Bioconversion of methyl protodioscin by Penicillium melinii cells

Bioconversion of methyl protodioscin (1) by Penicillium melinii was investigated. Seven bioconversion products were isolated and identified. Three of them were glycosidation products and were new compounds. Their structures were identified to be 3-O-[α-l-rhamnopyranosyl-(1 → 2)-{α-l-rhamnopyranosyl-(1 → 4)}-β-d-glucopyranosyl]-26-O-[β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl]-25(R)-furost-5,20(22)-diene-3β,26-triol (2), 3-O-[α-l-rhamnopyranosyl-(1 → 2)-{α-l-rhamnopyranosyl-(1 → 4)}-β-d-glucopyranosyl]-26-O-[β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl]-25(R)-furost-5-ene-3β,26-triol (3), 16β-[4′-methyl-5′-O-(β-d-glucopyranosyl-(1 → 6)-β-d-glucopyranosyl)-pentanoxyl]-pregn-5-en-3β-ol-20-one-O-α-l-rhamnopyranosyl-(1 → 2)-[α-l-rhamnopyranosyl-(1 → 4)]-β-d-glucopyranoside (4), respectively. To the best knowledge we known, this was the first time to find the type of furostanol saponins that had disugar at C-26. The proposed biosynthetic pathways of methyl protodioscin were drawn. Most bioconversion products showed considerable cytotoxic activities against HepG2, NCI-H460, MCF-7 and HeLa cell lines compared to methyl protodioscin.