Examination of the role of the acidic hydrogen in imparting selectivity of 7-(aminosulfonyl)-1,2,3,4-tetrahydroisoquinoline (SK and F 29661) toward inhibition of phenylethanolamine N-methyltransferase vs the α2-adrenoceptor

Article abstract of DOI:10.1021/jm960235e

7-(Aminosulfonyl)-1,2,3,4-tetrahydroisoquinoline (SK and F 29661, 1) is a potent inhibitor of the enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). In contrast to other inhibitors of PNMT, it is also highly selective toward PNMT in compar

Full text of DOI:10.1021/jm960235e

J . Med. Chem. 1997, 40, 3997-4005
3997
Articles
Exa m in a tion of th e Role of th e Acid ic Hyd r ogen in Im p a r tin g Selectivity of
7-(Am in osu lfon yl)-1,2,3,4-tetr a h yd r oisoqu in olin e (SK&F 29661) Tow a r d
In h ibition of P h en yleth a n ola m in e N-Meth yltr a n sfer a se vs th e r2-Ad r en ocep tor 1a
Gary L. Grunewald,* Vilas H. Dahanukar,1b Timothy M. Caldwell, and Kevin R. Criscione
Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045
Received J une 23, 1997X
7-(Aminosulfonyl)-1,2,3,4-tetrahydroisoquinoline (SK&F 29661, 1) is a potent inhibitor of the
enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). In contrast to other
inhibitors of PNMT, it is also highly selective toward PNMT in comparison with its affinity
toward the R2-adrenoceptor (PNMT Ki ) 0.55 µM, R2 Ki ) 100 µM, selectivity [R2 Ki/PNMT Ki]
) 180). A diverse set of compounds was synthesized and evaluated to probe the role of the
acidic hydrogen of the aminosulfonyl group of 1 in imparting this selectivity. Compounds were
designed to investigate the effect on selectivity of the acidity of the NH group [the 7-N-methyl
(compound 5) and 7-N-(p-chlorophenyl) (compound 4) derivatives of 1], the relative spatial
position of the acidic hydrogen [7-(N-(methylsulfonyl)amino)-1,2,3,4-tetrahydroisoquinoline (6)
and 7-((N-(methylsulfonyl)amino)methyl)-1,2,3,4-tetrahydroisoquinoline (8)], or the effect of
the substitution of an acidic phenolic group for the aminosulfonyl moiety [1-(aminomethyl)-6-
hydroxynaphthalene (23) and 8-hydroxy-1,2,3,4-tetrahydrobenz[h]isoquinoline (9)]. All of the
compounds studied displayed lower affinity for PNMT than 1, and nine of the eleven compounds
studied showed increased, rather than the desired decreased, affinity for the R2-adrenoceptor.
Specifically, compound 4, in which the aminosulfonyl NH group is more acidic than that in 1,
showed greatly reduced selectivity on account of increased R2-adrenoceptor affinity as compared
to 1 (PNMT Ki ) 2.6 µM, R2 Ki ) 6.3 µM, selectivity ) 2.4). Compound 8, in which the acidic
NH group is in the same region of space as that in 1, although the aminosulfonyl group is
reversed with respect to the aromatic ring, showed poor PNMT affinity and modest R2-
adrenoceptor affinity (PNMT Ki ) 330 µM, R2 Ki ) 18 µM, selectivity ) 0.055). Compound 9,
in which a phenolic group is in the same region of space as the acidic NH of 1, exhibited the
best R2-adrenoceptor affinity of any of the compounds studied (PNMT Ki ) 0.98 µM, R2 Ki )
0.078 µM, selectivity ) 0.080). Results from this study suggest that the selectivity of 1 is not
solely due to the presence of an acidic hydrogen on the 7-aminosulfonyl group of 1 but is likely
also dependent on some other property (e.g. electron-withdrawing character) of the aminosul-
fonyl group.
Phenylethanolamine N-methyltransferase (PNMT,
EC 2.1.1.28) catalyzes the conversion of the neurotrans-
mitter norepinephrine to epinephrine. The role of brain
epinephrine, which constitutes about 5-10% of the total
catecholamine content of the central nervous system
(CNS), is poorly understood due to the lack of a selective
PNMT inhibitor.2 Central epinephrine has been pos-
tulated to be involved in the control of blood pressure
and heart rate,3 control of the secretion of pituitary
hormones,3,4 control of exercise tolerance,5 and ethanol
intoxication.6 Demonstration of the antihypertensive
effect of PNMT inhibitors in spontaneously hypertensive
rats7 stimulated the interest to develop a potent inhibi-
tor of PNMT as a novel antihypertensive drug. How-
ever, most well-studied PNMT inhibitors exhibit high
affinity toward the R2-adrenoceptor.8 An exception was
SK&F 29661 (1), which exhibited high affinity for
PNMT and good selectivity for PNMT over the R2-
adrenoceptor (PNMT Ki ) 0.55 µM, R2 Ki ) 100 µM,
selectivity [R2 Ki/PNMT Ki] ) 180). In vivo administra-
tion of 1 decreased adrenal epinephrine levels, but
central epinephrine pools were unaffected. Autoradio-
graphic studies showed that 1 did not cross the blood-
brain barrier (bbb),9 presumably due to its low lipophi-
licity. As compared to 1, SK&F 64139 (2) was less
selective (PNMT Ki ) 0.20 µM, R2 Ki ) 0.021 µM,
selectivity ) 0.10), but was able to penetrate the bbb.10
A number of more lipophilic 1,2,3,4-tetrahydroisoquino-
line-7-sulfonanilides (3) were prepared and evaluated
by Blank et al.11 From that study it was concluded that
an acidic NH, rather than an acidic hydrogen such as
in SO2CH2(CdO)Ar, is essential for PNMT-inhibitory
activity. However, no data on these compounds for their
R2-adrenoceptor affinity were reported, and thus the
actual role of an acidic hydrogen, or an acidic NH of
the aminosulfonyl group, in imparting selectivity re-
mained to be evaluated. Because of the high potency
of 1 toward the inhibition of PNMT and its low affinity
for the R2-adrenoceptor, it seemed important to deter-
mine the reason for the selectivity of 1sis it the
presence of an acidic hydrogen, is it more specifically
the presence of an acidic NH as part of an aminosulfonyl
* To whom correspondence should be addressed.
X Abstract published in Advance ACS Abstracts, November 15, 1997.
S0022-2623(96)00235-X CCC: $14.00 © 1997 American Chemical Society

3998 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25
Grunewald et al.
Ta ble 1. In Vitro Activities of Inhibitors of PNMT and Binding
of [3H]Clonidine at the R2-Adrenoceptor
A
B
B/A
a
compd pKa PNMT Ki ( SEM (µM) R2 Ki ( SEM (µM) selectivity
1
4
5
6
7
10.0
7.8b
11.4
9.0
0.55 ( 0.04
2.6 ( 0.2
4.6 ( 0.3
48 ( 2
100 ( 20
6.3 ( 0.5
130 ( 10
11 ( 1
190 ( 10
18 ( 1
0.078 ( 0.002
1.6 ( 0.1
4.6 ( 0.1
2.1 ( 0.1
0.84 ( 0.03
2.2 ( 0.2
180
2.4
28
0.23
0.042
0.055
0.080
0.34
0.31
0.25
0.60
0.85
∼4500
330 ( 10
0.98 ( 0.06
8
9
11.9c
10.0
F igu r e 1. Alignment of compound 9 (gray) with SK&F 29661
(1, bold) showing the proximity of the lone pair (2.4 Å long)
on the oxygen of the phenolic hydroxy group of 9 with that on
the nitrogen of the aminosulfonyl group of 1. MNDO-optimized
geometries of 1 and 9 were fitted using the THIQ nitrogen
and two ends of a 2 Å long normal passing through the centroid
of the aromatic ring in the tetrahydroisoquinoline nucleus. The
closest distance between these lone pairs was about 0.23 Å.
Free rotation about the C-O bond in 9 and the SO2-N bond
in 1 was presumed to arrive at this distance.
21
22
23
27
28
4.7 ( 0.2
15 ( 2
8.4 ( 0.8
1.4 ( 0.1
2.6 ( 0.1
10.0
10.0
a
pKa values were based on literature data for the benzene
analogues,14 as the values for the substituted THIQ’s were
unavailable. For example, the pKa of 1 was based on PhSO2NH2,
which has a value of 10. Thus, while the pKa values listed will
not be exact, the relative values listed in the table should be
correct. b The pKa value was estimated based on known compounds
and substituent effects. The value for compound 4 was based on
PhSO2NHPh, which has a reported pKa of 8.4.14 A p-chloro
substituent lowers the pKa by approximately 0.6 (e.g. the pKa of
p-chloroaniline is 4.07,33a as compared to 4.69 for aniline33b and
the pKa of p-chlorophenol is 9.4,34 as compared to 10.0 for phenol),
and so the pKa for 4 was estimated as 7.8. c The value for
compound 8 was based on PhSO2NHCH2Ph, which has a reported
pKa of 11.25.14 Substitution of a methyl group for the phenyl
attached to the sulfonyl increases the pKa by approximately 0.7,
and so the pKa for 8 was estimated as 11.9 (e.g. the pKa of
CH3SO2NH2 is 10.7 [pKa value of 10.8 at 25 °C corrected to 20
°C], as compared to 10.0 for PhSO2NH2).14
droisoquinoline (THIQ) nucleus, and (3) the electron-
withdrawing effect of the (methylsulfonyl)amino group
is less than that of the aminosulfonyl group (σp ) 0.03
and 0.57, respectively). Because of the good PNMT
inhibition by 4,11 it was thought that there was some
steric bulk tolerance at this region of the active site of
PNMT, and so compound 7, which possesses no acidic
hydrogen, was included for comparison purposes. The
addition of a methylene spacer at the 7-position of 6
(compound 8) restores the acidic hydrogen to the same
region of space as that of 1. However, this also reduces
the acidity of 8 as compared to 1.
