Cross-metathesis and ring-closing metathesis reactions of amino acid-based substrates

Article abstract of DOI:10.1016/j.tet.2008.02.043

Olefin tethers of variable length, introduced into a natural amino acid (side-chain of Ser, Cys; N-terminus of Arg; C-terminus of Phe and Tic; and in both the side-chain and either the N- or C-terminus of Ser, Cys and Tyr), undergo metathesis on treatment with Grubbs' second generation catalyst. Side-chain linked dimers of Ser, Cys and Tyr were obtained by cross-metathesis, while olefin installation at the N- and C-terminus led to dimers of Arg and Phe (or Tic), respectively. Ring-closing metathesis of the doubly alkenylated derivatives of Ser, Cys and Tyr gave 12-, 20- and 24-membered macrocycles.

Full text of DOI:10.1016/j.tet.2008.02.043

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 3980e3997
www.elsevier.com/locate/tet
Cross-metathesis and ring-closing metathesis reactions
of amino acid-based substrates
Andrea J. Vernall a, Steven Ballet b,c, Andrew D. Abell a,c,
*
a Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
b Department of Organic Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
c School of Chemistry and Physics, University of Adelaide, North Terrace, Adelaide, SA 5005, Australia
Received 6 December 2007; received in revised form 30 January 2008; accepted 14 February 2008
Available online 5 March 2008
Abstract
Olefin tethers of variable length, introduced into a natural amino acid (side-chain of Ser, Cys; N-terminus of Arg; C-terminus of Phe and Tic;
and in both the side-chain and either the N- or C-terminus of Ser, Cys and Tyr), undergo metathesis on treatment with Grubbs’ second generation
catalyst. Side-chain linked dimers of Ser, Cys and Tyr were obtained by cross-metathesis, while olefin installation at the N- and C-terminus led to
dimers of Arg and Phe (or Tic), respectively. Ring-closing metathesis of the doubly alkenylated derivatives of Ser, Cys and Tyr gave 12-, 20- and
24-membered macrocycles.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Cross-metathesis (CM); Ring-closing metathesis (RCM); Amino acid dimerization; Cyclic amino acids
1. Introduction
a peptide can result in an improved pharmacological profile
relative to the monomer.7e13 For example, N-terminal linked
multimers of neurotensin exhibit improved binding affinities9
and the ‘tail-to-tail’ linkage of opioid pharmacophores allows
selective interaction with the different opioid subtype recep-
tors.8,11,14e16
Inter- and intramolecular cross-linking of peptides and pro-
teins is central to a number of important biological processes.1
Cross-linking of peptides (via biaryl dityrosine2 and cysteine
disulfide bond formation) helps to define protein structure
and hence function, while cross-linking of peptides to carbo-
hydrates is involved in immune recognition, cell-adhesion,
protease protection and inflammation.3e5 In addition, intramo-
lecular effects such as peptide backbone and/or side-chain am-
ide bond cross-linking6 and dimerization or oligomerization of
Ring-closing metathesis (RCM) and cross-metathesis (CM)
provide convenient and versatile methods by which to mimic
these important natural processes. Recent examples of the
use of CM include tethering of amino acids to sugars and fatty
acids,17 while RCM has been used to prepare low molecular
weight bioactive cyclic peptidomimetics18e22 and cyclic
amino acid-based building blocks.23 Secondary structures
such as a-helical structures,24 b-turn motifs25,26 and b-
strands27,28 can be stabilized by RCM. Olefin metathesis
also provides significant potential for the post-translational
modification of peptides and proteins by modification of a res-
idue in an existing peptide or protein, or by incorporating
a pre-derivatized residue into a solid phase synthesis protocol.
However, it is important to note that existing work in these
areas is, with few exceptions,17 limited to the use of non-
natural amino acids (e.g., allylglycine).29e33
Abbreviations: Boc2O, di-tert-butyl dicarbonate; BOP-Cl, bis(2-oxo-3-ox-
azolidinyl)phosphinic chloride; CM, cross-metathesis; DIPEA, N,N-diisopro-
pylethylamine; DMAP, 4-dimethylaminopyridine; EDCI, 1-ethyl-3-(30-
dimethylaminopropyl)carbodiimide hydrochloride; HATU, N,N,N0,N0-tetra-
methyl-O-(7-azabenzotriazol-1-yl)uronium hexafluorophosphate;
HOBt,
1-hydroxybenzotriazole; TBTU, O-(benzotriazol-1-yl)-N,N,N0,N0-tetramethyl-
uronium tetrafluoroborate; TEA, triethylamine; TFA, trifluoroacetic acid;
Tic, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid; Pbf, 2,2,4,6,7-penta-
methyldihydrobenzofuran-5-sulfonyl; RCM, ring-closing metathesis.
* Corresponding author. Tel.: þ61 8 83035996; fax: þ61 8 83034358.
E-mail address: andrew.abell@adelaide.edu.au (A.D. Abell).
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.043

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3981
O
PG = protecting group
R
CM
n
O-PG
PG-HN
Arg
R
O
2
O
R
R
O-PG
Phe
Tic
CM
N
H
Ser
Cys
O
n
CM
PG-HN
O
n
3
O
4
OH
O
Ser
Cys
H2N
Tyr
O
O
n
O
RCM
1
R
n
R
RCM
O
O-PG
PG-HN
n
N
n
O
H
O
5
6
Figure 1. Metathesis precursors 2e6.
Herein we report the synthesis of olefin-based derivatives of
natural amino acids (Fig. 1, 2e6) and their application in me-
tathesis-induced dimerization, conjugation and cyclization
studies. An olefin tether of controllable length is attached
via the side-chain of either serine or cysteine (see structure
2), the N-terminus (structure 3), the C-terminus (structure 4)
or a combination (5 and 6). Cysteine and serine were chosen
because they contain an appropriate side-chain functionality
(R) for modification and they provide an opportunity to
prepare stable mimics of natural disulfide bonds. Arginine
was selected as a type 3 olefin-containing derivative because
it represents an important branching point in multivalent var-
iants of biologically active peptides.9,10,34 Type 4 derivatives
provide precursors for the preparation of novel ‘tail-to-tail’
linked opioid ligands containing a C-terminal Phe or Tic,y
which are known to be critical for interaction with target re-
ceptor subtypes.11,8 Dienes 5 and 6 provide an opportunity
for the preparation of cyclic structures via RCM of the side-
chain to either the N- or C-terminus, respectively.
It is important to note that the alkene tether length of 2e6
can be tailored to a particular biological situation, for example
to study ligand interactions with receptors or enzymes by (i)
identifying the optimal olefin spacer length for potency, (ii)
providing long tethers to avoid steric problems known to be
a problem in bivalent opioid research,14,35 (iii) providing di-
meric structures capable of binding two active sites in receptor
complexes simultaneously.7,36
(Table 1, entries 1e4). The N-terminal acylated arginines 14
(88%) and 15 (83%) were prepared by coupling the hydrochlo-
ride salt of HeArg(Pbf)eOMe 13 to 4-pentenoic and 10-unde-
cenoic acid in the presence of the uronium salt TBTU (Table
1, entries 5 and 6). C2 and C8 olefin tethers were introduced at
the C-terminus of phenylalanine and the conformationally
constrained Phe analogue 1,2,3,4-tetrahydroisoquinoline-
3-carboxylic acid (Tic), by separate reactions of 16 and 19
with 3-butenol or with 9-decenol (Table 1, entries 7e10).
Precursors for RCM were prepared from cysteine, serine and
tyrosine (Table 1, entries 11e16). In particular, cysteine
methyl ester 22 was acylated with either 4-pentenoic acid (en-
try 11) or 10-undecenoic acid (entry 12), in the presence of
BOP-Cl, to give the N,S-diacylated products 23 and 24 in 85
and 44% yield, respectively. Serine methyl ester 25 was acyl-
ated with 4-pentenoic acid (entry 13) or 10-undecenoic acid
(entry 14), in the presence of HATU, to give the N,O-diacy-
lated products 26 (59%) and 27 (54%). The tyrosine-based
RCM precursors 29 (82%) and 30 (69%) were prepared simi-
larly from commercially available BoceTyr(OAllyl)eOH 28
on treatment with 3-butenol and 9-decenol, respectively.
2.2. Metathesis experiments (Tables 2e4)
The olefin tethered amino acid-based substrates (shown in
Table 1) were subjected to CM and RCM conditions and the
results are summarized in Tables 2e4. Cross-metathesis was
performed at a concentration of 0.05 M in the presence of
10 mol % Grubbs’ second generation catalyst 31 (Fig. 2). A re-
action time of 6 h (at reflux under a gentle flow of inert gas)
was sufficient to drive the reaction to completion. DMSO
was added at the completion of the reaction to facilitate re-
moval of generated ruthenium byproducts.52 A higher catalyst
loading of 20 mol % was used in the ring-closing experiments,
which were otherwise identical.
N-Boc-S-pentenoyl cysteine methyl ester 8 was treated with
Grubbs’ second generation catalyst 31 under the above condi-
tions to give olefin homodimer 33 in 45% yield (Table 2, entry
1). Similar treatment of N-Boc-S-decenoyl cysteine methyl es-
ter 9 gave the chain extended analogue 34 in 73% yield (Table
2, entry 2), while the two serine-based dimers (35 and 36)
2. Results and discussion
2.1. Preparation of the metathesis precursors (Table 1)
The side-chains of serine and cysteine were acylated with
4-pentenoic acid and 10-undecenoic acid, in the presence of
bis(2-oxo-3-oxazolidinyl)phosphinic chloride (BOP-Cl), to
give the alkene tether derivatives 8e12 suitable for metathesis
y
Dmt-Tic is a potent d-opioid receptor antagonist, the potency of which is
enhanced upon dimerization (see Ref. 11). These dimers are believed to be
useful for the treatment of drug addiction or alcohol dependence, but the op-
timum tether length to bind two active sites simultaneously remains to be
identified.

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A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
Table 1
Synthesis of metathesis precursors
Entry
Amino acid substrate
Conditions
Reaction product
n
Product (yield, %)
O
n
SH
S
1
2
2
8
8 (93)
9 (82)
7
a1
Boc
Boc
COOMe
N
H
Boc
Boc
COOMe
N
H
O
n
OH
3
4
2
8
11 (89)
12 (84)
O
10
b
COOMe
N
H
COOMe
H
N
H
H
N
HN
N
Pbf a
HN
Pbf a
NH
NH
5
6
2
8
14 (88)
15 (83)
13
c1
O
COOMe
N
COOMe
COOH
n
HCl.H2N
Boc
H
7
8
2
8
17 (87)
18 (86)
16
19
c2
Boc
O
N
H
n
N
H
O
9
2
8
20 (80)
21 (60)
c2
O
10
N
N
Boc
COOH
n
Boc
O
O
n
SH
S
11
12
2
8
23 (85)
24 (44)
O
22
25
a2
COOMe
H2N
H2N
COOMe
N
n
H
O
n
OH
13
14
O
2
8
26 (59)
27 (54)
O
d
COOMe
O
COOMe
O
N
H
n
15
16
2
8
29 (82)
30 (69)
28
c2
Boc
O
Boc
N
OH
N
H
n
H
O
O
Reagents and conditions: (a1) 4-pentenoic acid or 10-undecenoic acid (1.1 equiv), BOP-Cl (1.2 equiv), Et3N (2.4 equiv), CH2Cl2, 0 ꢀC then rt, 4 h; (a2) 4-pentenoic
acid or 10-undecenoic acid (1.1 equiv), BOP-Cl (1.2 equiv), Et3N (2.4 equiv), CH2Cl2, 0 ꢀC then rt, 18 h; (b) 4-pentenoic acid or 10-undecenoic acid (1.1 equiv),
EDCI (1.1 equiv), DMAP (0.01 equiv), CH2Cl2, rt, 16 h; (c1) 4-pentenoic acid or 10-undecenoic acid (1 equiv), TBTU (1.1 equiv), Et3N (3 equiv), CH2Cl2, rt, 2 h;
(c2) 3-butenol or 9-decenol (1 equiv), TBTU (1.1 equiv), Et3N (3 equiv), CH2Cl2, rt, overnight; (d) 4-pentenoic acid or 10-undecenoic acid (2.2 equiv), HATU
(2.4 equiv), DIPEA (4.8 equiv), DMF, rt, 16 h.
a
Protective group: Pbf, 2,2,4,6,7-pentamethyldihydrobenzofuran-5-sulfonyl.
were prepared from N-Boc-O-pentenoyl serine methyl ester 11
and 12 in isolated yields of 86 and 62%, respectively (Table 2,
entries 3 and 4). Catalyst 31 also induced dimerization of a-
amine acylated arginines 14 and 15 to give the desired self-
metathesis products 37 and 38 in respective yields of 74 and
66% (Table 2, entries 5 and 6). These results demonstrate
that the Pbf-protected guanidine functionality of the arginine
side-chain is compatible with catalyst 31, an important result
for the future preparation of multivalent variants of
biologically active peptides.9,10,32 Removal of the sulfonyl-
type protecting group of 14, on treatment with trifluoroacetic
acid,38 gave the water soluble guanidinium salt 39 as a possible
substrate for CM reactions under polar solvent conditions, as
an initial step towards extending the chemistry to an aqueous
environment. Second generation HoveydaeGrubbs catalyst 32
(0.05 equiv) was added to a solution of 39 in MeOH-d4 and the
1
reaction was monitored by H NMR. However, an overnight
reaction at 45 ꢀC returned only starting material 39, with

