Vasodilatory actions of xanthones isolated from a Tibetan herb,Halenia elliptica

In this study, six major xanthones, isolated and identified from Halenia elliptica were investigated for their vasodilatory actions in isolated rat coronary artery. The xanthones, including 1-hydroxy-2,3,5-trimethoxy-xanthone (HM-1), 1-hydroxy-2,3,4,7-tetramethoxy-xanthone (HM-2), 1-hydroxy-2,3,4,5-tetramethoxy-xanthone (HM-3), 1,7-dihydroxy–2,3,4,5-tetramethoxy-xanthone (HM-4), 1,5-dihydroxy-2,3-dimethoxy-xanthone (HM-5) and 1,7-dihydroxy-2,3-dimethoxy-xanthone (HM-7) caused vasodilation in the coronary artery pre-contracted with 1 μM 5-hydroxytryptamine (5-HT), with EC₅₀ values ranging from 1.4±0.1 μM (HM-1) to 6.6±1.4 μM (HM-2). The EC₅₀ values of the other xanthones were between those of HM-1 and HM-2. Removal of endothelium of the coronary artery led to decreases in the vasorelaxant effects of HM-1, HM-7 but not HM-2, HM-3, HM-4 and HM-5. Our results showed that xanthones isolated from Halenia elliptica are vasoactive substances which exhibit either endothelium-dependent or endothelium-independent mechanisms in rat coronary artery. The potency and mechanism(s) of the vasorelaxant effects of these xanthones may be relevant to the structure–activity differences in the level and the position of the substituent groups with the primary xanthone structure.     

Heptaoxygenated xanthones as anti-austerity agents from Securidaca longepedunculata

In a course of our search for anticancer agent based on a novel anti-austerity strategy, we found that the CHCl₃ extract of the roots of Securidaca longepedunculata (Polygalaceae), collected at Democratic Republic of Congo, killed PANC-1 human pancreatic cancer cells preferentially in nutrient-deprived medium (NDM). Phytochemical investigation on the CHCl₃ extract led to the isolation of 28 compounds including five new polymethoxylated xanthones [1,6,8-trihydroxy-2,3,4,5-tetramethoxyxanthone (1), 1,6-dihydroxy-2,3,4,5,8-pentamethoxyxanthone (2), 8-hydroxy-1,4,5,6-tetramethoxy-2,3-methylenedioxyxanthone (3), 4,6,8-trihydroxy-1,2,3,5-tetramethoxyxanthone (4), 4,8-dihydroxy-1,2,3,5,6-pentamethoxyxanthone (5)] and a new benzyl benzoate [benzyl 3-hydroxy-2-methoxybenzoate (6)]. Among them, 1,6,8-trihydroxy-2,3,4,5-tetramethoxyxanthone (1) and 1,6-dihydroxy-2,3,4,5,8-pentamethoxyxanthone (2) displayed the potent preferential cytotoxicity with PC₅₀ of 22.8 and 17.4 μM, respectively. They triggered apoptosis-like PANC-1 cell death in NDM with a glucose-sensitive mode.     

Mechanisms of the vasorelaxant effect of 1, 5-dihydroxy-2, 3-dimethoxy-xanthone, an active metabolite of 1-hydroxy-2, 3, 5-trimethoxy-xanthone isolated from a Tibetan herb, Halenia elliptica, on rat coronary artery

