Accraspiroketides A-B, Phenylnaphthacenoid-Derived Polyketides with Unprecedented [6 + 6+6 + 6] + [5 + 5] Spiro-Architecture.

Two novel polyketides, accraspiroketides A (1) and B (2), which feature unprecedented [6 + 6+6 + 6] + [5 + 5] spiro chemical architectures, were isolated from Streptomyces sp. MA37 ΔaccJ mutant strain. Compounds 1-2 exhibit excellent activity against Gram-positive bacteria (MIC = 1.5-6.3 µg/mL). Notably, 1 and 2 have superior activity against clinically isolated Enterococcus faecium K60-39 (MIC = 4.0 µg/mL and 4.7 µg/mL, respectively) than ampicillin (MIC = 25 µg/mL).

Algal-Derived Halogenated Sesquiterpenes from Laurencia dendroidea as Lead Compounds in Schistosomiasis Environmental Control.

Schistosomiasis has been controlled for more than 40 years with a single drug, praziquantel, and only one molluscicide, niclosamide, raising concern of the possibility of the emergence of resistant strains. However, the molecular targets for both agents are thus far unknown. Consequently, the search for lead compounds from natural sources has been encouraged due to their diverse structure and function. Our search for natural compounds with potential use in schistosomiasis control led to the identification of an algal species, Laurencia dendroidea, whose extracts demonstrated significant activity toward both Schistosoma mansoni parasites and their intermediate host snails Biomphalaria glabrata. In the present study, three seaweed-derived halogenated sesquiterpenes, (-)-elatol, rogiolol, and obtusol are proposed as potential lead compounds for the development of anthelminthic drugs for the treatment of and pesticides for the environmental control of schistosomiasis. The three compounds were screened for their antischistosomal and molluscicidal activities. The screening revealed that rogiolol exhibits significant activity toward the survival of adult worms, and that all three compounds showed activity against S. mansoni cercariae and B. glabrata embryos. Biomonitored fractioning of L. dendroidea extracts indicated elatol as the most active compound toward cercariae larvae and snail embryos.

Natural spirocyclic alkaloids and polyphenols as multi target dementia leads.

The U rhynchophylla, U tomentosa, Isatis indigotica Fortune, Voacanga Africana, herbal constituents, fungal extracts from Aspergillus duricaulis culture media, include spirooxindoles, polyphenols or bridged spirocyclic alkaloids. Their constituents exhibit specific and synergistic multiple neuroprotective properties including inhibiting of Aß fibril induced cytotoxicity, NMDA receptor inhibition in mice models of Alzheimer's disease (AD). The pioneering research from Woodward to Waldmann has advanced the synthesis of spirocyclic alkaloids. Furthermore, the elucidation of the genetic analysis, biochemical pathways that links strictosidine to the alkaloids akuammicine, stemmadenine, tabersonine, catharanthine, will now enable the biotechnological generation, also stimulate synthesis of related bridged spirocyclic alkaloids for medicinal investigations. From the value of spirocyclic structures as multi target dementia leads, we hypothesise that simpler Lipinski-like natural/synthetic alkaloid analogues may likewise be discovered that provide neurocognitive enhancing activities against dementia and AD.

Benzannulated 5,5-spiroketal sesquiterpenes from the roots of Angelica Pubescens.

Two new tetrahydrobenzannulated 5,5-spiroketal sesquiterpenes (1 and 2) and three novel benzannulated 5,5-spiroketal sesquiterpenes (3-5) namely angepubesins A-E, together with a new heliannane-type benzannulated sesquiterpene namely angepubesin F (6) and two known monoterpenes (7 and 8), were isolated from the roots of Angelica Pubescens. Their structures were identified by various spectroscopic analyses (NMR, MS, UV, IR), in combination with 13C NMR calculation as well as MAE, CMAE, DP4 + and MAEΔΔδ values analyses. The absolute configurations of 1-6 were determined by modified Mosher's method, ECD calculation and single-crystal X-ray diffraction (Cu Kα). Furthermore, the inhibitory activities of these isolated compounds against nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW264.7 macrophage cells were evaluated. The results showed that compounds 2-4, 6 and 7, especially 6, displayed markedly inhibitory effects on NO production in a concentration-dependent manner. Mechanical study revealed that compound 6 could significantly inhibit the expression of nitric oxide synthase (iNOS) protein at a concentration of 10 µM. In addition, compound 6 suppressed the activation of JAK-STAT and NF-κB pathways.

