The first synthesis and absolute configuration of glaucescenolide

The first synthesis of glaucescenolide (1), a cytotoxic sesquiterpene isolated from the liverwort, Schistochila glaucescens, was achieved by starting from 2,2,6-trimethylcyclohexanone (2). The absolute configuration of the naturally occurring 1 was confirmed as 5S,7S,10R.     

Chamigrenelactone, a polyoxygenated sesquiterpene with a novel structural type and devoid of halogen from Laurencia obtusa

A biogenetically interesting halogen-devoid metabolite chamigrenelactone 1, with a high oxygen-content, has been isolated from Laurencia obtusa from Isla Grande (Caribbean Panama). Its structure and stereochemistry were determined on the basis of spectral studies.     

Structure elucidation of some highly unusual tricyclic cis-caryophyllane sesquiterpenes from Marasmiellus troyanus

Three new unusual sesquiterpenes (1-3) were isolated from the tropical rainforest basidiomycete, Marasmiellus troyanus and their structure elucidation was achieved by NMR spectroscopy, single-crystal X-ray structural analysis and a modified Mosher’s ester method to determine the absolute stereochemistry of compound 1. These unusual metabolites are probably derived from the caryophyllane class of sesquiterpenes and a possible biosynthetic route to these compounds is proposed. These small natural products represent the best possible features of chemical diversity, being chiral and exhibiting extensive functional group chemistry highlighting the value of natural products as a screening resource for therapeutics discovery programmes.     

13-Chloro-3-O-β-d-glucopyranosylsolstitialin from Leontodon palisae: the first genuine chlorinated sesquiterpene lactone glucoside

Apart from a number of known sesquiterpenoids, a novel chlorinated sesquiterpene lactone glucoside--13-chloro-3-O-β-d-glucopyranosylsolstitialin--has been isolated from the Southwestern European plant Leontodon palisae (Asteraceae, tribe Lactuceae). The structure has been established by high resolution mass spectrometry and 1D as well as 2D NMR spectroscopy. The compound represents the first naturally occurring chlorinated sesquiterpene lactone glucoside. The cytotoxicity of the new compound and related ones was evaluated using the MTT assay.     

Artalbic acid, a sesquiterpene with an unusual skeleton from Artemisia alba (Asteraceae) from Sicily

From the aerial parts of Artemisia alba (Asteraceae) artalbic acid (1), a sesquiterpene with an unusual skeleton, was isolated. Its structure was elucidated on the basis of extensive proton, ¹³C and two-dimensional NMR experiments, as well as by transformation in its methyl ester derivative.     

Jiadifenlactone A,a novel diseco-prezizaane-type sesquiterpenoid from the fruits of Illicium jiadifengpi

Jiadifenlactone A (1), the first example of cleavage of bond [4, 9] of the seco-prezizaane-type sesquiterpenoid with a unique 9-membered ring moiety, together with its biosynthetic related compound 2, were isolated from the fruits of Illicium jiadifengpi. The structure of 1 and its relative configuration were determined by spectroscopic methods and single-crystal X-ray diffraction analysis. The inhibitory rates of compound 1 on the HBeAg and HBsAg expressions were 37.91 ± 2.78% and 17.21 ± 3.78%, respectively.     

New acorane sesquiterpenes isolated from the endophytic fungus Colletotrichum gloeosporioides SNB-GSS07

Looking for new anti-glycation compounds, four new acorane sesquiterpenes together with seven known molecules were isolated from Colletrotrichum gloeosporioides, an endophytic fungus of Sabicea cinerea. Their structures were established based on mass spectrometry and NMR, together with circular dichroism for their absolute configurations.     

Sulfur-containing sesquiterpenes from Thapsia villosa

Three new sesquiterpenoids bearing sulfurated ester groups have been isolated from the roots of Thapsia villosa L. Their structures have been elucidated by spectroscopic means. This is the first time that a methylthiopropionic acid ester is isolated from natural sources.     

