Deamination of Carbohydrate Amines and Related Compounds

Structural determination of the cell wall polysaccharide LCPS-1 in Lacticaseibacillus paracasei strain Shirota YIT 9029

The neutral polysaccharides LCPS-1 and LCPS-2 play functional roles in the cell wall of the lactic acid bacterium Lacticaseibacillus paracasei strain Shirota YIT 9029 (LcS; formerly Lactobacillus casei strain Shirota YIT 9029), which has long been used as a probiotic food product. Studies have shown that LCPS-1 is associated with the immunomodulatory functions of LcS. We hypothesized that the structure of LCPS-1 is crucial for elucidating the mechanism of action of LcS on host immune responses and aimed to solve the undetermined primary structure of LCPS-1. Our results showed that LCPS-1 has a molecular weight of >400 kDa and is composed of Glc, Rha, Gal, and GlcNAc, with a repeating structure. Using limited degradation reactions, including controlled Smith and deamination degradations, we obtained key fragments with low molecular weight. Subsequently, their structures were analyzed using NMR spectra and other analytical techniques. Further, we integrated the results for each key fragment to derive the complete structure of LCPS-1. Our results indicated that the most probable structure of LCPS-1 is composed of two types of units (X, Y), each with a basic structure of seven sugars in which the C2-position of Rha is substituted with an acetyl group. The structure of X is {6[Glcβ1-2] Galα1-3[2-OAc] Rhaβ1-4Glcβ1-4[Rhaα1-3] [Glcα1-6] Glcβ1-} and that of Y is {6[Glcβ1-2] Galα1-3[2-OAc] Rhaβ1-4Glcβ1-4[Rhaα1-3] [Glcα1-6)] GlcNAcβ1-}, which can be expressed as (X₆Y₁₂)_n. In this study, we identified the primary structure of LCPS-1, and our results may enable an improved understanding of the immunomodulatory abilities of LcS.

Use of Phenols as Nucleophiles in the Zbiral Oxidative Deamination of N-Acetyl Neuraminic Acid: Isolation and Characterization of Tricyclic 3-Keto-2-deoxy-nonulosonic Acid (KDN) Derivatives via an Intermediate Vinyl Diazonium Ion

It is well established that the N-nitrosoamide derived from peracetylated derivatives of N-acetyl neuraminic acid on treatment with a mixture of sodium isopropoxide and trifluoroethanol, followed by the addition of acetic acid, gives an oxidative deamination product, in which the AcN(NO)-C5 bond is replaced with a AcO-C5 bond with the retention of configuration, affording a practical synthesis of 2-keto-3-deoxy-d-glycero-d-galactononulosonic acid (KDN) derivatives. Application of other strong acids, including hydrogen fluoride, thioacetic acid, trifluoromethanesulfonic acid, and hydrogen azide, functions similarly to afford KDN derivatives functionalized at the 5-position. We describe our attempts to extend the range of useful nucleophiles employed in this oxidative deamination process to include phenols and thiophenols, resulting in the discovery of a new branch of the general reaction and the formation of a series of products resulting from substitution of the 5-acetamido group and of the 4-acetoxy group from neuraminic acid. A mechanistic rationale for the formation of these products is advanced according to which, in the absence of acids of pKa ≤ 8, the intermediate diazonium ion resulting from the elimination of acetic acid and nitrogen from the nitrosoacetamide undergoes elimination of acetic acid from the 4-position to afford a highly electrophilic alkenediazonium ion. Reversible conjugate addition of the nucleophile to the 4-position then initiates the reaction cascade leading to the ultimate products.

Synthesis of saccharocin from apramycin and evaluation of its ribosomal selectivity

We describe a straightforward synthesis of the apramycin biosynthetic precursor saccharocin from apramycin by regioselective partial azidation followed by stereoretentive oxidative deamination. Saccharocin was found to exhibit excellent selectivity for inhibition of the bacterial ribosome over the eukaryotic ribosomes indicating that its presence as a minor impurity in apramycin itself should not be problematic in the development of the latter as a clinical candidate.

