Strategies and methods for the attachment of amino acids and peptides to chiral [n]polynorbornane templates.

Article abstract of DOI:10.1039/b301980b

A versatile synthesis of amino acid and peptide functionalised [n]polynorbornane scaffolds is described. The frameworks are constructed using the stereoselective and regioselective cycloaddition of suitably functionalised chiral cyclobutene epoxides with similar norbornenes. The strategies employed allow a range of topologies to be accessed and a number of regioselectively addressable linkage points to be accommodated.

Full text of DOI:10.1039/b301980b

View Article Online / Journal Homepage / Table of Contents for this issue
Strategies and methods for the attachment of amino acids and
peptides to chiral [n]polynorbornane templates
Frederick M. Pfeffer*a and Richard A. Russellb
a Department of Chemistry, Trinity College Dublin, Dublin 2, Ireland. E-mail: pfefferf@tcd.ie;
Fax: ϩ353 1 671 2826; Tel: ϩ353 1 608 1306
b Centre for Chiral and Molecular Technologies, Deakin University, Geelong, 3216, Australia.
E-mail: rarcat@deakin.edu.au; Fax: ϩ61 3 925 17492; Tel: ϩ 61 3 925 17454
Received 20th February 2003, Accepted 4th April 2003
First published as an Advance Article on the web 25th April 2003
A versatile synthesis of amino acid and peptide functionalised [n]polynorbornane scaffolds is described.
The frameworks are constructed using the stereoselective and regioselective cycloaddition of suitably functionalised
chiral cyclobutene epoxides with similar norbornenes. The strategies employed allow a range of topologies to be
accessed and a number of regioselectively addressable linkage points to be accommodated.
amines. With this in mind, the specific inclusion of such func-
Introduction
tional groups, in well defined spatial arrangements, to poly-
norbornane frameworks was pivotal to the current investigation.
Examination of a typical polynorbornyl framework5 (Fig. 2)
reveals that carboxy edge functionality is introduced, in the
form of methyl esters, by means of the Mitsudo reaction of
a norbornene with dimethylacetylenedicarboxylate (DMAD)8
and as such is characteristic of ACE chemistry. Consequently, it
was decided to exclusively adopt carboxylic acids as attachment
points, and to use orthogonal protecting groups to enable
these points to be selectively addressed. Whilst methyl esters are
not ideal as an orthogonal protecting group, we have demon-
strated previously7 that the readily available di-tert-butylacetyl-
enedicarboxylate (DtBAD) is an efficient partner in the
Mitsudo reaction. Such a reaction leads ultimately to [n]poly-
norbornanes with tert-butyl edge esters, which in turn offer the
possibility of selective cleavage.
Macromolecules that exhibit a well-defined three-dimensional
structure have proven useful as templates in a range of appli-
cations including peptidomimetics.1 These scaffold-like mole-
cules impart a specific geometry to any attached peptide loops
or segments. Such TASP (Template Assembled Synthetic Pep-
tides)2 constructs have been successfully applied in small mole-
cule recognition3 and even protein surface recognition.4 For
successful peptide attachment, these molecules require select-
ively addressable points incorporated within their structure.
Polynorbornane frameworks are readily synthesised by
means of the ACE (Alkene ϩ Cyclobutene Epoxide) reaction.5
This reaction involves the thermal ring opening of cyclobutene
epoxides and subsequent 1,3-dipolar cycloaddition of the
resulting carbonyl ylides to functionalised norbornenes. Such
technology offers a versatile method for the synthesis of poly-
norbornane based frameworks of various geometries, both
linear and bent.6
As polynorbornyl scaffolds inherently possess a high degree
of structural rigidity they are ideally suited for use as molecular
templates. Additionally, polynorbornyl templates offer, depend-
ing upon their design, the capacity to be chiral and hence may
be synthesised as enantiomerically pure compounds. Whilst we
have recently introduced the concept of [n]polynorbornane
frameworks as rigid templates to which peptides can be
attached in a regiospecific manner,7 we herein report the precise
protocol to assembling peptide chains on chiral [n]polynor-
bornane templates. Furthermore, the methodology outlined is
equally well suited for attachment of other effectors e.g. DNA
intercalators via peptide chains.†
Fig. 2 Typical polynorbornyl framework.
Disconnection
To investigate the concept of regioselectively addressable
groups, framework 1 (Fig. 3), that included both benzyl esters
(end functionality) and tert-butyl esters (edge functionality)
was designed—benzyl esters are well established as orthogonal
to tert-butyl.9 Retrosynthetic analysis identified the orthogon-
ally protected epoxide 2 and norbornene endo ester 3 as neces-
sary components. This latter building block was seen as readily
obtainable from the Diels–Alder reaction of a suitable acryl-
ate with cyclopentadiene. Such reactions are well documented,
as is the endo preference of this cycloaddition.10 For future
Results and discussion
Several points on the [n]polynorbornyl framework have been
identified as suitable for peptide attachment (see Fig. 1) and
ideally, to complement traditional peptide synthetic method-
ology, these attachment points should be carboxylic acids or
Fig. 1 Sites for attachment to [n]polynorbornanes.
† Such endeavours are presently underway and will be reported in due
course.
Fig. 3 Disconnection of proposed template.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1845

View Article Online
applications it was thought the likelihood of interaction
between any attached peptide chains would be maximised if
they were directed in this pseudo-axial endo orientation.
Edge substitution
To explore the elaboration of the tert-butyl edge esters the syn-
thesis of the model [n]polynorbornyl framework 8 (Scheme 1)
was examined. The esters of 6 were cleanly cleaved with tri-
fluoroacetic acid (TFA) in dichloromethane. Coupling of the
resulting diacid 7 with glycine methyl ester using the combin-
ation of the water soluble 1-ethyl-3-(3Ј-dimethylaminopropyl)-
carbodiimide hydrochloride (EDCI) together with a catalytic
amount of 1-hydroxy-1,2,3-benzotriazole (HOBt)11 afforded
the desired amino acid functionalised framework 8 in 67%
yield.
Fig. 4 Possible stereoisomers.
cating that indeed, 1 had been produced as a single enantiomer
and was of the stereochemistry as indicated in Scheme 2. The
use of chiral starting materials allowed a successful route
to frameworks of type III to be developed and with it the
controlled positioning of the attachment points had been
achieved. From this point forward the racemic acid was used
only for validating synthetic pathways prior to chiral frame-
work construction.
The benzyl esters were selectively removed from 1 by means
of hydrogenation and the coupling reaction of the free acids
with glycine methyl ester attempted. Unfortunately, a range of
coupling reagents including carbodiimides,11 PyBop15 and
EEDQ16 failed to yield the desired product. This lack of
reactivity is probably due to steric hindrance as it is known that
polynorbornane frameworks are slightly curved in nature6 and
this exacerbates the known lesser reactivity of the endo position
of norbornanes relative to the exo position.17 Regardless of the
cause, a new approach to end functionalisation was required.
Scheme 1 Edge functionalisation. Reagents and conditions: (i) 1 : 1
TFA–DCM, RT, 4 h; (ii) H-Gly-OMe, EDCI, HOBt, NEt3, DMF, RT,
12 h.
End substitution and chirality
With the elaboration of tert-butyl esters established, we turned
our attention to combining these with orthogonal end func-
tionality. Benzyl ester 3 was synthesised from the readily
available endo-norbornene carboxylic acid 9,12 by means of
carbodiimide coupling with benzyl alcohol (Scheme 2).13 The
Mitsudo reaction of 3 with DtBAD proceeded smoothly as did
epoxidation of the product. The ACE reaction of this epoxide 2
Strategies
1
was also successful although the H NMR spectrum of the
Our initial strategy had been to build the complete framework
first and attach amino acids and peptides last (PATH A, Fig. 5).
An alternative approach, one that also made use of the nor-
bornene acid 3, was to attach the amino acids or peptides first
then construct the framework using the sequence of Mitsudo
reaction, epoxidation and ACE reaction (PATH B) and this
approach was subsequently evaluated.
product 1 revealed three tBu ester resonances.
Scheme 2 Synthesis of fully protected framework. Reagents and
conditions: (i) BnOH, EDCI, DMAP, NEt3, DCM, RT, 12 h;
(ii) RuH2(CO)(PPh3), DtBAD, benzene, 80 ЊC, 24 h; (iii) TBHP, tBuOK,
THF, RT, 12 h; (iv) 3, Sealed tube, THF, 140 ЊC, 12 h.
