| Abstract: | Leaf-gland Pigments from Labiatae: 22 Novel Diterpenoids (Coleons and Royleanones) from Plectranthus lanuginosus We report the isolation and structure elucidation of 22 novel diterpenoids (named lanugones A, B, C, D, E, F, G, H, I, J, K, K′, L, M, N, O, P, Q, R, S and (155)-coleon C ( 28 ) and (155)-coleon D ( 29 )) from the leaf-glands of the above-mentioned plant (see Table 1). Structurally they belong to the subgroups of royleanones and coleons with the following structural characteristics: 8-hydroxy-1-methyl-spi-ro2,5]oct-5-ene-4,7-diones, p-quinomethanes, extended (vinylogous) quinones, di-osphenols and diketones. Compounds 28 and 29 are (15S)-epimers of the already known coleon C and coleon D (with (15 R)-configuration), respectively. Furthermore, the already known 6,7-didehydroroyleanone ( 1 ) has been isolated in small amount. The present investigation has uncovered the broadest range of diverse chromo-phoric systems and oxydation levels so far found amongst diterpenoids in a single plant species. Most important for an understanding of the metabolic fate of an iso-propyl group is the full range found with the following metabolic stages: isopropyl-→ hydroxyisopropyl → dihydrofuran and spirocyclopropane → allyl- and 2-hydroxypropyl groups. |
