Tadalafil Cis-Intermediate Synthesis via Sulfolane Solvent
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Solution Overview
Problem
Existing methods for preparing the cis-intermediate compound of Formula II for Tadalafil are inefficient due to low yield, lengthy reaction times, and the use of hazardous reagents like trifluoroacetic acid, as well as the need for cumbersome synthetic steps and solvent handling challenges.
Innovation Solution
A process involving the reaction of D-tryptophan compound with a compound in the presence of sulfolane at elevated temperatures, allowing direct isolation of the cis-intermediate while the trans-isomer remains in solution, eliminating the need for hazardous chemicals and reducing the number of synthetic steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the Pictet-Spengler reaction is carried out using conventional methods (Path I or Path II), then the cis-intermediate of Formula II can be prepared, but the reaction involves hazardous reagents like trifluoroacetic acid, requires longer reaction times, and gives poor yield that needs separation from trans-intermediate
Solution Approach 1:
The patent changes the reaction parameters by using a different solvent system (ethyl acetate instead of conventional solvents) and optimizing temperature and time parameters to achieve high selectivity for the cis-intermediate without hazardous reagents
Solution Approach 2:
The patent replaces hazardous reagents like trifluoroacetic acid with safer, more environmentally friendly reagents and solvents that are easier to handle and dispose of, while maintaining or improving reaction efficiency
2Productivity
If Path II is used to prepare the cis-intermediate of Formula II, then the yield is improved, but the process becomes cumbersome involving four synthetic steps
Solution Approach 1:
The patent combines multiple synthetic steps into a single streamlined process by using a direct Pictet-Spengler reaction that selectively produces the cis-intermediate in one step, eliminating the need for separate purification and conversion steps required in Path II
3Productivity
If isopropanol is used as solvent in the Pictet-Spengler reaction, then the reaction can be carried out, but temperature control is difficult due to low boiling point and flash point, and peroxide contamination may cause side reactions
Solution Approach 1:
The patent replaces isopropanol with ethyl acetate as the solvent, which has a higher boiling point and flash point, making it safer and easier to handle during the reaction process without requiring stringent temperature control measures
Solution Approach 2:
The patent changes the solvent parameter from isopropanol to ethyl acetate, which fundamentally alters the safety and handling characteristics of the reaction system while maintaining its effectiveness as a reaction medium
4Manufacturing precision
If conventional workup procedures are used after the Pictet-Spengler reaction, then the product can be isolated, but additional acid-base treatment is required which complicates the process
Solution Approach 1:
The patent extracts or removes the need for complex acid-base treatment steps from the workup procedure by designing a reaction system that produces minimal byproducts and allows for simplified isolation of the cis-intermediate through standard filtration and concentration techniques
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
This process achieves high yield and purity of the cis-intermediate with ease of scale-up, eliminating the need for hazardous reagents and simplifying the separation of isomers, making it industrially viable.
Implementation Method 1
reacting a D-tryptophan compound of Formula III or a pharmaceutically acceptable salt thereof, with a compound of Formula IV, in the presence of sulfolane
Implementation Method 2
The reaction mixture is heated to about 50-100°C. (e.g., about 70-90°C.), stirred for 10-18 hours
Implementation Method 3
The reaction mixture is heated to about 50-100°C. (e.g., about 70-90°C.), stirred for 10-18 hours and then cooled to about 20-40°C. whereby the cis-intermediate of Formula II starts separating from the reaction mass as a solid
Data Source
AI summary
The present invention relates to a process for the preparation of cis-intermediate of Formula II,which is useful synthetic intermediates in the preparation of tadalafil.