Synthesis of amide-type fluoroalkene dipeptide isosteres by an intramolecular redox reaction

Article abstract of DOI:10.1021/jo900135t

We previously achieved NHC-mediated preparation of ester-type fluoroalkene dipeptide isosteres (ES-FADIs, 4) by an intramolecular redox reaction. In the present study, a cyanide ion-mediated reaction was successfully applied to the conversions of γ,γ-difl

Full text of DOI:10.1021/jo900135t

Synthesis of Amide-Type Fluoroalkene Dipeptide Isosteres by an
Intramolecular Redox Reaction
Yoko Yamaki,† Akira Shigenaga,† Jinglan Li,‡ Yasuyuki Shimohigashi,‡ and Akira Otaka*,†
Graduate School of Pharmaceutical Sciences, The UniVersity of Tokushima, 1-78-1 Shomachi,
Tokushima 770-8505, Japan, and Department of Chemistry, Research-Education Center of Risk Science,
Faculty of Sciences, Kyushu UniVersity, Fukuoka 812-8581, Japan
aotaka@ph.tokushima-u.ac.jp
ReceiVed January 21, 2009
We previously achieved NHC-mediated preparation of ester-type fluoroalkene dipeptide isosteres (ES-
FADIs, 4) by an intramolecular redox reaction. In the present study, a cyanide ion-mediated reaction
was successfully applied to the conversions of γ,γ-difluoro-R,ꢀ-enoylsilane 1 or 2 to amide-type
fluoroalkene isosteres (AM-FADIs, 5 or 6). The use of catalytic cyanide ion allowed synthesis of chiral
auxiliary incorporated FADI 15b which was then subjected to a diastereoselective R-alkylation reaction
to yield R-substituted FADIs 17. Furthermore, the presented amidation protocol was used for
straightforward incorporation of FADI into peptidyl resin.
Introduction
In a precedent article,1 the N-heterocyclic carbene (NHC)2-
mediated synthesis of ester-type fluoroalkene dipeptide isosteres3,4
(ES-FADIs, 4) was addressed. Incorporation of FADIs into the
peptide backbone requires the conversion of ES-FADI 4 to the
corresponding active acyl component, whereby hydrolysis of
the ester followed by activation of the resulting carboxy group
is involved.5 The fact that synthesis of ES-FADI 4 from γ,γ-
difluoro-R,ꢀ-enoylsilane 1 or 2 (or enals) is accomplished by
the NHC-mediated intramolecular redox reaction in the presence
of an appropriate alcohol such as EtOH indicates that replace-
FIGURE 1. Envisioned synthesis of amide-type fluoroalkene dipeptide
isosteres (AM-FADIs).
* Tel: +81-88-633-7283. Fax: +81-88-633-9505.
† The University of Tokushima.
‡ Kyushu University.
(1) Yamaki, Y.; Shigenaga, A.; Tomita, K.; Narumi, T.; Fujii, N.; Otaka, A.
J. Org. Chem. 2009, 74, 3272–3277.
(2) Much recent literature about the NHC-mediated reactions are listed in
ref 1.
ment of the alcohol with amines should result in the formation
of amide-type FADIs (AM-FADI 5 or 6; Figure 1).
Therefore, we examined the synthesis of AM-FADIs with
an intramolecular redox reaction leading to the straightforward
incorporation of FADIs into peptides. On the basis of the
knowledge obtained in the study on synthesis of AM-FADIs,
we attempted to prepare a chiral auxiliary-possessing FADI with
practical use in the auxiliary-guided stereoselective R-alkyla-
tions.
(3) For some recent reviews for FADIs, see: (a) Welch, J. T.; Allmendinger,
T. In Peptidomimetics Protocols; Kazmierski, W. M., Ed.; Humana Press:
Totowa, NJ, 1999; pp 357-384. (b) Couve-Bonnaire, S.; Cahard, D.; Pan-
necoucke, X. Org. Biomol. Chem. 2007, 5, 1151–1157.
(4) Recent examples of the synthesis of FADIs are listed in ref 1.
(5) Some recent examples of the incorporation of FADIs into peptides, see:
(a) Niida, A.; Tomita, K.; Mizumoto, M.; Tanigaki, H.; Terada, T.; Oishi, S.;
Otaka, A.; Inui, K.; Fujii, N. Org. Lett. 2006, 8, 613–616. (b) Tomita, K.; Narumi,
T.; Niida, A.; Oishi, S.; Ohno, H.; Fujii, N. Biopolymers 2007, 88, 272–278. (c)
Lamy, C.; Hofmann, J.; Parrot-Lopez, H.; Goekjian, P. Tetrahedron Lett. 2007,
48, 6177–6180. (d) Narumi, T.; Tomita, K.; Inokuchi, E.; Kobayashi, K.; Oishi,
S.; Ohno, H.; Fujii, N. Tetrahedron 2008, 64, 4332–4346.
(6) (a) Vora, H. U.; Rovis, T. J. Am. Chem. Soc. 2007, 129, 13796–13797.
(b) Bode, J. W.; Sohn, S. S. J. Am. Chem. Soc. 2007, 129, 13798–13799.
3278 J. Org. Chem. 2009, 74, 3278–3285
10.1021/jo900135t CCC: $40.75 2009 American Chemical Society
Published on Web 03/30/2009

Synthesis of AM-FADIs
SCHEME 1
FIGURE 2. Triazolium precatalysts.
Results and Discussion
The fact that the NHC derived from thiazolium salt 3 was
the catalyst used for the preparation of ES-FADI 4 prompted
us to utilize NHC in the presence of amines targeting the
preparation of AM-FADIs. First, the attempted reaction of γ,γ-
difluoro-R,ꢀ-enoylsilane 1 with 3 in the presence of 1,8-
diazabicyclo[5,4,0]undec-7-ene (DBU) resulted in failure to
afford the desired material. Recently, Rovis and Vora and Bode
and Sohn reported that triazolium salts 7 and 8 were effective
precatalysts for the NHC-mediated oxidation of aldehydes to
amides.6 On the basis of these reports, we also attempted to
use triazolium salt 9 (Figure 2).
ment.14 Then the resulting negative charge would move into
the π-electron system to give silyl fluorodienol ether 11 via the
pushing out of one fluorine atom. Attack of the liberated fluoride
ion to the silyl group followed by protonation with amines
should give acyl cyanide 13, whereby synthesis of AM-FADIs
would be achieved (Scheme 1).
Reaction of enoylsilane 1 with benzyl amine in the presence
of triazolium salt 9 and DBU (30 mol % each) in THF at room
temperature afforded the desired AM-FADI 5a in 15% isolated
yield with the accompanying 1,4-adduct of benzyl amine (19%).
Analogous with the fact that NHC-mediated synthesis of ES-
FADIs proceeds more efficiently at elevated temperature, the
reaction was conducted at 70 °C to give 5a in 28% yield. Aiming
to further increase the yield of the desired material 5a, we
attempted to fine-tune the reaction conditions utilizing additives6,7
such as HOAt,8 imidazole, or DMAP; however, all trials offered
no improvement in the amidation reaction. All cases examined
here were complicated by the competing 1,4-addition of benzyl
amine and the formation of unidentified materials.9 Therefore,
we speculated that the complete conversion of enoylsilane 1 to
the active acyl equivalent followed by addition of amines would
lead to the formation of 5a in improved yield. The use of a
stoichiometric amount of NHC prior to the addition of amines
was evaluated to achieve complete conversion. Starting enoyl-
silane 1 disappeared with treatment with precatalyst 9 (1.0 equiv)
in the presence of DBU (1.0 equiv); however, subsequent
addition of benzyl amine to the resulting reaction mixture did
not afford desired 5a in satisfactory yield.
To ensure the complete internal conversion of the enoylsilanes
to the corresponding cyano dienolate anion 12 as a precursor
for acyl cyanide 13, we subjected enoylsilane 1 or 2 to a reaction
with potassium cyanide (1.05 equiv) in the presence of 18-
crown-6 (1.05 equiv) followed by the addition of amines
including amino esters. Results are summarized in Table 1.
