Microbial Transformation of Spirolaxine, a Bioactive Undecaketide Fungal Metabolite from the Basidiomycete Sporotrichum laxum by Gianluca Nasini* a ), Adriana Bava a ), Giovanni Fronza a ), and Giuseppe Giannini b ) a )CNR-ICRM, Department of Chemistry, Materials and Chemical Engineering, Politecnico di Milano, via Mancinelli, 7, I-20123, Milano (phone: þ 39-2-23993046; fax: þ 39-2-23993080; e-mail: gianluca.nasini@polimi.it) b ) Sigma-TauS.P.A., Research and Development, via Pontina km 30,400, I-00040 Pomezia Incubation of (þ)-spirolaxine ( ¼ (3R)-5-hydroxy-7-methoxy-3-{5-[(2R,5R,7R)-2-methyl-1,6-dioxa- spiro[4.5]dec-7-yl]pentyl}-2-benzofuran-1(3H)-one; 1a) with Bacillus megaterium afforded two new mono- and one new dihydroxylated metabolite(s), all OH groups being introduced on the non-activated six-membered ring. In contrast, exposure of 1a to Cunninghamella echinulata gave rise to hydroxylation on the five-membered ring of the parent structure. The structures and absolute configurations of the new products 1b – e were deduced on the basis of MS and NMR data. The metabolite 1b was investigated, in comparison to 1a, for its cytotoxicity (sulforhodamin-B test) and for its antiproliferative activity towards bovine microvascular endothelial cells (BMEC). 1. Introduction. –(þ)-Spirolaxine (1a)and(þ)-sporotricale (2a) represent the major metabolites extracted from cultures of the white-rot fungus Sporotrichum laxum 1 ) (Basidiomycetae) [1]. These metabolites are structurally similar, both containing a 5- hydroxy-3-methoxyphthalide moiety linked through an oligomethylene chain to a spiro- acetal (as in 1a) or a hemi-acetal (as in 2a, which may also be present in the open form 2b).Spirolaxine(1a)hasbeenreportedtopossesscholesterol-loweringactivity[2].More recently, we reported its activity towards some endothelial cells and a variety of tumor cell lines (e.g. , LoVo and HL60 cells) [3]. The current interest in these types of compounds prompted us to determine the absolute configuration at all four stereogenic centers, which were all found to be ( R), on the basis of X-ray crystallographic and circular-dichroism (CD) experiments [4]. We also established the absolute configuration of sporotricale (2a)as(7R,13’R) [5]. Very recently, some synthetic approaches to the 5- O-methyl ethers of both (þ)-1a [6][7] and of 2a [8] were described. Spirolaxine (1a) belongs to a small group of fungal metabolites, produced by Phanerochaete species, that have received some attention for their inhibitory activity against the micro-aerophilic Gram-negative bacterium Helicobacter pylori [9], against which 1a exhibited the best activity. The present investigation was carried out to study the ability of some micro- organisms to accomplish structural modifications of the spirolaxine ring and to study the biological activity of the modified compounds with respect to the parent compound. CHEMISTRY & BIODIVERSITY – Vol. 4 (2007) 2772 # 2007 Verlag Helvetica Chimica Acta AG, Zürich 1 ) Now christened Phanerochaete chrysosporium.