Discovery of orally available tetrahydroquinoline-based glucocorticoid receptor agonists

Article abstract of DOI:10.1016/j.bmcl.2011.01.093

A series of tetrahydroquinoline derivatives were synthesized and profiled for their ability to act as glucocorticoid receptor selective modulators. Structure-activity relationships of the tetrahydroquinoline B-ring lead to the discovery of orally availabl

Full text of DOI:10.1016/j.bmcl.2011.01.093

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1697–1700
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of orally available tetrahydroquinoline-based glucocorticoid
receptor agonists
⇑
Andrew R. Hudson , Robert I. Higuchi, Steven L. Roach, Mark E. Adams, Angela Vassar,
Peter M. Syka, Dale E. Mais, Jeffrey N. Miner, Keith B. Marschke, Lin Zhi
Discovery Research, Ligand Pharmaceuticals, 11085 North Torrey Pines Road, Suite 300, La Jolla, CA 92037, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of tetrahydroquinoline derivatives were synthesized and profiled for their ability to act as
glucocorticoid receptor selective modulators. Structure–activity relationships of the tetrahydroquinoline
B-ring lead to the discovery of orally available GR-selective agonists with high in vivo activity.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 24 November 2010
Revised 19 January 2011
Accepted 20 January 2011
Available online 26 January 2011
Keywords:
Glucocorticoid
SGRM
SEGRA
Hormone
Tetrahydroquinoline
Prednisolone
Dexamethasone
Glucocorticoids (GCs) such as prednisolone 1 and dexametha-
sone 2 (Fig. 1) are effective treatments for the signs and symptoms
of inflammation.1,2 However severe side-effects associated with
chronic GC treatment, which include osteoporosis and hyperglyce-
mia, can limit long-term use.3 The glucocorticoid receptor (GR) is a
member of the nuclear receptor superfamily that includes steroid
hormone receptors androgen (AR), estrogen (ER), mineralocorti-
coid (MR) and progesterone (PR).4 Upon ligand binding, GR is able
to modulate gene transcription by directly binding to specific DNA
sequences within genes. Such transcriptional activation (TA) is
thought to be important for the regulation of glucose homeostasis
in the liver and may be responsible for several side-effects associ-
ated with chronic GC use.5,6 Alternatively, the receptor can directly
repress transcription by modulating the activity of inflammatory
highly selective for GR and demonstrated in vitro activity similar
to prednisolone (Fig. 1).
A liability of compound 3 that rendered it unsuitable for in vivo
profiling was poor hepatic microsomal stability. Compound 3
underwent rapid metabolism upon incubation with both human
(HLM) or rat liver microsomes (RLM) exhibiting a short half life
of <5 min.15 Here-in we describe SAR studies focused on the B-ring
of 3 in an effort to improve microsomal stability while retaining
high TR activity and GR selectivity. Such studies would help
OH
OH
O
O
HO
HO
OH
OH
mediators including NFjB and AP-1, the basis for the beneficial
H
H
Me
anti-inflammatory activity of GCs. Identifying GCs that are able
to separate transrepression (TR) from transactivation (TA) is an ac-
tive area of interest.7–13
We have previously disclosed a series of tetrahydroquinoline-
based non-steroidal glucocorticoid receptor agonists.14 Preliminary
optimization of both the C-6 aryl group and tetrahydroquinoline A-
ring lead to compound 3, a non-steroidal GC agonist which was
H
H
F
H
O
O
1
2
NH
Cl
Me
OH
Me
6
B
A
N
H
Me
Me
3
⇑
Corresponding author.
E-mail address: andyrhudson@gmail.com (A.R. Hudson).
