| CPC C07D 311/80 (2013.01) [C07D 221/06 (2013.01); C07D 335/04 (2013.01); A61P 3/00 (2018.01)] | 7 Claims | 
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               1. A compound of formula (1): 
              ![]() or a pharmaceutically acceptable salt or solvate thereof, 
                wherein: 
                Y, X1 and X2 are —O; 
                R1, R2, R3, R4, R5, and R6 are H; and 
                Z1 and Z2, independently, are NHR8; wherein 
              R8 is selected from methyl and propyl. 
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