Reverse Turn Induced π-Facial Selectivity during Polyaniline-Supported Cobalt(II) Salen Catalyzed Aerobic Epoxidation of N-Cinnamoyl l-Proline Derived Peptides
摘要:
A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereo-selectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d(6), and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction.
Polyaniline supported cobalt salen catalyses the facially selective aerobic epoxidation (oxygen/2-methylpropanal) of N-cinnamoyl proline derived peptides. A high diastereoselectivity is observed for peptides which are able to adopt a gamma- or beta -turn due to intramolecular hydrogen bonding. (C) 2000 Elsevier Science Ltd. Ail rights reserved.