WO2021083735A1

WO2021083735A1 - Process for the production of 1,6-anhydro sugars

Info

Publication number: WO2021083735A1
Application number: PCT/EP2020/079468
Authority: WO
Inventors: Steen ULDALL HANSEN; Tom KOCH SVENNESEN
Original assignee: Hepoligo Solutions Aps
Priority date: 2019-10-29
Filing date: 2020-10-20
Publication date: 2021-05-06

Abstract

Method for synthesizing 1,6-anhydro sugars – in particular sugars that may be used as intermediates for making fondaparinux.

Description

PROCESS FOR THE PRODUCTION OF 1,6-AN HYDRO SUGARS

Field of the invention

The present invention relates to a novel method for synthesizing 1 ,6-anhydro sugars - in particular sugars that may be used as intermediates for making fondaparinux.

Background of the invention

Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets (thrombocytes) and fibrin to form a blood clot to prevent blood loss. Even when a blood vessel is not injured, blood clots may form in the body under certain conditions.

A venous thrombus is a blood clot (thrombus) that forms within a vein. A common type of venous thrombosis is deep vein thrombosis (DVT), which is a blood clot in the deep veins of the leg. if the thrombus breaks off (embolizes) and flows towards the lungs, it can become a life-threatening pulmonary embolism (PE), a blood clot in the lungs.

When a thrombus is substantially large enough to reduce the blood flow to a tissue, hypoxia (oxygen deprivation) can occur and metabolic products such as lactic acid can accumulate. In arteries, this results predominantly from platelet activation and leads to heart attack, angina or stroke, whereas venous thrombosis results in inflammation and pulmonary emboli. The coagulation of blood is the result of a cascade of events employing various enzymes collectively known as activated blood coagulation factors.

Heparin is a powerful anticoagulant and has been used since the late 1930's in the treatment of thrombosis. Heparin is a polysulfated polysaccharide with alternating D- glucosamine (GlcN) and either D-glucuronic acid (GlcA) or L-iduronic acid (IdoA) units. Within its microheterogeneous chain is a particular pentasaccharide motif that binds and activates antithrombin, which then acts as an inhibitor of the blood coagulation cascade. In nature, heparin is a polymer of varying chain size. Unfractionated heparin as a pharmaceutical is heparin that has not been fractionated to sequester the fraction of molecules with low molecular weight. In contrast, low-molecular-weight heparin has undergone fractionation for the purpose of making its pharmacodynamics more predictable. However, active monitoring is needed during heparin therapy because serious complications such as heparin-induced thrombocytopenia, uncontrolled bleeding, and osteoporosis may occur. To avoid the problems associated with nature-sourced heparins, synthetic pentasaccharides, derived from the aforementioned antithrombin-binding sequence, have been developed. One such compound, fondapahnux, was developed and found to be safer and to display comparable to superior efficacy and pharmacological properties compared to unfractionated heparin and its low-molecular-weight variants, in reducing extension and recurrence of superficial venous thrombosis, and progression to symptomatic embolism.

The pharmaceutical compound fondapahnux consists of a sulfated pentasaccharide unit comprising the sugars D-glucosamine (building block A, C and E), D-glucuronic acid (building block D) and L-iduronic acid (building block B) as set forth in scheme 1 below.

Scheme 1

Sugar oligomers or oligosaccharides such as fondapahnux are assembled using coupling reactions, also known as glycosylation reactions, to “link” the sugar monomer building blocks together. The difficulty of these linking steps arises because of the required stereochemical relationship.

The chemical synthesis of fondapahnux is very demanding due to the regio- and stereochemical aspects of the assembly and the strategic placement of multiple sulfate groups.

A generic version of fondapahnux was developed by Alchemia (Australia) and is marketed in the United States by Dr. Reddy's Laboratories. EP1440077B1 discloses intermediates and processes for the chemical synthesis of fondapahnux and other heparin pentasaccharides. However, the synthesis method for fondapahnux disclosed in EP1440077 is also a very complex process and involves more than 50 steps with an estimated overall yield of less than 0.3%. US2014/0336369A1 (Apicore) discloses a chemical synthesis of fondaparinux in more than 50 steps with improved reaction conditions, resulting in reduced solvent quantities and a greater purity of the final fondaparinux product and with an overall yield of less than 0.3%.

US8742077B2 (Sanofi) discloses in scheme 2 (see end of column 6 to column 9) a process for the preparation of an 1,6-anhydro,2,3-epoxy-glucopyranose starting from D-glucose and comprising reacting D-glucose in anhydrous pyridine with TsCI, to obtain an intermediate corresponding to a compound of formula E1 of the method of the first aspect of the present application and further (in stage 3) reacting the mixture with the base MeONa (STAGE 3 - column 8, lines 49-53) to give an end product that is different from E2 end product of the method of the first aspect in the present application.

