46 THE SIMPLER NATURAL BASES 



Ergothioneine, Thiolhistidine-betaine, C 9 H 15 O 2 N 3 S. 



Tanret [1909] isolated from ergot a base of the composition 

 C 9 H 15 O 2 N 3 S and named it ergothioneine. 



Barger and Ewins [1911] have shown it to be the betaine of 

 thiolhistidine, as follows : 



I II III 



CH NH 



IV V 



On heating ergothioneine (I) with concentrated potassium 

 hydroxide solution, trimethylamine was given off almost quantitatively 

 and a yellow unsaturated acid (II) resulted, which still contained 

 sulphur and was almost insoluble m water. On boiling this acid with 

 dilute nitric acid, the sulphur was removed and iminazolylacrylic acid 

 (III) was formed and identified by comparison with a synthetic 

 specimen. This substance was subsequently shown by Hunter 

 [1912; Ch. II, urocanic acid] to be identical with urocanic acid from 

 dog's urine (see p. 36). On boiling ergothioneine with ferric chloride 

 the betaine of histidine itself is formed (IV) (see previous section). On 

 adding iodine in alcoholic solution two molecules combine to form the 

 quaternary iodide (V) which is much less soluble than the salts of ergo- 

 thioneine, to which it bears the same relationship as cystine does to 

 cystei'ne. By reduction with hydrogen sulphide this iodide is recon- 

 verted into ergothioneine. The crystals of the dimeric iodide have 

 the remarkable property of taking up excess of iodine from an aqueous 

 solution and becoming steel grey or blue, like narceine and other 

 substances. 



The biochemical (interest of ergothioneine is chiefly due to the 

 sulphur atom contained in the glyoxaline ring. Oddly enough the 



