THE FOLIC ACID GROUP 589 



Mallette, Taylor and Cain 141 was extremely effective in inhibiting the 

 growth of Streptococcus faecalis R. The effects of these pteridines and 

 related compounds on a number of organisms are indicated in Table 21. 

 The inhibitory effects of these pteridines are prevented in a competitive 

 manner by folic acid, particularly for Streptococcus faecalis R. The most 

 effective inhibitors of these pteridines are those with aromatic substitu- 

 ents in the 6,7-positions, e.g., 2,4-diamino-6,7-diphenylpteridine, 2,4- 

 diaminophenanthro(9,10-e)pteridine and 2,4-diaminoacenaphtho(l,2-e)- 

 pteridine. 



NH 2 



A n jTx 



I 



H 2 N— C C C 



N C C 



N N 



2 ,4-diamino-6 ,7-diphenylpteridine 



f\ 



2 ,4,-diamino-6 ,7-phenanthro(9 ,10-e)pteridine 



A large number of the pteridines indicated in Table 21 were prepared 

 in an effort to find more soluble derivatives with the same potent in- 

 hibitory properties as the 2,4-diaminopteridines with 6,7-aromatic sub- 

 stituents. However, substitution of the aromatic groups lowered the 

 activity, regardless of the nature of the substituent group. Acetylation of 

 the 2- or 4-amino groups did not appreciably alter the activity, but 

 methylation of these amino groups resulted in considerable loss of in- 

 hibitory power. 143 



The 2,4-diaminopteridines contrast markedly with the 2-amino-4- 

 hydroxypteridines which, though more closely related structurally to folic 

 acid, do not possess antibacterial activity; on the contrary, some have 

 very slight growth-stimulating effects. 140 



2,4-Diamino-6,7-diphenylpteridine inhibits the growth of Lactobacillus 

 arabinosus, which does not require exogenous folic acid. 140 Both p-amino- 



