1,4-Cyclohexanecarboxylates: Potent and selective inhibitors of phosophodiesterase 4 for the treatment of asthma

Article abstract of DOI:10.1021/jm970090r

Evaluation of a variety of PDE4 inhibitors in a series of cellular and in vivo assays suggested a strategy to improve the therapeutic index of PDE4 inhibitors by increasing their selectivity for the ability to inhibit PDE4 catalytic activity versus the ability to compete for high affinity [³H]rolipram-binding sites in the central nervous system. Use of this strategy led ultimately to the identification of cis-4-cyano-4-[3- (cyclopentyloxy)-4-methoxyphenyl]cyclohexane-1-carboxylic acid (1, SB 207499, Ariflo(TM)), a potent second-generation inhibitor of PDE4 with a decreased potential for side effects versus the archetypic first generation inhibitor, (R)-rolipram.

Full text of DOI:10.1021/jm970090r

821
J . Med. Chem. 1998, 41, 821-835
1,4-Cycloh exa n eca r boxyla tes: P oten t a n d Selective In h ibitor s of
P h osop h od iester a se 4 for th e Tr ea tm en t of Asth m a
Siegfried B. Christensen,*,† Aimee Guider,† Cornelia J . Forster,† J ohn G. Gleason,† Paul E. Bender,†
J oseph M. Karpinski,† Walter E. DeWolf, J r.,† Mary S. Barnette,‡ David C. Underwood,‡ Don E. Griswold,‡
Lenora B. Cieslinski,‡ Miriam Burman,‡ Steven Bochnowicz,‡ Ruth R. Osborn,‡ Carol D. Manning,‡
Marilyn Grous,‡ Leonard M. Hillegas,‡ J oan O’Leary Bartus,§ M. Dominic Ryan,| Drake S. Eggleston,|
R. Curtis Haltiwanger,| and Theodore J . Torphy‡,
Research and Development, SmithKline Beecham Pharmaceuticals, P.O. Box 1539, King of Prussia, Pennsylvania 19406-0939
Received February 11, 1997
Evaluation of a variety of PDE4 inhibitors in a series of cellular and in vivo assays suggested
a strategy to improve the therapeutic index of PDE4 inhibitors by increasing their selectivity
for the ability to inhibit PDE4 catalytic activity versus the ability to compete for high affinity
[3H]rolipram-binding sites in the central nervous system. Use of this strategy led ultimately
to the identification of cis-4-cyano-4-[3-(cyclopentyloxy)-4-methoxyphenyl]cyclohexane-1-car-
boxylic acid (1, SB 207499, ArifloTM), a potent second-generation inhibitor of PDE4 with a
decreased potential for side effects versus the archetypic first generation inhibitor, (R)-rolipram.
In tr od u ction
somewhat lesser extent in airway smooth muscle, has
made this isozyme an attractive target for novel anti-
asthmatic and antiinflammatory therapy.8,10,14-17
As would be predicted from the predominance of
PDE4 in immune and inflammatory cells and the
putative biological role of cAMP in these cells, PDE4
inhibitors exert broad antiinflammatory effects in
vitro.18-30 This suppression of inflammatory cell activ-
ity has been extended to several in vivo models of
inflammation.31-35 Thus, the antiinflammatory and
immunomodulatory activity displayed by PDE4 inhibi-
tors in a variety of in vitro and in vivo settings, coupled
with the relaxant activity of PDE4 inhibitors on human
isolated bronchi,36-38 support the concept that PDE4
inhibition represents a unique approach toward the
therapy of asthma. However, first-generation PDE4
inhibitors also possess certain dose-limiting side effects
resulting from an extension of their pharmacologic
mechanism of action (i.e., inhibition of PDE4 in inap-
propriate tissues). The side effects of primary concern
are nausea and vomiting,39-41 increased gastric acid
secretion,41,42 and potential psychotropic activity.41,43-46
The primary objective of our research effort has been
to identify novel, selective (for PDE4 versus other PDE
isozymes), orally active second-generation PDE4 inhibi-
tors as antiinflammatory and antiasthmatic agents with
decreased potential for the side effects reported for the
archetypic PDE4 inhibitor rolipram (Figure 1). To
achieve this goal, we adopted a strategy focused on
improving the selectivity of PDE4 inhibitors for their
ability to inhibit human monocyte-derived PDE4 cata-
lytic activity (herein designated LPDE4 activity)47 ver-
sus their ability to compete for high affinity (nanomolar)
[3H]rolipram-binding sites in the central nervous system
(CNS; this activity is herein designated HPDE4 activ-
ity),48 two divergent biochemical properties of rolipram.
Though the precise molecular nature of LPDE4 and
HPDE4 activity remains uncertain, kinetic and radio-
ligand binding studies on full-length and truncated
forms of recombinant human PDE4 suggest that these
The central role of cyclic nucleotides in regulating the
function of airway smooth muscle, inflammatory cells
and immune cells is well established.1-8 Compelling
evidence exists that cyclic 3′,5′-adenosine monophos-
phate (cAMP) is the second messenger that both medi-
ates airway smooth muscle relaxation and exerts a
broad inhibitory effect on the activity of immune and
inflammatory cells.7-10 Mechanistically, the intracel-
lular concentration of cAMP can be elevated either by
stimulation of adenylyl cyclase to increase the rate at
which cAMP is synthesized, as with â-adrenoceptor
agonists, or by inhibiting cyclic nucleotide phosphodi-
esterases (PDEs) to decrease the rate at which cAMP
is metabolized.
Cyclic nucleotide PDEs comprise a family of distinct,
cell-associated isozymes that inactivate cAMP or cyclic
3′,5′-guanosine monophosphate (cGMP) by catalyzing
hydrolysis of the 3′-phosphoester bond to form the
corresponding inactive 5′-nucleotide products. To date,
at least seven families of PDE isozymes have been
identified, each of which is encoded by a distinct gene
or family of genes.11,12 Though similar in their primary
hydrolytic role, these isozymes differ with respect to
their substrate specificity (or lack thereof), structure,
subunit organization, kinetic characteristics, allosteric
regulation by endogenous activators and inhibitors,
tissue and cellular distribution, and sensitivity to syn-
thetic inhibitors.8,13-15 Recognition of these differences
has greatly stimulated interest in PDEs as drug targets,
since these differences invite the possibility of targeting
compounds specifically for the isozyme that predomi-
nates in the tissue or cell of interest. In particular, the
dominant role of the cAMP-specific PDE (PDE4) in
nearly all immune and inflammatory cells, and to a
† Department of Medicinal Chemistry.
‡ Department of Pulmonary Pharmacology.
§ Department of Molecular Virology and Host Defense.
| Department of Physical and Structural Chemistry.
Department of Immunopharmacology.
S0022-2623(97)00090-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/12/1998

822 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6
Christensen et al.
Sch em e 1a
a
Reagents: (a) NaH, 15-crown-5, DMF; (b) 4-nitrobenzyl bro-
mide, THF; (c) 10% Pd/C, HCO2NH4, MeOH.
F igu r e 1. Structures of rolipram and 1.
activities arise from two distinct forms of the en-
zyme.47,49,50 While both forms appear to display cata-
lytic activity, rolipram binds to HPDE4 with a high
affinity (Kd ∼2 nM) and to LPDE4 with a low affinity
(Kd ∼100 nM). These forms differ with respect to their
relative sensitivity to inhibitors47,51,52 and to their
biological roles.51,52
Herein, we briefly describe the derivation of our
hypothesis that p oten t LP DE4 in h ibitor s w ith r e-
d u ced HP DE 4 a ct ivit y ver su s fir st-gen er a t ion
in h ibitor s w ou ld d isp la y good a n tiin fla m m a tor y
a ctivity w ith a d ecr ea sed p oten tia l for sid e effects.
We also describe the use of this strategy to design cis-
4-cyano-4-[3-(cyclopentyloxy)-4-methoxyphenyl]cyclo-
hexane-1-carboxylic acid [IUPAC name: c-4-cyano-4-[3-
(cyclopentyloxy)-4-methoxyphenyl]-r-1-cyclohexane-
carboxylic acid] (1, SB 207499, ArifloTM, Figure 1), a
potent and selective (versus other PDE isozymes) second-
generation inhibitor of PDE4 with a significant im-
provement in side-effect profile relative to the first-
generation inhibitor, (R)-rolipram.
curic chloride-mediated methanolysis61 of 11 provided
an approximately 11:1 mixture of the cis and trans
esters (12 and 13, respectively), which was separated
by flash chromatography on silica gel. Saponification
of the individual esters with potassium hydroxide in a
THF/methanol/water solvent mixture, followed by acidi-
fication with aqueous HCl, then provided the corre-
sponding carboxylic acids 1 and 14.
The synthesis of tetrazole 17 was accomplished by the
method of Duncia62 outlined in Scheme 3. EDC-medi-
ated coupling of 1 with 3-aminopropionitrile in meth-
ylene chloride in the presence of HOBt provided cya-
noethyl amide 15. Reaction of 15 with TMSN3 in the
presence of DEAD and PPh3 in THF provided protected
tetrazole 16, which was deprotected with sodium hy-
droxide in aqueous THF and then acidified with aqueous
HCl to provide 17.
Ketone 10 served as a convenient vehicle for the
examination of substituent effects at the benzylic posi-
tion of this class of cyclohexanone PDE4 inhibitors.
Thus, reductive decyanation63 of cyano ketone 10 with
sodium in liquid ammonia was accompanied by con-
comitant reduction of the ketone to provide alcohol 18
(Scheme 4). Oxidation of 18 with PCC64 to ketone 19,
followed by homologation as for ketone 10 in Scheme 2,
produced ketene dithioacetal 20. Hydrogen peroxide-
mediated hydrolysis of 20, followed by basic decomposi-
tion of the excess peroxide and then acidification with
aqueous HCl, provided the descyanocyclohexane car-
boxylic acid 21.65
Alternatively, treatment of 10 with methyl orthofor-
mate66 and catalytic p-toluenesulfonic acid in methanol
at reflux provided dimethyl ketal 22, the key intermedi-
ate used to prepare five additional benzylically modified
cyclohexanones (Scheme 5). Basic hydrogen peroxide-
mediated hydrolysis67 of the nitrile of 22 in aqueous
methanol produced ketal amide 23, which was deket-
alized to benzylic amide 24 in acidic acetone. Reduction
of the nitrile of 22 with DIBAl-H68 in toluene provided
ketal aldehyde 25. Simple hydrolysis of 25 with aque-
ous HCl in ethyl acetate produced benzylic aldehyde 26.
Homologation of 25 with the anion of dimethyl (di-
azomethyl)phosphonate69 generated at -78 °C in THF
with potassium tert-butoxide produced ketal acetylene
27, which was hydrolyzed as with 23 to benzylic
acetylene 28. Reduction of ketal aldehyde 25 with
Resu lts a n d Discu ssion
Ch em istr y. Rolipram was synthesized and resolved
as described previously.53 Independent treatment of
(R)- and (S)-rolipram with sodium hydride in anhydrous
DMF in the presence of 15-crown-5, followed by reaction
with 4-nitrobenzyl bromide, provided compounds 2 and
3, respectively (Scheme 1). Subsequent reduction of 2
to 4 and 3 to 5 was accomplished with 10% palladium
on carbon in the presence of excess ammonium formate
in MeOH.54
The synthesis of 1 is outlined in Scheme 2. Reductive
bromination of aldehyde 655 with 1,1,3,3-tetramethyl-
disiloxane and lithium bromide in the presence of
chlorotrimethylsilane56 was followed by reaction of the
product with sodium cyanide in DMF57 to provide benzyl
nitrile 7. Double Michael reaction58 of 7 in the presence
of excess methyl acrylate in acetonitrile using Triton-B
as base provided the pimelate 8. Dieckmann cycliza-
tion59 with sodium hydride in hot DME provided â-keto
ester 9, which was saponified and decarboxylated to
cyclohexanone 10 with sodium chloride in hot aqueous
DMSO.60 Cyclohexanone 10 was homologated by Peter-
son-type reaction with excess 2-lithio-2-(trimethylsilyl)-
1,3-dithiane61 to produce ketene dithioacetal 11. Mer-

