A. M. MAYER 



and 

 A. POLJ AKOFF-MAYBER 



Hebrew University 

 Jerusalem, Israel 



Counfiarlns and Their Role In Growth 



and GermlnatLon 



Coumarin derivatives are of comparatively wide occurrence in plants. 

 These compounds occur largely in the form of their glycosides; as a 

 result, even when present in high concentrations they are frequently 

 physiologically inactive [Dean (13), Wawzonek (80)]. Coumarin itself 

 has been shown to occur as the lactone; although being very active 

 physiologically, it is very difficult to detect, because of lack of a sensi- 

 tive method. In most plants it probably occurs only in very small 

 amounts. The glycoside of the opened lactone ring, melilotoside, has 

 also been found in plants. 



Coumarin does not give any very simple reactions and is not flu- 

 orescent. Only after alkaline hydrolysis does it give a diazo reaction 

 and show fluorescence on exposure to ultraviolet light. This is due to 

 the opening of the lactone ring which proceeds readily under alkaline 



conditions. 



The coumarin molecule is stable but undergoes substitution re- 

 actions fairly easily. Samuel (71) has measured the charge density of 

 coumarin, which resembles that of naphthalene. Thus, coumarm is 

 attacked by nucleophilic reagents at position 4 and is susceptible to 

 electrophilic substitution at positions 3, 6, and 8. 



Evidence for metabolism of coumarin is available only in a few 

 cases. Kosuge and Conn (25) studied the synthesis of coumarin in sweet 

 clover and concluded that trans-cinnamic acid is the most effective pre- 

 cursor. Synthesis was much more efficient in shoots than in roots. 

 Most of the other papers have been concerned with the breakdown of 

 coumarin and its derivatives. James et al. (22) have shown that aescule- 

 tin, a hydroxycoumarin derivative, is oxidized by phenolase. Mead 

 et al. (46) have shown that coumarin is hydroxylated in rabbits and 

 that as a result 3, 7, and 8 hydroxycoumarins are formed but neither 



[735] 