The use of cyanide anion gave satisfactory results in the
preparation of AM-FADIs as shown in Table 1. Dependent on
the increase in soluble KCN, disappearance of the starting
material 1 occurred efficiently to give the corresponding acyl
cyanide precursor (enolate anion 12) which was converted to
acyl cyanide 13 upon protonation by subsequently added amines.
Acylation of benzyl amine with the resulting cyanide in Et2O
progressed at a faster rate than in THF to afford amide 5a (Table
1, entries 1-4). The use of n-Bu4NCN as an easily soluble
cyanide source in organic solvents allowed enoylsilane 1 to be
consumed rapidly (within 1 min) to lead to the formation of 5a
at -78 °C (entry 5). Reactions of enoylsilane (1 or 2) with
amino acid derivatives, even with a sterically hindered valine
derivative, also proceeded efficiently to yield tripeptide mimetics
(5b, 5c, and 5d or 6b, 6c, and 6d, respectively) with high (Z)-
selectivity (entries 6-11).15 The reaction in DMF without 18-
crown-6 completed to give peptidomimetic 5b in quantitative
Consequently, the applicability of a cyanide anion alternate
to NHCs in the synthesis of AM-FADIs was next examined.10-13
We expected that the envisioned reaction would first give silyl-
protected cyanohydrin carbanion 10 via nucleophilic attack of
the cyanide ion to acylsilanes followed by Brook rearrange-
(13) Some recent examples of reaction of acylsilanes with cyanide anion,
see: (a) Reich, H. J.; Holtan, R. C.; Bolm, C. J. Am. Chem. Soc. 1990, 112,
5609–5617. (b) Takeda, K.; Ohnishi, Y. Tetrahedron Lett. 2000, 41, 4169–4172.
(c) Saleur, D.; Bouillon, J.-P.; Portella, C. Tetrahedron Lett. 2001, 42, 6535–
6537. (d) Tanaka, K.; Takeda, K. Tetrahedron Lett. 2004, 45, 7859–7861. (e)
Tanaka, K.; Masu, H.; Yamaguchi, K.; Takeda, K. Tetrahedron Lett. 2005, 46,
6429–6432.
(14) For reviews on the Brook rearrangement, see: (a) Brook, A. G.;
Bassindale, A. R. In Rearrangements in Ground and Excited States; de Mayo,
P., Ed.; Academic Press: New York, 1980; pp 149-221. (b) Brook, A. G. Acc.
Chem. Res. 1974, 7, 77–84. (c) Moser, W. H. Tetrahedron 2001, 57, 2065–
2084.
(7) Addition of additives such as HOAt,6a DMAP, or imidazole6b is
indispensable for the NHC-catalyzed redox amidation of aldehydes with amines.
(8) Carpino, L. A. J. Am. Chem. Soc. 1993, 115, 4397–4398.
(9) The NHC-mediated reaction of enals with amines needs the slow addition
of amines into the reaction mixtures.6b We also tried this protocol not to obtain
the desired material in high yield.
(10) Cyanide anion-mediated conversion of R-reducible aldehydes to esters,
see: (a) Roedig, A.; Hagedorn, F. Liebigs Ann. Chem. 1965, 683, 30–41. (b)
Yoshida, K.; Nomura, S.; Ban, Y. Tetrahedron Lett. 1985, 41, 5495–5501.
(11) Direct conversion of aldehydes to esters and amides using acetone
cyanohydrin was reported, see: Victor Paul Raj, I.; Sudalai, A. Tetrahedron Lett.
2005, 46, 8303–8306.
(15) In our system, reactions conducted at temperatures from 0 to 70 °C
generally gave approximately 95(Z):5(E)-diastereomeric mixture. The ratio was
easily determined by the NMR measurement of crude samples. (Z)-Fluoroalkene
3
compounds have coupling constants of JHF ) 35.3-37.0. (E)-Fluoroalkenes
3
have smaller coupling constants of JHF ) 20.0-21.2. Compounds possessing
(12) For review on acyl cyanides, see: Hu¨nig, S.; Schaller, R. Angew. Chem.,
Int. Ed. 1982, 21, 36–49.
(E)-geometry were obtained as (Z)/(E)-mixture, and further purification was not
conducted in this study.
J. Org. Chem. Vol. 74, No. 9, 2009 3279

Yamaki et al.
TABLE 1. Cyanide Ion-Mediated Synthesis of AM-FADIs
entrya
silane
amine (equiv)
solvent
temp (°C)
timeb (h)
product (yield %c (Z:E)d)
1
2
3
1
1
1
1
1
1
1
1
2
2
2
1
BnNH2 (1.05)
BnNH2 (1.05)
BnNH2 (5.0)
BnNH2 (5.0)
Et2O
THF
Et2O
THF
THF
THF
THF
THF
THF
THF
THF
DMF
0
0
0
0
2
5a (82 (92:8))
5a (73 (95:5))
5a (89 (93:7))
5a (85 (95:5))
5a (95 (100:0))
5b (93 (94:6))
5c (90 (94:6))
5d (84 (96:4))
6b (93 (95:5))
6c (88 (94:6))
6d (88 (95:5))
5b (quant. (95:5))
7.5
2.5
7.5
12
2
3
3
2
4
5e
6
BnNH2 (5.0)
-78
H-Gly-OEtg (5.0)
H-Val-OMeg (5.0)
H-Pro-OMeg (5.0)
H-Gly-OEtg (5.0)
H-Val-OMeg (5.0)
H-Pro-OMeg (5.0)
H-Gly-OEtg (5.0)
0
0
0
0
0
0
0
7
8
9
10
11
12f
4.5
2.5
2
a Prior to the addition of amines, reaction mixtures containing acylsilane, KCN, and 18-crown-6 were stirred at 0 °C until acylsilane disappeared (ca.
0.5-1 h). b Reaction time after addition of amines. c Combined yield. d E/Z ratios were determined by NMR analysis. e Instead of KCN/18-crown-6, 2
equiv of n-Bu4NCN was used. In this case, no (E)-isomer was detected. f Reaction was performed without 18-crown-6. g In situ formed amines from the
corresponding HCl salts and Et3N were used.
SCHEME 2
desired auxiliary-containing FADI 15a, albeit in low chemical
yield (37%, Table 2, entry 1). The reaction at an elevated
temperature did not improve the chemical yield. Addition of
such additives that promote the acylation of the auxiliary was
also not so effective (Table 2, entries 3-6). On the basis of
these results, we envisioned that the reason for the low chemical
yields was attributable to the stoichiometric amount of cyanide
anion as shown in Scheme 3.
yield (entry 12). The results obtained here encouraged us to
evaluate the straightforward incorporation of FADIs into pep-
tides by solid-phase peptide synthesis, reported later in this
study.
A reaction with a stoichiometric amount of cyanide anion
followed by 1,2-Brook rearrangement and a subsequent redox
reaction consumed the starting enoylsilane 1 to give dienolate
12, which, upon protonation by a chiral auxiliary, resulted in
the formation of acyl cyanide 13 and the nucleophilic amide
anion of the auxiliary. To the resulting acyl cyanide 13, two
courses of reactions are possible: one is the nucleophilic attack
of the auxiliary anion to give desired FADI 15a; the other is
the reaction with DMAP to give acyl-DMAP 16 which has
higher reactivity to the auxiliary anion than the acyl cyanide
13. Therefore, preferential formation of the acyl-DMAP seemed
to be the one critical issue to achieve high chemical yield in
the preparation of the FADIs. Using a stoichiometric amount
of the cyanide anion, the regenerated anion was involved in
the reversed reaction from 16 to 13, which probably attributed
to the low chemical yield. On the other hand, if a catalytic
amount of cyanide anion was used, we speculated that the
regenerated cyanide anion resulting from the reaction of the acyl
cyanide with DMAP could preferentially attack the remaining
enoylsilane 1 to lead to the unequivocal involvement of the acyl-
DMAP 16 in the acylation of the auxiliary. On the basis of this
assumption, a reaction using a catalytic amount of cyanide anion
was attempted. Treatment of 1 with KCN/18-crown-6 (0.1 equiv
each) and the oxazolidinone HXa in the presence of DMAP in
THF (0.1 M concentration) gave the Xa-FADI 15a in moderate
yield (59%). Increasing the concentrations of the reactants from
0.1 to 0.3 M improved the chemical yield (64%). A reaction
with Oppolzer’s sultam HXb with catalytic KCN completed in
2 h to yield the desired Xb-FADI 15b in 95% isolated yield,
whereas the stoichiometric reaction gave 15b in 44% yield
(Table 2, entries 9 and 10).
