S-23 (drug)

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S-23

Clinical data
Other names	Mastorin
Legal status
Legal status	US: Investigational New Drug
Identifiers
IUPAC name (2S)-N-(4-cyano-3-trifluoromethylphenyl)-3-(3-fluoro-4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide
CAS Number	1010396-29-8
PubChem CID	24892822
DrugBank	DB07419
ChemSpider	24715019
UNII	XDK89456WM
CompTox Dashboard (EPA)	DTXSID701045802
Chemical and physical data
Formula	C18H13ClF4N2O3
Molar mass	416.76 g·mol−1
3D model (JSmol)	Interactive image
SMILES C[C@](COC1=CC(=C(C=C1)Cl)F)(C(=O)NC2=CC(=C(C=C2)C#N)C(F)(F)F)O
InChI InChI=1S/C18H13ClF4N2O3/c1-17(27,9-28-12-4-5-14(19)15(20)7-12)16(26)25-11-3-2-10(8-24)13(6-11)18(21,22)23/h2-7,27H,9H2,1H3,(H,25,26)/t17-/m0/s1  Key:SSFVOEAXHZGTRJ-KRWDZBQOSA-N
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S-23, also known as Mastorin, is an investigational selective androgen receptor modulator (SARM) developed by GTX, Inc as a potential male hormonal contraceptive. It binds to the androgen receptor more strongly than older drugs such as andarine with a Ki of 1.7 nM, and in animal studies it showed both a good ratio of anabolic to androgenic effects, and dose-dependent suppression of spermatogenesis with spontaneous recovery after cessation of treatment.[1][2] It was encountered as a novel designer drug by 2020.[3]

1. ↑ Marhefka CA, Gao W, Chung K, Kim J, He Y, Yin D, et al. (February 2004). "Design, synthesis, and biological characterization of metabolically stable selective androgen receptor modulators". Journal of Medicinal Chemistry. 47 (4): 993–8. doi:10.1021/jm030336u. PMC 2040239. PMID 14761201.
2. ↑ Jones A, Chen J, Hwang DJ, Miller DD, Dalton JT (January 2009). "Preclinical characterization of a (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide: a selective androgen receptor modulator for hormonal male contraception". Endocrinology. 150 (1): 385–95. doi:10.1210/en.2008-0674. PMC 2630904. PMID 18772237.
3. ↑ "Масторин (S-23)". АИПСИН (in Russian). Retrieved 2 January 2026.