Biocatalytic Synthesis of Corticosteroid Derivatives by Toad-Derived Steroid C21-Hydroxylase

CsCYP21A, a steroid 21-hydroxylase from Bufo bufo gargarizans, exhibits unprecedented sequential oxidations. Optimizing Pichia pastoris biotransformation conditions enhanced C21-hydroxylation selectivity, converting 14 substrates to 21-hydroxylated products, with 10 conversions of >80% and 4 yields of >80%. Hydrocortisone production reached 1.5 g L^–1 day^–1 with 100 g/L wet biomass. CsCYP21A’s versatility enables integration into the synthesis of over 10 steroidal drugs, offering a sustainable biocatalytic platform for green pharmaceutical manufacturing.