N-hydroxypyridine-2(1H)-thione derivatives of carboxylic acids as activated esters. Part II. Applications in peptide synthesis

Amide bond formation: beyond the myth of coupling reagents

“…Many example of active esters have therefore been reported and include -O-succinimides, 150 -OBt and derivatives, 24 p-nitrophenol, 151 -OPfP, 152 -ODhbt, 153 and PTOC. 154 As this review focuses directly on coupling reagents, this useful method of amide-bond formation will not be discussed herein, but the reader is referred to Montalbetti's review for further details. 13…”

Chemical Synthesis of Natural Product Peptides: Coupling Methods for the Incorporation of Noncoded Amino Acids into Peptides

“…Barton has recently reported on the use of PTOC esters and arylsulfenamides for forming hindered dipeptides such as Z-Aib-Gly-OEt (95%) and Z-Aib-Sar-OEt (92%, Chart ) .…”

“…132 Barton has recently reported on the use of PTOC esters and arylsulfenamides for forming hindered dipeptides such as Z-Aib-Gly-OEt (95%) and Z-Aib-Sar-OEt (92%, Chart 25). 136 Amide bond formation according to this method is thought to proceed according to the mechanism shown in Chart 25. The PTOC ester can be generated in situ and coupled, but higher yields require that the active ester be prepared and isolated beforehand.…”

Formation of Enol Ethers by Radical Decarboxylation of α-Alkoxy β-Phenylthio Acids

“…A general literature procedure was followed to prepare the intermediate Barton ester. Acid 2b (0.057 g, 0.19 mmol) was dissolved in CH 2 Cl 2 (2 mL), and the flask was wrapped with aluminum foil.…”

“…Flash chromatography of the residue over silica gel (3.0 × 15.0 cm), using 50:1 hexane/EtOAc, afforded rac-methyl 3-(phenylsulfanyl)undecanoate as a colorless oil (1.4 g, 98%): 1 Dec-1-ene (2d). 42 A general literature procedure 43 was followed to prepare the intermediate Barton ester. Acid 2b (0.057 g, 0.19 mmol) was dissolved in CH 2 Cl 2 (2 mL), and the flask was wrapped with aluminum foil.…”