Synthesis of novel all-cis-functionalized cyclopropane template-assembled collagen models

Article abstract of DOI:10.1039/b103887g

An all-cis-functionalized cyclopropane template to connect the three peptide chains in a collagen model is designed. Stereoselective synthesis of cyclopropane-assembled collagen-model 2b with the minimum unit of Gly-Pro-Pro is based on a novel 1-seleno-2-silylethene [2 + 1] cycloaddition strategy. Reaction of the 1-seleno-2-silylethene 4 with triester-substituted olefin 5 in the presence of ZnI₂ gives [2 + 1] cycloadduct 6 stereoselectively. Cyclopropane 6 is selectively transformed into triol 10 in four steps. The reaction of 10 and three equivalents ofN-Boc-Pro-Pro-Gly-OH in the presence of WSC-DMAP and subsequent deprotection with TFA gives 2b.

Full text of DOI:10.1039/b103887g

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Synthesis of novel all-cis-functionalized cyclopropane template-
assembled collagen models†
Shoko Yamazaki,*a Mari Sakamoto,a Michiko Suzuri,a Masamitsu Doi,b Takashi Nakazawac
and Yuji Kobayashid
1
a Department of Chemistry, Nara University of Education, Takabatake-cho, Nara 630-8528,
Japan
b Department of Materials Science, Wakayama National College of Technology, Gobo,
Wakayama 644-0023, Japan
c Department of Chemistry, Nara Women’s University, Nara 630–8506, Japan
d Graduate School of Pharmaceutical Science, Osaka University, Suita, 565-1871, Japan
Received (in Cambridge, UK) 1st May 2001, Accepted 20th June 2001
First published as an Advance Article on the web 31st July 2001
An all-cis-functionalized cyclopropane template to connect the three peptide chains in a collagen model is designed.
Stereoselective synthesis of cyclopropane-assembled collagen-model 2b with the minimum unit of Gly-Pro-Pro is
based on a novel 1-seleno-2-silylethene [2 ϩ 1] cycloaddition strategy. Reaction of the 1-seleno-2-silylethene 4 with
triester-substituted olefin 5 in the presence of ZnI2 gives [2 ϩ 1] cycloadduct 6 stereoselectively. Cyclopropane 6 is
selectively transformed into triol 10 in four steps. The reaction of 10 and three equivalents of N-Boc-Pro-Pro-Gly-
OH in the presence of WSC–DMAP and subsequent deprotection with TFA gives 2b.
Cyclopropanes have more rigid skeletons than the cyclo-
Introduction
hexane skeleton of Kemp’s triacid.5 An all-cis-functionalized
cyclopropane template may be more effective at inducing the
collagen-like triple-helical structure for very short peptide
chains, compared with KTA. cis,cis-1,2,3-Tris(hydroxymethyl)-
cyclopropane derivative 2 and cis,cis-cyclopropane-1,2,3-tri-
carboxylic acid derivative 3 are newly designed cycloalkane
templates with potential application as collagen models
(Scheme 1).4,5 Cyclopropanes 2 and 3 have two sets of peptide
chains that are distinguishable owing to the presence of a sub-
stituent R on the cyclopropane ring. In the resulting desym-
metrized peptide chains assembled in the templates 2 and 3,
more detailed structural features may be analyzed by NMR
than in KTA-based model 1. In template model 2, the three
peptide chains are linked via the C-termini and in template 3
are linked at the N-termini, respectively. Although a number
of stereoselective cyclopropane syntheses are known,6,7 few
methods for all-cis-functionalized cyclopropanes are available.8
In this paper, we describe a stereoselective synthesis of template
model 2 based on a novel seleno(silyl)ethene [2 ϩ1] cyclo-
addition strategy.9
Collagen is the main protein constituent of bone, tendon, and
skin, which form the basic skeleton of the human body. This
characteristic function of collagen arises from its triple-helix
tertiary structure.1 The primary structure of the peptide chains
of collagen are mainly composed of trimer repeats of sequences
such as Gly-Pro-Hyp or Gly-Pro-Pro.2 Understanding the
dissociation–association mechanism of the three peptide chains
is of biophysical interest in order to elucidate the importance of
the triple-helix structure, and also to facilitate the design of
potential collagen-like synthetic materials that may have
improved properties. Towards this goal, a conformationally
constrained template-assembled synthetic collagen model has
been studied recently by Goodman.3 cis,cis-1,3,5-Trimethyl-
cyclohexane-1,3,5-tricarboxylic acid (Kemp’s triacid, KTA)4
was utilized as a template for a collagen model consisting of
three peptide chains 1 (Scheme 1). This all-cis cyclohexane-
Results and discussion
Reaction of 1-(phenylseleno)-2-(trimethylsilyl)ethene 4 with
triester-substituted olefin 5 in the presence of ZnI2 gave [2 ϩ 1]
cycloadduct 6 stereoselectively in 89% yield (Scheme 2). The
ethoxycarbonyl group on the least hindered face of cyclo-
propane 6 was chemoselectively reduced to mono alcohol 7
with NaBH4–LiCl in THF–EtOH in 75% yield.‡ Reaction of 7
with NaH–MeI in THF gave methoxymethylcyclopropane 8 in
97% yield. The methoxymethyl group was introduced to the
trans side and is for synthetic convenience; however, it may be
used as a handle for desymmetrization of the molecule and the
resulting differentiation of one of the three peptide chains in an
Scheme 1
assembled synthetic collagen model effectively induces the
collagen-like triple-helical structure for short peptide chains.