N6', N6''', and O4' Modifications to Neomycin Affect Ribosomal Selectivity without Compromising Antibacterial Activity

The synthesis of a series of neomycin derivatives carrying the 2-hydroxyethyl substituent on N6' and/or N6‴ both alone and in combination with a 4'-O-ethyl group is described. By means of cell-free translation assays with wild-type bacterial ribosomes and their hybrids with eukaryotic decoding A sites, we investigate how individual substituents and their combinations affect activity and selectivity at the target level. In principle, and as shown by cell-free translation assays, modifications of the N6' and N6‴ positions allow enhancement of target selectivity without compromising antibacterial activity. As with the 6'OH aminoglycoside paromomycin, the 4'-O-ethyl modification affects the ribosomal activity, selectivity, and antibacterial profile of neomycin and its 6'-N-(2-hydroxyethyl) derivatives. The modified aminoglycosides show good antibacterial activity against model Gram-positive and Gram-negative microbes including the ESKAPE pathogens Staphylococcus aureus, Klebsiella pneumoniae, Enterobacter cloacae, and Acinetobacter baumannii.

Stereoselective Synthesis of 5-epi-α-Sialosides Related to the Pseudaminic Acid Glycosides. Reassessment of the Stereoselectivity of the 5-Azido-5-deacetamidosialyl Thioglycosides and Use of Triflate as Nucleophile in the Zbiral Deamination of Sialic Acids

With a view to the eventual synthesis of glycosyl donors for the stereocontrolled synthesis of pseudaminic acid glycosides, the stereocontrolled synthesis of a d-glycero-d-gulo sialic acid adamantanylthioglycoside carrying an axial azide at the 5-position is described. The synthesis employs levulinic acid as nucleophile in the oxidative deamination of an N-acetylneuraminic acid thioglycoside leading to the formation of a 3-deoxy-d-glycero-d-galacto-2-nonulosonic acid (KDN) derivative selectively protected as 5-O-levulinate. Replacement of the levulinate by triflate enables introduction of the axial azide and hence formation of the glycosyl donor. A shorter synthesis uses trifluoromethanesulfonate as nucleophile in the oxidative deamination step when the 5-O-triflyl KDN derivative is obtained directly. Glycosylation reactions conducted with the 5-azido-d-glycero-d-gulo-configured sialyl adamantanylthioglycoside at -78 °C are selective for the formation of the equatorial glycosides, suggesting that the synthesis of equatorial pseudaminic acid glycosides will be possible as suitable donors become available. A comparable N-acetylneuraminic acid adamantanylthioglycoside carrying an equatorial azide at the 5-position was also found to be selective for equatorial glycoside formation under the same conditions, suggesting that reinvestigation of other azide-protected NeuAc donors is merited. Glycosylation stereoselectivity in the d-glycero-d-gulo series is discussed in terms of the side-chain conformation of the donor.

Structure of the acidic O-specific polysaccharide from Proteus vulgaris O39 containing 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid

The O-specific polysaccharide of Proteus vulgaris O39 was found to contain a new acidic component of Proteus lipopolysaccharides, 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid (di-N-acetylpseudaminic acid, Pse5Ac7Ac). The following structure of the polysaccharide was determined by NMR spectroscopy, including 2D 1H,(1)H COSY, TOCSY, ROESY, and 1H,(13)C HMQC experiments, along with selective cleavage of the polysaccharide by solvolysis with anhydrous trifluoromethanesulfonic (triflic) acid: -->8)-beta-Psep5Ac7Ac-(2-->3)-alpha-L-FucpNAc-(1-->3)-alpha-D-GlcpNAc-(1--> The structure established is unique among the O-specific polysaccharides, which is in accordance with classification of the strain studied into a separate Proteus serogroup.