It was recognised from the outset that three stereoisomers
would be produced from the ACE reaction of a racemic endo-
norbornene with an epoxide derived from such a norbornene
(Fig. 4). Two chiral C2v symmetric isomers (I and III) and a
meso compound (II) are produced in a 1 : 1 ratio of I&III : II.
For enantiomers I and III a single resonance was observed for
Fig. 5 Strategies for incorporating end functionality.
t
the Bu ester (δH = 1.46), however, the meso compound II
The carbodiimide mediated coupling of acid 9 with glycine
methyl ester provided 10 in 76% unoptimised yield (Scheme 3).
This derivative was successfully reacted under Mitsudo condi-
tions followed by epoxidation to provide the desired oxirane 13.
This result reinforces our previous findings that an amide NH is
tolerated if the cyclobutene to be epoxidised is activated by an
ester function.7 To our delight the ACE reaction of epoxide 13
with norbornene amino acid derivative 11 (synthesised as for 10
using alanine as the amino acid) provided the amino acid end
functionalised framework 14 in 41% yield. This framework is an
revealed two distinct resonances for the tBu esters (δH = 1.40 and
δH = 1.52). In order to construct a framework in which the
attachment points exhibit a well ordered and predetermined
topography the synthesis had to be pursued using a single
enantiomer of the norbornene endo-ester. Such optically pure
material was available using the (2S)-norbornene endo-acid
reported by Helmchen and coworkers.14 When the synthesis was
repeated using this optically pure norbornene no trace of the
meso product could be detected by NMR spectroscopy indi-
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1846

View Article Online
reaction of norbornene 11 and epoxide 20) was chosen for this
purpose as the C2 symmetric product would be easily recog-
nised from its NMR spectrum. Indeed, stirring framework 21
with 1 : 1 TFA–DCM ovenight (Scheme 5) cleanly cleaved the
tert-butyl esters then coupling of the diacid 22 with an excess
of glycine methyl ester for 48 hours provided the complete
peptidoframework 23 in 50% yield.
Scheme 3 End functionalisation using the ‘attach first’ strategy.
Reagents and conditions: (i) H-Gly-OMe (or H-Ala-OMe for 11),
EDCI, HOBt, DiPEA, DMF, RT, 12 h; (ii) 10, RuH2(CO)(PPh3),
t
DtBAD, benzene, 80 ЊC, 72 h; (iii) TBHP, BuOK, THF, RT, 14 h;
(iv) 11, Sealed tube, 140 ЊC, DCM, 12 h.
Scheme 5 Complete peptidoframework. Reagents and conditions: (i)
H-Ala-OMe, EDCI, HOBt, DiPEA, DMF, RT, 12 h; (ii) 11, Sealed
tube, DCM, 140 ЊC, 12 h; (iii) 1 : 1 TFA–DCM, RT, 12 h; (iv) H-Gly-
OMe, EDCI, HOBt, DiPEA, DMF, RT, 48 h.
example of the accommodation of three different groups: a
glycine at one end, alanine at the other and tert-butyl groups at
the edges.
Whilst this ‘attach first’ strategy was successful, there was
sound rationale why the failed strategy (PATH A, Fig. 5) was
the more appealing. Specifically, the high temperatures required
in the thermal ACE cycloaddition were seen as incompatible
with complex or valuable peptides which could be degraded or
racemised.
Accordingly, we devised a third strategy that obviated steric
concerns at the same time as minimising the risk of thermal
damage to peptide side chains.
To this end, a short regioselectively addressable, amino acid
spacer, attached to the [n]polynorbornane framework was
required. Commencing with chiral epoxide 2, the benzyl ester
was removed cleanly by hydrogenation and the resulting acid
coupled with glycine benzyl ester to afford 16 in 58% yield
(Scheme 4).
Conclusion
In summary we have established the necessary protocols to syn-
thesise chiral [n]polynorbornanes and to attach unlike amino
acids at the ends and like amino acids on the edges of these
frameworks. Furthermore we have shown how to extend small
polypeptides at the ends of the template. We believe this
approach has much to offer the field of peptidomimetics and we
are presently exploring the construction of looped peptides
using N- and C-terminals on chiral [n]polynorbornanes.
Experimental
NMR spectra were recorded on a Varian Unity Plus 300 MHz
spectrometer. Electrospray mass spectra (ES) were obtained
with a platform II single quadropole mass spectrometer
(Micromass, Altrincham, UK). High resolution mass spectra
(HRMS) were performed by the Centre for Molecular Archi-
tecture, Central Queensland University, Rockhampton. Melt-
ing points were performed on a Reichart hotstage microscope
and are uncorrected. Optical rotations were performed on
a Jasco DIP-1000 digital polarimeter using the Na D line
(589 nm) and 95% EtOH as solvent and are given in 10Ϫ1 deg
cm2 gϪ1 (concentrations are reported as mg × mLϪ1). Thin layer
chromatography was performed on Merck Kieselgel 60 F254
plates. Column chromatography was performed using Merck
Kieselgel 60 (70–230 mesh). All chromatography solvents were
AR grade. Dichloromethane was distilled from CaH2 and
either used fresh or stored over 4 Å sieves. Anhydrous N,N-di-
methylformamide was purchased from Aldrich Chemical Co.
Tetrahydrofuran was freshly distilled from Na/benzophenone
ketyl. Reagents were used as purchased except in the case of
tert-butyl hydroperoxide (TBHP) which was prepared from
commercial TBHP according to the method of Sharpless.18
Scheme 4 Definitive strategy for adding end functionality. Reagents
and conditions: (i) H2, Pd/C, EtOAc, 24 h; (ii) H-Gly-OBn (or H-Ala-
OMe for 17), EDCI, HOBt, DiPEA, DMF, RT, 12 h; (iii) Sealed tube,
DCM, 140 ЊC, 12 h; (iv) H2, Pd/C, EtOAc, 24 h; (v) H-Gly-Gly-OMe,
EDCI, HOBt, DiPEA, DMF, RT, 72 h.
Introduction of an amino acid in this manner is a further
example of the flexibility of this methodology for framework
construction. The ACE reaction of 16 with 11 produced
framework 17 which had a selectively addressable point for
attachment located a safe distance from the bulk of the nor-
bornene. The crucial test for the elaboration of 17 i.e. depro-
tection and coupling with GlyGlyOMe to produce 19 was
accomplished in 68% yield demonstrating conclusively that
this was the method of choice for end functionalisation.
Starting materials
Pure ( )-endo-norbornene-4-carboxylic acid 9 was obtained
using iodolactonisation followed by zinc mediated elimin-
ation.12 The (4S)-enantiomer of 9 was prepared by asymmetric
synthesis according to the method of Helmchen and co-
workers.14 The general epoxidation procedure is our modifi-
cation7 of the TBHP–base reaction originally published by
Meth-Cohn and coworkers.19
End and edge substitutions
General epoxidation procedure
With the successful synthesis of polynorbornane frameworks
having edge substitution and others that had end substitution,
our attention turned to a framework where both end and edge
positions had been addressed with amino acids. The alanine
end functionalised framework 21 (synthesised by the ACE
A solution of alkene (1.0 eq.) dissolved in freshly distilled THF
(∼10 mL : 100 mg substrate) under argon was cooled to 0 ЊC
whereupon TBHP (3.04 M in toluene, 1.5 eq.) was added with
stirring. The cold bath was maintained and after 10 min tBuOK
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1847

View Article Online
(0.3–0.5 eq.) was added in one portion. A slight yellow to
orange colour indicated that the reaction had commenced.
When TLC monitoring indicated the reaction was complete
(4–12 hours), the reaction was quenched by addition of 10%
Na2SO3 (1.5 eq.) and stirred for a further 10 min. This mix was
subsequently partitioned between dichloromethane–H2O (or
chloroform–H2O) and the organic phase separated. The aque-
ous phase was extracted twice more with dichloromethane (or
chloroform) and the combined organics dried (Na2SO4), filtered
and evaporated. Depending on the purity of the material
obtained the product was either isolated by chromatography
(EtOAc–hexane) and/or recrystallised (EtOAc–hexane).
