Woo Song Lee

Tyrosinase inhibitory polyphenols from roots of Morus lhou.

Twelve polyphenols (1-12) possessing tyrosinase inhibitory properties were isolated from the methanol (95%) extract of Morus lhou. The isolated compounds consisted of four flavanones (1-4), four flavones (5-8), and four phenylbenzofuranes (9-12). Moracin derivative 12 proved to be new a compound which was fully characterized. Compounds 1-12 were evaluated for both monophenolase and diphenolase (the two steps catalyzed by tyrosinase) inhibition to identify the structural characteristics required for mushroom tyrosinase inhibition. We observed that all parent compounds (1, 5, and 9) possessing an unsubstituted resorcinol group were highly effective inhibitors of monophenolase activity (IC(50) values of 1.3, 1.2, and 7.4 microM). The potency of the inhibitors diminished with alkyl substitution on either the aromatic ring or the hydroxyl functions. Interestingly, flavone 5 was shown to possess only monophenolase inhibitory activity, but flavanone 1 and phenylbenzofuran 9 inhibited diphenolase as well as monophenolase significantly. The inhibitory mode of these species was also dependent upon the skeleton: phenylbenzofuran 9 manifested a simple competitive inhibition mode for monophenolase and diphenolase; on the other hand flavanone 1 (monophenolase, k(3) = 0.1966 min(-1) microM(-1), k(4) = 0.0082 min(-1), and K(i)(app) = 0.0468 microM; diphenolase, k(3) = 0.0014 min(-1) microM(-1), k(4) = 0.0013 min(-1), and K(i)(app) = 0.8996 microM) and flavone 5 both showed time-dependent inhibition against monophenolase. Compound 1 operated according to the simple reversible slow binding model whereas compound 5 operated under the enzyme isomerization model.

Polyphenols from Broussonetia papyrifera Displaying Potent α-Glucosidase Inhibition

The organic extract of the roots of Broussonetia papyrifera showed extremely high alpha-glucosidase inhibitory activity with an IC50 of around 10 microg/mL. Due to its potency, subsequent bioactivity-guided fractionation of the chloroform extract led to 12 polyphenols, 1-12, 4 of which were identified as chalcones (1-4), another 4 as flavans (5-8), 2 as flavonols (9 and 10), and 2 others as the novel species benzofluorenones (11 and 12). Broussofluorenone A (11) and broussofluorenone B (12) emerged as new compounds possessing the very rare 5,11-dioxabenzo[b]fluoren-10-one skeleton. These compounds (1-12) were evaluated for alpha-glucosidase inhibitory activity to identify their inhibitory potencies and kinetic behavior. The most potent inhibitor, 10 (IC50=2.1 microM, Ki=2.3 microM), has an inhibitory activity slightly higher than that of the potent alpha-glucosidase inhibitor deoxynojirimycin (IC50=3.5 microM). The novel alpha-glucosidase inhibitors 11 (IC50=27.6 microM) and 12 (IC50=33.3 microM) are similar in activity to sugar-derived alpha-glucosidase inhibitors such as voglibose (IC50=23.4 microM). Interestingly, major constituents (1, 2, 6, 7, 9, and 10) of B. papyrifera displayed significant inhibitory activity with IC50 values of 5.3, 11.1, 12.0, 26.3, 3.6, and 2.1 microM, respectively. In kinetic studies, chalcones (1-4) exhibited noncompetitive inhibition characteristics, whereas the others (5-12) showed mixed behavior.

Xanthones with neuraminidase inhibitory activity from the seedcases of Garcinia mangostana.

This study was designed to gain deeper insights into the molecular properties of natural xanthones as neuraminidase inhibitors. A series of xanthones 1-12 was isolated from the seedcases of Garcinia mangostana and evaluated for bacteria neuraminidase inhibitory activity. Compounds 11 and 12 emerged to be new xanthones (mangostenone F, mangostenone G) which we fully spectroscopically characterized. The IC(50) values of compounds 1-12 were determined to range between 0.27-65.7 microM. The most potent neuraminidase inhibitor 10 which has an IC(50) of 270 nM features a 5,8-diol moiety on the B ring. Interestingly, structure-activity studies reveal that these xanthones show different kinetic inhibition mechanisms depending upon the arrangement of hydroxyl groups in the B ring. Compound 6 possessing a 6,7-diol motif on the B-ring operated under the enzyme isomerization model (k(5)=0.1144 microM(-1) s(-1), k(6)=0.001105 s(-1), and K(i)(app)=7.41 microM), whereas compound 10 possessing a 5,8-diol unit displayed simple reversible slow-binding inhibition (k(3)=0.02294 microM(-1) s(-1), k(4)=0.001025 s(-1), and K(i)(app)=0.04468 microM).

Inhibition and structural reliability of prenylated flavones from the stem bark of Morus lhou on β-secretase (BACE-1).

The action of β-secretase is strongly tied to the onset of Alzheimers disease. The development of inhibitors of β-secretase is thus critical to combating this disease, which threatens an ever increasing number of the population and grows in importance as the population ages. Herein we show that flavones from Morus lhou potently inhibit β-secretase. Our aim in this manuscript is to explore the inhibitory kinetics of natural compounds and develop a phamacophore model which details the critical features responsible for inhibitory activity. The IC(50) values of compounds for β-secretase inhibition were determined to range between 3.4 and 146.1 μM. Prenylated flavone 2 (IC(50)=3.4 μM) was 20 times more effective than its parent compound, noratocarpetin 1 (IC(50)=60.6 μM). The stronger activity was related with resorcinol moiety on B-ring and isoprenyl functionality at C-3. Kinetic analysis shows that the four effective compounds (1-4) have a noncompetitive mode of action. The binding affinity of flavones for β-secretase calculated using in silico docking experiments correlated well with their IC(50) values and noncompetitive inhibition modes.