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3983
longer reaction times resulting in some double bond isomeri-
zation.37 Catalyst 32 was employed in this study since it is re-
ported to promote CM in methanol, although Blechert and
Connon37 have reported that ammonium salts are often un-
reactive to CM and give rise to isomerization of the double
bond under the reaction conditions.
Dimers 41 through 44 were prepared as potential precursors
of bivalent opioid ligands, as discussed earlier (and in foot-
notey). Thus, dimerization of Phe-derived 17 and the longer
tethered analogue 18 gave 41 and 42 in yields of 68 and
76% (Table 2, entries 8 and 9). The analogous Tic-based sub-
strates 20 and 21 underwent CM to give the bivalent structures
Table 2
Self-metathesis compounds 33e46
Entry
Amino acid substrate
n
Substrate
Reaction product
n
Product (yield, %)
H
N
MeOOC
S
Boc
1
2
O
2
8
8
9
2
8
33 (45)
34 (73)
n
O
O
S
n
n
S
Boc
COOMe
N
H
Boc
COOMe
MeOOC
N
H
H
N
Boc
O
3
4
O
2
8
11
12
2
8
35 (86)
36 (62)
n
O
O
O
n
n
O
Boc
COOMe
N
H
Boc
N
H
COOMe
H
N
HN
Pbf
H
NH
HN
N
Pbf
O
NH
5
6
2
8
14
15
2
8
37 (74)
38 (66)
H
n
MeOOC
HN
N
COOMe
N
H
n
O
O
COOMe
N
n
H
Pbf
N
H
NH
H2N
NH2
H2N
NH2
NH
H
MeOOC
NH
O
N
n
O
7
2
39
2
40 (0)
n
N
O
COOMe
H
HN
COOMe
N
n
H
H2N
NH2
8
9
2
8
17
18
2
8
41 (68)
42 (76)
O
n
H
Boc
O
N
N
n
O
H
Boc
O
Boc
O
N
H
n
O
O
10
11
2
8
20
21
2
8
43 (89)
44 (56)
Boc
N
n
O
N
Boc
O
O
n
N
Boc
n
O
O
(continued)

3984
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
Table 2 (continued)
Entry
Amino acid substrate
n
Substrate
Reaction product
n
Product (yield, %)
O
H
N
MeO
O
n
Boc
n
O
n
12
1
45
1
46 (67)
O
Boc
OMe
N
H
Boc
OMe
O
N
H
O
Reagents and conditions: Grubbs’ second generation catalyst 31 (0.2 equiv), CH2Cl2, argon flow, reflux 6 h, then DMSO (50 equiv relative to 31), rt, 12 h. Entry 7:
HoveydaeGrubbs catalyst 32 (0.05 equiv), MeOH-d4, nitrogen flow, 45 ꢀC, 12 h to 3 days.37
Table 3
Cross-coupled metathesis products 47 and 48
Entry
CM partner 1
CM partner 2
Reaction product
n
m
Product (yield, %)
H
N
MeOOC
S
Boc
O
O
m
n
1
12
8
8
2
47 (51)
O
Boc
COOMe
MeOOC
N
H
H
N
Boc
S
2
12
9
8
8
48 (66)
O
O
m
n
O
Boc
COOMe
N
H
Reagents and conditions: 1 equiv of CM partner 1, 2 equiv of CM partner 2, Grubbs’ second generation catalyst 31 (0.2 equiv), CH2Cl2, argon flow, reflux 6 h, then
DMSO (50 equiv relative to 31), rt, 12 h.
Table 4
Ring-closing metathesis products 49e54
Entry
Amino acid substrate
n
Diene
Reaction product
n
Product (yield, %)
O
O
n
n
S
S
1
2
2
8
23
24
2
8
49 (74)
50 (43)
O
n
COOMe
COOMe
N
H
N
H
n
O
O
O
O
n
n
O
O
3
4
2
8
26
27
2
8
51 (45)
52 (15)
O
n
COOMe
O
COOMe
O
N
H
N
H
n
5
6
2
8
29
30
2
8
53 (0)
54 (62)
Boc
O
Boc
O
n
N
N
H
n
H
O
O
Reagents and conditions: Grubbs’ second generation catalyst 31 (0.2 equiv), CH2Cl2, argon flow, reflux 6 h, then DMSO (50 equiv relative to 31), rt, 12 h.
43 (89%) and 44 (56%) (Table 2, entries 10 and 11). This CM
strategy provides potential to access chimeric structures by
linking selective, olefin containing, pharmacophores. The
last example of self-metathesis dimerization involved cross-
linking commercially available N-Boc-O-allyl tyrosine methyl
ester 45 (Table 2, entry 12) to give 46 in a yield of 67%.

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3985
acid 50 (43%), the sample of which contained trace amounts
of a ring-contracted product presumably resulting from double
bond migration preceding RCM. The occurrence of double
bond migration in olefin metathesis is well known.41e43
The N,O-dipentenoyl serine analogues 26 and 27 were also
treated with catalyst 31 to give the 12-membered and 24-mem-
bered cyclic amino acids 51 (45%) and 52 (15%), respectively.
Traces of ring-contracted products were also present in the iso-
lated samples of 51 and 52, however, these were not purified or
characterized. Lactone 51 has been previously reported by
Schreiber.44 An attempted RCM with 29 gave only complex
mixtures, with none of the desired lactone 53 being observed
by NMR. This result is in accord with related work by Bressy
and Piva,45 which showed that an olefin tether containing
a minimum of four methylene units (i.e., n¼4) is needed to ob-
tain cyclic lactones of this type, albeit in low yield. Interest-
ingly, the longer tethered precursor 30 did give the desired
lactone 54 on treatment with 31 and in a respectable yield
of 62%. The configuration of the constituent double bonds
of 49 and 51 was assigned E on the basis of X-ray crystal
structures. As would be expected the cycles in the X-ray struc-
tures of 49 and 51 are almost identical (Fig. 3). The alkenes of
the larger cycles 50 and 52 were assigned E by analogy, the
thermodynamically more stable alkene isomer on the basis
of molecular modelling.
NMes
Cl
NMes
Cl
MesN
Ru
MesN
Ru
Ph
Cl
Cl
O
PCy3
31
32
Figure 2. Grubbs’ second generation catalyst 31 and HoveydaeGrubbs second
generation catalyst 32.
Structure 46 represents an analogue of a naturally occurring
tyrosine cross-linked dimer.2
Table 3 summarizes the results of cross-linking two differ-
ent amino acids using a CM strategy. The modified serine de-
rivative 12 was coupled to cysteine-based 8 upon treatment
with catalyst 31 to give the cross-linked product 47 in 51%
yield, along with the homodimer 33 as a result of the use of
a two-fold excess of 8 relative to 12. The serine derivative
12, containing the C8 alkene tether, was coupled to cysteine-
based 9 to give the mixed and extended dimer 48 in 66% yield.
Again, a self-metathesis dimer (34) was observed since 9 was
used in two-fold excess relative to 12. A statistical mixture of
the cross-metathesis product and the homodimers is expected,
as reactions between these types of olefins are considered to be
nonselective. Terminal olefins 8, 9 and 12 are prone to homo-
dimerization, whereas the homodimers themselves (disubsti-
tuted alkenes) are substrates for secondary metathesis
pathways.39
All self-metathesis and cross-metathesis products (Tables 2
and 3) were isolated as a single alkene isomer as evidenced by
1H and 13C NMR data. In each case this isomer was assigned
the thermodynamically more stable E configuration since ole-
fin metathesis using catalyst 31 is believed to occur under ther-
modynamic control.40 This assignment is supported by an
observed vicinal olefinic coupling constant of 15.2 Hz for 47.
Next a series of dienes (Table 4, entries 1e6) were reacted
with catalyst 31 in order to investigate RCM strategies. Diene
23 cyclized to give the 12-membered cysteine-based cyclic
amino acid 49 as a single isomer in 74% yield, the X-ray crys-
tal structure of which revealed an E geometry for the double
bond (see Fig. 3). Diene 24 similarly underwent RCM to
give the larger, 24-membered cysteine-based cyclic amino
2.3. Extension/application: dipeptidic moieties/PDF
inhibitors
Finally, we report studies on the synthesis of 56 as an initial
step towards the preparation of analogues of 55 (Fig. 4),
a known peptide deformylase (PDF) inhibitor that possesses
O
O
O
H
N
CO2Me
N
N
H
N
H
N
H
O
OH
O
S
O
55
56
Figure 4. Comparison of 56 to PDF inhibitor 5547 (metal-chelating warhead
circled).
Figure 3. X-ray crystal structures of 49 and 51.

3986
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
H
N
CO2Me
TFA.H
H
N
S
CO2Me
R
59
(i)
N
H
O
Boc
O
N
H
CO2H
H2N
CO2H
S
(ii)
O
57
58
R = Boc
60
61
(iii)
R = H.TFA
(iv)
O
O
H
N
H
CO2Me
N
CO2Me
N
H
N
(v)
H
O
O
O
S
S
62
56
O
Scheme 1. Synthesis of cyclic dipeptide 56. Reagents and conditions: (i) Boc2O (1.1 equiv), NaOH (1.1 equiv), water/tert-butyl alcohol (1:1 v/v), rt, 18 h (99%);
(ii) EDCI (1.3 equiv), HOBt (1.5 equiv), DIPEA (1.1 equiv), CH2Cl2, rt, 16 h (46%); (iii) TFA, CH2Cl2, rt, 18 h; (iv) 4-pentenoic acid (1.1 equiv), EDCI
(1.3 equiv), HOBt (1.5 equiv), DIPEA (1.1 equiv), CH2Cl2, rt, 16 h (72%, over two steps); (v) Grubbs’ second generation catalyst 31 (0.2 equiv), CH2Cl2, argon
flow, reflux 6 h, then DMSO (50 equiv relative to 31), rt, 12 h (65%).
antibacterial properties.46,47 Commercially available tert-
L-leucine 57 was treated with Boc2O in the presence of sodium
hydroxide to give Boc-protected 58 in quantitative yield
(Scheme 1). Boc-L-tert-leucine 58 and S-pentenoyl cysteine
methyl ester 59 were coupled on treatment with EDCI/HOBt
in CH2Cl2 to give 60 in 46%. The Boc group of dipeptide
60 was then removed using TFA in CH2Cl2 to give 61, which
was acylated with 4-pentenoic using EDCI/HOBt to give the
dipeptide diene 62 in 72% yield over two steps. This RCM
precursor was then cyclized on treatment with Grubbs’ second
generation catalyst 31 to give the 15-membered compound
E-56 in 65% yield. The double bond of 56 was again assigned
the thermodynamically more stable E configuration, as molec-
ular modelling suggests E-56 to be significantly more thermo-
dynamically stable than Z-56 (molecular models shown in
Fig. 5). It is interesting to note that a hydrogen bond is appar-
ent in both structures, between the N-pentenoyl carbonyl and
cysteine amide for the E isomer and between the thio ester
carbonyl and the tert-leucine amide for the Z. Ongoing work
is centred on converting the methyl ester of 56 into a metal-
chelating warhead as is found in 55 and studying biological
properties of this derivative.48
3. Conclusion
An olefin tether of variable length was introduced into nat-
ural amino acids via the side-chain (Ser, Cys), N-terminus
(Arg), C-terminus (Phe, Tic) or a combination of both (Ser,
Cys, Tyr) to provide substrates for metathesis (see Tables
1e4). Cross-metathesis of the side-chain derivatized Cys,
Ser and Tyr derivatives (8 and 9, 11 and 12 and 45) gave
33e36, 46 and 47 and 48, while dimerization of the Na-acyl
arginines 14 and 15 gave 37 and 38, respectively. The Phe
and Tic alkenyl esters 17 and 18 and 20 and 21 were cross-
linked to give dimers 41e44. Ring-closing metathesis of the
doubly alkenylated Cys, Ser and Tyr derivatives (23 and 24,
26 and 27 and 30) gave 12-, 20- and 24-membered macro-
cycles (49e52 and 54), with the alkene configuration of 49
and 51 being assigned the E configuration by X-ray crystallog-
raphy. The methodology was also applied to the synthesis of
a novel peptide deformylase inhibitor template 56.
The approach presented is general (using the side-chain of
serine and cysteine, and potentially aspartic/glutamic acid,
lysine and threonine) and versatile (length of olefin tether),
enabling access to analogues of natural peptide cross-links
Figure 5. Minimized energy structures of E-56 (a) and Z-56 (b).

