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• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07H—SUGARS; DERIVATIVES THEREOF; NUCLEOSIDES; NUCLEOTIDES; NUCLEIC ACIDS
  • C07H13/00—Compounds containing saccharide radicals esterified by carbonic acid or derivatives thereof, or by organic acids, e.g. phosphonic acids
  • C07H13/02—Compounds containing saccharide radicals esterified by carbonic acid or derivatives thereof, or by organic acids, e.g. phosphonic acids by carboxylic acids
  • C07H13/04—Compounds containing saccharide radicals esterified by carbonic acid or derivatives thereof, or by organic acids, e.g. phosphonic acids by carboxylic acids having the esterifying carboxyl radicals attached to acyclic carbon atoms
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P35/00—Antineoplastic agents
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P37/00—Drugs for immunological or allergic disorders
  • A61P37/02—Immunomodulators
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07H—SUGARS; DERIVATIVES THEREOF; NUCLEOSIDES; NUCLEOTIDES; NUCLEIC ACIDS
  • C07H1/00—Processes for the preparation of sugar derivatives
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07H—SUGARS; DERIVATIVES THEREOF; NUCLEOSIDES; NUCLEOTIDES; NUCLEIC ACIDS
  • C07H3/00—Compounds containing only hydrogen atoms and saccharide radicals having only carbon, hydrogen, and oxygen atoms
  • C07H3/06—Oligosaccharides, i.e. having three to five saccharide radicals attached to each other by glycosidic linkages

Definitions

• This invention relates methods of producing synthetic GM2s.
• the synthetic GM2s produced by the methods of the invention have greater than 95% purity, and have the same immunoreactivity with anti-GM2 antibodies as bovine brain- derived GM2s.
• Gangliosides are a class of molecules which are glycolipids. Different gangliosides have been identified as prominent cell surface constituents of various transformed cells, including melanoma, as well as other tumors of neuroectodermal origin. See, e.g., Ritter and Livingston, et al., Sem. Cane. Biol.. 2:401-409 (1991) and Oettgen, VCH Verlagstechnik (Weinheim Germany 1989), both of which are incorporated herein by reference.
• Gangliosides are known as mono-, di-, tri or polysialogangliosides, depending upon the degree of glycosylation with sialic acid residues.
• Abbreviations employed to identify these molecules include “GM1”, “GD3”, “GT1”, etc., with the “G” standing for ganglioside, "M” , “D” or M T”, etc. referring to the number of sialic acid residues, and the number or number plus letter (e.g., "GTla”), referring to the binding pattern observed for the molecule. See Lehninger, Biochemistry. pg.
• the onosialoganglioside GM2 has the structure:
• gangliosides There are difficulties unigue to the immunology of gangliosides, which are touched upon briefly here. First, while these molecules are prevalent on transformed cells, they are also common on certain normal cells, such as neural cells. There is a risk, in administering gangliosides to a subject, that the resulting antibody response will damage normal cells. Indeed, certain autoimmune pathologies, such as Guillain-Barre' Syndrome, are characterized by autoimmune antibodies reactive with GM1 or GQlb. See, e.g., Yuki, et al., J. Ex . Med.. 178:11771-1775 (1993); Aspinall, et al., Infect & I mun.. 6295) :2122-2125 (1994).
• gangliosides are secured via purification from tissue, such as bovine cranial tissues. Even under optimum conditions, the yields of pure gangliosides, in particular, GM2, are vanishingly small. Further, purification from mammalian tissue carries with it the risk of transmitting contaminants such as viruses, prion particles, and so forth. Alternate methodologies for securing ganglioside specific antibodies are thus highly desirable.
• This invention is directed to methods of synthesizing GM2.
• trisaccharide compound Ilia or Illb and glycosyl donor compound IV are glycosylated in the presence of a catalyst to obtain tetrasaccharide compound Va or Vb.
• the N-trichloroethyoxycarbonyl group is removed and the acetamido group is liberated from compound Va or Vb to obtain acetamino derivative compound Via or VIb.
• Compound Via or VIb is debenzylated and O-acetylated to obtain compound Vila or Vllb, which is then transformed into GM2.
• trisaccharide compound Ilia or Illb and glycosyl donor compound IV are glycosylated in the presence of a catalyst to obtain tetrasaccharide compound Va or Vb.
• the N-trichloroethyoxycarbonyl group is removed and the acetamido group is liberated from compound Va or Vb to obtain acet
• Illb and glycosyl donor compound VIII are glycosylated in the presence of a catalyst to obtain compound IXa or IXb.
