CONSTITUENTS OF THE BIOSPHERE 51 



(h) Pyridine Derivatives 



The simplest six-membered heterocyclic ring containing nitrogen is that 

 of pyridine. It can be prepared by cyclization of ethylallylamine followed 

 by dehydrogenation. 



Its formula is : 



H CH,=CH— CH,— NH— CH,— CH3. 



C \ ethylallylamine 



HC5 3CH 



II I 



HC 6 2 CH 



\ ^ ^ 



N 



pyridine 



It is present in the distillation product of bones and coal. It behaves 

 similarly to the benzene ring with regard to halogenation, nitration and 

 sulphonation, but the reactions are considerably slower. It is the ring 

 present in an important group of alkaloids. This group includes nicotine, 

 present in tobacco leaf in combination with malic and citric acids, and 

 which on oxidation yields nicotinic acid. 



H 



C^ HiC CHo 



y % II 



HC C HC CH2 



II I \ / 



HC CH N— CH3 



N 



Nicotine (Methylpyrrolidine-pyridine) 



H H 



y\ 



c 



HC C — COOH y^(^ C— CONH2 



» ' li I 



HC CH HC CH 



Nicotinic acid Amide of nicotinic acid (Nicotinamide) 



■n''^ ^n^ 



The amide of nicotinic acid, or nicotinamide, is a substance of very great 

 biological importance, for it is the active grouping in a whole series of 

 important coenzymes. Another important group of pyridine derivatives 

 comprises pyridoxin (also known as vitamin Bg, being a growth factor for 



