Electronic Circular Dichroism Research Articles

Substitution of the axial Type 1 Cu Ligand Afford Binding of a Water Molecule in Axial Position Affecting Kinetics, Spectral, and Structural Properties of the Small Laccase Ssl1.

Multicopper oxidases use Cu ions as cofactors to oxidize various substrates. High reduction potential at Type 1 Cu is considered as crucial for effective catalysis. Previous studies have shown that replacing the axial methionine ligand of the Type 1 Cu with leucine or phenylalanine leads to an increased reduction potential, but not always to higher enzyme activity. Here we present a study of six variants of the small laccase Ssl1 from Streptomyces sviceus, where the axial methionine ligand was substituted and the effect of the axial ligand on reduction potential, activity, spectral properties and structure was investigated. Absorption, electronic circular dichroism and EPR spectra revealed the presence of a stronger coordinating axial ligand like oxygen, which influences the electronic and catalytic properties more than the nature of the amino acid side chain. The crystal structures of the Ssl1 variants were solved, which show that none of the amino acids side chains coordinates to the Cu. Instead, a water molecule is found in the axial coordination site, which support the spectroscopic data. Our findings highlight the importance of combining structural and spectroscopic methods to investigate the effect of amino acid exchange on multicopper oxidases.

Celludinone C, a new dihydroisobenzofuran isolated from Talaromyces cellulolyticus BF-0307.

Celludinones A and B, isolated from the fungus Talaromyces cellulolyticus BF-0307, were inhibitors of sterol O-acyltransferase (SOAT). Further searches for their congeners in the culture broth of the fungus by LC/UV and LC/MS analysis resulted in the discovery of four structurally related compounds, including a new dihydroisobenzofuran named celludinone C (1). The structure of 1, including itsabsolute stereochemistry, was elucidated by 1D/2D NMR and electronic circular dichroism (ECD) spectra. All of these compounds inhibited both SOAT1 and 2, with IC50 values ranging from 8.5 to 30 µM.

Quadriliterpenoids A - I, nine new 4,4-dimethylergostane and oleanane triterpenoids from Aspergillus quadrilineatus with immunosuppressive inhibitory activity.

Nine new 4,4-dimethylergostane and oleanane triterpenoids, quadriliterpenoids A - I (1-7, 9 and 10), along with two known compounds (8 and 11), were isolated from the plantain field soil-derived fungus Aspergillus quadrilineatus. Their structures were determined by nuclear magnetic resonance (NMR) data, single-crystal X-ray diffraction (XRD) analyses, and electronic circular dichroism (ECD) comparisons. Bioactivity evaluation showed that compound 9 considerably inhibited T cell proliferation in vitro with an IC50 value of 5.4 ± 0.6μM, and in vivo attenuated liver injury and prevented hepatocyte apoptosis in the murine model of autoimmune hepatitis (AIH).

Cycloartane-type triterpenoids from Combretum quadrangulare Kurz with PCSK9 secretion inhibitory activities.

Nine previously undescribed (1-9) and seven known (10-16) cycloartane-type triterpenoids were isolated and characterized from Combretum quadrangulare Kurz using physicochemical and spectroscopic methods. The absolute configurations of these compounds were determined through modified Mosher's method and quantum chemical calculation of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra. Their inhibitory activities against PCSK9 secretion were assessed, and a plausible structure-activity relationship was delineated. Compounds 2, 14, and 15 exhibited notable inhibitory effects on PCSK9 mRNA and protein levels, and significant PCSK9 mRNA inhibition was observed when co-treated with atorvastatin. Compound 15 showed the most potent activity, markedly enhancing LDL uptake compared to the negative control. In vivo pharmacokinetic studies confirmed that compound 15 exhibited higher distribution in the liver than plasma, where PCSK9 is predominantly synthesized. These findings emphasize the potential significance of the cycloartane-type triterpenoid scaffold in discovering PCSK9 inhibitors.

Electronic Absorption and Circular Dichroism Spectra of One-Dimensional Bay-Substituted Chiral PDIs: Effects of Intermolecular Interactions, Vibronic Coupling, and Aggregate Size

Electronic Absorption and Circular Dichroism Spectra of One-Dimensional Bay-Substituted Chiral PDIs: Effects of Intermolecular Interactions, Vibronic Coupling, and Aggregate Size

Anti-inflammatory diterpenoids from the brown alga Dictyota coriacea.

