Total synthesis of trunkamide A, a novel thiazoline-based prenylated cyclopeptide metabolite from Lissoclinum sp.

Article abstract of DOI:10.1016/S0040-4020(03)00294-1

Full details of a total synthesis of the doubly prenylated cyclic peptide trunkamide A of marine origin, and also its C45 epimer, are described.

Full text of DOI:10.1016/S0040-4020(03)00294-1

Tetrahedron 59 (2003) 2713–2727
Total synthesis of trunkamide A, a novel thiazoline-based
prenylated cyclopeptide metabolite from Lissoclinum sp.
*
Benedict McKeever and Gerald Pattenden
School of Chemistry, University of Nottingham, Nottingham NG7 2RD, UK
Received 7 October 2002; revised 28 January 2003; accepted 20 February 2003
Abstract—Full details of a total synthesis of the doubly prenylated cyclic peptide trunkamide A of marine origin, and also its C45 epimer,
are described. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
modified as reverse prenyl ethers. In the previous paper we
described the successful synthesis of mollamide 3 which
demonstrated a strategy for the construction of these
compounds. In contemporaneous studies Uto and Wipf
described a total synthesis of the stereostructure 1b assigned
to trunkamide A by Bowden et al.3 However, the spectro-
scopic data recorded for the synthetic and natural materials
did not correlate. In a subsequent report these authors
showed that 1a was the correct stereostructure for natural
trunkamide A.6 More recently, a solid phase approach to
The marine environment has provided a rich source of
structurally novel and biologically important secondary
metabolites in recent years, many of which have attracted
chemists to their total synthesis and an evaluation of their
potential as chemotherapeutic agents.1 Amongst some of the
most intriguing marine natural products are hetero-
cyclic-based cyclopeptides which have been isolated from
a variety of organisms. Ascidians (sea squirts) of the genus
Lissoclinum have proven to be a particularly rich source of
these novel compounds.2 Trunkamide A 1 was isolated from
the colonial ascidian Lissoclinum sp. located in the Great
Barrier Reef in Australia.3 At the same time, the isolation of
the related patellins, e.g. patellin 6 2, were also reported.
Most cyclopeptides isolated from ascidians show only
moderate cytotoxicity. Trunkamide A, however, is reported
to have promising antitumour activity.4 The structures of
trunkamide A 1, patellin 6 2, along with other marine
cyclopeptides such as mollamide 3,5 are characterised by
the presence of serine/threonine residues which have been
Keywords: trunkamide A; thiazoline cyclopeptide; Lissoclinum sp..
*
Corresponding author. Tel.: þ44-115-9513530; fax: þ44-115-9513535;
e-mail: gp@nottingham.ac.uk
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00294-1

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B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
Scheme 1.
trunkamide A has been reported.7 In this paper we report the
full details of our own studies leading to a total synthesis of
trunkamide A 1a along with its C45 epimer 1b.8
peptide synthesis, i.e. from the amino terminus using acid-
labile Boc protecting groups.
Thus, our synthesis began with the elaboration of the
pentapeptide 6 via the thiodipeptide 11 (Scheme 2). Boc-L-
phenylalanine was first coupled with L-serine methyl ester 9
using DCC and HOBt as coupling reagents, leading to the
dipeptide 10 which was next protected as its TBS ether and
thionated using Lawesson’s reagent,9 and finally depro-
tected using TBAF to give 11 in good yield (57%,
four steps). Removal of the Boc protecting group from 11
and reaction of the resulting free amine with Boc-L-proline
in the presence of DCC and HOBt next gave the tripeptide
12. Removal of the Boc group in 12, followed by coupling
with Boc-L-alanine then provided the tetrapeptide 13.
Finally, removal of the Boc group in 13 and coupling of
the resulting amine with Boc-L-isoleucine led to the
pentapeptide 6.
2. Results and discussion
Following our successful synthesis of mollamide 3, we
designed a synthesis of the structure 1b reported for
naturally derived trunkamide A using a similar strategy.
Hence, the thiazoline ring in the natural product was to be
produced in the final step of the synthesis from the
thioamide-based cyclopeptide 4 (Scheme 1). We chose to
elaborate 4 from the heptapeptide 5 which we planned to
synthesise in a linear manner via the pentapeptide 6. The
introduction of the acid-labile reverse prenyl ether amino
acids 7 and 8 at a late stage in the synthesis should permit us
to construct the pentapeptide 6 by our preferred method of
Scheme 2. Reagents: (i) DCC, HOBt, DIPEA, DCM, 08C!rt; (ii) TBSCl, imidazole, DMF, rt, 90%; (iii) Lawesson’s reagent, benzene, 808C!rt, 92%;
(iv) TBAF, THF, rt, 93%; (v) AcCl, MeOH, rt.

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2715
Scheme 3. Reagents: (i) Ph3CCl, Et3N, DCM, rt, 96%; (ii) MsCl, Et3N, THF, 08C!658C, 97%; (iii) (a) TFA, MeOH, DCM, 08C; (b) TcBoc-OSu, Et3N, rt,
89%; (iv) BF3·OEt2, 2-methyl-3-buten-2-ol, rt, 69%; (v) 1.5 M LiOH, THF/MeOH, rt, 93%.
The synthesis of the amino acid 7 has been described
previously,10 and the amino acid 8 was synthesised using an
identical strategy (Scheme 3). Hence, following the
formation of the trityl-protected aziridine 15 from L-threo-
nine methyl ester 14, protecting group interconversion led
to the TcBoc (2,2,2-trichloro-tert-butyloxycarbonyl)-
protected aziridine 16. Ring opening of 16 by reaction
with 2-methyl-3-buten-2-ol in the presence of boron
trifluoride diethyl etherate then gave the amino acid 17
which was saponified leading to 8.
in 5, we were unable to induce macrolactamisation of the
zwitterion 19 to the desired cyclopeptide 4.
Subsequent investigations led us to suspect that the
thioamide bond in 19 and its proximity to the site of
macrolactamisation was the likely cause of the problem. In
order to test this suggestion we decided to form the
thiazoline ring in trunkamide A prior to macrolactamisation,
hence removing any potential interference of the thioamide
bond. This was a bold move in view of the ease with which
chiral thiazolines undergo epimerisation under both acidic
and basic conditions, with the likely consequence that we
would lose the stereochemical integrity at C45 (and possibly
C40) during the subsequent synthetic manipulations leading
to the cyclopeptide target.12 Hence, treatment of the
heptapeptide thioamide 5 with Burgess’ reagent13 resulted
in dehydration and cyclisation to the corresponding
substituted thiazoline 20 (Scheme 5). After removal of the
ester and amine protecting groups in 20, macrolactamisation
using DPPA14 successfully produced a cyclopeptide
The synthesis of the heptapeptide 5 from 6 was achieved
following removal of the Boc protecting group in 6,
coupling of the resulting amine with 7 in the presence of
EDC and HOBt, removal of the TcBoc protecting group
from the resulting hexapeptide 18 and a coupling reaction
with 8 under similar conditions (Scheme 4). Having
successfully constructed the macrocyclisation precursor 5,
we were disappointed, however, to find that, following the
removal of the TcBoc11 and methyl ester protecting groups
Scheme 4. Reagents: (i) AcCl, MeOH, rt; (ii) EDC, HOBt, DIPEA, DCM, 08C!rt, 72%; (iii) Cd/Pb, 1 M NH4OAc/THF (1:1), rt; (iv) EDC, HOBt, DCM,
08C!rt, 78% (two steps); (v) 1 M NaOH, MeOH, rt; (vi) DPPA, DIPEA, DMF, 258C!rt.

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B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
Scheme 5. Reagents: (i) Burgess’ reagent, THF, 658C, 92%; (ii) Cd/Pb, 1 M NH4OAc/THF (1:1), rt, 93%; (iii) 1 M NaOH, MeOH, rt; (iv) DPPA, DIPEA,
DMF, 258C!rt.
structure. However, as anticipated, analysis of the material
obtained clearly showed the presence of a mixture of
diastereomeric products. Following extensive semi-prepara-
tive HPLC, we were able to show that one of the product
diastereoisomers had NMR spectroscopic data which
corresponded to those of the target cyclopeptide 1b reported
for naturally derived trunkamide A.6 Furthermore, NMR
data for another diastereoisomer were identical with those
reported for natural trunkamide A.3 Unfortunately, at this
stage, we were unable to confirm the exact stereochemistry
of this particular compound which could have been any one
of the other three possible diastereoisomers.
Encouraged by the aforementioned successful macrocycli-
sation (Scheme 5), we speculated that if we replaced the
problematic thioamide bond in 19 with an amide bond then
our original macrocyclisation strategy, i.e. 5!4 (Scheme 1),
may prove more successful and allow us access to
diastereomerically pure material. Hence, we next decided
to synthesise the heptapeptide 25 and to examine its
macrocyclisation (Scheme 6). Thus, starting from the
dipeptide 10, the pentapeptide 23 was prepared by
sequential addition of L-proline, L-alanine and L-isoleucine.
Subsequent addition of the two reverse prenylated amino
acids 7 and 8 to 23 then gave the heptapeptide 25.
Scheme 6. Reagents: (i) AcCl, MeOH, rt; (ii) DCC, HOBt, DIPEA, DCM, 08C!rt; (iii) EDC, HOBt, DIPEA, DCM, 08C!rt, 60%; (iv) Cd/Pb, 1 M
NH4OAc/THF (1:1), rt, 94%; (v) EDC, HOBt, DCM, 08C!rt, 72%.

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2717
Scheme 7. Reagents: (i) Cd/Pb, 1 M NH4OAc/THF (1:1), rt, 98%; (ii) TBAH, THF, 08C; (iii) DPPA, DIPEA, DMF, 258C!rt, 35% (two steps); (iv) DAST,
DCM, 2158C; (v) H2S, Et3N, MeOH, rt.
After our disappointment at not being able to induce
macrocyclisation from the thioamide heptapeptide 5 we
were delighted to find that, following removal of the
TcBoc11 and methyl ester15 protecting groups in 25,
macrocyclisation proceeded smoothly and provided the
cyclopeptide 26 in a modest 35% yield (Scheme 7). The
macrocycle 26 was then elaborated to the trunkamide
structure 1b using a strategy described by Wipf et al.6,16 i.e.
cyclodehydration of 26 to the corresponding oxazoline,
subsequent thiolysis with H2S to the thioamide cyclopeptide
4, and reaction with DAST.17
formation of any other diastereoisomer (Scheme 8). After
careful purification by flash chromatography followed by
semi-preparative HPLC, comparison of the spectroscopic
data obtained for our synthetic material with those reported
for natural trunkamide A from Lissoclinum showed them to
be identical in all respects.
3. Conclusion
In summary, we have achieved a synthesis of trunkamide A
which has not only further demonstrated our approach to
the construction of this novel class of marine natural
products but also its potential for accessing other members
of the family. Our investigations have also shown that, in
agreement with the work of Wipf and Uto,6 the correct
structure for trunkamide A is 1a, and not 1b as originally
reported.
The cyclic peptide 1b was shown to be identical in all
respects with the trunkamide structure reported by Uto and
Wipf6 but its spectroscopic data differed significantly with
those reported by Bowden et al. for natural trunkamide A.3
Following the report of Uto and Wipf which revealed the
correct structure of trunkamide A, i.e. 1a rather than 1b,6a
we then decided to attempt to synthesise this epimeric
structure 1a. Instead of carrying out a new total synthesis of
natural trunkamide A from D- rather than L-phenylalanine,
however, we planned to effect conversion of epi-trunkamide
A 1b into trunkamide A 1a by selective epimerisation of the
‘incorrect’ C45 stereocentre. This was a somewhat risky
strategy in view of the potential for concurrent epimerisa-
tion at C40. However, we were encouraged to attempt this
conversion following previous observations that, under
suitably mild basic conditions, epimerisation is only seen at
the stereocentre which is positioned exocyclic to the
thiazoline ring.12b Indeed, we found that when 1b was
treated with methanolic pyridine at 50–558C it was slowly
converted into trunkamide A 1a with no detectable
4. Experimental
4.1. General
For general experimental details see the previous paper.
4.1.1. Boc-Phe-Ser-OMe (10).18 Diisopropylethylamine
(19.6 ml, 112 mmol) was added dropwise over 10 min to a
stirred suspension of L-serine methyl ester hydrochloride
9 (5.00 g, 32.1 mmol) in dichloromethane (200 ml) at
room temperature under an atmosphere of nitrogen.
On dissolution, the solution was cooled to 08C and then
Scheme 8.

