Asymmetric Synthesis of Axinellamines A and B

Axinellamines A and B are broad‐spectrum antibacterial pyrrole–imidazole alkaloids that have a complex polycyclic skeleton. A new asymmetric synthesis of these marine sponge metabolites is described herein, featuring an oxidative rearrangement and an anchimeric chlorination reaction.     

Structure revision of circumdatins A and B, benzodiazepine alkaloids produced by marine fungus Aspergillus ostianus, by X-ray crystallography

The structures of circumdatins A and B, pentacyclic alkaloids produced by Aspergillus ostianus, were revised from the previously reported betaine structures to unique oxepin ones by X-ray crystallography. The co-occurring known alkaloids, circumdatins D, E, and H, and a new compound reported here, circumdatin J, have a common framework.     

Total synthesis of clathculins A and B

Clathculins A and B represent a new class of vic-diamine alkaloids containing a PA2 unit as the basic structure. We report the first total syntheses of 1 and 2, which confirm the assigned structure of each. Dependence of their NMR spectroscopic behavior as a function of protonation state has been observed.     

Isatinones A and B, new antifungal oxindole alkaloids from Isatis costata

Two new oxindole alkaloids isatinone A (1) and B (2) have been isolated from Isatis costata, along with the known trisindoline. Their structures have been assigned on the basis of spectroscopic techniques and chemical studies. Both new compounds showed significant antifungal activity.     

Two novel indole alkaloids, Kopsiyunnanines A and B, from a Yunnan Kopsia

Two novel indole alkaloids having unusual skeletons were isolated from the aerial part of Yunnan Kopsia arborea. Kopsiyunnanine A (1) is a new class of bisindole alkaloid composed of vallesiachotamine (modified Corynanthe-type) and Aspidospermatan-type alkaloids. Kopsiyunnanine B (2) is a new Corynanthe-type oxindole alkaloid rearranged by D ring rotation.     

Virosaines A and B, two new birdcage-shaped Securinega alkaloids with an unprecedented skeleton from Flueggea virosa

Two new Securinega alkaloids, virosaines A (1) and B (2), were isolated from the twigs and leaves of Flueggea virosa. The structures and absolute configurations were elucidated by means of NMR, X-ray diffraction, and CD analyses. Compounds 1 and 2 represent the first examples of Securinega alkaloids bearing a 7-oxa-1-azabicyclo[3.2.1]octane ring system, whose plausible biogenetic pathways were also proposed.     

Total synthesis of the indole alkaloids henrycinol A and B

The total synthesis of new indole alkaloids henrycinol A and B were accomplished starting from l-tryptophan methyl ester. The key step is a stereochemically flexible Pictet–Spengler reaction governed by the presence or absence of an N-allyl group in the tryptophan precursor. The natural products henrycinol A and B were synthesized in good overall yield in eight and nine steps, respectively.     

Neoverataline A and B, two antifungal alkaloids with a novel carbon skeleton from Veratrum taliense

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.     

Haloxylines A and B, antifungal and cholinesterase inhibiting piperidine alkaloids from Haloxylon salicornicum

Haloxylines A (1) and B (2), new piperidine alkaloids, have been isolated from the chloroform soluble fraction of Haloxylon salicornicum and their structures elucidated by spectroscopic techniques including 2D-NMR. Both the compounds displayed antifungal and cholinesterase enzymes inhibitory potentials.     

Veramadines A and B, New Steroidal Alkaloids from Veratrum maackii var. japonicum

Two new steroidal alkaloids possessing a cevanine-type skeleton, veramadines A (1) and B (2), were isolated from the aerial parts of Veratrum maackii var. japonicum. The structures of 1 and 2 were elucidated on the basis of their spectroscopic data.     

Stephacidin A and B: two structurally novel,selective inhibitors of the testosterone-dependent prostate LNCaP cells

Two novel antitumor alkaloids, Stephacidin A and B, were isolated from the solid fermentation of Aspergillus ochraceus WC76466. Both alkaloids exhibit in vitro cytotoxicity against a number of human tumor cell lines; however, stephacidin B demonstrated more potent and selective antitumor activities, especially against prostate testeosterone-dependent LNCaP cells with IC50 value of 60 nM. The structures of stephacidin A and B were established on the basis of the NMR data and X-ray crystallography. With 15 rings and 9 chiral centers, stephacidin B represents one of the most structurally complex and novel alkaloids occurring in nature.     

Paxiphyllines A and B, new alkaloids from Daphniphyllum paxianum

Two new Daphniphyllum alkaloids with daphnicyclidin-type skeleton, paxiphyllines A (1) and B (2) were isolated from the twigs and the leaves of Daphniphyllum paxianum. Paxiphylline A (1) has an unprecedented additional carbon from a biogenetic perspective. The structures and relative configurations were elucidated on the basis of spectroscopic data.     

