Melanin acetylated derivative, and preparation method and application thereof

Abstract

This application relates to the field of bio-based functional materials technology, and in particular to a melanin acetylation derivative, its preparation method, and its applications. This application obtains a single compound (melanin acetylation derivative) with a well-defined structure (a mixture) by acetylation of a specific melanin monomer intermediate, thus solving the problem of the uncertain structure of natural melanin. This results in better stability and processability, facilitating quality control and standardized applications. The melanin acetylation derivative retains the conjugated structure and phenolic hydroxyl groups of the melanin core, exhibiting good UV absorption and antioxidant activity. The preparation method of the melanin acetylation derivative provided in this application is mild, requiring no high temperature or high pressure, and has simple post-processing, making it suitable for large-scale production.

Description

Technical Field

[0001] This application relates to the field of bio-based functional materials technology, and in particular to a melanin acetylation derivative, its preparation method, and its application. Background Technology

[0002] Melanin is a natural pigment widely found in organisms, possessing excellent UV absorption, antioxidant, and free radical scavenging capabilities. Natural melanin (such as eumelanin) is typically a highly cross-linked amorphous polymer formed through complex oxidative polymerization of monomers such as 5,6-dihydroxyindole (DHI) and its carboxylic acid derivatives (DHICA). While this complex polymer structure endows melanin with multiple functions, it also leads to problems such as poor solubility, difficulty in precisely controlling its structure, and large batch-to-batch variability, greatly limiting its application in high-end fields.

[0003] To improve the solubility and processing properties of melanin, existing technologies typically attempt to chemically modify it. Acetylation is a common modification method that can shield hydrophilic groups such as phenolic hydroxyl and amino groups in melanin molecules, increasing their hydrophobicity and potentially improving their solubility in water, thus facilitating color fastness in subsequent dyeing. However, directly acetylating high molecular weight melanin polymers often results in problems such as uneven reaction, difficulty in controlling the degree of modification, and unclear product structure.

[0004] Therefore, there is an urgent need in this field to develop a melanin acetylation derivative with a well-defined structure, controllable solubility, and ease of large-scale production, as well as its preparation method. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the prior art by providing a melanin acetylation derivative, its preparation method, and its application. The melanin acetylation derivative provided by this application has better stability and processability.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0007] This application provides a melanin acetylation derivative, the structural formula of which is shown in Formula (I); the melanin acetylation derivative is named N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide.

[0008]

[0009] Formula (I).

[0010] This application obtains a single compound (melanin acetylation derivative) with a well-defined structure by acetylation of a specific melanin monomer intermediate, rather than a mixture. This solves the problem of the uncertain structure of natural melanin, and has better stability and processability, which is beneficial for quality control and standardized application.

[0011] Among them, melanin acetylated derivatives retain the conjugated structure of the melanin core and phenolic hydroxyl groups, and have good UV absorption and antioxidant activity.

[0012] A preferred embodiment of the method for preparing the melanin acetylation derivative described in this application includes the following steps:

[0013] S1. Dissolve 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol in water, control the temperature during the reaction, and obtain a solution.

[0014] S2. Add an acetylation reagent dropwise to the solution in step S1. After the addition is complete, heat the solution to carry out the acetylation reaction and obtain the reaction product solution.

[0015] S3. Add ice water to the reaction product solution of step S2 to cool and stir to precipitate the product, then perform solid-liquid separation, dry the filter cake to obtain melanin acetylated derivative.

[0016] The reaction formula for preparing melanin acetylated derivatives in this application is as follows:

[0017]

[0018] This application utilizes phenylindole as a starting material to efficiently synthesize a structurally well-defined melanin acetylated derivative, resulting in a melanin acetylated derivative with improved stability and processability. The preparation method described in this application is mild, simple to operate, and yields high output, making it suitable for industrial production.

[0019] In a preferred embodiment of the preparation method of the melanin acetylated derivative described in this application, the temperature in step S1 is controlled at 0~5℃ using ice water.

