Synthesis of CMP-9''-modified-sialic acids as donor substrate analogues for mammalian and bacterial sialyltransferases

Cytidine-5'-monophospho-sialic acid (CMP-Neu5Ac) derivatives bearing a phenyl group in which the tether length between the phenyl group and the 9-position of Neu5Ac varied were synthesized and evaluated as substrates for sialyltransferases. In the synthesis of the compounds, a coupling reaction between methyl 5-acetamido-4,7,8-tri-O-acetyl-9-azido-3,5,9-trideoxy-beta-D-glycero-D-galacto-2-nonulopyranosonate and 2-cyanoethyl 2',3'-O,N4, triacetylcytidine-5'-yl N,N-diisopropylphosphoramidite was carried out and the phosphite derivative thus obtained was oxidized and then deprotected to yield CMP-9''-azido-Neu5Ac. Modification of the 9-amino group prepared by reduction of the azido groups was performed by the use of several phenyl-substituted alkylcarboxylic acid derivatives. Using these CMP-9''-modified-Neu5Ac analogues bearing the phenyl-substituted alkyl-amide group, sialyltransferase assays were performed with both rat liver alpha-(2-->6)-sialyltransferase and Photobacterium alpha-(2-->6)-sialyltransferase. These 9-modified analogues could be transferred to disaccharide acceptors, and a practical enzymatic synthesis using CMP-9''-modified-Neu5Ac yielded sialoside analogues and sialylglycoproteins in good yield. These experiments demonstrate that the Photobacterium sialyltransferase can be used in the synthesis of sialoside analogues having a large substituent at the 9-position of Neu5Ac.

Potential sialyltransferase inhibitors based on neuraminyl substitution by hetaryl rings

Replacement of the neuraminyl residue by a wide range of aryl rings in transition-state analogs of CMP-Neu5Ac led to readily accessible and potent inhibitors of alpha-(2-->6)- and alpha-(2-->3)-sialyltransferases. The synthesis of a series of potential sialyltransferase inhibitors in which the neuraminyl residue is replaced by hetaryl methylphosphonate residues (thiazole, benzothiazole, benzoxazole, benzothiophene and thiophene) is described in this paper.

Enzymatic synthesis of cytidine 5'-monophospho-N-acetylneuraminic acid

We have established an efficient method for enzymatic production of cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NeuAc) from inexpensive materials, N-acetylglucosamine (GlcNAc) and cytidine 5'-monophosphate (CMP). The Haemophilus influenzae nanE gene encoding GlcNAc 6-phosphate (GlcNAc 6-P) 2-epimerase and the Campylobacter jejuni neuB1 gene encoding N-acetylneuraminic acid (NeuAc) synthetase, both of whose products are involved in NeuAc biosynthesis, were cloned and co-expressed in Escherichia coli cells. We examined the synthesis of NeuAc from GlcNAc via GlcNAc 6-P, N-acetylmannosamine (ManNAc) 6-P, and ManNAc by the use of E. coli cells producing GlcNAc 6-P 2-epimerase and NeuAc synthetase, in expectation of biological functions of E. coli such as the supply of phosphoenolpyruvate (PEP), which is an essential substrate for NeuAc synthetase, GlcNAc phospholylation by the PEP-dependent phosphotransferase system, and dephospholylation of ManNAc 6-P. Eleven mM NeuAc was synthesized from 50 mM GlcNAc by recombinant E. coli cells with the addition of glucose as an energy source. Next we attempted to synthesize CMP-NeuAc from GlcNAc and CMP using yeast cells, recombinant E. coli cells, and H. influenzae CMP-NeuAc synthetase, and succeeded in efficient production of CMP-NeuAc due to a sufficient supply of PEP and efficient conversion of CMP to cytidine 5'-triphosphate by yeast cells.

Chemoenzymatic synthesis of CMP-sialic acid derivatives by a one-pot two-enzyme system: comparison of substrate flexibility of three microbial CMP-sialic acid synthetases

Three C terminal His6-tagged recombinant microbial CMP-sialic acid synthetases [EC 2.7.7.43] cloned from Neisseria meningitidis group B, Streptococcus agalactiae serotype V, and Escherichia coli K1, respectively, were evaluated for their ability in the synthesis of CMP-sialic acid derivatives in a one-pot two-enzyme system. In this system, N-acetylmannosamine or mannose analogs were condensed with pyruvate, catalyzed by a recombinant sialic acid aldolase [EC 4.1.3.3] cloned from E. coli K12 to provide sialic acid analogs as substrates for the CMP-sialic acid synthetases. The substrate flexibility and the reaction efficiency of the three recombinant CMP-sialic acid synthetases were compared, first by qualitative screening using thin layer chromatography, and then by quantitative analysis using high performance liquid chromatography. The N. meningitidis synthetase was shown to have the highest expression level, the most flexible substrate specificity, and the highest catalytic efficiency among the three synthetases. Finally, eight sugar nucleotides, including cytidine 5'-monophosphate N-acetylneuraminic acid (CMP-Neu5Ac) and its derivatives with substitutions at carbon-5, carbon-8, or carbon-9 of Neu5Ac, were synthesized in a preparative (100-200 mg) scale from their 5- or 6-carbon sugar precursors using the N. meningitidis synthetase and the aldolase.

