Chemo-Enzymatic Strategy for the Efficient Synthesis of Steroidal Drugs with 10α-Methyl Group and a Side Chain at C17-Position from Biorenewable Phytosterols

Steroidal pharmaceuticals with a 10α-methyl group or without the methyl group at C10-position are important medicines, but their synthesis is quite challenging, due to that the natural steroidal starting materials usually have a 10β-methyl group which is difficult to be inverted to 10α-methyl group. In this study, 3-((1R,3aS,4S,7aR)-1-((S)-1-hydroxypropan-2-yl)-7a-methyl-5-oxooctahydro-1H-inden-4-yl) propanoic acid (HIP-IPA, 2e) was demonstrated as a valuable intermediate for the synthesis of this kind of active pharmaceutical ingredients (APIs) with a side chain at C17-position. Knockout of a β-hydroxyacyl-CoA dehydrogenase gene and introduction of a sterol aldolase gene into the genetically modified strains of Mycobacterium fortuitum (ATCC 6841) resulted in strains N13Δhsd4AΩthl and N33Δhsd4AΩthl, respectively. Both strains transformed phytosterols into 2e. Compound 2e was produced in 62% isolated yield (25 g) using strain N13Δhsd4AΩthl, and further converted to (3S,3aS,9aS,9bS)-3-acetyl-3a,6-dimethyl-1,2,3,3a,4,5,8,9,9a,9b-decahydro-7H-cyclopenta[a]naphthalen-7-one, which is the key intermediate for the synthesis of dydrogesterone. This study not only overcomes a challenging synthetic problem by enabling an efficient synthesis of dydrogesterone-like steroidal APIs from phytosterols, the well-recognized cheap and readily available biobased raw materials, but also provides insights for redesigning the metabolic pathway of phytosterols to produce other new compounds of relevance to the steroidal pharmaceutical industry.