Abstract:2-Acetamido-2-deoxy-β-d-glucopyranose
(β-d-GlcpNAc), in O-glycosidic
linkage to the side chain
hydroxyls of serine (Ser) and threonine (Thr) residues, is often found
in nuclear and cytoplasmic proteins. The
“active ester” approach for solid phase glycopeptide synthesis
calls for the direct glycosylation of
N
α-(9-fluorenylmethyloxycarbonyl)amino acid pentafluorophenyl esters
(N
α-Fmoc-AA-OPfp's). The synthesis of
the required
Ser(β-d-GlcpNAc) and
Thr(β-d-GlcpNAc) building blocks poses
special problems arising … Show more
“…To date, N-Dts derivatives have been successfully transformed into the free amine using b-mercaptoethanol (BME), Nmethyl-mercaptoacetamide (MAc), and dithiothreitol (DTT). 473,474 Moreover, addition of tertiary amines like N,N-diisopropylethylamine was also found to greatly accelerate the thiolytic cleavage of the Dts group.…”
“…To date, N-Dts derivatives have been successfully transformed into the free amine using b-mercaptoethanol (BME), Nmethyl-mercaptoacetamide (MAc), and dithiothreitol (DTT). 473,474 Moreover, addition of tertiary amines like N,N-diisopropylethylamine was also found to greatly accelerate the thiolytic cleavage of the Dts group.…”
“…27 However, most researchers prefer to carry out deacetylation after glycopeptides have been released into solution, since the reaction can be more easily monitored. Both hydrazine-hydrate in methanol 28 and sodium methoxide in methanol [29][30][31] have been used successfully to effect solution deacetylation, with the latter more common. Catalytic sodium methoxide is believed to promote Zemplén transesterification, which occurs with neither b-elimination nor epimerization of the stereocenters.…”
Section: Optimization Of On-resin Removal Of O-acetyl Groupsmentioning
“…However, the necessity for laborious purification procedures, particularly after scale-up of the glycosylation reaction, can be a serious limitation. [118] Replacement of the N-acetyl group by strongly electronwithdrawing groups reduces the extent of oxazoline formation, and highly efficient glycosylations were reported when the Aloc-, [119] Troc- [120±122] or Dts-protected [123] donors were employed. A typical example is given in Scheme 11.…”
Despite the omnipresence of protein glycosylation in nature, little is known about how the attachment of carbohydrates affects peptide and protein activity. One reason is the lack of a straightforward method to access biologically relevant glycopeptides and glycoproteins. The isolation of homogeneous glycopeptides from natural sources is complicated by the heterogeneity of naturally occuring glycoproteins. It is chemical and chemoenzymatic synthesis that is meeting the challenge to solve this availability problem, thus playing a key role for the advancement of glycobiology. The current art of glycopeptide synthesis, albeit far from being routine, has reached a level of maturity that allows for the access to homogeneous and pure material for biological and medicinal research. Even the ambitious goal of the total synthesis of an entire glycoprotein is within reach. It is demonstrated that with the help of synthetic glycopeptides the effects of glycosylation on protein structure and function can be studied in molecular detail. For example, in immunology, synthetic (tumour-specific) glycopeptides can be used as immunogens to elicit a tumour-cell-specific immune response. Again, synthetic glycopeptides are an invaluable tool to determine the fine specificity of the immune response that can be mediated by both carbohydrate-specific B and T cells. Furthermore, selected examples for the use of synthetic glycopeptides as ligands of carbohydrate-binding proteins and as enzyme substrates or inhibitors are presented.
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