| CPC C07F 9/6533 (2013.01) [C07F 9/6512 (2013.01); C07F 9/65583 (2013.01); C07F 9/65616 (2013.01); C12N 15/113 (2013.01); C12N 2310/11 (2013.01); C12N 2310/314 (2013.01); C12N 2310/3233 (2013.01); C12N 2310/51 (2013.01)] | 2 Claims | 
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               1. A compound of Formula (X): 
              ![]() or a pharmaceutically acceptable salt thereof, wherein 
                R1 is a support-medium, and 
                R2 is, independently at each occurrence, selected from the group consisting of: 
              ![]()  and 
                wherein R2 is at each position from 1 to 25 and 5′ to 3′: 
              
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