Synthesis and evaluation of 3-aminopropionyl substituted fentanyl analogues for opioid activity

Article abstract of DOI:10.1016/j.bmcl.2006.06.040

An enkephalin analogue coupled to 'aminofentanyl' has been synthesized and tested for biological activities at the μ and δ opioid receptors. Aminofentanyl which represents a structural derivative of fentanyl has been synthesized by acylation of 1-(2-phenethyl)-4-(N-anilino)piperidine with phthaloyl protected β-alaninyl chloride in the presence of DIPEA, followed by deprotection with hydrazine hydrate. Aminofentanyl has also been successfully acylated with ethyl isocyanate, various acid anhydrides, to further investigate structure-activity relationships of these new fentanyl derivatives. Among the new derivatives compound 7 which carries a Tyr-d-Ala-Gly-Phe opioid message sequence showed good opioid affinity (1 nM at both δ and μ opioid receptors) and bioactivity (34.9 nM in MVD and 42 nM in GPI/LMMP bioassays).

Full text of DOI:10.1016/j.bmcl.2006.06.040

Bioorganic & Medicinal Chemistry Letters 16 (2006) 4946–4950
Synthesis and evaluation of 3-aminopropionyl substituted fentanyl
analogues for opioid activity
Ravil R. Petrov,a Ruben S. Vardanyan,a Yeon S. Lee,a Shou-wu Ma,b Peg Davis,b
Lucinda J. Begay,a Josephine Y. Lai,b Frank Porrecab and Victor J. Hrubya,*
aDepartment of Chemistry, University of Arizona, Tucson, AZ 85721, USA
bDepartment of Pharmacology, University of Arizona, Tucson, AZ 85721, USA
Received 27 April 2006; revised 13 June 2006; accepted 13 June 2006
Available online 7 July 2006
Abstract—An enkephalin analogue coupled to ‘aminofentanyl’ has been synthesized and tested for biological activities at the l and d
opioid receptors. Aminofentanyl which represents a structural derivative of fentanyl has been synthesized by acylation of 1-(2-phen-
ethyl)-4-(N-anilino)piperidine with phthaloyl protected b-alaninyl chloride in the presence of DIPEA, followed by deprotection with
hydrazine hydrate. Aminofentanyl has also been successfully acylated with ethyl isocyanate, various acid anhydrides, to further
investigate structure–activity relationships of these new fentanyl derivatives. Among the new derivatives compound 7 which carries
a Tyr-D-Ala-Gly-Phe opioid message sequence showed good opioid affinity (1 nM at both d and l opioid receptors) and bioactivity
(34.9 nM in MVD and 42 nM in GPI/LMMP bioassays).
ꢀ 2006 Elsevier Ltd. All rights reserved.
Depending on their nature all opiates can be broadly
divided into two categories: non-peptide and peptide
based. Morphine which occurs in nature represents one
of the most efficient analgesic drugs among the non-pep-
tide based opiates. Endogenous opioid peptides such as
endomorphins, enkephalins, and dynorphins occurring
naturally in the brain represent the second class of opi-
ates. The latter function as both neuromodulators and
hormones, and are responsible for a broad spectrum of
physiological effects. A common feature of these two clas-
ses of opiates is their binding to the three recognized opi-
oid receptor types: l, d, and j. A tremendous amount of
synthetic work was done to alter the potency, selectivity,
and bioavailability of these both classes of opioids.
