VITAMIN RFSEARCH 



which is active lor the growth of L. casei was drscrihcfl hy llni. hings, 

 Stokstad, Bohonos, and Slobodkin (20). 



The similarity of the biological activities of these several sub- 

 stances suggests that they also may have a similarity in chemical 

 structure. Concerning this chemical structure, Mitchell (32) pre- 

 sented evidence which showed that the ultraviolet absorption spectrum 

 of folic acid resembled that of xanthopterin (XIV). Addition of large 

 amounts of thymine (XV) was found to substitute (biological pre- 



COH N CO 



/'\/\ /\ 



N G COH HN GCH, 



I II I I II 



H2NC C CH OG CH 



\/\/ \/ 



N N NH . 



(XIV) (XV) 



cursor?) for folic acid according to Snell and Mitchell (51). Thus, 

 chemical relationships to the pterins and pyrimidincs are suggestive 

 possibilities. 



Precise determination of the chemical structure of these several 

 biological factors is probably necessary before the identity of any two 

 or more of them, and before exact similarities in chemical structure, can 

 be established with certainty. It is interesting that much of the micro- 

 biological characterization of folic acid, vitamin B^, and related factors 

 is being developed before the elucidation of their chemical structures. 

 This situation is somewhat the reverse of that for the vitamin Be group 

 since much of the chemical characterization of these factors was de- 

 veloped before the clarification of the microbiological aspects. 



On the Synthesis of Vitamins 



The methods of the organic syntheses of the synthetic vitamins 

 have been amply covered in appropriate review articles. These 

 methods exemplify the adaptation and modification of classical organic 

 laboratory reactions to the synthesis of the desired structure. 



The three asymmetric carbon atoms and the two fused five- 

 membered saturated heterocyclic nuclei of biotin present interesting 

 stereochemical features to the studies on the synthesis of this vitamin. 

 There are two racemates which have cis forms of the rings and two 



lOI 



