536 



BIOTIN 



CsHjsS 



— NH 



CO 



/ 

 — NH 



^ — NHCOOC2H6 

 IV 



CsHisS ' 



— NH2 

 — NH2 

 — NH2 



Biotin methyl ester (I) was converted into biotin hydrazide (II) by treat- 

 ment with hydrazine hydrate, and the corresponding azide (III) was pre- 

 pared from the hydrazide with the calculated amount of nitrous acid with- 

 out affecting the urea part of the molecule. When the azide was boiled 

 with ethanol, the corresponding ethyl urethane (IV) resulted. The urethane 

 was hydrolyzed with barium hydroxide to the triamine (V), thus simul- 

 taneously opening the urea ring. 



The triamine was subjected to the same oxidation procedures which 

 had been employed for the oxidation of the diaminocarboxylic, but no 

 adipic acid could be identified among the oxidation products. Thus, one 

 of the two carboxyl groups of the adipic acid must have been originally 

 present in the diaminocarboxylic acid, and it became highly probable 

 that the adipic acid formed by oxidation of the diaminocarboxylic acid 

 arose, not from a cyclic structure but from an aliphatic side chain 

 — CH2 — CH2 — CH2 — CH2 — COOH attached to a ring carbon in the biotin 

 molecule. 



The marked stability of the diaminocarboxylic acid toward hydrolytic 

 agents rendered unlikely structures in which the sulfur atom and an amino 

 group were attached to the same carbon atom. Such structures would be 

 unstable toward alkali and acid. This fact, together with the oxidative 

 formation of adipic acid, favored the assumption that biotin might contain 

 a tetrahydrothiophene nucleus with a n-valeric acid chain attached in the 

 |8 or a position, as depicted in formulas VI and VII, However, the possi- 

 bility could not have definitely been ruled out that the adipic acid might 

 have been formed from the decarboxylation of a malonic or a-substituted 



CO 



/\ 

 HN NH 



CO 



HN 



NH 



HC C-CHzCHj-CHzCHjCOOH HC CH 



II II 



H2C CH2 H2C CHCHjCHsCHrCHi-COOH 



\/ \/ 



s s 



VI 



VII 



