5-Bromo-1-hydroxybenzotriazole-7-sulphonic acid and derivatives. Synthesis and X-ray analysis of the pyridinium salt

We have now prepared the title acid 15a, its chloride 15b, phenyl ester 15c and dimethyl amide 15d, analysed the crystal structure of the pyridinium salt of 15a, and assessed the sulphonyl chloride 15b as a peptide coupling reagent. The formation of a peptide bond using 15b could involve an intramolecular capture of a highly activated carboxylic derivative analogous to that observed with a previously studied naphthosulfone, which should reduce the epimerisation