Total synthesis of the cytotoxic cyclopeptide mollamide, isolated from the sea squirt Didemnum molle

Article abstract of DOI:10.1016/S0040-4020(03)00293-X

Full details of a total synthesis of the novel reverse prenyl substituted cyclic peptide mollamide, isolated from the ascidian Didemnum molle, are described.

Full text of DOI:10.1016/S0040-4020(03)00293-X

Tetrahedron 59 (2003) 2701–2712
Total synthesis of the cytotoxic cyclopeptide mollamide,
isolated from the sea squirt Didemnum molle
*
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 novel reverse prenyl substituted cyclic peptide mollamide, isolated from the ascidian
Didemnum molle, are described. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
The marine environment has been a hugely important source
of structurally novel and biologically important natural
products for more than thirty years now.1 Among these
metabolites are the fascinating family of heterocycle-
containing cyclopeptides which have been isolated mainly
from ascidians (sea squirts), with much current interest
focusing on those isolated from the genus Lissoclinum.2 The
structures of these cyclopeptides are characterised by the
presence of highly modified amino acid residues present in
the form of thiazole, oxazole, thiazoline and oxazoline
moieties, e.g. lissoclinamide 4 1 and cyclodidemnamide 2.3
Mollamide 3 is a member of a rarer family of cyclopeptides
where the structure has been modified by inclusion of a
reverse prenyl unit associated as a serine ether residue. The
cyclopeptide has been isolated from the ascidian Didemnum
molle, and it is related to a group of about ten similar natural
products, including the doubly prenylated compound
trunkamide A 4.4,5 Like a number of these cyclopeptides,
mollamide displays moderate cytotoxicity against a range of
cell lines, with IC50 values of 1 mg/ml against P388 (murine
leukaemia) and 2.5 mg/ml against A549 (human lung
carcinoma), HT29 (human colon carcinoma) and CV1
(monkey kidney fibroblast) cells. Mollamide also inhibits
RNA synthesis with an IC50 of approximately 1 mg/ml. Its
unusual structure and interesting biological properties
2. Results and discussion
combined to make the compound a challenging synthetic
The structure of mollamide 3 was determined following
target and in this paper we report the full details of our
extensive NMR and degradation studies and ultimately by
synthesis of mollamide 3.6
X-ray crystallography. It includes a thiazoline ring,
characteristic of other cyclopeptides, e.g. lissoclinamide 4
1 and cyclodidemnamide 2, whose synthesis we have
described earlier.7,8 With due cognisance to the ease with
which thiazoline-based amino acids undergo racemisation
during synthesis and handling, we decided to follow the
successful synthetic strategy we developed for these related
cyclopeptide structures and elaborate the thiazoline unit in
Keywords: cyclopeptide; Didemnum molle; ascidians.
*
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)00293-X

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B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
Scheme 1.
mollamide from the thioamide-based cyclopeptide 5
(Scheme 1).9 This cyclopeptide, in turn, could be produced
from the heptapeptide 6 by macrolactamisation involving
the L-isoleucine/L-proline amide bond. We were
encouraged to choose this particular amide bond for
macrocyclisation due to the known resistance of carboxyl-
activated proline residues to base-catalysed epimerisation
during coupling reactions.
excellent 96% yield. Removal of the Boc protecting group
from 8 and a subsequent coupling with Boc-L-serine next
gave the tripeptide 9, which was then elaborated to the
tetrapeptide 10 using the thioacylating agent 15, prepared
using the method described by Rapoport et al. (Scheme 3).10
Hence, coupling of Boc-L-proline 12 with 4-nitro-1,2-
phenylenediamine gave the anilide 13 in 81% yield which,
on subsequent thionation led to the thioanilide 14. Reaction
of this compound with sodium nitrite under diazotisation
conditions next gave 15. After removal of the Boc group
from the tripeptide 9, reaction with 15 gave the tetrapeptide
10 and the synthesis of the pentapeptide 11 was then
completed following removal of the Boc protection from 10
and a coupling with Boc-L-phenylalanine to give 11 in 84%
yield.
While alternative strategies were investigated, we ulti-
mately decided to synthesise the heptapeptide 6 in a linear
manner. The synthesis began with the construction of the
pentapeptide 11, which was prepared in seven steps starting
from L-proline methyl ester 7 (Scheme 2). Hence, coupling
of 7 with Boc-L-isoleucine first gave the dipeptide 8 in an
Scheme 2. Reagents: (i) DCC, HOBt, DIPEA, DCM, 08C!rt; (ii) AcCl, MeOH, rt; (iii) Et3N, DCM, 08C!rt, 74%.

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
2703
i
Scheme 3. Reagents: (i) 4-nitro-1,2-phenylenediamine, NMM, BuOCOCl, THF, 2208C!rt, 81%; (ii) P4S10, Na2CO3, THF, 08C!rt, 95%; (iii) NaNO2,
AcOH, 08C, 93%.
Scheme 4. Reagents: (i) Ph3CCl, Et3N, DCM, rt, 98%; (ii) MsCl, Et3N, THF, 08C!658C, 98%; (iii) (a) TFA, MeOH, DCM, 08C; (b) P-OSu, Et3N, rt;
(iv) 2-methyl-3-buten-2-ol, BF3·OEt2, DCM, rt; (v) 1.5 M LiOH, THF/MeOH, rt.
In order to synthesise the reverse prenylated amino acid 21,
we used a strategy based on extensive studies carried out
earlier by Okawa et al.11 These authors had developed a
method for the synthesis of optically active b-alkoxy amino
acids involving the Lewis acid-assisted ring opening of
activated aziridines with alcohols. Thus, our synthesis of 21
began with formation of the chiral aziridine 18 in two steps
from homochiral L-serine methyl ester 16 (Scheme 4).
Selective protection of the amino group in 16 as the trityl
derivative 17, followed by treatment of 17 with methane-
sulfonyl chloride in THF using the procedure of
Zwanenburg et al. first gave the aziridine 18 in essentially
quantitative yield.12
presence of boron trifluoride diethyl etherate, giving the
amino acids 20a and 20b in acceptable yields. Saponifica-
tion of the methyl ester in 20a and 20b finally led to the
corresponding carboxylic acids 21a and 21b, respectively.
Removal of the Boc protection in the pentapeptide 11,
followed by reaction of the resulting amine with the
carboxylic acids 21a and 21b, in the presence of 1-(3-
dimethylaminopropyl)-3-ethyl carbodiimide (EDC) and
HOBt coupling reagents, smoothly gave the hexapeptides
22a and 22b, respectively, in modest yields (Scheme 5).
Removal of the carbamate protecting group in 22 next gave
the corresponding free amine 23. At this stage in the
synthesis the TcBoc group offered significant advantages.
While the removal of the PNZ group in 22a proceeded
smoothly,13 the subsequent purification proved problematic
due to difficulties in separating the by-products of the
reaction†. In contrast, removal of the TcBoc protection from
22b, using the conditions described by Ciufolini et al. was
clean and efficient and gave the amine product in an
excellent 88% yield.14
In order to facilitate efficient aziridine ring opening in 18, it
was necessary to replace the trityl group with an electron
withdrawing group and a protecting group had to be chosen
which could be removed under conditions which would
not affect the allyl ether group in any subsequent ring
opened product. Having investigated a number of alterna-
tives, we eventually identified two protecting groups, i.e. the
4-nitrobenzyloxycarbonyl (PNZ) and the 2,2,2-trichloro-
tert-butyloxycarbonyl (TcBoc) carbamate groups, as being
suitable for this purpose. The protecting group interconver-
sion 18!19 was achieved using a one-pot strategy in order
to avoid the isolation of the intermediate free aziridine,
which proved problematic in our hands. Hence, following
removal of the trityl protection from 18 using TFA,
basification with an excess of triethylamine and in situ
reprotection gave the aziridines 19a and 19b in 92 and 91%,
respectively. The ring opening of these aziridines was then
carried out by reaction with 2-methyl-3-buten-2-ol in the
The amine 23 was now coupled with Troc-protected
isoleucine, to give the heptapeptide 24. As with the PNZ
and TcBoc protecting groups used earlier, the Troc group
was chosen as protection for this residue due to the
possibility of removing it under conditions which would
†
In our initial studies we had made use of the PNZ protecting group, and
the synthesis was continued with the crude amine.6 Removal of the by-
products was only achieved on completion of the synthesis of mollamide
following preparative HPLC separation.

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B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
Scheme 5. Reagents: (i) AcCl, MeOH, rt; (ii) DIPEA, EDC, HOBt, DCM, 08C!rt; (iii) Zn, pH 6 phosphate buffer/THF (3:1), rt; (iv) Cd/Pb, 1 M
NH4OAc/THF (1:1), rt, 88%; (v) Troc-L-Ile, EDC, HOBt, DCM, 08C!rt, 78%.
Scheme 6. Reagents: (i) Cd/Pb, 1 M NH4OAc/THF (1:1), rt, 96%; (ii) TBAH, THF, 08C; (iii) DPPA, DIPEA, DMF, 258C!rt 52% (2 steps); (iv) DAST,
DCM, 2158C, 74%.

