Microbial transformation of diosgenin (1) using Absidia coerulea yielded five new polar metabolites, which were identified as (25R)-spirost-5-en-3β,7β,12β,25α-tetrol (2), (25S)-spirost-5-en-3β,7α,12β,25β-tetrol (3), (25S)-spirost-5-en-3β,7β,12β,25β-tetrol (4), (25R)-spirost-5-en-3β,7α,12β,25α-tetrol (5), and (25R)-spirost-5-en-3β,7β,12β,24β-tetrol (6). Their structures were established on the basis of mass spectrometry and multi-dimensional NMR spectroscopy. The characteristic transformations observed were C-7α, C-7β, C-12β, C-24β, C-25α, and C-25β hydroxylation. The cytotoxicity of compounds 1–6 was evaluated against the human myelogenous leukemia K562 cell line and squamous cell carcinoma KB parental cell lines. Compounds 2–6 exhibited weak cytotoxicity against K562 and KB cells and were less potent than the parent compound 1.
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