METHOD FOR THE ANALYSIS OF GLYCOSAMINOGLYCANS, HEPARINS AND THEIR DERIVATIVES BY NUCLEAR MAGNETIC RESONANCE Field of the invention

The present invention describes an analytical method by nuclear magnetic resonance (1H-NMR and 1H-13C HSQC) for the characterization of glycosaminoglycans in general, and heparins and low molecular weight heparins and their derivatives in particular, which allows their quantitative analysis. Background of the invention

Nuclear magnetic resonance (NMR) spectroscopy is one of the most important and widespread analytical techniques used in the characterization of glycosaminoglycans in general, and heparins and low molecular weight heparins and their derivatives in particular.

The possibility of performing both one-dimensional and two-dimensional experiments makes this technique highly sensitive for determining small variations in molecular structure, making it very advantageous for a suitable characterization of these compounds.

Glycosaminoglycans (GAGs) are linear and negatively charged polysaccharides with a mean molecular weight between 10– 100 KDa (The Structure of Glycosaminoglycans and their Interactions with Proteins. Gandhi NS and Mancera RL. Chem Biol Drug Des 2008; 72:455-482). There are two large groups of glycosaminoglycans: nonsulfated (such as hyaluronic acid) and sulfated (such as chondroitin sulfate, dermatan sulfate, keratan sulfate, heparin and heparan sulfate). Glycosaminoglycan chains are formed by disaccharide units or disaccharides composed of a uronic acid (D-glucuronic or L-iduronic) and an amino sugar (D-galactosamine or D- glucosamine).

Formula 1: General structure of the disaccharide unit for the different types of glycosaminoglycans Heparin is a polysaccharide from the glycosaminoglycan family, formed by uronic acid (L- iduronic or D-glucuronic acid) and D-glucosamine, linked alternatively. L-iduronic acid may be 2- O-sulfated and D-glucosamine, may be N-sulfated and/or 6-O-sulfated, and to a lesser extent N- acetylated or 3-O-sulfated (Mapping and quantification of the major oligosaccharides component of heparin. Linhardt RJ, Rice KG, Kim YS et al. Biochem J 1988; 254:781-787). The major disaccharide repeating unit corresponds to the trisulfated disaccharide, 2-O-sulfo L-iduronic acid (1→4) 2-N-sulfo-6-O-sulfo D-glucosamine.

The origin of this structural variability present in heparin oligosaccharide chains is found in their biosynthesis and in the mechanism regulating it. Thus, in the first stage of biosynthesis, a tetrasaccharide fragment formed by glucose-galactose-galactose-xylose is bound to a protein core, starting the biosynthesis of the glycoprotein chain. Next, glucuronic acid (GlcA) residues and N- acetylglucosamine (GlcNAc) residues are alternatively incorporated forming a polysaccharide chain of approximately 300 units. At the same as this chain elongation occurs, and due to the intervention of various enzymes, modifications occur therein. Thus, the action of N-deacetylase/N- sulfotransferase enzymes produce the N-deacetylation and N-sulfation of the GlcNAc units, turning them into N-sulfoglucosamine (GlcNS). A C5 epimerase catalyzes the transformation of certain units of GlcA into iduronic acid (IdoA), followed by a 2-O-sulfation due to action of a 2-O- sulfotransferase. Next, a 6-O-sulfotransferase, transfers a 6-O-sulfo group to GlcNS and GlcNAc units. Finally, a 3-O-sulfotransferase acts on certain N-sulfo-6-O-sulfoglucosamine (GlcNS6S) units generating N-sulfo-3,6-di-O-sulfoglucosamine (GlcNS3S6S) residues.

The apparently random and incomplete nature of the initial N-deacetylation is what is mainly responsible for the introduction of the structural heterogeneity in heparin in the first phase of its biosynthesis. Structural variability with regard to the degree and positions of sulfation is the result of the incomplete nature of modifications made by the biosynthetic enzymes that lead to the production of heparin sodium molecules with a variable disaccharide substitution pattern.

