3- and 4-pyridylalkyl adamantanecarboxylates: Inhibitors of human cytochrome P450(17α) (17α-hydroxylase/C17,20-lyase). Potential nonsteroidal agents for the treatment of prostatic cancer

Article abstract of DOI:10.1021/jm950749y

Various 3- and 4-pyridylalkyl 1-adamantanecarboxylates have been synthesized and tested for inhibitory activity toward the 17α-hydroxylase and C_17,20-lyase activities of human testicular cytochrome P450(17α). The 4-pyridylalkyl esters were much more inhibitory than their 3- pyridylalkyl counterparts. The most potent was (S)-1-(4-pyridyl)ethyl 1- adamantanecarboxylate (3b; IC₅₀ for lyase, 1.8 nM), whereas the (R)- enantiomer 3a was much less inhibitory (IC₅₀ 74 nM). Nearly as potent as 3b was the dimethylated counterpart, the 2-(4-pyridylpropan-2-yl) ester 5 (IC₅₀ 2.7 nM), which was also more resistant to degradation by esterases. In contrast to their 4-pyridyl analogs, the enantiomers of the 1-(3- pyridyl)ethyl ester were similarly inhibitory (IC₅₀ for lyase; (R)-isomer 8a 150 nM, (S)-isomer 8b 230 nM). Amides corresponding to the 4- pyridylmethyl ester 1 and the (S)-1-(4-pyridyl)ethyl ester 3b, respectively 11 and 15b, were much less inhibitory than their ester counterparts. On the basis of a combination of inhibitory potency and resistance to esterases, the ester 5 was the best candidate for further development as a potential nonsteroidal inhibitor of cytochrome P450(17α) for the treatment of prostate cancer.

Full text of DOI:10.1021/jm950749y

J . Med. Chem. 1996, 39, 3319-3323
3319
3
- a n d 4-P yr id yla lk yl Ad a m a n ta n eca r boxyla tes: In h ibitor s of Hu m a n
Cytoch r om e P 45017r (17r-Hyd r oxyla se/C17,20-Lya se). P oten tia l Non ster oid a l
Agen ts for th e Tr ea tm en t of P r osta tic Ca n cer
†
‡
Ferdinand C. Y. Chan, Gerard A. Potter, S. Elaine Barrie, Benjamin P. Haynes, Martin G. Rowlands,
J ohn Houghton, and Michael J arman*
Cancer Research Campaign Centre for Cancer Therapeutics at the Institute of Cancer Research, Cancer Research Campaign
Laboratory, 15 Cotswold Road, Sutton, Surrey SM2 5NG, U.K.
X
Received October 11, 1995
Various 3- and 4-pyridylalkyl 1-adamantanecarboxylates have been synthesized and tested
for inhibitory activity toward the 17R-hydroxylase and C17,20-lyase activities of human testicular
cytochrome P45017R. The 4-pyridylalkyl esters were much more inhibitory than their 3-pyr-
idylalkyl counterparts. The most potent was (S)-1-(4-pyridyl)ethyl 1-adamantanecarboxylate
(3b; IC50 for lyase, 1.8 nM), whereas the (R)-enantiomer 3a was much less inhibitory (IC50 74
nM). Nearly as potent as 3b was the dimethylated counterpart, the 2-(4-pyridylpropan-2-yl)
ester 5 (IC50 2.7 nM), which was also more resistant to degradation by esterases. In contrast
to their 4-pyridyl analogs, the enantiomers of the 1-(3-pyridyl)ethyl ester were similarly
inhibitory (IC50 for lyase; (R)-isomer 8a 150 nM , (S)-isomer 8b 230 nM). Amides corresponding
to the 4-pyridylmethyl ester 1 and the (S)-1-(4-pyridyl)ethyl ester 3b, respectively 11 and 15b,
were much less inhibitory than their ester counterparts. On the basis of a combination of
inhibitory potency and resistance to esterases, the ester 5 was the best candidate for further
development as a potential nonsteroidal inhibitor of cytochrome P45017R for the treatment of
prostate cancer.
Work from this laboratory has identified a series of
esters of 3- and 4-pyridylacetic acid and their R-alkyl-
ated derivatives as possessing inhibitory activity toward
steroidal 17R-hydroxylase/C17,20-lyase, a potential target
1
,2
enzyme for the treatment of prostate cancer.
The
F igu r e 1.
inhibitory activities of 4-pyridyl esters reported in the
earlier of these studies1 was in part rationalized in
terms of a partial overlay of key structural elements in
reversal of the ester linkage might influence inhibitory
potency, adversely or otherwise, a study of the effect of
such reversal was an additional aim, and has revealed
potent inhibitors. All the present compounds were
derivatives of 1-adamantanecarboxylic acid, chosen as
the acid component because of its ready availability,
coupled with the generally good inhibitory properties
found for adamantyl esters during previous studies.1
3
the active esters with the steroidal skeleton, with the
pyridyl nitrogen atom situated so as to coordinate with
the haem iron atom of this P450 enzyme. The results
2
of the later study suggested that an investigation of
individual enantiomers of compounds monosubstituted
in the methylene residue adjacent to the pyridyl sub-
stituent might have markedly different inhibitory po-
tencies.
