Total synthesis of the cyclic peptide Argyrin B

Article abstract of DOI:10.1002/1099-0690(200212)2002:23<3995::AID-EJOC3995>3.0.CO;2-P

The details of the total synthesis of Argyrin B, a natural product with immunosuppressive properties, are reported below. The two most unusual amino acid residues of this cyclic peptide are 4-methoxytryptophan and dehydroalanine, which were obtained by mo

Full text of DOI:10.1002/1099-0690(200212)2002:23<3995::AID-EJOC3995>3.0.CO;2-P

FULL PAPER
Total Synthesis of the Cyclic Peptide Argyrin B
Steven V. Ley*[a] and Alain Priour[a]
Keywords: Dehydroalanine / Immunology / Peptides / Total synthesis / Tryptophan
The details of the total synthesis of Argyrin B, a natural prod-
linear peptide was assembled in a most convergent fashion
uct with immunosuppressive properties, are reported below. then cyclisation followed by generation of the sensitive dehy-
The two most unusual amino acid residues of this cyclic pep-
tide are 4-methoxytryptophan and dehydroalanine, which
were obtained by modifying known synthetic methods. The
droalanine afforded synthetic Argyrin B (1).
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
ilarly the two way murine mixed-lymphocyte reaction
(MLR), a cellular model for alloantigenic-mediated T-cell
activation and proliferation,[9] was also inhibited by Argyrin
B. Cytotoxicity was low, since it did not affect the prolifera-
tion of human Jurkat T-cells. Argyrin B was further shown
to be a potent inhibitor of in vitro IgG production by
CD40 -stimulated murine and human B-cells.
The structure of Argyrin B (1) and its congeners was de-
termined by a combination of NMR spectroscopy, chemical
degradation and X-ray crystallographic analysis.[10] Argyrin
B (1) is a non-ribosomal bicyclic octapeptide with the cyclic
dipeptide 2-(1-aminoethyl)thiazole resulting from the hetero-
cyclisation of cysteine to the preceding carboxy group of
alanine.[11] The most unusual features in this molecule are
the novel 4-methoxytryptophan and the dehydroalanine res-
idues. Both tryptophans have the -configuration while am-
inobutyric acid and the alanine-derived thiazole have the -
configuration. Another unusual component is the sarcosine
unit, which is an N-methylated amino acid.
During the screening of myxobacteria[1] as a potential
source of new antibiotics, a group of cyclic peptides were
isolated from the Archangium gephyra strain and named the
Argyrins (Figure 1).[2] Further biological evaluation at Nov-
artis identified Argyrin B (1) as an immunosuppressant and
a possible drug development candidate in xenotransplant-
ation.[2,3]
Results and Discussion
Owing to its interesting biological profile and these un-
usual structural features, we have embarked on a total syn-
thesis of 1 and here wish to report full details of these ef-
forts.[12] In order to undertake this task we chose to use a
solution-phase synthesis as being the most reasonable ap-
proach to a molecule with this level of complexity. Al-
though a large variety of alternative coupling strategies for
the various amino acid fragments could be conceived, we
devised a plan, outlined in Figure 2, that would protect the
stereogenic centres at crucial stages of the synthesis. This
route also facilitates deprotection reactions, coupling
methods and the important late stage cyclisation process.
The route required, therefore, the preparation of suitably
protected fragments such as the thiazole 2, the tripeptide 3
and the tripeptide 4 containing the dehydroalanine com-
Figure 1. Structure of the Argyrins A-H
By using known biological assays for both murine[4Ϫ6]
and human B-cells,[7,8] Argyrin B was shown to be a potent
inhibitor of T-cell independent antibody formation. Sim-
[a]
Department of Chemistry, University of Cambridge,
Lensfield Road, Cambridge, CB2 1EW, UK
Fax: (internat) ϩ44-1223/336-442
E-mail: svl1000@cam.ac.uk
Eur. J. Org. Chem. 2002, 3995Ϫ4004  2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/02/1223Ϫ3995 $ 20.00ϩ.50/0
3995

S. V. Ley, A. Priour
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Scheme 2. Synthesis of 4-methoxytryptophan with aziridine
We next examined the use of the Schöllkopf auxiliary to
build the stereogenic centre of the amino acid
(Scheme 3).[19,20] Indole 5 was converted in three steps to
11. We then anticipated that conversion of the alcohol to a
suitable leaving group followed by substitution with the
chiral auxiliary 14 should generate adduct 15. However, all
attempts to isolate the intermediate 12 or to react it in situ
with 14 resulted in decomposition of the starting material.
We attribute these results to the high instability of the car-
bocation intermediate 13 compared to the relatively low re-
activity of 14 under the reaction conditions.
Figure 2. Retrosynthetic analysis of Argyrin B
ponent or a synthetic equivalent. Tripeptide 3 incorporates
the 4-methoxytryptophan unit, which itself derives from 4-
methoxyindole (5). The α-centre to the C-terminus of all
three fragments is achiral and therefore no epimerisation
problems arise during fragment coupling.
For the preparation of 2, we followed a straightforward
route[13] from N-Boc--alanine that involves transformation
to the thioamide 6 via the intermediate amide and thiol-
ation with Belleau’s reagent[14] (Scheme 1). Compound 6
was then reacted with ethyl bromopyruvate to afford an in-
termediate which, on treatment with trifluoroacetic anhyd-
ride and 2,6-lutidine, gave the thiazole 2.[15]
Next, the tripeptide 3 was assembled but this first re-
quired us to develop an efficient synthesis of the amino acid
4-methoxy--tryptophan. Initially we chose to rely on the
known regioselective opening of aziridine 7[16] by 4-methoxy-
Scheme 3. Synthesis of 4-methoxytryptophan with Schöllkopf aux-
iliary; reagents and conditions: (a) POCl3, DMF, room temp.
(84%); (b) NaH, PhSO2Cl, THF, room temp. (97%); (c) NaBH4,
EtOH/CH2Cl2, room temp. (68%)
[17]
indole in the presence of a Lewis acid such as Zn(OTf)2
[18]
or Sc(OTf)3
(Scheme 2). Despite steric and electronic
factors favouring the nucleophilic attack at the methylene
centre of 7, we obtained a mixture of regioisomers 8 and 9
which were extremely difficult to separate; the combined
yield was below 50%.
The third approach relied on an enzyme resolution route
using an immobilised Penicillin G acylase.[21,22] This re-
quired the synthesis of the racemic 4-methoxytryptophan
derivative 18 (Scheme 4). Indole 5 was converted quantitat-
ively to the gramine derivative 16. Methylation followed by
quenching with the enolate of 2-phenylacetylaminomalonic
acid diethyl ester gave 17. Saponification of the diester and
decarboxylation gave pure racemic phenylacetamide 18
after recrystallisation. The three-step sequence from indole
5 was readily performed on a ten gram scale, without the
need for column chromatography, in an overall 56% yield.
Scheme 1. Synthesis of fragment 2; reagents and conditions: (a)
EDC, HOBt, NH3, CH2Cl2, 0 °C; (b) Belleau’s reagent, THF, 0 °C
(quantitative, 2 steps); (c) i. BrCH2COCO2Et, KHCO3, DME; ii.
TFAA, 2,6-lutidine, DME, Ϫ15 °C (41%)
3996
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Total Synthesis of the Cyclic Peptide Argyrin B
FULL PAPER
form, since this is known to be unstable and prone to nucle-
ophilic attack. Most routes affording dehydroalanine in
peptide synthesis rely on the β-elimination of serine or cyst-
eine as the final step. Therefore, as a first approach to the
third fragment, we prepared the tripeptide 20 in which the
serine side chain was protected as a silyl ether (Scheme 6).
Although a model deprotection-dehydration sequence was
successful with 20 in generating dehydroalanine 4, all our
attempts to synthesise the real cyclic peptide failed to pro-
vide the target molecule.
Scheme 4. Synthesis of 4-methoxy--tryptophan by enzymatic res-
olution; reagents and conditions: (a) CH2NMe2ϩ·IϪ, CH3CN,
room temp. (99%); (b) (C2H5O2C)2CHNHCOCH2Ph, EtONa then
16 and MeSO4Me, EtOH, room temp. (82%); (c) i. NaOH, MeOH/
dioxane, 50 °C; ii. dioxane, 100 °C; iii. NaOH, MeOH/dioxane, 50
°C (69%); (d) Penicillin G acylase immobilised, MeOH/H2O, room
temp.; (e) CbzCl, NaHCO3, THF/H2O, room temp. (44%, 2 steps)
Scheme 6. Model study for dehydroalanine formation; reagents and
conditions: (a) nBu4Nϩ·FϪ, THF; (b) MsCl, NEt3, CH2Cl2; (c)
NEt3, CH2Cl2
Phenylacetamide 18 was treated with Penicillin G acylase
on the solid support, and, following filtration, washing of
the aqueous solution to remove unchanged starting mat-
erial and trapping of the free amino acid with CbzCl, pro-
vided carbamate 8 in a 44% yield (maximum yield 50%). We
did not investigate other methods, most notably the recently
published asymmetric hydrogenation which gives access to
both configurations of tryptophan derivatives.[23,24]
Consequently, we decided to use phenylselenocysteine to
generate dehydroalanine via oxidative β-elimination.[25,26]
The tripeptide 25, containing the phenylseleno group, was
constructed again following established protocols from N-
Boc--Serine (Scheme 7). This route proceeded via β-lac-
tone 22,[27] which, after ring opening, afforded selenide 23.
This was coupled with ethyl sarcosine using PyBroP [28] to
give 24 which, after deprotection to remove the Boc group,
was coupled with N-Boc-D-aminobutyric acid to give 25.
