Five phloroglucinol-monoterpene adducts from Eucalyptus grandis

Five new euglobals possessing the phlorogiucinol-monoterpene structure, eug lobals G8-G12, together with a known euglobal-IIc were isolated from the he xane fraction of the methanol extract of the leaves of Eucalyptus grandis. Euglobal-G8 is an adduct of formyl-isovaleroyl-phloroglucinol and gamma-ter pinene whereas -G9, -G10 and -G11 have the same phloroglucinol moiety fused with alpha-terpinene, while Euglobal-G12 has terpinolene fused with the sa me phloroglucinol moiety. The structures of these compounds were elucidated on the basis of spectral evidences. Biomimetic synthesis of euglobals sugg ests that these compounds are derived biogenetically by the Diels-Alder typ e cycloaddition of the corresponding terpenes with an ortho-quinone methide generated from grandinol. (C) 1998 Elsevier Science Ltd. All rights reserv ed.