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Title
| - Hantzsch-Type Three-Component Approach to a New Family ofCarbon-Linked Glycosyl Amino Acids. Synthesis ofC-Glycosylmethyl Pyridylalanines,
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Abstract
| - C-Glycosylmethyl pyridylalanines reported in this paper constitute a novel family of glycosyl aminoacids that contain a pyridine ring linking the carbohydrate and amino acid residues. These amino acidsmay serve to prepare nonnatural glycopeptides displaying firmly bound carbohydrate fragments througha rigid and highly stable tether. A viable route to these new hybrid molecules has been opened via thermallyinduced Hantzsch-type cyclocondensation using an aldehyde−ketoester−enamino ester system. To oneof these reagents was attached a C-glycosyl residue, while to another was bound an amino acid fragment.In a one-pot optimized methodology, the dihydropyridine was not isolated while its purification wascarried out by removal of unreacted material and side products using polymer-supported scavengers.Then the dihydropyridine (mixture of diastereoisomers) was oxidized by a polymer-bound oxidant togive the target pyridine bearing the two bioactive residues. In this way a range of eight compounds(58−68% yield) was prepared in which the elements of diversity were (i) the gluco and galactoconfigurations of the pyranose ring, (ii) the α- and β-configurations at the anomeric center, and (iii) thepositions of the carbohydrate and amino acid sectors in the pyridine ring. The orthogonal functionalgroup protection in these amino acids allowed their easy incorporation into oligopeptides via sequentialamino and carboxylic group coupling.
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