Structurally Diverse Diterpenoids from Sandwithia guyanensis

Bioassay-guided fractionation of an EtOAc extract of the trunk bark of Sandwithia guyanensis, using a chikungunya virus (CHIKV)-cell-based assay, afforded 17 new diterpenoids 1–17 and the known jatrointelones A and C (18 and 19). The new compounds included two tetranorditerpenoids 1 and 2, a trinorditerpenoid 3, euphoractines P-W (4–11), and euphactine G (13) possessing the rare 5/6/7/3 (4–7), 5/6/6/4 (8–11), and 5/6/8 (13) fused ring skeletons, sikkimenoid E (12), and jatrointelones J-M (14–17) possessing jatropholane and lathyrane carbon skeletons, respectively. Jatrointelones J (14) and M (17) represent the first naturally occurring examples of C-15 nonoxidized lathyrane-type diterpenoids. The structures of the new compounds were elucidated by NMR spectroscopic data analysis. The relative configuration of compound 16 and the absolute configurations of compounds 3–6 and 14 were determined by single-crystal X-ray diffraction analysis. In addition, jatrointelone K (15) was chemically transformed to euphor...