• Compound IXa or IXb is converted to acetamino derivative compound Via or VIb.
• Compound Via or VIb is debenzylated and O-acetylated to obtain compound Vila or Vllb, which is then transformed into GM2.
• trisaccharide compound Ilia or Illb and glycosyl donor compound X are glycosylated in the presence of a catalyst and the glycosylation product is in situ treated with zinc in acetic anhydride to obtain compound Via or VIb.
• Compound Via or VIb is debenzylated and O-acetylated to obtain compound Vila or Vllb, which is then transformed into GM2.
• Figure 1 is comprised of Figures IA, IB, and IC, and represents a schematic diagram of methods and compounds used to make GM2 in accordance with the invention
• Figure 2 represents thin-layer chromatography of the synthetic GM2 of the invention, stained with resorcinol for sialic acid containing compounds
• Figure 3 represents thin-layer chromatography of the synthetic GM2 of the invention, stained with iodine vapor for lipid containing compounds
• Figure 4 represents the immunoreactivity of the synthetic GM2 of the invention and bovine brain-derived GM2 with mAb 10.11, by ELISA;
• Figure 5 represents the immunoreactivity of the synthetic GM2 of the invention and bovine brain-derived GM2 with mAb 45.114, by ELISA;
• Figure 6 represents the immunoreactivity of synthetic GM2 of the invention and bovine brain-derived GM2 with sera obtained from a melanoma patient which had been vaccinated with bovine brain-derived GM2;
• Figure 7 represents immunoreactivity, by immune thin- layer chromatography, of the synthetic GM2 of the invention and bovine brain-derived GM2 with mAb 10.11.
• These compounds can be obtained using known sialyl donors (compound I ( Figure IA) wherein R is preferably ethyl) and known glycosyl acceptors (compound II, Figure IA, wherein R is preferably benzyl or pivaloyl).
• sialyl donors compound I ( Figure IA) wherein R is preferably ethyl
• glycosyl acceptors compound II, Figure IA, wherein R is preferably benzyl or pivaloyl.
• Tin(II) trifluoromethane-sulfonate, ytterbium(III) trifluoromethanesulfonate, copper (II) trifluoromethanesulfonate, silver(I) trifluoromethanesulfonate, and related metal trifluoromethanesulfonates are used as catalysts herein.
• N N-trichloroethyoxycarbonyl-acetamido-l-thio-b-D- galactopyranoside
• NMS N-iodosuccinimide
• trifluoromethanesulfonic acid leads to benzyl 0-(3,4,6-tri-0-acetyl-2-deoxy-2-(N- trichloroethoxycarbonyl)acetamido-b-D-galactopyranosy1)-(1- 4 )- ⁇ [methyl (5-acetamido-4,7,8,9-tetra- ⁇ -acetyl-3,5-dideoxy- D-glycero- ⁇ -D-galacto-2-nonulopyranosyl)onate]-(2-3) ⁇ -,2,6- di-O-benzyl-b-D-galactopyranosyl)-(1-4)-2,3,
• Compound Va or Vb is then subjected to removal of the N-trichloroethyoxycarbonyl group with the help of zink in acetic acid liberating the acetamido group and furnishing benzyl ⁇ -(2-acetamido-3,4,6-tri-0-acetyl-2- deoxy-b-D-galactopyranosyl)-(1-4)- ⁇ [methyl (5-acetamido- 4,7,8,9-tetra-0-acetyl-3,5-dideoxy-D-glycero- ⁇ -D-galacto-2- nonulopyranosyl)onatel]-(2-3) )-(2,6-di-O-benzyl-b-D- galactopyranosyl)-(l-4)-2,3,6-tri-0-benzyl- (compound Via, Figure IA) or -3,6-di-0-benzyl-2- ⁇ -pivaloyl- ⁇ /b-
• compounds IVa and IVb and structurally related compounds having selectively removable N-carbonyl moieties (for instance, benzyloxycarbonyl, allyloxycarbonyl, etc.) are ideal glycosyl donors for high glycoside yields at this hindered 4-hydroxy group of the galactose moiety. Additionally, they are accessible to direct liberation of the 2-acetaraido group at the required N-acetylgalactosamine moiety without leading to the intermediacy of a free amino group.
• N-carbonyl moieties for instance, benzyloxycarbonyl, allyloxycarbonyl, etc.
• a second method of synthesizing GM2 calls for the transformation of compound III into compound VI.