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3987
and bioconjugates. Bioactive (peptidic) monomers can be
linked at various positions, using the olefin tethered side-chain
and/or main-chain functionalities. The double bond in the me-
tathesis product also provides a point for further elaboration
and modification (e.g., via dihydroxylation or amino hydroxyl-
ation). RCM provides access to novel cyclic peptidomimetics
in two steps from the natural amino acids, where the length of
the olefin tether determines the ring size.
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
4.3. Molecular modelling
E- and Z-Configurations of cyclic compounds were con-
structed in silico using Schrodinger’s Maestro build function
¨
and minimized using the MMFFs forcefield in vacuo, which
is reputed to be best for comparing with crystal structures.53,54
The same forcefield was then used to perform a conforma-
tional search on each structure. Conformations within
12 kJ molꢁ1 of the lowest energy conformation were saved
to generate a low energy ensemble for each structure. Each
ensemble was then used to calculate the Boltzmann weighted
average energy of each compound allowing the most ther-
modynamically stable double bond configuration of each
compound to be identified.
4. Experimental
4.1. General
Thin Layer Chromatography (TLC) was performed on
a plastic sheet precoated with silica gel 60F254 (Merck) and
visualized using ultraviolet light, vanillin and/or potassium
permanganate dip. Column chromatography was performed
using 230e400 mesh Merck Silica Gel 60. CH2Cl2 was freshly
distilled from calcium hydride under an inert atmosphere and
4.4. Preparation of the metathesis substrates (Table 1)
˚
stored over 4 A molecular sieves. HPLC grade DMF was pur-
4.4.1. Synthesis of (2R)-2-tert-butoxycarbonylamino-
3-(pent-4-enoylsulfanyl)-propionic acid methyl ester 8
˚
chased from Aldrich and stored over 4 A molecular sieves.
Melting points (mp) were determined on an Electrothermal
apparatus and are uncorrected. Electrospray ionization mass
spectra were detected on a Micromass LCT TOF mass spec-
trometer, with a probe voltage of 3200 V, temperature of
Et3N (2.4 equiv) was added dropwise to a stirred solution of
4-pentenoic acid (267 mg, 2.67 mmol, 1.1 equiv) in dry
CH2Cl2 (15 mL) under an inert atmosphere. After stirring
for 20 min, this solution was added dropwise to a solution of
BOP-Cl (741 mg, 2.92 mmol, 1.2 equiv) in dry CH2Cl2
(15 mL) at 0 ꢀC. A solution of BoceL-CyseOMe (572 mg,
2.43 mmol, 1 equiv) in dry CH2Cl2 (15 mL) was then added
dropwise at 0 ꢀC. After 15 min the reaction was allowed to
warm to rt and stirring continued overnight. The solvent was
removed by evaporation under reduced pressure and the residue
dissolved in ethyl acetate. The solution was washed twice with
water (10 mL), and the combined organic layers were washed
with aqueous saturated sodium bicarbonate (10 mL), water
(10 mL) and brine (10 mL) sequentially. The combined organic
layers were dried (MgSO4), and the solvent removed by evapo-
ration under reduced pressure. The crude product was purified
by flash chromatography on silica (ethyl acetate/petroleum
ether, 1:4) to give 8 (717 mg, 93%) as a white solid.
1
150 ꢀC and a source temperature of 80 ꢀC. H NMR spectra
were obtained on a Varian Inova spectrometer, operating at
500 MHz. 13C NMR spectra were recorded on a Varian Inova
Unity 300 spectrometer, operating at 75 MHz. Solvents and
chemical shifts (d), using TMS (dH 0.00 ppm), CDCl3
(CHCl3 at dH 7.26 ppm, CDCl3 at dC 77.23 ppm) or CD3OD
(CHD2OD at dH 3.30 ppm, CD3OD at dC 49.3 ppm) as internal
standards, are reported for each compound.
4.2. X-ray crystallography
All measurements were made with a Seimens CCD area de-
˚
tector using graphite monochromized Mo Ka (l¼0.71073 A)
radiation at 92F. The data reduction was performed using
SAINT.49 Intensities were corrected for Lorentz and polariza-
tion effects and for absorption using SADABS. Space groups
were determined from systematic absences and checked for
higher symmetry. The structures were solved by direct
methods using SHELXS,50 and refined on F with all data using
full-matrix least squares procedures with SHELXL-97.51 All
non-hydrogen atoms were refined with anisotropic displace-
ment parameters. All hydrogen atoms were fixed in idealized
positions. Absolute structural determinations were based on
the Flack parameter. In all cases, final Fourier syntheses
showed no significant residual electron density in chemical
sensible positions.
HRMS (MþH) found 318.1375 (calcd for C14H24NO5S
318.1375); Rf (20% ethyl acetate/petroleum ether) 0.48; mp:
33e35 ꢀC; 1H NMR (CDCl3, 500 MHz) d 1.42 (s, 9H,
3
C(Me)3), 2.38 (m, 2H, COCH2CH2), 2.64 (t, 2H, J 7.5 Hz,
COCH2), 3.33 (m, 2H, CH2S), 3.73 (s, 3H, OCH3), 4.51 (br
m, 1H, NHCH(a)), 5.00 (dd, 1H, 2J 1.3 Hz, 3J 10.3 Hz,
CH]CHH), 5.04 (m, 1H, CH]CHH), 5.21 (br d, 1H, 3J
7.5 Hz, NH(a)), 5.76 (m, 1H, CH]CH2); 13C NMR
(CDCl3, 75 MHz) d 27.5, 28.6, 30.1, 42.3, 51.8, 52.4, 79.0,
115.3, 135.3, 154.4, 170.3, 196.6.
4.4.2. Synthesis of (2R)-2-tert-butoxycarbonylamino-
The crystallographic data have been submitted with the
Cambridge Crystallographic Data Centre. CCDC-676321
(compound 49) and CCDC-676322 (compound 51) contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
3-(undec-10-enoylsulfanyl)-propionic acid methyl ester 9
TEA (2.4 equiv) was added dropwise to a stirred solution of
10-decenoic acid (516 mg, 2.80 mmol, 1.1 equiv) in dry
CH2Cl2 (15 mL) under an inert atmosphere. After stirring
for 20 min, this solution was added dropwise to a solution of

3988
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
BOP-Cl (774 mg, 3.05 mmol, 1.2 equiv) in dry CH2Cl2
(15 mL) at 0 ꢀC. A solution of BoceL-CyseOMe (598 mg,
2.54 mmol, 1 equiv) in dry CH2Cl2 (15 mL) was then added
dropwise at 0 ꢀC. After 15 min the reaction was allowed to
warm to rt and stirring continued overnight. The solvent was
removed by evaporation under reduced pressure and the resi-
due dissolved in ethyl acetate. The solution was washed twice
with water (10 mL), and the combined organic layers were
washed with aqueous saturated sodium bicarbonate (10 mL),
water and brine (10 mL) sequentially. The combined organic
layers were dried (MgSO4), and the solvent removed by evapo-
ration under reduced pressure. The crude product was purified
by flash chromatography on silica (ethyl acetate/petroleum
ether, 1:4) to give 9 (840 mg, 82%) as a colourless oil.
0.01 equiv) and the solution was cooled to 0 ꢀC. EDCI (285 mg,
1.49 mmol, 1.09 equiv) was added, the solution was stirred at
0 ꢀC for 2 h and was then allowed to warm to rt with stirring over-
night. The solvent was removed by evaporation under reduced
pressure and the residue dissolved in ethyl acetate and water
(30 mL, 1:1 v/v). The organic layer was dried (MgSO4), and the
solvent removed by evaporation under reduced pressure. The
crude product was purified by flash chromatography on silica
(ethyl acetate/petroleum ether, 1:4) to give 12 (444 mg, 84%) as
a colourless oil.
HRMS (MþNa) found 408.2361 (calcd for C20H35NO6Na
1
408.2362); Rf (20% ethyl acetate/petroleum ether) 0.52; H
NMR (CDCl3, 500 MHz) d 1.26e1.45 (m, 10H, CH2), 1.43 (s,
9H, C(Me)3), 1.57 (m, 2H, COCH2CH2), 2.01 (m, 2H,
3
HRMS (MþNa) found 424.2119 (calcd for C20H35NO5SNa
424.2134); Rf (20% ethyl acetate/petroleum ether) 0.73; 1H
NMR (CDCl3, 500 MHz) d 1.26e1.47 (m, 10H, CH2), 1.42 (s,
9H, C(Me)3), 1.63 (m, 2H, COCH2CH2), 2.01 (m, 2H,
CO(CH2)7CH2), 2.27 (t, 2H, J 7.6 Hz, COCH2), 3.74 (s, 3H,
OCH3), 4.29 (dd, 1H, 3J 3.5 Hz, 2J 11.2 Hz, OCHH), 4.43 (dd,
1H, 3J 3.5 Hz, 2J 11.2 Hz, OCHH), 4.54 (m, 1H, NHCH), 4.90
(m, 1H, CH]CHH), 4.96 (m, 1H, CH]CHH), 5.27 (br d,
1H, 3J 8.0 Hz, NH), 5.78 (m, 1H, CH]CH2); 13C NMR
(CDCl3, 75 MHz) d 24.5, 27.9, 28.5, 28.7, 28.9, 29.0, 33.5,
33.6, 52.3, 52.7, 63.6, 79.7, 113.9, 138.7, 154.9, 170.0, 172.9.
3
CO(CH2)7CH2), 2.53 (t, 2H, J 7.6 Hz, COCH2), 3.32 (m, 2H,
CH2S), 3.73 (s, 3H, OMe), 4.51 (br m, 1H, NHCH(a)), 4.91 (m,
3
1H, CH]CHH), 4.97 (m, 1H, CH]CHH), 5.22 (br d, 1H, J
6.7 Hz, NH(a)), 5.79 (m, 1H, CH]CH2); 13C NMR (CDCl3,
75 MHz) d 25.0, 27.7, 28.3, 28.4, 28.5, 28.6, 28.7, 30.3, 33.2,
43.3, 51.9, 52.6, 79.1, 113.7, 138.3, 154.5, 170.4, 197.4.
4.4.5. Synthesis of Na-(2S)-pent-4-enoyl-Nu-(2,2,4,6,7-
pentamethyldihydro-benzofuran-5-sulfonyl)-arginine
methyl ester 14
4.4.3. Synthesis of (2S)-pent-4-enoic acid-(2-tert-butoxy-
carbonylamino-2-methoxycarbonyl)-ethyl ester 11
To a stirred solution of 4-pentenoic acid (0.053 mL,
0.76 mmol, 1 equiv) in dry CH2Cl2 (10 mL) were added Et3N
(0.32 mL, 2.26 mmol, 3 equiv) and TBTU (0.269 g,
0.84 mmol, 1.1 equiv). The solution was stirred at rt for 5 min
To a stirred solution of BoceL-SereOMe (2 g, 9.10 mmol,
1 equiv) and 4-pentenoic acid (1.04 g, 10.4 mmol, 1.14 equiv)
in dry CH2Cl2 (80 mL) was added DMAP (11 mg, 0.09 mmol,
0.01 equiv) and the solution was cooled to 0 ꢀC. EDCI (1.89 g,
9.92 mmol, 1.09 equiv) was added, the solution was stirred at
0 ꢀC for 2 h and was then allowed to warm to rt with stirring
overnight. The solvent was removed by evaporation under re-
duced pressure and the residue dissolved in ethyl acetate and
water (80 mL, 1:1 v/v). The organic layer was dried
(MgSO4), and the solvent removed by evaporation under re-
duced pressure. The crude product was purified by flash chro-
matography on silica (ethyl acetate/petroleum ether, 3:7) to
give 11 (2.51 g, 89%) as a white solid.
and
Nu-(2,2,4,6,7-pentamethyldihydro-benzofuran-5-sulfo-
nyl)-L-arginine methyl ester hydrochloride 13 (400 mg,
0.84 mmol, 1.1 equiv) was subsequently added. The reaction
was stirred for 2 h at rt and the reaction mixture was then diluted
with CH2Cl2 (10 mL) and extracted with 1 N aqueous HCl
(10 mL), aqueous saturated sodium bicarbonate (10 mL) and
brine (10 mL). The organic layer was dried (Na2SO4), filtered
and the solvent removed by evaporation under reduced pressure.
No further purification was needed (purity >95%). Compound
14 was isolated as a white foam (450 mg, 88%).
MS (MþH) found 523 (calcd for C25H39N4O6S 523.2512); Rf
(5% MeOH/CH2Cl2) 0.41; 1H NMR (CDCl3, 500 MHz) d 1.46
(s, 6H, Cquat(Me)2 (Pbf)), 1.55 (m, 2H, CH2(g)), 1.85 (m, 2H,
CH2(b)), 2.09 (s, 3H, C7Me (Pbf)), 2.32 (m, 4H, COCH2CH2),
2.51 (s, 3H, C4Me (Pbf)), 2.57 (s, 3H, C6Me (Pbf)), 2.96 (s,
2H, CH2 (Pbf)), 3.24 (m, 2H, CH2(d)), 3.72 (s, 3H, COOMe),
4.54 (m, 1H, CH(a)), 4.99 (m, 2H, CH]CHH and CH]CHH),
5.78 (m, 1H, CH]CH2), 6.27 (br s, 3H, C(d)NHC(]NH)NH),
HRMS (MþH) found 302.1601 (calcd for C14H24NO6
302.1604); Rf (30% ethyl acetate/petroleum ether) 0.67; mp:
35e37 ꢀC; 1H NMR (CDCl3, 500 MHz) d 1.42 (s, 9H,
C(Me)3), 2.32 (m, 2H, COCH2CH2), 2.39 (m, 2H, COCH2),
3.73 (s, 3H, OMe), 4.31 (dd, 1H, 3J 3.6 Hz, 2J 11.3 Hz,
3
2
OCHH), 4.41 (dd, 1H, J 3.6 Hz, J 11.3 Hz, OCHH), 4.54
(m, 1H, NHCH(a)), 4.98 (dd, 1H, 2J 1.4 Hz, 3J 10.3 Hz,
CH]CHcisHtrans), 5.02 (dd, 1H, 2J 1.4 Hz, 3J 17.2 Hz,
CH]CHcisHtrans), 5.27 (br d, 1H, 3J 8.0 Hz, NH(a)), 5.77 (m,
1H, CH]CH2); 13C NMR (CDCl3, 75 MHz) d 27.7, 28.1,
32.6, 52.0, 52.4, 63.5, 79.3, 115.0, 136.0, 154.7, 169.7, 171.8.
3
6.62 (d, 1H, J 6.6 Hz, NH(a)); 13C NMR (CDCl3, 75 MHz)
d 12.7, 18.1, 19.5, 25.5, 28.8, 29.6, 30.1, 35.5, 38.8, 43.4,
49.6, 52.7, 86.6, 118.9, 117.7, 124.8, 132.3, 133.1, 136.8,
138.5, 156.5, 158.9, 172.9, 173.8.
4.4.4. Synthesis of (2S)-undec-10-enoic acid-(2-tert-butoxy-
carbonylamino-2-methoxycarbonyl)-ethyl ester 12
To a stirred solutionofBoceL-SereOMe (300 mg, 1.37 mmol,
1 equiv) and 10-decenoic acid (287 mg, 1.56 mmol, 1.14 equiv) in
dry CH2Cl2 (10 mL) was added DMAP (2 mg, 0.01 mmol,
4.4.6. Synthesis of Na-(2S)-undec-10-enoyl-Nu-(2,2,4,6,7-
pentamethyldihydro-benzofuran-5-sulfonyl)-arginine
methyl ester 15
To a stirred solution of 10-undecenoic acid (0.15 mL,
0.76 mmol, 1 equiv) in dry CH2Cl2 (10 mL) were added

