Resorcinol derivatives

A topical pharmaceutical composition for lightening skin or reducing the pigmentation of skin in a human, comprising a pharmaceutically acceptable carrier, and a skin-lightening or pigmentation-reducing amount of a compound of formula I:

• or a pharmaceutically acceptable salt thereof, wherein:
• R1 is a (C3-C8)cycloalkyl ring or (C5-C8)cycloalkenyl ring, wherein either the cycloalkyl ring or cycloalkenyl ring is substituted by one to three substituents independently selected from the group consisting of cyano;
• halo;
• (C1-C6)alkyl;
• aryl;
• (C2-C9)heterocycloalkyl;
• (C2-C9)heteroaryl;
• aryl(C1-C6)alkyl-;
• ═O;
• ═CHO(C1-C6)alkyl;
• amino;
• hydroxy;
• (C1-C6)alkoxy;
• aryl(C1-C6)alkoxy-;
• (C1-C6)acyl;
• (C1-C6)alkylamino-;
• aryl(C1-C6)alkylamino-;
• amino(C1-C6)alkyl-;
• (C1-C6)alkoxy-CO—NH—;
• (C1-C6) alkylamino-CO—;
• (C2-C6)alkenyl;
• (C2-C6)alkynyl;
• hydroxy(C1-C6)alkyl-;
• (C1-C6)alkoxy(C1-C6)alkyl-;
• (C1-C6)acyloxy(C1-C6)alkyl-;
• nitro;
• cyano(C1-C6)alkyl-;
• halo(C1-C6)alkyl-;
• nitro(C1-C6)alkyl-;
• trifluoromethyl;
• trifluoromethyl(C1-C6)alkyl-;
• (C1-C6)acylamino-;
• (C1-C6)acylamino(C1-C6)alkyl-;
• (C1-C6)alkoxy(C1-C6)acylamino-;
• amino(C1-C6)acyl-;
• amino(C1-C6)acyl(C1-C6)alkyl-;
• (C1-C6)alkylamino(C1-C6)acyl-;
• ((C1-C6) alkyl)2amino(C1-C6)acyl-;
• —CO2R2;
• —(C1-C6)alkyl-CO2R2;
• —C(O)N(R2)2;
• —(C1-C6)alkyl-C(O)N(R2)2;
• R2ON═;
• R2ON═(C1-C6)alkyl-;
• R2ON═CR2(C1-C6)alkyl-;
• —NR2(OR2);
• —(C1-C6)alkyl-NR2(OR2);
• —C(O)(NR2R2);
• —(C1-C6)alkyl-C(O)(NR2OR2);
• —S(O)mR2;
• wherein each R2 is independently selected from hydrogen, (C1-C6)alkyl, aryl, or aryl(C1-C6)alkyl-;
• R3C(O)O—, wherein R3 is (C1-C6)alkyl, aryl, or aryl(C1-C6)alkyl-;
• R3C(O)O—(C1-C6)alkyl-;
• R4R5N—C(O)—O—;
• R4R5NS(O)2—;
• R4R5NS(O)2(C1-C6)alkyl-;
• R4S(O)2R5N—;
• R4S(O)2R5N(C1-C6)alkyl-;
• wherein m is 0, 1 or 2, and R4 and R5 are each independently selected from hydrogen or (C1-C6)alkyl;
• —C(═NR6)(N(R4)2);
• or —(C1-C6)alkyl-C(═NR6)(N(R4)2) wherein R6 represents OR2 or R2 wherein R2 is defined as above;
• with the proviso that the cycloalkenyl ring is not aromatic;
• with the proviso that R1 must be substituted by at least one of R3C(O)O—, R3C(O)O—(C1-C6)alkyl-, R2ON═, R2ON═(C1-C6)alkyl-, R2 ON═CR2(C1-C6)alkyl-, —NR2(OR2), R4R5NS(O)2—, R4R5NS(O)2(C1-C6)alkyl-, R4S(O)2R5N—, or R4S(O)2R5N(C1-C6)alkyl-.