102 



PTEROYLGLUTAMIC ACID 



glutamic acid in alkaline solution with platinum oxide as a catalyst takes 

 up 1 mole of hydrogen to form a colorless dihydro derivative with an ab- 

 sorption maxima at 284 mju in alkaline solution. In glacial acetic acid over 

 platinum 2 moles of hydrogen are taken up to form the tetrahydro deriva- 

 tive which has an absorption spectrum similar to that of the dihydro form. 

 Alkaline solutions of the dihydro derivative readily absorb oxygen to yield 

 PGA, whereas in acid solution reoxidation is less rapid. The tetrahydro 

 derivative is reoxidized to PGA by oxygen over platinum in glacial acetic 



25 - 



20 - 



15 - 



10 - 



5 - 



240 



280 



320 

 X, m/i 



Fig. 4. Ultraviolet absorption spectra: — 



hydro PGA at pH 11.0; dihj-dro PGA at pH 3.1 ; 



360 



400 



PGA at pH 11.0; di- 



tetrahydro PGA at 



pH 11.0; o.xidized dihydro PGA at pH 11.0. Courtesy /. Am. Chem. Soc. 



(O'Dell et al^^). 



acid. The ultraviolet absorption spectra of PGA, dihydro and tetrahydro 

 PGA, and reoxidized dihydro PGA are shown in Fig. 4 (O'Dell et al.-^). 



Reduction of 2-amino-4-hydroxypteridine-6-carboxy]ic acid in alkaline 

 solution with hydrogen over platinum oxide yields the tetrahydro form. 

 The reduced solutions rapidly absorb oxygen from the air to yield the 

 parent compound. It is interesting to note that the SilS-m^i absorption 

 band of pteroylglutamic acid disappears during formation of the di- or 

 tetrahydro derivatives, whereas the same band is shifted to longer wave- 

 lengths in the tetrahydro derivatives of 2-amino-4-hydroxypteridine-6-car- 

 boxylic acid and 2-amino-4-hydroxy-7-methylpteridine (Fig. 5, O'Dell et 



28 B. L. O'Dell, J. M. Vandenhelt, E. S. Bloom, and J. J. PfifTnor, J. Am. Chan. Soc. 

 69, 250 (1947). 