Examination of the effect on triple-helix formation by changing
the ring size of the template is of interest.
† Electronic supplementary information (ESI) available: 1H NMR
spectra of compounds 2a, 2b, 8–13, 15 and 17. See http://www.rsc.org/
suppdata/p1/b1/b103887g/
‡ The racemic alcohol 7 was separable by chiral column (CHIRALCEL
OF). This property should allow further development of asymmetric
template models.
1870
J. Chem. Soc., Perkin Trans. 1, 2001, 1870–1875
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b103887g

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stereochemistry was also supported by the observed vicinal
coupling constants. The coupling constants of vicinal protons
in cyclopropane rings are characteristic and the J-values are in
the region of those for cis-vicinal protons (8.9–9.2 Hz for the
unsymmetric cyclopropanes 6–9).9c,12
1
The H NMR spectra of 2a and 2b showed differentiation
between two equivalent chains and one chain. For example, in
2b two sets of glycine α-H are clearly distinguished [δ 3.79 (2H),
3.90 (2H) and 3.80 (1H), 3.92 (1H)]. Compounds 2a and 2b
can be used to connect further tripeptides to create a range of
collagen mimetics.
Synthesis of the cis,cis-cyclopropane-1,2,3-tricarboxylic acid
template 3 was attempted through intermediate 8 (Scheme 3).
Scheme 3
The cyclopropane 8 was directly oxidized to the carboxylic
acid by NaIO4–RuCl3 in CH3CN–CCl4–water,13 to give cis,cis-
cyclopropane-1,2,3-tricarboxylic acid derivative 13 in 61%
yield. Treatment of 13 with trifluoroacetic acid gave the
cis-cyclopropane-1,2-dicarboxylic acid 14. Reaction of 14
with two equivalents of glycine tert-butyl ester gave 15.
Attempted removal of the ethyl ester group of 15 to afford
the monoacid 16 was not successful. For example, hydrolysis
of 15 with LiOHؒH2O in THF gave imide 17. The cis stereo-
chemistry of the cyclopropanes 13–15 and 17 in Scheme 3
was also confirmed by 2D-NOESY. NOEs between 2-H and
3-H and/or between 2-H, 3-H and CH2OMe were observed.
The stereochemistry was supported by the observed cis-
vicinal coupling constants (9.3 Hz for 13, 8.5 Hz for 17) as
well.
Other routes were also attempted for the preparation of
all-cis three-amino-acid-connected cyclopropanes; however,
epimerization of the tert-butoxycarbonyl group in addition to
undesirable interaction of the cis-functional groups has pre-
vented success so far.
In summary, we have described the synthesis and preliminary
investigations of cyclopropane templates for collagen models.
Further studies on synthesis of collagen models with longer
chains and with three differentiated chains, and on synthesis of
other three-functionalized cyclopropane templates, are in pro-
gress. Furthermore, all-cis-functionalized cyclopropanes are
also attractive as templates for various chemical libraries and
peptidomimetics.14
Scheme 2
NMR study, as described above. Oxidation of 8 with NaIO4 in
aq. THF gave aldehyde 9 via sila-Pummerer reaction10 in 85%
yield. Aldehydo diester 9 was reduced by LiAlH4 in diethyl
ether to give triol 10 in 41% yield. The reaction of 10 and three
equivalents of N-Boc-glycine in the presence of WSC {1-[3-
(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride}–
DMAP [4-(dimethylamino)pyridine] in CH2Cl2 gave 11 in 83%
yield. Deprotection of 11 with trifluoroacetic acid then afforded
2a. The collagen model 2b with the minimum unit Gly-Pro-Pro
was obtained from 10. Protected derivative 12 was directly
prepared in 51% yield by the reaction of triol 10 and three
equivalents of N-Boc-Pro-Pro-Gly-OH using the same condi-
tions. Deprotection of 12 with trifluoroacetic acid gave 2b.§
The cis stereochemistry of the cyclopropanes in Scheme 2
was confirmed by 2D-NOESY. Thus, NOEs between 2-H and
3-H (the cyclopropane ring-numbering is shown in Scheme 2)
and/or between 2-H, 3-H and CH2OMe were observed. The
§ Molecular modelling of 2b shows the chains are too short to form a
triple helix. CD spectra of 2b in aqueous solution showed no positive
band at 220–240 nm at 24 ЊC, which is characteristic for a triple helix.11
J. Chem. Soc., Perkin Trans. 1, 2001, 1870–1875
1871

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MHz; CDCl3) Ϫ1.58 (SiMe3), 14.14 (CH2CH3), 25.28
(CHSeSi), 28.26 (tBu), 33.92 (C-3), 35.21 (C-2), 37.69 (C-1),
61.30 (OCH2CH3), 67.71 (CH2OH), 81.34 (OCMe3), 127.01
(p-C of Ph), 128.77 (m-C of Ph), 130.87 (C of Ph), 133.92 (o-C
Experimental
General methods
Mps were measured on a Yamato MP-21 melting point appar-
atus and are uncorrected. IR spectra were recorded with a
JASCO FT-IR 5000 spectrophotometer. NMR spectra were
recorded on a Varian INOVA 400 spectrometer. Chemical shifts
are reported in ppm relative to Me4Si or residual nondeuterated
solvent. J-Values are given in Hz. 1H and 13C assignments were
determined by COSY, TOCSY, NOESY, DEPT, HSQC and
HMBC. Mass spectra were recorded on a JEOL JMS700 or
JMS-SX-102 spectrometer at an ionizing voltage of 70 eV by EI
or FAB. All reactions were carried out under a nitrogen
atmosphere.
