Heptasaccharides

Enzymic fucosylation of an -acetyllactosamine-derived hexamer afforded two branched heptasaccharides and a difucosylated product. Substitutions occurred at 0-3 of the two glucosamine units other than that at the reducing end. A heptasaccharide anchor compound based on the inositol pentamer compound noted in reference 146, and carrying a GalNAc unit p-(l- 4)-linked on the central mannose moiety and a further a-(l- 2)-linked D-mannose unit on the non-reducing terminal mannose molecule, has been synthesized in a phosphory-lated form.  

Pokeweed lectin-B was determined by spectroscopic methods alone to have structure 20. A maltoheptaose derivative, produced by opening 0-methylated P-cyclodextrin, is reported in reference 186. 

The branched glucoheptaose 38, a repeating unit of lentinan which is used for anti-tumour purposes in China and Japan, has been synthesized.  

Two reports have appeared on the synthesis of GPI anchor hexasaccharide-inositol compounds which are heptasaccharide mimics. The first product, 43, is the anchor compound of Trypanosoma brucei, while the second, 44, is an analogous product of Leishmania parasites.  

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If processing occurs down to the core heptasaccharide (ManjiGIcNAclj), complex chains are synthesized by the addition of GIcNAc, removal of two Man, and the stepwise addition of individual sugars in reactions catalyzed by specific transferases (eg, GIcNAc, Gal, NeuAc transferases) that employ appropriate nucleotide sugars. 

Fig. 18.—Sequence of Heptasaccharide Isolated from RG-II. [Fragment-ions of the deuteropermethylated derivative are shown. Cleavages are all of the A, Type. (Rha = rhamnose, Ara = arabinose, AceA = aceric acid, MeFuc = 2-0-methylfucose, and Api = apiose).]...

Moreover, the one-pot sequential glycosylation method has been applied successfully to the rapid assembly of a branched heptasaccharide 73 (Scheme 2.23) [106],... 

Scheme 4.21 Mukaiyama s one-pot synthesis of phytoalexin-elicitor active heptasaccharide.

Warren and associates (18) have prepared a glycosyl azide derivative (15) of a heptasaccharide. This glycosyl azide was obtained from O-a-D-manno-pyranosyl-( 1 — 6)-0-[a-D-mannopyranosyl-( 1 — 3)-(9-a-D-mannopyrano syl-(l— 6)-0-a-D - mannopyranosyl - (1 — 3)] - O-fi- d - mannopyranosyl -(1 — 4) - O - (2 - acetamido - 2 - deoxy-/ -d-glucopyranosyl) - (1 — 4) - 2 -acetamido-2-deoxy-D-glucopyranose (12) by treatment of its peracetylated derivative 13 with trimethylsilyl trifuoromethanesulfonate, followed by reaction of the intermediary oxazoline 14 with trimethylsilyl azide. Reduction of the glycosyl azide 15 in the presence of Lindlar catalyst gave the glycosyla-mine derivative 16. The condensation of 16 with 1-tert-butyl N-(9-fluoren-... 

Scheme 1.7 Solid-phase synthesis of an immunogenic heptasaccharide by van Boom et al.

To date, heptasaccharide 47 is the largest oligosaccharide assembled on a solid support using only monosaccharide building blocks. This turns out to be an excellent demonstration of the efficiency of the (9-glycosyl trichloroacetimidate approach. 

In 1997 Nicolaou et al. published the assembly of a heptasaccharide phytoalexin elicitor (HPE, 16) on a solid support (Schemes 5.2-5.4).29 This oligosaccharide... 

Scheme 5.2 (a) Monosaccharide building blocks 1-3 selected for solid phase synthesis of heptasaccharide 16 (b) attachment of the first carbohydrate onto phenolic polystyrene through a new photocleavable o-nitrobenzyl-type linker29 (Bn = benzyl, Bz = benzoyl, Fmoc = 9-fluoromethyloxycarbonyl, Ph = phenyl, py = pyridine, TBDPS =t-butyldiphenylsilyl). 

Scheme 5.3 Stepwise assembly of the solid-phase-bound heptasaccharide thioglycosides as glycosyl donors and DMTST as activator.29...

Scheme 5.4 Photolytic cleavage of resin-bound heptasaccharide 15 and deprotection to yield the heptasaccharide phytoalexin elicitor 16.29...

Ley and coworkers13-18 are responsible for setting much of the stage on which our work is played. Showcased by the synthesis of the heptasaccharide shown in Scheme... 

Unverzagt, C., Synthesis of a Bianteimary Heptasaccharide by Regioselective Glycosylations. Uwgew. Chem. Int. Ed. 1994,33,1102-1104. 

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