Synthesis of Cyclic Peptidosulfonamides by Ring-Closing Metathesis

Abstract
N-Protected β-aminoethanesulfonyl chlorides (2a−e) were used in the preparation of sulfonamides 4, 8, 11a−c, and 15. Ring-closing metathesis of sulfonamides 4 and 8 did not lead to the expected nine-membered cyclic peptidosulfonamides. In contrast, the allylated peptidosulfonamides 11a−c and 15 turned out to be suitable precursor systems for ring-closing metathesis using second-generation Grubbs catalyst and nine-membered cyclic peptidosulfonamides were obtained in 47−60% yields. The possibility for incorporation of these cyclic peptidosulfonamides into a peptide sequence was illustrated by the incorporation of an amino acid on the “S”- or “N”-terminus leading to 16 and 18−20, respectively. A model of cyclic peptidosulfonamide 16 hints at an extended-like structure.