Methylthioninium Chloride Purification via Zwitterionic Intermediate Segmentation
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Solution Overview
Problem
Current methods for synthesizing Methylthioninium Chloride (MTC) result in products with high levels of metal and organic impurities, exceeding safety limits set by European health agencies, necessitating the development of methods for producing high-purity diaminophenothiazinium compounds.
Innovation Solution
A method involving oxidative coupling, isolation and purification of a zwitterionic intermediate, reduction of chromium(VI) to chromium(III), and additional treatment steps such as sulphide treatment, dimethyldithiocarbamate treatment, and organic extraction to achieve high purity, specifically including recrystallization and chloride salt formation, effectively reducing impurity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional synthesis methods are used to produce MTC, then production cost and simplicity are maintained, but the product contains high levels of metal and organic impurities exceeding safety limits
Solution Approach 1:
The synthesis process is divided into distinct segments: initial oxidative coupling to form the zwitterionic intermediate, isolation and purification of this intermediate, then ring closure to form final MTC. This segmentation allows impurities to be removed at the intermediate stage before final product formation, achieving high purity without requiring complex post-synthesis purification equipment
Solution Approach 2:
The zwitterionic intermediate is isolated and purified before the ring closure step that forms the final MTC product. This preliminary purification action removes metal and organic impurities at an early stage, preventing them from carrying through to the final product and eliminating the need for complex downstream purification equipment
2Manufacturing precision
If multiple purification steps are added to reduce impurity levels, then product purity improves, but manufacturing time and process complexity increase
Solution Approach 1:
Purification of the zwitterionic intermediate is performed preliminarily, before ring closure to form final MTC. This timing allows impurities to be removed when they are most accessible, achieving high purity in fewer steps and avoiding time-consuming repeated purification of the final product
Solution Approach 2:
The zwitterionic intermediate is extracted and isolated from the reaction mixture using standard extraction techniques. This extraction step efficiently removes the intermediate along with associated impurities in one operation, maintaining productivity while achieving purification
3Productivity
If chromium(VI) is used as oxidizing agent, then oxidative coupling reaction proceeds efficiently, but toxic chromium(VI) residues contaminate the product
Solution Approach 1:
Chromium(VI) is reduced to chromium(III) using sodium bisulfite or similar reducing agents. Chromium(III) is significantly less toxic and can be more easily removed from the product. This conversion transforms the harmful chromium(VI) residues into beneficial or manageable chromium(III) species that do not compromise product safety
Solution Approach 2:
Sodium bisulfite or similar reducing agents are introduced as intermediary substances to mediate the conversion of chromium(VI) to chromium(III). These intermediaries selectively reduce the toxic chromium species without affecting the desired MTC product, allowing efficient chromium removal while maintaining productivity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method yields MTC with extremely low levels of impurities, meeting and exceeding safety standards, resulting in the purest available pharmaceutical-grade MTC worldwide, suitable for medical treatments including Alzheimer's disease and pathogen inactivation.
Implementation Method 1
oxidative coupling of a thiosulfonate of a diamino benzene derivative with a further equivalent of a substituted aniline
Implementation Method 2
reduction of chromium(VI) to chromium(III)
Implementation Method 3
recrystallization and chloride salt formation, effectively reducing impurity levels
Implementation Method 4
additional treatment steps such as sulphide treatment, dimethyldithiocarbamate treatment, and organic extraction to achieve high purity
Data Source
AI summary
This invention pertains generally to the field of chemical synthesis and purification, and more specifically to methods of synthesizing and purifying certain 3,7 diamino-phenothiazin-5-ium compounds (referred to herein as “diaminophenothiazinium compounds”) including Methylthioninium Chloride (MTC) (also known as Methylene Blue). In one embodiment, the method comprises the steps of, in order: nitrosylation (NOS); nitrosyl reduction (NR); thiosulfonic acid formation (TSAF); oxidative coupling (OC); Cr(VI) reduction (CR); isolation and purification of zwitterionic intermediate (IAPOZI); ring closure (RC); chloride salt formation (CSF); one of: sulphide treatment (ST); dimethyldithiocarbamate treatment (DT); carbonate treatment (CT); ethylenediaminetetraacetic acid treatment (EDTAT); organic extraction (OE); and recrystallisation (RX). The present invention also pertains to the resulting (high purity) compounds, compositions comprising them (e.g., tablets, capsules), and their use in methods of inactivating pathogens, and methods of medical treatment and diagnosis, etc., for example, for tauopathies, Alzheimer's disease (AD), skin cancer, melanoma, viral diseases, bacterial diseases, or protozoal diseases. Wherein: each of R1 and R9 is independently selected from: —H; C1-4 alkenyl; and halogenated C1-4alkyl; each of R3NA and R3NB is independently selected from: C1-4 alkyl; C2-4alkenyl; and halogenated C4-1 alkyl; each of R7NA and R7NB is independently selected from: C1-4 alkyl; C2-4alkenyl; and halogenated C1-4 alkyl; and X is one or more anionic counter ions to achieve electrical neutrality.