Figure 2

Synthesis routes and structures for compounds 5, 9a-9u and 12a-12b. (A) Synthesis of compound 5 by Ugi-azide 4-CR. (B) Analogs synthesized for the structure-activity relationship studies. (C) Synthesis of diastereomers by the chiral isocyanide strategy. (D) X-ray crystal structure of the diastereomer 12b.