,2
Resu lts
The enantiomers of R-monoalkylated pyridyl acetic
esters are not appropriate synthetic targets for inves-
tigating this prediction. Racemization at physiological
pH of enantiomers of drugs which have a benzylic proton
at the chiral center is well-known.4 This problem should
be circumvented, allowing the effect on enzyme inhibi-
tory activity of chirality adjacent to the pyridyl residue
to be explored, by reversal of the ester linkage to give
compounds which we have termed “reverse esters”. The
structural relationship between such “reverse esters”
and the esters of the previous studies,1 which we have
here termed “normal esters”, is shown in Figure 1. The
synthesis and evaluation of “reverse esters” with defined
chirality at carbon R to a 4- or 3-pyridyl function was
the principal objective of the present study. Since
Ch em istr y. The target esters were prepared, as
exemplified for 4-pyridylmethyl 1-adamantanecarboxyl-
ate (1) by reacting 1-adamantanecarbonyl chloride with
the appropriate alkoxide generated from the pyridyl-
alkanol and n-butyllithium (Scheme 1). The chiral 1-(4-
pyridyl)ethyl esters 3a and 3b were prepared from the
commercially available chiral alcohols 2a and 2b. The
(R)-7a and (S)-7b enantiomers of 1-(3-pyridyl)ethanol
were prepared with high enantiomeric excess (ee)
(respectively 87% and 80%) by reducing 3-acetylpyridine
with the enantiomers of diisopinocampheylchloroborane,
,2
5
an efficient chiral reducing agent for aromatic prochiral
ketones. A single recrystallization of the appropriate
chiral 10-camphorsulfonate salts of the derived esters
afforded the corresponding 1-(3-pyridyl)ethyl esters 8a
and 8b of high enantiomeric purity (respective ee values
9
8% and 95%). The tertiary alcohols 2-(4-pyridyl)-
*
To whom enquiries should be addressed.
Present address: Chemical Company of Malaysia Berhad, P.O. Box
†
propan-2-ol (4) and the 3-pyridyl counterpart 9 required
for the preparation of the respective esters 5 and 10
were made by reacting the acetylpyridines with methyl-
lithium (Scheme 2).
1
4
0284, 50708 Kuala Lumpur, Malaysia.
‡
Present address: Chiroscience Ltd., Milton Rd, Cambridge CB4
WE, U.K.
X
Abstract published in Advance ACS Abstracts, J uly 1, 1996.
S0022-2623(95)00749-7 CCC: $12.00 © 1996 American Chemical Society

3
320 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Chan et al.
Sch em e 1a
Sch em e 3a
HO Py
Me
HO Py
Me
N
N
N3
a
TsO
H
b
(R)-2a
H
H
Me
Me
H
(
(
R)-2a: Py = 4-pyridyl
R)-7a: Py = 3-pyridyl
(S)-2b: Py = 4-pyridyl
(S)-7b: Py = 3-pyridyl
(
S)-13
a, b
a, b
c
N
H
N
N
Py
Me
Py
O
H2N
Me
O
d
O Me
H
H
O
O
Me
H
H
(
S)-15b
(S)-14
(
(
R)-3a: Py = 4-pyridyl
R)-8a: Py = 3-pyridyl
(S)-3b: Py = 4-pyridyl
(S)-8b: Py = 3-pyridyl
a
(
a) n-BuLi, tosyl chloride; (b) NaN3; (c) Pd/C, H2; (d) 1-ada-
a
mantoyl chloride.
(a) n-BuLi; (b) 1-adamantoyl chloride.
Sch em e 2a
rivative shows that the IC50 of (S)-enantiomer 3b was
40-fold lower against the lyase and 100-fold lower
against the hydroxylase than the IC50 of the correspond-
ing (R)-enantiomer 3a and that the (R)-enantiomer is
considerably less active than the unsubstituted com-
pound 1.
Me
Py
HO
Me
Py
a
O
Me
4: Py = 4-pyridyl
: Py = 3-pyridyl
9
Compared with their analogs in the 4-pyridyl series,
the 3-pyridyl derivatives 6, 8b, and 10 were much less
potent inhibitors. In marked contrast to 3a and 3b, the
enantiomers of the monomethylated 3-pyridyl deriva-
tives 8a and 8b were almost equipotent, and both more
active than the unsubstituted compound 6. The 4-5-
fold improvement in activity on dimethylation in this
series (compare 6 and 10, Table 1) was similar to that
seen in the present 4-pyridyl series (compare 1 and 5)
and to that seen in 3-pyridyl analogs in the “normal
ester” series. Thus, in the latter series, dimethylation
converted the moderate inhibitor isopinocampheyl 3-pyr-
idylacetate (IC50 for lyase, 88 nM, for hydroxylase, 260
nM) into a good one (respective values 14 and 29 nM).2
In view of the potential lability of esters toward
esterases (see below) in the body, which might hamper
their further development as potential drugs, some
corresponding amides were made. However, the amides
11 and 12 were each some 3 orders of magnitude less
potent than their ester counterparts 1 and 6. In an
attempt to improve potency, the amide counterpart 15b
of the most potent ester, the (S)-enantiomer 3b of the
monomethyl derivative, as well as the corresponding
racemate 15a were made. This (S)-enantiomer 15b was
about twice as inhibitory as the racemate 15a , implying
that, as with its ester counterpart 3b, this enantiomer
is much the more active. However, though showing a
similar improvement over its nonmethylated counter-
part 11 as did the corresponding ester 3b over 1, the
inhibitory activity of 15b remained some 2 orders of
magnitude less than that of 3b. Hence replacement of
the ester linkage in the present series of compounds by
an amide linkage was markedly detrimental to inhibi-
tory activity.
b, c
Py
O
O
Me Me
5
1
: Py = 4-pyridyl
0: Py = 3-pyridyl
a
(
a) MeLi; (b) n-BuLi; (c) 1-adamantoyl chloride.
