Antifungal activity of iridoid glycosides from the heartwood of Gmelina arborea

Gmelina arborea Linn. (Verbenaceae) is a deciduous broad-leaved tree widely distributed from Southeast Asia to South Asia (Greaves 1981) and all parts of this plant are used in medicine to cure various ailments (Rao et al. 1967; Tiwari 1995; Rechnagel and Glende 1973; Chanh et al. 1987). Trees of the Verbenaceae family contain iridoid glycosides (Jacke and Rimpler 1983; Rathore et al. 1989; Otsuka et al. 1991, 1992; Stuppner et al. 1993; Calis et ̧ al. 1994; Dellar et al. 1996; Hosny and Rosazza 1998; Hannedouche et al. 1999; Helfrich and Rimpler 1999; Ghisalberti 2000; Chowdhury et al. 2003). A total of 15 and 8 derivatives of 6-O-a-L-rhamnopyranosylcatalpols have been reported from the leaves of G. arborea (Hosny and Rosazza 1998) and the aerial parts of Holmskioldia sanguinea (Helfrich and Rimpler 1999), respectively. The aerial parts of Gmelina philippensis, which is the same genus of G. arborea, contains catalpol (Helfrich and Rimpler 2000). Iridoid glycosides have been found to possess a range of biological activities, i.e., antiinflammatory (Schapoval et al. 1998), antitumoral (Kapadia et al. 1996; Konoshima et al. 2000) and antioxidative (Chander et al. 1992). Cinnamate esters of catalpol from Westringia fruticosa and W. viminalis exhibited antifungal activity against the plant pathogenic fungus Cladosporium cucumerinum (Dellar et al. 1996). In the first part of this series, it was shown that four lignans contained in the heartwood of G. arborea showed antifungal activity against Trametes versicolor (Kawamura et al. 2004). In the present paper, we report on the isolation and identification of four iridoid glycosides from the same source and the determination of their antifungal activity.