| CPC C07H 21/02 (2013.01) | 15 Claims |
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1. A compound of formula (I):
![]() or a stereoisomer thereof, or a pharmaceutically acceptable salt thereof,
wherein:
R is selected from halogen, —C1-8alkyl, or —ORa, wherein Ra is hydrogen or —C1-8alkyl;
R1 and R2 are F;
X1 and X2, which are the same or different, are each independently O or S; and
Base1 and Base2, which are the same or different, are each independently
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