Biocatalytic Construction of Spiro-Oxazolidinones via Halohydrin Dehalogenase-Catalyzed Ring Expansion of Spiro-Epoxides

Spiro-oxazolidinones are highly valuable compounds in the fields of medicinal and organic chemistry; however, the methods for synthesizing these compounds have not been well established. Herein, we present a biocatalytic methodology for the construction of spiro-oxazolidinones through the halohydrin dehalogenase-catalyzed ring expansion of spiro-epoxides. By performing screening and protein engineering of halohydrin dehalogenases, both chiral and racemic spiro-oxazolidinones were synthesized in 24-47% yields (90-98% ee) and 69-98% yields, respectively. The biocatalytic method was also applied to the efficient synthesis of the drug fenspiride at a high substrate concentration of 200 mM (44 g/L). In addition, a chemo-enzymatic strategy was proposed to overcome the limitation of the maximum 50% yield inherent in the kinetic resolution process. Moreover, large-scale synthesis and representative transformations of the spiro-oxazolidinones were carried out to provide additional evidence of the practicality and applicability of the biocatalytic approach.