Figure 1. Steroidal and tetrahydroquinoline-based glucocorticoids.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.093

1698
A. R. Hudson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1697–1700
R5
R8
R5
The GR-mediated activity of the compounds was evaluated in a
R5
R8
number of biological assays. GR binding was determined using a
radiolabeled dexamethasone competitive binding assay with bacu-
lovirus-expressed GR.16 Direct TA by GR was measured in a
cotransfection (CTF) assay using an MMTV:luciferase reporter.17
TR activity was determined using a CTF E-selectin18 repression as-
say in HepG2 cells to determine repression of transcriptional acti-
OH
a
b
c
R7
N
H
R7
NH2
R7
N
H
R8
4
5
6
NH
R5
R5
Br
R7
OH
d
OH
vation mediated by NFj
B or AP-1.15 Compounds were also profiled
B
A
N
H
in an IL-6 ELISA assay12 to determine inflammatory cytokine
repression in primary neonatal human dermal fibroblast (NHDF)
cells as a further measurement of TR activity.
R7
N
H
R8
R8
8-31
7
Compounds within the series were synthesized as depicted
in Scheme 1. Skraup reaction19 of substituted aniline 4 followed
by hydroboration-oxidation gave racemic tetrahydroquinoline 6
as a single regioisomer. C-6 bromination followed by Suzuki
coupling with 1H-indol-7-ylboronic acid gave the desired ana-
logs 8–31.20 Starting from a variety of substituted anilines 4
we were able to access analogs with varied B-ring substitution
patterns.
Scheme 1. Representative synthetic route. Reagents and conditions: (a) Iodine,
acetone, 120 °C, sealed tube, 15 h; (b) BH3-THF, THF, then KOH, H2O2; (c) NBS,
CHCl3; (d) Pd(PPh3)4, 1H-indol-7-ylboronic acid, 2:1 PhMe/EtOH, 2 N Na2CO3,
100 °C, 15 h.
evaluate the suitability of the tetrahydroquinoline-based scaffold
for further SAR investigation and to aid profiling of representative
analogs in vivo.
Table 1
In vitro assay results for selected glucocorticoid receptor modulatorsa
Compd
R5
R7
R8
GR binding Ki (nM)
GRE activation agonist mode
E-Selectin repression
IL-6 repression
EC50 (nM)
Eff. (%)
IC50 (nM)
Eff. (%)
IC50 (nM)
Eff. (%)
1
3
8
9
10
11
Prednisolone
Cl
H
F
Me
Et
5.3 0.3
1.7 0.4
9.0
2.3 0.3
1.2 0.2
11.7
5.3 0.6
7.1 4.8
108 34
56 33
0.9 0.6
16 1.0
129 6.5
144 5.9
161 29
123 14
97 11
4.1 0.8
1.1 0.2
21 13
5.9 2.1
4.7 2.2
15 3.2
100 1.4
95 6.8
83 0.1
88 4.6
103 2.1
93 0.1
23 2.6
7.8 1.8
—
7.1 1.1
9.3 4.0
—
97 0.7
81 2.7
—
75 5.4
97 1.1
—
H
H
H
H
H
Me
Me
Me
Me
Me
169 25
12
13
14
H
H
H
Me
Me
Me
319
6.9
1.5
105 45
0.4 0.2
0.2 0.1
160 49
120 4.6
130 20
11 1.1
1.7 1.1
0.9 0.4
82 10
107 1.8
106 2.3
—
—
4.2 2.5
3.4 1.1
94 3.0
95 2.0
15
H
Me
6.0
34
122
5.5 1.7
95 4.7
3.8
68
16
17
H
H
Me
Me
3.5
3.7 1.7
40 12
127 3.3
152 29
3.1 1.2
—
94 6.7
—
14.4
—
51
—
19.6
18
19
H
H
Me
Me
16.6
1.3
5.7 0.9
9.6 3.1
120 1.3
173 18
6.5 0.5
5.3 0.8
95 8.1
96 1.2
16 15
16 2.2
78 14
64 5.9
CN
20
H
Me
10.4
112 40
168 62
7.8 7.1
84 0.9
—
—
21
22
23
24
25
26
27
28
29
30
31
H
H
H
H
H
Cl
H
F
Cl
F
Me
CF3
CHCH2
H
F
F
F
Me
Me
Me
Me
Me
F
F
F
Cl
H
1.8
36 17
40 29
205 92
—
18 0.6
89 17
11 4.6
16 10
1.3 0.1
480 0.4
0.6 0.2
134 17
162 29
165 45
—
110 12
126 7.7
193 49
156 17
139 7.6
100 8.3
138 16
21 19
1.7 0.3
42 19
—
13 4.2
17 1.6
7.7 1.3
3.8 1.0
3.9 1.3
301 38
1.5 0.7
96 3.5
97 1.1
79 1.1
—
91 1.4
86 3.0
95 1.3
89 3.8
97 2.8
72 0.1
100 2.7
26 9.4
4.1 1.7
—
—
—
82 4.8
64 6.3
—
—
—
0.9 0.8
38.3
106
3.1
8.0
2.4
5.0
1.0
157