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B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
Boc-L-phenylalanine (8.53 g, 32.1 mmol) and 1-hydroxy-
benzotriazole (4.78 g, 35.4 mmol) were added successively,
each in one portion. The suspension was stirred at 08C for a
further 15 min and then dicyclohexylcarbodiimide (7.29 g,
35.4 mmol) was added in one portion. The mixture was
allowed to warm to room temperature over the course of
51 h, then filtered, and the filtrate was evaporated in vacuo.
The residue was taken up in ethyl acetate (100 ml), filtered,
and the filtrate was then washed with 10% aqueous citric
acid solution (3£20 ml) followed by saturated aqueous
sodium bicarbonate solution (5£20 ml), with backwashing.
The combined organic extracts were dried and evaporated in
vacuo to leave the crude product which was purified by
chromatography on silica using diethyl ether as eluent to
give the dipeptide (8.66 g, 74%) as a yellow solid; mp
93–958C (ethyl acetate/hexane) (lit.18b mp 88–898C);
[a]D22¼þ17 (c 1.07, CHCl3) (lit.18a [a]D¼þ12.1 (c 1.02,
CH2Cl2)); found %: C, 59.3; H, 7.3; N, 7.5; calcd for
C18H26N2O6 %: C, 59.0, H, 7.15; N, 7.65; nmax (CHCl3)/
cm21 3427, 2955, 1744, 1682, 1490, 1455, 1393, 1369,
1156, 1056, 908; dH (360 MHz, CDCl3) 7.34–7.21 (5H, m,
Ph-H), 6.80 (1H, d, J¼7.2 Hz, NH), 5.02 (1H, br s, NHBoc),
4.60 (1H, app dt, J¼7.1, 3.5 Hz, CHCO2Me), 4.33 (1H, app
dt, J¼7.2, 6.8 Hz, CHCH2Ph), 3.97–3.88 (2H, m, CH2OH),
3.76 (3H, s, OCH3), 3.13 (1H, dd, J¼13.8, 6.3 Hz, CH2Ph),
3.07 (1H, dd, J¼13.7, 7.2 Hz, CH2Ph), 2.81 (1H, br s, OH),
1.41 (9H, s, C(CH3)3); dC (90 MHz, CDCl3) 171.8 (s), 170.7
(s), 155.8 (s), 136.6 (s), 129.4 (d), 128.7 (d), 127.0 (d), 80.5
(s), 62.8 (t), 56.0 (d), 55.0 (d), 52.7 (q), 38.2 (t), 28.3 (q);
m/z (ES) 389.1682 ([MþNa]þ, C18H26N2O6Na requires
389.1689).
(q), 25.7 (q), 18.1 (s), 25.6 (q), 25.7 (q); m/z (ES) 503.2583
([MþNa]þ, C24H40N2O6SiNa requires 503.2553).
Lawesson’s reagent9d (2.69 g, 6.65 mmol) was added in one
portion to a stirred solution of the aforementioned amide
(4.56 g, 9.50 mmol) in benzene (50 ml) at room temperature
under an atmosphere of nitrogen. The suspension was
heated under reflux for 2 h and then cooled to room
temperature and stirred for 26 h. The solvent was removed
in vacuo to leave a residue which was taken up in
dichloromethane and filtered. The filtrate was evaporated
in vacuo to leave the crude product which was purified by
chromatography on silica using 25% diethyl ether in light
petroleum (40–608C) as eluent to give the corresponding
thioamide (4.33 g, 92%) as a yellow oil; [a]2D5¼þ73 (c 1.33,
CHCl3); nmax (CHCl3)/cm21 3358, 2954, 2931, 2884, 2858,
1746, 1708, 1603, 1488, 1456, 1392, 1369, 1329, 1155,
1110, 1048, 1005, 981, 866, 839; dH (360 MHz, CDCl3)
8.19 (1H, d, J¼6.8 Hz, NHCvS), 7.32–7.22 (5H, m, Ph-
H), 5.24 (1H, br s, NHBoc), 5.12 (1H, app dt, J¼7.3, 2.8 Hz,
CHCO2Me), 4.65 (1H, app dt, J¼7.3, 7.2 Hz, CHCH2Ph),
4.06 (1H, dd, J¼10.3, 2.6 Hz, CH2OTBS), 3.98 (1H, dd,
J¼10.3, 3.1 Hz, CH2OTBS), 3.72 (3H, s, OCH3), 3.24 (1H,
dd, J¼13.9, 6.6 Hz, CH2Ph), 3.14 (1H, dd, J¼13.9, 7.4 Hz,
CH2Ph), 1.41 (9H, s, C(CH3)3), 0.84 (9H, s, SiC(CH3)3),
0.01 (6H, s, Si(CH3)2); dC (90 MHz, CDCl3) 203.5 (s),
169.4 (s), 154.9 (s), 136.5 (s), 129.3 (d), 128.7 (d), 127.1 (d),
80.4 (s), 62.3 (t), 59.6 (d), 52.6 (q), 41.9 (t), 28.3 (q), 25.7
(q), 18.2 (s), 25.5 (q), 25.6 (q); m/z (ES) 519.2355
([MþNa]þ, C24H40N2O5SSiNa requires 519.2325).
Tetrabutylammonium fluoride (3.43 g, 13.1 mmol) was
added in one portion to a stirred solution of the thioamide
(4.33 g, 8.73 mmol) in tetrahydrofuran (40 ml) at 08C under
an atmosphere of nitrogen. The suspension was warmed to
room temperature, stirred for 50 min and then evaporated in
vacuo. The residue was taken up in dichloromethane
(100 ml) and washed with water (3£30 ml), with back-
washing. The combined organic extracts were dried and
evaporated in vacuo to leave the crude product which was
purified by chromatography on silica using 50% diethyl
ether in light petroleum (40–608C) as eluent to give the
b-hydroxythioamide (3.09 g, 93%) as a cream foam;
[a]2D2¼þ64 (c 1.10, CHCl3); found %: C, 56.5; H, 7.0; N,
7.1; C18H26N2O5S requires %: C, 56.5; H, 6.85; N, 7.3; nmax
(CHCl3)/cm21 3428, 3358, 2980, 2956, 1743, 1698, 1603,
1489, 1456, 1394, 1369, 1326, 1155, 1102, 1054, 974, 906,
863; dH (360 MHz, CDCl3, 323 K) 8.32 (1H, d, J¼5.8 Hz,
NHCvS), 7.31–7.20 (5H, m, Ph-H), 5.21 (1H, d, J¼
6.8 Hz, NHBoc), 5.14 (1H, app dt, J¼7.1, 3.5 Hz, CHCO2
Me), 4.60 (1H, app dt, J¼7.3, 7.1 Hz, CHCH2Ph), 4.12 (1H,
ddd, J¼11.4, 5.1, 3.6 Hz, CH2OH), 3.94 (1H, ddd, J¼11.5,
7.1, 3.1 Hz, CH2OH), 3.74 (3H, s, OCH3), 3.21 (1H, dd,
J¼13.8, 6.6 Hz, CH2Ph), 3.16 (1H, dd, J¼13.8, 7.2 Hz,
CH2Ph), 2.43 (1H, br s, OH), 1.40 (9H, s, C(CH3)3); dC
(90 MHz, CDCl3) 204.5 (s), 169.8 (s), 155.7 (s), 136.4 (s),
129.3 (d), 128.5 (d), 126.9 (d), 80.7 (s), 62.2 (d), 61.4 (t),
59.8 (d), 52.8 (q), 41.6 (t), 28.2 (q); m/z (ES) 405.1470
([MþNa]þ, C18H26N2O5SNa requires 405.1460).
4.1.2. Boc-PheC{(CvS)NH}-Ser-OMe (11). Imidazole
(1.49 g, 21.9 mmol) was added in one portion to a stirred
solution of the dipeptide 10 (4.00 g, 10.9 mmol) in
dimethylformamide (50 ml) at 08C under an atmosphere
of nitrogen. The solution was stirred at 08C for 5 min and
then tert-butyldimethylsilyl chloride (2.47 g, 16.4 mmol)
was added in one portion. The mixture was stirred at room
temperature for 3 h, then diluted with ethyl acetate (50 ml)
and poured into water (200 ml). The layers were separated
and the aqueous fraction was then extracted with ethyl
acetate (5£40 ml). The combined organic extracts were
washed with water (5£50 ml), dried and evaporated in
vacuo to leave the crude product which was purified by
chromatography on silica using 40% diethyl ether in light
petroleum (40–608C) as eluent to give Boc-Phe-Ser(TBS)-
OMe (4.73 g, 90%) as a white solid; mp 101–1028C (ethyl
acetate/hexane); [a]D23¼þ22 (c 1.07, CHCl3); found %: C,
60.2; H, 8.45; N, 5.6; C24H40N2O6Si requires %: C, 60.0; H
8.4; N 5.8; nmax (CHCl3)/cm21 3430, 2954, 2931, 2884,
2858, 1747, 1711, 1678, 1489, 1456, 1368, 1297, 1157,
1110, 1049, 982, 864, 840; dH (360 MHz, CDCl3, 323 K)
7.32–7.21 (5H, m, Ph-H), 6.54 (1H, d, J¼8.2 Hz, NH), 4.91
(1H, br s, NHBoc), 4.61 (1H, app dt, J¼8.0, 3.3 Hz,
CHCO2Me), 4.41 (1H, app dt, J¼7.6, 6.9 Hz, CHCH2Ph),
4.03 (1H, dd, J¼10.1, 3.0 Hz, CH2OTBS), 3.78 (1H, dd,
J¼10.1, 3.5 Hz, CH2OTBS), 3.73 (3H, s, OCH3), 3.14 (1H,
dd, J¼13.9, 6.6 Hz, CH2Ph), 3.07 (1H, dd, J¼14.0, 6.9 Hz,
CH2Ph), 1.43 (9H, s, C(CH3)3), 0.86 (9H, s, SiC(CH3)3),
0.02 (6H, s, Si(CH3)2); dC (90 MHz, CDCl3) 171.0 (s),
170.3 (s), 155.1 (s), 136.5 (s), 129.3 (d), 128.6 (d), 126.9 (d),
80.0 (s), 63.4 (t), 55.6 (d), 54.2 (d), 52.3 (q), 38.5 (t), 28.2
4.1.3. Boc-Pro-PheC{(CvS)NH}-Ser-OMe (12). Acetyl
chloride (5 ml) was added dropwise over 5 min to a stirred
solution of the b-hydroxythioamide 11 (2.64 g, 6.91 mmol)

