Activity-guided isolation of the chemical constituents of Muntingia calabura usingaquinonereductaseinductionassay Bao-Ning Su a ,EunJungPark a ,JoseSchunkeVigo b ,JamesG.Graham a , Fernando Cabieses b ,HarryH.S.Fong a ,JohnM.Pezzuto a ,A.DouglasKinghorn a, * a Program for Collaborative Research in the Pharmaceutical Sciences and Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, Chicago, IL 60612, USA b Instituto Nacional de Medicina Tradicional (INMETRA), Minesterio de Salud, Jesus Maria, Lima, Peru Received 6 December 2002; received in revised form 24 January 2003 Abstract Activity-guidedfractionationofanEtOAc-solubleextractoftheleavesof Muntingia calabura collectedinPeru,usinganinvitro quinone reductase induction assay with cultured Hepa 1c1c7 (mouse hepatoma) cells, resulted in the isolation of a flavanone with an unsubstituted B-ring, (2R,3R)-7-methoxy-3,5,8-trihydroxyflavanone (5), as well as 24 known compounds, which were mainly flavanones and flavones. The structure including absolute stereochemistry of compound 5 was determined by spectroscopic (HRMS, 1D and 2D NMR, and CD spectra) methods. Of the isolates obtained, in addition to 5, (2S)-5-hydroxy-7-methoxy- flavanone,2 0 ,4 0 -dihydroxychalcone,4,2 0 ,4 0 -trihydroxychalcone,7-hydroxyisoflavoneand7,3 0 ,4 0 -trimethoxyisoflavonewerefoundto induce quinone reductase activity. # 2003ElsevierScienceLtd.Allrightsreserved. Keywords: Muntingia calabura;Elaeocarpaceae;(2R,3R)-trans-7-methoxy-3,5,8-trihydroxyflavanone; Quinone reductase induction assay 1. Introduction InductionofPhase2drug-metabolizingenzymessuch as quinone reductase (QR) is considered an effective strategy for achieving protection against the toxic and neoplasticeffectsofmanycarcinogens(Gerha¨useretal., 1997; Talalay, 2000). As part of our continuing search for novel, plant-derived cancer chemopreventive agents (Pezzuto, 1997; Kinghorn et al., 1998; Pezzuto et al., 1999),theleavesof Muntingia calabura L. (Elaeocarpa- ceae), collected in Peru, were chosen for detailed inves- tigation since their EtOAc-soluble extract significantly induced QR with cultured Hepa 1c1c7 (mouse hepa- toma) cells. Various parts of this tree have several documented medicinal uses in both Southeast Asia and tropical America (Kaneda et al., 1991; Nshimo et al., 1993).Therootshavebeenemployedasanemmenogo- gue in Vietnam and as an abortifacient in Malaysia. In the Philippines, the flowers of this species have been used to treat headaches, and as an antidyspeptic, anti- spasmodic, and diaphoretic. Infusions of the flowers of this plant are drunk as a tranquillizer and tonic in Colombia(Perez-Arbelaez,1975;Kanedaetal.,1991). In our previous work, several cytotoxic flavonoids and chalcones were isolated from the roots (Kaneda et al.,1991)andtheleavesandstems(Nshimoetal.,1993) of this species collected in the Philippines and in Thai- land, respectively. Other phytochemical investigations on this plant have resulted in the isolation of flavones and ellagic acid (Seetharaman, 1990). The volatile phe- nolic, sesquiterpene and furanoid constituents of the ripe fruits of M. calabura have been analyzed by GC– MS(Wong et al., 1996). This paper describes the isola- tionandstructureelucidationof24knowncompounds, (1–4, 6–14), and a new flavanone, (2R,3R)-7-methoxy- 3,5,8-trihydroxyflavanone (5), obtained using the QR induction assay to monitor fractionation (Chang et al., 1997; Dinkova-Kostova and Talalay, 2000). The 0031-9422/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0031-9422(03)00112-2 Phytochemistry 63 (2003) 335–341 www.elsevier.com/locate/phytochem * Corresponding author. Tel.: +1-312-996-0914; fax: +1-312-996- 7107. E-mail address: kinghorn@uic.edu (A.D. Kinghorn).