Cytotoxic Polyketide Metabolites from a Marine Mesophotic Zone Chalinidae Sponge-Associated Fungus Pleosporales sp. NBUF144.

Two new polyketide natural products, globosuxanthone F (1), and 2'-hydroxy bisdechlorogeodin (2), were isolated from the fungus Pleosporales sp. NBUF144, which was derived from a 62 m deep Chalinidae family sponge together with four known metabolites, 3,4-dihydroglobosuxanthone A (3), 8-hydroxy-3-methylxanthone-1-carboxylate (4), crosphaeropsone C (5), and 4-megastigmen-3,9-dione (6). The structures of these compounds were elucidated on the basis of extensive spectroscopic analysis, including 1D and 2D NMR and high-resolution electrospray ionization mass spectra (HRESIMS) data. The absolute configuration of 1 was further established by single-crystal X-ray diffraction studies. Compounds 1-5 were evaluated for cytotoxicity towards CCRF-CEM human acute lymphatic leukemia cells, and it was found that 1 had an IC50 value of 0.46 µM.

Synthesis of a Unique Psammaplysin F Library and Functional Evaluation in Prostate Cancer Cells by Multiparametric Quantitative Single Cell Imaging.

The spirooxepinisoxazoline alkaloid psammaplysin F (1) was selected as a scaffold for the generation of a unique screening library for both drug discovery and chemical biology research. Large-scale extraction and isolation chemistry was performed on a marine sponge (Hyattella sp.) collected from the Great Barrier Reef in order to acquire >200 mg of the desired bromotyrosine-derived alkaloidal scaffold. Parallel solution-phase semisynthesis was employed to generate a series of psammaplysin-based urea (2-9) and amide analogues (10-11) in low to moderate yields. The chemical structures of all analogues were characterized using NMR and MS data. The absolute configuration of psammaplysin F and all semisynthetic analogues was determined as 6R, 7R by comparison of ECD data with literature values. All compounds (1-11) were evaluated for their effect on cell cycle distribution and changes to cancer metabolism in LNCaP prostate cancer cells using a multiparametric quantitative single-cell imaging approach. These investigations identified that in LNCaP cells psammaplysin F and some urea analogues caused loss of mitochondrial membrane potential, fragmentation of the mitochondrial tubular network, chromosome misalignment, and cell cycle arrest in mitosis.

Bromo-spiroisoxazoline Alkaloids, Including an Isoserine Peptide, from the Caribbean Marine Sponge Aplysina lacunosa.

Three new bromotyrosine spiroisoxazoline alkaloids, lacunosins A and B (1 and 2) and desaminopurealin (3), were isolated from a MeOH extract of the marine sponge Aplysina lacunosa that showed modest α-chymotrypsin inhibitory activity. The structures of 1-3 share the spirocyclohexadienyl-isoxazoline ring system found in purealidin-R and several other Verongid sponge secondary metabolites. Compounds 1 and 2 are coupled to a glycine and an isoserine methyl ester, respectively. Alkaloid 3 is linked, contiguously, to an O-1-aminopropyl 3,5-dibromotyrosyl ether and, finally, to histamine through an amide bond. The planar structures of all three compounds were obtained from analysis of MS and 1D and 2D NMR data. The absolute configuration of the SIO unit of 1-3 was assigned by electronic circular dichroism (ECD). The isoserine amino acid residue in 2 was found to be a 1:1 mixture of epimers using a new Marfey's type reagent, derived from Trp-NH2. Allylic O-naphthoylation of the SIO subunit enhances the ECD spectrum of SIOs and improves discrimination of enantiomorphs. A unifying hypothesis is proposed that links the biosynthesis of several of the new compounds with previously reported analogues.

