Density Functional Theory (DFT)-Aided Structure Elucidation of Linear Diterpenes from the Irish Brown Seaweed .

Brown alga is an extraordinarily rich source of linear (acylic) diterpenes with enormous structural diversity. As part of our interest into secondary metabolites of the Irish seaweeds, here we report four new acyclic diterpenes (-) and seven known terpenoids (-) from the CHCl extract of . The planar structures of the new metabolites were elucidated by means of 1D and 2D NMR, HRMS, and FT-IR spectroscopy.

Oxygenated Acyclic Diterpenes with Anticancer Activity from the Irish Brown Seaweed .

Brown alga is a prolific source of bioactive acyclic (linear) diterpenes with high structural diversity. In the continuation of our investigations on Irish brown algae, we undertook an in-depth chemical study on the -hexanes and chloroform subextracts of that led to isolation of six new (-) and two known (-) acyclic diterpenes. Chemical structures of the compounds were elucidated by a combination of 1D and 2D NMR, HRMS, FT-IR, [α] and vibrational circular dichroism (VCD) spectroscopy.

Halogenated Diterpenes with In Vitro Antitumor Activity from the Red Alga .

Eight new (-) structurally diverse diterpenes featuring five different carbocycles were isolated from the organic extracts of the red alga collected from the coastline of the Ionian Sea in Greece. The structures of the new natural products, seven of which were halogenated, and the relative configuration of their stereocenters were determined on the basis of comprehensive spectroscopic analyses, including NMR and HRMS data. Compounds and were found to possess in vitro antitumor activity against one murine and five human cancer cell lines with mean IC values 15 and 16 μM, respectively.

Bifurcatriol, a New Antiprotozoal Acyclic Diterpene from the Brown Alga Bifurcaria bifurcata.

Linear diterpenes that are commonly found in brown algae are of high chemotaxonomic and ecological importance. This study reports bifurcatriol (1), a new linear diterpene featuring two stereogenic centers isolated from the Irish brown alga . The gross structure of this new natural product was elucidated based on its spectroscopic data (IR, 1D and 2D-NMR, HRMS).

Assignment of absolute configurations of highly flexible linear diterpenes from the brown alga Bifurcaria bifurcata by VCD spectroscopy.

Correct assignment of the stereogenic centers of highly flexible linear diterpenes (LDs) is challenging. Herein we report the first application of VCD spectroscopy for the absolute configuration determination of LDs of algal origin and provide experimental and computational procedures, such as a fragmentation approach, which will facilitate the use of VCD spectroscopy for configuration assignments of LDs.

Sulfated steroid-amino acid conjugates from the Irish marine sponge Polymastia boletiformis.

Antifungal bioactivity-guided fractionation of the organic extract of the sponge Polymastia boletiformis, collected from the west coast of Ireland, led to the isolation of two new sulfated steroid-amino acid conjugates (1 and 2). Extensive 1D and 2D NMR analyses in combination with quantum mechanical calculations of the electronic circular dichroism (ECD) spectra, optical rotation, and 13C chemical shifts were used to establish the chemical structures of 1 and 2. Both compounds exhibited moderate antifungal activity against Cladosporium cucumerinum, while compound 2 was also active against Candida albicans.

Terpenes from the red alga Sphaerococcus coronopifolius inhibit the settlement of barnacles.

In this study, we screened eight terpenes isolated from the organic extract of Sphaerococcus coronopifolius for their antifouling activity in order to find possible new sources of non-toxic or less toxic bioactive antifoulants. The anti-settlement activity (EC₅₀) and the degree of toxicity (LC₅₀) of S. coronopifolius metabolites was evaluated using larvae of the cirriped crustacean Amphibalanus (Balanus) amphitrite (cyprids and nauplii) as model organism.

Ioniols I and II, tetracyclic diterpenes with antibacterial activity, from Sphaerococcus coronopifolius.

Two naturally occurring diterpenes featuring unprecedented tetracyclic skeletons, ioniols I and II (1 and 2, resp.), along with two previously reported metabolites 3 and 4, were isolated from the organic extract of Sphaerococcus coronopifolius collected from the rocky coasts of Corfu island in the Ionian Sea. The structures of the new natural products, as well as their relative configuration, were elucidated on the basis of extensive spectral analysis, including 2D-NMR experiments.

Structure and antibacterial activity of brominated diterpenes from the red alga Sphaerococcus coronopifolius.

Four new tetracyclic brominated diterpenes, 1-4, were isolated from the organic extract of Sphaerococcus coronopifolius, collected from the rocky coasts of Corfu Island. The structures of the new natural products, as well as their relative configurations, were elucidated on the basis of extensive spectral analyses, including 2D-NMR experiments. The isolated metabolites were evaluated for their antibacterial activity against a panel of bacteria including multidrug-resistant (MDR) and methicillin-resistant Staphylococcus aureus (MRSA) with MIC values in the range of 16-128 microg/ml.

Structure and in vitro antitumor activity evaluation of brominated diterpenes from the red alga Sphaerococcus coronopifolius.

A novel bromoditerpene methyl ketone (1), two new bromoditerpene alcohols featuring a neodolastane (2), and a bromocorodienol skeleton (3), along with 13 previously reported metabolites (4-16) were isolated from the organic extract of Sphaerococcus coronopifolius collected from the rocky coasts of Corfu island in the Ionian Sea. The structures of the new natural products, as well as their relative stereochemistry, were elaborated on the basis of extensive spectral analysis, including 2D NMR experiments. The absolute stereochemistry of metabolite 3 was determined using the modified Mosher's method.

Sphaeroane and neodolabellane diterpenes from the red alga Sphaerococcus coronopifolius.

Investigation of minor metabolites in the extracts of the red alga Sphaerococcus coronopifolius collected from the rocky coasts of Corfu Island in the Ionian Sea yielded two new diterpene alcohols, sphaerollanes I, and II (1, 2) featuring neodolabellane skeletons, and the new sphaeroane diterpene alcohol 16-hydroxy-9S*-acetoxy-8-epi-isosphaerodiene-2 (3), along with two previously reported metabolites 4, 5. The structures of the new natural products, as well as their relative stereochemistry, were elucidated on the basis of extensive spectral analysis, including 2D-NMR experiments.

Brominated diterpenes with antibacterial activity from the red alga Sphaerococcus coronopifolius.

Four new brominated diterpenes (1, 2, 4, 5), along with two previously reported metabolites (3, 6), were isolated from the organic extract of Sphaerococcus coronopifolius, collected in Palaiokastritsa Bay at the west coast of Corfu Island. The structures of the new products, as well as their relative configuration, were established by means of spectroscopic data analyses, including 2D NMR experiments. The isolated metabolites were evaluated for their antibacterial activity against a panel of multidrug-resistant (MDR) and methicillin-resistant Staphylococcus aureus (MRSA) with MICs in the range 0.

Acetylene sesquiterpenoid esters from the green alga Caulerpa prolifera.

Sixteen secondary metabolites of the green alga Caulerpa prolifera have been isolated, and their chemical structures elucidated by analysis of their spectroscopic data. Two groups of metabolites have been established, with either a 1,2-dihydro- (2a-2i) or a 1,2,3,3'-tetrahydro-2,3-didehydro (3a-3f) caulerpenyne carbon backbone. The terminal vinyl acetoxy group of caulerpenyne was substituted by various fatty acid residues.