# Patent

## Title
Synthesis of sialooligosaccharide derivatives

## Abstract

The invention relates to a method for the synthesis of compounds of general formula (1A) and salts thereof wherein one of the R groups is an α-sialyl moiety and the other is H, X1 represents a carbohydrate linker, A is a D-glucopyranosyl unit optionally substituted with fucosyl, R1 is a protecting group that is removable by hydrogenolysis, the integer m is 0 or 1, by a transsialidation reaction.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the National Phase entry of PCT/EP2011/062184, which claims priority to European Patent Application No. 11166036.1, filed May 13, 2011 and Great Britain Patent Application No. 1012036.8, filed Jul. 16, 2010. The content of these applications is incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
The present invention relates to the enzymatic synthesis of sialooligosaccharide glycosides, and novel precursors and products taking part in the synthesis.
BACKGROUND OF THE INVENTION
Sialic acids are derivatives of the nine-carbon sugar neuraminic acid and encompass three parent molecules, N-acetyl-(Neu5Ac), N-glycolyl-(Neu5Gc) and deamino-neuraminic acid (3-deoxy-D-glycero-D-galacto-nonulosonic acid, KDN), which can be substituted at C-4, C-7, C-8 and C-9 by various moieties. They have many major biological roles, ranging from embryogenesis to neural plasticity to pathogen interactions. Although they may rarely occur in free form, they are usually found in chemical covalent linkage at the non-reducing terminus or in internal positions of oligosaccharide side-chains of glycoproteins and glycolipids. The linkages of sialic acids in which they are bound to penultimate sugars such as galactose, N-acetyl-galactosamine and N-acetyl-glucosamine are most commonly α-2,3- and α-2,6-ketosidic bonds.
Among sialoglycoconjugates, sialylated human milk oligosaccharides are of great importance which is directly linked to their unique biological activities such as antibacterial, antiviral, immune system and cognitive development enhancing activities. Sialylated human milk oligosaccharides are found to act as prebiotics in the human intestinal system helping to develop and maintain the intestinal flora. Furthermore they have also proved to be anti-inflammatory, and therefore these compounds are attractive components in the nutritional industry for the production of, for example, infant formulas, infant cereals, clinical infant nutritional products, toddler formulas, or as dietary supplements or health functional food for children, adults, elderly or lactating women, both as synthetically composed and naturally occurring compounds and salts thereof. Likewise, the compounds are also of interest in the medicinal industry for the production of therapeutics. In the human milk oligosaccharides the sialic acid residue is always linked to the terminal 3-O- and/or 6-O-position(s) of D-galactose via α-glycosidic linkage.
The availability of naturally occurring sialylated human milk oligosaccharides is limited. Mature human milk is the natural milk source that contains the highest concentrations of milk oligosaccharides (12-14 g/l), other milk sources are cow's milk (0.01 g/l), goat's milk and milk from other mammals. This low natural availability and difficult isolation methods are important motivations for the development of biotechnological and chemical methodologies for the production of these attractive compounds.
Approximately 200 HMOs have been detected from human milk by means of combination of techniques including microchip liquid chromatography mass spectrometry (HPLC Chip/MS) and matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FT ICR MS) (Ninonuevo et al. J. Agric. Food Chem. 54, 7471 (2006)), from which to date at least 115 oligosaccharides have been structurally determined (Urashima et al.: Milk Oligosaccharides, Nova Medical Books, NY, 2011). These human milk oligosaccharides can be grouped into 13 core units (Table 1). About a quarter of oligosaccharides contains sialic acid.







TABLE 1







13 different core structures of human milk oligosaccharides (HMOs)









No
Core name
Core structure












1
lactose (Lac)
Galβ1-4Glc


2
lacto-N-tetraose (LNT)
Galβ1-3GlcNAcβ1-3Galβ1-4Glc


3
lacto-N-neotetraose
Galβ1-4GlcNAcβ1-3Galβ1-4Glc



(LNnT)



4
lacto-N-hexaose (LNH)
Galβ1-3GlcNAcβ1-3(Galβ1-4GlcNAcβ1-6)Galβ1-4Glc


5
lacto-N-neohexaose
Galβ1-4GlcNAcβ1-3(Galβ1-4GlcNAcβ1-6)Galβ1-4Glc



(LNnH)



6
para-lacto-N-hexaose
Galβ1-3GlcNAcβ1-3Galβ1-4GlcNAcβ1-3Galβ1-4Glc



(para-LNH)



7
para-lacto-N-neohexaose
Galβ1-4GlcNAcβ1-3Galβ1-4GlcNAcβ1-3Galβ1-4Glc



(para-LNnH)



8
lacto-N-octaose (LNO)
Galβ1-3GlcNAcβ1-3(Galβ1-4GlcNAcβ1-3Galβ1-




4GlcNAcβ1-6)Galβ1-4Glc


9
lacto-N-neooctaose
Galβ1-4GlcNAcβ1-3(Galβ1-3GlcNAcβ1-3Galβ1-



(LNnO)
4GlcNAcβ1-6)Galβ1-4Glc


10
Iso-lacto-N-octaose
Galβ1-3GlcNAcβ1-3(Galβ1-3GlcNAcβ1-3Galβ1-



(iso-LNO)
4GlcNAcβ1-6)Galβ1-4Glc


11
para-lacto-N-octaose
Galβ1-3GlcNAcβ1-3 Galβ1-4GlcNAcβ1-3Galβ1-



(para-LNO)
4GlcNAcβ1-3Galβ1-4Glc


12
Lacto-N-decaose
Galβ1-3GlcNAcβ1-3[Galβ1-4GlcNAcβ1-3(Galβ1-



(LND)
4GlcNAcβ1-6)Galβ1-4GlcNAcβ1-6]Galβ1-4Glc


13
Lacto-N-neodecaose
Galβ1-3GlcNAcβ1-3[Galβ1-3GlcNAcβ1-3(Galβ1-



(LNnD)
4GlcNAcβ1-6)Galβ1-4GlcNAcβ1-6]Galβ1-4Glc









The isolation of sialooligosaccharides form human and other mammals' milk is rather difficult even in milligram quantities due to the presence of a large number of similar oligosaccharides. To date only analytical HPLC methodologies have been developed for the isolation of some sialooligosaccharides from natural source.
The synthesis of complex sialooligosaccharides follows multistep synthetic pathways utilising protection and deprotection strategies. Stereoselective chemical synthetic processes can become very complicated due to the extensive use of protecting groups. These strategies give sialylated oligosaccharides via stereoselective O-sialylation of appropriate protected glycosyl acceptors using glycosylhalide, thioglycoside or diethylphosphite donor activations. The use of either very expensive or very toxic chemicals for the sialylation such as mercury cyanide, mercury bromide and silver carbonate is one of the reasons that make these methodologies less attractive. Inefficient stereocontrol and/or poor yields likewise make(s) the strategies less suitable for further developments. Additionally, these strategies are characterized by severe purification difficulties.
In the case of enzymatic production of sialooligosaccharides, sialyltransferases and sialidases have been the preferred enzymes used. These complex enzymatic systems represent very expensive methodologies for scale-up production and difficult purification protocols are likewise a hindrance for further technology developments. Sialidases could not be used successfully in large scale production methodologies due to low yields and lack of regio- and stereoselectivity. Although in some cases sialyltransferase enzymes are found to be effective in the synthesis of complex sialooligosaccharides (e.g. the synthesis of 1-O-β-benzyl glycoside of 3′-O—(N-acetyl-neuraminosyl)-lactose sodium salt: WO 96/32492; the synthesis of 1-O-β-(4,5-dimethoxy-2-nitro)-benzyl glycoside of 3′-O—(N-acetyl-neuraminosyl)-lactose sodium salt: Cohen et al. J. Org. Chem. 65, 6145 (2000)), the need of CMP-activated sialic acid (cytidine 5′-monophosphosialic acid) as sialyl donor—whose availability is, in fact, rather limited—for transferring the sialic acid portion to the acceptor oligosaccharide restricts their usefulness.
The ability of N-acetyl-lactosamine benzyl glycoside and benzyl glycosides of mucin oligosaccharides from T. cruzi to act as substrate in transsialidase reaction has been studied (Lubineau et al. Carbohydr. Res. 300, 161 (1997); Agusti et al. Bioorg. Med. Chem. 15, 2611 (2007)).
Regioselective sialidation of unprotected or anomerically substituted galactose, lactose or N-acetyl-lactosamine derivatives by means of sialidases in poor yield has been reported (Thiem et al. Angew. Chem. Int. Ed. Eng. 30, 1503 (1991); Schmidt et al. Chem. Comm. 1919 (2000); Schmidt et al. J. Org. Chem. 65, 8518 (2000)).
Some biotechnological methodologies are also described using genetically modified bacteria, yeasts or other microorganisms. Such methods have serious drawbacks in regulatory processes due to limiting commercialisation opportunities.
Sialoglycoconjugates are known to be unstable under certain reaction conditions, such as to acid and base. Indeed, they are able to self-hydrolyse. Accordingly, conditions for preparation and purification of these compounds must be carefully selected.
In summary, isolation technologies have never been able to provide large quantities of sialooligosaccharides due to the large number of oligosaccharides present in the pool of natural origin, e.g. in human milk. Additionally, the presence of regioisomers characterized by extremely similar structures further made separation technologies unsuccessful. Enzymatic methodologies suffer from the low availability of enzymes, extremely high sugar nucleotide donor prices and regulatory difficulties due to the use of enzymes produced in genetically modified organisms. The preparation of oligosaccharides via biotechnology has huge regulatory obstacles due to the potential formation of several unnatural glycosylation products. Generally, all the chemical methods developed for the synthesis of sialooligosaccharides have several drawbacks which prevented the preparation of even multigram quantities of the target compounds (e.g. see the synthesis of 3′-O- and 6′-O-(N-acetyl-neuraminosyl)-lactose through the corresponding benzyl glycoside: Rencurosi et al. Carbohydr. Res. 337, 473 (2002)).
During the past decades the interest in the preparation and commercialisation of sialylated human milk oligosaccharides has been increasing steadily. There is still a need for novel methodologies which can simplify preparation and overcome or avoid purification problems encountered in prior art methods.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to a method for the synthesis of compounds of general formula 1A and salts thereof.




