Pycnanthuquinone C, an unusual 6,6,5-tricyclic geranyltoluquinone from the Western Australian brown alga Cystophora harveyi

Chemical investigation of the Western Australian marine brown alga Cystophora harveyi resulted in the isolation of the new linearly fused 6,6,5-tricyclic compound pycnanthuquinone C (1), in addition to four previously reported geranyltoluquinol derivatives. Structures were elucidated by interpretation of spectrometric data. Compounds with the same cyclic skeleton as 1 have been reported to be useful drug leads for the treatment of type 2 diabetes, while compounds 4 and 7 are known constituents of Chinese medicinal herbs. A biosynthetic scheme encompassing all of the geranyltoluquinol derivatives isolated from C. harveyi is proposed.