Ϫ105 (c = 43.0); δH(300 MHz, CDCl3, Me4Si) 1.27 (1H, d,
J = 8.3, H7syn), 1.42–1.49 (2H, m, H3endo, H7a), 1.92 (1H,
ddd, J = 12.9, J = 9.0, J = 3.7, H3exo), 2.91 (1H, s, H4), 2.98–
3.04 (1H, m, H2), 3.24 (1H, s, H1), 5.06 (1H, d, J = 12.5,
CHaHbAr), 5.09 (1H, d, J = 12.5, CHaHbAr), 5.88 (1H, dd,
J = 5.9, J = 2.9, H6), 6.19 (1H, dd, J = 5.6, J = 3.2, H5), 7.29–
7.40 (5H, m, ArH); δC(300 MHz, CDCl3, Me4Si) 29.22, 42.55,
43.34, 45.78, 49.61, 65.98, 128.03, 128.47, 132.26, 136.31,
137.79, 174.57; Found 228.1148, C15H16O2 requires 228.1150.
Di-tert-butyl 7ꢁ-benzyloxycarbonyl-(1ꢀ,2ꢁ,5ꢁ,6ꢀ)-tricyclo-
[4.2.1.02,5]nona-3-ene-3,4-dicarboxylate 4
The reaction of norbornene 3 (677 mg, 3.0 mmol) with DtBAD
(680 mg, 3.0 mmol) using RuH2(CO)(PPh3) (70 mg) in benzene
(10 mL) was performed in accordance with the method of
Mitsudo.8 A reaction time of 24 hours was required and the
crude product was purified by chromatography (1 : 20 EtOAc–
hexane, Rf = 0.30) to afford the title compound as a white,
crystalline, solid. For (7S): Yield 947 mg (70%);[α]2D3.3 = Ϫ10.3
(c = 61.0); mp 76–77 ЊC; δH(300 MHz, CDCl3, Me4Si) 1.22 (1H,
(1ꢀ,2ꢁ,3ꢀ,10ꢀ,11ꢁ,12ꢀ,13ꢁ,14ꢀ,21ꢀ,22ꢁ)-24-Oxaoctacyclo-
[10.10.1.13,10.114,21.02,11.04,9.013,22.015,20]pentacosa-4,6,8,15,17,19-
hexaene-1,12-dicarboxylic acid 7
The tert-butyl ester framework 6 (38 mg, 0.07 mmol) was stirred
in a 1 : 1 solution of TFA and dichloromethane for 4 hours. The
solution was concentrated to dryness to provide 30 mg (∼100%)
of the title compound as an off white solid that was used
directly in the next step; δH(300 MHz, CDCl3, Me4Si) 1.35 (2H,
d, J = 8.3, H23,25), 2.08 (4H, s, H2,11,13,22), 2.66 (2H, d,
J = 9.5, H23,25), 3.24 (4H, s, H3,10,14,21), 6.92–6.95 (4H, m,
ArH), 7.03–7.06 (4H, m, ArH); δC(300 MHz, CDCl3, Me4Si)
43.05, 45.59, 55.41, 88.59, 120.67, 125.63, 148.33, 171.29.
t
t
d, J = 11.0, H9syn), 1.47 (9H, s, CO2 Bu), 1.48 (9H, s, CO2 Bu),
1.41–1.65 (2H, m, H9a&H8endo), 1.82 (1H, ddd, J = 16.1,
J = 11.5, J = 4.6, H8exo), 2.29 (1H, d, J = 4.2, H1), 2.61–2.63
(2H, m, H5&6), 2.90 (1H, d, J = 2.9, H2), 2.91 (1H, dt, J = 11.0,
J = 4.6, H7), 5.10 (1H, d, J = 12.5, CHaHbAr), 5.17 (1H, d,
J = 12.5, CHaHbAr), 7.26–7.37 (5H, m, ArH); δC(300 MHz,
CDCl3, Me4Si) 28.03, 29.95, 32.02, 34.19, 37.68, 42.81, 45.06,
46.38, 66.15, 81.27, 81.36, 128.00, 128.05, 128.44, 136.08,
141.66, 142.37, 160.30, 160.43, 173.67; Found 455.2380,
C27H34O6 requires 455.2434.
1,12-Bis(methoxycarbonylmethylcarbamoyl)-(1ꢀ,2ꢁ,3ꢀ,10ꢀ,11ꢁ,
12ꢀ,13ꢁ,14ꢀ,21ꢀ,22ꢁ)-24-oxaoctacyclo[10.10.1.13,10.114,21.02,11
04,9.013,22.015,20]pentacosa-4,6,8,15,17,19-hexaene 8
.
To a nitrogen flushed solution of diacid 7 (30 mg, 0.07 mmol),
glycine methyl ester hydrochloride (20 mg, 0.16 mmol), triethyl-
amine (16 mg, 0.022 mL, 0.16 mmol) in dry DMF (1.0 mL) the
following were added in quick succession from pre-dried pre-
tared screw cap vials: EDCI (30 mg, 0.16 mmol) and hydroxy-
benzatriazole (20 mg, 0.16 mmol). The reaction was allowed to
stir overnight whereupon TLC indicated new material had
formed. Workup consisted of removal of DMF under high
vacuum, redissolving the crude material in chloroform (10 mL)
and washing with dilute HCl (10 mL), sat NaHCO3 (10 mL),
and water (10 mL). Drying over MgSO4, filtration and evapor-
ation yielded a crude material that after column chromato-
graphy (1 : 1–1 : 0 EtOAc–hexane, Rf[1 : 1 EtOAc–hexane] =
0.25) provided the title compound as a waxy white solid. Yield
27 mg (67%); mp 130–133 ЊC; δH(300 MHz, CDCl3, Me4Si) 1.46
(2H, d, J = 9.3, H23,25), 2.23 (4H, s, H2,11,13,22), 2.49 (2H, d,
J = 9.3, H23,25), 3.33 (4H, s, H3,10,14,21), 3.83 (6H, s, CO2Me
Gly), 4.29 (4H, d, J = 5.6, CH2 Gly), 6.91 (2H, t, J = 5.6, NH),
6.97–7.00 (4H, m ArH), 7.09–7.12 (4H, m ArH); δC(300 MHz,
CDCl3, Me4Si) 40.60, 43.55, 45.27, 52.55, 55.25, 90.91, 120.95,
125.80, 148.34, 169.19, 170.04; m/z (ES) 579.4 [C32H32N2O7 ϩ
Na]ϩ; Found 556.2202, C32H32N2O7 requires 556.2209.
Di-tert-butyl 8ꢁ-benzyloxycarbonyl-4-oxa-(1ꢀ,2ꢁ,3ꢀ,5ꢀ,6ꢁ,7ꢀ)-
tetracyclo[5.2.1.02,6.03,5]decane-3,5-dicarboxylate 2
The alkene diester 4 (200 mg, 0.44 mmol) in dry THF (20 mL)
was treated with TBHP (c = 3.0 M, 0.22 mL, 1.5 eq.) and MeLi
(c = 1.4 M, 0.22 mL, 0.7 eq.) in accordance with the standard
epoxidation method. A reaction time of 12 hours was required
and the crude product was purified by chromatography (1 : 8
EtOAc–hexane, Rf = 0.35) to yield the title compound as a crys-
talline solid. For (8S): Yield 180 mg (87%); [α]2D2.5 = Ϫ8.45 (c =
21.8); mp 93–96 ЊC; δH(300 MHz, CDCl3, Me4Si) 1.48 (10H,
t
s, CO2 Bu), 1.45–1.50 (1H, obscured, H10), 1.55 (1H, dm, J =
12.9, H9endo), 1.78 (1H, ddd, J = 11.2, J = 11.2, J = 4.6, H9exo),
1.97 (1H, d, J = 11.9, H10), 2.29 (1H, d, J = 3.9, H6), 2.36 (1H,
d, J = 3.9, H2), 2.73 (1H, d, J = 4.2, H1), 2.87 (1H, dt, J = 6.1,
J = 4.4, H7), 3.03 (1H, d, J = 4.2, H6), 5.09 (1H, d, J = 12.5,
CHaHbAr), 5.13 (1H, d, J = 12.5, CHaHbAr), 7.30–7.36 (5H,
m, ArH); δC(300 MHz, CDCl3, Me4Si) 27.98, 29.99, 34.78,
36.97, 40.24, 45.12, 46.03, 49.55, 64.02, 64.15, 66.23, 82.81,
82.86, 128.01, 128.08, 128.15, 128.49, 135.95, 162.89, 173.38.
