Teucrol, a decarboxyrosmarinic acid and its 4′-O-triglycoside, teucroside from Teucrium pilosum
Introduction
Plants of the family Lamiaceae are known for their high contents of flavonoids, essential oils and esters of caffeic acids (Banthorpe et al., 1989, Nawaar et al., 1989, Bisset, 1994, El-Ansari et al., 1995). The family is represented in Egypt by 15 genera, including 42 species, among which the genus Teucrium is of restricted occurrence (Täckholm, 1974) and only four of its species are growing wild in the western mediterranean coastal region and Sinai proper. In Egypt, infusion of the tender parts of these plants are used for treating dyspeptic complaints and biliary upsets (Boulos, 1983). As a part of our investigation of the constitutive phenolics of Lamiaceae we here describe the isolation and structure elucidation of the new phenolic ester, 9′-decarboxyrosmarinic acid, 3′,4′-dihydroxy-β-phenylethyl caffeate, or teucrol (1) and its triglycoside, 9′-decarboxyrosmarinic acid 4′-O-α-rhamnosyl-(1⁗→6‴)-O-β-galactosyl-(1‴→4″)-O-α-rhamnoside, teucroside, (2) from the aqueous ethanolic whole plant extract of T. pilosum.
The new compound (1) is of special interest as it represents the first reported occurrence of a caffeate ester of 3,4-dihydroxy-β-phenyl- ethanol. The related 2-(3,4-dihydroxyphenyl)ethenyl caffeate was reported to occur in callus cultures of several Lamiaceae species (Banthorpe et al., 1989). Its triglycoside (2) also, is interesting as it contains the new trioside, α-O-rhamnopyranosyl-(1→6)-β-O-galactopyranosyl (1→4)-α-O-rhamnopyranose. However, different glycosides of 3,4-dihydroxy-β-phenylethanol acylated with caffeic acid at their sugar moieties (e.g. orobanchin), have been previously reported to occur in Syringa vulgaris and Echinacea angustifolia (Stoll et al., 1950, Harborne, 1966, Birkofer et al., 1968).
Section snippets
Results and discussion
Ground dry shrublets of T. pilosum were exhaustively extracted with ethanol:H2O (3:1). Compounds (1 & 2) were isolated and purified by applying a combination of polyamide column chromatography followed by Sephadex LH-20 columns.
Compound (1), isolated as an off-white amorphous powder was found to exhibit chromatographic properties [fluorescent blue spot on paper chromatograms (PC) under UV light, changing to bright canary yellow colour on fuming with ammonia, high Rf-values in organic solvents
Experimental
NMR:Jeol EX-270 spectrometer, 270 MHz (1H NMR) and 67.5 MHz (13C NMR), respectively. 1H resonances were measured relative to TMS and 13C NMR resonances to DMSO-d6 and converted to TMS scale by adding 39.5. Typical conditions: spectral width=5000 Hz for 1H and 20000 Hz for 13C, 32 K data points and a flip angle of 45°C. FAB-MS: Finnigan MM-7070 instrument (VG Analytical). PC (descending): Whatman no. 1 paper, using solvent systems: (1) H2O; (2) 15% HOAc; (3) BAW (n-BuOH-HOAc-H2O, 4:1:5, upper
Acknowledgements
We are grateful to Dr. M. Nawwar, Professor of Phytochemistry, Division of Pharmaceutical Sciences, Dept. of Phytochemistry, NRC, Cairo, Egypt, for his valuable discussion throughout the course of the present study.
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