Carbocyclic[g]indole inhibitors of human nonpancreatic s-PLA2

Article abstract of DOI:10.1021/jm0401309

A vinyl azide cyclization method was used to synthesize three different carbocyclic[g]indole scaffolds as inhibitors of human nonpancreatic secretory phospholipase A₂. Each scaffold demonstrated potent enzyme activity in a chromogenic assay sys

Full text of DOI:10.1021/jm0401309

J. Med. Chem. 2005, 48, 893-896
893
Carbocyclic[g]indole Inhibitors of Human Nonpancreatic s-PLA2
J. Scott Sawyer,*,† Douglas W. Beight,† Edward C. R. Smith,† David W. Snyder,‡ Marcia K. Chastain,‡
Richard L. Tielking,‡ Lawrence W. Hartley,‡ and Donald G. Carlson‡
Discovery Chemistry Research and Technology and Cardiovascular Research, The Lilly Research Laboratories,
A Division of Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana 46285
Received July 8, 2004
A vinyl azide cyclization method was used to synthesize three different carbocyclic[g]indole
scaffolds as inhibitors of human nonpancreatic secretory phospholipase A2. Each scaffold
demonstrated potent enzyme activity in a chromogenic assay system, with select examples
also demonstrating potent activity in a secondary DOC/PC assay. Compound 11, representative
of the cyclopent[g]indole series, gave an IC50 of 10 nM for the inhibition of hnps-PLA2 in the
chromogenic assay.
Introduction
ary alcohol with sodium borohydride, then further
reduced with palladium and hydrogen. In the case of
compounds 23/24, Tebbe Reagent, followed by hydrolysis
in situ, was used to secure the acetyl intermediate,
which was then reduced with palladium and 1,4-
cyclohexadiene (see Supporting Information). Comple-
tion of the final examples was similar to Scheme 1,
where methyl ether 8 was demethylated, alkylated to
give oxoacetic ester 9, and treated with oxalyl chloride
and ammonia to provide ester 10. Simple hydrolysis
with aqueous hydroxide gave final acid 11. In the case
of N-acylsulfonamide compound 20, conversion was
effected via the treatment of 11 with benzenesulfon-
amide in the presence of EDC and a suitable base.
Excess levels of human nonpancreatic secretory phos-
pholipase A2 (hnps-PLA2) have been associated with a
number of disease states including arthritis, septic
shock, and atherosclerosis.1 While a number of different
inhibitors of hnps-PLA2 have been described,2 the indole
glyoxamide series exemplified by LY315920 (1) has been
the most thoroughly explored.3-5 In this study we
present the chemistry and SAR evaluation of a series
of carbocyclic[g]indole compounds representing a new
advance in the construction of potent sPLA2 inhibitors.
Chemistry
For each 6,7-fused carbocyclic ring system examined,
a different synthetic approach was required. Scheme 1
illustrates the route to 1,6,7,8-tetrahydrocyclopent[g]-
indole compounds 10 and 11 and is representative of
the strategy used for the remaining ring systems. In the
event, 2,3-dihydro-6-methoxy-1H-indene (2) was formy-
lated via a Vilsmeir procedure to provide aldehyde 3,
which was subsequently condensed with ethyl azido-
acetate giving R,â-unsaturated ester 4. Ring closure to
produce the 2-carbethoxy-substituted indole 5 was
achieved through thermal cyclization,6 although in the
case of the 6,7,8,9-tetrahydro-1H-benz[g]indole ex-
amples (compounds 21-24), rhodium(II) acetate dimer
was added to facilitate the reaction. As indicated for
compounds 10 and 11, targets requiring a 2-methyl
substituent were secured beginning with alkylation at
the 1-position, which was accompanied by partial hy-
drolysis of the ester. Treatment of the intermediate
mixture with base provided acid 6, which was then
reduced with lithium aluminum hydride to primary
alcohol 7. Further reduction via hydrogenolysis gave the
2-methyl intermediate 8.
