Incorporation of fluoroprolines to proctolin: Study on the effect of a fluorine atom toward peptidic conformation

Article abstract of DOI:10.1016/j.jfluchem.2007.12.005

In spite of quite small steric perturbation, substitution of proline (Pro) in the target pentapeptide proctolin (Arg-Tyr-Leu-Pro-Thr) for (4R)- as well as (4S)-4-fluoroproline led to apparent alteration of the pyrrolidine ring structure which eventually r

Full text of DOI:10.1016/j.jfluchem.2007.12.005

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Journal of Fluorine Chemistry 129 (2008) 286–293
www.elsevier.com/locate/fluor
Incorporation of fluoroprolines to proctolin: Study on the
effect of a fluorine atom toward peptidic conformation
Takamasa Kitamoto, Taeko Ozawa, Megumi Abe,
*
Shunsuke Marubayashi, Takashi Yamazaki
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology,
2-24-16 Nakacho, Koganei 184-8588, Japan
Received 15 December 2007; received in revised form 21 December 2007; accepted 22 December 2007
Available online 4 January 2008
Abstract
In spite of quite small steric perturbation, substitution of proline (Pro) in the target pentapeptide proctolin (Arg-Tyr-Leu-Pro-Thr) for (4R)- as
well as (4S)-4-fluoroproline led to apparent alteration of the pyrrolidine ring structure which eventually resulted in the significant conformational
change of the whole molecules which was assumed on the basis of their NOESY spectra.
# 2008 Elsevier B.V. All rights reserved.
Keywords: Fluorinated amino acid; Peptidic conformations; NOESY spectra
1. Introduction
Our research group has previously reported the synthesis
and conformational analysis of the fluorine-containing
enkephalin hexapeptide derivative and successfully demon-
strated that entry of three fluorine atoms to the terminal methyl
group of the threonine residue clearly changed the original
conformation, as our expectation, by elimination of the
hydrogen bonding [7].
Proline (Pro) possesses an exceptional cyclic secondary
amine structure among the 20 naturally occurring amino acids,
which has been drawing a special interest in the field of
medicinal chemistry. The peptide linkages composed of natural
amino acids usually exist exclusively as the s-trans conforma-
tion mainly due to steric reasons, but the proline-related amide
bond usually consists of a mixture of both s-cis and s-trans
conformers by their structural similarity [1] (Fig. 1). These
unique features sometimes affect their biological behavior like
the case of protein foldings, and the examples where only one of
the two isomers show bioactivity have been reported [2,3].
Therefore, incorporation of other elements or groups to the
proline ring in target peptides has become one of the central
methods for modification of the original biological activity.
Organofluorine compounds have played important roles in
various areas as agrochemicals, pharmaceuticals, and polymers
because fluorination can drastically affect the original chemical
and physical properties of molecules [4]. Fluorinated amino
acids [5] and peptides [6] are especially interesting as enzyme
inhibitors in the development of medicines.
During our continuing study in this field, we selected
biologically active proctolin 1 [8] (Arg-Tyr-Leu-Pro-Thr,
Fig. 2) known as neurohormone of insects and shellfishes as
the next target for investigation of the effect of a fluorine atom
towards molecular conformation of 1 when this atom was
substituted either for the pro-R or pro-S protons at the
4-position of Pro.
2. Results and discussion
2.1. Preparation of proctolin 1 and its monofluorinated
analogues 2 and 3
In Scheme 1 the synthetic sequence to assemble the target
compound 1 is shown. For coupling reactions, the urea-type
standard reagent WSCꢀHCl [9] was employed in the presence of
an additive HOBtꢀH2O [10] whose combination has advantages
for realizing high yield with a lower chance of undesirable
epimerization.
* Corresponding author. Tel.: +81 42 388 7038; fax: +81 42 388 7038.
E-mail address: tyamazak@cc.tuat.ac.jp (T. Yamazaki).
0022-1139/$ – see front matter # 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.12.005

T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
287
Fig. 1. Isomerism of the acylated Pro amide bond.
Fig. 2. Structure of Proctolin 1 (Arg-Tyr-Leu-Pro-Thr).
First, Boc-Tyr was condensed with Leu-OBnꢀTsOH under
the above condition to yield the dipeptide 4. Removal of the
Boc group of the dipeptide 5, prepared in a same manner as 4
from Boc-Pro and Thr-OBnꢀTsOH, followed by the coupling
with 4 after hydrogenolytic cleavage of the C-terminal benzyl
group furnished the tetrapeptide 6. Finally, the pentapeptide 7
was constructed by the WSC-mediated condensation of Boc-
deprotected 6 and Z-Arg(Z2) prepared following to the
synthetic method reported by Zervas et al. [11]. Catalytic
hydrogenation affected the spontaneous removal of the benzyl
ester and the Z groups at the same instance to provide the
desired target pentapeptide 1 as a single stereoisomer.
Scheme 2. Syntheses of fluoroprolines 10 and 12.
At the next stage, (2S,4S)- and (2S,4R)-4-fluoroproline
derivatives 10 [12] (Boc-flp-OBn) and 12 (Boc-Flp-OBn)
were prepared following to the procedure shown in Scheme 2.
The commercially available (4R)-4-hydroxyproline 8 (Hyp)
was protected as a benzyl ester by BnOH and a catalytic amount
of acid, and subsequently by (Boc)2O with a base to yield 9
which was further converted to Boc-flp-OBn 10 by the
fluorination using perfluoropropene diethylamine adduct [13]
(PPDA; Ishikawa reagent). Inversion of stereochemistry of the
hydroxy group in 9 by the Mitsunobu procedure [12a,14] prior
to the PDDA fluorination afforded the different diastereomer
Boc-Flp-OBn 12 in a stereospecific manner.
Fluorinated prolines 10 and 12 thus obtained were
incorporated to proctolin 1 instead of Pro. The same synthetic
protocol for 1 was used for the construction of both 2 and 3
(Schemes 3 and 4). Most of coupling reactions proceeded in
good to high yields, while CDMT [15] was found especially
effective in some specific steps such as preparation of the
dipeptide 13 and the pentapeptide 15. The final hydrogenolysis
was smoothly completed for 15 under an ambient pressure to
furnish 2 in a quantitative yield with a 2:1 isomeric ratio [16],
while the same process to 3 proceeded with difficulty under the
same condition. However, deprotection from 18 was eventually
realized under a 0.46 MPa pressure of H2 and 3 was afforded in
an acceptable yield in a 2:1 isomeric ratio [16].
