Home  About us  Contact
 

On-resin Cyclization (on-resin + cyclization)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Cyclic ,-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Conformational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical Calculations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005
Frank Büttner Dr.
Abstract The solution-phase synthesis of the simplest cyclic ,-tetrapeptide, cyclo(,-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic ,3 -tetrapeptide cyclo(-,3hPhe-,3hLeu-,3hLys-,3hGln-) (14) and the first cyclic ,3 -pentapeptide cyclo(-,3hVal-,3hPhe-,3hLeu-,3hLys-,3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(,-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-,3 -tetrapeptide causes stabilization of one dominating conformer. The cyclic ,3 -pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(,-Ala)4 (4) displays a Ci -symmetrical 16-membered ring with adjacent CO and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic ,-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities. [source]

cyclo(, -Asp- ,3 -hVal- ,3 -hLys) , Solid-Phase Synthesis and Solution Structure of a Water Soluble , -Tripeptide.

HELVETICA CHIMICA ACTA, Issue 11 2004
Preliminary Communication
The H2O-soluble cyclic ,3 -tripeptide cyclo(, -Asp- ,3 -hVal- ,3 -hLys) (4) was obtained by on-resin cyclization of the side-chain-anchored , -peptide 3 (Scheme). In aqueous solution, 4 adopts a structure with uniformly oriented amide bonds and all side chains in lateral positions (Fig.,3). [source]

Cyclic ,-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Conformational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical Calculations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005
Frank Büttner Dr.
Abstract The solution-phase synthesis of the simplest cyclic ,-tetrapeptide, cyclo(,-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic ,3 -tetrapeptide cyclo(-,3hPhe-,3hLeu-,3hLys-,3hGln-) (14) and the first cyclic ,3 -pentapeptide cyclo(-,3hVal-,3hPhe-,3hLeu-,3hLys-,3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(,-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-,3 -tetrapeptide causes stabilization of one dominating conformer. The cyclic ,3 -pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(,-Ala)4 (4) displays a Ci -symmetrical 16-membered ring with adjacent CO and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic ,-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities. [source]

Solid-Phase Synthesis of Dihydrovirginiamycin S1, a Streptogramin B Antibiotic

CHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004
Alex Shaginian
Abstract We describe the first solid-phase synthesis of dihydrovirginiamycin S1, a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1,, 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure,activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities. [source]