Dolastanes from the brown alga Dilophus spiralis: absolute stereochemistry and evaluation of cytotoxicity

Five new dolastanes (1-5) were isolated from the brown alga Dilophus spiralis. The structural elucidation of the isolated compounds and the assignment of relative stereochemistry were based on analyses of their spectroscopic data. The structure proposed for 1 was confirmed by single crystal X-ray diffraction analysis, whereas its absolute stereochemistry was determined using the modified Mosher's method. The cytotoxicity of 1-4 was evaluated against seven cell lines.     

Calyciphyllines H-M, new Daphniphyllum alkaloids from Daphniphyllum calycinum

Six new Daphniphyllum alkaloids, calyciphyllines H-M (1-6), were isolated from the leaves and stems of Daphniphyllum calycinum (Daphniphyllaceae). The structures and relative stereochemistry of 1-6 were elucidated on the basis of spectroscopic data, and the absolute stereochemistry of 3 was assigned by PGME method.     

Pregnanes with antiproliferative activity from the gorgonian Eunicella cavolini

Four new natural products (1-4), along with three previously reported metabolites (5-7), all belonging to the pregnane class of steroids were isolated from the organic extract of the gorgonian Eunicella cavolini. The structures and relative configurations of the isolated compounds were determined through NMR spectroscopic techniques and chemical interconversions, while their absolute stereochemistry was determined using the modified Mosher's method. Activity evaluation of 1-7 towards MCF-7 human breast cancer cells showed partial growth inhibitory effects for all metabolites bearing an 11α-acetoxy moiety.     

Yezo’otogirins A-C, new tricyclic terpenoids from Hypericum yezoense

Three new tricyclic terpenoids, yezo’otogirins A-C (1-3), were isolated from aerial parts of Hypericum yezoense. The structures including absolute stereochemistry of 1-3 were elucidated from the spectroscopic data and conformational analysis.     

Durumolides A-E, anti-inflammatory and antibacterial cembranolides from the soft coral Lobophytum durum

Chemical investigations on the acetone extract of the soft coral Lobophytum durum have afforded five new cembranoids with a trans-fused α-methylene-γ-lactone, durumolides A-E (1, 6, and 8-10), and five previously characterized cembrane-based diterpenoids (2-5 and 7). The structures of the isolated metabolites were elucidated through extensive spectroscopic analyses, while the relative stereochemistry of 4 was confirmed by X-ray diffraction analyses. Moreover, the absolute configurations of 3-5 and 8 were established by application of modified Mosher's method. The anti-inflammatory effects, antibacterial activities, and inhibition assay of HCMV (Human cytomegalovirus) endonuclease activity of these isolated metabolites 1-10 were evaluated in vitro.     

Labdane diterpenes with a new oxidation pattern from the marine pulmonate Trimusculus peruvianus

Four new labdane diterpenes, 1-4, with an unusual oxidation pattern have been isolated from the marine pulmonate Trimusculus peruvianus. The structure and stereochemistry of these compounds were determined by spectroscopic data and chemical transformations. The absolute stereochemistry of 4 was assigned by application of the modified Mosher method. These compounds exhibit in vitro moderate cytotoxic activity against human colon carcinoma cell lines.     

Senepodines B-E, new C22N2 alkaloids from Lycopodium chinense

Four new C₂₂N₂Lycopodium alkaloids, senepodines B-E (2-5), consisting of an octahydroquinoline ring and a quinolizidine ring have been isolated together with senepodine A (1) from the club moss Lycopodium chinense. The relative and absolute stereochemistry of 2-5 were determined by combination of NOESY correlations and chemical transformation, while the absolute configuration of 1 was assigned by exciton chirality method.     

The enantioselective synthesis of poison-frog alkaloids (−)-203A, (−)-209B, (−)-231C, (−)-233D, and (−)-235B″

The enantioselective synthesis of indolizidines (−)-203A, (−)-209B, (−)-231C, (−)-233D, and (−)-235B″ has been achieved and the absolute stereochemistry of both indolizidines 203A and 233D was established as 5S,8R,9S. The relative stereochemistry of natural 231C was established by the present asymmetric synthesis.     

