Tyrosinase inhibitors

A cosmetic composition for improving the aesthetic appearance of human skin comprising a cosmetically acceptable vehicle, and an effective amount of a compound according to formula I(a):

• wherein,
• R1 and R2 are independently selected from hydrogen, aliphatic C1-C12 hydrocarbon radicals;
• aromatic C1-C12 hydrocarbon radicals;
• aliphatic C1-C12 heterocycles, aromatic C1-C12 heterocycles, or combinations thereof;
• each of the foregoing optionally containing from 1-8 heteroatoms selected from halogen, O, N, and S and being optionally substituted with one or more groups R, and wherein R1 and R2 may together form a three- to six-membered ring, with the proviso that one of R1 and R2 are not hydrogen;
• R3 and R4 are independently selected from hydrogen, aliphatic C1-C12 hydrocarbon radicals;
• aromatic C1-C12 hydrocarbon radicals;
• aliphatic C1-C12 heterocycles, aromatic C1-C12 heterocycles, or combinations thereof;
• each of the foregoing optionally containing from 1-8 heteroatoms selected from halogen, O, N, and S and being optionally substituted with one or more groups R, and wherein R3 and R4 may together form a three- to six-membered heterocyclic ring, with the proviso that one of R3 and R4 are not hydrogen;
• R is selected, independently at each occurrence, from hydrogen, —F;
• —Cl;
• —Br;
• —I;
• ═O, —OH, —OR*;
• —NH2;
• —NHR*;
• —N(R*)2;
• —N(R*)3;
• —N(R*)—OH;
• —N(—O)(R*)2;
• —O—N(R*)2;
• —N(R*)—O—R*;
• —N(R*)—N(R*)2;
• —C═N—R*;
• —N═C(R*)2;
• —C═N—N(R*)2;
• —C(═NR*)—N(R*)2;
• —SH;
• —SR*;
• —CN;
• —NC;
• —(C═O)—R*;
• —CHO;
• —CO2H;
• —CO2−;
• —CO2R*;
• —(C═O)—S—R*;
• —O—(C═O)—H;
• —O—(C═O)—R*;
• —S—(C═O)—R*;
• —(C═O)—NH2;
• —(C═O)—N(R*)2;
• —(C═O)—NHNH2;
• —O—(C═O)—NHNH2;
• —(C═S)—NH2;
• —(C═S)—N(R*)2;
• —N(R*)—CHO;
• —N(R*)—(C═O)—R*;
• —(C═NR)—O—R*;
• —O—(C═NR*)—R*, —SCN;
• —NCS;
• —NSO;
• —SSR*;
• —N(R*)—C(═O)—N(R*)2;
• —N(R*)—C(═S)—N(R*)2;
• —SO2—R*;
• —O—S(═O)2—R*;
• —S(═O)2—OR*;
• —N(R*)—SO2—R*;
• —SO2—N(R*)2;
• —O—SO3;
• —O—S(═O)2—OR*;
• —O—S(═O)—OR*;
• —O—S(═O)—R*;
• —S(═O)—OR*;
• —S(═O)—R*;
• —NO;
• —NO2;
• —NO3;
• —O—NO;
• —O—NO2;
• —N3;
• —N2—R*;
• —N(C2H4);
• —Si(R*)3;
• —CF3;
• —O—CF3;
• —PR*2;
• —O—P(═O)(OR*)2;
• —P(═O)(OR*)2;
• C1-C8 perfluoroalkyl;
• an aliphatic C1-C8 hydrocarbon radical;
• a C1-C8 aromatic hydrocarbon radical;
• or a C1-C8 heteroaryl radical;
• where R* is independently at each occurrence hydrogen or a straight chained, branched, or cyclic C1-C20 hydrocarbon radical, which may be saturated, partially saturated, or aromatic, each of which may be optionally substituted with one or more groups R, or optionally substituted with 1-6 heteroatoms selected from nitrogen, oxygen, sulfur, or halogen;
• and cosmetically acceptable salts thereof.