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Mar. Drugs 2012, 10(8), 1741-1764; doi:10.3390/md10081741
Article

Natural Products from Antarctic Colonial Ascidians of the Genera Aplidium and Synoicum: Variability and Defensive Role

1,* , 2
, 1
, 3
, 3
, 4
, 2
 and 1
1 Department of Animal Biology (Invertebrates), Faculty of Biology, University of Barcelona, Av. Diagonal 643, Barcelona 08028, Catalunya, Spain 2 Institute of Biomolecular Chemistry, CNR, Via Campi Flegrei 34, Pozzuoli I-80078, Napoli, Italy 3 Department of Fundamental Chemistry, Faculty of Science, Campus Zapateira, University of La Coruña, A Coruña 15071, Spain 4 Department of Marine Science and Applied Biology, University of Alicante, Carretera San Vicente del Raspeig s/n, Alicante 03690, Spain
* Author to whom correspondence should be addressed.
Received: 29 June 2012 / Revised: 1 August 2012 / Accepted: 8 August 2012 / Published: 20 August 2012
(This article belongs to the Special Issue Deep-Sea Natural Products)
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Abstract

Ascidians have developed multiple defensive strategies mostly related to physical, nutritional or chemical properties of the tunic. One of such is chemical defense based on secondary metabolites. We analyzed a series of colonial Antarctic ascidians from deep-water collections belonging to the genera Aplidium and Synoicum to evaluate the incidence of organic deterrents and their variability. The ether fractions from 15 samples including specimens of the species A. falklandicum, A. fuegiense, A. meridianum, A. millari and S. adareanum were subjected to feeding assays towards two relevant sympatric predators: the starfish Odontaster validus, and the amphipod Cheirimedon femoratus. All samples revealed repellency. Nonetheless, some colonies concentrated defensive chemicals in internal body-regions rather than in the tunic. Four ascidian-derived meroterpenoids, rossinones B and the three derivatives 2,3-epoxy-rossinone B, 3-epi-rossinone B, 5,6-epoxy-rossinone B, and the indole alkaloids meridianins A–G, along with other minoritary meridianin compounds were isolated from several samples. Some purified metabolites were tested in feeding assays exhibiting potent unpalatabilities, thus revealing their role in predation avoidance. Ascidian extracts and purified compound-fractions were further assessed in antibacterial tests against a marine Antarctic bacterium. Only the meridianins showed inhibition activity, demonstrating a multifunctional defensive role. According to their occurrence in nature and within our colonial specimens, the possible origin of both types of metabolites is discussed.
Keywords: Antarctic colonial tunicates; deterrent activity; sea star Odontaster validus; amphipod Cheirimedon femoratus; antibacterial activity Antarctic colonial tunicates; deterrent activity; sea star Odontaster validus; amphipod Cheirimedon femoratus; antibacterial activity
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Núñez-Pons, L.; Carbone, M.; Vázquez, J.; Rodríguez, J.; Nieto, R.M.; Varela, M.M.; Gavagnin, M.; Avila, C. Natural Products from Antarctic Colonial Ascidians of the Genera Aplidium and Synoicum: Variability and Defensive Role. Mar. Drugs 2012, 10, 1741-1764.

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