1,4-Cyclohexanecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6 823
Sch em e 2a
a
Reagents: (a) LiBr, (Me2HSi)2O, TMSCl, MeCN; (b) NaCN, DMF; (c) excess methyl acrylate, MeCN, Triton-B; (d) NaH, DME, 85 °C;
(e) NaCl, H2O, DMSO, 150 °C; (f) lithium 2-(trimethylsilyl)-1,3-dithiane, THF, -78 °C; (g) HgCl2, HClO4, MeOH, 65 °C; (h) KOH, aqueous
MeOH, THF; (i) aqueous HCl.
Sch em e 3a
a
Reagents: (a) H2N(CH2)2CN, HOBt, EDC, CH2Cl2; (b) TMSN3, PPh3, DEAD, THF; (c) NaOH, aqueous THF; (d) aqueous HCl.
Sch em e 4a
a
Reagents (a) Na, NH3; (b) PCC, CH2Cl2; (c) lithium 2-(trimethylsilyl)-1,3-dithiane, THF, -78 °C; (d) TFA, H2O2, 85 °C; (e) NaOH; (f)
aqueous HCl.
sodium borohydride70 in DME provided benzylic hy-
droxymethyl ketal 29, which was hydrolyzed to the
benzylic (hydroxymethyl)cyclohexanone 30. Reaction of
29 with DAST71 in methylene chloride at -78 °C
produced the benzylic fluoromethyl ketal 31, which was
hydrolyzed with aqueous HCl in ethyl acetate to the
benzylic (fluoromethyl)cyclohexanone 32.
Compounds 33 and 34 (Table 1) were synthesized by
published procedures.72,73
Structural assignment for cis ester 12 and trans ester
13 was based initially on the expectation that the
thermodynamically more stable product (cis ester 12)
would be the major product, and on the resonance in
the NMR spectrum in CDCl3 for the R-methine proton

824 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6
Christensen et al.
Sch em e 5a
a
Reagents: (a) HC(OMe)3, p-TsOH (cat.), MeOH, reflux; (b) H2O2, K2CO3, MeOH/H2O; (c) p-TsOH (cat.), COMe2; (d) DIBAl-H, toluene;
(e) (MeO)2P(O)CHN2, KOtBu, THF, -78 °C; (f) 3 N HCl, EtOAc; (g) NaBH4, DME; (h) 1 N HCl, ether, reflux; (i) DAST, CH2Cl2, -78 °C;
(j) 1 N HCl, EtOAc.
Ta ble 1. Activity Profile of First-Generation PDE4 Inhibitors
at 2.36 ppm, a sharp, well-resolved triplet of triplets
displaying the apparent coupling constants (J ax,ax ) 12
Hz; J ax,eq ) 4 Hz) diagnostic of the axial proton in a
cyclohexane chair conformation.74 In contrast, the

1,4-Cyclohexanecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6 825
the initial steric and electronic structural requirements
for selective PDE4 inhibition were derived from the
inhibitory and specificity profiles of a series of active
site directed (competitive) PDE4 inhibitors, appropri-
ately modified congeners of rolipram. Using portions
of rolipram as a template, additional functionalities
expected to modify physicochemical properties while
maintaining or improving potency were explored. These
studies identified the 3-(cyclopentyloxy)-4-methoxyphen-
yl moiety a n d an appropriately positioned hydrogen
bond acceptor moiety as the minimum pharmacophoric
requirements for potent PDE4 inhibition, consistent
with results subsequently reported by other research-
ers.75 Thus, in our studies, cyclopentanone 33, a race-
mate, was comparable to (R)-rolipram in inhibition of
LPDE4 activity (Table 1), revealing that the NH func-
tion of the rolipram pyrrolidinone ring was unnecessary
for inhibition. Both (R)-rolipram and 33 were more
potent than (S)-rolipram by a factor of 2-4. The
carboxyl function of cyclopentanecarboxylate 34 served
as a slightly poorer hydrogen bond acceptor, with 34
(again, a racemate) 4-fold less potent than (R)-rolipram
as an inhibitor of LPDE4 activity. With respect to
HPDE4 activity, 33 and (S)-rolipram were some 9-fold
less potent than (R)-rolipram, while 34 was comparable
to (R)-rolipram in HPDE4 activity.
F igu r e 2. A view of 1 from its crystal structure showing the
numbering scheme employed. For clairity, only the higher
occupancy positions for the disordered cyclopentyl ring are
shown. Anisotropic displacement ellipsoids for non-hydrogen
atoms are shown at the 50% probability level. Hydrogen atoms
are displayed spheres of arbitrary size.
corresponding signal for trans ester 13 was a broadened,
distorted apparent six-line manifold with J app ) 4 Hz,
indicative of an equatorial proton in a cyclohexane chair
conformation.
Confirmation of the relative configuration of substit-
uents in cis ester 12 was obtained with the crystal
structure of its derived acid 1 (Figure 2). In the solid
state, the cyclohexane ring system of 1 possesses an
undistorted chair conformation. The nitrile and car-
boxylic acid moieties adopt a cisoid orientation relative
to one another, with the nitrile oriented axially and the
carboxylic acid oriented equatorially. The phenyl ring
of the 3-(cyclopentyloxy)-4-methoxyphenyl moiety oc-
cupies an equatorial orientation about the cyclohexane
chair, with a dihedral angle of 26.5° between the phenyl
ring and the mean plane of the cyclohexane ring. The
methyl group of the phenyl methoxy moiety is virtually
in-plane with the phenyl ring. The cyclopentyl sub-
stituent occupies two different orientations, the major
one (68%) illustrated in Figure 2 and the minor one in
which the ring system is rotated approximately +20°
about the phenyl carbon-oxygen bond.
The structural rigidity in solution of the cyclohex-
anone ring of descyano ketone 19 was apparent from
its NMR spectrum obtained in CDCl3. Specifically, the
resonance for the benzylic methine proton at 2.95 ppm
was a sharp, well-resolved triplet of triplets, displaying
the apparent coupling constants (J ax,ax ) 12 Hz; J ax,eq
) 3 Hz) characteristic of an axial proton in a cyclohex-
ane chair conformation. This unambiguously placed the
3-(cyclopentyloxy)-4-methoxyphenyl moiety in an equa-
torial orientation relative to the “pseudoequatorial”
carbonyl of the cyclohexanone ring.
Consistently, the configuration of the descyanocyclo-
hexanecarboxylic acid 21 again was evident from its
NMR spectrum in CDCl3. Here, a pair of triplet of
triplets centered at 2.45 and 2.40 ppm, with apparent
coupling constants of J ax,ax ) 12 Hz and J ax,eq ) 4 Hz,
clearly signaled axial orientations for the cyclohexane
C-4 and C-1 protons, respectively, and, therefore, a
transoid orientation for the equatorially oriented 3-(cy-
clopentyloxy)-4-methoxyphenyl and carboxylic acid moi-
eties. These conclusions were confirmed by more ex-
tensive 1D TOCSY and 1D NOE difference experiments
conducted in benzene-d6 at 300 K to improve signal
dispersion (data not shown).
In an effort to investigate the pharmacologic roles of
LPDE4 and HPDE4 activity, three of these four com-
pounds were evaluated for their ability to inhibit
antigen-induced bronchoconstriction in guinea pigs, an
antiallergic model,34 and to reverse reserpine-induced
hypothermia in the mouse, a standard model of psy-
chotropic activity.44,76 Upon either intravenous or oral
administration, (R)-rolipram, (S)-rolipram, and 34 were
essentially equipotent inhibitors of bronchoconstriction
in the guinea pig model (Table 1). In terms of their
ability to reverse reserpine-induced hypothermia in the
mouse, 34 was again equipotent to (R)-rolipram, while
(S)-rolipram was essentially inactive in this model,
consistent with reports on (R)- and (S)-rolipram by
earlier workers.77 While the approach used here to
compare antiallergic activity in the guinea pig with
reversal of hypothermia in the mouse using inhibitors
administered by the oral route is not without pitfalls,
particularly with regard to the impact that differences
in pharmacokinetics and drug disposition can have in
cross-species comparisons, results with these three
compounds suggested to us a tentative correlation
between inhibition of LPDE4 activity and peripheral
(antiinflammatory) effects on one hand and between
HPDE4 activity and central (CNS) effects on the other.
Parallel studies conducted with the rolipram enanti-
omers and their N-substituted derivatives strengthened
this tentative correlation. Thus, 4, the 4-aminobenzyl
derivative of (R)-rolipram, displayed LPDE4 activity
comparable to that of the parent with an 8-fold loss in
HPDE4 activity. Its enantiomer, 5, possessed an even
more interesting profile in vitro, with a 6-fold improve-
ment in LPDE4 activity and a 65-fold loss of HPDE4
activity relative to (R)-rolipram. Given that neither 4
nor 5 possessed significant oral activity in the guinea
pig model, these compounds were evaluated pharma-
cologically in a different way. Thus, the ability of these
compounds to inhibit antigen-induced bronchoconstric-
Str u ctu r e-Activity Rela tion sh ip s. The multiplic-
ity of PDE isozymes precluded a substrate-based design
strategy for an isozyme-selective PDE inhibitor. Thus,