Di-tert-butyl 4ꢁ,11ꢁ-bis(benzyloxycarbonyl)-16-oxa-(1ꢀ,2ꢁ,3ꢀ,
6ꢀ,7ꢁ,8ꢀ,9ꢁ,10ꢀ,13ꢀ,14ꢁ)-hexacyclo[6.6.1.14,6.110,13.02,7.09,14]-
heptadeca-1,8-dicarboxylate 1
Benzyl 2-endo-bicyclo[2.2.1]hept-5-enecarboxylate 313
To a nitrogen flushed solution of bicyclo[2.2.1]hept-5-ene-2-
endo-carboxylic acid 912 (500 mg, 3.6 mmol), triethylamine
(0.61 mL, 4.3 mmol) and benzyl alcohol (0.75 mL, 7.3 mmol) in
dichloromethane (5.0 mL), EDCI (830 mg, 4.3 mmol) was
added in one portion from a screw cap vial with stirring fol-
lowed by DMAP (88 mg, 0.7 mmol) in an analogous manner.
This reaction was stirred overnight whereupon the total volume
was diluted to 20 mL using dichloromethane. The solution was
washed with 1% HCl (20 mL) and the aqueous re-extracted
with dichloromethane (10 mL). The combined organics were
washed with H2O and again the aqueous re-extracted with di-
chloromethane (10 mL). Total organics were dried (Na2SO4),
filtered and evaporated with the residue being subject to chrom-
atography using 1 : 20 EtOAc–hexane (Rf = 0.35) as eluent to
The alkene 3 (12 mg, 0.05 mmol) and epoxide 2 (25 mg,
0.05 mmol) were combined in a sealed tube with THF (0.5 mL)
and heated overnight at 130 ЊC. The crude product was purified
by chromatography (1 : 6 EtOAc–hexane, Rf = 0.25) to furnish
the title compound as a waxy solid. For (4S,11S): Yield 22 mg
(60%); [α]2D2.9 = Ϫ9.2 (c = 21.8); mp 89–91 ЊC; δH(300 MHz,
CDCl3, Me4Si) 0.96 (2H, d, J = 9.9, H15&17), 1.46 (18H, s,
t
CO2 Bu), 1.52–1.62 (4H, m, H5α,5β,12α,12β), 1.93 (4H, dd,
J = 9.9, J = 6.6, H2,7,9&14), 2.13 (2H, s, H6&13), 2.40 (2H, d,
J = 9.9, H15&17), 2.48 (2H, d, J = 4.3, H3&10), 2.66–2.69 (2H,
m, H4&11), 5.08 (2H, d, J = 12.5, CHaHbAr), 5.24 (2H, d,
J = 12.5, CHaHbAr), 7.32–7.39 (10H, m, Ph); δC(300 MHz,
CDCl3, Me4Si) 28.17, 31.36, 35.75, 38.79, 42.07, 45.63, 50.49,
54.89, 66.37, 81.54, 89.54, 128.19, 128.55, 136.09, 167.78,
173.88; m/z (ES) 721.5 [C42H50O9 ϩ Na]ϩ.
yield a clear viscous oil. For (2S): Yield 690 mg (84%); [α]2D3.5
=
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1848

View Article Online
2-endo-(Methoxycarbonylmethylcarbamoyl)bicyclo[2.2.1]hept-
tBuOK (14 mg, 0.12 mmol) in accordance with the standard
5-ene 1010
method. A reaction time of 14 hours was required and the
crude product was purified by chromatography (1 : 1 EtOAc–
hexane Rf = 0.35) to yield the title compound as a slightly yel-
low coloured solid. For (8S): Yield 62 mg (70%); [α]2D3.6 = Ϫ2.46
(c = 14.4); mp 98–100 ЊC; δH(300 MHz, CDCl3, Me4Si) 1.47
A nitrogen covered solution of 2-endo-bicyclo[2.2.1]hept-5-ene-
carboxylic acid 9 (500 mg, 3.6 mmol) and glycine methyl ester
hydrochloride (400 mg, 3.2 mmol) in DMF (10 mL) was cooled
to 0 ЊC whereupon diisopropylethylamine (420 mg, 0.56 mL, 3.3
mmol), EDCI (700 mg, 3.7 mmol) and HOBt (430 mg, 3.2 mmol)
were added. The reaction mixture was stirred overnight at room
temperature whereupon TLC analysis indicated the reaction to
be complete. Workup consisted of removal of DMF under high
vacuum and partitioning of the residue between dichloromethane
(30 mL) and 2% HCl (20 mL). Re-extraction of the aqueous
using dichloromethane (2 × 20 mL) washing of the combined
organics with water (20 mL) followed by drying (MgSO4), filter-
ing and evaporation yielded near pure product. Purification could
be achieved using chromatography (3 : 7 EtOAc–hexane Rf =
0.40) or recrystallisation (Et2O). Yield 670 mg (76%); mp 101–102
ЊC (Found: C 62.97, H 7.36, N 6.60. C11H15NO3 requires C 63.14,
H 7.23, N 6.69%); δH(300 MHz, CDCl3, Me4Si) 1.31 (1H, d, J =
8.3, H7a), 1.38 (1H, ddd, J = 12.0, J = 4.4, J = 2.7, H3endo), 1.47
(1H, dq, J = 8.3, J = 2.4, H7syn), 1.96 (1H, ddd, J = 12.0, J = 9.3, J
= 3.7, H3exo), 2.93 (2H, m, H2&H4), 3.18 (1H, s, H1), 3.76 (3H,
s, CO2Me), 4.01 (2H, d, J = 5.1, CH2 Gly), 5.88 (1H, br s, NH),
6.02 (1H, dd, J = 5.6, J = 2.7, H6), 6.25 (1H, dd, J = 5.6, J = 2.9,
H5); δC(300 MHz, CDCl3, Me4Si) 29.87, 41.15, 42.68, 44.61,
46.19, 50.01, 52.31, 132.26, 137.87, 170.69, 174.50; Found
209.1053, C11H15NO3 requires 209.1052.
t
(18H, s, CO2 Bu), 1.46–1.61 (2H, obscured, H10a&H9endo),
1.74 (1H, ddd, J = 12.7, J = 11.2, J = 4.6, H9exo), 1.98 (1H, d,
J = 10.7, H10syn), 2.36 (1H, d, J = 3.9, H2), 2.46 (1H, d, J = 3.9,
H6), 2.72–2.79 (2H, m, H1&H8), 2.93 (1H, d, J = 3.4, H7), 3.75
(3H, s, CO2Me), 3.97 (1H, dd, J = 18.5, J = 5.4, CHaHb, Gly),
4.06 (1H, dd, J = 18.4, J = 5.2, CHaHb, Gly), 6.02 (1H, brt,
J = 4.9, NH); δC(300 MHz, CDCl3, Me4Si) 27.99, 29.57, 35.20,
37.00, 40.68, 41.26, 45.59, 46.05, 49.61, 52.33, 63.92, 64.19,
82.78, 82.86, 162.99, 163.337, 170.45, 172.63; m/z (ES) 452.6
[C23H33NO8 ϩ H]ϩ.
Di-tert-butyl 4ꢁ-(methoxycarbonylmethylcarbamoyl)-11ꢁ-
(1-methoxycarbonylethylcarbamoyl)-16-oxa-(1ꢀ,2ꢁ,3ꢀ,6ꢀ,
7ꢁ,8ꢀ,9ꢁ,10ꢀ,13ꢀ,14ꢁ)-hexacyclo[6.6.1.14,6.110,13.02,7.09,14]-
heptadeca-1,8-dicarboxylate 14
Epoxide 13 (20 mg, 0.043 mmol) and alkene 11 (15 mg, 0.067
mmol) were combined in a sealed tube with dichloromethane
(∼0.5 mL) and heated at 130 ЊC for 12 hours whereupon the
contents were concentrated to dryness and the crude product
purified by gradient chromatography (1 : 1–1 : 0 EtOAc–hexane,
Rf[1 : 1 EtOAc–hexane] = 0.15) to afford the title compound
as a white solid. Yield 12 mg (41%); mp 118–120 ЊC; δH(300
MHz, CDCl3, Me4Si) 0.99 (2H, d, J = 10.0, H15,17), 1.42 (3H,
2-endo-(1-Methoxycarbonylethylcarbamoyl)bicyclo[2.2.1]-
hept-5-ene 11
t
d, J = 7.3, CH(CH3) Ala), 1.515 (9H, s, CO2 Bu), 1.518 (9H, s,
t
CO2 Bu), 1.51–1.61 (4H, part. obscured, H5α,β,H12α,β), 2.08–
Synthesised as described for 10 using alanine methyl ester.
