Chemical structure and biological activity 



pure form and its activity similarly demonstrated. This substance is known as 

 Compound F (Steward and Shantz, 1954). It should be mentioned here that 

 a very large number of inactive substances have been fractionated and some 

 of them identified in the coco-nut milk. A variety of amino-acids, including 

 the recently discovered pipecolic acid, were isolated in pure form. None of 

 these functions is the specific response in question. 



The main new result to be reported is that Compound A has been re- 

 isolated (Shantz and Steward, 1955) and definitely identified as the quite 

 simple but rather unexpected substance, 1 :3-diphenylurea. This has been 

 established beyond any doubt by analysis, mixed melting point, completely 

 matching infra-red [Figure 6) and ultra-violet absorption spectra, and all 

 essential criteria for fastidious chemical identification. What is now quite 

 clear is that the response of various strains and varieties of carrot tissue to the 



h/ave/ength 

 Figure 6. 



diphenylurea is very variable. In some cases diphenylurea in presence of 

 casein hydrolysate may replace, in large part, the activity of whole coco-nut 

 milk, approaching at least 50 per cent of that activity. In other cases the 

 activity is small by comparison. The total concentration of diphenylurea 

 that could at its maximum be present in whole coco-nut milk is not large 

 (order of 01 p. p.m.) and it is quite clear that the coco-nut milk owes its 

 characteristic properties much more to the other substances that are present 

 therein than to the diphenylurea. In fact the paper in which this new 

 discovery has been communicated still makes cautious reservations because 

 the isolation of a relatively small amount of a substance like diphenylurea 

 from a very large amount of biological material requiring the use of large 

 amounts of reagents does raise the question whether the substance was 

 present as such in the coco-nut milk of the intact nut. While there is every 

 reason to believe that diphenylurea did so occur, the fact still remains that 

 this constitutes the first known case of the isolation from plants of a carbanilide. 

 Be that as it may, it is still a matter of great interest that here we have the 

 first case of the chemical identification of an active substance from coco-nut 

 milk, even though the total growth response produced by that substance may 

 not be as dramatic as that due to the coco-nut milk as a whole. 



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