Synthesis and human β-adrenoceptor activity of 1-(3,5-diiodo-4- methoxybenzyl)-1,2,3,4-tetrahydroisoquinolin-6-ol derivatives in vitro

Article abstract of DOI:10.1021/jm990463j

Trimetoquinol (1, TMQ) is a potent nonselective β-adrenergic receptor (AR) agonist and a thromboxane A₂/prostaglandin endoperoxide (TP) receptor antagonist, while 3',5'-diiodo-TMQ (2) exhibits β₃-AR selectivity. In search of selective β₃-AR agonists as potential drugs for the treatment of human obesity and type II diabetes mellitus, a series of 1-(3,5-diiodo-4- methoxybenzyl)-1,2,3,4-tetrahydroisoquinolin-6-ols has been prepared and evaluated for their biological activities at human β₁-, β₂-, and β₃-ARs expressed in Chinese hamster ovary (CHO) cells. The compounds have been synthesized by the Bischler-Napieralski cyclization of corresponding amides followed by NaBH₄ reduction, and the halogens in the aromatic ring A were introduced by direct halogenation of protected compound 11. Whereas halogen substitution in ring A reduced either potency or intrinsic activity on β₃- AR, the non-halogen-substituted compounds 8 and 10 were potent, selective, nearly full agonists for β₃-AR.

Full text of DOI:10.1021/jm990463j

J . Med. Chem. 2000, 43, 591-598
591
Syn th esis a n d Hu m a n â-Ad r en ocep tor Activity of 1-(3,5-Diiod o-4-
m eth oxyben zyl)-1,2,3,4-tetr a h yd r oisoqu in olin -6-ol Der iva tives in Vitr o
Yali He,† Victor I. Nikulin,† Sandeep S. Vansal,§ Dennis R. Feller,§ and Duane D. Miller*,†
Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee-Memphis, Memphis, Tennessee 38163,
and Department of Pharmacology, National Center for Natural Products Research, Research Institute of Pharmaceutical
Sciences, School of Pharmacy, University of Mississippi, University, Mississippi 38677
Received September 13, 1999
Trimetoquinol (1, TMQ) is a potent nonselective â-adrenergic receptor (AR) agonist and a
thromboxane A2/prostaglandin endoperoxide (TP) receptor antagonist, while 3′,5′-diiodo-TMQ
(2) exhibits â3-AR selectivity. In search of selective â3-AR agonists as potential drugs for the
treatment of human obesity and type II diabetes mellitus, a series of 1-(3,5-diiodo-4-
methoxybenzyl)-1,2,3,4-tetrahydroisoquinolin-6-ols has been prepared and evaluated for their
biological activities at human â1-, â2-, and â3-ARs expressed in Chinese hamster ovary (CHO)
cells. The compounds have been synthesized by the Bischler-Napieralski cyclization of
corresponding amides followed by NaBH4 reduction, and the halogens in the aromatic ring A
were introduced by direct halogenation of protected compound 11. Whereas halogen substitution
in ring A reduced either potency or intrinsic activity on â3-AR, the non-halogen-substituted
compounds 8 and 10 were potent, selective, nearly full agonists for â3-AR.
In tr od u ction
problems, including lack of â-AR selectivity, tissue
specificity, full agonist activity, drug toxicity, and a
short plasma half-life.17-19 Continuing to search for
potent and selective â3-AR agonists as potential drugs
for the treatment of obesity and NIDDM is a desirable
therapeutic goal.
Obesity results from a chronic imbalance between
energy intake from ingestion of food and energy expen-
diture by the body.1 The â3-adrenergic receptor (â3-AR)
plays a major role in mediating adipocyte lipolysis
(breakdown of fat) in white adipocyte tissue (WAT) and
thermogenesis in brown adipocyte tissue (BAT).2-6
Thermogenesis in BAT is initiated by the sympathetic
release of noradrenaline from sympathetic nerve end-
ings or treatment with â3-AR agonists which act pre-
dominantly via â3-ARs, to cause an activation of aden-
ylyl cyclase which, by increasing the concentration of
cAMP, regulates protein kinase A (PKA) and protein
phosphorylation. Active PKA stimulates a hormone-
sensitive lipase thereby releasing necessary free fatty
acids (FFAs) from the triglyceride stores in BAT and
WAT and phosphorylates cAMP response element bind-
ing protein (CREB) to increase uncoupling protein
(UCP)7 gene transcription.8,9 The FFAs act not only as
substrates for â-oxidation but also to overcome the
restraint on respiration exerted by purine nucleotides,
such as GDP, binding to UCP. Activation of UCP leads
to dissipation of the hydrogen gradient across the inner
mitochondial membrane and conversion of the gradient
energy to heat as a byproduct rather than ATP, thereby
uncoupling ATP synthesis from respiration.10,11
Our aim is to develop a compound of the tetrahy-
droisoquinoline class which possesses a high degree of
potency and selectivity for â3-AR and possesses minimal
side effects associated with an activation of the â1- and
â2-ARs. The lead compound, trimetoquinol (TMQ, 1;
Figure 1) is a potent nonselective â-AR agonist clinically
used in J apan as a bronchorelaxant.20-23 3′,5′-Diiodo-
TMQ (2; Figure 1) retains potent activity on â-AR
subtypes24 and exhibits selectivity for human â3-AR
versus â1- and â2-ARs.25 To improve the stability of
diiodo-TMQ, we focused on the modification of the
catechol moiety. The catechol portion is easily oxidized
in air, and the catechol moiety of these tetrahydroiso-
quinolines is also enzymatically unstable, being me-
tabolized by catechol O-methyltransferase (COMT). The
present study examines the structural requirements of
the aromatic A ring of diiodo-TMQ for optimum activity
at the â3-AR and investigates the effects of halogen
substituents at the 5- and/or 7-position of the 6-monophe-
nolic diiodo-TMQ system on â-AR subtypes. Compound
10 and its halogen derivatives were designed, synthe-
sized, and evaluated for their functional activities on
human â-AR subtypes. Non-catechol compound 8 (no
substituent at aromatic A ring of tetrahydroisoquinoline
system) was also synthesized and examined on â-AR
subtypes.