Next we tried to incorporate R-substitution in AM-FADIs.
Direct/one-pot R-alkylation of the possible dienolate intermedi-
ate 12 resulting from the treatment of enoylsilanes with KCN/
18-crown-6 was attempted. Reaction of 1 with KCN/18-crown-6
in THF at -78 °C followed by the addition of allyl bromide
and benzyl amine sequentially afforded the exclusively O-
allylated product 14 in 89% isolated yield (Scheme 2).
Transformation to tin enolates by the addition of Bu3SnCl,
Ph3SnCl, or Ph3SnCl/HMPA to the dienolate solution gave no
desired R-allylated product with the accompanying O-allylated
product and R-nonsubstituted benzyl amide 5a in varying ratios.
Although other possible procedures based on the direct/one-
pot strategy were ruled out, we decided to explore other
strategies where the synthesis of AM-FADIs with amide-type
chiral auxiliaries such as oxazolidinone (HXa)16 or sultam
(HXb)17 and subsequent chiral auxiliary-guided alkylation were
involved. We first examined the preparation of chiral auxiliary
X-possessing FADIs (X-FADI 15). Examination of the reactions
is summarized in Table 2.
Evans’ oxazolidinone HXa was first selected as an incorpo-
rated auxiliary. The reaction of enoylsilane 1 with a stoichio-
metric amount of KCN/18-crown-6 (1.05 equiv each) in THF
at 0 °C with stirring until the starting material disappeared
followed by addition of oxazolidinone (HXa) afforded the
(16) (a) Evans, D. A.; Bartoli, J.; Shih, T. L. J. Am. Chem. Soc. 1981, 103,
2127–2129. (b) Evans, D. A.; Ennis, M. D.; Le, T.; Mandel, N.; Mandel, G.
J. Am. Chem. Soc. 1984, 106, 1154–1156. (c) Evans, D. A.; Britton, T. C. J. Am.
Chem. Soc. 1987, 109, 6881–6883.
(17) (a) Oppolzer, W.; Chapuis, C.; Bernardinelli, G. HelV. Chim. Acta 1984,
67, 1397–1401. (b) Oppolzer, W.; Mills, R. J.; Reglier, M. Tetrahedron Lett.
1986, 27, 183–186. (c) Oppolzer, W. Tetrahedron 1987, 43, 1969–2004.
3280 J. Org. Chem. Vol. 74, No. 9, 2009

Synthesis of AM-FADIs
TABLE 2. Cyanide Ion-Mediated Synthesis of Chiral Auxiliary-Possessing FADIs
entry
auxiliary
KCN (equiv)
additive
time (h)
temp. (°C)
yielda (Z:Eb)
1
2
3
4
5
6
7
8
9
HXa
HXa
HXa
HXa
HXa
HXa
HXa
HXa
HXb
HXb
1.05
1.05
1.05
1.05
1.05
1.05
0.1
0.1
1.05
0.1
18
18
18
18
18
18
20
11
20
2
40
70
40
40
40
40
40
40
40
40
37
26 (94:6)
35 (95:5)
39 (95:5)
imidazole (1.1)
DMAP (1.1)
DMAP (10)
HOAt (1.1)
DMAP (1.1)
DMAP (1.1)
DMAP (1.1)
DMAP (1.1)
43 (95:5)
d
59 (c)
68 (92:8)
44 (c)
10
95 (93:7)
a Combined yield of (Z)- and (E)-isomers. b E/Z ratios were determined by NMR analyses. c Not determined. d No desired product was obtained.
SCHEME 3
SCHEME 4
organocopper followed by R-alkylation via transmetalation from
the resulting Cu-enolate to a corresponding Sn-enolate.21
Treatment of the auxiliary-possessing FADI with an organo-
copper reagent followed by a sequence of reactions consisting
of conversion to Sn-enolate and R-alkylation was next evaluated
(Scheme 4). The reaction of 15b with Gillman cuprate
(Me2CuLi·LiI·LiBr) followed by the subsequent addition of
Ph3SnCl/HMPA and allylbromide or benzyl bromide yielded
the R-alkylated product 17 in a highly diastereoselective
manner.22
Having the chiral auxiliary-incorporated FADI in high
chemical yield, we next examined the chiral auxiliary-guided
incorporation of a substitution at the R-position of the FADI
15. Initially attempted aldol reactions of 15b utilizing titanium18-
or borane-enolate19 did not afford satisfactory results to our
demands.20 Additionally, Na- or Li-enolate for R-alkylation was
proven to decompose.
Next, we turned our attention to the straightforward incor-
poration of FADIs into the peptide backbone by solid phase
protocols. As a model peptide, we selected a nociceptin/orphanin
FQ (N/OFQ) analogue.23 The N/OFQ is a neuropeptide char-
acterized by the following sequence: H-Phe-Gly-Gly-Phe-Thr-
Gly-Ala-Arg-Lys-Ser-Ala-Arg-Lys-Leu-Ala-Asn-Gln-OH. This
neuropeptide modulates several biological functions at the
peripheral and central levels by selectively activating an ORL1
(opioid receptor-like 1) receptor. Extensive efforts to develop
the receptor antagonist have continued, where an N/OFQ
analogue possessing N-terminal Phe-Ψ[CH2-NH]-Gly isostere
((Phe1Ψ(CH2-NH)Gly2)N/OFQ(1-13)-NH2, 18) is known to
Here, we became interested in the synthesis of R-substituted
FADIs by the reaction of γ,γ-difluoro-R,ꢀ-enoylsultam with an
(18) (a) Saksena, A. K.; Girijavallabhan, V. M.; Wang, H.; Liu, Y.-T.; Pike,
R. E.; Ganguly, A. K. Tetrahedron Lett. 1996, 36, 5657–5660. (b) Watson, R. J.;
Batty, D.; Baxter, A. D.; Hannah, D. R.; Owen, D. A.; Montana, J. G.
Tetrahedron Lett. 2002, 43, 683–685. (c) Bandur, N. G.; Harms, K.; Koert, U.
Synthesis 2007, 17, 2720–2730. (d) Beshore, D. C.; Smith, A. B., III. J. Am.
Chem. Soc. 2007, 129, 4148–4149.
(19) (a) Oppolzer, W.; Blagg, J.; Rodriguez, I.; Walther, E. J. Am. Chem.
Soc. 1990, 112, 2767–2772. (b) Wu, Y.; Liao, X.; Wang, R.; Xie, X.-S.; De
Brabander, J. K. J. Am. Chem. Soc. 2002, 124, 3245–3253. (c) Fraser, B.;
Permutter, P. J. Chem. Soc., Perkin Trans. 1 2002, 2896–2899.
(20) Hydroxymethylation is a useful transformation for the preparation of a
wide variety of FADIs. Reaction with paraformaldehyde or trioxane under various
conditions did not always lead to the reproducible result. No synthetically useful
result was obtained.
(21) Narumi, T.; Niida, A.; Tomita, K.; Oishi, S.; Otaka, A.; Ohno, H.; Fujii,
N. Chem. Commun. 2006, 4720–4722.
(22) No R-epimers were detected in the crude materials.
(23) For a recent review on the nociceptin/orphanin FQ peptide (N/OFQ),
see: Lambert, D. G. Nat. ReV. Drug DiscoVery 2008, 7, 694–710.
J. Org. Chem. Vol. 74, No. 9, 2009 3281

Yamaki et al.
exhibit partial agonistic activity.24 We were interested in the
replacement of the N-terminal reduced amide isoster unit in 18
with FADI (PheΨ(CFdCH)Gly).