2.2. Conformational analysis of proctolin 1 and its
monofluorinated analogues 2 and 3
Extensive studies have been carried out by the Raines’
research group [17] on disclosing the pyrrolidine ring structure
Scheme 1. Preparation of Arg-Tyr-Leu-Pro-Thr 1.

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T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
Fig. 3. NOESY correlation of 1.
material was further stabilized by the nꢁp* interaction of
amide oxygen with the methoxycarbonyl carbon atom [19].
With such basic information on the three-dimensional
shapes of Pro derivatives, NOESY spectrum of 1 obtained in
DMSO-d6 (Fig. 3) was analyzed. The amide bonds of Tyr-Leu
and Pro-Thr were determined to possess trans conformation on
the basis of the correlations between CH–C(O)NH–, including
the one between Leu and Pro which was strongly suggested by
the definite cross peak between Leu-a-CH and Pro-d-CH2.
Moreover, a number of cross peaks between Leu and Thr were
observed which led to anticipation that Leu-CO and Thr-NH
formed a hydrogen bond to construct g-turn conformation. In
addition, the zwitterionic interaction between the both terminal
amino acids Arg and Thr would also contribute to the close
proximity of the side chains of Leu and Thr. Absence of the
cross peak between Pro-a-CH and -g-CH2 expected the
pyrrolidine ring conformation of Pro as Cg-endo.
Scheme 3. Preparation of Arg-Tyr-Leu-flp-Thr 2.
in Pro derivatives. For example, Ac-Pro-OMe 19 was found to
exist as a conformational mixture of Cg-endo:Cg-exo = 66:34,
while introduction of only one fluorine to the 4-position of the
pyrrolidine ring of Pro affected this ratio quite significantly.
Thus, in spite of imposing the least steric perturbation, Ac-flp-
OMe 20 and Ac-Flp-OMe 21 [18] gave the isomeric preference
of endo:exo = 95:5 and 14:86, respectively, which was
explained as a result of the gauche effect. The amide cis:trans
ratios of 19–21 were 3.0, 4.0, and 1.2, respectively, in favor of
the trans form and the crystallographic analysis of 21 with the
Cg-exo-trans conformation led to the speculation that this
In case of compound 2, it was interesting to note that no long
range correlations were obtained from the NOESY spectrum
except for three cross peaks between adjacent amino acids
(Fig. 4). The pentapeptide 2 was proved to possess trans amide
conformation between Tyr-Leu and Pro-Thr similar to the
corresponding non-fluorinated counterpart 1. The cross peak
between Leu-a-CH and Pro-d-CH2 clearly demonstrated the
trans relationship of the amide linkage which allowed us to
assume the major isomer being trans. In addition, the Cg-exo
ring pucker of the pyrrolidine ring was deduced to be formed at
the flp residue on the basis of the obvious correlation between
a-CH and g-CH of flp, which was not found for 1. This Cg-exo
preference was totally contradicted to the issue already
discussed above. This reversal would be occurred to avoid
the undesirable electronic repulsive interaction of the fluorine
atom with the carbonyl oxygen at the same residue when Cg-
endo conformation was occupied. This conformational
Fig. 4. NOESY correlation of 2.
Scheme 4. Preparation of Arg-Tyr-Leu-Flp-Thr 3.

T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
289
4. Experimental
4.1. General
Most of reactions where an organic solvent was employed
were performed under argon with magnetic stirring using
flame-dried glassware. Anhydrous CH2Cl2 and THF were
purchased and used without further purification. DMF was
freshly distilled from CaH2. Unless otherwise noted, materials
were obtained from commercial suppliers and were used
without further purification. All protected amino acids (AAs)
for peptide syntheses were prepared by t-butyloxycarbonyla-
tion of an amino group or benzyl esterification of a carboxyl
group of non-protected AAs.
Fig. 5. NOESY correlation of 3.
Analytical thin-layer chromatography (TLC) was routinely
used for monitoring reactions by generally using a mixture of n-
hexane and ethyl acetate (v/v). Spherical neutral silica gel (63–
210 mm or 40–50 mm) was employed for column chromato-
graphy and flush chromatography, respectively.
Fig. 6. Plausible pyrrolidine ring structure of 3.
1H, 13C, and 19F NMR spectra were recorded (1H: 500,
400, or 300 MHz; 13C: 125, 100, or 75 MHz; 19F: 376 or
283 MHz) at room temperature whose data were reported
as follows: chemical shift (d scale) in parts per million
(ppm) downfield from Me4Si (d = 0.00) used as an internal
standard, number of protons (integration), multiplicity
(singlet, s; doublet, d; triplet, t; quartet, q; multiplet, m;
broad peak, br; etc.), and coupling constant (J, Hz). Infrared
(IR) spectra were reported in wave number (cmꢁ1). Optical
Rotation was measured as a MeOH solution by a cell with a
50 mm length. FAB mass spectra were measured in a positive
ion mode.
modification would be energetically favorable so that it could
keep g-turn conformation by forming the hydrogen bonding
between Leu-CO and Thr-NH by sacrificing the ring
conformational stability.
One of the most interesting points for the NOESY results of
3 would be the fact that, different from both 1 and 2, this
compound 3 possessed cis conformation at the Leu-Pro amide
bond which was assumed from the correlation between Pro-a-
CH and Leu-b-CH2 (Fig. 5). Furthermore, the pyrrolidine ring
in 3 indicated a similar tendency to the compound 2 with
occupying the opposite conformation to the expected Cg-exo
structure, and Cg-endo was the actual three-dimensional shape.
This phenomena would be understood from the fact that the Cg-
exo form would be encumbered by the steric hindrance of the i-
Bu group as supported by the cross peaks between protons in
this group and Pro-a-H (Fig. 6). The Cg-endo structure,
therefore, was presumed to be formed as the most stable
pyrrolidine ring conformation.
4.2. Experimental procedure
4.2.1. General procedure for the coupling of two amino
acids
Preparation of Boc-Tyr-Leu-OBn (4) is described as the
representative example. Boc-Tyr (8.44 g, 30.0 mmol) and Leu-
OBnꢀTsOH (11.8 g, 30.0 mmol, 1.0 equiv) in anhydrous
CH2Cl2 (100 mL) were added to a 200 mL two-necked
round-bottomed flask under argon. The mixture was cooled
to 0 8C with an ice/water bath, and WSCꢀHCl (6.33 g,
33.0 mmol, 1.1 equiv) and HOBtꢀH2O (5.05 g, 33.0 mmol,
1.1 equiv) were added in one portion, followed by the slow
addition of Et3N (4.6 mL, 33 mmol, 1.1 equiv). After 1 h, the
cold bath was removed, and the reaction mixture was stirred
overnight at room temperature. The reaction mixture was then
concentrated on a rotary evaporator and the residue was diluted
with water. The aqueous layer was extracted with AcOEt (three
times) and the combined organic layer was successively washed
with 5% NaHCO3 aq. (three times), 5% citric acid aq. (three
times), and brine (once). After this typical work-up procedure,
the extracts were dried over anhydrous MgSO4, filtered, and
evaporated. After purification by column chromatography, the
dipeptide compound, 4 (12.8 g, 26.5 mmol) was obtained as
white foam.
