Chiroptical properties of 2,3-dihydrobenzo[b]furan and chromane chromophores in naturally occurring O-heterocycles

Stereochemical insights into enantioselective antiplasmodial lignanamides from the twigs and leaves of Solanum erianthum

Stereochemical investigations on the twigs and leaves of Solanum erianthum afforded five pairs of lignanamide enantiomers and a previously undescribed phenolic amide (3). Particularly, two pairs of previously undescribed lignanamide racemates (1a/1b-2a/2b) represent the first case of natural products that feature an unreported 5/5-fused N/O-biheterocyclic core. Their structures, including the absolute configurations, were determined unambiguously by using spectroscopic analyses and electronic circular dichroism calculations. A speculative biogenetic pathway for 1-3 was proposed. Interestingly, these lignanamides exhibited enantioselective antiplasmodial activities against drug-sensitive Plasmodium falciparum 3D7 strain and chloroquine-resistant Plasmodium falciparum Dd2 strain, pointing out that chirality plays an important role in drug development.

Chiral separation and bioactivities of six pairs of enantiomeric dilignans from Magnolia officinalis var. biloba

Six pairs of enantiomeric dilignans, (+)/(-)-magdiligols A-F, have been isolated from an ethanolic extract of the barks of Magnolia officinalis var. biloba. Their chemical structures were elucidated by extensive spectroscopic analyses, NMR calculation with DP4+ analysis, and the electronic circular dichroism spectra calculation. (+)/(-)-1-3 possessed a dihydrobenzopyran ring, while a propyl chain of 1 was linked via ether bond. (+)/(-)-Magdiligols D and E ((+)/(-)-4 and 5) were dilignans possessing a furan ring. (+)-Magdiligol B ((+)/(-)-2), (+)/(-)-magdiligol C ((+)/(-)-3), and racemes 2, 3, and 5 showed potential hepatoprotective effects against APAP-induced HepG2 cell damage, increased the cell viability from 65.4% to 72.7, 78.7.76.6, 73.9, 77.9 and 73.2%, via decreasing the level of the live enzymes ALH and LDH consistently. (+)/(-)-Magdiligols B-D ((+)/(-)-2-4) and (+)/(-)-magdiligol F ((+)/(-)-6) exhibited significant antioxidative activity. (+)/(-)-Magdiligols B-C ((+)/(-)-2 and 3), (-)-magdiligol D ((-)-4), and (+)-magdiligol E ((+)-5) displayed significant PTP1B inhibitory activity with IC50 values 1.41-3.42 μM. (+)/(-)-Magdiligol B ((+)/(-)-2), and its raceme (2) demonstrated α-glucosidase inhibitory activity with the IC50 values 1.47, 2.88 and 1.85 μM, respectively.

Aromatic glycosides and lignans glycosides with their acetylcholinesterase inhibitory activities from the leaves of Picrasma quassioides

In this study, eight new natural products were isolated from the leaves of Picrasma quassioides. Spectroscopic techniques were used for the elucidation of their planar structures. Their absolute configurations were elucidated on the basis of electron circular dichroism (ECD) techniques combined with the P/M helicity rule for the 2,3-dihydrobenzofuran chromophore, and saccharide hydrolysis. Cholinesterase inhibitors are often used as Alzheimer's disease inhibitors.Thus, acetylcholinesterase and butyrylcholinesterase inhibitory activity of these eight compounds were tested, and results showed that only compound 6 showed weakly acetylcholinesterase inhibitory activity. In particular, molecular docking was used to illustrate the bindings between compound 6 and the active sites of AChE.

Neurotrophic phenolic glycosides from the roots of Armoracia rusticana

Armoracia rusticana P. G. Gaertner. belongs to the Brassicaceae family and has aroused scientific interest for its anti-inflammatory and anticancer activities. In a continuing investigation to discover bioactive constituents from A. rusticana, we isolated 19 phenolic glycosides including three undescribed flavonol glycosides and one undescribed neolignan glycoside from MeOH extract of this plant. Their structures were elucidated based on NMR spectroscopic analysis (1H, 13C, 1H-1H COSY, HSQC, and HMBC), HRESIMS, and chemical methods. The determination of their absolute configuration was accomplished by ECD and LC-MS analysis. All the compounds were assessed for their potential neurotrophic activity through induction of nerve growth factor in C6 glioma cell lines and for their anti-neuroinflammatory activity based on the measurement of inhibition levels of nitric oxide production and pro-inflammatory cytokines (i.e., IL-1β, IL-6, and TNF-α) in lipopolysaccharide-activated microglia BV-2 cells.

Diverse neolignans and lignans from an aqueous extract of the Angelica sinensis root head

Neolignans and lignans with diverse new chemical structures, including eleven pairs of separated chiral enantiomers [(+)-/(-)-1-(+)-/(-)-5, (+)-/(-)-8, (+)-/(-)-10, and (+)-/(-)-12-(+)-/(-)-15], two achiral compounds (6 and 9), and an unseparated racemate [(±)-11], together with a new natural product (7) and 21 known derivatives, were isolated from an aqueous extract of the Angelica sinensis root head (guitou). Among the chiral isolates, (+)-/(-)-13 and (+)-/(-)-15 were scalemic pairs with enantiomeric ratios of around 3:1 and 1.5:1, respectively, while others were enantiomeric equivalent pairs. This indicates that the diverse neolignans in A. sinensis are biosynthesized via different pathways with varying degrees of stereo-controlled manners.

