ent-Labdane and ent-kaurane diterpenoids from Chelonopsis odontochila with α-glucosidase inhibitory activity.

• Eleven new ent -labdane diterpenoids were isolated from C. odontochila. • Their absolute configurations were established by ECD, [ α ] D and X-ray methods. • One ent -labdane and four ent- kauranes showed α -glucosidase inhibitory activity. • Compounds 12 and 16 were mixed-type inhibitors with K i of 334.1 and 589.2 μM. • Docking study disclosed the importance of the carboxyl group at C-4 position. Eleven new ent -labdane diterpenoids, cheodontoins A-K (1 – 11), and thirteen known diterpenoids involving two ent -labdanes (12 – 13) and eleven ent- kauranes (14 – 24), were isolated from the active part of Chelonopsis odontochila (Lamiaceae) under the guidance of bioassay. The structures of cheodontoins A-K (1 – 11) were elucidated by extensive HRESIMS, 1D and 2D NMR, [ α ] D and ECD experiments, X-ray diffraction and quantum calculation. Interestingly, five nor- ent- labdanes (9 – 13) were obtained from this genus for the first time. One ent -labdane diterpenoid (12) and four ent- kaurane diterpenoids (16 , 19 , 23 , and 24) showed α -glucosidase inhibitory activity with IC 50 values of 326.5 ± 3.5, 599.1 ± 13.8, 620.1 ± 16.1, 185.0 ± 4.2, and 190.7 ± 11.6 μM, respectively. Compounds 12 and 16 were α -glucosidase mixed-type inhibitors with K i values of 334.1 and 589.2 μM according to the enzyme kinetics using Lineweaver-Burk and Dixon plots. Docking study manifested that compounds 12 and 23 well located in the catalytic pocket of α -glucosidase by hydrophobic effects with Trp1355, Trp1369, Phe1427, Phe1559, and Phe1560 residues. This study provides new insights for the antidiabetic effects of C. odontochila with ent -labdane and ent -kaurane diterpenoids as the active constituents. [ABSTRACT FROM AUTHOR]