Discovery and synthesis of a potent, selective and orally bioavailable EP4 receptor agonist

Article abstract of DOI:10.3987/COM-04-S(P)47

An optimized analog of prostaglandin E₂ which incorporates a γ-lactam in place of the cyclopentanone ring and which incorporates metabolically stabilized side chains, has been identified and shown to exhibit potent and selective EP4 receptor ag

Full text of DOI:10.3987/COM-04-S(P)47

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HETEROCYCLES, Vol. 64, 2004, pp. 437 - 446
Received, 7th October, 2004, Accepted, 30th November, 2004, Published online, 3rd December, 2004
DISCOVERY AND SYNTHESIS OF A POTENT, SELECTIVE AND
ORALLY BIOAVAILABLE EP4 RECEPTOR AGONIST†
Robert N. Young,* Xavier Billot,# Yongxin Han, Deborah A. Slipetz, Nathalie
Chauret, Michel Belley, Kathleen Metters, Marie-Claude Mathieu, Gillian M.
Greig, Danielle Denis, and Mario Girard
Merck Frosst Centre for Therapeutic Research, P.O. Box 1005, Pointe-Claire –
Dorval, Québec, Canada H9R 4P8. E-mail: ryoung@merck.com
#Gemin X Biotechnologies Inc., P.O. Box 477, Place du Parc, Montreal, Québec,
Canada, H2X 4A5
Abstract – An optimized analog of prostaglandin E2 which incorporates a
γ-lactam in place of the cyclopentanone ring and which incorporates metabolically
stabilized side chains, has been identified and shown to exhibit potent and
selective EP4 receptor agonism. The compound (2) (L-000902688) is also well
absorbed on oral dosing and exhibits a long half-life making it an excellent tool
for the study of the role of EP4 receptor in physiology and disease. An efficient
synthesis of 2 from a chiral synthon is described.
INTRODUCTION
Prostaglandin E2 (PGE2) (1) is a potent lipid hormone which elicits a variety of tissue specific and
sometimes conflicting biological activities in the body.1 It is now known that PGE2 interacts with four
distinct receptors2 and biological activities are presumably manifest depending on the predominant
receptor subtype in a given tissue. Studies have shown that in vivo administration of PGE2 can elicit bone
growth in rats3 and in humans4 and this anabolic activity has been attributed to interaction of PGE2 with
the EP4 receptor subtype5 which is found to be predominant in adult bone cells in rats.5 Thus, it has been
theorized that a selective EP4 agonist might provide a useful therapeutic to reverse the effects of
osteoporosis and that such a therapeutic might lack the potential side effects which would be associated
with interactions with the other EP receptors (EP1, EP2 and EP3).6 We and others have recently reported
the discovery of EP4 selective agonists6,7 and reports have shown that such agonists can elicit bone
†Dedicated to Dr. Pierre Potier on the occasion of his 70th birthday

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HETEROCYCLES, Vol. 64, 2004
growth in animals.8 Most of these agonists, however, exhibit short half-lives in vivo and/or are apparently
poorly bioavailable when given by the oral route. This report details of the discovery and synthesis of
(5R-[(1E)-4,4-difluoro-3R-hydroxy-4-phenylbut-1-en-1-yl]-1-[6-(1H-tetrazol-5-yl)hexyl]pyrrolidin-2-one
(L-000902688) (2) which is not only a highly potent and selective agonist at the EP4 receptor but also
embodies a degree of metabolic stability and solubility which allows it to be well absorbed and to exhibit
a long half-life in rats. This compound should prove to be a useful tool to study the role of the EP4
receptor in physiology and disease.
N
O
O
HN
O
N
N
R'
N
COOH
N
F
R
F
HO
R
H
HO
PGE2
OH
H
OH
2
3a; R=H; R'=tetrazole
3b; R=CH3; R'=COOH
3c; R,R= cypropyl; R'=COOH
DISCUSSION
Previous studies identified compound (3a) as an EP4 selective agonist with a degree of metabolic stability
and an i.v. terminal half-life of about two hours.6 Unfortunately, when dosed orally to rats, the compound
gave very low systemic blood levels. Considering that the compound contained a benzylic methylene
group which was potentially susceptible to metabolic transformation, several alkyl substituted analogs
(dimethyl (3b) and cyclopropyl (3c)) were previously prepared but were found to be significantly less
potent than the parent compound (3a).6 In further studies, we decided to introduce a geminal difluoro
group in this benzylic position, in part, based on the observation that the benzylic cyclopropyl analog (3c)
was 5-fold more potent that the corresponding dimethyl analog (3b) (see Table 2). We surmised that the
less sterically demanding difluoro analog could manifest further enhanced activity. We also noted reports
in the literature suggesting that similar difluoro analogs were potent prostaglandin receptor agonists.9
Synthesis of compound (2) proceeded in a relatively straight-forward fashion starting from the previously
prepared 7-(2R-formyl-5-oxopyrrolidin-1-yl)heptanenitrile (8). (Scheme). The synthesis of this aldehyde
which was derived from the corresponding hydroxymethyl compound (7) using Swern oxidation,10 could
be carried out in a convenient fashion using anhydrous work-up conditions (see experimental). Under
these conditions, the sensitive aldehyde (8) could be isolated directly in a non-hydrated form suitable for
direct reaction in the next step. The aldehyde was reacted with the anion derived from dimethyl
(3,3-difluoro-2-oxo-3-phenylpropyl)phosphonate (5) under standard Wittig-Horner conditions. (This

