Circulardichroismus—VIII

Isolation of Paraphaeoketones: A Plausible Biosynthetic Explanation for Paraphaeolactones via a Benzilic Acid Rearrangement Rather than a Favorskii Rearrangement

Paraphaeoketones A-C (1-3) were isolated from the culture broth of Paraphaeosphaeria sp. KT4192. Their structures and relative configurations were determined using spectroscopic analysis and verified through density functional theory (DFT)-based chemical shift calculations. The absolute configurations of these compounds were determined by comparing the experimental electronic circular dichroism (ECD) spectra with those based on DFT calculations. We also propose a plausible biosynthetic route to 1-3. While our prior studies on the isolation and structural elucidation of paraphaeolactones (e.g., 4) led us to suggest a Favorskii rearrangement for their biosynthesis, the isolation of 2 prompted the proposal of an alternative biosynthesis for 4, featuring a benzilic acid rearrangement of 2. Moreover, an in vitro conversion of 2 into 4 was achieved successfully, suggesting that a biosynthetic pathway for paraphaeolactones involving a benzilic acid rearrangement is more plausible than the previously presumed Favorskii rearrangement pathway. Arguments based on DFT calculations for these pathways are also described.

Cytotoxic Physalins from Aeroponically Grown Physalis acutifolia

Aeroponically grown Physalis acutifolia afforded five new and six known withanolides including 10 physalins. The structures of the new withanolides, acutifolactone (1), 5β,6β-epoxyphysalin C (2), 5α-chloro-6β-hydroxyphysalin C (3), and an inseparable mixture of 5β,6β-epoxy-2,3-dihydrophysalin F-3β-O-sulfate (4) and 5β,6β-epoxy-2,3-dihydrophysalin C-3β-O-sulfate (5), were elucidated by analysis of their spectroscopic data and chemical interconversions. The known withanolides were identified as physalins B (6), D (7), F (8), H (9), I (10), and U (11) by comparison of their spectroscopic data with those reported. Evaluation of 1-11 and the derivatives, 13 and 13a, obtained from 4 and 5 against a panel of four human cancer cell lines [NCI-H460 (non-small-cell lung), SF-268 (CNS glioma), PC-3 (prostate adenocarcinoma), and MCF-7 (breast adenocarcinoma)] and normal human lung fibroblast (WI-38) cells revealed that physalins 2, 3, 8, and 9 exhibited selective cytotoxic activity to at least one of the cancer cell lines tested compared to the normal cells and that 7, 10, and 11 were inactive up to a concentration of 10.0 μM. These data provided some preliminary structure-activity relationships and suggested that the mechanism of cytotoxic activity of physalins may differ from other classes of withanolides.

New meroterpenoids and C-methylated flavonoid isolated from Baeckea frutescens

Phytochemical investigation of the aerial parts of Baeckea frutescens resulted in the isolation of three new mono- or sesquiterpene-based meroterpenoids, frutescones S-U (1-3), and one pair of new (±)-5,7-dihydroxy-8-isobutyryl-6-methyldihydroflavonol (4). Their structures and absolute configurations were established by HR-ESI-MS, 1D and 2D NMR, and quantum chemical ECD calculation. Compound 1 exhibited inhibitory effect on NO production in LPS-activated RAW 264.7 macrophages with an IC₅₀ value being 0.81 μmol·L^-1.

Sesquiterpene glycosides from the roots of Codonopsis pilosula

Three new sesquiterpene glycosides, named codonopsesquilosides A−C (1−3), were isolated from an aqueous extract of the dried roots of Codonopsis pilosula. Their structures including absolute configurations were determined by spectroscopic and chemical methods. These glycosides are categorized as C₁₅ carotenoid (1), gymnomitrane (2), and eudesmane (3) types of sesquiterpenoids, respectively. Compound 1 is the first diglycoside of C₁₅ carotenoids to be reported. Compound 2 represents the second reported example of gymnomitrane-type sesquiterpenoids from higher plants. The absolute configurations were supported by comparison of the experimental circular dichroism (CD) spectra with the calculated electronic CD (ECD) spectra of 1−3, their aglycones, and model compounds based on quantum-mechanical time-dependent density functional theory. The influences of the glycosyls on the calculated ECD spectra of the glycosidic sesquiterpenoids, as well as some nomenclature and descriptive problems with gymnomitrane-type sesquiterpenoids are discussed.

