Abstract:
Compounds of the structure                            
     wherein R and R′ are H, alkyl or aryl and each Z, X, Y and X′ is H, acylamino, acyloxy, alkanoyl, alkoxycarbonyl, amino, alkyl, alkoxy, hydroxy, alkylamino, dialkylamino, arylamino, alkylaryl, diarylamino, halo, carboxyl or cyano; and Z can also be                            
     are effective UV blockers.

Description:
BACKGROUND OF THE INVENTION 
     The present application is directed to novel blockers of ultraviolet radiation formed by Perkin condensation of aromatic aldehyes with alpha-aryl acetic acids, followed by esterification with an alcohol. 
     Ultraviolet-blocking agents may be either inorganic or organic compounds. Inorganic UV blocking agents are effective by virtue of their reflective properties, while organic blocking agents absorb UV radiation and convert it to other forms of energy, mostly heat. Many organic compounds have been prepared and used as ingredients for sunscreening products. Compounds used for this purpose must be stable, nontoxic, and amenable to formulation. 
     The UV radiation permeating the earth&#39;s atmosphere has wavelengths ranging from about 290 nm to 400 nm. The radiation with wavelengths ranging from 290 to 320 nm is designated UVB radiation and is commonly referred to as the “burning rays.” The radiation with wavelengths ranging from 320 to 400 nm is designated UVA radiation and is commonly referred to as the “tanning rays.” Overdoses of either kind can cause inflammation, suppress the immune system, and damage DNA. 
     SUMMARY OF THE INVENTION 
     Compounds of the formula I:                           
     wherein R is H, linear or branched alkyl of 1 to 20 carbon atoms or aryl of5 to 20 carbon atoms; Z, X and Y are independently H, acylamino of 1 to 20 carbon atoms; acyloxy of  1  to 20 carbon atoms; alkoxycarbonyl of 2 to 20 carbon atoms; amino; linear or branched alkyl of 1 to 20 carbon atoms; linear or branched alkoxy of 1 to 20 carbon atoms; hydroxy; alkylamino of 1 to 20 carbon atoms; dialkylamino of 2 to 40 carbon atoms; arylamino of 5 to 20 carbon atoms; alkylaryl of  6  to 40 carbon atoms; diarylamino of 10 to 40 carbon atoms; halo, carboxyl, or cyano; n is an integer from 1 to 4, and Z can also be                           
     wherein R′ is independently selected from the same groups defining R; and X′ is independently selected from the same groups defining X; 
     possess a UV useful absorption spectrum with λ max  which make them suitable as UV blockers. 
     A preferred class of compounds includes those in which R is linear or branched alkyl; X is hydroxy; Z and Y are independently H or linear or branched alkoxy. In this class, the compounds wherein X is hydroxy; Y is H, n=2 and Z is alkoxy; and wherein X is hydroxy; Y n  is alkoxy, n=2, and Z is H are particularly preferred. 
     In the class of compounds where in Z is                           
     the compounds wherein R′ and R are independently linear or branched alkyl; Y n  is hydrogen, n=2; and X′ and X are hydroxy, are preferred. The indication of  means that the carbon-carbon double bond configuration may be E or Z. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 tabulates the molar absorbance of various tested sunscreen ingredients at 305 nm (UVB radiation) and at 350 nm (UVA radiation). 
     FIG. 2 shows graphically the molar extinction coefficients of the tested sunscreen ingredients at 305 nm (UVB radiation) and at 350 nm (UVA radiation) 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Compounds of formula I have been found which possess a UV absorption spectrum with a lambda (max) in the UVB radiation range (290-320 mm). Some of these compounds have an absorption spectrum which extends even into the UVA range which make them useful UVA and UVB blockers as well. 
     In the above formulas, linear and branched alkyl include, but are not limited to, methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, t-butyl, 2-ethyl-hex-1-yl and the like. 
     Aryl includes aromatic rings such as phenyl, naphthyl, anthracyl, and the like. 
     Acylamino includes RCONH— wherein R is alkyl or aryl as defined above. 
     Acyloxy includes RCOO— wherein R is hydrogen, alkyl or aryl as defined above. 
     Alkanoyl includes the group                           
     wherein R is hydrogen, alkyl or aryl as defined above. 
     Alkoxycarbonyl includes the group                           
     wherein R is alkyl as defined above. 
     Alkoxyl includes methoxy, propoxy, isopropoxy, and the like. 
     The groups alkylamino, dialkylamino, arylamino, alkylaryl and diarylamino include the definitions of alkyl and aryl as defined above. 
     Halo includes fluoro, bromo, iodo, chloro. 
     In general, the compounds of the invention may be prepared as follows:                           
     Compounds similar to Ic may be made from dialdehyde starting material.                           
     The compounds of the invention are useful as UV blockers. They may be utilized topically as a spray, oil, ointment, and the like with pharmaceutically acceptable carriers. As a topical agent, the amount of active ingredient in the carrier may be determined empirically by those of ordinary skill in the art. The compounds will typically be effective blockers of UVB radiation (290-320 nm) which is dangerous skin burning radiation. Some of the compounds will also be effective blockers of UVA radiation (320-400 nm) which is characterized as skin-tanning, but may nevertheless be harmful. 
     The compounds may also be used in industrial materials to protect from UV damage. For example, the compounds may be mixed into plastics for use in automobile parts, upholstery, and the like. 
     Compounds where R and R′ are independently linear or branched alkyl of 1 to 20 carbon atoms and X and X′ are hydroxy are particularly preferred. The groups R and R′ are preferably methyl or 3-octyl. 
     The groups Z and Y are preferably hydrogen or linear or branched alkoxy of 1 to 20 carbon atoms. Compounds where Y is H and Z is methoxy or Y i =Y 2 =methoxy and Z is H are preferred. 
     In the following examples, the 2-ethylhexyl ester Ia and a para-methoxy derivative Ib were synthesized for comparison to other esters currently in use as sunscreen agents. Another preferred compound, Ic, was synthesized for testing.                           
     EXAMPLE 1 
     
