Takahiko Isobe

Effects of phenolic compounds isolated from Rabdosia japonica on B16-F10 melanoma cells

Pedalitin isolated from the aerial part of Rabdosia japonica (Labiatae), exhibited cytotoxicity against the murine B16‐F10 melanoma cell line with an IC50 of 30 µm (9.5 µg/mL). As the cells were cultured with this flavone, melanin production was not suppressed, but rather enhanced. Quercetin isolated from the same source exhibited similar activities, but rutin showed neither activity. Copyright

THE STRUCTURE OF INFLEXIN

The structure of inflexin isolated from the leaves of Isodon inflexus has been determined as 1 by spectroscopic and chemical methods. Inflexin exhibits cytotoxicity, insect antifeedant and other bioactive properties.

Melanogenesis inhibitors from Rabdosia japonica.

The effects of the four major ent-kaurene diterpenoids isolated from the aerial part of Rabdosia japonica (Labiatae) on murine B16-F10 melanoma cells were investigated. Among the compounds tested, oridonin and nodosin most significantly suppressed cellular melanin production when the cells were cultured with these diterpenoids. However, oridonin and nodosin exhibited cytotoxicity against the same melanoma cells with an IC(50) of 1.1 μM (0.40 μg/ml) and of 1.3 μM (0.47 μg/ml) and almost complete lethality was observed at 4.0 μM and at 8.0 μM, respectively, and therefore observed melanogenesis inhibition is mainly due to its melanocytotoxic effect. Morphological observation showed that oridonin or nodosin treated B16-F10 melanoma cells induced dendrite structure. Diterpenoids quickly formed adducts partly in Dulbeccos Modified Eagles Medium (DMEM) containing 10% of fetal bovine serum (10% FBS-DMEM) before their application to the cells. Approximately 20% of oridonin formed adducts within the first 15 min. Notably, dihydronodosin exhibited inferior cytotoxicity (>85% cell viability at 100 μM) but still significantly suppressed melanogenesis (>55%) when murine B16-F10 melanoma cells were cultured with this diterpenoid derivatives. Hence, dihydronodosin can be a potential melanogenesis inhibitor.

Structure of isodomedin, a novel ent-kaurenoid diterpene

Chemical investigation of bitter principles from Isodon skikokianus var intermedius has led to the isolation and characterization of a new ent-kaurenoid, isodomedin, which exhibits antibacterial and cytotoxic activities as well as antifeedant activity against the African army worm.

Structure of effusin

The structure of a new spirosecokaureiie compound, effusin, isolated from Rabdosia effusus and possessing an insect growth inhibitor activity, has been determined from spectroscopic and chemical data.