The identification of the â3-AR2,12 in 1983 led to
intense interest in developing selective â3-AR ago-
nists13,14 for the treatment of various metabolic diseases,
such as obesity and non-insulin-dependent diabetes
mellitus (NIDDM).15,16 Most of the previously developed
â3-AR compounds have suffered from one or more
unacceptable pharmacokinetic or pharmacodynamic
Ch em istr y
* To whom correspondence should be addressed. Tel: 901-448-7530.
Fax: 901-448-6828. E-mail: dmiller@utmem.edu.
† University of Tennessee-Memphis.
The synthesis of compounds 8 and 10 is outlined in
Scheme 1. The starting materials (phenethylamines 3
§ University of Mississippi.
10.1021/jm990463j CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/03/2000

592 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4
He et al.
dichloroiodate (BTMACl2I)28,29 to afford the iodinated
derivatives which were separated by silica gel chroma-
tography using hexanes-ethyl acetate (8:1 to 6:1) as
eluent to give compounds 12 (69%), 13 (10%), and 14
(12%). Cleavage of the TFA protecting group in com-
pounds 12-14 with potassium carbonate and then
making HCl salts gave the desired iodinated compounds
15-17, respectively. The TFA protecting group in
compound 11 is necessary; otherwise, direct iodination
with BTMACl2I will form oxidation products instead of
the desired iodinated derivatives (data not presented).
The synthesis of compounds 20 and 21 is outlined in
Scheme 3. Direct bromination of protected compound
11 with pyridium tribromide (PyHBr3)30,31 provided the
brominated derivatives which were separated by silica
gel chromatography using hexanes-chloroform (2:1 to
1:2) as eluent to afford compounds 18 (76%) and 19
(16%). Deprotection of compounds 18 and 19 with
potassium carbonate and making the oxalic acid salts
gave the desired brominated compounds 20 and 21,
respectively. We also conducted the alternative route
for the synthesis of compound 19 from 11. Direct
bromination of compound 11 with bromine in glacial
acetic acid formed compound 19 in nearly quantitative
(99%) yield.
F igu r e 1. Molecular structures of trimetoquinol (1, TMQ),
diiodo-TMQ (2), and compounds 8, 10, 15-17, 20, and 21.
and 4) required for compounds 6 and 7, respectively,
are commercially available, while 3,5-diiodo-4-methoxy-
phenylacetyl chloride (5) was synthesized in four steps
from p-hydroxyphenylacetic acid.26 The phenethylamine
3 or 4 was condensed with 3,5-diiodo-4-methoxyphenyl-
acetyl chloride (5) to afford the corresponding phenyl-
acetamides 6 and 7, respectively. Bischler-Napieral-
ski27 cyclization of phenylacetamide (6 and 7) with
phosphorus oxychloride in acetonitrile resulted in the
dihydroisoquinoline, which was reduced with sodium
borohydride in methanol without purification to afford
compound 8 and the benzyloxy-protected tetrahydroiso-
quinoline 9, respectively. Deprotection of 9 with a
refluxing equivolume mixture of concentrated hydro-
chloride acid and methanol gave compound 10.
Biologica l Resu lts a n d Discu ssion
Chinese hamster ovary (CHO) cells expressing human
â1-, â2-, and â3-ARs and cAMP response element (CRE)-
luciferase (LUC) receptor gene (CRE-LUC) assay (see
Experimental Section) were employed to evaluate the
receptor functional activities of tested compounds.
Figure 2 shows the functional activities of compounds
8 (panel A) and 10 (panel B) on human â1-, â2-, and â3-
ARs.
We know that the catechol moiety of TMQ is impor-
tant for the receptor functional activities on both human
â1- and â2-ARs32 but is not indispensable for the activity
on human â3-AR.25 By removal of the catechol moiety
of diiodo-TMQ (2), compound 8 shows a significant
partial agonist activity on human â3-AR in both CRE-
LUC and cAMP-RIA assays and shows low intrinsic
activities on human â1- and â2-ARs. Compound 10 which
bears only a hydroxyl group at 6-position, lacking the
catechol moiety of diiodo-TMQ (2), shows full agonist
activity on human â3-AR and exhibits moderate selec-
Preparation of iodinated compounds 15-17 is out-
lined in Scheme 2. The synthesis first involved the
protection of secondary amine in tetrahydroisoquinoline
10 with trifluoroacetic anhydride (TFAA) to provide
compound 11. After the protection, compound 11 was
directly iodinated with benzyltrimethylammonium
Sch em e 1

(3,5-Diiodo-4-methoxybenzyl)tetrahydroisoquinolinols
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4 593
Sch em e 2
Sch em e 3
tivity for receptor functional activity of human â3-AR
versus human â1- and â2-ARs (Figure 2, Table 1). These
results are consistent with our previous findings25,32 and
also indicate that â3-AR agonists and new lead com-
pounds can be designed and synthesized by the modi-
fications of the aromatic A ring of diiodo-TMQ.
The biological results in Table 1 show that most of
the halogen substituents made on the aromatic A ring
of compound 10 decreased human â2- and â3-AR func-
tional activities in the cAMP-RIA assay, thus providing
very interesting findings. By introducing an iodo group
at the 5-position of compound 10, compound 15 in-
creases receptor functional activity on human â2-AR and
abolishes human â3-AR functional activity. Compound
20 bearing a bromine atom at the 5-position decreases
the receptor functional activity on both human â2- and
â3-ARs. These results indicate that introduction of
different halogen atoms at the 5-position (for example,
an iodo group in compound 15) provides a selective â2-
AR partial agonist. The introduction of an iodo group
at the 7-position of compound 10 provided compound
16 which results in a decrease in the functional activity
on human â3-AR, while it abolishes human â2-AR
functional activity. This result indicates that the binding
site of human â3-AR can tolerate a more bulky group,
like an iodo group, at the 7-position than that of â2-AR.
Therefore compound 16 is a partial agonist on the
human â3-AR and shows selectivity for the human â3-
AR versus human â2-AR (Table 1).