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2719
in methanol (50 ml) at 08C under an atmosphere of nitrogen.
The solution was stirred at room temperature for 3 h and
then evaporated in vacuo to leave the corresponding
hydrochloride salt (2.17 g, 99%) as a cream solid, which
was used without further purification.
then evaporated in vacuo to leave a residue which was taken
up in ethyl acetate (50 ml) and filtered. The filtrate was
washed with 10% aqueous citric acid solution (3£10 ml)
followed by saturated aqueous sodium bicarbonate solution
(5£10 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
crude product which was purified by chromatography on
silica using 50% ethyl acetate in diethyl ether as eluent to
give the tetrapeptide (1.85 g, 60%) as a cream foam; [a]2D7¼
263 (c 0.77, CHCl3); nmax (CHCl3)/cm21 3435, 3350,
2980, 1744, 1699, 1652, 1495, 1455, 1393, 1369, 1344,
1159, 1064, 865; dH (360 MHz, d6-DMSO, 343 K) 9.96
(1H, br s, NHCvS), 7.65 (1H, br s, NHCHCH2Ph), 7.27–
7.16 (5H, m, Ph-H), 6.50 (1H, br s, NHBoc), 5.05–4.99 (2H,
m, CHCO2Me and CHCH2Ph), 4.96 (1H, app t, J¼5.8 Hz,
OH), 4.35–4.33 (1H, m, CH(CH2)3N), 4.24 (1H, m,
CHCH3), 3.86 (1H, ddd, J¼11.3, 5.7, 5.7 Hz, CH2OH),
3.79 (1H, ddd, J¼11.4, 5.0, 5.0 Hz, CH2OH), 3.65 (3H, s,
OCH3), 3.57 (1H, m, CH2N), 3.46 (1H, m, CH2N), 3.18 (1H,
dd, J¼14.0, 4.8 Hz, CH2Ph), 2.95–2.88 (1H, m, CH2Ph),
1.99–1.65 (4H, m, CH2), 1.38 (9H, s, C(CH3)3), 1.18 (3H, d,
J¼7.1 Hz, CHCH3); dC (100 MHz, d6-DMSO, 333 K) 204.6
(s), 171.4 (s), 170.3 (s), 168.8 (s), 154.6 (s), 137.1 (s), 128.9
(d), 127.6 (d), 125.9 (d), 77.8 (s), 60.4 (d), 60.2 (t), 59.3 (d),
58.7 (d), 51.6 (q), 47.5 (d), 46.2 (t), 40.4 (t), 27.9 (t), 27.9
(q), 23.9 (t), 16.9 (q); m/z (ES) 573.2357 ([MþNa]þ,
C26H38N4O7SNa requires 573.2359).
Diisopropylethylamine (4.2 ml, 24 mmol) was added drop-
wise over 5 min to a stirred solution of the hydrochloride
salt (2.17 g, 6.81 mmol) in dichloromethane (30 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 10 min and then Boc-L-proline (1.47 g, 6.81 mmol)
and 1-hydroxybenzotriazole (1.01 g, 7.49 mmol) were
added successively in one portion. The suspension was
stirred at 08C for a further 15 min and then dicyclohexyl-
carbodiimide (1.55 g, 7.49 mmol) was added in one portion.
The mixture was allowed to warm to room temperature over
the course of 63 h and then evaporated in vacuo to leave a
residue which was taken up in ethyl acetate (50 ml) and
filtered. The filtrate was washed with 10% aqueous citric
acid solution (3£10 ml) followed by saturated aqueous
sodium bicarbonate solution (5£10 ml), with backwashing.
The combined organic extracts were dried and evaporated in
vacuo to leave the crude product which was purified by
chromatography on silica using 25% ethyl acetate in diethyl
ether as eluent to give the tripeptide (2.95 g, 90%) as a
cream foam; [a]2D4¼294 (c 0.99, CHCl3); found %: C, 57.3;
H, 7.0; N, 8.5; C23H33N3O6S requires %: C, 57.6; H, 6.9; N
8.8; nmax (CHCl3)/cm21 3406, 2979, 2955, 2886, 1745,
1682, 1603, 1556, 1496, 1455, 1393, 1369, 1327, 1158,
1127, 1062, 979, 892; dH (360 MHz, CDCl3, 323 K) 8.70
(1H, br s, NHCvS), 7.29–7.18 (5H, m, Ph-H), 6.76 (1H, d,
J¼8.2 Hz, NH), 5.13 (1H, app dt, J¼7.2, 3.5 Hz, CHCO2
Me), 5.07 (1H, m, CHCH2Ph), 4.20 (1H, dd, J¼8.6, 3.5 Hz,
CHNBoc), 4.05 (1H, ddd, J¼11.7, 5.7, 3.4 Hz, CH2OH),
3.95 (1H, ddd, J¼11.7, 7.2, 3.4 Hz, CH2OH), 3.75 (3H, s,
OCH3), 3.39–3.23 (4H, m, CH2NBoc and CH2Ph), 3.12
(1H, br s, OH), 2.07–1.98 (1H, m, CH2), 1.96–1.88 (1H, m,
CH2), 1.77–1.74 (1H, m, CH2), 1.60–1.55 (1H, m, CH2),
1.43 (9H, s, C(CH3)3); dC (90 MHz, CDCl3) 204.2 (s), 172.7
(s), 169.4 (s), 155.5 (s), 136.8 (s), 129.4 (d), 128.4 (d), 126.8
(d), 81.2 (s), 61.4 (t), 60.9 (d), 60.1 (d), 58.5 (d), 52.6 (q),
47.3 (t), 41.5 (t), 29.7 (t), 28.4 (q), 24.1 (t); m/z (ES)
502.1984 ([MþNa]þ, C23H33N3O6SNa requires 502.1988).
4.1.5. Boc-Ile-Ala-Pro-PheC{(CvS)NH}-Ser-OMe (6).
Acetyl chloride (1.5 ml) was added dropwise over 2 min to a
stirred solution of the tetrapeptide 13 (1.68 g, 3.06 mmol) in
methanol (15 ml) at 08C under an atmosphere of nitrogen.
The solution was stirred at room temperature for 11 h and
then evaporated in vacuo to leave the corresponding
hydrochloride salt (1.46 g, 98%) as a cream solid, which
was used without further purification.
Diisopropylethylamine (1.8 ml, 11 mmol) was added drop-
wise over 2 min to a stirred solution of the hydrochloride
salt (1.46 g, 3.00 mmol) in dichloromethane (15 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 15 min and then Boc-L-isoleucine (0.69 g,
3.0 mmol) and 1-hydroxybenzotriazole (0.45 g, 3.3 mmol)
were added successively in one portion. The suspension was
stirred at 08C for a further 15 min and then dicyclo-
hexylcarbodiimide (0.68 g, 3.3 mmol) was added in one
portion. The mixture was allowed to warm to room
temperature over 51 h and then evaporated in vacuo to
leave a residue which was taken up in ethyl acetate (50 ml)
and filtered. The filtrate was washed with 10% aqueous
citric acid solution (3£10 ml) followed by saturated
aqueous sodium bicarbonate solution (5£10 ml), with
backwashing. The combined organic extracts were dried
and evaporated in vacuo to leave the crude product which
was purified by chromatography on silica using 20%
acetone in diethyl ether as eluent to give the pentapeptide
(1.59 g, 80%) as a cream foam, mp 111–1138C; [a]2D4¼254
(c 0.93, CHCl3); found %: C, 57.6; H, 7.5; N, 10.3;
C32H49N5O8S requires %: C, 57.9; H, 7.4; N 10.55; nmax
(CHCl3)/cm21 3435, 2969, 2935, 2879, 1745, 1652, 1603,
1552, 1493, 1456, 1392, 1368, 1346, 1156, 1065, 976, 864;
dH (400 MHz, d6-DMSO, 343 K) 10.01 (1H, br s, NHCvS),
7.75 (1H, d, J¼7.4 Hz, NHCHCH3), 7.66 (1H, d, J¼7.8 Hz,
4.1.4. Boc-Ala-Pro-PheC{(CvS)NH}-Ser-OMe (13).
Acetyl chloride (4 ml) was added dropwise over 5 min to
a stirred solution of the tripeptide 12 (2.70 g, 5.66 mmol) in
methanol (40 ml) at 08C under an atmosphere of nitrogen.
The solution was stirred at room temperature for 7 h and
then evaporated in vacuo to leave the corresponding
hydrochloride salt (2.35 g) as a cream solid, which was
used without further purification.
Diisopropylethylamine (3.4 ml, 20 mmol) was added drop-
wise over 5 min to a stirred solution of the hydrochloride
salt (2.35 g, 5.66 mmol) in dichloromethane (25 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 10 min and then Boc-L-alanine (1.07 g, 5.66 mmol)
and 1-hydroxybenzotriazole (0.84 g, 6.2 mmol) were added
successively in one portion. The suspension was stirred at
08C for a further 15 min and then dicyclohexylcarbodiimide
(1.28 g, 6.22 mmol) was added in one portion. The mixture
was allowed to warm to room temperature over 24 h and

2720
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
NHCHCH2Ph), 7.29–7.17 (5H, m, Ph-H), 6.41 (1H, br s,
NHBoc), 5.06–4.99 (3H, m, CHCO2Me, CHCH2Ph and
OH), 4.57–4.54 (1H, m, CHCH3), 4.32–4.30 (1H, m,
CH(CH2)3N), 3.86–3.77 (3H, m, CH2OH and CHNHBoc),
3.65 (3H, s, OCH3), 3.65–3.58 (1H, m, CH2N), 3.48–3.44
(1H, m, CH2N), 3.17 (1H, dd, J¼14.0, 4.7 Hz, CH2Ph),
2.94–2.88 (1H, m, CH2Ph), 1.90–1.71 (5H, m, CH2 and
CH(CH3)CH2CH3), 1.44–1.34 (1H, masked m, CH2CH3),
1.39 (9H, s, C(CH3)3), 1.22 (3H, d, J¼6.8 Hz, CHCH3),
1.14–1.05 (1H, m, CH2CH3), 0.83 (3H, d, J¼7.2 Hz,
CH(CH3)CH2CH3), 0.82 (3H, app t, J¼7.3 Hz, CH2CH3);
dC (125 MHz, d6-DMSO, 333 K) 204.4 (s), 170.6 (s), 170.4
(s), 170.2 (s), 168.8 (s), 154.9 (s), 137.1 (s), 128.9 (d), 127.5
(d), 125.9 (d), 77.9 (s), 60.4 (d), 60.2 (t), 59.3 (d), 58.6 (d),
58.6 (d), 51.5 (q), 46.3 (t), 45.8 (d), 40.4 (t), 36.5 (d), 28.0
(t), 27.9 (q), 24.1 (t), 23.8 (t), 17.0 (q), 15.1 (q), 10.6 (q); m/z
(ES) 686.3242 ([MþNa]þ, C32H49N5O8SNa requires
686.3200).
4.1.7. (2S,3S)-Methyl 1-(2,2,2-trichloro-1,1-dimethyl-
ethoxycarbonyl)-3-methylaziridine-2-carboxylate (16).
Trifluoroacetic acid (0.58 ml, 7.5 mmol) was added drop-
wise over 1 min to a stirred solution of the aziridine
15 (1.33 g, 3.73 mmol) in dichloromethane (20 ml) and
methanol (0.15 ml, 3.7 mmol) at 08C under an atmosphere
of nitrogen. The solution was stirred at 08C for 30 min and
then triethylamine (2.6 ml, 19 mmol) was added dropwise
over 2 min. The mixture was stirred at 08C for a further
10 min, and then succinimidyl 2,2,2-trichloro-1,1-dimethyl-
ethyl carbonate20 (1.31 g, 4.11 mmol) in dichloromethane
(5 ml) was added over 5 min by cannula. The solution was
warmed to room temperature, stirred for 4.5 h and then
washed with 10% aqueous citric acid solution (3£10 ml)
and water (2£10 ml), with backwashing. The combined
organic extracts were dried and evaporated in vacuo to leave
the crude product which was purified by chromatography on
silica using chloroform as eluent to give the TcBoc aziridine
(1.06 g, 89%) as a cream solid; mp 55–588C (chloroform);
[a]1D6¼263 (c 0.72, CHCl3); nmax (CHCl3)/cm21 2955,
1733, 1458, 1388, 1370, 1299, 1154, 1128, 1083, 1050,
1027, 971, 896, 877; dH (400 MHz, CDCl3) 3.80 (3H, s,
OCH3), 3.21 (1H, d, J¼6.5 Hz, CHCO2Me), 2.85 (1H, dq,
J¼6.5, 5.7 Hz, CHCH3), 1.92 (3H, s, CH3), 1.91 (3H, s,
CH3), 1.38 (3H, d, J¼5.7 Hz, CHCH3); dC (100 MHz,
CDCl3) 167.6 (s), 158.8 (s), 105.8 (s), 89.6 (s), 52.6 (q), 40.0
(d), 39.2 (d), 21.3 (q), 21.2 (q), 12.8 (q); m/z (ES) 339.9918
([MþNa]þ, C10H14NO4Cl3Na requires 339.9886).
4.1.6. (2S,3S)-Methyl 1-trityl-3-methylaziridine-2-carb-
oxylate (15).19 Triethylamine (6.6 ml, 47 mmol) was added
dropwise over 5 min to a stirred suspension of threonine
methyl ester hydrochloride 14 (4.00 g, 23.6 mmol) in
dichloromethane (70 ml) at room temperature under an
atmosphere of nitrogen. On dissolution, the solution was
cooled to 08C and then triphenylmethyl chloride (6.57 g,
23.6 mmol) was added portionwise over 5 min. The
suspension was stirred at room temperature for 19 h and
then washed with 10% aqueous citric acid solution
(3£20 ml) and water (2£20 ml), with backwashing. The
combined organic extracts were dried and evaporated in
vacuo to leave trityl threonine methyl ester (8.50 g, 96%)19b
as a cream foam; dH (360 MHz, CDCl3) 7.49–7.46 (6H,
m, Ph-H), 7.29–7.17 (9H, m, Ph-H), 3.79 (1H, dq,
J¼7.4, 6.2 Hz, CHOH), 3.38 (1H, d, J¼7.5 Hz,
CHCO2Me), 3.16 (3H, s, OCH3), 1.20 (3H, d, J¼6.2 Hz,
CH3); dC (90 MHz, CDCl3) 173.7 (s), 145.5 (s), 129.0 (d),
128.0 (d), 126.7 (d), 70.8 (s), 69.8 (d), 62.6 (d), 51.8 (q),
19.0 (q); m/z (ES) 398.1721 ([MþNa]þ, C24H25NO3Na
requires 398.1732), which was used without further
purification.
4.1.8. TcBoc-Thr(dimethylallyl)-OMe (17). Boron tri-
fluoride diethyl etherate (1.6 ml, 13 mmol) was added
dropwise over 2 min to a stirred solution of the aziridine
16 (4.00 g, 12.6 mmol) in 2-methyl-3-buten-2-ol (60 ml) at
08C under an atmosphere of nitrogen. The solution was
warmed to room temperature, stirred for 46 h and then
diluted with dichloromethane (50 ml) and washed with
water (3£10 ml) and brine (2£10 ml), with backwashing.
The combined organic extracts were dried and evaporated in
vacuo to leave the crude product which was purified by
chromatography on silica using 10% ethyl acetate in light
petroleum (40–608C) as eluent to give the allyl ether
(3.21 g, 63%) as a pale yellow oil; [a]2D0¼þ13 (c 1.01,
CHCl3); nmax (CHCl3)/cm21 3435, 2980, 2953, 1750, 1724,
1602, 1493, 1458, 1386, 1370, 1314, 1153, 1118, 1090,
1069, 1000, 961, 899; dH (360 MHz, C6D6, 343 K) 5.67
(1H, dd, J¼17.6, 10.8 Hz, CHvCH2), 5.64 (1H, masked br
s, NH), 4.90 (1H, dd, J¼17.7, 1.0 Hz, CHvCH2), 4.86 (1H,
dd, J¼10.8, 1.1 Hz, CHvCH2), 4.33 (1H, m, CHCO2Me),
4.02 (1H, dq, J¼6.3, 2.4 Hz, CHCH3), 3.35 (3H, s, OCH3),
1.91 (3H, s, Cl3CC(CH3)2), 1.91 (3H, s, Cl3CC(CH3)2), 1.08
(3H, d, J¼6.3 Hz, CHCH3), 1.04 (3H, s, CH3), 1.03 (3H, s,
CH3); dC (90 MHz, C6D6, 333 K) 171.0 (s), 154.8 (s), 144.2
(d), 113.5 (t), 107.1 (s), 88.7 (s), 75.9 (s), 68.6 (d), 60.3
(d), 51.5 (q), 26.5 (q), 26.2 (q), 21.9 (q), 20.6 (q); m/z
(ES) 426.0601 ([MþNa]þ, C15H24NO5Cl3Na requires
426.0618).
Triethylamine (6.9 ml, 50 mmol) was added dropwise over
5 min to a stirred solution of trityl threonine methyl ester
(8.48 g, 22.6 mmol) in tetrahydrofuran (60 ml) at 08C under
an atmosphere of nitrogen. Methanesulfonyl chloride
(1.8 ml, 23 mmol) was added dropwise over 2 min and the
solution was stirred at 08C for 30 min and then at reflux for
48 h. The solvent was removed in vacuo to leave a residue
which was taken up in ethyl acetate (50 ml) and washed
with 10% aqueous citric acid solution (3£10 ml) followed
by saturated aqueous sodium bicarbonate solution
(2£10 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
aziridine (7.79 g, 97%) as a cream solid; dH (360 MHz,
CDCl3) 7.53–7.51 (6H, m, Ph-H), 7.30–7.18 (9H, m,
Ph-H), 3.74 (3H, s, OCH3), 1.88 (1H, d, J¼6.5 Hz,
CHCO2Me), 1.63 (1H, dq, J¼6.4, 5.5 Hz, CHCH3), 1.37
(3H, d, J¼5.4 Hz, CH3); dC (90 MHz, CDCl3) 170.8 (s),
144.0 (s), 129.5 (d), 127.7 (d), 126.9 (d), 75.1 (s), 51.9 (q),
36.0 (d), 34.9 (d), 13.4 (q); m/z (ES) 380.1623 ([MþNa]þ,
C24H23NO2Na requires 380.1626), which was used without
further purification.
4.1.9. TcBoc-Ser(dimethylallyl)-Ile-Ala-Pro-PheC
{(CvS)NH}-Ser-OMe (18). Acetyl chloride (0.9 ml) was
added dropwise over 1 min to a stirred solution of the
pentapeptide 6 (250 mg, 0.377 mmol) in methanol (9 ml) at
08C under an atmosphere of nitrogen. The solution was
warmed to room temperature, stirred for 3.5 h and then

