Novel pathway for the synthesis of arylpropionamide-derived selective androgen receptor modulator (SARM) metabolites of andarine and ostarine

Article abstract of DOI:10.1016/j.tetlet.2013.02.065

O-Dephenylandarine and O-dephenylostarine, two SARM metabolites relevant for doping control analysis, were synthesized in their endogenous (S)-forms as well as in terms of their racemates. The enantiopure (S)-metabolites were obtained after six steps in 20% and 23% overall yield, the slightly modified racemic route provided the compounds in 28% and 31% total yield, respectively.

Full text of DOI:10.1016/j.tetlet.2013.02.065

Tetrahedron Letters 54 (2013) 2239–2242
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Novel pathway for the synthesis of arylpropionamide-derived selective
androgen receptor modulator (SARM) metabolites of andarine and ostarine
Katharina M. Schragl a, Guro Forsdahl b, Guenter Gmeiner b, Valentin S. Enev a, , Peter Gaertner a,
⇑
⇑
a Institute of Applied Synthetic Chemistry, Vienna University of Technology, 1060 Vienna, Austria
b Doping Control Laboratory, Seibersdorf Labor GmbH, 2444 Seibersdorf, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
O-Dephenylandarine and O-dephenylostarine, two SARM metabolites relevant for doping control analy-
sis, were synthesized in their endogenous (S)-forms as well as in terms of their racemates. The enantio-
pure (S)-metabolites were obtained after six steps in 20% and 23% overall yield, the slightly modified
racemic route provided the compounds in 28% and 31% total yield, respectively.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 3 December 2012
Revised 18 February 2013
Accepted 20 February 2013
Available online 27 February 2013
Keywords:
Selective androgen receptor modulators
Andarine/ostarine metabolites
Arylpropionamides
Amide bond formation
Selective androgen receptor modulators (SARMs) have been
intensively investigated during the past decade, because of their
potential ability to replace anabolic–androgenic steroids in the
treatment of hypogonadism, muscle wasting, osteoporosis, or be-
nign prostatic hyperplasia. By showing the same effectiveness in
activating the androgen receptor, nonsteroidal SARMs seem to be
more tolerable concerning undesirable side effects as a result of
their markedly high selectivity to muscle and bone tissue.1–6
These promising first results inevitably also attracted athletes,
seeking enhanced physical performance and strength, willing to
achieve their goals even illegally by the misuse of drugs. Although
by now none of the lead candidates has received clinical approval,
the availability of andarine (S-4) (2a) via the internet as well as its
actual in-competition administration, resulting in an adverse ana-
lytical finding, has been reported.7–10 Accordingly, the whole class
of SARMs has been included in the list of prohibited substances by
the World Anti-Doping Agency (WADA) since 2008.
Andarine and structurally closely related ostarine (also referred
to as S-22) (2b) belong to the class of arylpropionamide-based
SARMs, which are structurally derived from the anti-androgen
bicalutamide (1) (Scheme 1). The latter was first synthesized by
Tucker et al.11–15 For the detection of SARMs for doping control
purposes, reference material in terms of the most abundant urinary
metabolites is needed. Possible targets for doping analysis were re-
vealed by a series of metabolism studies including in vitro and ani-
mal/human in vivo data.16–22 Besides other phase-I modifications
both drug candidates undergo hydrolysis of the ether linkage
resulting in the dephenylated molecules 3a and 3b. Due to
phase-II glucuronidation also the corresponding conjugates are de-
tected in human urine specimens after oral administration of
SARMs S-4 and S-22, respectively.21,22 Accordingly these glucuron-
ides have to be hydrolyzed prior to analysis. In 2008 Thevis and co-
workers synthesized andarine’s major metabolite O-dephenyland-
arine (3a).23
Herein, we want to present a new, simple route for the efficient
preparation of O-dephenylandarine (3a) and O-dephenylostarine
(3b). These metabolic products of 2a and 2b represent valuable ref-
erence substances, allowing the unequivocal proof of illicit SARM
administration by athletes (Scheme 1).
Based on the fact, that reference substances for routine doping
control purposes do not have to fulfill the criterion of enantiopuri-
ty, we first concentrated on the preparation of racemic 3a and 3b.
We succeeded in creating a short, highly cost-effective way, which
provides rac-3a in 28% and rac-3b in 31% yield over five reaction
steps (Scheme 2). The synthesis of racemic metabolites starts with
the epoxidation of methacrylic acid 4, with mCPBA24 to give rac-5
in 70% yield. The following formation of the amide bond between
rac-5 and anilines 6 represents the key step in the formation of
the arylpropionamide core structure. Our first attempts to achieve
this via activation of epoxy acid with isobutyl chloroformate,25
Yamaguchi reagent (2,4,6-trichlorobenzoyl chloride),26 or with
TBTU27 failed and resulted in a total loss of the starting material.
Most probably the lack of reaction is due to the poor
⇑
Corresponding authors. Tel.: +43 1 58801 163734; fax: +43 1 58801 16399
(V.S.E.); tel.: +43 1 58801 15421; fax: +43 1 58801 15492 (P.G.).
E-mail addresses: valentin.enev@tuwien.ac.at (V.S. Enev), peter.gaertner@
tuwien.ac.at (P. Gaertner).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.02.065

