A new anthraquinone glycoside from Rhamnus nakaharai and anti-tyrosinase effect of 6-methoxysorigenin

Plant anthraquinones: Classification, distribution, biosynthesis, and regulation

Anthraquinones are polycyclic compounds with an unsaturated diketone structure (quinoid moiety). As important secondary metabolites of plants, anthraquinones play an important role in the response of many biological processes and environmental factors. Anthraquinones are common in the human diet and have a variety of biological activities including anticancer, antibacterial, and antioxidant activities that reduce disease risk. The biological activity of anthraquinones depends on the substitution pattern of their hydroxyl groups on the anthraquinone ring structure. However, there is still a lack of systematic summary on the distribution, classification, and biosynthesis of plant anthraquinones. Therefore, this paper systematically reviews the research progress of the distribution, classification, biosynthesis, and regulation of plant anthraquinones. Additionally, we discuss future opportunities in anthraquinone research, including biotechnology, therapeutic products, and dietary anthraquinones.

A review of alpha-glucosidase inhibitors from plants as potential candidates for the treatment of type-2 diabetes

Diabetes mellitus is a multifactorial global health disorder that is rising at an alarming rate. Cardiovascular diseases, kidney damage and neuropathy are the main cause of high mortality rates among individuals with diabetes. One effective therapeutic approach for controlling hyperglycemia associated with type-2 diabetes is to target alpha-amylase and alpha-glucosidase, enzymes that catalyzes starch hydrolysis in the intestine. At present, approved inhibitors for these enzymes are restricted to acarbose, miglitol and voglibose. Although these inhibitors retard glucose absorption, undesirable gastrointestinal side effects impede their application. Therefore, research efforts continue to seek novel inhibitors with improved efficacy and minimal side effects. Natural products of plant origin have been a valuable source of therapeutic agents with lesser toxicity and side effects. The anti-diabetic potential through alpha-glucosidase inhibition of plant-derived molecules are summarized in this review. Eight molecules (Taxumariene F, Akebonoic acid, Morusin, Rhaponticin, Procyanidin A2, Alaternin, Mulberrofuran K and Psoralidin) were selected as promising drug candidates and their pharmacokinetic properties and toxicity were discussed where available.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11101-021-09773-1.

Assessment of Rhamnus alaternus Leaves Extract: Phytochemical Characterization and Antimelanoma Activity

Rhamnus alaternus (Rhamnaceae) has been used as a laxative, purgative, diuretic, antihypertensive, and depurative. However, few scientific research studies on its antimelanoma activity have been reported. This study aimed to investigate the in vitro antimelanoma effect of an enriched total oligomer flavonoid (TOF) extract, from R. alaternus, and to identify its phytochemical compounds. The chemical composition of TOF extract was assessed by HPLC-electrospray ionization tandem mass spectrometry (HPLC/ESI-MS²) analysis. Antimelanoma activity was determined on cultured tumor cell B16F10 by the crystal violet assay, the alkaline comet assay, acridine orange/ethidium bromide (AO/EB), annexin V-fluorescein isothiocyanate/ propidium iodide (V-FITC/PI) staining, the cell cycle distribution, and the wound healing assay. Regarding chemical composition, a mixture of quercetin diglucoside, quercetin-3-O-neohesperidoside, kaempferol-3-O-(2G-α-L-rhamnosyl)-rutinoside, rhamnetin hexoside, kaempferol-3-O-rutinoside, rhamnocitrin hexoside, pilosin hexoside, apigenin glucoside, and kaempferol-3-O-glucoside was identified as major phytochemical compounds of the extracts. TOF extract inhibits melanoma B16F10 cell proliferation in dose-dependent manner. The induction of apoptosis was confirmed by comet assay, AO/EB, and annexin V-FITC/PI test. TOF extract could also induce S phase cell cycle, inhibit, and delay the cell migration of B16F10 cells. The findings showed that TOF extract from R. alaternus could be a potentially good candidate for future use in alternative antimelanoma treatments.

Rhamnusalaternus Plant: Extraction of Bioactive Fractions and Evaluation of Their Pharmacological and Phytochemical Properties

Rhamnus alaternus, is a wild-growing shrub, belonging to the Rhamnaceae family. Widely distributed in the Mediterranean basin, R. alaternus is used in the usual medicine in numerous countries, mostly Tunisia, Algeria, Morocco, Spain, France, Italy, and Croatia. A large number of disorders-including dermatological complications, diabetes, hepatitis, and goiter problems-can be treated by the various parts of R. alaternus (i.e., roots, bark, berries, and leaves). Several bioactive compounds were isolated from R. alaternus, including flavonoids, anthocyanins, and anthraquinones, and showed several effects such as antioxidant, antihyperlipidemic, antigenotoxic, antimutagenic, antimicrobial, and antiproliferative. This review summarizes the updated information concerning the botanical description, distribution, extraction processes applied on R. alaternus, and its ethnopharmacology, toxicity, phytochemistry, and pharmacological effects.