“
Reverse amides” 11 and 12, corresponding to the
esters 1 and 6 and the racemic 1-(4-pyridyl)ethyl amide
15a ) and its (S)-enantiomer 15b analogous to ester 3b,
(
were made from the corresponding amines and 1-ada-
mantanecarbonyl chloride. The chiral amine 14 re-
quired as precursor to 15b had been obtained previ-
ously6 by resolution of the racemate by multiple
recrystallizations of its d-tartrate, but the recovery was
poor (20%). Here, it was synthesized (Scheme 3) in
three steps from the corresponding chiral alcohol 2a ,
based on a strategy employed7 in the synthesis of
selectively deuterated (S)-neopentyl tosylate from the
corresponding chiral neopentyl alcohol. The chiral
pyridyl azide 13 was prepared, with inversion of con-
figuration, by reacting the tosylate of 2a with NaN3 in
THF containing HMPA. Catalytic hydrogenation of 13
gave the amine 14, of 96% ee, in 49% overall yield.
In h ibition of Hu m a n Testicu la r 17r-Hyd r oxyl-
a se a n d C17,20-Lya se. Str u ctu r e-Activity Rela tion -
sh ip s. The most potent inhibitors of human testicular
steroidal 17R-hydroxylase/C17,20-lyase (Table 1) were the
-pyridyl ester 1 and its methylated derivatives 3b and
. In contrast to the situation with the “normal ester”
isopinocampheyl 4-pyridylacetate (IC50 for lyase, 5 nM;
for hydroxylase, 14 nM) and its dimethylated counter-
part (respective IC50 values 10 and 26 nM), dimethyl-
ation in the present “reverse ester” series gave a much
more potent inhibitor (compare 1 and 5). Indeed the
potency of 5 was comparable to that of our recently
described steroidal inhibitor 17-(3-pyridyl)androsta-
4
5
2
Ar om a t a se In h ib it ion . Ideally, if an inhibitor of
cytochrome P45017R is to be used clinically, it should be
selective for the target enzyme, and not inhibit other
cytochrome P450 enzymes. Esters of 4-pyridylacetic
acid have previously been identified as quite potent
1
5
4
,16-dien-3â-ol (IC50 for lyase, 2.9 nM; for hydroxylase,
nM) and more potent than the 17R-hydroxylase/C17,20-
lyase inhibitor ketoconazole (Table 1), which has been
used clinically. Comparison of the inhibitory activity
displayed by the enantiomers of the monomethyl de-
inhibitors of aromatase, the most active being 1-ada-
8
mantyl 4-pyridylacetate (IC50 0.09 µM). Aromatase is
a cytochrome P450 enzyme which catalyzes the conver-
sion of androstenedione, a product of the cytochrome
P45017R enzymic reaction, into estrone. Inhibition of
9

3
- And 4-(Pyridyl)alkyl Adamantanecarboxylates
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3321
Ta ble 1. Enzyme Inhibition Data
Y
Z
X
O R2 R1
substituents
Z
IC50 ( nM)a
IC50 (µM)a
c
compd
X
Y
R1
R2
C17,20-lyaseb
17R-hydroxylaseb
aromatase
1
3
3
5
6
8
8
1
1
1
1
1
O
O
O
O
O
O
O
O
NH
NH
NH
NH
CH
CH
CH
CH
N
N
N
N
CH
N
N
N
N
N
CH
CH
CH
CH
N
CH
N
N
H
Me
H
Me
H
Me
H
Me
H
H
H or Me
H
H
H
Me
Me
H
18
74
1.8
43
340
0.58
16
5.6
20
8
36
a
b
3.3
8.8
1500
580
840
2.7
460
150
230
92
1600
18000
430
210
26
a
H
b
0
1
2
5a
5b
Me
Me
H
4.6
51
390
7700
70000
1900
820
1.5
3.2
ND
ND
16
H
CH
CH
Me or H
Me
ketoconazole
65
a
IC50 values >200 nM were calculated using linear regression to fit the data to the Dixon equation. Those <200 nM were calculated
using nonlinear regression to fit the data to the median effect equation of Chou.14 The regression coefficients were >0.97. b The standard
errors for the hydroxylase and lyase IC50 values were <12% and averaged 5% of the IC50 value. The substrate concentration was 3 µM
c
in both assays. The standard errors for the aromatase IC50 values were <15% and averaged 8% of the IC50 value. The substrate
d
concentration was 0.38 µM in the assay. ND ) not determined.
