Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2010
Publication Date: August 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 17:(58)9476-9482. Interpretive Summary: The blue-green alga Oscillatoria perornata is a pest in commercial channel catfish (Ictalurus punctatus) production ponds in the southeastern United States. This blue-green alga produces 2-methylisoborneol (MIB) which accumulates in the flesh of catfish, giving them a “musty” off-flavor and thereby rendering them unpalatable. Compounds currently approved by United States Environmental Protection Agency to control off-flavor compound-producing blue-green alga are limited in their usefulness due to their persistence in the environment, lack of selectivity towards undesirable blue-green algae and little margin of safety between concentrations toxic towards algae and fish. As part of our continuing efforts in search for natural product-based agrochemicals, extracts from the leaves of a plant found in Texas were evaluated for algicidal, antifungal, and herbicidal activity. A compound isolated from the leaf extracts was found to be toxic towards O. perornata. 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 herbicidal activities. 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 disease-causing fungi in crops.
Technical Abstract: In our continuing search for natural algicides with selective toxicity towards the 2-methyl- isoborneol (MIB) -producing blue-green alga Oscillatoria perornata , the ethyl acetate extract from Amyris texana leaves was investigated by bioassay-guided fractionation. A chromene amide was isolated and identified as the active constituent 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 compared to the green alga S. capricornutum, the preferred type of phytoplankton in catfish aquaculture 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 of these analogs indicated the amide moiety is not essential for the algicide activity. A two- carbon chain with an isopropyl amine moiety in the form of a hydrochloride salt showed the optimum algicide activity. The amine analogs were not fungicidal in our bioassay, but the natural product amide showed antifungal activity. The alcohol and ester intermediates also showed antifungal activity. This is the first report of the algicidal activity of chromenes.