How is (2S)-2-Hydroxybutanoic acid (CAS: 3347-90-8) typically synthesized?

(2S)-2-Hydroxybutanoic acid can be synthesized through the chemical reduction of 2-keto-2-hydroxybutyric acid. Common synthetic routes involve the use of sodium borohydride as a reducing agent. This method yields high selectivity towards the (2S) enantiomer. Other approaches include the stereoselective epoxidation followed by reduction of an appropriate precursor. The final product's purity and enantiomeric excess can be enhanced through subsequent purification steps.