Disaccharides, 1 —> 6 linked synthesis

M. Blanc-Muesser, J. Defaye, and H. Driguez, Stereoselective thioglycoside syntheses. Part 4. A new approach to 1,4-linked-thio-disaccharides and synthesis of thiomaltose, J. Chem. Soc., Perkin Trans. 1, (1982) 15-18. 

In addition to oligomers obtained from the amino-acid (114), two other reports have described the synthesis of disaccharides linked through amide bonds. Hexosaminides (e.g. benzyl 2-amino-2-deoxy-a-D-glucopyranoside) have been condensed directly, or in the presence of DCC, with hexuronic acid derivatives (e.g. l,2 3,4-di-0-isopropylidene-a-D-galactopyranosyluronic acid) to give the corresponding A -acylamino derivatives [e.g. (128)], and a similar... 

Disaccharide, 997-999 1—>4 link in, 997-998 synthesis of, 1002 Dispersion forces, 62 alkanes and, 92 Disrotatory motion. 1183 Distortionless enhancement by... 

Martin and coworkers have used this strategy for synthesis of a- and P-(l,6)-linked C-disaccharides (Eq. 5.40).58... 

PCC in the presence of 4 A MS to afford the corresponding keto sugars (175, 176), which after Tebbe methylenation led to the corresponding exoglycals, valuable intermediates for the synthesis of C-disaccharides. Dondoni el al.159 made use of PCC in the presence of powdered 4 A MS to introduce suitable formyl groups in the carbohydrate, and allowing the synthesis of >6)-linked oligosaccharides,... 

Compound 33 also lends itself to the synthesis of 1,5-linked disaccharides. Thus, its condensation180 with 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide, and with methyl 2,3,4-tri-O-acetyl-a-D-glucopyranosyluronate bromide, respectively, yields the corresponding /3-D-linked disaccharides (97 and 98). 

In a synthesis of a partial structure of the GPI anchor of Trypanosoma brucd, three of the four glycosylations were realized with the zirconocene activator (Cp2ZrCl2/AgC104, 1 1 Scheme 8.8). First, the coupling of a 1-D-myo-inositol acceptor with a disaccharide donor gave a mixture (93 %) of the desired a-linked trisaccharide and its (3-isomer in a ratio... 

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]. 

Kusumoto and coworkers have found that the treatment of hemiacetal 1 with trifluoro- or trichloroacetic anhydride 94 (1 equiv) and trimethylsilyl perchlorate (0.2 equiv) selectively provides the corresponding anomeric ester intermediate 91 [152], Hemiacetal acylation occurs even in the presence of the alcohol acceptor. With Lewis acid assistance, the glycosyl ester intermediate is displaced to provide disaccharide products in good yields. This transformation allowed the synthesis of disaccharides 98 (81%) and 99 (91%). In some cases, acetic anhydride has been used as the electrophilic activator of hemiacetal donors and the reaction with thiol acceptors yields S-linked glycosides [153,154],... 

This procedure has been demonstrated to provide moderate yields and anomeric selectivity in oligosaccharide synthesis. For instance, the disaccharide 110 was obtained in 50% yield as a 1 2 a p ratio. The reaction side products were mainly the self-condensed donor (10-25%) and unreacted hemiacetal (5-10% or higher). Alternatively, the a-linked glycosides were favored with diethyl ether solvent. In this way, trisaccharide 111 was prepared from the disaccharide hemiacetal donor in 49% yield, favoring the a-anomer by 4 1. 

Stereoselective synthesis of higher aza disaccharides from C-linked carbo-(l-ami noacids was proposed by Indian scientists (Fig. 36).51... 

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