826 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6
Christensen et al.
Ta ble 2. Activity Profile of the Rolipram Enantiomers and N-(4-Aminobenzyl) Derivatives
tion in guinea pigs was compared with their ability to
Ta ble 3. Activity Profile of Cyclohexanone Derivatives
induce emesis in dogs78 when administered by the
intravenous route, another cross-species comparison
subject to the caveat noted above. In these studies, 5
was comparable in potency to (R)- and (S)-rolipram in
the guinea pig model, with 4 displaying unexpectedly
poor in vivo activity relative to its LPDE4 potency in
vitro. Compounds 4, 5, and (S)-rolipram were signifi-
cantly less potent than (R)-rolipram in their ability to
elicit emesis in the dog, consistent with their reduced
HPDE4 activity versus (R)-rolipram in vitro. Overall,
the trend of the data summarized in Tables 1 and 2
suggested that despite the caveat of cross-species com-
parison, decreasing the HPDE4 activity of PDE4 inhibi-
tors, and/or improving the selectivity of PDE4 inhibitors
for LPDE4 activity at the expense of HPDE4 activity,
could result in an improved therapeutic index.
LPDE4a
IC50 (nM)
HPDE4a
IC50 (nM)
compd
R
H/La
10
28
19
24
26
32
30
CN
CtCH
H
CONH2
CHO
CH2F
CH2OH
44
80
120
300
70
700
500
6000
7000
2.7
3.8
0.6
2.2
1.5
5.1
2.8
120
320
340
1180
2500
a
See corresponding footnotes from Table 1.
Thus, our synthetic efforts focused on construction of
a structurally simplified pharmacophore possessing
the requisite improvement in LPDE4 activity versus
HPDE4 activity. The five-membered pyrrolidinone ring
system of rolipram, the cyclopentanone of compound 33,
and the cyclopentane ring bearing the carboxyl moiety
of compound 34 all possess significant conformational
flexibility. Ring puckering allows the 3-(cyclopentyl-
oxy)-4-methoxyphenyl group to adopt either a pseudo-
axial or pseudoequatorial orientation with respect to the
carbonyl or carboxyl moieties of these compounds about
the five-membered ring. While molecular mechanics-
based conformational analysis (amber*/Macromodel/
Batchmin) coupled with molecular orbital calculations
(Gaussian94, 6-31G*//6-31G*) suggested that the pseu-
doequatorial conformation of each compound would be
energetically preferred, unambiguous assignment of an
active conformation of these five-membered rings was
not possible. For this, we sought a ring scaffold that
would (1) decrease conformational mobility, allowing
more rigid placement of key pharmacophore units in
order to derive a more well-defined pharmacophore
model; (2) avoid the issue of chirality to simplify both
structure activity relationship (SAR) interpretation and
synthetic efficiency; (3) provide flexibility in both the
synthesis and SAR development of alternative spacial
relationships among key pharmacophore units; and (4)
possess LPDE4 activity comparable to or better than
that of (R)-rolipram and 33 with a better selectivity for
LPDE4 activity versus HPDE4 activity than these
compounds.
A 1,4-substituted cyclohexane ring fulfilled all of these
criteria, as evidenced by the achiral cyclohexanone 19
(Table 3). Relative to (R)-rolipram, the structurally
rigid 19 (vide supra) possesses 2.5-fold better LPDE4
activity with a 25-fold reduction in HPDE4 activity, a
ca. 60-fold improvement. Likewise, relative to 33 (cf.
Table 2), 19 possesses 4-fold better LPDE4 activity with
a 1.5-fold reduction in HPDE4 activity, resulting in a
nominal 6-fold improvement in selectivity for LPDE4
versus HPDE4 activity. Comprehensive SAR studies
of substituents possessing a wide range of steric and
electronic properties at the benzylic position of cyclo-
hexanone 19 revealed that a third pharmacophore
element, a nitrile, improved both LPDE4 activity and
selectivity. As illustrated in Table 3 with selected
examples, cyano ketone 10 is roughly 2.5-fold more
potent and 4.5-fold more selective than 19 for LPDE4
activity. Replacement of the cyano moiety of 10 by an
acetylene (28), an amide (24), an aldehyde (26), a

1,4-Cyclohexanecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6 827
Ta ble 4. Activity Profile of 1 and Related Compounds
it is the lack of charge associated with 12, rather than
steric factors, which is important for the decrease in this
activity.
Finally, to confirm our previous observations concern-
ing the importance of the benzylic nitrile function in the
cyclohexanone series, we undertook synthesis and evalu-
ation of descyano compound 21 from 1. As expected
based on the previous SAR (cf. Table 3), the LPDE4
activity of 21 was some 12-fold less than that of 1,
although in this case removal of the nitrile had no effect
on HPDE4 activity, with 21 equipotent to 1.
Biologica l P r ofile of 1. Compound 1 is inactive
against PDEs 1, 2, 3, and 5 at concentrations up to 10
µM. Compound 1 potently and competitively inhibits
LPDE4 with a Ki ) 92 ( 6 nM. Compound 1 is nearly
equipotent with respect to LPDE4 activity (IC50 ) 95
nM) and HPDE4 activity (IC50 ) 120 nM). In contrast,
the HPDE4 activity (IC50 ) 5 nM) of (R)-rolipram is 60-
fold greater than its LPDE4 activity (IC50 ) 300 nM).
This represents a roughly 75-fold improvement over (R)-
rolipram in terms of the selectivity of 1 for LPDE4
versus HPDE4 (Table 5).
To illustrate the functional consequences of this
improvement in the selectivity of 1 versus (R)-rolipram
for LPDE4 versus HPDE4 activity (Table 5), the ability
of 1 and (R)-rolipram to decrease tumor necrosis factor-R
production by human isolated monocytes (hTNFR)51 was
compared with their ability to increase acid secretion
by isolated rabbit parietal glands.52 (R)-Rolipram and
1 inhibit lipopolysaccharide (LPS)-induced hTNFR re-
lease in a concentration-dependent manner, with IC50
values of 70 and 110 nM, respectively. (R)-Rolipram is
a potent acid secretagogue in rabbit parietal glands
(EC50 ) 4 nM). In marked contrast, 1 is a much weaker
acid secretagogue, with an EC50 ) 800 nM. Thus, while
(R)-rolipram is 17-fold more potent as an acid secreta-
gogue than as an inhibitor of hTNFR generation, 1 is
7-fold more potent as an inhibitor of hTNFR generation
than as an acid secretagogue, a 120-fold improvement.
These results are consistent with our previous conclu-
sions that inhibition of LPDE4 activity is associated
with suppression of hTNFR production,51 an antiinflam-
matory effect, whereas inhibition of HPDE4 activity
correlates with acid secretion,52 a side effect.
LPDE4a
HPDE4a
compd
R1
R2
R3 IC50 (nM) IC50 (nM) H/La
1
14
12
13
17
21
COOH
H
CO2CH3
H
5-tetrazole
COOH
H
CN
CN
CN
95
3410
530
1070
740
120
500
1000
700
110
120
1.3
0.15
1.9
COOH
H
CO2CH3 CN
0.7
H
H
CN
H
0.15
0.1
1200
a
See corresponding footnotes from Table 1.
fluoromethyl group (32), or a hydroxymethyl group (30)
produced progressively poorer LPDE4 activity, accom-
panied in these cases by a parallel loss in HPDE4
activity. It is assumed by analogy to compound 19 that,
in solution, the 3-(cyclopentyloxy)-4-methoxyphenyl moi-
ety of 10 adopts the equatorial orientation with the
nitrile in the axial orientation, as it is in the solid state
(data not shown), and that this is the conformation
producing LPDE4 inhibition.
Maintaining the benzylic nitrile, further examinations
of substituent effects focused on maintaining the LPDE4
activity and selectivity versus HPDE4 of 10 while
improving pharmaceutical properties within this class,
which prompted the synthesis of 1. Compound 1
displays a 2-fold reduction in inhibition of LPDE4
relative to 10 with identical HPDE4 activity (Table 4).
The importance of proper spatial positioning of the
carboxyl moiety relative to the 3-(cyclopentyloxy)-4-
methoxyphenyl and cyano moieties of the cyclohexane
ring is illustrated by comparison of 1 with its trans
isomer, 14. LPDE4 potency is profoundly influenced,
with 14 some 36-fold less potent than 1, while the
differential effect on HPDE4 activity is a comparatively
modest 4-fold loss. In the corresponding pair of dia-
stereomeric esters, differences between the isomers for
both activities are much less pronounced because of the
poor intrinsic potency of cis ester 12. Given that the
inhibition of LPDE4 activity by 12 is essentially equiva-
lent to that of the tetrazole 17, which, like 1, is ionized
and negatively charged at physiological pH, the poor
activity of 12 and 13 most likely results from a steric
constraint on inhibitor functionality in this region of the
enzyme active site. In contrast, the 8-9-fold decrease
in HPDE4 activity for 12 versus 1 and 17 suggests that
While these in vitro assay systems suggested an
improved therapeutic potential for 1, it was essential
to determine if this improvement was maintained in
vivo. Our first approach was to determine the anti-
allergic potency of 1 versus (R)-rolipram against antigen-
induced bronchoconstriction in the anesthetized guinea
pig34 and to compare this value with its emetic potency
Ta ble 5. Comparative Potencies of 1 and (R)-Rolipram
emesisd
ED50
(mg/kg, iv)
hTNFR
ID50
hypothermiaf
ED50
(mg/kg, po)
e
acid
antigen
LPDE4a
HPDE4a
hTNFR
secretionc
EC50 (nM)
provocationa
ID50 (mg/kg, iv)
b
compd
IC50 (nM)
IC50 (nM)
IC50 (nM)
(mg/kg, po)
(R)-rolipram
1
300
95
5
120
70
110
4
800
0.2
1.8
0.04
4.6
5.1
4.9
0.2
2.3
potency ratiog
3
0.04
0.6
0.005
0.1
0.01
1
0.09
a
b
See corresponding footnotes from Table 1. IC50 for inhibition of LPS-induced hTNFR generation from human monocytes; IC50 values
are the average of four to seven independent determinations. c EC50 for stimulation of acid secretion from rabbit parietal glands; EC50
values are the average of three to five independent determinations. Emesis in dogs (iv); see corresponding footnote from Table 2. e ID50
d
for inhibition of LPS-induced hTNFR generation in the mouse (po); ID50 values represent the mean response obtained from three to eight
g
animals. f ED50 for reversal of reserpine-induced hypothermia in the mouse (po); see corresponding footnote from Table 1. Potency ratio
represents the potency of 1 relative to (R)-rolipram, i.e., the value for (R)-rolipram divided by the value for 1.