Stereochemical evaluation of sesquiterpene quinones from two sponges of the genus Dactylospongia and the implication for enantioselective processes in marine terpene biosynthesis

Silver nitrate flash chromatography of the organic extract from the sponge Dactylospongia elegans has led to the isolation of three new sesquiterpene quinones isohyatellaquinone (7), 7,8-dehydrocyclospongiaquinone-2 (8) and 9-epi-7,8-dehydrocyclospongiaquinone-2 (9) together with the known quinones dictyoceratidaquinone (6), mamanuthaquinone (10), ilimaquinone (11), hyatellaquinone (12) and the sesterterpene furospinosulin (22). The relative stereochemistry of dictyoceratidaquinone (6) is assigned on the basis of NOESY analysis. A second species of Dactylospongia, thought to be new to science, was found to contain ent-(7) together with the new quinone neomamanuthaquinone (13). The isolation of antipodal sesquiterpenes from closely related species has implications for the stereochemical evaluation of terpene metabolites. The biosynthetic processes in these marine sponges may involve terpene synthases that do not discriminate chiral substrates or may result from the presence of multiple terpene synthases, each with differing enantioselectivity.     

Lacitemzine, a novel sesquiterpene acid from the Tunisian plant Pulicaria laciniata (Coss. et Kral.) Thell.

The flowers of Pulicaria laciniata (Coss. et Kral.) Thell. (Asteraceae) afforded a new sesquiterpene acid 1, named lacitemzine together with the three known compounds, 4-hydroxy-3-methoxypyridine 2, β-sitosterol-3-O-β-d-glucoside 3 and 1,3,5-trimethoxybenzene 4. The structure of compound 1, 2-(2,6-dimethyl-3,4,5,6,7,8,9,10-octahydro-5,8-oxaazulen-9-yl)acrylic acid, contains a guaiane skeleton and was elucidated by spectroscopic procedures including 2D-NMR and X-ray diffraction.     

Ptesculentoside, a novel norsesquiterpene glucoside from the Australian bracken fern Pteridium esculentum

A novel norsesquiterpene glucoside ptesculentoside has been isolated from the Australian bracken Pteridium esculentum, together with the known bracken carcinogen ptaquiloside and lesser amounts of caudatoside. The structure of ptesculentoside is determined by analysis of 1D and 2D NMR spectra, and via its conversion into previously known pterosin G.     

Synthesis and absolute configuration of annuionone A

Synthesis of both enantiomers of annuionone A (1), an allelopathic agent isolated from Helianthus annuus (sunflower), was accomplished. The absolute configuration of the naturally occurring 1 was determined to be 1S,5R,8R.     

Asymmetric total syntheses of heliannuol E and epi-heliannuol E

Asymmetric total syntheses of heliannuol E and epi-heliannuol E were achieved in 10 and 13 steps, respectively, from the commercially available starting materials. The syntheses feature an intramolecular attacking on the sulfate to form the dihydropyran ring of heliannuol E and an acyl transfer-secondary carbocation capture sequence to construct the dihydropyran ring of epi-heliannuol E.     

Chemical constituents of Ligularia virgaurea and its diversity in southwestern Sichuan of China

Chemical constituents of root extract and the nucleotide sequences of the atpB-rbcL intergenic region and the internal transcribed spacers (ITSs) of the ribosomal RNA gene were studied for Ligularia virgaurea var. virgaurea collected in southwestern Sichuan Province of China. Eleven samples were collected. Four of them were found to contain four new furanoeremophilanes, virgaurenones A-D, as well as a new eremophilanolide, virgaurenolide A. The other samples contained different furanoeremophilanes and their derivatives including nor-type of compounds, two of which were new. Diversity was found to be present in the nucleotide sequences as well. The chemical composition was found to be correlated with the ITS variation but not with the geographic distribution of the samples.     

Ecological leads for natural product discovery: novel sesquiterpene hydroquinones from the red macroalga Peyssonnelia sp.

