Copper‐Mediated Selenazolidine Deprotection Enables One‐Pot Chemical Synthesis of Challenging Proteins

While chemical protein synthesis has granted access to challenging proteins, the synthesis of longer proteins is often limited by low abundance or non‐strategic placement of cysteine residues, which are essential for native chemical ligations, as well as multiple purification and isolation steps. We describe the one‐pot total synthesis of human thiosulfate:glutathione sulfurtransferase (TSTD1). WT‐TSTD1 was synthesized in a C‐to‐N synthetic approach involving multiple NCL reactions, Cu^II‐mediated deprotection of selenazolidine (Sez), and chemoselective deselenization. The seleno‐analog Se‐TSTD1, in which the active site Cys is replaced with selenocysteine, was also synthesized with a kinetically controlled ligation with an N‐to‐C synthetic approach. The catalytic activity of the two proteins indicated that Se‐TSTD1 possessed only four‐fold lower activity than WT‐TSTD1, thus suggesting that selenoproteins can have physiologically comparable sulfutransferase activity to their cysteine counterparts.     

An Efficient One‐Pot Four‐Segment Condensation Method for Protein Chemical Synthesis

Successive peptide ligation using a one‐pot method can improve the efficiency of protein chemical synthesis. Although one‐pot three‐segment ligation has enjoyed widespread application, a robust method for one‐pot four‐segment ligation had to date remained undeveloped. Herein we report a new one‐pot multisegment peptide ligation method that can be used to condense up to four segments with operational simplicity and high efficiency. Its practicality is demonstrated by the one‐pot four‐segment synthesis of a plant protein, crambin, and a human chemokine, hCCL21.     

One‐Pot Four‐Component Synthesis of Tetrasubstituted Pyrroles

A convenient one‐pot four‐component synthesis of tetrasubstituted pyrroles was carried out through the reaction of butane‐2,3‐dione with α‐aminophosphorous ylides, obtained in situ from the 1 : 1 : 1 addition reaction between triphenylphosphine, dialkyl acetylenedicarboxylate, and ammonium acetate.     

One‐Pot Synthesis of Pyrazoles through a Four‐Step Cascade Sequence

A one‐pot synthesis of 3,4,5‐ and 1,3,5‐pyrazoles from tertiary propargylic alcohols and para‐tolylsulfonohydrazide has been accomplished. The pyrazoles are formed through a four‐step cascade sequence, including FeCl₃‐catalyzed propargylic substitution, aza‐Meyer–Schuster rearrangement, base‐mediated 6π electrocyclization, and thermal [1,5] sigmatropic shift. In this reaction, the 3,4,5‐ and 1,3,5‐pyrazoles are produced selectively according to different substituents in the starting alcohols.     

One‐Pot Synthesis of Cyclopropane‐Fused Cyclic Amidines: An Oxidative Carbanion Cyclization

A novel and efficient one‐pot method has been developed for the synthesis of cyclopropane‐fused bicyclic amidines on the basis of a CuBr₂‐mediated oxidative cyclization of carbanions. The usefulness of this unique multicomponent strategy has been demonstrated by the use of a wide variety of substrates to furnish novel cyclopropane‐containing amidines with a quaternary center in very good yields. This ketenimine‐based approach provides straightforward access to biologically active and pharmaceutically important 3‐azabicyclo[n .1.0]alkane frameworks under mild conditions. The synthetic power of this methodology is exemplified in the concise synthesis of the pharmaceutically important antidepressant drug candidate GSK1360707 and key intermediates for the synthesis of amitifadine, bicifadine, and narlaprevir.     

One‐Pot/Sequential Native Chemical Ligation Using N‐Sulfanylethylanilide Peptide

N‐Sulfanylethylanilide (SEAlide) peptides were developed with the aim of achieving facile synthesis of peptide thioesters by 9‐fluorenylmethyloxycarbonyl (Fmoc)‐based solid‐phase peptide synthesis (Fmoc SPPS). Initially, SEAlide peptides were found to be converted to the corresponding peptide thioesters under acidic conditions. However, the SEAlide moiety was proved to function as a thioester in the presence of phosphate salts and to participate in native chemical ligation (NCL) with N‐terminal cysteinyl peptides, and this has served as a powerful protein synthesis methodology. The reactivity of a SEAlide peptide (anilide vs. thioester) can be easily tuned with or without the use of phosphate salts. This interesting property of SEAlide peptides allows sequential three‐fragment or unprecedented four‐fragment ligation for efficient one‐pot peptide/protein synthesis. Furthermore, dual‐kinetically controlled ligation, which enables three peptide fragments simultaneously present in the reaction to be ligated in the correct order, was first achieved using a SEAlide peptide. Beyond our initial expectations, SEAlide peptides have served in protein chemistry fields as very useful crypto‐peptide thioesters. DOI 10.1002/tcr.201200007