828 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6
Christensen et al.
F igu r e 3. Inhibitory effect of 1 on antigen-induced bronchoconstriction and eosinophil infiltration in conscious guinea pigs.
Sensitized guinea pigs pretreated with chlorpheniramine (0.5 mg/kg) were placed in a plethysmograph and given an oral dose of
1 (10 or 30 mg/kg, dissolved in 90% PEG/10% H2O) 1 h prior to the administration of antigen (ovalbumin) by the aerosol route.
Pulmonary function (SGaw) was monitored over the next 10 min (left). The animals were removed and bronchoalveolar lavage
was performed 24 h after antigen challenge (right). The cells were isolated from the lavage fluid and differential cell counts
analyzed in stained cytospin preparations. Data are expressed as percent of total cell number. The dashed line represents the
percentage of eosinophils in unchallenged animals. The results obtained are the mean (SE of six to seven animals/group.
†
*†Significantly less than vehicle control: *(P < 0.05), (P < 0.01).
in dogs.78 After intravenous administration, (R)-rolip-
ram and 1 inhibit antigen-induced bronchoconstriction
with ID50 values of 0.2 and 1.8 mg/kg, respectively
(Table 5). A noteworthy observation from these studies
is that 1 has no effect on mean arterial pressure, pulse
pressure, or heart rate. (R)-Rolipram produces emesis
in the dog at 5-fold lower doses (ED50 ) 0.04 mg/kg, iv)
than those that inhibit bronchoconstriction in the guinea
pig. In contrast, intravenous 1 produces emesis in the
dog with an ED50 ) 4.6 mg/kg, 3-fold greater than its
ID50 for inhibiting antigen-induced bronchoconstriction
in the guinea pig. This yields an improved therapeutic
potential of slightly greater than 10-fold compared with
(R)-rolipram. These results demonstrate that the pos-
tulated improvement in therapeutic potential based
upon in vitro measurements is reflected in an in vivo
setting, though again the role of potential differences
in pharmacokinetics and drug disposition is unknown
in this cross-species comparison.
improvement over (R)-rolipram confirms our previous
in vivo results using the cross-species comparison.
Oral pharmacodynamics of 1 were assessed in both
the guinea pig and the mouse. Orally administered 1
(30 mg/kg) inhibits antigen-induced bronchoconstriction
in conscious guinea pigs with an estimated half-life of
4-5 h. In the mouse, orally administered 1 (30 mg/kg)
inhibits the production of mTNFR with an estimated
half-life of >10 h.
The activity of 1 also was examined in a guinea pig
model of the early-phase/late-phase response to antigen
(Figure 3).34 In this model, conscious sensitized guinea
pigs are placed in a plethysmograph and given an
aerosol challenge with ovalbumin. This results in mast
cell degranulation and the rapid development of an
early-phase response marked by bronchoconstriction.
This early-phase response resolves over a period of 30-
60 min. Beginning approximately 6 h after the antigen
challenge and continuing over a 24-h period, there is a
fulminant infiltration of inflammatory cells into the
airway. The most prominent of these cells, which can
be monitored by bronchoalveolar lavage, is the eosino-
phil. This infiltration of eosinophils into the airway is
analogous to the late-phase response in human asth-
matic patients. Previously, we have demonstrated that
(R)-rolipram administered orally 1 h prior to challenge
inhibited antigen-induced bronchoconstriction and eosi-
nophil influx in a dose-dependent manner.34 However,
at the doses used (1, 3 and 10 mg/kg), (R)-rolipram also
produces signs of CNS excitement (e.g., hyperpnea,
agitation, tremor) consistent with its previously reported
action in the guinea pig.80 Similar to (R)-rolipram, oral
administration of 1 (30 mg/kg) 1 h prior to antigen
challenge inhibits eosinophil influx by 65% (Figure 3).
In contrast to (R)-rolipram, 1 does not produce any signs
of CNS excitement at this dose. Thus, 1 prevents the
development of a late-phase reaction in the guinea pig
but, unlike rolipram, does so at a dose that produces
no overt CNS effects.
To confirm this improvement in therapeutic potential
without relying on a cross-species comparison, and to
demonstrate that this improvement could be maintained
upon administration by the oral route, our second
approach was to compare the ability of 1 and (R)-
rolipram to inhibit LPS-induced hTNFR generation from
human monocytes adoptively transferred into mice79
with their ability to reverse reserpine-induced hypo-
thermia in the same species. Upon oral administration,
(R)-rolipram and 1 inhibit LPS-induced hTNFR produc-
tion in a dose-dependent manner and with approxi-
mately equal potencies (ED50 ≈ 5 mg/kg). However,
when administered orally, (R)-rolipram (ED50 ) 0.2 mg/
kg) and 1 (ED50 ) 2.3 mg/kg) differ markedly in their
ability to reverse reserpine-induced hypothermia. (R)-
Rolipram is at least 20-fold more potent at reversing
reserpine-induced hypothermia than inhibiting hTNFR
production in vivo in the mouse, while 1 is only 2-fold
more potent in reversing reserpine-induced hypothermia
than it is at inhibiting hTNFR production. This 10-fold

1,4-Cyclohexanecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6 829
In summary (Table 5), 1 is a potent and competitive
inhibitor of PDE4, which is selective for PDE4 over the
other PDE isozymes and is 75-fold more selective than
(R)-rolipram with respect to LPDE4 activity versus
HPDE4 activity. In three models established to evalu-
ate the side-effect potential (acid secretagogue, emetic
and psychotropic effects) of PDE4 inhibitors, the overall
trend of the data suggests substantial improvement for
1 versus the first generation inhibitor (R)-rolipram (10-
120-fold, Table 5). Compound 1 is orally active in both
guinea pig and mouse models with excellent pharma-
codynamic properties.
among the first of a new generation of PDE4 inhibitors
specifically designed to possess an improved therapeutic
potential relative to first generation inhibitors (e.g.,(R)-
rolipram). Whether this comparative improvement
conveys clinical success remains to be determined.
Compound 1 continues to progress in clinical trials as
a novel therapy for the treatment of asthma.
Exp er im en ta l Section
(1) Cr ysta llogr a p h ic Stu d ies. A colorless plate of 1 with
approximate dimensions 0.6 × 0.2 × 0.1 mm was mounted on
a glass fiber with paratone for examination. Lattice param-
eters were determined at 223 K on an Enraf Nonius CAD-4
diffractometer equipped with graphite monochromated mo-
lybdenum radiation (λ Mo KR ) 0.710 73 Å) from the setting
angles of 25 high-order reflections. The systematic absences,
0k0 for k odd and h0l for l odd, indicated space group P21/c.
Intensity data were collected on the diffractometer using
variable speed ω-2θ scans where the final scan speed was
determined for each reflection from a prescan of its intensity.
Scan speeds varied from 1.27 to 5.5 deg min-1. Background
estimates were made by extending the scan 25% on each side
of the peak. Three intensity standards, monitored at regular
intervals, showed a negligible variation. Data were corrected
for backgrounds, Lorentz, and polarization effects. A total of
4384 data were collected to 2θ e 55° (-18 e h e 18; 0 e k e
18; 0 e l e 12), which gave 4128 unique data after averaging
of symmetry equivalents (Rint ) 0.02). The structure was
solved by direct methods.91 Atomic positions were refined with
anisotropic displacement parameters for all nondisordered
positions and for the highest occupancy conformer (68%) of the
cyclopentyloxy substituent. The lower occupancy positions
(32%) for the cyclopentyloxy group were refined with isotropic
temperature factors.92 The function minimized employing full-
matrix least-squares procedures was ∑w(Fo2 - Fc2)2. Weights,
w, were eventually assigned to the data as w ) 1/[σ2(Fo2) +
(0.0934P)2 + 0.87P] where P ) [MAX(Fo2,0) + 2Fc2]/3. Posi-
tions for the hydrogen atoms were determined from difference
Fourier maps. The positional and isotropic displacement
parameters for the hydrogen attached to the heteroatom were
refined. Other hydrogen atoms were included in idealized
positions riding on the atom to which they are attached with
isotropic displacement factors assigned as 1.2 times Ueq of the
attached atom. The refinement (on F2) converged (max ∆/σ )
0.002) to values of the conventional crystallographic residuals
R ) 0.056 for observed data and R ) 0.114 (wR2 ) 0.178) for
all data. A final difference Fourier map was featureless with
maximal residual density peaks between ( 0.24 e Å-3. Values
of the neutral atom scattering factors, including ∆f′ and ∆f ′′
for all non-hydrogen atoms, were from the International Tables
for X-ray Crystallography.93 Crystal data: C20H25NO4, Mr
(343.43), monoclinic, P21/c, a (14.244(2) Å), b (14.239(1) Å), c
(9.292(3) Å), â (107.06(1)°), V (1801.7(4) Å3), Z (4), Fcalc (1.266
g cm-3), µ (0.088 mm-1), F(000) (736).
Con clu sion s
Correlation of the central (CNS) effects of rolipram
with HPDE4 rather than LPDE4 activity, along with
the apparent separation between the central and pe-
ripheral (antiinflammatory) pharmacological effects of
PDE4 inhibitors, led us to a strategy focused on increas-
ing the potency of compounds for LPDE4 activity while
decreasing their HPDE4 activity. Our original observa-
tion that these divergent biological activities could be
separated by appropriate modification of PDE4 inhibi-
tors have been extended in subsequent SAR studies with
a number of different PDE4 inhibitors.47,50,81-86 One
crucial feature of this divergence in terms of drug
discovery is that HPDE4 activity is not present, or is
present at very low densities, in many tissues that
contain a considerable amount of LPDE4 activity. In
particular, HPDE4 is undetectable in most immune and
inflammatory cells, while the CNS appears to contain
a high proportion of this activity.48,51,86,87 This prompted
investigations of the relevance of HPDE4 to the func-
tional actions of PDE4 inhibitors by ourselves and
others using standard pharmacological approaches.
Thus, as judged by the rank-order potency of a variety
of PDE4 inhibitors for HPDE4 versus LPDE4 activity,
we and others have demonstrated that HPDE4 activity
strongly correlates with the following functional ef-
fects: (1) behavioral activity in rodents;76 (2) stimulation
of acid secretion from rabbit parietal glands;52 (3) emesis
in dogs78 and ferrets;86 (4) elevation of cAMP content
in guinea-pig eosinophils;88 (5) relaxation of guinea-pig
airway;89 and (6) inhibition of superoxide production
from human neutrophils.51 In contrast, by the same
criteria, inhibition of LPDE4 is linked with inhibiting
the following processes: (1) guinea pig mast cell de-
granulation;34 (2) antigen-driven proliferation of human
T-cells;30 (3) TNF-R generation in human monocytes;25,51
and (4) superoxide production from guinea pig eosino-
phils.90 Eosinophils are unique in that both LPDE4 and
HPDE4 activities are present and functionally impor-
tant.88,90
(2) Ch em istr y. Melting points were determined on a
Thomas-Hoover Unimelt capillary apparatus and are uncor-
rected. 1H NMR spectra were recorded at ambient tempera-
ture on a Bruker AM-250 or AM-400 spectrometer in the
indicated solvent, with chemical shifts reported as apparent
centers of multiplets in ppm (δ) downfield from internal TMS
and apparent first-order coupling constants reported in hertz.
Optical rotations were measured on a Perkin-Elmer model 241
polarimeter in a 1 dm cell. Elemental analyses were deter-
mined using a Perkin-Elmer 240C; the amorphous and/or
hygroscopic nature of certain compounds resulted in incorpo-
ration of fractions of water molecules into their elemental
analyses. Flash chromatography was conducted using silica
gel 60 (70-230 mesh ASTM) from E. Merck.
While the precise molecular nature of HPDE4 vis-a`-
vis LPDE4, as well as the consequent mechanistic
rationale for the differential rank-order potency of PDE4
inhibitors in producing these effects, remains unknown,
the demonstration that individual PDE4 inhibitors
produce different pharmacological effects with distinct
rank-order potencies has defined our strategy for a new
generation of compounds. Thus, cis-4-cyano-4-[3-(cy-
clopentyloxy)-4-methoxyphenyl]cyclohexane-1-carboxyl-
ic acid (1, SB 207499, ArifloTM), a potent and selective
(versus other PDE isozymes) inhibitor of PDE4, is
(R)-(+)-1-(4-Am in oben zyl)-4-[3-(cyclopen tyloxy)-4-m eth -
oxyp h en yl]p yr r olid in -2-on e (4). (R)-(-)-rolipram (1.8 g, 6.5
mmol) was added to a suspension of NaH (196 mg of an 80%
dispersion) in dry DMF (65 mL) containing 15-crown-5-ether
(1.28 mL). The suspension was stirred under an argon