14
56
20 0.1
19 3.1
16 3.0
—
44 2.9
68 4.6
52 6.6
—
F
Cl
F
Cl
F
H
2.5 1.0
11 5.6
90 2.3
a
EC50 and IC50 values determined from half-log concentration response curves. Agonist efficacies are represented as the percentage maximal response in comparison to
dexamethasone (100%). E-selectin repression efficacies are represented as a percent of maximal inhibition of the response induced by TNF and IL-1b. IL-6 repression
efficacies represent the percent of maximal inhibition of the response induced by IL-1b. Standard errors (SEM) represent the mean value of at least three separate experiments
with triplicate determinations. If no SEM is noted, value is from a single determinant. A hyphen (—) = not active and denotes <20% efficacy or potency >1 M.
a
l

A. R. Hudson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1697–1700
1699
Initially we assessed the importance of the C-5 chlorine atom of
3. Analog 8 (R5 = R7 = H, R8 = Me) exhibited greatly diminished
activity in both the GRE activation and E-selectin assay (Table 1).
Furthermore, the compound had no measurable IL-6 repression
activity. In contrast R5-substituted analogs 9 (R5 = F), 10 (R5 =
Me) and 11 (R5 = Et) demonstrated similar IL-6 repression activity
to compound 3. However both 10 (R5 = Me) and 11 (R5 = Et) lead to
the generation of distinct interconverting atropisomers.21 In an
effort to eliminate atropisomers we turned our attention to less
sterically demanding R5 groups that reduced the propensity to re-
strict rotation around the biaryl axis. Skraup reaction product
5 (R5 = Cl, R7 = H, R8 = Me) underwent aryl cyanation22 followed
by hydroboration–oxidation and subsequent nitrile reduction to
yield aldehyde 6 (R5 = CHO R7 = H, R8 = Me) which was reacted
with a number of hydroxylamines to probe steric tolerance at R5.
Oxime analog 12 was inactive in the IL-6 TR assay despite activity
in the E-selectin assay. Methyl-(13) and ethyl-(14) oxime analogs
were fully efficacious in both E-selectin and IL-6 repression assays
with potencies superior to steroidal GC prednisolone. These com-
pounds also avoided the added complication of atropisomerism.
Bulkier O-substituted oximes such as t-Bu (15) or benzyl (16) were
fully efficacious and potent in the E-selectin assay but showed re-
duced efficacy in the repression of IL-6 (68% and 51%, respectively).
Aldehyde 7 (R5 = CHO R7 = H, R8 = Me) underwent reaction with a
variety of phosphonium salts to introduce unsaturation at R5.23
Terminal alkene 17 showed no TR activity. Conjugated nitrile 18
One solution to this synthetic difficulty was to limit ourselves to
symmetrical anilines. We speculated that substitution at R7 in
conjunction with R5 should improve microsomal stability while
maintaining high GR-mediated activity. Skraup reaction of 3,5-
difluoro- or 3,5-dichloroaniline gave the corresponding dihydro-
quinoline product 5 (R5 = R7 = F or Cl) in acceptable yield (35% and
44%, respectively) which were subsequently processed to the target
compounds (Scheme 1). Compound 30 (R5 = R7 = Cl) showed very
weak GR-mediated activity. In contrast 31 (R5 = R7 = F) was fully effi-
cacious and potent in the E-selectin repression assay with activity in
the IL-6 repression assay similar to prednisolone (Table 1). Impor-
tantly the stability of 31 was substantially improved (Table 2) over
earlier analogs.