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
2705
not simultaneously affect the allyl ether residue. Removal of
the Troc group in 24,14 followed by saponification of the
methyl ester group using tetrabutylammonium hydroxide
(TBAH)15 and macrocyclisation using diphenylphosphoryl
azide (DPPA)16 next gave the macrocycle 5 (Scheme 6).
Finally, cyclodehydration of the b-hydroxy thioamide unit
in 5 to the corresponding thiazoline, in the presence of
diethylaminosulfur trifluoride (DAST)17 completed the total
deuterated solvent as internal standard. The following
abbreviations are used for designation of multiplicities: s,
singlet; d, doublet; t, triplet; q, quartet; dt, double triplet; dq,
double quartet; m, multiplet; app, apparent; br, broad. All
coupling constants, J, are recorded in Hertz (Hz) and are
uncorrected from peak printouts. 13C NMR spectra were
recorded on either a Bruker DPX 360 (90 MHz), a Bruker
AV 400 (100 MHz) or a Bruker DRX 500 (125 MHz) as
dilute solutions in deuterated solvents, as specified, on a
broad band decoupled mode, and the multiplicities deter-
mined using a DEPT sequence. Chemical shifts are quoted
in ppm on the d scale and are recorded relative to TMS or
residual non-deuterated solvent as internal standard. The
following abbreviations are used to denote multiplicities: s,
quaternary; d, tertiary methine; t, secondary methylene; q,
primary methyl. Mass spectra were recorded either on a VG
Autospec, MM-701CF, a VG Micromass 70E or a
Micromass LCT spectrometer using fast atom bombardment
(FAB) or electrospray (ES) techniques. Due to the soft
nature of these techniques, little fragmentation of the
compounds occurred and hence nominal mass and frag-
mentation data have not been included.
1
synthesis of mollamide 3. Comparison of the H and 13C
NMR spectra as well as [a]D measurement for our synthetic
material, with those reported for natural mollamide isolated
from D. molle showed the compounds to be identical.
3. Conclusion
In summary, we have achieved a synthesis of mollamide and
simultaneously demonstrated a method for the construction
of this important class of marine cyclopeptides. In addition,
we have further illustrated a concise method for the
incorporation of sensitive chiral thiazoline heterocycles
into complex natural products.
4.1.1. Boc-Ile-Pro-OMe (8).18 Diisopropylethylamine
(7.3 ml, 42 mmol) was added dropwise over 5 min to a
stirred solution of L-proline methyl ester hydrochloride 7
(2.00 g, 12.1 mmol) in dichloromethane (20 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 20 min and then Boc-L-isoleucine (2.79 g,
12.1 mmol) in dichloromethane (10 ml) was added drop-
wise over 10 min by cannula, followed by 1-hydroxybenzo-
triazole (1.79 g, 13.3 mmol) in one portion. The suspension
was stirred at 08C for a further 15 min and then
dicyclohexylcarbodiimide (2.74 g, 13.3 mmol) in dichloro-
methane (15 ml) was added dropwise over 10 min by
cannula. The mixture was allowed to warm to room
temperature over the course of 18 h, filtered, and then
evaporated in vacuo. The residue was taken up in ethyl
acetate (20 ml), filtered, and the filtrate was then 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 33% ethyl acetate in light petroleum (40–608C)
as eluent to give the dipeptide (3.97 g, 96%) as a pale yellow
oil; [a]2D4¼266 (c 1.16, CHCl3) (Lit.,18 [a]2D5¼287.2 (c
0.22, MeOH)); Found %: C, 59.9; H, 8.9; N, 8.0; Calcd for
C17H30N2O5 %: C, 59.6; H, 8.8; N, 8.2; nmax (CHCl3)/cm21
3437, 2966, 2934, 2878, 1744, 1704, 1644, 1495, 1455,
1392, 1368, 1318, 1156, 1090, 1045, 1022, 883; dH
(500 MHz, CDCl3) 5.14 (1H, d, J¼9.4 Hz, NHBoc), 4.53
(1H, dd, J¼8.6, 4.9 Hz, CHCO2Me), 4.29 (1H, dd, J¼9.3,
7.4 Hz, CHNHBoc), 3.84–3.80 (1H, m, CH2N), 3.72 (3H, s,
OCH3), 3.68–3.64 (1H, m, CH2N), 2.26–2.20 (1H, m,
CH2CHCO2Me), 2.07–1.95 (3H, m, CH2), 1.79–1.72 (1H,
m, CHCH3), 1.63–1.55 (1H, m, CH2CH3), 1.42 (9H, s,
C(CH3)3), 1.18–1.09 (1H, m, CH2CH3), 1.01 (3H, d,
J¼6.8 Hz, CHCH3), 0.91 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (90 MHz, CDCl3) 172.5 (s), 171.5 (s), 155.8 (s), 79.6 (s),
58.9 (d), 56.3 (d), 52.2 (q), 47.3 (t), 38.0 (d), 29.1 (t), 28.4
(q), 25.0 (t), 24.2 (t), 15.3 (q), 11.3 (q); m/z (FAB) 343.2233
([MþH]þ, C17H31N2O5 requires 343.2233).
4. Experimental
4.1. General details
Reactions were carried out under an atmosphere of nitrogen
or argon, otherwise, where specified, in air. Reactions
requiring anhydrous conditions were performed in flame-
dried apparatus. Organic solvents were routinely dried and
stored under a nitrogen atmosphere prior to use. Benzene,
diethyl ether and toluene solvents were dried over sodium
wire. Other organic solvents were dried by distillation as
follows: THF (sodium benzophenone ketyl), dichloro-
methane (calcium hydride) and methanol (magnesium).
Other organic solvents and reagents were purified according
to accepted literature procedures. Organic extracts were
dried over anhydrous magnesium or sodium sulphate and
then filtered under gravity. Solvents were removed under
reduced pressure on a Bu¨chi rotary evaporator. All reactions
were monitored by TLC using Merck silica gel 60 F254 pre-
coated aluminium plates which were visualised with
ultraviolet light and then developed with either basic
potassium permanganate solution or ceric ammonium
molybdate solution. Flash chromatography was performed
using Merck silica gel 60 as the stationary phase. All
¨
melting points were determined on a Reichert Kofler micro
hot-stage apparatus and are uncorrected. Specific rotations
were measured on a JASCO DIPA-370 polarimeter.
Solutions were prepared using spectroscopic grade solvents.
Microanalytical data were obtained on a Perkin–Elmer
240B elemental analyser. Infrared spectra were recorded on
a Perkin–Elmer 1600 series FT-IR instrument as dilute
solutions using spectroscopic grade solvents.
1H NMR spectra were recorded on either a Bruker DPX 360
(360 MHz), a Bruker AV 400 (400 MHz) or a Bruker DRX
500 (500 MHz) instrument as dilute solutions using
deuterated solvents as specified. Chemical shifts are quoted
in parts per million (ppm) on the d scale and are recorded
relative to tetramethylsilane (TMS) or residual non-

