title: Unusual orthogonality in the cleavage process of closely related chelating protecting groups for carboxylic acids by using different metal ions.
abstract: Three structurally related relay protecting groups for carboxylic acids that are based on chelating amines have been developed. These protecting groups can easily be introduced by coupling the carboxylic acid and the corresponding amine in the presence of 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU). In addition to being stable to a whole array of reaction conditions, these protecting groups are also stable under acidic and basic conditions, allowing them to be used in combination with the ester protection of carboxylic acids. The cleavage of these protecting groups is activated by the chelation of metal ions, involving an unusual coordination of the amide nitrogen. Despite their similarity, cleavage of these protecting groups is possible in both a stepwise and an orthogonal fashion by applying different metal salts.
authors.affiliation: Institut für Organische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg (Germany), Fax: (+49) 761-203-8705.
authors.forename: Stephan
authors.initials: S
authors.lastname: Mundinger
authors.forename: Uwe
authors.initials: U
authors.lastname: Jakob
authors.forename: Willi
authors.initials: W
authors.lastname: Bannwarth
keywords: amides; carboxylic acids; chelators; orthogonality; protecting groups