The substitutions of an iodo or bromo group at both
5- and 7-positions of compound 10 afforded compounds
17 and 21, respectively, which proved to be without any
significant agonist property on both human â2- and â3-
ARs, in comparison to those of compound 10 (Table 1).
This phenomenon is likely because the functional active
conformation on â2- or â3-AR could not be achieved by

594 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4
He et al.
TMQ is improved by removal of one or both hydroxyl
groups of the catechol nucleus and that halogen sub-
stitution of the 6-hydroxy compound 10 (at the 5-, 7-,
or 5,7-positions) reduced agonist activity and/or maxi-
mal effects for activation of this receptor.
Con clu sion s
Functional activity assays in vitro have demonstrated
that compound 10 is a potent full agonist while com-
pound 8 is a partial agonist at the human â3-AR. Both
compounds are selective for the â3-AR versus â1- and
â2-ARs. It has also been demonstrated that halogen
substitution on the aromatic A ring of compound 10 has
a role in the type and potency of biological activity
expressed. The introduction of an iodo substituent at
the 5-position of compound 10 converts it from a â3- into
a â2-AR agonist (compound 15), while compound 16
bearing an iodo group at the 7-position remains a partial
â3-AR agonist. A bromo substitution at the 5-position
(compound 20) results in the decrease of functional
activity on both â2- and â3-ARs. Iodo or bromo substitu-
tions at both 5- and 7-positions abolish nearly com-
pletely â2- and â3-AR intrinsic activity. We believe that
these new â3-AR agonists could offer therapeutic po-
tentials for treatment of obesity and NIDDM and serve
as lead compounds in our future research.
Exp er im en ta l Section
Ch em istr y. Melting points were determined on a Thomas-
Hoover capillary melting point apparatus and are uncorrected.
Infrared spectra were recorded on a Perkin-Elmer system 2000
FT-IR. Proton and carbon-13 magnetic resonance spectra were
obtained on a Bruker AX 300 spectrometer (300 and 75 MHz
for 1H and 13C, respectively). Chemical shift values are
reported as parts per million (δ) relative to tetramethylsilane
(TMS). Spectral data are consistent with assigned structures.
Elemental analyses were performed by Atlantic Microlab Inc.,
Norcross, GA, and found values are within 0.4% of the
theoretical values. Routine thin-layer chromatography (TLC)
was performed on silica gel on aluminum plates (silica gel 60
F 254, 20 × 20 cm; Aldrich Chemical Co. Inc., Milwaukee, WI).
Flash chromatography was performed on silica gel (Merck;
grade 60, 230-400 mesh, 60 Å). Tetrahydrofuran (THF) was
dried by distillation from sodium metal. Acetonitrile (MeCN)
and methylene chloride (CH2Cl2) were dried by distillation
from P2O5.
F igu r e 2. Concentration-response curves of compounds 8
(panel A) and 10 (panel B) on human â1-AR (9 lines), â2-AR
(b lines), and â3-AR (O lines) expressed in CHO cells. Drug-
induced changes in cellular cAMP were determined by the
CRE-LUC assay (see Experimental Section). Responses are
expressed relative to the maximal response produced by
10-6 M isoproterenol, and data represent the mean percent
response ( SEM of 6-10 experiments.
steric perturbation on the receptor binding site corre-
sponding to the aromatic A ring portion of diiodo-TMQ
analogues. These results indicate that marked differ-
ences exist in the receptor binding site or pocket of â1-,
â2-, and â3-ARs which interact with halogen substitu-
ents at the 5- and/or 7-position of compound 10. Our
findings indicate that the â3-AR selectivity of diiodo-
Ta ble 1. Agonist Potency (pKact) and Intrinsic Activity (IA) of TMQ Analoguesa
human â1-AR human â2-AR
human â3-AR
compd
pKact ( SEMb
IA ( SEMc
pKact ( SEM
IA ( SEM
pKact ( SEM
IA ( SEM
1. CRE-LUC Assayd
9.46 ( 0.09
MA
ISO
8
10
8.81 ( 0.12
MAe
5.71 ( 0.14
100
22
58
100
21
38
7.74 ( 0.07
7.54 ( 0.22
7.45 ( 0.09
100
62
90
6.36 ( 0.15
2. cAMP-RIA Assayd
TMQ
diiodo-TMQ
8
10
15
16
17
20
21
8.70 ( 0.11
8.11 ( 0.13
NDg
ND
ND
ND
ND
ND
ND
109
103
ND
ND
ND
ND
ND
ND
ND
8.33 ( 0.24f
8.84 ( 0.07
MA
95
52
15
44
65
4
6
26
3
8.60 ( 0.15
8.76 ( 0.20
8.20 ( 0.05
7.88 ( 0.24
MA
7.92 ( 0.32
MA
8.25 ( 0.47
MA
95
120
52
106
8
35
18
31
20
6.87 ( 0.07
6.77 ( 0.18
MA
MA
MA
MA
a
Human â1-, â2-, and â3-ARs were expressed in CHO cells. Data are expressed as means ( SEM. b pKact is -log of the molar concentration
of the drug which produces a cAMP response equal to 50% of its maximal response. c IA, intrinsic activity, expressed as the percentage
of a maximal analogue response relative to the maximal response (100%) of (R)-(-)-isoproterenol (ISO). See Experimental Section. e MA,
d
minimal activity. EC50 values were incalculable for compounds exhibiting IA less than 26%, and the observed IA values were determined
at 100 µM. f Data for (S)-(-)-TMQ. ND, not determined.
