Preparation method for removing ethyl impurities from isosulfur blue

Abstract

The invention discloses a preparation method for removing ethyl impurities from isosulfur blue, and belongs to the technical field of medicines. The technical problem to be solved is to provide the preparation method of the impurity for removing the ethyl from the isosulfur blue, which has the advantages of easily available raw materials, simple method and high purity and yield, so as to meet the accurate property research on the impurity for removing the ethyl from the isosulfur blue. According to the technical scheme, the preparation method is characterized by comprising the following steps: mixing 2-formylbenzene-1, 4-sodium disulfonate, N, N-diethyl aniline, acid and urea, and reacting to obtain 2-(bis (4-(diethylamino) phenyl) methyl) benzene-1, 4-disulfonic acid; 2-(bis (4-(diethylamino) phenyl) methyl) benzene-1, 4-disulfonic acid is subjected to an oxidation deethylation reaction in the presence of an oxidizing agent, and a crude product is obtained; and performing column chromatography purification to obtain the isothioblue ethyl-removed impurity.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical technology, and more specifically, to a method for preparing an isothiocyanate deethylated impurity. Background Technology

[0002] For understanding the technical content of this invention: Isothiazine, also known as purified patented blue violet, is a triarylmethane dye. As a novel lymphatic tracer, isothiazine is primarily used as a control reagent for lymphatic vessel mapping. It has excellent effects on lymph node localization, staining quickly and with long-lasting effects. It can significantly improve the accuracy and sensitivity of dye-based sentinel lymph node activity assays (SLNB) for breast cancer, making it an adjunct to lymphography and widely used in cancer treatment. Isothiazine injection (1%) is commonly used in a mapping procedure called lymph node marking, which allows for visual mapping of the lymphatic system through the injection area. It is frequently used for lymph node localization in breast cancer patients. Simultaneously, due to its lower cost and safety compared to radioactive technetium-99M sulfur colloid, the use of isothiazine as a guide for surgical resection of cancer cells is gradually increasing.

[0003] Impurity research is an important part of drug quality research and one of the key factors in drug quality assurance. As a pharmaceutical industry, it is essential to strictly control the impurity content in products. Research on material impurities helps optimize the drug synthesis process and quality control, ensuring the quality testing of each batch of raw materials. The deethylated impurity in isosulfur blue is an important part of its quality research. According to the draft of the United States Pharmacopeia / National Formulary for isosulfur blue published in July 2025, the name of the deethylated impurity is 2-{[4-(diethylimino)cyclohexyl-2,5-diene-1-ylidene][4-(ethylamino)phenyl]methyl}-4-sulfobenzenesulfonate sodium. The structural formula is shown in formula (1):

[0004] Equation (1) Relevant patent documents retrieved: This document, published in China (CN109721512A) on May 7, 2019, discloses a homogeneous oxidation synthesis method for isothiocyanate. Using acid blue as a raw material and tetravalent cerium salt as an oxidant, the method oxidizes acid blue in the presence of acid with water or a mixture of water and other solvents to obtain isothiocyanate. The reaction is carried out at -10 to -10°C, and the deethylation impurity is less than 0.15%. This method avoids the use of expensive oxidants like silver oxide and hazardous reagents like permanganate and dichromate, making it more environmentally friendly. The document mentions the need to control the deethylation impurity to less than 0.15% to ensure the quality of isothiocyanate. Furthermore, the background section details the difficulty in removing deethylation impurities from isothiocyanate, which affects its quality. For example, APICORE's patents US7662992, US8969616, and US9353050 report the following process routes for synthesizing isothiocyanate:

[0005] Relevant non-patent literature retrieved: The journal is titled "Synthetic Process and Quality Study of Isosulfur Blue, a Tumor Tracer," and the article is titled "Synthetic Process and Quality Study of Isosulfur Blue, a Tumor Tracer." The publication date is September 30, 2018. This article discloses the importance of the synthesis, purification, and quality control of isosulfur blue, and also mentions that the content of deethylated impurities in isosulfur blue needs to be controlled below ≤0.3%.