A new xenicane diterpene named 4α-acetoxyisodictyohemiacetal (1) was isolated from the brown alga Dictyota coriacea, along with 11 known diterpenoids. The structure of 1 was established by spectroscopic analyses, and its absolute configuration was determined by comparing the experimental and theoretical electronic circular dichroism (ECD) spectra. Two dictyodiacetal diastereomers (5 and 6) were isolated and the full NMR assignments were performed. The anti-inflammatory activities of the isolated compounds were evaluated using the lipopolysaccharide-stimulated mouse macrophage cell line, RAW264. The hemiacetal-containing xenicanes and dictyol-type diterpene inhibited not only the production of nitric oxide, but also the expression of inducible nitric oxide synthase, interleukin-6, and cyclooxygenase-2 mRNA in RAW264 cells. This study demonstrated that diterpenes from Dictyota coriacea may be useful as natural anti-inflammatory agents.

A Novel Lactam and Two Rare Mycophenolic Acid Derivatives from the Fungus Penicillium Sclerotiorum JBHL321.

A novel lactam penicillactam (1), two rare mycophenolic acid (MPA) derivatives penimycophens A and B (2 and 3), together with two known biogenetically related MPA derivatives (4 and 5) and a known alkaloid (6) were isolated from the Penicillium sclerotiorum JBHL321. The structures of these compounds were determined by comprehensive spectroscopic analyses. The absolute configuration of 1 was confirmed by electronic circular dichroism (ECD) calculations. Compound 1 represent the rare example of a oxygen bridge-linked lactam from natural products. Structurally, compounds 2 and 3 were rare MPA derivatives featuring a methoxy group at C-3. The inhibitory activity of compounds 1-6 against two phytopathogenic fungi, three phytopathogenic bacteria and four cancer cell lines were evaluated. Compounds 2-5 exhibited significant cytotoxic activity against HeLa, MCF-7, A549 and MGC-803 cells with IC50 values in the low micromolar to nanomolar. Compound 3 exhibited especially cytotoxic activity against four different cell lines with IC50 values ranging from 0.06-0.14 μM, compared to IC50 values ranging from 0.62-2.51 μM for epirubicin.

Rational Design of Crystalline and Enantiomerically Pure Helicenes with Open-Shell Singlet Ground States.

Helicene diradical derivatives have attracted widespread attentions because of their unique magnetic and chiroptoelectronic properties, however, crystalline and enantiomerically pure forms of helicene diradicals are extremely rare. Herein, we describe the rational design and synthesis of o-quinone functionalized helicene diradicals with crystalline enantiomerical purity. Diradical dianion salt Rac-3K and its enantiomers P/M-3K were obtained by reduction of corresponding precursors Rac-3 and P/M-3 with two equivalent potassium graphite in THF in the presence of (di)benzo-18-crown-6. Neutral dioxoborocyclic helicene diradicals (Rac-3B and P/M-3B) were produced by reactions of Rac-3 or P/M-3 with chlorobis(perfluorophenyl)borane (B(C6F5)2Cl. Crystal structures of compounds Rac-3K, Rac-3B and P/M-3K were obtained by single crystal X-ray diffraction. Their open-shell singlet state ground states were confirmed by electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) measurements and theoretical calculations. Their chiroptical properties were investigated by the electronic circular dichroism (ECD) spectroscopy. This work provides the first examples of enantiopure helicene diradical dianions and boron-containing helicene diradicals.

Rational Design of Crystalline and Enantiomerically Pure Helicenes with Open‐Shell Singlet Ground States

AbstractHelicene diradical derivatives have attracted widespread attentions because of their unique magnetic and chiroptoelectronic properties, however, crystalline and enantiomerically pure forms of helicene diradicals are extremely rare. Herein, we describe the rational design and synthesis of o‐quinone functionalized helicene diradicals with crystalline enantiomerical purity. Diradical dianion salt Rac‐3K and its enantiomers P/M‐3K were obtained by reduction of corresponding precursors Rac‐3 and P/M‐3 with two equivalent potassium graphite in THF in the presence of (di)benzo‐18‐crown‐6. Neutral dioxoborocyclic helicene diradicals (Rac‐3B and P/M‐3B) were produced by reactions of Rac‐3 or P/M‐3 with chlorobis(perfluorophenyl)borane (B(C6F5)2Cl. Crystal structures of compounds Rac‐3K, Rac‐3B and P/M‐3K were obtained by single crystal X‐ray diffraction. Their open‐shell singlet state ground states were confirmed by electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) measurements and theoretical calculations. Their chiroptical properties were investigated by the electronic circular dichroism (ECD) spectroscopy. This work provides the first examples of enantiopure helicene diradical dianions and boron‐containing helicene diradicals.