Finally, insecticidal activities were investigated briefly for
the pentapeptides 1–3. At the 500 ppm concentration, the Flp-
containing 3 showed a biological activity towards tortrix while
1 and 2 being inactive. On the other hand, only the non-
fluorinated 1 was found to be potent against spider mite.
3. Conclusion
In summary, we could clarify obvious conformational
change including alteration of the following proline-related
characteristic structures of the Cg-endo or Cg-exo pyrrolidine
ring conformations and cis or trans stereochemistry for the
amide linkage just by entry of only one fluorine atom to Pro.
Moreover, such conformational change would be one of the
important factors for appearance of biological activities in spite
of imposing the least steric perturbation. Our research group is
going to clarify the solid state conformations of the
pentapeptides 1–3 synthesized here by X-ray crystallographic
structure analysis for obtaining their three-dimensional feature.

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T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
4.2.2. General procedure for the deprotection of the C-
terminal BnO group and the N-terminal Boc group
equiv) and PNBOH (2.19 g, 13.1 mmol, 1.3 equiv) to a 100 mL
two-necked round-bottomed flask under argon. After cooling
the solution in a 0 8C bath, DIAD (2.6 mL, 13 mmol, 1.3 equiv)
was slowly added. The resulting solution was stirred overnight
at rt and then concentrated to a yellow oil under reduced
pressure. Adding n-hexane-AcOEt solution to the oil resulted in
the formation of a colorless solid which was separated by
vacuum filtration. This solid was not the desired product, but
most likely triphenylphosphine oxide and diisopropylhydra-
zine. The crude Boc-hyp(PNB)-OBn obtained as an oil from the
filtrate was used for the next step.
The C-terminal BnO deprotection of 4 is described as the
representative example. At 0 8C, 4 (4.02 g, 8.30 mmol) in MeOH
(8.3 mL) was added to 10% Pd/C (0.087 g, 0.98 mol%) under
argon in a 50 mL two-necked round-bottomed flask. After argon
wasreplacedwithhydrogenatthe same temperature, the reaction
mixturewas stirred for 6 h at room temperature. The catalyst was
then removed by filtration, and the filtrate was concentrated on a
rotary evaporator. Boc-Tyr-Leu-OH was used for the next
condensation reaction without further purification.
The N-terminal Boc deprotection of 5 is described as the
representative example. 5 (3.32 g, 8.17 mmol) in CH2Cl2
(5.0 mL) was added to a 100 mL round-bottomed flask at room
temperature. The solution was cooled to 0 8C with an ice/water
bath, and CF3CO2H (13 mL, 160 mmol) was slowly added, and
the mixture was stirred at 0 8C for 1 h. Excess CF3CO2H was
then removed as an azeotropic mixture with CH2Cl2. Boc-
deprotected H-Pro-Thr-OBnꢀCF3CO2H thus obtained was used
for the next condensation step without further purification.
To a solution of attained p-nitrobenzoic acid ester in THF
(60 mL) and H2O (20 mL) was added LiOHꢀH2O (0.44 g,
10 mmol, 1.0 equiv) at ꢁ10 8C. After stirring for 3 h, 4 N HCl
aq. was added to this solution until pH 1 with checking by pH-
test paper. The usual workup procedure and purification by
column chromatography afforded 11 (1.98 g, 6.18 mmol) as a
white foam.
4.3. Experimental data
4.2.3. Preparation of Boc-Hyp-OBn (9)
4.3.1. Boc-Tyr-Leu-OBn (4) [20]
(2S,4R)-4-Hydroxyproline (6.57 g, 50.1 mmol), toluene
(50 mL), BnOH (24 mL, 230 mmol, 4.6 equiv), and p-
TsOHꢀH2O (11.5 g, 60.4 mmol, 1.2 equiv) were added to a
200 mL round-bottomed flask. The mixture was refluxed for 2 h,
and the residue was then washed with Et2O (100 mL) and n-
hexane (100 mL) until it was crystallized. The resulting
precipitate was filtered off with suction and was washed with
n-hexane. Hyp-OBnꢀTsOH obtained as a white foam was used
for the next step.
Yield 88.4%. Rf 0.79 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.86 (d, J = 6.5 Hz, 3H), 0.87 (d, J = 7.0 Hz, 3H), 1.41 (s,
9H), 1.42–1.61 (m, 3H), 2.93–3.02 (m, 2H), 4.29 (br s, 1H),
4.60 (br s, 1H), 5.10 (d, J = 12.5 Hz, 1H), 5.14 (d, J = 12.5 Hz,
1H), 5.14 (br s, 1H), 6.42 (d, J = 8.0 Hz, 1H), 6.69 (d,
J = 8.5 Hz, 2H), 7.00 (d, J = 8.5 Hz, 2H), 7.31-7.38 (m, 5H).
13C NMR (500 MHz, CDCl3, d): 21.8, 22.7, 24.6, 28.2, 37.3,
41.4, 50.9, 55.8, 67.1, 80.4, 115.5, 127.8, 128.2, 128.4, 128.6,
130.4, 135.2, 155.1, 155.6, 171.3, 172.3.
Hyp-OBnꢀTsOH
(19.7 g,
50.0 mmol),
1,4-dioxane
(100 mL), H2O (50 mL), and Na2CO3 (5.83 g, 55.0 mmol,
1.1 equiv) were added to a 300 mL round-bottomed flask. The
mixture was cooled to 0 8C with an ice/water bath, and (Boc)2O
(12.2 g, 55.8 mmol, 1.1 equiv) was added in one portion. After
0.5 h, the cold bath was removed, and the reaction mixture was
stirred overnight at room temperature. It was concentrated on a
rotary evaporator and the residue was diluted with water. To this
solution was added 4 N HCl aq. until pH 1 checked by pH-test
paper. The usual workup procedure and purification by column
chromatography afforded 9 (13.0 g, 40.4 mmol) as an oil.
