The natural products chemistry of West Indian gorgonian octocorals

Synthetic studies towards furanocembrane diterpenes. A total synthesis of bis-deoxylophotoxin

Synthetic approaches to the furanocembrane family of natural products, e.g. lophotoxins, pukalides, bipinnatins, based on: i) an intramolecular cyclisation of an alpha,beta-unsaturated acyl radical intermediate into a conjugated enone, and ii) an intramolecular Stille coupling reaction involving a 2-stannylfuran and a vinyl iodide, are described. A total synthesis of bis-deoxylophotoxin , the probable biological precursor to the neurotoxin lophotoxin, isolated from species of the Pacific sea whip Lophogorgia, is then presented.

Phosphine-Mediated Reductive Condensation of γ-Acyloxy Butynoates: A Diversity Oriented Strategy for the Construction of Substituted Furans

Exposure of gamma-acyloxy butynoates to stoichiometric quantities of triphenylphosphine results in reductive condensation to afford substituted furans, by way of allenic ester intermediates. As gamma-acyloxy butynoates are readily obtained through condensation of ethyl propiolate with aldehydes followed by acylation, this method represents a powerful and mechanistically novel protocol for the convergent three-component construction of substituted furans.

Calyculaglycosides D and E, novel cembrane glycosides from the Caribbean gorgonian octocoral Eunicea species and structural revision of the aglycon of calyculaglycosides A-C

A recent investigation of the constituents of Eunicea sp. from Colombia and Puerto Rico has provided two novel cembrane glycosides, calyculaglycosides D (6) and E (7), and a new cembranoid diterpene in free form, (+)-nephthenol (4). Metabolites 6 and 7 possess a glycosyl-fused cembrane skeleton with a 1S configuration. Biogenetic considerations have led to a revision of the previously assigned dilophol skeleton of calyculaglycosides A-C, which was confirmed by extensive 2D NMR investigation and a chemical degradation study. Consequently, the true structures for calyculaglycosides A-C are 8-10, respectively, not 1-3. This is the first report of the occurrence of marine diterpene glycosides having a cembrane aglycon.

Studies toward the total synthesis of clavulactone

Synthetic studies directed toward a total synthesis of clavulactone are reported. In light of the analysis made in our previous work, cyclopentane 4a (a key intermediate in the present work) was synthesized through a radical-mediated ring closure of a rationally designed substrate 25. Using HWE reactions, the lower and upper side-chains of 4a were converted into an allyl chloride and an allyl cyanohydrin, respectively. Subsequent treatment of the allyl chloride/cyanohydrin in a highly diluted THF solution with sodium bis(trimethylsiliyl)amide led to intramolecular alkylation and thus completed a major endeavor in synthesizing the dolabellane framework, construction of the eleven-membered ring. SmI(2)-mediated lactonization as a model reaction for the formation of the alpha,beta-unsaturated delta-lactone segment of clavulactone is also described.

Tobacco cembranoids block behavioral sensitization to nicotine and inhibit neuronal acetylcholine receptor function

Cembranoids are cyclic diterpenoids found in tobacco and in marine invertebrates. The present study established that tobacco cembranoids inhibit behavioral sensitization to nicotine in rats and block several types of nicotine acetylcholine receptors (AChRs). 1) At the behavioral level, rat locomotor activity induced by nicotine was significantly increased after seven daily nicotine injections. This sensitization to nicotine was blocked by mecamylamine (1 mg/kg) and by the cembranoids eunicin, eupalmerin acetate (EUAC), and (4R)-2,7,11-cembratriene-4-6-diol (4R), each at 6 mg/kg. None of these compounds modified locomotor activity of nonsensitized rats. 2) In cells expressing human AChRs, cembranoids blocked carbamoylcholine-induced (86)Rb(+) flux with IC(50) in the low micromolar range. The cell lines used were the SH-EP1-halpha4beta2 cell line heterologously expressing human alpha4beta2-AChR, the SH-SY5Y neuroblastoma line naturally expressing human ganglionic alpha3beta4-AChR, and the TE671/RD cell line naturally expressing embryonic muscle alpha1beta1gammadelta-AChR. The tobacco cembranoids tested were 4R and its diastereoisomer 4S, and marine cembranoids tested were EUAC and 12,13-bisepieupalmerin. 3) At the molecular level, tobacco (4R and 4S) and marine (EUAC) cembranoids blocked binding of the noncompetitive inhibitor [(3)H]tenocyclidine to AChR from Torpedo californica electric organ. IC(50) values were in the submicromolar to low-micromolar range, with 4R displaying an order of magnitude higher potency than its diastereoisomer, 4S.

New metabolites from the West Indian sea feather Pseudopterogorgia bipinnata

Two diterpenes, a novel seco-furanocembranolide (3) and the highly oxygenated cembranolide bipinnatolide K (4), have been isolated from the West Indian gorgonian octocoral Pseudopterogorgia bipinnata. The chemical structures of these compounds were determined by 1D and 2D NMR spectroscopy in combination with IR, UV, and HRFABMS analyses.

Pseudopterane and norcembrane diterpenoids from the Caribbean sea plume Pseudopterogorgia acerosa

A chemical study of the common Caribbean sea plume Pseudopterogorgia acerosa from Puerto Rico has produced two previously undescribed secondary metabolites. One of them, 1, is a new representative of the pseudopterane family of diterpenes possessing the uncommon 3,4;5,6 diepoxyfuran moiety. The other metabolite, 2, is a rare norcembranolide diterpene. Their chemical structures, including relative stereochemistry, were established by detailed analysis of the spectral data in addition to NMR spectral comparisons with known pseudopterane and cembrane models.

New cembranolides from the gorgonian Eunicea succinea

A new chemical study of the Caribbean gorgonian Eunicea succinea collected in Puerto Rico afforded seven new cembranolides (1-5, 7, and 8). Excepting 1, the new compounds described here possess an unusual unsaturation at either position C-1, C-6, or C-8, and all but 8 possess the C-12R, C-13S stereochemistry usually ascribed to cembranolides from E. succinea. Their chemical structures were carefully established by a combination of chemical and spectroscopic methods in addition to detailed NMR spectral comparisons with known cembranolide models.