Emodin and syringaldehyde from Rhamnus pubescens (Rhamnaceae)

Rhamnus pubescens Sibth. & Sm. non Poir., originally from Greece, is a European species of Rhamnaceae (PANDORA Taxonomic Database System, 1999. Flora Europaea. Royal Botanic Garden Edinburgh, UK. Available on line at: http://www.rbge.org.uk/research/pandora.home.PANDORA Taxonomic Database System, 1999). Plant material was collected from San Jose, Costa Rica during August 1991 by Polybiotika, Costa Rica. A voucher specimen (MNL10067) has been maintained at the herbarium of the Institute of Grassland and Environmental Research, Aberystwyth, UK. BiotageTM 75 flash chromatography (silica gel, eluting with a step gradient of increasing polarity: n-hexane–EtOAc–MeOH) of the CH2Cl2 extract of leaves and stems of R. pubescens (0.97 kg) provided 9 fractions (1000 ml each). Flash fractions 2 (10% EtOAc in n-hexane) and 5 (40% EtOAc in n-hexane), respectively, afforded emodin (1, 1.9 mg) (SDBS, Integrated Spectral Database System for Organic Compounds, 1999. National Institute of Materials and Chemical Research Tsukuba, Ibaraki 305-8565, Japan. Available on-line at: http://www/aist.go.jp/RIODB/SDBS/menu-e.html.SDBS database, 1999; Coskun et al., 1990; Pouchert, 1983) and syringaldehyde (1.6 mg) (SDBS database, 1999) upon reverse phase HPLC purification (C18 preparative column, for 1, eluted isocratically with a mobile phase, water : acetonitrile : 0.1% TFA in ACETONITRILE=30 : 60 : 10, and for syringaldehyde, eluted with a gradient, water : acetonitrile : 0.1% TFA in ACETONITRILE=60 : 30 : 10, 55 ml/min. to 00 : 90 : 10 in 15 min, flow RATE=55 ml/min, detection at 210 nm). Structures of these compounds were determined on the basis of UV, LC-MS and NMR data, and also by direct comparison with the respective literature data.