Synthetic method of isoquinoline alkaloid N-oxide compound

Abstract

The invention discloses a synthesis method of an isoquinoline alkaloid N-oxide compound, which comprises the following steps: (1) taking 3, 4-dimethoxyphenylethylamine (I) as a raw material, and reacting to generate an intermediate compound (II); (2) taking the compound (II) as a raw material, and carrying out ring-closing dehydration reaction to obtain an intermediate compound (III); (3) taking the compound (III) as a raw material, and carrying out demethylation reaction to obtain an intermediate compound (IV); (4) dissolving the compound (IV) in a first organic solvent, adding a hydrogen peroxide aqueous solution, m-chloroperoxybenzoic acid or monoperoxyphthalic acid, and carrying out an N-oxidation reaction under a dark condition to generate an isoquinoline alkaloid N-oxide compound as shown in a formula (V); the synthesis method disclosed by the invention has the advantages that the raw materials are easy to obtain, the steps are simple and stable, the reaction quality process level can be increased, and sustainable industrial production is facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of pharmaceutical technology, and particularly relates to a method for synthesizing isoquinoline alkaloid N-oxide compounds. Background Art

[0002] Periodontitis is a local inflammatory response caused by the imbalance between local pathogenic bacteria and the host immune system. [1] Periodontitis can involve periodontal supporting tissues such as cementum, periodontal ligament, alveolar bone, and gingival tissue. The clinical manifestations are gingivitis, tooth loosening, alveolar bone resorption, and periodontal pocket formation. If the inflammation cannot be effectively controlled, the progressive destruction of periodontal tissues can lead to tooth loss and dentition defect. In addition to affecting pronunciation, eating, and aesthetics, periodontitis has also been proven to be a co-stimulatory factor for various systemic diseases such as diabetes, osteoporosis, rheumatoid arthritis, etc. [2] As one of the most common oral diseases worldwide, periodontitis has received increasing attention.

[0003] Litcubanine A (LA, namely Compound V in this application) is an isoquinoline alkaloid containing a special C-1 methyl group and N→O group, which was isolated by the applicant from Litsea cubeba, a plant of the genus Litsea in the Lauraceae family. [3] The isolation and extraction method thereof was disclosed in the article. Previous studies have found that LA can exert anti-inflammatory activity by inhibiting the NF-κB and MAPK signaling pathways, and showed good curative effects in the zebrafish caudal fin amputation model, the mouse dorsal wound healing model, and the mouse periodontitis model. [3-4] Chinese Patent ZL 2021 1 0395899.1 discloses a preparation method of LA and its derivatives, and the preparation method is to isolate and obtain from the 95% ethanol extract of Litsea cubeba. However, the yield of this method is low. At present, there is no report on the preparation of isoquinoline alkaloid N-oxide compounds by chemical synthesis methods.

[0004] References

[0005] [1]Slots J.Periodontitis:facts,fallacies and the future[J].Periodontol,2017 75(1):7-23.

[0006] [2]Fischer RG,Lira Junior R,Retamal-Valdes B,Figueiredo LC,MalheirosZ,Stewart B,Feres M.Periodontal disease and its impact on general health inLatin America.Section V:Treatment of periodontitis.Braz.Oral.Res.,2020,34(supp11):e026.

[0007] [3]Huan Xia,Yi-Tong Liu,Gui-Yang Xia,Yi Liu,Sheng Lin,Li-JiaGuo.Novel isoquinoline alkaloid Litcubanine A–a potential anti-inflammatorycandidate[J].Front.Immunol.,2021,12:685556.

[0008] [4]Yi-Tong Liu,Huan Xia,Gui-Yang Xia,Sheng Lin,Li-Jia Guo,Yi Liu.Theeffect of an isoquinoline alkaloid on treatment of periodontitis byregulating the neutrophils chemotaxis[J].J.Leukoc.Biol.,2021,110(3):475–484. Summary of the Invention

[0009] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for synthesizing isoquinoline alkaloid N-oxide compounds.

[0010] The technical solution of the present invention is outlined as follows:

[0011] A method for synthesizing isoquinoline alkaloid N-oxide compounds, comprising the following steps:

[0012] (1) Using 3,4-dimethoxyphenethylamine I as a raw material, reacting to generate intermediate compound II;

[0013] (2) Using compound II as a raw material, performing a ring-closing dehydration reaction to obtain intermediate compound III;

[0014] (3) Using compound III as a raw material, a demethylation reaction is carried out to obtain intermediate compound IV;

[0015] (4) Dissolve compound IV in a first organic solvent, add an aqueous hydrogen peroxide solution, m-chloroperoxybenzoic acid or monoperoxyphthalic acid, and carry out an N-oxidation reaction under light avoidance conditions to generate an isoquinoline alkaloid N-oxide compound, and the isoquinoline alkaloid N-oxide compound is shown in formula V;

[0016]

[0017] The first organic solvent is preferably dichloromethane, N,N-dimethylformamide or tetrahydrofuran.

