Cyclic peroxides and analogs: Antibacterial, antimalarial, and cytotoxic marine products from Xisha sponge Diacarnus sp.

A chemical investigation of the dichloromethane extract from the Xisha sponge Diacarnus sp. revealed seven undescribed norterpene cyclic peroxides, named diacarperoxides T-Z, and five unreported related norterpenes, named diacarnoids E-I, and eleven previously reported compounds. The structures of these isolated compounds, including their absolute configurations, were elucidated based on extensive spectroscopic analyses, electronic circular dichroism (ECD) calculations, Snatzke's method, [Rh2(OCOCF3)4]-induced ECD spectra, and modified Mosher's method. Bioassays were performed to assess the antibacterial activity against six pathogenic bacteria, cytotoxicities toward three cancer cell lines, and antimalarial activity against Plasmodium parasites. Most of the cyclic peroxides exhibited substantial antibacterial activity (MIC 1-8 µg/mL). Diacarperoxide W and nuapapuin A showed substantial antimalarial activity with IC50 values of 0.98 and 2.83 µM. Moreover, many compounds exhibited <50% cell survival rates, and IC50 values of 0.22-6.33 µM. The apoptosis assay showed that nuapapuin A induced cancer cell apoptosis in a dose-dependent manner.

Parameters of the Mouse Embryo Assay that affect detection of peroxides in mineral oil.

RESEARCH QUESTION: Can culture conditions influence the sensitivity of a Mouse Embryo Assay and its potential to detect peroxide-related toxicity in mineral oil samples? DESIGN: Protein type and concentration, embryo density and culture dish design were selected as the variables in the culture system with the potential to influence the assay's sensitivity. Fresh 1-cell mouse embryos were cultured under mineral oil samples with known peroxide concentrations. Protein type (human serum albumin [HSA] + α/ß-Globulins versus HSA versus bovine serum albumin [BSA]), concentration (5 mg/ml versus 0.5 mg/ml), embryo density (25 versus 3 µl/embryo) and culture dish (Petri versus micro-well dish) were adjusted to define the culture conditions with the highest sensitivity. RESULTS: High concentrations of peroxides can be easily detected by current quality control standards. However, for oil samples with a lower concentration of peroxides, supplementing the culture medium with 5 mg/ml of HSA + alpha/beta-globulins or with HSA resulted in an increased detection of embryo toxicity compared with when BSA was used as the protein supplement. The sensitivity of the assay was greatly reduced when embryos were cultured in groups and when certain micro-well dishes were used. CONCLUSIONS: Current quality control protocols may not be sensitive enough to identify low concentrations of peroxides, which, if undetected, can increase over time and become potentially harmful during gamete and embryo culture. The different parameters established in this study allow the sensitivity of the Mouse Embryo Assays to be optimized to specifically detect peroxides in mineral oil samples prior to their release into the market and their broad use in human IVF.

Identification of urate hydroperoxide in neutrophils: A novel pro-oxidant generated in inflammatory conditions.

Uric acid is the final product of purine metabolism in humans and is considered to be quantitatively the main antioxidant in plasma. In vitro studies showed that the oxidation of uric acid by peroxidases, in presence of superoxide, generates urate free radical and urate hydroperoxide. Urate hydroperoxide is a strong oxidant and might be a relevant intermediate in inflammatory conditions. However, the identification of urate hydroperoxide in cells and biological samples has been a challenge due to its high reactivity. By using mass spectrometry, we undoubtedly demonstrated the formation of urate hydroperoxide and its corresponding alcohol, hydroxyisourate during the respiratory burst in peripheral blood neutrophils and in human leukemic cells differentiated in neutrophils (dHL-60). The respiratory burst was induced by phorbol myristate acetate (PMA) and greatly increased oxygen consumption and superoxide production. Both oxygen consumption and superoxide production were further augmented by incubation with uric acid. Conversely, uric acid significantly decreased the levels of HOCl, probably because of the competition with chloride by the catalysis of myeloperoxidase. In spite of the decrease in HOCl, the overall oxidative status, measured by GSH/GSSG ratio, was augmented in the presence of uric acid. In summary, the present results support the formation of urate hydroperoxide, a novel oxidant in neutrophils oxidative burst. Urate hydroperoxide is a strong oxidant and alters the redox balance toward a pro-oxidative environment. The production of urate hydroperoxide in inflammatory conditions could explain, at least in part, the harmful effect associated to uric acid.

New Cembranoids and a Biscembranoid Peroxide from the Soft Coral Sarcophyton cherbonnieri.