The class of compounds known as 4-anilidopiperidines
represent the most powerful synthetic analgesics, which
include fentanyl and related compounds.1–13 Fentanyl is
a well-known l-selective synthetic analgesic (ED50
0.011 mg/kg) which is 50–100 times more potent than
morphine, has a short duration of action and an onset
of action almost immediately after intravenous adminis-
tration. Fentanyl, sufentanyl, and alfentanyl currently
represent the three most popular compounds used for
analgesia in clinical practice despite the fact that their
use results in side effects such as respiratory depression,
physical dependence, and rapid tolerance.14
Abbreviations: Ac, acetyl; Ac2O, acetic anhydride; Boc, tert-butyloxy-
carbonyl; DCC, N,N-dicyclohexylcarbodiimide; DCM, dichlorometh-
ane; DCU, N,N-dicyclohexylurea; DEPT, decoupled edited phase
transfer; DIPEA, diisopropylethylamine; DMF, N,N-dimethylform-
amide; DMSO, dimethylsulfoxide; hDOR, human d-opioid receptor;
DPDPE, c[D-Pen2,D-Pen5]enkephalin; DAMGO, [D-Ala2,NMePhe4,
Gly5-ol]enkephalin; Et, ethyl; Et2O, diethyl ether; EtOAc, ethyl acet-
ate; EtNCO, ethylisocyanate; GPI, guinea pig ileum; HOBt, 1-hydroxy-
benzotriazole; LMMP, longitudinal muscle myenteric plexus; rMOR,
rat l-opioid receptor; MVD, mouse vas deferens; Pht, phthaloyl; TEA,
triethylamine; TFA, trifluoroacetic acid.
An evident gap in the literature regarding incorporation
of amino acids and peptides into fentanyl chemistry has
encouraged us to investigate replacement of the propio-
nyl fragment of fentanyl with various amino acids. We
therefore sought to design a hybrid molecule based on
two distinct classes of opioid ligands: the peptide por-
tion derived from enkephalins and the non-peptide moi-
ety from a 4-anilidopiperidine series. This novel strategy
would be analogous to that used to create molecules
such as biphalin [(Tyr-D-Ala-Gly-Phe-NH)2], a dimeric
analogue of enkephalin with two peptide based
pharmacophores linked by a hydrazide bridge. The
Keywords: Fentanyl derivatives; Opioid agonists; Enkephalin
analogue.
*
Corresponding author. Tel.: +1 520 621 6332; fax: +1 520 621
8407; e-mail: hruby@u.arizona.edu
0960-894X/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.06.040

R. R. Petrov et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4946–4950
4947
original idea of incorporating 1- and 2-substituted fen-
tanyl analogues into peptides based on the structural
analogy between the aromatic rings of fentanyl and
the Tyr1 and Phe4 residues of the opioid peptides goes
back to the early 1980 with the resulting fentanyl ana-
logues showing very weak or no opioid activity, and
that study was limited to 1- and 2-substituted ana-
logues.15 The ability to incorporate and retain the char-
acteristic high opioid activity of 4-anilidopiperidines
into peptides holds numerous possibilities in the area
of drug design and their medicinal applications. For
example, attachment of the corresponding unit would
allow rather simple introduction of opioid activity into
any peptide of interest, which can be fruitful for
designing multiple ligands. The inherent l-opioid
receptor selectivity of fentanyl and its analogues would
allow, for instance, greater l-selectivity of opioid ana-
logues.16 Considering recent achievements in convert-
ing opioid agonists into antagonists,17 a combination
of peptide plus non-peptide opioid has a potential of
developing an antagonist of matching potency to fenta-
nyl. We expect that the highly lipophilic character of
the 4-anilidopiperidine moiety will increase cell perme-
ability of attached peptides, and consequently their
bioavailability.18 Furthermore, we anticipate that
replacement of the propionyl moiety of fentanyl with
amino acids and peptide residues will decrease the
toxicity associated with this class of analgesics.
nyl (BIOMOL Internationalꢁ, PA),19 is not described in
the literature, have prompted us to find a synthetic strat-
egy that would allow us to couple b-amino acids with
1-(2-phenethyl)-4-(N-anilino)-piperidine (2). This b-ala-
nine derivative would differ from the original structure
of fentanyl only by an amino group attached to the third
carbon of propionyl moiety.