Zottola et al (J. Org. Chem. 1989, 54, 6123 - 6125) discloses in the Experimental Section the reaction of D-glucose with p-tolylsulfonyl chloride (TsCI) in pyridine followed by reaction with NaOH (3N) + further purification. In this article is described a process for making 1,6- anhydro sugars on larger scale starting from either D-glucose or D-mannose. The process involves first reacting D-glucose with 1.5 eq. of toluenesulfonyl chloride in pyridine which results in a monotosylated product 2 (Scheme I). The product 2 is then further reacted with an unspecified amount of 3N NaOH to yield 1 ,6-anhydro sugars 3a or 3b. In the method of the first aspect of the present application is produced a ditosylated intermediate E1 (i.e. not monotosylated as in this article) e.g. due to that there is used a larger quantity of e.g. TsCI. The end product of this article is also different from E2 end product of the method of the first aspect in the present application.

In spite of certain improvements that have been made in the synthesis of fondaparinux, the available synthesis methods are still quite complex and provide low overall yields. Thus, there remains a need in the art for new and improved methods for efficient synthesis of fondaparinux and related compounds that provide a high yield and a high degree of stereoselective purity, and which employ less expensive reagents and fewer synthesis steps.

Summary of the invention

The problem to be solved by the present invention is to provide a novel method for synthesizing 1 ,6-anhydro sugars - in particular sugars that may be used as intermediates for making fondaparinux.

Working examples herein describe preferred examples/embodiments of the synthesis of compound 1 below.

As discussed herein compound 1 (1 ,6-anhydro-2-0-p-toluenesulfonyl^-D-glucose) is a preferred example of compounds of formula E2 of the method of the first aspect.

The article by Wei et al (Chin. J. Chem., 2009, (27), 1589-1592) describes the synthesis of compound 1 (compound 2 of scheme 1 on p1590) starting from Levoglucosan (1 ,6-anhydro- b-D-glucose - compound 1 of scheme 1 on p1590).

An advantage of the present invention is that it is a method starting from D-glucose, which is a common cheap compound - e.g. it is significantly cheaper than Levoglucosan. A further advantage of the method as described herein is that it can e.g. be adapted to a one-pot method taking place in a single reactor without purifying intermediate products.

The article by Wei et al discussed above also describes the synthesis of compound 2 (1 ,6- anhydro-2-azido-2-deoxy^-D-glucose) below (compound 3 of scheme 1 on p1590) from compound 1.

Starting from above discussed compound 1 (1,6-anhydro-2-0-p-toluenesulfonyl^-D- glucose), the article by Stanek and Cerny ( Synthesis , 1972, 698-699) describes the synthesis of the compound 3 ((1,6:2,3)-dianhydro^-D-mannose; compound 6 on p698) with the below following structure. Further, US2014/0336369A1 (Apicore) discloses use of compound 2 as an intermediate for making fondaparinux (see e.g. [0034] and [0028] where compound 2 is designated XXVII) and US2016/0264609A1 (Zhejiang Hisun Pharmaceutical) discloses use of compound 3 as an intermediate for making fondaparinux (see e.g. [0017]).

Thus, compound 1 may accordingly to the art be converted into compounds 2 or 3, which are known to be useful intermediates for making fondaparinux. A major advantage of the present invention is that compound 2 can be generated from compound 1 in only 2 process steps, compared to the 6 steps involved in the previously established process used by Apicore (see e.g. [0034]) and others in generating compound 2 when making fondaparinux.

As discussed above, working examples of the present invention describes herein preferred examples/embodiments of synthesis of compound 1.

As understood by the skilled person - one may make relatively routine changes (e.g. use of a different halide than chloride) to the specific methods of working examples herein and still achieve the herein described relevant improvements. A skilled person knows which solvents are compatible with which inorganic bases and which solvents are compatible with which organic bases. An example being the inorganic base potassium carbonate used with solvents such as water or methanol. Another example being the organic base 1,8- diazabicyclo(5.4.0)undec-7-ene DBU used with solvents such as pyridine or dichloromethane.