t
of Ph), 167.01 (CO2 Bu) and 169.46 (CO2Et); νmax (neat)/cmϪ1
3412, 2980, 1725, 1578, 1479, 1369, 1249, 1151, 862, 841 and
735; MS (EI) m/z 486; exact mass Mϩ, 486.1319 (Calc. for
C22H34O5SeSi: M, 486.1341) (Calc. for C22H34O5SeSi: C, 54.42;
H, 7.06. Found: C, 53.93; H, 6.88%).
2-tert-Butyl 1-ethyl 1-(methoxymethyl)-c-3-[(phenylseleno)-
(trimethylsilyl)methyl]cyclopropane-r-1,c-2-dicarboxylate 8
After removal of the mineral oil from sodium hydride (60%
dispersion in oil; 69 mg, 2.9 mmol) by washing with n-pentane,
THF (1.4 mL) was added and the mixture was cooled to 0 ЊC. A
THF (2.5 mL) solution of the alcohol 7 (0.93 g, 1.91 mmol) was
added dropwise to the mixture. After the reaction mixture had
been stirred for 30 min at 0 ЊC and for 1 h at room temperature,
it was cooled to 0 ЊC and iodomethane (0.18 mL, 412 mg,
2.9 mmol) was added. After the addition, the mixture was
stirred for 1.5 h at 0 ЊC. MeOH (69 µL) and water (1.6 mL) were
then added. The mixture was extracted with diethyl ether, the
extract was dried (MgSO4), and the solvent was evaporated off
in vacuo. The residue was purified by column chromatography
over silica gel and elution with hexane–diethyl ether (2 : 1) to
give 8 (926 mg, 97%), Rf 0.6, as a pale yellow oil; δH (400 MHz;
CDCl3) 0.036 (9H, s, SiMe3), 1.17 (3H, t, J 7.1, CH2CH3), 1.46
2-tert-Butyl 1,1-diethyl 2,3-cis-3-[(phenylseleno)(trimethylsilyl)-
methyl]cyclopropane-1,1,2-tricarboxylate 6
Optimization of the reaction conditions gave a better yield than
that described in ref. 9c. To a solution of 4 (2.66 g, 10.4 mmol)
in dichloromethane (24 mL), cooled to Ϫ78 ЊC, was added ZnI2
(4.99 g, 15.7 mmol), followed by a solution of 5 (3.69 g, 13.6
mmol) in dichloromethane (4 mL). The mixture was allowed to
warm to Ϫ40 ЊC and was stirred for 18 h. The reaction was
quenched by triethylamine (3.7 mL, 2.70 g, 26.7 mmol), and
then saturated aq. NaHCO3 (10 mL) was added to the mixture,
which was extracted with dichloromethane, and the organic
phase was washed with water, dried (Na2SO4), and evaporated
in vacuo. The residue was purified by column chromatography
over silica gel with hexane–diethyl ether (2 : 1) as eluent to give
6 (4.79 g, 89%), Rf 0.6, as a colorless oil; δH (400 MHz; CDCl3)
Ϫ0.002 (9H, s, SiMe3), 1.22 (3H, t, J 7.1, CH2CH3), 1.27 (3H, t,
J 7.1, CH2CH3), 1.45 (9H, s, tBu), 2.00 (1H, dd, J 13.5 and 9.4,
H-3), 2.62 (1H, d, J 9.4, H-2), 3.32 (1H, d, J 13.5, CHSeSi),
4.01–4.26 (4H, m, OCH2CH3), 7.19–7.22 (3H, m, m-, p-H of
Ph) and 7.61–7.64 (2H, m, o-H of Ph). The ring numbering is
shown in Scheme 2. Selected NOEs were between δ Ϫ0.002 and
1.45, δ 1.45 and 3.32, δ 1.45 and 4.01–4.26, and δ 2.00 and 2.62;
δC (100.6 MHz; CDCl3) Ϫ1.54 (SiMe3), 14.04 (CH2CH3), 23.46
(CHSeSi), 28.20 (tBu), 34.49 (C-2), 35.91 (C-3), 39.51 (C-1),
61.28 (OCH2CH3), 62.32 (OCH2CH3), 82.16 (OCMe3), 127.29
(p-C of Ph), 128.69 (m-C of Ph), 129.84 (C of Ph), 135.15
(o-C of Ph), 164.60 (CO), 167.99 (CO) and 169.57 (CO). The
spectroscopic data are in agreement with those described in ref.