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B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
4.1.2. Boc-Ser-Ile-Pro-OMe (9). Acetyl chloride (15 ml)
was added dropwise over 10 min to a stirred solution of the
dipeptide 8 (6.17 g, 18.0 mmol) in methanol (150 ml) at 08C
under an atmosphere of nitrogen. The solution was warmed
to room temperature, stirred for 6 h and then evaporated in
vacuo to leave the corresponding hydrochloride salt (5.11 g)
as a cream solid, which was used without further
purification.
dropwise over 15 min by cannula. The solution was allowed
to warm to room temperature over the course of 23 h and
then evaporated in vacuo. The crude product was purified by
chromatography on silica using 20% light petroleum (40–
608C) in ethyl acetate as eluent to give the tetrapeptide
(1.69 g, 74%) as a cream foam; [a]2D0¼2149 (c 0.96,
CHCl3); nmax (CHCl3)/cm21 3325, 2967, 2879, 1743, 1694,
1635, 1497, 1456, 1368, 1321, 1157, 1127, 1100, 1055, 998,
972, 876; dH (360 MHz, d6-DMSO, 333 K) 9.41 (1H, d,
J¼7.3 Hz, NHCvS), 7.76 (1H, d, J¼8.4 Hz, NH), 5.01–
4.98 (1H, m, CHCH2OH), 4.76 (1H, app t, J¼5.4 Hz, OH),
4.59 (1H, dd, J¼8.6, 3.4 Hz, CHCvS), 4.46 (1H, app t,
J¼8.3 Hz, CHCH(CH3)CH2CH3), 4.32 (1H, dd, J¼8.5,
5.3 Hz, CHCO2Me), 3.79–3.69 (3H, m, CH2OH and
CH2N), 3.62 (3H, s, OCH3), 3.60–3.54 (1H, m, CH2N),
3.49–3.35 (2H, m, CH2N), 2.25–2.13 (2H, m, CH2CHCO2-
Me and CH2CHCvS), 1.99–1.72 (7H, m, CH2 and
CHCH3), 1.57–1.46 (1H, m, CH2CH3), 1.35 (9H, s,
C(CH3)3), 1.17–1.04 (1H, m, CH2CH3), 0.90 (3H, d,
J¼6.8 Hz, CHCH3), 0.84 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (90 MHz, d6-DMSO, 323 K) 204.9 (s), 171.8 (s), 169.5
(s), 168.1 (s), 153.2 (s), 78.6 (s), 66.6 (d), 60.4 (t), 59.6 (d),
58.3 (d), 54.3 (d), 51.4 (q), 46.8 (t), 46.6 (t), 36.2 (d), 33.2
(t), 28.4 (t), 27.8 (q), 24.3 (t), 23.7 (t), 22.7 (t), 14.7 (q), 10.6
(q); m/z (ES) 565.2697 ([MþNa]þ, C25H42N4O7SNa
requires 565.2672).
Diisopropylethylamine (11.2 ml, 64.2 mmol) was added
dropwise over 10 min to a stirred solution of the
hydrochloride salt (5.11 g, 18.3 mmol) in dichloromethane
(100 ml) at 08C under an atmosphere of nitrogen. The
solution was stirred at 08C for 15 min and then Boc-L-serine
(3.76 g, 18.3 mmol) and 1-hydroxybenzotriazole (2.72 g,
20.2 mmol) were added successively in one portion. The
suspension was stirred at 08C for a further 15 min and then
dicyclohexylcarbodiimide (4.16 g, 20.2 mmol) was added
in one portion. The mixture was allowed to warm to room
temperature over the course of 18 h, filtered, and then
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£50 ml) followed
by saturated aqueous sodium bicarbonate solution
(3£50 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% light petroleum (40–608C) in ethyl acetate
as eluent to give the tripeptide (4.23 g, 55%) as a colourless
foam; [a]3D0¼285 (c 1.02, CHCl3); nmax (CHCl3)/cm21
3432, 2968, 2935, 2879, 1743, 1704, 1644, 1489, 1455,
1393, 1368, 1319, 1158, 1097, 1056, 1001, 867; dH
(360 MHz, CDCl3) 6.94 (1H, d, J¼8.1 Hz, NH), 5.48 (1H,
d, J¼6.6 Hz, NHBoc), 4.56 (1H, dd, J¼8.4, 7.5 Hz,
CHCH(CH3)CH2CH3), 4.53 (1H, dd, J¼8.6, 4.8 Hz,
CHCO2Me), 4.19 (1H, m, CHCH2OH), 4.01–3.98 (1H, m,
CH2OH), 3.87–3.80 (1H, m, CH2N), 3.72 (3H, s, OCH3),
3.72–3.64 (1H, m, CH2N), 3.59 (1H, dd, J¼11.3, 6.1 Hz,
CH2OH), 2.29–2.20 (1H, m, CH2CHCO2Me), 2.10–1.94
(3H, m, CH2), 1.91–1.84 (1H, m, CHCH3), 1.63–1.53 (1H,
m, CH2CH3), 1.45 (9H, s, C(CH3)3), 1.20–1.07 (1H, m,
CH2CH3), 1.04 (3H, d, J¼6.8 Hz, CHCH3), 0.91 (3H, app t,
J¼7.4 Hz, CH2CH3); dC (90 MHz, CDCl3) 172.3 (s), 171.5
(s), 171.0 (s), 155.8 (s), 80.1 (s), 63.0 (t), 59.0 (d), 55.5 (d),
55.0 (d), 52.2 (q), 47.4 (t), 37.2 (d), 29.0 (t), 28.3 (q), 25.0
(t), 24.3 (t), 15.2 (q), 11.1 (q); m/z (FAB) 430.2544
([MþH]þ, C20H36N3O7 requires 430.2553).
4.1.4. Boc-Phe-Proc{(CvS)NH}-Ser-Ile-Pro-OMe (11).
Acetyl chloride (2.5 ml) was added dropwise over 2 min to a
stirred solution of the tetrapeptide 10 (1.58 g, 2.92 mmol) in
methanol (25 ml) at 08C under an atmosphere of nitrogen.
The solution was warmed to room temperature, stirred for
5.5 h and then evaporated in vacuo to leave the correspond-
ing hydrochloride salt (1.39 g) as a pale yellow foam, which
was used without further purification.
Diisopropylethylamine (1.8 ml, 10 mmol) was added drop-
wise over 2 min to a stirred solution of the hydrochloride
salt (1.39 g, 2.90 mmol) in dichloromethane (25 ml) at 08C
under an atmosphere of nitrogen. The solution was stirred at
08C for 15 min and then Boc-L-phenylalanine (0.77 g,
2.9 mmol) and 1-hydroxybenzotriazole (0.43 g, 3.2 mmol)
were added successively in one portion. The suspension was
stirred at 08C for a further 15 min and then dicyclohexyl-
carbodiimide (0.66 g, 3.2 mmol) was added in one portion.
The mixture was allowed to warm to room temperature over
the course of 45 h and then evaporated in vacuo to leave a
residue which was taken up in ethyl acetate (25 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 ethyl acetate as eluent to
give the pentapeptide (1.68 g, 84%) as a colourless foam;
[a]2D3¼2110 (c 1.04, CHCl3); Found %: C, 58.7; H, 7.4; N,
10.0; C34H51N5O8S requires %: C, 59.2; H, 7.45; N, 10.15;
nmax (CHCl3)/cm21 3429, 3349, 2970, 2879, 1744, 1704,
1644, 1493, 1454, 1393, 1368, 1321, 1159, 1058, 1000, 868;
dH (400 MHz, d6-DMSO, 343 K) 9.58 (1H, d, J¼7.1 Hz,
NHCvS), 7.64 (1H, d, J¼7.9 Hz, NH), 7.29–7.20 (5H, m,
Ph-H), 6.62 (1H, br s, NHBoc), 4.96 (1H, m, CHCH2OH),
4.89 (1H, m, CHCvS), 4.73 (1H, m, OH), 4.47–4.43 (1H,
4.1.3. Boc-Proc{(CvS)NH}-Ser-Ile-Pro-OMe (10).
Acetyl chloride (3 ml) was added dropwise over 5 min to
a stirred solution of the tripeptide 9 (1.72 g, 4.02 mmol) in
methanol (30 ml) at 08C under an atmosphere of nitrogen.
The solution was warmed to room temperature, stirred for
2.5 h and then evaporated in vacuo to leave the correspond-
ing hydrochloride salt (1.54 g) as a cream solid, which was
used without further purification.
Triethylamine (1.2 ml, 8.4 mmol) was added dropwise over
1 min to a stirred solution of the hydrochloride salt (1.54 g,
4.21 mmol) in dichloromethane (50 ml) at 08C under an
atmosphere of nitrogen. The solution was stirred at 08C for
15 min and then a solution of the thioacylating agent 15
(1.59 g, 4.21 mmol) in dichloromethane (20 ml) was added

