Deodorizing activity of diterpenes from the leaves of Rabdosia trichocarpa and of several α,β-unsaturated carbonyl compounds against methanethiol

Fourteen diterpenes containing one novel compound from the leaves of Rabdosia trichocarpa had significant deodorizing activity against methanethiol (CH3SH), the main source of halitosis. The compounds generated from the reaction between oridonin, the main compound of the 14 diterpenes and CH3SH were isolated and determined to be two adducts, 17α-CH3S-oridonin and 17β-CH3S-oridonin. This implies that CH3SH reacted with oridonin, which had an exocyclic methylene group conjugated with a ketone, by 1,4-addition. Oridonin reduced the bad odor by converting CH3SH to these non-volatile compounds. Oridonin showed significant deodorizing effect in the basic pH range, and had almost no effect in the acidic pH range. The rate of the deodorizing action of oridonin was relatively faster than that of tea catechins, which are widely used as oral deodorizers. The deodorizing effect of several α, β-unsaturated carbonyl compounds against CH3SH was also determined.