Synthesis of sialyl chlorosides

Abstract

This invention belongs to the field of sialic acid synthesis, specifically relating to a method for synthesizing sialic acid chloroglycosides, which involves sialic acid esters, acid anhydrides, and MCl. n The reaction proceeds, followed by separation. This invention provides a method and mechanism for preparing sialic acid chloroglycosides, and this preparation method achieves superior reactivity, reaction efficiency, and conversion rate. Furthermore, it offers excellent environmental and cost advantages.

Description

Technical Field

[0001] This invention belongs to the field of synthesis, specifically relating to the synthesis of sialic acid compounds. Background Technology

[0002] Sialic acid is a class of nine-carbon sugar compounds widely found in organisms. N-Acetylneuraminic acid (Neu5Ac) is the most abundant type, and the term "sialic acid" generally refers to Neu5Ac. Unless otherwise specified in this article, sialic acid refers to Neu5Ac (formula A). Sialic acid is frequently linked to the ends of polysaccharides and glycoconjugates on the cell surface via glycosidic bonds, performing a variety of important biological functions. Sialic acid glycosides in organisms are all in the α-configuration; therefore, the stereoselective synthesis of α-sialic acid glycosides has always been one of the most challenging research areas in glycochemistry, and it is of great significance in the synthesis of novel anti-inflammatory, antiviral, and antitumor drugs and vaccines. N-acetyl-2-chloro-2-deoxyneuraminicacid methyl ester 4,7,8,9-tetraacetate (abbreviated as: sialic acid chloroglycoside, formula D) is not only the most classic sialic acid glycosyl donor, but also an intermediate in the synthesis of novel highly active sialic acid glycosyl donors (sialic acid thioglycosides, sialic acid phosphites or phosphates, sialic acid trifluoroacetylimine, etc.), and has always occupied an important position in the stereoselective synthesis of α-sialic acid glycosides.

[0003]

[0004] AN-acetylneuraminic acid (abbreviated as: sialic acid) structural formula

[0005]

[0006] Structural formula of BN-acetylneuraminic acid methyl ester (abbreviated as: methyl sialic acid)

[0007]

[0008] The structural formula of C.4,7,8,9-tetra-O-acetyl-N-acetylneuraminic acid methyl ester (abbreviated as: tetraacetylated sialic acid methyl ester)

[0009]

[0010] The structural formula of DN-acetyl-2-chloro-2-deoxyneuraminic acid methyl ester 4,7,8,9-tetraacetic acid ester (abbreviated as: sialic acid chloroglycoside)

[0011] Existing technologies all use the AcCl method to synthesize sialic acid chloroglycosides (Formula D), that is, first prepare sialic acid (Formula A) into methyl sialic acid (Formula B) or tetraacetylated methyl sialic acid (Formula C), and then react with (1) AcCl (ChemRxiv, 2020, 1-9; Chemical Communications, 2018, 54(74): 10487-10490; Angewandte Chemie, International Edition, 2016, 55(32): 9311-9315); (2) AcCl / 37% HCl (Angewandte Chemie, International Edition, 2010, 49(33): 5721-5725); (3) AcCl / AcOH (Synlett, 2002, (9): 1487-1490) or (4) AcCl / AcOH / gas HCl (Journal of Medicinal Chemistry, 2020, 63(11): 6134-6143) etc.

[0012] The main raw material for the current synthesis of sialic acid chloroglycosides is AcCl, a colorless, fuming liquid with a strong odor. It is highly irritating to the eyes and extremely corrosive. Even trace amounts of water in the reaction system will cause it to hydrolyze violently into AcOH and HCl. HCl also causes severe corrosion to equipment, requiring stringent production conditions. To ensure the reaction is effective, AcCl needs to be freshly distilled or HCl gas needs to be introduced simultaneously. To control the intensity of the reaction, AcCl must be added at the lowest possible temperature, and in a large excess (70-90 eq). After the reaction is complete, the excess AcCl must be removed by distillation. The reaction time is also very long, requiring stirring at room temperature in the dark for 1 to 5 days, resulting in high energy consumption and low efficiency. Summary of the Invention

[0013] In view of the problems of high cost, harsh operating environment, serious equipment wear and tear, and low reaction efficiency in the preparation methods of existing sialic acid chloroglycosides, the present invention aims to provide a non-acyl chloride method for preparing sialic acid chloroglycosides, which is an acyl chloride-free, low-cost method for synthesizing sialic acid chloroglycosides with excellent reaction efficiency and conversion rate.