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
2707
masked m, CHCH2Ph), 4.45 (1H, app t, J¼8.1 Hz,
CHCH(CH3)CH2CH3), 4.32 (1H, dd, J¼8.3, 5.2 Hz,
CHCO2Me), 3.77–3.73 (5H, m, CH2OH and CH2N), 3.62
(3H, s, OCH3), 3.59–3.53 (1H, m, CH2N), 3.13–3.02 (1H,
masked m, CH2Ph), 2.76–2.67 (1H, m, CH2Ph), 2.19–2.07
(2H, m, CH2CHCO2Me and CH2CHCvS), 1.97–1.78 (7H,
m, CH2 and CHCH3), 1.56–1.50 (1H, m, CH2CH3), 1.29
(9H, s, C(CH3)3), 1.16–1.07 (1H, m, CH2CH3), 0.91 (3H, d,
J¼6.8 Hz, CHCH3), 0.84 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (100 MHz, d6-DMSO, 333 K) 204.5 (s), 171.8 (s), 170.2
(s), 169.4 (s), 168.1 (s), 155.0 (s), 137.9 (s), 128.9 (d),
127.7 (d), 125.8 (d), 77.8 (s), 65.7 (d), 60.4 (t), 60.0 (d),
58.3 (d), 54.3 (d), 53.5 (d), 51.3 (q), 46.9 (t), 46.6 (t), 36.1
(d), 36.1 (t), 31.4 (t), 28.3 (t), 27.8 (q), 24.3 (t), 23.9 (t), 23.7
(t), 14.6 (q), 10.5 (q); m/z (ES) 712.3372 ([MþNa]þ,
C34H51N5O8SNa requires 712.3356).
in 2:1 ethyl acetate/hexane (20 ml) and washed with 5%
aqueous sodium bicarbonate solution (4£5 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 40% ethyl acetate in light petroleum (40–608C)
as eluent to give the thioanilide (495 mg, 95%) as a yellow
solid; mp 170–1738C (ethyl acetate/hexane); [a]2D1¼255 (c
0.65, DMSO); Found %: C, 52.3; H, 6.0; N, 15.0;
C16H22N4O4S requires %: C, 52.4; H, 6.05; N, 15.3; nmax
(DMSO)/cm21 3535, 3185, 1695, 1519, 1169, 831, 753; dH
(360 MHz, d6-DMSO, 343 K) 10.94 (1H, br s, NHCvS),
7.95 (1H, dd, J¼9.1, 2.6 Hz, Ar-H), 7.92 (1H, br s, Ar-H),
6.84 (1H, d, J¼9.0 Hz, Ar-H), 6.16 (2H, br s, NH2), 4.72
(1H, dd, J¼8.5, 4.6 Hz, CH), 3.60–3.53 (1H, m, CH2N),
3.48–3.42 (1H, m, CH2N), 2.40–2.30 (1H, m, CH2), 2.15–
2.03 (2H, m, CH2), 1.91–1.80 (1H, m, CH2), 1.43 (9H, s,
C(CH3)3); dC (125 MHz, d6-DMSO, 343 K) 206.9 (s), 153.7
(s), 150.2 (s), 135.5 (s), 124.3 (d), 122.3 (s), 113.7 (d), 78.9
(s), 67.0 (d), 46.8 (t), 32.9 (t), 27.8 (q), 23.2 (t); m/z (ES)
267.0893 ([(M2C5H8O2)þH]þ, C11H15N4O2S requires
267.0916).
4.1.5. Boc-proline 2-amino-5-nitroanilide (13). N-Methyl-
morpholine (5.1 ml, 46 mmol) was added dropwise over
5 min to a stirred solution of Boc-L-proline 12 (5.00 g,
23.2 mmol) in tetrahydrofuran (250 ml) at 2208C under an
atmosphere of nitrogen. The solution was stirred at 2208C
for 5 min, then isobutyl chloroformate (3.0 ml, 23 mmol)
was added dropwise over 5 min and the mixture was stirred
at 2208C for a further 10 min 4-nitro-1,2-phenylenediamine
(3.56 g, 23.2 mmol) was added portionwise over 5 min and
the mixture was stirred at 2208C for 2 h and then at room
temperature for 44 h. The solvent was removed in vacuo to
leave a residue which was taken up in ethyl acetate (250 ml)
and filtered. The filtrate was washed successively with 10%
aqueous citric acid solution (3£100 ml), saturated aqueous
sodium bicarbonate solution (3£100 ml) and brine
(2£50 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
crude product which was purified by recrystallisation with
ethyl acetate/hexane to give the anilide (6.53 g, 81%) as a
yellow solid; mp 200–2028C; [a]2D1¼270 (c 0.75, DMSO);
Found %: C, 54.95; H, 6.5; N, 15.8; C16H22N4O5 requires
%: C, 54.85; H, 6.3; N, 16.0; nmax (DMSO)/cm21 3567,
3355, 3198, 1704, 1595, 1548, 1240, 1174, 829, 776, 752;
dH (400 MHz, d6-DMSO, 353 K) 9.22 (1H, br s, NH), 8.19
(1H, br s, Ar-H), 7.85 (1H, dd, J¼9.0, 2.6 Hz, Ar-H), 6.81
(1H, d, J¼9.0 Hz, Ar-H), 6.17 (2H, br s, NH2), 4.30 (1H, dd,
J¼8.3, 4.3 Hz, CH), 3.49–3.36 (2H, m, CH2N), 2.24–2.21
(1H, m, CH2), 2.03–1.79 (3H, m, CH2), 1.41 (9H, s,
C(CH3)3); dC (100 MHz, d6-DMSO, ,1:1 mixture of
rotamers) 172.2 (s), 171.7 (s), 154.1 (s), 153.1 (s), 150.1
(s), 148.4 (s), 135.7 (s), 135.4 (s), 123.5 (d), 122.5 (d), 121.4
(s), 121.1 (s), 120.7 (d), 113.9 (d), 113.4 (d), 79.1 (s), 78.7
(s), 60.0 (d), 59.9 (d), 46.8 (t), 46.6 (t), 31.1 (t), 29.9 (t), 28.1
(q), 28.0 (q), 24.1 (t), 23.3 (t); m/z (ES) 373.1511
([MþNa]þ, C16H22N4O5Na requires 373.1488).
4.1.7. 1-(Boc-thionoprolinyl)-6-nitrobenzotriazole (15).
Sodium nitrite (57 mg, 0.82 mmol) was added in one
portion to a stirred solution of the thioanilide 14 (200 mg,
0.546 mmol) in glacial acetic acid (4 ml, diluted with 5%
water) at 08C. The solution was stirred at 08C for 30 min and
then ice water (50 ml) was added and the resulting
suspension was extracted with ethyl acetate (10 ml then
3£5 ml). The combined organic extracts were dried and
evaporated in vacuo to leave the nitrobenzotriazole
(192 mg, 93%) as an orange gum; [a]2D1¼215 (c 1.00,
CHCl3); nmax (CHCl3)/cm21 2978, 2884, 1688, 1601, 1542,
1455, 1394, 1368, 1350, 1264, 1158, 1129, 1075, 1056, 983,
955, 908, 894, 875, 834; dH (360 MHz, CDCl3, mixture of
rotamers) major rotamer: 9.72 (1H, dd, J¼2.1, 0.5 Hz, Ar-
H), 8.44 (1H, dd, J¼8.9, 2.1 Hz, Ar-H), 8.29 (1H, dd,
J¼8.9, 0.5 Hz, Ar-H), 6.21 (1H, dd, J¼9.0, 3.2 Hz, CH),
3.78–3.60 (2H, m, CH2N), 2.70–2.59 (1H, m, CH2), 2.17–
1.98 (3H, m, CH2), 1.49 (9H, s, C(CH3)3); minor rotamer:
9.74 (1H, dd, J¼2.1, 0.4 Hz, Ar-H), 8.48 (1H, dd, J¼9.0,
2.1 Hz, Ar-H), 8.35 (1H, d, J¼8.8 Hz, Ar-H), 6.24 (1H, dd,
J¼8.3, 3.1 Hz, CH), 3.78–3.60 (2H, m, CH2N), 2.70–2.59
(1H, m, CH2), 2.17–1.98 (3H, m, CH2), 1.25 (9H, s,
C(CH3)3); dC (100 MHz, CDCl3, mixture of rotamers) 209.6
(s), 208.1 (s), 154.4 (s), 153.5 (s), 149.7 (s), 149.5 (s), 148.8
(s), 132.2 (s), 132.0 (s), 122.2 (d), 122.0 (d), 121.6 (d), 121.3
(d), 113.1 (d), 112.9 (d), 80.4 (s), 67.9 (d), 67.7 (d), 47.3 (t),
47.0 (t), 34.6 (t), 33.6 (t), 28.6 (q), 28.3 (q), 23.9 (t), 23.2 (t),
which was used without further purification.
4.1.8. Tr-Ser-OMe (17).19a Triethylamine (8.9 ml,
64 mmol) was added dropwise over 10 min to a stirred
suspension of serine methyl ester hydrochloride 16 (5.00 g,
32.1 mmol) in dichloromethane (100 ml) at room tempera-
ture under an atmosphere of nitrogen. On dissolution, the
solution was cooled to 08C and then triphenylmethyl
chloride (8.96 g, 32.1 mmol) was added portionwise over
10 min. The suspension was warmed to room temperature,
stirred for 21 h and then washed with 10% aqueous citric
acid solution (3£20 ml) and water (2£20 ml), with back-
washing. The combined organic extracts were dried and
4.1.6. Boc-proline 2-amino-5-nitrothioanilide (14). Phos-
phorus pentasulfide (318 mg, 0.714 mmol) was added in one
portion to a stirred suspension of sodium carbonate (76 mg,
0.71 mmol) in tetrahydrofuran (25 ml) at room temperature
under an atmosphere of nitrogen and the mixture was stirred
at room temperature for 1 h. The solution was cooled to 08C,
then the anilide 13 (500 mg, 1.43 mmol) was added in one
portion and the mixture was stirred at 08C for 30 min and
then at room temperature for 2.5 h. The solvent was
removed in vacuo to leave a residue which was taken up

