María L. Souto

Evaluation of the effects of several zoanthamine-type alkaloids on the aggregation of human platelets.

Ten zoanthamine-type alkaloids from two marine zoanthids belonging to the Zoanthus genus (Zoanthus nymphaeus and Zoanthus sp.) along with one semisynthetic derivative were evaluated for their antiplatelet activities on human platelet aggregation induced by several stimulating agents. 11-Hydroxyzoanthamine (11) and a synthetic derivative of norzoanthamine (16) showed strong inhibition against thrombin-, collagen- and arachidonic acid-induced aggregation, zoanthenol (15) displayed a selective inhibitory activity induced by collagen, while zoanthaminone (10) behaved as a potent aggregant agent. These evaluations allowed us to deduce several structure-activity relationships and suggest some mechanisms of action for this type of compounds.

Structural determination and biosynthetic origin of two ester derivatives of okadaic acid isolated from Prorocentrum lima

Abstract The dinoflagellate Prorocentrum lima is responsible for the production of the toxins involved in the red tide phenomenon known as diarrhetic shellfish poisoning (DSP). In this paper we report on the isolation, structural elucidation and biosynthetic origin of two ester derivatives of okadaic acid on the basis of their spectroscopical data. Its biosynthetic origin was indicated by addition of labelled sodium [1- 13 C 1 ], [2- 13 C 2 ] and [1,2- 13 C 2 ] acetate to artificial cultures of the dinoflagellate.

Thyrsenols A and B, two unusual polyether squalene derivatives

Abstract Two new polyether squalene derivatives, thyrsenol A 2 and thyrsenol B 3, have been isolated from the red alga Laurencia viridis. Their structures, which possess an unusual enol-ether moiety, were determined through the interpretation of 2D-NMR spectral data. The relative stereochemistry is proposed on the basis of ROESY and NOEDIFF data. Their cytotoxic activities were evaluated.

TWO NEW ANTITUMORAL POLYETHER SQUALENE DERIVATIVES

Two new polyether squalene derivatives isodehydrothyrsiferol 2 and 10-epidehydrothyrsiferol 3 have been isolated from the red alga Laurencia viridis. Their structures were determined through the interpretation of 2D NMR spectra and their antitumoral activity was established.

New polyether squalene derivatives from Laurencia

Abstract Five new triterpenoid polyethers with a squalene carbon skeleton have been isolated from the red alga Laurencia viridis . Their structures were determined through the interpretation of 2D-NMR spectral data. The relative stereochemistry is proposed on the basis of ROESY and NOEDIFF data.

Novel marine polyethers

Abstract The red seaweed Laurencia viridis is a rich source of secondary metabolites derived from squalene. Novel polyethers, clavidol 4 , 3-epi-1111-dehydrothyrsiferol 5 , and lactodehydrothyrsiferol 6 , have been isolated and their structures established by spectroscopical methods. The relative stereochemistry proposed for these compounds is based on ROESY and NOEDIFF data. Possible biogenetic pathways are also discussed.

Several new squalene-derived triterpenes from Laurencia

Abstract Four new triterpenoids with a squalene carbon skeleton martiriol 7, pseudodehydrothyrsiferol 8, dioxepandehydrothyrsiferol 9 and 16-epihydroxydehydrothyrsiferol 10 have been isolated from the red alga Laurencia viridis. The structures were determined through the interpretation of their spectral data and the relative stereochemistries were proposed on the basis of ROESY and NOEDIFF data. Their cytotoxic activities were evaluated.

Nonterpenoid C15 Acetogenins from Laurencia marilzae

Eight new halogenated C(15) acetogenins, 1-8, were isolated from the organic extract of the red alga Laurencia marilzae. The structure elucidation and the assignments of the relative configurations were established by extensive use of spectroscopic studies, particularly 1D and 2D NMR data, while the absolute configurations of compounds 1 and 5 were determined by single-crystal X-ray diffraction analysis. Compounds 1, 2, 4, 5, and 7, along with the previously reported related cyclic ether obtusallene IV (9), were evaluated against six human solid tumor cell lines. All compounds were found to be essentially inactive (GI(50) > 10 μg/mL).

Evaluation of the cytotoxic activity of polyethers isolated from Laurencia.

In this paper, we report on the conformational analysis of several polyether triterpenes with a squalene carbon skeleton which exhibited significant cytotoxic activity using a Monte Carlo conformational search and spectroscopical data. These studies indicate that the conformation of the side chain C-14/C-19 and the arrangement and direction of this chain may be among the fundamental factors related to the activity of this type of metabolites.

Studies on Polyethers Produced by Red Algae

Two novel squalene-derived triterpenes, spirodehydrovenustatriol (3) and 14-keto-dehydrothyrsiferol (4) were isolated from the red alga Laurencia viridis, together with two new and unusual C17 terpenoids, adejen A (5) and B (6). These truncated structures possess structural similarities with other known squalene metabolites and their biogenetic origin has been proposed on the basis of an oxidative process of the squalene skeleton. All the structures were elucidated by extensive use of 2D NMR spectroscopic methods.