This amino acid was then coupled with methyl glycine by
standard peptide coupling techniques and, after removal of
the Cbz group, reacted with Nα-Cbz--tryptophan to afford
the tripeptide 3 in excellent yield (Scheme 5). The high en-
antioselectivity of the enzymatic hydrolysis was confirmed
1
by H NMR spectroscopy of tripeptide 3, which showed
only one diastereoisomer to be present.
Scheme 7. Synthesis of fragment 4 equivalent; reagents and condi-
tions: (a) DEAD, PPh3, THF, Ϫ78 °C to room temp.; (b) PhSe-
SePh, NaBH(OMe)3, EtOH then 22, room temp. (41%, 2 steps);
(c) HCl-Sar-OEt, PyBroP, DIPEA, CH2Cl2, room temp. (80%);
(d) TFA/CH2Cl2, room temp.; (e) Boc--Abu, EDC, HOBt, DI-
PEA, CH2Cl2, room temp. (84%, 2 steps)
Scheme 5. Synthesis of fragment 3; reagents and conditions: (a)
HCl·Gly-OMe, EDC, HOBt, DIPEA, CH2Cl2, room temp. (94%);
(b) H2, Pd/C, MeOH/aqueous HCl, room temp.; (c) Nα-Cbz--Trp,
EDC, HOBt, DIPEA, CH2Cl2, room temp. (81%, 2 steps)
With all the fragments in place, we could now apply the
proposed end-game strategy (Scheme 8). Removal of the
Cbz protection from 3 and coupling with the free acid from
2 gave pentapeptide 26 in 96% yield. Similarly, hydrolysis
Finally, the remaining coupling component 4 required of 26 to the acid and coupling with the Boc-deprotected
synthesis with dehydroalanine introduced as a masked fragment from 25 gave the fully assembled peptide 27. De-
Eur. J. Org. Chem. 2002, 3995Ϫ4004
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S. V. Ley, A. Priour
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Scheme 8. Synthesis of Argyrin B; reagents and conditions: (a) LiOH, THF/MeOH/H2O, room temp.; (b) H2, Pd/C, MeOH, room temp.;
(c) EDC, HOBt, CH2Cl2, room temp. (97%, 2 steps); (d) LiOH, THF/MeOH/H2O, room temp.; (e) TFA/CH2Cl2, room temp.; (f) EDC,
HOBt, DIPEA, CH2Cl2 (80%, 2 steps); (g) LiOH, THF/MeOH/H2O, room temp.; (h) Anisole/TFA, room temp.; (i) TBTU, HOBt,
DIPEA, CH2Cl2, room temp. (50Ϫ60%, 3 steps); (j) NaIO4, dioxane/H2O, room temp.; (k) NaHCO3, CH3CN/H2O, room temp. (66%,
2 steps)
ware cooled under vacuum. Acetonitrile, dioxane, DME, DMF,
methanol and ethanol were used as supplied. THF was distilled
over sodium/benzophenone and dichloromethane was distilled over
calcium hydride.
protection of 27 at the two termini and cyclisation (TBTU,
HOBt) afforded 28 in an overall yield of 50Ϫ60%. Lastly,
syn-elimination of the selenide was achieved using periodate
and bicarbonate to give Argyrin B (1), identical in all re-
spects to an authentic sample of the natural product.[29] 1
H
TLC was carried out on Merck 60 F254 silica gel plates and
visualised by UV irradiation (254 nm) or by staining with iodine
absorbed on silica gel, ninhydrin solution or with aqueous acidic
ammonium molybdate solution as appropriate. LCMS were re-
corded on a Micromass Platform MS using positive and negative
electrospray ionisation with a Hewlett Packard 1050 LC instrument
with detection by UV diode array. Flash column chromatography
was performed on silica gel with a Biotage Flash 40i system.
and 13C NMR spectra of a mixture of equivalent amounts
of synthetic and natural samples were identical to both sep-
arate samples, and [α]D values clearly matched.
Conclusion
In summary, we have achieved the first total synthesis of
a new cyclic peptide Argyrin B from 4-methoxyindole in a
5.8% overall yield with the longest linear sequence being 17
steps (23.4% yield from the enantiopure Nα-Cbz- 4-me-
thoxy--tryptophan 8, 12 steps). An enzymatic resolution
proved to be the most efficient and stereoselective method
to generate one -tryptophan component of this synthesis,
while oxidation and β-elimination of phenylselenocysteine
was the most reliable way to generate the dehydroalanine
residue in the fully assembled molecule.
Melting points were measured on a Reichert hot-stage apparatus
and are uncorrected. Mass spectra and accurate mass measure-
ments were obtained on a Kratos Q-TOF spectrometer using elec-
trospray (ϩESI) or a Kratos MS890MS spectrometer using elec-
tron impact (EI) or fast atom bombardment (FAB) techniques at
the Department of Chemistry, University of Cambridge. Optical
rotations were measured on a PerkinϪElmer model 343 polari-
meter. [α]D values are reported in 10Ϫ1 deg·cmϪ2·gϪ1, concentration
(c) in g per 100 mL. Infrared spectra were obtained on a
PerkinϪElmer ‘‘Spectrum One’’ spectrometer equipped with an At-
tenuated Total Reflectance (ATR) sampling accessory. 1H NMR
spectra were recorded at room temperature unless specified on
DPX-400 and DRX-600 Bruker spectrometers, at 400 or 600 MHz,
Experimental Section
with residual protic solvent CHCl3 as the internal reference (δH
ϭ
General Remarks: All reactions not involving aqueous reagents
were carried out under an argon atmosphere in oven-dried glass-
7.26 ppm). 13C NMR spectra were recorded at room temperature
unless specified on the same spectrometers at 100 or 150 MHz with
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Eur. J. Org. Chem. 2002, 3995Ϫ4004

Total Synthesis of the Cyclic Peptide Argyrin B
FULL PAPER
the central peak of CHCl3 as the internal reference (δC ϭ 77 ppm).
DEPT 135 and two dimensional NMR spectroscopy (COSY,
HMQC and HMBC) were used for the assignment of signals in the
1H and 13C NMR spectra. For convenience in the peak assignment
ide 6 as a light yellow solid (3.25 g, 100% yield); m.p. 104Ϫ105 °C;
Rf ϭ 0.29 (toluene/EtOAc, 3:2). MS: m/z (ϩESI) found 204.0929
[M], C8H16N2O2S (M, 204.1) requires 204.0932. [α]2D5 ϭ 69.1 (c ϭ
1, CHCl3). IR (solid): ν˜ ϭ 3373, 3289, 3191, 1674, 1512, 1243, 1154
of NMR spectra, the residues were numbered as follows: AlaThz ϭ cmϪ1 1H NMR (400 MHz, CDCl3): δ ϭ 1.43 [s, 9 H, C(CH3)3],
.
1, Trpϭ 2, 4-OMe-Trpϭ 3, Gly ϭ 4, Abuϭ 5, Sec/Dha ϭ 6, Sarϭ
7 (e.g. 2-CH2 stands for the methylene in Trp). Microanalysis were
performed in the microanalytical laboratories at the Department
of Chemistry, University of Cambridge.
1.45 (d, J ϭ 7 Hz, 3 H, CHCH3), 4.59 (br, 1 H, CHCH3), 5.53 (br,
1 H, α-NH), 8.07 (br, 1 H, NHAHB), 8.37 (br, 1 H, NHAHB) ppm.
13C NMR (100 MHz, CDCl3): δ ϭ 21.9 (CHCH3), 28.4 [C(CH3)3],
55.1 (CHCH3), 80.5 [C(CH3)3], 155.6 (CO2), 210.6 (CSNH2) ppm.
C8H16N2O2S (204.3): calcd. C 47.03, H 7.89, N 13.71; found C
46.99, H 7.81, N 13.75.
List of Abbreviations: Abu: α-aminobutyric acid; Ala: alanine; Bn:
benzyl; Boc: tert-butoxycarbonyl; Cbz: carbobenzyloxy; DEAD:
diethyl azodicarboxylate; Dha: dihydroalanine; DIPEA: N,N-diiso-
propylethylamine; DME: 1,2-dimethoxyethane; EDC: 1-(3-di-
methylaminopropyl)-3-ethylcarbodiimide hydrochloride; Gly: gly-
cine; HOBt: 1-hydroxybenzotriazole; Ig: immunoglobulin; IPA: 2-
propanol; PyBroP: bromo-tris-pyrrolidino-phosphonium hexa-
fluorophosphate; Phac: phenylacetyl; Sar: sarcosine; Sec: seleno-
cysteine; TBTU: 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyl-
uronium tetrafluoroborate; TFA: trifluoroacetic acid; TFAA: tri-
fluoroacetic anhydride; Thz: thiazole; Trp: tryptophan.