Discussion
Compounds were originally examined as inhibitors of
hnps-PLA2 in a chromogenic assay system utilizing a
synthetic substrate [1,2-bis(heptanoylthio)-1,2-dideoxy-
rac-glycero-3-phosphorylcholine] as previously described.4a
Mole fractions for each measurement are also presented
since the molar IC50 values are dependent on the lipid
concentration in the assay (Table 1).4c In general, it was
found that compounds containing saturated rings fused
to the 6,7-position of the indole ring proved to be very
potent at inhibiting the enzyme (compounds 11, 22, and
24). As previously noted in the original indole SAR,4c
the ethyl group at the 2-position was interchangeable
with methyl (compare compound pairs 1/19 and 22/24).
Adding a fluorine atom to the benzyl ring was tolerated
at the ortho and meta positions (compounds 13 and 15),
but less so at the para position (17), where an ap-
proximately 8-fold drop in potency was observed. N-
Acylsulfonamide 20 was equipotent with the correspond-
ing carboxylic acid 11, indicating that the space around
the acid binding site is sterically tolerant. An exchange
of unsaturation between the benzyl aromatic and car-
bocyclic rings of 22 produced the benzo-fused example
26, which was accomplished without loss of activity. As
observed with the original indole series, the precursor
esters for all of the carbocyclic[g]indoles tested were
approximately 10-fold less potent.
For examples requiring an ethyl group at the 2-posi-
tion (e.g., compounds 18/19), the intermediate acid 6
was treated with methyllithium to form the correspond-
ing acetyl derivative, which was reduced to the second-
* To whom correspondence should be addressed. Phone: 317-276-
7923. Fax: 317-276-1417. E-mail: jss.dcrt@lilly.com.
† Discovery Chemistry Research and Technology, The Lilly Research
Laboratories.
As a check on the results obtained in the chromogenic
assay, some of the more potent compounds were tested
‡ Cardiovascular Research, The Lilly Research Laboratories.
10.1021/jm0401309 CCC: $30.25 © 2005 American Chemical Society
Published on Web 01/19/2005

894 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 3
Brief Articles
Scheme 1a
a Reagents: (a) POCl3, DMF; (b) N3CH2COOEt, NaOEt; (c) toluene, heat; (d) BnBr, NaH; (e) aq. NaOH; (f) LiAlH4, THF; (g) H2, Pd(C),
THF, EtOAc, CHCl3; (h) BBr3, CHCl3; (i) methyl bromoacetate, Cs2CO3; (j) oxalyl chloride; (k) NH3; (l) LiOH, THF, MeOH, H2O.
Preparation of 3-(2,3-Dihydro-6-methoxy-1H-inden-5-
yl)-2-azido-2-propenoic Acid Ethyl Ester (4). Sodium (13.8
g, 0.600 mol) was dissolved in absolute ethanol (400 mL). After
cooling to -10 °C, a mixture of 2,3-dihydro-6-methoxy-1H-
indene-5-carboxaldehyde (3; 26.5 g, 0.150 mol) and ethyl
azidoacetate (72.0 g, 0.558 mol) in diethyl ether (100 mL) was
added dropwise in such a manner that the temperature did
not rise above -10 °C. The mixture was allowed to warm to
20 °C over 3 h. After gas evolution had ceased, the mixture
was poured into water (700 mL). The mixture was extracted
thrice with diethyl ether, and the combined organic fractions
were washed with water and saturated sodium chloride
solution, dried (sodium sulfate), filtered, and concentrated in
vacuo. The resulting oil was cooled to -10 °C for 24 h and
resulted in the formation of a solid. This material was slurried
in hexanes and collected via vacuum filtration (15.6 g). The
filtrate was concentrated in vacuo and purifed via chromatog-
raphy (silica gel, 5% ethyl acetate/95% hexane) to provide an
additional 7.3 g (53% total yield) of the title product as a yellow
crystalline material (single isomer, geometry not deter-
in the deoxycholate/phosphatidylcholine (DOC/PC) mixed
micelle assay, which uses higher levels of lipid (4 mM
vs 1.23 mM for the chromogenic assay) and less enzyme
(3 nM vs 16 nM for the chromogenic assay). Generally,
the DOC/PC mole fractions (Table 2) were found to be
approximately 8-fold lower than values observed for the
chromogenic assay, even though the IC50 values were
nearly the same. Comparison of mole fraction values
may be more indicative of absolute enzyme inhibitory
activity since they are independent of the lipid concen-
tration in each assay.
