Complex polysaccharides have been used as pharmaceutical interventions in a number of disease processes, including oncology, inflammatory diseases, and thrombosis. Examples of pharmaceutical interventions in this class are hyaluronic acid, an aid to wound healing and anti-cancer agent, and heparin, a potent anticoagulant and antithrombotic agent. Complex polysaccharides elicit their function primarily through binding soluble protein signaling molecules, including growth factors, cytokines and morphogens present at the cell surface and within the extracellular matrices between cells, as well as their cognate receptors present within this environment. In so doing, these complex polysaccharides effect critical changes in extracellular and intracellular signaling pathways important to cell and tissue function. For example, heparin binds to the coagulation inhibitor antithrombin III promoting its ability to inhibit factor IIa and Xa.
The invention concerns a method of identifying if a process including oxidation or oxidation followed by treatment with an acid was used to make a heparin sample, comprising: determining if a structural signature is absent from or present in the heparin sample and/or determining the amount of the structural signature in the heparin sample, wherein the absence or presence of the structural signature is determined using nuclear magnetic resonance (NMR), wherein the presence of the structural signature and/or the presence in an amount indicates that the the heparin sample was made by a process and the absence of the structural signature indicates that the heparin sample was not made by the process; and performing a step regarding the heparin sample if the heparin sample was made by the process, wherein the step is one or more of processing into a drug product, shipping, formulating, labeling, packaging, releasing into commerce, selling, and offering for sale the heparin sample; wherein the structural signature is one or more of:
wherein in structure B, X = H or SO3
In one embodiment, the heparin sample is an unfractionated heparin sample or low molecular weight heparin (LMWH) sample. Prefarably, the heparin sample is a LMWH sample.
In another embodiment, the heparin sample is an unfractionated heparin sample and the method includes selecting the unfractionated heparin sample for further processing to produce a LMWH sample.
In one embodiment, the method further includes selecting the heparin sample and processing the heparin sample to produce a drug product.
In one embodiment, the sample is an unfractionated heparin sample and the method further comprises depolymerizing the unfractionated heparin sample to produce a MWH sample.
In one embodiment, the absence or presence of structure A and structure B are determined.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
The drawings are first briefly described.
Figure 1 depicts 1H 1D-proton NMR spectra of an unfractionated heparin sodium (N-acetyl region). Figure 1A depicts the spectra of an unfractionated heparin sodium sample with spiked an over sulfated chondrotin sulfate standard. Figure 1 B depicts the spectra of the unfractionated heparin sodium that was not spiked with the standard. The peak marked with an asterisk represents the peak at 2.10 ppm.
Figure 2 depicts an expanded 1H 1D-NMR spectra of an unfractionated heparin sodium manufactured using process A (which does not include an oxidative processing step).
Figure 3 depicts an expanded 1H 1D-NMR spectra of an unfractionated heparin sodium manufactured using process B (which includes an oxidative processing step) with the presence of the signal at 2.10 ppm.
Figure 4 depicts an expanded 1H 1D-NMR spectra of an unfractionated heparin sodium treated with different oxidation procedures. Figure 4A depicts the spectra of an unfractionated heparin sodium treated with hydrogen peroxide; Figure 4 B depicts the spectra of an unfractionated heparin preparation treated with potassium permanganate.
Figure 5 depicts an expanded 1H 1D-NMR spectra of intermediates of a LMWH preparation before and after treatment with sodium periodate. Figure 5A depicts the spectra of a starting LMWH, intermediate 1, which has not been subjected to an oxidative process. Figure 5B depicts the spectra of intermediate 1, namely intermediate 2, after oxidation with sodium periodate.
Figure 6 depicts an expanded 1H 1D-NMR spectra of a porcine intestine heparan sulfate preparation before and after treatment with potassium permanganate and a porcine intestinal heparin sulfate enriched in reducing end N-acetylglucosamine residues. Figure 6A depicts the spectra of a porcine intestine heparan sulfate (HS) preparation. Figure 6B depicts the spectra of the HS preparation after oxidation with potassium permanganate. Figure 6C depicts the spectra of a porcine intestinal heparin sulfate enriched in reducing end N-acetylglucosamine residues (PI-HSNAc). Figure 6D depicts the spectra of the porcine intestinal heparin sulfate enriched in reducing end N-acetylglucosamine residues after oxidation with potassium permanganate (PI-HSNAcox).