Ethyl
(R)-2-(1-tert-Butoxycarbonylaminoethyl)thiazole-4-carb-
oxylate (2): Ethyl bromopyruvate (1.33 mL, 10.6 mmol) was added
to a suspension of finely powdered KHCO3 (2.55 g, 25.5 mmol)
and thioamide 6 (0.65 g, 3.18 mmol) which had been stirred in
DME (5 mL) at Ϫ15 °C for 5 minutes. After 1 minute, the mixture
was treated with a solution of 2,6-lutidine (3.15 mL, 27 mmol) and
trifluoroacetic anhydride (2.67 g, 12.7 mmol) in DME (3 mL) at
Ϫ15 °C. The reaction mixture was stirred for 3 hours at the same
temperature, poured into water (25 mL) and extracted with CHCl3
(3 ϫ 25 mL). The organic layers were combined, dried (Na2SO4)
and concentrated. The residue was purified by column chromato-
graphy (toluene/EtOAc, 6:1 then 5:1) and recrystallised from hex-
ane/Et2O to give thiazole 2 as a light yellow solid (0.39 g, 41%
yield); m.p. 85Ϫ86 °C (ref.[31] m.p. 89.5 °); Rf ϭ 0.21 (EtOAc/hex-
ane, 1:1); Rt ϭ 17.13 min [Rt (Boc--ThzAla-OEt) 13.87 min],
Chiralcel OD from DAICEL, 0.46 ϫ 25 cm, hexane/IPA, 95:5,
1 mL/min. MS: m/z (ϩESI) found 300.1158 [M], C13H20N2O4S (M,
300.1) requires 300.1144. [α]2D5 ϭ 40.8 (c ϭ 1, CHCl3). IR (solid):
Peptide Synthesis: Peptides were synthesised by solution-phase
methods using a racemisation-free fragment condensation (EDC
and HOBt). Boc or Cbz groups were used to protect the N-ter-
minus and were cleaved respectively by TFA in CH2Cl2 and hydro-
genolysis with Pd/C in MeOH. The C-terminus was protected as a
methyl or ethyl ester and cleaved by saponification with a slight
excess of LiOH in THF/MeOH/H2O. Reactions were monitored by
LCMS and TLC. Reaction mixtures were worked up with CH2Cl2
or in case of poor solubility with CHCl3/IPA (3:1). Purification
was performed by flash column chromatography with CH2Cl2 and
MeOH. Free N- and C-terminus intermediates were isolated and
used directly in the next step without purification.
1
ν˜ ϭ 3367, 3114, 1716, 1685, 1495, 1228 and 1156 cmϪ1. H NMR
(600 MHz, CDCl3): δ ϭ 1.39 (t, J ϭ 7 Hz, 3 H, CH2CH3), 1.43 [s,
9 H, C(CH3)3], 1.61 (d, J ϭ 6.5 Hz, 3 H, CHCH3), 4.40 (q, J ϭ
7 Hz, 2 H, CH2CH3), 5.10 (br. s, 1 H, α-CH), 5.22 (br. s, 1 H, α-
NH) and 8.07 (s, 1 H, C5-H) ppm. 13C NMR (150 MHz, CDCl3):
δ ϭ 14.3 (CH2CH3), 21.7 (CHCH3), 28.3 [C(CH3)3], 48.9 (α-CH),
61.4 (CH2CH3), 80.2 [C(CH3)3], 127.1 (C5-H), 147.2, 154.8, 161.3
and 174.8 (4 quat. C) ppm.
tert-Butyl (R)-(1-Thiocarbamoylethyl)carbamate (6): EDC (5.57 g,
29.1 mol) was added to a suspension of Boc--alanine (5 g,
26.4 mmol) and 1-hydroxybenzotriazole (3.92 g, 29 mmol) in
CH2Cl2 (250 mL) at 0 °C. The solution was warmed to room tem-
perature and stirred for 30 minutes. The solution was cooled to 0
°C and ammonia was condensed into the solution (20 drops). The
reaction mixture was warmed to room temperature, stirred for 30
minutes and then filtered. The mother liquor was concentrated and
purified by column chromatography (CH2Cl2 with 4% then 6%
MeOH) to give the amide as a white solid (4.99 g, 100%); m.p. 132
°C (ref.[30] m.p. 120Ϫ121 °C); Rf ϭ 0.22 (CH2Cl2 with 6% MeOH).
MS: m/z (ϩESI) found 211.1068 [MNaϩ], C8H16N2O3 (M, 188.1)
requires 211.1059. [α]2D5 ϭ 36.2 (c ϭ 1, CHCl3). IR (solid): ν˜ ϭ
3390, 3353, 3196, 1682, 1644, 1520, 1325, 1250 and 1165 cmϪ1. 1H
NMR (400 MHz, CDCl3): δ ϭ 1.36 (d, J ϭ 7 Hz, 3 H, CHCH3),
1.43 [s, 9 H, C(CH3)3], 4.21 (br, 1 H, CHCH3), 5.21 (br, 1 H, α-
NH), 5.93 (br, 1 H, NHAHB), 6.42 (br, 1 H, NHAHB) ppm. 13C
NMR (100 MHz, CDCl3): δ ϭ 18.4 (CHCH3), 28.3 [C(CH3)3], 49.6
(CHCH3), 80.1 [C(CH3)3], 155.6 and 175.5 ppm. C8H16N2O3
(188.2): calcd. C 51.05, H 8.57, N 14.88; found C 50.95, H 8.55,
N 14.77.
Diethyl 2-Phenylacetylaminomalonate: Phenylacetyl chloride
(5.95 mL, 45 mmol) was added dropwise to a solution of diethyl
aminomalonate hydrochloride (10 g, 47 mmol) and sodium hydro-
gen carbonate (9.92 g, 118 mmol) in Et2O (100 mL) and water
(100 mL) cooled at 0 °C. The solution was warmed to room tem-
perature, stirred for 1 hour and acidified with 3  aqueous HCl to
pH 2. The organic layer was washed with water (50 mL) then brine
(50 mL), dried (Na2SO4) and concentrated to give the amide as a
white fluffy solid (12.9 g, 98% yield); m.p. 68 °C; Rf ϭ 0.23 (Et2O/
hexane, 3:2). MS: m/z (ϩESI) found 294.1341 [MHϩ], C15H19NO5
(M, 293.1) requires 294.1341. IR (solid): ν˜ ϭ 3315, 1740, 1646,
1
1533, 1235, 1175 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 1.26 (t,
J ϭ 7 Hz, 6 H, OCH2CH3), 3.64 (s, 2 H, COCH2), 4.23 (m, 4 H,
OCH2CH3), 5.13 (d, J ϭ 7 Hz, 1 H, NHCH), 6.45 (br, 1 H,
NHCH), 7.35 (m, 5 H, arom. CH) ppm. 13C NMR (100 MHz,
CDCl3): δ ϭ 13.9 (OCH2CH3), 43.1 (COCH2), 56.5 (CHNH), 62.6
(OCH2CH3), 127.5 (arom. CH), 129 (arom. CH), 129.4 (arom.
CH), 134.1 (arom. C), 166.1 (CO), 170.6 (CO) ppm. C15H19NO5
(293.3): calcd. C 61.42, H 6.53, N 4.78; found C 61.39, H 6.43,
N 4.77.
Belleau’s reagent (5.05 g, 9.55 mmol) was added to a solution of
the amide (3 g, 15.9 mmol) in THF (100 mL) cooled at 0 °C. The
solution was warmed to room temperature, stirred for 40 minutes
and partitioned between ice (150 mL) and saturated aqueous
(4-Methoxy-1H-indol-3-ylmethyl)dimethylamine (16): A solution of
NaHCO3 (150 mL). This was extracted with Et2O (3 ϫ 150 mL). 4-methoxy indole (10 g, 68 mmol) in CH3CN (50 mL) was added
The organic layers were combined, washed with brine (150 mL),
dried (Na2SO4) and concentrated. The residue was purified by col-
umn chromatography (toluene/EtOAc, 8:2 then 7:3) to give thioam-
over 20 minutes to a suspension of N,N-dimethylmethyleneammo-
nium iodide (15 g, 81 mmol) in CH3CN (50 mL) and AcOH
(25 mL) at room temperature. The solution was stirred for 2 hours
Eur. J. Org. Chem. 2002, 3995Ϫ4004
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S. V. Ley, A. Priour
FULL PAPER
and partitioned between IPA and CHCl3 (1:3, 250 mL) and 10%
7.09 (m, 2 H), 7.13Ϫ7.22 (m, 3 H), 8.22 (d, J ϭ 8.5 Hz, 1 H),
aqueous NaOH (250 mL). The aqueous layer was extracted with 10.76 (br, 1 H, indole NH), 12.35 (br, 1 H, CO2H) ppm. 13C NMR
IPA/CHCl3 (1:3, 250 mL). The organic layers were combined, dried (100 MHz, [D6]DMSO): δ ϭ 29.2 (NHCHCH2), 42.5 (CH2Ph),
(Na2SO4) and concentrated to give gramine 16 as a white solid
54.1 and 55.4 (OCH3 and NHCHCH2), 99.3, 105.3, 110.6, 117.3,
(13.80 g, 99% yield); m.p. 137Ϫ138 °C (ref.[32] 136Ϫ138 °C). MS: 122.2, 122.8, 126.6, 128.5, 129.3, 136.7, 138.3, 154.5, 170.3,
m/z (ϩESI) found 205.1345 [MHϩ], C12H16N2O (M, 204.1) re-
quires 205.1341. IR (solid): ν˜ ϭ 3100, 1588, 1515, 1447, 1244, 1085,
174.3 ppm. C20H20N2O4 (352.4): calcd. C 68.17, H 5.72, N 7.95;
found C 67.93, H 5.80, N 7.84.
995, 726 cmϪ1 1H NMR (400 MHz, CDCl3): δ ϭ 2.32 [s, 6 H,
.
(S)-2-Benzyloxycarbonylamino-3-(4-methoxy-1H-indol-3-yl)pro-
pionic Acid (8): Aqueous 0.5  NaOH was added to a solution of
tryptophan 18 (0.815 g, 2.31 mmol) in MeOH (15 mL) and water
(120 mL) to set the pH to 7.6. The volume was adjusted with water
to 200 mL and penicillin G acylase immobilised (Penicillin G amid-
ase immobilised from E. coli, 150 U/g, [EC 3.5.1.11], from Fluka
(cat. number: 76428); 0.08 g, 9.6 U) was added. The reaction mix-
ture was shaken at room temperature in the dark. When the reac-
N(CH3)2], 3.82 (s, 2 H, CH2), 3.92 (s, 3 H, OCH3), 6.49 (d, 1 H,
arom. CH), 6.95 (d, 1 H, arom CH), 6.99 (br, 1 H, C2-H), 7.07 (m,
1 H, arom. CH), 8.18 (br, 1 H, NH) ppm. 13C NMR (100 MHz,
CDCl3): δ ϭ 45 (NCH3), 55 (OCH3), 55 (CH2), 99.5, 104.6, 112.8,
117.6, 122.4, 122.9, 137.9, 154.8 ppm. C12H16N2O (204.3): calcd. C
70.56, H 7.90, N 13.71; found C 70.36, H 7.81, N 13.42.
