Synthesis and Complement Inhibitory Activity of B/C/D-Ring Analogues of the Fungal Metabolite 6,7-Diformyl-3′,4′,4a′,5′,6′,7′,8′,8a′-octahydro-4,6′,7′-trihydroxy- 2′,5′,5′,8a′-tetramethylspiro[1′(2′H)-naphthalene-2(3H)-benzofuran] Barton J. Bradbury, †,§ Piotr Bartyzel, †,| Teodoro S. Kaufman, †,‡ Marcelo J. Nieto, † Robert D. Sindelar,* ,†,# Susanne M. Scesney, ⊥ Bruce R. Gaumond, ⊥ and Henry C. Marsh, Jr. ⊥ Department of Medicinal Chemistry and Laboratory of Applied Drug Design and Synthesis, School of Pharmacy, The University of Mississippi, University, Mississippi 38677, Research Institute of Pharmaceutical Sciences, School of Pharmacy, The University of Mississippi, University, Mississippi 38677, and Avant Immunotherapeutics, Inc., 119 Fourth Avenue, Needham, Massachusetts 02494-2725 Received September 26, 2002 This paper reports the synthesis and the bioassay of 4-methoxy- and 4-hydroxyspiro[benzofuran- 2(3H)-cyclohexane] partial analogues (5) of the complement inhibitory sesquiterpene fungal metabolite 6,7-diformyl-3′,4′,4a′,5′,6′,7′,8′,8a′-octahydro-4,6′,7′-trihydroxy-2′,5′,5′,8a′-tetra- methylspiro[1′(2′H)-naphthalene-2(3H)-benzofuran] (1a, K-76) and its silver oxide oxidized product (1b, K-76COOH). The described target compounds represent spirobenzofuran B/C/D- ring analogues lacking the A-ring component of the prototype structure. The target compounds were evaluated by the inhibition of total hemolytic complement activity in human serum. It was observed that the structurally simplified analogue 4-methoxyspiro[benzofuran-2(3H)- cyclohexane]-6-carboxylic acid (5a) exhibited an IC 50 ) 0.53 mM similar to the IC 50 ) 0.57 mM that was observed for the natural product derivative 1b. Exhibiting an IC 50 ) 0.16 mM, the three-ringed partial structure 6-carboxy-7-formyl-4-methoxyspiro[benzofuran-2(3H)-cyclo- hexane] (5k)was found to be the most potent target compound. Like the natural product, 5k appears to inhibit primarily at the C5 activation step and inhibits both the classical and alternative human complement pathways. Several other analogues inhibited complement activation in vitro at concentrations similar to those required for inhibition by the natural product 1b. Introduction Interest in the development of modulators of the complement cascade has recently increased because of a growing understanding of the role of complement in various disease processes. 1-5 This has led to attempts to identify structurally diverse complement inhibitory natural products and synthetic agents. 7 A microbial metabolite of the fungal species Stachybotrys comple- menti nov. sp. K-76, 6,7-diformyl-3′,4′,4a′,5′,6′,7′,8′,8a′- octahydro-4,6′,7′-trihydroxy-2′,5′,5′,8a′-tetramethylspiro- [1′(2′H)-naphthalene-2(3H)-benzofuran] (1a), and its oxidized derivative 1b have been shown to inhibit complement 6,7 and were examined in a wide variety of in vivo studies. 8-15 Their structure determination 15 and three total syntheses have been reported. 17-19 The reported experimental data demonstrating the complement inhibitory activity of 1b, its use in a number of animal disease models, and its unique chemical structure make it an interesting drug proto- type for further exploration. 7-9,12,14-20 In an attempt to elucidate the essential pharmacophore of compounds 1a and 1b, the natural product was used as a topographical model for the design of partial analogues retaining the desired complement inhibitory activity. Structurally, 1a * To whom correspondence should be addressed. Present address: Faculty of Pharmaceutical Sciences, The University of British Colum- bia, 2146 East Mall, Vancouver, BC V6T 1Z3, Canada. E-mail: sindelar@interchange.ubc.ca. Phone: 604-822-2343. Fax: 604-822- 3035. † Department of Medicinal Chemistry and Laboratory of Applied Drug Design and Synthesis, The University of Mississippi. § Present address: Achillion Pharmaceuticals, Inc., 300 George Street, New Haven, CT 06511. | Present address: NaPro BioTherapeutics, Inc., 6304 Spine Road, Unit A, Boulder, CO 80301. ‡ Present address: Instituto de Quimica Organica de Sintesis- IQUIOS, Casilla de Correo 991, (2000) Rosario, Argentina # Research Institute of Pharmaceutical Sciences, The University of Mississippi. ⊥ Avant Immunotherapeutics, Inc. 2697 J. Med. Chem. 2003, 46, 2697-2705 10.1021/jm0204284 CCC: $25.00 © 2003 American Chemical Society Published on Web 05/24/2003