BIOTIN 



NH,— q CH— C5H10 



I IQH.^SO MeOH 11 I KMnO, COOH HOOC. 



Cj C SO2 ^ I >C5H\o 



I I COOH HO3S/ 



COOH COOMe 



in agreement with the known behaviour of j3-amino acids. On oxida- 

 tion of the free acid with permanganate, 4 atoms of oxygen were 

 utilised and the product was a sulphocarboxylic acid, isolated as the 

 w-toluidine salt. To identify this sulphocarboxylic acid, it was fused 

 with alkali,^2 model experiments indicating that jS-sulphocarboxylic 

 acids yield unsaturated carboxylic acids by this procedure. An un- 

 saturated acid was in fact obtained and on hydrogenation, dl-oL^- 

 dimethylbutyric acid, (CHgjg . CH . CH(CH3) . COOH, was isolated. 



Various ^- and y-sulphonic acids derivable from this acid were 

 synthesised, and the methyl ester anilide of jS-carboxy-y-methylbutane- 

 sulphonic acid was shown to be identical with the corresponding 

 derivative of the sulphocarboxylic acid from biotin. 



This evidence therefore leads to the structure 



/o 



CH— CH.CH(CH3)2 



I I I 



NH CH CH2 



\ /\/ 

 CH S 



COOH 



for the a-biotin of egg-yolk. The difference between this formula and 

 that assigned to j8-biotin would account for the fact that the diamino 

 acid sulphone from a-biotin is so much more easily hydrolysed than 

 the corresponding compound from ^-biotin but, on the other hand, it 

 is a little difficult to believe that two molecules differing so markedly 

 from one another would possess the same highly specific growth- 

 promoting properties. 



Convincing as the above evidence apparently was, the formula 

 proposed for a-biotin was withdrawn by Kogl and his colleagues when 

 they learnt of the results obtained by the American workers on jS-biotin 

 and, on reconsideration of the evidence, they advanced the alternative 

 formula : 



CO 



/\ 

 NH NH 



1 I 

 CH— CH 



I I 



CH2 CH.CH.CH(CH3)2 



\/ I 



S COOH 



412 



