Di-An Sun

Biotransformation of Echinocystic acid (EA,1) using G. roseum CGMCC 3.3657 has been investigated, which leads to the isolation and identification of two novel Echinocystic acid derivatives, 4, 16α-dihydroxy-3,4-seco-olean-12-en-3,28-dioic acid (2) and 16α-hydroxy, A-homo-3α-oxa-olean-12-en-3-one-28-oic acid (3). Their structures have been elucidated by analysis of spectroscopic data. This biocatalysis could serve as an efficient tool complementary to classical chemical methods for the transformation of EA.

Three new (6, 9, and 12) and nine known steroidal saponins were obtained from the fermentation broth of pseudoprotodioscin (PPD) incubated with a fungus Gibberella fujikuroi CGMCC 3.4663. Structures of the metabolites were elucidated by 1-D (¹H, ¹³C), 2-D (HMBC, HSQC, NOESY) NMR, and HR-MS analyses. The biotransformation pathway of pseudoprotodioscin by Gibberella fujikuroi CGMCC 3.4663 was proposed. Compounds 1–11 were tested in vitro for their cytotoxic activities against two human cancer cell lines (HepG2 and Hela). Compounds 1, 6, 9, and 10 exhibited cytotoxic activity against HepG2 cells. Compound 10 exhibited cytotoxicity to Hela cells.

Biocatalysis of ursolic acid (UA 1) by Gliocladium roseum CGMCC 3.3657 was investigated. Baeyer–Villiger oxidation was found to occur during the reaction. Four metabolites were isolated from the cultures and their structures were identified as 21-oxo,A-homo-3a-oxa-urs-12-en-3-one-28-oic acid (2), 21-oxo-3,4-seco-ursan-4(23),12-dien-3,28-dioic acid (3), 21β-hydroxyl-A-homo-3a-oxa-urs-12-en-3-one-28-oic acid (4) and 21β-hydroxyl-3,4-seco-ursan-4(23),12-dien-3,28-dioic acid (5), based on their NMR and MS spectral data. All of the four metabolites were new and their anti-HCV activity was tested. Their biotransformation pathway was also proposed.

Microbial transformation of diosgenin (1) by suspended-cell cultures of the filamentous fungus Cunninghamella echinulata CGMCC 3.2000 was investigated. Incubation of the substrate diosgenin (1) with this fungus led to the isolation of three products: two known compounds, (25R)-spirost-5-en-3β,7β,12β-triol (2) and (25R)-spirost-5-en-3β,7β,11α-triol (3), and a new compound (25R)-spirost-5-en-3β,7α,11α-triol (4). The structural elucidations of the three compounds were achieved mainly by the MS, 1D and 2D NMR spectroscopic methods and comparison with known compounds. C. echinulata CGMCC 3.2000 has not been used before in the biotransformation of diosgenin (1).

Endophytic fungi were used not only for their producing bioactive products but also for their ability to transform natural compounds. An endophytic fungus, isolated from medicinal plant Huperzia serrata, was identified as Umbelopsis isabellina based on the internal transcribed spacer of ribosomal DNA (rDNA-ITS) region. It was used to transform ursolic acid (1), a pentacyclic triterpene. Incubation of ursolic acid with U. isabellina afforded three products, 3β-hydroxy-urs-11-en-28,13-lactone (2), 3β,7β-dihydroxy-urs-11-en-28,13-lactone (3), 1β,3β-dihydroxy-urs-11-en-28,13-lactone (4). Although product 2 was a known compound, it was first obtained by microbial transformation. Products 3 and 4 were new compounds. The structural elucidation of the three compounds was achieved mainly by the 1D- and 2D-NMR, MS, IR data. The endophytic fungus U. isabellina can hydroxyate the C12–C13 double bond at position 13 of ursolic acid 1 and form a five-member lactone effectively. In the meantime, this fungus can also introduce the hydroxyl group at C-1 or C-7 of ursolic acid 1.