Standard Fmoc-based solid phase protocols on the Rink amide
resin gave the protected peptide chain 19 corresponding to
N/OFQ(3-13), on which the Boc-protected FADI corresponding
to the L-Phe-Gly sequence was introduced under the reaction
conditions mentioned below. Conversion of the dienolate anion
such as 12 to the acyl cyanide requires the presence of an
appropriate proton source. Excessively added amines worked
as both proton sources and nucleophiles in the experiment shown
in Table 1. In the case of solid phase peptide synthesis, excess
carboxy components are used for amines on resin, and therefore,
a proton source which promotes amidation is necessary. For
this purpose, the general amidation promoter, 1-hydroxyben-
zotriazole (HOBt), was used. Conversion of enoylsilane 2 (5
equiv to the resin) to the corresponding dienolate was effected
by treatment with KCN (5.25 equiv) in DMF at room temper-
ature for 30 min. Then, reaction of the peptidyl resin with the
resulting mixture in the presence of HOBt was performed under
microwave irradiation conditions (12 min at 100 °C, measured
by the internal infrared sensor of the microwave apparatus).25
The attempted reaction proceeded smoothly in 12 min to yield
the protected resin corresponding to N/OFQ (1-13) analogue
20.DeprotectionofthecompletedresinwithTFA-thioanisole-m-
cresol-EDT-H2O (80:5:5:5:5, v/v) at room temperature for 1 h
gave crude deprotected (Phe1Ψ(CFdCH)Gly2)N/OFQ(1-13)-
NH2 20. HPLC analysis of crude peptides indicated that the
straightforward incorporation of the FADI unit was efficiently
achieved (Figure 3). HPLC purified N/OFQ analogue 20 was
subjected to the ligand-receptor competitive binding assay using
COS-7 cells expressing the human ORL1 receptor.26 Compared
with reference analogue 18, peptide 20 exhibited a 10-fold high
binding affinity (18, IC50 32.2 nM vs 20, 3.34 nM) although
the affinity was less than that of nociceptin itself (0.73 nM).
In conclusion, synthesis of amide-type FADIs (AM-FADIs)
from the enoylsilanes was accomplished by the intramolecular
redox reaction mediated by the cyanide anion in the presence
of a wide variety of amines. This redox type amidation protocol
was successfully applied to the synthesis of chiral auxiliary-
incorporated FADIs, which was then used for stereoselective
incorporation of R-substituent. Straightforward incorporation of
FADIs into peptidyl resin was also accomplished by reductive
amidation protocols under microwave irradiation conditions.
Experimental Section
FIGURE 3. Synthesis of N/OFQ analogue 20 and HPLC examination
of the straightforward incorporation of FADI into peptidyl resin.
Benzyl (5R,3Z)-5-[N-(tert-Butoxycarbonyl)amino]-4-fluoro-6-me-
thylhept-3-eneamide (5a) from 1 (Table 1, entries 1-5). To a
solution of KCN (7.8 mg, 0.12 mmol) and 18-crown-6 (32 mg,
0.12 mmol) in solvent (entry 1, Et2O, 1.0 mL; entry 2, THF, 1.0
mL; entry 3, Et2O, 0.5 mL; entry 4, THF, 0.5 mL) was added
substrate 1 (45 mg, 0.11 mmol) in solvent (entry 1, Et2O, 1.0 mL;
entry 2, THF, 1.0 mL; entry 3, Et2O, 0.5 mL; entry 4, THF, 0.5
mL) at 0 °C with additional stirring at this temperature for 1-2 h.
After complete consumption of starting material 1, benzylamine
(13 µL, 0.12 mmol for entries 1 and 2 or 48 µL, 0.57 mmol for
entries 3 and 4) was added to the reaction mixture at 0 °C. After
being stirred at 0 °C for the period indicated in Table 1, the reaction
was quenched by the addition of saturated NaHCO3(aq) and
extracted with Et2O. The extract was washed with 1 M HCl,
saturated NaHCO3(aq), and brine and dried over MgSO4. Concen-
tration under reduced pressure followed by column chromatography
on silica gel with EtOAc-n-hexane (1:4) gave the title compound
5a and its (E)-isomer (entry 1) or their mixture (entries 2-4). Entry
1: (Z):(E) ) 92:8 (88:12) in 82% combined yield (ratio in
parenthesis indicates the (Z)/(E) ratio of isolated materials). Entry
2: (Z):(E) ) 95:5 in 73% combined yield. Entry 3: (Z):(E) ) 93:7
in 89% combined yield. Entry 4: (Z):(E) ) 95:5 in 85% combined
yield.
(24) Guerrini, R.; Calo, G.; Rizzi, A.; Bigoni, R.; Bianchi, C.; Salvadori, S.;
Regoli, D. Br. J. Pharmacol. 1998, 123, 163–165.
(25) For a recent review on microwave irradiation, see: Kappe, C. O. Chem.
Soc. ReV. 2008, 37, 1127–1139.
(26) Li, J.; Isozaki, K.; Okada, K.; Matsushima, A.; Nose, T.; Costa, T.;
Shimohigashi, Y. Bioorg. Med. Chem. 2008, 16, 2635–2644.
For entry 5, 2 equiv of n-Bu4NCN were used for the cyanide
ion source for 30 min at -78 °C. Then, at -78 °C, a procedure
similar to that described above was applied for the preparation of
5a.
3282 J. Org. Chem. Vol. 74, No. 9, 2009

Synthesis of AM-FADIs
5a: white powder, mp 116-117 °C. [R]2D6 + 1.1 (c 1.24, CHCl3).
1H NMR (400 MHz, CDCl3, δ): 0.94 (d, J ) 6.8 Hz, 3H), 0.95 (d,
J ) 6.8 Hz, 3H), 1.38 (s, 9H), 1.89 (sext, J ) 6.8 Hz, 1H), 3.03
(dd, J ) 7.8 and 16.6 Hz, 1H), 3.15 (dd, J ) 7.8 and 16.6 Hz,
1H), 3.86 (dt, J ) 7.8 and 20.8 Hz, 1H), 4.41 (dd, J ) 5.8 and
14.8 Hz, 1H), 4.46 (dd, J ) 5.8 and 14.8 Hz, 1H), 4.69 (d, J ) 6.4
Hz, 1H), 4.99 (dt, J ) 7.8 and 36.4 Hz, 1H), 6.42 (br s, 1H),
7.23-7.33 (m, 5H). 13C NMR (75 MHz, CDCl3, δ): 18.3, 19.2,
28.1, 29.6, 31.2 (d, 5.0 Hz), 43.4, 57.8 (d, J ) 27.8 Hz), 79.7,
100.3 (d, J ) 13.6 Hz), 127.2, 127.5, 128.4, 138.2, 155.3, 159.6
(d, J ) 260.3 Hz), 170.0. HRMS (ESI), m/z: (M + Na+) calcd for
C20H29FN2NaO3, 387.2060; found, 387.2053. Anal. Calcd for
C20H29FN2O3: C, 65.91; H, 8.02; N, 7.69. Found: C, 65.94; H, 8.12;
N, 7.58.
and 20.0 Hz, 1H), 4.53 (dd, J ) 5.2 and 8.4 Hz, 1H), 4.74 (d, J )
8.2 Hz, 1H), 5.02 (dt, J ) 7.6 and 36.4 Hz, 1H), 6.15 (br d, J )
7.6 Hz, 1H). 13C NMR (75 MHz, CDCl3, δ): 17.8, 18.2, 18.8, 19.3,
28.3, 29.6, 31.1, 31.3 (d, J ) 5.0 Hz), 52.0, 57.1, 57.3 (d, J ) 27.8
Hz), 79.8, 99.8 (d, J ) 13.6 Hz), 155.2, 160.1 (d, J ) 259.7 Hz),
169.9, 170.3. HRMS (ESI), m/z: (M
+
Na+) calcd for
C19H33FN2NaO5, 411.2271; found, 411.2263. Anal. Calcd for
C19H33FN2O5: C, 58.74; H, 8.56; N, 7.21. Found: C, 58.44; H, 8.45;
N, 6.97.