HETEROCYCLES, Vol. 64, 2004
439
reagent was prepared from the corresponding keto-ester by reaction with DAST followed by addition of
the anion of dimethyl methanephosphonate). The resulting ketone (9) was reduced with sodium
Scheme
F F
O
F F
MePO(OMe)2
n-BuLi, 87%
OEt
DAST
91%
OEt
PO(OMe)2
O
O
O
4
5
O
O
O
a) NaH, DMF
CN
CN
(COCl)2
NH
N
N
Me
b) BrCH2(CH2)6CN
c) HCl (89% overall)
DMSO
100%
O Si Bu-t
OH
CHO
Me
8
7
6
O
N
O
5; NaH
(S)-CBS
CN
CN
N
F
F
THF, 0°C
74%
F
75%
F
R1
O
R2
9
10a; R1=OH, R2=OH
10b: R1=H, R2=OH
N
N
O
HN
O
HN
N
N
Bu3SnN3
95%
Bu3SnN3
N
N
N
N
10a
10b
F
F
F
F
H
HO
OH
H
2
11
borohydride to give a pair of diastereomeric alcohols (10a,b) in a ratio of ca. 2.5:1. These alcohols were
separated using chiral column chromatography to provide the pure diastereomeric alcohols (10a, 10b)
which were then reacted individually with tri-n-butylstannyl azide to provide the corresponding tetrazoles
(11, 2). Unfortunately the minor isomer (2) was found to correspond to the compound with the greater

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potency and which was subsequently shown to embody the natural R-stereochemistry at the 3-hydroxyl
position (see Table 1). This was in contrast to experience in the synthesis of 3a,b where the more potent
isomer predominated under most reducing conditions. An extensive evaluation of a variety of selective
reagents, many of which have been shown to provide the natural 15-R-hydroxyl stereochemistry in
reduction of 15-keto analogs of prostaglandins (Table 1) was unsuccessful. Reduction with (R)-2-methyl-
CBS-oxazaborolidine and catecholborane11 at -45°C gave a 10:1 ratio again favoring the undesired
diastereomer. However, the (S)-CBS reagent under the same conditions gave predominance of the
desired isomer. The reaction gave the same result when a smaller amount (0.6 eq.) of (S)-CBS reagent
was used. Separation of the diastereomers followed by conversion to the tetrazole yielded the desired
compound (2). For ease of handling, the compound was converted to its calcium salt which was a non-
hygroscopic solid suitable for in vivo studies.
Table 1: Reduction of difluoroketone 9
Conditions
Ratio 10a: 10b
NaBH4 (1.5 eq.), CeC13 (1 eq.), EtOH/H2O, -20°C
L-Selectide (1.1 eq.), THF, -78°C
2.5 : 1
2 : 1
(S)-Alpine-Hydride (1.05 eq.), THF, -78°C
Na(CN)BH3, MeOH/AcOH, 0°C
1 : 1 + other products
Mixture of 1,2- and 1,4-reduction
(R)-CBS (1 eq.), catecholborane (3 eq.), DCM, -40°C
(S)-CBS (1 eq.), catecholborane (3 eq.), DCM, -40°C
(S)-CBS(0.6 eq.), catecholborane (3.4 eq.), DCM, -40°C
(S)-CBS(0.1 eq.), catecholborane (3 eq.), DCM, -40°C
10 : 1
1 : 2
1 : 1.8
1 : 1 (incomplete reaction)
As noted in Table 2, 2 is very potent at the EP4 receptor with a Ki of 0.38 nM and also highly efficacious
showing an EC50 of 0.6 nM and is thus 3 to 5-fold more potent at the EP4 receptor than both the
previously optimized agonist compound (3a) and PGE2 itself.
Evaluated in in vitro incubations with rat and human hepatocytes, compound (2) showed a high degree of
metabolic stability and provided only small amounts of metabolites. The major metabolites had
molecular weights indicative of them being glucuronide conjugates presumably either at the tetrazole or
the hydroxyl function. Small amounts of oxidative metabolites (M + 16) were also observed but not