2708
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
evaporated in vacuo to leave trityl serine methyl ester
(11.69 g) as a cream solid; dH (360 MHz, CDCl3) 7.50–7.46
(6H, m, Ph-H), 7.29–7.16 (9H, m, Ph-H), 3.71 (1H, dd,
J¼10.2, 4.1 Hz, CH2OH), 3.59–3.51 (2H, m, CHCO2Me
and CH2OH), 3.29 (3H, s, OCH3); dC (90 MHz, CDCl3)
174.0 (s), 145.6 (s), 128.8 (d), 128.0 (d), 126.7 (d), 71.0 (s),
65.0 (t), 57.8 (d), 52.0 (q); m/z (ES) 384.1563 ([MþNa]þ,
C23H23NO3Na requires 384.1576), which was used without
further purification.
4.1.11. (2S)-Methyl 1-(2,2,2-trichloro-1,1-dimethyl-
ethoxycarbonyl)aziridine-2-carboxylate (19b). Trifluoro-
acetic acid (0.55 ml, 7.2 mmol) was added dropwise over
1 min to a stirred solution of the aziridine 18 (1.23 g,
3.58 mmol) in dichloromethane (20 ml) and methanol
(0.15 ml, 3.6 mmol) at 08C under an atmosphere of nitrogen.
The solution was stirred at 08C for 30 min and then
triethylamine (2.5 ml, 18 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-dimethylethyl
carbonate20 (1.25 g, 3.94 mmol) in dichloromethane (5 ml)
was added over 5 min by cannula. The solution was warmed
to room temperature, stirred for 15 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
(0.90 g, 83%) as a pale yellow oil; [a]1D6¼241 (c 0.57,
CHCl3); nmax (CHCl3)/cm21 2955, 1747, 1458, 1388, 1372,
1329, 1154, 1112, 1087, 1022, 971, 901, 876, 838; dH
(400 MHz, CDCl3) 3.78 (3H, s, OCH3), 3.14 (1H, dd,
J¼5.1, 3.1 Hz, CH), 2.63 (1H, dd, J¼3.2, 1.4 Hz, CH2), 2.47
(1H, dd, J¼5.1, 1.4 Hz, CH2), 1.96 (3H, s, CH3), 1.91 (3H,
s, CH3); dC (100 MHz, CDCl3) 168.6 (s), 157.9 (s), 106.0
(s), 89.7 (s), 52.8 (q), 35.0 (d), 31.5 (t), 21.3 (q), 21.1 (q);
m/z (FAB) 303.9934 ([MþH]þ, C9H13NO4Cl3 requires
303.9910).
4.1.9. (2S)-Methyl 1-tritylaziridine-2-carboxylate (18).12,19
Triethylamine (9.7 ml, 70 mmol) was added dropwise over
10 min to a stirred solution of trityl serine methyl ester 17
(11.48 g, 31.80 mmol) in tetrahydrofuran (85 ml) at 08C
under an atmosphere of nitrogen. Methanesulfonyl chloride
(2.5 ml, 32 mmol) was added dropwise at 08C over 2 min
and the solution was stirred at 08C for a further 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 (60 ml)
and washed with 10% aqueous citric acid solution
(3£20 ml) followed by saturated aqueous sodium bicarbon-
ate solution (2£20 ml), with backwashing. The combined
organic extracts were dried and evaporated in vacuo to leave
the aziridine (10.60 g, 97%) as a cream solid; mp 116–
1188C; dH (360 MHz, CDCl3) 7.51–7.46 (6H, m, Ph-H),
7.29–7.18 (9H, m, Ph-H), 3.74 (3H, s, OCH3), 2.25 (1H, dd,
J¼2.6, 1.6 Hz, CH2), 1.89 (1H, dd, J¼6.2, 2.7 Hz, CH), 1.41
(1H, dd, J¼6.2, 1.6 Hz, CH2); dC (90 MHz, CDCl3) 172.0
(s), 143.7 (s), 129.4 (d), 127.7 (d), 127.0 (d), 74.5 (s), 52.2
(q), 31.8 (d), 28.8 (t); m/z (ES) 366.1460 ([MþNa]þ,
C23H21NO2Na requires 366.1470), which was used without
further purification.
4.1.12. PNZ-Ser(dimethylallyl)-OMe (20a). Boron tri-
fluoride diethyl etherate (10 drops) was added to a stirred
solution of the aziridine 19a (502 mg, 1.79 mmol) in
dichloromethane (5 ml) and 2-methyl-3-buten-2-ol (10 ml)
at room temperature under an atmosphere of argon. The
solution was stirred at room temperature for five days, then
diluted with dichloromethane (20 ml) and washed with
water (3£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% diethyl ether in light petroleum (40–608C)
as eluent to give the allyl ether (492 mg, 75%) as a pale
yellow oil; [a]D23¼þ13 (c 1.79, CHCl3); nmax (CHCl3)/cm21
3437, 2979, 2954, 2882, 1732, 1609, 1556, 1495, 1457,
1379, 1349, 1146, 1077, 1016, 985, 895, 862, 842; dH
(500 MHz, CDCl3) 8.23 (2H, d, J¼8.7 Hz, Ar-H), 7.54 (2H,
d, J¼8.6 Hz, Ar-H), 5.72 (1H, dd, J¼17.9, 10.5 Hz, CH–
CH2), 5.71–5.69 (1H, masked d, NH), 5.25 (1H, d,
J¼13.5 Hz, Ar-CH2), 5.21 (1H, d, J¼13.4 Hz, Ar-CH2),
5.13–5.09 (2H, m, CHvCH2), 4.44 (1H, app dt, J¼8.9,
3.0 Hz, CHCO2Me), 3.77 (3H, s, OCH3), 3.77–3.75 (1H,
masked dd, CH2), 3.55 (1H, dd, J¼9.3, 3.2 Hz, CH2), 1.23
(3H, s, CH3), 1.22 (3H, s, CH3); dC (125 MHz, CDCl3)
171.0 (s), 155.7 (s), 147.7 (s), 143.9 (s), 143.0 (d), 128.1 (d),
123.8 (d), 114.5 (t), 75.7 (s), 65.5 (t), 62.7 (t), 54.7 (d), 52.5
(q), 25.6 (q), 25.5 (q); m/z (FAB) 367.1512 ([MþH]þ,
C17H23N2O7 requires 367.1505).
4.1.10. 2(S)-Methyl 1-(4-nitrobenzyloxycarbonyl)aziri-
dine-2-carboxylate (19a). Trifluoroacetic acid (0.45 ml,
5.8 mmol) was added dropwise over 1 min to a stirred
solution of the aziridine 18 (1.00 g, 2.92 mmol) in
dichloromethane (30 ml) and methanol (0.12 ml,
2.9 mmol) at 08C under an atmosphere of nitrogen. The
solution was stirred at 08C for 30 min and then triethylamine
(2.0 ml, 15 mmol) was added dropwise over 2 min. The
mixture was stirred at 08C for a further 5 min and then
succinimidyl 4-nitrobenzyl carbonate20 (0.86 g, 2.9 mmol)
was added in one portion. The solution was warmed to room
temperature, stirred for 24 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 1%
acetone in chloroform as eluent to give the PNZ aziridine
(0.75 g, 92%) as a cream solid; mp 70–728C (chloroform);
[a]2D1¼231 (c 0.90, CHCl3); nmax (CHCl3)/cm21 2956,
1748, 1609, 1530, 1496, 1456, 1393, 1378, 1350, 1323,
1170, 1140, 1112, 1089, 1044, 981, 860; dH (500 MHz,
CDCl3) 8.20 (2H, d, J¼8.8 Hz, Ar-H), 7.52 (2H, d,
J¼8.8 Hz, Ar-H), 5.25 (1H, d, J¼13.3 Hz, Ar-CH2),
5.20 (1H, d, J¼13.3 Hz, Ar-CH2), 3.74 (3H, s, OCH3),
3.15 (1H, dd, J¼5.2, 3.2 Hz, CH), 2.61 (1H, dd, J¼3.2,
1.2 Hz, CH2), 2.51 (1H, dd, J¼5.3, 1.3 Hz, CH2); dC
(125 MHz, CDCl3) 168.6 (s), 160.3 (s), 147.8 (s), 142.7 (s),
128.5 (d), 123.8 (d), 66.9 (t), 52.8 (q), 34.9 (d), 31.5 (t); m/z
(FAB) 281.0770 ([MþH]þ, C12H13N2O6 requires
281.0774).
4.1.13. TcBoc-Ser(dimethylallyl)-OMe (20b). Boron tri-
fluoride diethyl etherate (1.4 ml, 11 mmol) was added
dropwise over 2 min to a stirred solution of the aziridine
19b (1.63 g, 5.35 mmol) in 2-methyl-3-buten-2-ol (25 ml)
at 08C under an atmosphere of nitrogen. The solution was
warmed to room temperature, stirred for 16 h and then