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2721
evaporated in vacuo to leave the corresponding hydro-
chloride salt (226 mg) as a cream solid, which was used
without further purification.
and methanol (0.2 ml) at 08C. The solution was warmed to
room temperature, stirred for 2 h and then evaporated in
vacuo. The residue was taken up in ethyl acetate (5 ml) and
water (5 ml), cooled to 08C and then acidified with 2 M
aqueous hydrochloric acid solution with vigorous stirring.
The mixture was stirred at 08C for 5 min, the layers were
separated, and the aqueous layer was then extracted with
ethyl acetate (7£3 ml). The combined organic extracts were
dried and evaporated in vacuo to leave the corresponding
carboxylic acid (46 mg, 87%) as a colourless oil, which was
used without further purification.
Diisopropylethylamine (229 ml, 1.32 mmol) was added
dropwise over 1 min to a stirred solution of the hydro-
chloride salt (226 mg, 0.377 mmol) in dichloromethane
(6 ml) at 08C under an atmosphere of nitrogen. The solution
was stirred at 08C for 10 min and then the carboxylic
acid 710 (141 mg, 0.377 mmol) in dichloromethane (4 ml)
was added dropwise over 5 min by cannula followed by
1-hydroxybenzotriazole (56 mg, 0.41 mmol) in one portion.
The suspension was stirred at 08C for a further 15 min
and then 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (80 mg, 0.41 mmol) was added in one
portion. The mixture was allowed to warm to room
temperature over the course of 23 h and then evaporated
in vacuo. The residue was taken up in ethyl acetate (10 ml)
and washed with 10% aqueous citric acid solution (3£3 ml)
followed by saturated aqueous sodium bicarbonate solution
(5£3 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
crude product which was purified by chromatography on
silica using ethyl acetate as eluent to give the hexapeptide
(249 mg, 72%) as a cream foam; [a]2D2¼235 (c 1.13,
CHCl3); found %: C, 51.65; H, 6.3; N, 8.8; C40H59N6O10
SCl3 requires %: C, 52.1; H, 6.45; N 9.1; nmax (CHCl3)/
cm21 3416, 3331, 2974, 2879, 1727, 1652, 1550, 1489,
1456, 1386, 1370, 1147, 1064, 1001, 904, 872, 838; dH
(360 MHz, d6-DMSO, 343 K) 9.97 (1H, br s, NHCvS),
7.93 (1H, br s, NHCHCH3), 7.64 (1H, br s, NHCHCH2Ph),
7.46 (1H, br s, NHCHCH(CH3)CH2CH3), 7.28–7.18 (5H,
m, Ph-H), 6.89 (1H, br s, NHTcBoc), 5.83 (1H, dd, J¼17.6,
10.8 Hz, CHvCH2), 5.14 (1H, dd, J¼17.6, 1.3 Hz,
CHvCH2), 5.07 (1H, dd, J¼10.8, 1.3 Hz, CHvCH2),
5.05–4.97 (2H, m, CHCO2Me and CHCH2Ph), 4.95 (1H,
app t, J¼5.6 Hz, OH), 4.51 (1H, m, CHCH3), 4.33–4.31
(1H, m, CH(CH2)3N), 4.26 (1H, dd, J¼8.4, 7.4 Hz,
CHCH(CH3)CH2CH3), 4.11 (1H, app dt, J¼8.3, 6.1 Hz,
CHNHTcBoc), 3.86 (1H, ddd, J¼11.3, 5.6, 5.6 Hz,
CH2OH), 3.79 (1H, ddd, J¼11.3, 4.8, 4.8 Hz, CH2OH),
3.68–3.57 (1H, m, CH2N), 3.65 (3H, s, OCH3), 3.52–3.44
(3H, m, CH2OAllyl and CH2N), 3.18 (1H, dd, J¼14.0,
4.8 Hz, CH2Ph), 2.95–2.89 (1H, m, CH2Ph), 1.96–1.66
(5H, m, CH2 and CH(CH3)CH2CH3), 1.84 (6H, s, Cl3CC
(CH3)2), 1.48–1.38 (1H, m, CH2CH3), 1.23–1.21 (3H,
masked d, CHCH3), 1.21 (6H, s, CH3), 1.14–1.02 (1H, m,
CH2CH3), 0.84 (3H, d, J¼6.7 Hz, CH(CH3)CH2CH3), 0.82
(3H, app t, J¼7.3 Hz, CH2CH3); dC (125 MHz, d6-DMSO,
323 K) 204.7 (s), 170.6 (s), 170.3 (s), 169.9 (s), 168.9 (s),
168.7 (s), 153.3 (s), 143.4 (d), 137.2 (s), 129.0 (d), 127.6 (d),
126.0 (d), 113.5 (t), 106.3 (s), 86.9 (s), 74.9 (s), 62.2 (t), 60.5
(d), 60.3 (t), 59.3 (d), 58.6 (d), 56.3 (d), 55.1 (d), 51.7 (q),
46.4 (t), 46.0 (d), 40.5 (t), 37.0 (d), 28.1 (t), 25.3 (q), 25.1
(q), 23.9 (t), 23.9 (t), 21.2 (q), 16.8 (q), 15.0 (q), 10.7 (q);
m/z (ES) 943.2987 ([MþNa]þ, C40H59N6O10SCl3Na
requires 943.2977).
Cadmium–lead couple11 (709 mg, 5.70 mmol cadmium,
10% lead) was added in one portion to a rapidly stirred
solution of the hexapeptide 18 (105 mg, 0.114 mmol) in
tetrahydrofuran (1 ml) and 1N aqueous ammonium acetate
solution (1 ml) at room temperature. The mixture was
stirred vigorously at room temperature for 30 min and then
filtered, washing with water (3£2 ml) and ethyl acetate
(5£2 ml). The filtrate was cooled to 08C, then basified with
saturated aqueous sodium bicarbonate solution and stirred at
08C for 5 min. The layers were then separated and the
aqueous layer was extracted with ethyl acetate (6£5 ml).
The combined organic extracts were dried and evaporated in
vacuo to leave the amine (74 mg, 91%) as a white solid,
which was used without further purification.
A solution of the carboxylic acid 8 (45 mg, 0.12 mmol) in
dichloromethane (2 ml) was added dropwise over 2 min by
cannula to a stirred solution of the amine (74 mg,
0.10 mmol) in dichloromethane (2 ml) at 08C under an
atmosphere of nitrogen. 1-Hydroxybenzotriazole (16 mg,
0.12 mmol) was added, and the suspension was stirred at
08C for 15 min and then 1-(3-dimethylaminopropyl)-3-
ethylcarbodiimide hydrochloride (22 mg, 0.12 mmol) was
added. The mixture was allowed to warm to room
temperature over the course of 41 h and then evaporated
in vacuo. The residue was taken up in ethyl acetate (5 ml)
and washed with 10% aqueous citric acid solution (3£3 ml)
followed by saturated aqueous sodium bicarbonate solution
(5£3 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
crude product which was purified by chromatography on
silica using ethyl acetate as eluent to give the heptapeptide
(91 mg, 81%) as a cream foam; [a]2D2¼218 (c 1.06, CHCl3);
found %: C, 53.4; H, 6.7; N, 8.75; C49H74N7O12SCl3
requires %: C, 53.9; H, 6.8; N 9.0; nmax (CHCl3)/cm21
3412, 3326, 2978, 2934, 2879, 1723, 1674, 1546, 1488,
1456, 1383, 1148, 1064, 986, 873; dH (360 MHz, d6-DMSO,
343 K) 9.98 (1H, d, J¼6.7 Hz, NHCvS), 7.86 (1H, br s,
NHCHCH3), 7.71–7.63 (2H, m, NHCHCH2OAllyl and
NHCHCH2Ph), 7.47 (1H, d, J¼8.9 Hz, NHCHCH(CH3)-
CH2CH3), 7.27–7.18 (5H, m, Ph-H), 6.40 (1H, d, J¼8.4 Hz,
NHTcBoc), 5.90 (1H, dd, J¼17.6, 10.9 Hz, CHvCH2),
5.81 (1H, dd, J¼17.6, 10.8 Hz, CHvCH2), 5.15 (1H, dd,
J¼17.6, 1.1 Hz, CHvCH2), 5.13 (1H, dd, J¼17.6, 1.2 Hz,
CHvCH2), 5.07 (1H, dd, J¼10.8, 1.3 Hz, CHvCH2), 5.07
(1H, dd, J¼10.8, 1.2 Hz, CHvCH2), 5.04–4.99 (2H, m,
CHCO2Me and CHCH2Ph), 4.96 (1H, app t, J¼5.9 Hz,
OH), 4.51–4.42 (2H, m, CHCH3 and CHCH2OAllyl),
4.33–4.31 (1H, m, CH(CH2)3N), 4.26 (1H, dd, J¼8.2,
7.6 Hz, CHCH(CH3)CH2CH3), 4.06 (1H, dd, J¼8.7, 4.3 Hz,
CHNHTcBoc), 3.90–3.83 (1H, masked m, CH(CH3)
4.1.10. TcBoc-Thr(dimethylallyl)-Ser(dimethylallyl)-Ile-
Ala-Pro-PheC{(CvS)NH}-Ser-OMe (5). An aqueous
solution of lithium hydroxide (1.5 M, 0.91 ml, 1.4 mmol)
was added dropwise over 1 min to a stirred solution of the
allyl ether 17 (55 mg, 0.14 mmol) in tetrahydrofuran (2 ml)