Compounds 9 and 23 (a less conformationally con-
strained analogue of 9) were proposed because relatively
flat substituents are tolerated at the 7- and 8-positions
of THIQ at the PNMT active site12,13 and the hydroxyl
group in phenol has about the same pKa as that of the
aminosulfonyl group as in 1.14 In addition, the lone pair
on the oxygen of 9 is in a position in space near that
occupied by the lone pair on the aminosulfonyl nitrogen
in 1 (see Figure 1). Thus, 9 and 23 will allow assess-
ment of the effect of the acidic hydrogen, independent
of the aminosulfonyl group. Compound 21 is the non-
phenolic analogue of 23 and is included for comparison
purposes, as are the methoxy intermediates of 23
(compound 22) and 9 (compound 27). Compound 28 was
previously evaluated in our laboratory15 and is included
for comparison purposes as the 7-OH group is in the
same region of space as the acidic NH of 6.
group, or is some other factor responsible? We have
designed a diverse set of compounds to address these
points.
Compounds 4 and 5, which had been previously
synthesized,11 were chosen to explore the relative
importance of the acidity of the NH of 1. Addition of a
p-chlorophenyl moiety (4) to the aminosulfonyl group
of 1 greatly increased the acidity of the aminosulfonyl
group, while the addition of a methyl group (5) de-
creased the acidity as compared to 1. (See Table 1 for
pKa values of this and the other compounds presented
in this study.) Although either addition increased the
steric bulk near the aminosulfonyl group, both 4 and 5
exhibited good PNMT affinity,11 although no data for
their R2-adrenoceptor affinity were reported.
Ch em istr y
Compound 4 was prepared by the method of Blank
et al.11 Compound 5 was synthesized according to a
general literature procedure.11,16 Compound 6 was
synthesized from the readily available 1,2,3,4-tetrahy-
droisoquinoline (10) as outlined in Scheme 1. Nitration
of 10 according to the literature procedure17,18 afforded
a mixture of two regioisomers with the desired com-
Compound 6 possesses a reversed aminosulfonyl
[(methylsulfonyl)amino] group and differs from 1 in
several respects: (1) it is more acidic than 1, (2) the
acidic NH is closer to the aromatic ring of the tetrahy-

PNMT Inhibitors: Aminosulfonyl Acidic Hydrogen
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25 3999
Sch em e 1
Sch em e 3
Compounds 22 and 23 were readily synthesized from
6-methoxynaphthalene-1-carbonitrile.22 Attempts to
synthesize the benz[h]isoquinoline compound 27 by a
modified Pomeranz-Fritsch reaction23 on 6-methoxy-
1-naphthaldehyde (prepared by reduction of 6-methoxy-
naphthalene-1-carbonitrile with DIBAL-H) yielded the
tricyclic product 24 in poor yields (10 to 15% after
extensive purification). The difficulty in cyclization at
the â-position on naphthalene is due to its low reactiv-
ity.24 Hence, another approach based on the synthesis
of azasteroids was adopted.25 Commercially available
6′-methoxy-2′-propiononaphthone was converted to the
6′-methoxy-2′-naphthylpropionic acid (25) by the
Willgerodt reaction.26 This acid was subjected to the
Curtius reaction protocol (Scheme 3), and the interme-
diate isocyanate was cyclized to 26 by heating with
BF3‚Et2O.27 The R-position on the naphthalene nucleus
is more reactive than the â-position,24 and hence only
26 was obtained. It is interesting to note that failure
to form a seven-membered ring in the intramolecular
cyclization of isocyanate in the same ring system has
been observed.28 An alternate lengthy method has been
reported for the synthesis of 26.28 Protons H-5 and H-6
showed ortho coupling in the aromatic region of the
proton NMR spectrum of 26, confirming the assignment
of the structure. Such a coupling would be absent if
the intermediate isocyanate had cyclized in the alter-
nate mode at the â-position. Reduction followed by
demethylation gave the desired naphthol compound 9.
Sch em e 2
pound 11 purified by fractional crystallization in 29%
yield. The aromatic proton splitting pattern in the H
1
NMR spectrum was in accordance for the 7-substitution,
and this was further ascertained by a one-dimensional
difference nuclear Overhauser experiment, wherein the
irradiation of H-1 led to increased intensity of the
downfield aromatic proton (H-8). Protection of the
secondary amine as the trifluoroacetamide (12) followed
by catalytic reduction gave 13. Treatment of thearo-
matic amine with 1 equiv of mesyl chloride in the
presence of pyridine as the base led to monomesylation,
whereas in the presence of 2 equiv of mesyl chloride
bismesylation occurred. Removal of the trifluoroacetyl
group under mild conditions19,20 provided the desired
compounds 6 and 7.
In the attempted synthesis of the ((methylsulfonyl)-
amino)methyl compound 8 (Scheme 2), when the di-
amine 16 was diazotized under normal Sandmeyer
conditions, it failed to provide the nitrile 17. Addition
of the diazotized solution of 16 to a basic solution (pH
8-9) of KCN/CuCN resulted in decomposition and resin
formation. As a basic pH is required to avoid the
formation of HCN, a biphasic cyanation procedure21
using nickel(II) sulfate instead of cuprous cyanide was
employed and a 34% yield of 17 could be obtained after
column chromatography. Protection of the secondary
amine as its trityl derivative followed by reduction of
the nitrile yielded 19. Mesylation and subsequent
deprotection under acidic conditions provided compound
8.
Bioch em istr y
All the compounds were evaluated as their hydro-
chloride or hydrobromide salts for in vitro activity as
inhibitors of PNMT. In vitro PNMT affinity was as-
sessed by use of a standard radiochemical assay that
has been described previously for inhibitors.29 Bovine
adrenal PNMT used for the in vitro assay was purified
according to the procedure of Connett and Kirshner30
through the isoelectric precipitation step. Inhibition
constants were determined by using three different
concentrations of inhibitor, as previously described,29
with phenylethanolamine as the variable substrate. R2-
Adrenergic receptor binding assays were performed
using cortex obtained from male Sprague-Dawley
rats.31 [3H]Clonidine was used as the radioligand to
define the specific binding and phentolamine was used
to define the nonspecific binding. Clonidine was used
as the ligand to define R-adrenergic binding affinity to
simplify the comparison with previous results.

4000 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25
Grunewald et al.
Resu lts a n d Discu ssion
or selectivity with the presence of an acidic hydrogen
in the region of space being studied.
The results of biochemical evaluations of the com-
pounds are presented in Table 1. We have expressed
selectivity as a ratio of the R2 Ki versus the PNMT Ki.
Reversing the aminosulfonyl group, as in compound
6, moves the acidic hydrogen closer to the aromatic ring.
This increases the acidity of the hydrogen, but 6
displays reduced selectivity as a result of decreased
PNMT affinity and increased R2-adrenoceptor affinity.
The acidic hydrogen of 28 is in a similar region of space
as that of 6, and 28 also displays a lack of selectivity,
although it possesses good PNMT inhibitor activity.
Again, there is no correlation with the presence of an
acidic hydrogen in the given region of space with PNMT
affinity or selectivity.
Removal of the aminosulfonyl acidic hydrogen, as in
compound 7, reduces selectivity even more, primarily
due to greatly reduced PNMT potency, but this is likely
a result of steric interference with binding at the PNMT
active site, as 7 also showed the lowest R2-adrenoceptor
affinity of all the compounds in this study.
The exact binding mode of 1 at either the PNMT
active site or the R2-adrenoceptor is unknown. All of
the compounds in this study exhibited competitive
kinetics when binding to PNMT. If we assume that they
bind in a similar fashion at the PNMT active site, then
the acidic hydrogen of compounds 4, 5, 8, 9, and 23 will
be located in the same region of space as that in 1, while
the acidic hydrogen of compounds 6 and 28 will lie closer
to the THIQ aromatic ring. With regard to acidity, the
pKa of the acidic hydrogen in compounds 9, 23, and 28
is equivalent to that of 1, while for compounds 4 and 6
it is lower and for compounds 5 and 8, it is higher.14
Compounds 7, 21, 22, and 27 do not possess an acidic
hydrogen. As probes for the effect of the sulfonyl group,
compounds 4 and 5 are derivatives of 1, compounds 6-8
have the amine of the aminosulfonyl group reversed
with regard to the aromatic ring (i.e. the electron-
withdrawing effect of the (methylsulfonyl)amino group
is less than that of the aminosulfonyl group of 1), and
compounds 9, 22, 23, 27, and 28 possess electron-
donating hydroxy or methoxy groups.
Su m m a r y a n d Con clu sion
The results from this study indicate that the presence
of an acidic hydrogen of the aminosulfonyl group of 1
does not impart selectivity for PNMT over the R2-
adrenoceptor. The results also indicate that the acidic
NH group was not essential for the high PNMT-
inhibitory activity in THIQ-type inhibitors. However,
the interpretation of these data is dependent on all of
the compounds binding in a similar manner at the
PNMT active site and in a similar manner (although
not necessarily the same manner as for PNMT) at the
R2-adrenoceptor.32 Thus, in the case of 1, it is likely
some other factor (such as the presence of the sulfonyl
group on the aromatic ring) which plays a major role in
imparting selectivity between the PNMT active site and
the R2-adrenoceptor, and not its pKa.