Diethyl 2-(4-Methoxy-1H-indol-3-ylmethyl)-2-phenylacetylaminom-
alonate (17): A solution of sodium ethoxide (21% weight in EtOH, tion did not proceed further, as measured by HPLC, or when nearly
14.4 mL, 39 mmol) was added to a solution of diethyl 2-acetylam- 50% conversion was measured by HPLC or NMR spectroscopy,
ino-2-phenylmalonate (9.43 g, 32 mmol) stirred in absolute EtOH the solution was filtered. It was then acidified with 3  aqueous
(100 mL) at 0 °C. After 5 minutes gramine 16 (6.70 g, 32 mmol) was HCl to pH 1.5 and washed with EtOAc (3 ϫ 70 mL). The pH was
added in one portion. After 5 minutes dimethyl sulfate (4.6 mL,
48 mmol) was added dropwise. The solution was warmed to room
temperature, stirred for 2 hours and partitioned between Et2O
(150 mL) and water (150 mL). The reaction mixture was acidified
with 3  aqueous HCl to pH 3. The organic layer was washed with
water (100 mL), dried (Na2SO4) and concentrated. The residue was
adjusted to 7 with 10% aqueous NaOH. NaHCO3 (0.21 g,
2.5 mmol), THF (50 mL) and carbobenzyloxy chloride (0.19 mL,
1.3 mmol) were added successively. The reaction mixture was
stirred overnight at room temperature. The solution was partially
concentrated, acidified with 3  aqueous HCl to pH 2 and ex-
tracted with CH2Cl2 (3 ϫ 50 mL). The organic layers were com-
granulated in Et2O/hexane (3:2, 50 mL) to give malonate 17 as a bined, dried (Na2SO4) and concentrated. The residue was purified
white solid (11.9 g, 82% yield); m.p. 136Ϫ138 °C; Rf ϭ 0.34 (Et2O). by column chromatography (EtOAc/hexane, 3:2 with 0.5% AcOH)
MS: m/z (ϩESI) found 475.1839 [MNaϩ], C25H28N2O6 (M, 452.2) to give carbamate 8 as a white solid (0.376 g, 44% yield, maximum
requires 475.1845. IR (solid): ν˜ ϭ 3380, 3271, 1732, 1654, 1510, 50%); m.p. 152 °C; Rf ϭ 0.27 (EtOAc/hexane, 3:1 with 1% AcOH).
1
1197, 1083 cmϪ1. H NMR (400 MHz, CDCl3): δ ϭ 1.18 (t, J ϭ MS: m/z (ϩESI) found 391.1277 [MNaϩ], C20H20N2O5 (M, 368.1)
7 Hz, 6 H, OCH2CH3), 3.47 (s, 2 H, CH2Ph), 3.84 (s, 3 H, OCH3),
3.95 (s, 2 H, CCH2), 4.13 (dq, J ϭ 11 and 7 Hz, 2 H, OCHA-
requires 391.1270. [α]2D5 ϭ Ϫ52.8 (c ϭ 0.5, MeOH). 1H NMR
(400 MHz, [D6]DMSO, 60 °C): δ ϭ 2.95 (dd, J ϭ 14 and 10 Hz, 1
HBCH3), 4.22 (dq, J ϭ 11 and 7 Hz, 2 H, OCHAHBCH3), 6.46 H, NHCHAHB), 3.35 (dd, J ϭ 14 and 4 Hz, 1 H, NHCHAHB),
(d, 1 H, arom. CH), 6.59 (d, J ϭ 8 Hz, 1 H, C2-H), 6.68 (s, 1 H,
NHCO), 6.94 (d, 1 H, arom. CH), 7.07 (m, 1 H, arom. CH), 7.11
(m, 2 H, arom. CH); 7.21 (m, 3 H, arom. CH), 8.20 (br, 1 H, indole
3.83 (s, 3 H, OCH3), 4.30 (m, 1 H, NHCHCH2), 4.95 (m, 2 H,
CH2Ph), 6.44 (d, J ϭ 7 Hz, 1 H, arom. CH), 6.9Ϫ7 (m, 3 H, arom.
CH), 7.24Ϫ7.34 (m, 5 H, arom. CH), 7.41 (d, J ϭ 8 Hz, 1 H,
NH) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ 14.3 (OCH2CH3), NHCHCH2), 10.75 (br. s, 1 H, indole NH) ppm. 13C NMR
29.9 (CCH2), 43.8 (CH2Ph), 55.4 (OCH3), 62.5 (OCH2CH3), 68 (100 MHz, [D6]DMSO): δ ϭ 28.9 (NHCHCH2), 55.4 (OCH3), 55.9
(CCH2), 100, 105.1, 109.3, 118.3, 122.9, 123, 127.4, 129.1, 129.7, (NHCHCH2), 65.5 (CH2Ph), 99.2, 105.1, 110.6, 117.1, 122.1, 123,
135, 137.9, 154.8, 168.5, 169.8 ppm. C25H28N2O6 (452.5): calcd. C
66.36, H 6.24, N 6.19; found C 66.34, H 6.23, N 6.22.
127.8, 128, 128.6, 137.4, 138.2, 154.3, 156.3, 174.4 ppm.
Nα-Cbz-(4-OMe)Trp-Gly-OMe
(19): Diisopropylethylamine
3-(4-Methoxy-1H-indol-3-yl)-2-phenylacetylaminopropionic
Acid (0.19 mL, 1.08 mmol) and EDC (172 mg, 0.9 mmol) were added
successively to suspension of carboxylic acid (265 mg,
(18): A suspension of malonate 17 (11.9 g, 26 mmol) in MeOH/
dioxane (1:1, 120 mL) and 1.5  aqueous NaOH (60 mL) was
stirred for 2 hours at 50 °C. The solution was cooled to 0 °C,
a
8
0.72 mmol), glycine methyl ester hydrochloride (135 mg,
1.08 mmol) and 1-hydroxybenzotriazole (145 mg, 1.08 mmol) in
acidified with 3  aqueous HCl to pH 2 and extracted with CH2Cl2 CH2Cl2 (8 mL) at 0 °C. The reaction mixture was warmed to room
(100 mL). The organic layer was partially concentrated, diluted temperature and stirred for 2 hours. The solution was partitioned
with dioxane (30 mL) and stirred for 30 minutes at 100 °C. The between 0.1  aqueous HCl (4 mL) and CH2Cl2 (4 mL). The or-
solution was cooled to 0 °C and 1.5  aqueous NaOH (60 mL) was
added. The solution was stirred for 1 hour at room temperature,
partitioned with CH2Cl2 (100 mL) and acidified with 3  aqueous
ganic layer was washed with saturated aqueous ammonium chlor-
ide (4 mL), dried (Na2SO4) and concentrated. The residue was
purified by column chromatography (CH2Cl2 with 2% MeOH) to
HCl to pH 2. The aqueous layer was extracted with CH2Cl2 give dipeptide 19 (298 mg, 94% yield) as an oil; Rf ϭ 0.38 (CH2Cl2
(50 mL). The organic layers were combined, dried (Na2SO4) and
concentrated. The residue was recrystallised from EtOAc/Et2O to
with 5% MeOH). MS: m/z (ϩESI) found 462.1653 [MNaϩ],
C23H25N3O6 (M, 439.2) requires 462.1641. [α]2D5 ϭ Ϫ19.2 (c ϭ 1,
give two crops of racemic amino acid 18 as a white solid (6.4 g, MeOH). IR (film): ν˜ ϭ 3316, 1703, 1665, 1507, 1244, 1211 cmϪ1
.
69% yield); m.p. 153Ϫ156 °C; Rf ϭ 0.25 (EtOAc with 2% AcOH). 1H NMR (400 MHz, [D8]toluene, 60 °C): δ ϭ 3.25 (s, 3 H,
MS: m/z (ϩESI) found 375.1322 [MNaϩ], C20H20N2O4 (M, 352.1) CO2CH3), 3.39 (m, 1 H, NHCHCHAHB), 3.53 (dd, J ϭ 14 and 5.2,
requires 375.1321. IR (solid): ν˜ ϭ 3291, 1717, 1622, 1511, 1433,
1 H, NHCHCHAHB), 3.63 (s, 3 H, OCH3), 3.69 (m, 2 H, NHCH2),
1
1259, 1240 cmϪ1. H NMR (400 MHz, [D6]DMSO): δ ϭ 3.00 (dd, 4.69 (m, 1 H, NHCHCH2), 4.92 (s, 2 H, CH2Ph), 6.18 (d, J ϭ
J ϭ 14 and 10 Hz, 1 H, NHCHCHAHB), 3.35 (m, 1 H,
7 Hz, 1 H, NHCHCH2), 6.32 (d, J ϭ 8 Hz, 1 H, arom. CH), 6.43
NHCHCHAHB), 3.39 (s, 2 H, CH2Ph), 3.81 (s, 3 H, OCH3), 4.50 (br, 1 H, NHCH2), 6.66 (br, 1 H, ind. C2 H), 6.79 (d, J ϭ 8 Hz, 1
(m, 1 H, NHCHCH2), 6.42 (m, 1 H, arom. CH), 6.93 (m, 3 H), H, arom. CH), 6.9Ϫ7.1 (m, 6 H, arom. CH), 7.79 (br, 1 H, arom.