[0006] Furthermore, regarding the currently reported and publicly disclosed methods for the synthesis and preparation of isosulfur blue, including Aurobindo's patent IN2012 CH3509, INNOASSYNTH's patent US 7534911, Optimus' patents IN 2014 CH2658 and IN 2014 CH00263, DISHMAN's patent IN 2014 MU03879, and Jiming Pharmaceutical Technology (Suzhou) Co., Ltd.'s patent CN107573265A, all of these patents generate isosulfur blue deethylation impurities during the synthesis process, and these impurities are difficult to remove during purification.

[0007] Isosulfan blue is not currently included in the pharmacopoeias of various countries (China, the United States, Japan, etc.). The maximum daily dose of isosulfan blue is 30 mg per day. According to the ICH Q3A guideline "Impurities in New Drug Substances", the known impurities in drug substances with a maximum daily dose not exceeding 2 grams must be controlled to a content of ≤0.15%.

[0008] Currently, there is considerable research on the synthesis methods of isothiocyanate in China, but research on the preparation of its impurities is relatively limited. However, current drug application requirements for impurity research are quite stringent, and such research is beneficial for improving drug quality. Therefore, providing a method for preparing the deethylated impurity of isothiocyanate is of significant importance. Summary of the Invention

[0009] The purpose of this invention is to provide: A method for preparing isothiocyanate deethylated impurities, and related technologies, to solve the technical problems of providing a method for preparing isothiocyanate deethylated impurities with readily available raw materials, simple method, and high purity and high yield, so as to meet the technical problems of accurate property study of isothiocyanate deethylated impurities, or a combination thereof.

[0010] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0011] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0012] The definition of standard chemical terms can be found in the reference "Basic Organic Chemistry (Volumes 1 & 2)" by Xing Qiyi, Higher Education Press, 3rd Edition, 2005-06.

[0013] Unless otherwise stated, conventional methods within the scope of the art, such as mixing and stirring, shall be used.

[0014] Unless specifically defined herein, the use of all commercially available products herein employs standard techniques. For example, it may be carried out using the manufacturer's instructions for use with the kit, or in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0015] In a first aspect, the present invention provides: a method for preparing an isothiocyanate deethylated impurity, comprising the following steps: S1: Sodium 2-formylbenzene-1,4-disulfonic acid, N,N-diethylaniline, acid and urea are mixed and reacted to give 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid; S2: 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid was oxidized and deethylated in the presence of an oxidant to give the crude product; S3: Column chromatography was used to purify the isothiocyanate deethylated impurity.

[0016] In step S1, the molar ratio of sodium 2-formylbenzene-1,4-disulfonate and N,N-diethylaniline is 1:2.5-3.5.

[0017] Any point value or range between two points within the above range can achieve the technical effect of the present invention, including but not limited to 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, and 1:3.5.

[0018] In step S1, the molar ratio of sodium 2-formylbenzene-1,4-disulfonate and N,N-diethylaniline is further preferably 1:3.0.

[0019] In step S1, the acid is selected from at least one of acetic acid, sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, p-toluenesulfonic acid, or trifluoroacetic acid.

[0020] In step S1, the acid is further preferably acetic acid.

[0021] In step S1, the molar ratio of sodium 2-formylbenzene-1,4-disulfonate and urea is 1:0.5-1.5.

[0022] Any point value or the range between two points within the above range can achieve the technical effect of the present invention, including but not limited to 1:0.5, 1:0.75, 1:1.0, and 1:1.5.

[0023] In step S1, the molar ratio of sodium 2-formylbenzene-1,4-disulfonate and urea is further preferably 1:0.75.

[0024] In step S1, the reaction temperature is 115-120℃ (reflux) and the time is 4.5-5.5h.

[0025] In step S1, the reaction further includes a purification step.

[0026] In step S1, the purification is further preferably performed by pulping.

