Cytotoxic Phenolic Glucosides from Flowers ofEriogonum brevicaule

Abstract

The genus Eriogonum, wild buckwheat (Polygonaceae), comprises 150 species, mostly native to the West U. S. (1). Several species have had use in the past to treat colds, tuberculoses, bladder problems, skin cuts, and other ailments (2, 3). Whole plant extracts of eight species were screened for lP toxicity in mice, with one species (E. brevicaule Nutt.) exhibiting some lethality at 12.5mg/kg (4). The extract was also cytotoxic in the National Cancer Institute KB cell test at 18 pg/mI and showed marginal activity (TIC 118 and 132 in two tests) against P388 murine leukemia in mice (4). Antimicrobial activity of an extract of the native American medicinal plant F. umbellatum was traced to methyl gallate (5). Two alkaloids, hordenine and N-methyl-4-methoxyphenethylamine, were found in four Enogonum species, including F. brevicaule (6), while four gossypetin 7-methyl ether glycosides were found in E. nuduni (7).were collected on August 10, 1993 20km N. of Fort Collins, Colorado (Larimer Co.) and a voucher (FRS 479) deposited in the Colorado State University Herbarium.Extracts of leaves and flowers were quantitatively tested for cytotoxicity using the brine shrimp lethality (BSL) bioassay (8). For the assay, extracts and residues of chromatographic fractions were tested using two concentrations, 5 mg and 0.5 mg per vial, and each repeated twice. Colchicine was used as positive standard showing 100% mortality at 100ug/ml (ED50 = 15 ppm). Percent mortality was recorded after 24 h.Dried flowers (63.5g) and leaves (48.7g) were extracted separately with hexane/EtOAc (3 :2) and then MeOH. The MeOH extract of the flowers (8.5 g of residue) showed the strongest activity (100, 0.0% mortality at 5 and 0.5 mg/vial, respectively). The MeOH extract residue was fractionated (VLC, silica gel, 150g, CHCI3-MeOH mixtures). The fraction eluting with pure methanol (4.4 g) had the strongest activity (100, 10 % mortality). This material was fractionated (VLC, C18silica gel, 150g. H20-MeOH mixtures) with the most active fraction (1.7g; 100, 80% mortality) eluting with 40% MeOH. This residue was subjected to preparative TLC (silica gel, EtOAc/MeOH/H20 30:5:4) to yield 28mg of 1-/3-o-glucopyranosyloxy-3,5-dihydroxybenzene (R =0.48) (9) and 52mg of 1 -13-D-glucopyranosyloxy-3-methoxy-5-hydroxybenzene (R = 0.61) (10). These were identified by comparison of their 1H-and 13C-NMR spectra with those in the literature (9, 10). Copies of the original spectra are obtainable from the author of correspondence. Final lethalities were at 150 ppm for the isolated 3-methoxy-5-hydroxybenzene derivative and 1103 ppm for the 3,5-dihydroxybenzene derivative.This and previous studies (5, 6) suggest that further work on the possible medicinal potential of Eriogonum species is warranted.