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
2709
diluted with dichloromethane (25 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
(1.36 g, 65%) as a pale yellow oil; [a]2D4¼þ12 (c 1.74,
CHCl3); nmax (CHCl3)/cm21 3436, 2979, 2954, 2882, 1728,
1602, 1492, 1458, 1386, 1351, 1302, 1146, 1097, 1065,
1001, 984, 902; dH (360 MHz, C6D6, 333 K) 5.63 (1H,
masked br s, NH), 5.60 (1H, dd, J¼17.6, 10.8 Hz,
CHvCH2), 4.92 (1H, dd, J¼17.6, 1.1 Hz, CHvCH2),
4.90 (1H, dd, J¼10.8, 1.1 Hz, CHvCH2), 4.45 (1H, m,
CHCO2Me), 3.58 (1H, dd, J¼9.3, 3.4 Hz, CH2), 3.42 (1H,
dd, J¼9.3, 3.6 Hz, CH2), 3.33 (3H, s, OCH3), 1.91 (3H, s,
Cl3CC(CH3)2), 1.90 (3H, s, Cl3CC(CH3)2), 1.02 (6H, s,
CH3); dC (100 MHz, C6D6, 333 K) 170.5 (s), 154.1 (s),
143.4 (d), 114.0 (t), 107.1 (s), 88.8 (s), 75.6 (s), 63.0 (t), 55.1
(d), 51.7 (q), 25.6 (q), 25.5 (q), 21.8 (q); m/z (ES) 412.0443
([MþNa]þ, C14H22NO5Cl3Na requires 412.0461).
crude product which was purified by chromatography on
silica using 10% acetone in ethyl acetate as eluent to give
the hexapeptide (79 mg, 61%) as a cream foam; [a]1D9¼272
(c 1.13, CHCl3); nmax (CHCl3)/cm21 3411, 3338, 2956,
2933, 2879, 1738, 1643, 1558, 1491, 1454, 1349, 1320,
1144, 1077, 1000, 871; dH (360 MHz, d6-DMSO, 333 K)
9.59 (1H, d, J¼7.1 Hz, NHCvS), 8.20 (2H, d, J¼8.5 Hz,
Ar-H), 7.94 (1H, d, J¼7.9 Hz, NHCHCH2Ph), 7.69 (1H, d,
J¼8.5 Hz, NHCHCH(CH3)CH2CH3), 7.61 (2H, d,
J¼8.3 Hz, Ar-H), 7.27–7.15 (5H, m, Ph-H), 7.06 (1H, br
s, NHPNZ), 5.78 (1H, dd, J¼17.5, 10.8 Hz, CHvCH2),
5.17 (2H, br s, CH2Ar), 5.14–5.09 (1H, m, CHvCH2), 5.07
(1H, dd, J¼10.9, 1.3 Hz, CHvCH2), 4.99–4.97 (1H, m,
CHCH2OH), 4.86–4.77 (3H, m, CHCH2Ph, CHCvS and
OH), 4.45 (1H, app t, J¼8.3 Hz, CHCH(CH3)CH2CH3),
4.31 (1H, dd, J¼8.4, 5.1 Hz, CHCO2Me), 4.10 (1H, app dt,
J¼8.4, 5.9 Hz, CHCH2OAllyl), 3.82–3.51 (6H, m, CH2OH
and CH2N), 3.62 (3H, s, OCH3), 3.37–3.30 (2H, m,
CH2OAllyl), 3.19–3.12 (1H, masked m, CH2Ph), 2.81–
2.74 (1H, m, CH2Ph), 2.21–1.79 (9H, m, CH2 and CHCH3),
1.53–1.45 (1H, m, CH2CH3), 1.21–1.08 (1H, masked m,
CH2CH3), 1.17 (6H, s, CH3), 0.91 (3H, d, J¼6.8 Hz,
CHCH3), 0.83 (3H, app t, J¼7.4 Hz, CH2CH3); dC
(100 MHz, d6-DMSO, 323 K) 204.3 (s), 171.8 (s), 169.5
(s), 169.3 (s), 168.9 (s), 168.1 (s), 155.1 (s), 146.8 (s), 144.7
(s), 143.5 (d), 137.4 (s), 129.0 (d), 127.8 (d), 127.8 (d),
125.9 (d), 123.2 (d), 113.5 (t), 74.8 (s), 65.7 (d), 64.2 (t),
62.4 (t), 60.4 (t), 60.0 (d), 58.3 (d), 55.3 (d), 54.4 (d), 51.6
(d), 51.4 (q), 47.1 (t), 46.6 (t), 36.6 (t), 36.2 (d), 31.6 (t), 28.4
(t), 25.3 (q), 25.2 (q), 24.3 (t), 23.7 (t), 14.7 (q), 10.6 (q); m/z
(ES) 946.3989 ([MþNa]þ, C45H61N7O12SNa requires
946.3997).
4.1.14. PNZ-Ser(dimethylallyl)-Phe-Proc{(CvS)NH}-
Ser-Ile-Pro-OMe (22a). An aqueous solution of lithium
hydroxide (1.5 M, 0.55 ml, 0.82 mmol) was added dropwise
over 1 min to a stirred solution of the allyl ether 20a (60 mg,
0.16 mmol) in tetrahydrofuran (2 ml) and methanol (0.2 ml)
at 08C. The solution was warmed to room temperature,
stirred for 1.5 h and then evaporated in vacuo. The residue
was taken up in ethyl acetate (3 ml) and water (5 ml), then
cooled to 08C and acidified with 2 M aqueous hydrochloric
acid solution with vigorous stirring. After stirring at 08C for
10 min the layers were separated and the aqueous layer was
then extracted with ethyl acetate (5£2 ml). The combined
organic extracts were dried and evaporated in vacuo to leave
the carboxylic acid (58 mg) as a pale yellow oil, which was
used without further purification.
4.1.15. TcBoc-Ser(dimethylallyl)-Phe-Proc{(CvS)NH}-
Ser-Ile-Pro-OMe (22b). An aqueous solution of lithium
hydroxide (1.5 M, 2.5 ml, 3.8 mmol) was added dropwise
over 2 min to a stirred solution of the allyl ether 20b
(148 mg, 0.379 mmol) in tetrahydrofuran (4 ml) and
methanol (0.4 ml) at 08C. The solution was warmed to
room temperature, stirred for 45 min and then evaporated in
vacuo. The residue was taken up in ethyl acetate (5 ml) and
water (5 ml), then cooled to 08C and acidified with 2 M
aqueous hydrochloric acid solution with vigorous stirring.
After stirring at 08C for 5 min the layers were separated and
the aqueous layer was then extracted with ethyl acetate
(8£3 ml). The combined organic extracts were dried and
evaporated in vacuo to leave the carboxylic acid (140 mg,
98%) as a pale yellow oil, which was used without further
purification.
Acetyl chloride (0.1 ml) was added dropwise over 1 min to a
stirred solution of the pentapeptide 11 (100 mg,
0.145 mmol) in methanol (1 ml) at 08C under an atmosphere
of nitrogen. The solution was warmed to room temperature,
stirred for 5.5 h and then evaporated in vacuo to leave the
corresponding hydrochloride salt (88 mg, 97%) as a cream
solid, which was used without further purification.
Diisopropylethylamine (86 ml, 0.49 mmol) was added
dropwise over 1 min to a stirred solution of the hydro-
chloride salt (88 mg, 0.14 mmol) in dichloromethane (2 ml)
at 08C under an atmosphere of nitrogen. The solution was
stirred at 08C for 15 min and then the carboxylic acid 21a
(58 mg, 0.16 mmol) in dichloromethane (2 ml) was added
dropwise over 2 min by cannula, followed by 1-hydroxy-
benzotriazole (23 mg, 0.16 mmol) in one portion. The
suspension was stirred at 08C for a further 15 min and
then 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (32 mg, 0.16 mmol) was added in one
portion. The mixture was allowed to warm to room
temperature over the course of 24 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£2 ml)
followed by saturated aqueous sodium bicarbonate solution
(5£2 ml), with backwashing. The combined organic
extracts were dried and evaporated in vacuo to leave the
Acetyl chloride (0.2 ml) was added dropwise over 1 min to a
stirred solution of the pentapeptide 11 (270 mg,
0.392 mmol) in methanol (2 ml) at 08C under an atmosphere
of nitrogen. The solution was warmed to room temperature,
stirred for 6 h and then evaporated in vacuo to leave the
corresponding hydrochloride salt (245 mg) as a cream solid,
which was used without further purification.
Diisopropylethylamine (215 ml, 1.23 mmol) was added
dropwise over 1 min to a stirred solution of the hydro-
chloride salt (245 mg, 0.392 mmol) in dichloromethane
(5 ml) at 08C under an atmosphere of nitrogen. The solution
was stirred at 08C for 15 min and then the carboxylic acid

