Neoorthosiphonone A; a nitric oxide (NO) inhibitory diterpene with new carbon skeleton from Orthosiphon stamineus

From the aerial part of Orthosiphon stamineus from Hainan island of China, a diterpene named neoorthosiphonone A (1), having a novel carbon framework, has been isolated. Neoorthosiphonone A (1) possessed a unique unprecedented structural feature of eight-membered ring C in its structure, which may be biogenetically derived from its isopimarane precursor, orthosiphonone A, through the insertion of vinyl group into the C₁₃-C₁₄ bond. Neoorthosiphonone A (1) displayed potent inhibitory activity on the nitric oxide production in LPS-activated macrophage-like J774.1 cells with an IC₅₀ value of 7.08 μM, more potent than the positive control l-NMMA.