Figure 7 depicts an expanded 1H 1D-NMR spectra of a LMWH with high percentage of GlcNAc at the reducing end of the chain before and after treatment with potassium permanganate. Figure 7A depicts the spectra of the starting LMWH. Figure 7B depicts the spectra of LMWH after oxidation with potassium permanganate. The signal at 2.10 ppm is labeled and is greatly increased in this sample.
Figure 8 depicts 2D-NMR (HSQC) spectra of a heparan sulfate preparation with high percentage of GlcNAc at the reducing end of the chain before and after treatment with potassium permanganate. Figure 8B depicts the 2D-NMR (HSQC) spectra of a starting PI-HSNAc preparation. The signals arising from the reducing end GlcNAc are labeled. Figure 8D depicts the 2D-NMR (HSQC) spectra of the heparin sulfate preparation after oxidation with potassium permanganate (PI-HSNAcox).
Figure 9 depicts an expanded 1H 1D-NMR spectra of a heparin preparation subjected to periodate oxidation and subsequent acidic treatment.
Figure 10 depicts a 2D-NMR spectra of PI-HSNAcox. Figure 10A is a HSQC-DEPT spectra of PI-HSNAcox. The CH cross peaks are shown in the boxes. The cross peak at 4.37/58.9 ppm is highlighted. Figure 10B is a HMBC spectra of PI-HSNAcox. The long-range correlation between proton 4.37 ppm and a carbonyl group is indicated.
Figure 11 depicts a 1D-NMR spectra of PI-HSNAcox. Figure 11A depicts the 1D-NMR spectra of PI-HSNAcox. Figure 11B depicts the spectra of PI-HSNAcox after treatment with sodium borodeuteride and neutralization.
Figure 12 depicts a 2D-NMR spectra of PI-HSNAcox. Figure 12 A depicts the HSQC-TOSCY spectra of PI-HSNAcox recorded with a 20 ms mixing time. Figure 12 A depicts the HSQC-TOSCY spectra of PI-HSNAcox recorded with a 90 ms mixing time.
Figure 13 depicts an HSQC spectra of PI-HSNAcox. NMR assignments for the oxidized residues are indicated close to the relative contours.
Figure 14 depicts a negative-ion ESI-MS spectrum of the oxidized tetrasaccharide species containing four sulfates and one acetyl group (Dp4, S4, Ac1ox). The insert shows the well resolved isotopic peaks of oxidized tetrasaccharide.
Figure 15 depicts a 2D-NMR spectra of an unfractionated heparin preparation. Figure 15A depicts the spectra of an unfractionated heparin preparation that has not been oxidized. Figure 15 B depicts the unfractionated heparin preparation treated with KMnO4. The H1/C1 signal of GlcNAc α reducing end disappeared, while signals at 4.37/58.9 and 3.88/81.8 appeared (see circled signals). Signals due to linkage region (indicated with * in A are also missing.
Figure 16 depicts a reaction scheme outlining the formation of structure A (N-acetylglucosaminic acid; where X = H or SO3) generated as a result of potassium permanganate oxidation at the reducing end of chains. It is possible that further oxidation of structure A (if X=H) may result in the formation of a dicarboxylic acid (Structure B).
The disclosure is based, at least in part, on the finding that peaks within the N-
acetyl region of a 1
H 1D-NMR spectra of a heparin preparation are associated with characteristic structural signatures which reflect the process used to make the heparin preparation. For example, the presence of a peak at 2.10 ppm in a 1
H 1D-NMR spectra of unfractionated heparin represents a characteristic structural signature that is reflective of an oxidative processing step in the manufacture of unfractionated heparin. As another example, an increased amount of a structural signature associated with a peak at 2.08 ppm of a 1
H 1D-NMR spectra indicates an oxidized heparin preparation that has been subjected to acid treatment. Therefore, in some embodiments, a method described herein can include evaluating the absence, presence or amount of a structural signature associated with a peak in the N
-acetyl region of a 1
H 1D-NMR spectra of a heparin preparation. The N
-acetyl region refers to a region from about 1.8 ppm to 2.20 ppm, e.g., 1.9 ppm to 2.15 ppm, 2.0 ppm to 2.12 ppm, 2.02 ppm to 2.10 ppm of a 1
H 1D-NMR spectra. Presence means whether a structural signature can be detected. Amount refers to the amount, e.g., as % by weight or number.
