1. The isolation of aspalathin, the principal phenolic constituent in the leaves of Aspalathus linearis, is described and its properties are discussed. 2. The compound has been identified as 3'-C-beta-d-glucopyranosyl-2',3,4,4',6'-pentahydroxydihydrochalcone by the preparation and analysis of various derivatives, by photochemical oxidation to 2,3-dihydroiso-orientin and by nuclear-magnetic-resonance studies.
Certain varieties of A8palathus acuminatu8, particularly that due to the late Dr P. le F. Nortier, are used in South Africa for the manufacture of a beverage known as rooibos tea. The product has become increasingly popular during the past few years and is believed by many to have certain health-promoting properties. Although it has been reported to contain only traces of caffeine and only about 3 % of tannin (Reyneke, Coetzee & Bester, 1949), no detailed work on the composition of the latter has yet been published. The present study provides details of the isolation and characterization of two quercetin glycosides together with two rarely occurring C-glycosides of luteolin as the major flavone constituents of the green plant. EXPERIMENTAL AND RESULTS All melting points are corrected and were determined by the Kofier method. Mixed melting points were determined on equimolecular mixtures. Analyses of C, H, methoxyl and acetyl were by Weiler and Strauss, Oxford. Infrared spectra were recorded by Dr J. R. Nunn, National Chemical Research Laboratory, C.S.I.R.O., Pretoria, by the KBr-disk method. Isolation of the crude polyphenols Four 2-year-old bushes of the Nortier variety from a tea plantation in the Clanwilliam district were selected for sampling. During the harvesting season in February 1960, the top third of these bushes was removed and dried in an air current at 700 within 24 hr. of cutting. After drying for 12 hr., the leaves were separated from the stalks. The dried leaves (250 g.) were ground to a powder in a Wiley mill fitted with a 40-mesh sieve, and extracted three times with boiling water (800 ml.) for 10 min. The combined aqueous extracts were extracted continuously with chloroform (8 hr.) and ethyl acetate (48 hr.). The ethyl acetate in the collecting flask (600 ml.) was replaced every 8 hr. The combined ethyl acetate extracts (about 3-5 1.) were evaporated to dryness under reduced pressure on a water bath and the polyphenols were recovered as a light-yellow amorphous powder (20.08 g.).
1. The structures of orientin and iso-orientin have been investigated by periodic acid and ferric chloride oxidation of the tetra-O-methyl derivatives and by identification of the products of oxidation. 2. The preparation and properties of the 3',4',7-trimethyl ethers of orientin and iso-orientin are described, and the nuclear-magnetic-resonance spectra of orientin, iso-orientin and their tri- and tetra-O-methyl derivatives are discussed. 3. Orientin and iso-orientin are formulated as 8- and 6-C-beta-d-glucopyranosyl-luteolin respectively.
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