An efficient route to the α-methyl ester of L -glutamic acid, and its conversion into cis-5-hydroxy- L -pipecolic acid

The treatment of the N-benzyloxycarbonyl α-methyl esters of L-glutamine or L-asparagine with tert-butyl nitrite in refluxing acetonitrile results in selective hydrolysis of the amide group, giving optically pure Z-Glu-OMe (74%) or Z-Asp-OMe (88%); these are versatile chiral building blocks, and an efficient synthesis of cis-5-hydroxy-L-pipecolic acid from Z-Glu-OMe is described.