Glycopeptides, synthesis

Urge, L., Kollat, E., Hollosi, M., Laczko, I., Wroblewski, K., Thurin, J., and Otvos Jr., L. (1991) Solid-phase synthesis of glycopeptides synthesis of Na-fluorenylmethoxycarbonyl L-asparagine Nb-glyco-sides. Tetrahedron Lett. 32, 3445-3448. 

In fact, other studies have shown that TMSOTf catalyzes the glycosylation of a silylated acceptor with a silylated hemiacetal donor [49]. Nudel man s procedure was applied to the synthesis [1-glucuronide 30, isolated in 57% yield. Kiyoi and Kondo have applied the TMSOTf activation protocol to protected L-fucose hemiacetal donors for glycopeptide synthesis and obtained glycopeptide fragment 31 in 74% yield (a p, 20 1) [50], Posner and Bull have developed a procedure that uses excess TMSOTf in the presence of molecular sieves (SYLOSIV A4) to synthesize various l.l -linked disaccharides such as the galactopyranose dimer 32 [51,52]. 

The high specificity and stereoselectivity of enzymes, as well as the mild conditions under which they react, make enzyme-catalyzed reactions versatile tools in the synthesis of glycoconjugates. In some instances, an enzymic one-step transformation affords higher yields then the conventional and more-complex chemical synthesis. The application of enzymes in glycopeptide synthesis is under active development for selective deprotection and glycosylation purposes. 

Sequential solid-phase glycopeptide synthesis using glycosylated amino acid building blocks... 

Convergent glycopeptide synthesis with polymer-bound carbohydrates... 

Besides acetyl, benzoyl, and benzyl protecting groups for the carbohydrate hydroxyl groups, silyl, isopropylidene, and p-methoxybcnzyl groups have also been employed in solid-phase glycopeptide synthesis. The synthesis of a glycopeptide... 

Scheme 13.14 Synthesis of a sialyl Lewis A buiding block for solid-phase glycopeptide synthesis.

CONVERGENT GLYCOPEPTIDE SYNTHESIS WITH POLYMER-BOUND CARBOHYDRATES... 

Parallel synthesis of glycopeptides is not described in great detail since such synthesis was reviewed previously and may be regarded as an extension of conventional glycopeptide synthesis. 

Finally, solid-phase glycopeptide synthesis is highlighted in two chapters describing exciting new developments in this area. 

M Meldal, KJ Jense. Pentafluorophenyl esters for temporary protection of the a-carboxy group in solid phase glycopeptide synthesis. J Chem Soc Chem Commun 483, 1990. 

Scheme 10.1 Glycopeptide synthesis and a-chymotrypsin catalyzed release from the solid support, a) 25% TFA (CH2CI2) b) 0-(N-Boc-Phe)glycolic acid (7 eq), BOP, HOBt, DIEA b) 25% TFA (CH2CI2) c) Boc-Gly-OH (7 eq), BOP, HOBt, DIEA c) 25% TFA (CH2CI2) d) Boc-Asn(GlcNAcb)-OH (3 eq), BOP, DIEA e) galactosyl transferase, sialyl transferase f) CT, H2O, pH 7.0 g) ultrafiltration h) a-l,3-fuco-syltransferase, GDP-Fuc (2.5 eq), 0.1 M HEPES (pH 7.0), 95%.

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