| CPC C07F 5/025 (2013.01) | 15 Claims |
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1. A compound of formula (I), or a pharmaceutically acceptable salt thereof:
![]() wherein
R1 is —H or —C(O)CH(R1a)NHR1b; and
R1a is selected from —H, —(C1-C6) alkyl and CH2OR1c;
R1b is —H; or alternatively, R1a and R1b, together with the atom to which they are attached, form a 5-membered heterocyclic ring; and
R1c is H or —CH3.
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