Two new constituents from the aerial parts of Salvia miltiorrhiza Bge

Two new constituents: a neolignan, salignan A (1) and a phenolic acid, salside A (2), along with two known compounds (3, 4) have been isolated from the aerial parts of Salvia miltiorrhiza Bge. All structures were assigned on the basis of detailed spectroscopic analyses. The absolute configuration of 1 was characterised by electronic circular dichroism (ECD) spectroscopy. Compounds 1 and 3 exhibited moderate inhibitory effects on nitric oxide (NO) production in LPS-induced RAW264.7 cells, and the IC50 values are 11.58 and 10.73 μM, respectively. Compound 4 displayed moderate antioxidant activity to scavenge DPPH and ABTS radicals, and the IC50 values are 7.96 and 1.10 μM, respectively.

Identification of Small-Molecule Bioactive Constituents from the Leaves of Vaccinium bracteatum Confirms It as a Potential Functional Food with Health Benefits

The health benefits of Vaccinium bracteatum are well recorded in ancient Chinese medical books and were also demonstrated by modern researches. However, the relationship between its beneficial functions and specific chemical constituents has not been fully characterized. This study investigated the bioactive small-molecule constituents in the leaves of V. bracteatum, which afforded 32 compounds including ten new ones (1-9) and ten pairs of enantiomers (9-18). Their structures with absolute configurations were elucidated by spectroscopic methods, especially nuclear magnetic resonance (NMR) and electronic circular dichroism (ECD) analyses, with 1-4 bearing a novel revolving-door shaped scaffold. While half-compounds exhibited decent antioxidant activity by scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals, all except 19 and 20 exerted significant capturing activity against diammonium 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) radicals. In addition, the new iridoids 1, 5, 6, and 7 exerted apparent neuroprotective activity toward PC12 cells, with 1 being comparable to the positive control, and selective compounds also displayed anti-diabetic and anti-inflammatory properties by inhibiting α-glucosidase and NO production, respectively. The current work revealed that the bioactive small-molecule constituents could be closely related to the functional food property of the title species.

Lignans and a neolignan from an aqueous extract of Isatis indigotica roots

Four new lignans (1-4) and one new neolignan (5), along with two known lignan derivatives (6 and 7), were isolated from an aqueous extract of the Isatis indigotica root (ban lan gen). Their structures were determined by spectroscopic data analysis, chemical method, and theoretical calculation, for which 1 was proved by single-crystal X-ray diffraction. Compound 2 exhibited antiviral activity against influenza virus A/Hanfang/359/95 (H3N2) with an IC50 value of 11.1 µM and a selective index (SI) > 9, while 1 and 5 are the first examples of sulfonated lignan and neolignan from nature.

Atropisomeric 9,10-dihydrophenanthrene/bibenzyl trimers with anti-inflammatory and PTP1B inhibitory activities from Bletilla striata

Two pairs of novel trimeric dihydrophenanthrene-bibenzyl-dihydrophenanthrene enantiomers (1 and2), the first examples of a dihydrophenanthrene dimer linked to a bibenzyl or dihydrophenanthrene through a C-O-C bond (3 and4), and a pair of rare polymers with a bibenzyl connected to C-8' of the dihydrophenanthro[b]furan moiety via a methylene (5), together with four known compounds (6-9) were isolated from the tubers of Bletilla striata. Their structures including the absolute configurations were determined using spectroscopic data analysis and ECD and NMR calculations, combined with the exciton chirality method or the reversed helicity rule. The atropisomerism of dihydrophenanthrenes and related polymers was considered based on their chiral optical properties, and QM torsion profile calculations, which revealed the racemic mixture form of the polymers. Compounds 4, 5b, 6a and 7b significantly inhibited the production of NO in LPS-induced BV-2 cells, with IC₅₀ values ranging from 0.78 to 5.52 μM. Further mechanistic study revealed that 7b suppressed the expression of iNOS, and suppressed the phosphorylation of the p65 subunit to regulate the NF-κB signaling pathway. Furthermore, compounds 2b, 5a, 5b, 7a and 7b displayed significant protein tyrosine phosphatase 1B (PTP1B) inhibitory activities with IC₅₀ values of 3.43-12.30 μM.

