Chiral analysis of ostarine in commercially available products and doping control urine samples

Various substances classified as prohibited in sport by the World Anti-Doping Agency (WADA) comprise one or more chiral centers. One such substance is enobosarm ((2S)-3-(4-cyanophenoxy)-N-[4-cyano-3-(trifluoromethyl)phenyl]-2‑hydroxy-2-methylpropanamide, S-ostarine, S-22, MK-2866, GTx-024, VERU-024). Although ostarine is not an approved drug, it has been readily available via Internet-based suppliers, and to date it is unknown to what extent R-ostarine, S-ostarine, or a mixture of both is used in these products. Likewise, such information is not available with regards to urine samples that returned an adverse analytical finding in the context of sports drug testing programs and, hence, this pilot-study aimed at establishing a test method to provide first insights into the presence of R- and S-ostarine in commercially available products and in authentic doping control urine samples.

Here, a chiral liquid chromatographic - mass spectrometric method, employing a teicoplanin-containing (chiral) stationary phase that allows the differentiation of R- and S-enantiomers of ostarine, is presented. Ostarine products were extracted and diluted prior to analysis, while urine samples were prepared for analysis by enzymatic hydrolysis followed by liquid-liquid extraction.

Seven products declaring to contain ostarine were investigated, five of which were ordered via the Internet and two were confiscated and made available by a customs authority. Only 2 of the 5 purchased products contained ostarine. In these two products and the confiscated products, only the ostarine S-enantiomer was found. Further, five authentic doping control urine samples containing the target analyte were subjected to chiral analysis, also confirming the sole presence of the S-ostarine enantiomer.

The developed approach proved suitable for the separation of ostarine enantiomers, which adds further information e.g. in the context of illicit drug production, trafficking, and doping controls, especially when additional details are desirable that might assist in determining the origin of a drug or drug residue.