[0014] A method for synthesizing sialic acid chloroglycosides, comprising sialic acid ester of formula 1, acid anhydride of formula 2, and MCl n The reaction was carried out, and then the sialic acid chlorglycoside compound product of formula 3 was obtained by separation.

[0015]

[0016] The R mentioned is a C1 to C4 alkyl group;

[0017] R1 is H or a C1-C4 alkyl group;

[0018] The MCI mentioned n It is a covalent compound of metals M and Cl.

[0019] This invention provides a novel (R1CO)2O / MCl n A novel approach to the preparation of sialic acid chloroglycosides, which combines formula 1 with (R1CO)2O and MCl n The reaction, based on a novel reaction mechanism, successfully achieves the chlorination of the -OH group of the anomeric carbon and the acylation protection of other hydroxyl groups, enabling the successful preparation of the aforementioned sialic acid chloroglycosides. The method described in this invention achieves excellent reaction efficiency based on a novel reaction mechanism, obtaining product yields comparable to or even better than those obtained by the acyl chloride method in a shorter time. Furthermore, it significantly reduces production costs, equipment wear and tear, and improves the production environment, demonstrating significant advantages in terms of cost and environmental protection.

[0020] In this invention, in Formula 1, R is methyl or ethyl;

[0021] Preferably, in Formula 2, R1 is methyl or ethyl.

[0022] In this invention, Equation 2 and MC1 are used. n In conjunction with, further cooperate with MCI n By controlling the components together, synergy can be achieved, enabling the preparation of the novel preparation mechanism of Equation 3, improving reaction efficiency and conversion rate, and significantly reducing production costs.

[0023] Preferably, the MCl n It is at least one of aluminum chloride, zinc chloride, and GeCl4; preferably aluminum chloride and / or GeCl4. The research of this invention unexpectedly discovered that the preferred aluminum chloride has superior effects, helping to further improve the activation energy of the novel reaction mechanism, improve the conversion rate of the novel reaction mechanism, and not only that, it helps to improve the production environment and reduce material and equipment wear and tear costs.

[0024] Preferred ingredients include sialic acid ester of formula 1, acid anhydride of formula 2, and MCl. n The molar ratio is 1:(4-10):(0.5-2); more preferably 1:(4.5-5.5):(0.5-1.5).

[0025] Preferably, a catalyst is added to the reaction process, wherein the catalyst is an organic carboxylic acid or a pyridine amine. Studies have found that the addition of the catalyst helps to further improve the activity of the reaction mechanism described in this invention, and helps to further improve the efficiency and effectiveness of the reaction.

[0026] Further preferably, the catalyst is TFA (trifluoroacetic acid) or DMAP (4-dimethylaminopyridine), with TFA being the most preferred;

[0027] Preferably, the organic acid catalyst is used in a catalytic amount, for example, 0.01 to 0.5 times the molar amount of Formula 1.

[0028] In this invention, the reaction does not require the addition of a solvent, or DCM or DMF solvents are added.

[0029] In this invention, the reaction process is carried out in the dark.

[0030] Preferably, the reaction temperature is 15–50°C, more preferably 20–45°C. This invention can be carried out under mild and easily achievable conditions.

[0031] Preferably, the reaction time is 6–10 hours. In this invention, thanks to the novel reaction mechanism described above, reaction efficiency can be improved, achieving results comparable to or even better than AcCl in a shorter reaction time. Furthermore, it offers significant advantages in terms of environmental protection and cost.