Two new neolignans and an indole alkaloid from the stems of Nauclea officinalis and their biological activities

A pair of new diastereoisomers neolignans (1-2) and a new alkaloid (7) were isolated from the stems of Nauclea officinalis: naucleaoxyneolignoside A (1), naucleaoxyneolignoside B (2), (2S,3S)-javaniside (7), together with nine known compounds, 2S-3,3-di-(4-hydroxy-3-methoxyphenyl)-propane-1,2-diol (3), threo-1,2-bis-(4-hydroxy-3-methoxyphenyl)-propane-1,3-diol (4), nauclefine (5), angustidine (6), naucleoxoside A (8), naucleoxoside B (9), angustoline (10), (3S,19S)-3,14-dihydroangustoline (11), and (3S,19R)-3,14-dihydroangustoline (12).The structures of 1, 2 and 7 were elucidated by extensive spectroscopic methods and the known compounds were identified by comparison of their data with those reported in the literature. The absolution configurations of 1, 2, 7,11 and 12 were confirmed by the quantum chemical CD calculation method. Compounds 1-9 showed weak to moderate inhibitory activity on nitric oxide (NO) production induced by lipopolysaccharide in mouse macrophage RAW 264.7 cells in vitro with IC₅₀ values comparable to that of dexamethasone. In addition, compounds 1-9 were evaluated for the antibacterial and cytotoxic effects, and the results revealed that these compounds showed no anti-bacterial activity, and compounds 3-6 showed modest cytotoxic activity.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world's most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage "If you don't seek, you don't find". Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Characteristic guaiane sesquiterpenes from Daphne penicillata and ECD/NMR-based assignment of C-1 configuration

40 compounds including the first C17 homo-guaiane sesquiterpene (1) were isolated from Daphne penicillata and an efficient method using ECD/NMR strategy to access the C-1 configuration of characteristic guaiane sesquiterpenes has been developed.

Acmoxanthones A-E, New Lavandulated Xanthones from Hypericum acmosepalum N. Robson

Acmoxanthones A-E (1-5), five new lavandulylated xanthones, were isolated from the aerial parts of Hypericum acmosepalum, together with four known xanthones. Their structures with absolute configurations were elucidated on the basis of analysis of MS, NMR and chiroptical properties. A bioassay against high glucose-induced damage on human umbilical vein endothelial cells (HUVECs) showed ananixanthone (6) and osajaxanthone (7) had potential antioxidative damage activity with EC₅₀ values of 10.5 μg/mL and 7.6 μg/mL, respectively, while 3-hydroxy-2,4-dimethoxyxanthone (8) exhibited cytotoxic effect on the damaged cells with IC₅₀ values of 7.1 μg/mL.

Synthesis and HPLC-ECD Study of Cytostatic Condensed O,N-Heterocycles Obtained from 3-Aminoflavanones

Racemic chiral O,N-heterocycles containing 2-arylchroman or 2-aryl-2H-chromene subunit condensed with morpholine, thiazole, or pyrrole moieties at the C-3-C-4 bond were synthesized with various substitution patterns of the aryl group by the cyclization of cis- or trans-3-aminoflavanone analogues. The 3-aminoflavanone precursors were obtained in a Neber rearrangement of oxime tosylates of flavanones, which provided the trans diastereomer as the major product and enabled the isolation of both the cis- and trans-diastereomers. The cis- and trans-aminoflavanones were utilized to prepare three diastereomers of 5-aryl-chromeno[4,3-b][1,⁴]oxazines. Antiproliferative activity of the condensed heterocycles and precursors was evaluated against A2780 and WM35 cancer cell lines. For a 3-(N-chloroacetylamino)-flavan-4-ol derivative, showing structural analogy with acyclic acid ceramidase inhibitors, 0.15 μM, 3.50 μM, and 6.06 μM IC₅₀ values were measured against A2780, WM35, and HaCat cell lines, and apoptotic mechanism was confirmed. Low micromolar IC₅₀ values down to 2.14 μM were identified for the thiazole- and pyrrole-condensed 2H-chromene derivatives. Enantiomers of the condensed heterocycles were separated by HPLC using chiral stationary phase, HPLC-ECD spectra were recorded and TDDFT-ECD calculations were performed to determine the absolute configuration and solution conformation. Characteristic ECD transitions of the separated enantiomers were correlated with the absolute configuration and effect of substitution pattern on the HPLC elution order was determined.

Computational insight into the mechanism and origin of high regioselectivity in the ring-opening cyclization of spirocyclopropanes with stabilized sulfonium ylides by the DFT

Chromanes with high bioactivity play an important role in nature, and cyclization reactions of cyclopropanes with sulfonium ylides to form chromane skeletons have attracted great attention of scientists. The mechanism as well as origins of regioselectivity and stereoselectivity for the ring-opening/cyclization reactions between cyclohexane-1,3-dione-2-spirocyclopropanes and stabilized sulfonium ylides in CH₂Cl₂ were investigated by using the density functional theory (DFT) M06-2X/6-311+G(d,p)//M06-2X/6-31G(d,p) method combined with the SMD model. The calculated results revealed that the reaction process involved two key steps: the ring-opening step and the cyclization step, with the former being the rate-determining and stereoselectivity-determining step. The regioselectivity of the ring-opening step of spirocyclopropane indicated that the tertiary carbon was more preferential than the secondary one when sulfonium ylide attacked spirocyclopropane. The theoretical results confirmed that the stereoselectivity of the reaction to form the trans-isomer product is more favorable than the cis-isomer, and the calculated trans/cis ratio is in accordance with the experiment. Moreover, the conceptual density functional theory reactivity indices suggest that the electronic effect controls the regioselectivity. What is more, the stereoselectivity analyzed by weak non-covalent interaction also shows the importance of electronic effect. Graphical Abstract.