830 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6
Christensen et al.
atmosphere overnight at room temperature and then was
heated at 50-60 °C for 90 min to provide a solution of the
anion. 4-Nitrobenzyl bromide (2.79 g, 12.9 mmol) was dis-
solved in dry THF (70 mL), and the solution of anion was
added. The reaction mixture was stirred overnight, and the
THF was removed in vacuo. The resulting solution was poured
into ice water, was acidified with 3 N HCl, and was extracted
with EtOAc. The organic extract was washed six times with
water, was dried (Na2SO4), and was evaporated. The residue
was purified by flash chromatography, eluting with 1-3%
toluene in DMF (160 mL) under an argon atmosphere was
added NaCN (10.1 g, 206 mmol), and the resulting mixture
was stirred at room temperature for 18 h, then was poured
into cold water (600 mL), and was extracted three times with
ether. The organic extract was washed three times with water
and once with brine and was dried (K2CO3). The solvent was
removed in vacuo, and the residue was purified by flash
chromatography, eluting with 10% EtOAc/hexanes, to provide
1
7 as an off-white solid (17.7 g, 84%): mp 32-34 °C; H NMR
(400 MHz, CDCl3) δ 6.85 (m, 3H), 4.80 (m, 1H), 3.85 (s, 3H),
3.68 (s, 2H), 2.0-1.8 (m, 6H), 1.65 (m, 2H). Anal. (C14H17NO2)
C, H, N.
MeOH/CHCl3, to provide 2 as a yellow resin (570 mg, 21%):
1
[R]25 (0.61, methanol) ) +48.8°; H NMR (250 MHz, CDCl3)
D
δ 8.21 (d, J ) 9 Hz, 2H), 7.44 (d, J ) 9 Hz, 2H), 6.80 (d, J )
8 Hz, 1H), 6.70 (dd, J ) 8, 2 Hz, 1H), 6.67 (s,1H), 4.71 (m,
1H), 4.67 (d, J ) 15 Hz, 1H), 4.52 (d, J ) 15 Hz, 1H), 3.81 (s,
3H), 3.62 (t, J ) 9 Hz, 1H), 3.52 (p, J ) 7 Hz, 1H), 3.26 (dd, J
) 9, 9 Hz, 1H), 2.90 (dd, J ) 9, 18 Hz, 1H), 2.64 (dd, J ) 9, 18
Hz, 1H), 1.85-1.60 (br m, 8H).
Dim et h yl 4-Cya n o-4-[3-(cyclop en t yloxy)-4-m et h oxy-
p h en yl]p im ela te (8). To a solution of 7 (7 g, 30.3 mmol) in
CH3CN (200 mL) under an argon atmosphere was added a 40%
solution of Triton B in CH3OH (1.4 mL, 3.03 mmol), and the
mixture was heated to reflux. Methyl acrylate (27 mL, 303
mmol) was added carefully, and the reaction mixture was
maintained at reflux for 5 h and then was cooled. The mixture
was diluted with ether, was washed once with 1 N HCl and
once with brine, and was dried (MgSO4), and the solvent was
removed in vacuo. The solid residue was triturated with 5%
EtOH/hexane to provide 8 as a white solid (9 g, 74%): mp 81-
82 °C; 1H NMR (250 MHz, CDCl3) δ 6.97 (m, 3H), 4.78 (m,
1H), 3.85 (s, 3H), 3.62 (s, 6H), 2.6-2.1 (m, 8H), 2.0-1.8 (m,
6H), 1.6 (m, 2H). Anal. (C22H29NO6) C, H, N.
A solution of 2 (503 mg, 1.23 mmol) in anhydrous THF (6
mL) was treated with a suspension of ammonium formate (1.2
g, 19 mmol) and 10% Pd/C (120 mg) in MeOH. The suspension
was stirred for 2 h under argon. The reaction was filtered
through Celite and was washed with MeOH. The solvent was
removed in vacuo, and the residue was partitioned between
CH2Cl2 and water. After extracting, the organic layer was
washed twice with water, was dried (K2CO3), and was con-
centrated in vacuo. The resin was purified by flash chroma-
tography, eluting with a gradient of 50-100% EtOAc/CH2Cl2,
2-Car bom eth oxy-4-cyan o-4-[3-(cyclopen tyloxy)-4-m eth -
oxyp h en yl]cycloh exa n -1-on e (9). To a solution of 8 (5.9 g,
14.6 mmol) in dry DME (120 mL) under an argon atmosphere
was added NaH (80% suspension in mineral oil, 1.05 g, 43.8
mmol). The mixture was heated to reflux for 4.5 h, then was
cooled to room temperature, and was stirred for 16 h. Water
was added, and the reaction mixture was partitioned be-
tween ether and acidic water. The organic extract was dried
(MgSO4), and the solvent was removed in vacuo. The residue
was purified by flash chromatography, eluting with 3:1 hex-
anes/EtOAc, to provide 9 as a white foam (4.9 g, 93%): 1H
NMR (400 MHz, CDCl3) δ 10.8 (s, 1H), 6.99 (m, 2H), 6.87 (d,
J ) 8 Hz, 1H), 4.81 (m, 1H), 3.85 (s, 3H), 3.78 (s, 3H), 2.98 (d,
J ) 16 Hz, 1H), 2.80 (m, 1H), 2.65 (d, J ) 16 Hz, 1H), 2.48 (br
d, J ) 16 Hz, 1H), 2.26 (m, 1H), 2.16 (m, 1H), 2.0-1.7 (m,
6H), 1.6 (m, 2H). Anal. (C19H23NO3‚1/4H2O) C, H, N.
to provide 4 as a colorless oil (396 mg, 82%): [R]25 (0.56,
D
1
methanol) ) +72.5°; H NMR (250 MHz, CDCl3) δ 7.07 (d, J
) 8 Hz, 2H), 6.79 (d, J ) 8 Hz, 1H), 6.72-6.60 (m, 4H), 4.71
(m, 1H), 4.44 (d, J ) 14 Hz, 1H), 4.31 (d, J ) 14 Hz, 1H), 3.82
(s, 3H), 3.66 (s, 2H), 3.57 (t, J ) 9.6 Hz, 1H), 3.42 (p, J ) 8
Hz, 1H), 3.20 (dd, J ) 9.6, 9.6 Hz, 1H), 2.83 (dd, J ) 8 Hz, J
) 16 Hz, 1H), 2.55 (dd, J ) 8 Hz, J ) 16 Hz, 1H), 1.85-1.62
(br m, 8H). Anal. (C23H28N2O3‚1/5H2O) C, H, N.
(S)-(-)-1-(4-Am in oben zyl)-4-[3-(cyclopen tyloxy)-4-m eth -
oxyp h en yl]p yr r olid in -2-on e (5). Compound 3 was pro-
duced from (S)-(+)-rolipram by the reaction sequence described
for the preparation of 2. The residue was purified by succes-
sive flash chromatography, first eluting with 1-2% MeOH/
CHCl3, then eluting with 3:1 EtOAc/hexanes, to provide 3 as
a yellow resin (505 mg, 19%): [R]25D (0.61, methanol) ) -48.5°;
1H NMR (250 MHz, CDCl3) δ 8.21 (d, J ) 9 Hz, 2H), 7.44 (d,
J ) 9 Hz, 2H), 6.80 (d, J ) 8 Hz, 1H), 6.70 (dd, J ) 8, 2 Hz,
1H), 6.67 (s,1H), 4.71 (m, 1H), 4.67 (d, J ) 15 Hz, 1H), 4.52
(d, J ) 15 Hz, 1H), 3.81 (s, 3H), 3.62 (t, J ) 9 Hz, 1H), 3.52 (p,
J ) 7 Hz, 1H), 3.26 (dd, J ) 9, 9 Hz, 1H), 2.90 (dd, J ) 9, 18
Hz, 1H), 2.64 (dd, J ) 9, 18 Hz, 1H), 1.85-1.60 (br m, 8H).
4-Cya n o-4-[3-(cyclop en t yloxy)-4-m et h oxyp h en yl]cy-
cloh exa n -1-on e (10). A mixture of 9 (0.80 g, 2.15 mmol),
DMSO (16 mL), water (1 mL), and NaCl (0.8 g) under an argon
atmosphere was heated at 140-145 °C for 5 h. The reaction
mixture was cooled and was concentrated in vacuo. The
residue was purified by flash chromatography, eluting with
3:1 hexanes/EtOAc, to provide a yellow solid. Trituration with
hexanes/EtOAc yielded 10 as a white solid (0.52 g, 77%): mp
Compound 5 was produced from 3 by the reaction sequence
described for the preparation of 4. The resin was purified by
flash chromatography, eluting with a gradient of 50-75%
1
111-112 °C; H NMR (400 MHz, CDCl3) δ 7.01 (m, 2H), 6.87
(d, J ) 8 Hz, 1H), 4.80 (m, 1H), 3.85 (s, 3H), 2.90 (dt, J ) 6,
15 Hz, 2H), 2.56 (dt, J ) 2, 15 Hz, 2H), 2.47 (dt, J ) 3, 14 Hz,
2H), 2.24 (dt, J ) 4, 14 Hz, 2H), 2.0-1.8 (m, 6H), 1.63 (m,
2H). Anal. (C19H23NO3) C, H, N.
EtOAc/CH2Cl2, to provide 5 as a colorless resin (342 mg,
1
81%): [R]25 (0.63, methanol) ) -72.5°; H NMR (250 MHz,
D
CDCl3) δ 7.07 (d, J ) 8 Hz, 2H), 6.79 (d, J ) 8 Hz, 1H), 6.72-
6.60 (m, 4H), 4.71 (m, 1H), 4.44 (d, J ) 14 Hz, 1H), 4.31 (d, J
) 14 Hz, 1H), 3.82 (s, 3H), 3.66 (s, 2H), 3.57 (t, J ) 9.6 Hz,
1H), 3.42 (p, J ) 8 Hz, 1H), 3.20 (dd, J ) 9.6, 9.6 Hz, 1H),
2.83 (dd, J ) 8 Hz, J ) 16 Hz,1H), 2.55 (dd, J ) 8 Hz, J ) 16
Hz, 1H), 1.85-1.62 (br m, 8H). Anal. (C23H28N2O3‚1/5H2O) C,
H, N.
2-[4-Cya n o-4-[3-(cyclop en tyloxy)-4-m eth oxyp h en yl]cy-
cloh exylid en e]-1,3-d ith ia n e (11). To a solution of 2-(tri-
methylsilyl)-1,3-dithiane (9.25 mL, 48.7 mmol) in dry THF (80
mL) at 0 °C under an argon atmosphere was added rapidly
n-butyllithium (2.5 M in hexanes, 19.2 mL, 48 mmol). After
10 min, the mixture was cooled to -78 °C and a solution of 10
(7.53 g, 23 mmol) in THF (40 mL) was added. After 10 min,
aqueous NaCl was added, and the mixture was allowed to
warm to room temperature and was diluted with water. This
mixture was combined with the product of three substantially
similar reactions conducted on 10 (3.04, 6.01, and 6.1 g, 48.3
mmol total), the combined mixture was extracted three times
with CH2Cl2, the extract was dried (MgSO4), and the solvent
was evaporated. Purification by flash chromatography, eluting
with 10% EtOAc/hexanes, provided 11 as a white solid (26 g,
87%): mp 115-116 °C; 1H NMR (400 MHz, CDCl3) δ 6.96 (m,
2H), 6.84 (d, J ) 7 Hz, 1H), 4.80 (m, 1H), 3.84 (s, 3H), 3.30 (d,
J ) 15 Hz, 2H), 2.91 (t, J ) 6 Hz, 4H), 2.38 (dt, J ) 3, 14 Hz,
2-[3-(Cyclopen tyloxy)-4-m eth oxyph en yl]aceton itr ile (7).
To a solution of 655 (20 g, 90.8 mmol) in CH3CN (100 mL) was
added LiBr (15 g, 173 mmol) followed by the dropwise addition
of TMSCl (17.4 mL, 137 mmol). After 15 min, the reaction
mixture was cooled to 0 °C, 1,1,3,3-tetramethyldisiloxane (26.7
mL, 151 mmol) was added dropwise, and the resulting mixture
was allowed to warm to room temperature. After 3 h of
stirring, the mixture was separated into two layers. The lower
layer was removed, was diluted with CH2Cl2, and was filtered
through Celite. The filtrate was concentrated under reduced
pressure, was dissolved in CH2Cl2, and was refiltered. The
solvent was removed in vacuo to provide a light tan oil. To a
solution of this crude R-bromo-3-(cyclopentyloxy)-4-methoxy-