Accordingly, a first aspect of the present invention relates to a method for synthesizing a compound of formula E2 comprising reacting D-glucose according to reaction scheme below wherein the method comprises the following steps:

1): reacting D-glucose with 1.7 to 4 equivalents (preferably 2 - 2.5 equivalents) of Ri- SO2-X in the presence of a base A and optionally thereafter adding an acylating agent Rs-Y;

2) removing the majority of excess amounts of R1-SO2-X, base A, optionally R3-Y and acidic compounds generated in step 1) to get a composition comprising E1 and less than 25% (such as e.g. less than 10%) of the acidic compounds generated in step 1);

3) adding 1 to 1.5 equivalent of base B relative to D-glucose of step 1 ) to the composition comprising E1 of step 2) in a solvent Si at a temperature T;

4) obtaining the compound of formula E2; or wherein the method does not comprise a step of using an acylating agent of step 1 ) and f¾ in E1 is -H and wherein the method comprises the following steps: i): reacting D-glucose with 1.7 to 4 equivalents (preferably 2 - 2.5 equivalents) of Ri- SO2-X in the presence of a base A; ii) adding 3 to 4 equivalents of base B relative to D-glucose of step i) to the reaction mixture of step i) at a temperature T; iii) obtaining the compound of formula E2; and wherein when base B is added in step ii) there has not prior to this step ii) been performed a step that removes the majority of excess amounts of R1-SO2-X, base A and acidic compounds generated in step i) and the reaction mixture of step i) therefore comprises more than 75% (such as e.g. more than 90%) of the acidic compounds generated in step i); and wherein: Ri is 4-methylphenyl, phenyl, methyl, ethyl, terf-butyl, trichloromethyl, trifluoromethyl, benzyl or allyl; and

R2 is -H, acetyl, benzoyl, pivaloyl, thchloroacetyl or chloroacetyl; and

R3 is acetyl, benzoyl, pivaloyl, thchloroacetyl or chloroacetyl; and

X is -Cl (chloride), -O₃SR₁, -F (fluoride), -Br (bromide), or -I (iodide); and

Y is -Cl (chloride), -O2CR1, -F (fluoride), -Br (bromide), or -I (iodide); and base A is pyridine, 2,6-lutidine, dimethylaminopyridine (DMAP), triethylamine, diisopropylethylamine (DIEA), 1 ,4-diazabicyclo[2.2.2]octane (DABCO), imidazole, N- methylimidazole or a mixture of these; and base B is 1 ,8-diazabicyclo(5.4.0)undec-7-ene (DBU), potassium carbonate, cesium carbonate, sodium methoxide, sodium ethoxide, potassium terf-butoxide, tetrabutylammonium hydroxide, Amberlite IR-400 OH^®, cesium hydroxide, sodium hydroxide, potassium hydroxide or a mixture of these; and solvent Si is methanol, ethanol, butanol, water, dichloromethane, tetrahydrofuran, toluene or a mixture of these; and temperature T is selected to be below 100°C, preferably wherein temperature T is from 0°C to 20°C.

In relation to step 1) were in working examples herein made a reaction of D-glucose with around 2 to 2.5 equivalents of R1-SO2-X (used p-tolylsulfonyl chloride (TsCI)).

However, it is believed that it would work reasonably well by reacting D-glucose with around 1.7 to 4 equivalents equivalents of R1-SO2-X (such as preferably TsCI).

In above discussed prior art article of Zottola et al (J. Org. Chem. 1989, 54, 6123 - 6125) was only used 1.5 equivalent of TsCI.

In relation to step 2) - it is routine work for the skilled person to remove the majority of relevant compounds of earlier method steps - such as e.g. by standard filtration optionally followed by washing steps or e.g. by standard extraction step as illustrated in working examples herein. As understood by the skilled person in the present context - by making such standard removal steps one may routinely get “a composition comprising E1 and less than 25% of the acidic compounds generated in step 1)” as required in step 2) of the first aspect.

As evidently understood by the skilled person - when performing such removal steps there is also routinely removed other compounds than acid compounds - such as e.g. R1-SO2-X, base A and optionally R3-Y (if acylating agent R3-Y is used).

In a preferred embodiment, step 2 comprises:

2a): precipitating the compound of formula E1 by addition of a solvent (preferably water), wherein E1 precipitates in the solvent and the majority of acidic compounds generated in step 1) are soluble in the solvent followed by filtrating and optionally followed by washing; or

2b): extraction of the compound of formula E1.

It is routine work for the skilled person to identify a suitable solvent for the above discussed step 2a) - for instance a solvent that has herein relevant similar characteristic as water.

Step 3) relates the addition of “1 to 1.5 equivalent of base B relative to D-glucose of step 1 )” in a situation where the majority of acidic compounds has been removed in step 2) - the “1 to 1.5 equivalent” correspond to amounts of base B used in working examples herein.

In above discussed US8742077B2 (Sanofi) the majority of acidic compounds were removed in relation to the purification of a compound identical to E1 but then used significantly higher amount of base than the “1 to 1.5 equivalent” required in step 3) of the first aspect herein. For instance, the intermediate C^'(0.98 mol)(corresponds to E1) is in US8742077B2 reacted with the base sodium methoxide (2.12 mol - corresponding to 2.16 eq.) to yield the cyclised product I, which is different form E2.

