KARL FOLKERS 



milligrams of crystalline biotin (26). The difficult and tedious scheme 

 oi" hactionation involved a three million-fold purification. Kogl (26) 

 estimated that to produce one gram of their biotin from ordinary 

 yeast would have required 360 tons of the yeast as starting material. 

 Although he found egg yolk to contain ten times as much biotin as 

 yeast, the number of fresh eggs required for the production of one gram 

 of biotin would have cost about $165,000 in 1937. 



Special chemical steps or new techniques often have to be de- 

 vised or applied to the isolation process before the vitamin can be ob- 

 tained in sufficient amounts for the complete elucidation of its structure. 

 The improved yields (70) in the process for the isolation of thiamin 

 depended upon the elution of the vitamin from fuller's earth with 

 quinine acid sulfate instead of barium hydroxide and the introduction 

 of a benzoylation step for purification. Probably one of the most im- 

 portant factors contributing to the success of the isolation of additional 

 quantities of crystalline biotin was the application of the chromato- 

 graphic adsorption technique by du Vigneaud, Hofmann, Melville, 

 and Gyorgy (59) to concentrates of the vitamin which had been ob- 

 tained from beef liver (13). The concentrate contained 0.1% biotin, 

 and, after esterification, the material was chromatographed twice over 

 aluminum oxide. After the final sublimation and crystallization steps, 

 pure crystalline biotin methyl ester was obtained in 38% yield based 

 on the amount of the vitamin in the concentrate. 



On the Structure Determination of Vitamins 



Ordinarily, it is desirable to isolate any vmknown natural prod- 

 uct in a state of complete purity before the carrying out of chemical 

 reactions for establishment of molecular formula, identification of 

 functional groups, and finally the determination of structure. Special 

 attention to the question of purity is often justified, because natural 

 products are frequently isolated which are extremely difficult to sepa- 

 rate from final impurities of unknown but of allied properties. 



There are, however, exceptions to the purity requirement. 

 The isolation of calcium pantothenate in pure form was found by 

 Williams' group (67) to involve extraordinary difficulties, and it was 

 necessary to conduct the structure studies with a highly purified con- 

 centrate estimated to be about 90% pure (34,67). The establishment 



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