1, 5-Dihydroxy-2, 3-dimethoxy-xanthone (HM-5) is one of the naturally-occurring xanthones of a Tibetan medicinal herb Halenia elliptica. Recently, it has been shown that HM-5 is one of the phase I metabolites of 1-hydroxy-2, 3, 5-trimethoxy-xanthone (HM-1), the major active component of H. elliptica with potent vasorelaxant actions. This study investigated the vasorelaxant effect of HM-5 and its mechanism(s). HM-5 (0.35-21.9 microM) produced a concentration-dependent relaxation in rat coronary artery rings pre-contracted with 1 microM 5-hydroxytryptamine (5-HT), with an EC(50) of 4.40+/-1.08 microM. Unlike HM-1, the effect of HM-5 was endothelial-independent such that removal of the endothelium did not affect its vasodilator potency. Nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME, 100 microM), the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ, 10 microM) did not affect the vasodilatory effects of HM-5, thus confirming the non-involvement of endothelium related mechanisms. In endothelium-denuded coronary artery rings, the vasorelaxant effect of HM-5 was inhibited by a potassium channel blocker, TEA (10 mM), and 4-aminopyridine (4-AP, a K(v) blocker; 1 mM) but not by other K+ channel blockers such as iberiotoxin (100 nM), barium chloride (100 microM) and glibenclamide (10 microM). The involvement of Ca2+ channel was studied in artery rings pre-incubated with Ca2+-free buffer (intact endothelium or endothelium-denuded) and primed with 1 microM 5-HT or 60 mM KCl prior to the addition of CaCl2 to elicit contraction. In the 5-HT-primed preparations, HM-5 (34.7 microM) significantly inhibited the CaCl(2)-induced vasoconstriction (89.9% inhibition in intact endothelium artery rings; 83.3% inhibition in endothelium-denuded rings). In the KCl-primed preparations, HM-5 (34.7 microM) produced a 34% inhibition in endothelium-denuded rings. The same concentration of HM-5 inhibited (by 62.3%) the contractile response to 10 microM phorbol 12, 13-diacetate (PDA), a protein kinase C activator, in Ca2+-free solutions. Taken together, this study showed that the mechanisms of the vasorelaxant effects of HM-5 were distinctly different from those of its parent drug HM-1. The vasorelaxant effect of HM-5 was mediated through opening of potassium channel (4-AP) and altering intracellular calcium by partial inhibition of Ca2+ influx through L-type voltage-operated Ca2+ channels and intracellular Ca2+ stores.     

Antihypertensive and vasorelaxant effects of dihydrospinochalcone-A isolated from Lonchocarpus xuul Lundell by NO production: Computational and ex vivo approaches

Current work was conducted to evaluate the vasorelaxant effect of dihydrospinochalcone-A (1) and isocordoin (2), compounds type chalcone isolated from Lonchocarpus xuul, an endemic tree of the Yucatan Peninsula, Mexico. Compounds 1 and 2 were found to induce significant relaxant effect in a concentration-dependent manner on aortic rat rings pre-contracted with noradrenaline (NA, 0.1 μM). Compound 1 was the most active and its effect was endothelium-dependent (Emax = 79.67% and EC₅₀ = 21.46 μM with endothelium and Emax = 23.58% and EC₅₀ = 91.8 μM without endothelium, respectively). The functional mechanism of action for 1 was elucidated. Pre-incubation with l-NAME (unspecific nitric oxide synthase inhibitor), indomethacin (unspecific COX inhibitor), ODQ (soluble guanylyl cyclase inhibitor), atropine (cholinergic receptor antagonist), TEA (unspecific potassium channel blocker) reduced relaxations induced by 1. Oral administration of 50 mg/kg of compound 1 exhibited significant decrease in diastolic and systolic blood pressure in SHR rats. The heart rate was not modified. Compound 1 was docked with a crystal structure of eNOS. Dihydrospinochalcone-A showed calculated affinity with eNOS in the C1 binding pockets, near the catalytic site; Trp449, Trp447 and His373 through aromatic and π–π interactions, also His463 and Arg367 are the residues that make hydrogen bonds with the carbonyl and hydroxyl groups.In conclusion, dihydrospinochalcone-A induces a significant antihypertensive effect due to its direct vasorelaxant action on rat aorta rings, through NO/sCG/PKG pathway and potassium channel opening.     