2722
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
OAllyl), 3.86 (1H, ddd, J¼11.4, 5.6, 5.6 Hz, CH2OH), 3.79
(1H, ddd, J¼11.1, 5.3, 5.3 Hz, CH2OH), 3.67–3.58 (1H, m,
CH2N), 3.65 (3H, s, OCH3), 3.52–3.37 (2H, m, CH2OAllyl
and CH2N), 3.50 (1H, dd, J¼9.1, 4.9 Hz, CH2OAllyl), 3.17
(1H, dd, J¼14.0, 4.8 Hz, CH2Ph), 2.95–2.88 (1H, m,
CH2Ph), 1.99–1.67 (5H, m, CH2 and CH(CH3)CH2CH3),
1.85 (6H, s, Cl3CC(CH3)2), 1.48–1.38 (1H, m, CH2CH3),
1.25 (3H, s, CH3), 1.23 (3H, s, CH3), 1.23–1.20 (3H,
masked d, CHCH3), 1.20 (6H, s, CH3), 1.13–1.02 (1H, m,
CH2CH3), 1.07 (3H, d, J¼6.2 Hz, CH(CH3)OAllyl), 0.83
(3H, d, J¼6.7 Hz, CH(CH3)CH2CH3), 0.81 (3H, app t,
J¼7.3 Hz, CH2CH3); dC (90 MHz, d6-DMSO, 323 K) 204.7
(s), 170.6 (s), 170.3 (s), 169.8 (s), 168.9 (s), 168.8 (s), 153.2
(s), 143.8 (d), 143.4 (d), 137.2 (s), 129.0 (d), 127.6 (d),
126.0 (d), 113.6 (t), 113.4 (t), 106.3 (s), 87.0 (s), 75.5 (s),
74.9 (s), 68.1 (d), 62.4 (t), 60.5 (d), 60.3 (t), 59.3 (d), 59.3
(d), 58.6 (d), 56.3 (d), 52.8 (d), 51.7 (q), 46.4 (t), 46.0 (d),
40.5 (t), 36.8 (d), 28.1 (t), 26.5 (q), 25.3 (q), 25.2 (q), 25.2
(q), 23.9 (t), 23.9 (t), 21.3 (q), 21.2 (q), 18.8 (q), 16.8
(q), 15.0 (q), 10.8 (q); m/z (ES) 1112.4109 ([MþNa]þ,
C49H74N7O12SCl3Na requires 1112.4079).
(q), 25.2 (q), 25.2 (q), 23.9 (t), 23.9 (t), 21.3 (q), 18.7 (q),
16.8 (q), 15.0 (q), 10.8 (q); m/z (ES) 1072.4138 ([MþH]þ,
C49H73N7O11SCl3 requires 1072.4154).
4.1.12. Boc-Pro-Phe-Ser-OMe (21). Acetyl chloride (5 ml)
was added dropwise over 5 min to a stirred solution of the
dipeptide 10 (4.24 g, 11.6 mmol) in methanol (50 ml) at 08C
under an atmosphere of nitrogen. The solution was warmed
to room temperature, stirred for 3.5 h and then evaporated in
vacuo to leave the corresponding hydrochloride salt (3.36 g,
96%) as a cream solid, which was used without further
purification.
Diisopropylethylamine (6.8 ml, 39 mmol) was added drop-
wise over 5 min to a stirred solution of the hydrochloride
salt (3.36 g, 11.1 mmol) in dichloromethane (50 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 15 min and then Boc-L-proline (2.39 g, 11.1 mmol)
and 1-hydroxybenzotriazole (1.65 g, 12.2 mmol) were
added successively in one portion. The suspension was
stirred at 08C for a further 15 min and then dicyclohex-
ylcarbodiimide (2.52 g, 12.2 mmol) was added in one
portion. The mixture was allowed to warm to room
temperature over the course of 52 h and then evaporated
in vacuo to leave a residue which was taken up in ethyl
acetate (50 ml) and filtered. The filtrate was washed with
10% aqueous citric acid solution (3£10 ml) followed by
saturated aqueous sodium bicarbonate solution (5£10 ml),
with backwashing. The combined organic extracts were
dried and evaporated in vacuo to leave the crude product
which was purified by chromatography on silica using 50%
ethyl acetate in diethyl ether as eluent to give the tripeptide
(4.50 g, 87%) as a colourless foam; [a]2D5¼286 (c 1.13,
CHCl3); nmax (CHCl3)/cm21 3410, 2980, 2955, 2885, 1746,
1682, 1603, 1552, 1496, 1455, 1393, 1369, 1158, 1129,
1078, 977, 888; dH (360 MHz, CDCl3, 323 K) 7.33–7.20
(5H, m, Ph-H), 7.04 (1H, br s, NHCHCH2Ph), 6.54 (1H, d,
J¼8.1 Hz, NHCHCH2OH), 4.76–4.71 (1H, m, CHCH2Ph),
4.57 (1H, app dt, J¼7.6, 3.8 Hz, CHCO2Me), 4.22 (1H, dd,
J¼6.6, 5.6 Hz, CHNBoc), 3.92 (1H, ddd, J¼11.6, 7.7,
3.9 Hz, CH2OH), 3.86 (1H, ddd, J¼11.6, 6.1, 3.9 Hz,
CH2OH), 3.76 (3H, s, OCH3), 3.40–3.34 (1H, m, CH2-
NBoc), 3.30 (1H, ddd, J¼10.7, 7.8, 4.0 Hz, CH2NBoc),
3.17–3.12 (2H, m, CH2Ph), 2.09–2.01 (2H, m, CH2), 1.86–
1.78 (1H, m, CH2), 1.67–1.60 (1H, m, CH2), 1.41 (9H, s,
C(CH3)3); dC (90 MHz, CDCl3) 172.2 (s), 171.0 (s), 170.5
(s), 155.6 (s), 136.5 (s), 129.3 (d), 128.6 (d), 127.0 (d), 81.1
(s), 62.6 (t), 60.8 (d), 55.0 (d), 53.5 (d), 52.5 (q), 47.3 (t),
36.9 (t), 29.4 (t), 28.3 (q), 24.3 (t); m/z (ES) 486.2172
([MþNa]þ, C23H33N3O7Na requires 486.2216).
4.1.11. TcBoc-Thr(dimethylallyl)-Ser(dimethylallyl)-Ile-
Ala-Pro-Phe-Ser(thiazoline)-OMe (20). Burgess’ reagent21
(9 mg, 0.04 mmol) was added in one portion to a stirred
solution of the heptapeptide 5 (28 mg, 0.026 mmol) in
tetrahydrofuran (5 ml) at room temperature under an
atmosphere of nitrogen. The mixture was heated to reflux,
stirred for 30 min and then evaporated in vacuo to leave the
crude product which was purified by chromatography on
silica using ethyl acetate as eluent to give the thiazoline
(25 mg, 92%) as a cream foam; [a]2D0¼219 (c 0.93, CHCl3);
nmax (CHCl3)/cm21 3407, 2977, 2934, 2879, 1726,
1674, 1487, 1456, 1369, 1148, 1078, 1046, 986, 874; dH
(360 MHz, d6-DMSO, 343 K) 7.89 (1H, br s, NHCHCH2
Ph), 7.80 (1H, br s, NHCHCH3), 7.64 (1H, br s, NHCHCH2
OAllyl), 7.44 (1H, d, J¼8.4 Hz, NHCHCH(CH3)CH2CH3),
7.27–7.18 (5H, m, Ph-H), 6.36 (1H, d, J¼8.4 Hz,
NHTcBoc), 5.90 (1H, dd, J¼17.6, 10.8 Hz, CHvCH2),
5.82 (1H, dd, J¼17.6, 10.9 Hz, CHvCH2), 5.15 (1H,
d, J¼17.6 Hz, CHvCH2), 5.13 (1H, d, J¼17.6 Hz,
CHvCH2), 5.12–5.07 (1H, masked dd, CHCH2S), 5.07
(1H, d, J¼10.9 Hz, CHvCH2), 5.07 (1H, d, J¼10.8 Hz,
CHvCH2), 4.85 (1H, app dt, J¼7.6, 6.5 Hz, CHCH2Ph),
4.50–4.44 (2H, m, CHCH3 and CHCH2OAllyl), 4.37–4.35
(1H, m, CH(CH2)3N), 4.27 (1H, dd, J¼8.2, 7.2 Hz,
CHCH(CH3)CH2CH3), 4.07 (1H, dd, J¼8.5, 4.2 Hz,
CHNHTcBoc), 3.88 (1H, dq, J¼6.2, 4.3 Hz, CH(CH3)
OAllyl), 3.71 (3H, s, OCH3), 3.66–3.41 (6H, m, CH2N,
CH2S and CH2OAllyl), 3.17 (1H, dd, J¼14.0, 5.4 Hz,
CH2Ph), 3.04–2.99 (1H, masked dd, CH2Ph), 2.04–
1.69 (5H, m, CH2 and CH(CH3)CH2CH3), 1.85 (6H, s,
Cl3CC(CH3)2), 1.45 (1H, m, CH2CH3), 1.25 (3H, s, CH3),
1.24 (3H, s, CH3), 1.24–1.21 (3H, masked d, CHCH3), 1.21
(6H, s, CH3), 1.14–1.03 (1H, m, CH2CH3), 1.08 (3H, d,
J¼6.2 Hz, CH(CH3)OAllyl), 0.85–0.84 (3H, masked d,
CH(CH3)CH2CH3), 0.82 (3H, app t, J¼7.5 Hz, CH2CH3);
dC (125 MHz, d6-DMSO, 323 K) 174.8 (s), 170.8 (s), 170.4
(s), 170.1 (s), 169.8 (s), 168.8 (s), 153.1 (s), 143.8 (d), 143.4
(d), 137.1 (s), 129.0 (d), 127.8 (d), 126.0 (d), 113.6 (t), 113.4
(t), 106.3 (s), 87.0 (s), 77.6 (d), 75.5 (s), 74.9 (s), 68.1 (d),
62.4 (t), 59.1 (d), 59.1 (d), 56.3 (d), 52.8 (d), 52.2 (d), 51.9
(q), 46.3 (t), 45.9 (d), 38.2 (t), 36.9 (d), 34.2 (t), 28.4 (t), 26.5
4.1.13. Boc-Ala-Pro-Phe-Ser-OMe (22). Acetyl chloride
(9 ml) was added dropwise over 10 min to a stirred solution
of the tripeptide 21 (4.13 g, 8.93 mmol) in methanol (60 ml)
at 08C under an atmosphere of nitrogen. The solution was
warmed to room temperature, stirred for 3 h and then
evaporated in vacuo to leave the corresponding hydrochlo-
ride salt (3.53 g, 99%) as a white solid, which was used
without further purification.
Diisopropylethylamine (5.4 ml, 31 mmol) was added drop-
wise over 5 min to a stirred solution of the hydrochloride
salt (3.53 g, 8.84 mmol) in dichloromethane (50 ml) at 08C

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2723
under an atmosphere of nitrogen. The solution was stirred at
08C for 15 min and then Boc-L-alanine (1.67 g, 8.84 mmol)
and 1-hydroxybenzotriazole (1.31 g, 9.72 mmol) were
added successively in one portion. The suspension was
stirred at 08C for a further 15 min and then dicyclohex-
ylcarbodiimide (2.01 g, 9.72 mmol) was added in one
portion. The mixture was allowed to warm to room
temperature over the course of 47 h and then evaporated
in vacuo to leave a residue which was taken up in
dichloromethane (150 ml) and filtered. The filtrate was
washed with 10% aqueous citric acid solution (3£30 ml)
followed by saturated aqueous sodium bicarbonate solution
(5£30 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
crude product which was purified by chromatography on
silica using ethyl acetate as eluent to give the tetrapeptide
(4.12 g, 87%) as a colourless solid; mp 192–1938C (ethyl
acetate); [a]D23¼292 (c 0.51, CHCl3); nmax (CHCl3)/cm21
3435, 2981, 2955, 1745, 1678, 1548, 1495, 1455, 1393,
1369, 1346, 1158, 1067, 863; dH (360 MHz, d6-DMSO,
343 K) 7.84 (1H, d, J¼7.6 Hz, NHCHCH2OH), 7.56 (1H, br
s, NHCHCH2Ph), 7.28–7.16 (5H, m, Ph-H), 6.51 (1H, br s,
NHBoc), 4.78 (1H, app t, J¼5.8 Hz, OH), 4.55 (1H, app dt,
J¼8.3, 5.4 Hz, CHCH2Ph), 4.37 (1H, app dt, J¼7.7, 5.0 Hz,
CHCH2OH), 4.35–4.31 (1H, m, CH(CH2)3N), 4.25 (1H, br
s, CHCH3), 3.72 (1H, ddd, J¼10.9, 5.5, 5.5 Hz, CH2OH),
3.65 (1H, ddd, J¼10.6, 5.6, 5.6 Hz, CH2OH), 3.65 (3H, s,
OCH3), 3.59 (1H, m, CH2N), 3.47 (1H, m, CH2N), 3.12 (1H,
dd, J¼14.0, 5.0 Hz, CH2Ph), 2.92–2.86 (1H, m, CH2Ph),
2.01–1.70 (4H, m, CH2), 1.38 (9H, s, C(CH3)3), 1.17 (3H, d,
J¼6.9 Hz, CHCH3); dC (100 MHz, d6-DMSO, 333 K) 171.4
(s), 170.8 (s), 170.5 (s), 170.4 (s), 154.7 (s), 137.4 (s), 128.9
(d), 127.6 (d), 125.9 (d), 77.8 (s), 61.0 (t), 59.5 (d), 54.5 (d),
53.2 (d), 51.4 (q), 47.5 (d), 46.3 (t), 36.8 (t), 28.2 (t), 27.9
(q), 24.1 (t), 16.7 (q); m/z (ES) 557.2600 ([MþNa]þ,
C26H38N4O8Na requires 557.2587).
which was purified by chromatography on silica using 20%
acetone in ethyl acetate as eluent to give the pentapeptide
(3.73 g, 81%) as a colourless solid; mp 178–1808C (ethyl
acetate); [a]D23¼277 (c 0.50, CHCl3); nmax (CHCl3)/cm21
3420, 2970, 2878, 1746, 1673, 1548, 1494, 1455, 1368,
1156, 1078, 865; dH (360 MHz, d6-DMSO, 343 K) 7.85
(1H, d, J¼7.8 Hz, NHCHCH2OH), 7.75 (1H, d, J¼7.4 Hz,
NHCHCH3), 7.55 (1H, br s, NHCHCH2Ph), 7.28–7.16 (5H,
m, Ph-H), 6.37 (1H, br s, NHBoc), 4.77 (1H, br s, OH),
4.60–4.54 (1H, masked m, CHCH3), 4.57 (1H, app dt,
J¼8.3, 5.1 Hz, CHCH2Ph), 4.37 (1H, app dt, J¼7.7, 5.0 Hz,
CHCH2OH), 4.30 (1H, m, CH(CH2)3N), 3.85 (1H, dd,
J¼8.2, 7.8 Hz, CHNHBoc), 3.72 (1H, dd, J¼10.9, 5.3 Hz,
CH2OH), 3.68–3.65 (1H, masked dd, CH2OH), 3.65 (3H, s,
OCH3), 3.65–3.59 (1H, m, CH2N), 3.48 (1H, m, CH2N),
3.12 (1H, dd, J¼14.0, 5.2 Hz, CH2Ph), 2.92–2.85 (1H, m,
CH2Ph), 1.99–1.68 (5H, m, CH2 and CH(CH3)CH2CH3),
1.45–1.39 (1H, m, CH2CH3), 1.39 (9H, s, C(CH3)3), 1.20
(3H, d, J¼6.8 Hz, CHCH3), 1.17–1.05 (1H, m, CH2CH3),
0.83 (3H, d, J¼7.2 Hz, CH(CH3)CH2CH3), 0.82 (3H, app t,
J¼7.4 Hz, CH2CH3); dC (100 MHz, d6-DMSO, 333 K)
170.7 (s), 170.6 (s), 170.5 (s), 170.4 (s), 154.9 (s), 137.4 (s),
128.9 (d), 127.6 (d), 125.9 (d), 77.9 (s), 61.1 (t), 59.5 (d),
58.6 (d), 54.5 (d), 53.2 (d), 51.4 (q), 46.4 (t), 46.0 (d), 36.9
(t), 36.5 (d), 28.3 (t), 27.9 (q), 24.1 (t), 24.0 (t), 16.8 (q), 15.1
(q), 10.7 (q); m/z (ES) 670.3419 ([MþNa]þ, C32H49N5O9Na
requires 670.3428).
4.1.15. TcBoc-Ser(dimethylallyl)-Ile-Ala-Pro-Phe-Ser-
OMe (24). Acetyl chloride (0.75 ml) was added dropwise
over 1 min to a stirred solution of the pentapeptide 23
(500 mg, 0.773 mmol) in methanol (5 ml) at 08C under an
atmosphere of nitrogen. The solution was warmed to room
temperature, stirred for 3.5 h and then evaporated in vacuo
to leave the corresponding hydrochloride salt (450 mg) as a
cream solid, which was used without further purification.
4.1.14. Boc-Ile-Ala-Pro-Phe-Ser-OMe (23). Acetyl chlor-
ide (7.5 ml) was added dropwise over 5 min to a stirred
solution of the tetrapeptide 22 (3.80 g, 7.12 mmol) in
methanol (50 ml) at 08C under an atmosphere of nitrogen.
The solution was warmed to room temperature, stirred for
4 h and then evaporated in vacuo to leave the corresponding
hydrochloride salt (3.34 g) as a cream solid, which was used
without further purification.
Diisopropylethylamine (0.47 ml, 2.7 mmol) was added
dropwise over 1 min to a stirred solution of the hydro-
chloride salt (450 mg, 0.771 mmol) in dichloromethane
(5 ml) at 08C under an atmosphere of nitrogen. The solution
was stirred at 08C for 15 min and then a solution of the
carboxylic acid 710 (277 mg, 0.736 mmol) in dichloro-
methane (1 ml) was added over 1 min by cannula followed
by 1-hydroxybenzotriazole (115 mg, 0.848 mmol) in one
portion. The suspension was stirred at 08C for a further
15 min and then 1-(3-dimethylaminopropyl)-3-ethylcarbo-
diimide hydrochloride (163 mg, 0.848 mmol) was added in
one portion. The mixture was allowed to warm to room
temperature over the course of 43 h and then evaporated in
vacuo. The residue was taken up in ethyl acetate (10 ml) and
washed with 10% aqueous citric acid solution (3£3 ml)
followed by saturated aqueous sodium bicarbonate solution
(5£3 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
crude product which was purified by chromatography on
silica using 10% acetone in ethyl acetate as eluent to give
the hexapeptide (397 mg, 60%) as a colourless foam;
[a]2D2¼258 (c 0.51, CHCl3); found %: C, 52.9; H, 6.5; N,
9.1; C40H59N6O11Cl3 requires %: C, 53.0; H, 6.6; N, 9.3;
nmax (CHCl3)/cm21 3418, 2977, 2879, 1726, 1668, 1551,
1489, 1456, 1370, 1145, 1076, 905; dH (360 MHz,
d6-DMSO, 323 K) 8.06 (1H, br s, NHCHCH3), 7.98 (1H,
Diisopropylethylamine (4.3 ml, 25 mmol) was added drop-
wise over 5 min to a stirred solution of the hydrochloride
salt (3.34 g, 7.10 mmol) in dichloromethane (40 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 15 min and then Boc-L-isoleucine (1.64 g,
7.10 mmol) and 1-hydroxybenzotriazole (1.06 g,
7.81 mmol) were added successively in one portion. The
suspension was stirred at 08C for a further 15 min and then
dicyclohexylcarbodiimide (1.61 g, 7.81 mmol) was added
in one portion. The mixture was allowed to warm to room
temperature over the course of 28 h and then evaporated in
vacuo to leave a residue which was taken up in ethyl acetate
(50 ml) and filtered. The filtrate was washed with 10%
aqueous citric acid solution (3£10 ml) followed by
saturated aqueous sodium bicarbonate solution (5£10 ml),
with backwashing. The combined organic extracts were
dried and evaporated in vacuo to leave the crude product