Finally, compound 19 was evaluated in an ex vivo
model in transgenic mice expressing human sPLA2
protein.7 Animals were dosed with compound, and
serum enzyme activity at 1 and 2 h was evaluated in
the DOC/PC mixed micelle assay. At an oral dose of 0.3
mg/kg, compound 19 gave 83% inhibition of the enzyme
at the 1-h time point and 61% inhibition at the 2-h time
point. This compares favorably with compound 1, which
gave values of 65% and 55%, respectively, in this
assay.3b
1
mined): mp 64-66 °C. H NMR (CDCl3) δ 8.05 (s, 1H), 7.41
(s, 1H), 6.79 (s, 1H), 4.38 (q, J ) 7.3 Hz, 2H), 3.84 (s, 3H),
2.89 (q, J ) 7.3 Hz, 4H), 2.07 (quintet, J ) 7.3 Hz, 2H), 1.38
(t, J ) 7.3 Hz, 3H); MS FD+ m/e 287 (p); IR (CHCl3, cm-1
)
2961, 2122, 1704, 1081. Anal. Calcd for C15H17N3O3: C, 62.71;
H, 5.96; N, 14.62. Found: C, 62.46; H, 5.99; N, 14.40.
The present group of carbocyclic[g]indoles has proven
to have in vitro potency comparable to the hnps-PLA2
indole series represented by compound 1. Compounds
of this potency may be useful in delineating the role of
hnps-PLA2 in the treatment of human disease.
Preparation of 2-Carboethoxy-4-methoxy-1,6,7,8-tetra-
hydrocyclopent[g]indole (5). A mixture of 3-(2,3-dihydro-
6-methoxy-1H-inden-5-yl)-2-azido-2-propenoic acid ethyl ester
(4; 7.28 g, 25.3 mmol) in toluene (200 mL) was refluxed for 6
h. Upon cooling to room temperature, a crystalline precipitate
formed that was collected via vacuum filtration and washed
with hexanes to provide 3.38 g (52%) of the title product as
Experimental Section
1
white needles: mp 185-187 °C. H NMR (CDCl3) δ 8.97 (bs,
For general experimental parameters see Supporting In-
formation.
1H, NH), 7.36 (d, J ) 2.2 Hz, 1H), 6.46 (s, 1H), 4.41 (q, J )
7.0 Hz, 2H), 3.93 (s, 3H), 3.03 (q, J ) 6.6 Hz, 4H), 2.22 (quintet,
J ) 7.3 Hz, 2H), 1.42 (t, J ) 7.3 Hz, 3H); MS ES+ m/e 260 (p
+ 1); IR (CHCl3, cm-1) 3400, 1698, 1258. Anal. Calcd for C15H17-
NO3: C, 69.48; H, 6.61; N, 5.40. Found: C, 69.71; H, 6.62; N,
5.45.
Representative Procedure for the Preparation of
Carbocyclic[g]indole sPLA2 Inhibitors: Synthesis of
2-[[3-(2-Amino-1,2-dioxoethyl)-2-methyl-1-benzyl-1,6,7,8-
tetrahydrocyclopent[g]indol-4-yl]oxy]acetic Acid (11).
Preparation of 2,3-Dihydro-6-methoxy-1H-indene-5-car-
boxaldehyde (3). Phosphorus oxychloride (67.1 mL, 0.710
mol) was added to N,N-dimethylformamide (60 mL) at 0 °C.
After stirring for 0.5 h, 2,3-dihydro-6-methoxy-1H-indene (2;
50.0 g, 0.338 mol) was added and the resulting mixture heated
carefully at 80 °C for 4 h. The mixture was cooled to room
temperature, poured over crushed ice, and stirred for 18 h.
The resulting precipitate was collected via vacuum filtration.
Recrystallization (absolute ethanol) provided 43.5 g (73%) of
the title product as yellow plates: mp 73-74 °C.
