Highly potent growth hormone secretagogues

Article abstract of DOI:10.1016/j.bmcl.2007.04.050

During an effort to search for more potent growth hormone secretagogues, we discovered a class of compounds of which the best compound 8 was 7-fold more active in vitro than the best compound in the series we revealed before [Tata, J. R.; Lu, Z.; Jacks, T

Full text of DOI:10.1016/j.bmcl.2007.04.050

Bioorganic & Medicinal Chemistry Letters 17 (2007) 3657–3659
Highly potent growth hormone secretagogues
Zhijian Lu,a,* James R. Tata,a Kang Cheng,b Liente Wei,b
Wanda W.-S. Chan,b Bridget Butler,b Klaus D. Schleim,b
Thomas M. Jacks,b Gerard Hickeyb and Arthur A. Patchetta
aDepartment of Medicinal Chemistry, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
bDepartment of Biochemistry and Physiology, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
Received 21 February 2007; revised 11 April 2007; accepted 16 April 2007
Available online 25 April 2007
Abstract—During an effort to search for more potent growth hormone secretagogues, we discovered a class of compounds of which
the best compound 8 was 7-fold more active in vitro than the best compound in the series we revealed before [Tata, J. R.; Lu, Z.;
Jacks, T. M.; Schleim, K. D.; Cheng, K.; Wei, L.; Chan, W.-S.; Butler, B.; Tsou, N.; Leung, K.; Chiu, S.-H. L.; Hickey, G. J.; Smith,
R. G.; Patchett, A. A. Bioorg. Med. Chem. Lett. 1997, 7, 2319.]. Animal studies show that compound 8 can stimulate growth hor-
mone release at the oral dose as low as 0.06 mpk. Chemistry and biological studies are discussed.
Ó 2007 Published by Elsevier Ltd.
Growth hormone secretagogues were the subject of
intensive studies in past years due to their potential in
the clinic.1 In the previous communication, we described
a class of short acting growth hormone secretagogues
that were orally active (represented by ester
L-163,833).2 We were also interested in studying long
duration compounds that might closely mimic the natu-
ral pulsatile release of GH based on our clinic data from
MK-0677,1j another long duration secretagogue. In this
communication, we describe a series of potent long
duration spiroindane growth hormone secretagogues in
which the best compound 8 shows excellent in vitro
and in vivo activity (Fig. 1 and Scheme 1).
(50–80%). All amines RNH2 were commercially
available.
All the compounds were evaluated for their ability to
stimulate growth hormone in the rat pituitary cell as-
say.3 In our earlier article, we discussed that an ester
analog was a short acting secretagogue of GH.2 In order
to find alternative long duration GH secretagogues, we
decided to test if an amide analog in this series would
be of a longer duration of action in vivo. We first exam-
ined the primary amides. Both enantiomer 1 and 12 are
very potent. In fact, they are the most active analogs in
the respective series. The R isomer 1 is 4-fold more po-
tent than the S isomer 12. In general, the R isomers are
more active than the corresponding S isomers.
The synthesis of this class of compounds started from
chiral acid 18. Compound 18 and some related interme-
diates were discussed previously.2 Acid 18 was coupled
with benzyl alcohol to afford benzyl ester 19 in 75%
yield. Acidic cleavage of the Boc group followed by
EDC coupling with Boc-phenylpropyl amino acid gave
20 in 83% yield. Treatment of 20 with TFA and EDC
coupling of N-Boc a-methylalanine afforded compound
21 (87%). Final compounds were obtained by catalytic
hydrogenolysis and subsequent EDC coupling with
amine RNH2 and acidic cleavage of the Boc group
H
H
N
N
NH2
NH2
O
O
O
O
O
N
N
H
N
N
MeO2S
O
Keywords: Growth hormone secretagogues; Potent.
*
8
MK-0677
Figure 1. Potent growth hormone secretagogues.
Corresponding author. Fax: +1 732 594 9473; e-mail:
Zhijian_lu@merck.com
0960-894X/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2007.04.050