In general, all compounds showed reduced affinity
toward PNMT and, with the exceptions of 5 and 7,
showed increased R2-adrenergic affinity as compared to
1 (Table 1). For compounds 1, 4, and 5, the PNMT
affinity did not correlate with pKa (which would have
been the case if acidity was the determining factor);
however, both compounds 4 and 5 do possess additional
steric bulk which could complicate this interpretation.
It was noted that the R2-adrenoceptor affinity did
correlate with acidity for compounds 1, 4 and 5. The
pKa of compound 8 is comparable to that of 5, and the
acidic hydrogen occupies a similar region of space in
both molecules. However, the potency of 8 at PNMT is
considerably less and its R2-adrenoceptor affinity is
much greater, which would seem to indicate little
importance of the acidic hydrogen in determining af-
finity for PNMT or selectivity. However, as noted above,
there are significant differences in the electron-with-
drawing properties of the 7-substituents of compounds
1 and 8.
Exp er im en ta l Section
All reagents and solvents were reagent grade or were
purified by standard methods before use. Melting points were
determined in open capillaries on a Thomas-Hoover melting
point apparatus calibrated with known compounds but are
otherwise uncorrected. Proton nuclear magnetic resonance
spectra (1H NMR) were recorded on a Varian XL-300, a GE
QE-300 or a Bruker DRX-400 spectrometer with CDCl3 as the
solvent unless noted in the text, and chemical shifts are
reported in parts per million (ppm) relative to tetramethylsi-
lane (TMS, 0.00 ppm). Carbon nuclear magnetic resonance
spectra (13C NMR) were recorded on a Varian XL-300 or a
Bruker DRX-400 spectrometer with CDCl3 as the solvent, and
the chemical shifts are reported in ppm relative to CDCl3 (77.0
ppm). For the hydrobromide salts of the phenolic amines,
NMR spectra were recorded in deuterated dimethyl sulfoxide
(DMSO-d6), and the chemical shifts are reported relative to
DMSO (2.49 ppm for 1H and 39.5 ppm for 13C). Multiplicity
abbreviations: s, singlet; d, doublet; t, triplet; q, quartet; m,
multiplet; bs, broad singlet; e, exchangeable. Infrared spectra
were obtained on a Perkin-Elmer 1420 infrared spectropho-
tometer. Electron-impact mass spectra (EIMS) were obtained
When the THIQ portions of the low-energy conforma-
tions of 1 and 9 were superimposed, the lone pair on
the oxygen atom in 9 and the lone pair on the amino-
sulfonyl nitrogen of 1 were only 0.23 Å apart (Figure
1). If the unfavorable interaction responsible for the low
potency of 1 at the R2-adrenoceptor was occurring
through the acidic hydrogen or the lone pair, then 9
should also be a selective inhibitor. It was found that
9 was actually one of the least selective inhibitors of
those studied. Compound 23, a less conformationally
constrained analogue of 9, displayed a similar lack of
selectivity. Substitution of the phenolic hydrogen in 9
and 23 by a methyl group was found to reduce both
PNMT potency (as expected15) and R2-adrenoceptor
affinity slightly, as in compounds 27 and 22. Also,
compound 21, which does not possess a polar functional
group in the area of interest, has a higher affinity for
both PNMT and the R2-adrenoceptor than do 22 or 23.
Again, there is no apparent correlation of PNMT affinity
on
a Ribermag R10-10 mass spectrometer. The relative
intensities of the mass spectrum peaks are listed in paren-
theses. Preparative centrifugal thin-layer chromatography
(PCTLC) was performed on a Harrison Model 7924 Chroma-
totron (Harrison Research, Palo Alto, CA) using Merck silica
gel 60 PF254/CaSO4‚0.5H2O binder on 1, 2, or 4 mm thickness
plates. Analytical TLC was performed by using silica gel with
a fluorescent indicator coated on 1 × 3 in. glass plates in 0.2
mm thickness (Whatman MKGF silica gel 200 µm). Bulb to
bulb distillations were carried out on a Kugelrohr distillation
apparatus (Aldrich Chemical Co., Milwaukee, WI), and oven

PNMT Inhibitors: Aminosulfonyl Acidic Hydrogen
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25 4001
temperatures were recorded. Combustion analyses were
performed on a Hewlett-Packard Model 185B CHN analyzer
at the University of Kansas by Dr. Tho Ngoc Nguyen.
Amine hydrochloride salts were prepared by adding a
solution of methanolic HCl to a methanolic solution of the
amine, followed by crystallization of the resulting hydrochlo-
ride from MeOH-Et2O.
117 mmol) was added. The suspension was stirred in an ice
bath, trifluoroacetic anhydride (7.34 g, 4.94 mL, 34.9 mmol)
was added, and the mixture was allowed to stir for 24 h at
room temperature. The reaction mixture was poured onto ice
and extracted with CH2Cl2 (four times). The combined CH2-
Cl2 extracts were washed with 1 N HCl (four times) and brine
(once). The organic layer was dried over anhydrous Na2SO4,
and the solvent was removed under reduced pressure to yield
a yellow oil. The oil solidified on standing and was crystallized
from aqueous EtOH as pale buff needles (4.95 g, 80.6%, mp
66-67 °C): IR (KBr) 1685 (CO), 1520 (NO2), 1460, 1340 (NO2),
Compounds 1 and 2 were kindly provided by Smith Kline
and French Laboratories, Smith Kline Beecham Corp., Phila-
delphia, PA. S-Adenosyl-L-methionine was obtained from
Sigma Chemical Co. [methyl-3H]-S-Adenosyl-L-methionine
used in the radiochemical assay was purchased from New
England Nuclear Corp. (Boston, MA). Bovine adrenal glands
were obtained from Stinson Meat Processing (Ottawa, KS).
[3H]Clonidine used in the R2-adrenoceptor binding assay was
purchased from Amersham Corp. (Arlington Heights, IL).
7-((N-Meth ylam in o)su lfon yl)-1,2,3,4-tetr ah ydr oisoqu in -
olin e Hyd r och lor id e (5‚HCl). Compound 1 (58.1 mg, 0.274
mmol) was dissolved in dry THF (2 mL) and added to a
suspension of NaH (60% in mineral oil, 11.0 mg, 0.274 mmol)
in THF (2 mL) at 0 °C. The solution was stirred for 10 min.
A solution of MeI (13.0 µL, 0.206 mmol) in dry THF (1 mL)
was then added, and the solution was stirred for an additional
30 min. The reaction was quenched by the addition of water
(2 mL). The resulting solution was extracted with EtOAc
(three times), and the combined extracts were washed with
10% Na2CO3(aq) and brine. The organic phase was dried over
Na2SO4, and the solvent was removed under reduced pressure
to yield an off-white solid. Flash chromatography (flash silica
gel 32-63 µm, EtOAc as the eluent), followed by removal of
the solvent under reduced pressure yielded a colorless solid,
which was dissolved in methanol and converted to the hydro-
chloride salt. The solvent was removed and the residue
recrystallized from EtOH/hexane to yield 5‚HCl as white
needles (28.2 mg, 39.1%): mp (HCl) 243-244 °C; IR (KBr)
3150 (NH), 2900, 2800, 1410, 1320 (SO2), 1160 (SO2), 1130,
1
1200, 1140, 890 cm-1; H NMR (CDCl3) δ 8.15-8.05 (m, 2 H,
H-7, H-8), 7.40-7.32 (m, 1 H, H-6), 4.90-4.85 (m, 2 H, H-1),
4.00-3.89 (m, 2 H, H-3), 3.10-3.06 (m, 2 H, H-4); EIMS m/z
(relative intensity) 275 (M+ + 1, 16), 274 (M+, 100), 259 (10),
227 (25), 162 (14), 149 (35), 130 (15), 116 (26), 115 (30), 103
(28), 102 (14), 91 (31), 77 (69), 69 (45), 51 (34). Anal.
(C11H9F3N2O3) C, H, N.
7-Am in o-2-(tr iflu or oa cetyl)-1,2,3,4-tetr a h yd r oisoqu in -
olin e (13). Compound 12 (4.95 g, 18.1 mmol) was dissolved
in absolute EtOH, and PtO2 (0.05 g) was added. The reaction
mixture was hydrogenated at 50 psi until no further uptake
of H2 was seen (5 h). The suspension was filtered and
evaporated to afford a red oil that solidified on standing (3.68
g, 83.4%). The compound was crystallized from CH2Cl2-
hexanes as colorless crystals: mp 61-62 °C; IR (KBr) 3440
(NH2), 3360 (NH2), 1690 (CO), 1460, 1180, 1130, 820 cm-1; 1H
NMR (CDCl3) δ 6.96-6.90 (m, 1 H, ArH), 6.58-6.53 (m, 1 H,
ArH), 6.45-6.40 (m, 1 H, ArH), 4.67-4.62 (m, 2 H, H-1), 3.85-
3.77 (m, 2 H, H-3), 3.66 (bs, e, 2 H, NH2), 2.85-2.79 (m, 2 H,
H-4); EIMS m/z (relative intensity) 245 (M+ + 1, 14), 244 (M+,
100), 229 (20), 147 (M+ - COCF3, 11), 132 (12), 131 (19), 130
(23), 119 (85), 91 (27), 69 (45). Anal. (C11H11F3N2O) C, H, N.