Our initial attempts to employ traditional peptide cou-
pling reagents such as HBTU and DIC in the presence
of HOBt proved to be unsuccessful for coupling amino
acids to compound 2.20 On the other hand, attempts
to couple the corresponding Fmoc acid chloride in anhy-
drous (DCM and TEA) or biphasic (DCM/5% NaHCO3
in water) media gave low coupling yields and partial
cleavage of the Nb-Fmoc group. We have found that
the designed compound can be readily prepared by cou-
pling the phthaloyl protected acid chloride of b-alanine
with compound 2 in the presence of DIPEA or TEA,
followed by deprotection with hydrazine hydrate in
refluxing ethanol (Scheme 1). In contrast to a-phthaloyl
amino acids, attempted deprotection of phthaloyl group
of compound 3 with ethanolamine in refluxing ethanol
gave multiple products with only 35% yield of target
product 1. Thionyl chloride in refluxing toluene was
used to convert the phthaloyl protected b-alanine to its
acid chloride. The precursor of this reaction, compound
3,21 was obtained as a solid due to its low solubility in
organic solvents such as acetone or methanol which sig-
nificantly simplified the corresponding purification. We
also found that compound 122 could be prepared faster
via a single pot procedure: in this case synthesis and
hydrolysis of compound 3 were carried out in one flask,
and the compound 1 was purified by crystallization from
EtOAc. Compound 1 was advanced to the derivatives
4a–c by treatment with the corresponding acid anhy-
drides.23 The urea derivative 4d was accessed by the
treatment of 1 with EtNCO.24 Phthaloyl amino acid
chlorides were chosen in the synthesis of an enkephalin
analogue, even though deprotection of phthaloyl group
required rather harsh conditions which are routinely
avoided in peptide chemistry. We found that the
employment of phthaloylphenylalanyl chloride prepared
O
O
O
HO
H2N
N
N
N
N
N
N
O
Fentanyl
Carboxyfentanyl
Aminofentanyl (1)
The high pharmaceutical potential of the anilidopiperi-
dines, as well as the fact that aminofentanyl in contrast
to its commercially available counterpart, carboxyfenta-
O
O
O
O
R-Phe-N
H
N
N
RHN
N
N
HN
N
PhtN
N
N
H-Tyr-D-Ala-Gly-Phe-N
N
N
H
i
ii
Vii
iv, v
1: R =H
5: R = H
6:R = Ac
2
3
7
vi
iii
4a:R =Ac
4b:R = EtCO
4c: R = CF3CO
4d:R = EtNHCO
Scheme 1. Reagents and conditions: (i) Pht-AA-Cl (b-Ala), DIPEA , DCM, 0 ꢂC, 92%; (ii) N2H4ÆnH2O, ethanol, reflux, 63%; (iii) EtNCO or acid
anhydride, DIPEA, DCM, 65–97%; (iv) Boc-Phe-OH, DCC, DIPEA, DCM; (v) TFA, DCM, 94% (two steps); (vi) Ac2O, DIPEA, 72%; (vii) stepwise
chain elongation using (i) and (ii) (ethanolamine instead of N2H4ÆnH2O) methods for Gly (80%) and D-Ala (94%), and (iv) and (v) for Tyr (65%).

4948
R. R. Petrov et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4946–4950
Table 2. In vitro functional activity
by treatment with thionyl chloride in refluxing toluene
followed by coupling in the presence of TEA gave us a
completely racemized product.25 Although no racemiza-
tion of phthaloyl protected phenylalanine was reported
under less drastic conditions, such as activation with
oxalyl chloride at room temperature,26 Boc-Phe-OH
was used for corresponding coupling with DCC as a
condensing reagent. The reaction of 5 with Ac2O affor-
ded 6.27 We were pleased to obtain the desired peptides
in good yields after coupling the phthaloyl protected Na-
amino acid chlorides in the presence of DIPEA followed
by deprotection with ethanolamine, extraction with
DCM or EtOAc,28 drying over MgSO4, and evaporation
of the solvent. In the case of phthaloyl protected a-ami-
no acid chlorides, the duration of coupling was very fast
as monitored by TLC and a reaction time of 20–30 min
was sufficient and maintained throughout the synthesis.
The coupling of phthaloyl D-alanyl chloride was free of
racemization as confirmed by HPLC and NMR analy-
sis. Compounds 5 and intermediate peptides were used
for peptide synthesis without purification to obtain the
final product 7.29 Peptides 6 and 7 were used in biolog-
ical tests without further purification because their puri-
ty, as determined by HPLC analysis, was of 95%. It is
notable that isolation and purification of our com-
pounds were done conveniently by extracting with
Et2O (4a–d, 5, and 6) or 1/4 mixture of EtOAc/Et2O
(7),28 filtering through Celite (to remove salts or DCU
in the case of 5) and precipitating by passing dry HCl
through the solvent.
