ANALOGUES 



whilst xanthopterine was also eftective, but only in quantities approxi- 

 mately 1000-fold larger than folic acid. Xanthopterine was without 

 effect on Tenebrio. 



Pollen contains no folic acid, and royal jelly only 0-5 /xg. per 100 g.^ 

 so that folic acid appears to be of no significance in the development of 

 bee larvae as are apparently biotin and pantothenic acid (pages 390, 

 441)- 



References to Section 17 



1. L. Golberg, B. de Meillon and M. Lavoipierre, Nature, 1944, 154, 



608 ; /. Exp. Biol., 1945, 21, 90. 



2. L. Golberg and B. de Meillon, Nature, 1947, 160, 582. 



3. L. Golberg, B. de Meillon and J. F. Murray, ibid., 22. 



4. C. A. Grob, T. Reichstein andH. Rosenthal, Experientia, 1945, 1, 275. 



5. G. Fraenkel and M. Blewett, Nature, 1946, 157, 697 ; Biochem. J., 



1947, 41, 469. 



6. G. Kitzes, H. A. Schuette and C. A. Elvehjem, /. Nutrition, 1943, 



26, 241. 



18. ANALOGUES OF FOLIC ACID 



Pyrimidines 



J. L. Stokes ^ discovered that when L. helveticus was grown on a 

 medium deficient in folic acid, thymine (5-methyluracil, I) and its 

 nucleotide, thymidine, could be utilised instead, although a 5000-fold 

 concentration of thymine was required to produce the same effect. 

 According to K. K. Krueger and W. H. Peterson, 2 thymine did not com- 

 pletely replace vitamin Be as a growth factor for L. helveticus, although 

 it did for 5. faecalis R. Enterococci also required folic acid for growth 

 and these organisms likewise responded to thjonine. With S. faecalis 

 R,i, 3, 4 thymine was the only substance capable of replacing folic acid, 

 whereas with L. helveticus a response was obtained with some twenty 

 compounds related to thymine (I).^ Of these, the most effective, next 

 to thymine itself, was 2-hydroxy-5-methyl-4-thiopyrimidine (II), 

 whilst good responses were also obtained with 5-methyl-cytosine (III), 

 5-methyl-isocytosine (IV) and 2 : 4-diamino-5-methyl-pyrimidine (V). 



(I) N=C . OH (ID N=G . SH (ni) N=C . NH^ 



II II II 



HO . C C . CH3 HO . C C . CH3 HO . C C. CH, 



II II II II II II 



N— CH N— CH N— CH 



(IV) N=C . OH (V) N=C . NH2 



II ! I 



H2N . C C . CH3 H^N .0 C. CH3 



II II II II 



N— CH N— CH 



33 513 