Six new cembranoids, cherbonolides A-E (1⁻5) and bischerbolide peroxide (6), along with one known cembranoid, isosarcophine (7), were isolated from the Formosan soft coral Sarcophyton cherbonnieri. The structures of these compounds were elucidated by detailed spectroscopic analysis and chemical methods. Compound 6 was discovered to be the first example of a molecular skeleton formed from two cembranoids connected by a peroxide group. Compounds 1⁻7 were shown to have the ability of inhibiting the production of superoxide anions and elastase release in N-formyl-methionyl-leucyl-phenyl-alanine/cytochalasin B (fMLF/CB)-induced human neutrophils.

Peroxy steroids derived from plant and fungi and their biological activities.

Peroxides represent a large and interesting group of biologically active natural compounds. All these metabolites contain a peroxide group (R-O-O-R). This review describes studies of more than 60 peroxides isolated from plants and fungi. Most of the plant peroxy steroids exhibit high antiprotozoal (Plasmodium) activity with a confidence of up to 95%, while steroids harvested from fungi show more antineoplastic activity with a confidence of up to 94%. In addition, more than 20 different activities of both groups of peroxides with a probability of 78 to 90% have also been predicted using computer program PASS.

Plakortinic Acids A and B: Cytotoxic Cycloperoxides with a Bicyclo[4.2.0]octene Unit from Sponges of the Genera Plakortis and Xestospongia.

Plakortinic acids A (2) and B (3), two polyketide endoperoxides with a bicyclo[4.2.0]octene unit, were isolated as minor constituents from the sponge-sponge symbiotic association Plakortis halichondrioides-Xestospongia deweerdtae, along with known epiplakinic acid F (1). The structures of the mixture of two inseparable compounds were determined by spectroscopic analysis. Screening for cytotoxic activity of the mixture against two human tumor cell lines revealed that these compounds are very active at sub-micromolar concentration.

The First Casbane Hydroperoxides EBC-304 and EBC-320 from the Australian Rainforest.

Investigation of the Australian rainforest plant Croton insularis led to isolation of the first casbane hydroperoxide diterpenes EBC-304 and EBC-320. Extensive DFT and electronic circular dichroism (ECD) calculations in combination with 2D NMR spectroscopy determined the absolute configurations. EBC-304 and EBC-320 both display significant cytotoxicity.

A Norsesterterpene Peroxide from a Marine Sponge Hippospongia sp.

One new norsesterterpene peroxide, rhopaloic acid H (1), along with two known related metabolites 2 and 3, were isolated from a marine sponge Hippospongia sp. The structures of compounds were elucidated by means of IR, MS, and NMR techniques and comparison of the NMR data with those of known analogues. Evaluation of the cytotoxicities revealed that compound 2 exhibited significant cytotoxicity against DLD-1, Molt 4, T47D and K-562 cell lines, with IC50 values of 3.18, 0.69, 2.22 and 1.06 µg/mL, respectively. Moreover, compound 3 also showed significant K562 inhibitory activity, with IC50 value of 3.65 µg/mL.

Peroxide Natural Products from Plakortis zyggompha and the Sponge Association Plakortis halichondrioides-Xestospongia deweerdtae: Antifungal Activity against Cryptococcus gattii.

Cryptococcus gattii is a human pathogen and causative agent of a pernicious, sometimes fatal, disseminated fungal disease. Investigation of antifungal extracts of the marine sponge association Plakortis halichondrioides-Xestospongia deweerdtae and the sponge Plakortis zyggompha from the Bahamas led to the discovery and isolation of 6-epi-7,8-dihydroplakortide K (1), plakortide AA (2), and three new plakinic acids, N-P (4-6; unstable 1,2-dioxolanes bearing benzyl-substituted conjugated dienes), along with known plakinic acids L, K, and M.5 Chiroptical comparisons and DFT calculations of (13)C NMR chemical shifts were used to assign the absolute stereostructure of 4. The stereospecific base-promoted rearrangement-saponification of 1 to 10 was briefly investigated and showed tight kinetic control and stereospecific formation of the new C-2 stereocenter with inversion at C-3. Plakinic acid M and plakortides 9 and 11 exhibited antifungal activity against C. gattii (MIC90 = 2.4 to 36 µM), but plakinic acids N-P were inactive under the same conditions.

Cytotoxic sesquiterpenes from the endophytic fungus Pseudolagarobasidium acaciicola.

Twenty previously unknown compounds and two known metabolites, merulin A and merulin D, were isolated from the endophytic fungus Pseudolagarobasidium acaciicola, which was isolated from a mangrove tree, Bruguiera gymnorrhiza. Structures of the 20 compounds were elucidated by analysis of spectroscopic data. The absolute configuration of seven of these compounds was addressed by a single crystal X-ray analysis using CuKα radiation and an estimate of the Flack parameter. Three compounds also possessed a tricyclic ring system. Terpene endoperoxides isolated exhibited cytotoxic activity, while those without an endoperoxide moiety did not show activity. The endoperoxide moiety of sesquiterpenes has significant impact on cytotoxic activity, and thus is an important functionality for cytotoxicity. One terpene endoperoxide displayed potent cytotoxic activity (IC50 0.28µM), and selectively exhibited activity against the HL-60 cell line.