4000
Eur. J. Org. Chem. 2002, 3995Ϫ4004

Total Synthesis of the Cyclic Peptide Argyrin B
FULL PAPER
NH) ppm. 13C NMR (100 MHz, [D8]toluene, 60 °C): δ ϭ 29.4 CO2H) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ 9.5 and 9.7*
(NHCHCH2), 40.8 (NHCH2), 50.9 (CO2CH3), 54.5 (OCH3), 57.5 (CH2CH3), 25.6 (CH2), 27.3* and 28.2 [C(CH3)3], 54.4 and 55.7*
(NHCHCH2), 66.3 (CH2Ph), 99.6, 105.1, 110.8, 117.7, 122.4, 122.6, (α-CH), 80 and 81.6* [C(CH3)3], 155.6 and 157* (CO), 177.1 (CO)
127.4, 127.6, 128.1, 137.1, 138.3, 154.2, 156.3, 169.6, 172 ppm. ppm. C9H17NO4: calcd. C 53.19, H 8.43, N 6.89; found C 53.20,
C23H25N3O6 (439.5): calcd. C 62.86, H 5.73, N 9.56; found C 62.72, H 8.34, N 6.75.
H 5.78, N 9.46.
(S)-2-tert-Butoxycarbonylamino-3-phenylselanylpropionic Acid (23):
Diethyl azodicarboxylate (1.53 mL, 9.75 mmol) was added to a so-
(30 mg, 10% weight) was added to a solution of carbamate 19 lution of triphenylphosphane (2.55 g, 9.75 mmol) in THF (90 mL)
Nα-Cbz-Trp-(4-OMe)Trp-Gly-OMe (3): Palladium on charcoal
(297 mg, 0.68 mmol) and 3  aqueous HCl (0.24 mL) in methanol
(10 mL). The reaction mixture was purged with hydrogen three
times and stirred for 4 hours at room temperature. The suspension
was filtered through a plug of Celite, washed with methanol (2 ϫ
5 mL) and concentrated by coevaporation with toluene (2 ϫ 5 mL).
The amine was used directly in the next step.
at Ϫ78 °C. This was allowed to warm to room temperature and
then cooled to Ϫ78 °C. A solution of N-tert-butoxycarbonyl--ser-
ine (2 g, 9.75 mmol) in THF (15 mL) was added over 20 minutes.
After 20 minutes, the reaction mixture was warmed to room tem-
perature, stirred for 2 hours then concentrated. The residue was
triturated in EtOAc/hexane (20 mL, 1:1) and filtered. The liquor
was concentrated and purified by column chromatography (EtOAc/
hexane, 3:7). The β-lactone was used directly in the next step (NB
Storage of the β-lactone results in decomposition. It is recom-
mended to use the residue directly or to store the chromatography
fractions containing the product in the fridge overnight and con-
centrate the solution just prior to use.).
Diisopropylethylamine (0.13 mL, 0.74 mmol) and EDC (162 mg,
0.84 mmol) were added successively to a suspension of N-Carbo-
benzyloxy--tryptophan (3.43 g, 1.01 mmol), the amine and 1-hydro-
xybenzotriazole (139 mg, 1.01 mmol) in CH2Cl2 (10 mL) at 0 °C.
The reaction mixture was warmed to room temperature and stirred
for 2 hours. The solution was partitioned between 0.1  aqueous
HCl (10 mL) and CH2Cl2 (10 mL). The organic layer was washed Sodium trimethoxyborohydride (0.84 g, 6.57 mmol) was added to
with saturated aqueous ammonium chloride (10 mL), dried
(Na2SO4) and concentrated. The residue was purified by column
a solution of diphenyl diselenide (1.02 g, 3.27 mmol) in dry ethanol
(25 mL) at room temperature under argon. The resulting pale
chromatography (CH2Cl2 with 2.5% MeOH) to give tripeptide 3 as peach solution was stirred for 30 minutes then a solution of the β-
a glassy solid (342 mg, 81% yield); m.p. 119Ϫ124 °C; Rf ϭ 0.22 lactone in dry ethanol (5 mL) was added. The reaction mixture was
(CH2Cl2 with 4% MeOH). MS: m/z (ϩESI) found 648.2431
[MNaϩ], C34H35N5O7 (M, 625.3) requires 648.2434. [α]2D5 ϭ Ϫ34
(c ϭ 1, MeOH). IR (solid): ν˜ ϭ 3421, 3305, 1742, 1697, 1640, 1531
stirred for 2 hours and concentrated. The residue was partitioned
between aqueous saturated NaHCO3 (50 mL) and Et2O (50 mL).
The aqueous layer was washed with Et2O (20 mL), acidified with
and 1224 cmϪ1. 1H NMR (400 MHz, [D6]DMSO, 60 °C): δ ϭ 2.87 3  aqueous HCl to pH 2 and extracted with EtOAc (3 ϫ 50 mL).
(dd, 1 H, NHCHCHAHB), 3.07 (dd, 1 H, NHCHCHAHB), 3.12 The organic layers were combined, washed with brine (50 mL),
(dd, 1 H, NHCHCHCHD), 3.38 (dd, 1 H, NHCHCHCHD), 3.63 (s,
dried (Na2SO4) and concentrated to give amino acid 23 as a white
3 H, CO2CH3), 3.84 (m, 2 H, 4-CH2), 3.84 (s, 3 H, OCH3), 4.30 solid (1.37 g, 41% yield); m.p. 94Ϫ95 °C (ref.[26] m.p. 91Ϫ92 °C);
(m, 1 H, NHCHCH2), 4.65 (m, 1 H, NHCHCH2), 4.92 (s, 2 H, Rf ϭ 0.44 (CH2Cl2/MeOH, 9:1 with 2% AcOH). MS: m/z (ϩESI)
CH2Ph), 6.44 (d, 1 H, arom. CH), 6.90Ϫ7.07 (m, 7 H, arom. CH), found 368.0370 [MNaϩ], C14H19NO4Se (M, 345) requires 368.0377.
7.15Ϫ7.35 (m, 6 H, arom. CH and NHCHCH2), 7.55 (d, 1 H,
arom. CH), 7.84 (dd, 1 H, 4-α-NH), 7.92 (d, J ϭ 12 Hz, 1 H, MeOH)]. IR (solid): ν˜ ϭ 3300, 2930, 2519, 1729, 1652, 1413, 1220
NHCHCH2), 10.6 (br. s, 2 H) ppm. 13C NMR (100 MHz, cmϪ1 1H NMR (400 MHz, CDCl3): δ ϭ 1.41 [s, 9 H, C(CH3)3],
[α]2D5 ϭ Ϫ36.8 (c ϭ 1, MeOH) (ref.[26] [α]2D5 ϭ Ϫ38.1 (c ϭ 1,
.
[D6]DMSO, 60 °C): δ ϭ 28.3 (NHCHCH2), 29.6 (NHCHCH2), 3.35 (br, 2 H, CH2), 4.64 (br, 1 H, α-CH), 5.28 (br, 1 H, α-NH),
41.2 (4-CH2), 52 (4-CH3), 54.5 (NHCHCH2), 55.6 (3-OCH3), 56.2 7.26 (br, 3 H, arom. CH), 7.55 (br, 2 H, arom. CH) ppm. 13C NMR
(NHCHCH2), 65.9 (CH2Ph), 99.5, 105.4, 110.6, 110.8, 111.7, 117.7,
(100 MHz, CDCl3): δ ϭ 28.6 (CH3), 30.4 (CH2), 53.8 (α-CH), 81
118.7, 118.8, 121.2, 122.1, 122.5, 124.1, 127.82, 127. 85, 127.88, [C(CH3)3], 128.1 (arom. CH), 129.2 (arom. C), 129.6 (arom. CH),
128, 128.7, 136.6, 137.4, 138.4, 154.7 (4-CO2), 170.5 (CO), 171.9
(CO), 172.4 (CO) ppm. C34H35N5O7 (625.7): calcd. C 65.27, H
5.64, N 11.19; found C 65.06, H 5.66, N 11.06.
134.1 (arom. CH), 155.7 (CO), 175.5 (CO) ppm.
Boc-(Ph)Sec-Sar-OEt (24): Diisopropylethylamine (1.38 mL,
7.91 mmol) was added to a suspension of carboxylic acid 23
(0.91 g, 2.64 mmol), sarcosine ethyl ester hydrochloride (0.445 g,
2.90 mmol) and PyBroP (1.35 g, 2.90 mmol) in CH2Cl2 (20 mL)
at 0 °C. The reaction mixture was warmed to room temperature
and stirred for 3 hours. The solution was partitioned between satur-
ated aqueous ammonium chloride (20 mL) and CH2Cl2 (20 mL).
The aqueous layer was extracted with CH2Cl2 (20 mL). The organic
layers were combined, washed with water (20 mL), dried (Na2SO4)
and concentrated. The residue was purified by column chromato-
graphy (EtOAc/hexane, 3:7) to give dipeptide 24 as an oil (0.94 g,
80% yield); Rf ϭ 0.51 (EtOAc/hexane, 1:1). MS: m/z (ϩESI) found
467.1041 [MNaϩ], C19H28N2O5Se (M, 444.1) requires 467.1061.
(R)-2-tert-Butoxycarbonylaminobutyric Acid: Dioxane (20 mL) and
di-tert-butyl dicarbonate (4.1 g, 19.3 mmol) were added success-
ively to a solution of (R)-2-aminobutyric acid (2 g, 19.4 mmol) and
NaOH (0.77 g, 19.3 mmol) in water (20 mL) at 0 °C. The reaction
mixture was warmed to room temperature and stirred for 3 hours.