wherein one of the R groups is an α-sialyl moiety and the other is H, X1 represents a carbohydrate linker, A is a D-glucopyranosyl unit optionally substituted with fucosyl, R1 is a protecting group that is removable by hydrogenolysis, the integer m is 0 or 1, characterized in that a sialyl donor of formula SA-OR2 or salts thereof, wherein R2 can be a mono-, di- or oligosaccharide, glycolipid, glycoprotein or glycopeptide, cyclic or acyclic aliphatic group, or aryl residue, and SA is an α-sialyl moiety, is reacted with a sialyl acceptor of general formula 2A or a salt thereof




wherein X1, A, m and R1 are as defined above, under the catalysis of an enzyme having transsialidase activity.
In another aspect, the present invention provides compounds of general formula 1A′ and salts thereof




wherein one of the R groups is an α-sialyl moiety and the other is H, R1 is a protecting group that is removable by hydrogenolysis, A is a D-glucopyranosyl unit optionally substituted with fucosyl, integer m is 0 or 1, and X′ represents a carbohydrate linker, provided that 1-O-β-benzyl and 1-O-β-(4,5-dimethoxy-2-nitro)-benzyl glycosides of 3′-O—(N-acetyl-neuraminosyl)-lactose sodium salt, and 1-O-β-benzyl glycoside of 6′-O—(N-acetyl-neuraminosyl)-lactose sodium salt are excluded.



BRIEF DESCRIPTION OF THE FIGURES
The invention will be described in further detail hereinafter with reference to:
FIG. 1 which shows the 400 MHz 1H-NMR spectrum of benzyl 3′′′-O-sialyl-β-LNnT according to the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Whatever route is taken to synthesise an oligosaccharide, the final target unprotected oligosaccharide is soluble only in water, which presents challenges for the later steps of the synthesis. Organic solvents commonly used in synthetic manufacturing processes are not suitable for the reactions of the very final stages of the oligosaccharide synthesis.
The present invention provides new sialooligosaccharides protected in the anomeric position and methodology suitable for manufacturing thereof. The invention is based upon the utilisation of water soluble 1-O-protected oligosaccharide intermediates in transsialidation reaction, wherein the 1-O-protecting group chosen may be removed by hydrogenolysis. Preferably, the 1-O-protecting group should also provide to the oligosaccharide intermediate physical and chemical properties assisting powerful purification processes. For example, the introduction of an aromatic group such as a benzyl or substituted benzyl group as a hydrophobic moiety enables the derivatives to be soluble in organic protic solvents like alcohols while their water solubility also remains. This opens the possibility of using mobile phases having a wide range of water/alcohol proportions which can be applied in separation/purification techniques such as size exclusion or reverse phase chromatography. Moreover, with careful design of substituents on the aromatic group, crystalline compounds can in some cases be realized, which allows the development of powerful manufacturing procedures using crystallisation alone for product purifications. Furthermore, the benzylic 1-O-protecting group can be removed by catalytic reduction (hydrogenolysis) in the last step under mild and delicate conditions that prevent by-product formation, which is undoubtedly an advantage when at least one sialyl group is present in the target oligosaccharide. It is possible for the catalytic reduction to take place in aqueous solution.
General Terms
Throughout the present application the term “α-sialyl moiety” or “sialyl moiety” present in the sialyl donors and in the compounds of general formula 1, refers to glycosyl moieties of any naturally occurring or modified neuraminic or sialic acid derivatives and analogues thereof having an α-glycosidic linkage, as depicted by the example of N-acetyl neuraminic acid in Scheme 1. Preferred neuraminic acids are N-acetyl-(Neu5Ac), N-glycolyl-(Neu5Gc) and deamino-neuraminic acid (3-deoxy-D-glycero-D-galacto-nonulosonic acid, KDN). Also included are Neu5Ac, Neu5Gc and KDN derivatives that are derivatized with linkers, reactive functional groups, detectable labels or targeting moieties, and/or substituted at C-4, C-7-, C-8 and/or C-9, especially at C-9, with acyloxy, alkoxy, halogen or azido. More preferred O-substituents are acetyl (at C-4, C-7-, C-8 and/or C-9), lactyl (at C-9), methyl (at C-8), sulphate (at C-8) or phosphate (at C-8). The preferred substituents on the amino group are acyls including glycolyl and acetoacetyl as well.




The “protecting group that is removable by hydrogenolysis” refers to groups whose C—O bond to the 1-oxygen is cleaved by addition of hydrogen in the presence of catalytic amounts of palladium, Raney nickel or another appropriate metal catalyst known for use in hydrogenolysis, resulting in the regeneration of the OH group. Such protecting groups are well known to the skilled man and are discussed in Protective Groups in Organic Synthesis, P G M Wuts and T W Greene, John Wiley & Sons 2007. Suitable protecting groups include benzyl, diphenylmethyl (benzhydryl), 1-naphthylmethyl, 2-naphthylmethyl or triphenylmethyl (trityl) groups, each of which may be optionally substituted by one or more groups selected from: alkyl, alkoxy, phenyl, amino, acylamino, alkylamino, dialkylamino, nitro, carboxyl, alkoxycarbonyl, carbamoyl, N-alkylcarbamoyl, N,N-dialkylcarbamoyl, azido, halogenalkyl or halogen. Preferably, such substitution, if present, is on the aromatic ring(s). Particularly preferred protecting groups are benzyl or 2-naphthylmethyl groups optionally substituted with one or more groups selected from phenyl, alkyl or halogen. More preferably, the protecting group is selected from unsubstituted benzyl, unsubstituted 2-naphthylmethyl, 4-chlorobenzyl, 3-phenylbenzyl and 4-methylbenzyl. These particularly preferred and more preferable protecting groups have the advantage that the by-products of the hydrogenolysis are exclusively toluene, 2-methylnaphthalene, or substituted toluene or 2-methylnaphthalene derivatives, respectively. Such by-products can easily be removed even in multi ton scales from water soluble oligosaccharide products via evaporation and/or extraction processes.
Throughout the present description, the term “alkyl” means a linear or branched chain saturated hydrocarbon group with 1-6 carbon atoms, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, n-hexyl, etc.
The term “aryl” refers to a homoaromatic group such as phenyl or naphthyl.
In the present description, the term “acyl” represents an R′—C(═O)-group, wherein R′ may be H, alkyl (see above) or aryl (see above), such as formyl, acetyl, propionyl, butyryl, pivaloyl, benzoyl, etc. The alkyl or aryl residue may either be unsubstituted or may be substituted with one or more groups selected from alkyl (only for aryl residues), halogen, nitro, aryl, alkoxy, amino, alkylamino, dialkylamino, carboxyl, alkoxycarbonyl, carbamoyl, N-alkylcarbamoyl, N,N-dialkylcarbamoyl, azido, halogenalkyl or hydroxyalkyl, giving rise to acyl groups such as chloroacetyl, trichloroacetyl, 4-chlorobenzoyl, 4-nitrobenzoyl, 4-phenylbenzoyl, 4-benzamidobenzoyl, 4-(phenylcarbamoyl)-benzoyl, glycolyl, acetoacetyl, etc.
The term “alkyloxy” or “alkoxy” means an alkyl group (see above) attached to the parent molecular moiety through an oxygen atom, such as methoxy, ethoxy, t-butoxy, etc.
“Halogen” means fluoro, chloro, bromo or iodo.
“Amino” refers to a —NH2 group.
“Alkylamino” means an alkyl group (see above) attached to the parent molecular moiety through an —NH-group, such as methylamino, ethylamino, etc.
“Dialkylamino” means two alkyl groups (see above), either identical or different ones, attached to the parent molecular moiety through a nitrogen atom, such as dimethylamino, diethylamino, etc.
“Acylamino” refers to an acyl group (see above) attached to the parent molecular moiety through an —NH-group, such as acetylamino (acetamido), benzoylamino (benzamido), etc.
“Carboxyl” denotes an —COOH group.
“Alkyloxycarbonyl” means an alkyloxy group (see above) attached to the parent molecular moiety through a —C(═O)-group, such as methoxycarbonyl, t-butoxycarbonyl, etc.
“Carbamoyl” is an H2N—C(═O)-group.
“N-Alkylcarbamoyl” means an alkyl group (see above) attached to the parent molecular moiety through a —HN—C(═O)-group, such as N-methylcarbamoyl, etc.
“N,N-Dialkylcarbamoyl” means two alkyl groups (see above), either identical or different ones, attached to the parent molecular moiety through a >N—C(═O)-group, such as N,N-methylcarbamoyl, etc.
In the present description the term “salt” in connection with compounds of general formulae 1 and 2 and of formula SA-OR2, which contain at least one sialyl residue, means an associated ion pair consisting of the negatively charged acid residue and one or more cations in any stoichiometric proportion. Cations, as used in the present context are atoms or molecules with positive charge. The cation may be inorganic as well as organic cation. Preferred inorganic cations are ammonium ion, alkali metal, alkali earth metal and transition metal ions, more preferably Na+, K+, Ca2+, Mg2+, Ba2+, Fe2+, Zn2+, Mn2+ and Cu2+, most preferably K+, Ca2+, Mg2+, Ba2+, Fe2+ and Zn2+. Basic organic compounds in positively charged form may be relevant organic cations. Such preferred positively charged counterparts are diethyl amine, triethyl amine, diisopropyl ethyl amine, ethanolamine, diethanolamine, triethanolamine, imidazol, piperidine, piperazine, morpholin, benzyl amine, ethylene diamine, meglumin, pyrrolidine, choline, tris-(hydroxymethyl)-methyl amine, N-(2-hydroxyethyl)-pyrrolidine, N-(2-hydroxyethyl)-piperidine, N-(2-hydroxyethyl)-piperazine, N-(2-hydroxyethyl)-morpholine, L-arginine, L-lysine, oligopeptides having L-arginine or L-lysine unit or oligopeptides having free amino group on N-terminal, etc., all in protonated form. Such salt formations can be used to modify characteristics of the complex molecule as a whole, such as stability, compatibility to excipients, solubility and ability to form crystals.
Transsialidation Reactions
In accordance with the present invention there is provided a process for synthesizing sialooligosaccharides of general formula 1 and salts thereof wherein one of the R groups is an α-sialyl moiety and the other is H, X represents a carbohydrate linker, R1 is a protecting group that is removable by hydrogenolysis and the integer n is 0 or 1, characterized in that a sialyl donor of formula SA-OR2 and salts thereof, wherein R2 can be a mono-, di- or oligosaccharide, glycolipid, glycoprotein or glycopeptide, cyclic or acyclic aliphatic group, or aryl residue, and SA is an α-sialyl moiety, is reacted with a sialyl acceptor of general formula 2 and salts thereof, under the catalysis of an enzyme having transsialidase activity. The process is depicted in Scheme 2.




