NICOTINIC ACID (nIACIN) 



errors of the method, and D. Melnick and H. Field ^^ found that 

 hydrolysates sometimes contained substances that reacted with 

 aniUne or ^-aminoacetophenone to give colours indistinguishable from 

 the nicotinic acid colour, but that, in presence of cyanogen bromide, 

 these interfering side-reactions did not occur. They therefore recom- 

 mended that the base should not be included in the blank. Further 

 slight modifications were introduced by H. A. Waisman and C. A. 

 Elvehjem ^^ and by W. J. Dann and P. Handler.^^ The latter workers 

 stated that metol was preferable to other bases, as the colour produced 

 was more stable, but this preference for metol is not shared by other 

 workers. According to M. Swaminathan,^^ for example, aniline and 

 j3-naphthylamine give stronger colours than either metol or ^-amino- 

 acetophenone. He found that heating the test solution with cyanogen 

 bromide in alcohol gave colours two or three times as intense as those 

 obtained in aqueous solution. Alcoholic extracts of urine, however, 

 gave interfering red colours. 



Another base used in conjunction with cyanogen bromide is 

 />-aminophenol, which was said to be less affected by light and pK 

 than ^-aminoacetophenone.^^ w-Phenylene diamine, ^^ orthoform,^^ 

 procaine ^^ and ^-aminopropiophenone 22a have also been used. 

 Aniline would appear to be the base most generally used, with ^-amino- 

 acetophenone as a second favourite. The choice of base is, perhaps, 

 of less importance than other considerations, such as the procedures 

 used for preparing the nicotinic acid extract and for eliminating the 

 errors due to the existence of several forms of nicotinic acid, some 

 biologically active and others inactive. 



Metabolites of Nicotinic Acid and Nicotinamide 



One of these substances is the alkaloid, trigonelline, which occurs 

 in the seeds of Trigonella foenugraecum, Pisum sativum, Cannabis 

 sativa and Strophanthus spp. It is the betaine of nicotinic acid : 



CH, 



and may be present in human urine in relatively large amounts, 

 especially after the consumption of materials rich in trigonelline, such 

 as coffee. In addition, however, it is formed from nicotinic acid in 

 the human and animal organism and eliminated in the urine. It has 

 no anti-pellagra activity, so that methods of estimating nicotinic acid 

 in vegetable materials should be capable of distinguishing it from 



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