Several cyclic dipeptides were synthesized by refluxing methanolic solution of dipeptide methyl esters in high yield and purity. Cyclic dipeptides prepared by the Fischer method, the Nitecki method, and the present methanol-reflux method were compared with respect to yield and optical purity. The methanol-reflux method usually gave good results. High- performance liquid chromatography was effectively applied to detect racemization.
