Total synthesis of siomycin A: completion of the total synthesis

The total synthesis of siomycin A (1), a representative compound of the thiostrepton family of peptide antibiotics, was achieved by incorporating the five synthetic segments A (2), B (3), C (4), D (5), and E (6). The dehydropiperidine segment A (2) was esterified with the dihydroquinoline segment C (4), and the subsequent coupling with the beta-phenylselenoalanine dipeptide segment D (5) at the segment C portion followed by lactamization between the segments A and D gave segment A-C-D (27). This was amidated with the pentapeptide segment B (3) at the segment A portion followed by one-pot cyclization (between segments A and B) and elongation (with the beta-phenylselenoalanine dipeptide segment E (6) at the segment A portion), thus furnishing siomycin A (1).