a
IC50 (nM)
Compound
MVD
GPI/LMMP
1b
26.4%e
11%e
7b
34.9 4.9
33.3 6.1f
1%
42.0 16.3
108.0 49.0g
1%
7
Carboxyfentanyl
Fentanylc
Biphalind
9.45 4.05
0.72 0.20
3.45 0.45
40.0 13.0
a Values are means of four experiments.
b Tested in the base form.
c Data according to Ref. 15.
d Data according to Ref. 31.
e Percent inhibition of agonist activity at 1 lM.
f Small activity at j-opioid receptors.
g Effect is not reversed by naloxone.
smooth muscle preparations as described previously.33
IC50 values, relative potency estimates, and their associ-
ated errors were determined by fitting the data to the
Hill equation by a computerized non-linear least-square
method.
As reported in Table 1, compounds 1–6 showed weak
binding affinity at the opioid receptors. Compound 1
tested as a free base also showed weak in vitro activity.
Interestingly, although carboxyfentanyl was used to
raise antibodies against fentanyl, no data were available
in the literature about its opioid binding affinity. Our
tests showed that the binding affinity of carboxyfentanyl
is of the same magnitude as that of aminofentanyl
except the latter has higher l-opioid receptor selectivity
and bioactivity. Compound 7 which carries a Tyr-D-
Ala-Gly-Phe opioid message sequence showed good opi-
oid affinity and bioactivity. It is interesting to note that
this compound did not show any affinity for j-receptors
and was binding reversibly when tested in its neutral
form. In vivo studies of compound 7 are currently
underway and will be a subject of a separate report. This
study reveals that attachment of a b-aminoacid and its
N-acetylated analogues leads to substantial drop in opi-
oid binding affinity of corresponding fentanyl deriva-
tives. Thus, it appears that attachment of a peptide
bond to the propionyl moiety of fentanyl encounters
unfavorable interactions at the l- and particularly at
d-opioid binding sites. A comparison of the affinities
of compounds presented by Essawi and Portoghese,15
Montero et al.,34 and ours (4b, 4e, and 7) indicates that
propionyl moiety together with phenethyl part of fenta-
nyl play a very important role in opioid receptor binding
and activation.
Opioid binding affinities (see Table 1) of the new ana-
logues for the human d-opioid receptor (hDOR) or the
rat l-opioid receptor (rMOR) were determined by radi-
oligand competition analysis using DPDPE to label the
d-opioid receptor and DAMGO to label the l-opioid
receptor in cell membrane preparations from transfected
cells that stably express the respective receptor type.30
The functional bioactivity profiles of selected ligands
(see Table 2) were determined in MVD and GPI/LMMP
Table 1. Binding affinities
a
Binding IC50 (nM)
Compound
d
l
1b
13,000
36,000
n.c.
2080
1
3250
217
3
4a
8400
450
1030
451
4b
4c
12,100
6650
7600
0.99
146
4d
6
7b
29.9
2680
0.97
0.90
5400
3.3 0.45
1.4
In summary, we were able to identify some interesting
structure–activity relationships around the propionyl
moiety of fentanyl. Compound 7 which carries a Tyr-D-
Ala-Gly-Phe opioid message sequence showed good opi-
oid affinity and bioactivity suggesting that a novel class
of analgesics can be further developed utilizing this ap-
proach. Aminofentanyl was synthesized in good yield
by coupling of Nb-phthaloylalanyl chloride with 1-(2-
phenethyl)-4-(N-anilino)piperidine followed by hydroly-
sis with hydrazine hydrate. Phthaloyl amino acid
7
1.10
Carboxyfentanyl
Fentanylc
Biphalind
9400
246 41
2.6
a Values are means of two or three experiments (n.c. = no
competition).
b Tested in the base form.
c Data according to Ref. 31.
d Data according to Ref. 32.

R. R. Petrov et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4946–4950
4949
17. Schiller, P. W.; Weltrowska, G.; Nguyen, T. M. D.;
Lemieux, C.; Chung, N. N.; Lu, Y. Life Sci. 2003, 73, 691.
