CD73 inhibitors and pharmaceutical uses thereof

A compound of Formula I, or a pharmaceutically acceptable ester or salt thereof:

• where:
• W is oxygen, sulfur, nitrogen, or a methylene group;
• X is a moiety selected from phosphonyl (—P(═O)(OR)—), sulfonyl (—S(═O)2—), and carbonyl (—C(═O)—), where R is a hydrogen, an ester-forming group, or a protecting group;
• or X and W together form —(CR7R8)n, where n is an integer from 0 to 3, and R7 and R8 are independently selected from a hydrogen, a halogen, a hydroxyl group, and a lower alkyl group having 1 to 4 carbon atoms;
• Y is selected from phosphonate (—PO3R2), sulfonate (—SO3R), and carboxylate (—CO2R), where R is a hydrogen, an ester-forming group, or a protecting group;
• R1 is a hydroxyl group or a hydrogen;
• R2 is a chlorine or a hydrogen;
• and
• R3 and R4 are independently selected from a hydrogen, an alkyl group, an alkenyl group and an alkynyl group, where at least one of R3 and R4 has 1 to 30 carbon atoms, wherein at least one of R3 and R4 has 11 to 30 carbon atoms when W is O or S;
• or
• R3 and R4 are independently selected from a hydrogen and a ring system which is a monocycle, bicycle, tricycle, spiral-ring, fused-ring, or bridged-ring containing carbocyclic or heterocyclic ring system, the carbocyclic ring system being aromatic or non-aromatic, provided that R3 and R4 are not both hydrogen, and provided that the ring system is not a monocycle when W is O or S;
• or
• R3, R4, and the nitrogen atom to which they are attached form a heterocyclic system which is independently selected from a monocycle, a bicycle, a tricycle, a spiral-ring, a fused-ring, and a bridged-ring system.