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3989
Et3N (0.32 mL, 2.26 mmol, 3 equiv) and TBTU (0.269 g,
0.84 mmol, 1.1 equiv). The solution was stirred at rt for 5 min
and
11.25 mmol, 3 equiv) and TBTU (1.325 g, 4.125 mmol,
1.1 equiv). The solution was stirred at rt for 5 min and 9-de-
cen-1-ol (0.735 mL, 4.13 mmol, 1.1 equiv) was subsequently
added. The reaction was stirred overnight at rt and the reac-
tion mixture was then diluted with CH2Cl2 (20 mL) and ex-
tracted with 1 N aqueous HCl (20 mL), aqueous saturated
sodium bicarbonate (20 mL) and brine (20 mL). The organic
layer was dried (Na2SO4), filtered and the solvent removed
by evaporation under reduced pressure. The crude product
was purified by flash chromatography on silica (CH2Cl2/
MeOH, 99:1) to give 18 (1.30 g, 86%) as a glassy white
solid.
Nu-(2,2,4,6,7-pentamethyldihydro-benzofuran-5-sulfo-
nyl)-L-arginine methyl ester hydrochloride 13 (400 mg,
0.84 mmol, 1.1 equiv) was subsequently added. The reaction
was stirred for 2 h at rt and the reaction mixture was then diluted
with CH2Cl2 (10 mL) and extracted with 1 N aqueous HCl
(10 mL), aqueous saturated sodium bicarbonate (10 mL) and
brine (10 mL). The organic layer was dried (Na2SO4), filtered
and the solvent removed by evaporation under reduced pressure.
No further purification was needed (purity >95%). Compound
15 was isolated as a pale yellow oil (381 mg, 83%).
MS (MþH) found 607 (calcd for C31H51N4O6S 607.3451); Rf
(5% MeOH/CH2Cl2) 0.35; 1H NMR (CDCl3, 500 MHz) d 1.27
(m, 10H, C4eC8 CH2 undecenoyl), 1.46 (s, 6H, Cquat(Me)2
(Pbf)), 1.58 (m, 4H, C3 CH2 undecenoyl and CH2(g)), 1.65
and 1.85 (2m, 2H, C9 CH2 undecenoyl), 2.03 (m, 2H,
MS (MþNa) found 426 (calcd for C24H37NO4Na
1
426.2723); Rf (1% MeOH/CH2Cl2) 0.36; H NMR (CDCl3,
500 MHz) d 1.28 (br m, 10H, CH2 C3eC7 dec-9-enyl ester),
1.42 (s, 9H, C(Me)3), 1.61 (m, 2H, CH2 C2 dec-9-enyl ester),
2.05 (m, 2H, CH2 C8 dec-9-enyl ester), 3.07 (m, 2H, CH2Ar),
4.08 (t, 2H, 3J 7.0 Hz, CH2 C1 dec-9-enyl ester), 4.59 (dd, 1H,
3J 15.3, 6.0 Hz, CH(a)), 5.02 (m, 2H, CH]CH2), 5.05 (br s,
1H, NH(a)), 5.81 (m, 1H, CH]CH2), 7.15 (m, 2H, CH
arom), 7.25 (m, 3H, CH arom); 13C NMR (CDCl3, 75 MHz)
d 25.9, 28.4, 28.5, 29.0, 29.1, 29.2, 29.4, 33.9, 38.5, 54.6,
65.6, 79.8, 114.3, 127.0, 128.6, 129.4, 136.2, 139.2, 155.2,
172.0.
3
CH2(b)), 2.09 (s, 3H, C7Me (Pbf)), 2.20 (t, 2H, J 7.6 Hz, C2
CH2 undecenoyl), 2.51 (s, 3H, C4Me (Pbf)), 2.57 (s, 3H, C6Me
(Pbf)), 2.96 (s, 2H, CH2 (Pbf)), 3.25 (m, 2H, CH2(d)), 3.73 (s,
3H, COOMe), 4.54 (m, 1H, CH(a)), 4.98 (m, 2H, CH]CHH
and CH]CHH), 5.81 (m, 1H, CH]CH2), 6.24 (br s, 2H,
C(d)NHC(]NH)NH), 6.35 (br s, 1H, C(d)NHC(]NH)NH),
3
6.46 (d, 1H, J 6.6 Hz, NH(a)); 13C NMR (CDCl3, 75 MHz)
d 12.6, 18.1, 19.4, 25.5, 25.8, 28.8, 29.1, 29.3, 29.4, 29.5,
30.3, 36.5, 40.8, 43.5, 51.8, 52.7, 61.4, 86.6, 114.4, 117.7,
124.8, 132.5, 133.3, 138.5, 139.3, 156.5, 158.9, 172.9, 174.2.
4.4.9. Synthesis of (2S)-2-tert-butoxycarbonylamino-1,2,3,4-
tetrahydro-isoquinoline-3-carboxylic acid but-3-enyl
ester 20
4.4.7. Synthesis of (2S)-2-tert-butoxycarbonylamino-3-
phenyl-propionic acid but-3-enyl ester 17
To a stirred solution of BoceL-TiceOH 19 (300 mg,
1.08 mmol, 1 equiv) in dry CH2Cl2 (10 mL) were added
Et3N (0.450 mL, 3.26 mmol, 3 equiv) and TBTU (382 mg,
1.19 mmol, 1.1 equiv). The solution was stirred at rt for
5 min and 3-buten-1-ol (0.102 mL, 1.19 mmol, 1.1 equiv)
was subsequently added. The reaction was stirred overnight
at rt and the reaction mixture was then diluted with CH2Cl2
(10 mL) and extracted with 1 N aqueous HCl (10 mL), aque-
ous saturated sodium bicarbonate (10 mL) and brine
(10 mL). The organic layer was dried (Na2SO4), filtered and
the solvent removed by evaporation under reduced pressure.
The crude product was purified by flash chromatography on
silica (CH2Cl2/MeOH, 99:1) to give 20 (286 mg, 80%) as
a yellow oil.
To a stirred solution of BoceL-PheeOH (2 g, 7.5 mmol,
1 equiv) in dry CH2Cl2 (40 mL) were added Et3N (3.1 mL,
22.5 mmol, 3 equiv) and TBTU (2.65 g, 8.25 mmol, 1.1 equiv).
The solution was stirred at rt for 5 min and 3-buten-1-ol (0.
71 mL, 8.25 mmol, 1.1 equiv) was subsequently added. The re-
action was stirred overnight at rt and the reaction mixture was
then diluted with CH2Cl2 (40 mL) and extracted with 1 N aque-
ous HCl (20 mL), aqueous saturated sodium bicarbonate
(20 mL) and brine (20 mL). The organic layer was dried
(Na2SO4), filtered and the solvent removed by evaporation un-
der reduced pressure. The crude product was purified by flash
chromatography on silica (CH2Cl2/MeOH, 99:1) to give 17
(2.09 g, 87%) as a white solid.
MS (MþNa) found 354 (calcd for C19H25NO4Na
1
354.1784); Rf (1% MeOH/CH2Cl2) 0.40; H NMR (CDCl3,
MS (MþNa) found 342 (calcd for C18H26NO4Na 342.1681);
Rf (1% MeOH/CH2Cl2) 0.38; mp: 76e79 ꢀC; 1H NMR (CDCl3,
500 MHz) d 1.41 (s, 9H, C(Me)3), 2.34 (m, 2H, COCH2CH2),
500 MHz) d (cis/trans rotamer mixture) 1.46 and 1.53 (2s,
9H, cis/trans C(Me)3), 2.24 (m, 2H, COCH2CH2), 3.20 (m,
2H, CH2Ar), 4.07 (t, 2H, 3J 6.8 Hz, OCH2CH2), 4.48 and
3
3.07 (m, 2H, CH2Ar), 4.15 (t, 2H, J 6.7 Hz, OCH2CH2), 4.57
3
3
2
(dd, 1H, J 15.4, 6.2 Hz, CH(a)), 4.96 (br d, 1H, J 7.0 Hz,
NH(a)), 5.07 (m, 1H, CH]CH2), 5.70 (m, 1H, CH]CH2),
4.52 (2d, 1H, J 7.0 Hz, NCHHAr), 4.67 and 4.72 (2d, 1H,
2J 7.0 Hz, NCHHAr), 4.80 (apparent t, 0.5H, J 5.2 Hz,
CH(a) cis or trans), 5.01 (m, 2H, CH]CH2), 5.13 (dd,
0.5H, 3J 5.8, 3.3 Hz, CH(a) cis or trans), 5.62 (m, 1H,
CH]CH2), 7.16 (m, 4H, CH arom); 13C NMR (CDCl3,
75 MHz) d (cis/trans rotamer mixture) 28.5 and 28.6, 31.4
and 31.9, 33.1, 44.3 and 44.8, 52.7, 53.6, 54.5, 64.3, 80.7,
117.4 and 117.5, 126.4, 126.5, 126.7, 126.9, 127.0, 127.1,
128.0, 128.7, 132.0, 132.3, 133.8, 133.9, 134.7, 155.6 and
156.2, 171.6 and 172.9.
3
7.13 (apparent d, 2H, J 7.8 Hz, CH arom), 7.25 (m, 3H, CH
arom); 13C NMR (CDCl3, 75 MHz) d 28.5, 33.1, 38.9, 54.6,
64.6, 80.3, 117.7, 127.2, 128.7, 129.5, 133.8, 136.3, 155.9, 172.1.
4.4.8. Synthesis of (2S)-2-tert-butoxycarbonylamino-3-
phenyl-propionic acid dec-9-enyl ester 18
To a stirred solution of BoceL-PheeOH (1 g, 3.75 mmol,
1 equiv) in dry CH2Cl2 (20 mL) were added Et3N (1.55 mL,

3990
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3
4.4.10. Synthesis of (2S)-2-tert-butoxycarbonylamino-
1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid dec-9-
enyl ester 21
]CHCH2), 2.63 (t, 2H, J 7.3 Hz, COCH2), 3.35 (m, 2H,
CH2S), 3.72 (s, 3H, OMe), 4.77 (m, 1H, CH(a)), 4.97e5.06
(m, 4H, CH]CH2), 5.77 (m, 2H, CH]CH2), 6.28 (br d,
1H, J 7.1 Hz, NH(a)); 13C NMR (CDCl3, 75 MHz) d 28.5,
28.7, 29.7, 34.4, 42.19, 51.3, 51.8, 114.6, 115.2, 135.3,
136.3, 167.0, 171.8, 197.0.
3
To a stirred solution of BoceL-TiceOH 19 (300 mg,
1.08 mmol, 1 equiv) in dry CH2Cl2 (10 mL) were added
Et3N (0.450 mL, 3.26 mmol, 3 equiv) and TBTU (382 mg,
1.19 mmol, 1.1 equiv). The solution was stirred at rt for
5 min and 9-decen-1-ol (0.212 mL, 1.19 mmol, 1.1 equiv)
was subsequently added. The reaction was stirred overnight
at rt and the reaction mixture was then diluted with CH2Cl2
(10 mL) and extracted with 1 N aqueous HCl (10 mL), aque-
ous saturated sodium bicarbonate (10 mL) and brine
(10 mL). The organic layer was dried (Na2SO4), filtered and
the solvent removed by evaporation under reduced pressure.
The crude product was purified by flash chromatography on
silica (CH2Cl2/MeOH, 99:1) to give 21 (270 mg, 60%) as
a colourless oil.
4.4.12. Synthesis of (2R)-2-(undec-10-enoylamino)-3-
(undec-10-enoylsulfanyl)-propanoic acid methyl ester 24
To a stirred solution of 10-undecenoic acid (590 mg,
3.2 mmol, 2.2 equiv) in dry CH2Cl2 (10 mL) under an inert at-
mosphere was added dropwise Et3N (876 mg, 8.6 mmol,
5.9 equiv) at 0 ꢀC. After stirring for 20 min, this solution
was added dropwise to a solution of BOP-Cl (890 mg,
3.5 mmol, 2.4 equiv) in dry CH2Cl2 (20 mL) at 0 ꢀC. A solu-
tion of L-CyseOMe$HCl 22 (250 mg, 1.5 mmol, 1 equiv) in
dry CH2Cl2 (10 mL) was then added at 0 ꢀC. After 15 min
the reaction was allowed to warm to rt with stirring overnight.
The solvent was removed by evaporation under reduced pres-
sure and the residue dissolved in ethyl acetate (50 mL). The
solution was washed twice with water (25 mL) and the organic
layer washed twice with saturated aqueous sodium bicarbonate
(25 mL), water (25 mL) and brine solution (25 mL) sequen-
tially. The resulting organic layer was dried (MgSO4), and
the solvent was removed by evaporation under reduced pres-
sure. The crude product was purified by flash chromatography
on silica (ethyl acetate/petroleum ether, 1:1) to give 24
(300 mg, 44%) as a white solid.
MS (MþNa) found 438 (calcd for C25H37NO4Na
1
438.2723); Rf (1% MeOH/CH2Cl2) 0.31; H NMR (CDCl3,
500 MHz) d 1.25 (m, 10H, C3eC7 CH2 dec-9-enyl ester),
1.46 and 1.53 (2s, 9H, C(Me)3), 1.58 (br s, 2H, CH2 C2 dec-
9-enyl ester), 2.04 (m, 2H, CH2 C8 dec-9-enyl ester), 3.15
(m, 2H, CH2Ar), 4.00 (t, 2H, 3J 5.8 Hz, CH2 C1 dec-9-enyl es-
ter), 4.46 and 4.54 (2br s, 1H, NCHHAr), 4.65 and 4.74 (2br s,
1H, NCHHAr), 4.79 (apparent t, 1H, J 5.0 Hz, CH(a) cis or
trans), 4.99 (m, 2H, CH]CH2), 5.14 (dd, 3J 5.9, 3.0 Hz,
CH(a) cis or trans), 5.81 (m, 1H, CH]CH2), 7.17 (m, 4H,
CH arom); 13C NMR (CDCl3, 75 MHz) d (cis/trans mixture)
25.4, 28.1, 28.3, 28.6, 28.7, 28.8, 29.0, 31.0, 31.5, 33.4, 43.8
and 44.4, 52.3 and 54.1, 64.8, 80.2, 113.9, 126.0, 126.5,
127.5, 128.2, 130.9, 131.9, 132.7, 133.6, 138.8, 154.6 and
155.2, 171.1 and 171.7.
HRMS (MþH) found 468.3166 (calcd for C26H46NO4S
468.3148); Rf (50% ethyl acetate/CH2Cl2) 0.96; mp: 40e
1
41 ꢀC; H NMR (CDCl3, 500 MHz) d 1.30 (m, 20H, CH2),
1.59 (m, 4H, CH2), 2.00 (m, 4H, CH2CH]CH2), 2.16 (t,
2H, J 7.6 Hz, NHCOCH2), 2.52 (t, 2H, J 7.5 Hz, SCOCH2),
3.32 (pseudo d, 2H, J 5.5 Hz, CH2S), 3.71 (s, 3H, OMe), 4.76
3
3
4.4.11. Synthesis of (2R)-2-(pent-4-enoylamino)-3-(pent-4-
enoylsulfanyl)-propionic acid methyl ester 23
2
(m, 1H, NHCH), 4.89 (m, 2H, CH]CH2), 4.95 (ddd, 2H, J
To a stirred solution of 4-pentenoic acid (321 mg,
3.2 mmol, 2.2 equiv) in dry CH2Cl2 (10 mL) under an inert at-
mosphere was added dropwise Et3N (876 mg, 8.6 mmol,
5.9 equiv) at 0 ꢀC. After stirring for 20 min, this solution
was added dropwise to a solution of BOP-Cl (890 mg,
3.5 mmol, 2.4 equiv) in dry CH2Cl2 (20 mL) at 0 ꢀC. A solu-
tion of L-CyseOMe$HCl 22 (250 mg, 1.5 mmol, 1 equiv) in
dry CH2Cl2 (10 mL) was then added dropwise at 0 ꢀC. After
15 min the reaction was allowed to warm to rt with stirring
overnight. The solvent was removed by evaporation under re-
duced pressure and the residue dissolved in ethyl acetate
(50 mL). The solution was washed twice with water (25 mL)
and the organic layer washed twice with saturated aqueous so-
dium bicarbonate (25 mL), water (25 mL) and brine solution
(25 mL) sequentially. The resulting organic layer was dried
(MgSO4), and the solvent was removed by evaporation under
reduced pressure. The crude product was purified by flash
chromatography on silica (ethyl acetate/petroleum ether, 1:4)
to give 23 (372 mg, 85%) as a colourless oil.
1.6 Hz, 4J 3.4 Hz, 3J 17.1 Hz, CH]CH2), 5.77 (m, 2H,
CH]CH2), 6.24 (d, 1H, 3J 7.5 Hz, NH(a)); 13C NMR
(CDCl3, 75 MHz) d 25.2, 25.3, 28.5, 28.6, 28.7, 28.8, 28.9,
28.9, 29.0, 29.0, 30.2, 33.4, 33.5, 36.0, 43.6, 51.7, 52.3,
113.9, 113.9, 138.6, 138.7, 170.5, 172.8, 198.5.
4.4.13. Synthesis of (2S)-pent-4-enoic acid-[2-methoxy-
carbonyl-2-(pent-4-enoylamino)]-methyl ester 26
To a stirred solution of L-SereOMe$HCl 25 (200 mg,
1.7 mmol, 1 equiv) and 4-pentenoic acid (370 mg,
3.74 mmol, 2.2 equiv) in DMF (50 mL) were added DIPEA
(1.05 g, 8.16 mmol, 4.8 equiv) and HATU (1.53 g,
4.08 mmol, 2.4 equiv) and the solution was stirred overnight.
Water (100 mL) was added and the resulting solution extracted
with ethyl acetate (50 mL). The organic layer was then washed
with aqueous saturated sodium bicarbonate (25 mL), saturated
ammonium chloride (25 mL) and brine (25 mL). The organic
layer was dried (MgSO4), and the solvent was removed by
evaporation under reduced pressure. The crude product was
purified by flash chromatography on silica (ethyl acetate/
petroleum ether, 2:3) to give 26 (280 mg, 59%) as a pale
yellow oil.
HRMS (MþH) found 300.1273 (calcd for C14H22NO4S
300.1270); Rf (40% ethyl acetate/CH2Cl2) 0.61; 1H NMR
(CDCl3, 500 MHz) d 2.27 (m, 2H, COCH2), 2.36 (m, 4H,