18. Lee, K.; Jung, W.-H.; Park, C. W.; Hong, C. Y.; Kim, I.
C.; Kim, S.; Oh, Y. S.; Kwon, O. H.; Lee, S.-H.; Park, H.
D.; Kim, S. W.; Lee, Y. H.; Yoo, Y. J. Bioorg. Med. Chem.
Lett. 1998, 18, 2563.
chlorides proved to be highly efficient for coupling to a
sterically and electronically demanding amine. Amena-
bility of phthaloyl protected amino acid chlorides for
efficient solution-phase synthesis of enantiomerically
pure peptides was also demonstrated.
19. McConnell, R. I.; Benchikh, E. O.; Fitzgerald, S. P.;
Lamont, J. V. Eur. Patent 1312923, 2003.
20. Maryanoff, B. E.; Simon, E. J.; Gioannini, T.; Gorissens,
H. J. Med. Chem. 1982, 25, 913.
Acknowledgments
21. Compound 2 (10.0 g, 35.7 mmol) and DIPEA (9.2 g,
71.3 mmol) were dissolved in 100 mL of dry DCM. The
mixture was cooled in an ice-water bath. A solution of
phthaloyl b-alanine chloride (12.7 g, 53.5 mmol) in
100 mL DCM was added dropwise. The reaction mixture
was stirred overnight. The mixture was then diluted with
100 mL DCM and washed with 5% aqueous K2CO3. The
aqueous phase was extracted with DCM (2· 50 mL). The
combined organic layers were washed with brine and dried
over anhydrous magnesium sulfate. The product solidified
after solvent removal in vacuo. The resulting solid was
washed with small amounts of acetone and dried in vacuo.
Compound 3: yield: 15.8 g, mp 205 ꢂC, and as a hydro-
chloric salt 260 ꢂC (from Et2O); 1H NMR (500 MHz,
CDCl3): d 1.42 (qd, 2H, J1 = 12.1 Hz, J2 = 3.3 Hz), 1.80
(br d, 2H, J = 12.1 Hz), 2.14 (br t, 2H, J = 11.5 Hz) 2.32 (t,
2H, J = 7.4 Hz), 2.54 (m, 2H), 2.72 (m, 2H), 2.99 (br d,
2H, J = 11.5 Hz), 3.91 (t, 2H, J = 7.5 Hz), 4.64 (tt, 1H,
J1 = 12.1 Hz, J2 = 3.8 Hz), 7.14 (m, 5H), 7.25 (m, 2H),
7.34 (m, 3H), 7.66 (m, 2H), 7.77 (m, 2H); 13C NMR
(500 MHz, CDCl3): d 30.3, 33.4, 33.7, 34.3, 52.1, 52.9,
60.3, 123.0, 125.9, 128.2, 128.4, 128.5, 129.4, 130.3, 132.0,
133.7, 138.1, 140.1, 167.9, 169.4. MS: m/z 481.9 [M+H]+;
HRMS calcd: 481.2365; found: 481.2437.
This work was supported by grants from USPHS and
NIDA.
References and notes
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22. Compound 3 (15.6 g, 32.4 mmol) was heated at reflux with
50 mL of hydrazine hydrate and 200 mL of ethanol for
2 h. The reaction mixture was then cooled to 0 ꢂC. A bulky
precipitate, which appeared upon cooling, was removed by
filtration. The filtrates were concentrated in vacuo to
remove ethanol, taken into EtOAc, and washed with
saturated NaHCO3 solution. The aqueous phase was
extracted with EtOAc (2· 50 mL). The combined organic
layers were washed with brine, dried over anhydrous
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placed in a freezer. The resulting crystals were filtered and
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NMR (600 MHz, CDCl3): d 1.44 (qd, 2H, J1 = 12.2 Hz,
J2 = 3.6 Hz), 1.80 (br d, 2H, J = 12.2 Hz), 1.8 (s, 2H, NH2),
2.07 (t, 2H, J = 6.1 Hz), 2.15 (t, 2H, J = 11.5 Hz), 2.53 (m,
2H), 2.72 (m, 2H), 2.87 (t, 2H, J = 6.0 Hz), 2.99 (br d, 2H,
J = 11.5 Hz), 4.67 (tt, 1H, J1 = 12.1 Hz, J2 = 3.7 Hz), 7.09
(d, 2H, J = 8.0 Hz), 7.15 (m, 3H), 7.24 (t, 2H, J = 7.5 Hz),
7.37 (m, 3H); 13C NMR (600 MHz, CDCl3): d 30.4, 33.6,
37.9, 38.2, 52.1, 52.9, 60.2, 125.8, 128.1, 128.2, 128.4, 129.2,
130.3, 138.4, 140.0, 171.3. MS: m/z 352.1 [M+H]+; HRMS
calcd: 351.2311; found: 351.2375.