7-(N-(Meth ylsu lfon yl)am in o)-2-(tr iflu or oacetyl)-1,2,3,4-
tetr a h yd r oisoqu in olin e (14). Amine 13 (1.25 g, 5.12 mmol)
was dissolved in CH2Cl2 (15 mL), and pyridine (0.81 g, 0.83
mL, 10 mmol) was added, followed by mesyl chloride (0.71 g,
0.83 mL, 10 mmol). The orange reaction mixture was stirred
overnight, and the reaction was then quenched by the addition
of 1 N HCl. Extraction by CH2Cl2 (four times) followed by
drying and evaporation of the solvent yielded an orange-red
semisolid which was passed through a silica plug (CHCl3-
THF, 20:1, as the eluent). The yellow oil (1.26 g, 76.4%)
obtained was crystallized from CH2Cl2-hexanes to yield the
desired compound 14 as white plates: mp 109-111 °C; IR
(KBr) 3240 (NH), 1690 (CO), 1310 (SO2), 1180 (SO2), 1140,
1
1050, 895, 700 cm-1; H NMR (DMSO-d6) δ 9.77 (bs, e, 2 H,
NH2+), 7.68 (s, 1 H, ArH), 7.65 (d, 1 H, J ) 8 Hz, ArH), 7.54
(brs, ex, 1 H, NH), 7.46 (d, 1 H, J ) 8 Hz, ArH), 4.34 (s, 2 H,
H-1), 3.37 (s, 3 H, NCH3), 3.10 (t, 2 H, J ) 6 Hz, H-3), 2.55 (t,
2 H, J ) 6 Hz, H-4); 13C NMR (DMSO-d6) δ 138.4, 137.8, 131.1,
130.6, 130.6, 126.2, 44.1(C-1), 40.9 (C-3), 29.5 (NCH3), 25.6 (C-
4); CIMS m/z (relative intensity) 217 (M+ + 1, 100), 132 (10),
131 (15). Anal. (C10H14N2O2S‚HCl) C, H, N.
7-Nitr o-1,2,3,4-tetr a h yd r oisoqu in olin e Hyd r och lor id e
(11‚HCl). 1,2,3,4-Tetrahydroisoquinoline (11.6 g, 84.8 mmol)
was added dropwise with care to stirred ice-cold concentrated
H2SO4 (42.0 mL). Potassium nitrate (9.40 g, 93.0 mmol) was
then added in small portions, taking care that the temperature
of the reaction mixture did not rise above 5 °C. After being
stirred overnight at room temperature, the dark brown reac-
tion mixture was added carefully to a stirred ice-cold concen-
trated NH4OH solution. The basic red reaction mixture was
extracted with CHCl3 (three times), and the combined CHCl3
extracts were washed with brine (once) and dried over
anhydrous Na2SO4. Evaporation of the organic solvent gave
a dark brown oil (14.6 g) which was taken up in EtOH (65
mL) and cooled in an ice bath. Treatment of this reddish
solution with concentrated HCl (11 mL) yielded a viscous
yellow precipitate of the hydrochloride salt which was filtered
and crystallized from methanol (250 mL) to yield 11‚HCl as a
buff solid (5.36 g, 29.4%). An analytically pure sample was
obtained by crystallization from aqueous acetone (mp 260-
262 °C; lit.17 mp 261 °C): IR (KBr) 1585, 1520 (NO2), 1425,
1345 (NO2), 1090, 950, 740 cm-1; 1H NMR (DMSO-d6) δ 10.07
(bs, 2 H, NH2+), 8.21 (d, J ) 2.2 Hz, 1 H, H-8), 8.11 (dd, 1 H,
J ) 8.4, 2.4 Hz, H-6), 7.53 (d, J ) 8.6 Hz, 1 H, H-5), 4.39 (s, 2
H, H-1), 3.38 (t, J ) 5.9 Hz, 2 H, H-3), 3.17 (t, J ) 5.9 Hz, 2
H, H-4); 13C NMR (DMSO-d6) δ 145.8, 140.4, 131.0, 130.2,
122.0, 121.9, 43.0 (C-1), 39.7 (C-3), 24.9 (C-4); EIMS m/z
(relative intensity) 178 (M+ + 1), 177 (M+), 161, 149, 131 (M+
- NO2), 103, 102, 91, 77, 63, 51. Anal. (C9H10N2O2‚HCl) C,
H, N.
1110, 970, 750 cm-1 1H NMR (CDCl3) δ 7.44 (m, b, e, 1 H,
;
NH), 7.15-7.09 (m, 3 H, ArH), 4.77-4.70 (m, 2 H, H-1), 3.90-
3.80 (m, 2 H, H-3), 3.02 (s, 3 H, SO2CH3), 3.00-2.90 (m, 2 H,
H-4); EIMS m/z (relative intensity) 324 (M+ + 2, 5), 323 (M+
+ 1, 15), 322 (M+, 63), 243 (M+ - SO2Me, 72), 197 (34), 146
(13), 145 (13), 130 (68), 118 (29), 103 (27), 91 (100), 84 (18), 69
(31), 49 (41). Anal. (C12H13F3N2O3S) C, H, N.
7-(N-(Meth ylsu lfon yl)am in o)-1,2,3,4-tetr ah ydr oisoqu in -
olin e Hyd r och lor id e (6‚HCl). Trifluoroacetamide 14 (0.64
g, 2.0 mmol) was added to dry saturated methanolic ammonia
and stirred for 14 h at room temperature. The solvent was
removed under reduced pressure to yield a pale yellow oil (0.47
g, 83%) which solidified on addition of CH2Cl2. Recrystalli-
zation from CH2Cl2-hexanes gave 6 as a colorless solid: mp
180-181 °C dec; IR (KBr) 3300 (NH), 1310 (SO2), 1140 (SO2),
1
980, 820 cm-1; H NMR (DMSO-d6) δ 6.99 (s, 2 H, H-6, H-8),
6.88 (s, 1 H, H-7), 5.21 (bs, e, 2 H, NH, NHSO2Me), 3.89 (s, 2
H, H-1), 3.02 (t, J ) 5.8 Hz, 2 H, H-3), 2.88 (s, 3 H, SO2CH3),
2.69 (t, J ) 5.7 Hz, 2 H, H-4); 13C NMR (DMSO-d6) δ 136.6,
135.3, 130.7, 129.5, 118.2, 117.8, 47.7, 43.2, 38.3, 28.0.
The hydrochloride salt was crystallized from aqueous
MeOH: mp 263-264 °C dec; EIMS m/z (relative intensity) 226
(M+, 14), 225 (M+ - 1, 9), 197 (36), 147 (M+ - SO2Me, 12),
118 (22), 91 (88), 79 (13), 65 (100). Anal. (C10H14N2O2S‚HCl)
C, H, N.
7-(N,N-Bis(m eth ylsu lfon yl)a m in o)-2-(tr iflu or oa cetyl)-
1,2,3,4-tetr a h yd r oisoqu in olin e (15). Amine 13 (1.25 g, 5.12
mmol) was dissolved in CH2Cl2 (20 mL), and triethylamine
(2.59 g, 3.56 mL, 25.6 mmol) was added. The pale yellow
solution was stirred in an ice bath, and mesyl chloride (1.76
7-Nitr o-2-(tr iflu or oa cetyl)-1,2,3,4-tetr a h yd r oisoqu in o-
lin e (12). Compound 11‚HCl (5.00 g, 23.3 mmol) was sus-
pended in CH2Cl2 (20 mL), and to it pyridine (9.22 g, 9.42 mL,

4002 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25
Grunewald et al.
g, 1.21 mL, 15.4 mmol) was added dropwise. The reaction
mixture was stirred at room temperature for 48 h. The orange-
red reaction mixture was diluted with 1 N HCl and extracted
with CH2Cl2 (four times). The combined CH2Cl2 layers were
washed with 1 N HCl (four times) and brine (once). Evapora-
tion of the solvent after drying over Na2SO4 yielded a red foam
(1.80 g). Purification by PCTLC (silica, 4 mm) using CHCl3-
THF (20:1) as the eluent yielded 15 as a pale yellow foam (1.58
g, 77.3%). The compound was crystallized from CH2Cl2 as pink
plates: mp 149-150 °C; IR (KBr) 1690 (CO), 1360 (SO2), 1190,
1170, 1155, 1130, 970, 930, 750 cm-1; 1H NMR (CDCl3) δ 7.30-
7.15 (m, 3 H, ArH), 4.83-4.75 (m, 2 H, H-1), 3.89-3.85 (m, 2
H, H-3), 3.35 (s, 6 H, SO2CH3), 3.00-2.90 (m, 2 H, H-4); EIMS
m/z (relative intensity) 402 (M+ + 2, 3), 401 (M+ + 1, 6), 400
(M+, 27), 321 (M+ - SO2Me, 10), 289 (6), 259 (7), 243 (16), 242
(20), 241 (74), 130 (10), 116 (18), 84 (52), 79 (23), 49 (100).