2724
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
d, J¼7.6 Hz, NHCHCH2OH), 7.63 (1H, d, J¼8.1 Hz,
NHCHCH2Ph), 7.55 (1H, br s, NHCHCH(CH3)CH2CH3),
7.27–7.16 (5H, m, Ph-H), 7.09 (1H, br s, NHTcBoc), 5.82
(1H, dd, J¼17.6, 10.8 Hz, CHvCH2), 5.13 (1H, dd, J¼
17.6, 1.2 Hz, CHvCH2), 5.07 (1H, dd, J¼10.8, 1.1 Hz,
CHvCH2), 4.90 (1H, app t, J¼5.8 Hz, OH), 4.55 (1H, app
dt, J¼8.5, 5.0 Hz, CHCH2Ph), 4.51–4.47 (1H, m, CHCH3),
4.36 (1H, app dt, J¼7.6, 5.0 Hz, CHCH2OH), 4.28–4.22
(2H, m, CH(CH2)3N and CHCH(CH3)CH2CH3), 4.16–4.03
(1H, m, CHNHTcBoc), 3.72 (1H, ddd, J¼11.1, 5.6, 5.6 Hz,
CH2OH), 3.67–3.57 (2H, m, CH2OH and CH2N), 3.64 (3H,
s, OCH3), 3.50–3.41 (3H, m, CH2N and CH2OAllyl), 3.10
(1H, dd, J¼14.0, 4.8 Hz, CH2Ph), 2.86 (1H, dd, J¼14.0,
8.9 Hz, CH2Ph), 1.94–1.70 (5H, m, CH2 and CH(CH3)-
CH2CH3), 1.83 (6H, s, Cl3CC(CH3)2), 1.47–1.37 (1H, m,
CH2CH3), 1.19 (6H, s, CH3), 1.19 (3H, d, J¼6.5 Hz,
CHCH3), 1.12–1.02 (1H, m, CH2CH3), 0.82 (3H, d, J¼
6.7 Hz, CH(CH3)CH2CH3), 0.80 (3H, app t, J¼7.3 Hz,
CH2CH3); dC (90 MHz, d6-DMSO, 323 K) 170.8 (s), 170.6
(s), 170.5 (s), 170.0 (s), 168.8 (s), 153.4 (s), 143.4 (d), 137.5
(s), 129.0 (d), 127.7 (d), 125.9 (d), 113.6 (t), 106.3 (s), 87.0
(s), 74.9 (s), 62.2 (t), 61.1 (t), 59.5 (d), 56.3 (d), 55.1 (d),
54.5 (d), 53.2 (d), 51.5 (q), 46.5 (t), 46.1 (d), 36.9 (d), 36.9
(t), 28.4 (t), 25.3 (q), 25.2 (q), 24.1 (t), 23.9 (t), 21.3 (q), 16.5
(q), 15.0 (q), 10.8 (q); m/z (ES) 927.3165 ([MþNa]þ,
C40H59N6O11Cl3Na requires 927.3205).
atmosphere of nitrogen. 1-Hydroxybenzotriazole (69 mg,
0.51 mmol) was added in one portion and the suspension
was stirred at 08C for 10 min. 1-(3-Dimethylaminopropyl)-
3-ethylcarbodiimide hydrochloride (97 mg, 0.51 mmol) was
added in one portion and the mixture was allowed to warm
to room temperature over the course of 26 h and then
evaporated in vacuo. The residue was taken up in ethyl
acetate (10 ml) and washed with 10% aqueous citric acid
solution (3£3 ml) followed by saturated aqueous sodium
bicarbonate solution (5£3 ml), with backwashing. The
combined organic extracts were dried and evaporated in
vacuo to leave the crude product which was purified by
chromatography on silica using 10% acetone in ethyl
acetate as eluent to give the heptapeptide (352 mg, 72%) as
a cream foam; [a]2D0¼234 (c 0.55, CHCl3); found %: C,
54.55; H, 6.9; N, 8.9; C49H74N7O13Cl3 requires %: C, 54.7;
H, 6.9; N, 9.1; nmax (CHCl3)/cm21 3412, 2979, 2878, 1722,
1673, 1551, 1488, 1456, 1381, 1147, 1078, 986, 872; dH
(360 MHz, d6-DMSO, 343 K) 7.88–7.84 (1H, masked d,
NHCHCH3), 7.86 (1H, d, J¼7.7 Hz, NHCHCH2OH), 7.67
(1H, br s, NHCHCH2OAllyl), 7.55 (1H, br s, NHCHCH2
Ph), 7.46 (1H, d, J¼8.5 Hz, NHCHCH(CH3)CH2CH3),
7.27–7.16 (5H, m, Ph-H), 6.39 (1H, d, J¼7.1 Hz,
NHTcBoc), 5.90 (1H, dd, J¼17.6, 10.8 Hz, CHvCH2),
5.81 (1H, dd, J¼17.6, 10.8 Hz, CHvCH2), 5.15 (1H, dd,
J¼17.6, 1.2 Hz, CHvCH2), 5.13 (1H, dd, J¼17.6, 1.3 Hz,
CHvCH2), 5.07 (1H, dd, J¼10.8, 1.3 Hz, CHvCH2), 5.07
(1H, dd, J¼10.8, 1.3 Hz, CHvCH2) 4.76 (1H, app t,
J¼5.8 Hz, OH), 4.56 (1H, app dt, J¼8.3, 5.3 Hz, CHCH2
Ph), 4.51–4.42 (2H, m, CHCH3 and CHCH2OAllyl), 4.37
(1H, app dt, J¼7.6, 5.0 Hz, CHCH2OH), 4.29–4.25 (2H, m,
CH(CH2)3N and CHCH(CH3)CH2CH3), 4.07 (1H, dd, J¼
8.7, 4.3 Hz, CHNHTcBoc), 3.88 (1H, dq, J¼6.3, 4.4 Hz,
CH(CH3)OAllyl), 3.72 (1H, ddd, J¼11.0, 5.6, 5.6 Hz,
CH2OH), 3.68–3.57 (2H, m, CH2OH and CH2N), 3.65
(3H, s, OCH3), 3.52–3.40 (2H, m, CH2N and CH2OAllyl),
3.50 (1H, dd, J¼9.2, 5.0 Hz, CH2OAllyl), 3.11 (1H, dd,
J¼14.0, 5.1 Hz, CH2Ph), 2.92–2.85 (1H, m, CH2Ph), 1.99–
1.67 (5H, m, CH2 and CH(CH3)CH2CH3), 1.85 (6H, s,
Cl3CC(CH3)2), 1.50–1.38 (1H, m, CH2CH3), 1.25 (3H, s,
CH3), 1.23 (3H, s, CH3), 1.20 (6H, s, CH3), 1.20–1.19 (3H,
masked d, CHCH3), 1.13–1.03 (1H, m, CH2CH3), 1.07 (3H,
d, J¼6.2 Hz, CH(CH3)OAllyl), 0.84 (3H, d, J¼6.7 Hz,
CH(CH3)CH2CH3), 0.81 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (100 MHz, d6-DMSO, 323 K) 170.8 (s), 170.6 (s), 170.5
(s), 169.8 (s), 168.8 (s), 153.2 (s), 143.8 (d), 143.4 (d), 137.5
(s), 129.0 (d), 127.7 (d), 125.9 (d), 113.6 (t), 113.4 (t), 106.3
(s), 87.0 (s), 75.5 (s), 74.9 (s), 68.1 (d), 62.4 (t), 61.1 (t), 59.5
(d), 59.2 (d), 56.4 (d), 54.5 (d), 53.2 (d), 52.8 (d), 51.5 (q),
46.4 (t), 46.1 (d), 36.9 (t), 36.9 (d), 28.4 (t), 26.5 (q), 25.3
(q), 25.2 (q), 25.2 (q), 24.0 (t), 23.9 (t), 21.3 (q), 21.2 (q),
18.8 (q), 16.6 (q), 15.0 (q), 10.8 (q); m/z (ES) 1096.4287
([MþNa]þ, C49H74N7O13Cl3Na requires 1096.4308).
4.1.16. TcBoc-Thr(dimethylallyl)-Ser(dimethylallyl)-Ile-
Ala-Pro-Phe-Ser-OMe (25). An aqueous solution of
lithium hydroxide (1.5 M, 4.0 ml, 6.0 mmol) was added
dropwise over 5 min to a stirred solution of the allyl ether 17
(243 mg, 0.601 mmol) in tetrahydrofuran (5 ml) and
methanol (0.25 ml) at 08C. The solution was warmed to
room temperature, stirred for 4 h and then evaporated in
vacuo. The residue was taken up in diethyl ether (5 ml) and
water (5 ml), cooled to 08C and then acidified with 2 M
aqueous hydrochloric acid solution with vigorous stirring.
The mixture was stirred at 08C for 10 min, the layers were
separated, and the aqueous layer was then extracted with
diethyl ether (5£2 ml). The combined organic extracts were
dried and evaporated in vacuo to leave the corresponding
carboxylic acid (180 mg, 77%) as a colourless gum, which
was used without further purification.
Cadmium–lead couple11 (4.15 g, 33.6 mmol cadmium,
10% lead) was added in one portion to a rapidly stirred
solution of the hexapeptide 24 (608 mg, 0.671 mmol) in
tetrahydrofuran (6 ml) and 1N aqueous ammonium acetate
solution (6 ml) at room temperature. The mixture was
stirred vigorously at room temperature for 1.5 h and then
filtered, washing with water (5£3 ml) and ethyl acetate
(5£3 ml). The filtrate was cooled to 08C, then basified with
saturated aqueous sodium bicarbonate solution and stirred at
08C for 10 min. The layers were then separated and the
aqueous layer was extracted with ethyl acetate (5£3 ml).
The combined organic extracts were dried and evaporated in
vacuo to leave the amine (442 mg, 94%) as a colourless
solid, which was used without further purification.
4.1.17. Cyclo[Thr(dimethylallyl)-Ser(dimethylallyl)-Ile-
Ala-Pro-Phe-Ser] (26).6a Cadmium–lead couple11
(281 mg, 2.27 mmol cadmium, 10% lead) was added in
one portion to a rapidly stirred solution of the heptapeptide
25 (49 mg, 0.045 mmol) in tetrahydrofuran (0.5 ml) and 1N
aqueous ammonium acetate solution (0.5 ml) at room
temperature. The mixture was stirred vigorously at room
temperature for 1 h and then filtered, washing with water
(5£2 ml) and ethyl acetate (5£2 ml). The filtrate was cooled
A solution of the carboxylic acid 8 (180 mg, 0.461 mmol) in
dichloromethane (4 ml) was added dropwise over 5 min by
cannula to a stirred solution of the amine (317 mg,
0.452 mmol) in dichloromethane (6 ml) at 08C under an

