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CLAIMS
[Claim 1]
A compound represented by Formula (I) or a salt thereof: [Chemical Formula 11]

wherein, X is O or S;
a dotted line is a single bond or a double bond;
R1 is lower alkyl which optionally has one to four substituents selected from the Group G1, cycloalkyl which optionally has one to five substituents selected from the Group G2, or -lower alkylene-(cycloalkyl which optionally has one to five substituents selected from the Group G2);
R2 and R5 are the same or different from each other, and are H, lower alkyl or cycloalkyl;
R3 is -lower alkylene-X3-lower alkyl, -lower alkylene-X3-lower alkylene-(cycloalkyl which optionally has one to five substituents selected from the Group G2), -lower alkylene-(cycloalkyl which optionally has one to five substituents selected from the Group G2), or -lower alkylene-X3-(cycloalkyl which optionally has one to five substituents selected from the Group G2);
X3 is O or S(O)n, wherein n is 0, 1, or 2;

R4 is OH, NH2, or -O-lower alkyl and R6 is H; or R4 and R6 are linked to each other to form, together with -C(=O)-C-O- to which they are attached, 2,2-di(lower alkyl)-4-oxo-1,3-dioxolane-5,5-diyl;
the Group G1 consists of halogen, OH, -O-lower alkyl, -S-lower alkyl, and -O-(lower halogenoalkyl); and
the Group G2 consists of lower alkyl, halogen, lower halogenoalkyl, OH, -O-lower alkyl, -S-lower alkyl, and -O-lower halogenoalkyl. [Claim 2]
The compound or a salt thereof according to claim 1, wherein R4 is OH, NH2, or -O-lower alkyl and R6 is H. [Claim 3]
The compound or a salt thereof according to claim 2, wherein X is O, and a dotted line is a single bond or a double bond; or X is S, and a dotted line is a double bond. [Claim 4]
The compound or a salt thereof according to claim 3, wherein:
R1 is lower alkyl which optionally has one to four substituents selected from the group consisting of halogen, OH, and -O-lower alkyl; cycloalkyl which is optionally substituted by one to two lower alkyls; or -lower alkylene-(cycloalkyl which is optionally substituted by one to two lower alkyls);
R3 is -lower alkylene-X3-lower alkyl, -lower alkylene-X3-lower alkylene-(cycloalkyl which is optionally substituted by one to two lower alkyls), -lower alkylene-(cycloalkyl which is optionally substituted by one to two lower alkyls), or -lower alkylene-X3-(cycloalkyl which is optionally substituted by one to two lower alkyls); and
R2 and R5 are the same or different from each other, and are H or lower alkyl. [Claim 5]

The compound or a salt thereof according to claim 4, wherein:
R1 is lower alkyl which optionally has one to four substituents selected from the group consisting of halogen and OH; cycloalkyl; or -lower alkylene-cycloalkyl; and
R3 is -lower alkylene-S(O)n-lower alkyl, -lower alkylene-O-lower alkylene-cycloalkyl, -lower alkylene-S-lower alkylene-cycloalkyl, -lower alkylene-cycloalkyl, or -lower alkylene-S-cycloalkyl. [Claim 6]
The compound or a salt thereof according to claim 5, wherein R1 is lower alkyl, cycloalkyl, or -lower alkylene-cycloalkyl; R3 is -lower alkylene-S-lower alkyl, -lower alkylene-O-lower alkylene-cycloalkyl, -lower alkylene-S-lower alkylene-cycloalkyl, -lower alkylene-cycloalkyl, or -lower alkylene-S-cycloalkyl; R2 is H or lower alkyl; R5 is H; and R4 is OH. [Claim 7]
The compound or a salt thereof according to claim 6, wherein X is O, and a dotted line is a double bond; R1 is lower alkyl, or -lower alkylene-cycloalkyl; and R3 is -lower alkylene-S-lower alkyl, or -lower alkylene-cycloalkyl. [Claim 8]
The compound or a salt thereof according to claim 2, wherein X is O, and a dotted line is a double bond. [Claim 9]
The compound or a salt thereof according to claim 1, which is a compound selected from the group consisting of the following compounds, or a salt thereof: (2R,3R)-3-amino-2-{[2-(2-cyclopropylethyl)furo[3,2-c]pyridin-4-yl]methyl}-4-(ethylsulfanyl)-2-hydroxybutanoic acid, (2R,3S)-3-amino-5-cyclopropyl-2-{[2-(2-cyclopropylethyl)furo[3,2-c]pyridin-4-yl]methyl}-2-hydroxypentanoic acid, (2R,3R)-3-amino-2-{[2-(2-cyclopropylethyl)furo[3,2-c]pyridin-4-yl]methyl}-2-

hydroxy-4-(methylsulfanyl)butanoic acid, and (2R,3R)-3-amino-2-[(2-butyl-7-methylfuro[3,2-c]pyridin-4-yl)methyl]-2-hydroxy-4-(methylsulfanyl)butanoic acid. [Claim 10]
A pharmaceutical composition comprising the compound or a salt thereof according to claim 1. [Claim 11]
The pharmaceutical composition according to claim 10, which is an agent for treating nocturia. [Claim 12]
A pharmaceutical composition comprising the compound or a salt thereof according to claim 1 and an excipient. [Claim 13]
Use of the compound or a salt thereof according to claim 1 for production of a pharmaceutical composition for treating nocturia. [Claim 14]
Use of the compound or a salt thereof according to claim 1 for treating nocturia. [Claim 15]
The compound or a salt thereof according to claim 1 for treating nocturia. [Claim 16]
A method of treating nocturia comprising administering an effective amount of the compound or a salt thereof according to claim 1 to a subject.