[0027] In step S2, the oxidant is a tetravalent cerium salt.

[0028] In step S2, the tetravalent cerium salt is further selected from cerium ammonium nitrate or cerium ammonium sulfate.

[0029] In step S2, the molar ratio of 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid and the oxidant is 1:2-10.

[0030] Any point value or range between two points within the above range can achieve the technical effect of the present invention, including but not limited to 1:2, 1:2.5, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10.

[0031] In step S2, the molar ratio of 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid and the oxidant is further preferably 1:2.5.

[0032] In step S2, the reaction is carried out in the presence of a solvent.

[0033] In step S2, the solvent is further selected from at least one of water, acetone, isopropanol, ethanol, tetrahydrofuran, or acetonitrile.

[0034] In step S2, the solvent is more preferably water.

[0035] In step S2, the reaction is carried out in the presence of an acid.

[0036] In step S2, the acid is further selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, p-toluenesulfonic acid, or trifluoroacetic acid.

[0037] In step S2, the acid is more preferably sulfuric acid or phosphoric acid.

[0038] In step S2, the molar ratio of the acid to 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid is 1:1.0-2.0.

[0039] Any point value or the range between two points within the above range can achieve the technical effect of the present invention, including but not limited to 1:1.0, 1:1.25, 1:1.5, 1:1.75, and 1:2.0.

[0040] In step S2, the molar ratio of the acid to 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid is further preferably 1:1.25.

[0041] In step S2, the temperature of the oxidative deethylation reaction is 30-50℃ and the time is 10-14h.

[0042] Any point value or the range between two points within the above range can achieve the technical effect of the present invention, including but not limited to temperatures of 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, and 50℃; and times selected from 10h, 11h, 12h, 13h, and 14h.

[0043] In step S3, the eluent for column chromatography purification is methanol and dichloromethane in a volume ratio of 1:20.

[0044] The beneficial effects of this invention are as follows: This invention provides a method for preparing isosulfuron-derived deethylated impurity compounds. The starting materials are readily available, the synthetic route operates under mild conditions and is safe, and the yield and purity are good, meeting the requirements for the preparation of this impurity. This method is of great significance for the study of isosulfuron-derived impurities. It facilitates accurate property studies of isosulfuron-derived deethylated impurities and can be used as a reference standard in drug quality control. Attached Figure Description

[0045] Figure 1 The 1H NMR spectrum of the isothiocyanate deethylated impurity prepared in Example 1 of this invention; Figure 2 The carbon NMR spectrum of the isothiocyanate deethylated impurity prepared in Example 1 of this invention; Figure 3 This is the mass spectrum of the isothiocyanate deethylated impurity prepared in Example 1 of the present invention; Figure 4 The infrared absorption spectrum of the isothiocyanate deethylated impurity prepared in Example 1 of this invention. Detailed Implementation

[0046] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0047] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0048] Basic Example 1 Preparation of the isosulfur blue deethylated impurity intermediate 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid: In a 250 mL four-necked flask equipped with a thermometer and mechanical stirrer, sodium 2-formylbenzene-1,4-disulfonate (20 g, 64.5 mmol), N,N-diethylaniline (28.9 g, 193.5 mmol), urea (2.9 g, 48.4 mmol), and acetic acid (100 mL) were added. The mixture was stirred under reflux (118 °C) for 5 hours. Intermediate process analysis by HPLC (area percentage) showed that sodium 2-formylbenzene-1,4-disulfonate was less than 1.0%. The reaction solution was quenched with water (100 mL), filtered, and the solid was collected.

[0049] The solid was purified by pulping with water (200 mL), filtered, and the filter cake was washed twice with water (40 mL). It was then vacuum dried at 70 °C for 8 h to obtain the isosulfur blue deethylated impurity intermediate 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid with a purity of 99.1% and a yield of 88%.

[0050] The isosulfur blue deethylated impurity intermediate 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid was prepared and used in the following examples and comparative examples.

