Considerable interests have been attracted by isosteviol and its derivatives because of their large variety of bioactivities. In this project, a series of novel 15-and 16-substituted isosteviol derivatives were stereoselectively prepared by means of functional interconversions in ring D of the tetracyclic diterpene isosteviol. All compounds synthesized were characterized by analysis of NMR, IR, HR-MS data, and the configurations of 33 and 37 were confirmed by X-ray crystallographic analysis. The antibacterial activities in vitro of these isosteviol derivatives were investigated; the synthetic compounds were more active against Gram-positive than Gram-negative bacteria, and were especially active against Bacillus subtilis. Among them, compound 27 (MIC ¼ 1.56 mg/ml) exhibited the highest antibacterial activity and thus may be exploitable as a lead compound for the development of potent antibacterial agents.

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Two series of novel acylthiosemicarbazide and oxadiazole fused-isosteviol derivatives were synthesized based on the 19-carboxyl modification. The target compounds were evaluated for their cytotoxicities against three cancer cell lines (HCT-116, HGC-27, and JEKO-1) using an MTT assay. Lead compounds from the acylthiosemicarbazides (4) showed IC values in the lower micromolar range. For example, compounds (4i, 4l, 4m, 4r, and 4s) exhibited significant inhibitory activities against the three cell lines with IC values of 0.95-3.36 μm. Furthermore, 2D-HQSAR and 3D-topomer CoMFA analyses were established, which could be used to develop second generation of isosteviol derivatives as anticancer agents.