Vespers Op. 37

Chemoselective Reactions for the Synthesis of Glycoconjugates from Unprotected Carbohydrates

“…Glycosylamines constitute avery important class of glycoconjugates found in abundance in nature,m ost notably as the heterocyclic furanosylamineso fn ucleosides,b ut also in the form of pyranosylamines presentind iverse natural products. [46] The N-alkylg lycosylamines are cyclic hemiaminals analogous to the cyclic acetals found in O-alkylg lycosides;h owever, unlike O-glycosides they are able to equilibrate between the open-chain and cyclic forms, similarly to the hemiacetals of reducing sugars. They can freely undergo mutarotation via the open-chain form to the more stable configuration, which is often the b-anomer.I ti sb elieved that the equatorial preference resultsf rom nonbonded repulsion or steric effects in the a-anomer, [47] and thus it seems that the anomeric effect is less pronounced for the less electronegative nitrogen than for oxygen (Scheme 13).…”

“…Likewise, they are valuable building blocks for the construction of more complex neo-glycoconjugates through, for example, azide-alkyne cycloaddition chemistry (Section 4.2). [65] Severals trategies for their synthesis have been reported, as detailed in the followings ection.…”

“…[8b, 73e, 75] Furthermore, aw ide range of neo-glycosyl amide conjugates with biological activity relevant for medicinal chemistry have been synthesized. [65] Substantial effort has gone into the chemical synthesis of glycosyl amides Scheme21. One-pot synthesis of aM UC1 glycopeptide analogue from an unprotectedb iantennary N-glycan decasaccharide and the MUC1 peptide fragment.…”

“…Urea-, thiourea-, and thiocarbamate-linked N-glycosides constitute an emerging class of stable neo-glycoconjugates.T hey have found interesting applicationsa nd may be utilized as alternatives to glycosyl amides, which in somec ases can be problematic to synthesize. [65,75,100]…”