9c.
t
(9H, s, Bu), 1.70 (1H, dd, J 13.2 and 8.8, H-3), 2.24 (1H, d,
J 8.8, H-2), 3.37 (3H, s, OMe), 3.513 (1H, d, J 10.3, CHHOMe),
3.515 (1H, d, J 13.2, CHSeSi), 3.72 (1H, d, J 10.3, CHHOMe),
3.91–4.02 (2H, m, OCH2CH3), 7.18–7.21 (3H, m, m-, p-H of
Ph) and 7.56–7.58 (2H, m, o-H of Ph). Selected NOEs were
between δ 1.70 and 2.24, δ 1.70 and 3.513, δ 1.70 and 3.72, δ 2.24
and 3.513, and δ 2.24 and 3.72; δC (100.6 MHz; CDCl3) Ϫ1.55
(SiMe3), 14.10 (CH2CH3), 25.24 (CHSeSi), 28.27 (tBu), 31.74
(C-3), 33.24 (C-2), 35.91 (C-1), 58.81 (OCH3), 60.92 (OCH2-
CH3), 73.75 (CH2OMe), 81.04 (OCMe3), 126.80 (p-C of Ph),
128.66 (m-C of Ph), 131.02 (C of Ph), 133.88 (o-H of Ph),
167.77 (CO) and 168.72 (CO); νmax (neat)/cmϪ1 2980, 1740,
1578, 1479, 1369, 1309, 1249, 1154, 861, 839 and 737; MS (EI)
m/z 500; exact mass Mϩ, 500.1511 (Calc. for C23H36O5SeSi: M,
500.1497).
2-tert-Butyl 1-ethyl c-3-formyl-1-(methoxymethyl)-cyclo-
propane-r-1,c-2-dicarboxylate 9
To a solution of 8 (955 mg, 1.91 mmol) in THF (39 mL) were
added water (19.5 mL) and NaIO4 (2.043 g, 9.55 mmol). The
mixture was stirred for 4.5 h at room temperature. After
removal of THF in vacuo, saturated aq. NaHCO3 was added to
the residue. The mixture was extracted with diethyl ether 5
times, and the organic phase was washed with water, dried
(MgSO4), and evaporated in vacuo to give 9 (465 mg, 85%) as a
colorless oil; δH (400 MHz; CDCl3) 1.30 (3H, t, J 7.1, CH2CH3),
1.46 (9H, s, tBu), 2.18 (1H, dd, J 9.2 and 6.0, H-3), 2.40 (1H, d,
J 9.2, H-2), 3.35 (3H, s, OMe), 3.39 (1H, d, J 10.3, CHHOMe),
3.85 (1H, d, J 10.3, CHHOMe), 4.26 (2H, q, J 7.1, OCH2CH3)
and 9.71 (1H, d, J 6.0, CHO). Selected NOEs were between
δ 2.18 and 2.40, δ 2.18 and 3.39 and δ 2.40 and 3.39; δC (100.6
MHz; CDCl3) 14.12 (CH2CH3), 28.04 (tBu), 31.66 (C-2), 35.91
(C-3), 39.74 (C-1), 58.95 (OMe), 62.08 (OCH2CH3), 73.43
(CH2OMe), 82.77 (OCMe3), 166.71 (CO), 167.27 (CO) and
197.94 (CHO); νmax (neat)/cmϪ1 2984, 2936, 1729, 1715, 1458,
1396, 1373, 1323, 1228, 1152, 1112 and 1023; MS (FAB) m/z
287 (M ϩ H)ϩ; exact mass (M ϩ H)ϩ, 287.1507 (Calc. for
C14H23O6: m/z, 287.1495).
2-tert-Butyl 1-ethyl 1-(hydroxymethyl)-c-3-[(phenylseleno)-
(trimethylsilyl)methyl]cyclopropane-r-1,c-2-dicarboxylate 7
The cyclopropane 6 (4.52 g, 8.6 mmol) obtained as above was
dissolved in THF (24 mL), and anhydrous lithium chloride
(1.471 g, 34.2 mmol) and sodium borohydride (1.301 g, 34.2
mmol) were added successively at 0 ЊC. After addition of
ethanol (48 mL), the mixture was allowed to warm to room
temperature and was stirred overnight, then refluxed for 4 h
before being cooled with ice–water, acidifed by the gradual
addition of 10% aq. citric acid (37 mL), and concentrated in
vacuo. Water was added to the residue, which was extracted
with dichloromethane; the extract was dried (Na2SO4), and
evaporated in vacuo. The residue was purified by column
chromatography over silica gel and elution with hexane–diethyl
ether (2 : 1) to give 7 (3.15 g, 75%), Rf 0.2, as a pale yellow oil;
δH (400 MHz; CDCl3) 0.060 (9H, s, SiMe3), 1.18 (3H, t, J 7.1,
CH2CH3), 1.46 (9H, s, tBu), 1.66 (1H, dd, J 13.2 and 8.9, H-3),
2.17 (1H, d, J 8.9, H-2), 2.43 (1H, br, OH), 3.47 (1H, dd, J 11.8
and 6.4, CHHOH), 3.52 (1H, d, J 13.2, CHSeSi), 3.80 (1H, dd,
J 11.8 and 5.7, CHHOH), 3.96 (2H, q, J 7.1, OCH2CH3), 7.19–
7.23 (3H, m, m-, p-H of Ph) and 7.55–7.58 (2H, m, o-H of Ph).
