Diterpenes as nitric oxide secretion inhibitors from Kaempferia koratensis rhizomes

Kaempferia koratensis Picheans. (Zingiberaceae), known locally as "Proa Korat" or "Wan Proa Khao," is native to northeastern Thailand where it is widely used for its aromatic properties in the local cuisine. Given its potential for expanded applications in traditional medicines, and for foods and food supplements derived from certain Kaempferia species, this study focused on the metabolites of K. koratensis rhizomes and evaluated their in vitro anti-inflammatory properties. Eight new isopimarane diterpenoids were isolated, including five koratones A-E, two koratanes C and D, and a bisditerpenoid, named as koratensin, together with six known isopimarane diterpenoids. The anti-inflammatory properties were evaluated by inhibiting nitric oxide production, with curcumin used as a positive control. The results revealed that koratone B was the most potent isolate at 25 μg/mL with 36.54 ± 0.79 % inhibition and koratane D at 50 μg/mL with 58.85 ± 4.12 % inhibition. Molecular docking of koratone B suggested the inhibitory effect was due to an affinity for hydrogen bonding at the active site of iNOS. The physicochemical and pharmacokinetic properties of koratone B were calculated. These findings indicate that selected isopimarane diterpenoids from K. koratensis, such as koratone B, merit further developmental consideration to potentiate the observed biological response.