g

(3,5-Diiodo-4-methoxybenzyl)tetrahydroisoquinolinols
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4 595
N-P h en yleth yl-3,5-d iiod o-4-m eth oxyp h en yla ceta m id e
(6). 3,5-Diiodo-4-methoxyphenylacetyl chloride25 (0.52 g, 1.2
mmol) in CH2Cl2 (8 mL) was added dropwise to a stirred
mixture of phenethylamine (0.15 g, 1.2 mmol) in CH2Cl2 (3
mL) and K2CO3 (0.50 g, 3.6 mmol) in H2O (8 mL). The resulting
mixture was stirred for additional 1.5 h. The organic layer was
separated and the H2O layer was extracted with CH2Cl2 (10
mL × 2). The combined organic layer was washed successively
with 10% HCl solution (20 mL), saturated Na2CO3 solution
(20 mL), and brine (20 mL), dried over anhydrous MgSO4,
filtered, and concentrated to give an oily residue. The title
product was crystallized from ethyl acetate-hexanes to give
0.42 g (67%) of white needles: mp 157-158 °C; 1H NMR (300
MHz, CDCl3) δ 7.61 (s, 2H, ArH), 7.28 (m, 3H, ArH), 7.11 (m,
2H, ArH), 5.35 (br s, 1H, NH), 3.86 (s, 3H, MeO), 3.51 (q, J )
6.1 Hz, 2H, NCH2), 3.37 (s, 2H, COCH2), 2.79 (t, J ) 6.1 Hz,
2H, ArCH2); 13C NMR (75 MHz, CDCl3) δ 169.5 (CdO), 158.2
(C-O, Ar), 140.5, 138.6, 134.6, 128.8, 128.7, 126.7, 90.8 (C-I,
Ar), 60.7 (MeO), 41.7 (ArCH2CO), 40.8 (CH2N), 35.4 (ArCH2);
7.41 (m, 5H, ArH), 7.18 (m, 1H, ArH), 6.88 (m, 2H, ArH), 5.10
(s, 2H, ArCH2), 4.63 (dd, 1H, ArCHN), 3.74 (s, 3H, MeO), 3.35
(m, 2H, CH), 3.17-2.92 (m, 4H, ArCH2 and CH); 13C NMR
(75 MHz, DMSO-d6) δ 164.2 (HOOC-COOH), 157.5 (C-O, Ar),
157.4 (C-O, Ar), 140.6, 137.0, 136.6, 133.8, 128.4, 128.0, 127.8,
127.6, 124.9, 114.3, 113.6, 91.5, 69.2 (ArCH2O), 60.2 (MeO),
54.9 (ArCHN), 38.7, 37.5, 25.5 (ArCH2); IR (KBr) 3300-2400
(COOH, and NH), 1724 (CdO, acid), 1614, 1504 (CdC, Ar)
cm-1. Anal. (C24H23I2NO2‚0.5(COOH)2) C, H, N.
1-(3,5-Diiod o-4-m eth oxyben zyl)-1,2,3,4-tetr a h yd r oiso-
qu in olin -6-ol, Hyd r och lor id e (10). A solution of protected
isoquinoline 9 (0.88 g, 1.45 mmol) in an equivolume mixture
of MeOH and concentrated HCl (40 mL) was heated at reflux
for 5 h. After the end of the reaction was established by TLC,
the solvent was removed under vacuum to dryness which was
dissolved in MeOH (30 mL) and evaporated under vacuum
three times. The title product was crystallized from MeOH-
Et2O to give 0.45 g (56%) of white crystals: mp 233-234 °C;
1H NMR (300 MHz, DMSO-d6) δ 9.58 (s, 1H, ArOH), 9.16 (br
s, 1H, NH), 9.11 (br s, 1H, NH), 7.89 (s, 2H, ArH), 7.19 (d,
J ) 8.6 Hz, 1H, ArH), 6.65 (dd, J ) 8.6 Hz, J ) 2.4 Hz, 1H,
ArH), 6.60 (d, J ) 2.4 Hz, 1H, ArH), 4.61 (dd, 1H, ArCHN),
3.75 (s, 3H, MeO), 3.36 (m, 2H, CH), 3.15-2.82 (m, 4H, ArCH2
and CH); 13C NMR (75 MHz, DMSO-d6) δ 157.5 (C-O, Ar),
156.7 (C-O, Ar), 140.7, 136.4, 133.4, 127.9, 122.4, 114.8, 114.1,
60.2 (MeO), 55.1 (ArCHN), 39.0 (CHN, or ArCH2), 37.3 (ArCH2,
or CHN), 25.1 (ArCH2); IR (KBr) 3600-2400 (br, OH and NH),
1614 (NH bend), 1589, 1534, 1505 (CdC, Ar) cm-1. Anal.
(C17H17I2NO2‚HCl) C, H, N.
1-(3,5-Diiodo-4-m eth oxyben zyl)-2-tr iflu or oacetyl-1,2,3,4-
tetr a h yd r oisoqu in olin -6-ol (11). To a solution of isoquino-
line 10 (1.95 g, 3.5 mmol) in anhydrous THF (80 mL) was
added Et3N (2.44 mL, 17.5 mmol) and the resulting solution
was cooled to 0 °C in ice bath. Trifluoroacetic anhydride (3.68
g, 17.5 mmol) was added dropwise to the above solution, and
the mixture was stirred overnight at room temperature. After
the end of the reaction was established by TLC, the solvent
was removed under vacuum to dryness. The residue was
dissolved in CH2Cl2 (30 mL), washed successively with brine
(20 mL), 1 N HCl solution (20 mL), and brine (20 mL), dried
over anhydrous MgSO4, filtered, and evaporated to give a
residue. The title compound was crystallized from ethyl
acetate-hexanes to give 1.90 g (88%) of white crystals: mp
185.5-186.5 °C; 1H NMR (300 MHz, DMSO-d6) δ 9.37 (s, 1H,
ArOH), 7.72 (s, 2H, ArH), 7.23 (d, J ) 8.5 Hz, 1H, ArH), 6.65
(d, J ) 8.5 Hz, 1H, ArH), 6.57 (s, 1H, ArH), 5.46 (dd, 1H,
ArCHN), 3.82 (m, 2H, CH), 3.69 (s, 3H, MeO), 3.00 (m, 2H,
CH), 2.80 (m, 2H, ArCH2); 13C NMR (75 MHz, DMSO-d6) δ
156.9 (C-O, Ar), 156.1 (C-O, Ar), 154.4 (q, J ) 34.5 Hz, CF3-
CO), 140.4, 137.8, 133.9, 128.4, 125.3, 116.2 (q, J ) 287.3 Hz,
CF3), 114.6, 113.9, 90.5, 60.2 (MeO), 54.3 (ArCHN), 38.9, 38.9,
28.8 (ArCH2); IR (KBr) 3388 (OH), 1679 (CdO), 1612, 1512
(CdC, Ar) cm-1. Anal. (C19H16F3I2NO3) C, H, N.