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441
characterized. Compound (2) was found to have good oral bioavailability in the rat (15%) with a long
half-life (ca.12 h). When dosed orally to rats for four days at 1 mg/kg, blood levels peaked at
approximately 2 h after dosing at 20-25 nM and residual blood levels at time 0 on the fourth day (24 hr
after dosing on day 3) were 5 nM. Thus this dose can provide greater than 10 fold multiples of the EC50
throughout the dosing period. The rats, however, exhibited signs of abdominal discomfort and weight
loss suggesting that at least some of the gastrointestinal side effects associated with PGE2 may be
mediated through the EP4 receptor. Lower doses (0.1 and 0.3 mg/kg) were better tolerated and thus this
compound could serve as a useful tool to explore the in vivo effects of EP4 agonism in physiology.
Studies carried out to examine the effects of 2 on bone will be reported elsewhere.
Table 2: Agonist potency and radioligand binding affinity and selectivity.
Compound
Agonist
EC50
(nM)
EP4
Radioligand Binding
Ki (nM)
EP4
EP1
EP2
EP3-III
2800
DP
FP
IP
TP
2
>12000
3200
>4800
>8000
>6000
>6000
0.6 ± 0.1
0.38 ± 0.02
11
3a
3b
3c
1190(n=1)
690(n=1)
>13,000
>13,000
>13,000
>13,000
>13,000
>13,000
>13,000
10560
3340
>13,000
>13,000
>13,000
>13,000 >13,000 >13,000
>13,000 >13,000 >13,000
>13,000 >13,000 >13,000
2.5 ± 1.0
1.2 ± 0.2
62(n=1)
12(n=1)
nt
nt
PGE2
>100000 >20,000
3.0±0.4
0.8±0.07
9.1±1.5
4.9± 0.5 0.33±0.3 307±106 119±12
EXPERIMENTAL
Biological Assays
Receptor binding assays were performed using cell membranes from HEK 293ebna cells recombinantly
expressing the corresponding human prostanoid cDNA’s.12 EP4 agonist potency and efficacy were
evaluated utilizing a stable clone of pSV40-EP4 transfected into HEK293 cells that expresses
approximately 50 fmol/mg EP4 receptor. Whole cell cAMP assays were performed essentially as
described in Slipetz et al.13 with the following modifications. Assays were performed with cells in
suspension in a total of 0.2 mL HBSS containing 2 mM IBMX (phosphodiesterase type IV inhibitor).