We had previously described how relatively minor structural
changes within the scaffold can greatly alter hormone receptor
selectivity, thus cross-reactivity was closely monitored through-
out.12 Several compounds described within this study bound with
low nM potency to GR (Table 1). Generally alterations in the B-ring
had modest effects on receptor selectivity. Compound 31 retained
high receptor selectivity with >500 fold separation in binding to GR
(Ki = 2.5 nM) over PR (2100 nM), MR (1520 nM) or AR (1430 nM).
Analogs such as 21 (R7 = Cl) showed more pronounced binding
affinity to PR (190 nM) but separation in binding affinities re-
mained >100 fold.
High TR activity and GR selectivity coupled with improved
microsomal stability rendered 31 a suitable candidate for in vivo
profiling. A single-dose PK study of 31 demonstrated systemic
exposure upon oral administration in SD rats (30 mg/kg, AUC =
had activity comparable to nitrile 19 whereas
a,b-unsaturated
ketone 20 was inactive in the IL-6 repression assay. Throughout
the SAR study of the R5 position microsomal stability was moni-
tored and found to be poor. Only nitrile analog 19 exhibited a
marginally longer half-life compared to compound 3 (Table 2). Fur-
thermore, incremental improvements in compound potency upon
increasing steric bulk at R5 came at the expense of substantial in-
creases in molecular weight and compound lipophilicity.
35 3.3 lg h/mL, Cmax 3.6 0.6 lg/mL, apparent t1/2 = 3.2 0.7 h).
Compound 31 was subsequently profiled in a carrageenan-induced
paw edema (CPE) inflammation model.25 Acute edema was in-
duced by injection of pro-inflammatory agent carrageenan into
the hind paw of a rat. Compound 31 was given orally and paw vol-
ume measured 3 h later as an indication of anti-inflammatory
activity (Fig. 2). Compound 31 was fully efficacious and potent in
this model showing reduction in paw swelling back to no edema
levels with an ED50 of 6.6 mg/kg.
In conclusion SAR studies centered around the tetrahydroquin-
oline B-ring lead to the identification of non-steroidal GCs that
maintained high TR activity and GR selectivity but improved
hepatic microsomal stability. Substitution at R5 was important
for GR-mediated activity while derivatization at R7 necessary for
improved microsomal stability. In vivo characterization of repre-
sentative analog 31 via oral administration demonstrated full effi-
cacy in an acute model of inflammation with carrageenan-induced
swelling fully reversed after 3 h. Future studies that characterize
TR and TA activities based upon this chemical scaffold will follow.
We turned our attention to examine substitution at the R7 posi-
tion of the tetrahydroquinoline core. Switching the position of the
B-ring chlorine atom from R5 to R7 (21) lead to retention of high
GR-mediated activity. Analog 22 (R7 = F) was fully efficacious and
potent in the E-selectin assay but had diminished activity in the
repression of IL-6, consistent with previous analogs lacking
substitution at R5. Other R7-substituted analogs 23 (R7 = Me), 24
(R7 = CF3) and 25 (R7 = CH = CH2) had no activity in the IL-6 repres-
sion assay suggesting limited potential for further modification.
Importantly however both 21 and 22 showed improvement in
RLM and HLM (Table 2) compared to their R5-substituted
counterparts.
Replacement of R8 methyl group with fluorine (26) lead to sub-
stantially reduced TR activity, particularly in the IL-6 repression as-
say. Microsomal stability half-life for compound 26 was also low
(Table 2). R8-F analogs 27 and 28 also showed reduced efficacy in
the repression of IL-6. R8-Cl analog 29 was fully efficacious in
E-selectin but showed only partial efficacy (52%) in the IL-6 repres-
sion assay. Removal of the R8-Me group altogether lead to regioiso-
meric products24 of the modest yielding Skraup reaction requiring
separation by preparative HPLC and was not pursued further.