New phenylspirodrimane metabolites MBJ-0030, MBJ-0031, and MBJ-0032 isolated from the soil fungal strain Stachybotrys sp. f23793.

Chemical screening of culture medium from the soil fungus Stachybotrys sp. resulted in the isolation of the three new phenylspirodrimanes MBJ-0030 (1), MBJ-0031 (2) and MBJ-0032 (3). Their structures were determined by detailed analysis of spectroscopic data. The absolute configurations of 1-3 were determined by modified Mosher's and Marfey's methods. In addition, cytotoxic and antimicrobial evaluations of the compounds were conducted.

Chemical Constituents from Endophytic Fungus Annulohypoxylon cf. stygium in Leaves of Anoectochilus roxburghii.

The chemical investigation on endophytic fungus Annulohypoxylon cf. stygium in leaves of Anoectochilus roxburghii (Wall.) Lindl. has been performed. Sixteen compounds were isolated and their structures were identified as (-)-notoamide A, (-)-notoamide B, (+)-versicolamide B, notoamide C, notoamide D, stephacidin A, sterigmatocystin, dihydrosterigmatocystin, secosterigmatocystin, versiconol, averufanin, kipukasin D, kipukasin E, diorcinal, palmarumycin CP2 and (-)-(3R)-mellein methyl ether, respectively, by spectroscopic analysis and comparison with literature data. All the compounds were isolated from Annulohypoxylon genus for the first time. Sterigmatocystin and palmarumycin CP2 showed selective cytotoxic activities against HepG2, HeLa, MCF-7 and HT-29.

Versispiroketal A, an unusual tetracyclic bridged spiroketal from the sponge-associated fungus Aspergillus versicolor SCSIO 41013.

Versispiroketal A (1), an unprecedented 6/5/5/6 tetracyclic polyketide featuring a rarely encountered bridge-fused spiroketal skeleton, was isolated from the sponge-associated fungus Aspergillus versicolor SCSIO 41013. The structure and absolute configuration of 1 were unequivocally determined by comprehensive spectroscopic analysis, single-crystal X-ray diffraction analysis and quantum chemical ECD calculations. Compound 1 showed weak cytotoxicity against four cancer cell lines. A plausible biosynthetic pathway for 1 was also postulated.

New hexalactone derivatives and a pair of new oxaspiro-carbon epimeric glycosides from the fruits of Illicium lanceolatum.

Five new compounds (1-5), including three hexalactone derivatives (1-3) and a pair of new oxaspiro-carbon epimeric glycosides (4 and 5), and six known compounds (6-11) were obtained from the fruits of Illicium lanceolatum. The structures of the new compounds were elucidated using extensive spectroscopic data. The absolute configurations of compounds 1-3 were determined by an analysis of their CD spectra. It was determined that compounds 4 and 5, which are epimeric at C-5, possess the same 1-oxaspiro[4,5]decane-7α,8α,9ß-triol moiety. Plausible biogenetic pathways for 4 and 5 derived from the key precursor shikimic acid were proposed. Compounds 1-11 were all assayed on monosodium glutamate-induced human neuroblastoma SH-SY5Y cell damage. The results demonstrated that compounds 4, 5, and 8-10 possess potential neuroprotective effects. The anti-inflammatory, antiviral, and cytotoxic activities of 1-11 were also evaluated.

Hyperpatulols A-I, spirocyclic acylphloroglucinol derivatives with anti-migration activities from the flowers of Hypericum patulum.

Nine new spirocyclic acylphloroglucinol derivatives, hyperpatulols A-I (1-9), were characterized from the flowers of Hypericum patulum. Their structures were elucidated by the basic analysis of the obtained spectroscopic data, and their absolute configurations were assigned by both the electronic circular dichroism (ECD) exciton chirality method and ECD calculation. The evaluation of their anti-migration effects on U2-OS human osteosarcoma cells showed that compound 4 exhibited moderate inhibitory activity in a dose-dependent manner. Further pharmacological studies revealed that 4 could regulate the expression of the proteins Vimentin and E-cadherin.

