Bioactivity and chemistry of the genus Hortonia

The dichloromethane extracts of the leaves, stem bark, bark and the roots of the three species of the primitive endemic genus Hortonia, H. angustifolia, H. floribunda and H. ovalifolia, collected from nine geographical locations ranging from lower elevations (84-420 m) to higher (2000 m) showed comparable HPLC profiles and mosquito larvicidal and antifungal activities; protein analysis of the leaves of the three species of Hortonia showed identical peaks and bands. The two major metabolites (4S)-4-methyl-2-(11-dodecynyl)-2-butenolide (2) and (4S)-4-methyl-2-(11-dodecenyl)-2-butenolide (3), which were previously reported from all three plants, showed potent larvicidal activities. Compound 2 was excessively high in the extracts of the stem bark and the roots of all three species amounting to approximately 38 and 60%, respectively. A minor new butenolide (4), (4S)-4-methyl-2-((2R)-hydroxy-11-dodecenyl)-2-butenolide, with much reduced larvicidal activity and ishwarane (1), which showed antifungal activity, were also isolated from all three plants. Treatment of compound 2 with H₂/Pd-C afforded the completely reduced compound 5, which showed no larvicidal activity, indicating that unsaturation in both 2 and 3 is necessary for their bioactivity. The foregoing evidence showed that there are major similarities between the three species of Hortonia.