The solution was partially concentrated, acidified with 3  aqueous
HCl to pH 2 and extracted with EtOAc (2 ϫ 20 mL). The organic
layers were combined, washed with water (20 mL) and brine
(20 mL), dried (Na2SO4) and concentrated. The residue was puri-
fied by column chromatography (EtOAc/petroleum ether, 1:3 with
1% AcOH) to give the amide (3.45 g, 88% yield) as an oil; Rf ϭ
0.63 (EtOAc with 2.5% AcOH). MS: m/z (ϩESI) found 226.1046 [α]D25 ϭ Ϫ1.5 (c ϭ 1, CHCl3). IR (solid): ν˜ ϭ 3306, 2978, 2934, 1745,
[MNaϩ], C9H17NO4 (M, 203.1) requires 226.1055. [α]2D5 ϭ Ϫ9.0
1706, 1647, 1478, 1199, 1164 cmϪ1. H NMR (400 MHz, CDCl3,
4:1 rotamer ratio, the asterisk denotes minor rotamer peak): δ ϭ
1.25* and 1.26 (t, J ϭ 7 Hz, 3 H, CH2CH3), 1.41* and 1.43 [s, 9
1
(c ϭ 1, CHCl3). IR (solid): ν˜ ϭ 1710, 1510, 1394, 1368, 1159 cmϪ1
1H NMR (400 MHz, CDCl3, rotamer ratio 3:2, the asterisk denotes
.
minor rotamer peak): δ ϭ 0.94 and 0.96* (m, 3 H, CH2CH3), 1.41 H, C(CH3)3], 2.90* and 2.99 (s, 3 H, NCH3), 3.10 (dd, J ϭ 13 and
[s, 9 H, C(CH3)3], 1.71 and 1.86 (m, 2 H, CH2CH3), 4.04* and 4.26 7 Hz, 1 H, CHCHAHB), 3.21 (dd, J ϭ 13 and 6 Hz, 1 H,
(br, 1 H, α-CH), 5.14 and 6.45* (br, 1 H, α-NH), 11.19 (s, 1 H,
CHCHAHB), 3.93 (d, J ϭ 17 Hz, 1 H, CHAHBNCH3), 4.03 (d, J ϭ
Eur. J. Org. Chem. 2002, 3995Ϫ4004
4001

S. V. Ley, A. Priour
FULL PAPER
17 Hz, 1 H, CHAHBNCH3), 4.12 (q, J ϭ 7 Hz, 1 H, OCHA-
HBCH3), 4.18 (q, J ϭ 7 Hz, 1 H, OCHAHBCH3), 4.67* and 4.89
stirred for 2 hours at room temperature. The suspension was fil-
tered through a plug of Celite, washed with methanol (2 ϫ 5 mL)
m, 1 H, NHCH), 5.30* and 5.38 (d, J ϭ 8 Hz, 1 H, NHCH), 7.26 and concentrated by coevaporation with toluene (2 ϫ 5 mL). The
(m, 3 H, arom. CH), 7.54*and 7.58 (m, 2 H, arom. CH) ppm. 13C
NMR (100 MHz, CDCl3): δ ϭ 14.4* and 14.5 (CH2CH3), 28.6*
and 28.7 [C(CH3)3], 31 (CHCH2), 35.6* and 36.1 (NCH3), 48.8
(CHCH2), 50.1 (CH2NCH3), 61.7 (CH2CH3), 80.3 [C(CH3)3], 127.8
(arom. CH), 129.5 (arom. CH), 130.1 (arom. C), 133.4* and 133.7
(arom. CH), 155.4 (CO), 169 (CO), 171.8 (CO) ppm.
C19H28N2O5Se (443.4): calcd. C 51.47, H 6.37, N 6.32; found C
51.24, H 6.37, N 6.29.
resulting amine was used directly in the next step.
EDC (62 mg, 0.32 mmol) was added to a suspension of the carb-
oxylic acid, the amine and 1-hydroxybenzotriazole (52 mg,
0.39 mmol) in CH2Cl2 (10 mL) at 0 °C. The reaction mixture was
warmed to room temperature and stirred for 2 hours. The solution
was partitioned between water (5 mL) and CH2Cl2 (5 mL) and the
aqueous layer was extracted with CH2Cl2 (5 mL). The organic
layers were combined, washed with aqueous saturated ammonium
chloride (10 mL), dried (Na2SO4) and concentrated. The residue
was purified by column chromatography (CH2Cl2 with 4.5%
MeOH) to give pentapeptide 26 as a sticky solid (186 mg, 97%
yield); Rf ϭ 0.42 (CH2Cl2 with 10% MeOH). MS: m/z (ϩESI)
found 768.2800 [MNaϩ], C37H43N7O8S (M, 745.3) requires
N-Boc-D-Abu-(Ph)Sec-Sar-OEt (25): Trifluoroacetic acid (5 mL)
was added dropwise to a solution of carbamate 24 (0.319 g,
0.72 mmol) in CH2Cl2 (5 mL) at 0 °C. The reaction mixture was
warmed to room temperature and stirred for 30 minutes. The solu-
tion was concentrated by coevaporation with toluene (3 ϫ 5 mL)
and the resulting ammonium salt was used directly in the next step. 768.2792. [α]2D5 ϭ Ϫ45.0 (c ϭ 1, CHCl3). IR (solid): ν˜ ϭ 3320, 1654,
1507, 1246, 1164 cmϪ1. 1H NMR (400 MHz, CDCl3): δ ϭ 1.46 (m,
3 H, 1-CHCH3), 1.47 [s, 9 H, C(CH3)3], 3Ϫ3.2 (m, 3 H, NHCHCH2
and NHCHCHAHB), 3.44 (m, 1 H, NHCHCHAHB), 3.64 (s, 3 H,
3-CH3), 3.68 (s, 3 H, 4-OCH3), 3.81 (dd, J ϭ 18 and 5 Hz, 1 H, 4-
CHAHB), 4.01 (dd, J ϭ 18 and 6 Hz, 1 H, 4-CHAHB), 4.64 (m, 2
H, 2-NHCHCH2 and 3-NHCHCH2), 4.91 (m, 1 H, 1-CHCH3),
5.25 (d, J ϭ 7 Hz, 1 H, 1-NH), 6.36 (m, 1 H, arom. CH), 6.59 (m,
EDC (0.172 g, 0.90 mmol) and diisopropylethylamine (0.14 mL,
0.79 mmol) were added successively (addition of the base prior to
EDC results in the rapid formation of the diketopiperazine) to a
solution of the ammonium salt, (R)-2-tert-butoxycarbonylamino-
butyric acid (0.175 g, 0.86 mmol) and 1-hydroxybenzotriazole
(0.153 g, 1.13 mmol) in CH2Cl2 (10 mL) at 0 °C. The reaction mix-
ture was warmed to room temperature and stirred for 2 hours. The
2 H), 6.95 (m, 1 H, 4-NH), 6.95 (m, 1 H, arom. CH), 7.03 (m, 1
solution was partitioned between 0.1  HCl (10 mL) and CH2Cl2
H, NHCHCH2), 7.03 (m, 2 H, arom. CH), 7.13 (m, 1 H, arom.
(10 mL). The organic layer was washed with aqueous saturated am-
CH), 7.27 (m, 1 H, arom. CH), 7.52 (m, 1 H, arom. CH), 7.65 (m,
monium chloride (10 mL), dried (Na2SO4) and concentrated. The
residue was purified by column chromatography (CH2Cl2 with 1%
then 2% MeOH) to give tripeptide 25 as an oil (0.319 g, 84% yield);
Rf ϭ 0.26 (CH2Cl2 with 5% MeOH). MS: m/z (ϩESI) found
552.1584 [MNaϩ], C23H35N3O6Se (M, 529.2) requires 552.1589.
[α]D25ϭ 3.6 (c ϭ 1, CHCl3). IR (film): ν˜ ϭ 3309, 2972, 1744, 1716,
1 H, NHCHCH2), 7.90 (s, 1 H, 1-C5-H), 8.09 (br, 1 H, arom. NH),
8.94 (br, 1 H, arom. NH) ppm. 13C NMR (100 MHz, CDCl3): δ ϭ
21.6 (1-CHCH3), 26.9 (NHCHCH2), 27.9 (NHCHCH2), 28.3
[C(CH3)3], 41.1 (4-CH2), 49.1 (1-NHCHCH3), 52.1 (4-CH3), 54.9
(NHCHCH2), 55.2 (3-OCH3), 55.6 (NHCHCH2), 80.7 [C(CH3)3],
99.7, 105.3, 109.4, 110, 111.4, 117.4, 118.5, 119.5, 122, 122.5, 122.7,
123.2, 123.6, 127.2, 136.1, 138.1, 148.7, 153.8, 155.1, 161.6, 170.1,
171.6, 172.1, 174.8 ppm.
1
1642, 1493, 1366 and 1206 cmϪ1. H NMR (400 MHz, CDCl3, 3:1
rotamer ratio, the asterisk denotes minor rotamer peak): δ ϭ 0.93
and 0.92* (t, J ϭ 7.5 Hz, 3 H, 5-CH3), 1.25 and 1.22* (t, J ϭ 7 Hz,
3 H, OCH2CH3), 1.43 [s, 9 H, C(CH3)3], 1.6 (m, 1 H, 5-CHAHB), N-Boc-D-AlaThz-Trp-(4-OMe)Trp-Gly-D-Abu-(Ph)Sec-Sar-OEt
1.84 (m, 1 H, 5-CHAHB), 2.94 and 2.87* (s, 3 H, NCH3), 3.1 (dd,
J ϭ 13 and 7 Hz, 1 H, 6-CHAHB), 3.22 (dd, J ϭ 13 and 7 Hz, 1
(27): A 0.5  aqueous solution of LiOH (0.45 mL, 0.22 mmol) was
added to a solution of ester 26 (151 mg, 0.20 mmol) in THF/
H, 6-CHAHB), 3.91 (d, 1 H, 7-CHAHB), 4 (d, 1 H, 7-CHAHB), 4.09 MeOH/water (6:1.5:3 mL) at 0 °C. The reaction mixture was
(m, 1 H, 5-CH), 4.16 (q, J ϭ 7 Hz, 2 H, OCH2CH3), 5.16 and warmed to room temperature and stirred for 90 minutes. The solu-
4.90* (m, 1 H, 6-CH), 5.04 (br. s, 1 H, 5-NH), 6.95 (d, J ϭ 7 Hz,
tion was partitioned between 0.1  aqueous HCl (5 mL) and
1 H, 6-NH), 7.25 (m, 3 H, arom. CH), 7.56 and 7.52* (m, 2 H, CH2Cl2 (10 mL). The aqueous layer was extracted with CH2Cl2 (2
arom CH) ppm. 13C NMR (400 MHz, CDCl3): δ ϭ 9.8(5-CH3), ϫ 10 mL) and the organic layers were combined, dried (Na2SO4)
14.1 and 14* (OCH2CH3), 26.1 (5-CH2), 28.3 [C(CH3)3], 29.7 and and concentrated. The resulting carboxylic acid was used directly
29.9* (6-CH2), 36.4 and 35.2* (NCH3), 48.4 (6-CH), 49.7 (7-CH2), in the next step.
