In a series of food chain in aquatic world, phytoplankton is the bottom creature that supports the lives of animals. It has been soundly believed that phytoplankton is docile and never resists against its fate. This belief has been disputed by Hessen and van Donk, who reported that a unicellular green alga, Scenedesmus subspicatus, achieved morphological change into 2-, 4-, and 8-coenobia (colonies) when the water in which a crustacean Daphnia magna, a grazer of the alga, had been cultured (Daphnia water) was added to the cultivation medium. 1) They also found that the grazing rate of the coenobium morph was lower than that of the unicellular morph, owing to the increased size of the former. This metamorphosis was supposed to be a self-defense mechanism acquired by the green alga and triggered by a kairomone secreted from D. magna. Their report has aroused the interest of many scientists to attempt to identify the kairomone, 2-9) Recently, we reported identification of the Daphnia kairomones that cause the morphological change in a unicellular green alga Scenedesmus gutwinskii var. heterospina (NIES-802) at 10 Ϫ1 -10 3 ng/ml concentrations.
10,11)Here we report isolation and structure determination of aliphatic sulfates and sulfamates 1-13 as the Daphnia kairomones, which are active at ng-mg/ml concentration. To the best of our knowledge, compounds 1-3, 5-9 and 11-13 are new compounds. Their activity and structure correlation will be discussed elsewhere.Frozen Daphnia (10 kg; Aso Tropical Fish Co., Ltd., Osaka) was soaked with methanol (20 lϫ3), and the methanol solution was evaporated, the residue being treated with water (9 l). The mixture was successively extracted with hexane, dichloromethane, and butanol, and the most active butanol extract was separated by HPLC monitoring the activity to afford 1 (8.0 mg), 2 (0.5 mg), 3 (0.3 mg), 4 (3.8 mg), 5 (0.5 mg), 6 (8.0 mg), 7 (0.4 mg), 8 (0.8 mg) 9 (0.6 mg), 10 (1.5 mg), 11 (0.1 mg), 12 (0.2 mg), and 13 (1.5 mg).The molecular formula of 1 was established as H COSY spectrum of 1 led to a gross structure as 7-methyloctyl sulfate. To rule out the possibility that isolated substance is less active and it might still be contaminated with a minute amount of highly active compound, compound 1 was synthesized. The Wittig olefination of adipic semialdehyde methyl ester (14) with isopropyltriphenylphosphonium iodide gave the methyl ester 15. Reduction of the double bond under H 2 atmosphere over the Pd-C catalyst followed by LiAlH 4 re- New aliphatic sulfates and sulfamates were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). Their structures were determined by spectroscopic and synthetic studies.
