A compound of Formula I: ** Formula ** or a pharmaceutically acceptable salt or solvate thereof, wherein: G is R1 or a hydroxyl PG protecting group； R1 is hydrogen, alkyl, alkenyl, alkynyl, (cycloalkyl) alkyl, (heterocycle) alkyl, arylalkyl, or heteroarylalkyl, wherein its cycloalkyl, heterocycle, aryl and heteroaryl moieties are optionally substituted with 1, 2, or 3 substituents, each one independently selected from the group consisting of hydroxy, halo, haloalkyl, amino, alkylamino, dialkylamino, carboxy, and alkoxycarbonyl； R2 is (a) hydrogen, cyano, carboxy, alkoxycarbonyl, or carboxamido； or (b) alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocycle, aryl, heteroaryl, (cycloalkyl) alkyl, (cycloalkenyl) alkyl, (heterocycle) alkyl, arylalkyl, heteroarylalkyl, (arylalkoxy) carbonyl, or (heteroarylalkyl) carbonyl, any of which is optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, haloalkyl, amino, alkylamino, dialkylamino, carboxy, and alkoxycarbonyl； R3 and R4 are each independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocycle, aryl, heteroaryl, (cycloalkyl) alkyl, (cycloalkenyl) alkyl, (heterocycle) alkyl, arylalkyl, and heteroarylalkyl , wherein any of which, when different from hydrogen, is optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, haloalkyl, amino, alkylamino, dialkylamino, carboxy, and alkoxycarbonyl； R5 is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocycle, aryl, heteroaryl, (cycloalkyl) alkyl, (cycloalkenyl) alkyl, (heterocycle) alkyl, arylalkyl and heteroarylalkyl, wherein any of which, when different from hydrogen, is optionally substituted with 1, 2, or 3 substituents, each independently selected from the group consisting of hydroxy, halo, haloalkyl, amino, alkylamino