51.4 (5-CH), 61.3 and 61.7* (OCH2CH3), 79.9 [C(CH3)3], 127.5
Trifluoroacetic acid (2 mL) was added dropwise to a solution of
and 127.3* (arom. CH), 129.2 (arom. CH), 129.4 (quat. C), 133.2
carbamate 25 (117 mg, 0.22 mmol) in CH2Cl2 (3 mL) at 0 °C. The
and 133* (arom. CH), 155.4 [CO2C(CH3)3], 168.5 (CO), 170.9 and
reaction mixture was warmed to room temperature and stirred for
171* (CO), 171.6 (CO) ppm.
1 hour. The solution was concentrated by coevaporation with tolu-
N-Boc-D-AlaThz-Trp-(4-OMe)Trp-Gly-OMe (26): A 0.5  aqueous
ene (3 ϫ 5 mL) and the resulting ammonium salt was used directly
solution of LiOH (0.8 mL, 0.4 mmol) was added to a solution of in the next step.
ester 2 (0.1 g, 0.33 mmol) in THF/MeOH/water (4:1:2 mL) at 0 °C.
Diisopropylethylamine (39 µL, 0.22 mmol) and EDC (48 mg,
The reaction mixture was warmed to room temperature and stirred
for 2 hours. The solution was partitioned between 0.1  aqueous
HCl (10 mL) and CH2Cl2 (20 mL). The aqueous layer was ex-
tracted with CH2Cl2 (10 mL) and the organic layers were com-
bined, dried (Na2SO4) and concentrated. The carboxylic acid was
used directly in the next step.
0.25 mmol) were added successively to a suspension of the carb-
oxylic acid, the ammonium salt and 1-hydroxybenzotriazole
(43 mg, 0.32 mmol) in CH2Cl2 (15 mL) at 0 °C. The reaction mix-
ture was warmed to room temperature and stirred for 90 minutes.
The solution was partitioned between 0.1  aqueous HCl (10 mL)
and CH2Cl2 (20 mL). The aqueous layer was extracted with
CH2Cl2 (2 ϫ 15 mL). The organic layers were combined, washed
with aqueous saturated ammonium chloride (20 mL), dried
Palladium on charcoal (15 mg, 10% weight) was added to a solu-
tion of the carbamate 3 (161 mg, 0.26 mmol) in methanol (10 mL).
The reaction mixture was purged with hydrogen three times and (Na2SO4) and concentrated. The residue was purified by column
4002 Eur. J. Org. Chem. 2002, 3995Ϫ4004

Total Synthesis of the Cyclic Peptide Argyrin B
chromatography (CH2Cl2 with 5% MeOH) to give octapeptide 27 1 H, 1-α-NH), 8.45 (br. s, 1 H, ind. NH), 8.64 (d, J ϭ 7 Hz, 1 H,
FULL PAPER
as a sticky solid (185 mg, 80% yield); Rf ϭ 0.15 (CH2Cl2 with 6%
MeOH). MS: m/z (ϩESI) found 1165.3669 [MNaϩ],
C54H66N10O11SSe (M, 1142.4) requires 1165.3696. [α]2D5 ϭ 16.8 (c ϭ
2-α-NH), 8.66 (m, 1 H, 3-α-NH), 10.96 (br. s, 1 H, ind. NH) ppm.
13C NMR (150 MHz, CDCl3): δ ϭ 10.7 (5-CH3), 20 (1-CH3), 21.6
(5-CH2), 26.8 (2-CH2), 26.9 (3-CH2), 27.94 (6-CH2), 36.8 (7-CH3),
40.9 (4-CH2), 46.3 (1-α-CH), 50.2 (6-CH), 52 (2-α-CH), 52.1 (7-
1, CHCl3). IR (solid): ν˜ ϭ 3309, 3055, 2977, 2933, 1645, 1531,
1
1506, 1253, 1164, 732 cmϪ1. H NMR (400 MHz, [D6]DMSO, 90 CH2), 55 (5-CH), 56.1 (3-CH3), 57.6 (3-α-CH), 101.2 (arom. 3-CH),
°C): δ ϭ 0.86 (t, J ϭ 7.4 Hz, 3 H, 5-CH3), 1.18 (m, 3 H, 7-
CH2CH3), 1.40 [s, 9 H, 1-C(CH3)3], 1.43 (d, J ϭ 7 Hz, 3 H, 1-
CHCH3), 1.61 (m, 1 H), 1.73 (m, 1 H), 2.80Ϫ3.35 (m, 7 H), 2.98
106.2 (arom. C), 106.6 (arom. 3-CH), 108.3 (arom. C), 111.2 (arom.
2-CH), 116.4 (arom. 2-CH), 117.4 (arom. C), 119.3 (arom. 2-CH),
121.4 (arom. 2-CH), 122.7 (1-C5 H), 123.5 (arom. 3-CH), 123.6
(s, 3 H, 7-NCH3), 3.37 (m, 1 H), 3.76 (m, 2 H), 3.81 (s, 3 H, 3- (arom. 3-CH), 124.7 (arom. 2-CH), 126.5 (arom. C), 128.1 (arom.
CH3), 4.08 (m, 2 H, 7- CH2CH3), 4.08 (m, 1 H), 4.27 (m, 1 H),
6-CH), 128.1 (arom. 6-C), 129.5 (arom. 6-CH), 133.2 (arom. 6-
4.58 (m, 1 H), 4.70 (m, 1 H), 4.84 (m, 1 H, 1-CHCH3), 6.41 (dd, CH), 134.7 (arom. C), 138.4 (arom. C), 150.1 (1-C4), 152.4 (arom.
J ϭ 7 and 1.5, 1 H), 6.85Ϫ6.95 (m, 4 H), 7.01 (t, J ϭ 7.6 Hz, 1 C), 159.8, 167.5, 170.1, 171.6, 171.9, 172, 172.6 and 173.1 (7 CO
H), 7.09 (d, J ϭ 2 Hz, 1 H), 7.20Ϫ7.60 (m, 10 H), 7.79 (d, J ϭ 7.8 and 1-C2) ppm.
Hz, 1 H), 7.96 (d, J ϭ 7.4 Hz, 1 H), 8 (s, 1 H, 1-C5 H), 8.14 (br, 1
Argyrin B (1): Sodium periodate (17 mg, 80 µmol) was added to a
solution of phenyl selenide (28; 20 mg, 20 µmol) in water (4 mL)
and dioxane (4 mL) at room temperature. The solution was stirred
for 2 hours then diluted with water (10 mL) and extracted with
H), 10.42 (s, 1 H), 10.48 (s, 1 H) ppm. 13C NMR (150 MHz,
[D6]DMSO, 90 °C): δ ϭ 10.3, 14.3, 20.9, 25.9, 28.4, 28.7, 29.4, 36.2,
43, 49.2, 49.3, 54.2, 54.4, 55.3, 55.6, 60.9, 79.1, 99.8, 105.5, 110.3,
110.9, 111.7, 117.8, 118.7, 118.9, 121.3, 122.1, 122.6, 123.8, 124.2,
CHCl3/IPA (3:1, 2 ϫ 20 mL). The organic layers were combined,
127.4, 128.1, 129.5, 129.7, 130.5, 132.8, 136.8, 138.5, 149.6, 154.7,
washed with water (10 mL) and concentrated. The residue was dis-
155.4, 160.7, 169, 170.8, 171.5, 171.6, 172.2, 176.5 ppm.
solved into acetonitrile (4 mL) then water (2 mL) and saturated
aqueous NaHCO3 (2 mL) were added successively. The reaction
mixture was stirred for 2 days, diluted with water (10 mL) and ex-
tracted with CHCl3/IPA (3:1, 2 ϫ 20 mL). The organic layers were
combined, washed with water (10 mL), dried (Na2SO4) and concen-
trated. This was purified by column chromatography (CH2Cl2 with
a gradient of 1 to 4% of MeOH) to give Argyrin B (1; 11.2 mg,
66% yield) as a sticky solid; Rf ϭ 0.5 (CH2Cl2 with 10% MeOH).
MS: m/z (ϩESI) found 861.3113 [MNaϩ], C41H46N10O8S (M,
838.3) requires 861.3119. [α]2D5 (synthetic product) ϭ 92.2 (c ϭ 0.27,
acetone), [α]2D5 (natural product) ϭ 104 (c ϭ 2.9, acetone) (personal
communication Heinrich Steinmetz, GBF Naturstoffchemie,
Braunschweig, Germany. IR (film): ν˜ ϭ 3296, 1650, 1535 and 1254
Cyclo[D-AlaThz-Trp-(4-OMe)Trp-Gly-D-Abu-(Ph)Sec-Sar] (28): A
0.5  aqueous solution of LiOH (0.15 mL, 75 µmol) was added to
a solution of the ester 27 (74 mg, 65 µmol) in THF/MeOH/water
(2:0.5:1 mL) at 0 °C. The reaction mixture was warmed to room
temperature and stirred for 2 hours. The solution was partitioned
between 0.1  aqueous HCl (5 mL) and CH2Cl2 (10 mL). The
aqueous layer was extracted with CH2Cl2 (2 ϫ 10 mL). The organic
layers were combined, dried (Na2SO4) and concentrated. The re-
sulting carboxylic acid was used directly in the next step.
