566 THE BIOCHEMISTRY OF B VITAMINS 



glutamylglutamic acid 21_23 and later synthesized. 26 By synthesis, the 

 structure was established as N-pteroyldi-y-glutamylglutamic acid. 



OH 



C N r. * O 



N C C-CHVNH-^ VcO-CNH-CH-CH^CHo-Oo-NH-CH-CHj-CHj-COOH 



H 2 N-C C CH \=/ COOH COOH 



w 



N-pteroyldi-^-glutamylglutamic acid 



Another crystalline compound which prevents anemia in chicks, but is 

 not appreciably active for either Lactobacillus casei or Streptococcus 

 faecalis R, was isolated from yeast. 18 This compound was termed vitamin 

 B c conjugate, and later was demonstrated to be a pteroylhexaglutamyl- 

 glutamic acid. 27 An enzyme widely distributed in animal tissues 28 ~ 32 

 hydrolyzes the conjugate to a form which is active for Streptococcus 

 faecalis R and Lactobacillus casei. Folic acid was isolated after enzymatic 

 digestion of a concentrate of the conjugate from yeast. 14 



A fourth crystalline member 16 of the folic complex was isolated from 

 the fermentation liquors of Rhizopus nigricans and given the trivial name 

 rhizopterin. 33 This compound was subsequently shown to be N 10 -formyl- 

 pteroic acid and synthesized 34, 35 from pteroic acid which was previously 

 prepared synthetically in the course of studies on folic acid. 24 



OH O 



I II 



C N H— C 



N C C— CH 2 — N— f 



H 2 N— C C CH 



TJ N 



N l0 -formylpteroic acid (rhizopterin) 



The relative biological activities of these naturally occurring members 

 of the folic acid complex as well as a number of synthetic, related com- 

 pounds are indicated in Table 18. All activities, except those for rat and 

 man, represent the ability of derivatives to replace folic acid as an 

 essential nutritional factor under controlled experimental conditions. 



Supplementary folic acid is not ordinarily required by rats on a puri- 

 fied diet, but rats fed sulfaguanidine or succinylsulfathiazole in such a 

 purified diet grow slowly 6G and develop an anemia, an agranulocytosis, 

 a leucopenia, and a hypocellularity of bone marrow, 67, 68 which are cor- 

 rected by administration of folic acid. 55, 69 The effect of sulfonamides, 



