Antioxidant Quinonemethide Triterpenes from Salacia campestris by Paulo R. F. Carvalho, Dulce H. S. Silva, Vanderlan S. Bolzani, and Maysa Furlan* Instituto de Química, Universidade Estadual Paulista, CP 355, CEP14801-900, Araraquara, SP, Brazil (phone:  5516-201-6661; fax:  55-16-222-7932; e-mail: maysaf@iq.unesp.br) A new quinonemethide triterpene named as salacin, has been isolated from the root bark of Salacia campestris in addition to the known pristimerin, maytenin, 20a-hydroxymaytenin, and netzahualcoyene. Salacin was identified on the basis of NMR-spectral and mass spectrometric analysis. The free-radical scavenging activities of the quinonemethide triterpenes salacin (1), pristimerin (2), maytenin ( 3), 20a-hydroxymaytenin (4), and netzahualcoyene (5) towards DPPH have been evaluated and showed absorbance variation ( DA) of 19, 20, 39, 28, 55, and 10%, respectively, having rutin (74% at 50 mm) and BHT (7% at 50 mm) as standard compounds. 1. Introduction. ± Quinonemethide triterpenes are natural products of occurrence restricted to Hippocrateaceae and Celastraceae families. Several representatives of this class are claimed to be medicinally useful [1][2], as antimicrobial [3±5], anticancer [4][6][7], antimalarial [8], and spermicidal compounds [9]. Some Salacia species, e.g. , S. reticulata, S. oblonga, and S. chinesis , have long been used in India, Sri-Lanka, and China, respectively, as traditional medicines for treating rheumatism and skin diseases, and for their anti-inflammatory properties as well. Recent investigations have confirmed the hepatoprotective and antioxidant properties of S. reticulata, and disclosed the presence of catechins as the active principle [10] and aldose reductase inhibition by tingenin B, a quinonemethide from S.chinensis [11]. The antioxidant activity of organic compounds is dependent of few structural features that include, in most cases, the presence of phenolic OH-groups. Thus, flavonoids, lignans, phenylpropanoids, and other aromatic compounds have been the focus of a large number of publications dealing with antioxidant properties [12]. Antioxidant terpenes are rare, and the best known examples include rosmanol and carnosic acid derivatives, abietane diterpenes from sage ( Salvia officinalis) and rosemary ( Rosmarinus officinalis ), in which the phenolic moiety has been produced during their biosynthesis [13][14]. The antioxidant activities of the quinonemethide triterpenes celastrol, pristimerin, and acetylcelastrol have been previously assessed through demonstration of their lipid-peroxidation-inhibition effect in rat liver mitochondria [15]. On the other hand, no data are available on the free-radical scavenging activity of quinonemethide triterpenes. Useful information regarding the antioxidant activity of synthetic and natural products can be obtained from the measurement of their free-radical-scavenging properties, e.g. , in dilution assays on the reduction of the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) [16]. In the course of our studies on biosynthesis and bioactive compounds from Celastraceae and Hippocrateaceae species [12][17], we describe herein the occurrence CHEMISTRY & BIODIVERSITY ± Vol. 2 (2005) 367  2005 Verlag Helvetica Chimica Acta AG, Zürich