Synthesis and characterization of 14C-labelled sulfate conjugates of steroid oestrogens

Steroid oestrogens are typical endocrine-disrupting compounds in the environment and are excreted from the human and animals mainly as conjugates, including sulfate and glucuronide salts. The oestrogen conjugates are largely biologically inactive, but they can be de-conjugated and release free oestrogens, which usually exhibit strong oestrogenicity. Therefore, it is important to study the fate of oestrogen conjugates in the environment. However, because of the complexity of environmental matrixes, time-consuming pre-treatments of samples are usually required to reduce the interference of the matrixes. (14)C radioisotope can trace target substances and their degradation products at low concentrations in complex environmental samples and is therefore essential in such studies. We synthesized three oestrogen sulfates with (14)C-labelling at the ring, i.e. [3-(14)C]-estrone-3-sulfate ammonium salt, [3-(14)C]-17β-estradiol-17-sulfate ammonium salt, and [3-(14)C]-17β-estradiol-3,17-disulfate diammonium salt with radiochemical purities of >98% by sulfation of [3-(14)C]-labelled estrone and 17β-estradiol in dry pyridine with SO3 -triethylamine at room temperature or 90-95 °C, followed by hydrolysis with KOH-methanol solution and purification by preparative thin-layer chromatography on silica gel using an ammonia-containing eluent. The products were characterized by mass spectrometry and (13)C and (1)H nuclear magnetic resonance spectroscopy, using their corresponding non-labelled compounds. The (14)C-labelled oestrogen conjugates provide possibilities for studying their fate in soil and sediment environments as well as in the animal manure.