Novel seco-prezizaane sesquiterpenes from North American Illicium species

Three novel seco-prezizaane sesquiterpenes (1-3) were isolated from leaves of Illicium parviflorum (swamp star anise, yellow star anise), a species occurring endemically in central Florida. Compound 1, named cycloparvifloralone, possesses a hitherto unknown ring system with a cagelike acetal/hemiketal structure. Lactones 2 (cycloparviflorolide) and 3 (parviflorolide) which were obtained as an inseparable mixture, coexist in a hemiketal/keto equilibrium. It could be shown that a 4,7-hemiketal (4) occurs in an analogous fashion to pseudoanisatin 5, a known constituent of other Illicium species. From the fruits of Illicium floridanum the novel ortholactone 6 was isolated. The structures of the new compounds were elucidated by interpretation of their 1D and 2D homo- and heteronuclear NMR spectroscopic data. The modes of cyclization observed in 1, 2, 4, and 6 have not been described previously, and a biogenetic sequence is proposed for these compounds and further seco-prezizaane sesquiterpenes.