Further Furoclerodanes from Teucrium Genus

The review updates the results reported during the last four years on the chemistry of these diterpenoids.The interest for the furoclerodane diterpenoids (neo-clerodane skeleton) occurring in Teucriwn species (family Labiatae) seems to meet no pause.The main reason is their powerful insect antifeedant activity.The previous reviews1" are updated by the present report, concerning 19 new taxa @]us five reinvestigated) and 51 new natural products; in particular, some substances with transposed skeletons are attractive for the researcher.This genus is surely one of the richest sources of neo-clerodanes.The new taxa and products w i l l be reported mostly in chronological order, and for the new products the 2 3 .numbering used in the previous reviews ' wdl be continued.A paper escaped the previous review3 and published in 1990 referred to Teucrium grisebachii growing in ~r ~e n t i n a : ~ two furoclerodanes were isolated: one is the new hiacetylteumassilin (156), the other is 6-acetylteucjaponin B (20). claimed as a new derivative but in the fact previously known.5A reinvestigation of the extract of Teucriwn polium collected in Armenia (subspecies not indicated) yielded6 hdproducts named tepolin A and tepolin B; they were assigned the structures (157) and (1581, whose more peculiar detail is the occurrence of not lactonized 12-OH and 9a-COOH.Another reinvestigation was concerned with Teucrium pernyi.From this species, growing in South-East China, the teupernins A (115).B (105) and C (106) had been described by two chinese g ~o u p s .~" ' ~ In a second time, a product indicated as teupernin D (155) had been iso~ated.~'~Another product was then1' extracted and also named teupemin D, but its smcture, reported as 159, is quite different and shows an unprecedented carbomethoxy group on C-4.The nomenclature of these two products should be revised.In the same species also the known teucvidin (91).teuflin (93).montanin D (46) and teuscorodonin (68) were found."structurally more interesting are the nine furoclerodanes isolated"'12 from Teucrium brevifoliwn, growing in small areas of Greece and collected in the island of Karpathos.Teubrevin A (160) has a rearranged skeleton" arising from cleavage of the C-5lC-10 bond and formation of a C-1IC-6 linkage; teubrevin B (161) is its 8P-OH derivative."