Patent ID: 7923461

Claim:
A compound represented by the following formula [1] or a salt thereof, wherein A is —O—; B is alkylene or alkenylene; R 1 and R 2 are different, and are alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl, wherein the alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl is unsubstituted or substituted by halogen, cycloalkyl, aryl, adamantyl or amino; R 3 is a substituted or unsubstituted pyridine ring; R 5 and R 6 being the same or different, are hydrogen or alkyl; R 7 is hydrogen or alkyl; X is O or S; and each hydrogen of the said amino is unsubstituted or substituted by alkyl, alkoxycarbonyl, cycloalkyloxycarbonyl, arylalkoxycarbonyl or halogenoalkyloxycarbonyl.