Fucosyl phosphate

Fucosyl phosphate 36 also very efficiently glycosylated the C4 position of acceptor 32. The orthogonality of the activating conditions of thioglycosides and glycosyl phosphate donors was exploited in the synthesis of trisaccharide glycal 41 (Scheme 6.7A).32 Furthermore, the different reactivity of a- and p-glycosyl phosphates was... 

The critical intermediate in the outlined synthesis is the p-fucosyl phosphate, which can hardly be separated cleanly from the concomitant a isomer [65, 70], The ensuing coupling to the morpholidate-activated GMP proceeds sluggishly and is always accompanied by epimerization and hydrolysis. TTiis makes the synthesis a low-yielding process and impedes the isolation of the pure GDP-fucose from this reaction mixture. 

A series of peracetylated fucose analogs have been prepared by the chemical route described for the peracetylated P-fucosyl phosphate (Scheme 7) [87]. Two decisive improvements have been introduced with regard to the fully chemical synthesis of GDP-Fuc (Scheme 13). Firstly, the acetylated fucosyl phosphates used for the coupling reaction are more stable than the unprotected variety and they are far more soluble in the coupling solvent than the unprotected ones. This speeds up the diphosphate formation without any detectable, concomitant anomerization of... 

Fig. 7.—Elution Pattern for Lotus Extracts from L-Fucosyl-agarose. [Initial elution with 0.01 M sodium phosphate in saline, followed by elution with 0.1 M L fucose in 0.01 M phosphate buffer in saline (arrow) (see Ref. 20).]...

Glycosyl halides, reaction with ethyl potassium dithiocarbonates, 111 —, poly-O-acetyl-, solvolysis of, 39 Glyculosonic acids, 3-deoxy-, 253, 254 Glyoxal, bis(phenylhydrazone), 81 Guanosine, 5-(fucosyl dihydrogen pyrophosphate), 205 5-phosphate, 227 trihydrogen pyrophosphate, 205 —, 2-deoxy-, 5-triphosphate, 231 Guaran, 71, 75... 

The substrate, fucosyl-GMj, was separated from its product, GMj, by chromatography on a LiChrosorb-NH2 column (4 mm X 250 mm, 5 /urn). The mobile phase was a 25 75 mixture of 5 mM potassium phosphate buffer (pH 5.5) and acetonitrile. Similarly, fucosyl-GDib was separated from GDib. except the concentration of phosphate buffer was 20 mM Gangliosides were detected by their absorbance at 195 nm. 

To overcome the synthetic and inhibition problems, an integrated recycling system is applied. GTP and Fuc-l-P are transformed by GDP-fucosyl-pyro-phosphorylase to pyrophosphate and the activated donor (GDP-Fuc) [71]. This in turn in the presence of al-3/4-fucosyltransferase fucosylates the acceptor Gal)3l-4GlcNAc at the GlcNAc-3-position or the acceptor Gal)3l-3GlcNAc at the GlcNAc-4-position. The released GDP is phosphorylated to GTP with pyruvate kinase employing the activated phosphate donor phosphenol pyruvate, which in... 

Fucosyl transferases use GDP Fuc 10.59, which may be prepared on a gram scale from L-fucose (Adelhorst and Whitesides 1993 Veeneman etal. 1991). Hermann et al. (1993) proposed fucosylation with regeneration in a similar manner to one of the biosynthetic routes of fucose according to the reactions (10.15), whose similarity to reactions (10.9) to (10.12) will not escape the reader. The a-D-mannopyranosyl phosphate can be prepared rapidly by a non-enzymic route. 

Recently solutions of LiC104 in organic solvents were employed as media for the activation of various glycosyl donors. [22] In these solvents, glycosyl phosphates, glycosyl trichloroacetimidates and even the usually very stable glycosyl fluorides like the fucosyl donor 23 could be converted to glycosides like the trisaccharide 25 under neutral conditions and without the use of any further promotor (Scheme 8). 

The kinetics of the hydrolysis of D-glucosyl, D-mannosyl, D-galactosyl, and L-fucosyl a- and 3-phosphates between pH 1-6 have been determined. For the mono-anionic species the /3-anomers were hydrolysed 3-7 times faster than the a-anomers. Extended Hiickel calculations have shown that the difference in enthalpy between cyclic AMP and acyclic related phosphate esters is due to larger net exothermic solvation enthalpy in the former, ascribed to extra stabilization of the products of hydrolysis, due to their ability to form more stable hydrogen bonds with water. ... 

The in situ generation of GDP-Fuc from P-fucose-1-phosphate coupled with the transfer of the fucose moiety on to A -acetyllactosamine has also been probed on an analytical scale [96]. In the presence of GTP P-fucose-1-phosphate is converted to GDP-Fuc by GDP-fucose pyrophosphorylase. GDP-Fuc is then used by an a(l-3)fucosyl transferase to transfer the fucose moiety on to A -acetyllactosamine. The released GDP is recycled and phosphorylated to give GTP by a phosphokinase with phosphoenol pyruvate as phosphate source. The pyrophosphate produced in the complete cycle is decomposed by pyrophosphatase (see Scheme 16). 

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