Naphthyloxy compounds as plant growth regulators 



Hansch and Muir (1950) who postulated a two-point attachment involving 

 the carboxyl group and one or/Ao-position, and Wain (1953) who presented 

 much evidence in favour of a three-point attachment, an essential feature 

 of which was a hydrogen atom on the a-carbon atom, are well known. 



In order to explain the importance of certain positions in 2-naphthyloxy- 

 acetic acid for growth substance activity, it is necessary to postulate a four- 

 point, or in order to meet Wain's a-hydrogen requirement, a five-point 

 attachment theory. This would involve in addition to one hydrogen atom 

 on the a-carbon atom of the side-chain, and the carboxyl group, positions 1 , 

 4, and 5 in the nucleus. Substitution in these positions leads to inactivity, 

 whilst substitution in positions 6, 7, and 8 could reduce activity by hindering 

 close interlocking with the substrate molecule. This hindrance would be 

 greater the larger the substituent atom or group of atoms. Thus 8-nitro- 

 2-naphthyloxyacetic acid would be expected to be less active than the 

 corresponding 8-chloro compound, a fact which has already been noted. 

 Although it is possible on the basis of such a five-point attachment theory, 

 to explain all the known results so far obtained relating to 2-naphthyloxy- 

 acetic acid, several criticisms may be made not least of which is the fact that 

 an entirely hypothetical substrate, different from that postulated by Muir 

 and others for phenoxy growth substances is involved. Although different 

 types of growth substances may each have their own substrates, this seems 

 unlikely in view of the great similarity in the growth responses they produce. 



REFERENCES 



Aberg, B. (1951). On the growth substance activity of enantiomorphic a-(naph- 



thoxy) -propionic acids. Ark. Kemi. 3, 549. 

 Fawcett, C. H., Ingram, J. M. A., and Wain, R. L. (1952). /5-oxidation of w-phen- 



oxyalkylcarboxylic acids in the flax plant. Nature, 170, 887. 

 Grace, N. H. (1939). Physiological activity of a series of naphthylacetic acids. 



Canad. J. Res. (C) 17, 247. 

 Hansch, C, and Muir, R. M. (1950). The ortho effect in plant growth regulators. 



Plant Physiol. 25, 389. 

 James, P. M., and Woodcock, D. (1951). Synthesis of plant growth regulators. 



Part I. Substituted /3-naphthyIoxyacetic acids. J. chem. Soc. 3418. 

 James, P. M., and Woodcock, D. (1953). Synthesis of plant growth regulators. 



Part II. Dichloro-/?-naphthyloxyacetic acids. J. chem. Soc. 2089. 

 JoNSSON, A. (1955). Synthetic plant hormones. VIII. Relationship between chemical 



structure and plant growth activity in the arylalkyi-, aryloxyalkyl-, and indole- 



alkylcarboxylic acid series. Svensk. kem. Tidskr. 67, 166. 

 Leopold, A. C, and Guernsey, F. S. (1953). A theory of auxin action involving 



coenzyme A. Proc. nat. Acad. Sci. Wash., 39, 1105. 

 LucKWiLL, L. C. (1948). A method for the quantitative estimation of growth 



substances based on the response of tomato ovaries to known amounts of 2-naph- 



thoxy-acetic acid. J. hort. Sci. 24, 19. 

 LucKWiLL, L. C, and Woodcock, D. (1955). Plant growth regulators. I. The 



influence of side-chain length on the activity of cj-(2-naphthyloxy)-n-alkylcarboxylic 



acids for the induction of parthenocarpy in tomatoes. J. hort. Sci. 30, 109. 

 Maxell, M. (1953). Stereochemical studies on plant growth substances. LantbrHogsk. 



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