220 VITAMINS 



The K vitamins are derivatives of 1,4-naphthoquinone, and this structure, 

 or one readily convertible into it in the body, is essential for vitamin K 

 activity. In the accompanying formula of vitamin Ki the 1,4-naphtho- 

 quinone structure consists of rings A and B without the side chains 



Vitamin Ki, C31H46O2 



attached at positions 2 and 3. Synthetic 2-methyl-l,4-naphthoquinone 

 is even more active, gram for gram, than vitamin K, but the two are 

 of about equal activity when compared on a molecular weight basis. It 

 may be, as some have suggested, that in the body the K vitamins are 

 degraded to 2-methyl- 1,4-naphthoquinone or, as others believe, perhaps 

 the latter is used in the body to synthesize these vitamins. A number 

 of bacteria have been found to synthesize compounds possessing vitamin 

 K activity. Phthiocol (2-methyl-3-hydroxy- 1,4-naphthoquinone), a yel- 

 low pigment found first in the tubercle bacillus, is one such compound. 



Water-soluble derivatives of vitamin K (e.g., the sodium salt of 

 2-methyl- 1,4-naphthohydroquinone diphosphate) have been prepared 

 synthetically and are medically useful in certain cases (see below) . Both 

 menadione, as 2-methyl- 1,4 naphthoquinone is called, and the water- 

 soluble derivatives are in common use. 



The K vitamins are fat-soluble and, therefore, are dissolved by the 

 usual fat solvents such as ether and petroleum ether. They are stable 

 to heat, but are destroyed by alkalies, strong acids, oxidizing agents, and 

 sunlight. Solutions of vitamin K gradually lose their activity when sub- 

 jected to light from an ordinary electric light bulb. 



Prevalence of vitamin K deficiency 



The general distribution of vitamin K in foodstuffs doubtless is re- 

 sponsible for the fact that deficiencies seldom are encountered in the 

 adult. The vitamin apparently is also produced in the intestinal tract 

 through the agency of the bacteria normally present. Vitamin K prepara- 

 tions were used on man first in treatment of obstructive jaundice, a con- 

 dition in which a low concentration of prothrombin in the blood always 

 prevailed. Deficiency of vitamin K in this instance is related to lack 

 of bile, without which the vitamin is poorly absorbed from the intestinal 

 tract. Surgical removal of the obstruction was formerly accompanied 