Structural and serological studies of the related O-specific polysaccharides of Proteus vulgaris O21 and Proteus mirabilis O48 having oligosaccharide-phosphate repeating units

The O-specific polysaccharide chains (O-antigens) of the lipopolysaccharides (LPSs) of Proteus mirabilis O48 and Proteus vulgaris O21 were found to have tetrasaccharide and pentasaccharide repeating units, respectively, interlinked by a glycosidic phosphate. Polysaccharides and an oligosaccharide were derived from the LPSs by various degradation procedures and studied by 1H and 13C NMR spectroscopy, including 2D COSY, TOCSY, NOESY, H-detected 1H,13C and 1H,31P HMQC experiments. The following related structures of the repeating units of the O-antigens were established (top: Proteus mirabilis O48; bottom: Proteus vulgaris O21) The O-specific polysaccharide of P. vulgaris O21 has the same structure as that of Hafnia allvei 744 and PCM 1194 [Petersson C., Jachymek, W., Klonowska, A., Lugowski, C., Niedziela, T. & Kenne, L. (1997) Eur. J. Biochem., 245, 668-675], except that the GlcN residue carries the N-acetyl rather than the N-[(R)-3-hydroxybutyryl] group. Serological investigations confirmed the close relatedness of the Proteus and Hafnia O-antigens studied.

Polycarboxylates inhibit the glucan-binding lectin of Streptococcus sobrinus

Polycarboxylates, such as carboxymethylcellulose and hyaluronan, were found to be reversible inhibitors of the glucan-binding lectin of Streptococcus sobrinus. When the carboxylate groups were coupled to ethylenediamine, or reduced with carbodiimide-borohydride, inhibitory powers were lost. Similarly, N-deacetylated hyaluronan had poor inhibitory powers, probably due to the introduction of positive charges into the polymer. Other polymers, such as chondroitin sulfates, dextran sulfate, fetuin, heparin were not inhibitors. It appears that inhibition is based on repeating carboxylates, free of influence from ammonium groups. Such polymers have the property of complexing with metals. Earlier studies had concluded that the streptococcal lectin depended on manganese for activity. It is likely the carboxymethylcellulose and hyaluronan perturb essential metal coordination centers in the lectin. Polycarboxylates may have value in oral health care by acting on glucan-dependent microbial adhesion and biofilm formation.

ACTH-mediated glucocorticoid and mineralocorticoid production is inhibited by an inositolphosphoglycan and a glycosylphosphatidylinositol-phospholipase C is activated by the hormone in mammalian adrenocortical cells

In the present paper, we report that an inositolphosphoglycan (IPG), derived from a Trypanosoma cruzi glycoinositolphosphoceramide (LPPG), is able to inhibit ACTH-mediated accumulation of a glucocorticoid, cortisol, in calf adrenocortical cells. This IPG is also able to inhibit the stimulation by ACTH of the production of the main glucocorticoid, corticosterone and the main mineralocorticoid, aldosterone, in rat adrenocortical cells. Nitrous acid deamination confirmed that IPG is responsible for this inhibition. In order to study the involvement of glycosylphosphatidylinositol (GPI) in ACTH response in rat adrenal cortex, the activation of a phospholipase that hydrolyzes GPI (GPI-PLC) was evaluated. It was found that the release of alkaline phosphatase, a GPI-anchored enzyme, to the extracellular medium is increased in rat adrenocortical cells by ACTH treatment. In addition, ACTH stimulates the release of ceramide from the glycoinositolphosphoceramide purified from T. cruzi. These data suggest that ACTH activates a GPI-PLC in rat adrenal cortex, which is in agreement with our previous data in calf adrenocortical cells; thus, the hydrolysis of GPI provoked by ACTH takes place in different mammals and the IPG released could inhibit ACTH-mediated synthesis of aldosterone, corticosterone and cortisol.

The intercellular adhesin involved in biofilm accumulation of Staphylococcus epidermidis is a linear beta-1,6-linked glucosaminoglycan: purification and structural analysis