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IBMX and PGE2 or the test compound were added to the incubation mixture in DMSO to a final vehicle
concentration of 1.8% (v/v) (kept constant in all samples). The reaction was initiated by the addition of 1
x 105 cells per incubation, samples were incubated at 37°C for 10 min, and the reaction was terminated by
immersing the samples in boiling water for 3 min. Measurement of cAMP was performed by a
[125I]cAMP scintillation proximity assay. For in vivo and in vitro metabolism methods, see methods
described by Nicoll-Griffith et al.14
General Chemistry
NMR spectra were recorded as solutions in deuterochloroform or acetone-d6, unless otherwise stated, and
at field strength stated and using the solvent as internal standard. Preparative scale HPLC for enantiomer
separation was carried out using a ChiralPak AD™ (silica, coated with amylose tris(3,5-dimethylphenyl
carbamate)) HPLC columns from Chiral Technologies.
The chirality and relative stereochemistry of compound (10b) were determined by X-Ray analysis.
Ethyl difluoro(phenyl)acetate (4)- To a solution of ethyl benzoylformate (82 g, 460 mmol) in toluene
(100 mL) was added diethylaminosulfur trifluoride (DAST, 127 mL, 961 mmol) portionwise at rt (1/8 of
total amount each time, at 15-30 min intervals between each addition for the exothermic reaction to
subside). After addition of the last portion of DAST, the mixture was stirred for another 4 h at rt, after
which time it was poured into ice containing conc. NH4OH (500 mL). The mixture was then neutralized
with sat NH4Cl (1 L ) and conc. HCl and the product was extracted into EtOAc. The organic layer was
washed with 2N HCl, dried over Na2SO4 and evaporated. Pure acetate (4) (84.17 g, 91%) was obtained
after distillation (110-115°C, 25 mmHg). 1H NMR (500 MHz, acetone-d6) δ 7.62 (d, J = 9 Hz, 2H), 7.55
(m, 3H), 4.35 (q, J = 6 Hz, 2H), 1.27 (t, J = 6 Hz, 3H).
Dimethyl (3,3-difluoro-2-oxo-3-phenylpropyl)phosphonate (5) - To a solution of dimethyl
methanephosphonate (50 mL, 460 mmol) in THF (700 mL ) was added dropwise n-BuLi (2.5 M in
hexanes, 185 mL) at -78°C and this solution was stirred for another 20 min at the same temperature. Then,
a solution of acetate (4) (84.1 g, 420 mmol) in THF (200 mL ) was added at -78°C and the mixture was
stirred for another 4 h at the same temperature. The reaction was quenched by addition of a solution of
acetic acid (60 mL) in THF (100 mL ) at -78°C, followed by a half-saturated solution of NH4Cl at rt. The
product was extracted into i-PrOAc, dried over Na2SO4 and concentrated to dryness. Traces of solvents
were removed by co-evaporation with toluene and drying under high vacuum to yield the crude product
(5) (101.91 g, 87%) as an oil. 1H NMR (400 MHz, CDCl3) δ 7.65-7.40 (m, 5H), 3.77 (s, 3H), 3.74 (s, 3H),
3.35 (d, J = 22 Hz, 2H); MS 279.1 (M+1).