Computation-Assisted Structural Elucidation of Epoxyroussoeone and Epoxyroussoedione Isolated from Roussoella japanensis KT1651

The structures of epoxyroussoenone (1) and epoxyroussoedione (3) isolated from a culture broth of Roussoella japanensis KT1651 were determined. Although NMR spectra provided insufficient structural information, computation of the theoretical chemical shifts with DFT EDF2/6-31G* enabled us to elucidate not only the planar structure, but also the relative configuration. Their ECD (electric circular dichroism) spectra suggested the absolute configurations, which were confirmed with time-dependent DFT calculations employing BHandHLYP/TZVP. The ECD calculations for other stereoisomers yielded obviously different spectral profiles, thus confirming the relative structures of 1 and 3.

iNOS inhibitory activity of sesquiterpenoids and a monoterpenoid from the rhizomes of Curcuma wenyujin

Eleven new sesquiterpenoids, wenyujinins A-K (1-11), and a new monoterpenoid, wenyujinin L (12), were isolated from the rhizomes of Curcuma wenyujin. Their structures and relative configurations were elucidated using 1D and 2D NMR, X-ray crystallographic analysis, and HRESIMS data. The absolute configurations of 1, 2, 3, 4, 6, 8, 9, and 10 were determined by comparison of the experimental and calculated ECD spectra. The absolute configuration of 5 was determined from the ECD data of the [Rh2(OCOCF3)4] complex, whereas those of 7 and 12 were determined from the ECD spectra of the compounds alone. Compounds 7 and 7a strongly inhibited the induction of NO production by LPS, with IC50 values of 7.6 and 8.5 μM, respectively. Compounds 6 and 10 moderately inhibited NO production with IC50 values of 47.7 and 48.6 μM, respectively.

Guaiane-type sesquiterpenes from Curcuma phaeocaulis and their inhibitory effects on nitric oxide production

Ten new guaiane-type sesquiterpenes (1-10), phaeocaulisins A-J, and 18 known guaiane derivatives were isolated from rhizomes of Curcuma phaeocaulis. Their structures were established on the basis of extensive spectroscopic analyses, X-ray crystallographic analysis, and comparison with literature data. Compound 10 is the first example of a norsesquiterpene with this unusual skeleton isolated from the genus Curcuma. All of the isolated compounds were tested for inhibitory activity against LPS-induced nitric oxide production in RAW 264.7 macrophages. Compounds 1, 2, 20, and 22-24 inhibited nitric oxide production with IC50 values less than 2 μM. Preliminary structure-activity relationships for these compounds are discussed.

Arundinols A-C and arundinones A and B from the plant endophytic fungus Microsphaeropsis arundinis

Three new ent-eudesmane sesquiterpenoids, arundinols A-C (1-3), one isochroman-1-one, arundinone A (4), and a polyoxygenated benzofuran-3(2H)-one dimer, arundinone B (5), were isolated from the extract of a plant endophytic fungus, Microsphaeropsis arundinis. Their structures were elucidated primarily by NMR experiments, and 1 was confirmed by X-ray crystallography. The absolute configuration of 1 was assigned by X-ray crystallography using Cu Kα radiation, whereas those of the C-11 tertiary alcohols in 2 and 3 were deduced via the circular dichroism data of the in situ formed [Rh(2)(OCOCF(3))(4)] complexes. Arundinone B (5) represents the first dimeric benzofuran-3(2H)-one, showing cytotoxicity against T24 and A549 cells. The co-isolated known compound 6 showed a modest inhibitory effect against Staphylococcus aureus.