[0032] In this invention, after the reaction is completed, the reaction is quenched with a saturated ammonium chloride aqueous solution, followed by extraction and concentration with a hydrophobic solvent to obtain a crude product, which is then separated by chromatography to obtain the sialic acid chloroglycoside compound. The quenching solution is, for example, a saturated ammonium chloride aqueous solution. The hydrophobic solvent is, for example, at least one of EA and DCM. In the chromatographic separation stage, the eluent is a mixture of DCM and petroleum ether, preferably with a volume ratio of 2 to 4:1.

[0033] This invention discloses a preferred method for preparing sialic acid chloroglycosides, wherein methyl sialic acid (Formula B), Ac₂O, and MCl are prepared under an inert gas atmosphere. n The reaction was carried out under trifluoroacetic acid (TFA) catalysis at 20–45 °C with stirring in the dark for 6–10 h, in which methyl sialic acid, Ac₂O and MCl were involved. n The molar ratio of TFA to Ac2O was 1:(4-10):(0.5-2). The amount of TFA added as catalyst was determined. After the reaction was complete, a saturated NH4Cl aqueous solution was added to quench the reaction; the volume ratio of saturated NH4Cl aqueous solution to Ac2O was 5:1. Extraction was performed using CH2Cl2, with a volume ratio of CH2Cl2 to saturated NH4Cl aqueous solution of 1:1. The extract was washed with a saturated NaCl aqueous solution, and the solvent was removed by drying the extract with anhydrous Na2SO4 to obtain the crude product. The crude product was subjected to silica gel column chromatography (CH2Cl2:petroleum ether = 3:1, v / v) to remove the solvent, yielding sialic acid chloroglycoside.

[0034] In this invention, Formula 1, Formula 2, and MCln (Taking AlCl3 as an example) the product of formula 3 can be successfully prepared based on a completely new reaction pathway. The principle is as follows:

[0035]

[0036] The innovation of this invention lies in:

[0037] (1) This invention combines formulas 1, 2, and MCl. n The reaction avoids the use of AcCl and enables the preparation of Formula 3 based on a novel reaction mechanism. Furthermore, it exhibits superior reaction efficiency, achieving preparation results comparable to or even better than AcCl in a shorter reaction time. Moreover, the novel preparation approach described in this invention provides a favorable production environment and mild reaction conditions, significantly reducing production costs, effectively lowering the unit price of the target product, and minimizing equipment corrosion and wear.

[0038] (2) The operation is simple, the reaction time is short, the reagent cost is low, the energy consumption is low, and the overall cost is low. Attached Figure Description

[0039] Figure 1 The sialic acid chloroglycoside prepared in Example 1 1 H-NMR spectrum. Detailed Implementation

[0040] The present invention will be further described below with reference to examples. These examples are only for illustrating the present invention and do not limit the present invention. Examples 1 to 4 are the process of preparing sialic acid chloroglycoside according to the present invention; Comparative Example 1 is the preparation of sialic acid chloroglycoside by the existing method AcCl method.

[0041] Methyl sialic acid (Formula B) can be prepared using existing methods. For example, the preparation process is as follows: Under nitrogen protection, 10.0 g (32.3 mmol) of sialic acid (Formula A), 100 mL of anhydrous methanol, and 5 g of Dowex 50×8 (dried) are stirred at 35 °C in the dark for 2 h. The system becomes clear, and TLC (acetone:methanol = 8:1, v / v) shows that the reaction has reached its endpoint. After the reaction is complete, the resin is filtered off, the solvent is removed, and the mixture is dried under vacuum at 35 °C for 12 h to obtain 10.0 g (30.9 mmol) of methyl sialic acid, with a yield of 96%. Methyl sialic acid can be directly added to the next reaction without any further post-treatment.