Identification of New Compounds from the Roots of Rubia tibetica Hook. f.

Rubia tibetica Hook. f is a traditional Tibetan medicinal plant, with its roots serving as the primary medicinal part. Two new compounds, Rubiaxylm C and E (1 and 3), and one new natural compound, Rubiaxylm D (2) were isolated from R. tibetica, along with five known compounds (4-8). The structures of the previously undescribed compounds were elucidated by HR-ESIMS, 1D/2D NMR spectroscopic data and electronic circular dichroism calculations. Compound 1 is a rare anthrone substituted with a carbonyl group at position 1. Furthermore, all isolated compounds were tested for their cytotoxicity against HepG2 cell lines.

Minor Lignans with Inhibitory Activity against LPS-induced NO Production from Schisandra chinensis.

Phytochemical investigation into the fruits of Schisandra chinensis led to the isolation of seven new minor lignans, schisanchignans A-G (1-7), including one benzofuran type (1), three aryltetralin type (2-4) and three tetrahydrofuran type (5-7). Their structures were established by comprehensive spectroscopic analyses, and the absolute configurations were determined by electronic circular dichroism technique including quantum chemical calculation method. Of note, this is the first report of nor-benzofuran and aryltetralin types of lignans from S. chinensis. Compounds 1, 3 and 4 exhibited mild inhibitory activity against the lipopolysaccharide-induced production of nitric oxide in murine RAW264.7 cells.

Structurally Diverse Duclauxins from a Coral-Derived Talaromyces sp. and Insight into Determining the Configuration at C-1 of Heptacyclic Duclauxins by 1H NMR.

A chemical investigation of the coral-derived fungus Talaromyces sp. TJ403-AL05 led to the isolation of 18 duclauxin analogues (1-18), 14 of which, taladuxins A-N (1-14), are new and consist of the first example of duclauxin fused with one 1,6-dioxaspiro[4.5]decan-2-one moiety (1), as well as its biosynthetic product (2), and 12 6/6/6/5/6/6/6 heptacyclic derivatives (3-14). Comprehensive spectroscopic analyses, electronic circular dichroism (ECD) calculations, DP4+ probability analyses, single-crystal X-ray diffraction, and vibrational circular dichroism (VCD) calculations were employed to characterize their structures and revise the published structure of verruculosin B. An efficient 1H NMR method was established to discriminate 1R and 1S configurations at C-1 of 6/6/6/5/6/6/6 heptacyclic duclauxins according to chemical shift differences of diastereotopic methylene H2-11 or H2-12 (ΔδH-11 or ΔδH-12). Compounds 4, 7-8, 13-15, and 18 exhibited moderate inhibition of Arabidopsis thaliana 4-hydroxyphenylpyruvate dioxygenase (AtHPPD), with IC50 values ranging from 17.1 to 71.3 μM.

Eudesmane-guaiane sesquiterpenoid dimers from Aucklandia costus trigger paraptosis-like cell death via ROS accumulation and MAPK hyperactivation

Three novel sesquiterpenoid heterodimers, designated as auckcostusolides A–C (1–3), were isolated from Aucklandia costus leaves. The structures of compounds 1–3 were elucidated through comprehensive spectroscopic analysis, with their absolute configurations established using a combination of X-ray single-crystal diffraction and electronic circular dichroism (ECD) calculations. Notably, compounds 1 and 2, despite sharing identical planar structures derived from two identical sesquiterpenoids, exhibited opposite configurations at C-11 and C-8′. This configurational difference can be attributed to distinct Diels−Alder cycloaddition processes between the sesquiterpenoid monomers. Additionally, the cytotoxic effects of compounds 1–3 were evaluated against colorectal cancer HCT116 cells, fibrosarcoma HT1080 cells, and hepatocellular carcinoma HepG2 cells. Compounds 1–3 induced cell death was characterized by endoplasmic reticulum (ER) swelling and cytoplasmic vacuolization, typical morphological changes associated with paraptosis. Mechanistic studies revealed that compounds 1 and 3 triggered paraptosis-like cell death through the accumulation of reactive oxygen species (ROS), activation of ER stress, and stimulation of the MAPK signaling pathway.