In some embodiments, a method described herein can be used to determine if a heparin preparation (e.g., an unfractionated heparin preparation or a low molecular weight heparin (LMWH) preparation) is at risk for coloration. Some heparin preparations have limited shelf life due, at least in part, to the development of color is the preparation during storage. The phrase coloration means greater than 0.2 absorbance units in an accelerated stability test such as the calorimetric analysis described in U.S. Publication no.: 20080318328
As used herein, "acquiring a value" refers to any process that results in possession of the value. In an embodiment, acquiring a value comprises subjecting a sample to a process which results in a physical change in the sample or another substance, e.g., an analytical reagent or a device used in the analysis. Such methods comprise analytical methods, e.g., a method which include one or more of the following: separating a substance, e.g., an analyte, or a fragment or other derivative thereof, from another substance; combining an analyte, or fragment or other derivative thereof, with another substance, e.g., a buffer, solvent, or reactant; or changing the structure of an analyte, or a fragment of other derivative thereof, e.g., by breaking or forming a covalent or non covalent bond, between a first and a second atom of the analyte. Typical analytical methods include high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), capillary electrophoresis (CE) and mass spectroscopy (e.g., matrix-assisted laser desorption ionization-mass spectroscopy (MALDI-MS), electrospray ionization-mass spectroscopy (ESI-MS)), and fast protein liquid chromatography (FPLC).
In an embodiment, a party that practices the method performs the process. As used herein, "directly acquiring," refers to a process in which the party that practices the method performs the process. In an embodiment, a party that practices the method receives the value from another party. As used herein, "indirectly acquiring," refers to a process in which the party that practices the method receives the value from another party. Typically, even in embodiments characterized by indirect acquisition, some party has subjected a sample to a process as described above that results in a physical change in the sample or another substance. In an embodiment, a party that practices the method of evaluating instructs another party to perform the process, and e.g., a party that practices the method receives the value.
A heparin preparation, as used herein, is a preparation which contains heparin or a preparation derived there from, and thus includes unfractionated heparin, low molecular weight heparin (LMWH), ultra low molecular weight heparin (ULMWH) and the like.
The term "unfractionated heparin (UFH)" as used herein, is heparin purified from porcine intestinal mucosa. UFH can be used, e.g., as a starting material in the process to form a LMWH. Unfractionated heparin is commercially available from several vendors including Abbott, Organon, Riker, Invenex, Baxter, Calbiochem, Sigma or Upjohn. In some embodiments, the heparin is made by a process that includes an oxidation step. The oxidation step can include using at least one of: a permanganate salt peroxide, periodate, chlorine, chlorine dioxide, and combinations thereof. For example, the permanganate salt can be one or more of potassium permanganate, sodium permanganate, quaternary ammonium permanganate, hydrogen peroxide. Preferably, the oxidation step includes using a permanganate salt. In some embodiments, the heparin is made by a process that includes a reduction step, e.g., such as treatment with sodium borohydride, lithium aluminum hydride, or combinations thereof.
The heparin preparation can also be a LMWH preparation. Examples of LMWH preparations include, but are not limited to, an enoxaparin preparation (Lovenox™ or Clexane™); a dalteparin preparation (Fragmin™); a certoparin preparation (Sandoparin™ or Embollex); an ardeparin preparation (Normiflo™); a nadroparin preparation (Fraxiparin™); a parnaparin preparation (Fluxum™); a reviparin preparation (Clivarin™); a tinzaparin preparation (Innohep™ or Logiparin™), a fondaparinux preparation (Arixtra™), or a M118-REH preparation. In some embodiments, the LWMH preparation can be a LMWH preparation made by one or more of the following methods: fractionation using solvents (French Patent No.: 2,440,376
, U.S. Patent No.: 4,692,435
); fractionation using an anionic resin (French Patent No.: 2,453,875
); gel filtration (Barrowcliffe (1977) Thromb. Res. 12:27-36
); affinity chromatography (U.S. Patent No.: 4,401,758
); controlled depolymerization by means of a chemical agent including, but not limited to, nitrous acid (European Patent No.: 014 184 B1
, European Patent No.: 037 319 B1
, European Patent No.: 076 279 B1
, European Patent No.: 623 629 B1
, French Patent No.: 2,503,714
, U.S. Patent No. 4,804,652
and PCT Publication No.: WO 81/03276
), beta-elimination from a heparin ester (European Patent No.: 040 144 B1