Daphnoldines A and B,Two New Yuzurine Alkaloids with a Four‐Ring System,from the Fruits of Daphniphyllum oldhami

Two new yuzurine alkaloids, daphnoldines A ( 1 ) and B ( 2 ), possessing a rare four‐ring system, were isolated from the fruits of Daphniphyllum oldhami. Their structures were established on the basis of extensive spectroscopic analyses. Daphnoldine A ( 1 ) is the first example of Daphniphyllum alkaloids bearing a hydroxymethyl group at C(14).     

Wrightiamines A and B,two new cytotoxic pregnane alkaloids from Wrightia javanica

Two new pregnane alkaloids, wrightiamines A (1) and B (2), were isolated from the extract of the tropical Apocynaceous plant Wrightia javanica collected in Thailand, and their structures were elucidated by spectral data. Wrightiamine B (2) was preparaed from 3beta-hydroxy-5alpha-pregnan-20-one to establish the configuration of the C-20 position as S. Wrightiamine A (1) exhibited cytotoxic activity against vincristine-resistant murine leukemia P388 cells.     

Neolamarckines A and B, new indole alkaloids from Neolamarckia cadamba

Two new indole alkaloids, neolamarckines A and B (1, 2) were isolated from the leaves of Neolamarckia cadamba (Rubiaceae). Structural elucidation of 1 and 2 was performed by combination of 2D-NMR and circular dichroism (CD) spectra, and chemical correlations. Neolamarckine A (1) showed inhibition of inducible nitric oxide synthase (iNOS) dose dependently.     

Two New Iridoid Alkaloids,Daphmacropodosidines A and B,from Daphniphyllum macropodum

Two new iridoid alkaloids, daphmacropodosidines A ( 1 ) and B ( 2 ), together with two known ones, daphcalycinosidine B and caldaphnidine F, were isolated from the fruits of Daphniphyllum maropodum. Their structures were established by spectral methods, especially 2D NMR spectra (¹H,¹H‐COSY, HMQC, HMBC, and NOESY), as well as chemical means.     

Total syntheses of makaluvamines A, B, C, D and E, cytotoxic pyrroloiminoquinone alkaloids isolated from marine sponge bearing inhibitory activities against topoisomerase II

Syntheses of makaluvamines A, B, C, D and E (1 – 5), new members of tetrahydropyrroloiminoquinone alkaloids, have been successfully carried out. Particularly, olefin introduction for makaluvamines B and E could be achieved by Pd - mediated and E₂ type methodologies.     

Natural products, stylissadines A and B, specific antagonists of the P2X7 receptor, an important inflammatory target

The distribution of the P2X7 receptor in inflammatory cells suggests that P2X7 antagonists have a significant role to play in the treatment of inflammatory disease. We conducted a natural product high-throughput screening campaign to discover P2X7 receptor antagonists. The Australian marine sponge Stylissa flabellata yielded two new bisimidazo-pyrano-imidazole bromopyrrole ether alkaloids, stylissadines A (IC50 0.7 microM) and B (IC50 1.8 microM), as the specific bioactive constituents. The compounds inhibit BzATP-mediated pore formation in THP-1 cells. Also present in this extract was considerable nonspecific bioactivity in the hemeolysin specificity assay. A new pyrrole-imidazole alkaloid, konbu'acidin B, and the known pyrrole-imidazole alkaloids 4,5-dibromopalau'amine and massadine were also isolated and had nonspecific activity. ROESY and proton coupling constant data indicated that the stereochemistry at C12, C17, and C20 in 4,5-dibromopalau'amine should be revised to 12R, 17S, 20S. By analogy, the relative stereochemistry of palau'amine, 4-bromopalau'amine, styloguanidine, 3-bromostyloguanidine, and 2,3-dibromostyloguanidine should also be revised to 12R, 17S, 20S. Stylissadines A and B are the most potent natural product P2X7 antagonists to be isolated to date and provide a novel class of P2X7 receptor inhibitors. They are also the first examples of tetrameric pyrrole-imidazole alkaloids.     

Total synthesis of didemnimide A and B

The total synthesis of didemnimide A and didemnimide B, novel predator-deterrent alkaloids from the Caribbean mangrove ascidian Didemnum conchyliatum, is described.     

Kopsine and Danuphylline Alkaloids from Kopsia. Biomimetic Partial Synthesis of Danuphylline B

Two new indole alkaloids, 12‐methoxykopsine ( 6 ) and danuphylline B ( 7 ), were obtained from the leaf extract of the Malayan Kopsia species, K. arborea, and their structures established by spectroscopic analysis. An electrochemically‐mediated partial synthesis of the ring‐opened alkaloid, danuphylline B from the hexacyclic alkaloid, methyl N(1)‐de(methoxycarbonyl)chanofruticosinate was carried out.