Selected NOEs were between δ 1.66 and 2.17, δ 1.66 and 3.47,
δ 1.66 and 3.80, δ 2.17 and 3.47, and δ 2.17 and 3.80; δC (100.6
r-1-(Methoxymethyl)-1,t-2,t-3-tris(hydroxymethyl)cyclopropane
10
To LiAlH4 (89 mg, 2.1 mmol) was added diethyl ether (4.5 mL)
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J. Chem. Soc., Perkin Trans. 1, 2001, 1870–1875

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and the mixture was stirred for 1 h at room temperature, then
cooled to 0 ЊC, and a solution of 9 (201 mg, 0.7 mmol) in
diethyl ether (6.3 mL) was added with stirring. The resulting
mixture was allowed to warm to room temperature and was
stirred for 1 h. Saturated aq. Na2SO4 (2 mL) was then added to
the mixture, which was then extracted with diethyl ether 5 times,
and the organic phase was dried (MgSO4), and evaporated in
vacuo. The residue was purified by column chromatography
over silica gel with diethyl ether–MeOH (19 : 1) as eluent to give
10 (50 mg, 41%), Rf 0.2, as a colorless oil; δH (400 MHz; CDCl3)
1.36 (2H, m, H-2,3), 2.88 (2H, br s, OH), 3.34 (1H, m, OH),
3.35 (2H, s, CH2OMe), 3.38 (3H, s, OMe), 3.79 (4H, br s,
2,3-CH2OH) and 3.88 (2H, d, J 5.1, 1-CH2OH). Selected
NOEs were between δ 1.36 and 3.35; δC (100.6 MHz; CDCl3)
27.43 (C-2, -3), 30.06 (C-1), 58.68 (2-, 3-CH2OH), 59.10 (OMe),
61.50 (1-CH2OH) and 81.53 (CH2OMe); νmax (neat)/cmϪ1 3504,
2930, 1456, 1419, 1241, 1195, 1096 and 1023; MS (FAB) m/z
177 (M ϩ H)ϩ; exact mass (M ϩ H)ϩ, 177.1127 (Calc. for
C8H17O4: m/z, 177.1127).
was converted to Boc-Pro-Pro-Gly-OBzl by reaction with Boc-
Pro-OH, N-methyl morpholine and DCC in CH2Cl2 in 91%
yield. The product was converted to Boc-Pro-Pro-Gly-OH by
hydrogenation in the presence of Pd/C in methanol in 98%
yield.
Compound 12
To a solution of Boc-Pro-Pro-Gly-OH (184 mg, 0.50 mmol),
DMAP (5.6 mg, 0.046 mmol) and 10 (28 mg, 0.16 mmol) in
CH2Cl2 (1 mL) was added WSC (105 mg, 0.5 mmol) at 0 ЊC.
The mixture was stirred for 2 h at 0 ЊC, allowed to warm to
room temperature, and stirred overnight. After removal of the
solvent under reduced pressure, CH2Cl2 (20 mL) and water
(4 mL) were added to the residue. The organic phase was
extracted, washed with saturated aq. NaHCO3 (4 mL × 2)
and water (4 mL × 2), dried (Na2SO4), and evaporated in vacuo.
The residue was purified by column chromatography over silica
gel and elution with diethyl ether–MeOH (19 : 1) to give 12
(101 mg, 51%), Rf 0.3, as colorless crystals; mp 86–88 ЊC;
δH (400 MHz; CDCl3) 1.39 (s), 1.41 (s), 1.46 (s) (proportions
Compound 11
t
1 : 0.9 : 1.5, total 27H, Bu), 1.46 (2H, m, H-2, -3), 1.82–2.56
To a solution of Boc-Gly-OH (154 mg, 0.88 mmol), DMAP (10
mg, 0.08 mmol) and 10 (50 mg, 0.28 mmol) in CH2Cl2 (3.2 mL)
was added WSC (184 mg, 0.96 mmol) at 0 ЊC. The mixture was
stirred for 2 h at 0 ЊC, allowed to warm to room temperature,
and stirred overnight. After removal of the solvent under
reduced pressure, diethyl ether (40 mL) and water (2 mL) were
added to the residue. The organic phase was extracted, washed
successively with saturated aq. NaHCO3 (4 mL × 2) and water
(4 mL × 2), dried (MgSO4), and evaporated in vacuo. The resi-
due was purified by column chromatography over silica gel and
elution with diethyl ether–MeOH (19 : 1) to give 11 (150 mg,
83%), Rf 0.4, as a colorless viscous oil; δH (400 MHz; CDCl3)
(24H, m, Pro-β, -γ), 3.16–3.31 (2H, m, CH2OMe), 3.30 (3H, s,
OMe), 3.40–3.74 (12H, m, Pro-δ), 3.84–4.08 (6H, m, Gly-α),
4.15–4.29 (6H, m, CH2OCO), 4.31–4.35 (m), 4.41 (dd, J 8.4
and 4.4), 4.50 (dd, J 8.3 and 3.9), 4.70 (m) (proportions
1 : 0.8 : 1.0 : 1.5, total 6H, Pro-α), 7.61–7.64 (2H, m, Gly-NH)
and 8.62–8.63 (m, 1H, Gly-NH); δC (100.6 MHz; CDCl3) 22.20
(Pro-β or -γ), 23.12 (C-2, -3), 23.74 (Pro-β or -γ), 24.31 (Pro-β
or -γ), 24.69 (Pro-β or -γ), 25.01 (Pro-β or -γ), 25.29 (Pro-β or
-γ), 25.67 (Pro-β or -γ), 26.79 (Pro-β or -γ), 26.92 (Pro-β or -γ),
27.54 (C-1), 28.46 (tBu), 28.55 (tBu), 29.47 (Pro-β or -γ), 29.75
(Pro-β or -γ), 30.35 (Pro-β or -γ), 31.73 (Pro-β or -γ), 34.00
(Pro-β or -γ), 41.14 (Gly-α), 41.47 (Gly-α), 46.78 (Pro-δ), 46.99
(Pro-δ), 47.09 (Pro-δ), 47.23 (Pro-δ), 57.82 (Pro-α), 58.14 (Pro-
α), 58.80 (OMe), 59.50 (Pro-α), 59.66 (Pro-α), 61.02 (Pro-α),
61.10 (2-, 3-CH2OCO), 61.69 (1-CH2OCO), 76.25 (CH2OMe),
76.59 (CH2OMe), 79.59 (OCMe3), 79.73 (OCMe3), 80.06
(OCMe3), 153.75 (CO2 Bu), 154.65 (CO2 Bu), 154.92 (CO2 Bu),
169.27 (CO), 169.58 (CO), 171.50 (CO), 171.84 (CO), 171.94
(CO), 172.01 (CO), 172.08 (CO), 172.70 (CO) and 172.80 (CO);
νmax (KBr)/cmϪ1 2978, 2882, 1745, 1688, 1657, 1543, 1402 and
1165; MS (FAB) m/z 1252 (M ϩ Na)ϩ, 1230 (M ϩ H)ϩ; exact
mass (M ϩ Na)ϩ, 1252.6311 (Calc. for C59H91N9NaO19: m/z,
1252.6329), (M ϩ H)ϩ, 1230.6454 (Calc. for C59H92N9O19:
m/z, 1230.6510), Mϩ, 1229.6470 (Calc. for C59H91N9O19. M,
1229.6431).
