Full Papers Isolation, Synthesis, and Structure-Activity Relationships of Bioactive Benzoquinones from Miconia lepidota from the Suriname Rainforest 1 A. A. Leslie Gunatilaka, †,‡ John M. Berger, † Randy Evans, § James S. Miller, § Jan H. Wisse, ⊥ Kim M. Neddermann, | Isia Bursuker, | and David G. I. Kingston* ,† Department of Chemistry, M/C 0212, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, Bedrijf Geneesmiddelen Voorziening Suriname, Commissaris Roblesweg, Geyersluit, Suriname, Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri 63166-0299, and Bristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway, Wallingford, Connecticut 06492-7660 Received May 3, 2000 Bioactivity-directed fractionation of an EtOAc extract from the leaves of Miconia lepidota afforded the two benzoquinones 2-methoxy-6-heptyl-1,4-benzoquinone (1) and 2-methoxy-6-pentyl-1,4-benzoquinone (primin) (2). This is the first reported isolation of 1. Both quinones 1 and 2 exhibited activity toward mutant yeast strains based on Saccharomyces cerevisiae, indicative of their cytotoxicity and potential anticancer activity. A number of previously synthesized and new analogues were prepared and tested in the same strains. Compounds 1, 2, 2-methoxy-6-butyl-1,4-benzoquinone (5), and 2-methoxy-6-decyl-1,4- benzoquinone (6) were tested in two cytotoxicity assays. In the M109 tumor cell lines, quinones 1, 2, and 6 had an IC 50 value of 10 μg/mL. In the A2780 cell line, compounds 1, 2 and 5 had IC 50 values of 7.9, 2.9, and 3.2 μg/mL, respectively. In our continuing efforts to uncover bioactive constitu- ents from Suriname flora as part of an International Cooperative Biodiversity Group (ICBG) 2 program we ob- tained a sample of the plant Miconia lepidota DC. (Mela- stomataceae). Miconia is the largest genus of Melasto- mataceae with about 1000 species widely distributed in the New World tropics and one species in West Africa. Various species of Miconia are common components of forest understory throughout the neotropics, often with many species occurring sympatrically (more than one species of a genus at the same locality). M. lepidota is widespread in northern South America, occurring in all of the Guianas, adjacent Brazil, Venezuela, and Colombia. An EtOAc extract of the leaves of this plant exhibited a positive response to our bioassay using mutant yeast strains, which have been shown to respond to known cytotoxic agents, 2 and this extract was thus selected for detailed examination. Results and Discussion The EtOAc extract was partitioned between hexane and MeOH-H 2 O (80:20), and the aqueous layer was diluted with H 2 O to MeOH-H 2 O (60:40) and extracted with CHCl 3 to afford a bioactive CHCl 3 fraction. Repeated chromatog- raphy of this fraction on Si gel followed by reversed-phase chromatography on a C-18-bonded phase afforded the two bioactive compounds 1 and 2. The 1 H and 13 C NMR spectra of both 1 and 2 indicated clearly that they were simple alkylated benzoquinones, and this conclusion was supported by their mass spectra. Thus, the EIMS of 1 showed a molecular ion at m/z 236, with major fragment ions at m/z 179, 154, 153, 139, and 125, consistent with the formation of the fragments C 10 H 11 O 3 , C 8 H 10 O 3 ,C 8 H 9 O 3 ,C 7 H 7 O 3 , and C 6 H 5 O 3 . 3 The EIMS of 2 showed a molecular ion at m/z 208 and contained the same fragment ions as 1. Based on their 1 H and 13 C NMR data (Tables 2 and 3) and confirmed by COSY, HETCOR, and HMBC data, compounds 1 and 2 were assigned as the benzoquinones 2-methoxy-6-heptyl-1,4-benzoquinone and 2-methoxy-6-pentyl-1,4-benzoquinone (primin), respec- tively. These assignments were confirmed by comparison with literature data. 3 Quinone 1 has previously been synthesized as part of a structure-activity relationship study of primin-type ben- zoquinones as cell-mediated allergens causing contact dermatitis 3 and has been identified as a minor component of Primula obconica, 4 but it has not previously been isolated as a homogeneous compound. Previous phytochemical studies of various Miconia spp. have resulted in the isolation of primin (2), 5 its quinol analogue miconidin, 5,6 and several triterpenes. 7 Insect antifeedant, 5 antimicro- bial, 6,8 and antineoplastic 6,8 activities of primin and mi- conidin have also been evaluated. The bioactivity profiles for 1 and 2 in our yeast-based bioassays are depicted in Table 1. Both compounds exhib- ited moderate activity. However, it was interesting to note that quinone 1, having two additional carbon atoms in the side-chain, was significantly more active than its lower homologue, primin (2), in the Sc-7 yeast strain. Because of this apparent relationship between the length of the alkyl side chain and activity in the Sc-7 yeast assay, we prepared a number of additional 2-methoxy-6-alkyl-1,4-benzoquino- nes to determine whether the relationship was a general one. The previously reported quinones 1-7 were synthe- * To whom inquiries should be addressed. Tel.: (540) 231-6570. Fax: (540) 231-7702. E-mail: dkingston@vt.edu. † Virginia Polytechnic Institute and State University. ‡ Present address: Bioresources Research Facility, Office of Arid Lands Studies, University of Arizona, 250 E. Valencia Rd., Tucson, AZ 85706- 6800. § Missouri Botanical Garden. ⊥ Bedrijf Geneesmiddelen Voorziening Suriname. | Bristol-Myers Squibb Pharmaceutical Research Institute. 2 J. Nat. Prod. 2001, 64, 2-5 10.1021/np000219r CCC: $20.00 © 2001 American Chemical Society and American Society of Pharmacognosy Published on Web 11/23/2000