1,4-Cyclohexanecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6 831
2H), 2.22 (br d, J ) 14 Hz, 2H), 2.16 (m, 2H), 2.0-1.7 (m, 8H),
to provide 15 as a solid (0.54 g, 85%): mp 146-147 °C; 1H
NMR (400 MHz, CDCl3) δ 7.0 (d, J ) 2 Hz, 1H), 6.96 (dd, J )
8, 2 Hz, 1H), 6.85 (d, J ) 8 Hz, 1H), 6.0 (m, 1H), 4.8 (m, 1H),
3.85 (s, 3H), 3.54 (q, J ) 6 Hz, 2H), 2.67 (t, J ) 6 Hz, 2H),
2.27 (m, 3H), 2.13 (m, 2H), 2.03 (m, 2H), 1.8-2.0 (m, 9H), 1.6
(m, 2H). Anal. (C23H29N3O3) C, H, N.
1.65 (m, 2H). Anal. (C23H29N2S2) C, H, N.
Meth yl cis-a n d tr a n s-4-Cya n o-4-[3-(cyclop en tyloxy)-4-
m eth oxyp h en yl]cycloh exa n e-1-ca r boxyla te (12 a n d 13).
Perchloric acid (70%, 13.8 mL, 160 mmol) and mercuric
chloride (34.1 g, 126 mmol) were added to a solution of 11 (13
g, 31.3 mmol) in CH3OH (0.5 L) under an argon atmosphere,
and the mixture was heated at reflux for 2 h and then was
allowed to stir at room temperature for 42 h. The mixture
was diluted with CH2Cl2 and was filtered through Celite, and
the filtrate was combined with that of a similar reaction
conducted concurrently on the same scale. The mixture was
neutralized with aqueous NaHCO3 and was extracted three
times with CH2Cl2. The organic extract was washed three
times with aqueous sodium sulfite, was dried (MgSO4), and
was evaporated. Purification by flash chromatography, eluting
with 15% EtOAc/hexanes, provided the cis ester (12) as a white
solid (12.4 g, 56%): mp 119-120 °C; 1H NMR (400 MHz,
CDCl3) δ 7.00 (d, J ) 2 Hz, 1H), 6.96 (dd, J ) 2, 8 Hz, 1H),
6.85 (d, J ) 8 Hz, 1H), 4.80 (m, 1H), 3.84 (s, 3H), 3.72 (s, 3H),
2.36 (tt, J ) 4, 12 Hz, 1H), 2.25 (br d, J ) 13 Hz, 2H), 2.18
(dd, J ) 4, 13 Hz, 2H), 2.1-1.7 (m, 10H), 1.6 (m, 2H). Anal.
(C21H27NO4) C, H, N. The trans ester (13) was also isolated
cis-1-(2-Cya n oeth yl)-5-[4-cya n o-4-[3-(cyclop en tyloxy)-
4-m eth oxyp h en yl]cycloh exyl]tetr a zole (16). To a solution
of 15 (0.15 g, 0.37 mmol), PPh3 (0.19 g, 0.73 mmol) and TMSN3
(0.097 mL, 0.73 mmol), in dry THF (2 mL) at room tempera-
ture under an argon atmosphere was added dropwise DEAD
(0.12 mL, 0.73 mmol), and the mixture was stirred in the dark
for 24 h. Ceric ammonium nitrate (0.81 g, 1.48 mmol) in water
(10 mL) was added slowly at 0 °C to decompose the excess
TMSN3, the mixture was extracted three times with CH2Cl2,
the extract was dried (MgSO4), and the solvent was evapo-
rated. Purification by flash chromatography, eluting with 2:1
EtOAc/hexanes, followed by recrystallization from hexanes/
EtOAc, provided 16 as a white solid (0.03 g, 19%): mp 149-
1
150 °C; H NMR (250 MHz, CDCl3) δ 7.03 (m, 2H), 6.87 (d, J
) 8 Hz, 1H), 4.83 (m, 1H), 4.62 (t, J ) 6 Hz, 2H), 3.86 (s, 3H),
3.15 (t, J ) 6 Hz, 2H), 3.03 (m, 1H), 2.4 (m, 3H), 2.15 (m, 2H),
2.1-1.71 (m, 9H), 1.6 (m, 2H). Anal. (C23H28N6O2) C, H, N.
1
from this mixture as a solid (1.04 g, 5%): mp 50-51 °C; H
cis-4-Cya n o-4-[3-(cyclop en tyloxy)-4-m eth oxyp h en yl]-
1-(5-tetr a zolyl)cycloh exa n e (17). A mixture of 16 (0.098
g, 0.23 mmol) and NaOH (0.018 g, 0.46 mmol) in 10:1 THF/
water (5 mL) at room temperature under an argon atmosphere
was stirred overnight. The mixture was acidified with 3 N
HCl and was extracted three times with EtOAc, the extract
was dried (MgSO4), and the solvent was evaporated. Purifica-
tion by flash chromatography, eluting with 80:20:2 CHCl3/
CH3OH/water, followed by trituration with hexanes/EtOAc,
provided 17 as a white solid (0.038 g, 45%): mp 190-191 °C;
1H NMR (400 MHz, CDCl3) δ 7.0 (m, 2H), 6.88 (d, J ) 8 Hz,
1H), 4.83 (m, 1H), 3.86 (s, 3H), 3.3 (m, 1H), 2.37 (m, 3H), 2.2
(m, 2H), 2.0-1.8 (m, 9H), 1.52 (m, 2H). Anal. (C20H25N5O2‚
1/2H2O) C, H, N.
4-[3-(Cyclop en tyloxy)-4-m eth oxyp h en yl]cycloh exa n -1-
on e (19). Ammonia (30 mL) was condensed at -78 °C into a
flask containing 10 hexane-washed Na spheres (3-8 mm). To
this stirred mixture was added a solution of 10 (0.50 g, 1.6
mmol) in THF (10 mL). After 0.2 h, solid NH4Cl was added,
followed by ether and water. The mixture was warmed to
room temperature over 2 h, was extracted twice with ether,
was dried (MgSO4), and was evaporated. Purification by flash
chromatography, eluting with 4:1 hexanes/EtOAc, provided 18
as a white solid (0.26 g, 56%): mp 72 °C; 1H NMR (400 MHz,
CDCl3) δ 6.79 (d, J ) 9 Hz, 1H), 6.71 (m, 2H), 4.75 (m, 1H),
3.82 (s, 3H), 3.67 (m, 1H), 2.43 (m, 1H), 2.10 (m, 2H), 2.94-
1.83 (m, 7H), 1.58-1.39 (m, 8H).
NMR (400 MHz, CDCl3) δ 6.99 (d, J ) 2 Hz, 1H), 6.95 (dd, J
) 2, 8 Hz, 1H), 6.84 (d, J ) 8 Hz, 1H), 4.80 (m, 1H), 3.84 (s,
3H), 3.71 (s, 3H), 2.80 (m, J app ) 4 Hz, 1H), 2.24 (m, 2H), 2.1-
1.8 (m, 12H), 1.6 (m, 2H). Anal. (C21H27NO4‚3/4H2O) C, H, N.
cis-4-Cya n o-4-[3-(cyclop en tyloxy)-4-m eth oxyp h en yl]-
cycloh exa n e-1-ca r boxylic Acid (1). To a solution of 12
(0.12 g, 0.34 mmol) in CH3OH (0.9 mL, containing just enough
THF to solubilize the compound) under an argon atmosphere
was added a solution of KOH (0.06 g, 0.9 mmol) in water (0.7
mL). The resulting mixture was stirred at room temperature
for 1.5 h, then was poured into water, and was extracted with
EtOAc. The aqueous phase was acidified with 10% hydro-
chloric acid and was extracted twice with EtOAc. The organic
phase from the acid extraction was dried (Na2SO4) and was
concentrated under reduced pressure to provide 1 as a solid.
The solid was purified by flash chromatography, eluting with
4% CH3OH/CHCl3, to provide a white solid (0.05 g, 44%): mp
1
157 °C; H NMR (400 MHz, CDCl3) δ 7.01 (d, J ) 2 Hz, 1H),
6.97 (dd, J ) 2, 8 Hz, 1H), 6.86 (d, J ) 8 Hz, 1H), 4.81 (m,
1H), 3.85 (s, 3H), 2.42 (tt, J ) 4, 12 Hz, 1H), 2.25 (t, J ) 16
Hz, 4H), 2.04 (dd, J ) 2, 13 Hz, 2H), 1.98-1.75 (m, 6H), 1.63
1
(m, 2H); H NMR (400 MHz, CD3OD) δ 7.03 (m, 2H), 6.94 (d,
J ) 9 Hz, 1H), 4.83 (m, 1H), 3.80 (s, 3H), 2.41 (m, 1H), 2.15
(d, J ) 9 Hz, 4H), 2.0-1.7 (m, 10H), 1.6 (m, 2H). Anal. (C20H25
NO4) C, H, N.
-
tr a n s-4-Cyan o-4-[3-(cyclopen tyloxy)-4-m eth oxyph en yl]-
cycloh exa n e-1-ca r boxylic Acid (14). To a solution of 13
(0.68 g, 1.9 mmol) in CH3OH (8 mL, containing just enough
THF to solubilize the compound) under an argon atmosphere
was added water (4 mL) and KOH (0.32 g, 5.7 mmol). The
resulting mixture was stirred at room temperature for 24 h,
was acidified with 10% HCl, and was extracted three times
with 10% CH3OH/CH2Cl2. The organic extract was dried
(MgSO4) and was concentrated under reduced pressure. Pu-
rification by flash chromatography, eluting with 4% CH3OH/
CH2Cl2, provided a white semisolid (0.52 g), which was
triturated with ether to yield 14 as a white solid (0.43 g,
66%): mp 157-158 °C; 1H NMR (250 MHz, CD3OD) δ 6.97
(m, 3H), 4.80 (m, 1H), 3.80 (s, 3H), 2.76 (m, 1H), 2.19 (m, 2H),
2.0-1.7 (m, 12H), 1.6 (m, 2H). Anal. (C20H25NO4) C, H, N.
cis-4-Cya n o-4-[3-(cyclop en tyloxy)-4-m eth oxyp h en yl]-
cycloh exa n e-1-N-(2-cya n oeth yl)ca r boxa m id e (15). To a
solution of 1 (0.55 g, 1.6 mmol), HOBt (0.24 g, 1.76 mmol),
and 3-aminopropionitrile (0.11 g, 1.6 mmol) in CH2Cl2 (10 mL)
at 0 °C under an argon atmosphere was added EDAC‚HCl (0.34
g, 1.76 mmol), and the mixture was allowed to warm to room
temperature. After 6 h, the mixture was diluted with CH2-
Cl2, was washed twice with 10% aqueous K2CO3 and twice with
10% HCl, and was dried (MgSO4). The solvent was evapo-
rated, and the residue was crystallized from hexanes/EtOAc
To a suspension of PCC (0.29 g, 1.34 mmol) in CH2Cl2 (2
mL) was added a solution of 18 (0.26 g, 0.9 mmol) in CH2Cl2
(4 mL). After 4 h, the mixture was diluted with ether, was
stirred for 0.5 h, and was filtered through Celite, and the
filtrate was concentrated in vacuo. Purification by flash
chromatography, eluting with 4:1 hexanes/EtOAc, provided 19
1
as a white solid (0.24 g, 94%): mp 66-67 °C; H NMR (400
MHz, CDCl3) δ 6.81 (d, J ) 9 Hz, 1H), 6.75 (m, 2H), 4.78 (m,
1H), 3.83 (s, 3H), 2.95 (tt, J ) 3, 12 Hz, 1H), 2.51 (m, 4H),
2.21 (br m, 2H), 2.0-1.8 (m, 8H), 1.60 (m, 2H). Anal.
(C18H24O3‚1/7H2O) C, H, N.
2-[4-[3-(Cyclop en tyloxy)-4-m eth oxyp h en yl]cycloh exy-
lid en e]-1,3-d ith ia n e (20). To a solution of 2-(trimethylsilyl)-
1,3-dithiane (0.48 mL, 2.49 mmol) in dry tetrahydrofuran (5
mL) at 0 °C under an argon atmosphere was added rapidly
n-butyllithium (2.45 M in hexanes, 1.0 mL, 2.49 mmol). After
0.25 h, the mixture was cooled to -78 °C and a solution of 19
(0.24 g, 0.83 mmol) in THF (3 mL) was added. After 0.5 h,
aqueous NaCl was added, and the mixture was warmed to
room temperature and was diluted with water. The mixture
was extracted three times with CH2Cl2, the extract was dried
(MgSO4), and the solvent was evaporated. Purification by
flash chromatography, eluting with 10% EtOAc/hexanes, fol-
lowed by trituration from ether/hexanes, provided 20 as a

