Advances in the Chemistry of the Furanoditerphenoids from Teucrium Species

Abstract

This reviev describe5 the major advances reported during the last five years on the chemistry of these diterpenoids.1 Six years elapsed since the publication Of a review on the chemistry of the furoclerodane diterpenoids occurring in several species of genus Teucriwn (family Labiatae).During this time, some research groups were active in this field, and many more species vere investigated.The present paper aims at giving an up-to--date review on the results obtained after June 1980.It must be focused that specimens of the same botanical species, collected in different countries, showed a quite dissimilar qualitative content of diterpenoids.When the existence of subspecies is not recognized, these differences will be ascribed tentatively to the occurrence of chemotypes.As to the structure, all the new diterpenoids here reported do have the s-clerodane skeleton (synonimous, neo-clerodane), like the 1 products previously reported.The nomenclature s-clerodane or neo-clerodane is used indifferently through this paper. RECENT IGSEARCHESThis report starts vith the substances whose isolation had been announced in the 1 previous review . 1It had been reported the occurrence of auropolin in T.polium subsp.(Schreber) Arcangeli (= T.aurewn Schreber), Spanish chemotype, but it structure was not 2 ascertained.The elucidation of the structure as [ 2 5 ] showed that the usual C-20 -C-12 lactone or hemiacetal bridge is missing, and substituted by a C-20-C-7 hemiacetal bridge.The absolute stereostructure of auropolin, with C-12 in S configuration, was proved, except for its C-20 centre, by X-ray determination on the product of oxidation of [25], having the C-20-C-7 lactone bridge. 1The structure of teugin from T.fragile Boiss.had been given provisionally: it