Sesquineolignan and neolignan enantiomers from Triadica sebifera

Two pairs of new sesquineolignan enantiomers (1a/1b and 1c/1d), two pair of new 4',7-epoxy-8,3'-neolignan enantiomers (2a/2b and 3a/3b), and a pair of new 3',7-epoxy-8,4'-oxyneolignan enantiomers (4a/4b), along with two pairs of known 4',7-epoxy-8,3'-neolignan enantiomers (5a/5b and 6a/6b), were obtained from the stems and leaves of Triadica sebifera. The structures of the enantiomers were elucidated by spectroscopic analyses, and their absolute configurations were assigned by the experimental ECD spectra. Among them, compounds 5b, 6a and 6b showed inhibitory activities against NO production in activated microglial BV-2 cells, with IC₅₀ values of 14.3, 23.2 and 33.3 μM, respectively.

Miliusins; cytotoxic neolignans from the leaves of Miliusa sessilis

Eight undescribed neolignans and an undescribed propanoid dimer were isolated from the leaves of Miliusa sessilis, together with two known compounds, dehydrodieugenol A and dehydrodieugenol B. All structures were elucidated by extensive spectroscopic data analysis and the structure of (7S,8R)-5'-hydroxy-3,4-dimethoxy-4',7-epoxy-8,3'-neolign-8'-en-9-acetate (miliusin A) was further confirmed by X-ray crystallographic analysis. The absolute configurations were determined using circular dichroism (CD) data analysis and the modified Mosher's method. All isolated compounds were evaluated for their cytotoxic activities against four human cancer cell lines (HeLa, HN22, HepG2, and HCT116), including one normal-type cell line (HaCaT) using MTT assay. (7S,8R)-5'-hydroxy-3,4-dimethoxy-4',7-epoxy-8,3'-neolign-8'-en-9-ol (miliusin B) was found to exhibit the most promising cytotoxic effect against Hela cells with the lowest IC₅₀ value of 0.04 μM and the highest selective index of 187.8, highlighting miliusin B as an attractive candidate for cervical cancer drug development.

Phytochemical Investigation of Erodium oxyrrhynchum M. Bieb

We describe here the isolation of 1 previously unreported neolignan (7 S,8 R)-2′,3-dimethoxy-4′,7-epoxy-8,5′-neolignan-4,9,9′-triol-9′- O-β-d-glucopyranoside (1) and 4 flavonoid glycosides, quercetin 7- O-glucoside (2), Isoquercitrin (3), quercetin 3- O-rutinoside (4), narcissin (5), as well as 2 tannins, isomallotusinin (6), isocorilagin (7), from Erodium oxyrrhynchum M. Bieb. Structures were determined using 1-dimensional and 2-dimensional-nuclear magnetic resonance, liquid chromatography-mass spectrometry, infrared and ultraviolet spectroscopy, while stereochemistry was confirmed by circular dichroism and optical rotation.

Synthesis and antiproliferative activity of 6-naphthylpterocarpans

The Heck-oxyarylation of racemic 2-(1-naphthyl)- and 2-(2-naphthyl)-2H-chromene derivatives were carried out resulting diastereoselectively in (6S*,6aR*,11aR*)-6-(1-naphthyl)- and 6-(2-naphthyl)-pterocarpans as major products and bridged (6R*,12R*)-6,12-methanodibenzo[d,g][1,3]dioxocine derivatives as minor products. Antiproliferative activity of two 6-naphthylpterocarpans was identified by MTT assay against A2780 and WM35 human cancer cell lines with low micromolar IC50 values. The measured 0.80 and 3.51 μM IC50 values of the (6S*,6aR*,11aR*)-6-(1-naphthyl)pterocarpan derivative with 8,9-methylenedioxy substitution represent the best activities in the pterocarpan family. Enantiomers of the pterocarpan and dioxocine derivatives and their chiral 2-naphthylchroman-4-one and 2-naphthyl-2H-chromene precursors were separated by HPLC using chiral stationary phase. HPLC-ECD spectra were recorded and absolute configuration and low-energy solution conformations were determined by TDDFT-ECD calculations. Characteristic ECD transitions of the separated enantiomers were correlated with their absolute configuration.

Comparison of light absorption and oxidative potential of biodiesel/diesel and chemicals/diesel blends soot particles

Soot particles, mainly coming from fuel combustion, affect climate forcing through absorbing light and also result in adverse human health outcomes. Though biodiesel or additives blending with diesel was considered environmentally friendly, the understanding on absorbing and oxidative capacity of soot emitted from them are still unclear. The water-soluble organic carbon (WSOC) content, surface chemical structure, light absorption and oxidative potential (OP^DTT) of soot from biodiesel/diesel and chemicals/diesel blends were investigated utilizing total organic carbon analyzer, X-ray photoelectron spectrometer, ultraviolet-visible spectrophotometry and dithiothreitol (DTT) assay. The differences and correlations between soot properties were statistically analyzed. Chemicals/diesel blends soot owned significantly higher WSOC content, ratio of mass absorbing efficiency (MAE) in 250 and 365 nm (E₂/E₃), OP^DTT, and higher surface carbonyl content. Coconut biodiesel/diesel blends soot contained evidently higher aromatic carbon-oxygen single bond (Ar_C-O) content, and higher MAE₃₆₅. The individual comparison of biodiesel/diesel blends showed 20% coconut biodiesel blend owned the lowest WSOC, E₂/E₃ and OP^DTT, while highest Ar_C-O and MAE₃₆₅, representing strongest absorbing properties. Association analysis showed OP^DTT was significantly positively correlated with WSOC. Further, the evident negative correlation between MAE₃₆₅ and OP^DTT was observed. Our results showed coconut biodiesel/diesel blends soot induced lower levels of oxidative potential, whereas absorption of light was higher, which have far reaching consequences on climate forcing. Therefore, it is important to evaluate the balance point between light-absorbing properties and oxidative potential, under the wide use of biodiesel.