2710
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
21b (133 mg, 0.353 mmol) in dichloromethane (5 ml) was
added dropwise over 5 min by cannula, followed by
1-hydroxybenzotriazole (52 mg, 0.39 mmol) in one portion.
The suspension was stirred at 08C for a further 15 min and
then 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (74 mg, 0.39 mmol) was added in one
portion. The mixture was allowed to warm to room
temperature over the course of 33 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£4 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% light petroleum (40–608C) in ethyl acetate
as eluent to give the hexapeptide (148 mg, 40%) as a cream
foam; [a]1D9¼273 (c 0.98, CHCl3); nmax (CHCl3)/cm21
3414, 3336, 2974, 2879, 1729, 1643, 1489, 1455, 1386,
1364, 1322, 1147, 1077, 1001, 872, 840; dH (360 MHz,
d6-DMSO, 333 K) 9.61 (1H, d, J¼7.3 Hz, NHCvS), 7.94
(1H, br s, NHCHCH2Ph), 7.69 (1H, d, J¼8.4 Hz,
NHCHCH(CH3)CH2CH3), 7.28–7.18 (5H, m, Ph-H), 6.76
(1H, br s, NHTcBoc), 5.79 (1H, dd, J¼17.7, 10.8 Hz,
CHvCH2), 5.15–5.09 (1H, m, CHvCH2), 5.08 (1H, dd,
J¼10.8, 1.3 Hz, CHvCH2), 4.98–4.94 (1H, m, CHCH2-
OH), 4.90–4.72 (3H, m, CHCH2Ph, CHCvS and OH), 4.45
(1H, app t, J¼8.2 Hz, CHCH(CH3)CH2CH3), 4.31 (1H, dd,
J¼8.3, 5.0 Hz, CHCO2Me), 4.04 (1H, app dt, J¼8.3,
6.2 Hz, CHCH2OAllyl), 3.82–3.53 (6H, m, CH2OH and
CH2N), 3.62 (3H, s, OCH3), 3.33–3.32 (2H, m, CH2-
OAllyl), 3.13 (1H, masked m, CH2Ph), 2.77 (1H, dd,
J¼14.4, 9.1 Hz, CH2Ph), 2.20–1.83 (9H, m, CH2 and
CHCH3), 1.83 (6H, s, Cl3CC(CH3)2), 1.56–1.46 (1H, m,
CH2CH3), 1.24–1.04 (1H, masked m, CH2CH3), 1.17 (6H,
s, CH3), 0.91 (3H, d, J¼6.8 Hz, CHCH3), 0.84 (3H, app t,
J¼7.4 Hz, CH2CH3); dC (90 MHz, d6-DMSO, 323 K) 204.2
(s), 171.8 (s), 169.5 (s), 169.3 (s), 168.6 (s), 168.1 (s), 153.2
(s), 143.4 (d), 137.4 (s), 129.0 (d), 127.8 (d), 126.0 (d),
113.5 (t), 106.3 (s), 86.9 (s), 74.8 (s), 65.6 (d), 62.4 (t), 60.4
(t), 60.1 (d), 58.3 (d), 55.1 (d), 54.4 (d), 51.5 (d), 51.4 (q),
47.1 (t), 46.6 (t), 36.7 (t), 36.2 (d), 31.6 (t), 28.4 (t), 25.3 (q),
25.2 (q), 24.3 (t), 23.7 (t), 21.3 (q), 21.2 (q), 14.7 (q), 10.6
(q); m/z (ES) 969.3168 ([MþNa]þ, C42H61N6O10SCl3Na
requires 969.3133).
(2 ml) was added dropwise over 2 min by cannula to a
stirred solution of the amine 23 (124 mg, 0.167 mmol) in
dichloromethane (1 ml) at 08C under an atmosphere of
nitrogen. 1-Hydroxybenzotriazole (25 mg, 0.18 mmol) was
then added in one portion. The suspension was stirred at 08C
for 10 min and then 1-(3-dimethylaminopropyl)-3-ethyl-
carbodiimide hydrochloride (35 mg, 0.18 mmol) was added
in one portion. The mixture was allowed to warm to room
temperature over the course of 53 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 5% acetone in ethyl acetate as eluent to give the
heptapeptide (135 mg, 78%) as a cream foam; [a]2D4¼270
(c 1.03, CHCl3); nmax (CHCl3)/cm21 3415, 2966, 2933,
2879, 1741, 1644, 1556, 1492, 1454, 1364, 1322, 1141,
1079, 1000, 908, 836; dH (400 MHz, d6-DMSO) 9.75 (1H,
d, J¼7.4 Hz, NHCvS), 8.21 (1H, d, J¼8.5 Hz, NHCHCH2-
Ph), 7.92 (1H, d, J¼8.4 Hz, NHCHCH(CH3)CH2CH3), 7.83
(1H, d, J¼9.0 Hz, NHTroc), 7.74 (1H, d, J¼8.1 Hz,
NHCHCH2OAllyl), 7.27–7.14 (5H, m, Ph-H), 5.74 (1H,
dd, J¼17.6, 10.8 Hz, CHvCH2), 5.10 (1H, dd, J¼17.6,
1.3 Hz, CHvCH2), 5.07 (1H, dd, J¼10.8, 1.3 Hz,
CHvCH2), 4.96 (1H, app t, J¼5.4 Hz, OH), 4.95–4.90
(1H, masked m, CHCH2OH), 4.88–4.73 (2H, m, CHCH2Ph
and CHCvS), 4.83 (1H, d, J¼12.4 Hz, CH2CCl3), 4.76
(1H, d, J¼12.4 Hz, CH2CCl3), 4.41 (1H, app t, J¼8.4 Hz,
CHCH(CH3)CH2CH3), 4.38 (1H, app dt, J¼8.0, 5.8 Hz,
CHCH2OAllyl), 4.27 (1H, dd, J¼8.4, 5.4 Hz, CHCO2Me),
3.91 (1H, app t, J¼8.5 Hz, CHNHTroc), 3.79–3.64 (5H, m,
CH2OH and CH2N), 3.61 (3H, s, OCH3), 3.61–3.52 (1H, m,
CH2N), 3.32–3.25 (2H, m, CH2OAllyl), 3.11 (1H, dd,
J¼14.3, 4.1 Hz, CH2Ph), 2.74 (1H, dd, J¼14.4, 9.4 Hz,
CH2Ph), 2.20–2.01 (2H, m, CH2CHCO2Me and CH2-
CHCvS), 1.96–1.72 (8H, m, CH2 and CHCH3), 1.56–1.35
(2H, m, CH2CH3), 1.14 (3H, s, CH3), 1.14 (3H, s, CH3),
1.14–1.03 (2H, m, CH2CH3), 0.88 (3H, d, J¼6.7 Hz,
CHCH3), 0.81 (3H, app t, J¼7.4 Hz, CH2CH3), 0.78 (3H,
app t, J¼7.4 Hz, CH2CH3), 0.77 (3H, d, J¼6.8 Hz,
CHCH3); dC (100 MHz, d6-DMSO) 204.4 (s), 172.1 (s),
170.4 (s), 169.7 (s), 169.3 (s), 169.0 (s), 168.2 (s), 154.3 (s),
143.7 (d), 137.8 (s), 129.0 (d), 128.0 (d), 126.2 (d), 113.9 (t),
96.2 (s), 74.9 (s), 73.4 (t), 65.7 (d), 62.6 (t), 60.6 (t), 60.3 (d),
59.5 (d), 58.5 (d), 54.5 (d), 52.7 (d), 51.7 (d), 51.7 (q), 47.2
(t), 46.8 (t), 36.6 (t), 36.2 (d), 36.1 (d), 31.8 (t), 28.6 (t), 25.5
(q), 25.3 (q), 24.6 (t), 24.2 (t), 23.9 (t), 15.2 (q), 14.8 (q),
10.8 (q), 10.7 (q); m/z (ES) 1054.3730 ([MþNa]þ, C46H68-
N7O11SCl3Na requires 1054.3661).
4.1.16. Troc-Ile-Ser(dimethylallyl)-Phe-Proc-
{(CvS)NH}-Ser-Ile-Pro-OMe (24). Cadmium–lead
couple14 (1.17 g, 9.42 mmol cadmium, 10% lead) was
added in one portion to a rapidly stirred solution of the
hexapeptide 22b (179 mg, 0.189 mmol) in tetrahydrofuran
(2 ml) and 1N aqueous ammonium acetate solution (2 ml) at
room temperature. The mixture was stirred vigorously at
room temperature for 50 min and then filtered, washing with
water (5£1 ml) and ethyl acetate (5£1 ml). The filtrate was
cooled to 08C and then basified with saturated aqueous
sodium bicarbonate solution with vigorous stirring. After
stirring at 08C for 10 min the layers were 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 (124 mg, 88%) as a cream foam,
which was used without further purification.
4.1.17. Cyclo[Ile-Ser(dimethylallyl)-Phe-Proc-
{(CvS)NH}-Ser-Ile-Pro] (5). Cadmium–lead couple14
(807 mg, 6.52 mmol cadmium, 10% lead) was added in
one portion to a rapidly stirred solution of the heptapeptide
24 (135 mg, 0.131 mmol) in tetrahydrofuran (1.5 ml) and
1N aqueous ammonium acetate solution (1.5 ml) at room
temperature. The mixture was stirred vigorously at room
temperature for 40 min and then filtered, washing with
water (5£1 ml) and ethyl acetate (5£1 ml). The filtrate was
cooled to 08C and then basified with saturated aqueous
sodium bicarbonate solution with vigorous stirring. After
Troc-L-isoleucine (69 mg, 0.23 mmol) in dichloromethane

