Exploring the substrate stereoselectivity and catalytic mechanism of nonribosomal peptide macrocyclization in surugamides biosynthesis.

SurE, the first reported penicillin-binding protein-like thioesterase (PBP-like TE), is known as a new off-loading cyclase, which catalyzes heterochiral coupling in nonribosomal peptides (NRPs). However, the structural rationale for substrate stereoselectivity and enzymatic mechanism remains mysterious. Here, computational models, integrating MD simulations and QM/MM methods, unveiled SurE's substrate recognition and catalytic process. An oxyanion hole stabilized the C-terminal D-residue during recognition. Residue R446 anchored the substrate for macrocyclization. A vital hydrogen-bonding network (Y154, K66, N156), verified by mutation results, was responsible for the recognition of N-terminal L-residue and involvement in catalytic process with a calculated 19.4 kcal/mol energy barrier. Four novel-designed peptide precursors were effectively cyclized into cyclopeptides by SurE based on computational analysis. Our results provide a comprehensive understanding of SurE's catalytic mechanism and guiding design of versatile PBP-like TEs for novel macrocyclic NRPs.

The Linkage of Sulfonimidoyl Fluorides and Unactivated Alkenes via Hydrosulfonimidoylation.

Sulfur(VI) fluoride cleavage and exchanging linkage, a new generation of linkage chemistry, exhibits enormous potential for combining a range of functional molecules in an increasing number of fields. Herein, we established a metal-free linkage of unactivated alkenes and sulfonimidoyl fluorides via hydrosulfonimidoylation to construct sulfoximines within minutes. An intermolecular hydride transfer process is the key step, and it occurs via overlap of the LUMO in the sulfonimidoyl cation and HOMO in the unactivated alkene, which was confirmed via control experiments with deuterated compounds. DFT calculations further demonstrated the concerted process involving formation of the S-C(sp3 ) bond and hydride transfer. Remarkably, abundant natural products and pharmaceuticals with multiple heteroatoms and sensitive functional groups have been subjected to the current linkage reaction to achieve various sulfoximine linkages, furnishing the basis for drug discovery and drug conjugation.

Total Synthesis of (-)-Calycanthine via Iron-Catalyzed Stereoselective Oxidative Dimerization.

Dimeric cyclotryptamine alkaloids typically feature vicinal all-carbon quaternary stereocenters and four nitrogen atoms. In comparison with the actual biosynthetic tryptophan derivatives, we designed the 2N-featured monomer 7, aiming to construct vicinal all-carbon quaternary stereocenters via a one-step dimerization process to access the 4N-featured isomeric members of this family. In this work, we disclose the first synthetic route to access the skeleton of (-)-isocalycanthine, featuring an iron-catalyzed oxidative dimerization reaction in a catalytic single-step operation with an overwhelming control of the absolute and relative stereochemistry. This strategy has been successfully applied to the total synthesis of (-)-calycanthine and 16 isocalycanthine derivatives, which demonstrates a new synthetic pathway for dimeric cyclotryptamine alkaloids.