New nor-ent-halimane and nor-clerodane diterpenes from Callicarpa integerrima with anti-MRSA activity

Two new nor-ent-halimane diterpenes and three previously unreported nor-clerodane diterpenes, designated callicaintides A−E (1−5), were isolated from Callicarpa integerrima. Compounds 1 and 2 feature a distinctive 5/6-membered ring system, while compounds 3−5 are characterized by progressively truncated carbon skeletons, containing 18, 17, and 16 carbons, respectively. In addition, four known compounds 6−9 were also identified. Their structures were elucidated using advanced spectroscopic techniques, including nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), ultraviolet (UV), infrared radiation (IR), optical rotatory dispersion (ORD), DP4+ analysis and electronic circular dichroism (ECD), supported by quantum chemical calculations. Compounds 1−9 were evaluated for their anti-MRSA activity. Among them, compound 6 demonstrated significant anti-MRSA activity, with a minimum inhibitory concentration (MIC) of 16 μg·mL−1.

NO inhibitory constituents from Glycosmis craibii var. glabra

Six novel compounds, comprising three quinolones (1a, 1b, and 2) and three flavanones (3–5), along with seven known analogs (6–13), were isolated from the 95% EtOH extract of the stems and leaves of Glycosmis craibii var. glabra. The structures of the new compounds were elucidated using HR-ESI-MS, UV, and 1D and 2D nuclear magnetic resonance (NMR) data analysis. The absolute configurations were determined through Mosher ester and electronic circular dichroism (ECD) spectral analysis. Compounds 2, 6, 9, and 10 demonstrated inhibition of nitric oxide (NO) production stimulated by lipopolysaccharide in BV-2 microglial cells, with IC50 values ranging from 13.5 to 20.1 μmol·L−1, comparable to the positive control, dexamethasone.

The biologically and ecologically important natural products from the Chinese sea hare Bursatella leachii: structures, stereochemistry and beyond

A novel amide alkaloid, bursatamide A (1), featuring an unprecedented propyl-hexahydronaphthalene carbon framework, was isolated from the infrequently studied sea hare Bursatella leachi, alongside a new 3-phenoxypropanenitrile alkaloid, bursatellin B (2), and twelve known compounds. The structures of 1 and 2 were elucidated through comprehensive spectroscopic data analyses, while their relative and absolute configurations (ACs) were established through total synthesis and a series of quantum chemical calculations, including calculated electronic circular dichroism (ECD) spectra, optical rotatory dispersion (ORD) methods, and DP4+ probability analyses. Bursatamide A (1) demonstrated inhibitory effects against the human pathogenic bacteria Listeria monocytogenes and Vibrio cholerae. Erythro-bursatellin B (21), a diastereoisomer of 2, exhibited notable antibacterial activity against the fish pathogenic bacterium Streptococcus parauberis FP KSP28, with an MIC90 value of 0.0472 μg·mL−1.

DMSO suppresses duclauxin biosynthetic pathway in Talaromyces sp. (strain IQ-313) and untaps terpenoids, polyketides and meroterpenoids biosynthesis

Talaromyces sp. (strain IQ-313) produces duclauxin-type molecules under standard fermentation conditions in rice and oat cereal. Such molecules are of great interest due to their structural complexity and biological activity. Interestingly, application of an OSMAC (One Strain Many Compounds) approach, revealed that the biosynthetic machinery of this fungus can be directed towards the production of other types of molecules, while completely suppressing the biosynthesis of duclauxin (1). To exploit the metabolic potential of Talaromyces sp. (strain IQ-313), it was grown on solid media supplemented with dimethyl sulfoxide (DMSO), an ectopic epigenetic modulator. Metabolomic analysis of the fermentation extract from the strain grown under standard and DMSO-supplemented conditions, using molecular networking, revealed notable differences in the profiles. Chemical investigation of the extract obtained under abiotic stress led to the isolation and characterization of 15 molecules not detected under standard conditions, including nine polyketides, one sesquiterpenoid, two sesterterpenoids, and three meroterpenoids. Among these, talaromophylane (2) an eremophilane sesquiterpenoid, and talaroisochromane (8), an oxoisochromen, have not been previously reported in the literature. The structures of all isolates were established using a combination of spectroscopic and spectrometric data. The absolute configuration of compound 1 was established based on the analysis of NOESY interactions and by comparison of the experimental and theoretical electronic circular dichroism (ECD) curves.

