A compound of Formula ( 1-A): or a pharmaceutically acceptable salt thereof, wherein: R 3 is alkyl, alkenyl, carbocyclyl, heterocyclyl, aryl, or heteroaryl; each of R X and R Y is independently hydrogen, aryl, or alkyl, or R X and R Y are joined together to form a 3-10 membered heterocyclic ring; R 19 is hydrogen or alkyl; R 5 is absent or hydrogen; and represents a single or double bond, wherein when one is a double bond, the other is a single bond and R 5 is absent; a is 0; wherein 'alkyl' refers to an optionally substituted radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 20 carbon atoms; 'alkenyl' refers to an optionally substituted radical of a straight-chain or branched hydrocarbon group having from 2 to 20 carbon atoms, one or more carbon-carbon double bonds, and no triple bonds; 'carbocyclyl' refers to an optionally substituted radical of a non-aromatic cyclic hydrocarbon group having from 3 to 10 ring carbon atoms and zero heteroatoms in the non-aromatic ring system; 'heterocyclyl' refers to an optionally substituted radical of a 3- to 10-membered non-aromatic ring system having ring carbon atoms and 1 to 4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, sulfur, boron, phosphorus, and silicon; 'aryl' refers to a radical of an optionally substituted monocyclic or polycyclic 4n+2 aromatic ring system having 6-14 ring carbon atoms and zero heteroatoms provided in the aromatic ring system; and 'heteroaryl' refers to an optionally substituted radical of a 5-10 membered monocyclic or bicyclic 4n+2 aromatic ring system having ring carbon atoms and 1-4 ring heteroatoms provided in the aromatic ring system, wherein each heteroatom is independently selected from nitrogen, oxygen and sulfur. or a pharmaceutically acceptable salt thereof, wherein: R 3 is alkyl, alkenyl, carbocyclyl, heterocyclyl, aryl, or heteroaryl; each of R X and R Y is independently hydrogen, aryl, or alkyl, or R 3 is alkyl, alkenyl, carbocyclyl, heterocyclyl, aryl, or heteroaryl; each of R X and R Y is independently hydrogen, aryl, or alkyl, or R X and R Y are joined together to form a 3-10 membered heterocyclic ring; R 19 is hydrogen or alkyl; R 5 is absent or hydrogen; and represents a single or double bond, wherein when one is a double bond, the other is a single bond and R 5 is absent; a is 0; wherein 'alkyl' refers to an optionally substituted radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 20 carbon atoms; 'alkenyl' refers to an optionally substituted radical of a straight-chain or branched hydrocarbon group having from 2 to 20 carbon atoms, one or more carbon-carbon double bonds, and no triple bonds; 'carbocyclyl' refers to an optionally substituted radical of a non-aromatic cyclic hydrocarbon group having from 3 to 10 ring carbon atoms and zero heteroatoms in the non-aromatic ring system; 'heterocyclyl' refers to an optionally substituted radical of a 3- to 10-membered non-aromatic ring system having ring carbon atoms and 1 to 4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, sulfur, boron, phosphorus, and silicon; 'aryl' refers to a radical of an optionally substituted monocyclic or polycyclic 4n+2 aromatic ring system having 6-14 ring carbon atoms and zero heteroatoms provided in the aromatic ring system; and 'heteroaryl' refers to an optionally substituted radical of a 5-10 membered monocyclic or bicyclic 4n+2 aromatic ring system having ring carbon atoms and 1-4 ring heteroatoms provided in the aromatic ring system, wherein each heteroatom is independently selected from nitrogen, oxygen and sulfur. R 19 is hydrogen or alkyl; R 5 is absent or hydrogen; and represents a single or double bond, wherein when one is a double bond, the other is a single bond and R 5 is absent; a is 0; wherein 'alkyl' refers to an optionally substituted radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 20 carbon atoms; 'alkenyl' refers to an optionally substituted radical of a straight-chain or branched hydrocarbon group having from 2 to 20 carbon atoms, one or more carbon-carbon double bonds, and no triple bonds; 'carbocyclyl' refers to an optionally substituted radical of a non-aromatic cyclic hydrocarbon group having from 3 to 10 ring carbon atoms and zero heteroatoms in the non-aromatic ring system; 'heterocyclyl' refers to an optionally substituted radical of a 3- to 10-membered non-aromatic ring system having ring carbon atoms and 1 to 4 ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, sulfur, boron, phosphorus, and silicon; 'aryl' refers to a radical of an optionally substituted monocyclic or polycyclic 4n+2 aromatic ring system having 6-14 ring carbon atoms and zero heteroatoms provided in the aromatic ring system; and 'heteroaryl' refers to an optionally substituted radical of a 5-10 membered monocyclic or bicyclic 4n+2 aromatic ring system having ring carbon atoms and 1-4 ring heteroatoms provided in the aromatic ring system, wherein each heteroatom is independently selected from nitrogen, oxygen and sulfur.