The primary attachment to polymer surfaces followed by accumulation in multilayered cell clusters leads to biofilm production of Staphylococcus epidermidis, which is thought to contribute to virulence in biomaterial-related infections. We purified a specific polysaccharide antigen of biofilm-producing S. epidermidis 1457 and RP62A, which was recently shown to have a function in the accumulative phase of biofilm production by mediating intercellular adhesion (D. Mack, M. Nedelmann, A. Krokotsch, A. Schwarzkopf, J. Heesemann, and R. Laufs, Infect. Immun. 62:3244-3253, 1994). Following Sephadex G-200 gel filtration, this antigen was separated by Q-Sepharose chromatography into a major polysaccharide, polysaccharide I (> 80%), which did not bind to Q-Sepharose, and a minor polysaccharide, polysaccharide II (< 20%), which was moderately anionic. As shown by chemical analyses and nuclear magnetic resonance spectroscopy, polysaccharide I is a linear homoglycan of at least 130 beta-1,6-linked 2-deoxy-2-amino-D-glucopyranosyl residues. On average, 80 to 85% of them are N acetylated; the rest are non-N-acetylating and positively charged. Chain cleavage by deamination with HNO2 revealed a more or less random distribution of the non-N-acetylated glucosaminyl residues, with some prevalence of glucosaminyl-rich sequences. Cation-exchange chromatography separated molecular species whose content of non-N-acetylated glucosaminyl residues varied between 2 and 26%. Polysaccharide II is structurally related to polysaccharide I but has a lower content of non-N-acetylated D-glucosaminyl residues and contains phosphate and ester-linked succinate, rendering it anionic. Enzyme-linked immunosorbent assay inhibition with various monosaccharides revealed the beta-anomeric form and the acetylated amino group of the D-glucosaminyl residues as important for reactivity with the specific antiserum. The unbranched polysaccharide structure favors long-range contacts and interactions between polysaccharide strands and the cell wall and/or lectin-like proteins, leading to intercellular adhesion and biofilm accumulation. The structure of the polysaccharide is, so far, considered to be unique and, according to its function, is referred to as S. epidermidis polysaccharide intercellular adhesin (PIA).

Molecular weight manipulation of chitosan. I: Kinetics of depolymerization by nitrous acid

The kinetics of the depolymerization of chitosan in dilute aqueous HCl solutions by nitrous acid were studied. The rate of depolymerization is independent of the molecular weight of chitosan, first order with respect to the concentrations of both nitrous acid and glucosamine moieties, not catalysed by either hydrogen or chloride ions, and Arrhenius temperature dependent. Chitosan exhibits significantly decreased reactivity as the degree of deacetylation of the polymer increases. These results are consistent with a depolymerization reaction mechanism in which the rate-limiting step is nitrosation of the unprotonated amine by nitrous acidium ion.

The structure of the cyclic enterobacterial common antigen (ECA) from Yersinia pestis

Two antigenic acidic polysaccharides related to enterobacterial common antigen (ECA) were isolated from a vaccine strain of a pathogenic microorganism Yersinia pestis. The low molecular weight polysaccharide (LMP) is composed of equal amounts of 2-acetamido-2-deoxy-D-mannuronic acid, 4-acetamido-4,6-dideoxy-D-galactose (Fuc4NAc), and 2-amino-2-deoxy-D-glucose which is partially N- and partially 6-O-acetylated. The structure of the trisaccharide repeating unit was established by analyses of LMP and the completely N-acetylated LMP (LMP-NAc) using 1H and 13C NMR spectroscopy, including 2D COSY and 1D NOE spectroscopy. Deamination of LMP with nitrous acid gave a set of oligomers terminated with 2,5-anhydromannose and ranging from tri- to dodeca-saccharides, thus indicating a random distribution of free amino groups. FABMS analyses of LMP and LMP-NAc showed that LMP consists mainly of the cyclic tetramer of the trisaccharide repeating unit together with a small amount of the cyclic trimer and a very small amount of the cyclic pentamer and has, thus, the following structure: [formula: see text] where R is Ac or H (approximately 1:1), R' is Ac or H (approximately 1:4), and n = 4 (major), 3, 5 (minor). Small proportions of the linear trimer and the linear tetramer were also detected in the preparations. The high molecular weight polysaccharide is linear and has the same (or a very similar) repeating unit as LMP.