4.3.2. Boc-Pro-Thr-OBn (5) [21]
Yield 74.9%. Rf 0.61 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 1.18 (d, J = 6.5 Hz, 3H), 1.45 (s, 9H), 1.76–2.11 (m, 2H),
2.11–2.28 (m, 2H), 3.29–3.57 (m, 2H), 4.18–4.44 (br, 2H), 4.61
(dd, J = 2.2, 8.8 Hz, 1H), 5.18 (d, J = 12.0 Hz, 1H), 5.21 (d,
J = 12.5 Hz, 1H), 7.08 (br s, 1H), 7.26–7.46 (m, 5H). 13C NMR
(500 MHz, CDCl3, d): 20.0, 28.3, 47.1, 57.6, 60.0, 60.4, 61.0,
67.2, 68.7, 128.2, 128.4, 128.6, 135.2, 155.5, 170.6, 172.5,
175.0.
4.3.3. Boc-Tyr-Leu-Pro-Thr-OBn (6)
4.2.4. Preparation of Boc-flp-OBn (10)
Yield 72.0%. Rf 0.57 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.85 (d, J = 6.5 Hz, 3H), 0.89 (d, J = 7.0 Hz, 3H), 1.18 (d,
J = 6.0 Hz, 3H), 1.37–1.62 (m, 3H), 1.41 (s, 9H), 1.86–2.18 (m,
4H), 2.83–2.95 (m, 2H), 3.54–3.75 (m, 2H), 4.27–4.33 (m, 2H),
4.44–4.48 (m, 1H), 4.60 (dd, J = 3.2, 9.2 Hz, 1H), 4.70–4.76
(m, 1H), 5.15 (d, J = 12.5 Hz, 1H), 5.20 (d, J = 12.5 Hz, 1H),
5.23 (d, J = 8.5 Hz, 1H), 6.80 (d, J = 8.0 Hz, 1H), 6.93 (d,
J = 8.5 Hz, 2H), 7.25–7.37 (m, 5H), 7.41 (d, J = 8.5 Hz, 1H).
13C NMR (500 MHz, CDCl3, d): 20.1, 21.7, 23.1, 28.2, 38.0,
41.2, 47.6, 48.9, 55.7, 57.9, 60.0, 67.3, 68.5, 80.1, 115.5, 127.6,
128.1, 128.2 128.4, 128.5, 128.6, 130.2, 135.1, 155.2, 155.4,
171.0, 171.3, 171.5, 172.0. IR (KBr) n: 661, 740, 917, 1017,
1043, 1100, 1160, 1208, 1362, 1438, 1493, 1619, 1651, 2300,
9 (6.43 g, 2.20 mmol) in anhydrous CH2Cl2 (10 mL) was
added to a 50 mL two-necked round-bottomed flask under
argon. The mixture was cooled to 0 8C with an ice/water bath,
and PPDA (4.7 mL, 26 mmol, 1.3 equiv) was slowly added.
After 0.5 h, the cold bath was removed, and the reaction
mixture was refluxed for 1 h. It was concentrated on a rotary
evaporator and the residue was diluted with water. The usual
workup procedure and purification by column chromatography
afforded 10 (3.89 g, 12.0 mmol) as an oil.
4.2.5. Preparation of Boc-hyp-OBn (11)
9 (3.22 g, 10.0 mmol) was dissolved in anhydrous THF
(50 mL), and it was added with Ph3P (3.40 g, 13.0 mmol, 1.3
18
2950, 3270 cmꢁ1. ½aꢂD ꢁ59.6 (c 1.03, MeOH). mp 98–103 8C.

T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
291
HRMS-FAB (m/z): [M + H]+ calcd for C36H51N4O9, 683.3656;
found, 683.3698.
J = 12.5 Hz, 1H), 7.29–7.36 (m, 5H). 13C NMR (500 MHz,
CDCl3, d): 28.3, 37.5 (d, J = 20.6 Hz), 53.2 (d, J = 24.6 Hz),
66.9, 80.4, 91.2 (d, J = 174.8 Hz), 128.0, 128.3, 128.4, 135.5,
153.6, 171.5. (minor) 28.1, 36.6 (d, J = 20.6 Hz), 52.9 (d,
J = 22.6 Hz), 67.0, 80.4, 91.7 (d, J = 176.9 Hz), 128.1, 128.3,
128.5, 135.6, 154.0, 171.2. 19F NMR (283 MHz, CDCl3, d):
ꢁ174.28 to ꢁ173.50 (m).
4.3.4. Z-Arg(Z2)-Tyr-Leu-Pro-Thr-OBn (7)
Yield 37.4%. Rf 0.73 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.84 (d, J = 6.0 Hz, 3H), 0.87 (d, J = 6.5 Hz, 3H), 1.07 (d,
J = 6.5 Hz, 3H), 1.41-2.32 (m, 11H), 2.61–2.93 (m, 2H), 3.54–
3.65 (m, 2H), 3.74–3.98 (m, 2H), 4.16–4.25 (m, 1H), 4.25–4.37
(m, 1H), 4.53 (dd, J = 2.5, 9.0 Hz, 1H), 4.59–4.67 (m, 1H),
4.73–4.85 (m, 1H), 4.85–5.01 (m, 1H), 5.01–5.24 (m, 8H), 6.52
(d, J = 8.0 Hz, 2H), 6.65 (d, J = 7.5 Hz, 1H), 6.75 (d,
J = 8.5 Hz, 1H), 7.14 (d, J = 8.0 Hz, 1H), 7.15–7.27 (m,
20H), 7.26 (br s, 1H), 7.44 (d, J = 9.0 Hz, 1H). 13C NMR
(500 MHz, CDCl3, d): 20.0, 21.8, 23.2, 24.3, 24.7, 28.9, 41.7,
44.1, 47.4, 57.8, 59.8, 66.9, 67.1, 69.0, 115.3, 115.6, 127.3,
127.6, 127.8, 128.0, 128.2, 128.2, 128.3, 128.3, 128.4, 128.5,
128.8, 128.9, 130.2, 134.5, 135.3, 136.3, 155.7, 160.7, 163.3,
170.9, 172.1. IR (KBr) n: 660, 695, 738, 898, 1000, 1092, 1204,
1368, 1435, 1502, 1603, 1700, 2300, 2930, 3000, 3250,
4.3.8. Boc-hyp-OBn (11) [12a]
Yield 61.6%, 5:4 (E,Z isomeric ratio). Rf 0.43 (n-
1
Hexane:AcOEt = 3:2). H NMR (300 MHz, CDCl3, d): 1.34
(s, 9H), 2.11 (br d, J = 12.3 Hz, 1H), 2.25–2.40 (m, 1H), 3.24
(d, J = 9.3 Hz, 1H), 3.50–3.72 (m, 2H), 4.31–4.44 (m, 2H), 5.20
(s, 2H), 7.32–7.39 (m, 5H). (minor) 1.47 (s, 9H), 2.11 (br d,
J = 12.3 Hz, 1H), 2.25–2.40 (m, 1H), 3.34 (d, J = 9.9 Hz, 1H),
3.50–3.72 (m, 2H), 4.31–4.44 (m, 2H), 5.14 (d, J = 12.3 Hz,
1H), 5.31 (d, J = 12.3 Hz, 1H), 7.34–7.37 (m, 5H). 13C NMR
(300 MHz, CDCl3, d): 28.0, 38.5, 55.2, 57.9, 67.2, 70.0, 80.3,
128.0, 128.4, 128.5, 128.6, 135.0, 153.6, 174.4. (minor) 28.3,
37.7, 55.6, 57.7, 67.2, 71.0, 80.2, 128.2, 128.4, 128.5, 128.6,
135.2, 154.3, 174.5.
