Advances in Protecting Groups for Oligosaccharide Synthesis

Abstract

Carbohydrates contain numerous hydroxyl groups and sometimes amine functionalities which lead to a variety of complex structures. In order to discriminate each hydroxyl group for the synthesis of complex oligosaccharides, protecting group manipulations are essential. Although the primary role of a protecting group is to temporarily mask a particular hydroxyl/amino group, it plays a greater role in tuning the reactivity of coupling partners as well as regioselectivity and stereoselectivity of glycosylations. Several protecting groups offer anchimeric assistance in glycosylation. They also alter the solubility of substrates and thereby influence the reaction outcome. Since oligosaccharides comprise branched structures, the glycosyl donors and acceptors need to be protected with orthogonal protected groups that can be selectively removed one at a time without affecting other groups. This minireview is therefore intended to provide a discussion on new protecting groups for amino and hydroxyl groups, which have been introduced over last ten years in the field of carbohydrate synthesis. These protecting groups are also useful for synthesizing non‐carbohydrate target molecules as well.

Cysteine protecting groups: applications in peptide and protein science

“…The concept of protecting, and subsequently deprotecting, functional groups is of paramount importance in synthetic chemistry. [1][2][3] Protecting group strategies in particular feature extensively in the synthesis of peptides, whereby amino acid building blocks are coupled to one another via amide bonds. This is unsurprising, given the array of functional groups that are found within the 20 proteinogenic amino acids, including: amines, alcohols, thioethers, imidazole rings, and carboxylic acids.…”

Stereoselective Sc(OTf)3‐Catalyzed Aldol Reactions of Disubstituted Silyl Enol Ethers of Aldehydes with Acetals

“…TBS‐silyl enol ether 3 c reacted with acetal 4 a delivering 5 a with very similar selectivity, suggesting that the nature of the silyl group does not dramatically influence the mechanism of the reaction. To access free aldol products (R 4 =H), acetal 4 k possessing a removable allyl group [17] was also tested, and we were pleased to observe similar selectivities and yields for the diastereomeric pair 5 c and 5 d (from 3 a and 3 b , respectively). Aromatic aldehydes featuring substitution at either the para, meta or ortho‐position proceed with satisfactory levels of diastereoselectivity (Scheme 2, compare 5 e with 5 f and 5 g ).…”

“…Under the standard reaction conditions, Z ‐enolate 6 provided the anti ‐aldol derivatives 7 a – c , whereas the E ‐isomer gave the syn products 7 d – f in good yields with moderate to good selectivities. The relative stereochemistry of the aforementioned products can be determined by careful analysis of 1 H NMR J coupling constants ( J anti > J syn ) [18] and chemical correlation with published structures [17] …”

“…The relative stereochemistry of the aforementioned products can be determined by careful analysis of 1 H NMR J coupling constants (J anti > J syn ) [18] and chemical correlation with published structures. [17] Two striking aspects of the stereoselection in this aldol addition attracted our attention. First, the reaction is stereo-selective, with each stereoisomer of the enolate leading to a different diastereomer of the product.…”

Synthesis of structurally-defined polymeric glycosylated phosphoprenols as potential lipopolysaccharide biosynthetic probes

“…Protecting groups greatly inuence glycosylation reactivity, glycosylation stereoselectivity and deprotection efficiency. 27,28 These factors must be balanced with the complexity of the routes needed to assemble (usually monosaccharide) building blocks. Thus, great care was taken in choosing them in this investigation.…”