(E)-isomer of 5c: colorless oil. 1H NMR (400 MHz, CDCl3, δ):
0.95 (d, J ) 6.8 Hz, 6H), 1.04 (d, J ) 6.4 Hz, 6H), 1.43 (s, 9H),
1.85 (dsext, J ) 6.4 and 8.8 Hz, 1H), 2.18 (sext, J ) 6.8 Hz, 1H),
2.94 (ddd, J ) 3.0, 6.0, and 15.4 Hz, 2H), 3.22 (dd, J ) 10.4 and
15.4 Hz, 3H), 3.70 (s, 3H), 4.08 (dt, J ) 8.6 and 30.0 Hz, 1H),
4.49 (dd, J ) 5.6 and 8.8 Hz, 1H), 4.79 (d, J ) 8.6 Hz, 1H), 5.35
(ddd, J ) 6.0, 10.4, and 20.4 Hz, 1H), 6.79 (d, J ) 8.0 Hz, 1H).
Entry 8: Boc-D-Val-Ψ[(Z)CF)CH]-Gly-Pro-OEt (5d), (E)-
isomer of 5d ) 96:4, 84% combined yield.
(E)-isomer of 5a: colorless oil. 1H NMR (400 MHz, CDCl3, δ):
0.93 (d, J ) 6.8 Hz, 3H), 1.03 (d, J ) 6.8 Hz, 3H), 1.30 (s, 9H),
1.83 (dsext, J ) 6.8 and 9.0 Hz, 1H), 2.87 (dt, J ) 4.4 and 14.0
Hz, 1H), 3.22 (ddd, J ) 2.4, 12.0, and 14.0 Hz, 1H), 4.06 (dt, J )
9.0 and 29.6 Hz, 1H), 4.33 (dd, J ) 6.0 and 15.2 Hz, 1H), 4.48
(dd, J ) 6.0 and 15.2 Hz, 1H), 4.79 (d, J ) 8.0 Hz, 1H), 5.40
(ddd, J ) 5.2, 12.0, and 20.4 Hz, 1H), 7.21-7.32 (m, 5H), 7.48
(br s, 1H).
General Procedure for the Synthesis of Tripeptide Mimetics
(Table 1, entries 6-12). To a solution of KCN (7.8 mg, 0.12 mmol)
and 18-crown-6 (32 mg, 0.12 mmol) in solvent (0.5 mL of Et2O,
THF, or DMF in the absence of 18-crown-6) was added enoylsilane
1 or 2 (0.11 mmol) at 0 °C with additional stirring at this
temperature until complete consumption of the starting material.
To the reaction mixture was added a mixture of amino ester
hydrochloride (0.57 mmol) and triethylamine (79 µL, 0.57 mmol)
in solvent (0.5 mL of Et2O, THF, or DMF) at 0 °C. After being
stirring at this temperature for the period indicated in Table 1, the
reaction was quenched by the addition of NaHCO3(aq) and extracted
with Et2O. The resulting organic layer was washed with 1 M HCl,
saturated NaHCO3(aq), and brine and dried over MgSO4. Conden-
sation under reduced pressure followed by column chromatography
over silica gel with EtOAc-n-hexane (1:2) gave pure (Z)- and (E)-
isomers of FADI-containing tripeptide mimetics or pure (Z)-isomer
and (Z)/(E)-mixture.
1
5d: colorless oil. [R]D26 - 21.9 (c 3.09, CHCl3). H NMR (400
MHz, CDCl3, δ): 0.93 (d, J ) 6.8 Hz, 3H), 0.95 (d, J ) 6.8 Hz,
3H), 1.44 (s, 9H), 1.90-2.21 (m, 5H), 2.92 (dd, J ) 6.0 and 17.2
Hz, 1H, minor rotamer), 3.07-3.16 (m, 1H), 3.22 (dd, J ) 7.0 and
17.2 Hz, 1H), 3.49-3.59 (m, 1H), 3.61-3.68 (br, 1H), 3.72 (s,
3H, major rotamer), 3.76 (s, 3H, minor rotamer), 4.03 (hept, J )
9.2 Hz, 1H), 4.44 (dd, J ) 2.6 and 8.6 Hz, 1H, minor rotamer),
4.49 (dd, J ) 2.8 and 8.6 Hz, 1H, major rotamer), 4.70 (d, J ) 9.2
Hz, 1H), 5.09 (dt, J ) 37.6 and 7.0 Hz, 1H). 13C NMR (75 MHz,
CDCl3, δ, rotamer): 17.9, 19.2, 22.5, 24.7, 28.3, 29.2, 29.7 (d, J )
3.7 Hz), 29.7 (d, J ) 4.4 Hz), 30.1, 46.5, 46.9, 52.2 (major rotamer),
52.6, 57.0 (d, J ) 29.0 Hz), 58.7, 59.3, 79.6, 99.7 (d, J ) 13.7
Hz), 155.2, 158.7 (d, J ) 257.8 Hz), 169.0, 172.5, 172.7. HRMS
(ESI), m/z: (M + Na+) calcd for C19H31FN2NaO5, 409.2115; found,
409.2115.
(E)-isomer of 5d: colorless oil. 1H NMR (400 MHz, CDCl3, δ):
0.93 (d, J ) 6.8, 3H), 0.99 (d, J ) 6.8 Hz, 3H), 1.44 (s, 9H),
1.82-2.21 (m, 5H), 2.90 (dd, J ) 6.8 and 16.8 Hz, 1H, minor
rotamer), 3.07-3.16 (m, 2H), 3.53 (m, 1H), 3.68 (br s, 1H),
3.61-3.68 (br, 1H), 3.72 (s, 3H, major rotamer), 3.78 (s, 3H, minor
rotamer), 4.15 (dt, J ) 9.2 and 30.0 Hz, 1H), 4.48 (dd, J ) 3.2
and 8.4 Hz, 1H), 4.85 (d, J ) 9.2 Hz, 1H), 5.44 (dt, J ) 6.8 and
21.2 Hz, 1H).
Entry 5: Boc-D-Val-Ψ[(Z)CFdCH]-Gly-Gly-OEt (5b), (E)-
isomer of 5b ) 92:8, 62% combined yield.
5b: white powder, mp 89-90 °C. [R]2D6 + 14.9 (c 1.02, CHCl3).
1H NMR (400 MHz, CDCl3, δ): 0.97 (d, J ) 6.8 Hz, 6H), 1.28 (t,
J ) 7.2 Hz, 3H), 1.44 (s, 9H), 1.92 (sext, J ) 6.8 Hz, 1H), 3.06
(dd, J ) 7.8 and 16.6 Hz, 1H), 3.14 (dd, J ) 7.8 and 16.6 Hz,
1H), 3.92 (dt, J ) 7.8 and 20.4 Hz, 1H), 4.00 (d, J ) 5.2 Hz, 2H),
4.20 (q, J ) 7.2 Hz, 2H), 4.76 (d, J ) 7.8 Hz, 1H), 5.01 (dt, J )
7.8 and 36.4 Hz, 1H), 6.49 (br s, 1H). 13C NMR (75 MHz, CDCl3,
δ): 14.0, 18.3, 19.2, 28.2, 29.7, 30.9 (d, 5.0 Hz), 41.3, 57.7 (d, J )
27.2 Hz), 61.3, 79.7, 99.9 (d, J ) 13.0 Hz), 155.3, 159.8 (d, J )
260.3 Hz), 169.6, 170.3. HRMS (ESI), m/z: (M + Na+) calcd for
C17H29FN2NaO5, 383.1958; found, 383.1963. Anal. Calcd for
C17H29FN2O5: C, 56.65; H, 8.11; N, 7.77. Found: C, 56.42; H, 8.05;
N, 7.74.
Entry 9: Boc-L-Phe-Ψ[(Z)CFdCH]-Gly-Gly-OEt (6b), (E)-
isomer of 6b ) 95:5, 93% combined yield.
6b: white powder, mp 64-65 °C. [R]2D2 + 6.3 (c 1.04, CHCl3).