19
3350 cmꢁ1. ½aꢂD ꢁ48.5 (c 1.03, MeOH). mp 93–95 8C.
HRMS-FAB (m/z): [M + H]+ calcd for C61H73N8O14,
1141.5246; found, 1141.5208.
4.3.9. Boc-Flp-OBn (12) [12a]
Yield 70.0%, 2:1 (E,Z isomeric ratio). Rf 0.63 (n-Hexane:A-
4.3.5. Arg-Tyr-Leu-Pro-Thr (1) [21]
Yield 99.5%. 1H NMR (500 MHz, DMSO-d6, d): 0.71–1.01
(m, 9H), 1.07–2.27 (m, 11H), 2.62–2.95 (m, 2H), 3.02 (t,
J = 7.0 Hz, 2H), 3.14 (t, J = 6.2 Hz, 1H), 3.43-3.69 (m, 2H),
3.72–4.08 (m, 2H), 4.38–4.42 (m, 1H), 4.43–4.50 (m, 1H),
4.52–4.63 (m, 1H), 6.62 (d, J = 8.0 Hz, 2H), 6.94 (d, J = 8.0 Hz,
2H), 7.34 (d, J = 8.5 Hz, 1H), 7.97 (d, J = 8.0 Hz, 1H), 8.12 (d,
J = 6.5 Hz, 1H). 13C NMR (500 MHz, DMSO-d6, d): 19.2, 21.5,
23.2, 24.1, 24.5, 24.9, 28.5, 31.8, 36.5, 36.6, 40.6, 40.9, 46.7,
48.5, 53.4, 54.0, 57.5, 59.6, 66.2, 114.8, 127.5, 130.2, 155.8,
157.1, 170.2, 170.7, 170.8, 173.8.
cOEt = 1:1). H NMR (300 MHz, CDCl3, d): (Major) 1.36 (s,
1
9H), 1.96–2.08 (m, 1H), 2.51–2.67 (m, 1H), 3.63 (ddd, J = 3.3,
6.6, 36.6 Hz, 2H), 3.92 (ddd, J = 2.1, 12.9, 22.2 Hz, 1H), 4.45
(dd, J = 7.8, 9.0 Hz, 1H), 5.08–5.31 (m, 3H), 7.36 (br s, 5H).
(minor) 1.47 (s, 9H), 2.10–2.21 (m, 1H), 2.51–2.67 (m, 1H), 3.59
(ddd, J = 3.3, 6.6, 36.6 Hz, 2H), 4.54 (ddd, J = 8.4, 8.4, 8.4 Hz,
1H), 4.54 (t, J = 8.4 Hz, 1H), 5.08-5.31 (m, 3H), 7.36 (br s, 5H).
13C NMR (75 MHz, CDCl3, d): 27.9, 37.3 (d, J = 22.9 Hz), 52.7
(d, J = 22.3 Hz), 57.5, 66.7, 80.3, 90.8 (d, J = 178.6 Hz), 127.9,
128.0, 128.2, 128.3, 128.4, 135.1, 153.4, 172.2. (minor) 28.1,
36.3 (d, J = 22.9 Hz), 53.0 (d, J = 23.5 Hz), 57.3, 66.7, 80.2, 91.6
(d, J = 178.6 Hz), 127.9, 128.0, 128.2, 128.3, 128.4, 135.4,
153.9, 171.9. 19F NMR (283 MHz, CDCl3, d): ꢁ178.77 (ddddd,
J = 22.6, 22.9, 38.7, 38.7, 52.6 Hz). (minor) ꢁ178.09 (ddddd,
J = 22.6, 22.9, 36.5, 36.5, 52.6 Hz).
4.3.6. Boc-Hyp-OBn (9) [22]
Yield 80.8%, 2:1 (E,Z isomeric ratio). Rf 0.40 (Et2O). H
1
NMR (300 MHz, CDCl3, d): 1.34 (s, 9H), 2.01–2.10 (m, 1H),
2.22–2.34 (m, 1H), 2.40 (br s, 1H), 3.42–3.65 (m, 2H), 4.41–
4.53 (m, 2H), 5.13 (d, J = 12.3 Hz, 1H), 5.18 (d, J = 12.3 Hz,
1H), 7.32–7.37 (m, 5H). (minor) 1.45 (s, 9H), 2.01–2.10 (m,
1H), 2.22–2.34 (m, 1H), 2.40 (br s, 1H), 3.42–3.65 (m, 2H),
4.41–4.53 (m, 2H), 5.09 (d, J = 12.9 Hz, 1H), 5.26 (d,
J = 12.6 Hz, 1H), 7.32–7.37 (m, 5H). 13C NMR (300 MHz,
CDCl3, d): 27.6, 38.5, 54.0, 57.7, 66.2, 68.4, 79.9, 127.5, 127.9,
128.1, 135.0, 153.7, 172.6. (minor) 27.9, 37.8, 54.2, 57.4, 66.2,
69.1, 79.7, 127.7, 127.9, 128.0, 135.2, 154.2, 172.4.
4.3.10. Boc-flp-Thr-OBn (13)
Yield 63.8%. Rf 0.60 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 1.17 (d, J = 6.5 Hz, 3H), 1.46 (s, 9H), 2.01–2.84 (m, 2H),
3.55–3.88 (m, 2H), 4.30 (br, 1H), 4.48 (br s, 1H), 4.64 (dd,
J = 2.2, 8.8 Hz, 1H), 5.22 (??, 2H), 5.23 (td, J = 3.5, 52.0 Hz,
1H), 7.26 (br s, 1H), 7.30–7.38 (m, 5H). 13C NMR (125 MHz,
CDCl3, d): 19.7, 28.1, 37.7, 53.9 (d, J = 20.6 Hz), 57.0, 59.9,
67.2, 68.5, 81.7, 92.0 (d, J = 172.7 Hz), 128.2, 128.4, 128.6,
135.3, 154.7, 170.2, 172.1. 19F NMR (283 MHz, CDCl3, d):
ꢁ174.06 to ꢁ173.32 (m). (minor) ꢁ175.38 to ꢁ174.59 (m).