Cynanosides A-J, ten novel pregnane glycosides from Cynanchum atratum

Four novel 13,14:14,15-diseco-18-nor-pregnane-type steroidal glycosides, cynanosides A-D (1-4), and six novel 13,14:14,15-diseco-pregnane-type steroidal glycosides, cynanosides E-J (5-10) were isolated from the roots of Cynanchum atratum, together with one known compound, cynatratoside F (11). Their structures including the absolute stereochemistry were determined on the basis of spectroscopic analysis and chemical evidence, with combination of the modified Mosher method, the exciton chirality method and chemical transformations.     

Anti-inflammatory steroids from the octocoral Dendronephthya griffini

Five new steroids, griffinisterones A-E (1-5), were isolated from the octocoral Dendronephthya griffini. The structures of these compounds were elucidated by extensive spectroscopic analysis. The single-crystal X-ray crystallography on 1 allowed the determination of the 24R configuration in 1. The absolute stereochemistry of 5 was determined by the application of PGME method. Compounds 3 and 4 were found to significantly inhibit the accumulation of the pro-inflammatory iNOS protein of the LPS-stimulated RAW264.7 macrophage cells.     

Rakanmakilactones A-F, new cytotoxic sulfur-containing norditerpene dilactones from leaves of Podocarpus macrophyllus var. maki

Six new S-containing norditerpene dilactones, rakanmakilactones A-F (5-10), were isolated from the leaves of Podocarpus macrophyllus D. Don var. maki Endl., along with four known norditerpene dilactones (1-4). Their structures, stereochemistry and absolute configurations were determined by spectroscopic studies (HRMS, IR, ¹H, ¹³C and 2D NMR), and single-crystal X-ray analyses. Rakanmakilactones were found to have a cytotoxic effect against P388 murine leukemia cells.     

Cembradienes from the Caribbean sea whip Eunicea sp.

A new cembradiene diterpenoid 1, together with the known antiplasmodial cembradiene 2, was isolated from the sea whip Eunicea sp. collected from Santa Marta Bay on the Colombian Caribbean sea. The structures and absolute stereochemistry of 1-2 were determined by extensive spectroscopic analysis, chemical transformation of 2 to the new diterpenoid 3, and by using modified Mosher’s method. This is the first known report regarding the determination of the absolute configuration of 2.     

Xyloccensins Q-V, six new 8,9,30-phragmalin ortho ester antifeedants from the Chinese mangrove Xylocarpus granatum

Six new 8,9,30-phragmalin ortho esters, named xyloccensins Q-V (3-8), have been isolated from the stem bark of a Chinese mangrove Xylocarpus granatum, and their structures were elucidated on the basis of spectroscopic data and chemical means. The absolute stereochemistry of these compounds and xyloccensins O-P (1-2), revised as enantiomeric to all the phragmalins reported so far, was determined by application of the modified MTPA Mosher ester method and circular dichroism analysis. Both xyloccensins P and Q exhibited potent antifeedant activity against the third instar larvae of Mythimna separata (Walker) at a concentration of 500 ppm.     

Crucigasterins A-E, antimicrobial amino alcohols from the Mediterranean colonial ascidian Pseudodistoma crucigaster

Five new unsaturated 2-amino-3-alcohols, crucigasterins A-E (2-6), were isolated together with known related compound 7 from the Mediterranean ascidian Pseudodistoma crucigaster and characterised as diacetyl derivatives (2a-6a) by spectroscopic methods. The threo-relative configuration of the amino alcohol portion was inferred by NOE analysis of the oxazolidinone derivative of crucigasterin A (2) as well as by ¹³C NMR comparison with synthetic threo and erythro model compounds. The co-occurring metabolites were assumed to have the same relative configuration as 2 by comparison of the diagnostic carbon value of C-1. The absolute stereochemistry of compound 7 that had not been previously reported was determined by applying the modified Mosher’s method on the corresponding N-acetyl derivative. The same absolute configuration was suggested for the other co-occurring crucigasterins by biogenetic considerations. Antibacterial and antifungal activities of selected crucigasterins were also evaluated.     