Xanthones from Frasera albomarginata and F. speciosa

Seven 1-hydroxyxanthones have been isolated from the roots of Frasera albomarginata. There were 1-hydroxy-3,7-dimethoxy-, 1-hydroxy-3,5-dimethoxy-, 1,8-dihydroxy-3,5-dimethoxy-, 1-hydroxy-2,3,4,7-tetramethoxy-, 1-hydroxy-2,3,4,5-tetramethoxy-, 1-hydroxy-3,4,7-trimethoxy- and 1-hydroxy-2,3,5-trimethoxyxanthone. Six 1-hydroxyxanthones were obtained from the roots of F. speciosa. These were 1-hydroxy-2,3,4,5-tetramethoxy-, 1-hydroxy-2,3,4,7-tetramethoxy-, 1-hydroxy-2,3,5-trimethoxy-, 1,7-dihydroxy-2,3,4-trimethoxy-, 1,7-dihydroxy-2,3-dimethoxy- and 1,3-dihydroxy-4,5-dimethoxyxanthone.     

Synthesis,vasorelaxant activity and antihypertensive effect of benzo[d]imidazole derivatives

A series of 1H-benzo[d]imidazole analogues of Pimobendan, substituted at position 5 with either –CF₃ or –NO₂, were synthesized using a short synthetic route. All the nitro derivatives were potent, and exhibited a concentration- and partial endothelium-dependent vasorelaxant effects, with EC₅₀s <5 μM. 2-Methoxy-4-[5-nitro-1H-benzo[d]imidazol-2-yl]phenol (compound 13) was the most potent derivative of the series, showing an EC₅₀ value of 1.81 μM and E_max of 91.7% for ex vivo relaxant response in intact aortic rings, resulting in a 2.5-fold higher activity compared to Pimobendan. The closely related 5-CF₃ analogue (compound 8), was 19 times less potent than 13. The antihypertensive activity of compound 13 was evaluated at doses of 25, 50 and 100 mg kg^?1, using spontaneously hypertensive rats (SHR), showing a statistically significant dose-dependent effect.     

1,5-Benzodiazepine inhibitors of HCV NS5B polymerase

Optimization through parallel synthesis of a novel series of hepatitis C virus (HCV) NS5B polymerase inhibitors led to the identification of (R)-11-(4-benzyloxy-2-fluorophenyl)-6-hydroxy-3,3-dimethyl-10-(6-methylpyridine-2-carbonyl)-2,3,4,5,10,11-hexahydro-dibenzo[b,e][1,4]diazepin-1-one 11zc and (R)-11-(4-benzyloxy-2-fluorophenyl)-6-hydroxy-3,3-dimethyl-10-(2,5-dimethyloxazol-4-carbonyl)-2,3,4,5,10,11-hexahydro-dibenzo[b,e][1,4]diazepin-1-one 11zk as potent (replicon EC₅₀ = 400 nM and 270 nM, respectively) and selective (CC₅₀ > 20 μM) inhibitors of HCV replication. These data warrant further lead-optimization efforts.     

Syntheses of cytotoxic novel arctigenin derivatives bearing halogen and alkyl groups on aromatic rings

The new lignano-9,9′-lactones (α,β-dibenzyl-γ-butyrolactone lignans), which showed the higher cytotoxicity than arctigenin, were synthesized. The well-known cytotoxic arctigenin showed activity against HL-60 cells (EC₅₀ = 12 μM), however, it was inactive against HeLa cells (EC₅₀ > 100 μM). The synthesized (3,4-dichloro, 2′-butoxy)-derivative 55 and (3,4-dichloro, 4′-butyl)-derivative 66 bearing the lignano-9,9′-lactone structures showed the EC₅₀ values of 10 μM and 9.4 μM against HL-60 cells, respectively. Against HeLa cells, the EC₅₀ value of the derivative 66 was 27 μM. By comparing the activities with the corresponding 9,9′-epoxy structure (tetrahydrofuran compounds), the importance of the lactone structure of 55 and 66 for the higher activities was shown. The substituents on the aromatic ring of the lignano-9,9′-lactones affected the cytotoxicity level, observing more than 10-fold difference.     