B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
2711
stirring at 08C for 10 min, the layers were 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 (107 mg, 96%) as a cream solid,
which was used without further purification.
J¼7.4 Hz, CH2CH3); dC (90 MHz, CDCl3) 201.4 (s), 172.8
(s), 171.3 (s), 171.3 (s), 170.5 (s), 170.4 (s), 169.2 (s), 142.8
(d), 135.8 (s), 129.2 (d), 129.1 (d), 127.7 (d), 114.8 (t), 76.9
(s), 68.0 (d), 61.2 (t), 61.1 (d), 60.9 (t), 59.4 (d), 58.1 (d),
57.4 (d), 53.2 (d), 52.4 (d), 47.0 (t), 46.6 (t), 40.1 (t), 36.5
(d), 34.7 (d), 34.6 (t), 31.7 (t), 26.1 (q), 25.3 (t), 25.1 (q),
24.9 (t), 21.9 (t), 16.0 (q), 15.9 (q), 11.7 (q), 10.5 (q); m/z
(ES) 848.4302 ([MþNa]þ, C42H63N7O8SNa requires
848.4357).
An aqueous solution of tetrabutylammonium hydroxide
(40 wt%, 162 ml, 0.250 mmol) was added dropwise over
1 min to a stirred solution of the amine (107 mg,
0.125 mmol) in tetrahydrofuran (5 ml) at 08C. The solution
was stirred at 08C for 25 h and then additional aqueous
tetrabutylammonium hydroxide solution (40 wt%, 81 ml,
0.13 mmol) was added dropwise over 1 min. After stirring
at 08C for a further 6.5 h, the solution was neutralised with
2 M aqueous hydrochloric acid solution (188 ml,
0.375 mmol). The solution was stirred at 08C for a further
10 min, warmed to room temperature, and then evaporated
in vacuo, azeotroping several times with toluene, to leave
the amino acid, which was used without further purification.
4.1.18. Mollamide (3). Diethylaminosulfur trifluoride
(10 ml, 0.076 mmol) was added dropwise over 1 min to a
stirred solution of the cyclopeptide 5 (21 mg, 0.025 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. Dichloro-
methane (5 ml) and water (4 ml) were added, the layers
separated, and the aqueous layer was then extracted with
dichloromethane (5£1 ml). 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 mollamide (15 mg,
74%) as a colourless solid; mp 151–1538C (Lit.,4 mp 154–
1568C); [a]1D7¼240 (c 0.74, CHCl3) (Lit.,4 [a]2D5¼22.75 (c
0.08, CHCl3))‡; dH (500 MHz, CDCl3) 8.18 (1H, d,
J¼8.5 Hz, NHCHCH(CH3)CH2CH3), 8.09 (1H, d,
J¼8.6 Hz, NHCHCH2Ph), 7.32–7.24 (3H, m, Ph-H), 7.16
(2H, d, J¼6.9 Hz, Ph-H), 7.12 (1H, d, J¼4.6 Hz,
NHCHCH2OAllyl), 7.02 (1H, br s, NHCHCH(CH3)CH2-
CH3), 5.88 (1H, dd, J¼17.6, 10.9 Hz, CHvCH2), 5.31 (1H,
dd, J¼11.4, 5.6 Hz, CHCH2S), 5.15 (1H, d, J¼17.8 Hz,
CHvCH2), 5.14 (1H, d, J¼10.8 Hz, CHvCH2), 4.85 (1H,
ddd, J¼11.2, 8.5, 4.4 Hz, CHCH2Ph), 4.61 (1H, app d,
J¼7.3 Hz, CH(CH2)3N), 4.26 (1H, app d, J¼8.2 Hz,
CHCH(CH3)CH2CH3), 4.23 (1H, app dt, J¼10.6, 4.6 Hz,
CHCH2OAllyl), 4.16 (1H, app t, J¼8.4 Hz, CHCH(CH3)-
CH2CH3), 3.94 (1H, dd, J¼6.9, 4.6 Hz, CH(CH2)3N), 3.77
(1H, dd, J¼7.9, 4.2 Hz, CH2OAllyl), 3.77–3.71 (1H,
masked m, CH2N), 3.65 (1H, dd, J¼11.4, 5.6 Hz,
CHCH2S), 3.59–3.55 (1H, m, CH2N), 3.51 (1H, app dd,
J¼12.1, 7.1 Hz, CH2N), 3.34 (1H, app dd, J¼11.9, 7.2 Hz,
CH2N), 3.25 (1H, app t, J¼11.4 Hz, CH2S), 3.04 (1H, dd,
J¼11.9, 11.7 Hz, CH2Ph), 2.94 (1H, dd, J¼10.5, 7.9 Hz,
CH2OAllyl), 2.81 (1H, dd, J¼12.3, 4.4 Hz, CH2Ph), 2.66–
2.63 (1H, m, CH2), 2.00–1.81 (9H, m, CH2, CHCH3 and
CH2CH3), 1.77–1.71 (1H, m, CH2), 1.56–1.42 (2H, m, CH2
and CH2CH3), 1.38 (3H, s, CH3), 1.36 (3H, s, CH3), 1.35–
1.26 (1H, m, CH2CH3), 1.11 (3H, app t, J¼7.3 Hz,
CH2CH3), 1.11 (3H, d, J¼6.8 Hz, CHCH3), 0.94 (3H, d,
J¼6.8 Hz, CHCH3), 0.87 (3H, app t, J¼7.4 Hz, CH2CH3);
dC (100 MHz, CDCl3) 176.8 (s), 172.0 (s), 171.3 (s), 170.9
(s), 170.6 (s), 169.8 (s), 143.1 (d), 136.7 (s), 129.0 (d), 128.6
(d), 127.1 (d), 114.7 (t), 79.9 (d), 76.8 (s), 61.4 (d), 61.3 (t),
60.7 (d), 59.6 (d), 57.7 (d), 52.2 (d), 52.0 (d), 46.5 (t), 46.4
(t), 40.8 (t), 36.7 (d), 36.0 (d), 33.1 (t), 31.7 (t), 31.5 (t), 25.8
(q), 25.7 (t), 25.4 (q), 25.4 (t), 23.1 (t), 22.0 (t), 15.8 (q), 15.6
Diisopropylethylamine (48 ml, 0.28 mmol) was added
dropwise over 1 min to a stirred solution of the amino
acid in dimethylformamide (25 ml) at 258C under an
atmosphere of nitrogen. The solution was stirred at 258C
for 10 min and then diphenylphosphoryl azide16 (40 ml,
0.19 mmol) was added dropwise over 1 min. After 5 min at
258C, stirring was stopped and the solution was allowed to
slowly warm to room temperature and then stood at room
temperature for seven days. Ethyl acetate (20 ml) was added
and the solution was poured onto ice-cold water (50 ml).
The two layers were separated and the aqueous layer was
then extracted with ethyl acetate (6£10 ml). The combined
organic extracts were washed with water (6£30 ml) and
brine (1£30 ml), 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 cyclopeptide
(53 mg, 52%, 2 steps) as a cream foam; [a]1D7¼2280 (c
1.29, CHCl3); nmax (CHCl3)/cm21 3334, 2967, 2932, 2879,
1651, 1551, 1494, 1456, 1381, 1345, 1306, 1145, 1128,
1076, 1048, 993, 908, 876; dH (360 MHz, CDCl3) 8.66 (1H,
d, J¼7.7 Hz, NHCHCH2OH), 8.49 (1H, d, J¼4.0 Hz,
NHCHCH(CH3)CH2CH3), 8.08 (1H, d, J¼9.1 Hz,
NHCHCH2Ph), 7.96 (1H, d, J¼8.5 Hz, NHCHCH(CH3)-
CH2CH3), 7.37–7.28 (3H, m, Ph-H), 7.19 (1H, d, J¼5.3 Hz,
NHCHCH2OAllyl), 7.14–7.11 (2H, m, Ph-H), 5.94 (1H, dd,
J¼17.6, 10.8 Hz, CHvCH2), 5.20 (1H, dd, J¼17.6, 1.1 Hz,
CHvCH2), 5.17 (1H, dd, J¼10.8, 1.0 Hz, CHvCH2), 5.05
(1H, app d, J¼7.7 Hz, CHCH2OH), 4.60 (1H, ddd, J¼10.2,
9.4, 5.5 Hz, CHCH2Ph), 4.51 (1H, app d, J¼7.3 Hz,
CH(CH2)3N), 4.34–4.32 (1H, m, CH2OH), 4.26 (1H, dd,
J¼5.8, 4.3 Hz, CHCH(CH3)CH2CH3), 4.10 (1H, app t,
J¼8.7 Hz, CHCH(CH3)CH2CH3), 3.99 (1H, ddd, J¼9.6,
5.5, 4.2 Hz, CHCH2OAllyl), 3.81 (1H, app d, J¼6.8 Hz,
CH(CH2)3N), 3.72–3.64 (1H, m, CH2N), 3.69 (1H, dd,
J¼8.7, 4.0 Hz, CH2OAllyl), 3.58–3.31 (5H, m, CH2N,
CH2OH and OH), 3.42 (1H, dd, J¼9.9, 8.8 Hz, CH2OAllyl),
2.97 (1H, dd, J¼12.5, 10.4 Hz, CH2Ph), 2.87 (1H, dd,
J¼12.6, 5.5 Hz, CH2Ph), 2.60–2.56 (1H, m, CH2), 2.48–
2.39 (1H, m, CH2), 2.08–1.63 (9H, m, CH2, CH2CH3,
CHCH3), 1.54–1.40 (2H, m, CH2 and CH2CH3), 1.41 (3H,
s, CH3), 1.40 (3H, s, CH3), 1.29–1.14 (1H, m, CH2CH3),
1.04 (3H, d, J¼6.9 Hz, CHCH3), 0.97 (3H, app t, J¼7.3 Hz,
CH2CH3), 0.92 (3H, d, J¼6.7 Hz, CHCH3), 0.86 (3H, app t,
‡
While the [a]D measured for our synthetic mollamide was significantly
different from that reported for naturally derived material4 it was identical
to that obtained by ourselves from a sample of natural mollamide
([a]2D0¼238 (c 0.65, CHCl3)).

2712
B. McKeever, G. Pattenden / Tetrahedron 59 (2003) 2701–2712
(q), 11.4 (q), 10.6 (q); m/z (ES) 830.4238 ([MþNa]þ,
Soc., Perkin Trans. 1 2000, 883. (b) Norley, M. C.; Pattenden,
G. Tetrahedron Lett. 1998, 39, 3087. (c) Boden, C. D. J.;
Norley, M. C.; Pattenden, G. Tetrahedron Lett. 1996, 37, 9111.
9. (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.
C42H61N7O7SNa requires 830.4251).
Acknowledgements
We thank Dr P. Bradley and Dr C. D. J. Boden 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 for providing us with a sample of
natural mollamide and for helpful correspondence.
10. Shalaby, M. A.; Grote, C. W.; Rapoport, H. J. Org. Chem.
1996, 61, 9045.
11. Nakajima, K.; Neya, M.; Yamada, S.; Okawa, K. Bull. Chem.
Soc. Jpn 1982, 55, 3049.
12. Willems, J. G. H.; Hersmis, M. C.; de Gelder, R.; Smits, J. M.
M.; Hammink, J. B.; Dommerholt, F. J.; Thijs, L.;
Zwanenburg, B. J. Chem. Soc., Perkin Trans. 1 1997, 963.
13. Kumagai, T.; Abe, T.; Fujimoto, Y.; Hayashi, T.; Inoue, Y.;
Nagao, Y. Heterocycles 1993, 36, 1729.
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