Orelanin synthesis

Abstract

A method for preparing olelanine is disclosed. Tetramethylolelanine is demethylated to obtain olelanine.

Description

Technical Field

[0001] The present invention relates to a method for preparing orelanine.

Background Art

[0002] Orelanine (see formula I below) is a selective nephrotoxin that is present in relatively large amounts in some fungal species of the Cortinariaceae family.

Chem.

[0003] WO2010 / 040750 discloses that orelanine can be used in the treatment of renal cell carcinoma. Orelanine was taken up by human kidney cancer cells and killed them very efficiently, whether they were derived from primary tumors or metastatic tumor tissues. Cell death progressed for several days even after a temporary exposure to orelanine, indicating that the toxin was actively taken up and retained by the cells.

[0004] Orelanine formulations are being developed as therapeutic agents for renal cancer. Therefore, it is desirable to provide a safe and efficient synthetic route for orelanine.

[0005] Tiecco et al (Tetrahedron Vol.42, No.5, pages 1475 to 1485) disclose a synthetic route for orelanine. 3-Hydroxypyridine is converted to 2-bromo-3,4-dimethoxypyridine in a multi-step process. 2-Bromo-3,4-dimethoxypyridine is converted to orelanine as follows: a coupling reaction step with a nickel-phosphine complex; an oxidation step in the presence of excess m-chloroperbenzoic acid in chloroform; and a demethylation step at 120 °C for 5 hours with 48% hydrobromic acid.

[0006] The inventors are seeking to provide an improved synthetic route for orelanin. In particular, they are seeking a synthetic route that is safe, yields high yields, and does not require complex purification steps. [Overview of the project]

[0007] Accordingly, the present invention provides a method for preparing olelanine, which includes the following: The step of reacting the compound of formula (II) in the presence of pyridinium hydrochloride to obtain olelanine. [ka]

[0008] The inventors have discovered that reacting the compound of formula (II) in the presence of pyridinium hydrochloride yields olelanine in high yield and high purity. This reaction also avoids the gas generation that occurs in prior art processes when hydrobromic acid is used as a deprotective agent.

[0009] The present invention further provides compounds of formula (III): [ka] (In the formula, X - (This is a load charge counterion.)

[0010] The compound of formula (III) is an intermediate prepared during the purification step in an embodiment of the olelanine synthesis pathway. [Brief explanation of the drawing]

[0011] [Figure 1] This shows the synthetic pathway from 2-bromo-3,4-dimethoxypyridine to olelanine. [Modes for carrying out the invention]

[0012] Figure 1 shows the synthesis pathway of olelanine. It consists of the following four reaction steps: (i) Coupling of 2-bromo-3,4-dimethoxypyridine (Compound of Formula V) to obtain tetramethyloleoline (Compound of Formula IV) (ii) Purification of tetramethyloleoline (Compound of Formula IV) by reversible conversion to a salt of tetramethyloleoline (Compound of Formula III) (iii) Oxidation of tetramethyloleoline (Compound of Formula IV) to obtain tetramethylolelanine (Compound of Formula II) (iv) Demethylation of tetramethylolelanine (Compound of Formula II) to obtain olelanine (Compound of Formula I) These reaction steps are further detailed below:

[0013] Coupling of 2-bromo-3,4-dimethoxypyridine (Compound of Formula V) to obtain tetramethyloleoline (Compound of Formula IV) [Chemical formula] In one embodiment, the coupling is carried out in the presence of nickel(II) chloride, zinc, and triphenylphosphine. Nickel(II) chloride may be anhydrous nickel(II) chloride. Suitable solvents include dimethylformamide (DMF) or a mixture of tetrahydrofuran (THF) and DMF. The reaction can be carried out at a temperature of about 60 - 75 °C under reflux conditions.

[0014] The amount of nickel(II) chloride may be at least 0.2 equivalents and may be about 1 equivalent to achieve complete conversion.

[0015] Zinc may be highly activated zinc flakes (e.g., size - 325 mesh). Zinc may be present in excess (e.g., at least 1 equivalent, or at least 3 equivalents, or about 5.2 equivalents).

[0016] The reaction can be appropriately carried out under inert conditions (e.g., nitrogen atmosphere or argon atmosphere).

[0017] In one embodiment, a nickel complex is formed by placing triphenylphosphine in a reaction vessel, followed by zinc and then nickel chloride. The appearance of a dark red / brown color may indicate that the correct nickel complex has been formed.

[0018] In an alternative embodiment, the coupling of 2-bromo-3,4-dimethoxypyridine (Compound of Formula V) is carried out in the presence of a palladium(II) acetate catalyst. For example, the coupling can be carried out in the presence of 15% Pd(OAc)2, N-Bu4NI, EtNiPr2, and a DMF solvent.