Tricycloalternarenes F-H: three new mixed terpenoids produced by an endolichenic fungus Ulocladium sp. using OSMAC method

Three new mixed terpenoids, tricycloalternarenes (TCAs) F-H (1-3), together with ten known tricycloalternarenes (4-13), were isolated from the Czapek's culture of an endophytic fungus Ulocladium sp. Their structures were identified by extensive spectroscopic experiments (NMR and MS) and comparison with literature data. TCA 1b (5) showed weak activity against the Bacille Calmette-Guerin strain with the MIC of 125μg/mL. TCA 9b (10) exhibited strong cytotoxic activity against Hela cell line with IC50 of 8.58μM.

Naphthalenones from a Perenniporia sp. inhabiting the larva of a phytophagous weevil, Euops chinesis

The new naphthalenone derivatives perenniporides A-D (1-4) were isolated from solid cultures of a fungus Perenniporia sp. inhabiting the larva of Euops chinesis, a phytophagous weevil with high host specificity to the medicinal plant Fallopia japonica. The structures of 1-4 were elucidated primarily by NMR experiments, and 1 was confirmed by X-ray crystallography. The absolute configuration of 1 and 2 was assigned by electronic circular dichroism (ECD) calculations, whereas that of the C-10 tertiary alcohol in 3 was deduced via the CD data of the in situ formed [Rh(2)(OCOCF(3))(4)] complex and supported by the ECD data. Compound 1 showed antifungal activity against five plant pathogens.

The thermal and enzymatic taxifolin-alphitonin rearrangement

This report describes a detailed investigation of the thermal and enzymatic conversion of taxifolin to alphitonin. Chromatographic separation of the four dihydroquercetin stereoisomers 1-4 in combination with circular dichroism spectroscopy permitted elucidation of the kinetics of this rearrangement and characterization of the different reaction pathways involved. Our findings are corroborated by quantum chemistry calculations that reveal a unique cascade of tautomerization processes leading from taxifolin to alphitonin and also explain the racemization of alphitonin at room temperature. Furthermore, the substrate specificity toward (+)-taxifolin of an enzyme from Eubacterium ramulus catalyzing this intriguing rearrangement is demonstrated.

Molluscicidal metabolites from an assemblage of Palmyra Atoll cyanobacteria

Molluscicides can play an important role in the control of schistosomiasis because snails of the genus Biomphalaria act as intermediate hosts for the parasite. Schistosomiasis is one of 13 neglected tropical diseases with high morbidity and mortality that collectively affect one billion of the world's poorest population, mainly in developing countries. Thiopalmyrone (1) and palmyrrolinone (2), metabolites isolated from extracts of a Palmyra Atoll environmental assemblage of two cyanobacteria, cf. Oscillatoria and Hormoscilla spp., represent new and potent molluscicidal chemotypes against Biomphalaria glabrata (LC50=8.3 and 6.0 μM, respectively). A slight enhancement in molluscicidal effect (LC50=5.0 μM) was observed when these two natural products were utilized as an equimolar binary mixture.

Two new dihydrofuranoisoflavanones from the leaves of Lespedeza maximowiczi and their inhibitory effect on the formation of advanced glycation end products

Two new dihydrofuranoisoflavanones, 2',4',5-trihydroxy-[5''-(1,2-dihydroxy-1-methylethyl)-dihydrofurano(2'',3'':7,8)]-(3S)-isoflavanone (1) and 2', 4', 5-trihydroxy-[5''-(1,2-dihydroxy-1-methylethyl)-dihydrofurano(2'',3'':7,8)]-(3R)-isoflavanone (2) as well as one already-known compound, (+)-catechin (3), were isolated from an n-BuOH soluble fraction from the leaves of Lespedeza maximowiczi. Spectroscopic data was used to elucidate the structures of compounds 1 and 2. All of the isolates were evaluated in vitro for their inhibitory activity on the formation of advanced glycation end products (AGEs). Among these, compounds 1, 2, and 3 exhibited inhibitory activity against AGEs formation with IC(50) values of 20.6, 18.4, and 5.6 microM, respectively.