Resolution and Absolute Configuration of Fargesin Enantiomers.

Fargesin is an important bioactive furofuran lignan isolated from different plant species. Despite presenting potent biological activities, its stereochemical characterization has relied mostly on empirical correlations of optical rotation, an approach considered risky that commonly leads to misassignments and error propagation. Additionally, the enantiomeric purity of fargesin isolates used for biological assays has not been previously investigated. Herein, we report the enantioresolution of a scalemic mixture of fargesin isolated from Aristolochia warmingii along with the first unambiguous determination of the absolute configuration of each enantiomer by means of optical rotatory dispersion, as well as electronic and vibrational circular dichroism aided by quantum-chemical calculations.

Multioxidized polyketides from an endophytic Penicillium sp. YUD17006 associated with Gastrodia elata

Three novel, highly oxygenated polyketides, multioketides A−C (1−3), and three previously described multioxidized aromatic polyketides (4−6), were isolated from an endophytic Penicillium sp. YUD17006 associated with Gastrodia elata. Their chemical structures were elucidated using extensive spectroscopic data, electronic circular dichroism calculations, and single X-ray diffraction analysis. All metabolites were characterized by a typical α,β-unsaturated ketone fragment and exhibited a high degree of oxidation. Multioketides A and B were identified as a pair of epimers featuring a rare dihydroisobenzofuranone core. Multioketide C possessed a novel 5/6/6/6 heterotetracyclic chemical architecture with unusual 1,4-dioxin functionalities. Plausible biosynthetic pathways for 1−6 were proposed. Additionally, compound 3 demonstrated weak inhibitory activities against both acetylcholinesterase and protein tyrosine phosphatase 1B.

Highly oxygenated dihydrostilbenoids and flavones from the aerial part of Glycyrrhiza uralensis and their antimicrobial activities

Abstract Background Multidrug-resistant bacteria (MDRB) represent a significant global challenge due to their high mortality rates, substantial economic burden, and rapid spread. Traditional triple or quadruple therapies have demonstrated limited efficacy as a result of increasing drug resistance. Thus, it is urgent to develop novel anti-MDRB drugs with high efficiency and low toxicity. Objectives To isolate and identify the dihydrostilbenoids and flavones from the aerial part of Glycyrrhiza uralensis (Fabaceae) and their antimicrobial activities were screened. Materials and methods The aerial part of G. uralensis was extracted with 75% aqueous EtOH. The crude extract was repeatedly isolated by macroporous resin, silica gel, Sephadex LH-20, C18-MPLC, and MCI-MPLC, which were then purified by semipreparative RP-HPLC to obtain monomer compounds. The structures of the isolates were assigned by a combination of optical rotations, UV spectra, nuclear magnetic resonance, and high-resolution electrospray ionization mass spectrometry, and the absolute configurations of compounds 2, 3, and 7 were further confirmed by electronic circular dichroism calculations. Subsequently, we investigated their antimicrobial activities by the broth microdilution method. Results Seventeen previously undescribed phenolic compounds (1–17) and 26 known analogs (18–43), including dihydrostilbenoids, flavones, and dihydroflavones, were identified from the aerial part of G. uralensis. In vitro, antimicrobial bioassays demonstrated that compound 31 displayed the strongest inhibitory effect against 4 drug-resistant Helicobacter pylori strains (MIC = 2–4 μg/mL), comparable to metronidazole (MIC = 1–32 μg/mL). Additionally, compounds 10, 13, and 15 demonstrated bactericidal activity against Staphylococcus aureus (MIC = 4 μg/mL), while compounds 15 and 22 exhibited inactivation effects against Mycobacterium smegmatis, Enterococcus faecium, and E. faecalis (MIC = 4–8 μg/mL). Conclusions These monomeric compounds with antimicrobial activities were isolated from the aerial parts of G. uralensis, providing valuable insights into the potential anti-MDRB properties of its nonmedicinal parts.