[0020] The ice-water bath temperature control described in this application can prevent oxidative polymerization reactions from occurring due to excessively high temperatures.

[0021] In a preferred embodiment of the method for preparing the melanin acetylated derivative described in this application, in step S2, the molar ratio of 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol and the acetylation reagent in step S1 is 1:(0.8~2.0).

[0022] Preferably, the molar ratio of 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol and the acetylation reagent in step S1 is 1:(1.2~2.0).

[0023] This application uses 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diphenol and acetylation reagent in the above molar ratio range to make the reaction more complete.

[0024] In a preferred embodiment of the method for preparing the melanin acetylation derivative described in this application, the acetylation reagent includes acetic anhydride or acetyl chloride.

[0025] This application uses the aforementioned types of acetylation reagents to acetylate specific melanin monomer intermediates, generating the melanin acetylated derivatives of this application. This solves the problem of uncertain natural melanin structure and is beneficial for quality control and standardized application.

[0026] In a preferred embodiment of the method for preparing the melanin acetylation derivative described in this application, the temperature for the acetylation reaction in step S2 is 15-40°C, and the reaction time is 2-12 hours. Preferably, the temperature for the acetylation reaction in step S2 is 15-25°C.

[0027] The application uses the above-mentioned temperature range, which can ensure that the reaction proceeds normally and maintains substrate stability while ensuring the reaction rate.

[0028] In a preferred embodiment of the method for preparing the melanin acetylation derivative described in this application, the pH of the solution for the acetylation reaction in step S2 is 6-8; the pH is controlled by adjusting at least one of potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, and sodium bicarbonate. If the pH of the solution for the acetylation reaction is too low, it will lead to substrate decomposition; if the pH of the solution for the acetylation reaction is too high, it will lead to the reaction not proceeding.

[0029] In a preferred embodiment of the preparation method of the melanin acetylated derivative described in this application, the cooling control temperature in step S3 is 0~5℃.

[0030] In a preferred embodiment of the method for preparing the melanin acetylated derivative described in this application, in step S3, the mass ratio of ice water to the reaction product solution is (2~5):1. Preferably, the mass ratio of ice water to the reaction product solution is (3~5):1.

[0031] In a preferred embodiment of the method for preparing the melanin acetylated derivative described in this application, the solid-liquid separation method in step S3 includes vacuum filtration or centrifugation.

[0032] This application also provides the application of the above-mentioned melanin acetylation derivatives in fabric dyeing.

[0033] Preferably, the fabric comprises a cotton fabric.

[0034] The melanin acetylation derivative provided in this application can be used for dyeing cotton fabrics, and the dyeing effect is better.

[0035] Compared with the prior art, this application has the following beneficial effects:

[0036] This application provides a melanin acetylated derivative, its preparation method, and its applications. By acetylifying a specific melanin monomer intermediate, this application yields a single compound with a well-defined structure (the melanin acetylated derivative), rather than a mixture, thus solving the problem of the uncertain structure of natural melanin. This derivative exhibits better stability and processability, facilitating quality control and standardized applications. Furthermore, the melanin acetylated derivative retains the conjugated structure and phenolic hydroxyl groups of the melanin core, demonstrating excellent UV absorption and antioxidant activity. The preparation method of the melanin acetylated derivative provided in this application is mild, requiring no high temperature or high pressure, and involves simple post-processing, making it suitable for large-scale production. Attached Figure Description

[0037] Figure 1 The liquid phase diagram is for N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide;

[0038] Figure 2 The UV absorption spectrum of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide;

[0039] Figure 3 The mass spectrum of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide in cation mode;

[0040] Figure 4 The 1H NMR spectrum of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide;

[0041] Figure 5 Images of cotton fabrics dyed with different concentrations of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide. Detailed Implementation

[0042] To better illustrate the purpose, technical solution, and advantages of this application, the following description will be provided in conjunction with the accompanying drawings and specific embodiments.