Two new stilbenoids from Bletilla striata

Two new stilbenoids bletilol D (1) and bletilol E (2), together with five known compounds were isolated from Bletilla striata. Three of them (3, 4, and 7) were obtained from this genus for the first time. Their structures were elucidated by spectroscopic methods and comparing with data reported in literatures. The cytotoxic activities of compounds 1-7 against MCF-7 (human breast cancer) and A549 (human lung carcinoma) cell lines were evaluated by MTT assay. Compound 2 showed weak cytotoxicity against MCF-7 and A549 cell lines with IC₅₀ values of 36.32 ± 1.17 and 36.48 ± 1.12 μM, respectively, and 5 exhibited weak cytotoxicity against MCF-7 cell line with IC₅₀ value of 57.09 ± 2.03 μM.

Metachromins X and Y from a marine sponge Spongia sp. and their effects on cell cycle progression

New sesquiterpene quinones, metachromins X (1) and Y (2), together with the known metachromins C (3), J (4), and T (5), were isolated as inhibitors of cell cycle progression in the HeLa/Fucci2 cells. The structure of 1 was assigned by spectroscopic data and confirmed by a total synthesis. The planar structure of 2 was determined by interpretation of spectroscopic data, whereas its absolute configuration was analyzed by a combination of chiral HPLC and CD spectroscopy. Metachromins X (1) and C (3) arrested the cell cycle progression of HeLa/Fucci2 cells at S/G2/M phase.

Chemical Constituents from Ethanoic Extracts of the Aerial Parts of Leea aequata L., a Traditional Folk Medicine of Myanmar

We aimed at reporting the chemical constituents and antimicrobial activities of Leea aequata L., a traditional folk medicine used in Myanmar for the treatment of wounds and skin diseases. A new neolignan, (7S,8R)-9'-O-acetylcedrusin (1), a new lactam, (3S,4S)-4-chloro-3-hydroxypiperidin-2-one (2), along with 21 known compounds, including five lignans (3-7), four flavonoid glycosides (8-11), and others (12-23), were isolated from the ethanoic extract of the aerial parts of L. aequata. The structures of the new compounds were determined by NMR, MS, and ECD spectra. For all the antimicrobial tests of the 23 compounds, only 3,4,5-trihydroxybenzoic acid ethyl ester (17) showed weak inhibitory activities against Escherichia coli and Salmonella enterica subsp. enterica.

Quantum Reality in the Selective Reduction of a Benzofuran System

Two 2,3-disubstituted benzofurans (1 and 2), analogs of gamma-aminobutyric acid (GABA), were synthesized to obtain their 2,3-dihydro derivatives from the Pd/C-driven catalytic reduction of the double bond in the furanoid ring. The synthesis produced surprising by-products. Therefore, theoretical calculations of global and local reactivity were performed based on Pearson's hard and soft acids and bases (HSAB) principle to understand the regioselectivity that occurred in the reduction of the olefinic carbons of the compounds. Local electrophilicity (ω_k) was the most useful parameter for explaining the selectivity of the polar reactions. This local parameter was defined with the condensed Fukui function and redefined with the electrophilic (P_k⁺) Parr function. The similar patterns of both resulting sets of values helped to demonstrate the electrophilic behavior (soft acid) of the olefinic carbons in these compounds. The theoretical calculations, nuclear magnetic resonance, and resonance hybrids showed the moieties in each compound that are most susceptible to reduction.

A new anti-inflammatory lignan from Lonicerae Japonicae flos

One new lignan, loniceralanside A (1), together with three known compounds (2-4), were purified from Lonicerae Japonicae Flos. Their structures were determined by HR-ESI-MS, 1 D and 2 D NMR data. Compounds 2-4 were separated from the plant for the first time. The biological test showed that compound 1 had significant anti-inflammatory activity with inhibiting the release of β-glucuronidase induced by platelet-activating factor (PAF) in rat polymorphonuclear leukocytes (PMNs) (IC₅₀ = 3.05 µM).

Applications of OR/ECD/VCD to the structure elucidation of natural products

OR, ECD and VCD are powerful methods to determine the absolute configuration of natural products either applied independently or in combination.

