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Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.

The synthesis of privileged structures, which are potent drug candidates, is an impetus for drug discovery. The construction of heterocyclic framework furo[3,2-c]coumarins using a visible-light promoted photoredox neutral coupling of 3-bromo-4-hydroxycoumarins with commercially available alkynes has been reported. These reactions can be carried out at room temperature under visible light irradiation with good chemical yields. This work presents 17 furocoumarins, 12 of which are new. Three of the newly synthesized compounds show potent cytotoxicity, and one shows moderate acetylcholinesterase inhibitory activity with IC50 values of 2.16 ± 0.13 μM.

Three new polyketides, named daldinone F (1), nodulisporin G (2), and dalmanol C (3), together with five known compounds, 4-8, were isolated from cultures of Daldinia eschscholzii. The structures of the new compounds were elucidated by extensive NMR and MS analyses. Compound 1 showed moderate cytotoxic activity against SW480 cancer cells with an IC50 value of 9.59 μM, and its absolute configuration was determined by single crystal X-ray diffraction.

isolation, structure elucidation and cytotoxic activity of three new drimane sesquiterpenoids, astellolides C—E (I), and related hydroxybenzoates, astellolides F—I (II)

Ten new sesquiterpenoids including six brasilane-type sesquiterpenoids, diaporols J–O (1–6), a 3,6-cycloprecapnellane sesquiterpenoid, diaporol P (7), and three drimane sesquiterpenoids, diaporols Q–S (8–10) were isolated from Diaporthe sp., an endophytic fungus associated with the leaves of Rhizophora stylosa collected in Hainan Province, China. The structures of these compounds were elucidated by extensive analysis of NMR, MS, CD spectra and single crystal X-ray diffraction. Among them, compound 9 exhibited moderate cytotoxicity against the SW480 cell line with an IC50 value of 8.72 ± 1.32 μM.

The white croaker (Argyrosomus argentatus) derived Curvularia sp. IFB-Z10 produces curvulamine as a skeletally unprecedented alkaloid incorporating two undescribed extender units. Curvulamine is more selectively antibacterial than tinidazole and biosynthetically unique in the new extenders formed through a decarboxylative condensation between an oligoketide motif and alanine.

Along with four known compounds three new diterpenes, myrocin E (I), libertellenone J (II), and libertellenone K (III), are isolated from the culture of phomopsis sp.

isolation, structure elucidation, and cytotoxicity of five new stilbenolignans, hopeachinols E—I (I)—(III), and two new stilbenoids, hopeachinols J (IVa) and K (IVb)

isolation, structural determination and cytotoxic activity of two new compounds, amycomycin A (I), and amycomycin B (II) along with five known compounds

A highly efficient asymmetric reaction of Morita—Baylis—Hillman carbonates (I) and (IV) with alkyl mercaptans (II) is achieved in the presence of MgSO4 and (DHQD)2-PHAL as organocatalyst.

Precursor-fed cultivation of endophytic Chaetomium globosum1C51 afforded nine novel “unnatural” halogenated chaetoglobosins including those with more preferable immunosuppressive activity.

In addition to the title compounds (I) and (II), the polyphenol diptoindonesine G (III) is isolated from the ethanol extract of H.

Ligulaverin A 1, an eremophilane derivative with a novel carbon skeleton, was isolated from the medicinal plant Ligularia veitchiana, along with four analogues (ligulaverin B 2, ligulaverin C 3, ligulaverin D 4 and ligulaverin E 5). Their structures were elucidated by NMR techniques and X-ray diffraction. The biosynthetic route to this nineteen-carbon skeleton is discussed. © 1997 Elsevier Science Ltd.

The structure of a new diterpene, C30H46O11, with antibacterial activity against Pseudomonas aeruginose and Escherichia coli, isolated from the fresh whole plants of Ajuga lupulina (Labiatae) was established to be 2 beta-hydroxy-2-methylbutanoyl-3 alpha-lupulin (3-deoxy-14,15-dihydro-2-hydroxy-15-methoxycaryoptinol 2-methylbutanoate), by means of X-ray crystallographic analysis. The present study confirms that the two six-membered rings are in ideal chair conformations.

Wahlenbergioside, a new hydroxymethylglutaroyl phenylpropanoid glucoside, and a known compound, lobetyolin, were isolated from the methanol extract of Wahlenbergia marginata . The structures were determined by spectroscopic analysis and chemical degradations.

Repetitive chromatography of the methanol extract of the roots of Gentiana tibetica afforded two new secoiridoid glycosides and a novel antifungal anthranilic acid derivative, together with beta-sitosterol, daucosterol, oleanolic acid, loganic acid, gentiopicroside, sweroside, 2'-(2,3-dihydroxybenzoyl)sweroside, trifloroside, rindoside and macrophylloside A. The structures of the new products were determined mainly by spectroscopic methods as 8-hydroxy-10-hydrosweroside, isomacrophylloside and ethyl N-docosanoylanthranilate. Ethyl N-docosanoylanthranilate inhibited the growth of the human pathogenic fungi Candida albicans and Aspergillus flavus. The taxonomic significance of the constituent is discussed briefly.