[0043] In the following examples and comparative examples, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified. Furthermore, the raw materials used in each parallel experiment are the same.

[0044] The raw materials used in the following examples were provided by Nanjing Hegu Life Biotechnology Co., Ltd. Product structure identification: The synthesized product was sent to the Analysis and Testing Center of Nanjing Normal University for testing.

[0045] Product purity was determined by high performance liquid chromatography, as follows:

[0046] Chromatographic conditions: Mobile phase: gradient elution of methanol and pure water, as shown in Table 1:

[0047] Table 1 Elution gradient

[0048]

[0049] Wavelength 200 nm, flow rate 1.0 mL / min, sample solution: DMSO, injection volume: 10 μL, column temperature 35℃, run time 20 min. Column: Galasil EF C18M 4.6 mmid × 250 mm L (SN B06211801).

[0050] In the following examples and comparative examples, 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol was prepared using the engineered bacteria and fermentation method disclosed in the patent: A bio-based melanin precursor compound, bio-based melanin and its preparation method and application (application number 2026100009390), specifically the methods disclosed in Examples 1 and 2.

[0051] Example 1

[0052] This embodiment provides a method for preparing a melanin acetylated derivative, including the following steps:

[0053] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, about 320 mg) and 20 mL of water; place the reaction flask in an ice-water bath to cool to 0-5 °C to obtain a solution;

[0054] S2. Under continuous stirring, acetyl chloride (2.0 mmol, approximately 0.14 mL) is slowly added dropwise to the solution obtained in step S1. During the addition, the pH of the reaction system is maintained at 7.0 by adding 10% sodium carbonate solution. After the addition is complete, the ice-water bath is removed, and the reaction solution is heated to 25°C. The reaction is then stirred at this temperature for 3 hours. During the reaction, the reaction is monitored by thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v) until the starting material spot disappears, which is determined as the reaction endpoint, and the reaction product solution is obtained.

[0055] S3. Pour 80 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (mass ratio of ice water to reaction product solution is 4:1) for purification. A brownish-red solid precipitates out and is filtered. The filter cake is transferred to a vacuum drying oven and dried at 60℃ for 10 hours to obtain 345.2 mg of dried powdered product with a purity of 95.6% and a calculated yield of 81.42%. Mass spectrometry analysis determined the molecular weight to be 399.9 [M+H]+, and calculations determined the molecular weight to be 399.0 M / z.

[0056] The above product was identified and named N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide (i.e., melanin acetylation derivative).

[0057] The structural formula of the melanin acetylated derivative is shown in formula (I).

[0058]

[0059] Formula (I).

[0060] The liquid phase diagram of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide is shown below. Figure 1 As shown; UV absorption spectrum as shown Figure 2 As shown.

[0061] The cation mode mass spectrum of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide is shown below. Figure 3 As shown.

[0062] The 1H NMR spectrum of N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide is as follows: Figure 4 As shown.

[0063] Example 2

[0064] This embodiment provides a method for preparing a melanin acetylated derivative, including the following steps:

[0065] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stir bar, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, about 320 mg) and 20 mL of water; place the reaction flask in an ice-water bath to cool to 0-5 °C to obtain a solution;

[0066] S2. Under continuous stirring, acetic anhydride (2.0 mmol, approximately 0.19 mL) is slowly added dropwise to the solution obtained in step S1. During the addition, the pH of the reaction system is maintained at 6.0 by adding 20% ​​sodium hydroxide solution. After the addition is complete, the ice-water bath is removed, and the reaction solution is allowed to rise naturally to 20°C. The reaction is then stirred for 6 hours at this temperature. During the reaction, the reaction is monitored by thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v) until the starting material spot disappears, which is determined as the reaction endpoint, and the reaction product solution is obtained.

[0067] S3. Pour 100 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 5:1) for purification. A light brown solid precipitates out and is filtered. The obtained solid is transferred to a vacuum drying oven and dried at 50℃ for 12 hours to obtain 336.4 mg of dried powdered product with a purity of 96.1% and a calculated yield of 79.76%.