The use of significantly higher amount of base than the “1 to 1.5 equivalent” required in step 3) is further underlined in claim 6 of US8742077B2, where it is stated that the “cyclisation stage is carried out using from two to three equivalents of alkoxide”.

Step ii) of the first method relates to a one-pot related method (see e.g. working example herein), wherein when base B is added in step ii) there has not prior to this step ii) been performed a step that removes the majority of acidic compounds generated in step i) - i.e. the majority of earlier generated acidic compounds are still present - i.e. it is fundamentally a different method than e.g. described in US8742077B2 (Sanofi), where there is made a purification of a compound identical to E1 (see above).

In relation to step 4) and step iii) - as known to the skilled person, once the compound of formula E2 has been obtained it may e.g. be purified (e.g. to at least 40% purity w/w, to at least 80% purity w/w or to at least 95% purity w/w) - alternatively, the obtained compound of formula E2 may be used as such (e.g. without further purification) in e.g. subsequent chemical reactions.

Since a majority of earlier generated acidic compounds are still present when base B is added in step ii) - the present inventors identified (see e.g. working example herein) that one need to use around 2 to 2.5 equivalent base B to neutralise acidic components and therefore it is required in this step ii) to add “3 to 4 equivalents of base B relative to D- glucose of step i)” in order to have around “1 to 1.5 equivalent base B” that actually is “free” to make the required reaction/conversion of E2 to E1.

It may be preferred (as done in working example herein) to perform step ii) by adding 2 to 2.5 equivalent base B to the reaction mixture to neutralise acidic components and after a time period of at least 15 seconds (such as at least 1 minute or at least 5 minutes) adding 1 to 1.5 equivalent base B to the reaction mixture.

As discussed above, a compound of formula E2 may according to the art be used as a suitable intermediate for making fondaparinux. When a compound of formula E2 is reacted with an azide source (e.g. reaction of compound 1 to compound 2) a displacement takes place where the substituted sulfonyl group at the 02 position is displaced with an azido group and will thus in all cases create the exact structure of compound 2. Also, when a compound of formula E2 is reacted with a suitable base (e.g. reaction compound 1 to compound 3) a displacement takes place where the substituted sulfonyl group at the 02 position is displaced by the oxygen at the 03 position and thus in all cases produce the exact structure 3. In both cases the substituted sulfonyl group of general formula I acts as a leaving group.

Accordingly, a second aspect of the present invention relates to a process for producing fondaparinux comprising the following steps:

(i): synthesizing a compound of formula E2 according to the method of any of the preceding claims; and

(ii): use of the compound of formula E2 obtained in step (i) as an intermediate in a method for producing fondaparinux and thereby obtaining fondaparinux. Figure 1 herein shows a preferred example of producing fondaparinux of the second aspect herein.

Drawing

Figure 1: shows a preferred example of producing fondaparinux of the second aspect herein.

Detailed description of the invention

Prior to a discussion of the detailed embodiments of the invention is provided a definition of specific terms related to the main aspects and embodiments of the invention. All terms are defined in accordance with the skilled person’s normal understanding of the terms.

Definitions

The term "one-pot method" as used herein means two or more reactions that take place, in just one reactor, without isolating and purifying intermediate compounds, wherein all the reactants are added at the beginning of the first reaction or sequentially during the course of the reaction with no limitation as to the duration of time elapsing between introduction of sequentially added reactants.

The term “building block” or “monosaccharide building block” as used herein refers to the monosaccharide units that form the building blocks for the fondaparinux molecule and are monosaccharides labeled with the glucosamine unit on the right referred to as monosaccharide A and the next, an iduronic acid unit to its left as B and subsequent monosaccharide units, C (a glucosamine unit), D (glucuronic acid unit) and E (glucosamine unit) as shown in Scheme 1.

The terms "4-methylphenyl, phenyl, methyl, ethyl, trichloromethyl, trifluoromethyl, benzyl and allyl" as used herein are chemical groups which are substituents with structural formulas in accordance with lUPAC nomenclature or commonly accepted trivial names found in standard organic chemistry books like McMurry: Fundamentals of organic chemistry 7^th edition.

The terms “a” and “an” and “the” and similar referents as used in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context e.g. “a” or “an” means “one or more”.

The term “selected from a group consisting of: a, b, c and d” as used herein is intended to mean at least one member of a group consisting a, b, c and d” and includes both the individually group members and combinations thereof such as e.g. a+b and a+c and b+c.

