A cyclic peroxide 1 with an unusual phenethenyl side chain, together with the known peroxide 2 with a C4-sidechain have been isolated from a two-sponge association of Plakortis communis – Agelas mauritiana (Carter, 1883) collected near Mooloolaba, South-East Queensland, Australia. Metabolite purification was complicated by the presence of the free carboxylic acid groups in 1 and 2; therefore, diazomethane treatment was undertaken to afford methyl ester 3. Following RP-HPLC purification, the ring-opened analogues 4 and 5 were also obtained. The structures of the new compounds were elucidated on the basis of their 1D and 2D NMR and MS data, and by comparison with literature data. The relative configuration of the isolated peroxides was determined by the interpretation of JH-H values and comparison of the 13C chemical shift data with literature data for related compounds. The bromopyrrole alkaloid longamide (6) was also isolated.
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