Abstract
Synthetic approaches towards N-acetylgalactosamine (GalNAc) have been attracting considerable interest since this compound is known for its pivotal role in cell–cell interaction and receptor induced cell signaling. Herein, we present a synthetic route in which two of the four stereogenic centers present in the target compound are derived from enantiopure tartaric acid being selectively converted to epoxy alcohols. The key step is the Pd-catalyzed, stereo- and regioselective epoxide opening and subsequent nucleophilic substitution of an azide functionality. This approach enables the synthesis of the naturally D- and unnaturally L-configured GalNAc, as well as both enantiomers of the largely unknown N-acetylidosamine (IdoNAc).
Highlights
N-Acetylgalactosamine (GalNAc, Figure 1) and N-acetylidosamine (IdoNAc) belong to the group of 2-amino-2-deoxysugars, which can be found in a wide range of organisms as building blocks of, e.g., glycosaminoglycans, peptidoglycans or lipopolysaccharides [1]
A synthetic route was developed starting with both the D- and the L-epoxythreitol 5a and 5b. These isomers have been synthesized from D- (3a) and L-tartaric acid (3b), respectively, through an approach that has been published earlier by Iida et al (Scheme 1) [16]
After the C4-chain of tartaric acid has been extended by two carbon atoms resulting in compounds 4a and 4b, two new stereocenters have been introduced by Sharpless epoxidation [17,18]
Summary
N-Acetylgalactosamine (GalNAc, Figure 1) and N-acetylidosamine (IdoNAc) belong to the group of 2-amino-2-deoxysugars, which can be found in a wide range of organisms as building blocks of, e.g., glycosaminoglycans, peptidoglycans or lipopolysaccharides [1]. Flexible synthetic routes are required to access and probe the entire compound class of 2-amino-2-deoxysugars for further structure–activity relationship studies. Other approaches, novel synthetic concepts to fill the remaining methodological gaps for accessing the missing isomers of 2-amino sugars, as well as new derivatives are still highly desired.
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