Endothelium-dependent vasorelaxant effects of the essential oil from aerial parts of Alpinia zerumbet and its main constituent 1,8-cineole in rats

Vasorelaxant effects of essential oil of Alpinia zerumbet (EOAZ) and its main constituent, 1,8-cineole (CIN) were studied. In rat isolated aorta preparations with intact endothelium, EOAZ (0.01–3000 μg/ml) induced significant but incomplete relaxation of the phenylephrine-induced contraction, an effect that was abolished by removal of vascular endothelium. However, at the same concentrations (0.01–3000 μg/ml corresponding to 0.0000647–19.5 mM), CIN induced a complete vasorelaxant effects (IC₅₀=663.2±63.8 μg/ml) that were significantly reduced in endothelium-denuded rings (IC₅₀=1620.6±35.7 μg/ml). Neither EOAZ nor CIN affected the basal tonus of isolated aorta. Vasorelaxant effects of both EOAZ and CIN remained unaffected by the addition of tetraethylamonium chloride (500 μM) or indomethacin (10 μM) into the bath, but were significantly reduced by N^G-nitro-L-arginine methyl ester (100 μM). It is concluded that EOAZ induces a potent vasorelaxant effect that could not be fully attributed to the actions of the main constituent CIN, and appears totally dependent on the integrity of a functional vascular endothelium. The data is novel and corroborate the popular use of A. zerumbet for the treatment of hypertension.     

Hit to Lead optimization of a novel class of squarate-containing polo-like kinases inhibitors

A high throughput screening (HTS) hit, 1 (Plk1 K_i = 2.2 μM) was optimized and evaluated for the enzymatic inhibition of Plk-1 kinase. Molecular modeling suggested the importance of adding a hydrophobic aromatic amine side chain in order to improve the potency by a classic kinase H-donor–acceptor binding mode. Extensive SAR studies led to the discovery of 49 (Plk1 K_i = 5 nM; EC₅₀ = 1.05 μM), which demonstrated moderate efficacy at 100 mpk in a MiaPaCa tumor model, with no overt toxicity.     

Cytotoxic tetraoxygenated xanthones from the bark of Garcinia schomburgkiana

Two new tetraoxygenated xanthones, 6-O-demethyloliverixanthone and schomburgxanthone, together with cowanin, cowanol, fuscaxanthones A and B, 3-isomangostin hydrate, and 1,7-dihydroxyxanthone, were isolated from the bark of Garcinia schomburgkiana. Their structures were elucidated using 1-D and 2-D NMR techniques as well as chemical methods. Five of the isolated compounds were tested regarding their cytotoxicity against HeLa cells and the results showed that fuscaxanthone B and cowanin possessed remarkable activity with IC₅₀ values of 2.4 ± 0.2 and 2.7 ± 0.3 μg/ml, respectively, using an MTT assay.     

Discovery and structure–activity relationships study of novel thieno[2,3-b]pyridine analogues as hepatitis C virus inhibitors

Current treatment for hepatitis C is barely satisfactory, there is an urgent need to develop novel agents for combating hepatitis C virus infection. This study discovered a new class of thieno[2,3-b]pyridine derivatives as HCV inhibitors. First, a hit compound characterized by a thienopyridine core was identified in a cell-based screening of our privileged small molecule library. And then, structure activity relationship study of the hit compound led to the discovery of several potent compounds without obvious cytotoxicity in vitro (12c, EC₅₀ = 3.3 μM, SI >30.3, 12b, EC₅₀ = 3.5 μM, SI >28.6, 10l, EC₅₀ = 3.9 μM, SI >25.6, 12o, EC₅₀ = 4.5 μM, SI >22.2, respectively). Although the mechanism of them had not been clearly elucidated, our preliminary optimization of this class of compounds had provided us a start point to develop new anti-HCV agents.     

Ipomopsin and hymenain,two biscoumarins from seeds of Hymenaea courbaril

A new biscoumarin (7-hydroxy-6,6′-dimethoxy-3,7′-dicoumarinyl ether), named hymenain (1) and the known biscoumarin ipomopsin (2) were isolated from the germinated seeds of Hymenaea courbaril var. stilbocarpa. Their structures were elucidated by spectroscopic methods. Scopoletin was also detected in the extracts by TLC and GC–MS analyses. Hymenain and ipomopsin showed direct scavenging effect on a stable free radical, 2,2-diphenyl-1-picryl-hydrazyl (DPPH) with the EC₅₀ values of 100 and 300 μM, respectively.     