1.0
0.8
0.6
0.4
Table 2
Rat and human microsomal stability data for select compounds15
*
Vehicle
No Edema
Prednisolone
*
*
*
0.2
0.0
*
Compd
RLM t1/2 (min)
HLM t1/2 (min)
3
3.3
13
25
16
3.8
30
4.7
13
21
17
15
48
0.01 0.1
1
10
100
19
21
22
26
31
Compound 31 (mg/kg p.o)
Figure 2. In vivo anti-inflammatory activity of compound 31 in
a CPE mod-
el.⁄P <0.05 versus vehicle. Compound 31 ED50 6.6 mg/kg (95% confidence level ED50
4.7—9.2 mg/kg).

1700
A. R. Hudson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1697–1700
13. Takahashi, H.; Bekkali, Y.; Capolino, A. J.; Gilmore, T.; Goldrick, S. E.; Kaplita, P.
References and notes
V.; Liu, L.; Nelson, R. M.; Terenzio, D.; Wang, J.; Zuvela-Jelaska, L.; Proudfoot, J.;
Nabozny, G.; Thompson, D. Bioorg. Med. Chem. Lett. 2007, 17, 5091.
14. (a) Roach, S. L.; Higuchi, R. I.; Adams, M. E.; Liu, Y.; Karanewsky, D. S.;
Marschke, K. B.; Mais, D. E.; Miner, J. N.; Zhi, L. Bioorg. Med. Chem. Lett. 2008, 18,
3504; (b) Roach, S. L.; Higuchi, R. I.; Hudson, A. R.; Adams, M. E.; Syka, P. M.;
Mais, D. E.; Miner, J. N.; Marschke, K. B.; Zhi, L. Bioorg. Med. Chem. Lett. 2011, 21,
168.
15. Rat (CD-1, male) and human (mixed gender) liver microsomes were purchased
from BD Gentest (Franklin Lakes, NJ). Liver microsomal incubations were
conducted in triplicate. The incubation mixtures consisted of liver microsomes
1. Ali, S. L. Anal. Profiles Drug Subst. Excipients 1992, 21, 415.
2. Cohen, E. M. Anal. Profiles Drug Subst. 1973, 2, 163.
3. For recent reviews see (a) De Bosscher, K.; Haegeman, G. Mol. Endocrinol. 2010,
23, 281; (b) Schacke, H.; Berger, M.; Hansson, T. G.; McKerrecher, D.;
Rehwinkel, H. Expert Opin. Ther. Patent 2008, 18, 339; (c) Hudson, A. R.;
Roach, S. L.; Higuchi, R. I. Curr. Top. Med. Chem. 2008, 8, 750; (d) Takahashi, H.;
Razavi, H.; Thomson, D. Curr. Top. Med. Chem. 2008, 8, 521.
4. (a) Evans, R. M. Science 1988, 240, 889; (b) Rosen, J.; Day, A.;
Jones, T. K.; Jones, E. T. T.; Nadzan, A. M.; Stein, R. B. J. Med. Chem. 1995, 38,
4855.
5. Adcock, I. M.; Barnes, P. J. Biochem. Soc. Trans. 1996, 24, 267S.
6. Schacke, H.; Docke, W. D.; Asdullah, K. Pharmacol. Ther. 2002, 96,
23.
7. (a) Kym, P. R.; Kort, M. E.; Coghlan, M. J.; Moore, J. L.; Tang, R.; Ratajczyk, J. D.;
Larson, D. P.; Elmore, S. W.; Pratt, J. K.; Stashko, M. A.; Falls, H. D.; Lin, C. W.;
Nakane, M.; Miller, L.; Tyree, C. M.; Miner, J. N.; Jacobson, P. B.; Wilcox, D. M.;
Nguyen, P.; Lane, B. C. J. Med. Chem. 2003, 46, 1016; (b) Elmore, S. W.; Pratt, J.
K.; Coghlan, M. J.; Mao, Y.; Green, B. E.; Anderson, D. D.; Stashko, M. A.; Lin, C.
W.; Falls, D.; Nakane, M.; Miller, L.; Tyree, C. M.; Miner, J. N.; Lane, B. Bioorg.
Med. Chem. Lett. 2004, 14, 1721.