Anal. (C13H15F3N2O5S2) C, H, N.
to yellow-brown. To this mixture was added dropwise with
vigorous stirring the diazotized solution. Brisk evolution of
N2 was observed, and the reaction mixture was allowed to
warm to room temperature over a period of 2 h. The mixture
was warmed to 50 °C in an oil bath for 1 h, cooled to room
temperature, made basic with 1 N NaOH, and filtered through
Celite. The Celite bed was washed with CH2Cl2, the filtrate
was extracted with CH2Cl2 (three times), and the combined
organic layers were washed with brine (once). Removal of the
solvent after drying gave a dark black oil (0.60 g) which was
distilled bulb to bulb (100-105 °C, 0.15 mmHg) to afford a
colorless oil (0.30 g) which solidified on cooling. The compound
was further purified by PCTLC (silica, 2 mm) using CH2Cl2-
MeOH-NH4OH (250:20:1) as the eluent. Compound 17 was
obtained as a colorless solid (0.27 g, 33%, mp 92-94 °C): IR
(KBr) 3300 (NH), 2220 (CN), 1490, 1420, 950, 860, 820 cm-1
;
1H NMR (CDCl3) δ 7.37 (d, J ) 7.8 Hz, 1 H), 7.31-7.29 (m, 1
H), 7.17 (d, J ) 8 Hz, 1 H), 4.00 (s, 2 H, H-1), 3.12 (t, J ) 5.9
Hz, 2 H, H-3), 2.84 (d, J ) 5.9 Hz, 2 H, H-4), 1.8 (s, e, 1 H,
NH); 13C NMR (CDCl3) δ 140.6, 137.2, 130.0, 129.8, 129.3,
118.9, 109.2 (CN), 47.7 (C-1), 43.1 (C-3), 29.3 (C-4).
7-(N,N-Bis(m eth ylsu lfon yl)am in o)-1,2,3,4-tetr ah ydr oiso-
qu in olin e Hyd r och lor id e (7‚HCl). Trifluoroacetamide 15
(0.75 g, 1.9 mmol) was dissolved in 20% aqueous MeOH (12
mL). To that solution was added K2CO3 (0.28 g, 2.1 mmol),
and the solution was stirred for 10 h at room temperature.
The solvent was removed under reduced pressure, and the
yellow residue was suspended in water and extracted with
CH2Cl2 (three times). The combined CH2Cl2 extracts were
dried over Na2SO4 and evaporated to yield a yellow foam. This
compound was purified by PCTLC (silica, 2 mm) using CH2-
Cl2-MeOH-NH4OH (250:20:1) as the eluent. Compound 7
was isolated as a colorless solid (0.26 g, 46%): mp 170-171
The hydrochloride salt was crystallized from MeOH-Et2O
as a colorless solid: mp 298-300 °C dec; EIMS m/z (relative
intensity) 159 (M+ + 1, 3), 158 (M+, 34), 157 (M+ - 1, 100),
129 (95), 102 (21), 77 (11) 51 (16). Anal. (C10
H, N.
H10N2‚HCl) C,
7-Cyan o-2-(tr iph en ylm eth yl)-1,2,3,4-tetr ah ydr oisoqu in -
olin e (18). Triethylamine (1.12 g, 1.55 mL, 11.1 mmol) was
added to a solution of nitrile 17 (1.58 g, 10.0 mmol) in CH2Cl2
(15 mL). The solution was chilled in an ice bath, and
4-(dimethylamino)pyridine (0.12 g, 1.0 mmol) and triphenyl-
methyl chloride (4.18 g, 15.0 mmol) were added. After 14 h of
stirring, the reaction was quenched by the addition of water.
The reaction mixture was extracted with CH2Cl2 (three times),
and the combined CH2Cl2 extracts were dried and evaporated
to yield a yellow foam (4.93 g). The foam was purified by
chromatography (silica gel, CH2Cl2-hexanes-MeOH-NH4-
OH, 150:450:10:1, as the eluent) to yield 18 as a colorless fluffy
solid (3.47 g, 86.7%). Crystallization of the solid from CH2-
Cl2-hexanes gave colorless needles (mp softens at 195 °C and
melts completely at 202 °C): IR (KBr) 2210 (CN), 1480, 1440,
1070, 1035, 935, 740, 705 cm-1; 1H NMR (CDCl3) δ 7.54-7.51
(m, 6 H), 7.39-7.14 (m, 12 H), 3.44 (bs, 2 H, H-1), 3.06-3.02
(m, 2 H, H-3), 2.55 (bs, 2 H, H-4); 13C NMR (CDCl3) δ 142.1,
140.9, 137.6, 130.3, 129.5, 129.1, 127.9, 127.7, 126.3, 119.1
(CN), 109.1, 77.2 (CPh3), 50.5 (C-1), 45.8 (C-3), 30.2 (C-4);
EIMS m/z (relative intensity) 400 (0.1), 323 (M+ - Ph, 3), 243
(Ph3C+, 100), 165 (52), 105 (15), 91 (13), 51 (11). Anal.
(C29H24N2) C, H, N.
1
°C dec; H NMR (CDCl3) δ 7.27-7.00 (m, 3 H), 3.96 (s, 2 H,
H-1), 3.38 (s, 6 H, SO2CH3), 3.16-3.12 (m, 2 H, H-3), 2.83-
2.75 (m, 2 H, H-4), 1.98 (bs, e, 1 H, NH); 13C NMR (CDCl3) δ
137.9, 137.8, 130.8, 130.6, 128.2, 127.9, 48.0 (C-1), 43.3, 42.6,
28.9 (C-4).
The hydrochloride salt was crystallized from aqueous
methanol: mp 263-264 °C dec; IR (KBr) 1360 (SO2), 1335,
1150 (SO2), 950, 920, 760 cm-1; EIMS m/z (relative intensity)
305 (M+ + 1, 5), 304 (M+, 15), 303 (26), 275 (11), 225 (M+
-
SO2Me, 100), 209 (17), 146 (85), 119 (19), 118 (36), 116 (38),
91 (98), 79 (52), 65 (36), 43(32). Anal. (C11H16N2O4S2‚HCl) C,
H, N.
7-Am in o-1,2,3,4-tetr a h yd r oisoqu in olin e Dih yd r och lo-
r id e (16‚2HCl). In a Parr shaker bottle was placed 11‚HCl
(15.0 g, 69.9 mmol) dissolved in 95% EtOH (100 mL), and
concentrated HCl (10 mL), water (25 mL), and PtO2 (0.5 g)
were added. The mixture was hydrogenated at 50 psi until
no drop in pressure was observed (4 h). The yellowish
suspension was filtered through Celite and evaporated to
dryness to afford a yellowish solid which was made basic with
10% NaOH solution. Extraction of the basic solution with
CHCl3 (three times), followed by drying over anhydrous Na2-
SO4 and evaporation of the solvent, yielded a reddish yellow
solid (9.54 g, 92.2%): mp 110-112 °C (lit.17 mp 120-121 °C);
7-(Am in om eth yl)-2-(tr ip h en ylm eth yl)-1,2,3,4-tetr a h y-
d r oisoqu in olin e (19). To a solution of nitrile 18 (3.05 g, 7.61
mmol) in dry THF (20 mL) was added BH3‚THF complex (1 M
solution in THF, 10 mL, 10 mmol) dropwise. After addition
was complete, the mixture was refluxed under N2 for 18 h.
The reaction mixture was cooled, and MeOH was added to
quench excess borane. The solvent was removed under
reduced pressure and the residue was heated under N2 with
6 N NaOH (50 mL) for 3 h. The reaction mixture was
extracted with CH2Cl2 (four times) and evaporated to yield a
foamy solid (3.39 g). Purification by PCTLC (silica gel, 4 mm)
using CH2Cl2-MeOH-NH4OH (250:17:1) as the eluent yielded
compound 19 as a colorless foam (2.37 g, 76.9%). Crystalliza-
tion of this foam from CH2Cl2-hexanes afforded pale yellow
crystals: mp 109-110 °C; IR (KBr) 3430 (NH2), 3360 (NH2),
IR (KBr) 3400 (NH2), 3320 (NH2), 1500, 1440, 1300, 820 cm-1
;
1H NMR (CDCl3) δ 6.86 (d, J ) 7.8 Hz, 1 H, H-6), 6.51-6.47
(m, 1 H, H-8), 6.39-6.30 (bs, 1 H, H-5), 3.90 (s, 2 H, H-1), 3.08
(t, J ) 5.9 Hz, 2 H, H-3), 2.66 (t, J ) 5.9 Hz, 2 H, H-4); 13C
NMR (CDCl3) δ 144.0, 136.6, 129.8, 124.5, 113.4, 112.1, 48.2
(C-1), 44.1 (C-3), 28.2 (C-4).
The dihydrochloride salt was recrystallized from aqueous
MeOH as buff-colored needles: mp 290 °C dec; EIMS m/z
(relative intensity) 149 (M+ + 1, 5), 148 (M+, 38), 119 (100),
118 (29), 91 (19), 51 (11). Anal. (C9H12N2‚2HCl) C, H, N.
7-Cya n o-1,2,3,4-t et r a h yd r oisoq u in olin e H yd r och lo-
r id e (17‚HCl). The diamine 16 (0.75 g, 5.1 mmol) was
dissolved in concentrated HCl (1.75 mL) and water (2 mL) and
stirred in an ice bath, giving a red solution. To this solution
was added dropwise NaNO2 (0.35 g, 5.1 mmol) dissolved in
water (2 mL). After 15 min of stirring, a positive starch-iodide
test was obtained and the excess HNO2 was destroyed by the
addition of urea (0.10 g).