IR (KBr) 3285 (NH), 1633 (CdO), 1549, 1497 (CdC, Ar) cm-1
.
Anal. (C17H17I2NO2) C, H, N.
N -(3-Be n zyloxyp h e n yle t h yl)-3,5-d iiod o-4-m e t h oxy-
p h en yla ceta m id e (7). In the same manner as compound 6,
the title compound was prepared from 3,5-diiodo-4-methoxy-
phenylacetyl chloride (1.29 g, 3 mmol), NaOH (0.36 g, 9 mmol),
and 2-(3-benzyloxyphenyl)ethylamine (0.78 g, 3 mmol) which
in turn was obtained by reducing its corresponding nitro
precusor33 with LAH. Recrystallization from ethyl acetate-
hexanes affored 1.60 g (86%) of title compound as white
1
crystals: mp 117-119 °C; H NMR (300 MHz, CDCl3) δ 7.60
(s, 2H, ArH), 7.45-7.19 (m, 5H, ArH), 6.85 (dd, J ) 7.5 Hz,
J ) 2.1 Hz, 1H, ArH), 6.77 (d, J ) 2.1 Hz, 1H, ArH), 6.67 (d,
J
) 7.5 Hz, 1H, ArH), 5.42 (br s, 1H, NH), 5.05 (s, 2H,
ArCH2O), 3.83 (s, 3H, MeO), 3.49 (q, J ) 6.2 Hz, 2H, CH),
3.33 (s, 2H, ArCH2CdO), 2.75 (t, J ) 6.2 Hz, 2H, CH); 13C
NMR (75 MHz, CDCl3) δ 169.5 (CdO), 159.1 (C-O, Ar), 158.2
(C-O, Ar), 140.5, 140.1, 137.0, 134.6, 129.7, 128.6, 128.0, 127.5,
121.3, 115.3, 112.9, 90.7 (C-I, Ar), 70.0 (ArCH2O), 60.7 (MeO),
41.6 (CH2NH), 40.6 (ArCH2CdO), 35.4 (ArCH2); IR (KBr) 3316
(NH), 1635 (CdO), 1596, 1549, 1497 (CdC, Ar) cm-1. Anal.
(C24H23I2NO3) C, H, N.
1-(3,5-Diiod o-4-m eth oxyben zyl)-1,2,3,4-tetr a h yd r oiso-
qu in olin e, Hyd r och lor id e (8). A mixture of the correspond-
ing amide 6 (0.35 g, 0.67 mmol) and POCl3 (0.52 g, 3.36 mmol)
in anhydrous CH3CN (20 mL) was heated at reflux for 4 h.
Following cooling, the solvent and excess POCl3 were removed
under vacuum to dryness. The residue was dissolved in CH2-
Cl2 (20 mL), washed successively with brine (15 mL), saturated
Na2CO3 solution (2 × 15 mL), and brine (2 × 15 mL), dried
over anhydrous MgSO4, filtered, and concentrated to give an
oily residue. The oil was dissolved in MeOH (20 mL) and cooled
to 0 °C in an ice bath. A large excess NaBH4 (0.25 g, 6.27 mmol)
was added slowly in portions, and the resulting suspension
was stirred overnight at room temperature. After the end of
the reaction was established by TLC, the solvent was removed
under vacuum to dryness which was dissolved in CH2Cl2 (20
mL), washed successively with 10% NaOH solution (2 × 15
mL) and brine (2 × 15 mL), dried over anhydrous MgSO4, and
filtered; then 1 mL of 1 M HCl in Et2O was added to make
HCl salt. The title product was crystallized from MeOH-Et2O
to give 0.19 g (55%) of white crystals: mp 199-200 °C; 1H
NMR (300 MHz, DMSO-d6) δ 9.10 (br s, 2H, NH), 7.91 (s, 2H,
ArH), 7.27 (m, 4H, ArH), 4.77 (dd, 1H, ArCHN), 3.75 (s, 3H,
MeO), 3.43-2.91 (m, 6H, ArCH2 and CH); 13C NMR (75 MHz,
DMSO-d6) δ 157.5 (C-O, Ar), 140.7, 136.2, 132.1, 132.1, 128.9,
127.7, 126.8, 126.5, 60.2 (MeO), 55.2 (ArCHN), 39.0, 37.2, 24.9
(ArCH2); IR (KBr) 3436 (NH), 1587, 1532, 1495 (CdC, Ar)
cm-1. Anal. (C17H17I2NO‚HCl) C, H, N.
1-(3,5-Diiodo-4-m eth oxyben zyl)-5-iodo-2-tr iflu or oacetyl-
1,2,3,4-tetr a h yd r oisoqu in olin -6-ol (12), 1-(3,5-Diiod o-4-
m eth oxyben zyl)-7-iod o-2-tr iflu or oa cetyl-1,2,3,4-tetr a h y-
d r oisoq u in olin -6-ol (13), a n d 1-(3,5-Diiod o-4-m et h oxy-
ben zyl)-5,7-diiodo-2-tr iflu or oacetyl-1,2,3,4-tetr ah ydr oiso-
qu in olin -6-ol (14). A mixture of protected isoquinoline 11
(1.24 g, 2 mmol), benzyltrimethylammonium dichloroiodate
(BTMACl2I) (0.77 g, 2.2 mmol), and CaCO3 (1.40 g, 14 mmol)
in CH2Cl2 (20 mL) and MeOH (8 mL) was stirred for 5 h at
room temperature. After the starting material was consumed
nearly completely checked by TLC, the mixture was filtered,
and precipitate was washed with CH2Cl2 (2 × 10 mL). The
combined organic solvent was successively washed with 0.5
N Na2S2O3 solution (20 mL) and brine (20 mL), dried over
anhydrous MgSO4, filtered, and concentrated under vacuum
to dryness. The title products were separated by silica gel
chromatography using hexanes-ethyl acetate (8:1-6:1) as
eluent to afford 14 (0.25 g, 12%), 12 (1.01 g, 69%), and 13 (0.12
g, 10%).
