Novel amide derivative and whitening agent

A method of whitening skin, comprising applying to the skin a whitening agent comprising a compound represented by formula (V):

• wherein:
• R1, R2, R3, R4, R5, R6 and R7 are each independently a hydrogen atom, an alkyl group having a carbon number of 1 to 3, a hydroxyl group or an alkoxy group having a carbon number of 1 to 3, or R1 and R2, or R2 and R3 in combination optionally form a methylenedioxy group, provided that at least one of R1, R2, R3, R4 and R5 is a hydroxyl group;
• Z is a hydrogen atom;
• or a salt thereof,
• provided that the following compound and salts thereof are excluded:
• a compound wherein, when R1, R2, R5 and R7 are hydrogen atoms, and R6 is a hydroxyl group, then:
• R3 and R4 are hydroxyl groups, or
• R3 is a hydroxyl group and R4 is a methoxy group, or
• R3 and R4 are hydrogen atoms, or
• R3 is a methoxy group and R4 is a hydrogen atom.

A compound represented by formula (IV):

• wherein:
• R1, R2, R4, and R5 are each independently a hydrogen atom, an alkyl group having a carbon number of 1 to 3, a hydroxyl group or an alkoxy group having a carbon number of 1 to 3, or R1 and R2 in combination optionally form a methylenedioxy group;
• R3 is a hydroxyl group;
• R6 is a hydroxyl group;
• R7 is a hydrogen atom;
• X is a methylene group, an ethylene group, or a vinylene group;
• Z is a hydrogen atom;
• or a salt thereof,
• provided that the following compound and salts thereof are excluded:
• a compound wherein, when X is a vinylene group, and R1, R2, and R5 are hydrogen atoms, then
• R4 is a hydrogen atom, a methoxy group, or a hydroxyl group.

A method of whitening skin, comprising applying to the skin a whitening agent, comprising a compound represented by formula (I′):

• wherein:
• R1, R2, R3, R4 and R5 are each independently a hydrogen atom, an alkyl group having a carbon number of 1 to 3, a hydroxyl group or an alkoxy group having a carbon number of 1 to 3, or R1 and R2, or R2 and R3 in combination optionally form a methylenedioxy group, and at least one of R1, R2, R3, R4 and R5 is a hydroxyl group;
• X is a methylene group, an ethylene group, or a vinylene group;
• Y is a divalent group represented by formula:
• Z is a hydrogen atom, a hydroxycarbonyl group or an alkoxycarbonyl group having a carbon number of 1 to 3, and when Z is other than a hydrogen atom and a carbon atom bonded to Z contains an asymmetric center, the stereochemistry thereof may be any of (S), (R) and (SR);
• Ar is a substituent represented by formula (II):
• wherein:
• R6 and R7 are each independently a hydrogen atom, an alkyl group having a carbon number of 1 to 3, a hydroxyl group or an alkoxy group having a carbon number of 1 to 3, and * is a moiety bonded to Y;
• provided that the following compounds and salts thereof are excluded:
• (1) a compound wherein, when X is a vinylene group, Y is an ethylene group, R1, R2, R5 and R7 are hydrogen atoms, and R6 is a hydroxyl group, then
• R3 is a hydroxyl group and R4 is a hydrogen atom, or
• R3 is a hydroxyl group and R4 is a methoxy group, or
• R3 and R4 are hydroxyl groups;
• and
• (2) a compound wherein, when X is a vinylene group, Y is an ethylene group, and R1, R2, R5, R6 and R7 are hydrogen atoms, then
• R3 and R4 are hydroxyl groups.