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Mar. Drugs 2018, 16(10), 382; https://doi.org/10.3390/md16100382

New Sulfur-Containing Polyarsenicals from the New Caledonian Sponge Echinochalina bargibanti

1
Department of Chemistry, University of Turku, Vatselankatu 2, 20014 Turku, Finland
2
Laboratorio di Chimica Bioorganica, Dipartimento di Fisica, Università di Trento, Via Sommarive 14, I-38123 Trento, Italy
3
Istituto CNR per la Tecnologia delle Membrane, Unità di Padova, and Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo, 1-35131 Padova, Italy
4
LEMAR, IRD, UBO, CNRS, IFREMER, IUEM, 29280 Plouzané, France
5
Laboratoire Insulaire du Vivant et de l’Environnement, Université de la Nouvelle-Calédonie: EA 4243 BP 11106, 98802 Nouméa, Nouvelle-Calédonie, France
*
Author to whom correspondence should be addressed.
Received: 14 September 2018 / Revised: 3 October 2018 / Accepted: 9 October 2018 / Published: 11 October 2018
(This article belongs to the Special Issue Bioactive Compounds from Marine Sponges)
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Abstract

Arsenicin A (C3H6As4O3) was isolated from the New Caledonian poecilosclerid sponge Echinochalina bargibanti, and described as the first natural organic polyarsenic compound. Further bioguided fractionation of the extracts of this sponge led us to isolate the first sulfur-containing organic polyarsenicals ever found in Nature. These metabolites, called arsenicin B and arsenicin C, are built on a noradamantane-type framework that is characterized by an unusual As–As bonding. Extensive NMR measurements, in combination with mass spectra, enabled the assignment of the structure for arsenicin B (C3H6As4S2) as 2. The scarcity of arsenicin C and its intrinsic chemical instability only allowed the collection of partial spectral data, which prevented the full structural definition. After the extensive computational testing of several putative structures, structure 3 was inferred for arsenicin C (C3H6As4OS) by comparing the experimental and density functional theory (DFT)-calculated 1H and 13C NMR spectra. Finally, the absolute configurations of 2 and 3 were determined with a combined use of experimental and time-dependent (TD)-DFT calculated electronic circular dichroism (ECD) spectra and observed specific rotations. These findings pose great challenges for the investigation of the biosynthesis of these metabolites and the cycle of arsenic in Nature. Arsenicins B and C showed strong antimicrobial activities, especially against S. aureus, which is comparable to the reference compound gentamycin. View Full-Text
Keywords: antibacterial; arsenical; calculated NMR spectrum; density functional theory; natural products; NMR spectroscopy; structure elucidation; sulfur metabolite antibacterial; arsenical; calculated NMR spectrum; density functional theory; natural products; NMR spectroscopy; structure elucidation; sulfur metabolite
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Tähtinen, P.; Guella, G.; Saielli, G.; Debitus, C.; Hnawia, E.; Mancini, I. New Sulfur-Containing Polyarsenicals from the New Caledonian Sponge Echinochalina bargibanti. Mar. Drugs 2018, 16, 382.

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