Heparin is preferably used as sodium salt, but it can also be used as a salt of other alkaline or earth-alkaline metals and is mainly used as antithrombotic and anticoagulant medicine (Anticoagulant therapy for major arterial and venous thromboembolism. Tran HAM, Ginsberg JS. Basic principles and clinical practice. Colman RW, Marder VJ, Clowes AW, George JN, Goldhaber SZ (Ed). Lippincott Williams and Wilkins; 2006:1673-1688). Heparins can be classified depending on their molecular weight in: unfractionated heparin (UFH), Low Molecular Weight Heparin (LMWH) with a mean molecular weight lower than 8000 Da and Ultra Low Molecular Weight Heparin (ULMWH) with a mean molecular weight lower than 3000 Da (Chemoenzymatic synthesis of homogenous ultra low molecular weight heparins. Xu Y. et al. Science 2011; 334: 498-501). LMWH and ULMWH come from depolymerization of the original molecule of UFH and its manufacturing process may introduce certain characteristics of it in the molecule’s structure. Thus, the resulting molecule’s structure derives on the one hand from the structure of the heparin used as starting material and on the other hand from the characteristic residues generated and characteristic to the manufacturing method used.

The manufacturing process of enoxaparin sodium ( -elimination by alkaline treatment on benzyl ester of heparin in aqueous medium) and bemiparin sodium ( -elimination by alkaline treatment in non-aqueous medium) generates as majority species at the ends 4,5-unsaturated 2-O sulfo uronic acid (ΔU2S), at the non-reducing end, and 2-N-sulfo-6-O-sulfoglucosamine, at the reducing end of the molecule. Additionally, the non-reducing end may have structures of 4,5- unsaturated 2-O uronic acid (ΔU). At the reducing end of the aforementioned residue, it is possible to find 2-N-sulfo-6-O-sulfomannosamine (the alkaline treatment catalyzes the epimerization in C2), in addition to another two species of 1,6-anhydro derivatives: 2-N-sulfo-1,6- anhydroglucosamine (1,6-an.A) and 2-N-sulfo-1,6-anhydro-mannosamine (1,6-an.M).

Formula 2: Structures present at the reducing and non-reducing end in enoxaparin and bemiparin sodium.

Residues are also generated in other low molecular weight heparins related to their manufacturing process. For example, tinzaparin sodium, which is obtained by a method of β-elimination by treatment with heparinases, has at its non-reducing end the presence of 4,5-unsaturated 2-O sulfo uronic acid (ΔU2S).

Formula 3: Structures present at the reducing and non-reducing end in tinzaparin sodium

Dalteparin sodium is obtained by treatment with nitrous acid which generates a 2,5- anhydro mannitol residue at the reducing end of the molecule.

Formula 4: Structures present at the reducing and non-reducing end in dalteparin sodium

In the present specification,“monosaccharide residue present in heparin chains” identifies those monosaccharide residues or components that are typically present in LMWH/UFH/GAG chains. The list of these residues covers 4,5-unsaturated 2-O sulfo uronic acid (ΔU2S), 4,5- unsaturated uronic acid (ΔU), 2-N-sulfo-1,6-anhydroglucosamine (1,6-an.A), 2-N-sulfo-1,6- anhydro-mannosamine (1,6-an.M), 2-N-sulfo-6-O-sulfoglucosamine (ANS6S), 2,5-anhydro mannitol, N-sulfoglucosamine, glucuronic acid, N-sulfo-6-O-sulfoglucosamine, 2-O- sulfoiduronic acid, iduronic acid, N-sulfo-3-O-sulfoglucosamine, N-sulfo-3,6-di-O- sulfoglucosamine, galacturonic acid, Xylose, N-acetylglucosamine and N-acetyl-6-O- sulfoglucosamine.

NMR spectroscopy allows identification of the residues typical of the heparin and low molecular weight heparin manufacturing processes.

One of the advantages associated to the use of NMR for structural characterization is that, for its analysis, the samples do not require previous derivatizations or chromatographic fractionation. In other words, the sample is directly analysed by NMR, without the need for intermediate treatments. Nuclear magnetic resonance spectroscopy is used to determine the sequence of monosaccharide residues present in these compounds and unequivocally determines the N- acetylation and N- and O-sulfation points throughout the oligosaccharide chain. Additionally, this technique allows specifically determining the orientation of the anomeric bonds and distinguishing between the iduronic acid of glucuronic acid epimers. (Advancing Analytical Methods for Characterization of Anionic Carbohydrate Biopolymers. Langeslay D.J. PhD Thesis UC Riverside 2013). However, given the high degree of microheterogeneity and polydispersity of these compounds, the complete characterization of heparins and low molecular weight heparins is currently still a challenge.

