Dolabellane Skeleton Research Articles

Grob-Fragmentation-Enabled Approach to Clavulactone Analogues.

The novel synthetic strategy for dolabellane skeleton was realized, which allowed the synthesis of clavulactone analogues 26 and 27 in a concise and efficient manner. Salient transformations include a diastereoselective Mukaiyama aldol reaction, an intramolecular nucleophilic addition reaction, a Grob fragmentation reaction, and an efficient Mukaiyama-Michael addition reaction.

Antioxidative dolabellanes and dolastanes from brown seaweed Padina tetrastromatica as dual inhibitors of starch digestive enzymes

New dolabellanes {6-methoxy-dolabella-8(17),12-diene-10β,18-diol (1), 3-methoxy-dolabella-12(18)-ene-4β-ol (2), 3-methoxy-dolabella-10,18(19)-diene-5α,8β-diol (3)} and dolastanes {2,7-dimethoxy-14α-hydroxy-dolasta-1(15),9-diene (4) and 4,7-dimethoxy-9β,14α-dihydroxy-dolasta-1-ene (5)} were identified from brown seaweed Padina tetrastromatica (family Dictyotaceae), collected from the southeast coast of India. Compounds 1–3 were found to possess dolabellane skeleton with [9.3.0] cyclotetradecane framework whereas, 4–5 were composed of tricyclic diterpenes with linear arrangement of six-seven-five fused alicyclic rings. Compounds 3 and 5 registered greater antioxidative activities (IC50 ≤0.63 mg/mL) than other analogues (IC50 ≥0.65 mg/mL), whereas their attenuating potentials against carbolytics α-amylase and α-glucosidase (IC50 ∼0.12–0.14 mg/mL) were comparable with those displayed by acarbose (IC50 0.14-0.12 mg/mL). Bioactive potentials of titled compounds were assessed by electronic and lipophilic parameters. The lesser binding energies of 3 (−9.71 kcal/mol) and 5 (−8.59 kcal/mol) through molecular docking demonstrated their effective hydrogen bonding interactions with α-amylase. Thus, dolabellanes and dolastanes might be used as anti-diabetic and antioxidant leads to reduce the risk of hyperglycaemia.

Conformational effects and stereocontrol in synthesis studies of medium-ring dolabellane carbocycles

Stereoselective reactions are described which lead to functionalization of the dolabellane skeleton. The stereoselectivity is attributed to conformational effects imposed by the eleven-membered ring. An efficient pathway provides for the stereocontrolled synthesis of nonracemic 6(S)-hydroxy-4(E)-dolabellene-3-one 12 and related derivatives.

Semi-synthesis of oxygenated dolabellane diterpenes with highly in vitro anti-HIV-1 activity

Research on dolabellane diterpenes of brown algae Dictyota spp. has shown that these diterpenoids have strong anti-HIV-1 activity, but there are not data about antiviral activity of dolabellane diterpenes isolated from octocorals, which are antipodes of those isolated from the brown algae. Dolabellanes 13-keto-1(R),11(S)-dolabella-3(E),7(E),12(18)-triene (1) and β-Araneosene (2) were isolated from the Caribbean octocoral Eunicea laciniata, and both showed low anti-HIV-1 activity and low toxicity. Since it was shown that oxygenated dolabellanes from algae have better anti-HIV-1 activity, in this work some derivatives of the main dolabellane of E. laciniata1 were obtained by epoxidation (3), epoxide opening (4), and allylic oxidation (5). The derivatives showed significant improvement in the anti-HIV-1potency (100-fold), being compounds 3 and 5 the most active ones. Their high antiviral activities, along with their low cytotoxicity, make them promissory antiviral compounds; and it is worth noting that the absolute configuration at the ring junction in the dolabellane skeleton does not seem to be determinant in the antiviral potency of these diterpeneoids.

Structures and Antibacterial Activities of Minor Dolabellanes from the Brown Alga Dilophus spiralis

AbstractThirteen new minor diterpenes featuring the dolabellane skeleton (1–13) were isolated from the organic extracts of the brown alga Dilophus spiralis, collected in Elafonissos Island. The structures and relative configurations of the isolated natural products were elucidated on the basis of extensive analyses of their spectroscopic data (NMR, MS, IR). The absolute configuration of 1 was determined by using the modified Mosher's method, whereas the structure of 2 was confirmed by single‐crystal X‐ray diffraction analysis. The antibacterial activities of metabolites 1–9 and 13 were evaluated against six strains of Staphylococcus aureus, including multidrug‐ and methicillin‐resistant variants. Compounds 1 and 4 exhibited noteworthy levels of activity with MIC values in the range of 2–8 μg/mL.

Dolabellanes with antibacterial activity from the brown alga Dilophus spiralis.

