Monacolin K, a new hypocholesterolemic agent produced by a Monascus species.

Sir: In previous papers from our laboratory, ML236B, a metabolite of Penicillium citrinum that was isolated as an inhibitor of cholesterol synthesis1), was shown to have hypocholesterolemic activity in several animal species2,3). Further work in this laboratory to search for microbial metabolites having cholesterol-lowering activity led to the isolation of a new active compound (designated as monacolin K) produced by a Monascus species. The present paper describes isolation, physical and chemical properties and hypocholesterolemic effects of monacolin K. The strain of Monascus employed in the production of monacolin K, which was isolated from a food sample collected in Thailand, was classified as Monascus ruber and designated as Monascus ruber No. 1005. M. ruber No. 1005 was grown aerobically at 28°C in a medium containing 6% glucose, 2.5 % peptone, 0.5 % corn steep liquor (Corn Products Co., U.S.A.) and 0.5% ammonium chloride for 10 days. From the culture filtrate (5 liters), monacolin K was extracted with 5 liters of ethyl acetate at pH 3 and the extract was concentrated in vacuo to dryness. The resultant pellet was dissolved in 100 ml of benzene and the insoluble materials were removed by filtration. The filtrate was washed twice with 100 ml of 5 % NaCO3 and then mixed with 100 ml of 0.2 N NaOH with stirring at room temperature for 2 hours. The aqueous layers were pooled, adjusted to pH 3 with 6 N HCl and extracted twice with 100 ml of ethyl acetate. The solvent layer was collected and evaporated to dryness, giving 260 mg of an oily substance. This material was dissolved in a small volume of benzene, from which monacolin K was obtained as crystals. The compound was recrystallized from aqueous acetone, giving 87 mg of monacolin K as colorless crystals. Monacolin K melted at 157 159°C (dec.) and had a [a]2; value of +307.6° (c 1, methanol). The molecular formula, C24H3605 (Mw 404), was obtained by elemental analysis (Calcd.: C 71.31, H 8.91, O 19.78 %; Found C 71.56, H 8.85, 0 19.59%) and high resolution mass spectroscopy. The UV spectrum (methanol) showed maxima at 229, 237 and 246 nm (E,,., 550, 650 and 430, respectively) (Fig. 1). The IR spectrum (KBr) showed absorption bands at 3550, 2970, 1696 and 1220 cm -1 (Fig. 2). The 13C-NMR spectrum (CD3OD) indicated the presence of 2 ester carbonyl carbons (8 173.29 and 178.16), 4 methyl carbons (8 12.18, 14.13, 16.62 and 23.39) and methylene and methine carbons (Fig. 3). In addition to peaks at (m/e) 404 (M+), 302 (M102), 284 (M-120) and 224 (M-180), prominent peaks in the mass spectrum of monacolin K were observed at 198 (M-206), 172 (M-232), 159