Additionally, this technique can be used to obtain information on those structural residues associated to the production process of heparins and of low molecular weight heparins, such as the state of epimerization of uronic acids (iduronic acid vs. glucuronic acid), ratio of sulfated and nonsulfated 4,5-uronate residues at the non-reducing end (for low molecular weight heparins produced by a β-elimination method or treatment with heparinases).

Likewise, and due to its high sensitivity, this technique has been used as screening technique to determine impurities present in glycosaminoglycans (Analysis and characterization of heparin impurities. Beni S. et al. Anal Bioanal Chem 2011, 399:527-539).

In the state of the art, various NMR methods and experiments have been disclosed for the structural characterization of glycosaminoglycans in general, and heparins and low molecular weight heparins in particular. Thus, for example, ¹³ C-NMR spectroscopy has been used to determine the degree of sulfation in heparin sodium of different animal origin (Characterization of Sulfation Patterns of Beef and Pig Mucosal Heparins by Nuclear Magnetic Resonance. Casu B. et al. Arzneim.-Forsch./Drug Res.1996.46:472-477).

1H-NMR spectroscopy has been the most widely used technique for the study of these compounds since it is an abundant nucleus and with a high gyromagnetic ratio. The region between 1.8 - 2.1 ppm comprises the signals corresponding to the N-acetyl groups or methyl groups of the reducing ends which may be synthetically included. The region between 2.8– 4.6 ppm comprises the majority of the saccharide ring signals and has a high degree of overlapping between them, which makes it difficult to extract structural information directly from this area. Between 4.6 - 6.0 ppm are the signals corresponding to the anomeric protons. Since it is an area much less populated with signals, it is possible to extract a great deal of information from it. Furthermore, in the case of LMWHs obtained using a -elimination mechanism, it also contains the signals corresponding to H4 of the non-reducing ends of the molecule.

Two-dimensional experiments (2D NMR) allow the problems of one-dimensional experiments to be overcome, basically due to the overlapping of signals, and that also the spectra have two frequency dimensions and another signal intensity which allows them to become a powerful tool for assigning oligosaccharide structures derived from heparin (Characterization of currently marketed heparin products: composition analysis by 2D-NMR. Keire D.A. et al. Anal. Methods 2013.5:2984-2994).

TOCSY (TOtal Correlation SpectroscopY) spectra are an excellent starting point for the structural analysis of oligosaccharides since the information obtained in this allows the correlation of nuclei found in the same spin system, in this case all the protons within the same monosaccharide.

Another two-dimensional experiment of particular importance for the structural characterization of this type of compounds is ¹ H- ¹³ C HSQC (Heteronuclear Single-Quantum Correlation), which correlates chemical proton shifts with chemical shifts of carbon 13 and allows assigning the primary structures of oligosaccharides derived from GAGs and the monosaccharide composition (Structural elucidation of the tetrasaccharide pool in enoxaparin sodium. Ozug J. et al. Anal. Bioanal. Chem. 2002.403:2733-2744; Structural features of low molecular weight heparins affecting their affinity to antithrombin. Bisio A. et al. Thromb. Hemost.2009.102:865-873).

The increase in spectral dispersion achieved with this two-dimensional technique allows the quantification of the integrals of the signals which are superimposed in the corresponding one-dimensional spectra (Low-molecular-weight heparins: structural differentiation by two- dimensional nuclear magnetic resonance spectroscopy. Guerrini M. et al. Semin Thromb Hemost 2007.33:478-487).

Nuclear magnetic resonance is, by definition, a quantitative spectroscopy technique since the intensity of the resonance lines is directly proportional to the number of resonant nuclei (spin). This, in principle, makes it possible to precisely determine the quantity of molecular structures.

The increase in intensity of the magnetic fields used in NMR has allowed the limits of detection to significantly be reduced. However, the absence of precise methods that consider and control both the experimental methods and the processing and evaluation of the spectra means that measurements made on identical samples in various laboratories may significantly differ (Validation of quantitative NMR. Malz F. and Jancke H. Journal of Pharmaceutical and Biomedical Analysis 2005.38:813-823).