Seventeen diterpenes featuring the dolabellane skeleton (1-17) were isolated from the organic extracts of the brown alga Dilophus spiralis. Seven compounds are new natural products (1, 3, 5, 6, 11, 14, 15) and eight are structurally revised (2, 4, 7-10, 12, 13), among which three are reported for the first time from a natural source (4, 9, 10). The structure elucidation and the assignment of the relative configurations of the isolated natural products were based on detailed analyses of their spectroscopic data. The structure of metabolite 10 was confirmed by single-crystal X-ray diffraction analysis, whereas the absolute configurations of compounds 2, 4-10, 12, and 13 were determined using the modified Mosher's method on the semisynthetic product 18 and chemical interconversions. The antibacterial activities of compounds 1-18 were evaluated against six strains of Staphylococcus aureus, including multidrug- and methicillin-resistant variants.

Dolabellane-type diterpenoids with antiprotozoan activity from a southwestern Caribbean gorgonian octocoral of the genus Eunicea.

Ten new diterpenes, 1-10, having a dolabellane skeleton were isolated from a Colombian gorgonian coral of the genus Eunicea. Their structures, as well as those of known compounds 11-18, were determined on the basis of spectroscopic analysis and, in some instances, by chemical conversion and X-ray crystallographic analysis. The absolute structure of 7 was established by chemical conversion from 11, a co-occurring dolabellane congener of known absolute structure. Most of these diterpenoids showed antimalarial activity against the protozoan parasite Plasmodium falciparum.

New Dolabellane-Type Diterpenoids from the Okinawan Soft Coral of the Genus Clavularia

Abstract Two new diterpenoids, 2 and 4, having a dolabellane skeleton were isolated from the Okinawan soft coral of the genus Clavularia. Their structures were determined based on spectroscopic analysis, chemical conversion and X-ray crystallographic analysis. One of these diterpenoids showed cytotoxic activity against tumor cells.

Organozirconium methods for the efficient construction of the bicyclo[9.3.0]tetradecane dolabellane skeleton

Two highly convergent routes to the acetoxyodontoschismenol dolabellane skeleton are described. Both utilise efficient organozirconium based coupling reactions to rapidly assemble macro-cyclisation precursors. The first approach closes the key eleven membered ring of the dolabellane skeleton by an intramolecular Nozaki - Hiyama reaction, whereas the second uses an intramolecular α-sulphonyl carbanion - allyl iodide condensation.

Synthesis of the Dolabellane Diterpene Hydrocarbon (±)‐δ‐araneosene

AbstractThe racemic form of the bicyclic diterpene hydrocarbon δ‐araneosene (4), endowed with the dolabellane skeleton, was prepared from geraniol in two different ways. The more efficient route involved 13 steps and proceeded with an overall yield of 3.6% (average: 77% per step). With this reference sample at hand, the hitherto elusive metabolite (−)‐4, a likely biogenetic precursor of cycloaraneosene ((−)‐3) and sordaricin ((−)‐1), could finally be isolated in ≥ 99.5% purity from the neutral fractions of the mold Sordaria araneosa CAIN (Ascomycetes).

Chemical studies of north adriatic seaweeds-I new dolabellane diterpenes from the brown alga dilophus fasciola

From the brown alga Dilophus fasciola (Dictyotaceae) three new tetraoxygenated diterpenes ( 1-3) with a dolabellane skeleton were isolated. The structure of these was determined by spectral data and by means of chemical transformation. Two-dimensional NMR spectroscopy was proved to be a potent tool to establish the structures, the stereochemistry and to enable the assignment of all resonances in the NMR spectra. The new compounds were tested in ichthyotoxic and phytotoxic bioassays.

Structure and conformation of new diterpenes based on the dolabellane skeleton from a Dictyota species

From the brown alga Dictyota sp. we have isolated three new diterpenes ( 2, 3 and 6) of the dolabellane family. Their structures and conformations have been assigned on the basis of spectral studies, including proton difference decoupling and nuclear Overhauser enhancement difference spectroscopy, and chemical correlation.

A new diterpene from Aplysia dactylomela

From the digestive gland of the sea hare Aplysia dactylomela a new trioxygenated diterpene possessing the dolabellane skeleton was isolated. The structure was solved by spectral properties and X-ray diffraction analysis.

Diterpenes based on the dolabellane skeleton from dictyota dichotoma

From a variety of Dictyota dichotoma we have isolated, in addition to previously reported dolabellane ( 6-8) and perhydroazulene diterpenes ( 9,10), four new diterpenoids ( 2-5). Their structure have been elucidated by spectral analysis and chemical degradation. All the new dolabellane derivatives possess antimicrobial activity against gram-positive and gram-negative organisms.