Fluorescein Purification Process Using Segmentation and Intermediary Steps
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Solution Overview
Problem
Current methods for preparing fluorescein for pharmaceutical use face challenges in achieving high purity, low sodium chloride content, and minimizing the use of non-aqueous solvents like pyridine, while also requiring effective methods for identifying and quantifying low levels of impurities.
Innovation Solution
A process involving the conversion of commercial-grade fluorescein to O,O'-diacetylfluorescein using acetic anhydride, followed by hydrolysis with sodium hydroxide, treatment with charcoal to reduce color, and pH adjustment with hydrochloric acid to form a precipitate, which is then washed and filtered to achieve high purity, along with the use of HPLC and HPLC/MS methods for impurity quantification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional purification methods are used, then fluorescein can be prepared, but the purity is insufficient and impurities remain
Solution Approach 1:
The purification process is divided into multiple sequential steps: (1) conversion to diacetylfluorescein intermediate, (2) hydrolysis to release fluorescein, (3) charcoal treatment to adsorb impurities, and (4) pH adjustment for precipitation. This segmentation allows each step to target specific impurity types, achieving cumulative purification效果 that single-step methods cannot accomplish.
Solution Approach 2:
Diacetylfluorescein serves as a purification intermediary - the commercial grade fluorescein is converted to this less polar intermediate form, which can be more effectively purified through the subsequent hydrolysis and charcoal treatment steps, then converted back to fluorescein. This intermediary step enables separation of fluorescein from co-eluting impurities.
2Manufacturing precision
If pyridine is used as solvent, then purification can be achieved, but toxic non-aqueous solvents are introduced
Solution Approach 1:
The process changes the chemical parameters of the reaction medium by using aqueous acetic anhydride instead of pyridine. This parameter change maintains the ability to form the diacetylfluorescein intermediate while eliminating the toxic non-aqueous solvent, making the process suitable for pharmaceutical applications.
Solution Approach 2:
The invention replaces expensive and toxic pyridine with inexpensive, non-toxic aqueous acetic anhydride. The acetic anhydride serves its purpose in the reaction and can be easily removed, leaving no harmful residues in the final product.
3Manufacturing precision
If extensive purification steps are used, then purity increases, but production time and complexity increase
Solution Approach 1:
Multiple purification functions are merged into a single charcoal treatment step. The activated charcoal simultaneously adsorbs colored impurities, removes residual acetic anhydride, and eliminates other organic contaminants, replacing what would otherwise require multiple separate purification operations.
Solution Approach 2:
The process utilizes phase transition of fluorescein through pH-controlled precipitation. By adjusting pH to acidic conditions after hydrolysis, fluorescein precipitates from solution in high purity form, enabling easy separation from the aqueous phase containing water-soluble impurities.
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 process results in fluorescein that is substantially pure, low in color, and low in sodium chloride content, with significantly reduced related-substance impurities, improving yield and eliminating the need for pyridine, and providing a reliable method for determining purity.
Implementation Method 1
converting commercial grade fluorescein to O,O'-diacetylfluorescein using acetic anhydride as both solvent and reagent
Implementation Method 2
hydrolyzing diacetylfluorescein prepared from the commercial grade fluorescein, with sodium hydroxide in water to form fluorescein
Implementation Method 3
adding charcoal effective in reducing color number to the fluorescein in solution to form a fluorescein/charcoal mixture
Implementation Method 4
adjusting the pH to a level of from 1.0 to 2.5 using a hydrochloric acid solution with cooling during a period of from 2 to 4 hours to form a precipitate
Data Source
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AI summary
The present invention is directed to an improved process for producing substantially pure fluorescein, as well as to substantially pure fluorescein compositions prepared by the process. The invention is particularly directed to the provision of pharmaceutical compositions for use in angiography. The substantially pure fluorescein produced by the process of the present invention is low in color, low in sodium chloride content, and substantially free of pyridine.