostmannianum var. berbicense and standards were used to confirm their fragmentation behaviour. In negative ion mode, fragmentations of these three types of flavonoids revealed specific diagnostic ions which allowed us to identify aglycones in a crude plant extract. The major fragment ion obtained in MS/MS experiment for methoxylated chalcones is the neutral loss of a methyl radical whereas a H(2)O molecule is lost in the case of methoxylated dihydrochalcones. Methoxylated chalcones and flavanones isomers could be differentiated by the relative intensity ratio of [M-H-CH(3)]*(-) and [M-H-C(2)H(2)O](-) ions. Based on UV and MS data, a decision tree that includes UV lambda(max) absorptions and MS/MS diagnostic ions was built in order to obtain structural information of unknown compounds present in the extract. This tree was used to identify flavonoids in the ethyl acetate extract of P. hostmannianum var. berbicense leaves after analysis by high-performance liquid chromatography-diode array detection-atmospheric pressure chemical ionization ion trap multistage mass spectrometry. A total of 11 flavonoids were tentatively characterized based on the MS fragmentations pattern observed in MS(n) experiments.

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The bioassay-guided purification of an n-hexane extract from the leaves of Piper hostmannianum var. berbicense led to the isolation of four monoterpene or prenyl-substituted dihydrochalcones (1a, 1b, 2, 3) as well as the known compounds 2',6'-dihydroxy-4'-methoxydihydrochalcone (4), linderatone (5), strobopinin (6), adunctin E (7) and (-)-methyllinderatin (8). Their structures were established on the basis of NMR and X-ray analysis. (-)-Methyllinderatin, linderatone and 2',6'-dihydroxy-4'-methoxydihydrochalcone exhibited the most potent antiplasmodial activity with IC50 values of 5.64, 10.33 and 12.69 microM, respectively against both chloroquine-sensitive and resistant strains of Plasmodium falciparum (F32,FcB1). The activity of (-)-methyllinderatin was confirmed in vivo against Plasmodium vinckei petteri in mice (80% of reduction of parasitemia) at a dose of 20 mg/kg/day.

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