Novel stabilized activated derivatives of carbamic acid, their process of preparation and their use for the preparation of ureas
申请人:——
公开号:US20020143191A1
公开(公告)日:2002-10-03
Process for the preparation of stable activated derivatives of carbamic acid, comprising at least one protected amino group and an activated carbamic acid function, from an amino acid derivative in which the amino group is protected. The process includes: a) a step of transformation of the —COOH group of the amino acid derivative into a —CON
3
group to obtain an acyl azide; b) a step of transformation of the —CON
3
group of the acyl azide into a —NCO group to obtain an isocyanate; c) a step of treating the isocyanate to obtain a stable derivative of carbamic acid.
progress has been made toward the development of metal-free catalysts of enantioselective transformations, yet the discovery of organic catalysts effective at low catalyst loadings remains a major challenge. Here we report a novel synergistic catalyst combination system consisting of a peptide-inspired chiral helical (thio)urea oligomer and a simple tertiary amine that is able to promote the Michael reaction
an isoatomic and isostructural γ-aminoacid. The approach was extended to solid-phase techniques to accelerate the synthesis of longer and more functionalized sequences. Under optimized conditions, an octamer hybrid oligomer incorporating a central guanidinium linkage was obtained in good overall yield and purity. This work also reports data related to the structural consequences of urea by guanidinium
One fold to rule them all: New heterogeneous aliphatic backbonefoldamers belonging to the γ‐peptide superfamily and containing various combinations of urea/amide (U/A) and urea/carbamate (U/C) units are reported. Structural studies at atomic resolution reveal hydrogen‐bonded helical structures akin to that formed by cognate Un homooligomers.
Caught in a fold: A simple and efficient coupling strategy to make aliphaticoligoureafoldamers is reported. Crystal structures show that the pyrrolidine units (red; see picture) do not impair the 2.5‐helical folding of the oligoureas. This modular strategy enables assembly of long helical segments containing non‐adjacent pyrrolidine units as exemplified by the synthesis of a helix that is approximately