Novel diterpenes with cytotoxic, anti-malarial and anti-tuberculosis activities from a brown alga Dictyota sp.

Abstract

Two new diterpenes, (1E,2R*,3R*,4S*,6E,18S*)-4,18-dihydroxydictyolactone (1) and 8α,11-dihydroxypachydictyol A (2), together with fucoxanthin (3) and a known diterpene 4α-hydroxycrenulatane (4) were isolated from the methanol extract of the brown alga Dictyota sp. collected from Bangsaen Beach, Thailand. Their structures were determined by spectroscopic data. The relative stereochemistry of 1 was established by NOE difference and NOESY experiments. Compound 1 showed weak anti-tuberculosis activity while 2 displayed strong cytotoxicity against the NCI-H187 cell line, and potent anti-malarial activity. In addition, 3 was active against HSV-1 and malarial parasites.

Keywords:

• Dictyota
• Diterpene
• NCI-H187
• HSV-1
• Anti-malarial

Acknowledgements

This project was granted by the Thailand Research Fund and the Commission on Higher Education, Ministry of Education with Prof. Dr. Udom Kokpol as the mentor. Financial support from the centres for Innovation in chemistry: Postgraduate Education and Research Program in Chemistry (PERCH-CIC), Commission on Higher Education, Ministry of Eudcation is gratefully acknowledged. Thanks to Thidarat Noiraksa at the Institute of Marine Science, Burapha University, Bangsaen, Chonburi, Thailand, for the algal identification. Many thanks to Prof. Dr. Somsak Ruchirawat for access to high-resolution mass spectrometry, which was run by Nitirat Chimnoi at the Natural Product Chemistry Laboratory, Chulabhorn Research Institute, Thailand. Thanks also to Dr. Kanit Suwanborrirak, Faculty of Pharmacy, Chulalongkorn University for permission of the specific rotation measurements. We acknowledge the professional services provided by the National Centre for Genetic Engineering and Biotechnology (BIOTEC), Thailand for all the biological tests. Finally, thanks also to Dr. Preecha Phuwapraisirisan at the Department of Chemistry, Chulalongkorn University for MTPA reagents and his invaluable help.