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3991
HRMS (MþH) found 284.1494 (calcd for C14H22NO5
284.1498); Rf (40% ethyl acetate/CH2Cl2) 0.53; 1H NMR
(CDCl3, 500 MHz) d 2.35 (m, 8H, CH2CH2), 3.73 (s, 3H,
OMe), 4.33 (dd, 1H, 3J 3.7 Hz, 2J 11.5 Hz, OCHH), 4.43
(dd, 1H, 3J 3.7 Hz, 2J 11.5 Hz, OCHH), 4.83 (m, 1H,
NHCH(a)), 5.01 (m, 4H, CH]CH2), 5.78 (m, 2H,
CH]CH2), 6.32 (d, 1H, 3J 7.6 Hz, NH(a)); 13C NMR
(CDCl3, 75 MHz) d 28.3, 29.0, 32.8, 35.0, 51.3, 52.4, 63.4,
115.2, 115.3, 136.1, 136.5, 169.7, 172.1, 172.2.
and 4.51 (2apparent t, 3H, J 1.7 Hz, ArOCH2 and NHCH(a)),
3
3
4.95 (br d, 1H, J 7.6 Hz, NH(a)), 5.07 and 5.28 (2m, 2H, J
4
2
10.3 Hz, J 3.3 Hz, J 1.4 Hz, CH]CH2 ester), 5.09 and 5.40
2
4
3
(2m, 2H, J 1.8 Hz, J 3.5 Hz, J 17.3 Hz, CH]CH2 ether),
5.73 (m, 1H, CH]CH2 ester), 6.05 (m, 1H, CH]CH2 ether),
3
3
6.84 (d, 2H, J 8.8 Hz, CH arom), 7.04 (d, 2H, J 8.5 Hz, CH
arom); 13C NMR (CDCl3, 75 MHz) d 28.0, 32.6, 37.8, 54.6,
64.0, 68.5, 79.8, 114.6, 117.1, 117.2, 130.0, 133.1, 133.3,
155.8, 157.7, 172.0.
4.4.14. Synthesis of (2S)-undec-10-enoic acid-[2-methoxy-
carbonyl-2-(undec-10-enoylamino)]-ethyl ester 27
4.4.16. Synthesis of 3-(4-allyloxy-phenyl)-(2S)-2-tert-
butoxycarbonylamino-propionic acid dec-9-enyl ester 30
To a stirred solution of BoceL-Tyr(OAllyl)eOH 28 (1 g,
3.1 mmol, 1 equiv) in dry CH2Cl2 (20 mL) were added Et3N
(1.28 mL, 9.3 mmol, 3 equiv) and TBTU (1.095 g,
3.41 mmol, 1.1 equiv). The solution was stirred at rt for
5 min and 9-decen-1-ol (0. 608 mL, 3.41 mmol, 1.1 equiv)
was subsequently added. The reaction was stirred overnight
at rt and the reaction mixture was then diluted with CH2Cl2
(20 mL) and extracted with 1 N aqueous HCl (20 mL), aqueous
saturated sodium bicarbonate (20 mL) and brine (20 mL). The
organic layer was dried (Na2SO4), filtered and the solvent re-
moved by evaporation under reduced pressure. The crude prod-
uct was purified by flash chromatography on silica (CH2Cl2/
MeOH, 99:1) to give 30 (977 mg, 69%) as a pale yellow oil.
MS (MþNa) found 482 (calcd for C27H40NO5Na
To a stirred solution of L-SereOMe$HCl 25 (200 mg,
1.7 mmol, 1 equiv) and 10-undecenoic acid (680 mg,
3.74 mmol, 2.2 equiv) in DMF (50 mL) were added DIPEA
(1.05 g, 8.16 mmol, 4.8 equiv) and HATU (1.53 g,
4.08 mmol, 2.4 equiv), and the solution stirred overnight. Wa-
ter (100 mL) was added and the resulting solution extracted
with ethyl acetate (50 mL). The organic layer was washed
with aqueous saturated sodium bicarbonate (25 mL), saturated
ammonium chloride (25 mL) and brine (25 mL). The resulting
organic phase was dried (MgSO4) and the solvent removed by
evaporation under reduced pressure. The crude product was
purified by flash chromatography on silica (ethyl acetate/pe-
troleum ether, 2:3) to give 27 (409 mg, 54%) as a waxy oil.
HRMS (MþH) found 452.3378 (calcd for C26H46NO5
452.3376); Rf (30% ethyl acetate/CH2Cl2) 0.67; 1H NMR
(CDCl3, 500 MHz) d 1.31 (m, 20H, CH2), 1.58 (m, 4H,
CH2), 2.01 (m, 4H, CH2CH]CH2), 2.26 (m, 4H, COCH2),
3.74 (s, 3H, OMe), 4.32 (dd, 1H, 3J 3.5 Hz, 2J 11.4 Hz,
1
482.2985); Rf (1% MeOH/CH2Cl2) 0.38; H NMR (CDCl3,
500 MHz) d 1.29 (m, 10H, C3eC7 CH2 decenyl ester), 1.42
(s, 9H, C(Me)3), 1.59 (m, 2H, CH2 C2 decenyl ester), 2.05
(m, 2H, CH2 C8 decenyl ester), 3.02 (2br s, 2H, CH2Ar),
3
2
3
OCHH), 4.45 (dd, 1H, J 4.0 Hz, J 11.4 Hz, OCHH), 4.85
(m, 1H, NHCH(a)), 4.90 (m, 2H, HC]CHH), 4.96 (dd, 2H,
4.08 (t, 2H, J 6.7 Hz, CH2 C1 decenyl ester), 4.49 and 4.51
(2apparent t, 3H, J 1.8 Hz, ArOCH2 and CH(a)), 4.97 (br s,
3
3
4
2J 1.3 Hz, J 17.3 Hz, HC]CHH), 5.78 (m, 2H, CH]CH2),
1H, NH(a)), 4.93 and 5.27 (2m, 2H, J 10.1 Hz, J 3.6 Hz,
3
2
6.26 (d, 1H, J 7.8 Hz, NH(a)); 13C NMR (CDCl3, 75 MHz)
2J 1.3 Hz, CH]CH2 ester), 4.99 and 5.39 (2m, 2H, J 1.4,
d 24.5, 25.2, 28.5, 28.6, 28.7, 28.7, 28.8, 28.9, 29.0, 29.1,
33.4, 33.5, 35.6, 35.9, 51.4, 52.4, 63.3, 113.8, 113.9, 138.6,
138.6, 169.9, 173.0, 173.1.
17.4 Hz, 4J 3.4 Hz, CH]CH2 ether), 5.81 (m, 1H,
CH]CH2 ester), 6.05 (m, 1H, CH]CH2 ether), 6.83 (d,
3
3
2H, J 8.6 Hz, CH arom), 7.04 (d, 2H, J 8.6 Hz, CH arom);
13C NMR (CDCl3, 75 MHz) d 26.0, 28.5, 28.7, 29.1, 29.2,
29.3, 29.5, 33.9, 38.1, 55.4, 65.6, 69.0, 80.1, 114.4, 115.0,
117.7, 128.5, 130.5, 133.6, 139.3, 155.5, 157.9, 172.2.
4.4.15. Synthesis of 3-(4-allyloxy-phenyl)-(2S)-2-tert-
butoxycarbonylamino-propionic acid but-3-enyl ester 29
To a stirred solution of BoceL-Tyr(OAllyl)eOH 28 (1 g,
3.1 mmol, 1 equiv) in dry CH2Cl2 (20 mL) were added Et3N
(1.28 mL, 9.3 mmol, 3 equiv) and TBTU (1.095 g, 3.41 mmol,
1.1 equiv). The solution was stirred at rt for 5 min and 3-
buten-1-ol (0.293 mL, 3.41 mmol, 1.1 equiv) was subsequently
added. The reaction was stirred overnight at rt and the reaction
mixture was then diluted with CH2Cl2 (20 mL) and extracted
with 1 N aqueousHCl (20 mL), aqueoussaturated sodium bicar-
bonate (20 mL) and brine (20 mL). The organic layer was dried
(Na2SO4), filtered and the solvent removed by evaporation
under reduced pressure. The crude product was purified by flash
chromatography on silica (CH2Cl2/MeOH, 99:1) to give 29
(927 mg, 82%) as a glassy, colourless solid.
4.5. Cross-metathesis experiments (Tables 2 and 3)
4.5.1. General procedure
To a solution of alkene (2 equiv) in dry CH2Cl2 (w0.05 M)
was added Grubbs’ second generation catalyst 31 (0.2 equiv).
The solution was refluxed under a flow of inert gas for 6 h, and
DMSO added (50 equiv relative to catalyst 31) and stirred at rt
overnight. The solvent was removed by evaporation under re-
duced pressure to give the crude product.
4.5.2. Synthesis of (2R,2R)-2-tert-butoxycarbonylamino-3-
[7-(2-tert-butoxycarbonylamino-2-methoxycarbonyl-
ethylsulfanylcarbonyl)-hept-4-enoylsulfanyl]-propionic acid
methyl ester 33
MS (MþNa) found 398 (calcd for C21H29NO5Na
1
398.2046); Rf (1% MeOH/CH2Cl2) 0.36; H NMR (CDCl3,
500 MHz) d 1.42 (s, 9H, C(Me)3), 2.35 (m, 2H, COCH2CH2),
3.01 (m, 2H, CH2Ar), 4.14 (t, 2H, 3J 6.7 Hz, OCH2CH2), 4.50
Alkene 8 (30 mg, 0.09 mmol, 2 equiv) in dry CH2Cl2
(2 mL) was treated with Grubbs’ second generation catalyst