3658
Z. Lu et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3657–3659
NHBoc
Boc
N
Boc
N
O
N
a
b,c
BnO
HO
O
O
BnO
O
20
19
18
H
N
H
N
NH2.HCl
NHBoc
O
O
O
O
N
N
d,e
f,g,h
RHN
BnO
O
O
Scheme 1. Reagents: (a) BnOH, EDC, NMM,CH2Cl2; (b) TFA, CH2Cl2; (c) Boc-phenylpropyl amino acid, EDC, HOBT, NMM,CH2Cl2; (d) TFA,
CH2Cl2; (e) N-Boc-a-methylalanine, EDC, HOBT, NMM,CH2Cl2; (f) Pd/C, H2, MeOH; (g) RNH2, EDC, NMM,HOBT, CH2Cl2; (h) EtOAc/HCl.
In a series of R isomers, extension of the chain length re-
sults in a potency improvement. The 3-carbon straight
chain is optimal. The propyl amide 8 is as potent as
the allyl analog (10). However, the branched i-Pr amide
11 is 2-fold less potent than 8. Introduction of a terminal
hydroxyl group at the carbon chain affords very active
analogs and their potency seems insensitive to the length
change of the chain (4–6). Replacement of the hydroxyl
with methyl sulfonamide results in a better GH secreta-
gogue (7). Bulky groups like phenyl cause a drop in po-
tency (9). The S isomer series displays a similar trend
(13–17). One interesting observation is that the R iso-
mers of the amides are more active than the correspond-
ing S isomers; however, the S isomers of the esters are
more potent than the R isomers instead.2 Due to insuf-
ficient structural information at the receptor level, it was
unclear why the ester series showed a different SAR
from the amide series. Nonetheless, in general, the
amides are more active than the esters. The SAR of
these amides is summarized in Table 1. For comparison,
the data for the ester analogs can be referred to our
earlier paper.2
Table 1. SAR studies of amide analogs in the in vitro assay
H
H
N
N
NH2.HCl
NH2.HCl
O
O
O
O
N
S
N
RHN
R
RHN
O
O
Compound
R
EC50 (nM)
Compound
R
EC50 (nM)
1
2
H
Me
0.09
0.4
12
13
14
15
16
17
H
Me
0.35
3.8
3
Et
0.9
Et
2.1
4
–(CH2)2OH
–(CH2)3OH
–(CH2)4OH
–(CH2)2NHMs
Pr
0.51
0.41
0.44
0.21
0.15
1.2
–(CH2)2OH
–(CH2)3OH
–(CH2)4OH
0.45
0.85
0.73
5
6
7
8
MK-0677
L-163,833
1.5
1.0
9
Ph
Allyl
10
11
0.14
0.3
i-Pr
Data from the rat pituitary cell assay. All EC50 are normalized against our internal standards. Single data point.