7. Huang, B. S.; Deutsche, K. H.; Lalinde, N. L.; Terrell, R.
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23. Selected data. Compound 4a: 1H NMR (500 MHz,
CDCl3) d 1.45 (qd, 2H, J1 = 12.3 Hz, J2 = 3.7 Hz), 1.80
(br d, 2H, J = 12.6 Hz), 1.93 (s, 3H), 2.10 (t, 2H,
J = 5.7 Hz), 2.15 (td, 2H, J1 = 12.0 Hz, J2 = 1.8 Hz), 2.54
(m, 2H), 2.72 (m, 2H), 3.01 (br d, 2H, J = 11.7 Hz), 3.39
(dt, 2H, J1 = 5.9 Hz, J2 = 5.3 Hz), 4.63 (tt, 1H,
J1 = 12.2 Hz, J2 = 3.9 Hz), 6.52 (t, 1H, J = 5.3 Hz), 7.06
(m, 2H), 7.16 (m, 3H), 7.25 (t, 2H, J = 7.4 Hz), 7.38 (m,
3H); 13C NMR (500 MHz, CDCl3): d 23.3, 30.4, 33.7,
34.9, 35.1, 52.4, 52.9, 60.3, 125.9, 128.2, 128.4, 128.5,
129.4, 130.1, 137.8, 139.9, 169.7, 171.5. MS: m/z 394.2
[M+H]+; HRMS calcd: 393.2416; found: 393.2509.
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Lemieux, C. J. Med. Chem. 1989, 32, 698.

4950
R. R. Petrov et al. / Bioorg. Med. Chem. Lett. 16 (2006) 4946–4950
Compound 4b: 1H NMR (500 MHz, CDCl3): d 1.13 (t,
(CH2), 33.7 (CH2), 34.6 (CH2), 35.0 (CH2), 38.7 (CH2),
52.3 (CH), 52.9 (CH2), 54.4 (CH), 60.3 (CH2), 125.8 (CH),
126.6 (CH), 128.2 (CH), 128.3 (CH), 128.4 (CH), 129.1
(CH), 129.3 (CH), 130.1 (CH), 136.6 (Cq), 137.8 (Cq),
139.9 (Cq), 169.6 (C@O), 170.5 (C@O), 170.8 (C@O). MS:
m/z 541.2 [M+H]+; HRMS calcd: 540.3100; found:
540.3157.
3H, J = 7.6 Hz), 1.45 (qd, 2H, J1 = 12.1 Hz, J2 = 3.7 Hz),
1.80 (br d, 2H, J = 12.1 Hz), 2.10 (t, 2H, J = 5.7 Hz), 2.16
(m, 2H), 2.17 (q, 2H, J = 7.6 Hz), 2.54 (m, 2H), 2.73 (m,
2H), 3.01 (br d, 2H, J = 11.7 Hz), 3.40 (dt, 2H,
J1 = 5.8 Hz, J2 = 5.4 Hz), 4.63 (tt, 1H, J1 = 12.1 Hz,
J2 = 3.9 Hz), 6.53 (t, 1H, J = 5.4 Hz, NH), 7.05 (m, 2H),
7.16 (m, 3H), 7.25 (t, 2H, J = 7.5 Hz), 7.38 (m, 3H); 13C
NMR (500 MHz, CDCl3): d 9.7, 29.6, 30.3, 33.6, 34.9,
52.3, 52.8, 60.2, 125.9, 128.2, 128.4, 128.5, 129.4, 129.9,
137.8, 139.9, 171.6, 173.4. MS: m/z 408.1 [M+H]+; HRMS
calcd: 407.2573; found: 407.2659.