Ta ble 2. Comparative Rates of Hydrolysis of Selected Esters
this enzyme would reduce the level of circulating
by Rat Liver Microsomal Esterase at 37 °C
estrogens which would stimulate the production of
compd
hydrolysis t1/2 (min)
gonadotrophins, which in turn would stimulate the
1
0
<1a
testicular production of androgens. For these reasons,
the inhibition of human placental aromatase by the
1
3
3
5
a
b
0.5
0.5
“reverse esters” was studied. The reverse ester coun-
>60b
terpart 1 of 1-adamantyl 4-pyridylacetate was much less
inhibitory (Table 1), and all other compounds studied
were even less so. The decrease in potency progressing
from the R-unsubstituted compounds (e.g. 1, IC50 0.58
µM) to their dimethylated counterparts (e.g. 5, IC50 20
a
No substrate detectable at 1 min. b No hydrolysis at 60 min.
Ta ble 3. Extent of Hydrolysis of Selected Esters by Rat and
Mouse Liver Microsomes and by Blood from Rat, Mouse, and
Human at 37 °C
1
-3
µM) has been noted for “normal ester” counterparts
and has been ascribed to the occupancy by one of the
methyl groups of a region, the position occupied by C(2)
% substrate metabolized at 1 h
rat
mouse
1
1
of the steroid substrate, intolerant of steric bulk.
compd microsomes blood microsomes blood human blood
Compound 5 has comparable inhibitory activity toward
aromatase to ketoconazole (Table 1), but has much less
activity against aromatase relative to its activity against
cytochrome P45017R.
1
5
100a
0
100b
0
100c
13
100b
2
45
0
a
No substrate detectable at 5 min. b 97% substrate hydrolyzed
at 10 min. c 97% substrate hydrolysed at 2 min.
Resista n ce to Hyd r olysis by Ester a se. Esters of
the present study are intrinsically susceptible to hy-
drolysis by esterases in vivo. A combination of good
inhibitory activity toward the target enzyme and high
resistance to esterases is essential if a compound is to
be a candidate for further preclinical development. A
rat liver microsomal preparation was used as a source
of esterase for preliminary evaluation of the effect of
methylation R to the ester linkage on the susceptibility
animal test systems, but proved less labile in human
blood, with 45% being metabolized in 1 h. 3-Pyridyl
derivatives were not examined, since hydrolysis rates
by esterases had been previously found to be similar
for analogous 3- and 4-pyridyl derivatives.
Con clu sion s. This study set out to investigate the
importance to the inhibitory activity of chirality at the
position R to the 3- and 4- pyridyl substituents, by
utilizing derivatives not susceptible to racemization. The
study has identified several potent inhibitors of cyto-
chrome P45017R and confirmed what features are neces-
sary for resistance to esterase activity. The ester 5, on
the basis of high inhibitory potency and resistance to
degradation, merits further assessment as a potential
nonsteroidal inhibitor of cytochrome P45017R for use
against prostatic cancer.
2
1
2
of esters to hydrolysis or to oxidative cleavage.
Se-
lected compounds were studied in more detail for their
stability toward mouse hepatic microsomal esterase and
in blood from mouse, rat, and human.
The 4-pyridylmethyl ester 1 and both enantiomers
(3a ,b) of the 1-(4-pyridyl)ethyl ester were rapidly hy-
drolyzed by the rat microsomes (Table 2). The corre-
sponding ester 5 of the tertiary alcohol 4 was resistant,
being unaffected after 1 h. In further studies, 5 also
proved completely resistant to hydrolysis in rat and
human blood, though minor degradation was detected
by mouse microsomes (13-15%) and in mouse blood
Exp er im en ta l Section
Ch em ica l Meth od s. 1H NMR spectra (250 MHz) (internal
Me Si ) δ 0) were determined in CDCl (unless otherwise
4
3
(2%). The ester 1 was completely hydrolyzed by the
indicated) using a Bruker AC 250 spectrometer. Infrared

3
322 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Chan et al.
spectra were determined with a Perkin-Elmer 1720X spec-
trometer. Mass spectra (electron impact, 70 eV) were obtained
by direct insertion with a VG 7070H spectrometer and VG
50:1, gave 6 (422 mg, 78%) as an oil: IR υmax 1728 cm-1; NMR
δ 1.71 and 1.91 (2s, 12, adamantyl CH
CH), 5.11 (s, 2, OCH
pyridyl H-4), 8.56 (m, 1, pyridyl H-6), 8.61 (m, 1, pyridyl H-2).
Anal. (C17 ) C, H, N.
2
), 2.02 (s, 3, adamantyl
2
), 7.30 (m, 1, pyridyl H-5), 7.66 (m, 1,
2
235 data system. Melting points were determined with a
Reichert micro hot stage apparatus and are uncorrected.
Chromatography refers to column chromatography on silica
gel (Merck Art. 15111) with solvent indicated applied under
positive pressure. Petroleum ether refers to the fraction with
bp 60-80 °C. Elemental analyses were determined by CHN
Analysis Ltd., South Wigston, Leicester, England.