• This method consists of the use of 0-(3,4,6-tri-0-acetyl-2-deoxy- 2-trichloroacetamido- ⁇ -galactopyranosyl)trichloroacetimidate (compound VIII, Figure IB) as glycosyl donor, for instance, with Ilia or Illb as glycosyl acceptors having the low reactive 4-hydroxy group of the galactose moiety.
• new catalysts are used for the attachment of the Neu5Ac residue to the lactose moiety, thus providing (2-3)-connected GM3 type intermediates.
• the GalNAc residue is attached at the low reactive 4-OH group of the Gal moiety to obtain GM2-tetrasaccharide.
• Methods with lead in the deprotection steps to free amino groups frequently result in low yields due to difficulties in the removal of the protecting groups, and/or in side reactions (lactam formation with the ester group of the Neu5Ac residue).
• the invention described herein provides methods which allow for a readily removable auxiliary group at the 2-acetamido group or for a substitute of the 2-acetamido group of the GalNAc residue.
• the required enhancement of the glycosyl donor properties with the direct liberation of the 2- acetamido group is gained without resorting to the free amine and its subsequent N-acetylation.
• Y can be any readily removable oxycarbonyl, thiorcarbonyl or aminocarbonyl derivative, including, but not limited to, 2,2,2-tribromoethoxycarbonyl, allyloxycarbonyl, benzyloxycarbonyl, 4- nitrophenylethoxycarbonyl or trichloromethylthiocarbonyl.
• 1,3,4,6-Tetra-0-acetyl-2-amino-2-deoxy-b-D-galactopyranose was prepared as described by R. Bergmann et al., Chem. Ber. Vol. 64, p.
• N-iodosuccinimide (168 mg, 0.75 mmol) and trifluoromethanesulfonic acid (.67 ⁇ L, 0.075 mmol) were added successively and the mixture was stirred for 30 minutes until TLC (toluene/acetone, 3:1) indicated complete reaction.
• the mixture was diluted with dichloromethane and washed with saturated aqueous NaHC0 3 , 1 M Na 2 S 2 0 3 solution and water, dried with MgS0 4 and concentrated. The residue was purified by silica gel column chromatography (toluene/acetone, 3:1) to afford compound V (61%).
• Debenzylation of compounds Via and b and subsequent O- acetylation to produce compounds VII a and b was performed using standard procedures.
• a mixture of compound Via (85 mg, 51 ⁇ mol) and 10% Pd-C (15 mg) in Me0H-CH 3 C00H (8 L, 5:1) was stirred for 2 hours at room temperature under H 2 . After filtration, the solution was concentrated. Without purification, a mixture of the residue, acetic anhydride (1 mL) , pyridine (1 mL) , and 4-dimethylaminopyridine (12 mg, 0.10 mmol) was stirred overnight at room temperature and then concentrated.
• Example 2 A second method for the synthesis of compound VI is provided. This method requires the preparation of glycosyl donor compound VIII. This was performed via the following procedures starting from galactosamine: Trichloroacetyl chloride (3.88 mL, 34.8 mmol) was added dropwise at room temperature within 30 minutes to a vigorously stirred solution of D-galactosamine hydrochloride (5 g, 23.4 mmol) and NaHC0 3 (5.84 g, 69 mmol) in water (46 mL) . The mixture was stirred for 1 hour, neutralized with 1 M HCI, concentrated and dried in vacuo . The residue was stirred for 3 hours at 0°C with MeOH (50 mL) .
• Transformation into compound VIII was performed as follows: A solution of l,3,4,6-tetra- ⁇ -acetyl-2-deoxy-2- trichloroacetamide-a,b-D-galactopyranose (1.73 g, 3.5 mmol) and hydrazine acetate (355 mg, 3.9 mmol) in DMF (20 mL) was stirred for 2 hours at 0 Q C, and then diluted with EtOAc (60 mL) , washed with saturated aqueous NaCl and water, dried with MgS0 4 , and concentrated.
• Example 3 A third method for the synthesis of compound VI is provided. This method requires the preparation of glycosyl donor X ( Figure IC) .
• Compound X contains a 2,2,2-trichloroethoxycarbonyl group, which can be replaced by any structurally related, electron withdrawing group including, but not limited to, 2,2,2- tribromoethoxylcarbonyl, 2,2,2-trifluoroethoxycarbonyl or 4- nitrophenylethoxycarbonyl.
• the purity of the synthetic GM2 obtained by the procedure described in Example 1 was analyzed.
• the GM2 was subjected to thin layer chromatography utilizing techniques known to those skilled in the art.
• the GM2 was visualized with resorcinol/HCl and iodine vapor as indicated in the brief description of the figures.