Pharmacologically-motivated marine natural product investigations have yielded a large variety of structurally unique compounds with interesting biomedical properties, but the natural roles of these molecules often remain unknown. While secondary metabolites may function as antimicrobial chemical defenses, few studies have examined this hypothesis. In the present investigation, chromatographic fractions from 69 collections of Fijian red macroalgae representing at least 43 species were evaluated for growth inhibition of three microbial pathogens and saprophytes of marine macrophytes. At least one microbe was suppressed by fraction(s) of all evaluated algae, suggesting that antimicrobial defenses are common among tropical seaweeds. From these leads, peyssonoic acids A-B (1-2), novel sesquiterpene hydroquinones, were isolated from the crustose red alga Peyssonnelia sp. At ecologically realistic concentrations, both compounds inhibited growth of Pseudoalteromonas bacteriolytica, a bacterial pathogen of marine algae, and Lindra thalassiae, a fungal pathogen of marine algae, and exhibited modest antineoplastic activity against ovarian cancer cells. The peyssonoic acids included one novel carbon skeleton and illustrated the utility of ecological studies in natural product discovery.     

An expeditious protocol for sesquiterpene-cored functionalized arenes from S-(−)-citronellal

An expeditious straightforward synthesis of sesquiterpene-cored arenes functionalized with electron-withdrawing or electron-donating substituents is described and illustrated by Michael addition of S-(−)-citronellal on functionalized 2H-pyran-2-one in a single step at room temperature. The reaction was further generalized by synthesizing isoprenylated 9,10-dihydrophenanthrene-2-carbonitrile using 5,6-dihydro-2-oxo-4-sec-amino-2H-benzo[h]chromene-3-carbonitriles and S-(−)-citronellal under similar reaction conditions.     

A new sesquiterpene from Caragana intermediia

A new alloaromadendrane-type sesquiterpene,(-)-alloaromadendrane-3β,9β-diol(1),has been isolated from the aerial part of Caragana intermediia.The structure of (-)-alloaromadendrane-3β,9β-diol(1)was established by spectroscopic methods, including X-ray analysis that provided its relative stereochemistry.Bioassay showed that (-)-alloaromadendrane-3β,9β-diol (1)possesses anti-pyricularia oryzae P-2b activity with MIC value of 10μg/mL.     

Synthesis of quinone/hydroquinone sesquiterpenes

ent-Halimic acid has been used in the synthesis of the quinone/hydroquinone sesquiterpenes (−)-aureol, (−)-smenoqualone, (−)-neomamanuthaquinone and in the formal synthesis of (−)-cyclosmenospongine.     

Asymmetric total synthesis of (+)-curcutetraol and (+)-sydonol

The asymmetric total syntheses of (+)-curcutetraol and (+)-sydonol, phenolic bisabolane-type sesquiterpenoids having chiral tertiary alcohol moiety in the o-position of a phenol, were achieved in high enantiomeric excesses (99% ee). The chiral tertiary benzylic alcohol moiety of these compounds was constructed by an asymmetric synthesis using an easily available chiral aminal, (−)-(2R,5S)-2-methoxycarbonyl-3-phenyl-1,3-diazabicyclo[3.3.0]octane. The absolute configurations of both (+)-curcutetraol and (+)-sydonol have been assumed to be S-configuration based on the stereochemical course of the well established asymmetric synthesis used in the syntheses.     

Kunzeanones A, B, and C: novel alkylated phloroglucinol metabolites from Kunzea ambigua

Three new metabolites, kunzeanones A (1), B (2), and C (3), along with three known compounds, cryptostrobin (4), (+)-spathulenol (5), and (−)-globulol (6), were isolated from the non-polar fraction of the dried leaves of Kunzea ambigua (Myrtaceae), which shows ichthyotoxicity toward a small fish, medaka. The structures of these new compounds were elucidated as condensates of alkylated phloroglucinol with methylflavanone and germacrane-type sesquiterpene, respectively, on the basis of spectral analyses including 1-D and 2-D NMR spectra. The stereochemistries of kunzeanones A and B were determined by X-ray crystallographic analysis. A sesquiterpene, (+)-spathulenol (5), among the isolates was characterized as the ichthyotoxic principle of the extract.