t
1.45 (27H, s, Bu), 1.50 (2H, m, H-2, -3), 3.26 (2H, br s,
CH2OMe), 3.31 (3H, s, OMe), 3.90 (6H, d, J 5.9, Gly-α), 4.26–
4.31 (4H, m, 2-, 3-CH2OCO), 4.34 (2H, s, 1-CH2OCO) and 5.20
(br s, NH). Selected NOEs were between δ 1.50 and 3.26 and
δ 4.26–4.31 and 4.34; δC (100.6 MHz; CDCl3) 23.24 (C-2, -3),
27.66 (C-1), 28.40 (tBu), 42.46 (Gly-α), 58.85 (OMe), 61.16 (2-,
3-CH2OCO), 61.71 (1-CH2OCO), 76.39 (CH2OMe), 80.17
t
t
t
t
(OCMe3), 155.89 (CO2 Bu) and 170.30 (HNCH2CO); νmax
(KBr)/cmϪ1 3400, 2982, 1750, 1725, 1520, 1369 and 1170; MS
(EI) m/z 647; exact mass Mϩ, 647.3229 (Calc. for C29H49N3O13:
M, 647.3265).
Compound 2a
TFA (0.32 mL) was added to 11 (20 mg, 0.031 mmol) at 0 ЊC
and the solution was stirred for 2 h. Removal of the solvent
under reduced pressure gave 2a quantitatively as a colorless
viscous oil; δH (400 MHz; D2O) 1.48 (2H, m, H-2, -3), 3.15 (3H,
s, OMe), 3.19 (2H, s, CH2OMe), 3.76 (4H, s, Gly-α), 3.78 (2H, s,
Gly-α), 4.29 (4H, d, J 7.8, 2-, 3-CH2OCO) and 4.31 (2H, s,
1-CH2OCO). Selected NOEs were between δ 1.48 and 3.76 and
δ 4.29 and 4.31; δC (100.6 MHz; D2O) 24.16 (C-2, -3), 28.02
(C-1), 40.93 (Gly-α), 41.01 (Gly-α), 59.01 (OMe), 63.84 (2-,
3-CH2OCO), 64.52 (1-CH2OCO), 77.82 (CH2OMe), 117.24
(C, q, JCF 291.5, CF3), 163.82 (C, q, JCF 35.9, CF3CO), 168.81
(CO) and 169.01 (CO); νmax (neat)/cmϪ1 3000, 1760, 1748, 1684,
1653, 1634, 1435 and 1417; MS (FAB) m/z 370 (M ϩ Na)ϩ,
348 (M ϩ H)ϩ; exact mass (M ϩ Na)ϩ, 370.1596 (Calc. for
C14H25N3NaO7: m/z, 370.1590); (M ϩ H)ϩ, 348.1779 (Calc.
for C14H26N3O7: m/z 348.1771).
Boc-Pro-Pro-Gly-OH was prepared by standard liquid-phase
peptide-synthesis methods. Reaction of glycine, p-TsOH, and
benzyl alcohol in benzene gave Gly-OBzlؒTsOH in 77% yield.