[0042] Example 1: Preparation of sialic acid chloroglycoside

[0043] Under argon protection, 1.0 g (3.09 mmol) of methyl sialic acid, Ac₂O, AlCl₃, and 100 μL of TFA were stirred at 25 °C in the dark for 8 h. The molar ratio of methyl sialic acid, Ac₂O, and AlCl₃ was 1:5:1.2. TLC (CH₂Cl₂:petroleum ether = 3:1, v / v) showed that the reaction had reached its endpoint. After the reaction was completed, saturated NH₄Cl aqueous solution was added to quench the reaction. The volume ratio of saturated NH₄Cl aqueous solution to Ac₂O was 5:1. Extraction was performed with CH₂Cl₂. The volume ratio of CH₂Cl₂ to saturated NH₄Cl aqueous solution was 1:1. The extract was washed with saturated NaCl aqueous solution. The extract was dried over anhydrous Na₂SO₄ to remove the solvent and obtain the crude product. The crude product was subjected to silica gel column chromatography (CH₂Cl₂:petroleum ether = 3:1, v / v). After removing the solvent, 1.32 g (2.59 mmol) of sialyl chloroglycoside was obtained, with a yield of 84%.

[0044] The product spectrum information is as follows:

[0045] 1H NMR (500MHz, CDCl3) δ5.51–5.36(m,3H),5.35–5.28(m,1H),5.17(dt,J=14.6,7.3H z,1H),4.44(dd,J=12.5,2.2Hz,1H),4.39(t,J=11.4Hz,1H),4.25–4.11(m,2H),4. 07(dd,J=12.5,6.0Hz,1H),3.88(s,3H),2.79(dd,J=13.8,4.4Hz,1H),2.26(dd,J= 22.6,9.6Hz,2H),2.12(s,5H),2.09(s,5H),2.08(s,3H),2.06(s,4H),1.96(s,1H).

[0046] Example 2

[0047] Compared to Example 1, the difference lies in the screening of preparation conditions (including reaction temperature, whether a solvent is added, Cl source, and whether a catalyst is used). The operation and structure are shown in Table 1:

[0048] Table 1

[0049]

[0050] It is evident that the method described in this invention can achieve superior preparation efficiency and conversion rate.

[0051] Example 3: Preparation of sialic acid chloroglycosides according to the present invention

[0052] Under argon protection, 1.0 g (3.09 mmol) of methyl sialic acid, Ac₂O, GeCl₄, and 100 μL of TFA were stirred at 20 °C in the dark for 6 h. The molar ratio of methyl sialic acid, Ac₂O, and GeCl₄ was 1:5:0.5. TLC (CH₂Cl₂:petroleum ether = 3:1, v / v) showed that the reaction was complete. After the reaction was completed, saturated NH₄Cl aqueous solution was added to quench the reaction. The volume ratio of saturated NH₄Cl aqueous solution to Ac₂O was 5:1. Extraction was performed with CH₂Cl₂. The volume ratio of CH₂Cl₂ to saturated NH₄Cl aqueous solution was 1:1. The extract was washed with saturated NaCl aqueous solution. The extract was dried over anhydrous Na₂SO₄ to remove the solvent and obtain the crude product. The crude product was subjected to silica gel column chromatography (CH₂Cl₂:petroleum ether = 3:1, v / v). After removing the solvent, 1.34 g (2.63 mmol) of sialyl chloroglycoside was obtained, with a yield of 85%.

[0053] Example 4

[0054] Under argon protection, 1.0 g (3.09 mmol) of methyl sialic acid, Ac₂O, and 100 μL of TFA were stirred at 25 °C in the dark for 2 h. AlCl₃ was added, and the reaction continued for another 8 h. TLC (CH₂Cl₂:petroleum ether = 3:1, v / v) showed that the reaction was complete, with a molar ratio of methyl sialic acid, Ac₂O, and AlCl₃ of 1:5:1.2. After the reaction was complete, a saturated aqueous NH₄Cl solution was added to quench the reaction (volume ratio of saturated NH₄Cl solution to Ac₂O: 5:1). The mixture was extracted with CH₂Cl₂ (volume ratio of CH₂Cl₂ to saturated NH₄Cl solution: 1:1). The extract was washed with a saturated NaCl solution. The extract was dried over anhydrous Na₂SO₄ to remove the solvent, yielding a crude product. The crude product was subjected to silica gel column chromatography (CH₂Cl₂:petroleum ether = 3:1, v / v), and after solvent removal, 1.29 g (2.54 mmol) of sialyl chloroglycoside was obtained, with a yield of 82%.