, U.S. Patent No.: 5,389,618
), periodate (EP 287477
), sodium borohydride (EP 347588
, EP 380943
), ascorbic acid (U.S. Patent No.: 4,533,549
), hydrogen peroxide (U.S. Patent No.: 4,629,699
, U.S. Patent No.: 4,791,195
), quaternary ammonium hydroxide from a quaternary ammonium salt of heparin (U.S. Patent No.: 4,981,955
), alkali metal hydroxide (European Patent No.: 380 943
, European Patent No.: 347 588
), by an enzymatic route (European Patent No.: 064 452
, U.S. Patent No.: 4,396,762
, European Patent No.: 244 235
, European Patent No.: 244 236
; U.S. Patent No.: 4,826,827
; U.S. Patent No.: 3,766,167
), by means of irradiation (European Patent No.: 269 981
), and other methods or combinations of methods such as those described in U.S. Patent No.: 4,303,651
, U.S. Patent No.: 4,757,057
, U.S. Publication No.: 2007/287683
, PCT Publication No.: WO 2009/059284
and PCT Publication No.: WO 2009/059283
In some embodiments, a heparin preparation, e.g., an unfractionated heparin preparation, can be selected for further processing based upon the absence, presence or amount of a structural signature that indicates the method used to make the heparin preparation. For example, an unfractionated heparin preparation can be selected for further processing, e.g., into a LMWH preparation. The unfractionated heparin preparation can be selected for further processing, e.g., by one or more of the methods described above.
The disclosure also features a database that correlates the presence or amount of a structural signature associated with a peak in the N
-acetyl region of a 1
H 1D-NMR spectra, e.g., a peak at 2.08 ppm of Figure 9 and/or the peak at 2.10 ppm of Figure 1, with a method used to make the heparin preparation (e.g., a method that includes oxidation or oxidation followed by treatment with an acid), and use of such a database, e.g., in a method described herein. The term "database" refers to a collection of data. Typically, it is organized so that its contents can easily be accessed, managed, and updated. In one embodiment, the database is configured or managed to ensure its integrity and quality, to minimize content beyond records described herein, and to allow controlled access. The database is presented or memorialized on a medium. The medium can be, e.g., a traditional paper medium or other medium which displays printed or written symbols which can be directly (e.g., without the aid of a computer) used by a human being. Such a database can exist as a set of printed tables, or a card catalogue, which, e.g., show the relationship of the structural signature to the method used to produce the heparin preparation. The database can also be presented or memorialized in electronic or other computer readable form. These embodiments can range from simple spreadsheets to more complex embodiments. The database need not be deposited on a single unit of medium, e.g., in a single table or book, or on a single computer or network. A database, e.g., can combine a traditional medium as described above with a computer-readable medium. Typically, the database will contain a collection of records, wherein each record relates a structural signature to a method of manufacture by way of a correlative function. The database can be organized in a number of ways, e.g., as a relational database. Typically the database is in a format that can be searched for specific information or records by techniques specific to each database. A computer database is typically a structured collection of records stored in a computer or computers so that a program can consult it to answer queries.
Reference Values and Standards
A reference standard, by way of example, can be a value determined from a reference heparin preparation (e.g., a commercially available heparin preparation or a heparin preparation made by a particular method). For example, a reference standard can be a value for the presence of a structural signature in a preparation, e.g., a reference heparin preparation. The reference standard can be numerical or non-numerical, e.g., it can be a qualitative value, e.g., yes or no, or present or not present at a preselected level of detection, or graphic or pictorial. The reference standard can also be values for the presence of more than one structural signature in a sample. For example, the reference standard can be a map of structures (e.g., structures associated with peaks in the N
-acetyl region of 1
H-1D-NMR spectra) present in a heparin preparation when analyzed by a separation method described herein. The reference standard can also be a release standard (a release standard is a standard which should be met to allow commercial sale of a product) or production standard, e.g., a standard which is imposed, e.g., by a party, e.g., the FDA, on a heparin or LMWH.
Detection of Structural Signatures
The absence, presence or amount of a structural signature associated with a peak in the N
-acetyl region of a 1
H 1D-NMR spectra can be determined by nuclear magnetic resonance (NMR).