832 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6
Christensen et al.
1
white solid (0.1 g, 31%): mp 90-92 °C; H NMR (400 MHz,
1H), 3.85 (s, 3H), 2.60-2.25 (m, 8H), 2.0-1.75 (m, 6H), 1.62
CDCl3) δ 6.79 (d, J ) 9 Hz, 1H), 6.71 (m, 2H), 4.76 (m, 1H),
3.81 (s, 3H), 3.28 (d, J ) 13 Hz, 2H), 2.88 (m, 4H), 2.64 (m,
1H), 2.15 (m, 2H), 2.01-1.80 (m, 10H), 1.58 (m, 2H), 1.45 (m,
2H). Anal. (C22H30O2S2) C, H.
(m, 2H). Anal. (C19H24O4) C, H.
4-[3-(Cyclop en tyloxy)-4-m eth oxyp h en yl]-4-eth yn ylcy-
cloh ex-1-on e (28). To a solution of KOtBu (0.155 g, 1.38
mmol) in dry THF (5 mL) under an argon atmosphere at -78
°C was added a solution of dimethyl (diazomethyl)phospho-
nate69 (ca. 88% pure, 0.24 g, 1.38 mmol). After 0.25 h, a
solution of 25 (0.42 g, 1.15 mmol) in dry THF (5 mL) was added
dropwise, and the mixture was allowed to stir at -78 °C under
an argon atmosphere for 5 h. Aqueous HOAc was added, and
the mixture was concentrated, was partitioned between
CH2Cl2 and water, and was extracted twice. The organic
extract was dried (MgSO4) and was evaporated. Purification
by flash chromatography, eluting with 3:1 hexanes/EtOAc,
provided 27 as an oil (0.13 g, 32%): 1H NMR (250 MHz, CDCl3)
δ 7.16 (d, J ) 2 Hz, 1H), 7.06 (dd, J ) 2, 8 Hz, 1H), 6.82 (d, J
) 8 Hz, 1H), 4.80 (m, 1H), 3.83 (s, 3H), 3.25 (s, 3H), 3.19 (s,
3H), 2.40 (s, 1H), 2.08-1.75 (m, 14H), 1.60 (m, 2H).
A mixture of 27 (0.13 g, 0.36 mmol) and p-TsOH (catalytic
amount) in acetone (5 mL) was stirred under an argon
atmosphere at room temperature for 1.5 h. The mixture was
concentrated, was diluted with EtOAc, and was washed with
water. The organic extract was dried (MgSO4) and the solvent
was removed in vacuo to provide 28 as an oil (0.11 g, 97%):
1H NMR (250 MHz, CDCl3) δ 7.16 (d, J ) 2 Hz, 1H), 7.07 (dd,
J ) 2, 8 Hz, 1H), 6.84 (d, J ) 8 Hz, 1H), 4.80 (m, 1H), 3.84 (s,
3H), 2.99 (dt, J ) 6, 14 Hz, 2H), 2.56 (s, 1H), 2.44 (d, J ) 14
Hz, 2H), 2.30-2.10 (m, 6H), 2.00-1.75 (m, 6H), 1.60 (m, 2H).
Anal. (C20H24O3‚1/2H2O) C, H.
4-[3-(Cyclop en t yloxy)-4-m et h oxyp h en yl]-4-(h yd r oxy-
m eth yl)cycloh exa n -1-on e (30). To a solution of 25 (0.24 g,
0.66 mmol) in DME (5 mL) under an argon atmosphere was
added NaBH4 (0.05 g, 1.3 mmol), and the mixture was stirred
at room temperature for 0.75 h. Water was added, the mixture
was partitioned between ether and water and was extracted
twice with ether, and the organic extract was dried (K2CO3)
and was evaporated to provide 29 as an oil (0.19 g, 79%): 1H
NMR (250 MHz, CDCl3) δ 6.85, (m, 3H), 4.75 (m, 1H), 3.84 (s,
3H), 3.47 (m, 2H), 3.19 (s, 3H), 3.13 (s, 3H), 2.12 (m, 2H), 1.95-
1.75 (m, 8H), 1.75-1.60 (m, 4H), 1.43 (m, 2H). Compound 29
(0.15 g, 0.41 mmol) in ether (2 mL) was treated with 1 N HCl
(2 mL), and the mixture was stirred vigorously and gently
heated for 10 min. The mixture was extracted with ether, the
organic extract was washed with 5% aqueous Na2CO3 and was
dried (K2CO3), and the solvent was removed in vacuo. Puri-
fication by flash chromatography, eluting with 25% EtOAc/
CHCl3, provided 30 as a wax (0.06 g, 56%): 1H NMR (250 MHz,
CDCl3) δ 7.03-6.87 (m, 3H), 4.78 (m, 1H), 3.88 (s, 3H), 3.53
(m, 2H), 2.60-2.47 (m, 2H), 2.40-2.30 (m, 3H), 2.0-1.73 (m,
9H), 1.60 (m 2H). Anal. (C19H26O4) C, H.
4-[3-(Cyclopen tyloxy)-4-m eth oxyph en yl]-4-(flu or om eth -
yl)cycloh exa n -1-on e (32). A solution of 29 (0.37 g, 1.02
mmol) in CH2Cl2 (5 mL) was added dropwise to a solution of
(diethylamido)sulfur trifluoride (0.14 mL, 1.02 mmol) at -78
°C under an argon atmosphere. The mixture was allowed to
warm to room temperature, and after 0.75 h, 5% aqueous
Na2CO3 was added. The mixture was extracted with CHCl3,
the organic extract was dried (MgSO4), and the solvent was
removed in vacuo to provide 31 as a yellow oil (0.3 g, 80%):
1H NMR (250 MHz, CDCl3) δ 6.85-6.65, (m, 3H), 4.75 (m, 1H),
3.83 (s, 3H), 3.23 (s, 3H), 3.16 (s, 3H), 2.80 (d, J ) 24 Hz, 2H),
2.0-1.5 (m, 16H).
tr a n s-4-[3-(Cyclop en t yloxy)-4-m et h oxyp h en yl]cyclo-
h exa n e-1-ca r boxylic Acid (21). To a suspension of 20 (0.09
g, 0.23 mmol) in 4:1 CH3CN/water (5 mL) was added TFA (0.06
mL, 0.78 mmol). After 1 h of heating at 60-65 °C, the mixture
was cooled to 30 °C, 30% aqueous H2O2 (0.32 mL, 3.13 mmol)
was added, and the temperature was increased to 80 °C. After
0.75 h, the mixture was cooled to 40 °C and 10% aqueous
NaOH (3 mL) was added. The mixture was acidified with 3
N HCl, was extracted three times with CH2Cl2, and was dried
(MgSO4), and the solvent was evaporated. Purification by
flash chromatography, eluting with 95:5 CHCl3/CH3OH, pro-
1
vided 21 as a white solid (0.03 g, 45%): mp 156-158 °C; H
NMR (400 MHz, CDCl3) δ 6.80 (d, J ) 9 Hz, 1H), 6.72 (m,
2H), 4.77 (m, 1H), 3.82 (s, 3H), 2.45 (tt, J ) 4, 12 Hz, 1H),
2.40 (tt, J ) 4, 12 Hz, 1H), 2.15 (br d, J ) 11 Hz, 2H), 2.01-
1.78 (m, 7H), 1.70-1.45 (m, 7H). Anal. (C19H26O4) C, H.
4-(Am in oca r b on yl)-4-[3-(cyclop en t yloxy)-4-m et h oxy-
p h en yl]cycloh exa n -1-on e (24). A mixture of compound 10
(0.5 g, 1.6 mmol), trimethyl orthoformate (0.21 mL, 1.9 mmol),
and a catalytic amount of p-TsOH in CH3OH (20 mL) was
heated gently under an argon atmosphere for 2 h. The mixture
was cooled, was partitioned between aqueous sodium carbon-
ate and EtOAc, and was extracted twice with EtOAc. The or-
ganic extract was dried (K2CO3), and the solvent was removed
in vacuo to provide compound 22 as an oil (0.57 g, 99%). A
solution of 22 (0.34 g, 0.95 mmol) and powdered potassium
carbonate (0.7 g, 5.1 mmol) in CH3OH (20 mL) and water (4
mL) at 0 °C was treated with H2O2 (30% solution, 2.55 mL).
The mixture was allowed to warm to room temperature, and
after 7 days, brine was added and the mixture was extracted
with CH2Cl2. The organic extract was washed twice with brine
and was dried (K2CO3), and the solvent was removed in vacuo.
Purification by flash chromatography provided the ketal amide
23 (0.055 g, 15%), along with recovered 22 (0.25 g): 1H NMR
(250 MHz, CDCl3) δ 6.95 (m, 2H), 6.83 (d, J ) 8 Hz, 1H), 5.30
(br s, 2H), 4.75 (m, 1H), 3.83 (s, 3H), 3.25 (s, 3H), 3.19 (s, 3H),
2.40 (m, 2H), 2.13 (m, 3H), 1.87-1.53 (m, 11H).
A mixture of 23 (0.055 g, 0.15 mmol) and p-TsOH (catalytic
amount) in 20% aqueous acetone (5 mL) was stirred under an
argon atmosphere at reflux for 8 h. The mixture was cooled,
was diluted with water, and was extracted with CH2Cl2. The
organic extract was dried (MgSO4), and the solvent was
removed in vacuo to provide 24 as a hygroscopic, amorphous
material (0.035 g, 72%): 1H NMR (250 MHz, CDCl3) δ 7.0 (m,
2H), 6.90 (d, J ) 8 Hz, 1H), 5.35 (m, 2H), 4.75 (m, 1H), 3.85
(s, 3H), 2.7-2.5 (m, 4H), 2.45-2.30 (m, 4H), 1.95-1.80 (m, 6H),
1.63 (m, 2H). Anal. (C19H25NO4‚3/8H2O) C, H, N.
4-[3-(Cyclop en t yloxy)-4-m et h oxyp h en yl]-4-for m ylcy-
cloh exa n -1-on e (26). A solution of 22 (0.57 g, 1.6 mmol) in
toluene (20 mL) at room temperature under an argon atmo-
sphere was treated with a solution of DIBAl-H (1.5 M in
toluene, 2.7 mL, 4 mmol). After 2 h, a solution of saturated
aqueous sodium bisulfite was added, and the mixture was
extracted twice with EtOAc. The organic extract was washed
with 5% aqueous Na2CO3 and was dried (K2CO3), and the
solvent was removed in vacuo to provide 25 as an oil (0.55 g,
96%): 1H NMR (250 MHz, CDCl3) δ 9.33 (s, 1H), 6.85 (d, J )
1 Hz, 2H), 6.79 (s, 1H), 4.75 (m, 1H), 3.83 (s, 3H), 3.19 (s, 3H),
3.16 (s, 3H), 2.0-1.8 (m, 10H), 1.6 (m, 6H).
Compound 25 (0.1 g, 0.28 mmol) in EtOAc (2 mL) was
treated with 3 N HCl (5 mL), and the mixture was stirred
vigorously and gently heated for 10 min. The mixture was
extracted twice with EtOAc, the organic extract was washed
with 5% aqueous Na2CO3 and was dried (K2CO3), and the
solvent was removed in vacuo. This material, combined with
that obtained from an identical reaction, was purified by flash
chromatography, eluting with 2% EtOAc/CHCl3, to provide 26
as a white solid (0.1 g, 57%): mp 55-57 °C; 1H NMR (250
MHz, CDCl3) δ 9.50 (s, 1H), 6.90 s, 2H), 6.82 (s, 1H), 4.75 (m,
Compound 31 (0.35 g, 0.95 mmol) in EtOAc (2 mL) was
treated with 1 N HCl (2 mL), and the mixture was stirred
vigorously and gently heated for 10 min. The mixture was
extracted with EtOAc, the organic extract was washed with
5% aqueous Na2CO3 and was dried (MgSO4), and the solvent
was removed in vacuo. Purification by flash chromatography,
eluting with 25% EtOAc/hexanes, followed by trituration with
ether/hexanes, provided 32 as a white solid (0.075 g, 24%): mp
1
72-74 °C; H NMR (250 MHz, CDCl3) δ 6.83-6.70, (m, 3H),
4.75 (m, 1H), 3.80 (s, 3H), 2.80 (d, J ) 24 Hz, 2H), 2.65 (dt, J
) 8, 18 Hz, 2H), 2.35-2.13 (m, 4H), 2.0-1.75 (m, 8H), 1.6 (m,
2H). Anal. (C19H25FO3) C, H.