In another flask, a solution of NaOH (0.50 g in 1.5 mL water)
and KCN (1.63 g in 5 mL water) was prepared, and benzene
(5 mL) was added. This suspension was chilled in an ice bath,
and to it was added a solution of Ni2SO4‚6H2O (1.3 g, 5 mmol
in 2.5 mL water). The color of the resulting mixture changed
1480, 1440, 1030, 740, 705 cm-1 1H NMR (CDCl3) δ 7.56-
;
7.54 (m, 6 H, ArH), 7.27-7.05 (m, 12 H, ArH), 3.73 (s, 2 H,
H-1), 3.45 (bs, 2 H, ArCH2NH2), 2.98-2.96 (m, 2 H, H-3), 2.52
(bs, 2 H, H-4), 1.49 (bs, e, 2 H, NH2); 13C NMR (CDCl3) δ 142.2,
140.1, 136.1, 133.2, 129.0, 128.6, 127.3, 125.8, 125.0, 124.6,
76.4 (CPh3), 50.6 (C-1), 46.2, 45.9, 29.4 (C-4); EIMS m/z
(relative intensity) 404 (M+, 0.3), 327 (M+ - Ph, 4), 243 (Ph3C+,
91), 165 (100), 132 (25), 115 (26), 91 (56), 77 (35), 51 (27). Anal.
(C29H28N2) C, H, N.
7-((N -(Me t h ylsu lfon yl)a m in o)m e t h yl)-2-(t r ip h e n yl-
m eth yl)-1,2,3,4-tetr a h yd r oisoqu in olin e (20). A solution of
amine 19 (2.10 g, 5.19 mmol) in dry CH2Cl2 (20 mL) was chilled

PNMT Inhibitors: Aminosulfonyl Acidic Hydrogen
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25 4003
brown needles (0.56 g, 82%): mp 256-258 °C dec; IR (KBr)
in an ice bath, and triethylamine (0.58 g, 0.79 mL, 5.7 mmol)
was added. After addition of mesyl chloride (0.65 g, 0.45 mL,
5.4 mmol), the mixture was stirred at room temperature for
16 h. The reaction was quenched with 1 N NaOH and
extracted with CH2Cl2 (four times). The combined CH2Cl2
layers were dried and evaporated to yield a white foam (2.59
g) which was passed through a silica gel plug (CHCl3-THF,
20:1, as the eluent) to yield a colorless solid (2.21 g, 88.4%):
mp 185-187 °C dec; IR (KBr) 3270 (NH), 1320 (SO2), 1145
1
3270 (OH), 1610, 1600, 1580, 1240, 1210, 870, 800 cm-1; H
NMR (DMSO-d6) δ 9.85 (bs, e, 1 H, OH), 8.35 (bs, e, 3 H, NH3+),
8.01 (d, J ) 9.2 Hz, 1 H), 7.75 (d, J ) 7.7 Hz, 1 H), 7.46-7.38
(m, 2 H), 7.23-7.14 (m, 2 H), 4.47 (s, 2 H, CH2); 13C NMR
(DMSO-d6) δ 155.5, 135.1, 129.8, 127.5, 125.7, 125.2, 125.2,
124.1, 119.1, 109.7, 39.4 (CH2); EIMS m/z (relative intensity)
174 (M+ + 1, 10), 173 (M+, 100), 172 (M+ - 1, 93), 157 (25),
145 (26), 144 (20), 128 (31), 127 (48), 115 (74). Anal. (C11H11
-
(SO2), 1130, 1070, 740, 710 cm-1
;
1H NMR (CDCl3) δ 7.55-
NO‚HBr) C, H, N.
7.52 (m, 6 H, ArH), 7.28-7.09 (m, 12 H, ArH), 4.69 (bs, e, 1
H, NH), 4.20-4.18 (m, 2 H, H-1), 3.43 (bs, 2 H, CH2NH), 2.98-
2.96 (m, 2 H, H-3), 2.82 (s, 3 H, SO2CH3), 2.56-2.45 (m, 2 H,
H-4); 13C NMR (CDCl3) δ 142.4, 142.3, 136.9, 135.0, 133.6,
129.2, 127.6, 126.1, 125.5, 77.4 (CPh3), 50.9 (C-1), 46.9, 46.3,
40.9 (SO2CH3), 29.6 (C-4); EIMS m/z (relative intensity) 482
(M+, 0.1), 405 (M+ - Ph, 2), 244 (26), 243 (Ph3C+, 100), 165
(64), 91 (15). Anal. (C30H30N2O2S) C, H, N.
7-((N-(Meth ylsu lfon yl)a m in o)m eth yl)-1,2,3,4-tetr a h y-
d r oisoqu in olin e Hyd r och lor id e (8‚HCl). To a solution of
compound 20 (2.0 g, 4.1 mmol) in acetone (25 mL) was added
3 N HCl (10 mL). The solution was stirred for 12 h at room
temperature, and the acetone was removed under reduced
pressure. The aqueous layer was washed with CH2Cl2 (four
times) and evaporated to yield a colorless solid (1.04 g, 75.9%).
Crystallization from aqueous MeOH yielded colorless
needles: mp 224-226 °C dec; EIMS m/z (relative intensity)
241 (M+ + 1, 4), 240 (M+, 17), 239 (M+ - 1, 53), 211 (19), 159
(15), 145 (22), 132 (74), 131 (100), 117 (18), 115 (17), 103 (18),
77 (41), 51 (15). Anal. (C11H16N2O2S‚HCl) C, H, N.
3,4-Dih yd r o-8-m e t h oxy-b e n z[h ]isoq u in olin -1(2H )-
on e (26). (6′-Methoxy-2′-naphthyl)-3-propionic acid26 (1.00 g,
4.34 mmol) was treated with oxalyl chloride (3.4 mL, 39.1
mmol) for 2 h at room temperature, and the dark brown-red
reaction mixture was evaporated to dryness. Dry benzene was
added to the residue and evaporated to remove the traces of
oxalyl chloride. The acid chloride was dissolved in acetone (5
mL) and chilled in an ice bath, and sodium azide (0.61 g, 9.3
mmol), dissolved in a minimum amount of water, was added.
After the completion of the addition the reaction mixture was
allowed to warm to room temperature and was stirred for 1
h. The biphasic reaction mixture was quenched with ice and
extracted with toluene (three times), and the combined organic
extracts were dried over anhydrous Na2SO4. The dark brown
toluene extract was heated to reflux for 3 h. The solvent was
removed to afford a dark brown oil which showed a charac-
teristic band for the isocyanate group in the IR at 2300 cm-1
.
The oil was refluxed under nitrogen for 14 h with BF3‚Et2O (5
mL), the reaction mixture was quenched with ice and extracted
with CH2Cl2 (three times). The combined extracts were dried
over anhydrous Na2SO4 and the solvent was evaporated to
yield a dark brown solid (0.98 g), which was purified by flash
chromatography (hexanes-EtOAc, 1:1, as the eluent) to yield
a pale brown solid (0.75 g, 76%). The compound was crystal-
lized from EtOAc-hexanes as a pale pink shiny crystalline
solid: mp 171-172 °C (lit.28 mp 170-172 °C); IR (KBr) 3190
A small amount of the hydrochloride salt was neutralized
with 5% NH4OH, and the solution was extracted with CH2Cl2
(four times). The colorless solid obtained by evaporation of
the CH2Cl2 extracts was crystallized from CH2Cl2-hexanes as
small colorless crystals: mp 144-145 °C; IR (KBr) 3300 (NH),
1500, 1300 (SO2), 1140 (SO2), 1070, 980, 850, 800 cm-1 1H
;
1
(NH), 1660 (CO), 1620, 1475, 1235, 1165, 1025, 830 cm-1; H
NMR (DMSO-d6) δ 7.4 (bs, e, 1 H, NH), 7.11-6.98 (m, 3 H,
ArH), 4.12 (s, 2 H, CH2NHSO2Me), 3.93 (s, 2 H, H-1), 3.05 (t,
2 H, J ) 5.8 Hz, H-3), 2.77 (s, 3 H, SO2CH3), 2.73 (t, 2 H, J )
5.8 Hz, H-4); 13C NMR (DMSO-d6) δ 134.8, 133.7, 132.8, 127.9,
124.2, 124.0, 46.8, 45.0, 42.3, 39.1, 27.4.
NMR (CDCl3) δ 9.34 (d, 1 H, J ) 9.6 Hz, H-6), 7.78 (d, 1 H, J
) 8.4 Hz, H-5), 7.28-7.24 (m, 2 H, H-7 and H-9), 7.16 (bs, e,
1 H, NH), 7.13-7.10 (m, 1 H, H-10), 3.91 (s, 3 H, OCH3), 3.56-
3.50 (m, 2 H, H-3), 3.05 (t, 2 H, J ) 6.6 Hz, H-4); 13C NMR
(CDCl3) δ 167.3 (CO), 157.1, 137.4, 134.6, 131.4, 128.3, 127.1,
125.9, 123.8, 120.0, 106.3, 55.2 (OCH3), 39.3 (C-3), 30.0 (C-4);
EIMS m/z (relative intensity) 228 (M+ + 1, 18), 227 (M+, 100),
199 (8), 198 (40), 170 (74), 155 (36), 139 (15), 128 (18), 127
(47), 126 (18), 99 (13), 77 (18), 63 (13). Anal. (C14H13NO2) C,
H, N.
