Phytochemistry and pharmacology of natural prenylated flavonoids

Prenylated flavonoids are a special kind of flavonoid derivative possessing one or more prenyl groups in the parent nucleus of the flavonoid. The presence of the prenyl side chain enriched the structural diversity of flavonoids and increased their bioactivity and bioavailability. Prenylated flavonoids show a wide range of biological activities, such as anti-cancer, anti-inflammatory, neuroprotective, anti-diabetic, anti-obesity, cardioprotective effects, and anti-osteoclastogenic activities. In recent years, many compounds with significant activity have been discovered with the continuous excavation of the medicinal value of prenylated flavonoids, and have attracted the extensive attention of pharmacologists. This review summarizes recent progress on research into natural active prenylated flavonoids to promote new discoveries of their medicinal value.

Isobavachalcone: A comprehensive review of its plant sources, pharmacokinetics, toxicity, pharmacological activities and related molecular mechanisms

Isobavachalcone (IBC), also known as isobapsoralcone, is a natural flavonoid widely derived from many medicinal plants, including Fabaceae, Moraceae, and so forth. IBC has been paid more and more attention by researchers in recent years due to its pharmacological activity in many diseases. This review aims to describe in detail the plant sources, pharmacokinetics, toxicity, pharmacological activities, and molecular mechanisms of IBC on various diseases. We found that IBC can be obtained not only by extraction but also by chemical synthesis. Pharmacokinetic studies have shown that IBC has low bioavailability, but can penetrate the blood-brain barrier and is widely distributed in the brain. Its pharmacological activities mainly include anticancer, antibacterial, anti-inflammatory, antiviral, neuroprotective, bone protection, and other activities. In particular, IBC shows strong anti-tumor and anti-inflammatory therapeutic potential due to its anti-cancer and anti-inflammatory activities. However, due to its hepatotoxicity, there may be more drug interactions. Therefore, more and more in-depth studies are needed for its clinical application. Mechanically, IBC can induce the production of reactive oxygen species (ROS), inhibit AKT, ERK, and Wnt pathways, and promote apoptosis of cancer cells through mitochondrial or endoplasmic reticulum pathways. IBC can inhibit the NF-κB pathway and the production of multiple inflammatory mediators by activating NRF2/HO-1 pathway, thus producing anti-inflammatory effects. Moreover, we discussed the limitations of current research on IBC and put forward some new perspectives and challenges, which provide a strong basis for clinical application and new drug development of IBC in the future.

The Antioxidant Activity of Prenylflavonoids

Prenylated flavonoids combine the flavonoid moiety and the lipophilic prenyl side-chain. A great number of derivatives belonging to the class of chalcones, flavones, flavanones, isoflavones and other complex structures possessing different prenylation patterns have been studied in the past two decades for their potential as antioxidant agents. In this review, current knowledge on the natural occurrence and structural characteristics of both natural and synthetic derivatives was compiled. An exhaustive survey on the methods used to evaluate the antioxidant potential of these prenylflavonoids and the main results obtained were also presented and discussed. Whenever possible, structure-activity relationships were explored.

Natural and Bioinspired Phenolic Compounds as Tyrosinase Inhibitors for the Treatment of Skin Hyperpigmentation: Recent Advances

One of the most common approaches for control of skin pigmentation involves the inhibition of tyrosinase, a copper-containing enzyme which catalyzes the key steps of melanogenesis. This review focuses on the tyrosinase inhibition properties of a series of natural and synthetic, bioinspired phenolic compounds that have appeared in the literature in the last five years. Both mushroom and human tyrosinase inhibitors have been considered. Among the first class, flavonoids, in particular chalcones, occupy a prominent role as natural inhibitors, followed by hydroxystilbenes (mainly resveratrol derivatives). A series of more complex phenolic compounds from a variety of sources, first of all belonging to the Moraceae family, have also been described as potent tyrosinase inhibitors. As to the synthetic compounds, hydroxycinnamic acids and chalcones again appear as the most exploited scaffolds. Several inhibition mechanisms have been reported for the described inhibitors, pointing to copper chelating and/or hydrophobic moieties as key structural requirements to achieve good inhibition properties. Emerging trends in the search for novel skin depigmenting agents, including the development of assays that could distinguish between inhibitors and potentially toxic substrates of the enzyme as well as of formulations aimed at improving the bioavailability and hence the effectiveness of well-known inhibitors, have also been addressed.

A New Bioactive Secondary Metabolite from Artocarpus elasticus

Detailed phytochemical investigation has been carried out on the bark of Artocarpus elasticus Reinw. ex Blume, which led to the isolation of artonin E (1), a new dihydrobenzoxanthone derivative named elastixanthone (2), cycloartobiloxanthone (3) and artobiloxanthone (4). Structures of these compounds were elucidated on the basis of various spectroscopic (UV, IR, 1D-NMR and 2D-NMR) and MS data. Compounds 1-3 displayed outstanding scavenging activity for 1,1-diphenylpicrylhydrazyl (DPPH) with IC50 values of 11.5, 21.6 and 40.0 μg/mL, respectively. In addition, compounds 1-3 displayed broad spectrum antimicrobial activities against thirteen different bacterial strains when tested using the disc diffusion assay. Cytotoxic screening revealed that artonin E (1) constantly exhibited strong cytotoxic activity against human estrogen receptor (ER+) positive breast cancer (MCF-7) and human estrogen receptor (ER-) negative (MDA-MB 231) cells in comparison with the other two, with IC50 values of 2.6 and 13.5 μg/mL, respectively, without being toxic towards the WRL68 (human normal liver) cell line (IC50 value more than 30 μg/mL). However, the compound was inactive against HepG2 (human liver carcinoma) cancer cells.