Hyung Jae Jeong

Neuraminidase inhibitory activities of flavonols isolated from Rhodiola rosea roots and their in vitro anti-influenza viral activities

Five flavonols (3, 5, and 9-11) were isolated from Rhodiola rosea, and compared with commercially available flavonoids (1, 2, 4, 6-8, and 12-14) to facilitate analysis of their structure-activity relationship (SAR). All compounds (1-14) showed neuraminidase inhibitory activities with IC(50) values ranging from 0.8 to 56.9 microM. The in vitro anti-influenza virus activities of flavonoids 1-6, 8-12, and 14 were evaluated using two influenza viral strains, H1N1 (A/PR/8/34) and H9N2 (A/Chicken/Korea/MS96/96), testing their ability to reduce virus-induced cytopathic effect (CPE) in MDCK cells. We found that the activity of these compounds ranged from 30.2 to 99.1 microM against H1N1- and 18.5 to 133.6 microM against H9N2-induced CPE. Of compounds 1-14, gossypetin (6) exhibited the most potent inhibitory activity, with IC(50) values of 0.8 and 2.6 microM on neuraminidases from Clostridium perfringens and recombinant influenza virus A (rvH1N1), respectively. In contrast, kaempferol (3) exhibited the highest activity against two influenza viruses, H1N1 and H9N2 with EC(50) values of 30.2 and 18.5 microM, respectively. Activity depended on the position and number of hydroxy groups on the flavonoids backbone. In kinetic studies, all isolated compounds behaved as noncompetitive inhibitors.

In vitro anti-rotavirus activity of polyphenol compounds isolated from the roots of Glycyrrhiza uralensis

We evaluated the ability of six polyphenols isolated from the roots of Glycyrrhiza uralensis to inactivate rotaviruses, specially G5P[7] and G8P[7]. Upon finding that all polyphenols possessed anti-rotavirus activity, we evaluated whether these properties were attributable to direct inhibition of the binding of rotavirus to cells and/or to inhibition of viral replication. Using the virucidal assay, we found that all six compounds directly inhibited rotavirus binding, with activity being dependent on the type of virus. The 50% effective inhibitory concentrations (EC(50)) of the six compounds were 18.7-69.5 μM against G5P[7] and 14.7-88.1 μM against G8P[7], respectively. Five of the six compounds inhibited hemagglutination activity. Moreover, the CPE inhibition assay showed that five compounds inhibited viral replication with EC(50) values of 12.1-24.0 μM against G5P[7] and 12.0-42.0 μM against G8P[7], respectively. RT-PCR showed that the compounds suppressed viral RNA synthesis in TF-104 cells. Interestingly, the anti-rotavirus activities of four compounds were attributable to inhibition of both viral absorption and viral replication. These results suggest that compounds isolated from the roots of G. uralensis may be potent anti-rotavirus agents in vivo, acting by inhibiting both viral absorption and viral replication.

Biosynthesis of antibiotic prodiginines in the marine bacterium Hahella chejuensis KCTC 2396

Aims:  Hahella chejuensis KCTC 2396 produces red pigments, showing antibacterial and algicidal activities. The main red‐coloured metabolite of the pigments was identified as antibiotic prodigiosin. With the expectation that the red pigments are a mixture of a series of close relatives, the aim of the present study is to detect new antibiotic prodigiosin analogues and to analyse the biosynthetic pattern for prodiginines in KCTC 2396.

Characteristic of alkylated chalcones from Angelica keiskei on influenza virus neuraminidase inhibition

As part of our ongoing effort to develop influenza virus neuraminidase (NA) inhibitors from various medicinal plants, we utilized bioassay-guided fractionation to isolated six alkylated chalcones (1-6) from Angelica keiskei. Xanthokeistal A (1) emerged as new compound containing the rare alkyl substitution, 6,6-dimethoxy-3-methylhex-2-enyl. When we tested the ability of these individual alkyl substituted chalcones to inhibit influenza virus NA hydrolysis, we found that 2-hydroxy-3-methyl-3-butenyl alkyl (HMB) substituted chalcone (3, IC(50)=12.3 μM) showed most potent inhibitory activity. The order of potency of substituted alkyl groups on for NA inhibition was HMB>6-hydroxyl-3,7-dimethyl-octa-2,7-dienyl>dimethylallyl>geranyl. All NA inhibitors screened were found to be reversible noncompetitive inhibitors.

