Progress toward the Total Synthesis of Callipeltin A (I):  Asymmetric Synthesis of (3S,4R)-3,4-Dimethylglutamine

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 key feature of this approach is the generation of three adjacent stereogenic centers using the same camphorsultam chiral auxiliary.