1H NMR (400 MHz, CDCl3, δ): 1.28 (t, J ) 7.0 Hz, 3H), 1.40 (s,
9H), 2.96 (d, J ) 7.2 Hz, 2H), 3.03 (d, J ) 7.6 Hz, 2H), 3.90 (d,
J ) 5.6 Hz, 1H), 4.20 (q, J ) 7.0 Hz, 2H), 4.43 (m, 1H), 4.79 (m,
1H), 4.86 (dt, J ) 7.6 and 35.6 Hz, 1H), 6.06 (br s, 1H), 7.18-7.31
(m, 5H). 13C NMR (75 MHz, CDCl3, δ): 14.1, 28.2, 31.0, 38.1,
41.3, 53.1 (d, J ) 29.1 Hz), 61.4, 80.1, 100.2 (d, J ) 13.0 Hz),
126.8, 128.6, 129.2, 136.4, 154.8, 159.4 (d, J ) 259.6 Hz), 169.6,
170.0. HRMS (ESI), m/z: (M + Na+) calcd for C21H29FN2NaO5,
431.1958; found, 431.1974.
(E)-isomer of 6b: colorless oil. 1H NMR (400 MHz, CDCl3, δ):
1.26 (t, J ) 7.0 Hz, 3H), 1.42 (s, 9H), 2.51 (dd, J ) 4.4 and 15.2
Hz, 1H), 2.82-2.99 (m, 3H), 3.80 (dd, J ) 5.2 and 17.6 Hz, 1H),
3.90 (dd, J ) 5.6 and 17.6 Hz, 1H), 4.17 (q, J ) 7.0 Hz, 2H), 4.66
(m, 1H), 4.79 (br d, J ) 7.2 Hz, 1H), 5.24 (ddd, J ) 6.8, 10.0, and
20.0 Hz, 1H), 6.84 (br s, 1H), 7.20-7.31 (m, 5H).
Entry 10: Boc-L-Phe-Ψ[(Z)CFdCH]-Gly-Val-OMe (6c), (E)-
isomer of 6c ) 94:6 (determined by NMR measurement of the
crude materials), 88% combined yield.
(E)-isomer of 5b: colorless oil. 1H NMR (400 MHz, CDCl3, δ):
0.95 (d, J ) 6.8 Hz, 3H), 1.04 (d, J ) 6.8 Hz), 1.27 (t, J ) 7.2
Hz), 1.45 (s, 9H), 1.85 (dsext, J ) 6.8 and 8.8 Hz, 1H), 2.89 (ddd,
J ) 4.0, 6.0, and 14.4 Hz, 1H), 3.22 (ddd, J ) 2.0, 11.4, and 14.4
Hz, 1H), 3.96 (dd, J ) 6.0 and 9.2 Hz, 2H), 3.89-4.24 (m, 1H),
4.8 (q, J ) 7.2 Hz, 2H), 4.83 (d, J ) 8.4 Hz, 1H), 4.38 (ddd, J )
6.0, 11.4, and 20.8 Hz, 1H), 7.39 (br s, 1H).
Entry 6: 5b, (E)-isomer of 5b ) 94:6, 93% combined yield.
Entry 7: Boc-D-Val-Ψ[(Z)CFdCH]-Gly-Val-OMe (5c), (E)-
isomer of 5c ) 94:6, 90% combined yield.
6c: white powder, mp 118-120 °C. [R]2D6 + 13.9 (c 1.04, CHCl3).
1H NMR (400 MHz, CDCl3, δ): 0.89 (d, J ) 6.8 Hz, 3H), 0.92 (d,
J ) 6.8 Hz, 3H), 1.38 (s, 9H), 2.14 (dsept, J ) 5.6 and 6.8 Hz,
1H), 2.88-3.11 (m,, 4H), 3.73 (s, 3H), 4.48-4.51 (m, 1H), 4.50
(dd, J ) 5.6 and 8.8 Hz, 1H), 4.71 (br s, 1 H), 4.93 (dt, J ) 7.2
and 36.4 Hz, 1H), 6.09 (br s, 1H), 7.17-7.31 (m, 5H). 13C NMR
(75 MHz, CDCl3, δ): 17.9, 18.9, 28.2, 31.1, 31.3 (d, J ) 4.7 Hz),
5c: white powder, mp 97-99 °C. [R]2D6 + 35.8 (c 1.05, CHCl3).
1H NMR (400 MHz, CDCl3, δ): 0.90 (d, J ) 6.8 Hz, 3H), 0.93 (d,
J ) 6.8 Hz, 3H), 0.96 (d, J ) 6.8 Hz, 3H), 0.97 (d, J ) 6.8 Hz,
3H), 1.44 (s, 9H), 1.93 (sext, J ) 6.8 Hz, 1H), 2.16 (sext, J ) 6.8
Hz, 1H), 3.09 (d, J ) 7.6 Hz, 2H), 3.73 (s, 3H), 3.98 (dt, J ) 8.2
J. Org. Chem. Vol. 74, No. 9, 2009 3283

Yamaki et al.
38.4, 52.1, 52.7 (d, J ) 31.5 Hz), 57.2, 80.0, 99.8 (d, J ) 13.1
Hz), 126.9, 128. 5, 129.2, 136.3, 154.7, 159.6 (d, J ) 259.0 Hz),
1H), 3.80 (dd, J ) 6.8 and 18.0 Hz, 1H), 4.04 (dt, J ) 9.0 and
21.2 Hz, 1H), 4.17-4.24 (m, 2H), 4.67 (m, 1H), 4.75 (d, J ) 9.0
Hz, 1H), 5.10 (dt, J ) 6.8 and 36.8 Hz, 1H), 7.19-7.36 (m, 5H).
13C NMR (75 MHz, CDCl3, δ): 18.2, 19.3, 28.3, 30.9 (d, 5.0 Hz),
37.7, 55.1, 57.3 (d, J ) 27.2 Hz), 66.3, 79.7, 98.5 (d, J ) 13.0
Hz), 127.3, 128.9, 129.4, 135.1, 153.3, 155.2, 159.4 (d, J ) 260.1
169.7, 172.3. HRMS (ESI), m/z: (M
C23H33FN2NaO5, 459.2271; found, 459.2252.
+
Na+) calcd for
(E)-isomer of 6c: colorless oil. 1H NMR (400 MHz, CDCl3, δ):
0.89 (d, J ) 6.8 Hz, 3H), 0.92 (d, J ) 6.8 Hz, 3H), 1.42 (s, 9H),
2.13 (sept, J ) 6.0 Hz, 1H), 2.86-3.11 (m, 4H), 3.68 (s, 3H), 4.42
(dd, J ) 5.6 and 8.8 Hz, 1H), 4.51-4.67 (m, 1H), 4.71 (br d, J )
6.4 Hz, 1H), 5.22 (ddd, J ) 5.6, 10.7, and 20.0 Hz, 1H), 6.66 (br
d, J ) 8.8 Hz 1H), 7.17-7.31 (m, 5H).
Hz), 170.3. HRMS (ESI), m/z: (M
C23H31FN2NaO5, 457.2115; found, 457.2109.