6-Ben zyloxy-1-(3,5-d iiodo-4-m eth oxyben zyl)-1,2,3,4-tet-
r a h yd r oisoqu in olin e, Oxa la te (9). The title compound was
prepared from compound 7 (3.19 g, 5.09 mmol) in the same
manner as compound 8. Rerystallization from MeOH-Et2O
affored 1.26 g (76%) of compound 9 as white crystals: mp 197-
198 °C; 1H NMR (300 MHz, DMSO-d6) δ 7.84 (s, 2H, ArH),
1
14: mp 114-115 °C; H NMR (300 MHz, CDCl3) δ 7.49 (s,
2H, ArH), 7.13 (s, 1H, ArH), 5.93 (br s, 1H, ArOH), 5.47 (dd,

596 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4
He et al.
1H, ArCHN), 4.04 (m, 2H, CH), 3.86 (s, 3H, MeO), 3.61 (m,
1H, ArCH2), 3.11-2.76 (m, 3H, ArCH2 and CH); 13C NMR (75
MHz, CDCl3) δ 158.3 (C-O, Ar), 155.7 (q, J ) 36.0, COCF3),
153.0 (C-O, Ar), 140.8, 137.8, 137.8, 136.0, 129.7, 116.2 (q,
J ) 286.5 Hz, CF3), 90.3 (C-I, Ar), 89.8 (C-I, Ar), 79.6 (C-I,
Ar), 60.8 (MeO), 54.2 (ArCHN), 40.1 (ArCH2), 40.0 (q, J ) 3.8
Hz), 30.9 (ArCH2); IR (KBr) 3425 (OH), 1683 (CdO), 1535 (Cd
C, Ar) cm-1. Anal. (C19H14F3I4NO3) C, H, N.
CH), 2.92 (m, 2H, ArCH2); 13C NMR (75 MHz, DMSO-d6) δ
157.5 (C-O, Ar), 154.8 (C-O, Ar), 140.9, 137.3, 136.6, 136.2,
127.7, 94.8 (C-I, Ar), 91.5 (C-I, Ar), 84.3 (C-I, Ar), 60.2
(MeO), 54.0 (ArCHN), 38.3, 37.0 (ArCH2), 32.5 (ArCH2); IR
(KBr) 3437 (OH), 1585, 1534 (CdC, Ar) cm-1. Anal. (C17H15I4-
NO2‚HCl) C, H, N.
1-(3,5-Diiod o-4-m et h oxyb en zyl)-5-b r om o-2-t r iflu or o-
a cetyl-1,2,3,4-tetr a h yd r oisoqu in olin -6-ol (18). A solution
of pyridium tribromide (PyHBr3) (0.96 g, 3 mmol) in anhydrous
THF (50 mL) was added dropwise to a solution of isoquinoline
11 (1.24 g, 2 mmol) in THF (50 mL) over a 45-min period. The
resulting solution was stirred for an additional 4 h at room
temperature. After the starting material was consumed, the
solution was filtered, treated with 2% NaHSO3 solution, and
concentrated under reduced pressure to dryness. The title
product was purified by silica gel chromatography using
hexanes-chloroform (2:1-1:2) as eluent and crystallized from
ethyl acetate-hexanes to give 0.94 g (76%) of white crystals.
Meanwhile, compound 19 (0.25 g, 16%) was also obtained from
12: mp 80-81 °C; 1H NMR (300 MHz, CDCl3) δ 7.47 (s,
2H, ArH), 6.88 (d, J ) 8.4 Hz, 1H, ArH), 6.82 (d, J ) 8.4 Hz,
1H, ArH), 5.54 (br s, 1H, ArOH), 5.45 (dd, 1H, ArCHN), 4.06
(m, 1H, CH), 3.93 (m, 1H, CH), 3.78 (s, 3H, MeO), 3.55 (m,
1H, CH), 2.93-2.78 (m, 3H, CH); 13C NMR (75 MHz, CDCl3)
δ 158.1 (C-O, Ar), 155.8 (q, J ) 36.0 Hz, COCF3), 154.4 (C-
O, Ar), 140.7, 136.6, 136.3, 129.0, 128.1, 116.3 (q, J ) 285.8
Hz, CF3), 113.5, 92.9 (C-I, Ar), 90.2 (C-I, Ar), 60.8 (MeO),
54.8 (ArCHN), 40.3 (q, J ) 3.8 Hz), 40.2 (ArCH2), 35.5 (ArCH2);
IR (KBr) 3374 (OH), 1681 (CdO), 1603, 1533 (CdC, Ar) cm-1
.
Anal. (C19H15F3I3NO3‚0.15C6H14) C, H, N.
1
1
this procedure: mp 162-163 °C; H NMR (300 MHz, CDCl3)
13: mp 151-152 °C; H NMR (300 MHz, CDCl3) δ 7.48 (s,
2H, ArH), 7.06 (s, 1H, ArH), 6.81 (s, 1H, ArH), 5.45 (dd, 1H,
ArCHN), 4.14 (m, 1H, CH), 3.95 (m, 1H, CH), 3.87 (s, 3H,
MeO), 3.65 (m, 1H, ArCH2), 2.95 (m, 2H, CH), 2.78 (m, 1H,
ArCH2); 13C NMR (75 MHz, CDCl3) δ 158.1 (C-O, Ar), 156.0
(q, J ) 36.0 Hz, COCF3), 154.1 (C-O, Ar), 140.9, 137.2, 136.3,
135.5, 128.2, 116.3 (q, J ) 286.0 Hz, CF3), 114.5, 90.2 (C-I,
Ar), 83.1 (C-I, Ar), 60.8 (MeO), 54.7 (ArCHN), 40.2 (q, J )
3.8 Hz), 40.2, 28.7 (ArCH2); IR (KBr) 3396 (OH), 1682 (CdO),
δ 7.48 (s, 2H, ArH), 6.92 (d, J ) 8.7 Hz, 1H, ArH), 6.81 (d,
J ) 8.7 Hz, 1H, ArH), 5.72 (br s, 1H, ArOH), 5.56 (dd, 1H,
ArCHN), 4.00 (m, 2H, CH), 3.84 (s, 3H, MeO), 3.59 (m, 1H,
ArCH2), 2.93 (m, 3H, CH); 13C NMR (75 MHz, CDCl3) δ 158.1
(C-O, Ar), 155.8 (q, J ) 36.0 Hz, COCF3), 151.7 (C-O, Ar),
140.7, 136.3, 133.3, 128.0, 127.8, 116.3 (q, J ) 288.8 Hz, CF3),
114.4, 112.4, 90.2 (C-I, Ar), 60.8 (MeO), 54.7 (ArCHN), 40.1
(ArCH2), 39.7 (q, J ) 3.7 Hz), 30.1 (ArCH2); IR (KBr) 3430
(OH), 1692 (CdO), 1581, 1534 (CdC, Ar) cm-1. Anal. (C19H15F3-
BrI2NO3) C, H, N.