New Metabolites from the South China Sea Sponge Diacarnus megaspinorhabdosa.

Chemical investigation on CH2Cl2 extract of the marine sponge Diacarnus megaspinorhabdosa resulted in the isolation of two new farnesylacetone derivatives 1-2, a new γ-lactone 3, a known dinorditerpenone 4 and four known norsesterterpene peroxides 5-8. Their structures were elucidated by using one and two dimensional (1D and 2D)-NMR, high resolution-electrospray ionization (HR-ESI)-MS, and comparison with the literature. Compounds 1 and 2 were cis/trans-olefinic isomers and determined through nuclear Overhauser effect spectroscopy (NOESY) experiment. The absolute configuration of 3 was established by comparison of circular dichroism (CD) data with known lactones. The cytotoxic activities of the compounds were evaluated against five cancer cell lines, and compound 3 showed moderate cytotoxicity activities against cancer cell lines HeLa, H446, NCI-H460, SGC-7901 and MCF-7, with IC50 values in the range of 18.5 to 47.1 µM.

Supercritical CO2 extract and essential oil of aerial part of Ledum palustre L.--Chemical composition and anti-inflammatory activity.

The anti-inflammatory activity of two extracts from the aerial parts of Ledum palustre has been reported. The volatile oil was obtained by supercritical fluid extraction (SFE) and the essential oil by hydrodistillation (HD). The oils were analysed by gas chromatography-mass spectrometry to monitor their composition. Both extracts shared as main compound (41.0-43.4%) ledol (23.3-26.7%) and ascaridole (15.1-4.5%). The anti-inflammatory activity was evaluated by the subcutaneous carrageenan injection-induced hind paw oedema. The treated animals received essential oil (SFE and HD), the reference group received ketoprofen or piroxicam and the control group received NaCl 0.9%. A statistical analysis was performed by the Student t-test. The results show that L. palustre essential oil enhanced a significant inhibition of oedema (50-73%) for HD oil and (52-80%) for SFE oil. These results were similar to those obtained with piroxicam (70%) and ketoprofen (55%).

Antileishmanial activity of essential oil from Chenopodium ambrosioides and its main components against experimental cutaneous leishmaniasis in BALB/c mice.

UNLABELLED: Chenopodium ambrosioides have been used during centuries by native people to treat parasitic diseases. AIMS OF THE STUDY: To compare the in vivo anti-leishmanial activity of the essential oil (EO) from C. ambrosioides and its major components (ascaridole, carvacrol and caryophyllene oxide). MATERIALS AND METHODS: Anti-leishmanial effect was evaluated in BALB/c mice infected with Leishmania amazonensis and treated with the EO, main compounds and artificial mix of pure components by intralesional route at 30 mg/kg every 4 days during 14 days. Diseases progression and parasite burden in infected tissues were determined. RESULTS: EO prevented lesion development compared (p<0.05) with untreated animals and treated with vehicle. In addition, the efficacy of EO was also statistically superior (p<0.05) compared with the glucantime-treated animals. No potential effects were observed with pure components treatment. Mix of pure compounds cause death of animals after 3 days of treatment. CONCLUSIONS: Our results demonstrate the superiority of EO against experimental cutaneous leishmaniasis caused by L. amazonensis.

Prenylated indolediketopiperazine peroxides and related homologues from the marine sediment-derived fungus Penicillium brefeldianum SD-273.

Three new indolediketopiperazine peroxides, namely, 24-hydroxyverruculogen (1), 26-hydroxyverruculogen (2), and 13-O-prenyl-26-hydroxyverruculogen (3), along with four known homologues (4-7), were isolated and identified from the culture extract of the marine sediment-derived fungus Penicillium brefeldianum SD-273. Their structures were determined based on the extensive spectroscopic analysis and compound 1 was confirmed by X-ray crystallographic analysis. The absolute configuration of compounds 1-3 was determined using chiral HPLC analysis of their acidic hydrolysates. Each of the isolated compounds was evaluated for antibacterial and cytotoxic activity as well as brine shrimp (Artemia salina) lethality.

In vitro pharmacological and toxicological effects of norterpene peroxides isolated from the Red Sea sponge Diacarnus erythraeanus on normal and cancer cells.

Eight cyclic peroxide norterpenoids, compounds 1-8, have been isolated and characterized from the Red Sea sponge Diacarnus erythraeanus, including two new norsesterterpene derivatives (3, 4). Among these metabolites, (-)-muqubilin A (5) (nine cell lines analyzed) and the new compounds 3 and 4 (seven cell lines analyzed) displayed mean IC50 growth inhibitory concentrations in vitro of <10 µM, while the remaining compounds (1, 6-8) were inactive in these cancer cell lines. Compound 5 displayed no selectivity between normal and cancer cells in terms of in vitro growth inhibition. Quantitative video microscopy analysis carried out on (-)-muqubilin A-treated cells validated the data obtained by means of the MTT colorimetric assay, while flow cytometry analysis revealed ROS production but no induction of apoptosis in cancer cells.