An advantage of providing compounds of general formula 1 is the more simple purification of the sialylated oligosaccharide 1-O-protected glycosides compared to the unglycosylated sialooligosaccharides. Since there is no formation of free sialic acid as a side product, and due to the different polarity of the reaction compounds, isolation of the products by reverse phase or size exclusion chromatography is possible. In the case of reverse phase chromatography when water is used, compounds of general formula 1 migrate much more slowly than the very polar compounds present in the reaction mixture, thus the polar compounds can be eluted smoothly. Compounds of general formula 1 can be then washed from the column with e.g. alcohol.
Enzymes Having Transsialidase Activity
Enzymes having transsialidase activity and suitable for the purpose of the method of making sialooligosaccharides claimed in the present application can be selected from sialidase and transsialidase enzymes.
Sialidases (EC 3.2.1.18), classified in the GH33 family, are retaining enzymes with the ability of hydrolyzing the α-linkage of the terminal sialic acid, mainly those bound to galactose with α-2-3 or α-2-6 linkage, of various sialoglycoconjugates. They are found particularly in diverse virus families and bacteria, and also in protozoa, some invertebrates and mammals. Some bacterial sialidases can be used to scavenge sialic acids from sialylated glycoprotein, glycolipids or other glycoconjugates for nutrients for bacterial cell growth.
Although sialidases are characterized by their hydrolytic activity, under appropriate reaction conditions they are able to catalyze the transfer of a sialic acid unit to an asialo acceptor by a transsialidation reaction giving rise to the formation of sialoglycoconjugates. Sialidases from pathogen bacteria or viruses such as Bacteroides fragilis, Clostridium species (e.g. C. perfringens), Corynebacterium diphtherias, Haemophilus parasuis, Pasteurella multocida, Pseudomonas aeruginosa, Salmonella typhimurium, Streptococcus pneumoniae, Tannerella forsythia, Vibrio cholerae or Newcastle disease virus and from non-pathogenic bacteria or viruses such as Actinomyces viscosus, Arthrobacter species or Micromonospora viridifaciens are capable of acting as a catalyst for a sialylation reaction due to their transsialidase activity with α-2-3 and/or α-2-6 selectivity. As to the regioselectivity, the ratio between the α-2-3- and α-2-6-linked products varies depending on the enzymes and/or the acceptors. For example sialidases from A. ureafaciens, C. perfringens and V. cholerae have good α-2-6 selectivity, whereas those from S. typhimurium and Newcastle disease virus have good to excellent preference for formation of the α-2-3 linkage.
Recently, sialidases from Bifidobacterium species like Bifidobacterium bifidum and Bifidobacterium longum subsp. infantis have been identified, cloned and characterized. These sialidases can cleave and so recognize both α-2,3- and α-2,6-linked sialosides. Sialidases from Bifidobacterium longum subsp. infantis have a consistent preference for α-2,6-linkage whereas sialidases from Bifidobacterium bifidum have a consistent preference for α-2,3-linkage.
In order to improve regioselectivity and/or conversion of the transsialidation reaction the sialidases may be subjected to alteration by various engineering techniques.
In rational engineering novel altered enzymes (mutants) are created by point mutation. The mutation generally affects the active site of the enzyme. Replacement of the catalytic nucleophile with a non-nucleophilic residue results in the formation of an inactive mutant or an altered enzyme with reduced transglycosylation activity due the lack of an appropriate environment for the formation of the reactive host-guest complex for transglycosylation. However, in the presence of a more active sialyl donor than the natural one, the mutated enzyme is able to transfer efficiently the sialyl residue to a suitable acceptor. Rational engineering of enzymes generally requires reliance on the static 3D protein structure. These altered enzymes may be devoid of product hydrolysis activity.
A second technique called directed evolution strategy comprises random mutagenesis of the selected natural sialidase enzyme thus creating a library of enzyme variants each of which are altered in a single or multiple positions. They may be inserted into suitable microorganisms such as E. coli or S. cerevisiae for producing recombinant variants with slightly altered properties. Clones expressing improved enzymes are then identified with a fast and reliable screening method, selected and brought into a next round of the mutation process. The recurring cycles of mutation, recombination and selection are continued as far as mutant(s) with the desired activity and/or specificity is/are evolved.
With regard to transsialidases, the first transsialidase enzyme described was found in Trypanosoma cruzi, a protozoa which causes Chagas disease. Since that time transsialidases have been detected in several other trypanosome types such as Trypanosoma brucei gambiense, Trypanosoma brucei rhodesiense, Trypanosoma brucei brucei and Trypanosoma congolense. Moreover, the existence of transsialidases has been shown in Endotrypanum types, in Corynebacterium diphtherias and even in the human plasma.
Transsialidases differ from sialidases in that, in addition to the hydrolytic activity towards sialic acids of the sialidases, the former have more considerable sialic acid transfer activity. Transsialidases can transfer sialic acids, preferably α-2,3-bonded sialic acids, from a donor molecule to an acceptor derivative, which is preferably a terminal galactose moiety with β-interglycosidic linkage. As a result of this transfer, an α-glycosidic bond is be formed between the sialic acid and the acceptor. However, if there is no suitable acceptor, the transsialidase hydrolyses the sialic acid.
It is possible to produce directed transsialidase enzyme mutants wherein the hydrolase activity is effaced in favour of the transsialidase action, e.g. by altering the amino acid sequence. After creating a library of altered genes by mutagenesis and/or recombination, they may be inserted into suitable microorganisms such as E. coli or S. cerevisiae for producing recombinant variants with slightly altered properties. Clones expressing improved enzymes are then identified, isolated and can be used for the desired purpose. For example, based on sequence and structure comparisons, sialidase from Trypanosoma rangeli may be mutated at six positions, wherein the resulting mutant is able to display a significant level of trans-sialidase activity (Paris et al. J. Mol. Biol. 345, 923 (2005)).
Preferably, the enzyme having transsialidase activity may be selected from sialidases or transsialidases derived from Bifidobacterium longum subsp. infantis ATCC 15697, Bifidobacterium bifidum JCM1254, Bifidobacterium bifidum S17, Bifidobacterium bifidum PRL2010, Bifidobacterium bifidum NCIMB 41171, Trypanosoma cruzi, etc.
More preferably the enzyme having transsialidase activity may be selected from sialidases or transsialidases as defined according to the following deposit numbers: gi|213524659 (Bifidobacterium longum subsp. infantis ATCC 15697, SEQ ID NO: 1), gi|213523006 Bifidobacterium longum subsp. infantis ATCC 15697, SEQ ID NO: 2), gi|309252191 (Bifidobacterium bifidum S17, SEQ ID NO: 3), gi|309252190 (Bifidobacterium bifidum S17, SEQ ID NO: 4), gi|310867437 (Bifidobacterium bifidum PRL2010, SEQ ID NO: 5), gi|310867438 (Bifidobacterium bifidum PRL2010, SEQ ID NO: 6), gi|224283484 (Bifidobacterium bifidum NCIMB 41171, SEQ ID NO: 7), gi|224283485 (Bifidobacterium bifidum NCIMB 41171, SEQ ID NO: 8), gi|334283443 gi|47252690 (Bifidobacterium bifidum JCM1254, SEQ ID NO: 9), gi|47252690 (T. cruzi, SEQ ID NO: 10), gi|432485 (T. cruzi, SEQ ID NO: 11). Particularly preferred sialidases/transsialidases with transsialidase activity are listed in the following Table 2:







