65 AURANTOSIDES A AND B, TETRAMIC ACID GLYCOSIDES, FROM THE MARINE SPONGE THEONELLA SP.
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The marine sponge Theonella sp., from which we isolated cyclotheonamides, contained orange pigments associated with cytotoxicity. The isolation and structure elucidation of two metabolites are the subject of this paper. The BuOH phase of the initial solvent partitioning scheme was successively purified by Sephadex LH2O and reverse-phase chromatographies to yield aurantosides A and B (1 and 2, respectively). Aurantoside A had a molecular formula of C_<36>H_<46>N_2O <15>Cl_2 as revealed by the FABMS, NMR spectra, and elemental analysis. Its gross structure was determined by the interpretation of 2D NMR spectra to be a tetramic acid glycoside: one side chain was a dichlorinated conjugated heptaene, while the other was a methylenecarboxyamide; xylopyranose, arabinopyranose, and a 5-deoxypentofuranose, whose hydroxyl group on C2 was methylated, were linked via nitrogen to the pyrrolidone ring, in order. Aurantoside B gave almost superimposable NMR spectra to that of 1, except for the absence of O-methyl group. Detailed analysis of spectral data indicated that the 2-O-methyl group of the 5-deoxypentose unit of aurantoside A was replaced by a hydroxyl group in aurantoside B.
