Progress toward the total synthesis of callipeltin A (I): Asymmetric synthesis of (3S,4R)-3,4-dimethylglutamine

[GRAPHICS] During the total synthesis of the novel cyclic depsipeptide callipeltin A ( 1), the unit (3S,4R)-3,4-dimethylglutamine, was successfully synthesized by asymmetric Michael addition and subsequent electrophilic azidation. The ke y feature of this approach is the generation of three adjacent stereogenic centers using the same camphorsultam chiral auxiliary.