The structures of three new shishididemniols from a tunicate of the family Didemnidae

Three new serinolipid derivatives, shishididemniols C (1), D (2), and E (3), were isolated as antibacterial constituents of a tunicate of the family Didemnidae. Their planar structures were elucidated by interpretation of NMR and MS data, whereas the absolute stereochemistry was determined by chemical conversions. Shishididemniols C (3), D (4), and E (5) exhibited antibacterial activity against the fish pathogenic bacterium Vibrio anguillarum.     

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.     

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.     

Novel alkaloids, paxdaphnines A and B with unprecedented skeletons from the seeds of Daphniphyllum paxianum

Two novel Daphniphyllum alkaloids with unprecedented skeletons, namely paxdaphnines A (1) and B (2), have been isolated from the seeds of Daphniphyllum paxianum. Paxdaphnine A (1) is a 19-nor-Daphniphyllum alkaloid with highly caged skeleton, and paxdaphnine B (2) is the first 1,19-bisnor-Daphniphyllum alkaloid. The relative structures of 1 and 2 were elucidated by spectral methods, and their unique biosynthetic pathway postulated. The absolute structure of 1 was determined by X-ray diffraction of the iodide derivative (1a) of 1, and the absolute stereochemistry of 2 was proposed by correlation with the biosynthetic pathway for 1.     

A novel chlorinated norsesquiterpenoid and two related new metabolites from the soft coral Paralemnalia thyrsoides

A structurally unique chlorinated norsesquiterpenoid, paralemnolin A (1), along with two new metabolites, paralemnolin B (2) and C (3), have been isolated from the soft coral Paralemnalia thyrsoides. Their structures were determined by extensive spectroscopic analyses. Single-crystal X-ray diffraction analysis of 1 further establish the absolute stereochemistry of 1.     

Phormidinines A and B, novel 2-alkylpyridine alkaloids from the cyanobacterium Phormidium sp.

Novel 2-alkylpyridine alkaloids, phormidinines A (1) and B (2), were isolated from cyanobacterium Phormidium sp. Their structures were determined by spectroscopic analysis. The absolute stereochemistry of 1 was established by the modified Mosher’s method.     

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.     

New antimitotic bicyclic peptides, celogentins D-H, and J, from the seeds of Celosia argentea

Six new bicyclic peptides, celogentins D-H (1-5) and J (6) have been isolated from the seeds of Celosia argentea, and the structures including its absolute stereochemistry were determined by using extensive NMR methods and chemical means. Celogentins E-H (2-5) and J (6) showed potent inhibition of tubulin polymerization, while the inhibitory activity of celogentin D (1) was modest. Structure-activity relationship study indicates that ring size of the bicyclic ring system including unusual β^s-Leu, Trp, and His residues would be important for their biological activity.     

Cytotoxic sesterterpenes, 6-epi-ophiobolin G and 6-epi-ophiobolin N, from marine derived fungus Emericella variecolor GF10

Two new sesterterpenes, 6-epi-ophiobolin G (1) and 6-epi-ophiobolin N (3), and six known ophiobolins were isolated from the extracts of the fungus, Emericella variecolor GF10, which was separated from marine sediment. The planar structures of the new compounds were deduced from analysis of the 2D NMR spectra, and the stereochemistry was determined by extensive examination of the NOESY spectrum. Additionally, the configuration of the C-6 proton in ophiobolin G (2) was revised from α to β, and the unsolved stereochemistry of ophiobolin H (4) was determined by its physicochemical evidence and the chemical correlation with ophiobolin K (8). Ophiobolin K (8) showed cytotoxic activity against various tumor cell lines, including adriamycin-resistant mouse leukemia cells (P388), with IC₅₀ of 0.27-0.65 μM.     

Revised structure and structure-activity relationship of bisebromoamide and structure of norbisebromoamide from the marine cyanobacterium Lyngbya sp.

Novel potent cytotoxic peptides bisebromoamide (1) and norbisebromoamide (2) have been isolated from the marine cyanobacterium Lyngbya sp. The planar structure of these peptides was elucidated through the extensive application of 1D and 2D NMR techniques. The absolute stereostructure of 1 was determined by chemical degradation followed by chiral HPLC analysis. Recently, Tao and co-workers achieved synthesis of bisebromoamide, and the configuration of thiazoline moiety was revised. We re-investigated the stereochemistry of thiazoline moiety of 1. The structure-activity relationships of bisebromoamide (1) were investigated with the use of natural and synthetic analogs. Furthermore, bisebromoamide (1) potently inhibited protein kinase: the phosphorylation of ERK in NRK cells by PDGF-stimulation was selectively inhibited by treatment with 10-0.1 μM of 1.     

