Reverse RNA Phosphoramidites for 5' to 3' Synthesis
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Solution Overview
Problem
The chemical synthesis of RNA molecules with 3′-end modifications, particularly those requiring lipophilic or chromophore ligands, faces challenges such as low coupling efficiency and purity issues due to the limitations of conventional 3′→5′ synthesis methodologies.
Innovation Solution
Development of reverse RNA monomer phosphoramidites for 5′→3′ direction synthesis, which allows for efficient and clean oligo synthesis with higher coupling efficiency and purity, enabling modifications at the 3′-end and reducing impurities like N+1 species that affect HPLC and gel purification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional 3'→5' synthesis methodology is used for RNA synthesis with 3'-end modifications, then synthesis can be performed, but coupling efficiency is low and purity is reduced
Solution Approach 1:
The patent applies reverse synthesis methodology by synthesizing RNA in the 5'→3' direction instead of the conventional 3'→5' direction. This inversion of the synthesis direction allows the 3'-end to be synthesized last, providing a free 3'-OH group that can be efficiently modified with lipophilic or chromophore ligands without the impurity issues associated with conventional methods. The reverse phosphoramidite chemistry enables higher coupling efficiency and purity simultaneously.
2Ease of manufacture
If conventional 3'→5' synthesis is used, then RNA can be synthesized, but N+1 species impurities are generated that broaden peaks during HPLC and gel purification
Solution Approach 1:
By inverting the synthesis direction to 5'→3', the patent eliminates the formation of N+1 species impurities that occur in conventional 3'→5' synthesis. The reverse phosphoramidite chemistry ensures that each coupling step adds only one nucleotide unit, preventing the formation of over-coupled impurities that would otherwise require additional purification steps and broaden peaks during HPLC and gel purification.
3Adaptability or versatility
If 3'-end modified RNA is synthesized using conventional methods, then modifications can be introduced, but additional purifications are generally required
Solution Approach 1:
The patent performs preliminary action by synthesizing the RNA backbone in the 5'→3' direction with a free 3'-OH group already in place before introducing the 3'-end modification. This preliminary synthesis approach allows direct coupling of lipophilic or chromophore ligands to the 3'-end without requiring additional purification steps, as the reverse synthesis methodology inherently produces cleaner products with fewer impurities.
Data Source
AI summary
The present invention provides building blocks and methods for synthesizing very pure RNA in a form that can efficiently be modified at the 3′ end. Reverse RNA monomer phosphoramidites have been developed for RNA synthesis in 5′→3′ direction, leading to very clean oligo synthesis that allows for the introduction of various modifications at the 3′-end cleanly and efficiently. Higher coupling efficiency per step have been observed during automated oligo synthesis with the reverse RNA amidites disclosed herein, resulting in a greater ability to achieve higher purity and produce very long oligonucleotides. The use of the reverse RNA phosphoramidites in the synthetic process of this invention leads to oligonucleotides free of N+1 species.