28. The aqueous solution was adjusted to pH
NaHCO3.
8 with
29. Selected data. Compound 7: 1H NMR (600 MHz,
DMSO-d6): d 1.16 (d, 3H, J = 6.9 Hz), 1.19 (br q,
2H, J = 12.0 Hz), 1.69 (br d, 2H, J = 10.8 Hz), 1.9–2.04
(m, 4H), 2.44 (m, 2H), 2.58–2.66 (m, 3H), 2.80 (dd,
1H, J1 = 13.3 Hz, J2 = 9.4 Hz), 2.86–2.97 (m, 4H), 3.17
(m, 1H), 3.25 (m, 1H), 3.5 (br s, 2H, NH2), 3.56 (t,
1
Compound 4c: H NMR (500 MHz, CDCl3): d 1.48 (qd,
2H, J1 = 12.2 Hz, J2 = 3.3 Hz), 1.81 (br d, 2H,
J = 12.2 Hz), 2.17 (t, 2H, J = 5.5 Hz), 2.19 (t, 2H,
J = 11.5 Hz), 2.56 (m, 2H), 2.74 (m, 2H), 3.04 (br d,
2H, J = 11.5 Hz), 3.50 (dt, 2H, J1 = 5.8 Hz, J2 = 5.4 Hz),
4.62 (tt, 1H, J1 = 12.2 Hz, J2 = 3.9 Hz), 7.07 (m, 2H), 7.16
(m, 3H), 7.25 (m, 2H), 7.41 (m, 3H), 7.69 (br t, 1H,
J = 5.4 Hz, NH); 13C NMR (500 MHz, CDCl3): d 30.2,
33.6, 33.9, 35.6, 52.6, 52.8, 60.2, 126.0, 128.3, 128.5, 128.8,
129.6, 129.9, 137.6, 139.9, 156.7, 156.9, 171.1. MS: m/z
448.1 [M+H]+; HRMS calcd: 447.2134; found: 447.2221.
1H,
J = 6.2 Hz),
3.60
(dd,
1H,
J1 = 16.8 Hz,
J2 = 5.5 Hz), 3.72 (dd, 2H, J1 = 6.1 Hz, J2 = 16.6 Hz),
4.22 (m, 1H), 4.36 (dt, 1H, J1 = 8.6 Hz, J2 = 5.2 Hz),
4.45 (tt, 1H, J1 = 12.0 Hz, J2 = 3.2 Hz), 6.71 (d, 2H,
J = 8.3 Hz), 7.02 (d, 2H, J = 8.2 Hz), 7.12–7.21 (m,
10H), 7.23 (t, 2H, J = 7.6 Hz), 7.43 (dd, 1H,
J1 = 7.0 Hz, J2 = 6.8 Hz), 7.47 (t, 2H, J = 7.1 Hz), 7.89
(t, 1H, J = 5.1 Hz), 7.94 (d, 1H, J = 8.2 Hz), 8.29 (br s,
1H), 8.32 (br s, 1H); 13C (part. assigned using 13C
DEPT-90 and DEPT-135) NMR (500 MHz, CDCl3): d
17.8 (CH3), 30.0 (CH2), 32.9 (CH2), 34.3 (CH2), 35.2
(CH2), 37.6 (CH2), 42.1 (CH2), 48.5 (CH), 51.9(CH),
52.5 (CH2), 54.3 (CH), 55.8 (CH), 59.5 (CH2), 115.0
(CH), 117.8 (Cq), 125.7 (CH), 126.1 (CH), 127.9 (CH),
128.1 (CH), 128.2 (CH), 128.5 (CH), 129.0 (CH), 129.3
(CH), 130.1 (CH), 130.3 (CH), 137.8 (Cq), 138.4 (Cq),
140.4 (Cq), 155.9 (Cq), 168.5 (C@O), 169.4 (C@O),
170.7 (C@O), 172.5 (C@O), 173.4 (C@O); MS: m/z
790.3 [M+H]+; HRMS calcd: 789.4214; found:
789.4271.