• the synthetic GM2 contained one major band, which was resorcinol and orcinol positive.
• the synthetic GM2 co- migrated with bovine brain-derived GM2.
• three major bands were detectable after staining with orcinol and resorcinol in the lanes containing 5 and 10 ⁇ g synthetic GM2.
• One band migrated slightly faster, and two bands migrated slightly slower than the main GM2 band (see Figure 2).
• Base treatment comprised treatment with 0.05 M NaOH in MeOH, at 50 ° C, for one hour.
• iodine vapor only the main GM2 band was detectable (see Figure 3).
• the purity of the GM2 synthesized by the method described in Example l was found to be greater than 95%, as determined by thin layer chromatography.
• the purity of the final product in the described process is dependent upon the purity of the starting materials. In the data described herein, the 95% would be improved, perhaps to 99%, if practical starting materials of higher purity, e.g., fatty acids with 99% higher purity, were available.
• the term "GM2" actually refers to a backbone structure, and while the glycoside chains which are described are constant, there is a certain amount of variability possible because of natural variability in fatty acid composition of the molecules. Hence, it is better to refer to GM2 in the plural ( M GM2s”), or to "a family of molecules, all of which possess the GM2 backbone structure".
• Example 5 The antigenicity of the GM2 synthesized by the method described in Example 1 was compared with the antigenicity of bovine brain-derived GM2. To do this, the synthetic GM2 was tested by ELISA for reactivity with various GM2 antisera. To perform the ELISA, antibody titration and GM2 antigen (both synthetic and bovine brain-derived) titration were performed. The synthetic GM2 was recognized by three different GM2-reactive antisera. These antisera included murine monoclonal antibody 10.11 ( Figure 4), human monoclonal antibody 45.114 ( Figure 5), and sera from a melanoma patient which was immunized with a vaccine containing bovine brain-derived GM2 ( Figure 6).
• Table 1 shows that the synthetic GM2 and the bovine brain-derived GM2 were recognized by the same antibodies by ELISA. Specifically, both synthetic and bovine brain-derived GM2 were recognized by monoclonal antibody 10.11, antibody 45.114, and patient sera immunized with a vaccine containing bovine brain-derived GM2. Neither the synthetic GM2 nor the bovine brain-derived GM2 was recognized by monoclonal antibodies R24 (which is an anti- GD3 monoclonal antibody) or F31, a glycolipid-recognizing antibody. Similarly, neither synthetic GM2 nor bovine brain-derived GM2 were recognized by sera from a patient which had not previously been immunized with a vaccine containing bovine brain-derived GM2. TABLE 1
• TITER anti-GM2 mAb 10.11 (mlgM) >0.39 ⁇ g/ml >0.39 ⁇ g/ml mAb 45.114 (hlgM) 1:4 1:8 pat. serum 1:3200 1:3200 (bovine brain GM2 vaccine) anti-GD3 mAb R24 (mlgG) others mAb F31 (mlgM) pat. serum neg. pool
• Example 6 The antigenicity of synthetic GM2 was compared with the antigenicity of bovine brain-derived GM2 utilizing immune thin-layer chromatography techniques known to those skilled in the art. Monoclonal antibody 10.11 ( Figure 7) was used in the chromatography.
• one main band and two minor bands were immunoreactive with monoclonal antibody 10.11.
• the main band co-migrated with bovine brain- derived GM2, while both minor bands migrated slightly faster than the main GM2 band (see Figure 7).
• the two minor bands which were immunoreactive with the anti-GM2 monoclonal antibodies are likely all GM2 species, which differ in ceramide composition from the major band, which contains C18:0 and dl8:l. No band migrating below the main GM2 band stained specifically with monoclonal antibody 10.11.
• Rabbits were immunized with either synthetic GM2 obtained by the method described in Example 1 or bovine brain-derived GM2 in order to induce the production of anti- GM2 antibodies.
• the rabbits were immunized four times at three week intervals with 200 ⁇ g GM2 for the first two immunizations and 100 ⁇ g GM2 for subsequent injections. Freund's adjuvant was utilized. After three months, two additional immunizations, at three week intervals, were given.
• Sera from the immunized animals was tested for immunoreactivity. It was found that sera from both synthetic GM2-immunized rabbits and bovine brain-derived GM2-immunized rabbits had low titers of IgM and IgG anti-GM2 antibodies. Both sera had the same low levels of i munogenicity. This indicates that the synthetic GM2 and the bovine brain-derived GM2 are not distinguished by the immune system.

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