+
Na+) calcd for
(1R,5′R,3′Z)-5′-{[N-(tert-Butoxycarbonyl)amino]-4′-fluoro-6′-me-
thylhept-3′-enoyl}bornane-10,2-sultam (15b; Table 2, entry 10). To
a mixture of KCN (1.0 mg, 0.015 mmol), 18-crown-6 (4.0 mg,
0.015 mmol), and 1 (59 mg, 0.15 mmol) in THF (0.5 mL) was
added a solution of (1R)-bornane-10,2-sultam (34 mg, 0.16 mmol)
and DMAP (20 mg, 0.17 mmol) in THF (0.5 mL) at 0 °C under
argon atmosphere. The reaction was stirred at 40 °C for 2 h and
then quenched with saturated NaHCO3(aq). The mixture was
extracted with Et2O, and the resulting extract was washed with
brine. After being dried over MgSO4, the extract was condensed
under reduced pressure to give residues. Column chromatographical
purification over silica gel with EtOAc-n-hexane (1:4) gave the
title compound 15b as white powder (67.1 mg, 95%): mp 57-60
°C. [R]2D1 + 95.9 (c 1.05, CHCl3). 1H NMR (400 MHz, CDCl3, δ):
0.94 (d, J ) 6.8 Hz, 3H), 0.95 (d, J ) 6.8 Hz, 3H), 0.97 (s, 3H),
1.15 (s, 3H), 1.28-1.44 (m, 2H), 1.44 (s, 9H), 1.87-1.92 (m, 4H),
2.03- 2.12 (m, 2H), 3.44 (d, J ) 14.0 Hz, 1H), 3.49-3.56 (m,
2H), 3.62 (dd, J ) 6.8 and 18.4 Hz, 1H), 3.86 (dd, J ) 5.2 and 7.2
Hz, 1H), 3.99 (dt, J ) 8.8 and 20.4 Hz, 1H), 4.72 (d, J ) 8.8 Hz,
1H), 5.04 (dt, J ) 6.8 and 36.8 Hz, 1H). 13C NMR (75 MHz, CDCl3,
δ): 18.2, 19.3, 19.8, 20.8, 26.4, 28.3, 30.3, 30.5 (d, J ) 5.0 Hz),
32.8, 38.3, 44.6, 47.8, 48.5, 52.8, 57.1, 57.2 (d, J ) 25.4 Hz), 65.3,
79.6, 98.4 (d, J ) 12.4 Hz), 155.2, 159.3 (d, J ) 260.3 Hz), 169.0.
HRMS (ESI), m/z: (M + Na+) calcd for C23H37FN2NaO5S,
495.2305; found, 495.2298.
Entry 11: Boc-L-Phe-Ψ[(Z)CFdCH]-Gly-Pro-OMe (6d), (E)-
isomer of 6d ) 95:5 (determined by NMR measurement of the
crude materials), 88% combined yield.
1
6d: colorless oil. [R]D26 - 33.0 (c 1.07, CHCl3). H NMR (400
MHz, CDCl3, δ): 1.37 (s, 9H), 1.97-2.19 (m, 5H), 2.88 (m, 1H),
2.99 (dd, J ) 6.4 and 14.4 Hz, 1H), 3.07 (dd, J ) 6.2 and 16.4 Hz,
1H), 3.19 (dd, J ) 7.6 and 17.2 Hz, 1H), 3.42-3.49 (m, 1H),
3.56-3.60 (m, 1H), 3.72 (s, 3H, major rotamer), 3.77 (s, 3H, minor
rotamer), 4.37 (dd, J ) 3.0 and 8.4 Hz, 1H, minor rotamer), 4.45
(dd, J ) 3.6 and 8.4 Hz, 1H, major rotamer), 4.65 (br, 1H), 5.03
(dt, J ) 6.4 and 37.6 Hz, 1H). 13C NMR (75 MHz, CDCl3, δ,
rotamer): 22.5, 24.7, 28.2, 29.2, 29.7, 29.7 (d, J ) 4.4 Hz), 31.5,
38.6, 46.5, 46.9, 52.2, 52.6, 58.7, 59.3, 79.8, 99.7 (d, J ) 11.8
Hz), 126.7, 128.4, 129.3, 136.6, 154.7, 158.5 (d, J ) 256.5 Hz),
168.8, 172.3. HRMS (ESI), m/z: (M
+
Na+) calcd for
C23H31FN2NaO5, 457.2115; found, 457.2131.
(E)-isomer of 6d: Characteristic signal for (E)-isomer. 1H NMR
(400 MHz, CDCl3 δ): 5.36 (dt, J ) 20.8 and 7.2 Hz, 1H).
Entry 12: 5b, (E)-isomer of 5b ) 95:5 (determined by NMR
measurement of the crude materials); 100% combined yield.
O-Allylated Diene 14. Conversion of enoylsilane 1 to dienolate
12 was performed by the procedure described above. To the
resulting mixture was added ally bromide (5.0 equiv) with stirring
at 0 °C for 2 h. Then benzyl amine (5.0 equiv) was added to the
mixture. After 2 h reaction at 0 °C, usual workup procedures were
applied to the isolation of the products (89% isolated yield).
Obtained products were proven to be a mixture of diastereomers
at the diene part of the O-allylated diene by NMR measurement.
Compound 14: colorless oil. 1H NMR (400 MHz, CDCl3, δ): 0.95
(d, J ) 6.8 Hz, 6H), 1.45 (s, 9H, major isomer), 1.46 (s, 9H, minor
isomer), 1.94 (sept, J ) 6.8 Hz, 1H), 3.85 (br s, 1H, minor isomer),
4.03 (dt, J ) 20.2 and 8.8 Hz, 1H), 4.41 (d, J ) 5.2 Hz, 1H, minor
isomer), 4.51 (d, J ) 5.6 Hz, 1H, major isomer), 4.73 (br d, J )
8.8 Hz, 1H), 5.04 (d, J ) 10.0 Hz, 1H, minor isomer), 5.11 (d, J
) 17.2 Hz, 1H, minor isomer), 5.33 (d, J ) 10.0 Hz, 1H, major
isomer), 5.40 (d, J ) 17.2 Hz, 1H, major isomer), 5.69 (dd, J )
12.0 and 33.2 Hz, 1H, minor isomer), 5.80-5.96 (m, 2H), 6.27 (d,
J ) 11.2 Hz, 1H, major isomer), 6.43 (d, J ) 11.2 Hz, 1H, minor
isomer). 13C NMR (75 MHz, CDCl3, δ): 19.0, 19.3, 28.3, 30.3,
57.5 (d, J ) 24.8 Hz), 71.1, 72.1, 80.0, 100.4 (d, J ) 9.9 Hz),
114.6, 116.2 (d, J ) 6.2 Hz), 119.4, 119.8, 126.8 (d, J ) 5.6 Hz),
131.3, 131.7, 155.1, 161.2 (d, J ) 273.8 Hz). HRMS (ESI), m/z:
(M + H+) calcd for C17H26FN2O3, 325.1927; found, 325.1927.
(4R,5′R,3′Z)-5′-{[N-(tert-Butoxycarbonyl)amino]-4′-fluoro-6′-me-
thylhept-3′-enoyl}-4-benzyl-2-oxazolidinone (15a; Table 2, entry
8). To a mixture of KCN (2.0 mg, 0.030 mmol), 18-crown-6 (8.0
mg, 0.030 mmol), and 1 (117 mg, 0.300 mmol) in THF (0.5 mL)
was added a solution of (4R)-benzyl-2-oxazolidinone (266 mg, 1.50
mmol) and DMAP (40 mg, 0.33 mmol) in THF (0.5 mL) at 0 °C
under argon. After being stirred at 40 °C for 11 h, the reaction was
quenched by the addition of saturated NaHCO3(aq) and extracted
with Et2O. The extract was washed with brine and dried over
MgSO4. Removal of solvent under reduced pressure followed by
column chromatography over silica gel with EtOAc-n-hexane (1:
4) gave the title compound 15a as white powder: mp 97-100 °C.
[R]2D1 - 23.0 (c 1.19, CHCl3). 1H NMR (400 MHz, CDCl3, δ): 0.95
(d, J ) 6.4 Hz, 3H), 0.98 (d, J ) 6.8 Hz, 3H), 1.45 (s, 9H), 1.93
(sext, J ) 6.8 Hz, 1H), 2.78 (dd, J ) 9.6 and 13.6 Hz, 1H), 3.30
(dd, J ) 3.0 and 13.6 Hz, 1H), 3.74 (dd, J ) 6.8 and 18.0 Hz,
(1R,5′R,2′S,3′Z)-{5′-[N-(tert-Butoxycarbonyl)amino]-4′-fluoro-6′-
methylhept-2′-(prop-2′′-enyl)-3′-enoyl}bornane-10,2-sultam (17a).