[0018] Advantages of the present invention:

[0019] The synthesis method of the present invention has easily available raw materials, simple and stable steps, can increase the process level of the reaction quality, and is conducive to sustainable industrial production. Description of the drawings

[0020] Figure 1 Are TLC chromatograms of LA, LA-1, and LA-2, where A is the view of the TLC silica gel plate under an ultraviolet lamp (254 nm), and B is the view of the TLC silica gel plate sprayed with ninhydrin solution and heated until the spots are clearly developed, under daylight;

[0021] Figure 2 Are HPLC chromatograms of LA, LA-1, and LA-2;

[0022] Figure 3 Is the single crystal structure of LA-3. Specific embodiments

[0023] The following further describes the present invention in detail with reference to specific embodiments. Reagents or instrument equipment not indicating the manufacturer are regarded as conventional products that can be purchased on the market.

[0024] Example 1

[0025] A synthesis method of an isoquinoline alkaloid N-oxide compound, comprising the following steps

[0026] (1) Add raw material 3,4-dimethoxyphenethylamine I (3.62 g, 20.0 mmol) to a 250 mL round-bottom flask, add dichloromethane (100 mL), stir to dissolve at room temperature, cool to 0 - 5 °C and stir. Slowly add acetyl chloride (2.34 g, 30.0 mmol) dropwise within 5 min, continue to stir at 0 - 5 °C for 10 min, slowly add triethylamine (4.00 g, 40.0 mmol) dropwise within 20 min. After the addition is complete, react at 0 - 5 °C for 1 h; Monitor the reaction by TLC until completion, warm to room temperature, add water (100 mL) for extraction, dry the organic phase, and distill under reduced pressure to obtain intermediate compound II (4.24 g, 19.0 mmol) with a yield of 95%;

[0027] (2) Add intermediate compound II (3.35 g, 15.0 mmol) to a 250 mL round-bottom flask, add acetonitrile (100 mL), phosphorus oxychloride (6.80 g, 45.0 mmol) (phosphorus pentoxide or phosphorus pentachloride with the same molar amount can also be added), heat to reflux, and carry out ring-closing dehydration reaction for 5 h. Remove the solvent under reduced pressure, add 50 mL of ethyl acetate, extract with 10% sodium carbonate aqueous solution by mass fraction, extract the aqueous phase with ethyl acetate 5 times, combine the organic phases and dry, and obtain intermediate compound III (1.72 g, 8.4 mmol) by silica gel column chromatography with a yield of 56%;

[0028] (3) Add intermediate compound III (1.02 g, 5.0 mmol) to a 100 mL round-bottom flask, add 30% HBr aqueous solution by mass concentration (40 mL), heat to reflux, and carry out demethylation reaction for 10 h. Monitor the reaction by TLC until completion, remove the solvent under reduced pressure, dilute with ethyl acetate and extract with saturated sodium bicarbonate aqueous solution, extract the aqueous phase with ethyl acetate 5 times, combine the organic phases and dry, and obtain intermediate compound IV (0.57 g, 3.0 mmol) by silica gel column chromatography with a yield of 60%;

[0029] (4) Add intermediate compound IV (0.57 g, 3.0 mmol) to a 100 mL round-bottom flask, add dichloromethane (30 mL) and stir to dissolve, stir at room temperature, add 85% m-chloroperbenzoic acid (0.90 g, 5 mmol) in three portions, and carry out N-oxidation reaction for 2 h under light-shielded conditions. Monitor the reaction by TLC until completion, and obtain isoquinoline alkaloid N-oxide compound V (0.42 g, 2.0 mmol), abbreviated as LA-1, by silica gel column chromatography with a yield of 68%.

[0030]

[0031] Identification of LA-1

[0032] Compound LA-1. Purple-red powder; HR-ESI-MS: m / z 208.09669 [M+H] + (calcd for C 11 H 14 NO 3 , 208.09717); 1 1H NMR (600 MHz, DMSO) and 13 13C NMR (150 MHz, DMSO) data are shown in Table 1.

[0033] Table 1 Compound LA-1 1 1H 13 and 13C NMR (600 MHz) data (measured in DMSO)

[0034]

[0035] LA-1 obtained through Example 1 was identified by NMR and high-resolution mass spectrometry data as Litcubanine A (LA, i.e., Compound V of this application).