TABLE 2







Preferred sialidases/transsialidases









GI number in




GenBank

SEQ ID


Database
Organism
NO:












gi|213524659
Bifidobacterium longum subsp. infantis
1



ATCC 15697



gi|213523006
Bifidobacterium longum subsp. infantis
2



ATCC 15697



gi|309252191
Bifidobacterium bifidum S17
3


gi|309252190
Bifidobacterium bifidum S17
4


gi|310867437
Bifidobacterium bifidum PRL2010
5


gi|310867438
Bifidobacterium bifidum PRL2010
6


gi|224283484
Bifidobacterium bifidum NCIMB 41171
7


gi|224283485
Bifidobacterium bifidum NCIMB 41171
8


gi|334283443
Bifidobacterium bifidum JCM1254
9


gi|47252690
Trypanosoma cruzi
10


gi|432485
Trypanosoma cruzi
11









It is envisaged that sialidase/transsialidase enzyme mutants retaining transsialidase activity and having a sequence similarity/homology to the sequence of the above mentioned enzyme sequences having transsialidase activity of at least 70%, more preferably at least 80%, even more preferably at least 85%, even more preferably at least 90% and most preferably at least 95% or even 97%, 98% or 99% as compared to the entire wild type sequence on amino acid level.
Preferably, the sequence similarity is at least 90%, more preferably 95%, 97%, 98% or most preferably 99%. Preferably, said trans-sialidase activity is at least 75% of that of the native form of the enzyme, more preferably at least 90% and still more preferably at least 100%.
Sialidases and transsialidases possess a broader donor and acceptor specificity than the sialyl transferases used in prior art processes, and so can be used in a particularly wide variety of reactions. Sialidases/transsialidases are therefore more advantageous for industrial utilisation than are sialyltransferases previously used.
Donors for Sialidases/Transsialidases
It is known that, upon infection of an organism with T. cruzi, the transsialidase in T. cruzi scavenges sialic acids from sialoglycoconjugates of the host's organism and efficiently sialylates its own surface mucin in order to mask its own epitope.
After numerous intensive investigations it has been found that a huge number of natural and synthetic sialic acid containing derivatives can act as sialyl donors in transsialidation reactions. Thus sialyl donor compounds of general formula SA-OR2 defined above can provide a substrate to be transferred by transsialidases to the acceptor. Transsialidases do not transfer pure sialic acid or CMP-sialic acid (which is, in fact, a β-sialide) to the acceptor, the presence of a sialic acid with an α-anomeric aglycon or α-anomeric substituent is a requisite for the transsialidase reactions. Typical natural sialyl donors can be selected from, but are not limited to, 3′-O-sialyl-lactose, fetuin, gangliosides, O- or N-linked glycopeptides, all of which contain a sialic acid α-2,3-linked to a terminal β-galactoside residue, or polysialic acid with α-2,8-linkage. Among synthetic sialosides 2-O-(4-methylumbelliferyl)- or 2-O-(optionally substituted phenyl)-α-D-sialosides, more commonly 2-O-(p-nitrophenyl)-α-D-sialoside, are of preference.
Acceptors for Sialidases/Transsialidases
Transsialidase acceptors used in transsialidation reaction disclosed above are characterized by general formula 2 and salts thereof which are R1-galactopyranosides (when n is 0) or oligosaccharide R1-glycosides whose terminal sugar moiety on the non-reducing end is galactopyranose (when n equals 1). The terminal galactopyranosyl unit is bound preferably with a β-glycosidic linkage.
The anomeric hydroxyl group of compounds of general formula 2 are protected with R1 groups that can be removed by hydrogenolysis. As set out previously, such groups include optionally substituted benzyl and naphthylmethyl groups. Benzyl or 2-naphthylmethyl groups optionally substituted with phenyl, alkyl or halogen are preferred R1-groups, and among them unsubstituted benzyl, unsubstituted 2-naphthylmethyl, 4-chlorobenzyl, 3-phenylbenzyl or 4-methylbenzyl groups are of particular preference.
When n is 1, the structural element X, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl glucosamine, galactose, fucose and sialic acid.
In a preferred method n is 1 and linker X corresponds to formula —(X1)m-A-forming acceptors of general formula 2A or salts thereof




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, and integer m is 0 or 1. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.

When m is 0, the terminal D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 2B




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 2C or salts thereof




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the terminal galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a lacto-N-biosyl or N-acetyl-lactosaminyl terminal disaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred method group X2 is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 2D or salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently an N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R8 is selected form the groups characterized by general formulae 5 and 6,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, and R9 is selected from H, α-sialyl moiety, a group of general formula 5 and a group of general formula 6.
According to a further preferred method, the compound of general formula 2D and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y, when attached to another N-acetyl-lactosaminyl group (p=2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 5, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 6, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 2B, 2C or 2D and salts thereof as defined above represents the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having unsubstituted terminal galactosyl residue. Preferably, the sialyl substituent is N-acetyl neuraminyl group.
Particularly preferably, the compound of general formula 2B, 2C or 2D and salts thereof as defined above is selected from the group of R1-glycosides of Galβ1-4Glc (lactose), Galβ1-4(Fucα1-3)Glc (3-O-fucosyllactose), Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LNT), Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LNnT), Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (LNFP II), Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc (LNFP III), Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-4)Glc (LNFP V), Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNDFH II), Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (LSTb), Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNDFH III), or salts thereof. The R1-glycosides may be alpha or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
A typical synthesis of compounds of general formula 2 comprises the treatment of galactose, or oligosaccharides having a galactopyranosyl unit at the nonreducing terminal, with acetic anhydride and sodium acetate at 50-125° C., followed by Lewis acid catalyzed glycosylation using R1—OH, preferably benzyl/substituted benzyl alcohols, in organic solvent such as DCM, toluene, THF, etc. Subsequently, compounds of general formula 2 are obtained via a final Zemplén deprotection of the glycosylated products.
According to another typical anomeric O-protection procedure, fully or partially protected galactose or oligosaccharides having a galactopyranosyl unit at the nonreducing end with a free anomeric OH in a dipolar aprotic solvent such as DMF, DMSO, N-methylpyrrolidone, hexamethylphosphoramide (HMPA), N,N′-dimethylhexahydropyrimidine-2-one (DMPU), THF, dioxane, acetonitrile, etc., or mixture thereof, is O-alkylated in the presence of a strong base and R1—X wherein X is a leaving group selected from halogen, alkylsulfonyloxy like mesyl, triflyl, etc. and arylsulfonyl like benzenesulfonyl, tosyl, etc. Preferred alkylating agents are benzyl or 1- or 2-naphthylmethyl halogenides optionally substituted with one or more groups selected from phenyl, alkyl or halogen. The strong base is able to deprotonate the anomeric OH chemoselectively due to its more acidic character when an equivalent amount or a slight excess (1 to 1.5 equiv.) of base is used. The strong base suitable for activating the anomeric OH is typically taken from the group of alkali metal or alkaline earth metal hydrides or alkoxides such as NaH, KH, CaH2, NaOMe, NaOtBu, KOtBu, inorganic hydroxides, potassium carbonate, etc. The alkylation agent is added in an equivalent amount or a slight excess (1 to 1.5 equiv.). The reaction is carried out between −10 and 80° C., preferably at a low temperature during whole course of the reaction or at a low temperature during the addition of the reagents/reactants and an elevated temperature in the later stages of the course of the reaction. Benzyl/substituted benzyl glycosides of general formula 2 can be obtained after usual work-up.
In a further aspect, the present invention relates to providing compounds of general formula 2A′ and salts thereof




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, integer m is 0 or 1, provided that a) when m is 0, then group A is substituted with fucosyl, and b) the compound differs to 1-O-β-benzyl-LNT, 1-O-β-(4-hydroxymethylbenzyl)-LNnT and 1-O-β-benzyl-LNnT. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.

When m is 0, the terminal D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 2B′ and salts thereof




wherein R3 is fucosyl. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 2C′ and salts thereof




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the terminal galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a lacto-N-biosyl or N-acetyl-lactosaminyl terminal disaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred method group X2 is galactose optionally substituted with sialyl or oligosaccharide residue representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 2D′ or salts thereof.




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently an N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R8 is selected form the groups characterized by general formulae 5 and 6,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, and R9 is selected from H, α-sialyl moiety, a group of general formula 5 and a group of general formula 6.
According to a further preferred embodiment, the compound of general formula 2D′ and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y, when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 5, when attached to Y, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 6, when attached to Y, is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 2C′ or 2D′ and salts thereof as defined above represents the R1-glycosides lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having unsubstituted terminal galactosyl residue. Preferably, the sialyl substituent is N-acetyl neuraminyl group.
Particularly preferably, the compound of general formula 2A′ and salts thereof as defined above is selected from the group of R1-glycosides of Galβ1-4(Fucα1-3)Glc (3-O-fucosyllactose), Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LNT), Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LNnT), Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (LNFP II), Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc (LNFP III), Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNFP V), Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNDFH II), Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (LSTb), Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNDFH III), or salts thereof. The R1-glycosides may be alpha or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
Products of Transsialidation Reaction
As set forth above, the transsialidation reaction claimed in the present application produces compounds of general formula 1 and salts thereof




wherein one of the R groups is an α-sialyl moiety and the other is H, X represents a carbohydrate linker, R1 is a protecting group that is removable by hydrogenolysis and the integer n is 0 or 1, from compounds of general formula 2 and salts thereof. R1 group includes optionally substituted benzyl and naphthylmethyl groups, among which benzyl or 2-naphthylmethyl groups optionally substituted with phenyl, alkyl or halogen are preferred R1-groups, and among them unsubstituted benzyl, unsubstituted 2-naphthylmethyl, 4-chlorobenzyl, 3-phenylbenzyl or 4-methylbenzyl groups are of particular preference.
When n is 1, the structural element X, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl glucosamine, galactose, fucose and sialic acid.
In a preferred method n is 1 and linker X corresponds to formula —(X1)m-A-forming sialylated products of general formula 1A and salts thereof




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, and integer m is 0 or 1. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.
When m is 0, the D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 1B and salts thereof.