In one embodiment, the absence, presence or amount of a structural signature is determined using 1D-NMR or 2D-NMR. The 2D-NMR can be carried out using homonuclear (e.g., COSY, TOCSY, NOESY and ROESY) and/or heteronuclear (e.g., HSQC, HSQC-DEPT, HMQC-COSY, HSQC-TOSCY and HMBC) spectroscopy. The peaks depicted in many of the Figures were obtained using 1
H 1D-NMR. The general procedure for the 1
H 1D-NMR was as follows: an unfractionated heparin sample (approximately 20 mg) was dissolved in 0.7 ml of D2
O (deuterium oxide, 99.96 % atom D) and transferred to a 5mm NMR tube. Proton (1
H) 1D-NMR spectra were acquired on a 600 MHz Varian VNMRS spectrometer equipped with a 5mm triple resonance probe. Data were acquired at 25° C, with presaturation of the water signal, for 16 - 32 scans and a 10 second delay. The NMR spectrum was collected with a spectral window of 14 to -2 ppm. Samples were calibrated either using an added internal standard (0.1 % w/v TSP; methyl protons set at 0.00 ppm), or by setting the major N
-acetyl methyl proton signal of heparin to 2.045 ppm.
The initial experiments performed confirmed that a peak at 2.10 ppm is not over sulfated chondrotin sulfate (OSCS), a contaminant sometimes found in heparin. The results indicated that OSCS shows a major distinct peak at 2.15 ppm that is well resolved from the peak at 2.10 ppm (Figure 1).
NMR was also used to analyze unfractionated heparin preparations obtained from different sources to understand the potential origin of the peak at 2.10 ppm. Figure 2 shows an unfractionated heparin preparation made by process A and which does not contain the signal at 2.10 ppm, whereas Figure 3 shows an unfractionated heparin preparation made by a different process, process B, and which does contain the signal at 2.10 ppm. This indicates that the different processing conditions can have an effect on observation of the peak at 2.10 ppm. The unfractionated heparin preparation analyzed in Figure 3 underwent an oxidative processing step (process B), whereas the unfractionated heparin preparation analyzed in Figure 2 did not undergo an oxidative processing step (process A). Thus, the peak at 2.10 ppm observed in the 1
H 1D-NMR of unfractionated heparin arises due to oxidative processes that the heparin has been subjected to during manufacturing. This oxidative processing modifies the chemical environment around the N
-acetylglucosamine residue, thereby giving rise to the peak at 2.10 ppm.
Based on these initial observations, a low molecular weight heparin (LMWH) preparation that had been subjected to an oxidative process was evaluated. 1
H 1D-NMR data obtained on intermediates from a process used to make a LMWH preparation indicated that oxidation with sodium periodate yielded a LMWH preparation that shows the appearance of signals in the 2.10 ppm region. In Figure 5, the top panel shows the starting LMWH sample (Intermediate 1 which has not been subjected to oxidation and which does not have a detectable signal at 2.10 ppm. This LMWH intermediate was subjected to oxidation with sodium periodate. After oxidation, the resulting LMWH preparation, (Intermediate 2; bottom panel of Figure 5), showed the presence of signals at 2.09 and 2.10 ppm. The presence of these signals is likely due to a change in the environment of the N
-acetyl groups present on the glucosamine residues adjoining the uronic acid residues in heparin that have been oxidized as a result of periodate treatment. It is also worth noting that agents like permanganate follow similar mechanisms of oxidation, and permanganate is commonly used in heparin oxidation processes during purification.
Further experiments were performed to determine whether a modification on or near the N
-acetylglucosamine (GlcNAc) residue occurred when the residue was present internally within the chain, or at the reducing end of the chain. To test this, a preparation of porcine intestinal heparan sulfate with a high number of chains having an internal GlcNAc (PI-HS) was subjected to oxidation with potassium permanganate (PI-HSox
). In conjunction, a sample of porcine intestinal heparan sulfate enriched in reducing end N-acetylglucosamine residues (PI-HSNAc) was prepared and subjected to the same oxidation with potassium permanganate (PI-HSNAcox
) as the porcine intestinal heparin sulfate.
In addition, a low molecular weight heparin preparation prepared by enzymatic digestion that has a high percentage of GlcNAc at the reducing ends of the chains in the sample was subjected to permanganate oxidation. Both preparations were subjected to the same oxidation conditions.
