Chemistry of 1,2-Anhydro Sugars

Abstract

The 1,2-anhydro sugars are a class of valuable and versatile intermediates in carbohydrate chemistry. In the first part of this article, a review is given on preparation methods of 1,2-anhydro sugars that are suitably protected. Protected 1,2-anhydro sugars have been widely used as glycosyl donors for the synthesis of glycosyl compounds such as oligosaccharides and nucleosides. In the second part, a brief history and the chemistry of unprotected 1,2-anhydro sugars is described. In the past few years, our research group has developed protection-free methods for synthesis of glycosyl compounds through unprotected 1,2-anhydro sugars as reactive intermediates based on the concept of 'direct anomeric activation'. In this article, the one-step preparation of glycosyl compounds such as thioglycoside derivatives and glycosyl azides by using formamidinium-type dehydrating agents is presented. Furthermore, the initial results on the first detection of unprotected 1,2-anhydro sugar intermediates by NMR measurements are shown along with their full structure characterizations.

Protecting-group-free glycosylation of phosphatidic acid in aqueous media

“…To assess whether the DMC/TEA-mediated condensation reaction proceeded via the previously proposed 1,2-anhydro glucose intermediate, 11 coupling with 2-deoxyglucose as a glycosyl donor was attempted (Table 1, entry 19). The absence of a reliably detectable product strongly supports the hypothesis that the reaction proceeds via the 1,2-anhydro-α- d -glucopyranosyl intermediate (Fig.…”

Recent advances in stereoselective 1,2-cis-O-glycosylations

“…In addition to various furanosyl phosphate donors (Figures 1Ac,d, 2B1) (Mayfield et al, 2020), the suitably protected mannosyl and rhamnosyl diphenylphosphate donors have been reported to be activated with the bis-thiourea catalyst as one of the organocatalytic approaches (Bradshaw et al, 2018;Loh, 2018 recent reviews, Mayfield et al, 2020;Park et al, 2017; ) afforded 1,2-cis glycoside in a highly selective manner (Li et al, 2020). It is noteworthy that a Schreiner thiourea catalyst with a halogen bond donor such as 2-iodoimidazolium salt has been developed to afford 1,2-cis N-glycoside from glycosyl trichloroacetimidate and amide of protected Asn (Li G et al, 2018). Pyrilium salt as an alternative organocatalyst effectively promotes the glycosylation of α and β-glycosyl trichloroacetimidate via S N 2-type inversion to afford β-(1,2cis manno-) and α-(1,2-cis gluco-) glycosides, respectively (Figure 2B2) (Nielsen et al, 2022).…”

Carbohydrate‐Derived Dienes as Building Blocks for Pharmaceutically Relevant Molecules

“…[8 -11] Furthermore, these carbohydrate-based diene building blocks can be converted into useful intermediates using various transformations, including cycloadditions, electrophilic/nucleophilic additions, and aromatization reactions (Scheme 2). Although various reviews have covered synthetic transformations of unique carbohydrate-based scaffolds, such as the functionalization of glycals, [12][13][14] 1,2-and 1,6-anhydrosugars, [15,16] and CÀ H activations, [17,18] to the best of our knowledge the chemistry of carbohydratebased dienes has not been reviewed recently. Given the progress made over the past several decades, and the great utility of carbohydrate-based dienes as important building blocks, we herein summarize their various applications in the preparation of different natural products and pharmaceutically relevant derivatives.…”