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a 3′-O-sialyl-lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 1C and salts thereof




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the sialyl-galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a sialyl-lacto-N-biosyl or sialyl-N-acetyl-lactosaminyl terminal trisaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred method to synthesize sialyl oligosaccharide derivatives, group X2 in compounds of general formula 1C and salts thereof is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 1D and salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4 is selected form the groups characterized by general formulae 3 and 4,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, one of the R groups is an α-sialyl moiety and the other is H, and R5 is selected from H, α-sialyl moiety, group of general formula 3 and group of general formula 4.
According to a further preferred method, the compound of general formula 1D and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y (p=2), when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 3, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 4, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 1B, 1C or 1D and salts thereof as defined above represents the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having sialyl substituent in 3-OH or 6-OH of a terminal galactosyl residue. Preferably, the sialyl substituent(s) is/are N-acetyl-neuraminyl group(s).
Particularly preferably, the compound of general formula 1B, 1C or 1D and salts thereof as defined above is selected from the group of R′-glycosides of Neu5Acα2-3Galβ1-4Glc (3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-6Galβ1-4Glc (6′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-4(Fucα1-3)Glc (3-O-fucosyl-3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LST a), Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LST c), Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FLST a), Neu5Acα2-6Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-4)Glc, Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3 (Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3 (Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (DSLNT), Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FDSLNT I), Neu5Acα2-6Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FDSLNT II), Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FLST c), Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc or salts thereof. The R1-glycosides may be alpha- or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
In case of selective α-2-3 sialidation, the transsialidation reaction claimed in the present application produces compounds of general formula 1-3 and salts thereof




wherein SA is an α-sialyl moiety, X represents a carbohydrate linker, R1 is a protecting group that is removable by hydrogenolysis and the integer n is 0 or 1, from compounds of general formula 2 and salts thereof. R1 group includes optionally substituted benzyl and naphthylmethyl groups, among which benzyl or 2-naphthylmethyl groups optionally substituted with phenyl, alkyl or halogen are preferred R1-groups, and among them unsubstituted benzyl, unsubstituted 2-naphthylmethyl, 4-chlorobenzyl, 3-phenylbenzyl or 4-methylbenzyl groups are of particular preference.
When n is 1, the structural element X, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl glucosamine, galactose, fucose and sialic acid.
In a preferred method n is 1 and linker X corresponds to formula —(X1)m-A-forming sialylated products of general formula 1-3A and salts thereof




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, and integer m is 0 or 1. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.
When m is 0, the D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 1-3B and salts thereof




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a 3′-O-sialyl-lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 1-3C and salts thereof




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the sialyl-galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a sialyl-lacto-N-biosyl or sialyl-N-acetyl-lactosaminyl terminal trisaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred method to synthesize sialyl oligosaccharide derivatives, group X2 in compounds of general formula 1-3C and salts thereof is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 1-3D and salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4′ is selected form the groups characterized by general formulae 3-3 and 4-3,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, SA is α-sialyl moiety and R5′ is selected from H, α-sialyl moiety, group of general formula 3-3 and group of general formula 4-3.
According to a further preferred embodiment, the compound of general formula 1-3D and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y (p=2), when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 3-3, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 4-3, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 1-3B, 1-3C or 1-3D and salts thereof as defined above represents the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having sialyl substituent in 3-OH of a terminal galactosyl residue, and salts thereof. Preferably, the sialyl substituent(s) is/are N-acetyl neuraminyl group(s).
Particularly preferably, the compound of general formula 1-3B, 1-3C or 1-3D and salts thereof as defined above is selected from the group of R1-glycosides of Neu5Acα2-3Galβ1-4Glc (3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-4(Fucα1-3)Glc (3-O-fucosyl-3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LST a), Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FLST a), Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (DSLNT), Neu5Acα2-3Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FDSLNT I), Neu5Acα2-3Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FDSLNT II), Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc and salts thereof. The R1-glycosides may be alpha- or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
In case of selective α-2-6 sialidation, the transsialidation reaction claimed in the present application produces compounds of general formula 1-6 and salts thereof




wherein SA is an α-sialyl moiety, X represents a carbohydrate linker, R1 is a protecting group that is removable by hydrogenolysis and the integer n is 0 or 1, from compounds of general formula 2 and salts thereof. R1 group includes optionally substituted benzyl and naphthylmethyl groups, among which benzyl or 2-naphthylmethyl groups optionally substituted with phenyl, alkyl or halogen are preferred R1-groups, and among them unsubstituted benzyl, unsubstituted 2-naphthylmethyl, 4-chlorobenzyl, 3-phenylbenzyl or 4-methylbenzyl groups are of particular preference.
When n is 1, the structural element X, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl glucosamine, galactose, fucose and sialic acid.
In a preferred method n is 1 and linker X corresponds to formula —(X1)m-A-forming sialylated products of general formula 1-6A and salts thereof.




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, and integer m is 0 or 1. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.
When m is 0, the D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 1-6B and salts thereof




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a 3′-O-sialyl-lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 1-6C and salts thereof.




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the sialyl-galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a sialyl-lacto-N-biosyl or sialyl-N-acetyl-lactosaminyl terminal trisaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred method to synthesize sialyl oligosaccharide derivatives, group X2 in compounds of general formula 1-6C and salts thereof is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 1-6D and salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4′′ is selected from the groups characterized by general formulae 3-6 and 4-6,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, SA is α-sialyl moiety and R5′′ is selected from H, α-sialyl moiety, group of general formula 3-6 and group of general formula 4-6, or salts thereof.
According to a further preferred embodiment, the compound of general formula 1-6D and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y (p=2), when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 3-6, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 4-6, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 1-6B, 1-6C or 1-6D and salts thereof as defined above represents the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having sialyl substituent in 6-OH of a terminal galactosyl residue, and salts thereof. Preferably, the sialyl substituent(s) is/are N-acetyl neuraminyl group(s).
Particularly preferably, the compound of general formula 1-6B, 1-6C or 1-6D and salts thereof as defined above is selected from the group of R1-glycosides of Neu5Acα2-6Galβ1-4Glc (6′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-6Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LST c), Neu5Acα2-6Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3 (Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FLST c), Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc or salts thereof. The R1-glycosides may be alpha- or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
It should be emphasized that some compounds represented by general formula 1 and salts thereof defined above and obtainable in the transsialidation reaction disclosed in the present application are novel. Thus the invention relates to providing novel compounds of general formula 1A′ and salts thereof




wherein one of the R groups is an α-sialyl moiety and the other is H, R1 is a protecting group that is removable by hydrogenolysis, A is a D-glucopyranosyl unit optionally substituted with fucosyl, integer m is 0 or 1, and X1 represents a carbohydrate linker, provided that 1-O-β-benzyl and 1-O-β-(4,5-dimethoxy-2-nitro)-benzyl glycosides of 3′-O—(N-acetyl-neuraminosyl)-lactose sodium salt, and 1-O-β-benzyl glycoside of 6′-O—(N-acetyl-neuraminosyl)-lactose sodium salt are excluded. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.
When m is 0, the D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 1B′ and salts thereof




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a 3′-O-sialyl-lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 1C′ and salts thereof.




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the sialyl-galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a sialyl-lacto-N-biosyl or sialyl-N-acetyl-lactosaminyl terminal trisaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred embodiment, group X2 in compounds of general formula 1C′ and salts thereof is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 1D′ and salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4 is selected form the groups characterized by general formulae 3 and 4,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, one of the R groups is an α-sialyl moiety and the other is H, and R5 is selected from H, α-sialyl moiety, group of general formula 3 and group of general formula 4.
According to a further preferred embodiment, the compound of general formula 1D′ and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y (p=2), when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 3, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 4, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 1B′, 1C′ or 1D′ and salts thereof as defined above is selected from the group consisting of the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having sialyl substituent in 3-OH or 6-OH of a terminal galactosyl residue, and salts thereof. Preferably, the sialyl substituent(s) is/are N-acetyl neuraminyl group(s).
Particularly preferably, the compound of general formula 1A′ and salts thereof as defined above is selected from the group consisting of R1-glycosides of Neu5Acα2-3Galβ1-4Glc (3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-6Galβ1-4Glc (6′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-4(Fucα1-3)Glc (3-O-fucosyl-3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LST a), Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LST c), Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FLST a), Neu5Acα2-6Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-4)Glc, Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-4)Glc, Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3 (Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3 (Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (DSLNT), Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FDSLNT I), Neu5Acα2-6Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FDSLNT II), Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FLST c), Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc or salts thereof. The R1-glycosides may be alpha- or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
In one embodiment within the group of compounds of general formula 1A′ and salts thereof the present invention relates to α-2-3-sialylated compounds of general formula 1′-3A and salts thereof




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, and integer m is 0 or 1. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.
When m is 0, the D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 1′-3B and salts thereof




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a 3′-O-sialyl-lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 1′-3C and salts thereof




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the sialyl-galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a sialyl-lacto-N-biosyl or sialyl-N-acetyl-lactosaminyl terminal trisaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred embodiment, group X2 in compounds of general formula 1′-3C and salts thereof is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 1′-3D and salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4′ is selected from the groups characterized by general formulae 3-3 and 4-3,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, SA is α-sialyl moiety and R5′ is selected from H, α-sialyl moiety, group of general formula 3-3 and group of general formula 4-3.
According to a further preferred embodiment, the compound of general formula 1′-3D and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y (p=2), when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 3-3, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 4-3, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 1′-3B, 1′-3C or 1′-3D and salts thereof as defined above is selected from the group consisting of the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having sialyl substituent in 3-OH of a terminal galactosyl residue, and salts thereof. Preferably, the sialyl substituent(s) is/are N-acetyl-neuraminyl group(s).
Particularly preferably, the compound of general formula 1′-3B, 1′-3C or 1′-3D and salts thereof as defined above is selected from the group consisting of R1-glycosides of Neu5Acα2-3Galβ1-4Glc (3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-4 (Fucα1-3)Glc (3-O-fucosyl-3′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LST a), Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3 (Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FLST a), Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3 (Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3 (Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (DSLNT), Neu5Acα2-3Galβ1-3 (Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FDSLNT I), Neu5Acα2-3Galβ1-3 (Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FDSLNT II), Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc or salts thereof. The R1-glycosides may be alpha- or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
In another embodiment within the group of compounds of general formula 1A′ and salts thereof the present invention relates to α-2-6-sialylated compounds of general formula 1′-6A and salts thereof.