       
                 
         
             
             
         
      
     
     To a mixture of 3,5-dimethoxybenzaldehyde (5.0 g, 30 mM) and p-hydroxyphenyl acetic acid (4.57 g, 30 mM) under nitrogen atmosphere was added acetic anhydride (10 ml) and triethylamine (4.2 ml, 30 mM). After being stirred at 130-140° C. for 18 hours, the mixture was cooled to 20° C. Concentrated HCl (20 mL) was added to the reaction mixture slowly in 5 minutes, keeping temperature between 20-30° C. The light yellow precipitate obtained was filtered (wet˜10 g) and dissolved in CH 2 Cl 2  (150 mL). Methylene chloride solution was extracted with 2M aqueous NaOH solution (3×75 ml). The aqueous layers were pooled together and washed with CH 2 Cl 2  (50 mL). The aqueous layer thus obtained was acidified, maintaining a temperature at 25-30° C., with concentrated HCl (˜40 mL) to pH 1 and stirred for 2 hours at room temperature. The product was filtered and washed with ice cold water (2×20 mL) to give crude product (˜11 g). The crude product was recrystallized from EtOH—H 2 ) (4:1, 50 mL) mixture to yield white crystals of 1,(3.20 g, 35.5%). 
     A mixture of 1 (1.0 g, 3.2 mM), 2-ethyl hexan-1-o1 and p-toluenesulfonic acid (250 mg) were taken in toluene (5 mL) and refluxed for 7 hours with continuous removal of water, diluted with ethyl acetate and washed with saturated bicarbonate solution. The organic layer was dried on anhydrous magnesium sulfate and evaporated. The crude product was purified by chromatography on SiO 2  gel (Hexanes: EtOAc-4:1). UV (EtOH) λ max  228, 286, 410 nm;  1 HNMR (CDCl 3 ): 7.69 (s, 1H), 7.09 (d, J=8.8 Hz, 2H), 6.81 (d, J=8.8 Hz, 2H), 6.32 (t, J=2 Hz, 1H), 6.25 (d, J=2 Hz, 2H), 4.10 (d, J=5.2 Hz, 2H), 3.56 (s, 6H), 1.57-0.84 (m, 15H). 
     EXAMPLE 2 
     