In the following description, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one having ordinary skill in the art that the invention may be practiced without these specific details. In some instances, well-known features may be omitted or simplified so as not to obscure the present invention. Furthermore, reference in the specification to phrases such as "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of phrases such as "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment. Embodiments of the present invention are described below, by way of examples only.

A method for synthesizing a compound of formula E2

Applicants have found that by reacting D-glucose with compounds containing a functional sulfonyl halide group having the general formula R1-SO2-X where X is a suitable leaving group such as halogen in the presence of a suitable base, 1 ,6-anhydro-2-0-sulfonyl sugars of formula E2 can be produced fast and at low cost and in good yield.

It is routine work for the skilled person to identify suitable sulfonyl halide groups which can react with D-glucose in the presence of a suitable base to prepare 1 ,6-anhydro-2-0-sulfonyl sugars of formula E2. In one embodiment of the present invention the sulfonyl halide is any functional sulfonyl halide having the general formula R1-SO2-X which can react with D- glucose. In a preferred embodiment R1-SO2-X is p-toluenesulfonyl chloride. When Ri is p- toluenesulfonyl chloride, 1 ,6-anhydro-2-0-p-toluenesulfonyl^-D-glucose (compound 1) is prepared.

In another embodiment Ri is any functional chemical group bound to a sulfonyl halide group that can react with D-glucose in the presence of a suitable base in a method forming 1 ,6- anhydro-2-O-sulfonyl sugars of formula E2. In a further embodiment Ri is a functional chemical group selected from the group consisting of 4-methylphenyl, phenyl, methyl, ethyl, trichloromethyl, trifluoromethyl, benzyl and allyl. In a preferred embodiment, Ri is 4-methylphenyl.

Sulfonyl halide groups are sulfonyl functional groups singly bonded to a halogen atom or Ri substituted sulfonate groups (-O₃SR1). The stability of sulfonyl halides decreases in the order fluorides>chlorides>bromides>iodides. In one embodiment of the present invention X is selected from the group consisting of, -Cl (chloride), -F (fluoride), -Br (bromide), and -I (iodide). In another embodiment X is -O₃SR1 (Ri substituted sulfonate). In a preferred embodiment X is chloride.

The method for synthesizing a compound of formula E2 from D-glucose comprises reacting D-glucose with R1-SO2-X in the presence of a suitable base A. In one embodiment of the present invention the base A is any suitable base A capable of mediating the reaction of D- glucose with R1-SO2-X. In another embodiment base A is selected from the group consisting of pyridine, 2,6-lutidine, dimethylaminopyridine (DMAP), triethylamine, diisopropylethylamine (DIEA), 1 ,4-diazabicyclo[2.2.2]octane (DABCO), imidazole and N- methylimidazole. In a preferred embodiment, base A is pyridine.

Without being limited to theory it is believed that during the reaction, of D-glucose with R- SO2-X in the presence of a suitable base A an intermediate product E1 is created as shown below. This intermediate product is then converted into E2 in the presence of a second base B.

In one embodiment of the present invention base B is any suitable base capable of mediating the conversion of compound E1 to compound E2. In another embodiment of the present invention base B is selected from the group consisting of 1,8- diazabicyclo(5.4.0)undec-7-ene (DBU), potassium carbonate, cesium carbonate, sodium methoxide, sodium ethoxide, potassium terf-butoxide, tetrabutylammonium hydroxide, Amberlite IR-400 OH^®, cesium hydroxide, sodium hydroxide and potassium hydroxide. In a further embodiment, base B is selected from the group consisting of DBU and sodium methoxide. In a preferred embodiment base B is 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), NaOMe or a mixture of DBU and NaOMe.

As described above one advantage of the method of the present invention is that it is a method starting from D-glucose, which is a common low cost compound commercially available in bulk quantities. A further advantage of the method as described herein is that it can be performed as one-pot method taking place in a single reactor without isolating nor purifying the intermediate compound E1.

Accordingly, in one embodiment of the present invention the method of the first aspect and any relevant embodiments thereof, is a one-pot method.

In another embodiment, the intermediate compound E1 may be precipitated or purified before it is the converted to E2.

The skilled person knows how to purify 1,6-anhydro sugars such as E2 from solutions by chromatography and crystallization. In one embodiment of the present invention the purification of the compound of formula E2 of the first aspect and any relevant embodiments thereof comprises column chromatography. In another embodiment, the purification of the compound of formula E2 of the first aspect and any relevant embodiments thereof comprises column chromatography using silica gel and a solvent system with a dichloromethane/methanol mixture or a dichloromethane/ethyl acetate mixture. In a further embodiment of the present invention the dichloromethane/methanol mixture is a gradient from (DCM/MeOH 1:0 to 30:1 to 20:1 to 10:1).

