Diastereomer-Enriched PCTA Gadolinium Complexes for Stability
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Solution Overview
Problem
Existing gadolinium-based contrast agents for medical imaging face challenges such as undesired lanthanide release, stability issues, and cerebral deposition, particularly with PCTA-based chelating ligands having lower thermodynamic stability and producing mixtures of stereoisomers with varying physicochemical properties.
Innovation Solution
A novel process for synthesizing a gadolinium complex with a diastereoisomerically enriched PCTA-based chelating ligand, involving isomeric enrichment of an intermediate hexaacid complex to predominantly produce the most stable diastereoisomers II-RRR and II-SSS, enhancing thermodynamic and kinetic stability while maintaining high relaxivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PCTA-based chelating ligands are used for gadolinium complex synthesis, then the relaxivity is improved (superior to other GBCAs with r1 up to 11-12 mM−1·s−1), but the thermodynamic stability is worsened (lower thermodynamic constant compared to other cyclene-based macrocycles)
Solution Approach 1:
The patent applies parameter changes by modifying the stereochemical configuration of the PCTA-based chelating ligand. Specifically, it uses diastereoisomerically enriched PCTA ligands with controlled (R) or (S) configurations at specific chiral centers, which changes the spatial arrangement and electronic properties of the complex, thereby improving thermodynamic stability while preserving the high relaxivity characteristic of PCTA-based agents.
2Ease of manufacture
If conventional synthesis methods for PCTA-based gadolinium complexes are used, then the synthesis is relatively easy, but the product is a mixture of stereoisomers with varying physicochemical properties, leading to inconsistent stability and relaxivity
Solution Approach 1:
The patent applies preliminary action by using diastereoisomerically enriched PCTA ligands before the gadolinium complexation step. The ligands are pre-synthesized with controlled stereochemistry (enriched in either (R) or (S) configurations), ensuring that the final gadolinium complex inherits this stereochemical purity. This preliminary control of stereoisomer composition simplifies the overall synthesis while guaranteeing consistent physicochemical properties.
3Productivity
If gadolinium-based contrast agents are administered repeatedly for diagnostic examinations or therapeutic monitoring, then the diagnostic and therapeutic efficacy is improved, but the risk of undesired lanthanide release and cerebral deposition increases
Solution Approach 1:
The patent applies beforehand cushioning by designing gadolinium complexes with enhanced thermodynamic stability through diastereoisomerically enriched PCTA ligands. This increased stability acts as a protective buffer that prevents gadolinium release even under repeated administration conditions, thereby cushioning against the harmful effects of NSF and cerebral deposition while maintaining the ability to administer the contrast agent multiple times for diagnostic and therapeutic purposes.
Data Source
AI summary
The present invention relates to a complex of formula (II) constituted of at least 80% of a diastereoisomeric excess comprising a mixture of isomers II-RRR and II-SSS of formulae:The present invention also relates to a process for preparing said complex of formula (II), and also to two synthetic intermediates.