[0051] Example 1 A method for preparing isothiocyanate deethylated impurities: In a 500 mL four-necked flask equipped with a thermometer, mechanical stirrer, and constant-pressure dropping funnel, intermediates 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid (10.0 g, 18.3 mmol), cerium ammonium nitrate (25.1 g, 45.8 mmol), water (200 mL), and sulfuric acid (2.3 g, 22.9 mmol) were added. The mixture was reacted at 35 °C for 14 hours. HPLC (area percentage) analysis of the intermediate process showed that the starting material was less than 5.0% and the deethylated impurity was greater than 70%. The pH was adjusted to 7-10 with 20% sodium carbonate solution, and the mixture was filtered. The filtrate was concentrated under reduced pressure. 100 g of 200-300 mesh silica gel was added to the filter residue. The mixture was then purified using an eluent (methanol:dichloromethane = 1:20, volume ratio) to obtain 5.3 g of isosulfur blue deethylated impurity with a purity of 96.2% and a yield of 53%. Its 1H NMR spectrum, 1C NMR spectrum, mass spectrum, and infrared absorption spectrum are as follows: Figures 1-4 As shown.

[0052] Example 2 A method for preparing isothiocyanate deethylated impurities: In a 500 mL four-necked flask equipped with a thermometer, mechanical stirrer, and constant-pressure dropping funnel, intermediates 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid (10.0 g, 18.3 mmol), cerium ammonium nitrate (50.2 g, 91.5 mmol), water (200 mL), and sulfuric acid (2.3 g, 22.9 mmol) were added. The mixture was reacted at 35 °C for 12 hours. HPLC (area percentage) analysis of the intermediate process showed that the starting material was less than 5.0% and the deethylated impurity was greater than 70%. The pH was adjusted to 7-10 with 20% sodium carbonate solution, and the mixture was filtered. The filtrate was concentrated under reduced pressure. 100 g of 200-300 mesh silica gel was added to the filter residue. The mixture was then purified using an eluent (methanol:dichloromethane = 1:20, volume ratio) to obtain 5.1 g of isosulfur blue deethylated impurity with a purity of 95.4% and a yield of 51%.

[0053] Example 3 A method for preparing isothiocyanate deethylated impurities: In a 500 mL four-necked flask equipped with a thermometer, mechanical stirrer, and constant-pressure dropping funnel, intermediate 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid (10.0 g, 18.3 mmol), cerium ammonium sulfate (11.7 g, 45.8 mmol), water (200 mL), and sulfuric acid (2.3 g, 22.9 mmol) were added. The mixture was reacted at 45 °C for 14 hours. HPLC (area percentage) analysis of the intermediate process showed that the starting material was less than 5.0% and the deethylated impurities were greater than 65%. The pH was adjusted to 7-10 with 20% sodium carbonate solution, filtered, and the filtrate was concentrated under reduced pressure. 200 mL of [unspecified substance] was added to the filter residue. 100 g of 300-mesh silica gel was purified by separation using an eluent (methanol:dichloromethane = 1:20, volume ratio) to obtain 4.7 g of isosulfur blue deethylated impurity with a purity of 95.9% and a yield of 47%.

[0054] Example 4 A method for preparing isothiocyanate deethylated impurities: In a 500 mL four-necked flask equipped with a thermometer, mechanical stirrer, and constant-pressure dropping funnel, intermediates 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid (10.0 g, 18.3 mmol), cerium ammonium nitrate (25.1 g, 45.8 mmol), water (200 mL), and phosphoric acid (2.6 g, 85 wt%, 22.9 mmol) were added. The mixture was reacted at 35 °C for 12 hours. HPLC (area percentage) analysis of the intermediate process showed that the starting material was less than 5.0% and the deethylated impurities were greater than 65%. The pH was adjusted to 7-10 with 20% sodium carbonate solution, filtered, and the filtrate was concentrated under reduced pressure. 200 mL of [unspecified substance] was added to the filter residue. 100 g of 300-mesh silica gel was purified by separation using an eluent (methanol:dichloromethane = 1:20, volume ratio) to obtain 4.9 g of isosulfur blue deethylated impurity, with a purity of 95.6% and a yield of 49%.

