14 



FORMATION IN PLANTS 



II 



TABLE 1 



PRO-VITAMINS A 



W. Oroshnik, /. Am. Chem. Soc. 67 (1945) 1627. — O. Isler, W. Huber, A. Ronco 

 and M. Kofler, Experientia 2 (1946) 31. - — See also Festschrift 'Emil Barell', Basle 1946, 



P- 31- 



J. F. Arens and D. A. van Dorp, Nature 157 (1946) 190. — P. Karrer, E. Jucker 

 and E. Schick, Helv. Chim. Acta 2g (1946) 704. — I. M. Heilbron, E. R. H. Jones, and 

 D. G. O'SuLLiVAN, Nature 157 (1946) 485; /. Chem. Soc, 1946, 866. 



and its chemical constitution have now been clarified. In order to exhibit 

 vitamin A activity a compound must contain an unsubstituted j8-ionone ring 

 and the unsaturated side-chain present in axerophtol (vitamin A). a-Semi- 

 carotenone^' possesses the unsaturated side chain but not the ^-ionone ring 

 and is biologically inactive. ^-Euionone^^ contains an unsubstituted ^-ionone 

 ring but not the complete side chain and is incapable of replacing vitamin A 

 in experiments with animals*. 



Steric relationships also play a part in the biological activity of a pro- 

 vitamin A. Most of the investigations in this field are due to Zechmeister and 



I. M. Heilbron, E. R. H. Jones and their collaborators (of. I. M. Heilbron, 

 Pedlar Lecture, /. Chem. Soc, 1948, 3S6; I. M. Heilbron, E. R. H. Jones and R. W. 

 Richardson, ibid., 1949, 287; I. M. Heilbron, E. R. H. Jones, D. G. Lewis and B. C. L. 

 Weedon, ibid., 1949, 2023) have recently synthesized a number of partly demethylated 

 and acetylenic analogues of vitamin A acid and have shown that they exhibit some 

 growth-promoting properties. This work is providing important new evidence concerning 

 the relationships between chemical constitution and vitamin A activity. 



References p. ly-ig. 



