Phenolic Constituents and Antioxidant Properties of Xanthosoma violaceum Leaves PATRIZIA PICERNO, † TERESA MENCHERINI, † MARIA ROSARIA LAURO, † FRANCESCO BARBATO, ‡ AND RITA AQUINO* ,† Dipartimento di Scienze Farmaceutiche and Scuola di Specializzazione in Scienza e Tecnologia Cosmetiche, University of Salerno, Invariante 11/C, 84084 Fisciano, Salerno, Italy, and Dipartimento di Chimica Farmaceutica e Tossicologica, University of Naples Federicio II, via D. Montesano, 80131 Naples, Italy An extract of Xanthosoma violaceum leaves was subjected to a polyphenol profile determination, including total polyphenols, and antioxidant activity evaluation. Analysis of the extract resulted in the isolation of a new flavone C-glycoside, apigenin 6-C--D-glucopyranosyl-8-C--D-apiofuranoside (1), as well as known flavone C-glycosides, including vitexin (2), isovitexin (3), isovitexin 4′-O- rhamnopyranoside (4), apigenin 6-C-[-D-glucopyranosyl-(1f6)--D-glucopyranoside] (5), and apigenin 6,8-diC--D-glucopyranoside (6). The antioxidant activity of the extract was assessed by means of two different in vitro tests: bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical (DPPH test) and peroxidation induced by the water-soluble radical initiator 2,2′-azobis(2-amidinopropane) hydrochloride, on mixed dipalmitoylphosphatidylcholine/linoleic acid unilamellar vesicles (LP-LUV test). In both tests used, the extract and a fraction II showed a significant antioxidant/free-radical scavenging effect (fraction II, EC 50 ) 11.6 µg/mL) in comparison to R-tocopherol (EC 50 ) 10.1 µg/mL). KEYWORDS: Xanthosoma violaceum; new cocoyams; C-glycosyl flavones; free-radical scavenging/ antioxidant activity INTRODUCTION X. Violaceum Schott (Araceae) is a herbaceous perennial plant of tropical American origin, widely distributed in Dominican Republic, Puerto Rico, Guatemala, and Ecuador; its roots and cormels are typical tropical crops (1, 2). Because many developing countries in the tropics depend on Xanthosoma species, collectively known as “new” cocoyams, as a source of carbohydrates (2), these edible aroids are an unexploited source of food and industrial starches. Among the Xanthosoma species, X. sagittifolium (L) Schott is generally considered as the main cultivated species and therefore the composition of its cormels and leaves has been studied with regard to minerals (3), carbohydrates (3), phenols (4), and carotenoids (5), whereas the phenolic composition of X. Violaceum leaves is unknown. In our continuing search for antioxidative plant extracts from Central and South American species (6-8), Xanthosoma Vio- laceum was investigated phytochemically and biologically. An analytical preliminary evaluation of a polar leaf extract (EXV) of X. Violaceum showed high levels of phenolic compounds, especially flavones, whose effectiveness as antioxidant agents is reported in the literature (9, 10). In this study we investigated the in vitro antioxidant and free-radical scavenging activities of EXV extract determined both in homogeneous solution, employing the bleaching of the stable 1,1-diphenyl-2-picryl- hydrazyl radical (DPPH test), and in a membrane system employing, as an experimental model, the peroxidation induced by the water-soluble radical initiator 2,2′-azobis(2-amidinopro- pane) hydrochloride, on mixed dipalmitoylphosphatidylcholine/ linoleic acid unilamellar vesicles (LP-LUV test). Since the interaction with the microenvironment of the lipid cell bilayers plays a key role in the membrane-dependent antioxidant activity, the employment of both in vitro tests may give useful informa- tion on the actual effectiveness and suitability of potential antioxidants (7). Also, the total phenolic content of the extract was determined, the major constituents were isolated and their chemical structures established, and the flavone quantitative analysis was obtained by an HPLC analytical method. MATERIAL AND METHODS General Experimental Procedures. Melting points are uncorrected. UV spectra were obtained with a Perkin-Elmer 550 SE spectropho- tometer. For NMR experiments, a Bruker DRX-600 spectrometer was used, operating at 599.2 MHz for 1 H and 150.9 MHz for 13 C and using the UXNMR software package; DEPT, 1 H- 1 H DFQ-COSY (double- quantum filtered COSY), and 1 H- 13 C HSQC and HMBC experiments were obtained using conventional pulse sequences. 1D TOCSY (11) (selective excitation spectra) were acquired as previously reported (6). Chemical shifts are expressed in δ (ppm) referring to the following solvent center peaks: δH 3.34 and δC 49.0 for CD3OD. The FABMS * To whom correspondence should be addressed. Tel: ++39 89 962814. Fax: ++39 89 962828. E-mail: aquinorp@unisa.it. † University of Salerno. ‡ University of Naples Federicio II. J. Agric. Food Chem. 2003, 51, 6423-6428 6423 10.1021/jf030284h CCC: $25.00 © 2003 American Chemical Society Published on Web 09/17/2003