Gly-OBzؒTsOH was converted to Boc-Pro-Gly-OBzl by reac-
tion with Et3N, Boc-Pro-OH, and DCC in CH2Cl2 quanti-
tatively The product was converted to TFAؒPro-Gly-OBzl by
reaction with TFA in CH2Cl2 in 66% yield. TFAؒPro-Gly-OBzl
Compound 2b
TFA (0.17 mL) was added to 12 (20 mg, 0.016 mmol) at 0 ЊC
and the solution was stirred for 2 h. Removal of the solvent
under reduced pressure gave 2b (20 mg, 100%) as a pale yellow
oil; δH (400 MHz; D2O) 1.41 (2H, t-like, J 5.6, H-2, -3), 1.73–
1.94 (18H, m, Pro-γ, -β), 2.14–2.22 (3H, m, Pro-β), 2.32–2.43
(3H, m, Pro-β), 3.14 (3H, s, OMe), 3.13–3.28 (8H, m, CH2OMe,
Pro-δ), 3.39–3.45 (3H, m, Pro-δ), 3.50–3.55 (3H, m, Pro-δ), 3.79
(2H, d, J 17.9, Gly-α), 3.80 (1H, d, J 17.9, Gly-α), 3.90 (2H, d,
J 17.9, Gly-α), 3.92 (1H, d, J 17.9, Gly-α), 4.18 (4H, d, J 5.6, 2-,
3-CH2OCO), 4.23 (2H, s, 1-CH2OCO), 4.31–4.34 (3H, m,
Pro-α) and 4.43–4.47 (3H, m, Pro-α); δC (100.6 MHz; D2O)
24.10 (C-2, -3), 24.81 (Pro-γ), 25.55 (Pro-γ), 28.00 (C-1), 29.32
(Pro-β), 30.44 (Pro-β), 42.18 (Gly-α), 47.55 (Pro-δ), 48.65
(Pro-δ), 58.98 (OMe), 60.05 (Pro-α), 61.47 (Pro-α), 63.09 (2-,
3-CH2OCO), 63.51 (1-CH2OCO), 117.25 (C, q, JCF 292, CF3),
163.83 (C, q, JCF 35.6, CF3CO), 171.92 (CO), 171.98 (CO),
175.10 (CO) and 175.16 (CO); νmax (neat)/cmϪ1 3400, 1734,
1694, 1684, 1667, 1653, 1647, 1634, 1570, 1557, 1541, 1470, and
1456; MS (FAB) m/z 930 (M ϩ H)ϩ; exact mass (M ϩ H)ϩ,
930.4933 (Calc. for C44H68N9O13: m/z, 930.4937).
J. Chem. Soc., Perkin Trans. 1, 2001, 1870–1875
1873

View Article Online
2-tert-Butyl 1-ethyl 3-hydrogen 1-(methoxymethyl)cyclopropane-
r-1,c-2,c-3-tricarboxylate 13
νmax (KBr)/cmϪ1 3280, 3000, 1750, 1735, 1628, 1549, 1369,
1228 and 1154; MS (FAB) m/z 495 (M ϩ Na)ϩ, 473 (M ϩ H)ϩ;
exact mass (M ϩ H)ϩ, 473.2491 (Calc. for C22H37N2O9: m/z,
473.2499).
Compound 8 (203 mg, 0.41 mmol) was dissolved in a mixture
of CH3CN (4.3 mL), CCl4 (4.3 mL), and water (5.5 mL); NaIO4
(1.052 g, 4.93 mmol) was then added, followed by RuCl3ؒxH2O
(14 mg, ≈0.067 mmol). After 5 h of stirring at room temper-
ature, the solution was diluted with diethyl ether. The layers
were separated, and the aq. layer was extracted with diethyl
ether. The combined organic layers were dried (MgSO4), and
concentrated in vacuo. The residue was purified by column
chromatography over silica gel and elution with hexane–diethyl
ether (1 : 9) to give 13 (75 mg, 61%), Rf 0.6, as pale yellow
crystals; mp 108–110 ЊC; δH (400 MHz; CDCl3) 1.28 (3H, t,
J 7.1, CH2CH3), 1.48 (9H, s, tBu), 2.33 (1H, d, J 9.3, H-2), 2.46
(1H, d, J 9.3, H-3), 3.36 (3H, s, OMe), 3.57 (1H, d, J 10.1,
CHHOMe), 3.77 (1H, d J 10.1, CHHOMe) and 4.20–4.27 (2H,
m, OCH2CH3). The ring numbering is shown in Scheme 3.
Selected NOEs were between δ 2.33 and 2.46, δ 2.33 and 3.57,
δ 2.33 and 3.77, δ 2.46 and 3.57, and δ 2.46 and 3.77; δC (100.6
MHz; CDCl3) 13.86 (CH2CH3), 27.92 (tBu), 29.26 (C-3), 29.99
(C-2), 36.46 (C-1), 58.92 (OMe), 62.34 (OCH2CH3), 72.05
(CH2OMe), 83.96 (OCMe3), 168.39 (CO), 169.18 (CO) and
169.20 (CO); νmax (KBr)/cmϪ1 2990, 1745, 1731, 1371 and 1154;
MS (FAB) m/z 303 (M ϩ H)ϩ; exact mass (M ϩ H)ϩ, 303.1435
(Calc. for C14H23O7. m/z, 303.1444).
Compound 17
To a solution of 15 (40 mg, 0.085 mmol) in THF (1 mL) was
added LiOHؒH2O (3.6 mg, 0.085 mmol) at room temperature.