Brasilane sesquiterpenoids and dihydrobenzofuran derivatives from Aspergillus terreus [CFCC 81836]

Brasilanones A-F and asperterreusines A-C, undescribed brasilane sesquiterpenoids and dihydrobenzofuran derivatives, were isolated from the marine-derived fungus Aspergillus terreus [CFCC 81836]. Their structures with absolute configurations were elucidated on the basis of spectroscopic data, X-ray crystallographic analyses, and electronic circular dichroism (ECD) calculations. Brasilanones A-F are unusual brasilane sesquiterpenoids with an α,β-unsaturated ketone unit, interestingly, brasilanones B-D are stereo isomers. All of the isolates were evaluated for their inhibitory activities against NO production and cytotoxic activities against five human cancer cell lines (HL-60, SW-480, A-549, MCF-7, and SMMC-7721). Brasilanones A and E showed moderate inhibitory effect with NO inhibition rates of 47.7% (p < 0.001) and 37.3% (p < 0.001) at the concentration of 40 μM. Asperterreusines A showed cytotoxicity against HL-60 and SW-480 cell lines with IC₅₀ values of 15.3 and 25.7 μM, respectively.

Solvation of 2-(hydroxymethyl)-2,5,7,8-tetramethyl-chroman-6-ol revealed by circular dichroism: a case of chromane helicity rule breaking

The primary goal of this work is to clarify why 2-(hydroxymethyl)-2,5,7,8-tetramethyl-chroman-6-ol {(S)-TMChM} deviates from the chromane helicity rule under solvent change. The rule, applicable to determining the absolute configuration of molecules containing the chromane chromophore, binds the sign of the 1Lb Cotton effect (CE) with the helicity of the dihydropyran ring. In case of TMChM, however, this CE exhibits extreme solvent dependence: it is negative in non-coordinating solvents and positive in coordinating ones, irrespective of the helicity of the heterocyclic ring. TD-DFT calculations using PCM and hybrid solvation models were performed to explain origin of this phenomenon. It turned out that the 1Lb CE sign directly depends on the position of the phenolic OH group at carbon atom C6 (OHC6). In the absence of interactions with solvents (as in CCl4 or nC6H14) or when a solvent plays proton donor role (as in CHCl3), the OHC6 lies in the phenyl plane and the 1Lb CE sign follows the P/M helicity rule. In contrast, in proton acceptor solvents, like DMSO, CH3OH or CH3CN, the OHC6 group is deflected from the phenyl plane, and the 1Lb CE sign of individual (S)-TMChM conformers depends on the sector in which the OHC6 is located. Thus, in solution, the 1Lb CE sign is an average over different orientations of the OHC6 group and can be positive (as in DMSO and CH3OH) or negative (as in CH3CN) which means that it does not follow the chromane helicity rule. The impact of OHC6 on the 1Lb CE sign and thus the conclusions for the stereochemistry of chromans are demonstrated here for the first time. Additionally, a comparison of experimental and simulated ECD spectra, supported by VCD data, allowed to determine the geometry of intermolecular clusters formed in different solvents.

Anti-HIV and cytotoxic biphenyls, benzophenones and xanthones from stems, leaves and twigs of Garcinia speciosa

Eleven previously undescribed compounds, including four benzophenones (garciosones A-D), four xanthones (garciosones E-H) and three biphenyls (garciosines A-C), along with eighteen known compounds were isolated from the stems, leaves and twigs of Garcinia speciosa Wall. (Clusiaceae). Their structures were established by extensive spectroscopic analysis. For garciosines A-C, the structures were confirmed by single crystal X-ray diffraction analysis. Most of the isolated compounds were evaluated for their cytotoxic activity and anti-HIV-1 activity using the syncytium inhibition assay and HIV-1 reverse transcriptase (RT) assay. The known compounds, 4,6,3',4'-tetrahydroxy-2-methoxybenzophenone and macluraxanthone, displayed significant cytotoxic activity with the ED₅₀ in the range of 1.85-11.76 μM. 1,5-Dihydroxyxanthone exhibited the most potent anti-HIV activity against syncytium formation with EC₅₀ < 17.13 μM (SI > 25.28) and 2-(3,3-dimethylallyl)-1,3,7-trihydroxyxanthone was the most active compound in the HIV-1 reverse transcriptase assay with IC₅₀ value of 58.24 μM. Structure-activity relationship of some isolated compounds were also discussed.

Gardenifolins A-H, Scalemic Neolignans from Gardenia ternifolia: Chiral Resolution, Configurational Assignment, and Cytotoxic Activities against the HeLa Cancer Cell Line

From the tropical plant Gardenia ternifolia Schumach. and Thonn. (Rubiaceae), eight stereoisomeric 2,3-dihydrobenzo[b]furan neolignans, named gardenifolins A-H (1a-d and 2a-d), were isolated and fully structurally characterized. Reversed-phase chromatography of a stem bark extract afforded two peaks, viz. mixtures I and II, each one consisting of two diastereomers and their respective enantiomers. They were resolved and stereochemically analyzed by HPLC on a chiral phase coupled to electronic circular dichroism (ECD) spectroscopy, giving single ECD spectra of all eight stereoisomers. The double-bond geometries (E or Z) of the gardenifolins A-H and their relative configurations (cis or trans) at the stereogenic centers C-7 and C-8 in the dihydrofuran ring system were assigned by 1D and 2D NMR methods, in particular, using NOE difference experiments, whereas the absolute configurations of the isolated enantiomers were established by ECD spectroscopy by applying the reversed helicity rule. The individual pure gardenifolin isomers A-H showed the most different cytotoxic effects against the human cancer HeLa cell line, with 1d and 2a displaying the highest activities, with IC₅₀ values of 21.0 and 32.5 μM, respectively. Morphological experiments indicated that gardenifolin D (1d) induces apoptosis of HeLa cells at 25 μM.