The complexity of the nuclear magnetic resonance spectra of glycosaminoglycans in general, and heparins and low molecular weight heparins and their derivatives in particular, has meant that to date no specific validation methods have been developed which allow quantification of its characteristic signals, and therefore, the suitable characterization and differentiation of these compounds.

Hence, the inventors of the present invention have managed to overcome this obstacle in the state of the art, managing to develop a method which enables unequivocally differentiating heparins from one another. Thanks to the method developed in the present invention, the percentage values of monosaccharide composition obtained make it possible to differentiate between low molecular weight heparins obtained by different manufacturing processes and also heparin sodium and other glycosaminoglycans. Summary of the invention

The inventors of the present invention have developed a method which allows the quantification of the characteristic signals of glycosaminoglycans in general, and heparins and low molecular weight heparins and their derivatives in particular, through the use of one-dimensional nuclear magnetic resonance of ¹ H-NMR and/or two-dimensional nuclear magnetic resonance of ¹ H- ¹³ C HSQC. The quantification of these signals allows determining the monosaccharide composition of the oligosaccharide chains of each one of these compounds, which is characteristic of the compound.

In consequence, in a first aspect the invention it provides a method for the analysis of a composition containing monosaccharide residues present in, or coming from, heparin chains by means of ¹ H-NMR one-dimensional nuclear magnetic resonance and/or ¹ H- ¹³ C HSQC two- dimensional nuclear magnetic resonance comprising the steps of:

a) Providing a composition including at least one monosaccharide residue present in heparin chains and obtaining its spectrum of ¹ H-NMR one-dimensional nuclear magnetic resonance and/or ¹ H- ¹³ C HSQC two-dimensional nuclear magnetic resonance using dimethylmalonic acid (DMMA) as internal reference, and

b) Identifying in the NMR spectrum the presence or the absence of at least one signal of at least one residue selected from the group consisting of: 4,5-unsaturated 2-O sulfo uronic acid (ΔU2S), 4,5-unsaturated uronic acid (ΔU), 2-N-sulfo-1,6-anhydroglucosamine (1,6- an.A), 2-N-sulfo-1,6-anhydro-mannosamine (1,6-an.M), 2-N-sulfo-6-O-sulfoglucosamine (ANS6S), 2,5-anhydro mannitol, N-sulfoglucosamine, glucuronic acid, N-sulfo-6-O- sulfoglucosamine, 2-O-sulfoiduronic acid, iduronic acid, N-sulfo-3-O-sulfoglucosamine, N-sulfo-3,6-di-O-sulfoglucosamine, galacturonic acid, Xylose, N-acetylglucosamine and N-acetyl-6-O-sulfoglucosamine, characterized in that the presence of said signals in a determined relative proportion of its normalized integrals with respect to DMMA, or the absence thereof, forms a pattern which allows identifying the heparin which the monosaccharide residue comes from comparing the pattern obtained in the analysis with a standard pattern previously obtained for different heparins in the same conditions.

The suitable quantification of the characteristic signals of these products and of their monosaccharide composition or characteristic residues, allows suitably differentiating polysaccharides from one another and their origin, and in the case of the low molecular weight heparins, to confirm that the products have been manufactured according to the declared method.

This quantification of the residues is obtained in percentage values and in relative form to the complete structure of each heparin. Obtaining a characteristic“photo” of each one of the structures, which allows an unequivocal deduction and identification both of the heparin analysed and of the process whereby it has been obtained. In this way, the process of the present invention can be used as both a quality system or method (to assess if the heparins analysed correspond to an identified standard or are being adulterated) and as method of analysis and determination of characteristic signals of new structures of heparins, of which the method of the invention can later be used as quality system or method.

Furthermore, the approval with the health authorities of biosimilars and/or generics of certain low molecular weight heparins, as is the case of Enoxaparin sodium, occurs after a suitable exercise of comparability between the biosimilar/generic and the reference molecule, which must demonstrate, among other aspects, the suitable degree of structural similarity between both products. One of the basic aspects on a structural level that it is necessary to demonstrate is that the relative proportion of the monosaccharides that form their oligosaccharide chains and after statistical evaluation, fulfil biosimilarity criteria. For them, the method of the present invention is especially selective.