Antiangiogenic effect of chamigrane endoperoxides from a Thai mangrove-derived fungus.

As part of our ongoing efforts to investigate natural products with potential for use as cancer treatments, we have recently disclosed the cytotoxicity of unique nor-chamigrane (1) and chamigrane (2, 3) endoperoxides from a Thai mangrove-derived fungus. Reinvestigation of this fungus in a large-scale fermentation led to the isolation of an additional new chamigrane endoperoxide (4) and one known analogue (5). Among these isolated metabolites, compound 3 (merulin C) exhibited potent antiangiogenic activity mainly by suppression of endothelial cell proliferation and migration in a dose-dependent manner, and its effect is mediated by reduction in the phosphorylation of Erk1/2. Merulin C also displayed promising activity in a rat aortic ring sprouting (ex vivo) and a mouse Matrigel (in vivo) assay.

Cytotoxic norsesquiterpene peroxides from the endophytic fungus Talaromyces flavus isolated from the mangrove plant Sonneratia apetala.

Four new norsesquiterpene peroxides, named talaperoxides A-D (1-4), as well as one known analogue, steperoxide B (5, or merulin A), have been isolated from a mangrove endophytic fungus, Talaromyces flavus. Their structures were elucidated mainly by 1D and 2D NMR. Structures of 1, 2, and 5 were further confirmed by single-crystal X-ray diffraction, and their absolute configurations were also determined using copper radiation. Cytotoxic activities of compounds 1-5 were evaluated in vitro against human cancer cell lines MCF-7, MDA-MB-435, HepG2, HeLa, and PC-3. Compounds 2 and 4 showed cytotoxicity against the five human cancer cell lines with IC50 values between 0.70 and 2.78 µg/mL.

Bioactive Cycloperoxides Isolated from the Puerto Rican Sponge Plakortis halichondrioides.

Two new five-membered-ring polyketide endoperoxides, epiplakinic acid F methyl ester (1) and epiplakinidioic acid (3), and a peroxide-lactone, plakortolide J (2), were isolated from the Puerto Rican sponge Plakortis halichondrioides, along with two previously reported cyclic peroxides, 4 and 5. The structures of the new metabolites were determined by spectroscopic and chemical analyses. The absolute stereostructures of 1, 2, and 5 were determined by degradation reactions followed by application of Kishi's method for the assignment of absolute configuration of alcohols. Biological screening of cycloperoxides 1-5 and semisynthetic analogues 7-12 for cytotoxic activity against various human tumor cell lines revealed that compounds 3, 4, and 11 are very active. Upon assaying for antimalarial and antitubercular activity, some of the compounds tested showed strong activity against the pathogenic microbes Plasmodium falciparum and Mycobacterium tuberculosis.

Norterpenoids and related peroxides from the formosan marine sponge Negombata corticata.

Six norterpenes including negombatoperoxides A and B (4 and 5), the inseparable epimers negombatoperoxides C and D (6 and 7), negombatodiol (8), and negombatolactone (9), in combination with three known compounds, (+)-nuapapuin B (1), (+)-nuapapuin B methyl ester (2), and (+)-aikupikoxide C (3), were isolated from the Formosan marine sponge Negombata corticata. In addition, 6,6-dimethylundecane-2,5,10-trione (10) was isolated for the first time from a natural source. Their structures, including relative configurations, were elucidated on the basis of interpretation of spectroscopic data and by the application of the empirical rule established by Capon and MacLeod. The absolute configurations of 8 and 9 were established by the application of Mosher's method and comparison of CD data with known lactones, respectively. Cytotoxicity of these isolates against human breast carcinoma, human liver carcinoma, and human lung carcinoma cell lines was evaluated.

Prenylated benzophenone peroxide derivatives from Hypericum sampsonii.

Two new prenylated benzophenone peroxide derivatives, peroxysampsones A and B (1 and 2, resp.), together with a known compound, plukenetione C (3), were isolated from the roots of the Chinese medicinal plant Hypericum sampsonii, and their structures were elucidated by detailed spectral analysis. These compounds are the unusual peroxides of polyprenylated benzophenone derivatives, containing the unique caged moiety of 4,5-dioxatetracyclo[9.3.1.1(9,13).0(1,7)]hexadecane-12,14,15-trione. In the biological test, peroxysampsone A (1) showed comparable activity with norfloxacin against a NorA over-expressing multidrug-resistant (MDR) strain of Staphylococcus aureus SA-1199B.