Z. Lu et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3657–3659
Table 2. In vitro response of growth hormone secretagogues
3659
26–30; (b) Jungheim, L. N. 222nd ACS National Meeting,
Chicago, IL, 2001, August 26–30; (c) Nargund, R. P.; Ye,
Z.; Tata, J. R.; Lu, Z.; Barakat, K.; Hong, Q.; Bakshi, R.;
Gao, Y.; Tamvakopoulos, C.; Colwell, L.; Feighner, S.;
Hreniuk, D.; Pong, S.; Cheng, K.; Schleim, K.; Jacks, T.;
Strack, A.; Hickey, G.; Howard, A.; Van der Ploeg, L.;
Bailey, A.; Smith, R.; Patchett, A. A. 222nd ACS National
Meeting, Chicago, IL, 2001, August 26–30; (d) Carpino, P.
A.; Lefker, B. A.; Toler, S. M.; Pan, L. C.; Hadcock, J. R.;
Murray, M. C.; Cook, E. R.; Dibrino, J. N.; DeNinno, S.
L.; Chidsey-Frink, K. L.; Hada, W. A.; Inthavongsay, J.;
Lewis, S. K.; Mangano, F. M.; Mullins, M. A.; Nickerson,
D. F.; Ng, O.; Pirie, C. M.; Ragan, J. A.; Rose, C. R.; Tess,
D. A.; Wright, A. S.; Yu, L.; Zawistoski, M. P.; MacLean,
D. B.; Pettersen, J. C.; DaSilva-Jardine, P. A.; Wilson, T.
C.; Thompson, D. D. 222nd ACS National Meeting,
Chicago, IL, 2001, August 26–30; (e) Nagata, R.; Tokuna-
ga, T.; Hume, W. E.; Umezome, T.; Okazaki, K.; Ueki, Y.;
Kumagai, K.; Nagamine, J.; Seki, H.; Taiji, M.; Noguchi,
H. 222nd ACS National Meeting, Chicago, IL, 2001,
August 26–30; (f) Carpino, P. A.; Mangano, F. M.; Lefker,
B. A.; Toler, S. M.; Pan, L. C.; Cook, E. R.; Dibrino, J. N.;
Chidsey-Frink, K. L.; Hada, W. A.; Inthavongsay, J.;
Mullins, M. A.; Nickerson, D. F.; Ng, O.; Pirie, C. M.;
Rose, C. R.; Tess, D. A.; Wright, A. S.; Zawistoski, M. P.;
DaSilva-Jardine, P. A.; Thompson, D. D. 222nd ACS
National Meeting, Chicago, IL, 1999, August 23–27; (g)
Chen, M.-H.; Pollard, P. P.; Cheng, K.; Wei, L.; Chan, W.
W.-S.; Butler, B.; Jacks, T. M.; Smith, R. G.; Patchett, A.
A. Bioorg. Med. Chem. Lett. 1999, 9, 1261; (h) Shoen, W.
R.; Pisano, J. M.; Prendergast, K.; Wyvratt, M. J.; Fisher,
M. H.; Cheng, K.; Chan, W.-S.; Butler, B.; Smith, R. G.;
Ball, R. G. J. Med. Chem. 1994, 37, 897, For more recent
work in this area, see; (i) DeVita, R. J.; Bochis, R.;
Frontier, A. J.; Kotliar, A.; Fisher, M. H.; Shoen, W. R.;
Wyvratt, M. J.; Cheng, K.; Chan, W.-S.; Butler, B.; Jacks,
T. M.; Hickey, G. J.; Schleim, K. D.; Leung, K.; Chen, Z.;
Chiu, S.-H. L.; Feeney, W. P.; Cunningham, P. K.; Smith,
R. G. J. Med. Chem. 1998, 41, 1716; (j) Patchett, A. A.;
Nargund, R. P.; Tata, J. R.; Chen, M. H.; Barakat, K. J.;
Johnston, D. B. R.; Cheng, K.; Chan, W.-S.; Butler, J. B.;
Hickey, G. J.; Jacks, T. M.; Schleim, K.; Pong, S.-S.;
Chaung, L.-Y. P.; Chen, H. Y.; Frazier, E.; Leung, K. H.;
Chiu, S.-H.; Smith, R. G. Proc. Natl. Acad. Sci. U.S.A.
1995, 92, 7001; (k) Yang, L.; Morriello, G.; Leung, K.;
Jacks, T. M.; Cheng, K.; Schleim, K. D.; Smith, R. G.;
Patchett, A. A. Bioorg. Med. Chem. Lett. 1999, 9, 1761; (l)
Barakat, K. J.; Cheng, K.; Chan, W.-S.; Butler, B.; Jacks,
T. M.; Schleim, K. D.; Hora, D. F., Jr.; Hickey, G. J.;
Smith, R. G.; Patchett, A. A.; Nurgund, R. P. Bioorg. Med.
Chem. Lett. 1998, 8, 1431; (m) Nargund, R. P.; Patchett, A.
A.; Bach, M. A.; Murphy, M. G.; Smith, R. G. J. Med.
Chem. 1998, 41, 3103; (n) Nargund, R. P.; Van der Ploeg, L.
H. T. In Annual Reports In Medicinal Chemistry; Bristol, J.
A., Ed.; Academic: San Diego, 1997; Vol. 32, pp 221–230,
and references cited therein; (o) DeVita, R. J.; Wyvratt, M.
J. Drugs Fut. 1996, 21, 273.
Compound
Dog GH release
iv (mpk) po (mpk)
Respondersa
1
0.25
0.125
0.25
4/4
5/6
2
3
0.10
6/7
4/4
4
0.50 (weak)
0.06
0.125
8
MK-0677
0.01
0.025
6/6
8/10
a Doses shown represent the lowest dose where 4-fold elevations over
basal GH levels were recorded.
Five compounds in the R isomer series were evaluated
in vivo for their ability to stimulate the release of GH
in beagle dog model as summarized in Table 2. The min-
imum effective dose that caused at least a 4-fold increase
in serum GH levels was regarded as a positive response.
In general, the alkyl amides responded better than the
more polar analogs (2, 3 and 8 vs 1 and 4). Compound
8 (the propyl analog) performed the best compared to
the shorter chain analogs (Me analog 2 and Et analog
3). Another observation we had during the study of this
class of compounds was that the female animals gener-
ally responded better than the male counterpart. All
compounds tested in vivo have a long duration of
action. The GH levels remain well above the basal level
even after 2 h. In case of the short acting series, the level
of GH returned to the base line after 1.5 h.2 In the same
assay, compound 8 showed similar duration of action to
MK-0677 at 1 mpk. There was no follow-up chronic
study for these compounds. Therefore it remains unclear
whether these amide analogs would mimic the natural
pulsatile release of GH or affect IGF-I level in vivo.
Compared to MK-0677, compound 8 is 10-fold more
potent in vitro and 2-fold more potent in vivo.
In summary, a new class of potent GH secretagogues
has been reported. The best compound 8 is not only
highly potent in the rat pituitary cell assay but also
orally active at a very low dose in dogs to stimulate
growth hormone.
Acknowledgments
We would like to thank Amy Bernick for mass spec-
trometry support; and Dr. Gerard Kieczykowski and
Peter Cicala of Basic Chemistry Preparation Laboratory
for large scale synthesis of key intermediates.
2. Tata, J. R.; Lu, Z.; Jacks, T. M.; Schleim, K. D.; Cheng, K.;
Wei, L.; Chan, W.-S.; Butler, B.; Tsou, N.; Leung, K.;
Chiu, S.-H. L.; Hickey, G. J.; Smith, R. G.; Patchett, A. A.
Bioorg. Med. Chem. Lett. 1997, 7, 2319.
3. Cheng, K.; Chan, W.-S.; Barreto, A.; Convey, E. M.;
Smith, R. G. Endocrinology 1989, 124, 2791.
References and notes
1. (a) Smith, R. G.; Sun, Y.; Smith, A. G. A.; Howard, A.;
Feighner, S.; Dean, D.; Narguard, R. P.; Patchett, A. A.
222nd ACS National Meeting, Chicago, IL, 2001, August