wherein A is a D-glucopyranosyl unit optionally substituted with fucosyl, X1 represents a carbohydrate linker, and integer m is 0 or 1. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation.
When m is 0, the D-galactopyranosyl unit is directly coupled to group A through an interglycosidic linkage. Preferably, the interglycosidic linkage is a 1-4 linkage thus forming compounds of general formula 1′-6B and salts thereof




wherein R3 is fucosyl or H. More preferably the interglycosidic linkage between the galactose and the glucose portion is β thus giving rise to a 3′-O-sialyl-lactose derivative. In an even more preferable embodiment aglycon —OR1 is also in β orientation.
When m is 1, the structural element X1, as carbohydrate linker, means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure. The monosaccharide building units of the carbohydrate linker can be any naturally occurring 5-, 6- or 9-carbon containing sugar derivatives, with the most frequently occurring units being glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Preferably, linker X1 is represented by the formula —B—X2— thus forming compounds of general formula 1′-6C and salts thereof.




wherein group B is an N-acetyl-glucosaminopyranosyl unit optionally substituted with fucosyl and/or sialyl, and linker X2 means a mono-, di-, tri-, tetra-, penta- or oligosaccharide representing a linear or a branched structure having the monosaccharide building units selected from glucose, N-acetyl-glucosamine, galactose, fucose and sialic acid. Group —OR1 is linked to the anomeric carbon (C1) atom of the D-glucopyranosyl ring, preferably in β orientation. In preference, the sialyl-galactosyl group is attached to group B through 1-3 or 1-4 interglycosidic linkage forming thus a sialyl-lacto-N-biosyl or sialyl-N-acetyl-lactosaminyl terminal trisaccharide moieties, respectively. In a further favoured method, a fucosyl substituent may be coupled to the 3-OH or 4-OH group of unit B and/or to the 3-OH group of unit A, and/or sialyl may be connected to 6-OH of unit B.
In a more preferred embodiment, group X2 in compounds of general formula 1′-6C and salts thereof is galactose optionally substituted with sialyl or oligosaccharide representing a linear or a branched structure having the saccharide building units selected from N-acetyl-lactosamine, lacto-N-biose, fucose and sialic acid, forming thus human milk oligosaccharide derivatives represented by general formula 1′-6D and salts thereof




wherein R1 is a group removable by hydrogenolysis, R3 is H or fucosyl unit, Y is independently N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4′′ is selected form the groups characterized by general formulae 3-6 and 4-6,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, SA is α-sialyl moiety and R5′′ is selected from H, α-sialyl moiety, group of general formula 3-6 and group of general formula 4-6.
According to a further preferred method, the compound of general formula 1′-6D and salts thereof as defined above is characterized by its linkages and attached moieties, wherein

    
    
        an N-acetyl-lactosaminyl group in group Y (p=2), when attached to another N-acetyl-lactosaminyl group, is coupled with 1-3 interglycosidic linkage,
        the group of general formula 3-6, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the group of general formula 4-6, when attached to Y (p=1, 2), is coupled with 1-3 interglycosidic linkage,
        the fucosyl residue if attached to a N-acetyl-lactosaminyl group present in Y is linked to the N-acetyl-glucosamine of the N-acetyl-lactosaminyl group with 1-3 interglycosidic linkage,
        the α-sialyl residue if attached to a N-acetyl-lactosaminyl present in Y is linked to the galactose of the N-acetyl-lactosaminyl group with 2-6 interglycosidic linkage.
    
    


In a further aspect, the compound of general formula 1′-6B, 1′-6C or 1′-6D and salts thereof as defined above represents the R1-glycosides of lactose, lacto-N-neotetraose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-neohexaose, para-lacto-N-octaose and lacto-N-neooctaose, lacto-N-tetraose, lacto-N-hexaose, lacto-N-octaose, iso-lacto-N-octaose, lacto-N-decaose and lacto-N-neodecaose optionally substituted with one or more sialyl and/or fucosyl residue and having sialyl substituent in 6-OH of a terminal galactosyl residue, and salts thereof. Preferably, the sialyl substituent(s) is/are N-acetyl neuraminyl group(s).
Particularly preferably, the compound of general formula 1′-6B, 1′-6C or 1′-6D and salts thereof as defined above is selected from the group of R1-glycosides of Neu5Acα2-6Galβ1-4Glc (6′-O—(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-6Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LST c), Neu5Acα2-6Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-6Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FLST c), Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-6Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc or salts thereof. The R1-glycosides may be alpha- or beta-anomers. Preferably, said R1-glycosides are the beta-anomers.
Other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which are given for illustration of the invention and are not to be limiting thereof.
EXPERIMENTAL
1. Synthesis of Sialyl Acceptors
A) General procedure: lactose (5 g, 14.6 mmol) and TsOH.H2O (0.2 g, 1.05 mmol) were added in one portion to a mixture of DMF (20 ml) and benzaldehyde dimethyl acetal (5.5 ml, 35.4 mmol, 2.4 eq.) at room temperature. The reaction mixture was stirred strongly at 70° C. under exclusion of humidity for 1 hour. After cooling triethyl amine (0.15 ml) was added then the volatile components (MeOH, triethyl amine, remaining benzaldehyde dimethyl acetal) were removed in vacuo. To the reaction mixture the benzyl bromide derivative (1.5 eq.)—predissolved in 5-10 ml of DMF, if the reagent is a solid—was added and the mixture was cooled to 0° C. for 20 min. Still under cooling NaH (0.8 g of a 55% dispersion on mineral oil, 1.3 eq.) was added in one portion and the mixture was stirred under cooling until the hydrogen formation stopped then at room temperature for 2-3 hours. Methanol (2 ml) was added carefully and the reaction was stirred for a further 5 min. The reaction mixture was portioned between 100 ml of DCM and 100 ml of water and extracted. The water layer was back-extracted twice with 100 ml of DCM. The combined organic phases were evaporated, the residue was dissolved in 100 ml of acetonitrile and extracted with 100 ml of hexane. The acetonitrile was distilled off and the residue was taken up in isopropanol (10 ml) and isopropyl ether (50 ml) at 50° C. The clear solution was cooled to −20° C. for or overnight. The crystals obtained were filtered off and washed twice with TBME and dried. Recrystallization may be carried out from a mixture of TBME ( ̃50 ml) and ethanol ( ̃20 ml).
4-Chlorobenzyl 4′,6′-O-benzylidene-β-lactoside
Yield: 1.71 g
4-Methylbenzyl 4′,6′-O-benzylidene-β-lactoside
Yield: 3.20 g
3-Phenylbenzyl 4′,6′-O-benzylidene-β-lactoside
Yield: 2.70 g
2-Naphthylmethyl 4′,6′-O-benzylidene-β-lactoside
Yield: 1.77 g
B) To a mixture of one of the above benzylidene acetals (500 mg) in methanol (10 ml) and water (0.5 ml) TFA was added at room temperature and the reaction mixture was stirred for 2-4 hours under exclusion of humidity then evaporated. The remaining material was co-evaporated with ethanol 3-4 times giving a crude solid, which, after drying, may be recrystallized from a mixture of methanol ( ̃10-35 ml) and water ( ̃0-2 mL).
4-Chlorobenzyl β-lactoside
Yield: 333 mg
13C-NMR (75.1 MHz, D2O): δ=135.25, 133.67, 130.30, 128.70, 103.00, 101.13, 78.39, 75.44, 74.89, 74.49, 72.88, 72.58, 71.03, 70.83, 68.62, 61.11, 60.13.
4-Methylbenzyl β-lactoside
Yield: 439 mg
13C-NMR (75.1 MHz, D2O): δ=138.91, 133.50, 129.37, 129.07, 103.01, 100.96, 78.43, 75.44, 74.87, 74.52, 72.90, 72.59, 71.47, 71.03, 68.63, 61.11, 60.17, 20.34.
3-Phenylbenzyl β-lactoside
Yield: 438 mg
13C-NMR (75.1 MHz, d6-DMSO/d4-MeOH/D2O 8:1:1): δ=140.29, 140.24, 138.88, 129.13, 129.02, 127.66, 126.88, 126.83, 126.03, 125.90, 103.95, 102.03, 80.76, 75.65, 75.07, 75.00, 73.34, 73.28, 70.66, 69.81, 68.27, 60.56.
2-Naphthylmethyl β-lactoside
Yield: 378 mg
13C-NMR (75.1 MHz, D2O/d6-DMSO): δ=134.96, 133.24, 133.12, 128.59, 128.31, 128.08, 127.46, 126.98, 126.90, 126.79, 103.26, 101.59, 78.89, 75.62, 75.09, 74.81, 73.14, 72.81, 71.33, 71.14, 68.75, 61.22, 60.39.
C)




10 g (8.13 mmol) of benzyl 2,3,6,2′,6′-penta-O-(4-chlorobenzoyl)-4′-O-benzoyl-β-lactoside and 10 g (1.6 equiv.) of methyl N-trichloroacetyl-3,6,2′,3′,4′6′-hexa-O-acetyl-1-thio-lactosaminide were dissolved in 35 ml of dry CHCl3 under argon. To this solution 3.7 g of NIS and 490 mg of AgOTf were added at rt, and the stirring was continued for approx. 20 min. Triethyl amine (5 ml) was added to the slurry, diluted with CH2Cl2 (500 ml) and then extracted 2× with sodium thiosulphate solution (10%), the organic phase was separated, dried with MgSO4, filtered, concentrated, and the syrup was chromatographed on a column of silica-gel, using a gradient of CH2Cl2: acetone 98:2→95:5. Yield: 12.7 g, 80%. MS (ESP): 1972.1 [M+Na]+, 1988.1 [M+K]+, 1948.2 [M-H]−, 1984.0 [M+Cl]−. 13C NMR (CDCl3) δ: 101.2, 100.7, 100.0, 98.8 (anomeric carbons).




