A natural diterpenoid kamebacetal A with anti-tumor activity: Theoretical and experimental study

Kamebacetal A (1) is an ent-kaurane diterpenoid isolated from Isodon racemosa (Hemsl) Hara. This natural product exhibits significant cytotoxicity against human Bel-7402 and HO-8910 tumor cells. The geometrical conformation of 1 has been optimized at the B3LYP/6-311+G(d) level of theory. The results indicated that the calculated geometric parameters are close to the X-ray crystal structure. The theoretical 13C NMR chemical shifts of 1 were also calculated at the GIAO-B3LYP level of theory with different basis sets. The calculated NMR chemical shifts are in closer agreement with the experimental results. cular electrostatic potential (MEP) map was used in an attempt to identify key features of the kamebacetal A to account for its anti-tumor activity. MEP investigations reveal that compound 1, which shows anti-tumor activity, possesses electron-rich regions that extend over the hydroxyl and carbonyl groups of compound 1. The data generated in this study is valuable as it provides an insight into kamebacetal A molecular and structure–activity relationships.