[0055] Comparative Example 1: Preparation of sialic acid chloroglycosides by existing method (AcCl method)

[0056] 1.0 g (3.09 mmol) of methyl sialic acid was placed in a 50 mL round-bottom flask, and 15 mL of freshly distilled AcCl was added dropwise at 0 °C. The mixture was stirred under argon protection in the dark for 2 h, and then transferred to 25 °C to continue the reaction for 8 h. TLC (CH2Cl2:petroleum ether = 3:1, v / v) showed that the reaction was complete. After the reaction was completed, excess AcCl was removed by vacuum distillation, and the crude product was obtained by distillation twice with CH2Cl2. The crude product was subjected to silica gel column chromatography (CH2Cl2:petroleum ether = 3:1, v / v) to remove the solvent, yielding 1.37 g (2.69 mmol) of sialic acid chloroglycoside, with a yield of 59%.

[0057] The novel preparation mechanism of this invention can achieve comparable or even superior preparation performance compared to the AcCl method.

[0058] Raw material preparation cost accounting: The raw material prices are all from the quotations on October 26, 2022, from the Chemical Channel of Business Society.

[0059] Industrial-grade AcCl costs 8000 yuan / ton. Based on the minimum addition amount of 70 eq for the AcCl method and a yield of 59%, the main raw material reagent cost for producing 1 kg of sialic acid chloroglycoside, excluding methyl sialic acid, is 146 yuan.

[0060] Industrial-grade Ac2O costs 5800 yuan / ton, and industrial-grade AlCl3 costs 8500 yuan / ton. Based on a molar ratio of methyl sialic acid, Ac2O and AlCl3 of 1:5:1.2 and a yield of 84%, the main raw material reagent cost for producing 1 kg of sialic acid chloroglycoside, excluding methyl sialic acid, is only 10 yuan.

[0061] In addition to lower raw material costs, this invention also avoids harsh preparation environments and equipment corrosion and wear, resulting in a significant reduction in processing costs.

[0062] In summary, the preparation method described in this application has a novel preparation principle, superior reaction efficiency and conversion rate, and significant advantages in terms of raw material cost, equipment cost, and environmental protection.

Claims

1. A method for synthesizing sialic acid chloroglycosides, characterized in that, Sialate of Formula 1, anhydride of Formula 2, and MCl n The reaction was carried out, and then the sialic acid chlorglycoside compound product of formula 3 was obtained by separation. Formula 1 Formula 2 Formula 3 The R mentioned is a C1~C4 alkyl group; R1 is methyl; The MCI mentioned n It is at least one of aluminum chloride, zinc chloride, and GeCl4.

2. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, In Formula 1, R is methyl or ethyl.

3. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, Formula 1 sialic acid ester, Formula 2 acid anhydride, MCl n The molar ratio is 1:(4~10):(0.5~2).

4. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, A catalyst is also added during the reaction process, which is an organic carboxylic acid or DMAP.

5. The method for synthesizing sialic acid chloroglycosides as described in claim 4, characterized in that, The catalyst is TFA.

6. The method for synthesizing sialic acid chloroglycosides as described in claim 4, characterized in that, The amount of organic carboxylic acid used is the catalytic amount.

7. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, The reaction does not require the addition of a solvent, or may contain DCM or DMF solvent.

8. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, The reaction was carried out in the dark.

9. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, The reaction temperature is 15~50℃.

10. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, The reaction temperature is 20~45℃.

11. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, The reaction time is 6-10 hours.

12. The method for synthesizing sialic acid chloroglycosides as described in claim 1, characterized in that, After the reaction was completed, the reaction was quenched with a saturated ammonium chloride aqueous solution, followed by extraction and concentration with a hydrophobic solvent to obtain the crude product, which was then separated by chromatography to obtain the sialic acid chlorglycoside compound.

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