[0068] Example 3

[0069] This embodiment provides a method for preparing a melanin acetylated derivative, including the following steps:

[0070] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, approximately 320 mg) and 20 mL of water. Cool the reaction flask to 0-5°C in an ice-water bath to obtain a solution;

[0071] S2. Under continuous stirring, acetic anhydride (2.0 mmol, approximately 0.19 mL) is slowly added dropwise to the solution obtained in step S1. During the addition, the pH of the reaction system is maintained at 7.8 by adding 5% sodium hydroxide solution. After the addition is complete, the ice-water bath is removed, and the reaction solution is allowed to naturally heat up to 15°C. The reaction is then stirred for 8 hours at this temperature. During the reaction, the reaction is monitored by thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v) until the starting material spot disappears, which is determined as the reaction endpoint, and the reaction product solution is obtained.

[0072] S3. Pour 100 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 3:1) for purification. A brown solid precipitates out. Filter the solid and transfer it to a vacuum drying oven. Dry the solid at 70℃ for 8 hours to obtain 348.2 mg of dried powdered product with a purity of 95.2%. The calculated yield is 81.78%.

[0073] Examples 2-3 used the same reaction substrate and the same reaction principle as Example 1, and had the same experimental phenomena. The products could be identified by TLC spotting. They were all N-[1-(acetylamino)-2-[5-(5,6-dihydroxy-1H-indol-4-yl)-3,4-dihydroxyphenyl]ethyl]acetamide (i.e. melanin acetylation derivatives).

[0074] Example 4

[0075] This embodiment provides a method for preparing a compound, including the following steps:

[0076] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, approximately 320 mg) and 20 mL of water. Cool the reaction flask to 0-5°C in an ice-water bath to obtain a solution;

[0077] S2. Under continuous stirring, acetyl chloride (1.4 mmol, approximately 0.1 mL) is slowly added dropwise to the solution obtained in step S1. During the addition, the pH of the reaction system is maintained at 7.5 by adding 10% sodium carbonate solution. After the addition is complete, the ice-water bath is removed, and the reaction solution is heated to 40°C and stirred for 3 hours. During the reaction, the reaction is monitored by thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v). TLC monitoring shows that new by-product spots are generated and the starting material spots have not completely disappeared. The reaction is then terminated, and the reaction product solution is obtained.

[0078] S3. Pour 100 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 2:1) for purification. A brown solid precipitates out. Filter the solid and transfer it to a vacuum drying oven. Dry it at 60℃ for 10 hours. After treatment, 319.5 mg of light brown solid product is obtained with a purity of 68.5% and a yield of 54.0%.

[0079] The results showed that excessively high reaction temperatures led to the decomposition of raw materials and an increase in side reactions, resulting in a significant decrease in yield.

[0080] Example 5

[0081] This embodiment provides a method for preparing a compound, including the following steps:

[0082] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, approximately 320 mg) and 20 mL of water. Cool the reaction flask to 0-5°C in an ice-water bath to obtain a solution;

[0083] S2. Under continuous stirring, acetic anhydride (0.8 mmol, approximately 0.076 mL) was slowly added dropwise to the solution obtained in step S1. The pH of the reaction system was maintained at 7.0 by adding 20% ​​sodium hydroxide solution. After the addition was complete, the ice-water bath was removed, and the reaction solution was slowly heated to 25°C. The reaction was continued to be stirred at this temperature for 6 hours. During the reaction, the reaction was monitored by TLC (evolving solvent: dichloromethane / methanol = 10 / 1, v / v). The TLC monitoring showed a faint target product spot, but the starting material spot was still present in large quantities. The reaction was then terminated, and the reaction product solution was obtained.