3992
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
31 (8 mg, 0.009 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (petroleum ether/ethyl acetate, 7:3) to
give 33 (13 mg, 45%) as a brown oil.
HRMS (MþH) found 743.4714 (calcd for C38H67N2O12
743.4694); Rf (5% ethyl acetate/CH2Cl2) 0.45; 1H NMR
(CDCl3, 500 MHz) d 1.28 (m, 18H, CH2), 1.44 (s, 18H,
C(Me)3), 1.58 (m, 6H, CH2), 1.96 (m, 4H, ]CHCH2), 2.28 (t,
4H, 3J 7.5 Hz, COCH2), 3.75 (s, 6H, OMe), 4.30 (m, 2H,
OCH2), 4.44 (m, 2H, OCH2), 4.55 (m, 2H, NHCH(a)), 5.27 (br
HRMS (MþH) found 607.2354 (calcd for C26H43N2O10S2
1
607.2359); Rf (20% ethyl acetate/petroleum ether) 0.48; H
3
NMR (CDCl3, 500 MHz) d 1.42 (s, 18H, C(Me)3), 2.31 (m,
d, 2H, J 8.0 Hz, NH(a)), 5.36 (m, 2H, CH]CH); 13C NMR
3
4H, ]CHCH2), 2.59 (t, 4H, J 7.4 Hz, COCH2), 3.32 (m,
(CDCl3, 75 MHz) d 24.7, 28.2, 28.9, 29.1, 29.2, 29.4, 29.5,
32.4, 33.8, 52.6, 52.8, 63.9, 80.1, 130.2, 155.0, 170.2, 173.2.
4H, SCH2), 3.72 (s, 6H, OMe), 4.50 (m, 2H, NHCH(a)),
3
5.23 (br d, 2H, J 7.4 Hz, NH(a)), 5.41 (m, 2H, CH]CH);
13C NMR (CDCl3, 75 MHz) d 24.6, 28.2, 31.0, 43.5, 53.0,
52.6, 80.1, 129.1, 155.0, 170.9, 197.6.
4.5.6. Synthesis of (2S,2S)-2-{7-[1-methoxycarbonyl-4-(N0-
methyl-guanidino)-butylcarbamoyl]-hept-4-enoylamino}-5-
(N0-2,2,4,6,7-pentamethyldihydro-benzofuran-5-sulfonyl-
guanidino)-pentanoic acid methyl ester 37
Alkene 14 (100 mg, 0.19 mmol, 2 equiv) in dry CH2Cl2
(5 mL) was treated with Grubbs’ second generation catalyst
31 (16 mg, 0.019 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/methanol, 9:1) to give 37
(75 mg, 74%) as a light brown oil.
4.5.3. Synthesis of (2R,2R)-2-tert-butoxycarbonylamino-3-
[19-(2-tert-butoxycarbonylamino-2-methoxycarbonyl-
ethylsulfanylcarbonyl)-nonadec-10-enoylsulfanyl]-
propionic acid methyl ester 34
Alkene 9 (50 mg, 0.12 mmol, 2 equiv) in dry CH2Cl2
(5 mL) was treated with Grubbs’ second generation catalyst
31 (10 mg, 0.012 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (petroleum ether/ethyl acetate, 7:3) to
give 34 (35 mg, 73%) as a brown oil.
HRMS (MþH) found 1017.4802 (calcd for C48H73N8O12S2
1
1017.4711); Rf (10% MeOH/CH2Cl2) 0.25; H NMR (CDCl3,
500 MHz) d 1.46 (s, 12H, C(Me)2 (Pbf)), 1.57 (m, 4H,
CH2(g)), 1.80 (m, 4H, CH2(b)), 2.09 (s, 6H, C7Me (Pbf)),
2.32 (m, 8H, COCH2CH2), 2.50 (s, 6H, C4Me (Pbf)), 2.56
(s, 6H, C6Me (Pbf)), 2.96 (s, 4H, CH2 (Pbf)), 3.19 (m, 4H,
CH2(d)), 3.72 (s, 6H, COOMe), 4.53 (m, 2H, CH(a)), 5.46
(m, 2H, CH]CH), 6.34 (br s, 6H, C(d)NHC(]NH)NH),
6.97 (br s, 2H, NH(a)); 13C NMR (CDCl3, 75 MHz) d 12.6,
18.1, 19.4, 25.9, 26.5, 27.1, 28.5, 28.8, 29.6, 36.0, 40.8,
43.4, 52.1, 52.6, 86.6, 117.7, 124.8, 129.7, 132.3, 133.1,
138.4, 156.6, 158.9, 172.8, 173.6.
HRMS (MþH) found 775.4224 (calcd for C38H67N2O10S2
1
775.4237); Rf (30% ethyl acetate/petroleum ether) 0.56; H
NMR (CDCl3, 500 MHz) d 1.24 (m, 20H, CH2), 1.41 (s,
18H, C(Me)3), 1.60 (m, 4H, COCH2CH2), 1.92 (m, 4H,
]CHCH2), 2.52 (m, 4H, COCH2), 3.30 (br m, 4H, SCH2),
3.71 (s, 6H, OMe), 4.49 (br m, 2H, NHCH(a)), 5.22 (br d,
3
2H, J 7.9 Hz, NH(a)), 5.34 (m, 2H, CH]CH); 13C NMR
(CDCl3, 75 MHz) d 25.5, 28.2, 28.7, 28.9, 29.1, 29.1, 29.5,
30.8, 32.4, 43.9, 52.5, 53.0, 80.0, 130.2, 154.9, 170.9, 198.4.
4.5.4. Synthesis of (2S)-oct-4-enedioic acid bis-(2-tert-
butoxycarbonylamino-2-methoxycarbonyl-ethyl) ester 35
Alkene 11 (50 mg, 0.17 mmol, 2 equiv) in dry CH2Cl2 (5 mL)
was treated with Grubbs’ second generation catalyst 31 (14 mg,
0.017 mmol, 0.2 equiv) according to the general procedure. The
crude product was purified by flash chromatography on silica
(CH2Cl2/ethylacetate, 9:1) to give 35(42 mg,86%)asabrownoil.
HRMS (MþH) found 575.2818 (calcd for C26H43N2O12
575.2816); Rf (10% ethyl acetate/CH2Cl2) 0.44; 1H NMR
(CDCl3, 500 MHz) d 1.39 (s, 18H, C(Me)3), 2.23 (m, 4H,
]CHCH2), 2.31 (m, 4H, COCH2), 3.70 (s, 6H, OMe), 4.27
(m, 2H, OCH2), 4.38 (m, 2H, OCH2), 4.51 (m, 2H, NHCH(a)),
5.32 (br m, 2H, NH(a)), 5.38 (m, 2H, CH]CH); 13C NMR
(CDCl3, 75 MHz) d 27.4, 28.1, 33.6, 52.6, 52.7, 64.0, 80.2,
129.2, 155.0, 170.2, 172.4.
4.5.7. Synthesis of (2S,2S)-2-{19-[1-methoxycarbonyl-4-(N0-
methyl-guanidino)-butylcarbamoyl]-nonadec-10-
enoylamino}-5-(N0-2,2,4,6,7-pentamethyldihydro-
benzofuran-5-sulfonyl-guanidino)-pentanoic acid
methyl ester 38
Alkene 15 (100 mg, 0.17 mmol, 2 equiv) in dry CH2Cl2
(5 mL) was treated with Grubbs’ second generation catalyst
31 (14 mg, 0.017 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/methanol, 95:5) to give 38
(64 mg, 66%) as a light brown foam.
HRMS (MþH) found 1185.6671 (calcd for C60H97N8O12S2
1
1185.6589); Rf (5% MeOH/CH2Cl2) 0.20; H NMR (CDCl3,
500 MHz) d 1.25 (m, 20H, CH2 C3eC7), 1.46 (s, 12H, C(Me)2
(Pbf)), 1.57 (m, 8H, CH2(g) and CH2 C2), 1.71 and 1.83 (2m,
4H, CH2(b)), 1.97 (m, 4H, CH2 C8), 2.09 (s, 6H, C7Me (Pbf)),
2.22 (t, 4H, 3J 7.3 Hz, CH2 C1), 2.50 (s, 6H, C4Me (Pbf)), 2.56
(s, 6H, C6Me (Pbf)), 2.96 (s, 4H, CH2 (Pbf)), 3.22 (m, 4H,
CH2(d)), 3.71 (s, 6H, COOMe), 4.51 (m, 2H, CH(a)), 5.35 (m,
2H, CH]CH), 6.30 (br s, 6H, C(d)NHC(]NH)NH), 6.68 (br
s, 2H, NH(a)); 13C NMR (CDCl3, 75 MHz) d 12.1, 17.6, 18.9,
25.1, 25.3, 28.3, 28.5, 28.9, 29.0, 29.1, 29.4, 32.1, 35.6, 40.3,
43.0, 51.5, 52.1, 86.1, 117.2, 124.3, 130.1, 131.9, 132.7,
138.0, 156.1, 158.5, 172.4, 173.7.
4.5.5. Synthesis of (2S)-icos-10-enedioic acid bis-(2-tert-
butoxycarbonylamino-2-methoxycarbonyl-ethyl) ester 36
Alkene 12 (60 mg, 0.13 mmol, 2 equiv) in dry CH2Cl2
(5 mL) was treated with Grubbs’ second generation catalyst
31 (14 mg, 0.017 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/ethyl acetate, 9:1) to give 36
(30 mg, 62%) as a brown oil.

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3993
4.5.8. Synthesis of (2S,2S)-2-tert-butoxycarbonylamino-3-
phenyl-propionic acid 6-(2-tert-butoxycarbonylamino-3-
phenyl-propionyloxy)-hex-3-enyl ester 41
Alkene 17 (110 mg, 0.34 mmol, 2 equiv) in dry CH2Cl2
(7 mL) was treated with Grubbs’ second generation catalyst
31 (28 mg, 0.034 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/methanol, 99:1) to give 41
(70 mg, 68%) as a white solid.
75 MHz) d 28.6 and 28.7, 31.5 and 32.0, 44.3 and 44.9, 52.8
and 54.6, 64.7, 80.8, 126.5 and 126.6, 126.9 and 127.0, 127.1
and 127.4, 128.1, 128.3, 128.8, 132.1, 133.6, 133.8, 133.9,
134.7, 155.5 and 156.1, 171.4 and 172.8.
4.5.11. Synthesis of (2S,2S)-2-tert-butoxycarbonyl-1,2,3,4-
tetrahydroisoquinoline-3-carboxylic acid 18-(2-tert-
butoxycarbonyl-1,2,3,4-tetrahydroisoquinolyloxy)-octadec-
9-enyl ester 44
HRMS (MþH) found 611.3331 (calcd for C34H47N2O8
Alkene 21 (80 mg, 0.2 mmol, 2 equiv) in dry CH2Cl2
(5 mL) was treated with Grubbs’ second generation catalyst
31 (16 mg, 0.02 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/methanol, 99:1) to give 44
(45 mg, 56%) as a brown oil.
1
611.3254); Rf (1% MeOH/CH2Cl2) 0.27; mp: 50e52 ꢀC; H
NMR (CDCl3, 500 MHz) d 1.41 (s, 18H, C(Me)3), 2.32 (m,
4H, OCH2CH2), 3.12 (m, 2H, CH2(b)), 4.14 (t, 4H, 3J
3
6.8 Hz, OCH2), 4.60 (dd, 2H, J 15.0, 5.2 Hz, CH(a)), 5.04
(br s, 2H, NH(a)), 5.45 (m, 2H, CH]CH), 7.18 (apparent d,
4H, J 7.3 Hz, CH arom), 7.30 (m, 6H, CH arom); 13C NMR
(CDCl3, 75 MHz) d 28.5, 32.0, 38.6, 54.5, 64.8, 80.1, 127.2,
128.4, 128.7, 129.5, 136.3, 155.3, 172.1.
HRMS [M(ꢁBoc)þH] found 703.4692 (calcd for
C43H63N2O6 703.4608); Rf (1% MeOH/CH2Cl2) 0.29; 1H NMR
(CDCl3, 500 MHz) d (cis/trans mixture) 1.21 (m, 20H, CH2),
1.46 and 1.52 (2s, 22H, C(Me)3 and CH2 C2), 1.97 (m, 4H, CH2
3
4.5.9. Synthesis of (2S,2S)-2-tert-butoxycarbonylamino-3-
phenyl-propionic acid 18-(2-tert-butoxycarbonylamino-3-
phenyl-propionyloxy)-octadec-9-enyl ester 42
Alkene 18 (210 mg, 0.52 mmol, 2 equiv) in dry CH2Cl2
(11 mL) was treated with Grubbs’ second generation catalyst
31 (42 mg, 0.052 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/methanol, 99:1) to give 42
(119 mg, 76%) as a brown oil.
C8), 3.20 and 3.30 (m, 4H, CH2(b)), 4.04 (t, 4H, J 7.1 Hz,
2
OCH2 C1), 4.52 and 4.58 (2d, 2H, J 3.6 Hz, NCH2Ar cis or
trans), 4.70 and 4.76 (2br s, 2H, NCH2Ar cis or trans), 4.83 (ap-
parent t, 1H, J 5.4 Hz, CH(a) cis or trans), 4.79 (dd, 1H, 3J 6.8,
3.0 Hz, CH(a) cis or trans), 5.43 (m, 2H, CH]CH), 7.16 (m,
8H, CH arom); 13C NMR (CDCl3, 75 MHz) d 25.9, 28.5 and
28.6, 28.7 and 28.8, 29.4, 29.5, 29.7, 31.5 and 32.0, 32.8, 44.3
and 44.8, 52.8 and 54.5, 65.4, 80.7, 126.4 and 126.5, 126.8 and
126.9, 127.0 and 127.1, 128.0 and 128.7, 130.5, 132.1 and
132.4, 133.1 and 134.1, 155.0 and 155.7, 171.7 and 172.2.
HRMS (MþH) found 779.5411 (calcd for C46H71N2O8
1
779.5132); Rf (1% MeOH/CH2Cl2) 0.24; H NMR (CDCl3,
500 MHz) d 1.28 (m, 20H, CH2), 1.42 (s, 18H, C(Me)3),
1.57 (m, 4H, CH2), 1.97 (m, 4H, ]CHCH2), 3.07 (m, 4H,
CH2(b)), 4.07 (t, 4H, 3J 6.7 Hz, OCH2), 4.56 (dd, 2H, 3J
16.2, 6.7 Hz, CH(a)), 4.99 (br d, 2H, 3J 8.1 Hz, NH(a)),
5.39 (m, 2H, CH]CH), 7.13 (apparent d, 4H, J 7.6 Hz, CH
arom), 7.26 (m, 6H, CH arom); 13C NMR (CDCl3, 75 MHz)
d 26.1, 28.6, 28.7, 29.4, 29.5, 29.6, 29.9, 32.9, 38.8, 54.7,
65.8, 80.1, 127.2, 128.8, 129.6, 130.6, 136.4, 155.3, 172.2.
4.5.12. Synthesis of (2S,2S)-2-tert-butoxycarbonylamino-3-
(4-{4-[4-(2-tert-butoxy-carbonyl amino-2-methoxycarbonyl-
ethyl)-phenoxy]-but-2-enyloxy}-phenyl)-propionic acid
methyl ester 46
Alkene 45 (100 mg, 0.3 mmol, 2 equiv) in dry CH2Cl2
(5 mL) was treated with Grubbs’ second generation catalyst
31 (24 mg, 0.03 mmol, 0.2 equiv) according to the general
procedure. The crude product was purified by flash chroma-
tography on silica (CH2Cl2/MeOH, 99:1) to give 46 (66 mg,
67%) as a brown oil.
4.5.10. Synthesis of (2S,2S)-2-tert-butoxycarbonyl-1,2,3,4-
tetrahydroisoquinoline-3-carboxylic acid 6-(2-tert-
butoxycarbonyl-1,2,3,4-tetrahydroisoquinolyloxy)-hex-3-
enyl ester 43
HRMS (MþH) found 643.3242 (calcd for C34H47N2O10
1
643.3152); Rf (1% MeOH/CH2Cl2) 0.31; H NMR (CDCl3,
500 MHz) d 1.44 (s, 18H, C(Me)3), 3.02 (m, 4H, ArCH2),
3.70 (s, 6H, OMe), 4.55 (m, 6H, ArOCH2 and CH(a)), 4.98
Alkene 20 (60 mg, 0.18 mmol, 2 equiv) in dry CH2Cl2 (5 mL)
was treated with Grubbs’ second generation catalyst 31 (15 mg,
0.018 mmol, 0.2 equiv) according to the general procedure.
The crude product was purified by flash chromatography onsilica
(CH2Cl2/MeOH, 99:1) to give 43 (51 mg, 89%) as a brown oil.
HRMS (MþH) found 632.3176 (calcd for C36H47N2O8
3
(d, 2H, J 8.0 Hz, NH(a)), 6.07 (m, 2H, CH]CH), 6.83 (d,
3
3
4H, J 8.0 Hz, CH arom), 7.03 (d, 4H, J 8.0 Hz, CH arom);
13C NMR (CDCl3, 75 MHz) d 28.5, 37.8, 52.3, 54.8, 67.9,
80.1, 115.0, 128.5, 128.6, 130.5, 152.5, 157.8, 172.6.
1
632.3254); Rf (1% MeOH/CH2Cl2) 0.25; H NMR (CDCl3,
4.5.13. Synthesis of (2R,2S)-13-(2-tert-butoxy-
500 MHz) d (cis/trans mixture) 1.46 and 1.52 (2s, 18H,
C(Me)3), 2.13 (m, 4H, OCH2CH2), 3.15 (m, 4H, CH2(b)), 3.97
carbonylamino-2-methoxycarbonyl-ethylsulfanylcarbonyl)-
tridec-10-enoic acid 2-tert-butoxycarbonylamino-2-
methoxycarbonyl-ethyl ester 47
To a solution of O-decenoyl serine 12 (20 mg, 0.05 mmol,
1 equiv) and S-pentenoyl cysteine 8 (33 mg, 0.1 mmol,
2 equiv) in dry CH2Cl2 (2 mL) was added Grubbs’ second gen-
eration catalyst 31 (9 mg, 0.01 mmol, 0.2 equiv). The solution
3
2
(t, 4H, J 6.0 Hz, OCH2), 4.47 and 4.53 (2d, 2H, J 7.2 Hz,
NCH2Ar cis or trans), 4.67 and 4.72 (2d, 2H, 2J 3.3 Hz, NCH2Ar
cis or trans), 4.79 (apparent t, 1H, J 5.7 Hz, CH(a) cis or trans),
4.79 (dd, 1H, 3J 6.0, 3.3 Hz, CH(a) cis or trans), 5.22 (m, 2H,
CH]CH), 7.13 (m, 8H, CH arom); 13C NMR (CDCl3,

