A new labdane diterpene from Vitex negundo

Context: Vitex negundo Linn. (Verbenaceae) seeds are pepper substitute and occasionally used as a condiment for edible purposes. The seeds also find use for analgesia, sedation, rheumatism and joint inflammation in folk medicine. Objective: To isolate and characterize bioactive constituents from V. negundo seeds. Materials and methods: The ethanol extract of V. negundo seeds was subjected to repeated column chromatography. Chemical structures were elucidated by detailed spectroscopic analyses on the basis of NMR, IR, and MS data. Several pathogenic fungi isolates were employed to evaluate the antifungal activity of the isolated compound. Results: Chemical investigations of the seed extract afforded a new labdane diterpenoid, named negundol (1a + 1b), as an inseparable mixture of two diastereoisomers in a 5:4 ratio. Their structures were identified as (rel 3S, 5S, 8R, 9R, 10S, 13S, 16S)-3-acetoxy-9, 13-epoxy-16-hydroxy-labda-15, 16-olide (1a), and (rel 3S, 5S, 8R, 9R, 10S, 13S, 16R)-3-acetoxy-9, 13-epoxy-16-hydroxy-labda-15, 16-olide (1b). Compound 1 was active as an antifungal agent with MIC80 values in the range of 16-64 μg/mL. Discussion and conclusion: The presence of compound 1 in V. negundo is of chemotaxonomic significance, since plants under the genus Vitex are chemically characterized with labdane diterpenoids. Compound 1 exhibited potential antifungal activity and may be considered a lead compound for promising antifungal agent.