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7-[(2R)-2-({[tert-Butyl(dimethyl)silyl]oxy}methyl)-5-oxopyrrolidin-1-yl]heptanenitrile - To a mixture
of NaH (60% in oil, 34.7 g, 870 mmol) in DMF (600 mL) was added a solution of (5R)-5-({[tert-
butyl(dimethyl)silyl]oxy}methyl)pyrrolidin-2-one (6)15 (142.2 g, 620 mmol) in DMF (600 mL) at rt Then,
sodium iodide (10 g, 667 mmol) and 7-bromoheptanenitrile (158 g, 828 mmol) were added and the
mixture was stirred between 30 and 40°C for 30 min (with cooling to control the exothermic reaction) and
then at 50°C for 2 h and at rt overnight. The mixture was poured into 3 L of ice-cold half-saturated NH4Cl
and the products were extracted in EtOAc. (2x1.5 L). The combined organic solutions were washed with
water (2x1.6 L) and brine (1 L), dried over Na2SO4, filtered, and concentrated. Purification of a small
sample by flash chromatography on silica gel eluting with a 20% acetone:toluene provided pure 7-[(2R)-
1
2-({[tert-butyl(dimethyl)silyl]oxy}methyl)-5-oxopyrrolidin-1-yl]heptanenitrile as an oil. H NMR (500
MHz, acetone-d6) δ 3.85 (dd, J = 2, 10 Hz, 1H), 3.75 (m, 1H), 3.69 (dd, J = 3, 10 Hz, 1H), 3.48 (m, 1H),
3.04 (m, 1H), 2.48 (t, J = 8 Hz, 2H), 2.30 (m, 1H), 2.13 (m, 2H), 1.86 (m, 1H), 1.70-1.42 (m, 6H), 1.34
(m, 2H), 0.92 (s, 9H), 0.10 (2s, 6H); MS 339.3 (M+1).
7-[(2R)-2-Hydroxymethyl-5-oxopyrrolidin-1-yl]heptanenitrile (7) – To the crude 7-[(2R)-2-({[tert-
butyl(dimethyl)silyl]oxy}methyl)-5-oxopyrrolidin-1-yl]heptanenitrile dissolved in THF (1.2 L) was
added 1N HCl (300 mL). The mixture was stirred at rt for 3 days, then the solvents were evaporated to
dryness and the remaining traces of solvents co-evaporated twice with toluene. Purification by flash
chromatography on silica gel (2.8 kg) eluting with a solvent gradient (acetone:toluene 40:60 to
1
acetone:ethanol:toluene 65:10:25) provided 7 (123.8 g, 89%, 2 steps) as an oil. H NMR (500 MHz,
acetone-d6) δ 3.78 (m, 2H), 3.60 (m, 2H), 3.08 (m, 1H), 2.47 (t, J = 7 Hz, 2H), 2.38 (m, 1H), 2.25 (m, 1H),
2.12 (m, 1H), 1.93 (m, 1H), 1.65 (m, 3H), 1.50 (m, 3H), 1.37 (m, 2H); MS 225.1 (M+1).
7-[(2R)-2-Formyl-5-oxopyrrolidin-1-yl]heptanenitrile (8) - Oxalyl chloride (34 mL, 388 mmol) was
added portionwise to a solution of DMSO (30 mL, 423 mmol) in CH2Cl2 (500 mL) at -72°C and the
mixture was stirred at this temperature for 20 min. Then, a solution of the alcohol (7) (73.16 g, 326 mmol)
in CH2Cl2 (200 mL) was added slowly and the mixture was stirred at -72°C for 30 min. Triethylamine
(135 mL, 960 mmol) was then added slowly and the mixture was stirred again at -72°C for 45 min after
which it was warmed to -15°C. Ether (800 mL) was added and the solid Et3N·HCl was removed by
filtration through celite and was washed with cold ether:CH2Cl2 1:1 (800 mL). The solvents were
evaporated and the remaining oil was redissolved in THF:ether 1:1 (600 mL) and filtered again to remove
more Et3N·HCl. Evaporation of the solvents afforded the crude aldehyde (8) (72.5 g, 326 mmol) as an oil.
1H NMR (400 MHz, CDCl3) δ 9.62 (s, 1H), 4.15 (m, 1H), 3.65 (m, 1H), 3.10 (m, 1H), 2.45 (m, 2H), 2.35
(m, 3H), 2.10 (m, 1H), 1.68 (m, 2H), 1.52 (m, 4H), 1.35 (m, 2H).
7-{(2R)-2-[(1E)-4,4-Difluoro-3-oxo-4-phenylbut-1-en-1-yl]-5-oxopyrrolidin-1-yl}heptanenitrile (9) -

