Chemical structure and biological activity 



If ( — ) amphetamine is used in the same way with the racemic acid, the 

 product which crystallizes out is 



O— CH— CO— NH— CH CH2 (m.p. 164-5°; [a]^' +39-0 

 r^]/\ I I /\ (c= 2-00 in toluene)), 



CI 



and the (+)-( — ) remains in solution. 



The ( — )-( — ) product is again readily purified by recrystallization fi-om 

 methanol and on hydrolysis gives the pure (— ) a-(2:4-dichlorophenoxy)- 

 propionic acid and ( — ) amphetamine. 



These phenyl ?,fopropylamides of hormone acids in general have been the 

 subject of considerable biological study in our greenhouse apart from the 

 acids themselves and represent an entirely new hormone-type product which 

 has great possibilities in practical application. They can be made from any 

 hormone acid whether potentially optically active or not but, of course, 

 should have their major usefulness in connection with the more active one of 

 a potentially optically active pair of acids. In this connection they would 

 have the following advantages : 



(i) they are readily obtained pure without tedious recrystallizations; 



(ii) they are made from a readily available base which is easily recoverable 

 if desired ; 



{Hi) they are made from the racemic acid directly without having to use 

 the pure (+) or (— ) acid at all; 



(iv) they contain the most active half of the hormone acid ; 



(v) they have a low molecular weight; 



(vi) they have extremely low solubility in water. 



The last property may seem to be a disadvantage, but our experience, for 

 instance in apple blossom thinning, has led us to the conclusion that a spray 

 of a comparatively insoluble compound formulated in a wettable form such as 

 for instance 1-naphthylacetamide has at least the advantage over the corre- 

 sponding acid or salt, that it will not cause damage to the trees when used 

 carelessly, since its maximum solubility is not very far from the concentration 

 needed for blossom thinning. Even apart from this advantage, it also does a 

 consistently superior job and is today being widely used. The amphetamides 

 of (+) a-(2:4:5-trichlorophenoxy)propionic acid, a-(2-naphthoxy)propionic 

 acid, and a- (1-naphthyl) propionic acid (see below) are expected to be 

 particularly useful, 



RESOLUTION OF a- ( 1 -NAPHTHYL) PROPIONIC ACID 



Since we have been prominent in the manufacture and uses of 1-naphthyl- 

 acetic acid and its derivatives since the early days of plant hormone applica- 

 tion, it was natural that we should look into the possibilities of the homologues. 

 The activity of the (o-homologues of 1-naphthylacetic acid was studied by 

 Grace (1939), who found a similar alternate spacing of activity with length 

 of side-chain as was found in the substituted phenoxy series by Synerholm and 



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