[0055] Comparative Example 1 A method for preparing isothiocyanate deethylated impurities: In a 250 mL four-necked flask equipped with a thermometer and mechanical stirrer, sodium 2-formylbenzene-1,4-disulfonate (2 g, 6.4 mmol), N,N-diethylaniline (2.9 g, 19.3 mmol), urea (0.04 g, 0.6 mmol), and acetic acid (10 mL) were added. The mixture was stirred under reflux (118 °C) for 5 hours. HPLC (area percentage) analysis of the intermediate process showed that more than 20% of the sodium 2-formylbenzene-1,4-disulfonate remained, indicating incomplete reaction.

[0056] Comparative Example 2 A method for preparing isothiocyanate deethylated impurities: In a 100 mL three-necked flask equipped with a thermometer, mechanical stirrer, and constant-pressure dropping funnel, intermediates 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid (2.0 g, 3.7 mmol), cerium ammonium nitrate (3.0 g, 5.5 mmol), water (40 mL), and sulfuric acid (0.5 g, 4.6 mmol) were added. The mixture was reacted at 35 °C for 14 hours. HPLC (area percentage) analysis of the intermediate process showed that more than 20% of the raw material remained, and the deethylated impurities were less than 2%.

[0057] Comparative Example 3 A method for preparing isothiocyanate deethylated impurities: In a 100 mL three-necked flask equipped with a thermometer, mechanical stirrer, and constant-pressure dropping funnel, intermediates 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid (2.0 g, 3.7 mmol), cerium ammonium nitrate (5.0 g, 9.2 mmol), water (40 mL), and sulfuric acid (0.5 g, 4.6 mmol) were added. The mixture was reacted at 5 °C for 14 hours. HPLC (area percentage) analysis of the intermediate process showed that the starting material was less than 5.0% and the deethylated impurities were less than 1%.

[0058] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing an isosulfur blue deethylated impurity, characterized in that, Includes the following steps: S1: Sodium 2-formylbenzene-1,4-disulfonic acid, N,N-diethylaniline, acid and urea are mixed and reacted to give 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid; S2: 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid was oxidized and deethylated in the presence of an oxidant to give the crude product; S3: Column chromatography was used to purify the isothiocyanate deethylated impurity.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of sodium 2-formylbenzene-1,4-disulfonate and N,N-diethylaniline is 1:2.5-3.

5.

3. The preparation method according to claim 1, characterized in that, In step S1, the acid is selected from at least one of acetic acid, sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, p-toluenesulfonic acid, or trifluoroacetic acid.

4. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of sodium 2-formylbenzene-1,4-disulfonate and urea is 1:0.5-1.

5.

5. The preparation method according to claim 1, characterized in that, In step S1, the reaction temperature is 115-120℃ and the time is 4.5-5.5h.

6. The preparation method according to claim 1, characterized in that, In step S2, the oxidant is a tetravalent cerium salt; the tetravalent cerium salt is selected from cerium ammonium nitrate or cerium ammonium sulfate.

7. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid and the oxidant is 1:2-10.

8. The preparation method according to claim 1, characterized in that, In step S2, the reaction is carried out in the presence of a solvent; the solvent is selected from at least one of water, acetone, isopropanol, ethanol, tetrahydrofuran, or acetonitrile; the reaction is carried out in the presence of an acid; the acid is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, methanesulfonic acid, p-toluenesulfonic acid, or trifluoroacetic acid; the molar ratio of the acid to 2-(bis(4-(diethylamino)phenyl)methyl)benzene-1,4-disulfonic acid is 1:1.0-2.

0.

9. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the oxidative deethylation reaction is 30-50℃ and the time is 10-14h.

10. The preparation method according to claim 1, characterized in that, In step S3, the eluent for column chromatography purification is methanol and dichloromethane in a volume ratio of 1:20.

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