Structure of the core oligosaccharide in the lipopolysaccharide isolated from Aeromonas salmonicida ssp. salmonicida

The core oligosaccharide isolated from the lipopolysaccharide of Aeromonas salmonicida ssp. salmonicida has been investigated by methylation analysis, NMR spectroscopy (13C and 1H), oxidation with periodate and chromium trioxide, and Smith degradation. The following structure is proposed: [Formula: see text]

Application of high-resolution n.m.r. spectroscopy to the elucidation of the structure of the specific capsular polysaccharide of Streptococcus pneumoniae type 7F

The specific capsular polysaccharide of Streptococcus pneumoniae type 7F (American type 51) is a high-molecular-weight neutral polymer composed of 2-acetamido-2-deoxy-D-galactose, 2-acetamido-2-deoxy-D-glucose, D-glucose, D-galactose, L-rhamnose, and 2-O-acetyl-L-rhamnose residues. N.m.r. spectroscopy (1H and 13C), in conjunction with composition and methylation analyses, and periodate oxidation data, showed the polysaccharide to be a branched polymer with a repeating heptasaccharide unit having the following structure. (formula; see text)

Analysis of linkage positions in 2-acetamido-2-deoxy-D-glucopyranosyl residues by the reductive-cleavage method

The fate of methylated 2-acetamido-2-deoxy-D-glucopyranosyl residues under reductive-cleavage conditions was investigated by using methyl 2-(acetylmethylamino)-2-deoxy-3,4,6-tri-O-methyl-beta-D-glucopyran oside (1), its alpha anomer (8), and fully methylated lacto-N-tetraitol as test compounds. Treatment of 1 with triethylsilane and trimethylsilyl trifluoromethanesulfonate in dichloromethane gave rise to (1,2-dideoxy-3,4,6-tri-O-methyl-alpha-D-glucopyrano)-2,3-dimethyl- [2,1-d]-2- oxazolinium trifluoromethanesulfonate. Quenching of the reaction by addition of aqueous sodium hydrogencarbonate resulted in hydrolysis of the oxazolinium salt. Compound 8 was fully stable to reductive-cleavage conditions. Thus, participation by the 2-acetamido group is necessary for glycosidic carbon-oxygen bond-cleavage to occur. Treatment of methyl 2-deoxy-2-(ethylmethylamino)-3,4,6-tri-O-methyl-alpha,beta-D-gluco pyranoside under reductive-cleavage conditions resulted in some anomerization, but neither hydrolysis nor reductive cleavage of the glycosidic carbon-oxygen bond was observed, as expected. Reductive cleavage of fully methylated lacto-N-tetraitol gave the products predicted on the basis of these and prior model studies, including 3-O-acetyl-2-(acetylmethylamino)-2-deoxy-4,6-di-O-methyl-D-glucopy ranose derived from the 3-linked 2-acetamido-2-deoxy-beta-D-glucopyranosyl residue.

Insulin-stimulated hydrolysis of a novel glycolipid generates modulators of cAMP phosphodiesterase

Insulin action may involve the intracellular generation of low molecular weight substances that modulate certain key enzymes. The production of two substances that regulate the activity of adenosine 3',5'-monophosphate phosphodiesterase was evaluated in cultured myocytes by incorporation of radiolabeled precursors. Insulin caused the rapid hydrolysis of a chemically undefined membrane glycolipid, resulting in the production of two related complex carbohydrates as well as diacylglycerol. Both the glycolipid precursor and the aqueous products were monitored by labeling with radioactive inositol and glucosamine. Depletion of the labeled precursor and the appearance of labeled water-soluble products and diacylglycerol occurred within 30 seconds after hormone treatment and was followed by rapid resynthesis of the precursor. The aqueous products that were radioactively labeled appeared chromatographically and electrophoretically identical to phosphodiesterase modulating activities produced by insulin from the same cells. The purified radiolabeled and bioactive substances had similar chemical properties. Hydrolysis of the glycolipid precursor and subsequent generation of products could be reproduced by incubation of extracted lipids with a phosphatidylinositol-specific phospholipase C. These studies suggest that insulin stimulates an endogenous, selective phospholipase C activity that hydrolyzes a novel glycolipid, resulting in the generation of a complex carbohydrate-phosphate substance containing inositol and glucosamine that may mediate some of the actions of the hormone.

