The Recombinant 3-Ketosteroid Δ ¹ -Dehydrogenase Catalyzed Δ ¹ -Dehydrogenation toward Total Synthesis of Vamorolone by Combining with Flow in Situ Silicon Nucleophile Annelation Process/Desilylation

The recombinant 3-ketosteroid Δ1-dehydrogenase from Rhodococcus erythropolis PR4 (KstD-Re1) catalyzed the Δ1-dehydrogenation of ester (1a) to access vamorolone-21-ester (2a). After modification of the structure and examination of the reaction carefully, the recombinase (KstD-Re1) with position 194 changing from Val to Gly and 318 changing from Tyr to tryptophan (Trp, W) was screened as the best catalyst. Other steroids like androstenedione, progesterone, testosterone, hydroxyprogesterone, and hydrocortisone acetate were also tolerated well in this Δ1-dehydrogenation. The molecular docking of 1a with KstD-Re1 was also disclosed. We found that the dual base (NaOH/K2CO3)-mediated hydrolysis of 2a formed vamorolone in 94.0% yield and 99.6% purity, meeting the International Conference Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) quality standards. Staring from the readily available and inexpensive 16α-methyl-4,9-androstadiene-3,17-dione (3), ester 1a could be generated in 80.5% total yield through cyanidation/silyl etherification, in situ silicon nucleophile annelation process (SNAP)/desilylation, and substitution. Notably, a continuous-flow in situ SNAP/desilylation in a microchannel reactor was developed to produce chloride (5) in 91.7% yield, which not only improved the yield dramatically but also avoided the harsh reaction conditions and side reactions such as desilylation, C–Cl bond cleavage and flipping of 16-CH3. Compared to previously reported synthetic routes to vamorolone, our approach offers advantages like low cost, higher yield, mild reaction conditions, excellent product quality, and gram-scale synthesis.