Investigation of the nucleotide triphosphate substrate specificity of Homo sapiens UDP-N-acetylgalactosamine pyrophosphorylase (AGX1).

Nucleotide sugars are essential glycosyl donors for Leloir-type glycosyltransferases. The UDP-N-acetylgalactosamine pyrophosphorylase (UDP-GalNAc PP; AGX1) from Homo sapiens catalyzes the synthesis of UDP-N-acetylgalactosamine from N-acetylgalactosamine 1-phosphate and UTP. In this Letter, we systematically studied nucleotide substrate specificity of AGX1 during its uridyltransfer reaction, and described the capability of AGX1 to catalyze dUTP and dTTP to their corresponding nucleotide sugars for the first time. Furthermore, using such a eukaryotic enzyme, we synthesized dUDP-GalNAc and dTDP-GalNAc in multiple mg scale in vitro efficiently and rapidly.

Synthesis and biological evaluation of new UDP-GalNAc analogues for the study of polypeptide-alpha-GalNAc-transferases.

A series of three O-methylated UDP-GalNAc analogues have been synthesised using a divergent strategy from a 3,6-di-O-pivaloyl GlcNAc derivative. The biological activity of these probes toward polypeptide-alpha-GalNAc-transferase T1 has been investigated. This study shows that this glycosyltransferase exhibits a very high substrate specificity.

Syntheses of unnatural N-substituted UDP-galactosamines as alternative substrates for N-acetylgalactosaminyl transferases.

UDP-GalNAc analogues with slight modifications in the 2-acetamido group of the GalNAc moiety are prepared in order to study their role in the mechanism of the N-acetylgalactosaminyl transferase mediated glycosylation step. The analogues with N-propionyl-, N-butyryl- and N-bromoacetyl-groups were synthesized, utilizing Khorana's morpholidate coupling method starting from D-galactosaminyl-1-phosphate after selective N-acylation of its amino group with the appropriate N-acyloxysuccinimides. Furthermore, in addition to UDP-galactosamine its 2-azido analogue has been efficiently prepared involving a metal catalyzed diazo transfer reaction.

Synthesis of novel donor mimetics of UDP-Gal, UDP-GlcNAc, and UDP-GalNAc as potential transferase inhibitors.

For the enzymatic transfer of galactose, N-acetylglucosamine, and N-acetylgalactosamine, UDP-Gal (1), UDP-GlcNAc (2), and UDP-GalNAc (3) are employed, and UDP serves as a feedback inhibitor. In this paper the synthesis of the novel UDP-sugar analogues 4, 5, and 6 as potential transferase inhibitors is described. Compounds 4-6 feature C-glycosidic hydroxymethylene linkages between the sugar and nucleoside moieties in contrast to the anomeric oxygens in the natural derivatives 1-3.

The synthesis of high-specific-activity UDP-[6-3H]galactose, UDP-N-[6-3H]acetylgalactosamine, and their corresponding monosaccharides.

Tritiated uridine-5'-diphosphogalactose (UDP-[3H]Gal) has been widely used to study oligosaccharide biosynthesis and structure. It can be synthesized either chemically or enzymatically using galactose oxidase to oxidize the hydroxyl moiety at C-6 to an aldehyde (6-aldo-UDP-Gal), which is then reduced back to the alcohol with tritiated sodium borohydride. Although the enzymatic approach is simple and efficient, there are several problems associated with it. First, incomplete oxidation to the aldehyde reduces the final specific activity. Second, if the galactose oxidase is not removed from the 6-aldo-UDP-Gal prior to reduction, the resulting UDP-[6-3H]Gal can be reoxidized to 6-aldo-UDP-[6-3H]Gal. We present evidence for the occurrence of this compound in one commercially obtained preparation of UDP-[6-3H]Gal. Finally, if an excess of 6-aldo-UDP-Gal is used for good yield, it is necessary to quench the reduction with nonradioactive borohydride, again reducing the final specific activity. We have devised a rapid, inexpensive, and efficient synthesis of UDP-[6-3H]Gal that circumvents all of these problems. Galactose oxidase is used to produce 6-aldo-UDP-Gal and the completeness of this reaction is confirmed on polyethyleneimine (PEI) cellulose TLC plates. The 6-aldo-UDP-Gal is purified on silica gel 60 TLC plates. This purified compound is then reduced with tritiated sodium borohydride, with the aldehyde present in excess. Unreacted 6-aldo-UDP-Gal is then purified away from the product UDP-[6-3H]Gal by chromatography on PEI cellulose. Radiochemically pure UDP-[6-3H]Gal with a specific activity of 10 Ci/mmol was obtained using the above scheme.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of uridine 5'-(2-acetamido-2,4-dideoxy-4-fluoro-alpha-D-galactopyranosyl) diphosphate and uridine 5'-(2-acetamido-2,6-dideoxy-6-fluoro-alpha-D-glucopyranosyl) diphosphate.

Benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside was converted into its 4-O-(methylsulfonyl) derivative (2) by treatment with methanesulfonyl chloride in pyridine. Displacement of the methylsulfonyloxy group of 2 with fluoride ion afforded benzyl 2-acetamido-3,6-di-O-benzyl-2,4-dideoxy-4-fluoro-alpha-D-galactopyranosi de, which on hydrogenolysis, followed by acetylation, furnished 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-4-fluoro-D-galactopyranose. Treatment of this and of 2-acetamido-1,3,4-tri-O-acetyl-2,6-dideoxy-6-fluoro-D-glucopyranose with trimethylsilyl trifluoromethanesulfonate in 1,2-dichloroethane at approximately 50 degrees afforded the 4-deoxy-4-fluoro- or the 6-deoxy-6-fluoro-oxazolines (5) and (11), respectively. Reaction of 5 and 11 with dibenzyl phosphate in 1,2-dichloroethane produced the alpha-linked dibenzyl phosphate derivatives 6 and 12, respectively. Catalytic hydrogenation of 6 provided 2-acetamido-3,6-di-O-acetyl-2,4-dideoxy-4-fluoro-alpha-D-galactopyranosy l phosphate (7), and that of 12 gave 2-acetamido-3,4-di-O-acetyl-2,6-dideoxy-6-fluoro-alpha-D-glucopyranosyl phosphate (13). Coupling of 7 and 13 with uridine 5'-monophosphomorpholidate in dry pyridine at approximately 37 degrees, followed by O-deacetylation, furnished the title compounds, respectively, isolated and characterized as their respective dilithium salts.

Synthesis of UDP-N-[1-14C]acetyl D-glucosamine and UDP-N-[1-14C]acetyl-D-galactosamine from [1-14C]acetate.

Procedures for the preparation of UDP-N-[1-14C]acetyl-D-glucosamine and UDP-N-[1-14C]acetyl-D-galactosamine with very high specific activities are described. The overall yield based on the amount of [1-14C]acetate used is greater than 80%. The N-acetyl-D-glucosamine-alpha-1-phosphate used in this synthesis is prepared by phosphorylation of tetraacetyl-D-N-acetylglucosamine with crystalline phosphoric acid. N-acetyl-D-glucosamine-alpha-1-phosphate is then deacetylated in anhydrous hydrazine with hydrazine sulfate as a catalyst. D-glucosamine-alpha-1-phosphate is N-acetylated with [14C]acetate using N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline as the coupling agent. The acetylated product is coverted to the UDP derivative with yeast UDP-N-acetyl-D-glucosamine pyrophosphorylase. UDP-N-[1-14C]acetylgalactosamine is prepared by acetylation of UDP-galactosamine using [1-14C]acetate and N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline. UDP-galactosamine is prepared enzymatically using galactokinase and galactose-1-phosphate uridyltransferase. The labeled products, isolated and characterized by ion-exchange and paper chromatography, were active as substrates in glycosyl transferase systems.