3994
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
was stirred at reflux under a flow of inert gas for 6 h, and
DMSO added (50 equiv relative to 31) and stirred at rt over-
night. The solvent was removed by evaporation under reduced
pressure to give the crude product, which was purified by flash
chromatography on silica (petroleum ether/ethyl acetate, 3:2)
to give 47 (18 mg, 51%) as a brown oil.
stirred at reflux under a flow of inert gas for 6 h, and DMSO
added (50 equiv relative to 31) and stirred overnight at rt.
The solvent was removed by evaporation under reduced pres-
sure to give the crude product, which was purified by flash
chromatography on silica (petroleum ether/ethyl acetate, 1:4)
to give 49 (23 mg, 74%) as a white solid. Recrystallization
by slow evaporation from CH2Cl2/ethyl acetate gave crystals
suitable for X-ray crystallography.
HRMS (MþH) found 675.3527 (calcd for C32H55N2O11S
1
675.3527); Rf (40% ethyl acetate/petroleum ether) 0.76; H
NMR (CDCl3, 500 MHz) d 1.24 (m, 10H, CH2), 1.42 (s, 9H,
C(Me)3), 1.43 (s, 9H, C(Me)3), 1.56 (m, 2H, CH2), 1.94 (m,
2H, ]CHCH2(CH2)7CO), 2.29 (m, 4H, OCOCH2,
]CHCH2CH2CO), 2.59 (t, 2H, 3J 7.5 Hz, SCOCH2), 3.32 (br
m, 2H, CH2S), 3.72 (s, 3H, OMe), 3.74 (s, 3H, OMe), 4.29 (m,
1H, OCHH), 4.43 (m, 1H, OCHH), 4.50 (m, 1H, NHCH(a)),
HRMS (MþH) found 272.0960 (calcd for C12H18NO4S
272.0957); Rf (20% ethyl acetate/petroleum ether) 0.48; mp:
146e147 ꢀC; 1H NMR (CDCl3, 500 MHz) d 2.02 (m, 1H,
COCHHCH2), 2.26e2.43 (m, 5H, ]CHCH2, COCHHCH2),
2.62 (m, 1H, COCHHCH2), 2.69 (m, 1H, COCHHCH2), 3.45
(m, 2H, CH2S), 3.74 (s, 3H, OMe), 4.80 (m, 1H, NHCH(a)),
5.33 (m, 1H, CH]CH), 5.41 (m, 1H, CH]CH), 5.85 (br s,
1H, NH(a)); 13C NMR (CDCl3, 75 MHz) d 29.0, 29.4, 29.5,
37.5, 42.7, 51.9, 52.6, 128.2, 131.8, 170.8, 172.4, 199.1.
3
4.54 (m, 1H, NHCH(a)), 5.22 (br d, 1H, J 7.4 Hz, NH(a)),
5.27 (br d, 1H, 3J 8.5 Hz, NH(a)), 5.33 (dt, 1H, J 6.7, 15.2 Hz,
CH]CH), 5.42 (dt, 1H, J 6.6, 15.2 Hz, CH]CH); 13C NMR
(CDCl3, 75 MHz) d 24.7, 27.1, 28.2, 28.4, 28.9, 29.1, 29.2,
29.3, 30.9, 32.4, 33.9, 43.8, 52.6, 52.6, 52.9, 53.0, 63.9, 80.1,
80.2, 127.1, 132.3, 154.9, 155.1, 170.3, 170.9, 173.2, 197.8.
4.6.2. Synthesis of (3R)-5,24-dioxo-1-thia-4-aza-
cyclotetracos-14-ene-3-carboxylic acid methyl ester 50
To a solution of alkene 24 (50 mg, 0.11 mmol, 1 equiv) in
dry CH2Cl2 (5 mL) was added Grubbs’ second generation cat-
alyst 31 (18 mg, 0.02 mmol, 0.2 equiv). The solution was
stirred at reflux under a flow of inert gas for 6 h, and DMSO
added (50 equiv relative to 31) and stirred overnight at rt.
The solvent was removed by evaporation under reduced pres-
sure to give the crude product, which was purified by flash
chromatography on silica (ethyl acetate/petroleum ether, 3:7)
to give 50 (20 mg, 43%) as a white solid.
HRMS (MþH) found 440.2843 (calcd for C24H42NO4S
440.2835); Rf (30% ethyl acetate/petroleum ether) 0.58; mp:
94e96 ꢀC; 1H NMR (CDCl3, 500 MHz) d 1.30 (m, 16H,
CH2), 1.60 (m, 8H, CH2), 2.00 (m, 4H, CH2CH]CH2), 2.16
(m, 2H, NHCOCH2), 2.55 (m, 2H, SCOCH2), 3.33 (m, 2H,
SCH2), 3.75 (s, 3H, OCH3), 4.77 (m, 1H, NHCH(a)), 5.31
(m, 2H, CH]CH), 6.16 (d, 1H, 3J 8.0 Hz, NH(a)); 13C
NMR (CDCl3, 75 MHz) d 25.9, 25.2, 27.9, 28.2, 28.7, 28.7,
28.8, 28.9, 29.2, 29.4, 29.4, 29.6, 30.0, 32.0, 32.1, 36.8,
43.9, 52.3, 52.7, 130.8, 130.9, 170.8, 173.1, 199.9.
4.5.14. Synthesis of (2R,2S)-19-(2-tert-butoxy-
carbonylamino-2-methoxycarbonyl-ethylsulfanylcarbonyl)-
nonadec-10-enoic acid 2-tert-butoxycarbonylamino-2-
methoxycarbonyl-ethyl ester 48
To a solution of O-decenoyl serine 12 (20 mg, 0.05 mmol,
1 equiv) and S-decenoyl cysteine 9 (42 mg, 0.10 mmol,
2 equiv) in dry CH2Cl2 (2 mL) was added Grubbs’ second gen-
eration catalyst 31 (9 mg, 0.01 mmol, 0.2 equiv). The solution
was stirred at reflux under a flow of inert gas for 6 h, and
DMSO added (50 equiv relative to 31) and stirred overnight
at rt. The solvent was removed by evaporation under reduced
pressure to give the crude product, which was purified by flash
chromatography on silica (petroleum ether/ethyl acetate, 7:3)
to give 48 (26 mg, 66%) as a brown oil.
HRMS (MþH) found 759.4453 (calcd for C38H67N2O11S
1
759.4466); Rf (30% ethyl acetate/petroleum ether) 0.74; H
NMR (CDCl3, 500 MHz) d 1.26 (m, 20H, CH2), 1.41 (s, 9H,
C(Me)3), 1.43 (s, 9H, C(Me)3), 1.59 (m, 4H, COCH2CH2),
3
1.93 (m, 4H, ]CHCH2), 2.27 (t, 2H, J 7.6 Hz, OCOCH2),
3
2.53 (t, 2H, J 7.5 Hz, SCOCH2), 3.31 (br m, 2H, SCH2),
4.6.3. Synthesis of (3S)-5,12-dioxo-1-oxa-4-aza-cyclododec-
8-ene-3-carboxylic acid methyl ester 51
3.72 (s, 3H, OMe), 3.74 (s, 3H, OMe), 4.29 (m, 1H, OCHH),
4.42 (m, 1H, OCHH), 4.50 (m, 1H, NHCH(a)), 4.54 (m, 1H,
To a solution of alkene 26 (110 mg, 0.39 mmol, 1 equiv) in
dry CH2Cl2 (10 mL) was added Grubbs’ second generation
catalyst 31 (66 mg, 0.08 mmol, 0.2 equiv). The solution was
stirred at reflux under a flow of inert gas for 6 h, and DMSO
added (50 equiv relative to 31) and stirred overnight at rt.
The solvent was removed by evaporation under reduced pres-
sure to give the crude product, which was purified by flash
chromatography on silica (CH2Cl2/ethyl acetate, 1:1) to give
51 (45 mg, 45%) as brown crystals. Recrystallization by
slow evaporation from CH2Cl2/ethyl acetate gave colourless
crystals suitable for X-ray crystallography.
3
NHCH(a)), 5.23 (br d, 1H, J 7.7 Hz, NH(a)), 5.27 (br d,
3
1H, J 8.3 Hz, NH(a)), 5.35 (m, 2H, CH]CH); 13C NMR
(CDCl3, 75 MHz) d 24.7, 25.5, 28.21, 28.8, 28.8, 28.9, 29.0,
29.0, 29.1, 29.1, 29.2, 29.2, 29.5, 30.9, 32.5, 33.9, 40.3,
43.9, 52.6, 52.6, 52.9, 53.0, 64.0, 80.1, 80.3, 130.2, 130.3,
155.0, 155.1, 170.3, 170.9, 173.3, 198.5.
4.6. Ring-closing metathesis experiments (Table 4)
4.6.1. Synthesis of (3R)-5,12-dioxo-1-thia-4-aza-
cyclododec-8-ene-3-carboxylic acid methyl ester 49
To a solution of alkene 23 (34 mg, 0.11 mmol, 1 equiv) in
dry CH2Cl2 (2 mL) was added Grubbs’ second generation cat-
alyst 31 (19 mg, 0.02 mmol, 0.2 equiv). The solution was
HRMS (MþH) found 256.1183 (calcd for C12H18NO5
256.1185); Rf (30% ethyl acetate/petroleum ether) 0.47; mp:
1
151e153 ꢀC; H NMR (CDCl3, 500 MHz) d 2.09e2.44 (m,
3
2
8H, CH2CH2), 3.76 (s, 3H, OMe), 4.24 (dd, 1H, J 3.8 Hz, J