The Spirocyclic Imine from a Marine Benthic Dinoflagellate, Portimine, Is a Potent Anti-Human Immunodeficiency Virus Type 1 Therapeutic Lead Compound.

In this study, we aimed to find chemicals from lower sea animals with defensive effects against human immunodeficiency virus type 1 (HIV-1). A library of marine natural products consisting of 80 compounds was screened for activity against HIV-1 infection using a luciferase-encoding HIV-1 vector. We identified five compounds that decreased luciferase activity in the vector-inoculated cells. In particular, portimine, isolated from the benthic dinoflagellate Vulcanodinium rugosum, exhibited significant anti-HIV-1 activity. Portimine inhibited viral infection with an 50% inhibitory concentration (IC50) value of 4.1 nM and had no cytotoxic effect on the host cells at concentrations less than 200 nM. Portimine also inhibited vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped HIV-1 vector infection. This result suggested that portimine mainly targeted HIV-1 Gag or Pol protein. To analyse which replication steps portimine affects, luciferase sequences were amplified by semi-quantitative PCR in total DNA. This analysis revealed that portimine inhibits HIV-1 vector infection before or at the reverse transcription step. Portimine has also been shown to have a direct effect on reverse transcriptase using an in vitro reverse transcriptase assay. Portimine efficiently inhibited HIV-1 replication and is a potent lead compound for developing novel therapeutic drugs against HIV-1-induced diseases.

Cytotoxic Spliceostatin Analogs from Pseudomonas sp.

Two new spliceostatin analogs, designed as spliceostatins J and K (1 and 2), were isolated and identified from the culture of Pseudomonas sp., along with two known ones, FR901464 (3) and spliceostatin E (4). Their structures were elucidated by detailed interpretation of their spectroscopic data, especially 2D-NMR and HR-ESI-MS. Spliceostatin J (1) represented the first example of spliceostatins bearing an unusual hexahydrofuro[3,4-b]furan moiety. Biological assay showed all the isolated compounds except 1 displayed potent cytotoxic activities against two cancer cell lines (MDA-MB-231 and A-549). Structure-activity-relationship studies revealed that the tetrahydropyran ring in spliceostatin analogs was necessary for their bioactive retention.

Recent progress in the isolation, bioactivity, biosynthesis, and total synthesis of natural spiroketals.

Covering: 2011 to July 2017.Spiroketal (spiroacetal), a common moiety in numerous natural products, drugs and functional molecules, has been a central topic in organic chemistry for a long time. Owing to their structural diversity, important bioactivity and functional irreplaceability, natural spiroketals have attracted the interest of natural product chemists, medical chemists, biological chemists, agricultural chemists, synthetic chemists, and chemical biologists. In this review, we focus on the overview of the isolation, bioactivity, biosynthesis and total synthesis of spiroketals from 2011 to July 2017.

Antiplasmodial and trypanocidal activity of violacein and deoxyviolacein produced from synthetic operons.

BACKGROUND: Violacein is a deep violet compound that is produced by a number of bacterial species. It is synthesized from tryptophan by a pathway that involves the sequential action of 5 different enzymes (encoded by genes vioA to vioE). Violacein has antibacterial, antiparasitic, and antiviral activities, and also has the potential of inducing apoptosis in certain cancer cells. RESULTS: Here, we describe the construction of a series of plasmids harboring the complete or partial violacein biosynthesis operon and their use to enable production of violacein and deoxyviolacein in E.coli. We performed in vitro assays to determine the biological activity of these compounds against Plasmodium, Trypanosoma, and mammalian cells. We found that, while deoxyviolacein has a lower activity against parasites than violacein, its toxicity to mammalian cells is insignificant compared to that of violacein. CONCLUSIONS: We constructed E. coli strains capable of producing biologically active violacein and related compounds, and propose that deoxyviolacein might be a useful starting compound for the development of antiparasite drugs.

Separation and determination of corynoxine and corynoxine B using chiral ionic liquid and hydroxypropyl-ß-cyclodextrin as additives by field-amplified sample stacking in capillary electrophoresis.