[0019] In an alternative to the coupling of 2-bromo-3,4-dimethoxypyridine, tetramethyloleoline (Compound of Formula IV) can be prepared by coupling 2-iodo-3,4-dimethoxypyridine using the same reagents and conditions as for 2-bromo-3,4-dimethoxypyridine.

[0020] Purification of tetramethyloleoline (Compound of Formula IV) by reversible conversion to the salt of tetramethyloleoline (Compound of Formula III)

Chemical formula

[0021] In one embodiment, tetramethyloleline (compound of formula IV) is purified by converting tetramethyloleline (compound of formula IV) to a salt of tetramethyloleline (compound of formula III). Subsequently, as a simple purification step for tetramethyloleline (compound of formula IV), the salt is reverse-converted back to tetramethyloleline (compound of formula IV). In this approach, chromatographic purification is not required, and extraction is sufficient to obtain tetramethyloleline (compound of formula IV) of a suitable purity.

[0022] In one method according to this embodiment, tetramethyloleline (compound of formula IV) is dissolved in dichloromethane at room temperature. Hydrochloric acid is added to obtain tetramethyloleline dihydrochloride. Tetramethyloleline dihydrochloride is vacuum filtered while washing with dichloromethane. Tetramethyloleline dihydrochloride is neutralized with a base (e.g., sodium carbonate). The obtained tetramethyloleline (compound of formula IV) can be extracted into dichloromethane.

[0023] In another method according to this embodiment, tetramethyloleline (compound of formula IV) is dissolved in dichloromethane at room temperature. Oxalic acid is added to obtain tetramethyloleline dioxalate. Tetramethyloleline dioxalate is vacuum filtered while washing with dichloromethane. Tetramethyloleline dioxalate is neutralized with a base (e.g., sodium carbonate). The obtained tetramethyloleline (compound of formula IV) can be extracted into dichloromethane.

[0024] The compound of formula (III) is 2X - The load includes a counterion represented by . As an alternative to two counterions with a single negative charge, the counterion is a single counterion with a charge of -2 (i.e., X 2- ) may be. The load charge counterion may be a halide ion, preferably a chloride. The load charge counterion may be a dioxalate anion.

[0025] Oxidation of tetramethyloleline (compound of formula IV) to obtain tetramethylolelanine (compound of formula II) [ka] In one embodiment, oxidation is carried out in the presence of m-chloroperbenzoic acid (m-CPBA). The solvent may be dichloromethane. Other usable solvents include THF, ethyl acetate, and DMF. Vacuum filtration may be used to remove byproducts.

[0026] The amount of m-CPBA required to achieve rapid conversion may be at least 2 equivalents, or at least 3 equivalents.

[0027] Tetramethylolelanine (compound of formula II) can be purified by adding methyl tert-butyl ether (MTBE) and crystallizing tetramethylolelanine from the solution. The crystals are then properly washed with MTBE and filtered under vacuum.

[0028] Demethylation of tetramethylolelanine (compound of formula II) to obtain olelanine (compound of formula I). [ka] Demethylation of tetramethylolelanine (compound of formula II) with hydrobromic acid can yield olelanine, but this is accompanied by gas generation. The inventors sought to provide an alternative route for olelanine. Surprisingly, the inventors discovered that pyridinium hydrochloride yields high-purity olelanine from tetramethylolelanine (compound of formula II), thereby avoiding the need for chromatographic purification and enabling safe scale-up without significant gas generation.

[0029] The amount of pyridinium hydrochloride is at least 8 molar equivalents, and probably about 25 molar equivalents.

[0030] Pyridinium hydrochloride may be purchased as a reagent or prepared in situ by adding pyridine and hydrochloric acid. In this specification, both the terms “pyridinium hydrochloride” and “pyridine hydrochloride” are used to describe the reaction products of pyridine and hydrochloric acid. Another appropriate term is “pyridinium chloride.”

[0031] The reaction temperature may be in the range of 25–200°C, 50–150°C, 80–125°C, or 95–110°C, or approximately 105°C. The inventors have found that effective deprotection occurs at temperatures lower than those typically used in the demethylation step.

[0032] The typical reaction duration may be approximately 1 hour, or up to 24 hours.

[0033] The solvent may be n-methylpyrrolidone (NMP). Other possible solvents include dimethylimidazolidinone, DMF, NMP, DMA, sulfolane, and 1,4-dichlorobenzene. The reaction can also be carried out in the absence of a solvent.

[0034] The reaction can be carried out appropriately under inert conditions (e.g., a nitrogen or argon atmosphere).

[0035] Olelanine can be purified by methods known to those skilled in the art. In one method, olelanine is crystallized from solution and subjected to vacuum filtration and washing with water and ethanol. The olelanine can then be treated with hydrochloric acid, followed by treatment with sodium carbonate. This acidification / basicization can be repeated once or multiple times.