The inventors of the present invention have verified that, although the structural characterization by nuclear magnetic resonance has been widely used for characterization of these compounds, however, in the literature there are no quantitative analysis methods of glycosaminoglycan analysis by means of NMR. The absence of these methods prevents the suitable comparability between identical samples studied and assessed under not suitably established experimental conditions.

Thus, it is possible to find in the literature publications wherein the values of relative proportion which are provided for the different component residues of these compounds significantly differ from one another, which clearly indicates that they are inadequate methods (Generic versions of enoxaparin available for clinical use in Brazil are similar to the original drug. Glauser B.F., Vairo B.C., Oliveira C.P.M., Cinelli L.P., Pereira M.S. and Mourao P.A.S. J Thromb Haemost 2011.9;1419-1422).

With the aim of establishing a selective quantitative method to determine the proportion of the signals corresponding to these residues present in the structure of these compounds, which allows the suitable comparison between results and which makes it possible to avoid the error associated to the conditions in which NMR experiments are performed, the inventors have found that the use of dimethylmalonic acid (DMMA) as internal standard in 1H NMR and HSQC experiments for the relative quantification of the signals corresponding to the different component monosaccharides is suitable, since among other aspects it has a longitudinal relaxation time (T1), of under 1 second similar to the T1 of the anomeric protons and carbons (Molecular Weight of Heparin using 13C Nuclear Magnetic Resonance Spectroscopy. Desai U.R. and Linhardt R.J., J Pharm Sci 1995.84(2);212-215), which allows a good transfer of polarization and, therefore, an increase in intensity of the signals, which makes it suitable for this purpose.

Thus, the process for NMR analysis of these compounds is characterized, in first place, by the use of dimethylmalonic acid as internal standard for the quantification of the characteristic signals of these products, both using ¹ H-NMR and ¹ H- ¹³ C HSQC.

Surprisingly, it has been found that the selection dimethylmalonic acid (DMMA) as internal standard in its application both to ¹ H-NMR and ¹ H- ¹³ C HSQC allows the quantitative determination by percentage means of the characteristic signals in glycosaminoglycans typically related to heparins with high specificity, accuracy, repeatability and linearity and between the signal of the NMR spectrum and the concentration of the characteristic residues of the glycosaminoglycan analysed which enables development of a quantitative analysis method of said glycosaminoglycans non-existent to date. Brief description of the figures

Figure 1: Diagram of the heparin biosynthesis process

Figure 2: Specificity. ¹ H-NMR spectra

Figure 3: Specificity. ¹ H- ¹³ C HSQC spectra

Figure 4: ¹ H-NMR linearity

Figure 5: ¹ H- ¹³ C HSQC linearity

Figure 6: ¹ H-NMR spectrum of enoxaparin sodium

Figure 7: ¹ H- ¹³ C HSQC spectrum of enoxaparin sodium Abbreviations and acronyms

The following abbreviations and acronyms are used in the present specification: NMR: Nuclear magnetic resonance

HSQC: Heteronuclear Single-Quantum Correlation

GAG: Glycosaminoglycan

UFH: Unfractionated heparin

LMWH: Low Molecular Weight Heparin

ULMWH: Ultra Low Molecular Weight Heparin

Da: Dalton

ΔU2S: 4,5-unsaturated 2-O sulfo uronic acid

ΔU: 4,5-unsaturated uronic acid

1,6-an.A: 2-N-sulfo-1,6-anhydroglucosamine

1,6-an.M: 2-N-sulfo-1,6-anhydro-mannosamine

TOCSY: TOtal Correlation SpectroscopY

TSP: Sodium salt of 3-(Trimethylsilyl)-Propionic-D4 acid

DMMA: Dimethylmalonic acid

MHz: Megahertz

ppm: part per million

: chemical shift

SW: Spectral width

TD: Time domain

T1: Longitudinal relaxation time

ANS: N-sulfoglucosamine

G: Glucuronic acid

ANS6S: N-sulfo-6-O-sulfoglucosamine

I2S: 2-O-sulfoiduronic acid

I: Iduronic acid

ANS3S: N-sulfo-3-O-sulfoglucosamine

Gal: Galacturonic acid

Xyl: Xylose

ANAc: N-acetylglucosamine

A6S: 6-O-sulfoglucosamine

A6OH: Glucosamine G2S: Sulfoglucuronic 2-O acid

M: Mannosamine

MNS6S: N-sulfo-6-O-sulfomannosamine

Epox: Epoxide

red: anomer

red: β anomer Detailed description of the invention

Experimental assays

The quantitative NMR assays have been performed using a Bruker AVIII-600 o AVIII-800 nuclear magnetic resonance (NMR) spectrometer. Reagents used were deuterium oxide (D ₂ O) 99.9%, sodium salt of 3-(Trimethylsilyl)-Propionic-D4 acid (TSP) and Dimethylmalonic acid (DMMA, standard for quantitative NMR, TraceCERT grade) as internal standard.