H21NO
2
(R)-(+)-1-(3-P yr id yl)et h yl 1-Ad a m a n t a n eca r b oxyla t e
(8a ). The method followed that described for 1, but using (R)-
(+)-1-(3-pyridyl)ethanol [7a , 87% ee; prepared by asymmetric
reduction of 3-acetylpyridylridine with (1S)-(+)-B-chlorodiiso-
5
pinocampheylborane ] (0.62 g, 5.0 mmol) in THF (20 mL),
4
-P yr id ylm eth yl 1-Ad a m a n ta n eca r boxyla te (1). To
-pyridylmethanol (1.2 g, 11.0 mmol) in THF (40 mL) at -18
C was added n-butyllithium (2.5 M, 4.2 mL, 10.5 mmol) in
hexane dropwise with stirring. After 10 min a solution of
-adamantanecarbonyl chloride (2.0 g, 10.0 mmol) in THF (10
n-butyllithium (2.5 M; 2.0 mL, 5.0 mmol) in hexane, and
1-adamantanecarbonyl chloride (1.09 g, 5.5 mmol) in THF (5
mL). Chromatography, on elution with Et O-petroleum
2
4
°
ether-Et
3
N, 100:50:1, gave 8a (1.16 g, 81%) as an oil: [R]
D
1
+29.9° (c 2, MeOH), 87% ee. Recrystallization of the (1R)-(-
mL) was added, and stirring continued at room temperature
for 30 min. The mixture was poured into water, basified with
)-10-camphorsulfonate salt from EtOAc, and reliberation of the
free base, afforded 8a with 98% ee: [R]
D
+33.7° (c 2, MeOH):
IR υmax 1728 cm ; NMR δ 1.54 (d, 3, J ) 6.5 Hz, CHCH ),
1.72 and 1.90 (2s, 12, adamantyl CH ), 2.03 (s, 3, adamantyl
CH), 5.88 (q, 1, J ) 6.5 Hz, CHCH ), 7.30 (m, 1, pyridyl H-5),
7.65 (m, 1, pyridyl H-4), 8.56 (m, 1, pyridyl H-6), 8.63 (m, 1,
-
1
saturated aqueous NaHCO
Et O extracts were combined, dried (Na
trated. Chromatography, on elution with petroleum ether-
Et
3
, and extracted with Et
2
O. The
3
2
2
CO ), and concen-
3
2
3
2
O-Et
petroleum ether); IR υmax 1730 cm ; NMR δ 1.74 and 1.96
2s, 12, adamantyl CH ), 2.05 (s, 3, adamantyl CH), 5.12 (s, 2,
), 7.24 (d, 2, J ) 5.7 Hz, pyridyl H-3, H-5), 8.60 (d, 2,
pyridyl H-2, H-6). Anal. (C17 ) C, H, N.
3
N, 100:50:1, gave 1 (0.95 g, 35%): mp 57-58 °C
-
1
+
(
(
2
pyridyl H-2); MS m/z 285 (M ). Anal. (C18H23NO ) C, H, N.
2
(S)-(-)-1-(3-P yr id yl)et h yl 1-Ad a m a n t a n eca r b oxyla t e
(8b). The method followed that described for 1, but using (S)-
(-)-1-(3-pyridyl)ethanol [7b, 80% ee; prepared by asymmetric
reduction of 3-acetylpyridine with (1R)-(-)-B-chlorodiiso-
OCH
2
H
21NO
2
(
R)-(+)-1-(4-P yr id yl)et h yl 1-Ad a m a n t a n eca r b oxyla t e
5
(
(
3a ). The method followed that described for 1, but using (R)-
+)-1-(4-pyridyl)ethanol (2a , >99% ee, Fluka Chemie AG,
Buchs, Switzerland, 369 mg, 3.0 mmol) in THF (12 mL),
pinocampheylborane ] (0.49 g, 4.0 mmol) in THF (16 mL),
n-butyllithium (2.5 M; 1.6 mL, 4.0 mmol) in hexane, and
1-adamantanecarbonyl chloride (0.87 g, 4.4 mmol) in THF (4
mL). Chromatography, as described for 8a , gave 8b (0.92 g,
n-butyllithium (2.5 M, 1.2 mL, 3.0 mmol) in hexane, and
1
(
-adamantanecarbonyl chloride (656 mg, 3.3 mmol) in THF
3 mL). Chromatography, on elution with petroleum ether-
Et O-Et N 200:50:1, afforded 3a (754 mg, 88%): [R] +25.8°
c 1, CHCl ); IR υmax 1730 cm ; NMR δ 1.50 (d, 3, J ) 6.6 Hz,
CHCH ), 1.73 and 1.93 (2s, 12, adamantyl CH ), 2.04 (s, 3,
adamantyl CH), 5.80 (q, 1, J ) 6.6 Hz, OCH), 7.23 (d, 2, J )
.1 Hz, pyridyl H-3, H-5), 8.58 (d, 2, pyridyl H-2, H-6); MS
81%) as an oil: [R]
D
-27.6° (c 2, MeOH), 80% ee. Recrystal-
lization of the (1S)-(+)-10-camphorsulfonate salt, and relib-
2
3
D
eration of the free base, afforded 8b with 95% ee, [R] -32.7°
(c 2, MeOH). IR, NMR, and MS data were the same as for
8a .
2-(3-P yr id yl)p r op a n -2-ol (9). The method followed that
for 4, but using methyllithium (1.4 M; 14 mL, 20 mmol) in
D
-
1
(
3
3
2
6
+
m/z 285 (M ). The hydrochloride of 3a was obtained by
passing HCl gas through a solution in Et O: mp 164-166 °C.
Anal. (C18 Cl) C, H, N; Cl: found, 10.50; required,
1.02.