4.3.7. Boc-flp-OBn (10) [12]
Yield 60.1%, 5:4 (E,Z isomeric ratio). Rf 0.64 (n-
1
Hexane:AcOEt = 1:1). H NMR (500 MHz, CDCl3, d): 1.34
19
½aꢂD ꢁ53.9 (c 1.04, MeOH). mp 118–119 8C. Anal. Calcd for
(s, 9H), 2.31–2.42 (m, 1H), 2.50 (dd, J = 15.0, 17.5 Hz, 1H),
3.58–3.73 (m, 2H), 4.46 (d, J = 9.5 Hz, 1H), 5.12 (s, 2H), 5.20
(dm, J = 52.0 Hz, 1H), 7.29–7.36 (m, 5H). (minor) 1.46 (s, 9H),
2.28 (ddd, J = 4.5, 9.5, 14.5 Hz, 1H), 2.44 (dd, J = 4.5, 9.5 Hz,
1H), 3.76–3.89 (m, 2H), 4.60 (d, J = 9.5 Hz, 1H), 5.09 (d,
J = 12.5 Hz, 1H), 5.20 (dm, J = 52.0 Hz, 1H), 5.27 (d,
C21H29FN2O6: C, 59.42; H, 6.89; N, 6.60. Found: C, 59.59; H,
6.81; N, 6.57.
4.3.11. Boc-Tyr-Leu-flp-Thr-OBn (14)
Yield 64.7%. Rf 0.39 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.86–0.94 (m, 6H), 1.18 (d, J = 6.5 Hz, 3H), 1.40 (s, 9H),

292
T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
1.28–1.72 (m, 3H), 2.11–2.82 (m, 2H), 2.81–3.12 (m, 2H),
3.58–4.12 (m, 2H), 4.18–4.46 (m, 2H), 4.50–4.65 (m, 1H), 4.59
(dd, J = 2.5, 8.5 Hz, 1H), 4.66–4.91 (d, J = 9.8, 1H), 5.12 (d,
J = 12.5, 1H), 5.14 (d, J = 13.0, 1H), 5.06–5.23 (m, 1H), 5.21–
5.29 (br, 1H), 6.64 (d, J = 8.0 Hz, 2H), 6.92 (d, J = 8.5 Hz, 2H),
6.97 (d, J = 8.0 Hz, 1H), 7.22 (d, J = 8.5, 1H), 7.26–7.38 (m,
5H). 13C NMR (125 MHz, CDCl3, d): 20.0, 22.8, 23.0, 24.4,
28.3, 33.8, 37.1, 40.9, 52.0, 55.8, 58.1, 58.5, 67.4, 75.8, 115.6,
121.4, 127.6, 128.2, 128.3, 128.4, 128.6, 128.6, 130.3, 135.1,
155.2, 170.5, 170.5, 170.8, 171.5, 172.4.
(d, J = 22.2 Hz, 1H), 4.25–4.30 (m, 1H), 4.44 (t, J = 7.8 Hz,
1H), 4.65 (dd, J = 3.0, 9.6 Hz, 1H), 5.14–5.32 (m, 3H), 7.17 (d,
J = 9.3 Hz, 1H), 7.36 (m, 5H). (minor) 1.18 (d, J = 8.1 Hz, 3H),
1.45 (s, 9H), 2.39–2.60 (br m, 2H), 2.80 (br s, 1H), 3.51 (dd,
J = 3.3, 36.0 Hz, 1H), 3.88 (d, J = 22.2 Hz, 1H), 4.25–4.30 (m,
1H), 4.44 (t, J = 7.8 Hz, 1H), 4.62 (dd, J = 2.7, 9.6 Hz, 1H),
5.14–5.32 (m, 3H), 6.78 (d, J = 8.4 Hz, 1H), 7.36 (m, 5H). 13C
NMR (75 MHz, CDCl3, d): 19.7, 28.0, 35.7 (d, J = 21.1 Hz),
53.4 (d, J = 22.3 Hz), 57.7, 58.3, 67.0, 68.5, 80.8, 91.8 (d,
J = 176.8 Hz), 127.9, 128.2, 128.4, 135.0, 154.6, 170.5, 171.7.
(minor) 20.0, 28.0, 37.8 (d, J = 21.7 Hz), 53.2 (d, J = 21.1 Hz),
57.3, 58.9, 67.0, 67.4, 80.8, 91.1 (d, J = 178.0 Hz), 127.9,
128.2, 128.4, 135.0, 154.2, 170.5, 172.8. 19F NMR (283 MHz,
CDCl3, d): ꢁ177.63 (ddddd, J = 20.6, 20.6, 36.5, 36.6,
57.1 Hz). (minor) ꢁ178.80 (ddddd, J = 19.8, 19.8, 36.5,
36.5, 57.1 Hz). IR (KBr) n: 765, 972, 1034, 1074, 1116,
1166, 1207, 1249, 1318, 1378, 1409, 1456, 1540, 1674, 1698,
19F NMR (283 MHz, CDCl3, d): ꢁ172.34 to ꢁ171.73 (m).
IR (KBr) n: 658, 731, 920, 1037, 1157, 1202, 1358, 1419, 1500,
19
1639, 2340, 2980, 3290, 4170 cmꢁ1. ½aꢂD ꢁ53.9 (c 1.04,
MeOH). mp 115–117 8C. HRMS-FAB (m/z): [M + H]+ calcd
for C36H50FN4O9, 701.3562; found, 701.3535.