1599, 1533 (CdC, Ar) cm-1. Anal. (C19H15F3I3NO3‚0.11C6H14
C, H, N.
)
1-(3,5-Diiod o-4-m eth oxyben zyl)-5,7-d ibr om o-2-tr iflu o-
r oa cetyl-1,2,3,4-tetr a h yd r oisoqu in olin -6-ol (19). A solution
of Br2 (0.26 g, 1.62 mmol) in AcOH (5 mL) was slowly added
to an ice-bath-cooled solution of protected isoquinoline 11 (0.50
g, 0.81 mmol) in AcOH (10 mL). The mixture was allowed to
warm to room temperature and stirred for 4 h. After the end
of the reaction was established by TLC, the solution was
concentrated to 2 mL and crystals were precipitated. The
acrystals was filtered and recrystallized from ethyl acetate-
hexane to afford 0.11 g (86%) of title compound as white
1-(3,5-Diiod o-4-m eth oxyben zyl)-5-iod o-1,2,3,4-tetr a h y-
d r oisoqu in olin -6-ol, Hyd r och lor id e (15). A mixture of
protected isoquinoline 12 (0.62 g, 0.83 mmol) in MeOH (30 mL)
and K2CO3 (1.50 g, 10.90 mmol) in H2O (10 mL) was heated
at reflux for 1 h. After the end of reaction was established by
TLC, the solvent was removed under reduced pressure to
dryness which was extracted with CH2Cl2 (3 × 20 mL). The
combined organic layer was dried over anhydrous MgSO4 and
filtered, and then 1 mL of 1 M HCl in Et2O was added to make
HCl salt. The title product was crystallized from MeOH-Et2O
to give 0.40 g (70%) of white crystals: mp 235-236 °C; 1H
NMR (300 MHz, DMSO-d6) δ 10.60 (s, 1H, ArOH), 9.21 (br s,
2H, NH2), 7.88 (s, 2H, ArH), 7.09 (d, J ) 8.7 Hz, 1H, ArH),
6.82 (d, J ) 8.7 Hz, 1H, ArH), 4.66 (dd, 1H, ArCHN), 3.75 (s,
3H, MeO), 3.36 (m, 2H, CH), 3.01 (m, 2H, CH), 2.92 (m, 2H,
ArCH2); 13C NMR (75 MHz, DMSO-d6) δ 157.5 (C-O, Ar),
156.3 (C-O, Ar), 140.7, 136.2, 135.8, 127.9, 124.4, 113.0, 91.6
(C-I, Ar), 91.6 (C-I, Ar), 60.2 (MeO), 54.8 (ArCHN), 38.8, 37.2,
32.2 (ArCH2); IR (KBr) 3431 (OH), 1595, 1563, 1534 (CdC,
Ar) cm-1. Anal. (C17H16I3NO2‚HCl) C, H, N.
1
crystals: mp 191-192 °C; H NMR (300 MHz, CDCl3) δ 7.58
(s, 2H, ArH), 6.95 (s, 1H, ArH), 5.97 (s, 1H, ArOH), 5.50 (dd,
1H, ArCHN), 4.40 (m, 2H, CH), 3.83 (s, 3H, MeO), 3.57 (m,
1H, CH), 2.90 (m, 3H, CH); 13C NMR (75 MHz, CDCl3) δ 158.3
(C-O, Ar), 155.8 (q, J ) 36.0 Hz, COCF3), 148.8 (C-O, Ar),
140.8, 135.9, 133.4, 130.5, 129.0, 116.3 (q, J ) 286.5 Hz, CF3),
112.2, 107.8, 90.3 (C-I, Ar), 60.8 (MeO), 54.3 (ArCHN), 40.0
(ArCH2), 39.4 (q, J ) 3.8 Hz), 30.1 (ArCH2); IR (KBr) 3380
(OH), 1689 (CdO), 1603, 1533 (CdC, Ar) cm-1. Anal. (C19H14F3-
Br2I2NO3‚1.3C6H14) C, H, N.
1-(3,5-Diiodo-4-m eth oxyben zyl)-5-br om o-1,2,3,4-tetr ah y-
d r oisoqu in olin -6-ol, Oxa la te (20). A mixture of the pro-
tected isoquinoline 18 (0.30 g, 0.43 mmol) in MeOH (25 mL)
and K2CO3 (1.2 g, 8.68 mmol) in H2O (10 mL) was stirred
overnight at room temperature. The resulting solution was
concentrated under vacuum to 5 mL, and crystals were
precipitated which were filtered, washed with H2O and CHCl3,
and dissolved in MeOH; then 1.1 equiv of oxalic acid was added
to make salt. The title compound was crystallized from
MeOH-Et2O to give 0.28 g (99%) of white crystals: mp 227.5-
228 °C; 1H NMR (300 MHz, DMSO-d6) δ 7.74 (s, 2H, ArH),
6.98 (d, J ) 8.5 Hz, 1H, ArH), 6.80 (d, J ) 8.5 Hz, 1H, ArH),
4.60 (dd, 1H, ArCHN), 3.73 (s, 3H, MeO), 3.40 (m, 2H, CH),
3.24 (m, 2H, CH), 2.92 (m, 2H, CH); 13C NMR (75 MHz, DMSO-
d6) δ 163.9 (HOOC-COOH), 157.4 (C-O, Ar), 153.7 (C-O, Ar),
140.6, 136.3, 132.9, 126.8, 124.8, 114.2, 111.4, 91.5 (C-I, Ar),
60.2 (MeO), 54.7 (ArCHN), 38.1 (ArCH2), 37.4, 26.9 (ArCH2);
IR (KBr) 3600-2400 (br, NH and OH), 1712 (CdO), 1645, 1611
(NH bend), 1534 (CdC, Ar) cm-1. Anal. (C17H16NBrI2O2‚1.75-
(COOH)2) C, H, N.