S)-(-)-1-(4-P yr id yl)et h yl 1-Ad a m a n t a n eca r b oxyla t e
3b). The method was the same as for 3a , but using (S)-(-)-
-(4-pyridyl)ethanol (2b, Fluka AG, 369 mg, 3.0 mmol), and
provided 3b (774 mg, 90%): [R] -24.4° (c 1, CHCl ); IR, NMR,
and MS data were the same as for 3a . The hydrochloride of
b had mp 164-166 °C. Anal. (C18 Cl) H, N, Cl; C:
found, 67.89; required, C, 67.17.
-(4-P yr id yl)p r op a n -2-ol (4). A solution of methyllithium
1.4 M; 30 mL, 42 mmol) in Et O was added dropwise to a
Et
mL). Chromatography, on elution with Et
ether-Et N, 30:10:1, afforded 9 (1.26 g, 46%) as an oil: NMR
δ 1.58 (s, 6, CMe ), 7.22 (m, 1, pyridyl H-5), 7.85 (m, 1, pyridyl
2
O and 3-acetylpyridine (2.2 mL, 20 mmol) in dry THF (40
2
2
O-petroleum
H
24NO
2
3
1
2
(
H-4), 8.32 (m, 1, pyridyl H-6), 8.65 (m, 1, pyridyl H-2); MS
+
(
1
m/z 137 (M ).
2-(3-P yr idyl)pr opan -2-yl 1-Adam an tan ecar boxylate (10).
The method followed that for 5, but using 2-(3-pyridyl)propan-
2-ol (9, 0.69 g, 5.0 mmol), and provided 10 (1.06 g, 71%) as an
oil: IR υmax 1730 cm ; NMR δ 1.71 (s, 6, CMe
(2s, 12, adamantyl CH ), 2.02 (s, 3, adamantyl CH), 7.25 (m,
1, pyridyl H-5), 7.65 (m, 1, pyridyl H-4), 8.48 (m, 1, pyridyl
H-6), 8.63 (m, 1, pyridyl H-2). Anal. (C19 ) C, H, N.
D
3
-
1
3
H
24NO
2
2
), 1.77 and 1.94
2
2
(
2
H25NO
2
stirred solution of 4-acetylpyridine (4.65 mL, 42 mmol) in dry
THF (100 mL) at -76 °C, and the deep blue solution was
allowed to reach ambient temperature. After 24 h the mixture
4-P yr id ylm eth yl Ad a m a n ta n eca r boxa m id e (11). To a
solution of 4-(aminomethyl)pyridine (1.08 g, 10 mmol) in dry
THF (25 mL) was added 1-adamantanecarbonyl chloride (1.987
g, 10 mmol). After stirring for 3 h at room temperature, the
was partitioned between Et
CO , and the Et O phase was concentrated. Chromatography,
on elution with EtOAc-CH Cl -Et N, 60:40:1, gave 4 (2.59
g, 45%) as an oil: NMR δ 1.58 (s, 6, CMe ), 7.40 (d, 2, J ) 6.2
Hz, pyridyl H-3, H-5), 8.55 (d, 2, pyridyl H-2, H-6); MS m/z
2
O and saturated aqueous NaH-
3
2
reaction mixture was added to H
aqueous NaHCO , extracted with Et
(Na CO ), and concentrated. Chromatography, on elution with
petroleum ether-Et O-Et N, 20:20:1, gave 11 (1.9 g (70%):
2
O, treated with saturated
2
2
3
3
2
O and EtOAc, dried
2
2
3
2
3
+
-1
1
37 (M ).
mp 177-178 °C (from toluene); IR υmax 3332 cm (NH str),
1635 (CdO str); MS m/ z 270 (M ). Anal. (C17H22NO) C, H,
+
2
-(4-P yr idyl)pr opan -2-yl 1-Adam an tan ecar boxylate (5).
The method followed that described for 1, but using 2-(4-
pyridyl)propan-2-ol (4, 0.69 g, 5.0 mmol) in THF (20 mL),
n-butyllithium (2.5 M; 2.0 mL, 5.0 mmol) in hexane, and
N.
3-P yr id ylm eth yl Ad a m a n ta n eca r boxa m id e (12). By
the foregoing procedure, but using 3-(aminomethyl)pyridine
(1.08 g, 10 mmol), compound 12 was prepared: mp 129-130
1
-adamantanecarbonyl chloride (1.09 g, 5.5 mmol) in THF (6
mL). Chromatography, on elution with Et O-petroleum
ether-Et N, 150:50:1, gave 5 (1.06 g, 71%) as an oil: IR υmax
2
°C (from toluene). Anal. (C17H22NO) C, H, N.
3
-
(S)-(-)-1-(4-P yr id yl)eth yl Azid e (13). To a solution of
(R)-(+)-1-(4-pyridyl)ethanol (2a , 369 mg, 3.0 mmol) in THF (10
mL) at 0 °C was added n-butyllithium (1.6 M in hexane, 1.88
mL, 3.0 mmol), followed after 5 min by p-toluenesulfonyl
chloride (572 mg, 3.0 mmol). After stirring for a further 30
1
1
730 cm ; NMR δ 1.71 (s, 6, CMe
adamantyl CH ), 2.02 (s, 3, adamantyl CH), 7.23 (d, 2, J )
.1 Hz, pyridyl H-3, H-5), 8.56 (d, 2, J ) 6.1 Hz, pyridyl H-2,
H-6). Anal. (C19 ) C, H, N.