Structural determination of the capsular polysaccharide of Neisseria meningitidis group I: a two-dimensional NMR analysis

The capsular polysaccharide antigen of Neisseria meningitidis group I was isolated by Cetavlon precipitation and purified by ion-exchange chromatography. The structure of the I polysaccharide was determined largely by comprehensive proton and carbon-13 nuclear magnetic resonance studies in which both one-dimensional and two-dimensional experiments were carried out directly on the I polysaccharide. The I polysaccharide is composed of the repeating unit----4)alpha-L-GulpNAcA(1----3)[4-OAc]beta-D-ManpNA-cA(-- --in which the former residue adopts the 4C1 (L) conformation and the latter residue adopts the 4C1 (D) conformation. The one-bond coupling between the anomeric carbon and proton (1J13C,H) of the 2-acetamido-2-deoxy-beta-D-mannuronopyranosyl residue is not consistent with its beta-D configuration. This anomalous value of 1J13C,H for this residue is due to through-space anisotropy effects on its anomeric proton, generated by the proximity of the carboxyl group of the neighboring 2-acetamido-2-deoxy-alpha-L-guluronopyranosyl residue. The O-acetyl substituents of the I polysaccharide are essential for its antigenicity to group I polysaccharide-specific antibodies.

Structural studies of the Vibrio cholerae O-antigen

The dominant part of the O-antigen of Vibrio cholerae is a homopolysaccharide composed of (1 leads to 2)-linked 4-amino-4,6-dideoxy-alpha-D-mannopyranosyl (perosaminyl) residues, in amino groups of which are acylated by 3-deoxy-L-glycero-tetronic acid. Most of the amino sugar is decomposed during acid hydrolysis. Treatment of the polymer with anhydrous hydrogen fluoride, which cleaves the glycosidic linkages but does not cause N-deacylation, followed by acid hydrolysis under mild conditions, produced the monomer in good yield. Treatment of the N-deacylated polysaccharide with nitrous acid caused deamination with concomitant rearrangements, typical of 4-amino-4-deoxyhexopyranosyl residues in which the amino group occupies an equatorial position.

The carbohydrate-protein binding region in keratan sulfate from bovine cornea. I. Isolation and partial characterization

We present a defined chemical method for the isolation of the oligosaccharide linking the protein to the disaccharide units of keratan sulfate from bovine corneas. 1) Hydrazinolysis removes the amino acids from the peptido keratan sulfate, and leads to deacetylation of the glucosamine residues but does not split off the sulfate groups. 2) NaB3H4 reduction selectively labels the reducing terminal glucosamine of the chain by converting it to [3H]glucosaminitol. 3) Nitrous acid deamination splits the glycosidic bonds of glucosamine and converts this sugar into 2,5-anhydromannose but also leads to several derivatives of the free terminal [3H]glucosaminitol. 4) Na12CN treatment stabilizes the reactive 2,5-anhydromannose and the terminal compounds containing aldehyde groups in a cyanhydrin reaction. 5) The oligosaccharide structure between the glucosamine residue at the reducing end and the first glucosamine of the disaccharide chain is not degraded by this procedure and is obtained intact and in labelled form. The data so far obtained on this part of the cornea keratan sulfate show that it is heterogeneous and contains besides the terminal glucosamine, mannose and fucose in a similar ratio as found in undegraded keratan sulfate. The predominant compound probably contains three neutral sugar residues.

Structural studies of the capsular polysaccharide from Streptococcus pneumoniae type 1

The capsular polysaccharide from Streptococcus pneumoniae type 1 is composed of D-galactopyranosyluronic acid residues and 2-acetamido-4-amino-2,4,6-trideoxy-D-galactopyranosyl residues. The latter sugar, previously unknown in Nature, was not isolated but was identified from the products obtained on deamination of the polymer. Using n.m.r. spectroscopy, methylation analysis, and Smith degradation as the principal methods of structural investigation, it is concluded that the polysaccharide is composed of trisaccharide repeating-units having the structure: leads to 3)-alpha-Sugp-(1 leads to 4)-alpha-D-GalpA-(1 leads to 3)-alpha-D-GalpA-(1 leads to, in which Sug denotes the new sugar.