8. Schäcke, H.; Schottelius, A.; Döcke, W.-D.; Strehlke, P.; Jaroch, S.; Schmees, N.;
Rehwinkel, H.; Hennekes, H.; Asadullah, K. Proc. Natl. Acad. Sci. 2004, 101,
227.
9. (a) Thompson, C. F.; Quraishi, N.; Ali, A.; Mosley, R. T.; Tata, J. R.; Hammond, M.
L.; Balkovec, J. M.; Einstein, M.; Ge, L.; Harris, G.; Kelly, T. M.; Mazur, P.; Pandit,
S.; Santoro, J.; Sitlani, A.; Wang, C.; Williamson, J.; Miller, D. K.; Yamin, T. T.;
Thompson, C. M.; O’Neill, E. A.; Zaller, D.; Forrest, M. J.; Carballo-Jane, E.; Luell,
S. Bioorg. Med. Chem. Lett. 2007, 17, 3354; (b) Shah, N.; Scanlan, T. S. Bioorg. Med.
Chem. Lett. 2004, 14, 5199.
10. (a) Barker, M.; Clackers, M.; Copley, R.; Demaine, D. A.; Humphreys, D.; Inglis,
G. G. A.; Johnston, M. J.; Jones, H. T.; Haase, M. V.; House, D.; Loiseau, R.; Nisbet,
L.; Pacquet, F.; Skone, P. A.; Shanahan, S. E.; Tape, D.; Vinader, V. M.;
Washington, M.; Uings, I.; Upton, R.; McLay, I. M.; MacDonald, S. J. F. J. Med.
Chem. 2006, 49, 4216–4231; (b) Betageri, R.; Zhang, Y.; Zindell, R. M.; Kuzmich,
D.; Kirrane, T. M.; Bentzien, J.; Cardozo, M.; Capolino, A. J.; Fadra, T. N.; Nelson,
R. M.; Paw, Z.; Shih, D.-T.; Shih, C.-K.; Zuvela-Jelaska, L.; Nabozny, G.; Thomson,
D. S. Bioorg. Med. Chem. Lett. 2005, 15, 4761.
11. (a) Regan, J.; Lee, T. W.; Zindell, R. M.; Bekkali, Y.; Bentzien, J.; Gilmore, T.;
Hammach, A.; Kirrane, T. M.; Kukulka, A. J.; Kuzmich, D.; Nelson, R. M.;
Proudfoot, J. R.; Ralph, M.; Pelletier, J.; Souza, D.; Zuvela-Jelaska, L.; Nabozny,
G.; Thomson, D. S. J. Med. Chem. 2006, 49, 7887; (b) Biggadike, K.; Boudjelal, M.;
Clackers, M.; Coe, D. M.; Demaine, D. A.; Hardy, G. W.; Humphreys, D.; Inglis, G.
G. A.; Johnston, M. J.; Jones, H. T.; House, D.; Loiseau, R.; Needham, D.; Skone, P.
A.; Uings, I.; Veitch, G.; Weingarten, G. G.; McLay, I. M.; MacDonald, S. J. F. J.
Med. Chem. 2007, 50, 6519.
(0.5 mg microsomal protein/mL), test article (1
lM), MgCl2 (3 mM),
alamethicin (50 g/mg microsomal protein), NADPH-generating system
l
(1 mM NADP, 5 mM glucose-6-phosphate, 1 U/mL glucose-6-phosphate
dehyrogenase), and UDPGA (5 mM) in a total volume of 0.5 mL potassium
phosphate buffer (15 mM, pH 7.4). The metabolic reaction was initiated by the
addition of cofactor (NADPH-generating system and UDPGA) and carried out in
a 37 °C water bath. At 0, 5, 10, and 20 min after incubation, a 60
the sample was withdrawn. The enzyme reaction was stopped by mixing the
60 aliquot with ice-cold acetonitrile (300 L) including an analytical
lL aliquot of
lL
l
internal standard. The mixtures were centrifuged for 30 min at 3000 rpm at
4 °C, and analysis of the supernatant was performed by HPLC-MS/MS (API4000
or API4000-QTRAP (Applied Biosystems, Foster City, CA)). In vitro metabolic
half-life was calculated using the percent remaining of test article versus the
time elapsed.
