Jing-Jie Zhang

Discovery of antifungal constituents from the Miao medicinal plant Isodon flavidus

ETHNOPHARMACOLOGICAL RELEVANCE Leigong Mountain is an area in the Southwest of China where there is a high incidence rate of athletes foot, but the Miao people, a Chinese minority who reside in this mountainous area have suffered less from this disease due to their use of the herbal medicine Isodon flavidus (Hand.-Mazz.) H. Hara. AIM OF THE STUDY The present study is to identify the active chemical constituents responsible for antifungal effects of the folk medicine plant. MATERIALS AND METHODS The natural compounds were separated from the methanol extract of the twigs and leaves of I. flavidus by phytochemical study using chromatographic methods, and their chemical structures were determined by analysis of the spectroscopic data including 1D and 2D NMR spectra. The absolute configuration of fladin A (1) was further confirmed by X-ray crystallographic analysis. The compounds were evaluated for their antifungal activity against the athletes foot fungus Trichophyton rubrum. They were further evaluated for their antimicrobial and anti-biofilm activity against the dental pathogens Streptococcus mutans, Porphyromonas gingivalis and Candida albicans. RESULTS Phytochemical and biological studies of I. flavidus led to the discovery of two antifungal compounds, fladin A (1) and lophanic acid (2). Fladin A (1) is a novel diterpene with an unprecedented cyclic ether group formed between C-4 and C-9. Lophanic acid (2) displayed inhibition activity against the athletes foot fungus Trichophyton rubrum with an MIC value of 7.8μg/mL, and fladin A (1) also showed inhibition activity against the fungus with a MIC value of 62.5μg/mL. CONCLUSIONS Our identification of two antifungal compounds provided strong evidence for the Miao people to use I. flavidus as a medicinal plant for treatment of athletes foot disease. The very different chemical structures of the active compounds from those in the market presents them as potential antifungal lead compounds for follow-up study.

Crystal constructure of 16(S)-methyl-6α-carboxy-1, 15-dioxo-6, 7-seco-ent-kaur-2-en-7, 20-olide, C20H24O6

Abstract C20H24O6, orthorhombic, P212121 (no. 19), a = 7.697(14) Å, b = 13.91(2) Å, c = 16.75(3) Å, V = 1794 Å3, Z = 4, Rgt(F) = 0.0430, wRref(F2) = 0.1087, T = 293 K.

Crystal structure of ent-1β-acetoxy-7α,14α-di-hydroxy-7β,20-epoxykaur-16-en-15-one, C22H30O6

Abstract C22H30O6, monoclinic, P21/c (no. 14), a = 11.1339(16) Å, b = 6.1262(9) Å, c = 14.771(2) Å, β = 103.567(5)°, V = 1867.9(12) Å3, Z = 2, Rgt(F) = 0.0430, wRref(F2) = 0.1165, T = 293 K.

Crystal structure of 7β,14β,15β-trihydroxy-1α-acetoxy-7α,20-epoxy-ent-kaurane, C22H32O6

Abstract C22H30O6, monoclinic, P21 (no. 14), a = 9.111(3) Å, b = 9.535(3) Å, c = 11.331(4) Å, β = 92.703(4)°, V = 983.3(5) Å3, Z = 2, Rgt(F) = 0.0418, wRref(F2) = 0.1152, T = 293 K.

Crystal structure of 1-oxo-6,15-dihydroxy-6,7-seco-ent-kaura-2,16-dien-7,20-olide monohydrate, C20H26O5 · H2O

C20H28O6, orthorhombic, P212121 (no. 19), a = 7.444(2) Å, b = 14.026(3) Å, c = 17.298(4) Å, V = 1806.0 Å, Z = 4, Rgt(F) = 0.036, wRref(F ) = 0.086, T = 293 K.