A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
3995
11.5 Hz, OCHH), 4.63(m, 1H, OCHH), 4.98 (m, 1H, NHCH(a)),
NaOH (34 mg, 0.84 mmol, 1.1 equiv) in water/tert-butyl alco-
hol (1 mL/1 mL). The reaction mixture was stirred overnight
at rt and was extracted three times with ethyl acetate
(5 mL). The combined organic layers were washed with satu-
rated aqueous sodium bicarbonate solution (5 mL), and the
combined water phases were acidified to pH 1.5e2.0. The wa-
ter phase was extracted four times with ethyl acetate (5 mL)
and the combined organic phases were washed with brine
solution, dried (MgSO4), and the solvent removed by evapora-
tion under reduced pressure to give 58 (175 mg, 99%) as a col-
ourless solid.
HRMS (MþH) found 232.1485 (calcd for C11H22NO4
232.1471); mp: 122e123 ꢀC; 1H NMR (CDCl3, 500 MHz)
d 1.01 (s, 9H, C(Me)3Leu), 1.43 (s, 9H, C(Me)3Boc), 4.11 (d,
1H, 3J 7.2 Hz, CH(a)), 5.08 (d, 1H, 3J 8.3 Hz, NH); 13C
NMR (CDCl3, 75 MHz) d 26.4, 28.2, 34.4, 61.6, 79.8,
155.6, 176.2.
3
5.39 (ddt, 2H, J 6.3, 11.5, 15.1 Hz, CH]CH), 5.92 (d, 1H,
3J 8.6 Hz, NH(a)); 13C NMR (CDCl3, 75 MHz) d 28.8, 28.9,
34.3, 36.4, 51.0, 52.5, 61.1, 130.0, 130.3, 169.6, 171.9, 172.9.
4.6.4. Synthesis of (2S)-5,24-dioxo-1-oxa-4-aza-
cyclotetracos-14-ene-3-carboxylic acid methyl ester 52
To a solution of alkene 27 (119 mg, 0.26 mmol, 1 equiv) in
dry CH2Cl2 (10 mL) was added Grubbs’ second generation
catalyst 31 (45 mg, 0.05 mmol, 0.2 equiv). The solution was
stirred at reflux under a flow of inert gas for 6 h, and DMSO
added (50 equiv relative to 31) and stirred overnight at rt.
The solvent was removed by evaporation under reduced pres-
sure to give the crude product, which was purified by flash
chromatography on silica (ethyl acetate/petroleum ether, 3:7)
to give 52 (17 mg, 15%) as a brown solid.
HRMS (MþH) found 424.3068 (calcd for C24H42NO5
424.3063); Rf (30% ethyl acetate/petroleum ether) 0.30; mp:
88e90 ꢀC; 1H NMR (CDCl3, 500 MHz) d 1.28 (m, 20H,
CH2), 1.59 (m, 4H, CH2), 1.99 (m, 4H, CH2CH]CH2), 2.24
(m, 4H, COCH2), 3.76 (s, 3H, OMe), 4.41 (m, 2H, OCH2),
4.83 (m, 1H, NHCH(a)), 5.30 (m, 2H, CH]CH), 6.17 (d, 1H,
3J 7.7 Hz, NH(a)); 13C NMR (CDCl3, 75 MHz) d 25.2, 25.9,
28.1, 28.8, 28.8, 28.9, 29.0, 29.1, 29.1, 29.3, 32.1, 33.9, 34.2,
36.6, 51.6, 52.8, 63.1, 130.8, 130.8, 170.0, 172.9, 173.3.
4.7.2. Synthesis of (2S,2R)-2-(2-tert-butoxycarbonylamino-
3,3-dimethyl-butyrylamino)-3-(pent-4-enoylsulfanyl)-
propionic acid methyl ester 60
To N3-pentenoyl cysteine 8 (1 g, 3.15 mmol, 1 equiv) in
CH2Cl2 (50 mL) was added TFA (9.4 mL, 40 equiv) and the
solution was stirred overnight. Removal of the solvent by
evaporation under reduced pressure yielded TFA salt 59 with
a quantitative yield. Salt 59 (3.15 mmol) was added to a mix-
ture of BoceL-TleeOH 58 (831 mg, 3.6 mmol, 1.14 equiv),
DIPEA (0.6 mL, 1.1 equiv), EDCI (782 mg, 4.1 mmol,
1.3 equiv) and HOBt (713 mg, 4.73 mmol, 1.5 equiv) and
stirred at rt overnight. The reaction mixture was then diluted
with CH2Cl2 (50 mL) and extracted with 1 N aqueous HCl
(50 mL), aqueous saturated sodium bicarbonate (50 mL) and
brine (50 mL). The organic layer was dried (Na2SO4), filtered
and the solvent removed by evaporation under reduced pres-
sure. The crude product was purified by flash chromatography
on silica (ethyl acetate/CH2Cl2, 1:4) to give 60 (620 mg, 46%)
as a pale yellow oil.
4.6.5. (15-Oxo-2,14-dioxa-bicyclo[16.2.2]docosa-
1(21),4,18(22),19-tetraen-16-yl)-carbamic acid tert-butyl
ester 54
To a solution of alkene 30 (100 mg, 0.22 mmol, 1 equiv) in
dry CH2Cl2 (100 mL) was added Grubbs’ second generation
catalyst 31 (30 mg, 0.033 mmol, 0.15 equiv). The solution
was stirred at reflux under a flow of inert gas for 6 h, and
DMSO added (50 equiv relative to 31) and stirred overnight
at rt. The solvent was removed by evaporation under reduced
pressure to give the crude product, which was purified by flash
chromatography on silica (CH2Cl2/methanol, 99:1) to give 54
(59 mg, 62%) as a light brown foam.
HRMS (MþH) found 431.2214 (calcd for C20H35N2O6S
1
431.2216); Rf (40% ethyl acetate/petroleum ether) 0.75; H
HRMS (MþH) found 432.2748 (calcd for C25H38NO5
1
432.2672); Rf (1% MeOH/CH2Cl2) 0.24; H NMR (CDCl3,
NMR (CDCl3, 500 MHz) d 0.99 (s, 9H, C(Me)3Leu), 1.43 (s,
3
500 MHz) d 0.80e1.40 (m, 10H, CH2), 1.47 (s, 9H, C(Me)3),
1.82e2.16 (m, 2H, CH2 C2), 2.24 and 2.40 (2m, 2H,
CH2CH]CH2), 2.76 and 3.15 (2m, 2H, ArCH2), 3.81e4.01
(m, 4H, ArOCH2 and OCH2 C1), 4.49 (m, 1H, CH(a)), 5.13
(br s, 1H, NH(a)), 5.32 (m, 1H, OCH2CH]CH), 5.47 (m, 1H,
OCH2CH]CH), 6.79 (m, 2H, CH arom), 7.04 (m, 2H, CH
arom); 13C NMR (CDCl3, 75 MHz) d 26.0, 28.6, 27.8, 29.0,
29.8, 30.5, 32.1, 32.4, 39.1, 55.4, 65.2, 68.1, 77.5, 114.2,
114.6, 127.9, 129.3, 130.4, 132.5, 133.1, 156.2, 158.6, 172.4.
9H, C(Me)3Boc), 2.29 (m, 2H, COCH2CH2), 2.36 (t, 2H, J
7.0 Hz, COCH2CH2), 3.30 (dd, 1H, 3J 5.0 Hz, 2J 14.2 Hz,
3
2
SCHH), 3.46 (dd, 1H, J 4.6 Hz, J 14.2 Hz, SCHH), 3.70
3
(s, 3H, OMe), 4.02 (d, 1H, J 8.3 Hz, CH(a)Leu), 4.86 (m,
3
1H, CH(a)Cys), 4.98 (d, 1H, J 10.1 Hz, NH(a)Leu), 5.04 (m,
2H, CH]CH2), 5.81 (m, 1H, CH]CH2), 6.38 (d, 1H, 3J
7.7 Hz, NH(a)Cys); 13C NMR (CDCl3, 75 MHz) d 26.7, 28.2,
29.2, 30.1, 33.8, 35.2, 51.5, 52.5, 68.6, 80.4, 115.3, 136.8,
155.5, 170.6, 172.3, 199.5.
4.7. Application: preparation of PDF inhibitor analogue 56
(Scheme 1)
4.7.3. Synthesis of (2S,2R)-2-[3,3-dimethyl-2-(pent-4-
enoylamino)-butyrylamino]-3-(pent-4-enoylsulfanyl)-
propionic acid methyl ester 62
4.7.1. Synthesis of (2S)-2-tert-butoxycarbonylamino-3,3-
dimethyl-butyric acid 58
Boc2O (182 mg, 0.84 mmol, 1.1 equiv) was added to a solu-
tion of L-tert-leucine 57 (100 mg, 0.76 mmol, 1 equiv) and
Dipeptide 60 (620 mg, 1.44 mmol, 1 equiv) was treated
with TFA (analogous to Section 4.7.2). TFA salt 61
(1.44 mmol) and 4-pentenoic acid (164 mg, 1.6 mmol,
1.14 equiv) were treated with EDCI (358 mg, 1.87 mmol,

3996
A.J. Vernall et al. / Tetrahedron 64 (2008) 3980e3997
4. Cobb, B. A.; Kasper, D. L. Eur. J. Immunol. 2005, 35, 352e356.
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1.3 equiv) and HOBt (326 mg, 2.16 mmol, 1.5 equiv) analo-
gous to procedure given in Section 4.7.2. The crude product
was purified by flash chromatography on silica (ethyl ace-
tate/CH2Cl2, 1:4) to give 62 (430 mg, 72%) as a colourless oil.
HRMS (MþH) found 413.2115 (calcd for C20H32N2O5S
413.2110); Rf (20% ethyl acetate/CH2Cl2) 0.20; 1H NMR
(CDCl3, 500 MHz) d 0.99 (s, 9H, C(Me)3), 2.35 (m, 8H,
9. Hultsch, C.; Pawelke, B.; Bergmann, R.; Wuest, F. Bioorg. Med. Chem.
2006, 14, 5913e5920.
10. Stewart, J. M. Peptides 2004, 25, 527e532.
3
2
COCH2CH2), 3.28 (dd, 1H, J 5.4 Hz, J 14.2 Hz, SCHH),
3.46 (dd, 1H, 3J 4.6 Hz, 2J 14.2 Hz, SCHH), 3.72 (s, 3H,
OMe), 4.42 (d, 1H, 3J 8.6 Hz, CH(a)Leu), 4.83 (m, 1H,
CH(a)Cys), 4.98e5.11 (m, 4H, CH]CH2), 5.82 (m, 2H, CH]
CH2), 6.05 (d, 1H, 3J 8.6 Hz, NH(a)Leu), 6.35 (d, 1H, 3J
7.7 Hz, NH(a)Cys); 13C NMR (CDCl3, 75 MHz) d 26.4, 28.4,
28.9, 29.8, 32.9, 33.5, 34.7, 51.5, 52.2, 67.0, 115.0, 115.1,
136.4, 136.6, 170.2, 172.3, 173.1, 198.6.
11. Li, T.; Fujita, Y.; Shiotani, K.; Miyazaki, A.; Tsuda, Y.; Ambo, A.; Sasaki,
Y.; Jinsmaa, Y.; Marczak, E.; Bryant, S. D.; Salvadori, S.; Lazarus, L. H.;
Okada, Y. J. Med. Chem. 2005, 48, 8035e8044.
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15. Jinsmaa, Y.; Miyazaki, A.; Fujita, Y.; Li, T.; Fujisawa, Y.; Shiotani, K.;
Tsuda, Y.; Yokoi, T.; Ambo, A.; Sasaki, Y.; Bryant, S. D.; Lazarus,
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4.7.4. Synthesis of (3S,6R)-6-tert-butyl-5,8,15-trioxo-1-thia-
4,7-diaza-cyclopentadec-11-ene-3-carboxylic acid methyl
ester 56
To a solution of diene 57 (230 mg, 0.60 mmol, 1 equiv) in
CH2Cl2 (10 mL) was added Grubbs’ second generation cata-
lyst 31 (102 mg, 0.12 mmol, 0.2 equiv). The solution was
stirred at reflux under a flow of inert gas for 6 h, and DMSO
(50 equiv relative to catalyst 31) added and stirred overnight
at rt. The solvent was removed by evaporation under reduced
pressure to give the crude product, which was purified by flash
chromatography on silica (100% ethyl acetate) to give 56
(140 mg, 65%) as white solid.
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Kay, S.; Walters, D. E.; Koh, Y.; Mitsuya, H. J. Med. Chem. 2005, 48,
3576e3585.
20. Goudreau, N.; Brochu, C.; Cameron, D. R.; Duceppe, J.-S.; Faucher,
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HRMS (MþH) found 385.1796 (calcd for C18H29N2O5S
385.1797); Rf (ethyl acetate) 0.51; 1H NMR (CDCl3,
500 MHz) d 0.99 (s, 9H, C(Me)3), 2.20 (m, 4H, ]CHCH2
(3H), COCH2 (1H)), 2.44 (m, 3H, ]CHCH2 (1H), COCH2
(2H)), 2.57 (m, 1H, COCH2), 3.11 (dd, 1H, 3J 3.9 Hz, 2J
14.5 Hz, SCHH), 3.46 (dd, 1H, 3J 9.5 Hz, 2J 14.5 Hz,
SCHH), 3.73 (s, 3H, OMe), 4.59 (m, 2H, CH(a)), 5.52 (m,
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3
3
2H, HC]CH), 5.86 (d, 1H, J 9.7 Hz, NH), 6.41 (d, 1H, J
7.4 Hz, NH); 13C NMR (CDCl3, 75 MHz) d 26.5, 27.2, 27.6,
29.6, 34.1, 35.4, 35.7, 52.7, 52.9, 65.5, 129.7, 130.2, 170.8,
172.3, 172.5, 200.2.
27. Loughlin, W. A.; Tyndall, J. D. A.; Glenn, M. P.; Fairlie, D. P. Chem. Rev.
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Acknowledgements
The authors would like to thank the Australian Research
Council (grant 20103228) for the financial support. A.J.V.
thanks the Foundation for Research, Science and Technology
for a Top Achiever Doctoral Scholarship. We also thank
Prof. Ward Robinson (University of Canterbury, New Zealand)
and Dr. Chris Sumby (University of Adelaide, Australia) for
the preparation of all crystallographic data.
31. Pernerstorfer, J.; Schuster, M.; Blechert, S. Chem. Commun. 1997,
1949e1950.
32. Gibson, S. E.; Gibson, V. C.; Keen, S. P. Chem. Commun. 1997,
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34. Hultsch, C.; Berndt, M.; Bergmann, R.; Wuest, F. Appl. Radiat. Isot. 2007,
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