a) Equipment conditions

- Frequency: 1H: 600 / 800 MHz, 13C: 150,9 / 201.2 MHz

- Temperature: 298 K

b) Acquisition parameters (quantitative ¹ H NMR)

- 90º pulse: it is determined from a qualitative 1H spectrum

- Acquisition window: SW=10-12 ppm/TD=64-128k

- Inter scans delay d1 must fulfil the condition d1+AQ≥20s

- No. of scans: 12

c) Acquisition parameters (HSQC)

- 90º pulse: it is determined from a qualitative ¹ H spectrum

- Acquisition window: SW2 ( ¹ H)=6 ppm / TD(F2)=1k

SW1 ( ¹³ C)= 120 ppm / TD(F1)=256-384

- Time between pulses d1 =1.8-2 s

- No. of scans: 12

d) Processing parameters ( ¹ H)

- Processing window: SI=64-256K

- Window function: None

- Phase adjustment: manual

- Baseline adjustment: automatic (abs)

e) Processing parameters (HSQC)

- Processing window: SI(F2)=2k - Processing function: QSINE, SSB=2

- Phase adjustment: manual

- Baseline adjustment: automatic

f) Preparation of the sample the following solutions were prepared:

- Solution A [TSP] 1mg/ mL

- Solution B [D2O-TSP] 0.002 mg/mL: 40 µL A [TSP] + 19.96 mL D2O, Total volume = 20 mL

- Solution C [DMMA] 1.2 mg/ mL

- Test sample: 50 mg of product to study in 500 µL of the solution B [D2O-TSP] and add 100 µL of solution C [DMMA] of dimethylmalonic acid and place in 5 mm-diameter NMR tube.

g) Process

The NMR tube containing the sample is introduced in the spectrometer. Then, the homogeneity of the magnetic field is adjusted and the harmony of the wave is optimized for the ¹ H and ¹³ C nuclei. A qualitative ¹ H spectrum is then performed, with parameters similar to the aforementioned, except the following:

Time between pulses d1 =1-2s

No. of scans: 1-4

Then, the value of the 90º pulse is determined with automatic pulse program (TOPSPIN). Next, the quantitative ¹ H spectrum is performed, with the parameters indicated in the analytical method and the 90º pulse value (P1) previously determined. After the HSQC spectrum is obtained with the aforementioned parameters. The spectra obtained are then processed according to the aforementioned parameters, taking as chemical shift reference, the TSP-d4 signal at 0 ppm.

The dimethylmalonic acid signal appears at the following chemical shifts:

- ¹ H NMR: singlet that appears at 1.2-1.4 ppm

- HSQC: signal at 1.2-1.4 and 26-27 ppm

The parameters assessed to determine validation of the method for quantitative NMR have been the following:

Specificity

It determines the capacity of the analytical method for measuring and/or identifying, simultaneously or separately the analytes of interest, unequivocally, in presence of other chemical substances that may be present in the sample.

The data obtained in the ¹ H NMR spectra in these experiments, were:

Sample Composition Chemical shift, ppm

It is verified that there is no interference between signals neither in the ¹ H NMR or ¹ H ¹³ C- HSQC spectra (Figures 2 and 3). This demonstrates that the method is capable of discriminating without interferences the signals forming the structure of the compound to study, from that of other products present in the sample such as the solvent (deuterium oxide, D ₂ O), the internal standard (dimethylmalonic acid, DMMA) and the chemical shift reference (TSP-d4). Limit of quantification and linearity

Under these parameters, on the one hand, the minimum quantity of analyte that may be suitably quantified precisely and accurately is determined and, on the other hand, the capacity of the method to obtain results directly (by means of mathematical transformations) proportional to the concentration of the analyte in the sample, within an established interval.