24. Selected data. Compound 4d: 1H NMR (500 MHz,
CDCl3): 1.10 (t, 3H, J = 7.2 Hz), 1.46 (qd, 2H,
d
J1 = 12.0 Hz, J2 = 2.9 Hz), 1.79 (br d, 2H, J = 11.9 Hz),
2.11 (t, 2H), 2.14 (br t, 2H, J = 11.4 Hz), 2.55 (m, 2H),
2.73 (m, 2H), 3.02 (br d, 2H, J = 11.4 Hz), 3.16 (m, 1H),
3.34 (dt, 2H, J1 = 5.8 Hz, J2 = 5.4 Hz), 4.61 (tt, 1H,
J1 = 12.1 Hz, J2 = 3.8 Hz), 5.04 (br s, 1H, NH), 5.54 (br
s, 1H, NH), 7.06 (m, 2H), 7.16 (m, 3H), 7.26 (m, 2H), 7.38
(m, 3H); 13C NMR (500 MHz, CDCl3): d 15.4, 30.3, 33.6,
35.1, 35.9, 52.3, 52.9, 60.2, 125.9, 128.2, 128.4, 129.4,
130.1, 137.9, 139.9, 158.3, 171.9. MS: m/z 423.1 [M+H]+;
HRMS calcd: 422.2682; found: 422.2752.
25. Petrov, R. R.; Vardanyan, R. S.; Nichol, G. S.; Carducci,
M. D.; Ma, S.-W.; Lai, J. Y.; Hruby, V. J. Acta Cryst.
2006, E62, o2815.
30. (a) Polt, R.; Porreca, F.; Szabo, L.; Bilsky, E. J.; Davis, T.
P.; Horvath, R.; Abbruscato, T. J.; Yamamura, H. J.;
Hruby, V. J. Proc. Natl. Acad. Sci. U.S.A. 1994, 91, 7114;
(b) Misicka, A.; Lipkowski, A. W.; Horvath, R.; Davis, P.;
Kramer, T. H.; Yamamura, H. I.; Hruby, V. J. Life Sci.
1992, 51, 1025.
26. Stephen, W. H. Org. Proc. Dev. 1999, 3, 241.
27. Selected data. Compound 6: 1H NMR (500 MHz, CDCl3):
d 1.41 (qd, 2H, J1 = 12.2 Hz, J2 = 4 Hz), 1.77 (br d, 2H,
J = 12.6 Hz), 1.89 (m (part. overlap.), 1H), 1.93 (s, 1H),
2.02 (ddd, 1H, J1 = 16.9 Hz, J2 = 6.7 Hz, J3 = 4.9 Hz),
2.13 (br dd, 2H, J1 = 11.9 Hz, J2 = 4.3 Hz), 2.53 (m, 2H),
2.71 (m, 2H), 2.98 (m (part. overlap), 2H), 3.0 (br d (part.
overlap.), 2H, J = 7 Hz), 3.28 (m, 1H), 3.36 (m, 1H), 4.58
(tt, 1H, J1 = 12.1 Hz, J2 = 3.8 Hz), 4.61 (dt, 1H,
J1 = 7.5 Hz, J2 = 7.3 Hz), 6.68 (d, 1H, J = 8.0 Hz, NH),
6.75 (t, 1H, J = 5.9 Hz, NH), 7.04 (m, 2H), 7.14–7.28 (m,
10H), 7.37 (m, 3H); 13C (assigned using 13C DEPT-90 and
DEPT-135) NMR (500 MHz, CDCl3): d 22.9 (CH3), 30.3
31. Yeadon, M.; Kitchen, I. Neuropharmacology 1988, 27,
345.
32. Lipkowski, A. W.; Misicka, A.; Davis, P.; Stropova, D.;
Janders, J.; Lachwa, M.; Porreca, F.; Yamamura, H. I.;
Hruby, V. J. Bioorg. Med. Chem. Lett. 1999, 9, 2763.
33. Kramer, T. H.; Davis, P.; Hruby, V. J.; Burks, T. F.;
Porreca, F. J. Pharmacol. Exp. Ther. 1993, 266, 577.
34. Montero, A.; Goya, P.; Jagerovic, N.; Callado, L. F.;
Meana, J. J.; Giron, R.; Goicoechea, C.; Martin, M. I.
Bioorg. Med. Chem. 2002, 10, 1009.