Biotransformation of 22-hydroxy-23,24-bisnorchol-4-ene-3-one by Gibberella fujikuroi CICC 40272-A to discover novel C22 steroid derivatives

Abstract

The microbial transformation of steroids offers a sustainable and selective approach to synthesize pharmacologically valuable derivatives. This study investigated the biotransformation of 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) by Gibberella fujikuroi CICC 40272-A to produce novel C22 steroid derivatives. Among seven screened fungal strains, G. fujikuroi exhibited superior regio- and stereo-selective hydroxylation activity. High performance liquid chromatography (HPLC) and thin layer chromatography (TLC) analyses revealed the formation of a major metabolite, identified as 7β,11α-dihydroxy-23,24-bisnorchol-4-ene-3-one (7β,11α-diOH-HBC) via NMR and MS, confirming the introduction of two hydroxyl groups at positions 7β and 11α. Optimization of fermentation conditions through single-factor and orthogonal experiments demonstrated that a medium containing 50 g/L galactose, 10 g/L NaNO₃, and pH 5.5, combined with 3 % inoculum, 1 g/L 4-HBC, and 96 h transformation time, achieved a maximum transformation rate of 65.88 %. Methanol (2 % v/v) was identified as the optimal cosolvent, enhancing substrate solubility while minimizing cytotoxicity. The study highlights G. fujikuroi CICC 40272-A as an effective biocatalyst for stereoselective steroid hydroxylation, providing an efficient and eco-friendly strategy to produce 7β,11α-diOH-HBC. These findings advance the application of microbial systems in pharmaceutical synthesis, emphasizing their potential to replace energy-intensive chemical processes in steroid derivative production.

Keywords: 4-HBC; 7β,11α-diOH-HBC; Biocatalyst; Gibberella fujikuroi; Microbial transformation; Steroid hydroxylation.