To a suspension of CuI (66 mg, 0.35 mmol) in THF (1.0 mL) was
added dropwise a solution of MeLi ·LiBr complex in Et2O (1.5 M,
0.46 mL, 0.69 mmol) at -78 °C under argon, and the mixture was
stirred for 10 min at 0 °C. To the resulting organocopper reagent
was added dropwise a solution of the N-enoyl sultam 15b (40 mg,
0.085 mmol) in THF (1.5 mL) at -78 °C. The mixture was stirred
for 30 min at -78 °C, and HMPA (24 µL, 1.4 mmol) was added
dropwise to the mixture. After stirring for 30 min at -78 °C, a
solution of triphenyltin chloride (67 mg, 0.17 mmol) in THF (1.5
mL) was added dropwise; the mixture was then stirred for 30 min
at -40 °C, and allyl bromide (59 µL, 0.70 mmol) was added
dropwise. The mixture was stirred for 20 h at -40 °C. The reaction
was quenched at -40 °C by addition of a 1:1 saturated NH4Cl,
28% NH4OH solution with additional stirring at room temperature
for 30 min. The mixture was extracted with Et2O, and the extract
was washed with brine and dried over MgSO4. Concentration under
reduced pressure followed by column chromatography over silica
gel with EtOAc-n-hexane (1:5) gave the title compound 17a (37
1
mg, 84%) as colorless oil. [R]2D0 73.47 (c 1.11, CHCl3). H NMR
(400 MHz, CDCl3, δ): 0.92 (d, J ) 6.4 Hz, 3H), 0.93 (d, J ) 6.4
Hz, 3H), 0.97 (s, 3H), 1.16 (s, 3H), 1.24-1.40 (m, 2H), 1.44 (s,
9H), 1.85-1.91 (m, 4H), 2.03-2.08 (m, 2H), 2.36 (m, 1H), 2.53
(m, 1H), 3.43 (d, J ) 13.6 Hz, 1H), 3.50 (d, J ) 13.6 Hz, 1H),
3.87-3.97 (m, 2H), 4.21 (dt, J ) 7.0 and 8.0 Hz, 1H), 4.71 (d, J
) 9.2 Hz, 1H), 4.90-5.02 (m, 1H), 5.01 (d, J ) 9.2 Hz, 1H), 5.07
(d, J ) 17.2 Hz, 1H), 5.71-5.81 (m, 1H). 13C NMR (75 MHz,
CDCl3, δ): 18.6, 19.3, 19.9, 20.8, 26.4, 28.3, 30.3, 32.8, 38.3, 38.6,
40.7, 44.6, 47.7, 48.3, 53.1, 57.6 (d, J ) 25.4 Hz), 65.2, 79.6, 104.1
(d, J ) 11.8 Hz), 117.8, 134.0, 155.1, 158.0 (d, J ) 260.3 Hz),
172.5. HRMS (ESI), m/z: (M + Na+) calcd for C26H41FN2NaO5S,
535.2618; found, 535.2611.
(1R,2′S,5′R,3′Z)-{2′-Benzyl-5′-[N-(tert-butoxycarbonyl)amino]-4′-
fluoro-6′-methylhept-3′-enoyl}bornane-10,2-sultam (17b). Experi-
mental procedures identical to those used for the preparation of
3284 J. Org. Chem. Vol. 74, No. 9, 2009

Synthesis of AM-FADIs
17a were employed. Forty milligrams (0.085 mmol) of 15b was
converted to the title compound 17b (38 mg, 79%) as a colorless
(25 µL), and H2O (25 µL) at room temperature for 2 h. After
removal of resin by filtration, ice-cold dry Et2O was added to the
residue. The resulting powder was collected by centrifugation and
then washed three times with ice-cold dry Et2O. The crude peptide
was dissolved in 0.1% TFA(aq) solution (400 µL) and analyzed
by HPLC. Analytical HPLC condition: linear gradient of solvent
B in solvent A, 2-40% over 30 min. Retention time ) 17.9 min.
MS (ESI-IT): (M + 2H+) calcd for C62H104FN21O14, 691.9; found,
692.0. As reference peptides in HPLC analysis, N/OFQ(3-13)-
NH2 was obtained after deprotection identical to those employed
for peptide 20.
1
oil. [R]2D1 67.3 (c 1.14, CHCl3). H NMR (400 MHz, CDCl3, δ):
0.71 (s, 1H), 0.86-0.90 (m, 6H), 0.88 (s, 3H), 1.25-1.36 (m, 2H),
1.45 (s, 9H), 1.74-1.85 (m, 5H), 1.93-1.98 (m, 1H), 2.79 (dd, J
) 7.2 and 13.2 Hz, 1H), 3.11 (dd, J ) 8.0 and 13.2 Hz, 1H), 3.36
(d, J ) 14.0 Hz, 1H), 3.41 (d, J ) 14.0 Hz, 1H), 3.78 (br, 1H),
3.90 (dt, J ) 9.0 and 24.0 Hz, 1H), 4.45 (dt, J ) 8.4 and 7.2 Hz,
1H), 4.64 (d, J ) 9.0 Hz, 1H), 4.97 (dd, J ) 9.2 and 36.0 Hz, 1H),
7.14-7.26 (m, 5H). 13C NMR (75 MHz, CDCl3, δ): 18.5, 19.1,
19.8, 20.5, 26.4, 28.3, 30.4, 32.7, 38.2, 40.4, 43.0 (d, J ) 3.1 Hz),
44.6, 47.6, 48.1, 53.0, 57.6 (d, J ) 26.0 Hz), 65.0, 79.5, 104.3 (d,
J ) 12.4 Hz), 127.1, 128.2, 129.5, 137.5, 155.1, 158.2 (d, J )
259.8 Hz), 172.3. HRMS (ESI), m/z: (M + Na+) calcd for
C30H43FN2NaO5S, 585.2761; found, 585.2774.
N/OFQ(3-13)-NH2. Analytical HPLC condition: linear gradient
of solvent B in solvent A, 2-40% over 30 min. Retention time )
11.9 min. MS (ESI-IT): (M + 2H+) calcd for C50H90N20O13, 589.4;
found, 589.5.
Synthesis of Protected Peptide Resin [N/OFQ(3-13)-NH2]
(19). Protected peptide resin was manually constructed by Fmoc-
based solid-phase synthesis. Fmoc deprotection was achieved by
20% piperidine in DMF (10 min). Fmoc-amino acids were coupled
by treatment with 3 equiv of reagents [Fmoc-amino acid, diiso-
propylcarbodiimide (DIPCDI), and HOBt ·H2O] to free amino
groups on the resin in DMF for 2 h.
Receptor-Binding Assay. The receptor-binding assay with cell
membranes was conducted in a 96-well format according to
literature.26 The receptor-binding potencies of synthetic peptides
were assessed by the radio-ligand ([3H]nociceptin) receptor-binding
assay using COS-7 cell membrane preparations expressing human
ORL1-Ga fusion receptors. The binding potency of each peptide
was estimated as the IC50 value, the peptide concentration at which
the half-maximal inhibition is achieved.
[Phe1-Ψ(CFdCH)-Gly2]Nociceptin(1-13)-NH2 (20). After pre-
activation of acylsilane 2 (10.6 mg, 0.021 mmol) with KCN (1.60
mg, 0.022 mmol) in DMF (0.10 mL) for 30 min, the protected
peptide resin 19 (51.0 mg, 4.25 µmol) in a microwave vial (0.2-0.5
mL) was treated with the resulting activated species and HOBt ·H2O
(3.2 mg, 0.02 mmol) in DMF (0.10 mL). The vial was equipped
with a magnetic stir bar and capped with a rubber septum. The
above mixture was shaken vigorously and then heated in the
microwave for 12 min at 100 °C (as measured by the IR sensor of
the microwave apparatus). Then the vessel was cooled, and the
resin was washed with DMF and CH2Cl2. The resulting protected
peptidyl resin (10 mg) was treated with thioanisole (25 µL)-TFA
(400 µL) in the presence of m-cresol (25 µL), 1,2-ethanedithiol
Acknowledgment. This research was supported in part by a
Grant-in-Aid for Scientific Research (KAKENHI). A.S. is
grateful for research grants from the Takeda Science Foundation.
Supporting Information Available: Copies of 1H NMR and
13C NMR spectra of compounds 5a, 5b, 5c, 5d, 6b, 6c, 6d, 14,
15a, 15b, 17a, and 17b. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO900135T
J. Org. Chem. Vol. 74, No. 9, 2009 3285