Molecular structure and pseudopolymorphism of squamtin A from Annona squamosa

The cyclopeptide, squamtin A (1, formula: C₃₉H₆₀O₁₁N₈S), was found to crystallized in two pseudopolymorphisms, i.e. 1·(H₂O)_3.5 and 1·(H₂O)_3.9. The composition of the amino acids and their linkage sequences are the same. The main differences between the two kinds of crystals lie in the positions and occupancies of the water molecules, the positions of the sulfur atoms and the conformation of the side chains. The absolute configuration of 1 is established by X-ray analysis in combination with the Marfey's analysis of its hydrolysates.     

Photo-induced synthesis and in vitro biological activity of a Sansalvamide A analog

Photoinduced single electron transfer (SET) cyclization processes for synthesis of a Sansalvamide A analog containing double pharmacophores (cyclicpeptides and O-phthalimide moiety) is described to develop novel antitumor cyclopeptide drug. The resultant compound is active in drug-sensitive HeLa, HepG-2 and MCF-7 cell lines. Specifically, the title compound was found to inhibit MCF-7 cells with an IC₅₀ value of 15 μM (13.4 μg/mL), which may serve as a potential candidate for antitumor drug development.     

Late‐Stage Peptide Diversification through Cobalt‐Catalyzed C−H Activation: Sequential Multicatalysis for Stapled Peptides

Bioorthogonal late‐stage diversification of structurally complex peptides has enormous potential for drug discovery and molecular imaging. In recent years, transition‐metal‐catalyzed C?H activation has emerged as an increasingly viable tool for peptide modification. Despite major accomplishments, these strategies largely rely on expensive palladium catalysts. We herein report an unprecedented cobalt(III)‐catalyzed peptide C?H activation, which enables the direct C?H functionalization of structurally complex peptides, and sets the stage for a multicatalytic C?H activation/alkene metathesis/hydrogenation strategy for the assembly of novel cyclic peptides.     

On-resin cyclization and antimicrobial activity of Laterocidin and its analogues

Total synthesis of cyclodecapeptide antibiotics from Bacillus laterosporus, laterocidin and its analogues, was accomplished for the first time by solid-phase peptide synthesis followed by traceless on-resin cyclization of the linear precursors with protection of α-carboxyl group on the Asp residue by Dmab as a temporary blocking group for on-resin head-to-tail cyclization, in which the carboxyl group of side chain of Asp was linked to Rink resin. Single alanine substitution or Asn substitution (Asp¹⁰→Asn¹⁰) demonstrated improvements in antibacterial activity. Of note, d-Phe² and Pro⁴ play an important role in on-resin head-to-tail cyclization and exerting antibacterial activity of Laterocidin.