Purified using column chromatography (3 : 7 EtOAc–hexane Rf
= 0.35). For (2S): Yield 84%; [α]2D0.8 = Ϫ142.3 (c = 80.1); mp 89–
90 ЊC (sublimed > 80 ЊC); δH(300 MHz, CDCl3, Me4Si) 1.24
(1H, d, J = 8.3, H7a), 1.31 (3H, d, J = 7.1, CH(CH3) Ala), 1.30–
1.35 (1H, m, H3endo), 1.37 (1H, dq, J = 8.3, J = 2.0, H7syn),
1.86 (1H, ddd, J = 12.7, J = 9.3, J = 3.7, H3exo), 2.82–2.87 (2H,
m, H2&H4), 3.12 (1H, s, H1), 3.68 (3H, s, CO2Me), 4.55 (1H,
quint, J = 7.3, CH(CH3) Ala), 5.93 (1H, dd, J = 5.6, J = 2.7, H6),
6.04 (1H, brd, J = 6.6, NH), 6.16 (1H, dd, J = 5.6, J = 2.9, H5);
δC(300 MHz, CDCl3, Me4Si) 18.22, 29.43, 42.54, 44.39, 46.03,
47.67, 49.78, 52.16, 132.05, 137.43, 173.56, 173.611; Found
223.1205, C12H17NO3 requires 223.1208.
2.21 (6H, m, H2,6,7,9,13,14), 2.33 (2H, s, H3,10), 2.42–2.49
(2H, m, H15,17), 2.54 (2H, dt, J = 10.5, J = 5.9, H4,11), 3.778
(3H, s, CO2Me), 3.781 (3H, s, CO2Me), 4.02 (1H, dd, J = 18.5,
J = 4.9, CHaHb Gly), 4.15 (1H, dd, J = 18.3, J = 5.3, CHaHb
Gly), 4.60 (1H, quint, J = 7.1, CH(CH3) Ala), 5.92 (1H, br t,
J = 5.1, NH Gly), 5.97 (1H, d, J = 7.3, NH Ala); δC(300 MHz,
CDCl3, Me4Si) 18.62, 28.17, 28.24, 30.87, 30.90, 36.15, 36.29,
38.82, 41.33, 42.46, 42.50, 46.61, 46.66, 48.11, 49.80, 49.82,
52.37, 52.44, 55.06, 55.14, 81.56, 89.61, 89.72, 168.04, 168.19,
170.49, 172.28, 172.98, 173.43.
Di-tert-butyl 7ꢁ-carboxylic acid-(1ꢀ,2ꢁ,3ꢀ,5ꢀ,6ꢁ,7ꢀ)-4-oxa-
tetracyclo[5.2.1.02,6.03,5]decane-3,5-dicarboxylate 15
Di-tert-butyl 7ꢁ-methoxycarbonylmethylcarbamoyl-(1ꢀ,2ꢁ,5ꢁ,
6ꢀ)-tricyclo[4.2.1.02,5]non-3-ene-3,4-dicarboxylate 12
A solution of benzyl ester epoxide 2 (66 mg, 0.14 mmol) and 2%
acetic acid (2 drops) in EtOAc (10 mL) was stirred under a
hydrogen atmosphere in the presence of a 10% palladium on
carbon catalyst (∼10 mg) for 24 hours whereupon TLC indi-
cated consumption of starting material. The reaction mixture
was carefully filtered through Celite to remove the catalyst, the
filter cake being washed thoroughly with EtOAc to ensure all
product was collected. The solvent was removed under reduced
pressure and the residue completely dried under high vacuum
to provide a slightly impure material that was used directly in
the next step. Yield 53 mg (∼100%); δH(300 MHz, CDCl3,
The reaction of alkene 10 (40 mg, 0.19 mmol) with DtBAD
(60 mg, 0.26 mmol) using RuH2(CO)(PPh3) (10 mg) in benzene
(5.0 mL) was performed in accordance with the method of Mit-
sudo.8 A reaction time of 72 hours was required and the crude
product was purified by means of gradient chromatography
(1 : 1–1 : 0 EtOAc–hexane, Rf[1 : 1 EtOAc–hexane] = 0.15) to
afford the title compound as a viscous oil. For (7S): Yield 90
mg (98%); [α]2D5.0 = ϩ2.4 (c = 18.6); δH(300 MHz, CDCl3, Me4Si)
t
1.25 (1H, d, J = 11.9, H9a), 1.48 (18H, s, CO2 Bu), 1.56 (1H, d,
t
t
Me4Si) 1.48 (9H, s, CO2 Bu), 1.49 (9H, s, CO2 Bu), 1.48–
1.57 (2H, obscured, H10a&H9endo), 1.80 (1H, ddd, J = 16.3,
J = 11.5, J = 4.9, H9exo), 1.99 (1H, d, J = 10.0, H10syn),
2.36 (1H, d, J = 3.9, H6), 2.47 (1H, d, J = 3.7, H2), 2.75 (1H, d,
J = 3.9, H1), 2.88 (1H, dt, J = 11.2, H8), 3.06 (1H, d, J = 3.7,
H7); δC(300 MHz, CDCl3, Me4Si) 27.94, 29.86, 34.82, 36.89,
40.15, 44.81, 45.97, 49.47, 63.97, 64.06, 82.84, 82.94, 162.76,
162.97, 179.11; m/z (ES) 381.3 [C20H28O7 ϩ H]ϩ.
J = 10.9, H9syn), 1.65 (1H, dm, J = 12.5, H8endo), 1.79 (1H,
ddd, J = 15.6, J = 11.0, J = 4.6, H8exo), 2.29 (1H, d, J = 4.2, H1),
2.48 (1H, d, J = 4.2, H6), 2.72 (1H, d, J = 3.2, H5), 2.78–2.85
(1H, m, H7), 2.86 (1H, d, J = 3.2, H2), 3.75 (3H, s, CO2Me),
4.05 (2H, m, CH2 gly), 6.02 (1H, brt, NH); δC(300 MHz, CDCl3,
Me4Si) 28.10, 28.11, 29.54, 32.52, 34.21, 38.21, 41.30, 42.42,
46.07, 46.57, 52.30, 81.40, 81.46, 141.29, 142.29, 160.60, 160.73,
170.45, 172.98; m/z (ES) 893.6 [C46H66N2O14ϩNa]ϩ(dimer).