[0084] S3. Pour 100 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 4:1) for purification. A brown solid precipitates out. Filter the solid and transfer it to a vacuum drying oven. Dry it at 60℃ for 10 hours. After treatment, 186.8 mg of brown solid is obtained with a purity of 86.5% and a yield of 39.87%.

[0085] The results showed that insufficient acylation dosage led to incomplete reaction, which was the main reason for the reduced yield.

[0086] Example 6

[0087] This embodiment provides a method for preparing a compound, including the following steps:

[0088] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, approximately 320 mg) and 20 mL of water. Cool the reaction flask to 0-5°C in an ice-water bath to obtain a solution;

[0089] S2. Under continuous stirring, acetic anhydride (1.2 mmol, approximately 0.11 mL) was slowly added dropwise to the solution obtained in step S1. The pH of the reaction system was maintained at 6.8 by adding 10% sodium bicarbonate solution. After the addition was complete, the ice-water bath was removed, and the reaction solution was rapidly heated to 40°C. The reaction was stirred for 2 hours. During the reaction, the reaction was monitored by TLC (evolving solvent: dichloromethane / methanol = 10 / 1, v / v). The TLC monitoring showed that the starting material spot disappeared, but several unidentified byproduct spots appeared. The reaction was then terminated, and the reaction product solution was obtained.

[0090] S3. Pour 100 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 4:1) for purification. A brown solid precipitates out. Filter the solid and transfer it to a vacuum drying oven. Dry it at 60℃ for 10 hours. After treatment, 256.1 mg of dark brown solid is obtained with a purity of 49.5% and a yield of 31.28%.

[0091] The results showed that although reaction conditions with excessively high temperatures and excessively short reaction times could accelerate the reaction, they also exacerbated side reactions, resulting in unsatisfactory yields and product purity.

[0092] Example 7

[0093] This embodiment provides a method for preparing a melanin acetylated derivative, including the following steps:

[0094] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, approximately 320 mg) and 20 mL of water. Place the reaction flask in an ice-water bath and maintain the temperature at 0-5°C to obtain a solution;

[0095] S2. Under continuous stirring, acetic anhydride (1.8 mmol, approximately 0.17 mL) is slowly added dropwise to the solution obtained in step S1. During the addition, the pH of the reaction system is maintained at 6.8 by adding 10% sodium bicarbonate solution. After the addition is complete, the reaction system is kept in an ice-water bath (2-5℃) and stirred for 12 hours. During the reaction, the reaction progress is monitored by thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v) to determine the reaction endpoint and obtain the reaction product solution.

[0096] S3. Pour 60 mL of ice water (0-2℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 4:1) for purification. A dark brown solid precipitates out and is filtered. The obtained solid is transferred to a vacuum drying oven and dried at 50℃ for 16 hours to obtain 315.4 mg of dried powdered product with a purity of 96.10% and a calculated yield of 74.78%.

[0097] The results showed that if the reaction temperature was too low, the reaction time needed to be extended by more than four times in order to achieve a yield and purity similar to that of Example 1.

[0098] Example 8

[0099] This embodiment provides a method for preparing a melanin acetylated derivative, including the following steps:

[0100] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, about 320 mg) and 20 mL of water; place the reaction flask in an ice-water bath to cool to 0-5 °C to obtain a solution;

[0101] S2. Under continuous stirring, acetyl chloride (1.4 mmol, approximately 0.1 mL) is slowly added dropwise to the solution obtained in step S1. During the addition, the pH of the reaction system is maintained at 7.5 by adding 10% sodium carbonate solution. After the addition is complete, the ice-water bath is removed, and the reaction solution is slowly heated to 25°C. The reaction is then stirred at this temperature for 3 hours. During the reaction, the reaction is monitored by thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v) until the starting material spot disappears, which is determined as the reaction endpoint, and the reaction product solution is obtained.

[0102] S3. Pour 40 mL of ice water (0-5℃) into the reaction product solution obtained in step S2 (the mass ratio of ice water to reaction product solution is 4:1) for purification. A brown solid precipitates out and is filtered. The filter cake of the obtained solid is transferred to a vacuum drying oven and dried at 60℃ for 10 hours to obtain 278.4 mg of dried powdered product with a purity of 92.1% and a calculated yield of 63.26%.