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K. M. Schragl et al. / Tetrahedron Letters 54 (2013) 2239–2242
NC
F
O
O
S
∗
F3C
N
H
OH
O
bicalutamide (Casodex) (1)
R1
R2
R1
O
O
F3C
N
H
O
F3C
N
H
OH
OH
OH
andarine (2a): R1 = NO2, R2 = NHAc
ostarine (2b): R1 = CN, R2 = CN
(S)-O-dephenylandarine (3a) : R1 = NO2
(S)-O-dephenylostarine (3b): R1 = CN
Scheme 1. Chemical structures of bicalutamide and the urinary metabolites of andarine and ostarine.
Scheme 2. Synthesis of racemic O-dephenylandarine and O-dephenylostarine.
nucleophilicity of the aromatic amino group, which is additionally
deactivated by the electron-withdrawing nitro or cyano substitu-
ent. Finally, according to the Crich procedure28, the DIPEA-salt of
epoxy acid rac-5 was reacted with in situ generated isocyanates
729 to give intermediate 8 which after decarboxylation yielded
the desired epoxyamide rac-9 together with the corresponding
chlorohydrins rac-10. The formation of the latter could be ex-
plained by the presence of chloride ions in the reaction mixture
due to the application of triphosgene. Conversion of rac-10 to
rac-9 was easily achieved by treatment of the corresponding chlo-
rohydrine with DBU to give rac-9a and rac-9b, respectively, in good
yields over three steps. For the epoxide opening reaction several

K. M. Schragl et al. / Tetrahedron Letters 54 (2013) 2239–2242
2241
Scheme 3. Synthesis of (S)-O-dephenylandarine and (S)-O-dephenylostarine.
conditions were screened. Where the reaction of rac-9 with 2 N
References and notes
NaOH led to amide cleavage, various acidic reagents proved to be
efficient. The best results were obtained by refluxing of rac-9 in a
DMF/water mixture30 to give rac-O-dephenylandarine (3a) in 75%
yield and rac-O-dephenylostarine (3b) in 72% yield.
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ee).33
Comparison of these synthetic metabolites with excretion sam-
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ine specimens after oral administration of SARMs S-4 and S-22,
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(S)-compounds. Starting from isotopically labeled educts, either
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Acknowledgment
27. Ballet, S.; Feytens, D.; Buysse, K.; Chung, N. N.; Lemieux, C.; Tumati, S.;
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29. The isocyanates were obtained by following a modified procedure of Glorius;
see: Willwacher, J.; Rakshit, S.; Glorius, F. Org. Biomol. Chem. 2011, 9, 4736–
4740.
We wish to thank Professor Egon Erwin Rosenberg (Vienna Uni-
versity of Technology) for performing the HRMS-measurements.
Supplementary data
30. Jiang, J. L.; Xiu, Z.; Hua, R. Synth. Commun. 2008, 38, 232–238.
31. Gao, Y.; Hanson, R. M.; Klunder, J. M.; Ko, S. Y.; Masamune, H.; Sharpless, K. B. J.
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Supplementary data (experimental procedure and spectral
data) associated with this article can be found, in the online ver-
sion, at http://dx.doi.org/10.1016/j.tetlet.2013.02.065.
32. Shao, H.; Zhu, Q.; Goodman, M. J. Org. Chem. 1995, 60, 790–791.