Cytotoxic bromoditerpenes from the red alga Sphaerococcus coronopifolius

Three new brominated diterpenes (1, 2, 8), along with six previously reported metabolites (3-7, 9), were isolated from the organic extract of Sphaerococcus coronopifolius, collected in Palaiokastritsa bay at the west coasts of Corfu Island. The structures of the new natural products, as well as their relative stereochemistry, were established by means of spectral data analyses, including 2D experiments. The absolute stereochemistry of 2 and 4 as well as the structure revision of the previously reported metabolite 3 were established by X-ray crystallographic analyses. The cytotoxicity of the isolated metabolites was evaluated against the NSCLC-N6-L16 and A549 human lung cancer cell lines.     

Eight new limonoids from Turraea pubescens

Eight new ring B-seco limonoids, turrapubesic acids A-C (1-3) and turrapubesins C-G (4-8), along with turraflorin E and isoazadironolide were isolated from the twigs and leaves of Turraea pubescens. Turrapubesic acids A-C (1-3) are a group of ring B-seco limonoid 17-carboxylic acids with a new C₂₃ skeleton, and turrapubesin C (4) incorporates an unprecedented 1,30-oxygen bridge. The structures including absolute stereochemistry of 1-8 were established on the basis of extensive NMR spectroscopic analysis and CD study. The cytotoxicity of the isolates against the P-388 and A-549 cells was evaluated.     

Novel antifungal polyene amides from the myxobacterium Cystobacter fuscus: isolation, antifungal activity and absolute structure determination

Three new unstable metabolites, (6E,10Z)-2′-O-methylmyxalamide D (1), 2′-O-methylmyxalamide D (2) and (6E)-2′-O-methylmyxalamide D (3) were isolated from the myxobacterium Cystobacter fuscus. The planar structures were elucidated by spectroscopic analyses to be geometrical isomers of a polyene amide related to a myxobacterial metabolite, myxalamide D (4). Their absolute stereochemistry was determined by synthesis of degradation products. Antifungal activities of 1-3 as well as their acetates were evaluated against the phythopathogenic fungus Phythopthora capsici.     

Aplysiols A and B, squalene-derived polyethers from the mantle of the sea hare Aplysia dactylomela

Two novel triterpenoids, aplysiols A (5) and B (6), have been isolated, together with structurally related known metabolites, from a South China Sea collection of the anaspidean mollusc Aplysia dactylomela. The structures of 5 and 6 were determined mainly by spectroscopic NMR techniques. The absolute stereochemistry of compound 5 was deduced by Mosher's method as well as by biogenetical consideration, whereas the absolute stereochemistry of compound 6 was established also using an integrated NMR-QM (Quantum Mechanical) approach, based on the combination of ¹³C NMR chemical shifts and ^2,3J_C-H coupling constant DFT (density functional theory) calculations.     

The absolute configuration determination of naturally occurring diacetylenic spiroacetal enol ethers from Artemisia lactiflora

Six new naturally occurring diacetylenic spiroacetal enol ethers, Lactiflodiynes A-F (1-6), together with five known congeners (7-11), were isolated from the whole plant of Artemisia lactiflora (Compositae). The structures were elucidated by extensive spectroscopic methods, X-ray crystallography, chemical transformations, and CD. The absolute configuration of Lactiflodiyne A (1) was determined to be 2R, 5S, 6S, and 7R by an X-ray crystallographic diffraction experiment using Mo Kα radiation with the absolute parameter of 0.01(8). In combination with CD, the absolute configurations of compounds 2-11 were confirmed by chemical transformations using 1 as the starting material.     

New phlegmarane-type, cernuane-type, and quinolizidine alkaloids from two species of Lycopodium

Two new phlegmarane-type alkaloids, cermizines A (1) and B (2), three new quinolizidine alkaloids, cermizine C (3) and senepodines G (4) and H (5), and a new C₁₆N₂ type alkaloid consisting of a quinolizidine and a piperidine ring, cermizine D (6), as well as two new cernuane-type alkaloids, cernuine N-oxide (7) and lycocernuine N-oxide (8), have been isolated together with cernuine (9) and lycocernuine (10) from the club moss Lycopodium cernuum and L. chinense. The relative stereochemistry of 1-4 and 6, and the absolute stereochemistry of 5, 7, and 8 were elucidated by combination of NOESY correlations, modified Mosher's method, chemical transformations, and computational methods. Cermizine D (6) might be a biosynthetic intermediate of cernuane-type alkaloids such as 7-10.