Preparation of 1-Benzyl-2-carboxy-4-methoxy-1,6,7,8-
tetrahydrocyclo-pent[g]indole (6). To a slurry of a 60% oil
suspension of sodium hydride (7.00 g, 0.175 mol) in N,N-
dimethylformamide (350 mL) was added 2-carbethoxy-4-
methoxy-1,6,7,8-tetrahydrocyclopent[g]indole (5; 34.5 g, 0.133
mol) and the resulting mixture stirred for 15 min. Benzyl
bromide (21.0 mL, 0.176 mol) was added and the mixture
allowed to stir at room temperature for 48 h. The mixture was
dissolved in approximately 300 mL of 1:1 methanol/tetra-

Brief Articles
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 3 895
250 °C (dec). 1H NMR (DMSO-d6) δ 12.68 (bs, 1H), 7.29 (s,
1H), 7.22 (m, 3H), 6.80 (d, J ) 7.0 Hz, 2H), 6.52 (s, 1H), 5.94
(bs, 2H), 3.89 (s, 3H), 2.93 (m, 2H), 2.84 (t, J ) 7.3 Hz, 2H),
1.94 (quintet, J ) 7.3 Hz, 2H); MS ES+ m/e 322 (p + 1); IR
(KBr, cm-1) 3000, 1662, 1610, 1497. Anal. Calcd for C20H19-
NO3: C, 74.75; H, 5.96; N, 4.36. Found: C, 74.59; H, 5.64; N,
4.38.
Table 1. Inhibitory Activity of Carbocyclic[g]indoles against
Human Nonpancreatic Secretory Phospholipase A2
(Chromogenic Assay)
Preparation of 1-Benzyl-2-hydroxymethyl-4-methoxy-
1,6,7,8-tetrahydrocyclopent[g]indole (7). A solution of
1-benzyl-2-carboxy-4-methoxy-1,6,7,8-tetrahydrocyclopent[g]-
indole (6; 3.21 g, 10.0 mmol) in tetrahydrofuran (70 mL) was
treated carefully with lithium aluminum hydride (0.58 g, 15
mmol) at room temperature for 18 h. Additional small portions
of lithium aluminum hydride were added until the conversion
of starting material was complete via TLC. The reaction was
quenched by the addition of excess sodium sulfate decahydrate
and the resulting suspension filtered. The filtrate was dried
(sodium sulfate), filtered, and concentrated in vacuo to provide
a quantitative yield of the title compound as white crystals.
An analytical sample was obtained by recrystallization (ethyl
1
acetate/hexanes): mp 135-140 °C. H NMR (CDCl3) δ 7.20-
7.30 (m, 3H), 6.91 (d, J ) 7 Hz, 2H), 6.64 (s, 1H), 6.54 (s, 1H),
5.62 (s, 2H), 4.63 (s, 2H), 3.97 (s, 3H), 3.03 (t, J ) 7 Hz, 2H),
2.97 (t, J ) 7 Hz, 2H), 2.20 (bs, 1H), 2.08 (quintet, J ) 7 Hz,
2H); MS ES+ m/e 308 (p + 1); IR (CHCl3, cm-1) 2944, 1595,
1497. Anal. Calcd for C20H21NO2: C, 78.15; H, 6.89; N, 4.56.
Found: C, 78.52; H, 6.82; N, 4.61.
Preparation of 1-Benzyl-2-methyl-4-methoxy-1,6,7,8-
tetrahydrocyclo-pent[g]indole (8). To a nitrogen-purged
solution of 1-benzyl-2-hydroxymethyl-4-methoxy-1,6,7,8-tetra-
hydrocyclopent[g]indole (7; 2.0 g, 6.5 mmol) and chloroform
(3 mL) in 1:1 tetrahydrofuran/absolute ethanol (200 mL) was
added 10% palladium-on-carbon (400 mg). The resulting
suspension was hydrogenated at 45-50 psi for 18 h. The
mixture was filtered through Celite and concentrated in vacuo
to provide a solid. Chromatography (silica gel, 7% ethyl
acetate/93% hexanes) provided 0.50 g (26%) of the title
compound as a white solid: mp 128-130 °C. 1H NMR (CDCl3)
δ 7.24 (m, 3H), 6.88 (d, J ) 7.0 Hz, 2H), 6.46 (s, 1H), 6.40 (bs,
1H), 5.42 (s, 2H), 3.93 (s, 3H), 3.00 (t, J ) 7.3 Hz, 2H), 2.93 (t,
J ) 7.7 Hz, 2H), 2.28 (s, 3H), 2.05 (quintet, J ) 7.3 Hz, 2H);