To assess the limit of quantification and the linearity the integrals of the DMMA NMR signals are quantified (i.e. the integral of the NMR signal area corresponding to DMMA) on enoxaparin sodium doped at 7 levels of concentration of the internal standard, from independent weighings and in triplicate. These levels correspond to the following working concentrations:

- 0.2 mM: 13.5 % of the working concentration

- 0.3 mM: 20.3 % of the working concentration

- 0.76 mM: 50 % of the working concentration

- 1.2 mM: 80.1 % of the working concentration

- 1.5 mM: 100 % of the working concentration

- 1.8 mM: 120 % of the working concentration

- 2.27 mM: 150.2 % of the working concentration

The acceptance criteria established to fulfil this linearity criterion is that in the line obtained the correlation coefficient for both experiments is≥ 0.99. In Figures 4 and 5 the graphic is represented which represents the DMMA signal integral values vs. DMMA concentration (mM), for the ¹ H NMR and ¹ H ¹³ C-HSQC spectra. The acceptance criterion is easily fulfilled both for one and the other.

The limit of quantification is established for a DMMA concentration of 0.20 mM. Thus, the signals of the samples studied with intensity less than the intensity of the DMMA signal corresponding to this concentration, cannot be suitably quantified and, therefore, they cannot be taken to determine the relative proportion of the residues present in the molecule.

Accuracy

It expresses the proximity between the value which is accepted conventionally as true or reference value and the experimental value found. To calculate the experimental value of the concentration of the samples to evaluate it considers the equations of the line obtained in the previous section on linearity.

The accuracy is expressed as recovery percentage in the valuation of a known quantity of internal standard:

Where:

Xm: mean value found

µ: value accepted as true

The acceptance criteria established is that the recovery values are between 70.0-130.0 % for the concentration corresponding to the concentration limit and 80.0-120.0 % for the other levels. The data obtained for the ¹ H NMR and HSQC experiments were the following:

The conclusion drawn from this assay both for the ¹ H NMR and HSQC experiment is the suitability in compliance with the acceptance criteria for the accuracy parameters for those signals corresponding to the sample, with intensity higher than that of the limit of quantification.

Precision - Repeatability

The variability is studied of the method by performing a series of analyses on the same sample in the same operating conditions in a same laboratory and in a short period of time.

To do this, three consecutive analyses were performed for each concentration. The repeatability of a method is expressed as the coefficient of variation (CV) of a series of measurements and is mathematically calculated as follows:

Where:

s: standard deviation

X: arithmetic means of the results.

The acceptance criteria established to fulfil these accuracy criteria is that the coefficient of variation for all levels is≤ 7%.

The data obtained for both experiments was the following:

The conclusion drawn from this assay both for the ¹ H NMR and HSQC experiment is the suitability in compliance with the acceptance criteria for the accuracy parameters for those signals corresponding to the sample, with intensity higher than that of the limit of quantification. EXAMPLES

The following specific examples provided below serve to illustrate the nature of the present invention. These examples are included only for illustration purposes and have not to be interpreted as limitations to the invention which are claimed here. EXAMPLE 1

Study by ¹ H NMR of enoxaparin sodium.

50 mg of enoxaparin sodium are dissolved in 500 µL of a D ₂ O-TSP (solution B) solution and 100 µL of DMMA solution (solution C) are added. The resulting solution is introduced in a 5 mm diameter tube.

The resulting DMMA concentration in the solution to analyse is 1.5 mM.

The experiments are performed in a Bruker AVIII-800 nuclear magnetic resonance spectrometer.

The main signals identified are as follows:

Once the values of the integrals of the signals both of DMMA and the rest of the residues have been obtained, the normalized values are obtained of said residues dividing the value of its integrals by the value of the integral corresponding to the DMMA signal. This normalization can be performed since the concentration of the internal standard is kept constant with respect to the residue concentration for all experiments, thus avoiding the inter-experimental variability that may arise in the analysis of a series of several product batches.