Guaiane-type sesquiterpenes from Curcuma wenyujin and their inhibitory effects on nitric oxide production

Four new guaiane-type sesquiterpenes (1S,4S,5S,10R)-zedoarondiol, zedoalactones D, E, and F (1-4), along with 10 known ones (5-14), were isolated from Curcuma wenyujin Y.H. Chen et C. Ling. The structures of these new compounds were elucidated by spectroscopic methods. The inhibitory effects of compounds 1-14 on nitric oxide production in lipopolysaccharide-activated macrophages were evaluated.

Structure determination and absolute configuration of cannabichromanone derivatives from high potency Cannabis sativa

Three new cannabichromanone derivatives were isolated from high potency cannabis, along with the known cannabichromanone. Full spectroscopic data, including the use of electronic circular dichroism and Mosher ester analysis to determine the absolute configuration of these compounds, are reported. All isolates were tested for antimicrobial, antimalarial, antileishmanial and anti-oxidant activity.

Two Novel Glycosidic Triterpene Alkaloids from the Stem Barks of Machilus yaoshansis

[structure: see text] Two unusual glycosidic triterpene alkaloids, machilaminosides A (1) and B (2), have been isolated from the stem barks of Machilus yaoshansis. Their structures were elucidated by detailed spectroscopic analysis. A possible biogenetic origin of 1 and 2 mediated by the coupling of 2-O-beta-D-glucopyranosyl-cucurbitacin I, respectively, with urea and adenosine was postulated. 1 and 2 showed nonselective cytotoxic activities against several human cancer cell lines as well as TNF-alpha secretion inhibitory activities.

Shellfish poisons

In our ongoing search for bioactive metabolites from marine organisms, novel shellfish poisons have been isolated. Pinnatoxins, which are amphoteric polyether compounds, were purified from the Okinawan bivalve Pinna muricata. Pinnatoxins show acute toxicity against mice and activate Ca2+ channels. Two novel alkaloids, pinnamine and pinnaic acid, were also obtained from P. muricata. Pinnaic acid inhibits cytosolic phospholipase (cPLA2). Pteriatoxins, which are pinnatoxin analogs, were isolated from the Okinawan bivalve Pteria penguin. A nanomole-order structure determination of pteriatoxins was achieved by the detailed analysis of 2D-NMR and ESI-TOF MS/MS. This review covers the isolation, structure determination, bioactivity, synthesis, and biogenesis of these shellfish poisons and related compounds.

Circular dichroism, a powerful tool for the assessment of absolute configuration of flavonoids

Circular dichroism is a powerful tool for establishing the absolute configuration of flavonoids and proanthocyanidin analogues. It has been utilized to study the configuration of flavanones, dihydroflavonols (3-hydroxyflavanones), flavan-3-ols, flavan-4-ols, flavan-3,4-diols, flavans, isoflavans, isoflavanones, pterocarpans, 6a-hydroxypterocarpans, rotenoids, 12a-hydroxyrotenoids, neoflavonoids, 3,4-dihydro-4-arylcoumarins, 4-arylflavan-3-ols, auronols, homoisoflavanones, proanthocyanidins, and various classes of biflavonoids. Results relevant to the correlation of circular dichroic data and the absolute configuration of the diastereoisomers of some of the above classes of compounds will be discussed.

Total structural assignment and absolute configuration of terreinol by 13C and 1H NMR

The carbon-carbon connectivity of terreinol, a new metabolite isolated from Aspergillus terreus, and its previous (13)C assignments were confirmed by a two-dimensional INADEQUATE experiment using a few milligrams of the compound with natural (13)C abundance. The carbon-carbon correlations were determined by computational analysis (with >99% probability) of this experiment. Additionally, the absolute configuration of terreinol was achieved indirectly via its corresponding secondary alcohol by the modified Mosher method allied to conformational analysis. The shielding effect of the phenyl group of methoxytrifluoromethylphenylacetic acid (MTPA) on the substituents of the carbonylic centre gave a fully regular Deltadelta(SR) sign distribution, allowing reliable assignment of the R configuration for terreinol.