The results from these experiments are shown in Figures 6 and 7. Oxidation of the heparan sulfate preparation with permanganate resulted in a very small increase of the peak at 2.10 ppm (Figure 6B). In contrast, the heparin sulfate preparation enriched in reducing end N-acetylglucosamine was oxidized, there was an intense signal at 2.10 ppm (Figure 6D), indicating that the oxidative chemistry had a significant influence on the N-acetylglucosamine residues at the reducing end position of the heparin chain. In addition, when the LMWH preparation that has a high percentage of GlcNAc at the reducing end was oxidized, there was a dramatic increase in the peak at 2.10 ppm (Figure 7). These results suggest that the structure resulting in the peak at 2.10 ppm arises from N-acetylglucosamine at or near the reducing end of the chain.
These experiments demonstrate that signals in the N
-acetyl region of the 1
H 1D-NMR spectra of unfractionated heparins can be indicative of different processing steps undertaken during the manufacture of heparin.
The presence of reducing α and β N-acetylglucosamine residues in PI-HSNAc and PI-HSNAcox
was confirmed by multidimensional experiments, i.e., COSY, TOCSY and HSQC. The HSQC spectra showed that after oxidation, the signals arising from GlcNAc at the reducing end are no longer observed (Figure 8). Comparison between HSQC spectra of PI-HSNAc (Figure 8B) and PI-HSNAcox
(Figure 8D) demonstrate that signals due to reducing α and β anomeric signals of the reducing end N-acetylglucosamine residues disappeared after potassium permanganate treatment, while peaks due to internal N-acetylglucosamine (5.4-5.3/100.3-98.8 ppm) did not increase in intensity.
Concomitantly, two distinct cross peaks appear at 4.37/ 58.9 ppm and 3.88/81.8 ppm (Figure 8C) after potassium permanganate oxidation. An HSQC-DEPT experiment assigned the peak at 4.37/58.9 ppm to a -CH residue (Figure 10A). A COSY experiment recorded in 10 % deuterated water showed a cross peak between an amide proton (from the N
-acetyl group) at 7.99 ppm and the peak at 4.37 ppm, while a NOESY experiment acquired in 10% deuterated water correlated the amide proton at 7.99 ppm to the CH3
signal at 2.10 ppm. These data suggest that the peak at 4.37 ppm arises due to the H2 of the oxidized N
-acetylglucosamine residue. In addition, HMBC analysis showed a long-range correlation between the proton at 4.37/ 58.9 ppm and a carbonyl group (Figure 10B). To determine if the carbonyl group belonged either to an aldehydic or carboxylic moiety, two experiments were performed. Firstly, the sample was acidified to pH 4.1 and an HSQC experiment was recorded. The experiment showed that the cross peak at 4.37/ 58.9 ppm shifted to 4.47/58.3 ppm as a function of the pH of the solution, consistent with a CH group adjacent to a carboxylic acid moiety. In addition, PI-HSNAcox was treated with sodium borodeuteride (10% w/w) for 60 minutes at 4°C and, after neutralization, was analyzed by 1HNMR (Figure 11). The intensity of the signal at 2.10 ppm did not decrease after reduction, indicating that the methyl group of the oxidized N
-acetylglucosamine residue is adjacent to a carboxylic acid group. Furthermore, COSY and TOCSY experiments do not show any correlation of this peak (4.37 ppm) with signals present in the anomeric region, indicating that C1 does not have a corresponding proton. This observation supports the assignment of the C1 as a carboxylic acid moiety.