The residue was dissolved in anisole (0.5 mL) and the solution was
cooled to 0 °C before trifluoroacetic acid (5 mL) was added. The
reaction mixture was warmed to room temperature and stirred for
20 minutes. The solution was concentrated by coevaporation with
toluene (3 ϫ 5 mL). The resulting amine was used directly in the
next step.
1
cmϪ1. H NMR (600 MHz, CDCl3): δ ϭ 0.87 (t, J ϭ 7 Hz, 3 H,
5-CH3), 1.05 (dd, J ϭ 17 and 5 Hz, 1 H, 4-CHAHB), 1.72 (d, J ϭ
7 Hz, 3 H, 1-CH3), 1.88 (m, 1 H, 5-CHAHB), 2 (m, 1 H, 5-CHAHB),
2.85 (dd, J ϭ 15 and 3 Hz, 1 H, 2-CHAHB), 3.09 (s, 3 H, 7-CH3),
3.32 (dd, J ϭ 15 and 4 Hz, 1 H, 3-CHAHB), 3.39 (d, J ϭ 17.1 H,
7-CHAHB), 3.49 (m, 1 H, 3-CHAHB), 3.49 (m, 1 H, 4-CHAHB),
3.55 (dd, J ϭ 15 and 3 Hz, 1 H, 2-CHAHB), 3.98 (m, 1 H, 5-CH),
4.21 (m, 1 H, 3-α-CH), 4.34 (s, 3 H, 3-CH3), 4.53 (m, 1 H, 4-NH),
4.71 (d, 1 H, 6-CHAHB), 4.97 (d, J ϭ 17 Hz, 1 H, 7-CHAHB), 5
(d, 1 H, 6-CHAHB), 5.07 (m, 1 H, 2-α-CH), 5.42 (d, J ϭ 8 Hz, 1
H, 2-C4 H), 5.48 (m, 1 H, 1-α-CH), 6.34 (m, 1 H, 2-C5 H), 6.81 (d,
J ϭ 7 Hz, 1 H, 5-NH), 6.82 (d, J ϭ 2 Hz, 1 H, 3-C2 H), 6.89 (m,
1 H, 2-C6 H), 6.91 (m, 1 H, arom. 3-CH), 6.96 (d, J ϭ 2 Hz, 1 H,
2-C2 H), 7.05 (d, J ϭ 8 Hz, 1 H, 2-C7 H), 7.33 (m, 2 H, arom. 3-
CH), 8.04 (s, 1 H, 1-C5 H), 8.35 (d, J ϭ 2 Hz, 1 H, arom. 3-NH),
8.59 (d, J ϭ 7 Hz, 1 H, 2-α-NH), 8.77 (d, 1 H, 3-α-NH), 8.81 (d,
J ϭ 9 Hz, 1 H, 1-α-NH), 9.36 (s, 1 H, 6-NH), 10.63 (br. s, 1 H,
arom. 2-NH) ppm. 13C NMR (150 MHz, CDCl3): δ ϭ 10.4 (5-
CH3), 20.4 (1-CH3), 21.1 (5-CH2), 26.6 (2-CH2), 26.9 (3-CH2), 37.2
(7-CH3), 40.5 (4-CH2), 45.2 (1-α-CH), 51 (7-CH2), 52.1 (2-α-CH),
54.3 (5-CH), 56.1 (3-CH3), 57.8 (3-α-CH), 99.3 (6-CH2), 101.3
(arom. 3-CH), 105.7 (arom. C), 106.6 (arom. 3-CH), 108.4 (arom.
C), 111.3 (arom. 2-CH), 115.9 (arom. 2-CH), 117.4 (arom. C),
119.2 (arom. 2-CH), 121.2 (arom. 2-CH), 122.7 (1-C5 H), 123.6
(arom. 3-CH), 123.7 (arom. 3-CH), 125.5 (arom. 2-CH), 126.5
(arom. C), 134.8 (arom. C), 136.9 (6-α-C), 138.4 (arom. C), 150.4
(1-C4), 152.3 (arom. C), 159.8 (CO), 166.8 (CO), 168.2 (CO), 169.3
(CO), 170 (CO), 170.8 (1-C2), 171.4 (CO), 172.9 (CO) ppm.
Diisopropylethylamine (45 µL, 250 µmol) and TBTU (42 mg, 130
µmol) were added successively to a solution of the linear peptide
and 1-hydroxybenzotriazole (17 mg, 130 µmol) in CH2Cl2 (100 mL)
at room temperature. The reaction mixture was stirred for 2 hours,
concentrated and purified by column chromatography (CH2Cl2
with a gradient of 0.5 to 4% MeOH) to give the cyclic peptide 28
as a sticky solid (32 mg, 50% yield); Rf ϭ 0.2 (CH2Cl2 with 5%
MeOH). MS: m/z (ϩESI) found 1019.2786 [MNaϩ],
C47H52N10O8SSe (M, 996.3) requires 1019.2753. [α]2D5 ϭ 55.8 (c ϭ
1, CHCl3). IR (film): ν˜ ϭ 3304, 1653 and 1536 cmϪ1 1H NMR
.
(600 MHz, CDCl3): δ ϭ 0.87 (t, J ϭ 7 Hz, 3 H, 5-CH3), 1.21 (m,
1 H, 4-CHAHB) 1.73 (d, J ϭ 7 Hz, 3 H, 1-CH3), 1.81 (m, 1 H, 5-
CHAHB), 1.97 (m, 1 H, 5-CHAHB), 2.87 (dd, J ϭ 15 and 3 Hz, 1
H, 2-CHAHB), 3.12 (s, 3 H, 7-CH3), 3.16 (m, 1 H, 6-CHAHB), 3.18
(m, 1 H, 7-CHAHB) 3.28 (dd, J ϭ 15 and 4 Hz, 1 H, 3-CHAHB),
3.33 (dd, J ϭ 13 and 8 Hz, 1 H, 6-CHAHB), 3.44 (m, 1 H, 4-
CHAHB), 3.44 (m, 1 H, 3-CHAHB), 3.53 (dd, J ϭ 15 and 3 Hz, 1
H, 2-CHAHB), 3.92 (m, 1 H, 5-CH), 4.18 (d, 1 H, 3-α-CH), 4.31
(s, 3 H, 3-CH3), 4.48 (m, 1 H, 4-NH), 4.48 (m, 1 H, 6-α-CH), 4.90
(d, J ϭ 17 Hz, 1 H, 7-CHAHB), 5.04 (m, 1 H, 2-α-CH), 5.26 (m, 1
H, 1-α-CH), 5.54 (m, 1 H, arom. 2-CH), 6.42 (m, 1 H, arom. 2-
CH), 6.57 (br. s, 1 H, 5-NH), 6.76 (br. s, 1 H, ind. C2 H), 6.92 (m,
1 H, arom. 3-CH), 6.92 (m, 1 H, arom. 2-CH), 7.01 (d, J ϭ 2 Hz,
1 H, ind. C2 H), 7.13 (d, J ϭ 8 Hz, 1 H, arom. 2-CH), 7.29 (m, 3
H, arom. 6-CH), 7.33 (m, 2 H, arom. 3-CH), 7.56 (m, 2 H, arom.
X-ray Crystal Structure determination of 8: Crystal data:
6-CH), 8 (s, 1 H, 1-C5 H), 8.27 (s, 1 H, 6-NH), 8.32 (d, J ϭ 7 Hz, C20H20N2O5, Mw ϭ 368.38, colourless prism 0.42 ϫ 0.25 ϫ
Eur. J. Org. Chem. 2002, 3995Ϫ4004
4003

S. V. Ley, A. Priour
FULL PAPER
[10]
[11]
[12]
L. Vollbrecht, H. Steinmetz, G. Höfle, L. Oberer, G. Rihs, G.
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For a preliminary communication of this work see: S. V. Ley,
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1983, 24, 3815Ϫ3818.
0.10 mm, monoclinic P21 (No. 4), a ϭ 11.5678(10), b ϭ 5.0122(2),
3
˚
˚
c ϭ 15.9392(13) A, β ϭ 107.451(3)°, V ϭ 881.62(11) A , T ϭ 230(2)
K, DX ϭ 1.388 g.cmϪ3, λ ϭ 0.71073 A, µ ϭ 0.101 mmϪ1, Nonius
˚
Kappa CCD diffractometer, 1.85° Ͻ θ Ͻ 27.79°, 5220 measured
reflections, 3510 independent, 2961 with I Ͼ 2σ(I). The structure
was solved by direct methods (SHELXS-97) and refined by least-
squares (SHELXL-97) using Chebyshev weights on F02 to R1 ϭ
0.046, wR2 ϭ 0.113 [I Ͼ 2σ(I)], 249 parameters, all H atoms in
calculated positions except H10 (the carboxylic acid proton) which
was located and refined successfully, goodness-of-fit on F2 1.16,
[13]
[14]
[15]
[16]
[17]
[18]
[19]
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residual electron density 0.33 e·A
.
CCDC-187559 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033; E-mail:
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This work was financially supported by the Novartis Research Fel-
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European Trust (AP). We thank Prof. Dr. G. Höfle from the GBF,
Braunschweig, for an authentic sample of Argyrin B (1) and Dr J.
E. Davies for determining the crystal structure of 8.
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[O02363]
4004
Eur. J. Org. Chem. 2002, 3995Ϫ4004