Kuroshines A and B,new alkaloids from Zoanthus kuroshio

A chemical investigation of Zoanthus kuroshio has yielded two new alkaloids, kuroshines A (1) and B (2). The compounds possess a densely functionalized ring system on the basis of the zoanthamine frames. The structures of 1 and 2 were elucidated through interpretation of spectroscopic methods, especially 2D NMR techniques (COSY, HMQC, HMBC, and ROESY). The absolute stereochemistry of 1 was further confirmed by an X-ray single crystallographic analysis using a mirror Cu-Kα radiation.     

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.     

Conformational analysis and absolute stereochemistry of ‘spongian’-related metabolites

New degraded and rearranged diterpenoids, 5-8, have been isolated from the Antarctic sponge Dendrilla membranosa. The structure and relative stereochemistry of these compounds were determined by spectroscopic data. The absolute stereochemistry of 5 was determined by spectroscopic data using a chiral reagent. Conformational studies allowed us to assign also the absolute stereochemistry of 6-8, as well as those previously isolated spongian-derived metabolites with known relative stereochemistries.     

Lyconadins C and F, new Lycopodium alkaloids from Lycopodium complanatum

New Lycopodium alkaloids, lyconadins C (1) and F (2), were isolated from the club moss Lycopodium complanatum. Lyconadin C (1) is a new C₁₆N₂-type Lycopodium alkaloid possessing unique fused-tetracyclic ring system consisting of a cycloheptene ring fused to a decahydroquinoline and pyridone rings. Lyconadin F (2) possesses a primary amide moiety in its molecular, which is the first example of Lycopodium alkaloids. Biogenetically, lyconadins C (1) and F (2) might be related to lyconadins A (4) and B (5). The structures and relative stereochemistry of 1 and 2 were elucidated on the basis of spectroscopic data. The absolute stereochemistry of 2 was elucidated by chemical correlations with lyconadin B (5) through hemiaminal form of lyconadin F (3).     

An unusual indole alkaloid with anti-adenovirus and anti-HSV activities from Alstonia scholaris

A novel alkaloid, 17-nor-excelsinidine (1), possessing an unusual 1-azoniatricyclo [4.3.3.0] undecane moiety was isolated from the twigs and leaves of Alstonia scholaris alongside its biogenetically related strictamine (2). The structure and absolute stereochemistry of compound 1 were rigorously determined by a combination of NMR spectroscopy and X-ray crystallography. The 17-nor-excelsinidine (1) and strictamine (2) showed significant inhibitory activity against herpes simplex virus (HSV) and adenovirus (ADV).     

Daphniglaucins D-H, J, and K, new alkaloids from Daphniphyllum glaucescens

Five new fused-hexacyclic alkaloids, daphniglaucins D (1), E (2), F (3), G (4), and H (5), and two new yuzurimine-type alkaloids, daphniglaucins J (6) and K (7), have been isolated from the leaves of Daphniphyllum glaucescens, and the structures and relative stereochemistry were elucidated on the basis of spectroscopic data and chemical means.     

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 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.     

Amarusine A,a new dioxaspiro[4.4]nonane derivative with a butyrolactone ring from Pleioblastus amarus

Amarusine A (1), a new polyketide derivative possessing an unusual dioxaspiro[4.4]nonane derivative with a butyrolactone ring, was isolated from the leaves of Pleioblastus amarus. The structure and absolute stereochemistry of compound 1 were rigorously determined using UV, IR, HRESIMS, and 1D and 2D NMR techniques and by comparing experimental and calculated electronic circular dichroism (ECD) spectra. Amarusine A (1) exhibits a good antioxidant activity for scavenging the DPPH radical. A possible biosynthetic pathway was postulated.     

Pre-schisanartanins C-D and propintrilactones A-B, two classes of new nortriterpenoids from Schisandra propinqua var. propinqua

Four new nortriterpenoids, pre-schisanartanins C and D (1-2) with pre-schisanartane backbone, and propintrilactones A and B (3-4) possessed wuweiziartane framework, were isolated from the acetone extract of the stems of Schisandra propinqua var. propinqua. Their structures were characterized by extensive spectroscopic analyses. Compounds 3 and 4 existed as a pair of slowly interconverting diastereomers at room temperature; their absolute configuration was established by CD methods. Compounds 1-4 showed no cytotoxicity against K562, A549, and HT-29 human cancer cells.