BIOTIN 



and T. J. de Man ^ suggested that the sulphur formed part of a ring. 

 The diamino-carboxylic acid on oxidation with nitric acid or potas- 

 sium permanganate yielded, amongst other compounds, adipic acid.^ 

 Biotin methyl ester was converted via the hydrazide into an azide 

 which, with boiling absolute alcohol, yielded an ethyl urethane, 

 CigHgiOgNgS.^' ^ By the action of hydrochloric acid, this gave a 

 monoamine, CgHi^ONgS (IV), and both this and the urethane were 

 converted by the action of barium hydroxide into the same triamine, 

 CgHigNgS (V). The monoamine had the same structure as biotin, 

 except that the carboxyl group was replaced by an amino group, 

 whilst the triamine corresponded to the diamino-carboxylic acid 

 referred to above. Unlike the diamino acid, however, the triamine 

 did not give adipic acid on oxidation with nitric acid or potassium 

 permanganate, whence it was concluded that the carboxyl group of 

 adipic acid was the carboxyl group originally present in biotin, the 

 adipic acid resulting from a side-chain and not from a cyclic structure. 



By the action of concentrated hydrochloric acid at 200° C, biotin 

 sulphone was converted "^ into the sulphone of the diamino carboxylic 

 acid (IV) which, on treatment with phosgene, was reconverted into the 

 original biotin sulphone. 



Of the several formulae proposed by du Vigneaud and his col- 

 leagues,^ formula I (R = H) was shown to be correct.^ 



In the first place, hydrogenolysis of biotin with Raney nickel 

 yielded desthiobiotin (VII) which on acid hydrolysis yielded a desthio- 

 diamino-carboxylic acid, C9H20O2N2 (VIII). This, on oxidation with 

 alkaline periodate, gave pimelic acid ; treatment with phenanthrene- 

 quinone gave a quinoxaline. Secondly, exhaustive methylation of the 

 diaminocarboxylic acid, followed by acid hydrolysis, yielded small 

 amounts of thiophan-2 -valeric acid (IX). ^ 



These reactions are summarised in the schematic representation 

 on pages 408 and 409. 



Chemical Constitution of a-Biotin 



The constitution of a-biotin, prepared from egg-yolk, was investi- 

 gated by F. Kogl and his colleagues. It was hydrolysed *» ^^ by con- 

 centrated hydrochloric acid at 200° C, giving a diamino-carboxylic 

 acid, C9H18O2N2S, suggesting the presence of a cyclic urea group. On 

 oxidation with alkaline permanganate, biotin sulphone was obtained 

 and it was suggested that the sulphur atom was part of a ring. 



Biotin methyl ester added on i mole of methyl iodide to give 

 methyl biotin sulphonium iodide, whilst on oxidation of the ester, 

 biotin sulphone methyl ester was obtained. This on vigorous hydro- 

 lysis yielded a Cg-diamino-sulphocarboxylic acid, thus proving that 

 the urea group and the sulphur atom were present in different rings ; 



41:0 