In another embodiment of the present invention the purification of the compound of formula E2 of step 3) of the first aspect and any relevant embodiments thereof comprises crystallization using a toluene/ethyl acetate mixture. In a further embodiment, the toluene/ethyl acetate mixture is mixture of toluene/ethyl acetate in from 10:1 to 1 :10, such as from 5:1 to 1 :5. In a preferred embodiment, the toluene/ethyl acetate mixture is a mixture of toluene/ethyl acetate in (5:1).

A process for producing fondaoarinux As explained above the article by Wei et al describes the synthesis of compound 2 (1 ,6- anhydro-2-azido-2-deoxy^-D-glucose) from compound 1. Further US2014/0336369A1 (Apicore) discloses use of compound 2 (designated XXIV in US2014/0336369A1 [0034]) as an intermediate for making fondaparinux (see e.g. [0028] and examples therein) where XXIV can be modified into a XXVII monomer and XXVII monomers may then be linked to form a disaccharide XL, XLIII and XX dimers may then be linked to form a tetrasaccharide, XLVII tetramer and XLV monomer may be linked to form a pentasaccharide (XLVIII) pentamer. The XLVIII pentamer is an intermediate that may be converted through a series of reactions to fondaparinux sodium. This strategy described in US2014/0336369A1 provides an efficient method for kilogram preparation of fondaparinux in high yields and high stereoselective purity.

In addition, Stanek and Cerny (Synthesis, 1972, 698-699) describes the synthesis of compound 3 from compound 1 and, US2016/0264609A1 (Zhejiang Hisun Pharmaceutical) discloses use of compound 3 as an intermediate for making fondaparinux (see e.g. [00017] where a DC disaccharide intermediate is prepared as set forth in scheme 1 above.). This DC disaccharide intermediate may be applied in the subsequent synthesis of fondaparinux. Thus, compound 1 may accordingly to the art be converted into compounds 2 or 3, which are known to be useful intermediates for making fondaparinux.

In one embodiment of the present invention the process of the second aspect is a process wherein step (i) is made by synthesizing a compound of formula E2, wherein R1-SO2-X is p- toluenesulfonyl chloride and the compound of formula E2 is 1 ,6-an hydro-2 -O-p- toluenesulfonyl^-D-glucose (compound 1).

In another embodiment, the process of the second aspect or any relevant embodiments is a process, wherein compound 1 obtained in step (i) is converted into compound 2 or 3 as intermediates for producing fondaparinux and thereby obtaining fondaparinux.

In a further embodiment, the process of the second aspect or any relevant embodiments is a process, wherein compound 1 obtained in step (i) is converted into building blocks C or E as intermediates for producing fondaparinux and thereby obtaining fondaparinux.

Figure 1 herein shows a preferred example of producing fondaparinux of the second aspect. EXAMPLES

The following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention in any way as many variations and equivalents that are encompassed by the present invention will become apparent to those skilled in the art upon reading the present disclosure.

The following abbreviations are used herein:

Acetate (Ac); Acetic acid (AcOH); Benzyl (Bn); 1 ,8-Diazabicyclo[5.4.0]undec-7-ene (DBU); Dichloromethane (DCM); Ethyl acetate (EtOAc); Magnesium sulfate (MgSC ); Methanol (MeOH); Sodium hydrogen carbonate (NaHCOs); Sodium methoxide (NaOMe); Sulfuric acid (H2SO4); f-butyldimethylsilyl (TBS); p-toluenesulfonyl chloride also known as tosyl chloride, 4-methylbenzenesulfonyl chloride, (4-methylphenyl)sulfonyl chloride, p-tolylsulfonyl chloride (TsCI).

Example 1 (Acylation and precipitation):

Synthesis of 1,6-anhydro-2-0-p-toluenesulfonyl-R-D-glucose - Compound 1, which is a compound of formula E2

To D-glucose (180.0 g, 1.00 mol) was added dry pyridine (2.0 L) in a reactor and the suspension stirred while kept under Argon for 15 min. The mixture was then cooled to - 20°C. Then p-toluenesulfonyl chloride (418 g, 2.20 mol) was divided in 5 portions and added over 7 hrs as a solid with vigorous stirring. The reaction mixture was kept at -20°C for another 17 hrs. Then the cooling was removed and added acetic anhydride (312 mL, 3.30 mol) and DMAP (1.2 g, 0.01 mol). After 6 hrs water (5 L) was slowly added with stirring which resulted in precipitation of a white solid. The liquid phase was removed by filtration and to the remaining solid was added MeOH (1 L) and stirred 2 hrs. The solution was again filtered and the white fine precipitate was dried in the reactor. The precipitate was dissolved in DCM (2 L) and MeOH (2 L). To this solution was added NaOMe (207 mL, 5.4 M in MeOH, 1.12 mol) drop wise over 90 min. and stirred another 30 min. The solvents were evaporated and the product separated from salts and base line impurities by Flash short column chromatography using DCM/MeOH (1 :0 to 20:1 to 15:1). This gave a product mixture that could be crystallized to yield 1 (180 g, 66%).

