CHEMISTRY OF THE AUXINS 



109 



acids, is thus similar to the relation between the two female 

 sex hormones, theelol (trihydroxyoestrin) and theelin (keto- 

 hydroxyoestrin). The structure of the C13 residue was 

 worked out by breakdown experiments (Kogl and Erxleben, 

 1934), while finally the synthesis of a dicarboxylic acid 

 identical with the oxidation product III, ("auxin-glutaric 

 acid") (Kogl and Erxleben, 1935) confirmed the following 

 formulae for auxin a and 6: 



CH3 



C2H5— CH— CH- 



CH2 



\ 

 C2H5— CH— CH 



C— CHOH.CH2.CHOH.CHOH.COOH 



auxin a, auxentriolic acid 



CH 



CH3 



CH. 



C2H5— CH— CH— C— CHOH.CH0.COCH2.COOH 



CH2 



auxin h, auxenolonic acid 



C2H5— CH— CH— CH 



CH3 



A remarkable property of both auxin a and h is their 

 spontaneous inactivation. This, which occurs in the solid 

 crystalline state, involves no oxidation because it may take 

 place in vacuo and in the dark, being complete in 1-2 months 

 (Kogl, Erxleben, and Haagen Smit, 1933). Analysis of the 

 inactive product ("pseudo-auxin") showed no change in 

 composition or molecular weight, so that the change must 

 be one of isomerization. Study of the ultra-violet spectra 

 (Koningsberger, 1936; Kogl, 1936a) has shown that it con- 

 sists of a shift of the double bond from the ring to the side- 

 chain, the 5 — OH group shifting to the ring; this produces 

 an asymmetric C atom, which explains the formation of two 

 optically isomeric "pseudo-auxins" from auxin a: 