HSQC-TOCSY experiments show additional correlations between the peak at 4.37/ 58.9 ppm and signals at 4.21/73.6 ppm, 3.88/81.8 ppm, and 4.12/72.8 ppm (Figure 12). Assignment of these cross peaks was performed by analysis of HMQC-COSY and HSQC-TOCSY experiments recorded with different mixing times, and are reported in Table 1 below and in Figure 13. Additional cross peaks at 3.80/64.4 ppm and 3.72/64.4 ppm were also observed in the HSQC spectra of all the samples treated with potassium permanganate. HSQC-DEPT spectra indicate that these signals arise from CH2
moieties (Figure 10A). Correlations between the peaks at 3.80 and 3.72 ppm and other protons of the oxidized residue could not clearly be identified by COSY and TOCSY experiments due to severe overlapping with other heparin signals. However, the proximity of the HSQC peaks at 3.80/64.4 ppm and 3.72/64.4 ppm to the H6,6'/C6 of 6-O
acetylglucosamine residues, and the appearance of these signals upon treatment with potassium permanganate, suggests assignment of these peaks to H6,6'/C6 of 6-0-desulfated N
-acetylglucosaminic acid. The chemical shift assignments of the residue generated by potassium permanganate treatment are consistent with a 4-substituted N-
acetylglucosaminic acid (Uchiyama et al. (1990) J. Biol. Chem., 265:7753-7759
Table 1. NMR assignment of the oxidized reducing end (N-acetylglucosaminic acid)
| ||Heparin/Heparan Sulfate|
|*These chemical shifts correspond to the residue that is non-sulfated at the 6-O position|
Based on these results, two possible structures that can give rise to the peak at 2.10 ppm have been determined. The structures are:
wherein, in structure B, X = H or SO3
Mass spectrometry was applied as an orthogonal analytical technique to support the structural assignment. The mass difference between N
-acetylglucosamine and N
-acetylglucosaminic acid at the reducing end is expected to be +16 Da. The PI-HSNAcox sample was digested with Heparinase I and analyzed by gel permeation chromatography, followed by mass spectrometry.
The results showed that some acetylated species have 16 Da higher mass than the corresponding non-oxidized N
-acetylglucosamine species (Supplementary Figure 5). This observation further substantiates our claim of an oxidized -COOH moiety present at C1 of the reducing end N
Finally, to confirm whether our observations on the model compound (PI-HSNAc) could be extended to unfractionated heparin, UFH lot 2 was subjected to oxidation with potassium permanganate. In unfractionated heparin samples the amount of N
-acetylglucosamine at the reducing end is usually very low (below 1% of the total glucosamine content, as estimated by NMR). Therefore, HSQC experiments of heparin acquired with a sufficient number of scans allow detection of a small peak at 5.20/93.4 ppm belonging to α reducing N
-acetylglucosamine (Figure 6A). Potassium permanganate oxidation of UFH lot 2 caused disappearance of the α reducing N
-acetylglucosamine signal and appearance of cross peaks at 4.37/ 58.9 ppm and 3.88/81.8 ppm (Figure 15). This result demonstrates that, similar to the situation for PI-HSNAc, potassium permanganate oxidation of unfractionated heparin results in the formation of an N-
acetylglucosaminic acid residue at the reducing end of the chain.
Experiments were also conducted to show that certain peaks in the N
-acetyl region can result from different chemical processing steps of heparin. For example, periodate oxidized heparin was submitted to acidic treatment. The treatment on an oxidized heparin preparation with an acid resulted in an increase of a peak at 2.08 ppm (Figure 9). Some minor peaks in the 2.10 ppm region were also observed.
These experiments described above show that the peak at 2.10 ppm in the 1
H 1D-NMR spectra of heparin is not OSCS and instead is a characteristic structural signature that is reflective of an oxidative processing step in the manufacture of unfractionated heparin. Based upon the experiments described above, the scheme provided likely results in structures A and B of Figure 16. Oxidation agents, such as KMnO4
, react with the reducing N
-acetyl glucosamine moieties to generate a modified N-
acetylglucosaminic acid residue (Structure A) at the reducing end of the heparin chain. In this situation, the newly formed signal at 4.37 ppm/58.9 ppm in the HSQC spectrum can be assigned to the proton at the C2 position of the newly generated N
-acetylglucosaminic acid. It is also possible that further oxidation of this structure may occur, resulting in the formation of a dicarboxylic acid (Structure B), however no confirmation of this structure is provided at present. This scheme (Figure 16), also explains why the appearance of the signal at 2.10 ppm in the 1H-NMR spectrum is dependent on the presence of reducing end N
-acetylglucosamine. Finally, since the formation of these structures results from oxidation conditions, we anticipate that other oxidation conditions, beyond potassium permanganate, could also potentially result in the formation of such structures.
In conclusion, it was found that oxidation conditions result in the conversion of N
-acetylglucosamine residues at the reducing end of heparin chains to an N-
acetylglucosaminic acid which yields a characteristic signal at 2.10 ppm in the 1H-NMR spectrum of the heparin. Therefore, this signal does not arise from an impurity or contaminant present within heparin, but rather represents a part of the heparin chain itself.
Modifications and variations of the methods in accordance with the invention are possible within the scope of the appended claims.