Three new ester glycosides with cytotoxic activity from the seeds of Caesalpinia sappan

Three new ester glycosides, named as Caesateroside A (1), Caesateroside B (2) and Caesateroside C (3) were obtained from the seeds of Caesalpinia sappan. The new structures of compounds 1-3 were elucidated by analyzing their 1 D NMR, 2 D NMR and HR-ESI-MS spectra. Compounds 1-3 showed weak-moderate cytotoxicity against Hela and HepG-2 human cancer cell lines.

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.

Isolation and identification of new anthraquinones from Rhamnus alaternus L and evaluation of their free radical scavenging activity

From the butanolic and the ethyl acetate extracts of Rhamnus alaternus L root bark and leaves, three new anthraquinone glycosides, alaternosides A-C (1,4,6,8 tetrahydroxy-3 methyl anthraquinone 1-O-ß-D-glucopyranosyl-4,6-di-O-α-L-rhamnopyranoside (1); 1,2,6,8 tetrahydroxy-3 methyl anthraquinone 8-O-ß-D-glucopyranoside (2) and 1, 6 dihydroxy-3 methyl 6 [2'-Me (heptoxy)] anthraquinone (3)) were isolated and elucidated together with the two known anthraquinone glycosides, Physcion-8-O-rutinoside (4) and emodin-6-O-α-L-rhamnoside (5) as well as with the known kaempferol-7-methylether (6), β-sitosterol (7) and β-sitosterol-3-O-glycoside (8). Their chemical structures were elucidated using spectroscopic methods (1D-, 2D-NMR and FAB-MS). Free radical scavenging activity of the isolated compounds was evaluated by their ability to scavenge DPPH^. free radicals. Compounds (3), (4) and (6) showed the highest activity with IC₅₀ values of 9.46, 27.68 and 2.35 μg/mL, respectively.

A new cadinane sesquiterpenoid glucoside with cytotoxicity from Abelmoschus sagittifolius

A new cadinane sesquiterpenoid glucoside, 2β,7,3-trihydroxycalamenene 3-O-β-d-glucoside (1) together with six known compounds, N-(p-trans-coumaroyl)-N-methyl tyramine (2), Cleomiscosin A (3), 9,12,13-trihydroxy-10,15-heptadecadienoic acid (4), Cytochalasin B (5), Marmesinin (6) and N-(p-trans-coumaroyl) tyramine (7) were obtained from the stem bark of Abelmoschus sagittifolius. The new structure of compound 1 was elucidated by analysing its ¹H and ¹³C-NMR, ¹H-¹H COSY, HSQC, HMBC, NOESY and HR-ESI-MS spectra. Compounds 1-7 showed moderate cytotoxicity against Hela and HepG-2 human cancer cell lines.

An optimized protocol for anthraquinones isolation from Rhamnus frangula L

Different from works described in the literature, which use expansive analytical methods to separation of anthraquinones derivatives (AQs), this communication reported a simple and inexpensive methodology to get them. In this way, the expensive commercial AQs: Chrysophanol, physcione and emodine were extracted from plant material (Rhamnus frangula L.) and isolated by classical column chromatography technique under optimised binary mobile phase gradients (CHCl₃ : AcOEt(a), a = 1 to 5%) in excellent yields.

Screening of Peruvian Medicinal Plants for Tyrosinase Inhibitory Properties: Identification of Tyrosinase Inhibitors in Hypericum laricifolium Juss

Tyrosinase inhibitors are of far-ranging importance in cosmetics, medicinal products, and food industries. Peru is a diverse country with a wide variety of plants that may contain excellent anti-tyrosinase inhibitors. In the present study, the tyrosinase inhibitory properties of 50 medicinal plant extracts from Peru were investigated using tyrosinase assay. Among plant extracts, those that showed an inhibition rate >50% were Hypericum laricifolium Juss., Taraxacum officinale F.H.Wigg., and Muehlenbeckia vulcanica Meisn., with H. laricifolium Juss. showing the greatest anti-tyrosinase activity. Although H. laricifolium Juss. has been widely used as a medicinal plant by Peruvians, little is known regarding its bioactive components and effects on tyrosinase activity. For this reason, we attempted to discover tyrosinase inhibitors in H. laricifolium Juss. for the first time. The bioactive components were separated by Sephadex LH-20 chromatography and eluted with 100% methanol. Eight compounds were discovered and characterized by high-performance liquid chromatography coupled with diode array detection (HPLC-DAD): protocatechuic acid, p-hydroxybenzoic acid, chlorogenic acid, vanilic acid, caffeic acid, kaempferol 3-O-glucuronide, quercetin, and kaempferol. In addition, the concentration of these compounds required for 50% inhibition (IC₅₀) of tyrosinase activity were evaluated. Quercetin exhibited the strongest tyrosinase inhibition (IC₅₀ 14.29 ± 0.3 μM). Therefore, the Peruvian plant H. laricifolium Juss. could be a novel source for anti-tyrosinase activity.