Topical compositions and methods for skin lightening

1. A method for reducing pigmentation of human skin comprising topically applying to an area of the skin in need thereof a composition comprising, in a topically acceptable vehicle, an effective amount of a compound having the structure of formula (I):

wherein, R N are independently selected at each occurrence from hydrogen or C 1- C 12 hydrocarbons, optionally containing from 1-8 heteroatoms selected from halogen, O, N, and S and combinations thereof; and wherein two groups R N on the same nitrogen atom may together form a three- to six-membered ring;

R a is independently selected from hydrogen, —F; —Cl; —Br; —I; —OH, —OR*; —NH 2 ; —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; —CO 2 H; —CO 2 − ; —CO 2 R*; —(C═O)—S—R*; —O—(C═O)—H; —O—(C═O)—R*; —S—(C═O)—R*; —(C═O)—NH 2 ; —(C═O)—N(R*) 2 ; —(C═O)—NHNH 2 ; —O—(C═O)—NHNH 2 ; —(C═S)—NH 2 ; —(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 ; —SO 2 —R*; —O—S(═O) 2 —R*; —S(═O) 2 —OR*; —N(R*)—SO 2 —R*; —SO 2 —N(R*) 2 ; —O—SO 3 − ; —O—S(═O) 2 —OR*; —O—S(═O)—OR*; —O—S(═O)—R*; —S(═O)—OR*; —S(═O)—R*; —NO; —NO 2 ; —NO 3 ; —O—NO; —O—NO 2 ; —N 3 ; —N 2 —R*; —N(C 2 H 4 ); —Si(R*) 3 ; —CF 3 ; —O—CF 3 ; —PR* 2 ; —O—P(=O)(OR*) 2 ; —P(=O)(OR*) 2 ; C 1 -C 8 perfluoroalkyl; an aliphatic C 1 -C 8 hydrocarbon radical; a C 1 -C 8 aromatic hydrocarbon radical; or a C 1 -C 8 heteroaryl radical;

X 1 and X 2 are independently selected from oxygen, sulfur, or NR N ;

R* is independently at each occurrence hydrogen or a straight chained, branched, or cyclic C 1 -C 20 hydrocarbon radical, optionally substituted with one or more groups R a or with 1-6 heteroatoms selected from nitrogen, oxygen, sulfur, or halogen and combinations thereof;

ring “A” is a five or six-membered optionally aromatic ring, z 1 is —C—, —N—, —NL 1 -, or —CL 1 -;

and z 2 -z 6 are independently selected from —N—, —NH—, —NR—, —O—, —S—, —CH—, —CR—, —CR*—, and in the case where ring “A” is a five membered ring, z 4 is a bond (i.e., it is absent); where L 1 is group —V—(CH 2 ) r —(CH═CH) s —X b —(CH 2 ) y —(CH═CH) z —X c —, where X a , X b , and X c are independently a bond (i.e., absent), —O—, —S—, —NH—, —NR*— and “r,” “s,” “y,” and “z” are independently at each occurrence integers from 0-2;

Ω is selected from H, R*, OH, OR*, or NR N R N , wherein R N and R* are as defined above;

and n and m are independently integers from 0-6;

and topically acceptable salts thereof, for a time sufficient to reduce the pigmentation of said human skin.

2. The method of claim 1 , wherein the compound has the structure of formula (II):

3. The method according to claim 1 , wherein said composition is applied at least once daily for a period of at least four weeks.