Bicyclic pyridine derivative

A compound represented by formula I

• or a pharmaceutically acceptable salt thereof,
• wherein
• X is an oxygen atom or a sulfur atom,
• n is 0,
• R1 is a hydrogen atom, optionally substituted C1-6 alkyl, or optionally substituted C3-6 alkenyl,
• R2a and R2b are each independently a hydrogen atom, a halogen atom, optionally substituted C1-6 alkyl, or optionally substituted C6-10 aryl, or R2a and R2b, together with a carbon atom to which they are attached, form a 3- to 6-membered saturated carbocyclic ring,
• R3a, R3b, and R3c are each independently a hydrogen atom, optionally substituted C1-6 alkyl, a halogen atom, —OR4, or optionally substituted C6-10 aryl,
• R4 is optionally substituted C1-6 alkyl or optionally substituted 3- to 6-membered saturated carbocyclic ring, and
• R5a and R5b are each independently a hydrogen atom or optionally substituted C1-6 alkyl, or R5a and R5b, together with a carbon atom to which they are attached, form a 3- to 6-membered saturated carbocyclic ring,
• wherein,
• the optionally substituted C1-6 alkyl and optionally substituted C3-6 alkenyl are optionally substituted with a halogen atom, hydroxy, or C1-6 alkoxy, and
• the optionally substituted C6-10 aryl and optionally substituted 3- to 6-membered saturated carbocyclic ring are optionally substituted with a halogen atom, hydroxy, C1-6 alkyl, or C1-6 alkoxy,
• provided that the following (1) to (19) are is excluded:
• (1) a compound wherein n is 0, X is an oxygen atom, and R2a and R2b are hydrogen atoms.