Plant Tissue Cult. 11(2) : 159-172, 2001 (December)

Two New Quinones from Lithospermum erythrorhizon Hairy Root Cultures

A. F. M. Feroj Hasan, Masaharu Kyo and Hiroshi Fukui

Applied Bioresource Science, United Graduate School of Agricultural Sciences, Ehime University (Kagawa University Campus), Kagawa 761-0795, Japan

Key words: Lithospermum erythrorhizon, New quinones, Hairy root culture

Abastract

Hairy root cultures of Lithospermum erythrorhizon Sieb. et Zucc. (Boraginaceae) produce large amounts of shikonins (red naphthoquinone derivatives) as normal secondary metabolities in a hormone-free and ammonium nitrate-depleted MS liquid medium. However, we recently found that the culture in MS medium (without hormones) induced the production and secretion of two new quinone compounds, tentatively named hydroxyechinofuran B (brown) and rhizonone (colorless), accompanied with the inhibition of hairy root growth and the reduced production of shikonin derivatives. Hydroxyechinofuran B (15 mg) and rhizonone (20 mg) were isolated from the medium of the hairy root culture (15 liter). Their structures were elucidated as 2-[4-(E-4-hydroxymethyl-3-pentenyl)-furan-2-yl]-1, 4-benzoquinone (hydroxycehinofuran B) and 5a-methyl-5a, 6, 10b, 10c-tetrahydro-2H-anthra [9,1-bc]furan-7, 10-dione (rhizonone) based on the spectroscopic data (UV, IR, MS and NMR) and some chemical reactions. When the developed and dried TLC plate was sprayed with a suspension of spores of Cladosporium fulvum, rhizonone showed stronger antifungal activity compared to shikonin derivatives. The hydroxyechinofuran B and rhizonone are considered to be derived from geranylhydroquinone, a key biosynthetic precursor of shikonin. This unique carbon skeleton of rhizonone has not been known in the compounds isolated from the L. erythrorhizon plant. The novel carbon skeleton of rhizonone indicates that L. erythrorhizon prossesses three types of biogenetic pathways from geranylhydroquinone to three endo-products (shikonins, echinofurans and rhizonone). The undifferentiated cells cultured in the same liquid medium did not produce and secrete the two new quinones.

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