MS ES+ m/e 292 (p + 1); IR (KBr, cm-1) 2939, 1596, 1497,
1251. Anal. Calcd for C20H21NO: C, 82.44; H, 7.26; N, 4.81.
Found: C, 82.14; H, 7.29; N, 4.83.
Preparation of 2-[(2-Methyl-1-benzyl-1,6,7,8-tetrahy-
drocyclopent[g]indol-4-yl)oxy]acetic Acid Methyl Ester
(9). A solution of 1-benzyl-2-methyl-4-methoxy-1,6,7,8-tetrahy-
drocyclopent[g]indole (8; 2.2 g, 7.6 mmol) in chloroform (40 mL)
was treated with boron tribromide (2.8 mL, 30 mmol) at 0 °C.
The mixture was warmed to room temperature and stirred for
2.5 h. The mixture was poured into water and extracted with
chloroform. The organic layer was washed once with water,
once with saturated sodium chloride solution, dried (sodium
sulfate), filtered, and concentrated in vacuo to provide an
unstable blue oil. A solution of this material in N,N-dimethyl-
formamide (35 mL) was treated with cesium carbonate (3.21
g, 9.10 mmol) and methyl bromoacetate (0.86 mL, 9.1 mmol)
at room temperature. After stirring for 18 h, the mixture was
poured into water and extracted with ethyl acetate. The
organic layer was washed once with water and once with
saturated sodium chloride solution, dried (sodium sulfate),
filtered, and concentrated in vacuo. Chromatography (silica
gel, 10% ethyl acetate/90% hexanes) provided 0.43 g (16%) of
a Chromogenic assay system; mean values ( SEM for a mini-
mum of three determinations. b Mole fraction is the IC50 concen-
tration divided by the total lipid concentration (1230 µM).
Table 2. Inhibitory Activity of Selected Carbocyclic[g]indoles
against Human Nonpancreatic Secretory Phospholipase A2
(DOC/PC assay)
compd
IC50 (µM)a
mole fractionb
1
0.007c
0.006
0.007
0.003
0.016
0.017
0.004
1.8 × 10-6
1.5 × 10-6
1.8 × 10-6
7.5 × 10-7
4.0 × 10-6
4.2 × 10-6
1.0 × 10-6
11
19
20
22
24
26
1
the title product as a white solid: mp 135-138 °C. H NMR
a DOC/PC assay system; single-point determination. b Mole
fraction is the IC50 concentration divided by the total lipid
concentration (4000 µM). c Data from ref 4c.
(CDCl3) δ 7.22 (m, 3H), 6.88 (d, J ) 7.0 Hz, 2H), 6.47 (s, 1H),
6.36 (s, 1H), 5.42 (s, 2H), 4.76 (s, 2H), 3.82 (s, 3H), 3.00 (t, J
) 7.3 Hz, 2H), 2.90 (t, J ) 7.3 Hz, 2H), 2.29 (s, 3H), 2.04
(quintet, J ) 7.0 Hz, 2H); MS ES+ m/e 350 (p + 1).
