A compound represented by the general formula (I) or a salt thereof: wherein, -X<；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00001"/>；Y- represents -CH=CH-, -CH2-CH2- or the like, <；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00002"/>；between R<；1 >；and the carbon atom at 4'-position represents a single bond or a double bond, <；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00003"/>；between R<；2 >；and the carbon atom at 5-position represents a single bond or a double bond, and for example, 1) when -X<；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00004"/>；Y- represents -CH=CH- or -CH2-CH2-, and <；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00005"/>；between R<；1 >；and the carbon atom at 4'-position represents a double bond, R<；1 >；represents =C(R<；11>；)(R<；12>；) (wherein R<；11 >；represents a lower alkyl group or the like and R<；12 >；represents a hydrogen atom or the like) or the like, and R<；2 >；represents a hydroxyl group or the like, or R<；2 >；may be combined together with the carbon atom at 5-position to form a carbonyl group, and 2) when -X<；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00006"/>；Y- represents -CH=CH- or -CH2-CH2-, and <；custom-character file="US20040087519A1-20040506-P00900.TIF" wi="20" he="20" id="custom-character-00007"/>；between R<；1 >；and the carbon atom at 4'-position represents a single bond, R<；1 >；represents -OCH(R<；1a>；)(R<；1b>；) (wherein R<；1a >；represents a lower alkyl or the like and R<；1b >；represents a hydrogen atom or the like) or the like, and R<；2 >；represents a hydroxyl group or the like.
