| CPC C07F 9/65517 (2013.01) [A61K 9/0019 (2013.01); A61K 9/0053 (2013.01); A61K 31/665 (2013.01); C07D 317/48 (2013.01)] | 8 Claims |

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1. A compound of Formula (III):
![]() or a pharmaceutically acceptable salt thereof, wherein:
X is independently selected from the group consisting of:
(a) —C(O)OCH(R4)OP(O)OR11(OR12),
(b) —CH2OC(O)R3, and
(c) —C(O)(CH2)nZaR5;
wherein:
n is 3 or 4;
R1 and R2 are each independently —C1-6alkyl or —C3-6cycloalkyl;
R3 is selected from the group consisting of: —C1-6alkyl, C3-6cycloalkyl, —C1-6haloalkyl, aryl, and heteroaryl;
R4 is H, —C1-6alkyl or C3-6cycloalkyl;
R5 is selected from the group consisting of: —C(O)R3, —C(O)OR3, —P(O)OR11(OR12), an amino acid, and a peptide;
Za is O or NR4;
R11 and R12 are each independently H, —C1-6alkyl, —C1-6heteroalkyl, —C3-6cycloalkyl, —C1-6haloalkyl, aryl or heteroaryl, wherein —C1-6alkyl, —C1-6heteroalkyl, —C3-6cycloalkyl, —C1-6haloalkyl, aryl or heteroaryl is unsubstituted or substituted with one or more —C1-6alkyl, —C1-6heteroalkyl, —C3-6cycloalkyl, —C1-6haloalkyl, aryl or heteroaryl.
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