4.3.12. Z-Arg(Z2)-Tyr-Leu-flp-Thr-OBn (15)
26
Yield 37.1%. Rf 0.49 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.85–0.93 (m, 6H), 1.09 (d, J = 6.5 Hz, 3H), 1.18–1.35 (m,
2H), 1.38–1.73 (m, 5H), 1.95–3.13 (m, 4H), 3.72–4.08 (m, 4H),
4.20–4.33 (m, 1H), 4.39–4.52 (m, 1H), 4.54 (dd, J = 2.0,
9.0 Hz, 1H), 4.55–4.66 (m, 1H), 4.66–4.82 (m, 1H), 4.84–4.97
(m, 1H), 4.98–5.20 (m, 8H), 5.15–5.30 (m, 1H), 6.54 (d,
J = 7.5 Hz, 2H), 6.79 (d, J = 8.0 Hz, 2H), 7.10 (br s, 1H), 7.22
(d, J = 6.5 Hz, 1H), 7.24–7.37 (m, 20H). 13C NMR (125 MHz,
CDCl3, d): 19.8, 19.9, 21.8, 23.0, 23.2, 24.4, 24.8, 24.8, 29.6,
29.6, 29.6, 29.7, 29.8, 53.8, 57.6, 59.0, 66.8, 66.8, 66.9, 66.9,
67.0, 67.0, 67.0, 67.1, 67.1, 67.2, 67.2, 68.1, 69.0, 115.2, 127.4,
127.8, 127.9, 128.0, 128.1, 128.1, 128.3, 128.4, 128.4, 128.6,
128.7, 128.8, 128.9, 130.2, 134.5, 155.2, 155.6, 170.6, 170.7,
172.1. 19F NMR (283 MHz, Acetone-d6, d): ꢁ172.80 to
ꢁ171.90 (m). IR (KBr) n: 705, 778, 1000, 1078, 1204, 1370,
1744, 2337, 2354, 2364, 2929, 2978, 3410 cmꢁ1. ½aꢂD ꢁ65.3 (c
0.11, MeOH). mp 134–136 8C. HRMS-FAB (m/z): [M + H]+
calcd for C21H30FN2O6, 425.2088; found, 425.2085.
4.3.15. Boc-Tyr-Leu-Flp-Thr-OBn (17)
Yield 71.4%. Rf 0.54 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.84 (d, J = 7.0 Hz, 3H), 0.87 (d, J = 6.0 Hz, 3H), 1.22 (d,
J = 6.5 Hz, 3H), 1.41 (s, 9H), 1.44 (m, 2H), 1.54 (m, 1H), 2.18–
2.30 (m, 1H), 2.40–2.53 (m, 1H), 2.76–2.96 (m, 2H), 3.73 (dd,
J = 3.0, 35.5 Hz, 1H), 3.97 (br m, 1H), 4.25–4.33 (m, 4H),
4.61–4.65 (m, 2H), 4.72 (dd, J = 8.5, 14.0 Hz, 1H), 5.19 (br m,
2H), 5.27 (d, J = 9.0 Hz, 1H), 5.33 (br m, 1H), 6.62 (br m, 1H),
6.67 (d, J = 8.5, 2H), 6.92 (d, J = 8.5 Hz, 2H), 7.34–7.38 (m,
5H), 7.49 (d, J = 8.5 Hz, 1H), 7.61 (s, 1H). 13C NMR
(125 MHz, CDCl3, d): 19.8, 21.8, 22.7, 24.1, 28.1, 35.6 (d,
J = 22.7 Hz), 38.0, 41.2, 50.2, 54.0 (d, J = 22.7 Hz), 55.3, 58.0,
58.6, 67.2, 68.2, 79.8, 91.8 (d, J = 179.8 Hz), 115.4, 128.0,
128.3, 128.4, 130.1, 134.9, 155.2, 155.4, 170.8, 171.6, 171.8. IR
(KBr) n: 699, 745, 846, 1013, 1066, 1175, 1252, 1370, 1452,
1521, 1662, 1882, 1936, 2235, 2311, 2395, 2494, 2606, 2756,
2815, 2888, 2973, 3083, 3294, 3487, 3538, 3623, 3742, 3822,
19
1425, 1500, 1602, 1630, 1700, 3020, 3300 cmꢁ1. ½aꢂD ꢁ46.4 (c
0.70, MeOH). mp 97–101 8C. HRMS-FAB (m/z): [M]+ calcd
for C61H71FN8O14, 1158.5074; found, 1158.5077.
4.3.13. Arg-Tyr-Leu-flp-Thr (2)
Yield 99.1%, 2:1 (E,Z isomeric ratio). 1H NMR (500 MHz,
DMSO-d6, d): 0.73–1.02 (m, 9H), 1.16–1.77 (m, 7H), 2.14–
2.49 (m, 2H), 2.62–2.90 (m, 2H), 2.85–3.13 (m, 2H), 3.55–4.24
(m, 5H), 4.24–4.78 (m, 3H), 5.24 (d, J = 54.0 Hz, 1H), 6.64 (dd,
J = 8.2, 13.8 Hz, 2H), 7.00 (dd, J = 8.0, 30.0 Hz, 2H), 7.16 (d,
J = 5.5 Hz, 1H), 7.88 (br s, 1H), 8.39 (br s, 1H). 13C NMR
(125 MHz, DMSO-d6, d): 18.4, 21.4, 23.2, 24.1, 30.5, 31.9,
34.7, 36.0, 36.4, 36.8, 48.6, 53.4 (d, J = 20.5 Hz), 53.8, 57.2,
58.7, 65.6, 92.3, 114.8, 127.6, 130.1, 155.8, 157.2, 169.0, 170.8,
171.1, 171.7, 173.5, 174.4. 19F NMR (283 MHz, DMSO-d6, d):
ꢁ172.29 to ꢁ171.21 (m). IR (KBr) n: 594, 808, 832, 880, 914,
964, 1081, 1174, 1244, 1388, 1444, 1517, 1636, 2960,
3862, 3942 cmꢁ1
.
19F NMR (283 MHz, CDCl3, d): ꢁ177.74
26
(ddddd, J = 20.4, 20.6, 38.7, 38.7, 54.8 Hz). ½aꢂD ꢁ51.2 (c
0.11, MeOH). mp 97–102 8C. HRMS-FAB (m/z): [M + H]+
calcd for C36H50FN4O9, 701.3562; found, 701.3569.
4.3.16. Z-Arg(Z2)-Tyr-Leu-Flp-Thr-OBn (18)
Yield 71.6%. Rf 0.65 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 0.85 (d, J = 5.5 Hz 3H), 0.87 (d, J = 6.0 Hz, 3H), 1.06 (d,
J = 6.0 Hz, 3H), 1.39–1.64 (br m, 7H), 2.14–2.22 (m, 1H),
2.40–2.51 (m, 1H), 2.59–2.83 (m, 2H), 3.72–3.81 (m, 1H), 3.88
(br s, 1H), 4.13 (br m, 1H), 4.25–4.31 (m, 2H), 4.49 (br m, 1H),
4.55 (dd, J = 1.5, 9.5 Hz, 1H), 4.63 (m, 1H), 4.81–4.95 (m, 3H),
5.04–5.21 (m, 8H), 5.27–5.31 (m, 1H), 6.00 (br m, 1H), 6.52 (d,
J = 7.5 Hz, 2H), 6.65 (d, J = 7.5 Hz, 2H), 7.19 (d, J = 6.5 Hz,
1H), 7.25 (m, 20H), 7.31 (br s, 1H), 7.62–7.79 (m, 1H), 9.27 (br
s, 1H), 9.41–9.44 (br m, 1H). 13C NMR (125 MHz, CD3OD, d):
11.0, 17.0, 19.0, 20.1, 22.0, 26.4, 33.6 (d, J = 20.6 Hz), 34.8,
38.2, 42.0, 47.1, 51.8 (d, J = 22.7 Hz), 52.8, 56.1, 56.4, 58.0,
64.3, 64.6, 64.7, 65.1, 66.4, 90.0 (d, J = 177.8 Hz), 112.8,
19
3310 cmꢁ1. ½aꢂD ꢁ53.4 (c 0.82, MeOH). mp 181–186 8C.