A sensitive, fast, and effective method, field-amplified sample stacking (FASS) in capillary electrophoresis, has been established for the separation and determination of corynoxine and corynoxine B. Hydroxypropyl-ß-CD (HP-ß-CD) and tetrabutylammonium-L-glutamic acid (TBA-L-Glu) were used as additives in the separation system. Electrokinetic injection was chosen to introduce sample from inlet at 10 kV for 50 s after a water plug (0.5 psi, 4 s) was injected to permit FASS. The running buffer (pH 6.1) was composed of 40 mM sodium dihydrogen phosphate solution, 130 mM HP-ß-CD, and 10 mM TBA-L-Glu and the separation voltage was 20 kV. Under the optimum conditions, corynoxine and corynoxine B were successfully enriched and separated within 12 min and the sensitivity was improved approximately by 700-900 folds. Calibration curves were in a good linear relationship within the range of 62.5-5.00 × 103  ng/mL for both corynoxine and corynoxine B. The limits of detection (S/N = 3) and quantitation (S/N = 10) were 14.9, 45.2 ng/mL for corynoxine and 11.2, 34.5 ng/mL for corynoxine B, respectively. Finally, this method was successfully applied for the determination of corynoxine and corynoxine B in the stems with hooks of Uncaria rhynchophylla and its formulations.

Bistachybotrysins A-C, three phenylspirodrimane dimers with cytotoxicity from Stachybotrys chartarum.

Bistachybotrysins A-C (1-3), three phenylspirodrimane dimers representing an unusual [6,6,7,6]-tetracyclic skeleton with a central 2,10-dioxabicyclo[4.3.1]decan-7-ol core fused with two phenyl units, were isolated from a fungal strain, Stachybotrys chartarum CGMCC 3.5365. The structures of 1-3 were elucidated through extensive spectroscopic data analysis, including Mo2(AcO)4-induced and calculated electronic circular dichroism (ECD). 1 and 2 exhibited potent cytotoxicity against four human tumor cell lines with IC50 values in the range of 2.8-7.5 µM. Furthermore, a possible biogenesis for 1-3 is proposed.

Bioactive spiropyrrolizidine oxindole alkaloid enantiomers from Isatis indigotica Fortune.

Four pairs of new spiropyrrolizidine oxindole enantiomers (1a/1b-4a/4b) were isolated from the leaves of Isatis indigotica Fortune. Their structures and absolute configurations were elucidated by a combination of NMR spectroscopic analyses, experimental and calculated electronic circular dichroism (ECD) and the assistance of quantum chemical predictions (QCP) of 13C NMR chemical shifts. Notably, all the isolated spiropyrrolizidine oxindoles are reported as natural products for the first time. The biosynthetic pathway of these unique structures was proposed to be formed by cycloaddition reaction. In addition, all the compounds were evaluated for their inhibitory effects on ß-amyloid aggregation by ThT assay, and the optically pure compounds 1a/1b and 2a/2b exhibited better Aß1-42 aggregation inhibition potency (85.8% and 73.6%, 71.5% and 75.8%, respectively) at a concentration of 20 µM, compared with the positive control curcumin (57.0%). The difference of the inhibitory pattern caused by chirality was also explained by molecular docking studies.

Cyclopiamines C and D: Epoxide Spiroindolinone Alkaloids from Penicillium sp. CML 3020.

Cyclopiamines C (1) and D (2) were isolated from the extract of Penicillium sp. CML 3020, a fungus sourced from an Atlantic Forest soil sample. Their structures and relative configuration were determined by 1D and 2D NMR, HRMS, and UV/vis data analysis. Cyclopiamines C and D belong to a small subset of rare spiroindolinone compounds containing an alkyl nitro group and a 4,5-dihydro-1 H-pyrrolo[3,2,1- ij]quinoline-2,6-dione ring system. NMR and MS/HRMS data confirmed the presence of an epoxide unit (C-17-O-C-18) and a hydroxy group at C-5, not observed for their known congeners. Cytotoxic and antimicrobial activities were evaluated.