1-(3,5-Diiod o-4-m eth oxyben zyl)-7-iod o-1,2,3,4-tetr a h y-
d r oisoqu in olin -6-ol, Hyd r och lor id e (16). In the same man-
ner as compound 15, the title compound was prepared from
the protected isoquinoline 13 (0.30 g, 0.40 mmol). Recrystal-
lization from MeOH-Et2O affored 0.14 g (51%) of compound
16 as white crystals: mp 231-232 °C; 1H NMR (300 MHz,
DMSO-d6) δ 10.38 (s, 1H, ArOH), 9.11 (br s, 2H, NH2), 7.81
(s, 2H, ArH), 7.43 (s, 1H, ArH), 6.65 (s, 1H, ArH), 4.54 (dd,
1H, ArCHN), 3.74 (s, 3H, MeO), 3.31 (m, 2H, CH), 3.11 (m,
1H, ArCH2), 2.99 (m, 2H, CH), 2.84 (m, 1H, ArCH2); 13C NMR
(75 MHz, DMSO-d6) δ 157.4 (C-O, Ar), 155.8 (C-O, Ar),
140.83, 137.1, 136.3, 133.6, 124.6, 114.2, 91.4 (C-I, Ar), 82.5
(C-I, Ar), 60.2 (MeO), 54.3 (ArCHN), 38.7, 38.4, 37.2 (ArCH2);
IR (KBr) 3600-2400 (br, OH and NH), 1592, 1534, 1502 (Cd
C, Ar) cm-1. Anal. (C17H16I3NO2‚HCl) C, H, N.
1-(3,5-Diiod o-4-m et h oxyb en zyl)-5,7-d iiod o-1,2,3,4-t et -
r a h yd r oisoqu in olin -6-ol, Hyd r och lor id e (17). In the same
manner as compound 15, the title compound was prepared
from the protected isoquinoline 14 (0.19 g, 0.22 mmol).
Recrystallization from MeOH-Et2O affored 0.15 g (86%) of
compound 17 as white crystals: mp 233-234 °C; 1H NMR (300
MHz, DMSO-d6) δ 9.72 (s, 1H, NH), 9.65 (s, 1H, ArOH), 9.58
(s, 1H, NH), 7.88 (s, 2H, ArH), 7.49 (s, 1H, ArH), 4.61 (dd, 1H,
ArCHN), 3.76 (s, 3H, MeO), 3.42 (m, 2H, CH), 3.17 (m, 2H,
1-(3,5-Diiod o-4-m et h oxyb en zyl)-5,7-d ib r om o-1,2,3,4-
tetr a h yd r oisoqu in olin -6-ol, Oxa la te (21). In the same
manner as compound 20, the title compound was prepared
from the protected isoquinoline 19 (0.28 g, 0.36 mmol) and K2-

(3,5-Diiodo-4-methoxybenzyl)tetrahydroisoquinolinols
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 4 597
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CO3 (1.2 g, 8.68 mmol). Recrystallization from MeOH-Et2O
generated 0.24 g (92%) of white crystalline title compound: mp
220-221 °C; 1H NMR (300 MHz, DMSO-d6) δ 7.82 (s, 2H,
ArH), 7.40 (s, 1H, ArH), 4.58 (dd, 1H, ArCHN), 3.75 (s, 3H,
MeO), 3.42 (m, 2H, CH), 3.22 (m, 2H, CH), 2.91 (m, 2H,
ArCH2); 13C NMR (75 MHz, DMSO-d6) δ 164.0 (HOOC-
COOH), 157.4 (C-O, Ar), 150.1 (C-O, Ar), 140.8, 136.6, 133.0,
130.3, 127.6, 114.4, 109.5, 91.3 (C-I, Ar), 60.2 (MeO), 54.4
(ArCHN), 37.8, 37.4 (ArCH2), 27.4 (ArCH2); IR (KBr) 3600-
2400 (br, NH and OH), 1724 (CdO), 1694 (NH bend), 1534
(CdC, Ar) cm-1. Anal. (C17H15Br2I2NO2‚0.5(COOH)2) C, H, N.
cAMP Resp on se Elem en t (CRE)-Lu cifer a se (LUC)
Recep tor Gen e (CRE-LUC) Assa y. CHO cells stably ex-
pressing human â1-, â2-, or â3-AR populations were transfected
with a 6 CRE-LUC plasmids (gift from Dr. Himmler, Vienna,
Austria) using electroporation with a single 70-ms, 150-V
pulse.34 The transfected CHO cells were seeded at a density
of 40 000/well in 96-well microtiter plates (culturplate, Pack-
ard) and allowed to grow for 20 h. After 20 h, the cells were
treated with varying drug concentrations (10-11-10-4 M) for
4 h. Following drug exposures, the cells were lysed and
luciferase activity was measured using the LucLite assay kit
(Packard). Changes in light production were measured by a
Topcount luminometer (Packard). Data were analyzed in
duplicate at each concentration and expressed as a percent
luciferase response relative to the maximum response to (-)-
isoproterenol (10-6 M). Results are expressed as the mean (
SEM of n ) 5-16.
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xanthine (IBMX), and 1 mM L-ascorbic acid for 30 min at 37
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methyl ester/antibody precipitated
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Ack n ow led gm en t. We are grateful for the support
of this research from the National Institutes of Health
(Grant 1 R41 DK52238-01) and Molecular Design
International (MDI). We also thank Dr. Richard Fertel
(Department of Pharmacology, The Ohio State Univer-
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body for the cAMP radioimmunoassay.
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