Microbial transformation of the triterpene nigranoic acid in Trichoderma sp.

Two new metabolites were obtained by microbial transformation of the triterpene nigranoic acid (3,4-secocyloarta-4 (28), 24 (Z)-diene-3,26-dioic acid), (1) in the culture of Trichoderma sp. JY-1, a fungus obtained from the branches of Kadsura angustifolia. Their structures were established as 15α, 16α-dihydroxy-3,4-secocyloarta-4 (28), 17 (20), 17 (E), 24 (E)-triene-3,26-dioic acid (2) and 16α, 20α-dihydroxy-18 (13 → 17β) abeo-3,4-secocyloarta-4 (28), 12 (13), 24 (Z)-triene-3,26-dioic acid (3) by analysis of NMR and MS data and by analogy with the data for the substrate nigranoic acid (1). Compound 2 was found to possess an unusual 17(20), 17 (E)-ene structure while compound 3 featured an unprecedented 18(13 → 17β)-abeo-secocyloarta skeleton. Additionally, compounds 1–3 showed weak anti-HIV activity with EC₅₀ values of 10.5, 8.8 and 7.6 μg/mL, therapeutic index values (CC₅₀/EC₅₀) of 8.48, 9.12 and 10.1, respectively.     

Synthesis and biological evaluation of imidazole thioacetanilides as novel non-nucleoside HIV-1 reverse transcriptase inhibitors

A series of 2-(1-aryl-1H-imidazol-2-ylthio)acetamide [imidazole thioacetanilide (ITA)] derivatives were synthesized and evaluated as potent inhibitors of human immunodeficiency virus type-1 (HIV-1). Among them, the most potent HIV-1 inhibitors were 4a5 (EC₅₀ = 0.18 μM), and 4a2 (EC₅₀ = 0.20 μM), which were more effective than the lead compound L1 (EC₅₀ = 2.053 μM) and the reference drugs nevirapine and delavirdine. The preliminary structure–activity relationship (SAR) of the newly synthesized congeners is discussed.     

Comparing anti-HIV,antibacterial, antifungal,micellar, and cytotoxic properties of tricarboxylato dendritic amphiphiles

Three series of homologous dendritic amphiphiles—RCONHC(CH₂CH₂COOH)₃, 1(n); ROCONHC(CH₂CH₂COOH)₃, 2(n); RNHCONHC(CH₂CH₂COOH)₃, 3(n), where R = n-C_nH_2n+1 and n = 13–22 carbon atoms—were assayed for their potential to serve as antimicrobial components in a topical vaginal formulation. Comparing epithelial cytotoxicities to the ability of these homologues to inhibit HIV, Neisseria gonorrhoeae, and Candida albicans provided a measure of their prophylactic/therapeutic potential. Measurements of the ability to inhibit Lactobacillus plantarum, a beneficial bacterium in the vagina, and critical micelle concentrations (CMCs), an indicator of the potential detergency of these amphiphiles, provided additional assessments of safety. Several amphiphiles from each homologous series had modest anti-HIV activity (EC₅₀ = 110–130 μM). Amphiphile 2(18) had the best anti-Neisseria activity (MIC = 65 μM), while 1(19) and 1(21) had MICs against C. albicans of 16 and 7.7 μM, respectively. Two measures of safety showed promise as all compounds had relatively low cytotoxic activity (EC₅₀ = 210–940 μM) against epithelial cells and low activity against L. plantarum, 1(n), 2(n), and 3(n) had MICs ? 490, 1300, and 940 μM, respectively. CMCs measured in aqueous triethanolamine and in aqueous potassium hydroxide showed linear dependences on chain length. As expected, the longest chain in each series had the lowest CMC—in triethanolamine: 1(21), 1500 μM; 2(22), 320 μM; 3(22), 340 μM, and in potassium hydroxide: 1(21), 130 μM; 3(22), 40 μM. The CMC in triethanolamine adjusted to pH 7.4 was 400 μM for 1(21) and 3900 μM for 3(16). The promising antifungal activity, low activity against L. plantarum, relatively high CMCs, and modest epithelial cytotoxicity in addition to their anti-Neisseria properties warrant further design studies with dendritic amphiphiles to improve their safety indices to produce suitable candidates for antimicrobial vaginal products.     