Three new cyclopeptides, including halolitoralin A (a cyclic hexapeptide), halolitoralin B and C (two cyclic tetrapeptides), together with three known cyclic dipeptides, cyclo(Pro-Val), cyclo(Pro-Leu) and cyclo(Ile-Val) were isolated from the ferment broth of a marine sediment-derived Halobacillus litoralis YS3106. The cyclopeptides show surprisingly simple architectures with highly repeated residue units, which showed moderate antifungal and weak antitumor activities in vitro.

Andrographolide, a diterpene lactone from Andrographis paniculata, has multiple pharmacological activities. And its acetylated derivatives showed improved antitumour activities. Herein, a total of ten lipases and four proteases were tested for regioselective acylation(s) of andrographolide by vinyl acetate in acetone. Although the enzyme activity was markedly source-dependent, the highest conversion with better initial reaction rate was achieved with immobilized Candida antarcticalipase B (Novozym 435), which displayed higher operational stability. The regioselective acylation at the 14-hydroxyl of the lactone was established by a combination of spectroscopic methods including 1H and 13C NMR, DEPT, ESI-MS and FTIR spectra of the transformed product. The present work accommodated a feasible enzymatic approach for preparing andrographolide monoester, which possesses obvious advantages over the multi-step chemical process in terms of excellent regioselectivity, simplicity, environmental friendliness and mild reaction conditions.

Chaetoglobins A (1) and B (2), two azaphilone alkaloid dimers with an unprecedented skeleton, were characterized from an endophytic fungus Chaetomium globosum with the former ascertained to be a significant cytotoxin valuable for anti-tumor drug discovery.

Cephalosol (1), a potent antimicrobial secondary metabolite with a new carbon skeleton, was characterized from the culture of Cephalosporium acremonium IFB-E007 that used to reside as an endophyte in Trachelospermum jasminoides (Apocynaceae). Its structure and absolute configuration were unambiguously determined by spectroscopic and computational approaches.

Two new phytotoxic gamma-lactones, pestalotines A and B (1 and 2, resp.), along with 4-oxo-4H-pyran-3-acetic acid (3) and 6-hydroxyramulosin (=3,4,4a,5,6,7-hexahydro-6,8-dihydroxy-3-methyl-1H-2-benzopyran-1-one; 4), were isolateded from the culture of Pestalotiopsis sp. HC02, a fungus residing in the Chondracris rosee gut. Structures of the new metabolites were elucidated on the basis of their IR, NMR, and MS data. Pestalotines A and B (1 and 2, resp.) significantly inhibited the radical growth of Echinochloa crusgalli with IC(50) values of 1.85 x 10(-4) and 2.50 x 10(-4) M, respectively, comparable to that of 2-(2,4-dichlorophenoxy)acetic acid (0.94 x 10(-4) M) used as a positive control.

Along with the known secondary metabolites lumichrome, physcion, and emodin-1,6-dimethyl ether, three alkaloids named penicidones A-C (1-3) were isolated from the culture of Penicillium sp. IFB-E022, an endophytic fungal strain residing in the stem of Quercus variabilis (Fagaceae). The structures of penicidones A-C were established by a correlative interpretation of spectroscopic data including IR, UV and HR-ESI-MS, as well as by analysis of a set of 1D and 2D NMR experiments. The stereochemistry of compounds 1 and 2 was obtained by comparison of the optical rotation with those of vermistatin and its analogues. Penicidones A-C were the first group of natural products possessing a penicidone framework. Compounds 1-3 exhibited moderate cytotoxicity against four cancer cell lines.

Carpesilipskyin 1, a novel coumarin dimer which possesses a unique isopropyl side chain, together with two new sesquiterpene lactones, carabrol isovalerate 2 and 2'-hydroxy-4',6'-dimethoxy-benzoylcarpesiolin 3 have been isolated from the methanol extract of the aerial parts of the title herbal plant followed by structure elucidation on the basis of spectral data.

A new xanthene-based, polycyclic metabolite, paranolin (= (2R,3aS,12aR)-3,3a-dihydro-3a-hydroxy-8-(hydroxymethyl)-2-(1-hydroxy-1-methylethyl)-9-methoxy-10-methylfuro[3,2-d]xanthen-6(2H)-one; 1) was isolated from a culture of Paraphaeosphaeria nolinae (IFB-E011), an endophytic fungus residing in the normal stem of the artemisinin-producing plant Artemisia annua (Asteraceae). The structure of 1 was elucidated by extensive spectroscopic analyses. Although not substantially active against the human colon (SW1116) and human cervical carcinoma (Hela) cell lines, this metabolite seems to be the first example of a xanthene-derived secondary metabolite. Its possible biosynthetic origin (Scheme) and its significance as a phyllogenetic marker are discussed in brief.

