Sunscreen compositions and methods of use thereof

1. A method of reducing or preventing harmful effects of solar radiation on skin comprising, applying a composition, the composition comprising:

one or more agents that provide a UV-B filter; and,

an effective amount of a compound of formula I:

wherein

R 1 and R 2 are, independently, hydrogen, an alkyl group, or, taken together, NR 1 R 2 comprise a heterocyclic ring;

R 3 and R 4 are, independently, selected from hydrogen and pi electron donating groups;

R b and R c are, independently, hydrogen, hydroxy(lower)alkyl, (lower)alkanoyl(lower)alkyl, (lower)alkyl, (lower)alkoxycarbonyl(lower)alkyl, (lower)alkenyl, carboxy(lower)alkyl, carboxy(lower)alkyloxyimino, alkoxycarbonyl, (C 6 or C 10 ) aryl, (C 5 or C 9 ) heteroaryl, wherein the heteroaryl group contains one oxygen, one sulfur or one nitrogen, or Ar(lower)alkyl;

Y is S, O, or N—R′ where R′ is aryl, heteroaryl or lower alkyl;

Z is N or C—R b ; and

X- is a pharmaceutically acceptable anion;

wherein the compound of the formula I is not a 3-[2-(4-diethylaminophenyl)-2-oxoethy]thiazolium salt.

2. The method of claim 1 , wherein the effective amount of the compound of the formula I is between about 0.5% and about 10% by weight of the composition.

3. The method of claim 1 , wherein at least one of R 3 or R 4 is a halogen.

4. The method of claim 1 , wherein at least one of R 3 or R 4 is OH.

5. The method of claim 1 , wherein R 1 and R 2 are, independently, hydrogen or a lower alkyl group.

6. The method of claim 1 , wherein the composition further comprises a suitable carrier for topical application to human skin.

7. The method of claim 1 , wherein the one or more agents that provide a UV-B filter are selected from the group consisting of paramethoxycinnamic acid esters and octyl salicylate.

8. The method of claim 1 , wherein the composition further comprises one or more agents that provide a UV-A filter.

9. The method of claim 8 , wherein the UV-A filter is selected from the group consisting of dibenzoylmethane derivatives, 4-(1,1-dimethylethyl)-4′-methoxydibenzoylmethane, and 4-isopropyl dibenzoylmethane.

10. A sunscreen composition for the reduction or prevention of harmful effects of solar radiation on skin comprising:

one or more agents that provide a UV-B filter; and,

an effective amount of a compound of the formula I:

wherein

R 1 and R 2 are, independently, hydrogen, an alkyl group, or, taken together, NR 1 R 2 comprise a heterocyclic ring;

R 3 and R 4 are, independently, selected from hydrogen and pi electron donating groups;

R b and R c are, independently, hydrogen, hydroxy(lower)alkyl, (lower)alkanoyl(lower)alkyl, (lower)alkyl, (lower)alkoxycarbonyl(lower)alkyl, (lower)alkenyl, carboxy(lower)alkyl, carboxy(lower)alkyloxyimino, alkoxycarbonyl, (C 6 or C 10 ) aryl, (C 5 or C 9 ) heteroaryl, wherein the heteroaryl group comprises one heteroatom, selected from oxygen, sulfur or nitrogen, or Ar(lower)alkyl;

Y is S, O or N—R′ where R′ is aryl, heteroaryl or lower alkyl;

Z is N or C—R b ;

X- is a pharmaceutically acceptable anion;

wherein the compound of the formula I is not a 3-[2-(4-diethylaminophenyl)-2-oxoethyl]thiazolium salt; and,

a suitable carrier for application to the skin.

11. The composition of claim 10 , wherein the effective amount of the compound of the formula I is between about 0.5% and about 10% by weight of the composition.

12. The composition of claim 10 , wherein the one or more agents that provide a UV-B filter are selected from the group consisting of paramethoxycinnamic acid esters and octyl salicylate.

13. The composition of claim 10 , wherein the composition further comprises one or more agents that provide a UV-A filter.

14. The method of claim 13 , wherein the UV-A filter is selected from the group consisting of dibenzoylmethane derivatives, 4-(1,1-dimethylethyl)-4′-methoxydibenzoylmethane, and 4-isopropyl dibenzoylmethane.

15. The composition of claim 10 , wherein the composition further comprises one or more sunscreen active agents.

16. The method of claim 15 , wherein the one or more sunscreen active agents are selected from the group consisting of para aminobenzoic acid, avobenzone, cinoxate, dioxybenzone, homosalate, menthyl anthranilate, octocrylene, octyl methoxycinnamate, oxybenzone, padimate O, phenylbenzimidazole sulfonic acid, sulisobenzone, trolamine salicylate, titanium dioxide, zinc oxide, diethanolamine methoxycinnamate, digalloy trioleate, ethyl dihydroxypropyl PABA, glyceryl aminobenzoate, lawsone with dihydroxyacetone, red petrolatum, homomenthyl salicylate, Benzophenone-3, Uvinul MS-40, Uvasorb MET/C, and Neo Heliopan 303 or mixtures thereof.

17. The composition of claim 10 , wherein the composition further comprises one or more components selected from the group consisting of emollients, humectants, dry-feel modifiers, waterproofing agents, insect repellants, antimicrobial preservatives, antioxidants, chelating agents, fragrances and moisturizers.

18. The composition of claim 10 , wherein the composition is in the form of an emulsion.

19. The emulsion of claim 18 , further comprising a hydrophobic component that imparts film-forming and waterproofing characteristics to the emulsion.

20. The emulsion of claim 19 , wherein the hydrophobic component is a polymer selected from the group consisting of a copolymer comprising octadecene-1 and maleic anhydride monomers, polyanhydride resin, and a copolymer comprising vinyl pyrollidone and eicosene monomers.