Di-tert-butyl 8ꢁ-(methoxycarbonylmethylcarbamoyl)-4-oxa-
(1ꢀ,2ꢁ,3ꢀ,5ꢀ,6ꢁ,7ꢀ)-tetracyclo-[5.2.1.02,6.03,5]decane-3,5-dicarb-
oxylate 13
Di-tert-butyl 8ꢁ-(1-methoxycarbonylethylcarbamoyl)-4-oxa-
(1ꢀ,2ꢁ,3ꢀ,5ꢀ,6ꢁ,7ꢀ)-tetracyclo[5.2.1.02,6.03,5]decane-3,5-dicarb-
oxylate 20
A solution of alkene diester 12 (80 mg, 0.18 mmol) in dry THF
(10.0 mL) was treated with TBHP (0.104 mL, 0.3 mmol) and
A solution of epoxyacid 15 (53 mg, 0.14 mmol) and alanine
methyl ester hydrochloride (25 mg, 0.18 mmol) in DMF
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1849

View Article Online
(2.0 mL) was prepared under nitrogen and to it diisopropylethyl
amine (23 mg = 30 µl, 0.18 mmol), EDCI (40 mg, 0.21 mmol)
and HOBt (5 mg) were added and the reaction allowed to stir
overnight. The solvent was removed under high vacuum and
the residue taken up in dichloromethane (10 mL) and washed
with sat. citric acid (5.0 mL) followed by water (5.0 mL). The
organic was dried (Na2SO4) filtered and evaporated to yield a
product which when chromatographed (1 : 4 EtOAc–hexane
Rf = 0.30) provided the title compound as a clear viscous
oil. For (8S): Yield 20 mg (31%); [α]2D2.7 = Ϫ11.4 (c = 26.0);
δH(300 MHz, CDCl3, Me4Si) 1.38 (3H, d, J = 7.1, CH(CH3)
Di-tert-butyl 4ꢁ-(1-carboxymethylcarbamoyl)-11ꢁ-(1-methoxy-
carbonylethylcarbamoyl)-(1ꢀ,2ꢁ,3ꢀ,6ꢀ,7ꢁ,8ꢀ,9ꢁ,10ꢀ,13ꢀ,14ꢁ)-
16-oxahexacyclo[6.6.1.14,6.110,13.02,7.09,14]heptadeca-1,8-dicarb-
oxylate 18
A solution of benzyl ester 17 (40 mg, 0.022 mmol) and 1 M acetic
acid (2 drops) in EtOAc (20 mL) was stirred for 24 hours with a
catalytic amount of palladium on carbon (< 5 mg) under an
atmosphere of hydrogen. After 24 hours TLC analysis of the
reaction mixture indicated that all starting material had been
consumed. Workup consisted of removal of catalyst by filtration
(Whatman no. 1), followed by concentration in vacuo that pro-
vided a crude product which, when examined by NMR displayed
no benzyl resonances. This material was used directly in the next
step without further purification. Yield 28 mg (79%); δH(300 MHz,
CD3OD, Me4Si) 1.02 (1H, d, J = 8.8), 1.03 (1H, d, J = 9.8), 1.38
t
Ala), 1.47 (18H, s, CO2 Bu), 1.41–1.59 (2H, obscured m,
H10a&H9endo), 1.72 (1H, ddd, J = 16.1, J = 12.7, J = 4.9,
H9exo), 1.98 (1H, d, J = 10.5, H10syn), 2.35 (1H, d, J = 3.9,
H2), 2.47 (1H, d, J = 3.9, H6), 2.68–2.75 (2H, m, H1&H8),
2.93 (1H, d, J = 3.4, H7), 3.74 (3H, s, CO2Me), 4.52
(1H, quint, J = 7.3, CH(CH3) Ala), 6.01 (1H, brd, J = 7.1,
NH); δC(300 MHz, CDCl3, Me4Si) 18.39, 28.00, 29.55, 35.20,
37.04, 40.66, 45.56, 46.12, 48.10, 49.59, 52.42, 64.00, 64.16,
82.74, 82.80, 163.05, 163.27, 171.99, 173.43; m/z (ES) 488.3
[C24H35NO8 ϩ Na]ϩ.
t
(3H, d, J = 7.1, CH(CH3) Ala), 1.54 (9H, s, CO2 Bu), 1.56 (9H, s,
t
CO2 Bu), 1.49–1.61 (4H, m), 2.08–2.18 (4H, m), 2.26–2.29 (2H,
m), 2.33–2.38 (2H, m), 2.41–2.45 (2H, m), 2.58–2.69 (2H, m),
3.76 (3H, s, CO2Me), 3.87–3.92 (2H, m, CH2 gly), 4.32 (1H, q, J =
7.3, CH(CH3) Ala), 8.10 (1H, brt, NH), 8.19 (1H, brd, NH);
δC(300 MHz, CD3OD, Me4Si) 18.23, 21.61, 29.34, 30.38, 32.28,
32.37, 37.69, 37.90, 41.27, 42.94, 45.27, 47.91, 48.28, 49.01, 50.63,
50.71, 52.15, 52.22, 53.63, 57.33, 57.39, 61.84, 67.85, 84.05, 84.15,
91.96, 92.13, 170.91, 170.92, 173.73, 175.32, 176.23, 176.82.
Di-tert-butyl 8ꢁ-(benzyloxycarbonylmethylcarbamoyl)-4-oxa-
(1ꢀ,2ꢁ,3ꢀ,5ꢀ,6ꢁ,7ꢀ)-tetracyclo[5.2.1.02,6.03,5]decane-3,5-dicarb-
oxylate 16
Di-tert-butyl 4ꢁ-[1-{[(methoxycarbonylmethylcarbamoyl)-
methyl]carbamoyl}methylcarbamoyl]-11ꢁ (1-methoxycarbonyl-
ethylcarbamoyl)-16-oxa-(1ꢀ,2ꢁ,3ꢀ,6ꢀ,7ꢁ,8ꢀ,9ꢁ,10ꢀ,13ꢀ, 14ꢁ)-
hexacyclo[6.6.1.14,6.110,13.02,7.09,14]heptadeca-1,8-dicarboxylate
19
Synthesised as for 20 using glycine benzyl ester. Purified
by column chromatography (1 : 3 EtOAc–hexane Rf = 0.35)
to afford
a colourless, slightly viscous oil. For (8S):
Yield 58%; [α]2D1.3 = Ϫ6.6 (c = 30.7); δH(300 MHz, CDCl3, Me4Si)
t
t
1.47 (9H, s, CO2 Bu), 1.48 (9H, s, CO2 Bu), 1.47–1.48 (1H,
obs, H10a), 1.58 (1H, ddd, J = 12.9, J = 5.4, J = 2.7, H9endo),
1.74 (1H, ddd, J = 12.7, J = 11.5, J = 4.6, H9exo), 1.99
(1H, d, J = 10.5, H10syn), 2.36 (1H, d, J = 3.9, H2),
2.47 (1H, d, J = 3.9, H6), 2.72–2.79 (2H, m, H1, H8), 2.94
(1H, d, J = 3.4, H7), 4.00 (1H, dd, J = 18.6, J = 4.9, CHA-
HB), 4.11 (1H, dd, J = 18.6, J = 4.9, CHAHB), 5.18 (2H, s,
CH2Ar), 6.02 (1H, t, J = 5.1, NH), 7.30–7.40 (5H, m,
ArH); δC(300 MHz, CDCl3, Me4Si) 27.99, 29.59, 35.20, 36.99,
40.66, 41.44, 45.59, 46.06, 49.61, 63.92, 64.18, 67.20, 82.78,
82.85, 128.38, 128.52, 128.61, 135.05, 163.00, 163.33, 169.88,
172.63.
