Pressurized Hot Water Extraction as a Viable Bioprospecting Tool: Isolation of Coumarin Natural Products from Previously Unexamined Correa (Rutaceae) Species

Gaafar AR, Gurusamy R, Akbar I. Synthesis of anthraquinone-connected coumarin derivatives via grindstone method and their evaluation of antibacterial, antioxidant, tyrosinase inhibitory activities with molecular docking, and DFT calculation studies

Anthraquinones and coumarins have excellent pharmacological activities and are an important class of natural plant metabolites with various biological activities. In this study, anthraquinone-9,10-dione and coumarin derivatives were combined to develop a novel anthraquinone-connected coumarin-derivative sequence. The synthesised novel anthraquinone-connected coumarin derivatives (1a-t) were screened for in vitro antibacterial, antioxidant, and tyrosinase inhibitory activities. The antibacterial activities of the synthesised compounds (1a-t) were tested against both gram-positive and gram-negative bacteria. Specifically, compound 1t was more active against E. aerogenes than ciprofloxacin. With regard to antioxidant activity, compound 1o (50.68 % at 100 μg/mL) was highly active compared to the other compounds, whereas it was less active than the standard BHT (76.74 % at 100 μg/mL). In terms of compound 1r (9.31 ± 0.45 μg/mL) was highly active against tyrosinase inhibitory activity compared with kojic acid (10.42 ± 0.98 μg/mL). In the molecular docking study, compound 1r had a higher docking score (-8.8 kcal mol-1) than kojic acid (-1.7 kcal mol-1). DFT calculations were performed to determine the energy gap of highly active compound 1r (ΔE = 0.11) and weakly active compound 1a (ΔE = 0.12). In this study, we found that every molecule displayed significant antibacterial, antioxidant, and tyrosinase inhibitory properties. Based on these reports, compounds 1r and 1t may act as multi-target agents.

Isolation and Biomimetic Oxidation of Prenylbruceol A, an Anticipated Meroterpenoid Natural Product from Philotheca myoporoides

Reinvestigation of the coumarin meroterpenoids of Philotheca myoporoides using pressurized hot water extraction (PHWE) procedures led to the isolation of prenylbruceol A, a proposed biosynthetic precursor of seven previously reported bruceol derivatives, prenylbruceols B-H. Protobruceol-I, ostruthin, dipetalactone, and a new dihydrocoumarin natural product were isolated alongside prenylbruceol A. A biomimetic singlet oxygen ene reaction of prenylbruceol A allowed the semisynthesis of prenylbruceols B, C, and D.

Pressurized Hot Water Extraction and Capillary Electrophoresis for Green and Fast Analysis of Useful Metabolites in Plants

The search for useful compounds from plants is an important research area. Traditional screening that involves isolation and identification/quantitation is tedious, time consuming, and generates a significant amount of chemical waste. Here, we present a simple, fast, and green strategy to assess ≥0.1% wt/wt quantities of useful compounds in plants/spices using pressurized hot water extraction using a household espresso machine followed by chemical analysis using capillary electrophoresis. Three demonstrations with polygodial, cinnamaldehyde, coumarin, and shikimic acid as target metabolites are shown. Direct analysis of extracts was by the developed micellar electrokinetic chromatography and capillary zone electrophoresis methods. The approach, which can be implemented in less developed countries, can process many samples within a day, much faster than traditional techniques that would normally take at least a day. Finally, 0.8–1.1% wt/wt levels of shikimic acid were found in Tasmanian-pepperberry and Tasmanian-fuschia leaves via the approach.

Phytochemical profile of the rare, ancient clone Lomatia tasmanica and comparison to other endemic Tasmanian species L. tinctoria and L. polymorpha

An investigation of the previously unexamined ancient Tasmanian clone Lomatia tasmanica W. M. Curtis (Proteaceae) and two other endemic species Lomatia tinctoria R. Br. and Lomatia polymorpha (Labill.) R. Br. was undertaken. This represents the first extensive natural products study in which individual phytochemical components have been isolated and identified from these three Lomatia species. Extraction of L. tasmanica leaves provided the naphthoquinone juglone (0.34% w/w), and n-alkanes nonacosane and heptacosane (0.30% w/w combined). L. polymorpha afforded the flavonoid glycosides dihydroquercetin 3-O-β-D-xyloside (0.22% w/w) and quercetin 3-O-β-d-glucose (0.14% w/w), as well as the naphthalene glucoside 1,4,8-trihydroxynaphthalene-1-O-β-d-glucose (0.04% w/w) and 4-O-p-coumaroyl-d-glucose (0.03% w/w). In addition, both L. polymorpha and L. tinctoria contained juglone (0.32% w/w and 0.58% w/w, respectively). L. polymorpha provided tetracosan-1-ol, hexacosan-1-ol and octacosan-1-ol (0.07% w/w combined), while L. tinctoria gave nonacosane (0.13% w/w). Analysis of three individual specimens from each of the three species demonstrated consistency in the respective phytochemical profiles of these populations and tentatively suggests limited intraspecific variation.

Arbutin Derivatives Isolated from Ancient Proteaceae: Potential Phytochemical Markers Present in Bellendena, Cenarrhenes, and Persoonia Genera

Extensive phytochemical studies of the paleoendemic Tasmanian Proteaceae species Bellendena montana, Cenarrhenes nitida, and Persoonia gunnii were conducted employing pressurized hot water extraction. As part of these studies, six novel glycosides were isolated, including rare examples of glycoside-containing natural products featuring tiglic acid esters. These polar molecules may represent potential phytochemical markers in ancient Proteaceae.

Extraction of isoflavones from Puerariae lobata using subcritical water

As an alternative to organic solvents, subcritical water was employed for the first time as an effective solvent for the extraction of isoflavones from Puerariae lobata. Optimum experimental conditions for the extraction of the four main isoflavones were established by single factor experiments, and the optimum experimental conditions for total isoflavone extraction were established further by response surface methodology. With an extraction time of 45 min and a liquid/solid ratio of 1 : 20, the extraction yields of puerarin, 3′-methoxypuerarin, and daidzin reached maxima at extraction temperatures of 120 °C, 140 °C and 200 °C, respectively. Moreover, puerarin, 3′-methoxypuerarin and daidzin were degraded and produced various byproducts due to hydrothermal reactions at higher temperatures. The maximum extraction yields of the total isoflavones were obtained by response surface methodology (extraction time of 45 min, solid/liquid ratio of 1 : 15 and extraction temperature of 120 °C). Compared to conventional solvents, subcritical water utilized less solvent and required a shorter extraction time.

Four main isoflavones from Puerariae lobata were successfully extracted using subcritical water. Maximum yields of total isoflavones by response surface methodology were obtained.

Extraction of carboxylic acid-containing diterpenoids from Dodonaea viscosa via pressurised hot water extraction

Pressurised hot water extraction (PHWE) was employed to effect the extraction of two carboxylic acid-containing ent-labdane diterpenoids from Dodonaea viscosa. The different extraction profile provided by PHWE in this case suggests that this recently developed method also has applications as a complementary tool for natural products extraction.