Discovery and efficient synthesis of a biologically active alkaloid inspired by thiostrepton biosynthesis

Thiostrepton, a natural peptide macrocycle, is of great interest due to its structural complexity and numerous biological activities, including anti-bacterial, anti-tumor, and anti-plasmodial activities. The quinaldic acid (QA) moiety-containing side ring (loop 2) was proven to play an important role in carrying out these functions. Previously, we proposed biosynthetic logic for thiostrepton loop 2 and demonstrated the formation mechanism of QA. Herein, we report the discovery and efficient synthesis of a biologically active alkaloid, that is, a key intermediate involved in the thiostrepton biosynthetic pathway. A chemo-enzymatic method was performed to synthesize the molecule, and a series of analogs were prepared for bioassays, which included the examination of anti-bacterial and anti-tumor activities.