THE VITAMIN B a GROUP 



661 



reported that 2,4,5-trimethyl-3-hydroxypyridine and 2-methyl-3-hy- 

 droxy-4-ethoxymethyl-5-hydroxymethylpyridine inhibited the growth 

 of excised tomato roots, but did not show that the toxicity was prevented 

 by pyridoxine. These and other inhibitory analogues of the vitamin B c 

 group are listed in Table 37. The analogues, with one exception, contain 

 one or more of the following variations from the structure of pyridoxine: 

 2-ethyl group replacing the 2-methyl group, a methyl group replacing an 

 hydroxymethyl group, or either an amino or alkyoxyl group replacing 

 an hydroxyl group. These types are illustrated by the following inhibitory 

 analogues: 



CH 2 OH 



I 



H0 :A 



-CH 2 OH 



2-ethyl-8-hydroxy-4,5-bis 

 (hydroxymethyl)pyridine 



CH 3 



I 

 HO— if^'S— CH 2 OH 



desoxypyridoxine 



CH 2 OCH 3 



CH 2 OH 



-CH 2 OH 



£-methyl-3-hydroxy-4-inethoxymethyl- 

 5-hydroxymethylpyridine 



-CH 2 NH 2 



2-m ethyl-3-amino-Jf-hydroxy- 

 methyl-5-aminomethylpyridine 



2-Ethyl-3-hydroxy-4,5-bis(hydroxymethyl)pyridine. The index at which 

 the ethyl homologue of pyridoxine inhibits the growth of Ceratostomella 

 ulmi is approximately 50. 25 At that ratio of analogue to vitamin, no 

 growth occurs, but at a ratio of 10, approximately half-maximal growth 

 is obtained. This analogue is as effective as pyridoxine in stimulating the 

 growth of excised tomato roots (Table 35). 24 This high activity in replac- 

 ing the vitamin for one organism and the very potent inhibiting action 

 on another organism illustrate that a line of demarkation cannot be 

 drawn between stimulatory and inhibitory properties of analogues of 

 metabolites. 



Desoxypyridoxines. Investigation of the vitamin activity of analogues 

 of pyridoxine led to the discovery that 2,4-dimethyl-3-hydroxy-5-hy- 

 droxymethylpyridine (a desoxypyridoxine) was very toxic for pyridoxine- 

 deficient chicks. 65 Day-old female single comb White Leghorn chicks, 

 after being maintained on an adequate diet for three days, were placed 

 on a purified diet deficient in pyridoxine for a period of six days before 

 administration of the desoxypyridoxine. Administration of as little as 