-P yr id ylm et h yl 1-Ad a m a n t a n eca r boxyla t e (6). The
2
), 1.71 and 1.90 (2s, 12,
2
6
H
25NO
2
3
3
min at 0 °C, a suspension of NaN (585 mg, 9.0 mmol) in
method followed that described for 1, but using 3-pyridyl-
carbinol (240 mg, 2.2 mmol) in THF (10 mL), n-butyllithium
hexamethylphosphoramide (HMPA) (Aldrich Chemical Co.,
Gillingham, Dorset, U.K.) (6 mL) was added and the mixture
allowed to attain room temperature. After 1 h, it was poured
(
2.5 M; 0.84 mL, 2.1 mmol) in hexane, and 1-adamantanecar-
bonyl chloride (397 mg, 2.0 mmol) in THF (2 mL). Chroma-
tography, on elution with petroleum ether-Et O-Et N, 200:
into H
2
O (50 mL) and extracted with Et
2
O (2 × 50 mL), and
2
3
the extracts were dried (Na
2
CO ) and concentrated. Chroma-
3

3
- And 4-(Pyridyl)alkyl Adamantanecarboxylates
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3323
tography on elution with hexane-Et
2
O-Et
-65.7° (c 1.0, CHCl
); NMR δ 1.55 (d, 3, J ) 6.8 Hz, CHCH
), 7.26 (d, 2, J ) 6.1 Hz, pyridyl H-2, H-6), 8.63
d, 2, pyridyl H-3, H-5).
S)-(-)-1-(4-P yr id yl)eth yla m in e (14). A solution of the
azide 13 (400 mg, 2.7 mmol) in MeOH (5 mL) containing 5%
Pd/C (60 mg) was stirred under H for 30 min, then filtered,
and concentrated. Chromatography on elution with CH Cl
3
N, 100:50:1, gave
incubated in the presence of the esterase inhibitor phenyl-
methylsulfonyl fluoride (0.1 mM). Half-lives were derived from
the plots of the natural log of % ester remaining against time.
1
3 (333 mg, 75%) as an oil: [R]
D
3
); IR υmax
3
), 4.63
-
1
2
096 cm (N
3
(q, 1, CHCH
3
(
Ack n ow led gm en t. This work was supported by
grants from the Cancer Research Campaign. Financial
support from British Technology Group (to G.A.P. and
S.E.B.) and Cancer Research Campaign Technology (to
S.E.B.) is also gratefully acknowledged. We thank Mr.
P. StQuintin for assistance with the preparation of
compounds 11 and 12 and Mr. M. H. Baker for deter-
mining the mass spectra.
(
2
2
2
-
EtOAc-Et
8 °C at 4.0 mmHg: [R]
R]
CHCH
.1 Hz, pyridyl H-3, H-5), 8.54 (d, 2, pyridyl H-2, H-6).
R,S)-1-(4-P yr id yl)et h yl 1-Ad a m a n t a n eca r b oxa m id e
3
N, 300:50:1 f 100:50:1, gave 14 (214 mg, 65%): bp
-24.9° (c 1.5, EtOH) of 96% ee (lit.6
9
[
D
D
-26.6° for homochiral 14); NMR δ 1.39 (d, 3, J ) 6.8 Hz,
3
2 3
), 1.65 (s, 2, NH ), 4.10 (1, q, CHCH ), 7.27 (d, 2, J )
6
(
Refer en ces
(
15a ). To a stirred solution of (R,S)-1-(4-pyridyl)ethylamine
(
1) McCague, R.; Rowlands, M. G.; Barrie, S. E.; Houghton, J .
Inhibition of Enzymes of Estrogen and Androgen Biosynthesis
by Esters of 4-Pyridylacetic Acid. J . Med. Chem. 1990, 33, 3050-
3055.
(85 mg, 0.70 mmol; prepared as for 14 but from (R,S)-1-(4-
2 2
pyridyl)ethanol) in CH Cl (4 mL) was added pyridine (0.2 mL)
and then 1-adamantanecarbonyl chloride (278 mg, 1.4 mmol).
After 1 h, the mixture was concentrated. Chromatography,
(2) Rowlands, M. G.; Barrie, S. E.; Chan, F. C. Y.; Houghton, J .;
J arman, M.; McCague, R.; Potter, G. A. Esters of 3-Pyridylacetic
on elution with hexane-EtOAc-Et
3
N, 100:50:1, gave 15a as
white crystals (181 mg, 91%): mp 201-203 °C (from cyclo-
Acid Which Combine Potent Inhibition of 17R-Hydroxylase/C17,20
-
Lyase (Cytochrome P45017R) With Resistance to Esterase
-
1
hexane); IR υmax 1633 cm ; NMR δ 1.46 (d, 3, J ) 6.9 Hz,
CHCH ), 1.74 (s, 6, adamantyl CH ), 2.07 (s, 3, adamantyl CH),
.08 (q, 1, CHCH ), 5.80 (s, 1, NH), 7.21 (d, 2, J ) 6.0 Hz,
pyridyl H-3, H-5), 8.55 (d, 2, pyridyl H-2, H-6); MS m/ z 284
Hydrolysis. J . Med. Chem. 1995, 38, 4191-4197.
