How is (4R)-4-Cyano-L-proline (CAS: 273221-93-5) typically synthesized?

(4R)-4-Cyano-L-proline can be synthesized using a multi-step process. One common method involves the reaction of L-proline with cyanogen chloride in the presence of a base such as sodium hydroxide. The reaction is typically carried out in a solvent like methanol or ethanol, with high selectivity and yield. The product is then purified through techniques such as recrystallization or chromatography.