Chemical Constituents from the Aerial Parts of Cyrtopodium paniculatum

We report the first phytochemical study of the neotropical orchid Cyrtopodium paniculatum. Eight new compounds, including one phenanthrene 1, one 9,10-dihydro-phenanthrene 2, one hydroxybenzylphenanthrene 3, two biphenanthrenes 4–5, and three 9,10 dihydrophenanthrofurans 6–8, together with 28 known phenolic compounds, mostly stilbenoids, were isolated from the CH₂Cl₂ extract of its leaves and pseudobulbs. The structures of the new compounds were established on the basis of extensive spectroscopic methods.

(1) H NMR-Guided Isolation of Formyl-Phloroglucinol Meroterpenoids from the Leaves of Eucalyptus robusta

Nine formyl-phloroglucinolmeroterpenoids (FPMs), namely, eucalrobusones A-I (1-9), were isolated from the leaves of Eucalyptus robusta by tracking the phenolic hydroxyl (1) H NMR peaks. The Snatzke helicity rules for the Cotton effects of twisted benzene rings were applied to elucidate the absolute configurations of the FPMs. These findings, along with NMR spectroscopy, the circular dichroism (CD) exciton chirality method, and CD calculations, allowed complete structures for the FPMs to be assigned. Eucalrobusones A-F (1-6) are novel adducts formed between a formyl-derived carbon atom on the phloroglucinol ring and monoterpene and sesquiterpene components. Eucalrobusones G-I (7-9) are the first examples of FPMs with cubebane part structures connected by an unusual 1-oxaspiro[5.5]undecane subunit. Among these isolates, eucalrobusone C (3) showed significant cytotoxicity against HepG2, MCF-7, and U2OS cancer cell lines, with IC50 values less than 10 μm. Compound 3 significantly blocks cell proliferation in MCF-7 cells and induces MCF-7 cell death through apoptosis.

Enantiomeric Lignans and Neolignans from Phyllanthus glaucus: Enantioseparation and Their Absolute Configurations

Eight pairs of enantiomeric neolignans, norlignans, and sesquineolignans (1a/1b–8a/8b), together with five known neolignans (9a/9b and 10–12), have been isolated from 70% acetone extract of the whole plants of Phyllanthus glaucus Wall. (Euphorbiaceae). The racemic or partial racemic mixtures were successfully separated by chiral HPLC using different types of chiral columns with various mobile phases. Their structures were elucidated on the basis of extensive spectroscopic data. The absolute configurations of 2a/2b were determined by computational analysis of their electronic circular dichroism (ECD) spectrum, and the absolute configurations of other isolates were ascertained by comparing their experimental ECD spectra and optical rotation values with those of structure-relevant compounds reported in literatures. Compounds 4a/4b featured unique sesquineolignan skeletons with a novel 7-4′-epoxy-8′-8′′/7′-2′′ scaffold, consisting of an aryltetrahydronaphthalene and a dihydrobenzofuran moiety. The planar structures of compounds 2, 3, 7, and 8 were documented previously; however, their absolute configurations were established for the first time in this study. The antioxidant activities of 1a/1b–8a/8b were evaluated using DPPH free radical scavenging assay, and the results demonstrated that compounds 1b and 3b showed potent DPPH radical scavenging activities with IC₅₀ values of 5.987 ± 1.212 and 9.641 ± 0.865 μg/mL, respectively.

Enantiomeric Neolignans and a Sesquiterpene from Solanum erianthum and Their Absolute Configuration Assignment

One pair of new C-8-C-3'/C-7-O-C-4' linked neolignan enantiomers (1a/1b) and one new guaiane sesquiterpene (2) first featuring the 1(2),9(10)-conjugated double bond were isolated from the stems of Solanum erianthum (Solanceae). Their structures were characterized on the basis of extensive spectroscopic analyses, especially from their 2D nuclear magnetic resonance (NMR) spectra. The absolute configurations of 1a/2b were rigorously elucidated by electronic circular dichroism (ECD) experiments combined with the reversed helicity rule for the 2,3-dihydrobenzo[b]furan chromophore, and compound 2 is the first report on the sterochemical assignment of a guaiane sesquiterpene by using the allylic axial chirality rule for the conjugated diene chromophore in combination with the calculated ECD spectrum.

A comparative study on hulled adlay and unhulled adlay through evaluation of their LPS-induced anti-inflammatory effects, and isolation of pure compounds

Coicis semen (=the hulled seed of Coix lacryma-jobi L. var. ma-yuen (Rom.Caill.) Stapf; Gramineae), commonly known as adlay and Job's tears, is widely used in traditional medicine and as a nutritious food. Bioassay-guided fractionation of the AcOEt fraction of unhulled adlays, using measurement of nitric oxide (NO) production on lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells, led to the isolation and identification of two new stereoisomers, (+)-(7'S,8'R,7″S,8″R)-guaiacylglycerol β-O-4'-dihydrodisinapyl ether (1) and (+)-(7'S,8'R,7″R,8″R)-guaiacylglycerol β-O-4'-dihydrodisinapyl ether (2), together with six known compounds, 3-8. Compounds 3 and 4 exhibited inhibitory activities on LPS-induced NO production with IC50 values of 1.4 and 3.7 μM, respectively, and suppressed inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein expressions in RAW 264.7 macrophage cells. Simple high-performance liquid chromatography with ultraviolet detection (HPLC/UV) was used to compare the AcOEt fraction of unhulled adlays responsible for the anti-inflammatory activity in RAW 264.7 cells and the inactive AcOEt fraction of hulled adlays.