A new marasmane sesquiterpene, named lactapiperanol E (1), was isolated from the fruiting bodies of Russula foetens together with a known sesquiterpene lactapiperanol A (2). Their structures were established on the basis of spectral methods (MS, IR, 1D and 2D NMR experiments).

A novel nitrogen-containing compound, named xylactam (1), was isolated from the fruiting bodies of ascomycete Xylaria euglossa together with two known compounds penochalasin B2 and neoechinulin A. Their structures were elucidated on the basis of spectral data.

An antimicrobial cerebroside, pinelloside, was isolated from the air-dried tubers of Pinellia ternata (Thunb.) Breit. Its structure was determined as 1-O-beta-D-glucopyranosyl-(2S,3R,4E,11E)-2-(2'R-hydroxyhexadecenoylamino)-4,11-octadecadiene-1,3-diol by chemical transformation and extensive spectroscopic analyses (IR, MS, 1H and 13C NMR, DEPT as well as 2D NMR techniques HMBC, HMQC, 1H-1H COSY and NOESY). The antimicrobial assay showed that this compound was inhibitory to the growth of Bacillus subtilis, Staphylococcus aureus, Aspergillus niger and Candida albicans, with minimum inhibitory concentrations (MICs) of 20, 50, 30 and 10 microg/ml, respectively. The MICs of penicillin G against bacteria B. subtilis, S. aureus, E. coli, P. fluorescens and H. pylori were 0.80, 0.34, 0.56, 1.34 and 0.92, and those of ketoconazole against fungi A. niger, C. albicans and T. rubrum 0.90, 0.65 and 1.0 microg/ml, respectively.

Bioassay-guided fractionation of the ethanol extract of the roots and rhizomes of Veratrum taliense yielded two new and thirteen known steroidal alkaloids. The structures of the two new compounds, neoverataline A and B, were established by extensive spectroscopic analyses to be 3,4-secocevane-4,9-olid-14,15,16,20-tetra-ol-3-oic acid and 3,4-secocevane-4,9-olid-7,14,15,16,20-penta-ol-3-oic acid, respectively, and are a novel carbon skelton. All of the fifteen alkaloids were subjected to in vitro antifungal assays, which showed that the verazine- (veramitaline, stenophylline B, stenophylline B-3-O-β- d -glucopyranoside, veramiline-3-O-β- d -glucopyranoside) and jerveratrum-type (jervine, jervine-3-O-β- d -glucopyranoside) alkaloids exhibited strong antifungal activities against the phytopathogenic fungus Phytophthora capisis with MICs of 160, 120, 160, 80, 80 and 120 μg·L−1, respectively. Furthermore, the verazine-type alkaloids stenophylline B, stenophylline B 3-O-β- d -glucopyranoside and veramiline 3-O-β- d -glucopyranoside were shown to also inhibit the growth of another fungal phytopathogen Rhizoctonia cerealis with MICs of 160, 120 and 120 μg mL−1. The MICs of triadimefon (an antifungal agrochemical used herein as a positive control) against P. capisis and R. cerealis were 120 and 80 μg mL−1, respectively. A preliminary structure–activity relationship regarding these alkaloids has been formulated.

Leptosphaerone (1), a metabolite with a new C skeleton, was isolated from the AcOEt extract of the culture of Leptosphaeria sp., an endophytic fungus (strain number: IV403) found in Artemisia annua. The structure of 1 was elucidated on the basis of spectral analyses, including homo- and hetero-nuclear correlation NMR experiments (HMQC and HMBC), with its absolute configuration determined by CD and NOED studies.

D-glucopyranosid e and stenophylline B-3-0-~D-glucopyranoside) and two novel steroidal alkaloids . The structures of the new compounds have been established by a combination of spectroscopic methods as 3angeloylzygadenine-I3-N-oxide and (20S,25S)-22,26-epiminocholesta-5,22-diene-3I3,12a.-diol (named veramitaline). The chemotaxonomic significance of the isolates are discussed briefly. . Most of Veratrum species, distributing mainly in the temperate regions of the Northern Hemisphere, are well known for their pharmacological potentials. Although a lot of Veratrum plants have been examined chemically to lead to the characterization of more than ninety steroidal alkaloids, much renewed attention is being paid to biologically active and/or structurally novel alkaloidal principles presumably due to their diversified biological actIvIties and structural novelties as reported recently. 1-4 As a follow-up to the phytochemical attention to Veratrum taliense Loes. f. (Liliaceae) , a frequently used traditional Chinese medicine. S • 6 The reinvestigation of the roots and rhizomes of the title species was undertaken. The results are discussed in the present paper. 4