Once the normalized values of the residues have been obtained, the relative percentage of each one of them is calculated in accordance with the following formula:

To clarify the steps performed, the results obtained are shown for a series of four samples M1, M2, M3 and M4 of enoxaparin sodium:

In the experiments performed, the following integral values of each one of the signals selected were obtained:

where M corresponds to sample. To obtain the normalized values of the integrals of the signals under study, they are divided by the value of the DMMA integral:

And finally, from these normalized values, the relative proportion of each one of these signals is calculated with respect to the set of all the signals:

The quantification of the characteristic and well-differentiated signals of enoxaparin sodium (generally those corresponding to the anomeric protons, H1) are shown in the following table with the observed relative proportion values:

Signal Chemical shift, ppm Relative proportion, %

The set of the signals corresponding to the peaks found in a determined NMR spectrum, whether one-dimensional ¹ H-NMR and/or two-dimensional ¹ H- ¹³ C HSQC, or the absence thereof, in the relative proportions of its normalized integrals indicated by the parameter “relative proportion (%)” is what in the present specification is called“signal pattern” or simply “pattern”. EXAMPLE 2

The same solution used in example 1, is used to perform the study by ¹ H- ¹³ C HSQC. The main signals identified are as follows:

ANS6S red

These signals can be associated to monosaccharide components of the molecule, so that their quantification allows determination of their monosaccharide composition.

The integrals for each one of these signals were normalized from the value set for the DMMA integral, using the same process explained for the ¹ H NMR experiments. The quantification of the characteristic signals of enoxaparin sodium is shown in the following table:

These experiments demonstrate that, using the experimental conditions described above, it is possible to obtain an analysis method by nuclear magnetic resonance ( ¹ H-NMR and ¹ H- ¹³ C HSQC) of glycosaminoglycans in general, and of heparins and low molecular weight heparins and their derivatives in particular, which allows their quantitative analysis. EXAMPLE 3

Study by ¹ H NMR of bemiparin sodium.

The main signals identified are as follows:

H5 I2S 4.836

The quantification of the characteristic and well-differentiated signals of bemiparin sodium (generally those corresponding to the anomeric protons, H1) are shown in the following table, with the values of relative proportions observed for a series of six samples.

EXAMPLE 4

The same solution used in example 3, is used to perform the study by ¹ H- ¹³ C HSQC. The main signals identified are as follows:

These signals can be associated with the monosacaridic components of the molecule, so that their quantification allows determining its monosacaridic composition.

The integrals of each one of these signals were normalized starting from the value established for the integral of DMMA, using the same procedure explained for the experiments ¹ H RMN. The quantification of the signals characteristic of bemiparin sodium are shown in the following table:

EXAMPLE 5

Study by ¹ H NMR of dalteparin sodium.

The main signals identified are as follows:

The quantification of the characteristic and well-differentiated signals of dalteparin sodium (generally those corresponding to the anomeric protons, H1) are shown in the following table, with the values of relative proportions observed for a series of six samples. Signal Chemical shift, ppm Relative proportion, % EXAMPLE 6

The same solution used in example 5, is used to perform the study by ¹ H- ¹³ C HSQC. The main signals identified are as follows:

These signals can be associated with the monosacaridic components of the molecule, so that their quantification allows the determination of their monosacaridic composition.

The integrals of each one of these signals were normalized starting from the value established for the integral of DMMA, using the same procedure explained for the experiments ¹ H RMN. The quantification of the signals characteristic of dalteparin sodium are shown in the following table:

EXAMPLE 7

Study by ¹ H NMR of tinzaparin sodium.

The main signals identified are as follows:

The quantification of the characteristic and well-differentiated signals of tinzaparin sodium (generally those corresponding to the anomeric protons, H1) are shown in the following table, with the values of relative proportions observed for a series of six samples.

EXAMPLE 8

The same solution used in example 7, is used to perform the study by ¹ H- ¹³ C HSQC. The main signals identified are as follows:

These signals can be associated with the monosacaridic components of the molecule, so that their quantification allows the determination of their monosacaridic composition.

The integrals of each one of these signals were normalized starting from the value established for the integral of DMMA, using the same procedure explained for the experiments ¹ H RMN. The quantification of the signals characteristic of tinzaparin sodium are shown in the following table:

These experiments show that, using the above-described experimental conditions, it is possible to obtain a method of analysis by nuclear magnetic resonance ( ¹ H-RMN y ¹ H- ¹³ C HSQC) of glycosaminoglycans in general and of heparins and low molecular weight heparins and their derivatives in particular, which allows their quantitative analysis.