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To a solution of the phosphonate (5) (90.7 g, 326 mmol) in THF (500 mL) was added NaH 60% in oil (13
g, 325 mmol) at 0°C, and the reaction mixture was stirred at rt for 1.5 h. Then, at -10°C, a solution of
crude aldehyde (8) (72.5 g, 326 mmol) in THF (300 mL) was added and the resulting mixture was stirred
at rt overnight. A half-saturated solution of NH4Cl (800 mL) was added and the product was extracted
with i-PrOAc, dried over Na2SO4, concentrated and purified by filtration through silica gel (1.8 kg) using
1
a gradient of EtOAc:hexanes (65 to 100%) as eluent to yield 9 (90.33 g, 74%) as an oil. H NMR (400
MHz, acetone-d6) δ 7.60 (m, 5H), 7.05 (dd, J=10, 14 Hz, 1H), 6.82 (d, J=14 Hz, 1H), 4.44 (m, 1H), 3.45
(m, 1H), 2.82 (m, 1H), 2.47 (t, J=7 Hz, 2H), 2.40-2.20 (m, 3H), 1.84 (m, 1H), 1.61 (m, 2H), 1.43 (m, 4H),
1.26 (m, 2H).
7-{(2R)-2-[(1E,3R)-4,4-Difluoro-3-hydroxy-4-phenylbut-1-en-1-yl]-5-oxopyrrolidin-
1-yl}heptanenitrile (10b) - To a solution of the ketone (9) (27.74 g, 74.1 mmol) and (S)-2-methyl-CBS-
oxazaborolidine (47 mL of a 1M solution in toluene) in CH2Cl2 (340 mL) maintained at -40°C was added
slowly a 1M solution of catecholborane in THF (250 mL). The mixture was then warmed up slowly
to -20°C, at which point the reaction was found to be complete by TLC. The reaction was quenched with
2N HCl and the mixture was stirred at rt overnight. Methanol (75 mL) was then added and the resulting
mixture was filtered through celite. The organic layer was separated and the aqueous layer was
reextracted with i-PrOAc. The combined organic phases were dried over Na2SO4, concentrated and
purified by filtration through silica gel using a gradient of EtOAc:hexanes (60 to 100%) and
ethanol:EtOAc 15% as eluents to yield an oil (21 g, 75%) consisting of a 1.8:1 mixture of 10b and its 3S
isomer (10a). The two isomers were separated by chiral HPLC on a ChiralPak AD column (20 µm, 5x50
cm, eluent 25% i-PrOH/hexane, flow rate 80 mL/min, detection at 264 nm; on an analytical column
eluting with 20% i-PrOH/hexane at 1 mL/min, the retention time of the 3S isomer (10a) and compound
(10b) are respectively 10.2 and 16.5 min). The fractions containing the more polar isomer (10b) were
concentrated and the crystallized solid triturated in ether. mp 89-90°C, 1H NMR (500 MHz, acetone-d6) δ
7.52 (m, 5H), 5.72 (m, 2H), 5.04 (br s, 1H, OH), 4.67 (m, 1H), 4.14 (m, 1H), 3.42 (m, 1H), 2.72 (m, 1H),
2.47 (t, J = 7 Hz, 2H), 2.20 (m, 3H), 1.65 (m, 3H), 1.45 (m, 4H), 1.28 (m, 2H).
(5R)-5-[(1E,3R)-4,4-Difluoro-3-hydroxy-4-phenylbut-1-en-1-yl]-1-[6-(1H-tetrazol-
5-yl)hexyl]pyrrolidin-2-one (2) – To the nitrile (10b) (31.82 g, 84.5 mmol) was added azidotributyltin
(45.3 g, 136 mmol) and the mixture was heated to 120°C for 6 h. The reaction mixture was then dissolved
in boiling acetone (150 mL), then diluted with toluene (150 mL) and purified by flash chromatography on
silica gel (1 kg) with a gradient of acetone:toluene:AcOH 20:80:0 to 40:60:2 as eluent to yield 2 (33.67 g,
95%) as an oil. 1H NMR (500 MHz, acetone-d6) δ 7.57-7.47 (m, 5H), 5.72 (m, 2H), 4.67 (m, 1H), 4.17 (m,
H), 3.42 (m, 1H), 2.97 (t, J = 7 Hz, 2H), 2.73 (m, 1H), 2.30-2.17 (m, 3H), 1.80 (m, 2H), 1.66 (m, 1H),
1.42 (m, 4H) 1.30 (m, 2H); MS 420.3 (M+1).

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Calcium salt of (5R)-5-[(1E,3R)-4,4-difluoro-3-hydroxy-4-phenylbut-1-en-1-yl]-1-[6-(1H-tetrazol-
5-yl)hexyl]pyrrolidin-2-one - The tetrazole (2) (37.64 g, 89.7 mmol) was dissolved in a small amount of
hot methanol and diluted with deionized water. Calcium hydroxide (3.996 g, 54 mmol) was then added
and the mixture was stirred at rt for 30 min. The excess amount of calcium hydroxide was removed by
filtration and the methanol was evaporated. The aqueous solution was washed twice with ether and the
product was freeze-dried. The gummy solid was finally triturated into acetone:hexane 3:1 (270 mL),
filtered under nitrogen and dried under high vacuum to yield a white solid (35.48 g, 90%), mp 140°C
(decomp). 1H NMR (500 MHz, methanol-d4) δ 7.52-7.42 (m, 5H), 5.80 (dd, J = 7, 15 Hz, 1H), 5.64 (dd, J
= 10, 15 Hz, 1H), 4.55 (m, 1H), 4.15 (m, H), 3.38 (m, 1H), 2.85 (t, J = 7 Hz, 2H), 2.72 (m, 1H), 2.36 (m,
2H), 2.24 (m, 1H), 1.76 (m, 2H), 1.68 (m, 1H), 1.50-1.32 (m, 4H) 1.28 (m, 2H).
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