Synthesis of orthogonally protected cyclic homooligomers from sugar amino acids.
Two new families of orthogonally protected cyclic homooligomers with two to four sugar units were synthesized from pyranoid sugar amino acids. Cyclic oligomers composed of amide-linked sugar amino acids (1-3) were prepared by cyclization of linear oligomers of the novel orthogonally protected pyranoid sugar amino acid 12 using a solution-phase coupling method. These orthogonally protected cyclic molecules can be selectively or fully deprotected, affording the macrocycles ready to further functionalization. The straightforward reduction of the amide bonds in the cyclic oligomers 1-3 gave the corresponding amine-linked macrocycles 4-6. This kind of amine-linked carbohydrate-based cyclic oligomer has never been reported before. These flexible molecular receptors could be studied as molecular hosts for molecular, cationic, and anionic recognition. Conformational analysis by molecular modeling (AM1) showed that all of the deprotected cyclic trimers and tetramers preferred a (4)C(1) chair conformation with oxygen atoms of the sugar ring located on the interior of the cavity and the secondary hydroxyl groups outward. In the amide-linked macrocycles, all of the amide bonds are in s-trans conformation. The estimated size of the internal cavity is about 4.5 A for the cyclic trimer and 6.9 A for the cyclic tetramer. The amine-linked macrocycles displayed similar conformational behavior with a slight decrease in internal cavity.
Ménand
Mickaël
M
Synthèse, Structure et Fonction des Molécules Bioactives, CNRS UMR 7613, Université Pierre et Marie Curie, 4 Place Jussieu, F-75005 Paris, France.
Blais
Jean-Claude
JC
Hamon
Louis
L
Valéry
Jean-Marc
JM
Xie
Juan
J
D000596:Amino Acids / Q000737:chemistry*; D000606:Amino Sugars / Q000737:chemistry*; D002236:Carbohydrate Conformation; D020650:Combinatorial Chemistry Techniques; D018360:Crystallography, X-Ray; D003500:Cyclization; D008958:Models, Molecular; D015394:Molecular Structure; D009844:Oligosaccharides / Q000138:chemical synthesis*
D000596:Amino Acids; D000606:Amino Sugars; D009844:Oligosaccharides