II. CHEMISTRY 



103 



Hj'drogcuation of pteroyltrigliitamic acid with a palladium catalyst at 

 pH 1 results in rapid biological inactivation and liberation of p-amino- 

 benzoyltriglutamic acid (Hutchings et alJ^*). Reduction of PGA with zinc 

 in acid solution also cleaves the bond between the nitrogen of the p-amino- 

 benzoic acid and the methylene carbon attached to the pteridine ring. Thus 

 the reduced form of PGA is unstable in acid solution and rapidly splits to 

 give the free aromatic amine. 



Fig. 5. Ultraviolet absorption spectra of pterins: — — 2-amino-4-hydroxy-6- 



carboxypteridine at pH 11.0; — ■ tetrahydro-2-amino-4-hydrox}^-6-carbo.xy- 



pteridine at pH 11.0; ■ tetrahydro-2-amino-4-hydro.\y-6-carbo.xypteridine at pH 



3.0; 2-amino-4-hydrox3'-6-carbo.xy-7-methyltetrah3'dropteridine at pH 11. 



Courtesy /. Am. Chem. Soc. (O'Dell et al}^). 



2. Other Reactions 



Cosulich and Smith-^ observed that treatment of PGA with cold nitrous 

 acid yields X'^-nitrosopteroylglutamic acid with biological activity approxi- 

 mately equal to that of PGA for the chick and for S. faecalis R. It will be 

 recalled that nitrous acid has also been used to remove the 2-amino group 

 of N'^-formylpteroic acid (rhizopterin) (Wolf et al.^°). Heating PGA with 

 formic acid and acetic anhydride gives N'^-formylpteroylglutamic acid 

 (Gordon et aZ.'O- Stokstad et al.^- found that irradiation of PGA with sun- 



" D. B. Cosulich and J. M. Smith, Jr., J. Am. Chem. Soc. 71, 3574 (1949). 



30 D. E. Wolf, R. C. Anderson, E. A. Kaczka, S. A. Harris, G. E. Arth, P. L. South- 

 wick, R. Mozingo, and K. Folkers, J. Am. Chem. Soc. 69, 2753 (1947). 



3' M. Gordon, J. M. Ravel, R. E. Eakin, and W. Shive, /. Am. Chem. Soc. 70, S78 

 (1948). 



32 E. L. R. Stokstad, D. Fordham, and A. deGrunigen, /. Biol. Chem. 167, 877 (1947). 