The mixture was stirred overnight. After removal of the solvent
under reduced pressure, CH2Cl2 and water were added to the
residue and acidified with KHSO4. The organic phase was
extracted, dried (Na2SO4), and evaporated in vacuo. The residue
was purified by column chromatography over silica gel and elu-
tion with diethyl ether–MeOH (9 : 1) to give 17 (27.5 mg, 76%),
Rf 0.7, as a colorless oil; δH (400 MHz; CDCl3) 1.45 (9H, s, tBu),
t
1.46 (9H, s, Bu), 2.71 (1H, d, J 8.5, H-3), 2.82 (1H, d, J 8.5,
H-2), 3.38 (3H, s, OMe), 3.82 (1H, d, J 10.6, CHHOMe), 3.87
(2H, d, J 5.0, HNCH2CO), 3.97 (1H, d, J 10.6, CHHOMe),
3.99 (2H, s, NCH2CO) and 6.46 (1H, J 5.0, t, NH). Selected
NOEs were between δ 2.71 and 2.82, δ 2.71 and 3.82, δ 2.71 and
3.97, δ 2.82 and 3.82, δ 2.82 and 3.97, and δ 2.71 and 6.46;
δC (100.6 MHz; CDCl3) 28.02 (tBu), 28.05 (tBu), 29.65 (C-3),
36.57 (C-2), 37.63 (C-1), 40.62 (NCH2CO), 42.41 (HNCH2-
CO), 59.17 (OMe), 67.16 (CH2OMe), 82.46 (OCMe3), 82.70
(OCMe3), 165.08 (CO), 166.05 (CO), 168.50 (CO), 170.89 (CO)
and 171.81 (CO); νmax (neat)/cmϪ1 3320, 2982, 2940, 1742, 1725,
1715, 1684, 1541, 1419, 1373, 1232 and 1158; MS (FAB) m/z,
449 (M ϩ Na)ϩ, 427 (M ϩ H)ϩ.
1-Ethyl 2,3-dihydrogen 1-(methoxymethyl)cyclopropane-r-1, c-2,
c-3-tricarboxylate 14
TFA (0.37 mL) was added to 13 (32 mg, 0.11 mmol) at 0 ЊC and
the solution was stirred for 15 min. Removal of the solvent
under reduced pressure gave 14 (29 mg, 100%) as colorless crys-
tals, mp 106–108 ЊC; δH (400 MHz; CDCl3) 1.25 (3H, t, J 6.7,
CH2CH3), 2.55 (2H, s, H-2, -3), 3.40 (3H, s, OMe), 3.71 (2H, s,
CH2OMe) and 4.24 (2H, q, J 6.7, OCH2CH3). Selected NOEs
were between δ 2.55 and 3.71; δC (100.6 MHz; CDCl3) 13.51
(CH2CH3), 29.39 (C-2, -3), 37.26 (C-1), 59.10 (OMe), 63.09
(OCH2CH3), 72.60 (CH2OMe), 168.44 (CO2Et) and 172.80
(CO2H); νmax (KBr)/cmϪ1 3400, 3000, 2900, 1740, 1713, 1439,
1234, 1201 and 1110; MS (FAB) m/z 247 (M ϩ H)ϩ; exact mass
(M ϩ H)ϩ, 247.0821 (Calc. for C10H15O7: m/z, 247.0818) (Calc.
for C10H14O7: C, 48.78; H, 5.73; O, 45.49. Found: C, 48.54; H,
5.74; O, 45.14%).
Acknowledgements
We are grateful to Dr K. Yamamoto (Osaka University) and
Dr Shigeo Umetani (Kyoto University) for measurement of
mass spectra and elemental analysis. We thank Ms Etsuko
Tanigawa for experimental assistance.
References
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Compound 15
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Et3N (0.125 mL, 90.4 mg, 0.83 mmol) was added to glycine tert-
butyl ester hydrochloride (139 mg, 0.83 mmol) in THF (0.76
mL). To the solution were added HOBt (223 mg, 1.65 mmol)
and 14 (108.5 mg, 0.41 mmol). The mixture was cooled to 0 ЊC
and a solution of DCC (177 mg, 0.86 mmol) in THF (0.38 mL)
was added. The reaction mixture was stirred for 1 h at 0 ЊC,
allowed to warm to room temperature, and stirred overnight.
After removal of the insoluble dicyclohexylurea (DCU), the
filtrate was concentrated under reduced pressure. The residue
was dissolved in CH2Cl2 and the organic phase was washed
successively with saturated aq. NaHCO3, 2 M aq. citric acid,
saturated aq. NaHCO3, and water (2 mL), dried (Na2SO4), and
evaporated in vacuo. The residue was purified by column
chromatography over silica gel with diethyl ether–MeOH
(19 : 1) as eluent to give 15 (106 mg, 54%), Rf 0.3, as colorless
crystals, mp 91–93 ЊC; δH (400 MHz; CDCl3) 1.17 (3H, t, J 7.1,
CH2CH3), 1.45 (18H, s, tBu), 2.33 (2H, s, H-2, -3), 3.36 (3H, s,
OMe), 3.64 (2H, s, CH2OMe), 3.88 (2H, dd, J 18.3 and 4.9,
Gly-α), 3.95 (2H, dd, J 18.3 and 5.2, Gly-α), 4.13 (2H, q, J 7.1,
OCH2CH3) and 7.67 (2H, dd, J 5.2 and 4.9, NH). Selected
NOEs were between δ 2.33 and 3.64; δC (100.6 MHz; CDCl3)
13.95 (CH2CH3), 28.09 (tBu), 31.59 (C-2, -3), 35.14 (C-1), 42.42
(Gly-α), 59.01 (OMe), 61.65 (OCH2CH3), 73.36 (CH2OMe),
82.14 (OCMe3), 167.18 (CO), 168.55 (CO) and 168.67 (CO);
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T. Takada, T. Imanishi, Y. Moriguchi and S. Yamabe, J. Org. Chem.,
1874
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1875