16. (a) Elmore, S. W.; Coghlan, M. J.; Anderson, D. D.; Pratt, J. K.; Green, B. E.; Wang,
A. X.; Stashko, M. A.; Lin, C.-W.; Tyree, C. M.; Miner, J. N.; Jacobson, P. B.;
Wilcox, D. M.; Lane, B. C. J. Med. Chem. 2001, 44, 4481.
17. Guido, E. C.; Delorme, E. O.; Clemm, D. L.; Stein, R. B.; Rosen, J.; Miner, J. N. Mol.
Endocrinol. 1996, 10, 1178.
18. Thiesen, H.-J. Immunol. Methods 1997, 1, 315.
19. For a review of the Skraup quinoline synthesis see: Hudson, A. R. In Name
Reactions; Li, J. J., Ed., fourth ed.; Springer, 2009; pp 509–510.
20. All compounds were tested as racemic mixtures of a single diastereoisomer.
Previous studies have demonstrated that the activity within this series
predominates in a single enantiomer. See Ref. [14].
21. Distinct atropisomers were observed by 1H NMR (DMSO-d6). Variable
temperature 1H NMR (DMSO-d6) demonstrated that signals corresponding to
each atropisomer broaden and coalesce to a single multiplicity at temperatures
above 50 °C.
22. Conditions for the synthesis of compound 5 (R5 = CN, R7 = H, R8 = Me); Chloride
5
(R5 = Cl, R7 = H, R8 = Me), Zn(CN)2 (0.5 equiv), Pd(dba)3 (4 mol %), dppf
(8 mol %) and Zn powder (25 mol %) were heated in dry DMA (c = 0.2 M) at
150 °C for 15 h. Aqueous work-up followed by purification by flash
chromatography gave 5 in 58% yield.
23. Reagents for reaction of aldehyde
phosphonium ylides: Compound 7 (R5 = CHCH2, R7 = H, R8 = Me): MePPh3Br,
n-BuLi, THF, 0 °C, 0.5 h. Compound
(R5 = CHCH2CN, R7 = H, R8 = Me):
(OEt)2P(O)CH2CN, NaH, THF, rt, 15 h. Compound
(R5 = CHCH2C(O)Me,
R7 = H, R8 = Me): (OEt)2P(O)C(O)Me, NaH, DME, 50 °C, 3 h.
7
(R5 = CHO, R7 = H, R8 = Me) with
7
12. (a) Hudson, A. R.; Roach, S. L.; Higuchi, R. I.; Phillips, D. P.; Bissonette, R. P.;
Lamph, W. W.; Yen, J.; Li, Y.; Adams, M. E.; Valdez, L. J.; Cuervo, C.; Kallel, E. A.;
Gharbaoui, C. J.; Mais, D. E.; Miner, J. N.; Marschke, K. B.; Rungta, D.;
Negro-Vilar, A.; Zhi, L. J. Med. Chem. 2007, 50, 4699; (b) Ardecky, R. J.; Hudson,
A. R.; Phillips, D. P.; Tyhonas, J. S.; Deckhut, C.; Lau, T. L.; Li, Y.; Martinborough,
E. A.; Roach, S. L.; Higuchi, R. I.; Lopez, F. J.; Marschke, K. B.; Miner, J. N.;
Karanewsky, D. S.; Negro-Vilar, A.; Zhi, L. Bioorg. Med. Chem. Lett. 2007, 17,
4158.
7
24. Skraup reaction of 3-chloro-5-fluoroaniline gave a 32% yield of a 3:1 mixture of
tetrahydroquinoline regioisomers favoring 5 (R5 = F, R7 = Cl, R8 = H) over 5
(R5 = Cl, R7 = F, R8 = H) which required separated by preparative HPLC.
25. Walz, D. T.; Martino, M. J.; Griffin, C. L.; Misher, A. Arthritis Rheum. 1970, 42,
2060.