Efficient one-step synthesis of diastereoisomeric cyclic dipeptides from amino acids: three diastereoisomers of cyclo-L-isoleucyl-L-isoleucine

Cyclic dipeptides formed by the self-condensation of amino acids in ethane-1,2-diol comprise readily separable diastereoisomeric mixtures which, in the case of isoleucine, affords three isomers in good yield.