[0103] The results showed that reducing the volume ratio of ice water to the reaction product solution in the post-processing step led to a decrease in product yield.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing a compound, comprising the following steps:

[0106] S1. In a 100 mL three-necked round-bottom flask equipped with a magnetic stirrer, add 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol (1 mmol, approximately 320 mg) and 20 mL of water. Cool the reaction flask to 0-5°C in an ice-water bath to obtain a solution;

[0107] S2. Acetic anhydride (1.8 mmol, approximately 0.17 mL) was slowly added dropwise to the solution obtained in step S1 under continuous stirring. No alkali solution was added to adjust the pH during the reaction; the initial pH of the reaction solution was approximately 4.0, and it decreased further as the reaction proceeded. After the addition was complete, the ice-water bath was removed, and the reaction solution was allowed to naturally heat to 18°C ​​and stirred for 8 hours. During the reaction, thin-layer chromatography (TLC, developing solvent: dichloromethane / methanol = 10 / 1, v / v) was used for monitoring. TLC monitoring showed that the starting material spot remained essentially unchanged. Only a small amount of brownish-black tar-like substance was obtained after treatment; the target product was not detected.

[0108] The results showed that when the pH of the reaction system was too low, the amine was protonated, the nucleophilicity decreased sharply, and an effective N-acetylation reaction could not occur.

[0109] Application Example 1

[0110] Different mass concentrations (45 g / L, 40 g / L, 35 g / L, 30 g / L) of the product from Example 1 were dispersed in an aqueous solution at pH 5. Fabrics (such as cotton, silk, or wool) were immersed in the dye bath at a liquor ratio of 1:20, and slowly immersed with shaking at 60°C for 30 minutes. The dyed fabrics were then dried at temperatures below 80°C. The final dyeing effect of the fabric is shown in the image. Figure 5 The image shown is a staining effect diagram of the product from Example 1 with a concentration of 30 g / L-45 g / L.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A melanin acetylated derivative, characterized in that, The structural formula of the melanin acetylated derivative is shown in formula (I); Formula (I).

2. The method for preparing the melanin acetylation derivative as described in claim 1, characterized in that, Includes the following steps: S1. Dissolve 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol in water, control the temperature during the reaction, and obtain a solution. S2. Add an acetylation reagent dropwise to the solution in step S1. After the addition is complete, heat the solution to carry out the acetylation reaction and obtain the reaction product solution. S3. Add ice water to the reaction product solution of step S2 to cool down and stir to precipitate the product. Then perform solid-liquid separation, dry the filter cake, and obtain melanin acetylated derivative. In step S1, ice water is used to control the temperature at 0~5℃; In step S2, the molar ratio of 4-[5-(2,2-diaminoethyl)-2,3-dihydroxyphenyl]-1H-indole-5,6-diol and the acetylation reagent in step S1 is 1:(0.8~2.0). In step S2, the temperature for acetylation is 15-40°C, and the reaction time is 2-12 hours.

3. The method for preparing the melanin acetylation derivative as described in claim 2, characterized in that, The acetylation reagent includes acetic anhydride or acetyl chloride.

4. The method for preparing the melanin acetylation derivative as described in claim 2, characterized in that, The pH of the solution for the acetylation reaction in step S2 is 6-8; the pH is controlled by adjusting at least one of potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, and sodium bicarbonate.

5. The method for preparing the melanin acetylated derivative as described in claim 2, characterized in that, In step S3, the cooling control temperature is 0~5℃.

6. The method for preparing the melanin acetylation derivative as described in claim 2, characterized in that, In step S3, the mass ratio of ice water to the reaction product solution is (2~5):

1.

7. The application of the melanin acetylation derivative as described in claim 1 in fabric dyeing.

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