[0036] Example 2

[0037] Synthesis method of isoquinoline alkaloid N-oxide compounds, including the following steps

[0038] (1) 3,4-Dimethoxyphenethylamine I (3.62 g, 20.0 mmol) was added to a 250 mL round-bottom flask, acetic anhydride (50 mL) was added, the temperature was raised to reflux and stirred for 2 h. After the reaction was monitored by TLC and completed, acetic anhydride was removed under reduced pressure, water and ethyl acetate were added for extraction, the organic phase was dried, and the intermediate compound II (4.37 g, 19.0 mmol) was obtained by distillation under reduced pressure, with a yield of 98%;

[0039] (2)-(3) are the same as (2)-(3) in Example 1;

[0040] (4) The intermediate compound IV (0.30 g, 1.6 mmol) was added to a 50 ml round-bottom flask, N,N-dimethylformamide (15 ml) was added and stirred to dissolve, stirred at room temperature, 30% aqueous hydrogen peroxide solution (0.09 g) was added in three portions, and N-oxidation reaction was carried out for 6 h under light-shielded conditions. After the reaction was monitored by TLC and completed, the isoquinoline alkaloid N-oxide compound (V) (0.22 g, 1.0 mmol), i.e., LA-2, was obtained by silica gel column chromatography, with a yield of 66%.

[0041] The synthesized compounds LA-1, LA-2 and the isoquinoline alkaloid N-oxide compound (V) LA isolated from the 95% ethanol extract of Litsea cubeba were analyzed by thin layer chromatography and HPLC, and the results are as Figure 1 、Figure 2 as shown

[0042] Figure 1 are TLC chromatograms of LA, LA-1, and LA-2 (developer condition: dichloromethane - methanol 15:1; color developer: ninhydrin solution)

[0043] Figure 2 HPLC chromatograms of LA, LA-1, and LA-2 (HPLC analysis chromatographic conditions: CAPCELL-PAK-MGⅡC 18 (4.6 mm × 250 mm, 5 μm) chromatographic column, water (A) with (0.5% trifluoroacetic acid) - mobile phase acetonitrile (B), gradient elution (0.01 - 45.00 min, 5% - 95% B; 45.01 - 50.00 min, 95% B; 50.01 - 55.00 min, 5% B), flow rate 1.0 mL·min -1 , column temperature 32°C)

[0044] The above experimental results show that LA-1 and LA-2, identified and analyzed by TLC and HPLC data, are consistent with LA isolated from the 95% ethanol extract of Litsea cubeba, indicating that this method is feasible.

[0045] Example 3

[0046] A method for synthesizing isoquinoline alkaloid N-oxide compounds, comprising the following steps

[0047] (1)-(3) are the same as (1)-(3) in Example 1;

[0048] (4) Intermediate compound IV (0.45 g, 2.3 mmol) is added to a 50 ml round-bottom flask, and tetrahydrofuran (25 ml) is added and stirred to dissolve. Stir at room temperature, and m-chloroperbenzoic acid (0.71 g, 3.9 mmol) is added in three portions. Under light-shielded conditions, the N-oxidation reaction is carried out for 3 h. After monitoring the reaction completion by TLC, silica gel column chromatography is used to obtain isoquinoline alkaloid N-oxide compound (V) (0.31 g, 1.5 mmol), namely LA-3, with a yield of 65%. The synthesized compound LA-3 is cultured into single crystals, and its single crystal data are measured. The structure of LA-3 is the same as that of LA (see Figure 3 ), indicating that the method shown in this example can also obtain LA.

Claims

1. A method for synthesizing isoquinoline alkaloid N-oxide compounds, characterized in that The steps include: (1) Using 3,4-dimethoxyphenylethylamine (I) as a raw material, reacting to generate an intermediate compound (II); (2) using compound (II) as a raw material, performing a ring-closing dehydration reaction to obtain an intermediate compound (III); (3) using compound (III) as a raw material, performing a demethylation reaction to obtain an intermediate compound (IV); (4) dissolving compound (IV) in a first organic solvent, adding aqueous hydrogen peroxide, m-chloroperbenzoic acid or monoperoxyphthalic acid, and performing N-oxidation reaction under light-shielding conditions to generate an isoquinoline alkaloid N-oxide compound, wherein the isoquinoline alkaloid N-oxide compound is represented by formula (V); 2. The synthesis method according to claim 1, characterized in that The first organic solvent is dichloromethane, N,N-dimethylformamide or tetrahydrofuran.

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