(3) Laughton, C. A.; Neidle, S. Inhibitors of the P450 Enzymes
Aromatase and Lyase. Crystallographic and Molecular Modelling
Studies Suggest Structural Features of Pyridylacetic Acid
Derivatives Responsible for Differences in Enzyme Inhibitory
Activity. J . Med. Chem. 1990, 33, 3055-3060.
3
2
5
3
+
(
M ). Anal. (C18
24 2
H N O) C, H, N.
(
S)-(-)-1-(4-P yr id yl)eth yl 1-Ad a m a n ta n eca r boxa m id e
(4) Pepper, C.; Smith, H. J .; Barrell, K. J .; Nicholls, P. J .; Hewlins,
M. J . Racemisation of Drug Enantiomers by Benzylic Proton
Abstraction at Physiological pH. Chirality 1994, 6, 400-404.
(
15b). By the foregoing method, but using (S)-(-)-1-(4-
pyridyl)ethylamine (14, 85 mg, 0.70 mmol), 15b (185 mg, 93%)
was obtained as a white solid, mp 159-160 °C (from cyclo-
(
5) Chandrasekharan, J .; Ramachandran, P. V.; Brown, H. C.
Diisopinocampheylchloroborane, a Remarkably Efficient Chiral
Reducing Agent for Aromatic Prochiral Ketones. J . Org. Chem.
hexane), [R] -35.7° (c 0.6, MeOH), having IR, NMR, and MS
D
data identical with those of 15a .
1
985, 50, 5446-5448.
En zym e In h ibitor y Activities. The hydroxylase and
lyase assays were carried out as described previously using
(6) J aeger, D. A.; Broadhurst, M. D.; Cram, D. J . A 4-Pyridyl Group
Attached to a Carbon Acid Introduces an Isoinversion Compo-
nent into the Base-Catalyzed Racemization of the System. J .
Am. Chem. Soc. 1973, 95, 7525-7526.
2
3
3
3
µM [ H]progesterone or 3 µM [ H]-17R-hydroxyprogesterone
as substrate. The enzyme concentration was estimated to be
e4 nM. Under the conditions used, the K values ((SE) were
(
7) Stephenson, B.; Solladi e´ , G.; Mosher, H. S. Neopentyl Displace-
ment Reactions without Rearrangement. J . Am. Chem. Soc.
1972, 94, 4184-4189.
m
0
.2 ( 0.05 and 2.2 ( 0.15 µM, respectively. The reagents and
conditions for the assays for inhibition of aromatase enzyme
from the microsomal fraction of human placenta were as
previously described.
androstenedione, was 38 ( 5 nM.
Hyd r olysis of Ester s by Micr osom a l a n d Blood Es-
(8) Potter, G. A.; Barrie, S. E.; J arman, M.; Rowlands, M. G. Novel
Steroidal Inhibitors of Human Cytochrome P45017R
(17R-Hydroxylase/C17,20-lyase): Potential Agents for the Treat-
ment of Prostatic Cancer. J . Med. Chem. 1995, 38, 2463-2471.
1
3
The K
m
((SE) for the substrate,
(
9) Van Wauwe, J . P.; J anssen, P. A. J . Is there a Case for P-450
Inhibitors in Cancer Treatment? J . Med. Chem. 1989, 32, 2231-
2239.
ter a ses. Esters were incubated with, and extracted from, liver
microsomal preparations as described previously and extracts
subjected to HPLC (see below). The stability of the esters was
also assessed in mouse, rat, and human blood. Thus esters
2
(10) Bhatnagar, A. S.; Mueller, P. H.; Schenkel, L.; Trunet, P. F.;
Beh, I.; Schieweck, K. Inhibition of Estrogen Biosynthesis and
its Consequences on Gonadotrophin Secretion in the Male. J .
Steroid Biochem. Mol. Biol. 1992, 41, 437-443.
(0.25 mg) were incubated at 37 °C with blood (4.5 mL) and
(
11) Brueggemeier, R. W.; Floyd, E. E.; Counsell, R. E. Synthesis and
Biochemical Evaluation of Inhibitors of Oestrogen Biosynthesis.
J . Med. Chem. 1978, 21, 1007-1011.
aliquots (0.5 mL) removed at various times up to 1 h. An
internal standard (25 µg) was added before deproteinization
of the sample with acetonitrile (0.5 mL); for example, for
compounds 3a and 3b, the internal standard was compound
(
12) Guengerich, F. P. Oxidative Cleavage of Carboxylic Esters by
Cytochrome P-450. J . Biol. Chem. 1989, 262, 8459-8462.
13) Foster, A. B.; J arman, M.; Leung, C.-S.; Rowlands, M. G.; Taylor,
G. N. Analogues of Aminoglutethimide: Selective Inhibition of
Cholesterol Side-Chain Cleavage. J . Med. Chem. 1983, 26, 50-
54.
(
1
.
Aliquots (100 µL) of the supernatant obtained after
centrifugation were analyzed by HPLC. The HPLC system
consisted of a 15 cm Apex column containing 5 µm of C18
stationary phase with a mobile phase comprising 10 mM
sodium phosphate buffer, pH 6.8, and acetonitrile (44:56).
Esters were detected by their UV absorption at 229 and 254
nm. No hydrolysis was observed when the esters were
(
14) Chou, T. C. Derivation and Properties of Michaelis-Menten Type
and Hill Type Equations for Reference Ligands. J . Theor. Biol.
1
976, 39, 253-276.
J M950749Y