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35
33. Enantiomeric excess was determined by the Mosher ester method; see: Dale, J.
A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969, 34, 2543–2549.
34. Selected data
Compound (S)-3b: mp 113–115 °C. ½ ꢀ ꢁ 28:1 (c 0.585, MeOH) [lit.
a 2D0
½
a 2D1
ꢀ
ꢁ 42:2 (c 0.945, MeOH), 100% ee]. 1H NMR (400 MHz, CD3OD): d = 8.37
(1H, s, HAr), 8.10 (1H, d, J = 8.5 Hz, HAr), 7.91 (1H, d, J = 8.5 Hz, HAr), 3.85 (1H, d,
2J = 11.1 Hz, HO–CH2), 3.52 (1H, d, 2J = 11.1 Hz, HO–CH2), 1.38 (3H, s, Me). 13C
NMR (100 MHz, CD3OD): d = 177.0 (q, C@O), 144.1 (q, CAr), 137.1 (t, CAr), 134.2
Compound (S)-3a: mp 119–120 °C. ½a D20
ꢀ
ꢁ 21:2 (c 0.480, MeOH). 1H NMR
(400 MHz, CD3OD): d = 8.37 (1H, d, J = 2.2 Hz, HAr), 8.14 (1H, dd, J = 8.9 and
2.2 Hz, HAr), 8.03 (1H, d, J = 8.9 Hz, HAr), 3.85 (1H, d, 2J = 11.1 Hz, HO–CH2), 3.53
(1H, d, 2J = 11.1 Hz, HO–CH2), 1.39 (3H, s, Me). 13C NMR (100 MHz, CD3OD):
d = 177.0 (q, C@O), 144.2 (q, CAr), 143.9 (q, CAr), 127.9 (t, CAr), 125.3 (q,
2
1
(q, JCF = 32.4 Hz, CAr), 123.9 (q, JCF = 272.9 Hz), 123.7 (t, CAr), 118.7 (t,
3JCF = 5.1 Hz), 116.7 (q, CN), 104.6 (q, CAr), 77.6 (q, C(Me)), 69.4 (t, HO–CH2),
22.6 (s, Me). IR (neat): 3447 (NH, OH), 3298 (OH), 2226 (CN), 1688 (CO), 1504,
1325, 1124, 1049, 620 cmꢁ1. HRMS (ESI): m/z [MꢁH]ꢁ calcd for C12H11F3N2O3:
287.0649; found: 287.065.
1
3
2JCF = 33.7 Hz), 124.1 (t, CAr), 123.5 (q, JCF = 271.7 Hz), 119.6 (t, JCF = 5.9 Hz),
77.6 (q, C(Me)), 69.4 (t, HO–CH2), 22.6 (s, Me). IR (neat): 3448 (NH, OH), 3305
(OH), 1686 (CO), 1527 (NO), 1320 (NO), 1141, 1044, 901, 759 cmꢁ1. HRMS
(ESI): m/z [MꢁH]ꢁ calcd for C11H11F3N2O5: 307.0547; found: 307.0554.
35. Fujino, A.; Asano, M.; Yamaguchi, H.; Shirasaka, N.; Sakoda, A.; Ikunaka, M.;
Obata, R.; Nishiyama, S.; Sugai, T. Tetrahedron Lett. 2007, 48, 979–983.