       
                 
         
             
             
         
      
     
     To a mixture of 4-methoxybenzaldehyde (4.48 g, 33 mM) and p-hydroxyphenyl acetic acid (5.0 g, 33 mM) under nitrogen atmosphere was added acetic anhydride (10 mL) and triethylamine (7.3 mL, 53 mM). After being stirred at 130-140° C. for 2 hours, the mixture was poured in ice and 5% acqueous HCl (100 mL) was added. The precipitate obtained was taken up in 2N NaOH (150 mL) and filtered through Celite. Filtrate was acidified with concentrated HCl solid precipitated was washed with water. Repeated crystallization from MeOH— water mixture yielded pure 2, 2.44 g. 
     A mixture of 2 (1.92 g, 7.1 mM), 2-ethyl hexan-1-o1 (1.67 g, 12.8 mM) and p-toluenesulfonic acid (0.50 g) were taken in toluene (10 mL) and refluxed for 2.5 hours with continuous removal of water, diluted with ethyl acetate and washed with saturated bicarbonate solution followed by brine. The organic layer was dried on anhydrous magnesium sulfate and evaporated. The crude product was purified by chromatography on SiO 2  gel (Hexanes: EtOAc-4:1). UV (EtOH) λ max  227, 300;  1 HNMR (CDCl 3 ): 7.75 (s, 1H), 7.06 (d, J=8.8 Hz, 2H), 7.03 (d, J=8.8 Hz, 2H), 6.81 (d, J=8.8 Hz, 2H, 6.69 (d, J=8.8 Hz, 2H), 4.09 (d, J=6.0 Hz, 2H), 3.75 (s, 3H), 1.58-0.83 (m, 15H). 
     EXAMPLE 3 
     
       
                 
         
             
             
         
      
     
     To a mixture of terephthaldicarboxaldehyde (2.0 g, 14.9 mM) and p-hydroxyphenyl acetic acid (4.57 g, 30 mM) under nitrogen atmosphere was added acetic anhydride (10 ml) and triethylamine (6.7 mL, 48 mM). After being stirred at 135-140° C. for 2 hours, the mixture was poured in ice and concentrated HCl (20 mL) was added. The precitate obtained was filtered and taken up in 2N NaOH (150 mL). The clear orange solution was acidified with concentrated HCl (30 mL). The yellow solid precipitate was washed with water to yield 3. The product was dried at 50° C. for two days. 
     Sulfuric acid (1 mL) was added to a suspension of crude product 3, in MeOH and refluxed for 18 hours. The reaction mixture was cooled to room temperature, the solid precipitated was filtered was filtered and washed with fresh methanol. Pale yellow solid obtained was dried overnight at 50° C. to yield 1.3 g of the compound Ic. UV (EtOH) λ max  230, 305, 350 nm;  1 HNMR (DMSO-d 6 ): 9.57(s, 2H), 7.57 (s, 2H), 6.92 (d, J=9.2 Hz, 4H), 6.92 (s, 4H), 6.73 (d, J=9.2 Hz, 4H), 3.67 (s, 6H). 
     EXAMPLE 4 
     Compounds Ia, Ib and Ic, were compared to the following commerical sunscreening agents: 
     HMB: 2-Hydroxy-4-methoxybenzophenone 
     CDA: 2-Ethylhexyl 2-cyano-3,3-diphenylacrylate 
     PMC: 2-Ethylhexyl 4-methoxycinnamate 
     DAB: 2-Ethylhexyl 4-(dimethylamino)benzoate 
     SAL: 2-Ethylhexyl salicylate 
     The UV spectra were obtained in ethanol for each of these compounds, and their molar extinction coefficients were calculated. The extinction coefficients at 305 nm (UVB) and at 350 nm (UVA) were tabulated and graphed for comparison. 
     FIGS. 1 and 2 summarize the results of these comparisons of absorption of the active ingredients of sunscreening agents. Ordinarily, as absorption at 305 nm increases, absorption at 350 nm decreases. However, it was found that Compound Ib absorbs well at 350 nm and at 305 nm and Compound Ic absorbs UV radiation almost equally well at 305 nm and 350 nm.