HRMS-FAB (m/z): [M]+ calcd for C30H47FN8O8, 666.3501;
found, 666.3465.
4.3.14. Boc-Flp-Thr-OBn (16)
Yield 56.0%. Rf 0.69 (AcOEt). 1H NMR (500 MHz, CDCl3,
d): 1.21 (d, J = 6.3 Hz, 3H), 1.45 (s, 9H), 2.39–2.60 (br m, 2H),
3.20 (d, J = 6.9 Hz, 1H), 3.56 (dd, J = 3.0, 36.3 Hz, 1H), 3.83

T. Kitamoto et al. / Journal of Fluorine Chemistry 129 (2008) 286–293
293
[5] (a) P. Kukhar, V.A. Soloshonok (Eds.), Fluorine-Containing Amino
Acids: Synthesis and Properties, Wiley, Chichester, UK, 1995;
(b) X.-L. Qiu, W.-D. Meng, F.-L. Qing, Tetrahedron 60 (2004) 6711–
6745;
125.4, 125.6, 125.8, 125.8, 125.9, 126.0, 126.1, 126.3, 128.0,
133.0, 133.6, 134.5, 134.8, 153.3, 153.6, 158.3, 161.4, 168.2,
169.5, 169.6, 170.6. 19F NMR (283 MHz, CDCl3, d): ꢁ177.92
to ꢁ177.23 (m). (minor) ꢁ177.20 to ꢁ177.60 (m). IR (KBr) n:
705, 745, 848, 915, 1007, 1094, 1248, 1374, 1448, 1516, 1645,
1710, 2316, 2386, 2473, 2602, 2688, 2773, 2885, 2967, 3037,
3086, 3293, 3372, 3486, 3547, 3627, 3704, 3747, 3817, 3863,
(c) A. Sutherland, C.L. Willis, Nat. Prod. Rep. 17 (2000) 621–631.
Recent examples about fluorinated amino acids synthesis;
(d) g-F1-Leu D. Padmakshan, S.A. Bennett, G. Otting, C.J. Easton,
Synlett, (2007) 1083–1084;
(e) g-F1-Thr J. Steinreiber, K. Fesko, C. Mayer, C. Reisinger, M. Schur-
mann, H. Griengl, Tetrahedron, 63 (2007) 8088–8093.
[6] (a) V.A. Soloshonok, K. Mikami, T. Yamazaki, J.T. Welch, J.F. Honek
(Eds.), Current Fluoroorganic Chemistry. New Synthetic Directions,
Technologies, Materials and Biological Applications, ACS, Washington,
D.C., 2007;
26
3941 cmꢁ1. ½aꢂD ꢁ36.4 (c 0.11, MeOH). mp 87–91 8C.
HRMS-FAB (m/z): [M + H]+ calcd for C61H72FN8O14,
1159.5152; found, 1159.5161.
4.3.17. Arg-Tyr-Leu-Flp-Thr (3)
(b) M. Molteni, C. Pesenti, M. Sani, A. Volonterio, M. Zanda, J. Fluorine
Chem. 125 (2005) 1735–1743;
Yield 68.9%, 2:1 (E,Z isomeric ratio). 1H NMR (500 MHz,
DMSO-d6, d): 0.88 (d, J = 7.0 Hz, 6H,), 0.95 (d, J = 4.5 Hz,
3H), 1.24–1.64 (br m, 7H), 2.09–2.44 (m, 2H), 2.68 (dd, J = 9.0,
13.5 Hz, 1H), 2.84–2.89 (m, 1H), 3.02 (br m, 2H), 3.11 (t,
J = 6.0 Hz, 1H), 3.71 (dd, 1H, J = 10.0, 37.5 Hz), 3.98 (br m,
3H), 4.47 (br m, 1H), 4.54–4.60 (m, 2H), 5.35 (d, 1H,
J = 54.0 Hz), 6.62 (d, 2H, J = 7.5 Hz), 6.95 (d, 2H, J = 8.5 Hz),
7.46 (br s, 1H), 7.53 (br s, 1H), 8.01 (br s, 1H), 8.08 (d, 1H,
J = 7.5 Hz), 9.27 (br s, 1H). 13C NMR (125 MHz, DMSO-d6,
d): 19.9, 22.0, 23.4, 24.4, 25.1, 29.3, 32.0, 35.9 (d, J = 20.6 Hz),
37.4, 40.5, 41.0, 49.0, 49.2, 53.8, 54.4, 58.8 (d, J = 18.6 Hz),
67.4, 93.0 (d, J = 175.8 Hz), 115.3, 130.6, 137.2, 156.2, 157.4,
170.6, 171.2, 171.6, 174.6. 19F NMR (283 MHz, CD3OD, d):
ꢁ176.01 to ꢁ175.42 (m). (minor) ꢁ176.92 to ꢁ176.34 (m). IR
(KBr) n: 625, 731, 772, 793, 802, 822, 833, 977, 1108, 1175,
1204, 1393, 1444, 1522, 1656, 2330, 2360, 2689, 2828, 2863,
(c) R.I. Mathad, F. Gessier, D. Seebach, B. Jaun, Helv. Chim. Acta 88
(2005) 266–280;
(d) F. Gessier, C. Noti, M. Rueping, D. Seebach, Helv. Chim. Acta 86
(2003) 1862–1870;
(e) P. Wadhwani, S. Afonin, M. Ieronimo, J. Buerck, A.S. Ulrich, J. Org.
Chem. 71 (2006) 55–61.
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pyl)carbodi imide hydrochloride:
24
2934, 2976, 3199, 3391, 3788, 3840 cmꢁ1. ½aꢂD ꢁ39.6 (c 0.11,
MeOH). mp 166–169 8C. HRMS-FAB (m/z): [M]+ calcd for
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¨
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