Abstract
L-Aspartic acid building blocks bearing galactosyl moieties were used to synthesise glycolipid mimetics of variable hydrocarbon chain length. The glycolipids were readily prepared through amide bond formation using the TBTU/HOBt coupling methodology. It was observed that, under these conditions, activation of the α-carboxylic acid of the intermediates led to near complete racemisation of the chiral centre if the reaction was carried out in the presence of a base such as triethylamine. The enantiomerically pure glycolipids were obtained after careful consideration of the synthetic sequence and by performing the coupling reactions in the absence of base.
Highlights
Synthetic glycomimetics have been the subject of much research activity in the field of carbohydrate chemistry
The carboxylic acid present on the aspartic acid side chain offers the possibility for attachment of mono or oligosaccharides, while both the amino and carboxylic acid groups at the α-carbon allow for further functionalization
In this study we report our investigations towards the synthesis of galactosylated building blocks based on: (i) orthogonally protected; (ii) enantiomerically pure and (iii) commercially available L-aspartic acid derivatives, as we intend to expand their application to the preparation of glycolipid mimetics
Summary
Synthetic glycomimetics have been the subject of much research activity in the field of carbohydrate chemistry. Glycolipid mimetics [6], in particular synthetic derivatives of biologically relevant ceramides (such as galactosyl ceramides, shown in Figure 1a), have attracted the attention of many carbohydrate chemists over recent years [7]. Amino acids that allow for side chain functionalization with glycosyl moieties, such as serine and aspartic acid, have been popular choices as the starting point for the preparation of glycolipid analogues [8,9]. The carboxylic acid present on the aspartic acid side chain offers the possibility for attachment of mono or oligosaccharides, while both the amino and carboxylic acid groups at the α-carbon allow for further functionalization. Due to the biological relevance of N-linked glycosides, this type of building blocks has been used predominantly in the synthesis of glycopeptides and glycopeptoids and numerous examples of such compounds can be found in the literature [10,11,12,13]
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