Example 2 (Extraction):

1,6-anhydro-2-0-p-toluenesulfonyl-R-D-glucose (1 ).

To D-glucose (150.0 g, 0.833 mol) was added dry pyridine (1.4 L) in a reactor and the suspension stirred while kept under Argon for 15 min. The mixture was then cooled to - 20°C. Then p-toluenesulfonyl chloride (348 g, 1.83 mol) was divided in 3 portions and added over 3 hrs as a solid with vigorous stirring. After the first portion of p-toluenesulfonyl chloride (115.9 g) was added the reaction was cooled in an icebath and second portion (108.5 g) after 1 h and third portion (123.6 g) after 3 hrs. The reaction mixture was kept at 0°C for another 7 hrs and then left over night at room temperature. To the reactor was then added DCM (2 L), ice (1 .5 kg) and slowly a solution of 4M H2SO4 (1 .75 L) until pH ~ 3 while the temperature was maintained at below 30°C. The organic phase was separated via an outlet in the bottom of the reactor and more DCM (1 L) added to the reactor and after stirring the second organic phase is combined with the first in a second reaction vessel. To the mixture was added EtOH (0.3 L) and DBU (131 ml_, 0.87 mol) was added over 45 min. with stirring. After another 75 min. the reaction was quenched by adding AcOH (12 ml.) and the organic phase washed with a mixture of water/brine (800 mL/200 ml_). The aqueous phase was extracted with DCM (2x500 mL) and the combined organic phase dried over MgSC , filtered and evaporated. The dark oil obtained was purified by flash column chromatography using a gradient (DCM/EtOAc 1 :0 to 10:1 to 2:1 to 1 :1) yielding 1 (104.7 g, 40%). To remove traces of impurities the product was crystallized from a mixture of toluene/EtOAc (5:1) by heating to above 60°C until everything is dissolved and upon cooling a white precipitate formed that was isolated by filtration.

Example 3 (One pot):

1,6-anhydro-2-0-p-toluenesulfonyl^-D-glucose (1 ).

A)To D-glucose (24.5 g, 0.136 mol) was added dry pyridine (0.25 L) in a reactor and the suspension stirred while kept under Argon for 15 min. The mixture was then cooled to - 20°C. Then p-toluenesulfonyl chloride (30.8 g, 0.162 mol) was added as a solid with vigorous stirring. The reaction was then warmed to 0°C over 1 hr by external cooling with ice. After another 45 min. more toluenesulfonyl chloride (25.9 g, 0.136 mol) was added as a solid and the reaction maintained at 0-5°C for another 16 hrs.

B) To the mixture at 0°C was then added in portion DCM (100 mL) and NaOMe (56 mL of a 5.4 M solution in MeOH) over 20 min. while stirring vigorously.

C) After another 10 min. 1 ,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (30.4 mL, 0.204 mol) was added over 30 min. with stirring. The external cooling was removed and reaction stirred for another 4.5 hrs.

To the reactor was then added DCM (0.3 L), water (0.2 L) and slowly a solution of 4M H₂SO₄ (0.86 L) until pH ~ 3 while the temperature is maintained at below 30°C using external cooling. The organic phase is separated via an outlet in the bottom of the reactor and more DCM (0.1 L) added to the reactor and after stirring the second organic phase is combined with the first and the organic phase washed with a mixture of NaHCOs(sat.) /brine (50 mL/200 ml_). The organic phase was dried over MgSC , filtered and evaporated. The dark oil obtained was purified by flash column chromatography using a gradient (DCM/EtOAc 1:0 to 10:1 to 2:1 to 1 :1) yielding 1 (17.2 g, 40%). To remove traces of impurities the product was crystallized from a mixture of toluene/EtOAc (5:1) by heating to above 60°C until everything is dissolved and upon cooling a white precipitate formed that was isolated by filtration

Following literature procedures (US2014/0336369A1 and US2016/0264609A1), gram scale quantities of well established building blocks C and E derivatives used in the industrial preparation of the pharmaceutical fondaparinux sodium have been prepared according to the reaction scheme below.