1-(Am in om eth yl)-6-m eth oxyn a p h th a len e Hyd r och lo-
r id e (22‚HCl). 6-Methoxynaphthalene-1-carbonitrile22 (2.00
g, 10.9 mmol) was dissolved in dry THF (10 mL), and
BH3‚Me2S complex (2 M solution in THF, 6 mL, 12.0 mmol)
was added dropwise to this red-brown solution. After heating
to reflux for 3 h, the solvent was removed by evaporation, and
the resulting red-yellow residue was carefully acidified with
methanolic HCl (20 mL). After the mixture was heated to
reflux for 12 h, a suspension was obtained which was cooled
to room temperature, and the solvent was evaporated to yield
a yellow solid. The solid was dissolved in 10% HCl (30 mL),
and the solution was washed with Et2O (four times). The
aqueous layer was cooled and made basic with KOH pellets.
Extraction of the aqueous layer with Et2O (four times) followed
by evaporation of the Et2O extracts yielded a yellow solid (1.69
g). Purification by PCTLC (silica, 4 mm) using CH2Cl2-
MeOH-NH4OH (250:25:1) as the eluent yielded a yellowish-
white solid (1.42 g, 69.6%, mp 58-60 °C): 1H NMR (CDCl3) δ
7.92 (d, 1 H, J ) 9.1 Hz), 7.62 (d, 1 H, J ) 8.2 Hz), 7.36 (t, 1
H, J ) 7.6 Hz), 7.26 (d, 1 H, J ) 7 Hz), 7.14-7.12 (m, 2 H),
4.21 (s, 2 H), 3.86 (s, 3 H), 1.59 (s, e, 2 H); 13C NMR (CDCl3)
δ 157.2, 138.8, 135.0, 126.4, 126.3, 126.1, 124.7, 122.1, 118.5,
106.6, 55.1, 43.9.
The hydrochloride salt was crystallized from MeOH-Et2O
as colorless shiny fluffy needles: mp 268-270 °C dec; IR (KBr)
3030, 1615, 1600, 1510, 1260, 1230, 1020, 830, 810 cm-1; EIMS,
m/z (relative intensity) 188 (M+ + 1, 14), 187 (M+, 100), 171
(M+ - CH3, 25), 144 (33), 127 (27), 128 (29), 115 (100), 114
(27), 102 (12), 89 (19), 77 (22), 63 (43). Anal. (C12H13NO‚HCl)
C, H, N.
1-(Am in om et h yl)-6-h yd r oxyn a p h t h a len e H yd r ob r o-
m id e (23‚HBr ). Amine 22 (0.50 g, 2.7 mmol) was heated to
reflux with 48% HBr (10.5 mL) for 3 h. The reaction mixture
was cooled and concentrated in vacuo to give a reddish brown
solid which was crystallized from MeOH-Et2O as pale reddish
8-Meth oxy-1,2,3,4-tetr a h yd r oben z[h ]isoqu in olin e Hy-
d r och lor id e (27‚HCl). Amide 26 (1.26 g, 5.54 mmol) was
dissolved in dry THF (10 mL) and refluxed under N2 with
BH3‚Me2S complex (2 M solution in THF, 8.3 mL, 16.6 mmol)
for 14 h. The excess borane was destroyed with methanol, and
the solvent was removed to yield a semisolid. The semisolid
was refluxed with concentrated HCl (2 mL) and MeOH (10
mL) for 4 h. The resulting white suspension was cooled, made
basic with KOH pellets, and extracted with CH2Cl2 (three
times). The combined extracts were dried over anhydrous Na2-
SO4, and the solvent was evaporated to yield a yellow solid
(1.30 g). PCTLC (4 mm, silica gel; CH2Cl2-MeOH-NH4OH,
250:17:1, as the eluent) yielded a colorless solid (1.01 g,
85.6%): mp 84-86 °C; mp (HCl) 228-229 °C dec; IR (KBr)
3250 (NH), 1620, 1600, 1240, 1160, 1120, 1030, 850, 820 cm-1
;
1H NMR (CDCl3) δ 7.64 (d, 1 H, J ) 9.1 Hz, H-6), 7.51 (d, 1 H,
J ) 8.4 Hz, H-5), 7.14-7.08 (m, 3 H, H-7, H-9 and H-10), 4.32
(s, 2 H, H-1), 3.88 (s, 3 H, OCH3), 3.15 (t, 2 H, J ) 5.8 Hz,
H-3), 2.85 (t, 2 H, J ) 5.8 Hz, H-4), 2.12 (s, e, 1 H, NH); 13C
NMR (CDCl3) δ 156.8, 133.1, 130.3, 129.8, 128.5, 125.8, 125.1,
123.3, 118.2, 106.7, 55.1 (OCH3), 45.4 (C-1), 43.4 (C-4), 29.6
(C-3).
The hydrochloride salt was crystallized from i-PrOH-MeOH
as a colorless fluffy solid: mp 228-229 °C; EIMS m/z (relative
intensity) 214 (M+ + 1, 16), 213 (M+, 88), 212 (M+ - 1, 63),
198 (M+ - CH3, 8), 185 (22), 184 (100), 169 (19), 141 (36), 139
(15), 115 (33), 86 (17), 84 (25), 49 (35). Anal. (C14H15NO‚
HCl‚0.75H2O) C, H, N.
8-Hyd r oxy-1,2,3,4-tetr a h yd r oben z[h ]isoqu in olin e Hy-

4004 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25
Grunewald et al.
(2) Fuller, R. W. Overview and Concluding Remarks. In Epinephrine
in the Central Nervous System. Proceedings of the International
Symposium on Brain Epinephrine; Stolk, J ., U’Prichard, D.,
Fuxe, K., Eds.; Oxford Press: London, 1987; pp 366-369.
(3) Ho¨kfelt, T.; Fuxe, K.; Goldstein, M.; J ohansson, G. Immunohis-
tochemical Evidence for the Existence of Adrenaline Neurons
in the Rat Brain. Brain Res. 1974, 66, 235-251.
(4) Crowley, W. R.; Terry, L. C.; J ohnson, M. D. Evidence for the
Involvement of Central Epinephrine Systems in the Regulation
of Luteinizing Hormone, Prolactin, and Growth Hormone Re-
lease in Female Rats. Endocrinology 1982, 110, 1102-1107.
(5) Trudeau, F.; Brisson, G. R.; Pe´ronnet, F. PNMT Inhibition
Decrease Exercise Tolerance in the Rat. Physiol. Behav. 1992,
52, 389-392.
(6) Mefford, I. N.; Lister, R. G.; Ota, M.; Linnoila, M. Antagonism
of Ethanol Intoxication in Rats by Inhibitors of Phenylethano-
lamine N-Methyltransferase. Alcoholism 1990, 14, 53-57.
(7) Saavedra, J . M. Adrenaline Levels in Brain Stem Nuclei and
Effects of a PNMT Inhibitor on Spontaneously Hypertensive
Rats. Brain Res. 1976, 166, 283-292.
(8) Toomey, R. E.; Horng, J . S.; Hemrick-Luecke, S. K.; Fuller, R.
W. R2-Adrenoceptor Affinity of Some Inhibitors of Norepineph-
rine N-Methyltransferase. Life Sci. 1981, 29, 2467-2472.
(9) Pendleton, R. G.; Gessner, G.; Weiner, G.; J enkins, B.; Sawyer,
J .; Bondinell, W.; Intoccia, A. Studies on SK&F 29661, an Organ
Specific Inhibitor of Phenylethanolamine N-Methyltransferase.
J . Pharmacol. Exp. Ther. 1979, 208, 24-30.
(10) Sauter, A. M.; Lew, J . Y.; Baba, Y.; Goldstein, M. Effect of
Phenylethanolamine N-Methyltransferase and Dopamine â-hy-
droxylase Inhibition on Epinephrine Levels in the Brain. Life
Sci. 1977, 21, 261-266.
(11) Blank, B.; Krog, A. J .; Weiner, G.; Pendleton, R. G. Inhibitors
of Phenylethanolamine N-Methyltransferase and Epinephrine
Biosynthesis. 2. 1,2,3,4-Tetrahydroisoquinoline-7-sulfonanilides.
J . Med. Chem. 1980, 23, 837-840.
(12) Rafferty, M. F.; Borchardt, R. T.; Grunewald, G. L. Directional
Probes of the Hydrophobic Component of the Aromatic Ring
Binding Site of Norepinephrine N-Methyltransferase. J . Med.
Chem. 1982, 25, 1204-1208.
(13) Grunewald, G. L.; Carter, A. E.; Sall, D. J .; Monn, J . A.
Conformational Preference for the Binding of Biaryl Substrates
and Inhibitors to the Active Site of Phenylethanolamine N-
Methyltransferase. J . Med. Chem. 1988, 31, 60-65.
d r obr om id e (9‚HBr ). Compound 27 (0.50 g, 2.3 mmol) was
refluxed with 48% HBr (9.4 mL) under N2 for 5 h to yield a
pink suspension which was evaporated to remove excess HBr.