Structural characteristics of flavanones and flavones from Cudrania tricuspidata for neuraminidase inhibition.

The structural characteristics of flavonoids (1-3 and 6-8) from the root of Cudrania tricuspidata required for neuraminidase inhibition were studied and compared with commercially available flavonoids (4, 5, and 9-12). Alkylated flavanones (1-3) display better inhibition than the corresponding parent compound 4. Importantly, flavanone 1 bearing a C-8 hydrated prenyl group showed extremely high inhibition with IC(50) of 380 nM. On the other hand, the parent flavone 5 was more effective than alkylated analogues (6-8). Isolated inhibitors (1-3 and 6-8) showed noncompetitive inhibition in kinetic studies. The binding affinity of flavanones (1-4) for neuraminidase in in silico docking experiments correlated well with their IC(50) values and noncompetitive inhibition mode.

Influenza Virus Neuraminidase Inhibitory Activity of Phlorotannins from the Edible Brown Alga Ecklonia cava

Influenza A virus infections continue to pose a major threat to humans and several animal species. Neuraminidase (NA) is one of the most promising targets for the development of drugs against influenza viruses because of its critical role in the viral life cycle. During the course of a search for NA inhibitors from edible natural sources, we found that the ethyl acetate layer of ethanol extracts of Ecklonia cava showed extremely high NA-inhibitory activity (72.1% inhibition at 30 μg/mL). Bioactivity-guided fractionation of the ethyl acetate layer yielded five phlorotannins, identified as phloroglucinol (1), eckol (2), 7-phloroeckol (3), phlorofucofuroeckol (4), and dieckol (5). The inhibitory activities of these compounds (1-5) against NAs from group-1 (A/Bervig_Mission/1/18 [H1N1], A/PR/8/34 [H1N1]) and group-2 (A/Hong Kong/8/68 [H3N2], A/Chicken/Korea/MS96/96 [H9N2]) influenza A were evaluated to determine potencies and kinetic behavior. Analyses using various in vitro influenza A virus NA assays showed that all five phlorotannin derivatives were selective NA inhibitors. Of the phlorotannins, phlorofucofuroeckol (4) exhibited the most potent inhibitory activities toward group-1 NAs (IC₅₀ values, 4.5 and 14.7 μM), whereas dieckol (5) potently inhibited group-2 NAs. Kinetic analyses indicated that compounds 1-5 were all noncompetitive. Notably, these noncompetitive inhibitors synergized with oseltamivir to enhance the NA-inhibitory effects of oseltamivir.

Syntheses and reactions of the diethyl α-alkynylmalonates involving the generation of conjugated allenyl esters as the latent active species: A new approach to the development of cysteine proteinase inhibitors

Abstract Various diethyl α-alkynylmalonates (DAM) having potential as cysteine proteinase inhibitors were synthesized by treatment of diethyl acetyliminomalonate (or ketomalonate) with several lithium acetylides. Hydrolytic decarboxylation of the DAM under the mild basic conditions afforded oxazole derivatives or allenyl esters which caused the Michael type reaction with EtSH.

New intramolecular spiro-endo-mode ring closure of allenyl (methoxy-substituted phenyl)alkyl ketones

Abstract Allenyl ketones bearing a (mono-, di-, or tri-methoxy-substituted phenyl)alkyl group were submitted to a new intramolecular geminal spiro-endo-mode cyclization reaction using BF 3 ·OEt 2 , ZnI 2 , and AlCl 3 to give the corresponding bicyclic spiro compounds.

Novel heterocyclic ring-expansion and/or dehydration-hydration reactions of propargylic and allenylic hydroxy γ-lactams in the presence of strong base or Lewis acid

Abstract Dehydration-hydration products were obtained in good yields by the treatment of propargylic hydroxy γ-lactams with some Lewis acids. Several propargylic and allenylic hydroxy γ-lactams were successfully converted to the corresponding ring-expanded benzazepines in various yields via a tandem decyclization-cyclization process in the presence of (TMS)2NLi, (TMS)2NNa, or n-BuLi under reflux conditions in THF.

Mass production of rubusoside using a novel stevioside-specific β-glucosidase from Aspergillus aculeatus.

Rubusoside (R) is a natural sweetener and a solubilizing agent with antiangiogenic and antiallergic properties. However, currently, its production is quite expensive, and therefore, we have investigated nine commercially available glycosidases to optimize an economically viable R-production method. A stevioside (ST)-specific β-glucosidase (SSGase) was selected and purified 7-fold from Aspergillus aculeatus Viscozyme L by a two-step column chromatography procedure. The 79 kDa protein was stable from pH 3.0 to pH 7.0 at 50-60 °C. Hydrolysis of ST by SSGase produced R and steviol monoglucosyl ester as determined by (1)H and (13)C nuclear magnetic resonance (NMR). Importantly, SSGase showed higher activity toward ST than other β-linked glucobioses. The optimal conditions for R production were 280 mM ST and 16.6 μL of SSGase at pH 5.1 and 63 °C. This is the first discussion detailing the production of R by enzymatic hydrolysis of ST and is useful for the food additive and pharmaceutical industries.