Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2010
Publication Date: 8/9/2010
Citation: Meepagala, K.M., Schrader, K., Burandt, C., Wedge, D.E., Duke, S.O. 2010. New class of algicidal compounds and fungicidal activities derived from a chromene amide of Amyris texana. Journal of Agricultural and Food Chemistry. 58:9476-9482. Interpretive Summary: The blue-green alga, Oscillatoria perornata is a pest in commercial catfish (Ictalurus punctatus) production ponds in the southeastern United States. This blue green alga produces 2-methyl isoborneol (MIB) which accumulates in the flesh of catfish, giving them a "musty" off flavor and thereby rendering them unpalatable. The agents currently approved by United States Environmental Protection Agency to control off-flavor compound-producing blue-green alga, copper-based products and diuron (3-[3,4-dichlorophenyl]-1,1-dimethylurea), are limited in their usefulness due to their persistence in the environment, lack of selectivity towards noxious blue-green algae and little margin of safety between phytotoxic and ichthyotoxic concentrations. As an alternative to these synthetic algicides, we are screening natural compounds and extracts from plants to discover selective and environmentally-safe algicides for use in catfish aquaculture. As part of our continuing efforts in search for natural product-based agrochemicals, the leaves of Amyris texana were extracted and investigated for algicidal, antifungal, and phytotoxic constituents. Bioassay-guided fractionation of this extract led to the isolation of an active compound. The structure of this compound was determined to be a chromene amide by spectroscopic methods. To improve the selective algicidal activity and provide water solubility, a series of chromene analogs were synthesized and evaluated for algicidal activity using a rapid bioassay. In addition, the chromene analogs were evaluated for antifungal and phytotoxic activities. Hydrochloride salts of a chromene amine analog showed improved water solubility and selectivity towards O. perornata with comparable activity to that of the naturally-occurring chromene amide. Some of these analogs also showed fungicidal activity against several agriculturally important pathogenic fungi Colletotrichum fragariae, C. gloeosporiodes, C. acutatum, and Botrytis cineara and Fusarium oxysporum. Botrytis cineara was the most sensitive among the fungal species that we tested.
Technical Abstract: In our continuing search for natural algicides with toxicity towards the 2-methyl- isoborneol (MIB) -producing blue-green alga Oscillatoria perornata, with relatively little effect on other types of algae, the ethyl acetate extract of Amyris texana leaves was investigated by bioassay-guided fractionation. A chromene amide was isolated and identified as the activeconstituent in the ethyl acetate extract by bioassay-guided fractionation, followed by NMR spectroscopic analysis. This chromene amide had significant, selective algicidal activity against O. perornata over S. capricornutum, the preferred type of phytoplankton in catfish aquacutlure ponds. In an attempt to improve the selective algicidal activity and water solubility, a series of chromene amine analogs were synthesized and evaluated. Structure activity studied of these analogs indicated the amide moiety is not essential for the algicide activity. A two cabon chain with isopropyl amine moiety in a form of a HCl salt showed the optimum algicide activity. The amine analogs were not fungicidal in our bioassay. The natural product amide showed antifungal activity. The alcohol and ester intermediates showed antifungal activity. This is the first report of the algicide activity of chromenes.