Production of cytidine 5'-monophospho-N-acetyl-beta-D-neuraminic acid (CMP-sialic acid) using enzymes or whole cells entrapped in calcium pectate-silica-gel beads

The present study focuses on the application of immobilization technology to enzymic sugar syntheses. The paper describes an improved silica-alginate matrix established for entrapment and encapsulation. The replacement of alginate with pectate provided enhanced chemical resistance of the matrix, which allows the use of 1% (w/v) polyphosphate in reaction mixtures. Polylysine, a reagent for silica condensation, was replaced by a much cheaper alternative, namely polyethyleneimine. The proposed design was applied in the production of cytidine 5'-monophospho-N-acetyl-beta-D-neuraminic acid (CMP-sialic acid) by immobilized recombinant enzymes or Escherichia coli cells containing overexpressed enzymes. A comparison between these two strategies was made. On the basis of the results we conceptualized a system to synthesize sialyloligosaccharides by using a biocatalyst entrapped in calcium pectate-silica gel beads.

Production of cytidine 5'-monophosphate N-acetylneuraminic acid using recombinant Escherichia coli as a biocatalyst

An Escherichia coli strain expressing three recombinant enzymes, i.e., cytidine 5'-monophosphate (CMP) kinase, sialic acid aldolase and cytidine 5'-monophosphate N-acetylneuraminic acid (CMP-NeuAc) synthetase, was utilized as a biocatalyst for the production of CMP-NeuAc. Both recombinant E. coli extract and whole cells catalyzed the production of CMP-NeuAc from CMP (20 mM), N-acetylmannosamine (40 mM), pyruvate (60 mM), ATP (1 mM), and acetylphosphate (60 mM), resulting in 90% conversion yield based on initial CMP concentration used. It was confirmed that endogenous acetate kinase can catalyze not only the ATP regeneration in the conversion of CMP to CDP but also the conversion of CDP to CTP. On the other hand, endogenous pyruvate kinase and polyphosphate kinase could not regenerate ATP efficiently. The addition of exogenous acetate kinase to the reaction mixture containing the cell extract increased the conversion rate of CMP to CMP-NeuAc by about 1.5-fold, but the addition of exogenous inorganic pyrophosphatase had no influence on the reaction. This E. coli strain could also be employed as an enzyme source for in situ regeneration of CMP-NeuAc in a sialyltransferase catalyzed reaction. About 90% conversion yield of alpha2,3-sialyl-N-acetyllactosamine was obtained from N-acetyllactosamine (20 mM), CMP (2 mM), N-acetylmannosamine (40 mM), pyruvate (60 mM), ATP (1 mM), and acetyl phosphate (80 mM) using the recombinant E. coli extract and alpha2,3-sialyltransferase.

A convenient synthesis of nucleoside monophosphate-N-acetylneuraminic acids (NMP-Neu5Ac)

Reaction of sialyl phosphites 2a,b with acetyl-protected ribonucleoside monophosphates 3C, 3U, 3A and 3G furnished without addition of a catalyst directly the corresponding beta-configurated sialyl ribonucleoside monophosphates 4C, 4U, 4A and 4G, respectively. Treatment of these compounds with sodium methanolate in methanol and sodium hydroxide afforded the disodium salts of CMP-Neu5Ac (1C), UMP-Neu5Ac (1U), AMP-Neu5Ac (1A), and GMP-Neu5Ac (1G).

Chemoenzymatic galactosialylation with integrated cofactor regeneration

As a precursor for the chemical synthesis of sialylated oligosaccharides, the trisaccharide glycoside Neu5Ac alpha (2-8)Gal beta (1-4)GlcNAc beta (1-O)-pent-4-ene was synthesized starting from GlcNAc beta (1-O)-pent-4-ene, UDP-glucose and N-acetylneuraminic acid in a one pot reaction employing galactosyltransferase and alpha (2-6)sialyltransferase in a complete cofactor regeneration system.

The preparation of CMP-sialic acids by using CMP-acylneuraminate synthase from frog liver immobilized on sepharose 4B

A preparation of frog liver CMP-acylneuraminate synthase (2-10-fold enriched over the homogenate) obtained from DEAE-Sephadex A-50 chromatography of a 105,000g liver supernatant was bound to Sepharose 4B by the CNBr method. The enzyme retained 80-100% activity on binding and showed similar properties to the purified soluble enzyme from the same source with respect to Km, pH optimum and inhibition. The bound enzyme was stable to temperatures above 40 degrees C, in contrast with the soluble enzyme, and could be stored for 4 months at 2 degrees C with loss of 20% activity. The bound enzyme was used preparatively for the synthesis of radioactive and non-radioactive CMP-N-acetylneuraminic acid and CMP-N-glycolloylneuraminic acid. With suitable substrate concentrations and ratios, yields of 80% and over can be achieved.