A solution of acid 18 (20 mg, 0.030 mmol), glycyl-glycine methyl
ester (100 mg, 0.68 mmol) and diisopropylethylamine (105 mg,
0.14 mL, 0.81 mmol) in dry DMF (2.5 mL) was prepared under
nitrogen and to it EDCI (200 mg, 1.0 mmol) and HOBt (10 mg)
were added in quick succession from screw cap vials. The reaction
mixture was subsequently stirred for 72 hours. Workup consisted
of removal of solvent under high vacuum, redissolving the resi-
due in dichloromethane (10 mL) and washing of this organic
solution with saturated citric acid (2 × 5 mL) followed by water
(5 mL). The combined organics were set aside and the combined
aqueous extracted with a second portion of dichloromethane
(10 mL), the total organics combined, dried (Na2SO4), filtered
and evaporated to yield a crude that when subject to chromato-
graphy (10 : 99 : 1 MeOH–EtOAc–NH4OH Rf = 0.15) provided
the title compound as a waxy white solid. For (4S,11S): Yield 16
mg (68%); [α]2D3.1 = Ϫ23.8 (c = 10.4); mp 198–200 ЊC; δH(300 MHz,
CDCl3, Me4Si) 0.97 (2H, d, J = 9.5, H15, H17), 1.39 (3H, d, J =
Di-tert-butyl 4ꢁ-(benzyloxycarbonylmethylcarbamoyl)-11ꢁ-(1-
methoxycarbonylethylcarbamoyl)-16-oxa-(1ꢀ,2ꢁ,3ꢀ,6ꢀ,7ꢁ,8ꢀ,
9ꢁ,10ꢀ,13ꢀ,14ꢁ)-hexacyclo[6.6.1.14,6.110,13.02,7.09,14] heptadeca-
1,8-dicarboxylate 17
t
t
Epoxide 16 (40 mg, 0.076 mmol) and alkene 11 (40 mg,
0.17 mmol) were combined in a sealed tube with dichloro-
methane (∼0.5 mL) and heated at 130 ЊC for 12 hours. The
tube was subsequently cracked and the contents concentrated
to dryness to afford a crude product that was purified by
chromatography (1 : 1 EtOAc–hexane Rf = 0.15) to yield the
title compound as a glassy solid. For (4S,11S): Yield 41 mg
(70%); [α]2D1.0 = Ϫ29.6 (c = 26.7); mp 107–109 ЊC; δH(300
MHz, CDCl3, Me4Si) 0.99 (2H, d, J = 9.3, H15,H17), 1.41
7.0, CH(CH3) Ala), 1.48 (9H, s, CO2 Bu), 1.50 (9H, s, CO2 Bu),
1.44–1.56 (4H, m, H5α,H5β,H12α,H12β), 2.05 (1H, d, J = 6.9,
H7), 2.08 (3H, br s, H6,H9,H14), 2.12 (1H, d, J = 3.7, H13), 2.18
(1H, d, J = 6.6, H2), 2.31 (1H, d, J = 4.0, H3), 2.35–2.36 (2H, m,
H15,H10), 2.40 (1H, d, J = 10.3, H17), 2.47–2.52 (1H, m, H4),
2.59 (1H, dt, J = 10.9, J = 4.8, H11), 3.72 (3H, s, CO2Me), 3.75
(3H, s, CO2Me), 3.99–4.05 (6H, m, CH2 × 3 gly × 3), 4.56 (1H,
quint, J = 7.3, CH(CH3) Ala), 6.04 (1H, d, J = 7.3, NH Ala), 6.71
(1H, t, J = 5.5, NH gly), 7.15 (1H, t, J = 5.1, NH gly), 7.23 (1H, t,
J = 5.1, NH gly); δC(300 MHz, CDCl3, Me4Si) 18.63, 28.24, 28.33,
30.61, 30.92, 36.13, 36.31, 38.92, 38.96, 41.26, 42.64, 42.86, 43.10,
43.49, 46.66, 46.76, 48.25, 49.91, 49.99, 52.42, 52.52, 55.15, 55.56,
81.87, 82.26, 89.65, 90.01, 168.19, 169.03, 169.50, 170.20, 170.27,
172.48, 173.46, 174.18; m/z (ES) 789.5 [C39H56N4O13 ϩ H]ϩ;
Found 788.3841 C39H56N4O13 requires 788.3844.
t
(3H, d, J = 7.1, CH(CH3) Ala), 1.49 (9H, s, CO2 Bu), 1.52
t
(9H, s, CO2 Bu), 1.45–1.61 (4H, m, H5α,H5β,H12α,H12β),
2.08–2.21 (6H, m, H2,H6,H7,H9,H13,H14), 2.33 (2H, s,
H3,H10), 2.42–2.59 (4H, m, H15,H17,H4,H11), 3.78 (3H,
s, CO2Me), 4.04 (1H, dd, J = 18.6, J = 4.6, CHaHb gly), 4.21
(1H, dd, J = 18.6, J = 5.4, CHaHb gly), 4.60 (1H, quint,
J = 7.1, CH(CH3) Ala), 5.21 (2H, s, CH2Ar), 5.92 (1H, t, J = 4.9,
NH gly), 5.97 (1H, d, J = 7.1, NH Ala), 7.34–7.40 (5H, m,
ArH); δC(300 MHz, CDCl3, Me4Si) 18.64, 28.17, 28.23, 30.85,
30.90, 36.17, 36.30, 38.83, 41.49, 42.49, 46.66, 48.11, 49.80,
52.46, 55.06, 55.10, 67.21, 81.56, 81.58, 89.62, 89.73, 128.39,
128.52, 128.63, 135.15, 168.06, 168.18, 169.97, 172.30, 173.00,
173.44.
Di-tert-butyl 4ꢁ,11ꢁ-bis(1-methoxycarbonylethylcarbamoyl)-16-
oxa-(1ꢀ,2ꢁ,3ꢀ,6ꢀ,7ꢁ,8ꢀ,9ꢁ,10ꢀ,13ꢀ,14ꢁ)-hexacyclo[6.6.1.14,6.
110,13.02,7.09,14]heptadeca-1,8-dicarboxylate 21
Epoxide 20 (30 mg, 0.06 mmol) and alkene 11 (20 mg, 0.09
mmol) were combined in a sealed tube with dichloromethane
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1850

View Article Online
(∼0.5 mL) and heated for 6 hours at 140 ЊC. The tube was
subsequently cracked and the contents concentrated to dryness
to produce a crude product that was purified by gradient
chromatography (1 : 1 EtOAc–hexane–1 : 0 EtOAc–hexane,
Rf[1 : 0 EtOAc–hexane] = 0.75) to afford a white solid. For
(4S,11S): Yield 47 mg (90%); [α]2D5 = Ϫ50.7 (c = 21.2); mp 122–
125 ЊC; δH(300 MHz, CDCl3, Me4Si) 0.97 (2H, d, J = 9.8,
H15,H17), 1.40 (6H, d, J = 7.1, CH(CH3) Ala), 1.51 (18H, s,
H5α,H12α), 1.70 (2H, dd, J = 12.4, J = 2.7, H5β,H12β), 2.13
(2H, d, J = 5.9, H7,H14), 2.26 (4H, m, H2,H9,H6,H13), 2.34
(2H, d, J = 10.0, H15,H17), 2.54–2.58 (2H, m, H4,H11),
2.69 (2H, brs, H3,H10), 3.75 (6H, s, CO2Me), 3.82 (6H, s,
CO2Me), 4.50–4.67 (6H, brm, CH2 gly, CH(CH3) Ala); δC(300
MHz, CD3OD, Me4Si) 13.27, 25.84, 31.88, 34.08, 35.42, 36.98,
41.76, 43.13, 45.55, 47.90, 48.34, 51.22, 86.55, 164.83, 166.7,
168.45; m/z (ES) 719.4 [C34H46N4O13ϩH]ϩ; Found 718.3050,
C34H46N4O13 requires 718.3061.
t
CO2 Bu), 1.50–1.59 (4H, obscured m, H5α,H5β,H12α,H12β),
2.08 (2H, d, J = 6.6, H7,H14), 2.12 (2H, d, J = 3.9, H6,H13),
2.19 (2H, d, J = 6.6, H2,H9), 2.31 (2H, d, J = 4.1, H3,H10), 2.42
(2H, d, J = 8.9, H15,H17), 2.49 (2H, dt, J = 10.5, J = 4.6,
H4,H11), 3.77 (s, 6H, CO2Me), 4.59 (2H, q, J = 7.1, CH(CH3)
Ala), 5.99 (2H, d, J = 7.1, NH ); δC(300 MHz, CDCl3, Me4Si)
18.6, 28.14, 30.87, 36.27, 38.80, 42.46, 46.60, 48.08, 49.75,
53.43, 55.03, 81.59, 89.64, 168.14, 172.27, 173.44; m/z (ES)
711.6 [C36H52N2O11 ϩ Na]ϩ.
References
1 S. Anderson, H. L. Anderson and J. K. Sanders, Acc. Chem. Res.,
1993, 26, 469–475; G. Tuchscherer and M. Mutter, J. Biotechnol.,
1995, 41, 197–210; J. Schneider and J. Kelly, Chem. Rev., 1995, 95,
2169–2187.
2 I. Eggleston and M. Mutter, Chem. Br., 1996, 39–41; M. Mutter,
P. Dumy, G. Tuchscherer, P. Garrouste, C. Lehmann, M. Mathieu,
C. Peggion, S. Peluso and A. Razaname, Angew. Chem., Int. Ed.
Engl., 1996, 35, 1482–1485; G. Olsen, D. Bolin, M. Bonner,
M. Bos, C. Cook, D. C. Fry, B. J. Graves, M. Hatanda, D. E. Hill,
M. Kahn, V. S. Madison, V. K. Rusiecki, R. Sarabu, J. Sepinwall,
G. P. Vincent and M. E. Voss, J. Med. Chem., 1993, 36, 3039–3049;
G. Nikiforovich, M. Mutter and C. Lehmann, Biopolym. (Pept.
Sci.), 1999, 50, 361–372.
