The present invention provides a compound having an excellent inhibitory action on melanin production and being useful as a whitening agent, and a skin external preparation containing the compound. The whitening agent of the present invention comprises, as an active ingredient, a heterocyclic compound represented by formula (1) or a pharmacologically acceptable salt thereof:
wherein A is C
1-6
alkyl, C
5-6
cycloalkyl, benzyl, benzylcarbonyl, benzoyl, phenyl, pyridyl or pyrimidyl; Ra is H, C
1-6
alkyl, or C
2-6
alkenyl; “
” represents a single bond or a double bond wherein n=1 or 2; Y is S or O; and R
3
and R
4
are each independently H, C
1-6
alkyl, hydroxy-C
1-6
alkyl, C
2-7
acyl, phenyl, pyridyl, pyrimidyl, etc.;with the proviso that at least one R
3
is a group other than C
1-3
alkyl in the case where: the hetero ring containing Y is a thiazoline ring; R
4
═Ra═H; X
1
═X
2
═CH; and either p =0 or R
5
═C
1-6
alkyl.
本发明提供了一种具有优异的抑制
黑色素生成作用并且可用作美白剂的化合物,以及含有该化合物的皮肤外用制剂。本发明的美白剂包含以下异构化合物作为活性成分:式(1)或其药学上可接受的盐,其中,A是C1-6烷基、C5-6环烷基、苄基、苯甲酰基、苯甲酰基、苯基、
吡啶基或
嘧啶基;Ra是氢、C1-6烷基或C2-6烯基;“”表示单键或双键,其中n=1或2;Y是S或O;R3和R4分别独立地是氢、C1-6烷基、羟基-C1-6烷基、C2-7酰基、苯基、
吡啶基、
嘧啶基等;但当:异杂环含有Y是
噻唑环;R4═Ra═H;X1═X2═CH;且p=0或R5═C1-6烷基时,至少一个R3是除了C1-3烷基以外的基团。