Biflavonoids from Torreya nucifera displaying SARS-CoV 3CLpro inhibition

Abstract As part of our search for botanical sources of SARS-CoV 3CLpro inhibitors, we selected Torreya nucifera, which is traditionally used as a medicinal plant in Asia. The ethanol extract of T. nucifera leaves exhibited good SARS-CoV 3CLpro inhibitory activity (62% at 100μg/mL). Following bioactivity-guided fractionation, eight diterpenoids (1–8) and four biflavonoids (9–12) were isolated and evaluated for SARS-CoV 3CLpro inhibition using fluorescence resonance energy transfer analysis. Of these compounds, the biflavone amentoflavone (9) (IC50 =8.3μM) showed most potent 3CLpro inhibitory effect. Three additional authentic flavones (apigenin, luteolin and quercetin) were tested to establish the basic structure–activity relationship of biflavones. Apigenin, luteolin, and quercetin inhibited 3CLpro activity with IC50 values of 280.8, 20.2, and 23.8μM, respectively. Values of binding energy obtained in a molecular docking study supported the results of enzymatic assays. More potent activity appeared to be associated with the presence of an apigenin moiety at position C-3′ of flavones, as biflavone had an effect on 3CLpro inhibitory activity.

Selective and slow-binding inhibition of shikonin derivatives isolated from Lithospermum erythrorhizon on glycosyl hydrolase 33 and 34 sialidases

Sialidases are enzymes that catalyze the hydrolysis of sialic acid residues from various glycoconjugates, which are widely found in a number of viral and microbial pathogens. In this study, we investigated the biological evaluation of isolated six shikonins (1-6) and three shikonofurans (7-9) from Lithospermum erythrorhizon. The nine isolated compounds 1-9 showed strong and selective inhibition of glycosyl hydrolase (GH) 33 and -34 sialidases activities. In GH33 bacterial-sialidase inhibition assay, the inhibitory activities against GH33 siadliase of all shikonofuran derivatives (7-9) were greater than shikonin derivatives (1-6). Shikonofuran E (8) exhibited the most potent inhibitory activity toward GH33 sialidases (IC(50)=0.24μM). Moreover, our detailed kinetic analysis of these species unveiled that they are all competitive and simple reversible slow-binding inhibitors. Otherwise, they showed different inhibitory capacities and kinetic modes to GH34 viral-sialidase activity. All the naphthoquinone derivatives (1-6) were of almost equal efficiency with IC(50) value of 40μM and shikonofurans (7-9) did not show the significant inhibitory effect to GH34 sialidase. Kinetic analyses indicated that naphthoquinones acted via a noncompetitive mechanism.

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.

Dieckol, a SARS-CoV 3CLpro inhibitor, isolated from the edible brown algae Ecklonia cava

Graphical abstract Phlorotannins have been isolated and are the first of their type showing competitively inhibitory activity toward SARS-CoV 3CLpro. Dieckol showed the most potent SARS-CoV 3CLpro trans/cis-cleavage inhibitory effects with high association rate.

Tanshinones as selective and slow-binding inhibitors for SARS-CoV cysteine proteases

Abstract In the search for anti-SARS-CoV, tanshinones derived from Salvia miltiorrhiza were found to be specific and selective inhibitors for the SARS-CoV 3CLpro and PLpro, viral cysteine proteases. A literature search for studies involving the seven isolated tanshinone hits showed that at present, none have been identified as coronaviral protease inhibitors. We have identified that all of the isolated tanshinones are good inhibitors of both cysteine proteases. However, their activity was slightly affected by subtle changes in structure and targeting enzymes. All isolated compounds (1–7) act as time dependent inhibitors of PLpro, but no improved inhibition was observed following preincubation with the 3CLpro. In a detail kinetic mechanism study, all of the tanshinones except rosmariquinone (7) were identified as noncompetitive enzyme isomerization inhibitors. However, rosmariquinone (7) showed a different kinetic mechanism through mixed-type simple reversible slow-binding inhibition. Furthermore, tanshinone I (5) exhibited the most potent nanomolar level inhibitory activity toward deubiquitinating (IC50 =0.7μM). Additionally, the inhibition is selective because these compounds do not exert significant inhibitory effects against other proteases including chymotrysin, papain, and HIV protease. These findings provide potential inhibitors for SARS-CoV viral infection and replication.

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.