3 C. Still, R. Boyce, G. Li, P. Nestler and T. Suenaga, J. Am. Chem.
Soc., 1994, 116, 7955–7956; H. De Muynck, A. Madder, N. Farcy,
P. De Clerq, N. M. Oerez-Payan, L. M. Ohberg and A. P. Davis,
Angew. Chem., Int. Ed. Engl., 2000, 39, 145–148; R. Fitzmaurice,
G. Kyne, D. Douheret and J. Kilburn, J. Chem. Soc., Perkin Trans. 1,
2002, 841–864.
4 Y. Hamuro, M. Calama, H. Park and A. Hamilton, Angew. Chem.,
Int. Ed. Engl., 1997, 36, 2680–2683; H. Park, Q. Lin, Y. Hamuro,
C. Lee and A. Hamilton, Biopolym. (Pept. Sci.), 1998, 47, 285–297;
H. Park, Q. Lin and A. Hamilton, J. Am. Chem. Soc., 1999, 121,
8–13.
5 R. Warrener, A. Schultz, D. Butler, D. Margetic, I. Mahadacan and
R. Russell, J. Chem. Soc., Chem. Commun., 1997, 1023–1024.
6 R. Warrener, D. Butler and R. Russell, Synlett, 1998, 566–573;
R. Warrener, D. Margetic, A. Amarasekara and D. Butler, Org.
Lett., 1999, 1, 199–202.
7 R. Warrener, D. Butler, D. Margetic, F. Pfeffer and R. Russell,
Tetrahedron Lett., 2000, 41, 4671–4675; F. Pfeffer and R. Russell,
J. Chem. Soc., Perkin Trans. 1, 2002, 2680–2685.
8 T. Mitsudo, K. Kokuryo, T. Shinsugi, Y. Nakagawa and
Y. Takegami, J. Org. Chem., 1979, 44, 4492–4496; T. Mitsudo,
H. Naruse, T. Kondo, Y. Ozaki and Y. Watanabe, Angew. Chem.,
Int. Ed. Engl., 1994, 33, 580–581.
4ꢁ,11ꢁ-Bis(1-methoxycarbonylethylcarbamoyl)-16-oxa-(1ꢀ,2ꢁ,
3ꢀ,6ꢀ,7ꢁ,8ꢀ,9ꢁ,10ꢀ,13ꢀ,14ꢁ)hexacyclo[6.6.1.14,6.110,13.02,7.09,14]-
heptadeca-1,8-dicarboxylic acid 22
A 1 : 1 solution of TFA in dry dichloromethane (1.0 mL)
was added quickly in one portion to a nitrogen flushed round
bottom flask containing the alanyl-alanine-di-tert-butyl ester
framework 20 (40 mg, 0.058 mmol) and a magnetic stirrer. The
resultant solution was stirred under a nitrogen atmosphere
overnight whereupon TLC analysis indicated complete con-
sumption of starting material. Solvent was removed in vacuo
and complete dryness achieved using high vacuum. For
(4S,11S): Yield 27 mg (81%); [α]2D6 = Ϫ57.1 (c = 24.0); mp 270 ЊC
(140 ЊC polymerisation, 170 ЊC partial decomposition with
odour, 240–270 ЊC slow decolourisation and decomposition);
δH(300 MHz, CD3OD, Me4Si) 1.02 (2H, d, J = 9.8, H15,H17),
1.36 (6H, d, J = 7.3, CH(CH3) Ala), 1.50 (2H, td, J = 11.2,
J = 4.2, H5α,H12α), 1.56–1.62 (2H, m, H5β,H12β), 2.14–2.16
(4H, m, H6,H7,H13,H14), 2.32 (2H, d, J = 6.6, H2,H9), 2.39
(2H, d, J = 9.0, H15,H17), 2.49 (2H, d, J = 4.2, H3,H10), 2.60
(2H, dt, J = 11.0, J = 4.6, H4,H11), 3.76 (6H, s, CO2Me), 4.38
(2H, q, J = 7.3, CH(CH3) Ala); δC(300 MHz, CD3OD, Me4Si)
17.25, 31.53, 36.99, 40.51, 44.33, 47.11, 49.61, 51.31, 52.83,
56.55, 172.43, 174.72, 175.28; m/z (ES) 577.3 [C28H36N2O11
ϩ
H]ϩ.
9 T. Greene, P. Wuts, Protective Groups in Organic Synthesis,
John Wiley & Sons, New York, 1991; M. Bodansky, Peptide
Chemistry: A Practical Textbook-2nd Revised Edition, Springer–
Verlag, Berlin, 1993.
10 W. Oppolzer, in Comprehensive Organic Synthesis, ed. I. Fleming
and B. Trost, Pergamon Press, Oxford, 1991, 5, 316–395; I. Fleming,
Frontier Orbitals and Organic Chemical Reactions, Wiley Inter-
science, London, 1976.
11 M. Miklolajczyk and P. Kielbasinski, Tetrahedron, 1981, 37, 233–
284; L. Carpino, J. Am. Chem. Soc., 1993, 115, 4397–4398.
12 W. Konig and R. Geiger, Chem. Ber., 1970, 103, 788–798;
M. Nakazaki, K. Naemura and H. Kadowski, J. Org. Chem., 1978,
43, 4947–4951; W. Boehme, E. Schipper, W. Scharpf and J. Nichols,
J. Am. Chem. Soc., 1958, 80, 5488–5495.
13 W. Steglich and B. Neises, Angew. Chem., Int. Ed. Engl., 1978, 17,
522–524; M. Dhaon, R. Olsen and K. Ramasamy, J. Org. Chem.,
1982, 47, 1962–1965.
14 T. Poll, A. Sobczac, H. Hartmann and G. Helmchen, Tetrahedron
Lett., 1985, 26, 3095–3098.
15 J. Hans, R. Driver and S. Burke, J. Org. Chem., 1999, 64, 1430–1431;
J. Coste, D. Le-Nguyen and B. Castro, Tetrahedron Lett., 1990, 31,
205–208.
16 X. Nie, M. Wang and Z. Huang, Synthesis, 2000, 1439–1443;
B. Bellau and G. Malek, J. Am. Chem. Soc., 1968, 90, 1651–1652.
17 H. Brown and M. Ravindranathan, J. Am. Chem. Soc., 1978, 100,
1865–1869.
1,8-Bis(methoxycarbonyl-methylcarbamoyl)-4ꢁ,11ꢁ-bis(1-
methoxycarbonylethylcarbamoyl)-16-oxa-(1ꢀ,2ꢁ,3ꢀ,6ꢀ,7ꢁ, 8ꢀ,
9ꢁ,10ꢀ,13ꢀ,14ꢁ)-hexacyclo[6.6.1.14,6.110,13.02,7.09,14]heptadecane
23
A solution of the preceding diacid 22 (27 mg, 0.047 mmol),
glycine methyl ester hydrochloride (25 mg, 0.20 mmol), diiso-
propylethylamine (15 mg, 0.020 mL, 0.12 mmol) in dry DMF
(1.0 mL) was prepared under nitrogen and to this solution the
following were added successively from screw cap vials: EDCI
(35 mg, 0.18 mmol) and HOBt (5 mg). The reaction was sub-
sequently stirred at room temperature for a total of 48 hours.
Workup consisted of removal of solvent under high vacuum,
redissolving the residue in dichloromethane (10 mL). This
organic solution was washed with saturated citric acid (2 ×
5 mL) and water (5 mL). The combined organics were set aside
and the combined aqueous extracted with a second portion of
dichloromethane (10 mL), the total organics combined, dried
(Na2SO4), filtered and evaporated to afford a crude that when
subject to gradient chromatography (1 : 1 EtOAc–hexane–1 : 10
MeOH–EtOAc, Rf[1 : 10 MeOH–EtOAc] = 0.35) afforded the
title compound as a waxy solid. For (4S,11S): Yield 17 mg
(50%); mp 104–106 ЊC; [α]2D3.5 = Ϫ20.5 (10.5); δH(300 MHz,
CDCl3, Me4Si) 1.04 (2H, d, J = 10.3, H15,H17), 1.36 (6H, d,
J = 7.3, CH(CH3) Ala), 1.57 (2H, td, J = 12.2, J = 4.6,
18 G. Hill, B. Rossiter and K. B. Sharpless, J. Org. Chem., 1983, 48,
3607–3608.
19 O. Meth-Cohn, C. Moore and H. Taljaard, J. Chem. Soc.,
Perkin Trans. 1, 1988, 2663–2674.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 1 8 4 5 – 1 8 5 1
1851