1,4-Cyclohexanecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 6 833
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(3) Biology. LPDE4 activity and HPDE4 activity were
assayed as described previously using monocyte-derived hu-
man recombinant LPDE4 produced in yeast and HPDE4
derived from rat brain preparations.47 Ki values were deter-
mined as described previously.47 PDEs 1, 2, and 5 were
isolated from canine tracheal smooth muscle and assayed as
described previously.94 PDE3 was isolated from guinea-pig
cardiac ventricle and was assayed as described previously.95
The remaining in vitro and in vivo assays were conducted
according to the procedures described for (R)-rolipram and/or
other PDE4 inhibitors in the references cited in the text of
this manuscript.
(19) Peachell, P. T.; Undem, B. J .; Schleimer, R. P.; MacGlashan, D.
W.; Lichtenstein, L. M.; Cieslinski, L. B.; Torphy, T. J . Prelimi-
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Ack n ow led gm en t. The authors gratefully acknowl-
edge Edith A. Reich for elemental analyses and Dr.
Charles W. DeBrosse for valuable discussions.
Su p p or tin g In for m a tion Ava ila ble: Tables of elemental
analyses and crystallographic data (crystal data and structural
refinements, bond distances, bond angles, positional param-
eters and anisotropic displacement parameters) (6 pages).
Ordering information is given on any current masthead page.
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