The resulting pale red solid was crystallized from aqueous
MeOH and ether to yield the pale pink crystalline hydrobro-
mide (0.45 g, 68%): mp 295-296 °C dec; IR (KBr) 3310 (OH),
2940, 2820, 1510, 1260, 1245, 950, 800 cm-1; 1H NMR (DMSO-
d6) δ 9.81 (bs, e, 1 H, OH), 9.34 (bs, e, 2 H, NH2+), 7.73 (d, 1
H, J ) 9.8 Hz, H-6), 7.63 (d, 1 H, J ) 8.3 Hz, H-5), 7.24-7.15
(m, 3 H, H-7, H-9 and H-10); 4.62 (s, 2 H, H-1), 3.46-3.30 (m,
2 H, H-3), 3.15-3.01 (m, 2 H, H-4); 13C NMR (DMSO-d6) δ
155.2, 133.4, 127.3, 126.4, 126.1, 124.0, 123.6, 123.4, 118.9,
109.0, 41.7 (C-1), 40.4 (C-3), 25.0 (C-4); EIMS m/z (relative
intensity) 200 (M+ + 1, 14), 199 (M+, 85), 198 (M+ - 1, 77),
171 (21), 170 (100), 169 (26), 141 (20), 115 (25). Anal.
(C13H13NO‚HBr) C, H, N.
Ra d ioch em ica l Assa y for P NMT Affin ity. The assay
used in this study has been described elsewhere.29 Briefly, a
typical assay mixture consisted of 50 µL of 0.5 M phosphate
buffer (pH 8.0), 25 µL of 10 mM unlabeled S-adenosyl-L-
methionine (AdoMet), 5 µL of [methyl-3H]AdoMet, containing
approximately 3 × 105 dpm (specific activity approximately
15 mCi/mmol), 25 µL of substrate solution (phenylethanola-
mine), 25 µL of inhibitor solution, 25 µL of the enzyme
preparation, and sufficient water to achieve a final volume of
250 µL. After incubation for 30 min at 37 °C, the reaction
mixture was quenched by addition of 250 µL of 0.5 M borate
buffer (pH 10.0) and was extracted with 2 mL of toluene-
isoamyl alcohol (7:3). A 1 mL portion of the organic layer was
removed and transferred to a scintillation vial and diluted with
cocktail for counting. The mode of inhibition was ascertained
to be competitive in all cases reported in Table 1 by inspection
of the 1/V vs 1/S plots of the data. All assays were run in
duplicate with three inhibitor concentrations over a 5-fold
range. Ki values were determined by a hyperbolic fit of the
data.
r2-Ad r en ocep tor Ra d ioliga n d Bin d in g Assa y. The ra-
dioligand receptor binding was performed according to the
method of U’Prichard et al.31 Male Sprague-Dawley rats were
decapitated, and the cortexes were dissected out and homog-
enized in 20 volumes (w/v) of ice-cold 50 mM Tris‚HCl buffer
(pH 7.7 at 25 °C). Homogenates were centrifuged thrice for
10 min at 50000g with resuspension of the pellet in fresh buffer
between spins. The final pellet was homogenized in 200
volumes (w/v) of ice-cold 50 mM Tris‚HCl buffer (pH 7.7 at 25
°C). Incubation tubes containing [3H]clonidine (specific activ-
ity ca. 19.2 mCi/mmol, final concentration 4.0 nM), various
concentrations of drugs, and an aliquot of freshly resuspended
tissue (800 µL) in a final volume of 1 mL were used. Tubes
were incubated at 25 °C for 30 min, and the incubation was
terminated by rapid filtration under vacuum through GF/B
glass fiber filters. The filters were rinsed with three 5 mL
washes of ice-cold 50 mM Tris buffer (pH 7.7 at 25 °C). The
filters were counted in vials containing premixed scintillation
cocktail. Nonspecific binding was defined as the concentration
of bound ligand in the presence of 2 µM phentolamine. All
assays were run in quadruplicate with 5 inhibitor concentra-
tions over a 16-fold range. IC50 values were determined by a
log-probit analysis of the data and Ki values were determined
by the equation Ki ) IC50/(1 + [clonidine]/KD), as all Hill
coefficients were approximately equal to 1.
(14) King, J . F. Chapter 6: Acidity. In The Chemistry of Sulphonic
Acids, Esters and Their Derivatives; Patai, S., Rappoport, Z.,
Eds.; J ohn Wiley & Sons, Ltd.: West Sussex, 1991; pp 252-
253.
(15) Sall, D. J .; Grunewald, G. L. Inhibition of Phenylethanolamine
N-Methyltransferase (PNMT) by Aromatic Hydroxy-Substituted
1,2,3,4-Tetrahydroisoquinolines: Further Studies on the Hy-
drophilic Pocket of the Aromatic Ring Binding Region of the
Active Site. J . Med. Chem. 1987, 30, 2208-2216.
(16) J ung, M. E.; Kaas, S. M. Facile Synthesis of a Substituted
Bicyclo[4.2.1]nonane via an Anionic [1,3]-Sigmatropic Shift: Use
of Long Range 2D HETCOR and Difference NOE in Structure
Determination. Tetrahedron Lett. 1989, 30, 641-644.
(17) McCoubrey, A.; Mathieson, D. W. Isoquinolines. Part III. The
Nitration of 3,4-Dihydro and 1,2,3,4-Tetrahydroisoquinolines. J .
Chem. Soc. 1951, 2851-2853.
(18) Ajao, A. F.; Bird, C. W. The Preparation and Oxidative Dimer-
ization of 2-Acetyl-7-hydroxy-1,2,3,4-tetrahydroisoquinoline. A
New Approach to Tetrahydroisoquinoline Synthesis. J . Hetero-
cycl. Chem. 1985, 22, 329-331.
(19) Bergeron, R. J .; McManis, J . S. Reagents for the Stepwise
Functionalization of Spermine. J . Org. Chem. 1988, 53, 3108-
3111.
(20) Imazawa, M.; Eckstein F. Facile Synthesis of 2′Amino-2′deoxy-
ribofuranosyl Purines. J . Org. Chem. 1979, 44, 2039-2041.
(21) McRae, J . A. The Preparation of 1-Naphthoic Nitrile from
1-Naphthylamine. J . Am. Chem. Soc. 1930, 52, 4550-4552.
(22) J acobs, S. A.; Harvey, R. G. Synthesis of Conjugated Nitrile from
a Benzylic Ketone via a Cyanotrimethylsilane Adduct: 3,4-
Dihydro-6-methoxynaphthalene-1-carbonitrile. J . Org. Chem.
1983, 48, 5134-5135.
(23) Bevis, M. J .; Forbes, E. J .; Naik, N. N.; Uff, B. C. The Synthesis
of Isoquinolines, Indoles and Benzthiophen by an Improved
Pomeranz-Fritsch Reaction, Using Boron Trifluoride in Trifluo-
roacetic Anhydride. Tetrahedron 1971, 27, 1253-1259.
(24) Stock, L. M. Aromatic Substitution Reactions; Prentice-Hall:
Inc.: Englewood Cliffs, NJ , 1968; pp 73-76.
(25) Kessar, S. V.; Sobti, A. K.; J oshi, G. S. Azasteroids. Part VII.
Synthesis of 7-Hydroxy-2-methoxy-7, 8, 9, 10-tetrahydrobenzo-
[j]phenanthridine. J . Chem. Soc. C 1971, 259-261.
(26) Grunewald, G. L.; Borchardt, R. T.; Rafferty, M. F.; Krass, P.
Conformationally Defined Adrenergic Agents. 5. Conformational
Preferences of Amphetamine Analogues for Inhibition of Phen-
ylethanolamine N-Methyltransferase. Mol. Pharmacol. 1981, 20,
377-381.
Molecu la r Mod elin g Stu d ies. Molecular modeling was
performed using the Sybyl software package (version 6.00,
Tripos Associates, Inc., St. Louis, MO) on an IBM RS/6000
(Models 560 and 350) work station. The MNDO method in
the semiempirical molecular orbital package (MOPAC, version
5.0 at the Sybyl interface) was used. The FIT command was
used in fitting 9 with 1.
Ack n ow led gm en t. This work was supported by
U.S. Public Health Service Grant NIH HL-34193.
Refer en ces
(1) (a) Presented at the 206th American Chemical Society National
Meeting, Chicago, IL, August 22-27, 1993, Abstract MEDI 168.
(b) Taken in large part from the Ph. D. dissertation of V.H.D.,
University of Kansas, 1994.

PNMT Inhibitors: Aminosulfonyl Acidic Hydrogen
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 25 4005
(27) J acques, J .; Horeau, A. Ne 149.- Structure Mole´culaire et activite´
Œstroge`ne. (VI). Pre´paration de Quelques de´rive´s L’acide Am-
phihydroxynaphtyl â-propionique (Acide Alle´nolique). (No.
149.sMolecular Structure and Estrogenic Activity. (VI). Prepa-
ration of Some Derivatives of Amphihydroxynaphthyl â-Propi-
onic Acid (Allenolic Acid).) Bull. Soc. Chim. Fr. 1948, 15, 711-
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(29) Wrobel, J .; Dietrich, A.; Gorham, B. J .; Sestanj, K. Conforma-
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(31) U’Prichard, D. C.; Greenberg, D. A.; Synder, S. H. Binding
Characteristics of Radiolabeled Agonists and Antagonists at
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(32) A comparative molecular field analysis (CoMFA) study in our
laboratory of 72 compounds for PNMT and 74 compounds for
the R2-adrenoceptor has indicated that there may be two binding
modes which are dependent on the lipophilicity of the aromatic
substituent. Unpublished results with V. Dahanukar and R.
J alluri.
(33) (a) Perrin, D. D. Dissociation Constants of Organic Bases in
Aqueous Solutions; Butterworth: London, 1965; p 68. (b) Ibid.;
p 58.
(34) Kortu¨m, G.; Vogel, W.; Andrussow, K. Dissociation Constants
of Organic Acids in Aqueous Solutions; Butterworth: London,
1961; p 445.
J M960235E