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2725
to 08C, then basified with saturated aqueous sodium
bicarbonate solution and stirred at 08C for 10 min. The
layers were then separated and the aqueous layer was
extracted with ethyl acetate (6£3 ml). The combined
organic extracts were dried and evaporated in vacuo to
leave the amine (38 mg, 96%) as a cream solid, which was
used without further purification.
(t), 36.4 (d), 31.6 (t), 29.8 (t), 29.3 (t), 26.9 (q), 25.8 (q), 25.7
(q), 24.9 (q), 24.7 (t), 21.8 (q), 21.3 (t), 16.3 (q), 15.3 (q),
11.4 (q); m/z (ES) 862.4652 ([MþNa]þ, C43H65N7O10Na
requires 862.4691).
4.1.18. Cyclo[Thr(dimethylallyl)-Ser(dimethylallyl)-Ile-
Ala-Pro-PheC{(CvS)NH}-Ser] (4).6a Diethylamino-
sulfur trifluoride (14 ml, 0.10 mmol) was added dropwise
over 1 min to a stirred solution of the cyclopeptide 26
(78 mg, 0.093 mmol) in dichloromethane (1.5 ml) at 2158C
under an atmosphere of nitrogen. The solution was stirred at
2158C for 35 min and then additional diethylaminosulfur
trifluoride (14 ml, 0.10 mmol) was added dropwise over
1 min. The mixture was stirred at 2158C for 30 min, then
quenched with saturated aqueous sodium bicarbonate
solution (2 ml) and warmed to room temperature. The
layers were separated, the aqueous layer was extracted with
dichloromethane (5£1 ml), and the combined organic
extracts were then dried and evaporated in vacuo. The
residue was purified by chromatography on silica using 30:1
chloroform/methanol as eluent to give the oxazoline
cyclopeptide (37 mg, 50%)6a as a colourless solid; dH
(360 MHz, CDCl3) 8.20 (1H, d, J¼6.9 Hz, NHCHCH2Ph),
8.06 (1H, d, J¼6.7 Hz, NHCHCH(CH3)OAllyl), 7.47 (1H,
d, J¼7.0 Hz, NHCHCH2OAllyl), 7.27 (1H, d, J¼5.3 Hz,
NHCHCH3), 7.14–7.11 (3H, m, Ph-H), 7.01–6.98 (2H, m,
Ph-H), 6.22 (1H, d, J¼10.0 Hz, NHCHCH(CH3)CH2CH3),
5.93 (1H, dd, J¼17.6, 10.8 Hz, CHvCH2), 5.73 (1H, dd,
J¼17.6, 10.9 Hz, CHvCH2), 5.31 (1H, d, J¼17.4 Hz,
CHvCH2), 5.29 (1H, d, J¼10.8 Hz, CHvCH2), 5.15 (1H,
dd, J¼10.9, 0.8 Hz, CHvCH2), 5.12 (1H, dd, J¼17.6,
0.7 Hz, CHvCH2), 4.94 (1H, ddd, J¼7.0, 5.2, 5.0 Hz,
CHCH2Ph), 4.89–4.87 (1H, m, CH(CH2)3N), 4.72–4.55
(5H, m, CHCH3, CHCH(CH3)CH2CH3, CH2O and
CHCH2O), 4.49–4.45 (2H, m, CHCH(CH3)OAllyl and
CHCH2OAllyl), 3.95 (1H, dq, J¼6.4, 5.2 Hz, CH(CH3)
OAllyl), 3.89 (1H, dd, J¼9.2, 2.2 Hz, CH2OAllyl), 3.47
(1H, dd, J¼9.2, 3.2 Hz, CH2OAllyl), 3.44–3.37 (2H, m,
CH2N), 3.17 (1H, dd, J¼14.0, 5.1 Hz, CH2Ph), 2.96 (1H,
dd, J¼14.0, 5.4 Hz, CH2Ph), 2.60–2.55 (1H, m, CH2),
2.45–2.38 (1H, m, CH(CH3)CH2CH3), 1.98–1.90 (2H, m,
CH2), 1.70–1.59 (1H, m, CH2), 1.48 (3H, s, CH3), 1.39 (3H,
s, CH3), 1.27 (3H, s, CH3), 1.24 (3H, s, CH3), 1.15 (3H, d,
J¼6.6 Hz, CHCH3), 1.12–1.01 (2H, m, CH2CH3), 0.95
(3H, d, J¼6.9 Hz, CH(CH3)CH2CH3), 0.94 (3H, app t,
J¼7.1 Hz, CH2CH3), 0.76 (3H, d, J¼6.5 Hz, CH(CH3)
OAllyl); dC (90 MHz, CDCl3) 172.7 (s), 170.7 (s), 170.3 (s),
170.1 (s), 169.0 (s), 167.7 (s), 142.6 (d), 142.2 (d), 136.5 (s),
129.6 (d), 128.3 (d), 126.8 (d), 115.7 (t), 115.1 (t), 77.8 (s),
76.0 (s), 70.8 (t), 67.9 (d), 67.0 (d), 62.0 (t), 59.8 (d), 57.5
(d), 56.2 (d), 56.0 (d), 49.3 (d), 47.8 (d), 47.3 (t), 37.9 (t),
36.6 (d), 27.3 (q), 25.8 (q), 25.8 (q), 25.6 (q), 25.5 (t), 25.2
(t), 23.7 (t), 19.0 (q), 18.3 (q), 16.1 (q), 12.1 (q); m/z (ES)
844.4569 ([MþNa]þ, C43H63N7O9Na requires 844.4585).
An aqueous solution of tetrabutylammonium hydroxide
(40 wt%, 57 ml, 0.087 mmol) was added dropwise over
1 min to a stirred solution of the amine (38 mg, 0.044 mmol)
in tetrahydrofuran (1.5 ml) at 08C. The solution was stirred
at 08C for 3 h and then neutralised with 2 M aqueous
hydrochloric acid solution (44 ml, 0.087 mmol). The
mixture was stirred at 08C for a further 10 min, then
warmed to room temperature and evaporated in vacuo,
azeotroping several times with toluene, to leave the amino
acid, which was used without further purification.
Diisopropylethylamine (17 ml, 0.096 mmol) was added
dropwise over 1 min to a stirred solution of the amino
acid in dimethylformamide (8.7 ml) at 258C under an
atmosphere of nitrogen. The solution was stirred at 258C
for 15 min and then diphenylphosphoryl azide14 (14 ml,
0.066 mmol) was added dropwise over 1 min. The mixture
was stirred at 258C for a further 5 min, stirring was then
stopped, and the solution was allowed to slowly warm to
room temperature and stood at room temperature for 7 days.
Ethyl acetate (10 ml) was added and the solution was then
poured into ice-cold water (20 ml). The layers were
separated and the aqueous layer was extracted with ethyl
acetate (5£5 ml). The combined organic extracts were
washed with water (3£20 ml) and brine (1£20 ml), and then
dried and evaporated in vacuo. The residue was purified by
chromatography on silica using 40% acetone in ethyl
acetate as eluent to give the cyclopeptide (13 mg, 35%, two
steps) as a colourless solid, mp 167–1698C (lit mp 167–
1698C); [a]2D0¼280 (c 0.61, CHCl3), [lit [a]2D3¼294 (c 0.60,
CHCl3]; dH (360 MHz, CDCl3) 7.88 (1H, d, J¼6.8 Hz,
NHCHCH2OH), 7.34–7.13 (6H, m, Ph-H and NHCHCH2
OAllyl), 7.09 (1H, d, J¼7.7 Hz, NHCHCH2Ph), 6.97 (1H, d,
J¼8.8 Hz, NHCHCH(CH3)CH2CH3), 6.67 (1H, d, J¼
6.4 Hz, NHCHCH(CH3)OAllyl), 6.49 (1H, d, J¼5.2 Hz,
NHCHCH3), 5.77 (1H, dd, J¼17.6, 10.9 Hz, CHvCH2),
5.75 (1H, dd, J¼17.5, 10.9 Hz, CHvCH2), 5.21–5.09 (4H,
m, CHvCH2), 4.79 (1H, app dt, J¼6.5, 3.3 Hz, CHCH2
OH), 4.75–4.65 (2H, m, CHCH2OAllyl and CHCH2Ph),
4.46 (1H, dq, J¼7.0, 5.6 Hz, CHCH3), 4.35–4.33 (1H, m,
CH(CH2)3N), 4.23 (1H, dq, J¼6.4, 1.2 Hz, CH(CH3)
OAllyl), 4.19–4.03 (3H, m, CHCH(CH3)CH2CH3,
CHCH(CH3)OAllyl and CH2OH), 3.97–3.90 (1H, m,
CH2OH), 3.74 (1H, dd, J¼9.2, 1.8 Hz, CH2OAllyl),
3.62 (1H, dd, J¼9.3, 2.0 Hz, OH), 3.42–3.33 (4H, m,
CH2OAllyl, CH2N and CH2Ph), 3.06–2.99 (1H, m, CH2Ph),
2.34–2.29 (1H, m, CH2), 1.95–1.52 (4H, m, CH2 and
CH(CH3)CH2CH3), 1.36–1.10 (20H, m, CH3, CHCH3,
CH(CH3)OAllyl and CH2CH3), 0.99 (3H, d, J¼6.6 Hz,
CH(CH3)CH2CH3), 0.94 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (90 MHz, CDCl3) 172.2 (s), 171.6 (s), 170.9 (s), 170.7
(s), 170.3 (s), 170.0 (s), 169.4 (s), 143.1 (d), 142.8 (d), 136.6
(s), 129.0 (d), 128.9 (d), 127.4 (d), 115.1 (t), 114.5 (t), 76.2
(s), 75.8 (s), 66.8 (d), 64.1 (t), 62.4 (t), 61.0 (d), 60.8 (d),
57.8 (d), 55.8 (d), 54.3 (d), 53.8 (d), 48.7 (d), 46.8 (t), 38.2
Hydrogen sulfide gas was bubbled through a stirred solution
of the oxazoline cyclopeptide (37 mg, 0.045 mmol) in
methanol/triethylamine (2:1, 3 ml) for 5 min at room
temperature under an atmosphere of nitrogen. The solution
was stirred at room temperature for 51 h, then evaporated in
vacuo and the residue was purified by chromatography on
silica using 20% acetone in ethyl acetate as eluent to give
the thioamide cyclopeptide (37 mg, 97%) as a cream solid,

