Chem. Pharm. Bull. 55(1) 118—123 (2007)

perform regioand stereo-selective reactions on organic compounds. The different possible microbial reactions include oxidation, reduction, and degradative reactions. Many of these reactions allow the production of new compounds that would be extremely difficult to synthesize chemically. For instance hydroxylation at inactivated methylene is a very common microbial reaction. The results obtained from microbial transformations are quite often similar to those obtained from mammal biotransformations. The parallel relationship between mammals and microbial transformations is due to the fact that many fungi, such as the filamentous fungus Cunninghamella, utilize the enzyme cytochrome P-450 monoxygenase in the metabolism of xenobiotics. This enzyme system is analogous to the enzyme system used by mammals, allowing microbial transformations to be used successfully as in vitro models for mammalian drug metabolism. A lead bioactive compounds can also be generated through microbial transformations of natural products. The metabolic products often have improved bioactivity with minimal toxicity compared to the parent natural product. In our continuing effort to discover new bioactive natural products, we decided to do biotransformation studies of sclareolide (1) using whole cell cultures of different fungi. Sclareolide (1) is a minor constituent of the vascular plant Arnica angustifolia and is commercially available. Compound 1 has shown modest cytotoxcity against breast (MCF7), colon (CKCO-1), lung (H-1299) and skin (HT-144) human cancer cell lines. For this project, we screened five different fungi, namely Mucor plumbeus (ATCC 4740), Cunninghamella blakesleeana (ATCC 9245), Cunninghamella echinulata (ATCC 9244), Curvularia lunata (ATCC 12017) and Aspergillus niger (ATCC 1004), for their capability to metabolize compound 1. During these biotransformation experiments, we discovered that Cunninghamella blakesleeana (ATCC 9245) metabolized compound 1 into O-sclareolide (2), 3b ,6a-dihydroxysclareolide (3) and 9-hydroxysclareolide (4), along with three known metabolites, 1b ,3b-dihydroxysclareolide (5), 3-oxosclareolide (6) and 3b-hydroxysclareolide (7). Biotransformation experiments of compound 1 with Cunninghamella echinulata (ATCC 9244) also yielded two new compounds, 5-hydroxysclareolide (8), and 7b-hydroxysclareolide (9) along with two known compounds 5 and 7. NMR spectroscopic methods were used to establish the structures of compounds 2—9. Compounds 2—9 were found to exhibit modest acetylcholinesterase inhibitory activity. To the best of our knowledge, biotransformation of 1 into 2 is a novel ether-forming microbial reaction. In this paper we report the biotransformations of 1 and structure elucidation of compounds 2—9 as well as their bioactivity data.