10 g (5.1 mmol) of tetrasaccharide prepared above was dissolved in MeOH (110 ml) and a solution of NaOMe (1 M in MeOH) was added until pH 10 was attained. The solution was stirred at 40° C. for 5 h, then was neutralized by addition of Amberlite IR 120H+ resin, the resin was filtered off, and the filtrate was evaporated to dryness. The residue was dissolved in warm DMF (10 ml) and added dropwise to iPr2O (150 ml) and the suspension was stirred for an additional 3 h. The precipitate was filtered off, washed with iPr2O (2×20 ml) and dried to yield 4.2 g of product as off-white powder (91%). MS (ESP): 900.1 [M-H]−. 13C NMR (D2O) δ: 105.6, 105.5, 104.2, 103.7 (anomeric carbons).




35 g of a compound of the tetrasaccharide prepared above was dissolved in 110 ml of MeOH and 110 ml of aqueous KOH (7.5 g) solution and the mixture was stirred at rt. for id. The mixture was then chilled with an ice-bath, neutralized by HCl-gas and concentrated to dryness. The resulting crude brown glass was then acetylated with pyridine (150 ml) and acetic anhydride (150 ml) at rt. for 1 d. The solution was concentrated, the syrup was dissolved in CH2Cl2, the organic phase was extracted with 1M HCl-solution and then with sat. NaHCO3-solution, dried with MgSO4, filtered and concentrated to yield 43 g of brown foam, which was subjected to column chromatography using CH2Cl2:acetone 8:2 as eluent. 13C NMR (CDCl3) δ: 101.2, 100.8, 100.4, 99.2 (anomeric carbons).




140 g (107.5 mmol) of the peracetylated tetrasaccharide prepared above was dissolved in 1.5 L of MeOH, NaOMe-solution (1M) was added until pH 10, and the mixture was stirred at 50° C. overnight. The product crystallized from the reaction mixture. The mixture is allowed to cool to rt., then it was chilled, filtered, the filtrate was washed with cold EtOH, then dried to yield 69 g of benzyl β-LNnT as a white powder (86.5 mmol, 80%). 13C NMR (D2O) δ: 105.6, 105.5, 105.4, 103.6 (anomeric carbons). Mp. 284-286° C.
D) General Procedure for the Preparation of a Neutral HMO Benzyl/Substituted Benzyl Glycoside
A selected neutral HMO (1 equiv.) was dissolved/suspended in 1-10 volumes (g/mL) of DMF, DMSO or a mixture thereof. The reaction mixture was cooled to 0° C. and benzyl bromide/substituted benzyl bromide (1.2-1.4 equiv.) was added. A strong base such as sodium hydride, potassium hydride, calcium hydride, potassium t-butoxide, sodium t-butoxide (1.2-1.4 equiv) was added at 0-40° C. and the reaction mixture was stirred for 6-24 hours at 0-60° C. Subsequently, water was added to quench the excess of base and the reaction mixture was stirred at RT for 30 minutes. The resulting reaction mixture was concentrated and purified in reverse phase chromatography, silica gel chromatography, ion-exchange chromatography, size-exclusion chromatography, etc. or crystallized giving rise to the desired benzylated/substituted benzylated neutral HMO compound in 70-80% yields.
1-O-β-(4-methylbenzyl)-LNnT
1H NMR (D2O): 7.3 (dd, 4H), 4.88 (d, 1H), 4.7 (m), 4.54 (d, 1H), 4.48 (d, 1H), 4.42 (d, 1H), 4.34 (d), 4.0-3.5 (m), 3.34 (dd, 1H).
13C NMR (D2O): 184.2, 177.6, 173.7, 141.5, 136.1, 131.9, 131.4, 105.6, 105.5, 105.4, 103.6, 93.2, 84.7, 81.5, 81.0, 80.8, 78.0, 77.6, 77.4, 77.1, 75.5, 75.2, 74.8, 74.0, 73.6, 72.9, 63.7, 62.8, 58.9, 56.4, 25.9, 22.9.
1-O-β-(4-chlorobenzyl)-LNnT
1H NMR (D2O): 7.4 (s, 4H), 4.9 (d, 1H), 4.72 (m), 4.52 (d, 1H), 4.8 (d, 1H), 4.42 (d, 1H), 4.16 (d, 1H), 4.0-3.52 (m).
13C NMR (D2O): 138.9, 177.6, 138.3, 137.9, 136.2, 131.3, 105.6, 105.5, 105.4, 103.7, 93.2, 86.1, 84.7, 81.5, 81.0, 80.8, 78.0, 77.5, 77.4, 77.2, 77.1, 75.5, 75.2, 74.9, 63.7, 58.9, 57.8, 56.4, 24.8.
1-O-β-benzyl-LNT
1H-NMR (D2O, 400 MHz) δ 2.03 (s, 3H, CH3CONH), 3.35 (dd, 1H, J=8.1 8.5 Hz, H-2), 3.49 (m, 1H, H-5′′), 3.53 (m, H-2′′), 3.65 (m, 1H, H-3′′′), 3.57 (dd, 1H, J=8.1 9.0 Hz, H-4′′), 3.58 (m, 1H, H-5), 3.59 (dd, 1H, J=7.7 10.0 Hz, H-2′), 3.62 (m, 1H, H-3), 3.63 (m, 1H, H-4), 3.71 (m, 1H, H-5′), 3.71 (m, 1H, H-5′′′), 3.73 (dd, 1H, J=3.3 10.0 Hz, H-3′), 3.76 (m, 2H, H-6ab′′′), 3.76 (m, 2H, H-6ab′), 3.80 (m, 1H, H-6a′′), 3.80 (dd, 1H, J=5.0 12.2 Hz, H-6a), 3.82 (dd, 1H, J=8.1 10.5 Hz, H-3′′), 3.90 (m, 1H, H-6b′′), 3.90 (dd, 1H, J=8.4 10.5 Hz, H-2′′), 3.92 (d, 1H, J=3.3 Hz, H-4′′), 3.98 (dd, 1H, J=1.6 12.2 Hz, H-6b), 4.15 (d, 1H, J=3.3 Hz, H-4′), 4.44 (d, 1H, J=7.7 Hz, H-1′), 4.45 (d, 1H, J=7.7 Hz, H-1′′′), 4.56 (d, 1H, J=8.1 Hz, H-1), 4.73 (d, 1H, J=8.4 Hz, H-1′), 4.76 (d, 1H, J=11.7 Hz, CH2Ph), 4.94 (d, 1H, J=11.7 Hz, CH2Ph), 7.40-7.50 (m, 5H, Ph).
13C-NMR (D2O, 100 MHz) δ 24.9 (CH3CONH), 57.4 (C-2′′), 62.8 (C-6), 63.2 (C-6′′), 63.7 (C-6′′′), 63.7 (C-6′), 71.0 (C-4′), 71.2 (C-4′′′), 71.3 (C-4′′), 72.7 (C-2′), 73.4 (C-2′′′), 74.2 (CH2Ph), 75.2 (C-3′′′), 75.5 (C-2), 77.1 (C-3), 77.5 (C-5′), 77.6 (C-5′′′), 77.9 (C-5), 78.0 (C-5′′), 81.1 (C-4), 84.7 (C-3′), 84.8 (C-3′′), 103.7 (C-1), 105.3 (C-1′′), 105.6 (C-1′), 106.2 (C-1′′), 131.1 (Ph), 131.4 (2C, Ph), 131.5 (2C, Ph), 139.2 (Ph), 177.7 (CH3CONH).
M.p. 245° C. (dec.). [α]D22=−10.3 (c=1, H2O).
1-O-β-(4-methylbenzyl)-LNT
1H-NMR (D2O, 300 MHz) δ 1.97 (s, 3H), 2.29 (s, 3H), 3.27 (dd, 1H, J=8.1 8.5 Hz), 3.39-3.87 (m, 21H), 3.92 (dd, 1H, J=1.8 12.3 Hz), 4.09 (d, 1H, J=3.3 Hz), 4.37 (d, 1H, J=8.1 Hz), 4.38 (d, 1H, J=7.8 Hz), 4.47 (d, 1H, J=8.1 Hz), 4.65 (d, 1H, J=11.7 Hz), 4.67 (d, 1H, J=8.1 Hz), 4.83 (d, 1H, J=11.7 Hz), 7.22 (d, 2H, J=8.1 Hz), 7.30 (d, 2H, J=8.1 Hz).
13C-NMR (D2O, δ5.4 MHz) δ 23.1, 25.0, 57.7, 62.8, 63.2, 63.7, 63.8, 71.0, 71.1, 71.3, 72.7, 73.4, 74.1, 75.2, 75.5, 77.1, 77.5, 77.6, 77.9, 78.0, 81.1, 84.7, 84.8, 103.6, 105.3, 105.7, 106.2, 131.7 (2C), 132.0 (2C), 136.2, 141.5, 177.7.
2. Trans-Sialylation Reactions
General procedure: a solution of 2-O-(p-nitrophenyl)-α-D-sialoside (25 mmol) and the appropriate sialyl acceptor (35 mmol) in degassed incubation buffer (1.0 m, 100 mM Tris/HCl, pH 7.5, 50 mg BSA, 0.02% NaN3) was incubated with recombinant transsialidase from T. cruzi (80 μl, 1.3 mg/ml) at 23° C. for 24 h. The reaction was monitored by TLC (butanol/acetic acid/water 5:2:2). After completion, the enzyme was denatured and centrifuged before the supernatant is lyophilized. The dry residue was dissolved in water and purified by biogel chromatography (P-2 Biogel, 16×900 mm) with water or by reverse phase chromatography. The yields vary between 45-85%.
4-Chlorobenzyl 3′-O—(N-acetyl-neuraminosyl)-β-lactoside
1H-NMR (500 MHz, D2O): δ [ppm]=7.46-7.42 (m, 4H, H(a/b)arom); 4.91 (d, 1H, CH2a-Bn); 4.74 (d, 1H, CH2b-Bn); 4.55-4.52 (m, 2H, H-1/H-1′); 4.11 (dd, 1H, H-3′); 2.76 (dd, 1H, H-3′′eq); 2.04 (s, 3H, COCH3); 1.81 (dd, 1H, H-3′′ax).
J(a,b)-Bn=11.8; J2′,3′=9.9; J3′,4′=2.9; J3′′ax,3′′eq=12.4; J3′′ax,4′′=12.1; J3′′eq,4′′=4.5 Hz.
13C-NMR (126 MHz, D2O): δ [ppm]=135.2, 133.5 (quart. Carom); 130.2 (CHa-arom); 128.6 (CHb-arom); 102.6 (C-1′); 101.1 (C-1); 51.7 (C-5′′); 39.6 (C-3′′); 22.0 (COCH3).
4-Methylbenzyl 3′-O—(N-acetyl-neuraminosyl)-β-lactoside
1H-NMR (500 MHz, D2O): δ [ppm]=7.36 (d, 2H, H-aarom); 7.28 (d, 2H, H-barom); 4.89 (d, 1H, CH2a-Bn); 4.72 (d, 1H, CH2b-Bn); 4.54-4.52 (m, 2H, H-1/H-1′); 4.12 (dd, 1H, H-3′); 2.76 (dd, 1H, H-3′′eq); 2.35 (s, 3H, CH3-Tol); 2.04 (s, 3H, COCH3), 1.81 (dd, 1H, H-3′′ax).
J(a,b)arom=7.9; J(a,b)-Bn 11.5; J2′,3′=9.9; J3′,4′=3.0; J3′′ax,3′′eq=12.5; J3′′,4′′=12.2; J3′′eq,4′′=4.6 Hz.
13C-NMR (126 MHz, D2O): δ [ppm]=138.8, 133.4 (quart. Carom); 129.3 (CHa-arom); 129.0 (CHb-arom); 102.6 (C-1′); 100.9 (C-1); 99.8 (C-2′′), 51.7 (C-5′′); 39.6 (C-3′′); 22.0 (COCH3); 20.2 (CH3-Tol).
2-Naphthylmethyl 3′-O—(N-acetyl-neuraminosyl)-β-lactoside
1H-NMR (500 MHz, D2O): δ [ppm]=7.99-7.97 (m, 4H, H-arom); 7.62-7.59 (m, 3H, H-arom); 5.10 (d, 1H, CH2a-Bn); 4.95 (d, 1H, CH2b-Bn); 4.60 (d, 1H, H-1); 4.53 (d, 1H, H-1′); 4.12 (dd, 1H, H-3′); 2.77 (dd, 1H, H-3′′eq); 2.04 (s, 3H, COCH3); 1.81 (dd, 1H, H-3′′ax).
J(a,b)-Bn=11.9; J1,2=8.0; J1′,2′=7.9; J2′,3′=9.9; =3.0; J3′′ax,3′′eq=12.5; J3′′ax, 4′′=12.1; J3′′eq,4′′=4.6 Hz.
13C-NMR (126 MHz, D2O): δ [ppm]=128.3, 127.9, 127.7, 127.6, 126.6, 126.5 (CHarom); 102.6 (C-1′); 101.1 (C-1); 51.7 (C-5′′); 22.0 (COCH3).
3-Phenylbenzyl 3′-O—(N-acetyl-neuraminosyl)-β-lactoside
1H-NMR (400 MHz, D2O): δ [ppm]=7.75-7.44 (m, 9H, H-arom); 4.99 (d, 1H, CH2a-Bn); 4.82 (d, 1H, CH2b-Bn); 4.57 (d, 1H, H-1); 4.53 (d, 1H, H-1′); 4.13 (dd, 1H, H-3′); 2.78 (dd, 1H, H-3′′eq); 2.05 (s, 3H, COCH3); 1.82 (dd, 1H, H-3′′ax).
J(a,b)-Bn=11.8; J1,2=8.0; =7.9; J2′,3′=9.9; J3′,4′=3.1; J3′′ax,3′′eq=12.5; J3′′ax,4′′=12.0; J3′′eq,4′′=4.6 Hz.
13C-NMR (100 MHz, D2O): δ [ppm]=140.9, 140.3, 137.5 (quart. Carom); 129.4, 129.2, 127.9, 127.8, 127.1, 127.0, 126.9, (CHarom); 102.7 (C-1′); 101.2 (C-1); 99.6 (C-2′′); 51.8 (C-5′′); 39.7 (C-3′′); 22.1 (COCH3).
Benzyl 3′′′-O—(N-acetyl-neuraminosyl)-β-LNnT
1H-NMR (400 MHz, D2O): see FIG. 1.