[0036] Currently, the present invention will be described by reference to examples (not intended to limit the present invention). [Examples]

[0037] Demethylation of tetramethylolelanine (compound of formula II) to obtain olelanine (compound of formula I). Comparative Example 1 - Hydrogen bromide and acetic acid 0.5 g of tetramethylolelanine was reacted with neat hydrogen bromide (33%) in acetic acid. The reaction occurred in a sealed tube at 125°C. Olelanine was formed with approximately 10% impurities and an uncorrected yield of 70–85%. Scaling up this methodology would require special equipment suitable for high-pressure corrosive media.

[0038] Comparative Example 2 - Hydrogen Bromide and Acetic Acid Tetramethylolelanine (8) was reacted with neat hydrogen bromide (33%) in acetic acid. Half-batch synthesis was used to control the exothermic reaction and excessive gas generation. The reaction proceeded gradually under a slow flow of nitrogen. Several fresh additions of acid were necessary to accelerate the conversion, using a total of approximately 50 equivalents of hydrogen bromide. The crude product was filtered and separated, and analysis by NMR showed that several decomposition impurities had formed, indicating an olelanine content of approximately 40%. Due to problems with gas generation, this approach was concluded to be unsuitable for large-scale use.

[0039] Comparative Example 3 - Boron Tribromide Tetramethylolelanine was reacted with excess boron tribromide in dichloromethane. The temperature was controlled from -4 to 0°C, and then from 0 to 25°C. Decomposition of N-oxide and formation of impurities were observed. This reaction did not produce olelanine.

[0040] Comparative Example 4 - Hydrogen Iodide 39.5 mg of tetramethylolelanine was reacted with hydrogen iodide in a sealed vial in the dark. No olelanine was produced overnight at room temperature. Upon heating, decomposition and iodination reactions occurred.

[0041] Example 1 - Pyridine hydrochloride 22 mg of tetramethyloleranine was reacted with an excess amount of pyridine hydrochloride overnight at 80°C. This yielded a mixture of oleranine, monodeprotected methyloleranine, and the starting material in a ratio of 10:3:0.3.

[0042] Example 2 - Pyridine hydrochloride 1.74 g of tetramethyloleranine was reacted with 25 equivalents of pyridine hydrochloride in NMP. The reaction mixture was heated from 25°C to 105°C. To control the quench, the reaction mixture was cooled before adding water, stirred for 30 minutes, and then isolated by vacuum filtration through P3 filter paper. Oleranine was obtained in high purity. The residual solvents were detected as follows: NMP 30 45 ppm, pyridine 53 61 ppm, ethanol 817 ppm.

[0043] Example 3 - Pyridine hydrochloride 48.05 g of olelanine was prepared by reacting tetramethylolelanine with 25 equivalents of pyridine hydrochloride in NMP. The reaction mixture was heated from 25°C to 105°C. The olelanine product was treated with hydrochloric acid, and then with sodium carbonate. This acidification / basicization was repeated several times. The calculated yield was 79.5%.

Claims

1. A method for preparing orelanin, The method comprising the step of reacting a compound of formula (II) in the presence of a pyridinium hydrochloride to obtain olelanine. 【Chemistry 1】

2. The method according to claim 1, wherein the reaction of the compound of formula (II) is carried out at a temperature in the range of 80 to 125°C.

3. The method according to claim 2, wherein the reaction of the compound of formula (II) is carried out at a temperature of about 105°C.

4. The method according to any one of claims 1 to 3, further comprising the step of reacting a compound of formula (IV) to obtain a compound of formula (II). 【Chemistry 2】

5. The method according to claim 4, wherein a compound of formula (IV) is reacted with m-chloroperbenzoic acid.

6. The method according to claim 4 or 5, wherein the compound of formula (II) is purified by crystallizing the compound of formula (II) from a solution containing methyl tert-butyl ether.

7. Furthermore, the method according to any one of claims 4 to 6, comprising the step of reversibly converting the compound of formula III to purify the compound of formula IV: 【Transformation 3】 (In the formula, X - (This is a load charge counterion.)

8. The method according to claim 7, wherein the compound of formula (IV) is reacted with hydrochloric acid.

9. The method according to claim 7, wherein a compound of formula (IV) is reacted with oxalic acid.

10. The method according to any one of claims 4 to 9, further comprising the step of reacting a compound of formula (V) to obtain a compound of formula (IV). 【Chemistry 4】

11. The method according to claim 10, wherein the compound of formula (IV) is reacted in the presence of nickel(II) chloride, zinc, and triphenylphosphine.

12. Compound of formula (III): 【Transformation 5】 (In the formula, X - (This is a load charge counterion.)

13. X - The compound according to claim 12, wherein the ion is a halide ion, preferably a chloride.

14. 2X - The compound according to claim 12, wherein the compound is a dioxalate anion.

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