Preparation of 2-[[3-(2-Amino-1,2-dioxoethyl)-2-meth-
yl-1-benzyl-1,6,7,8-tetrahydrocyclo-pent[g]indol-4-yl]oxy]-
acetic Acid Methyl Ester (10). A solution of 2-[(2-methyl-
1-benzyl-1,6,7,8-tetrahydrocyclopent[g]indol-4-yl)oxy]acetic acid
methyl ester (9; 0.38 g, 1.1 mmol) in methylene chloride (8
mL) was cooled to 0 °C and treated with oxalyl chloride (0.47
hydrofuran and treated with aqueous 5 N sodium hydroxide
solution at 50 °C until nearly all of the precipitate had
dissolved. The mixture was filtered and the filtrate adjusted
to pH 2 with concentrated hydrochloric acid. The resulting
precipitate was collected via vacuum filtration, washed with
water, and dried under vacuum at 40 °C for 48 h to provide
37.5 g (87%) of the title product as a white solid: mp 248-

896 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 3
Brief Articles
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mL, 5.4 mmol). The resulting mixture was stirred for 1 h and
concentrated in vacuo. The residue was dissolved in methylene
chloride and concentrated in vacuo. The residue was again
dissolved in methylene chloride (5 mL) and treated with a 1
M solution of ammonia in dioxane (10 mL). The mixture was
stirred for 30 min and concentrated in vacuo. The resulting
material was slurried in hot ethyl acetate, and the resulting
solids were collected via vacuum filtration to provide 0.28 g
(61%) of the title compound as a bright yellow solid: mp 226-
228 °C. 1H NMR (DMSO-d6) δ 7.63 (bs, 1H), 7.30 (m, 4H), 6.92
(d, J ) 7.3 Hz, 2H), 6.50 (s, 1H), 5.54 (s, 2H), 4.71 (s, 2H),
3.70 (s, 3H), 2.96 (t, J ) 7.3 Hz, 2H), 2.82 (t, J ) 7.3 Hz, 2H),
2.41 (s, 3H), 1.96 (quintet, J ) 7.0 Hz, 2H); IR (CHCl3, cm-1
)
3154, 1640, 1406. FAB+ MS exact mass calculated for
C24H25N2O5: m/z ) 421.1763 (p + 1). Found: 421.1768. Anal.
Calcd for C24H24N2O5: C, 68.56; H, 5.75; N, 6.66. Found: C,
68.29; H, 5.85; N, 6.51.
Preparation of 2-[[3-(2-Amino-1,2-dioxoethyl)-2-meth-
yl-1-benzyl-1,6,7,8-tetrahydrocyclopent[g]indol-4-yl]oxy]-
acetic Acid (11). A solution of 2-[[3-(2-amino-1,2-dioxoethyl)-
2-methyl-1-benzyl-1,6,7,8-tetrahydrocyclopent[g]indol-4-yl]oxy]-
acetic acid methyl ester (10; 95 mg, 0.23 mmol) in a 1:1 mixture
of methanol/tetrahydrofuran (1 mL) was treated with excess
1 M lithium hydroxide for 19 h at room temperature. The
mixture was concentrated in vacuo, diluted with water, and
acidified with 5 N hydrochloric acid. The resulting precipitate
was collected via vacuum filtration and recrystallized (absolute
ethanol) to provide 65 mg (71%) of the title product as yellow
crystals: mp 255-257 °C. 1H NMR (DMSO-d6) δ 12.84 (bs,
1H, OH), 7.69 (bs, 1H), 7.33 (m, 4H), 6.92 (d, J ) 7.0 Hz, 2H),
6.46 (s, 1H), 5.54 (s, 2H), 4.61 (s, 2H), 2.95 (t, J ) 7.0 Hz, 2H),
2.82 (t, J ) 7.3 Hz, 2H), 2.42 (s, 3H), 1.96 (quintet, J ) 7.0
Hz, 2H); MS ES+ m/e 407 (p + 1). Anal. Calcd for C23H22N2O5:
C, 67.97; H, 5.46; N, 6.89. Found: C, 68.07; H, 5.31; N, 7.22.
The following assays have been previously described: chro-
mogenic assay;4a DOC/PC assay;4c transgenic human sPLA2
mouse model.3b
Supporting Information Available: Detailed synthetic
methods for the preparation of compounds in Table 1, including
analytical and spectroscopic data. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) (a) Uhl, W.; Nevalainen, T. J.; Bu¨chler, M. W., Eds. Phospho-
lipase A2: Basic and Clinical Aspects in Inflammatory Diseases;
S. Karger, AG: Basel, 1997. (b) Kovanen, P. T.; Pentika¨inen,
M. O. Secretory Group II Phospholipase A2: A Newly Recognized
Acute-Phase Reactant With a Role in Atherogenesis. Circ. Res.
2000, 86, 610-612.
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