REFERENCE LIST

1 : EP1440077

2: US2014/0336369A1 (Apicore) 3: Wei et al (Chin. J. Chem., 2009, (27), 1589-1592)

4: Stanek and Cerny ( Synthesis , 1972, 698-699)

5: US2016/0264609A1 (Zhejiang Hisun Pharmaceutical)

6: McMurry: Fundamentals of organic chemistry 7^th edition 7: US8742077B2 (Sanofi) 8: Zottola et al (J. Org. Chem. 1989, 54, 6123 - 6125)

Claims

1. A method for synthesizing a compound of formula E2 comprising reacting D-glucose according to reaction scheme below

wherein the method comprises the following steps:

1): reacting D-glucose with 1.7 to 4 equivalents of R1-SO2-X in the presence of a base A and optionally thereafter adding an acylating agent R3-Y;

2) removing the majority of excess amounts of R1-SO2-X, base A, optionally R3-Y and acidic compounds generated in step 1) to get a composition comprising E1 and less than 25% of the acidic compounds generated in step 1);

4) obtaining the compound of formula E2; wherein the method does not comprise a step of using an acylating agent of step 1) and f¾ in E1 is -H and wherein the method comprises the following steps: i): reacting D-glucose with 1.7 to 4 equivalents of R1-SO2-X in the presence of a base A; ii) adding 3 to 4 equivalents of base B relative to D-glucose of step i) to the reaction mixture of step i) at a temperature T; iii) obtaining the compound of formula E2; and wherein when base B is added in step ii) there has not prior to this step ii) been performed a step that remove the majority of excess amounts of R1-SO2-X, base A and acidic compounds generated in step i) and the reaction mixture of step i) therefore comprises more than 75% of the acidic compounds generated in step i); and wherein:

Ri is 4-methylphenyl, phenyl, methyl, ethyl, terf-butyl, trichloromethyl, trifluoromethyl, benzyl or allyl; and

R2 is -H, acetyl, benzoyl, pivaloyl, trichloroacetyl or chloroacetyl; and

R3 is acetyl, benzoyl, pivaloyl, trichloroacetyl or chloroacetyl; and

2. The method of claim 1 , wherein Ri is 4-methylphenyl.

3. The method of any of the preceding claims, wherein step 1) is reacting D-glucose with 2 to 2.5 equivalents of R1-SO2-X or step i) is reacting D-glucose with 2 to 2.5 equivalents of R1-SO2-X.

4. The method of any of the preceding claims, wherein X is chloride.

5. The method of claim 4, wherein R1-SO2-X is p-toluenesulfonyl chloride and the compound of formula E2 is 1,6-anhydro-2-0-p-toluenesulfonyl^-D-glucose (compound 1).

6. The method of any of the preceding claims, wherein base A is pyridine.

7. The method of any of the preceding claims, wherein base B is 1 ,8- diazabicyclo(5.4.0)undec-7-ene (DBU), NaOMe or a mixture of DBU and NaOMe.

8. The method of any of the preceding claims, wherein the method of claim 1 comprises the following steps:

1): reacting D-glucose with 1.7 to 4 equivalents of R1-SO2-X in the presence of a base A and optionally thereafter adding an acylating agent R₃-Y;

2) removing the majority of excess amounts of R1-SO2-X, base A, optionally R₃-Y and acidic compounds generated in step 1) to get a composition comprising E1 and less than 25% of the acidic compounds generated in step 1);

4) obtaining the compound of formula E2.

9. The method of claim 8, wherein step 1 is reacting D-glucose with R1-SO2-X in the presence of a base A and thereafter adding an acylating agent R₃-Y.

10. The method of claim 9, wherein Y is -O2CCH₃ (acetate) and wherein Rsand R2 are acetyl.

11. The method of any of claims 8 to 10, wherein solvent Si is methanol.

12. The method of any of claims 8 to 11 , wherein step 2 comprises:

2b): extraction of the compound of formula E1.

13. The method of any of claims 1 to 7, wherein the method of claim 1 comprises the following steps: i): reacting D-glucose with 1.7 to 4 equivalents of R1-SO2-X in the presence of a base A; ii) adding 3 to 4 equivalents of base B relative to D-glucose of step i) to the reaction mixture of step i) at a temperature T; iii) obtaining the compound of formula E2; and wherein step ii) comprises: adding 2 to 2.5 equivalent base B to the reaction mixture to neutralise acidic components and after a time period of at least 15 seconds (such as at least 1 minute) adding 1 to 1.5 equivalent base B to the reaction mixture.

14. A process for producing fondaparinux comprising the following steps:

(ii): use of the compound of formula E2 obtained in step (i) as an intermediate in a method for producing fondaparinux and thereby obtaining fondaparinux.

15. The process for producing fondaparinux of claim 14, wherein step (i) is made according to the method claim 5.