## Claims

1. Method for the synthesis of compounds of human milk oligosaccharides of Formula 1-3D and salts thereof



wherein Y is independently an N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, integer p is independently 0, 1 or 2, R4′ is selected from Formulae 3-3 or 4-3,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, SA is α-sialyl moiety, and R5′ is selected from the group consisting of H, α-sialyl moiety, a group of Formula 3-3, and a group of Formula 4-3;
wherein R1 is a protecting group that is removable by hydrogenolysis, in which a sialyl donor of formula SA-OR2 and salts thereof, wherein R2 is a mono-, di- or oligosaccharide, glycolipid, glycoprotein or glycopeptide, cyclic or acyclic aliphatic group, or aryl residue, and SA is an α-sialyl moiety, is reacted with a sialyl acceptor of Formula 2D and salts thereof





wherein R1 is as defined above and is a group removable by hydrogenolysis, in which a sialyl donor of formula SA-OR3 is H or fucosyl unit, Y is independently an N-acetyl-lactosaminyl group optionally substituted with a sialyl and/or fucosyl residue, p is an integer independently selected from 0, 1 or 2, R8 is selected form Formulae 5 or 6,




wherein R6 is H or fucosyl residue, R7H or α-sialyl moiety, and R9 is selected from the group consisting of H, α-sialyl moiety, a group of Formula 5 and a group of Formula 6, under the catalysis of an enzyme having transsialidase activity.

2. The method according to claim 1, wherein the enzyme having transsialidase activity is selected from sialidases derived from Bifidobacterium species and transsialidases derived from Trypanosoma cruzi.

3. The method according to claim 1, wherein the enzyme having transsialidase activity is an engineered enzyme.

4. The method according to claim 1, wherein the sialyl donor is selected from the group consisting of 2-O-(p-nitrophenyl)-α-D-sialoside, 2-O-(4-methylumbelliferyl)-α-D-sialoside, fetuin and 3′-O-sialyl-lactose.

5. The method according to claim 1, wherein R1 is selected from the group consisting of benzyl or 2-naphthylmethyl groups optionally substituted with at least one group selected from the group consisting of phenyl, alkyl or halogen.

6. Method for the synthesis of compounds selected from the group consisting of R1-glycosides of Neu5Acα2-3Galβ1-4(Fucα1-3)Glc (3-O-fucosyl-3′-O-(N-acetyl-neuraminosyl)-lactose), Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LST a), Neu5Acα2-3Galβ1-GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FLST a), Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc, Neu5Acα2-3Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (DSLNT), Neu5Acα2-3Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (FDSLNT I), Neu5Acα2-3Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (FDSLNT II), Neu5Acα2-3Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Neu5Acα2-3Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc and salts thereof
wherein R1 is a protecting group that is removable by hydrogenolysis, in which a sialyl donor of formula SA-OR2 and salts thereof, wherein R2 is a mono-, di- or oligosaccharide, glycolipid, glycoprotein or glycopeptide, cyclic or acyclic aliphatic group, or aryl residue, and SA is an α-sialyl moiety, is reacted with a sialyl acceptor selected from the group of R1-glycosides of Galβ1-4(Fucα1-3)Glc (3-O-fucosyllactose), Galβ1-3GlcNAcβ1-3Galβ1-4Glc (LNT), Galβ1-4GlcNAcβ1-3Galβ1-4Glc (LNnT), Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc (LNFP II), Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4Glc (LNFP III), Galβ1-3GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNFP V), Galβ1-3(Fucα1-4)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNDFH II), Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4Glc (LSTb), Galβ1-3(Neu5Acα2-6)(Fucα1-4)GlcNAcβ1-3Galβ1-4Glc, Galβ1-3(Neu5Acα2-6)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Galβ1-4GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc, Galβ1-4(Fucα1-3)GlcNAcβ1-3Galβ1-4(Fucα1-3)Glc (LNDFH III), or salts thereof, under the catalysis of an enzyme having transsialidase activity.

7. The method according to claim 6, wherein R1 is selected from the group consisting of benzyl or 2-naphthylmethyl groups optionally substituted with at least one group selected from the group consisting of phenyl, alkyl or halogen.

8. The method according to claim 6, wherein the enzyme having transsialidase activity is selected from sialidases derived from Bifidobacterium species and transsialidases derived from Trypanosoma cruzi.

9. The method according to claim 6, wherein the enzyme having transsialidase activity is an engineered enzyme.

10. The method according to claim 6, wherein the sialyl donor is selected from the group consisting of 2-O-(p-nitrophenyl)-a-D-sialoside, 2-O-(4 methylumbelliferyl)-α-D-sialoside, fetuin and 3′-O-sialyl-lactose.