Grindelane diterpenoids from Stevia subpubescens

Four new 9R,13R-epoxylabdane diterpenes (1-4) and a known clerodane derivat ive, 3,3 beta-epoxy-5 beta,10 beta-cis- 17 alpha,20 alpha-clerod-13(14)-en- 15,16-olide, were isolated from the leaves of Stevia subpubescens. The stru ctures, which correspond to the grindelane class of diterpenoids, were eluc idated by NMR data, chemical correlation, and single-crystal X-ray diffract ion analysis of monoacetate 5. The absolute configuration of 1-4 is based o n the optical activity of ketone 3 as compared with data of closely related substances.