2726
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
mp 184–1868C; [a]D20¼264 (c 0.48, CHCl3);dH (500 MHz,
CDCl3) 9.47 (1H, d, J¼6.8 Hz, NHCvS), 7.35–7.21 (7H,
m, Ph-H, NHCHCH2Ph and NHCHCH2OAllyl), 6.97 (1H,
d, J¼8.7 Hz, NHCHCH(CH3)CH2CH3), 6.70 (1H, d, J¼
6.6 Hz, NHCHCH(CH3)OAllyl), 6.56 (1H, d, J¼5.4 Hz,
NHCHCH3), 5.77 (1H, dd, J¼17.7, 10.5 Hz, CHvCH2),
5.75 (1H, dd, J¼17.6, 10.3 Hz, CHvCH2), 5.33 (1H, app
dt, J¼6.5, 3.2 Hz, CHCH2OH), 5.19–5.10 (3H, m,
CHvCH2), 5.18 (1H, d, J¼17.9 Hz, CHvCH2), 5.00–
4.96 (1H, m, CHCH2Ph), 4.76–4.74 (1H, m, CHCH2
OAllyl), 4.61 (1H, dq, J¼6.8, 5.8 Hz, CHCH3), 4.36–4.31
(2H, m, CH(CH2)3N and CH2OH), 4.26–4.23 (1H,
m, CH(CH3)OAllyl), 4.19 (1H, dd, J¼9.8, 8.8 Hz,
CHCH(CH3)CH2CH3), 4.09–4.02 (2H, m, CHCH(CH3)
OAllyl and CH2OH), 3.76 (1H, dd, J¼9.3, 1.6 Hz, CH2
OAllyl), 3.69 (1H, dd, J¼14.0, 4.1 Hz, CH2Ph), 3.38 (1H,
dd, J¼9.3, 3.5 Hz, CH2OAllyl), 3.30–3.24 (2H, m, CH2N
and OH), 2.93 (1H, dd, J¼13.8, 11.7 Hz, CH2Ph), 2.86 (1H,
app t, J¼10.3 Hz, CH2N), 2.36–2.30 (1H, m, CH2), 1.89–
1.81 (2H, m, CH2 and CH(CH3)CH2CH3), 1.68–1.56 (3H,
m, CH2 and CH2CH3), 1.34 (3H, d, J¼7.1 Hz, CHCH3),
1.29 (3H, s, CH3), 1.26 (3H, s, CH3), 1.25 (3H, s, CH3), 1.22
(3H, d, J¼6.0 Hz, CH(CH3)OAllyl), 1.21 (3H, s, CH3),
1.19–1.11 (1H, m, CH2CH3), 1.01 (3H, d, J¼6.6 Hz,
CH(CH3)CH2CH3), 0.93 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (125 MHz, CDCl3) 201.5 (s), 172.2 (s), 171.6 (s), 170.7
(s), 170.3 (s), 169.8 (s), 168.9 (s), 143.1 (d), 142.7 (d), 137.0
(s), 129.1 (d), 128.9 (d), 127.4 (d), 115.3 (t), 114.6 (t), 76.2
(s), 75.9 (s), 66.8 (d), 64.0 (d), 62.8 (t), 62.4 (t), 61.0 (d),
60.8 (d), 59.0 (d), 57.8 (d), 53.8 (d), 48.8 (d), 46.6 (t), 41.4
(t), 36.0 (d), 31.6 (t), 27.0 (q), 25.8 (q), 25.8 (q), 24.9 (q),
24.7 (t), 21.9 (q), 21.4 (t), 16.4 (q), 15.4 (q), 11.3 (q); m/z
(ES) 878.4479 ([MþNa]þ, C43H65N7O9SNa requires
878.4462).
CHCH2OAllyl), 4.00 (1H, dq, J¼6.5, 5.2 Hz, CH(CH3)
OAllyl), 3.91 (1H, dd, J¼9.3, 2.3 Hz, CH2OAllyl), 3.67
(1H, dd, J¼11.4, 9.5 Hz, CH2S), 3.62 (1H, app t, J¼
11.3 Hz, CH2S), 3.51 (1H, dd, J¼9.3, 3.4 Hz, CH2OAllyl),
3.47–3.35 (2H, m, CH2N), 3.22 (1H, dd, J¼14.0, 5.4 Hz,
CH2Ph), 2.95 (1H, dd, J¼14.1, 5.8 Hz, CH2Ph), 2.59–2.55
(1H, m, CH2), 2.46–2.40 (1H, m, CH(CH3)CH2CH3),
2.01–1.84 (2H, m, CH2), 1.68–1.60 (1H, m, CH2), 1.51
(3H, s, CH3), 1.42 (3H, s, CH3), 1.36–1.26 (2H, m,
CH2CH3), 1.29 (3H, s, CH3), 1.26 (6H, s, CHCH3 and CH3),
1.19 (3H, d, J¼6.7 Hz, CH(CH3)OAllyl), 0.97 (3H, d,
J¼6.2 Hz, CH(CH3)CH2CH3), 0.95 (3H, app t, J¼6.4 Hz,
CH2CH3); dC (100 MHz, CDCl3) 172.6 (s), 171.8 (s), 170.7
(s), 170.4 (s), 170.3 (s), 169.8 (s), 169.2 (s), 142.7 (d), 142.2
(d), 136.4 (s), 129.6 (d), 128.2 (d), 126.8 (d), 115.8 (t), 115.1
(t), 77.9 (s), 77.8 (d), 76.0 (s), 67.3 (d), 62.0 (t), 59.7 (d),
57.6 (d), 56.4 (d), 56.1 (d), 53.6 (d), 47.8 (d), 47.3 (t), 40.5
(t), 36.5 (d), 35.8 (t), 29.8 (t), 27.4 (q), 25.9 (q), 25.7 (q),
25.5 (q), 25.2 (t), 23.9 (t), 18.9 (q), 18.4 (q), 16.2 (q), 12.2
(q); m/z (ES) 860.4321 ([MþNa]þ, C43H63N7O8SNa
requires 860.4357).
4.1.20. Trunkamide A (1a). Pyridine (48 ml, 0.59 mmol)
was added to a solution of epi-trunkamide A 1b (10 mg,
0.012 mmol) in methanol (0.1 ml) at room temperature. The
solution was heated to 508C, stood at this temperature for 9
days and then evaporated in vacuo. The residue was purified
by chromatography on silica using 30:1 chloroform/metha-
nol as eluent and then by HPLC using 25% isopropanol in
hexane as eluent† to give trunkamide A (3 mg, 32%) as a
viscous oil; [a]D23¼221 (c 0.26, CHCl3) (lit.6a [a]D¼223.1
(c 0.06, CHCl3));‡ dH (360 MHz, CDCl3) 7.97 (1H, d,
J¼6.4 Hz, NHCHCH(CH3)OAllyl), 7.56 (1H, d, J¼7.8 Hz,
NHCHCH2OAllyl), 7.29–7.21 (4H, m, Ph-H and
NHCHCH2Ph), 7.17 (1H, d, J¼7.7 Hz, NHCHCH3),
7.15–7.12 (2H, m, Ph-H), 6.32 (1H, d, J¼9.6 Hz,
NHCHCH(CH3)CH2CH3), 5.93 (1H, dd, J¼17.6, 10.8 Hz,
CHvCH2), 5.75 (1H, dd, J¼17.6, 10.9 Hz, CHvCH2),
5.28 (1H, dd, J¼17.5, 0.6 Hz, CHvCH2), 5.25 (1H, dd,
J¼10.8, 0.7 Hz, CHvCH2), 5.17–5.11 (1H, masked ddd,
CHCH2Ph), 5.16 (1H, dd, J¼10.9, 0.9 Hz, CHvCH2), 5.12
(1H, dd, J¼17.5, 0.9 Hz, CHvCH2), 4.93 (1H, app t,
J¼9.6 Hz, CHCH2S), 4.63–4.56 (3H, m, CHCH(CH3)CH2
CH3, CHCH2OAllyl and CHCH(CH3)OAllyl), 4.51 (1H,
dq, J¼6.5, 5.7 Hz, CHCH3), 4.39 (1H, app t, J¼6.0 Hz,
CH(CH2)3N), 4.04 (1H, dq, J¼6.5, 5.1 Hz, CH(CH3)
OAllyl), 3.91 (1H, dd, J¼9.1, 2.1 Hz, CH2OAllyl), 3.73
(1H, dd, J¼11.3, 9.7 Hz, CH2S), 3.64 (1H, dd, J¼11.2,
9.7 Hz, CH2S), 3.55–3.49 (2H, m, CH2N), 3.46 (1H, dd,
J¼9.1, 3.2 Hz, CH2OAllyl), 3.25 (1H, dd, J¼13.9, 5.7 Hz,
CH2Ph), 2.95 (1H, dd, J¼14.0, 5.9 Hz, CH2Ph), 2.40–2.33
(1H, m, CH(CH3)CH2CH3), 2.27–2.22 (1H, m, CH2),
1.96–1.87 (3H, m, CH2), 1.49 (3H, s, CH3), 1.39 (3H, s,
CH3), 1.35–1.18 (2H, m, CH2CH3), 1.27 (3H, s, CH3), 1.25
(3H, s, CH3), 1.22 (3H, d, J¼6.6 Hz, CHCH3), 1.07 (3H, d,
J¼6.5 Hz, CH(CH3)OAllyl), 0.96 (3H, d, J¼6.9 Hz,
CH(CH3)CH2CH3), 0.94 (3H, app t, J¼7.4 Hz, CH2CH3);
4.1.19. C45 epi-Trunkamide A (1b).6a Diethylaminosulfur
trifluoride (9.6 ml, 0.073 mmol) was added dropwise over
1 min to a stirred solution of the thioamide cyclopeptide 4
(28 mg, 0.033 mmol) in dichloromethane (0.5 ml) at 2158C
under an atmosphere of nitrogen. The solution was stirred at
2158C for 1 h, then quenched with saturated aqueous
sodium bicarbonate solution (1 ml) and warmed to room
temperature. The layers were separated, the aqueous layer
was extracted with dichloromethane (6£0.5 ml), and the
combined organic extracts were then dried and evaporated
in vacuo. The residue was purified by chromatography on
silica using 30:1 chloroform/methanol as eluent to give epi-
trunkamide A (20 mg, 72%) as a viscous oil; [a]2D4¼210
(c 0.50, CHCl3) (lit.6a [a]D22¼210.4 (c 0.5, CHCl3)); dH
(400 MHz, CDCl3) 8.45 (1H, d, J¼7.1 Hz, NHCHCH2Ph),
8.17 (1H, d, J¼7.1 Hz, NHCHCH(CH3)OAllyl), 7.56 (1H,
d, J¼7.0 Hz, NHCHCH2OAllyl), 7.30 (1H, d, J¼5.5 Hz,
NHCHCH3), 7.18–7.14 (3H, m, Ph-H), 7.12–7.07 (2H, m,
Ph-H), 6.26 (1H, d, J¼10.0 Hz, NHCHCH(CH3)CH2CH3),
5.96 (1H, dd, J¼17.6, 10.8 Hz, CHvCH2), 5.76 (1H, dd,
J¼17.6, 10.9 Hz, CHvCH2), 5.32 (1H, dd, J¼17.5, 0.4 Hz,
CHvCH2), 5.30 (1H, dd, J¼10.8, 0.7 Hz, CHvCH2), 5.17
(1H, dd, J¼10.8, 0.9 Hz, CHvCH2), 5.14 (1H, dd, J¼17.5,
0.9 Hz, CHvCH2), 5.07–4.97 (2H, m, CHCH2S and
CHCH2Ph), 4.85 (1H, app d, J¼7.5 Hz, CH(CH2)3N),
4.68–4.58 (1H, masked dq, CHCH3), 4.67 (1H, dd, J¼10.0,
3.2 Hz, CHCH(CH3)CH2CH3), 4.61 (1H, dd, J¼6.8, 5.5 Hz,
CHCH(CH3)OAllyl), 4.47 (1H, app dt, J¼6.5, 2.9 Hz,
†
HPLC separation was performed on an Agilent 1100 LC system using a
Hichrom Nucleosil 100-5 ID silica column (4.6 mm£25 cm). Mobile
phase: 25% IPA in hexane; detection: UV 254 nm; flow rate: 1 ml/min;
retention time: 8 min (trunkamide A), 30 min (C45 epi-trunkamide A).
In the original report the [a]D for natural trunkamide A was erroneously
given as [a]D¼2231 (c 0.06, CHCl3).3
‡

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2713–2727
2727
(b) Cava, M. P.; Levinson, M. I. Tetrahedron 1985, 41, 5061.
dC (100 MHz, CDCl3) 173.3 (s), 171.1 (s), 170.9 (s), 170.6
(s), 170.2 (s), 170.1 (s), 168.7 (s), 142.7 (d), 142.1 (d), 135.7
(s), 129.7 (d), 128.4 (d), 127.2 (d), 115.8 (t), 115.0 (t), 78.2
(d), 77.9 (s), 76.0 (s), 67.3 (d), 62.3 (t), 60.0 (d), 57.9 (d),
56.5 (d), 55.4 (d), 52.8 (d), 47.8 (d), 47.1 (t), 39.9 (t), 36.5
(d), 36.4 (t), 28.6 (t), 27.4 (q), 25.8 (q), 25.8 (q), 25.7 (q),
25.6 (t), 23.8 (t), 18.6 (q), 18.1 (q), 16.1 (q), 12.0 (q); m/z
(ES) 860.4320 ([MþNa]þ, C43H63N7O8SNa requires
860.4357).
´
(c) Lajoie, G.; Lepine, F.; Maziak, L.; Belleau, B. Tetrahedron
Lett. 1983, 24, 3815. (d) Clausen, K.; Thorsen, M.; Lawesson,
S.-O. Tetrahedron 1981, 37, 3635.
10. See preceding paper for details of the preparation of this
compound; McKeever, B.; Pattenden, G. Tetrahedron 2003,
59, 2701.
11. Dong, Q.; Anderson, C. E.; Ciufolini, M. A. Tetrahedron Lett.
1995, 36, 5681.
12. (a) Boden, C. D. J.; Pattenden, G.; Ye, T. Synlett 1995, 417.
(b) Wipf, P.; Fritch, P. C. Tetrahedron Lett. 1994, 35, 5397.
(c) Yonetani, K.; Hirotsu, Y.; Shiba, T. Bull. Chem. Soc. Jpn
1975, 48, 3302. (d) Hirotsu, Y.; Shiba, T.; Kaneko, T. Bull.
Chem. Soc. Jpn 1970, 43, 1870. (e) Konigsberg, W.; Hill, R. J.;
Craig, L. C. J. Org. Chem. 1961, 26, 3867.
Acknowledgements
We thank Dr P. Bradley and Dr M. Norley for their interest
in this work and Knoll Pharmaceuticals for their support via
a research scholarship (to B. M.). We also thank Professor
B. F. Bowden and Professor P. Wipf for their helpful
correspondence.
13. Wipf, P.; Miller, C. P. Tetrahedron Lett. 1992, 33, 6267 (see
also Ref. 12b).
14. Shioiri, T.; Ninomiya, K.; Yamada, S. J. Am. Chem. Soc. 1972,
94, 6203.
15. Abdel-Magid, A. F.; Cohen, J. H.; Maryanoff, C. A.; Shah,
R. D.; Villani, F. J.; Zhang, F. Tetrahedron Lett. 1998, 39,
3391.
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