Synthesis of the main long-term dihydroxylated metabolite of LGD-4033 as reference material for doping control analysis

Code: 21A17EP

LGD-4033 (Ligandrol), is a Selective Androgen Receptor Modulator (SARM) with a pyrrolidinyl-benzonitrile core structure. Although it displays promising muscle-and bone-anabolic properties, it is not yet
a drug approved for clinical use and it is included in the World Anti-Doping Agency’s (WADA’s) Prohibited List. Nonetheless, lately numerous related adverse analytical findings have been reported by
doping control laboratories worldwide.

Prior studies related to the detection of LGD-4033’s illicit use by LC–MS analysis of human urine have indicated two isomeric dihydroxylated metabolites as the preferred target analytes. Their monitoring could extend the detection for at least twenty-one days post-administration of the parent compound. For doping control laboratories to check, improve and properly validate their methods of detection of these metabolites it is crucial that relevant reference materials are available for comparison of chromatographic retention times and mass spectrometric properties. However, these compounds are not readily available and their structure has only partially been elucidated. Furthermore, their bis-hemiaminal nature questions their stability for long-term handling and storage. To address the abovementioned challenges, proposed herein is the chemical synthesis of all possible diastereoisomers of the main dihydroxylated LGD-4033 metabolite. Two alternative synthetic approaches that employ as starting material either the parent compound or commercially available building blocks will be investigated at small scale. NMR and LC-MS analysis of the synthesized diastereoisomers in comparison with the ones reported for the targeted metabolite is anticipated to clarify its stereochemistry and stability. To secure material to be distributed among WADA accredited laboratories, the synthesis of the diastereoisomer(s) that match the chromatographic and mass spectrometric properties of the in vivo observed metabolite(s) and exhibit stability that permits their use a reference material will be pursued at a larger scale.

Main findings

The main objective of this project was to secure through chemical synthesis reference material for the main dihydroxylated metabolite of LGD-4033 (M5b), a long-term marker for the detection of the illicit use of this WADA-banned SARM employing LC-HRMS/MS methods.

In the course of the project, the originally proposed structure for this metabolite was revised to (4R,5R)-4-{[4-cyano-3-(trifluoromethyl)phenyl]amino}-6,6,6trifluoro-5-hydroxyhexanoic acid. This material was synthesized in multi-mg scale, and shown, by LC-HRMS/MS and NMR, to be identical to the metabolite detected in post-administration urine samples. Thus, it can serve as reference material for this important metabolic marker. Details can be found in the research article Organic & Biomolecular Chemistry 2022, 20, 9112–9116. https://doi.org/10.1039/D2OB01907H and in the international patent application PCT/EP2023/063907, which has been published in WIPO under publication number WO2024046605 (publication date 07.04.2024) (https://patentscope.wipo.int/search/en/detail.jsf?docId=WO2024046605).

Furthermore, two diastereoisomeric pyrrolidinone-type derivatives—the 4{(5R)-2-oxo-5-[(1R)-2,2,2-trifluoro-1-hydroxyethyl]pyrrolidin-1-yl}-2-(trifluoromethyl)benzonitrile and the 4-{(5R)-2-oxo-5-[(1S)-2,2,2-trifluoro-1-hydroxyethyl]pyrrolidin-1-yl}-2-(trifluoromethyl)benzonitrile)—as well as the (4R,5S)diastereoisomer of M5b were synthesized and fully characterized (specific optical rotation, IR, 1H and 13C NMR, HRMS).

LC-HRMS/MS comparison of the above synthetic materials with a postadministration urine sample, obtained in the frame of a previous related excretion study, revealed that:

1. the (4R,5S)-diastereoisomer of M5b corresponds to the minor dihydroxylated long-term metabolite of LGD-4033 (M5a), which elutes in the same chromatographic window with M5b and is monitored simultaneously by WADA-accredited laboratories during their ITP;

2. the two synthesized pyrrolidinones correspond to two of the pyrrolidinonetype metabolites (M2) detected in LGD-4033 post-administration urine samples;

3. they are true metabolites and not, as previously suggested, analytical artifacts.

Some of the above results have been published in ChemPlusChem 2024, e202300634. https://doi.org/10.1002/cplu.202300634

The efficient synthetic sequence developed for M5b was adapted for the preparation of molecules that could correspond to the (R,R)-diastereoisomer of the ring-opened hydroxylated metabolite M4, and two of the potential isomers of the trishydroxylated metabolite M6. Their comparison (LC-HRMS/MS) with the corresponding in vivo-observed metabolites allowed structural elucidation of these metabolites.

Finally, a targeted metabolic investigation of a post-administration human urine sample, employing as reference material a pyrrole derivative that was obtained in the course of synthetic studies performed in the frame of the project, suggested that it corresponds to a new, not previously reported, short-term metabolite of LGD-4033.