Food Byproducts as a New and Cheap Source of Bioactive Compounds: Lignans with Antioxidant and Anti-inflammatory Properties from Crataegus pinnatifida Seeds

During the process of manufacturing hawthorn (Crataegus pinnatifida) juice and jam, a significant quantity of byproducts (leaves, seeds) is generated. The antioxidant and anti-inflammatory bioassay-guided fractionation of the extract of hawthorn seeds has led to the isolation of eight new lignans, hawthornnins A-H (1-8), and seven known analogues (9-15). Their structures were elucidated by spectroscopic techniques, including 1D and 2D NMR and CD spectra. The radical-scavenging effects of all isolated compounds were investigated. 1-6 and 8 showed moderate activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH), whereas 1-6 and 14 displayed good 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical-scavenging activities that were even more potent than that of trolox. In addition, all isolates were evaluated for their anti-inflammatory activities by detecting the nitric oxide (NO) and tumor necrosis factor α (TNF-α) production by the LPS-induced murine macrophage cell line RAW264.7, and compounds 1-7, 13, and 14 exhibited potent inhibition of NO and TNF-α production. The structure-activity relationships of isolated lignans were also examined, and the results obtained show that C. pinnatifida seeds can be regarded as a potential new and cheap source of antioxidants and inflammation inhibitors.

Bioactive Sesquiterpenes and Lignans from the Fruits of Xanthium sibiricum

Seven new sesquiterpenes (1, 3-8), a new sesquiterpene natural product (2), and two new lignans (9 and 10), together with 15 known compounds, were isolated from the fruits of Xanthium sibiricum. The structures of the new compounds were established by NMR spectroscopic analysis, ECD calculations, and Mo2(OAc)4-induced circular dichroism, with the structures of 1 and 4 confirmed by single-crystal X-ray diffraction. Compound 1 is the first example of a 3/5/6/5 tetracyclic eudesmane sesquiterpene lactone formed at C-6 and C-7. In turn, compound 4 is the first example of a natural xanthane tetranorsesquiterpene, while compounds 5-8 are the first xanthane trinorsesquiterpenes found to date. Compounds 8, 11-15, 17, and 24 exhibited indirect anti-inflammatory activity by suppressing the lipopolysaccharide-induced proinflammatory factors in BV2 microglial cells, with IC50 values between 1.6 and 8.5 μM. Furthermore, compounds 13 and 17 exhibited anti-inflammatory activity against ear edema in mice produced by croton oil, with inhibition rates of 46.9% and 37.7%, respectively. Compounds 8, 11, 12, 23, and 24 exhibited potent activity against influenza A virus (A/FM/1/47, H1N1) with IC50 values between 3.7 and 8.4 μM.

Diarylheptanoids of Curcuma comosa with Inhibitory Effects on Nitric Oxide Production in Macrophage RAW 264.7 Cells

Eight new diarylheptanoids, a 1.2:1 mixture of (3S)- and (3 R)-1-(4-hydroxyphenyl)-7-phenyl-(4 E,6 E)-4,6-heptadien-3-ol (1a and 1b), a racemic mixture of (3S)- and (3 R)-1-(4-hydroxyphenyl)-3-methoxy-7-phenyl-(4 E,6 E)-4,6-heptadiene (2a and 2b), a ca. 1:1 mixture of (3S)- and (3 R)-1-(4-hydroxy-3-methoxyphenyl)-3-methoxy-7-phenyl)-(4 E,6 E)-4,6-heptadiene (3a and 3b), 3-acetoxy-1-(3,4-dihydroxyphenyl)-7-phenylheptan-5-ol (4), (3 R)-1-(4,5-dihydroxyphenyl)-7-phenyl-(6 E)-6-hepten-3,2′-epoxide (5), and thirteen known diarylheptanoids, 6-12, a 3:1 mixture of 13a and 13b, and 14-17, were isolated from the rhizomes of Curcuma comosa from Sakon Nakhon, northeastern part of Thailand. The isolated compounds were evaluated for their antiinflammatory activities on the inhibition of lipopolysaccharide-induced nitric oxide production in macrophage RAW 264.7 cells and the diarylheptanoids 1a and 1b mixture and 14 exhibited potent inhibitory activity.

Enantiomeric neolignans and sesquineolignans from Jatropha integerrima and their absolute configurations

Two pairs of new sesquineolignan enantiomers, 1a/1b and 2a/2b, one pair of new neolignan enantiomer, 4a/4b, and two new neolignans, 3a and 5a, together with seven known analogues were isolated from the trunks of Jatropha integerrima.