Design,synthesis, antiviral and cytostatic activity of ω-(1H-1,2,3-triazol-1-yl)(polyhydroxy)alkylphosphonates as acyclic nucleotide analogues

The efficient synthesis of a new series of polyhydroxylated dibenzyl ω-(1H-1,2,3-triazol-1-yl)alkylphosphonates as acyclic nucleotide analogues is described starting from dibenzyl ω-azido(polyhydroxy)alkylphosphonates and selected alkynes under microwave irradiation. Selected O,O-dibenzylphosphonate acyclonucleotides were transformed into the respective phosphonic acids. All compounds were evaluated in vitro for activity against a broad variety of DNA and RNA viruses and for cytostatic activity against murine leukemia L1210, human T-lymphocyte CEM and human cervix carcinoma HeLa cells. Compound (1S,2S)-16b exhibited antiviral activity against Influenza A H3N2 subtype (EC₅₀ = 20 μM—visual CPE score; EC₅₀ = 18 μM—MTS method; MCC >100 μM, CC₅₀ >100 μM) in Madin Darby canine kidney cell cultures (MDCK), and (1S,2S)-16k was active against vesicular stomatitis virus and respiratory syncytial virus in HeLa cells (EC₅₀ = 9 and 12 μM, respectively). Moreover, compound (1R,2S)-16l showed activity against both herpes simplex viruses (HSV-1, HSV-2) in HEL cell cultures (EC₅₀ = 2.9 and 4 μM, respectively) and feline herpes virus in CRFK cells (EC₅₀ = 4 μM) but at the same time it exhibited cytotoxicity toward uninfected cell (MCC ⩾ 4 μM). Several other compounds have been found to inhibit proliferation of L1210, CEM as well as HeLa cells with IC₅₀ in the 4–50 μM range. Among them compounds (1S,2S)- and (1R,2S)-16l were the most active (IC₅₀ in the 4–7 μM range).     

The ameliorating effects of 2,3-dihydroxy-4-methoxyacetophenone on scopolamine-induced memory impairment in mice and its neuroprotective activity

We isolated 2,3-dihydroxy-4-methoxyacetophenone, a neuroprotective compound from Cynenchum paniculatum in our previous study.The present study was conducted to investigate the possible neuroprotective effect of 2,3-dihydroxy-4-methoxyacetophenone that has been previously isolated from Cynenchum paniculatum on hippocampal neuronal cell line, HT22 cells and its possible cognitive-enhancing effect on scopolamine-induced amnesia in mice.Neuroprotective effect against glutamate-induced neurotoxicity in HT22 cells was evaluated by MTT assay. Also, cognitive enhancing effect against scopolamine (1 mg/kg, ip) induced learning and memory deficit was measured by Morris water maze test. Oral administered of 2,3-dihydroxy-4-methoxyacetophenone (1, 10, 20, 40 and 50 mg/kg) to amnesic mice induced by scopolamine. In Morris water maze test, 2,3-dihydroxy-4-methoxyacetophenone (50 mg/kg) improved the impairment of spatial memory induced by scopolamine. 2,3-Dihydroxy-4-methoxyacetophenone protect HT22 cells on glutamate induced cell-death in a dose-dependent manner (EC₅₀ value: 10.94 μM). Furthermore, 2,3-dihydroxy-4-methoxyacetophenone was found to inhibit [Ca²⁺] accumulation in HT22 cells and had antioxidantive activity. The results showed that 2,3-dihydroxy-4-methoxyacetophenone exert neuroprotective and cognitive-enhancing activities through its antioxidant activity. We suggest that 2,3-dihydroxy-4-methoxyacetophenone improves cognitive function and may be helpful for the treatment of Alzheimer’s disease.