Structures of Nonylphenol Isomers and their Estrogenic Activity

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4-Nonylphenol (NP) is known as an environmental endocrine disruptor and widely used in many industrial applications, as plastic additive, antioxidant and raw material of nonylphenol polyethoxylate (NPEO), which is a nonionic surface-active agent. Commercial NP prepared by the alkylation of phenol with nonene isomers ("propylene trimer") is a mixture of more than 31 components.Preparative fractionation of a commercial NP mixture using high performance liquid chromatography (HPLC) gave fifteen NP isomers (NP-A : 4-(2,4-dimethylheptan-4-yl)phenol, NP-B : 4-(2,4-dimethylheptan-2-yl)phenol, NP-C : 4-(3,6-dimethylheptan-3- yl)phenol, NP-D : 4-(4-ethyl-2-methylhexan-2-yl)phenol, NP-E(diastereomer of NP-G) : 4-(3,5-dimethylheptan-3-yl)phenol, NP-F : 4-(2,5-dimethylheptan-2-y1)phenol, NP-G (diastereomer of NP-E), NP-H : 4-(4-methyloctan-4-yl)phenol, NP-I : 4-(3-ethy1-2- methylhexan-2-yl)phenol, NP-J(diastereomer of NP-L) : 4-(3,4-dimethylheptan-4-yl)phenol, NP-K(diastereomer of NP-P) : 4-(3,4- dimethylheptan-3-yl)phenol, NP-L (diastereomer of NP-J), NP-M : 4-(2,3-dimethylheptan-2-yl)phenol, NP-N : 4-(3-methyloctan- 3-yl)phenol), and NP-P(diastereomer of NP-K). All of fifteen NP isomers isolated from NP mixture possessed tertiary a-carbon having at least one methyl group in their chemical structures, and were synthesized by two different synthetic methods. NP-I (racemate), one of synthetic NP isomer, showed strong estrogenic activity than the others on recombinant yeast screen system. Optical resolution of racemic NP-I using HPLC and elucidation of its absolute structure were studied to clear the optical isomeric effect for estrogenic activity.