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Mar. Drugs 2014, 12(9), 5021-5034; doi:10.3390/md12095021

Didemnaketals F and G, New Bioactive Spiroketals from a Red Sea Ascidian Didemnum Species

1
Natural Products Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah 21589, Kingdom of Saudi Arabia
2
Suez Canal University Hospital, Suez Canal University, Ismailia 41522, Egypt
3
Department of Natural Products, Faculty of Pharmacy, King Abdulaziz University, Jeddah 21589, Kingdom of Saudi Arabia
4
Department of Pharmacognosy, Faculty of Pharmacy, Suez Canal University, Ismailia 41522, Egypt
5
Department of Pharmacognosy, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
6
Department of Pharmacognosy and Medicinal Chemistry, Faculty of Pharmacy, Taibah University, Al Madinah Al Munawwarah 3001, Kingdom of Saudi Arabia
7
Department of Pharmacognosy, Faculty of Pharmacy, Al-Azhar University, Assiut Branch, Assiut 71524, Egypt
8
Department of Pharmacology and Cancer Therapy & Research Center, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
*
Author to whom correspondence should be addressed.
Received: 24 July 2014 / Revised: 5 September 2014 / Accepted: 9 September 2014 / Published: 25 September 2014
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Abstract

In continuation of our ongoing efforts to identify bioactive compounds from Red Sea marine organisms, a new collection of the ascidian Didemnum species was investigated. Chromatographic fractionation and HPLC purification of the CH2Cl2 fraction of an organic extract of the ascidian resulted in the identification of two new spiroketals, didemnaketals F (1) and G (2). The structure determination of the compounds was completed by extensive study of 1D (1H, 13C, and DEPT) and 2D (COSY, HSQC, and HMBC) NMR experiments in addition to high-resolution mass spectral data. Didemnaketal F (1) and G (2) differ from the previously reported compounds of this class by the lack the terminal methyl ester at C-1 and the methyl functionality at C-2. Instead, 1 and 2 possess a methyl ketone moiety instead of the terminal ester. Furthermore, didemnaketal F possesses a disubstituted double bond between C-2 and C-3, while the double bond was replaced by a secondary alcohol at C-3 in didemnaketal G. In addition, they possess the unique spiroketal/hemiketal functionality which was previously reported in didemnaketal E. Didemnaketals F (1) and G (2) displayed moderate activity against HeLa cells with of IC50s of 49.9 and 14.0 µM, respectively. In addition, didemnaketal F (1) displayed potent antimicrobial activity against E. coli and C. albicans. These findings provide further insight into the biosynthetic capabilities of this ascidian and the chemical diversity as well as the biological activity of this class of compounds. View Full-Text
Keywords: Red Sea ascidian; Didemnum species; spiroketals; didemnaketals F and G; HeLa cells; antiproliferative and cytotoxic activity; antimicrobial activity Red Sea ascidian; Didemnum species; spiroketals; didemnaketals F and G; HeLa cells; antiproliferative and cytotoxic activity; antimicrobial activity
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Shaala, L.A.; Youssef, D.T.; Ibrahim, S.R.; Mohamed, G.A.; Badr, J.M.; Risinger, A.L.; Mooberry, S.L. Didemnaketals F and G, New Bioactive Spiroketals from a Red Sea Ascidian Didemnum Species. Mar. Drugs 2014, 12, 5021-5034.

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