Pyridone dipeptides - Synthesis of a novel peptide chromophore

Article abstract of DOI:10.1002/ejoc.200500156

Sequential elimination of two water molecules transfers the diols 2 and 3 into the pyridone dipeptide 1. Both dehydration steps become part of the peptide synthesis under appropriate reaction conditions. A straightforward strategy for the incorporation of 1 in oligopeptide sequences is presented here. As part of the oligopeptide backbone, 1 has a local rigidifying effect which was studied in the cyclic octapeptides 16 and 25. Both cyclopeptides exhibit conformational averaging although a fixed conformation was identified for the 1-Phe tripeptide fragment of octapeptide 25. The pyridone dipeptide 1 serves also as a fluorescence label and the UV/Vis-spectroscopic properties of tetrapeptide 13 are investigated here. The peptide backbones of the two cyclic octapeptides 16 and 25 arrange a pair of chromophores 1 in close vicinity of each other. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejoc.200500156

FULL PAPER
Pyridone Dipeptides – Synthesis of a Novel Peptide Chromophore
Peter Tremmel[a] and Armin Geyer*[b]
Dedicated to Horst Kessler on the occasion of his 65th birthday
Keywords: Peptidomimetics / Peptides / Heterocycles / Lactams / Bicyclic dipeptides / Amino acids
Sequential elimination of two water molecules transfers the
diols 2 and 3 into the pyridone dipeptide 1. Both dehydration
steps become part of the peptide synthesis under appropriate
reaction conditions. A straightforward strategy for the incor-
poration of 1 in oligopeptide sequences is presented here. As
part of the oligopeptide backbone, 1 has a local rigidifying
effect which was studied in the cyclic octapeptides 16 and
25. Both cyclopeptides exhibit conformational averaging al-
though a fixed conformation was identified for the 1-Phe tri-
peptide fragment of octapeptide 25. The pyridone dipeptide
1 serves also as a fluorescence label and the UV/Vis-spectro-
scopic properties of tetrapeptide 13 are investigated here.
The peptide backbones of the two cyclic octapeptides 16 and
25 arrange a pair of chromophores 1 in close vicinity of each
other.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
Dipeptide lactams impose conformational constraints on
peptides by restricting the peptide bond (ω) to the trans
conformation and ψ1 to about –120°.[1] Therefore, bicyclic
dipeptide lactams like the β-turn dipeptide (BTD, n = 1)
were proposed as surrogates of the type IIЈ β-turn motif.[2]
Yet, the overall constraint fixed by a bicyclic dipeptide is
closer to a right angle (90°) than to a hairpin turn (180°)
and the concept of β-turn mimetics was challenged by the
observation that 7,5-bicyclic thiazolidine lactams (n = 2)
occupy the i to i+1 positions of a β-turn, independently of
the chirality of neighbouring amino acids.[3] Smaller lactam
rings (n = 0, 1) are flattened and minima of –140° or 60°
are expected for φ1.[4] The pyridone dipeptide 1 combines
an NH donor and CO acceptor of parallel orientation (φ1
= 180°) and a thiaproline ring which induces a close to right
angle in the peptide structure (φ2 = –60° to –90°). The syn-
thetic strategy presented here extends our earlier approach
towards bicyclic thiazolidine lactams. Sequential elimi-
nation of two water molecules transfers the sugar precursor
into an aromatic ring. Only few protocols convert sugars
into hydrocarbons by repeated dehydration.[5] Pyridone
rings find application as peptide mimetics.[6] To the best of
our knowledge, the synthesis of a pyridine ring from a sugar
precursor has never been described before.
Results and Discussion
Synthesis
The diastereomeric thiazolidine lactam dipeptides 2 (6R)
and 3 (6S) are obtained in only four steps from d-aldurono-
2,5-lactone (4) and l-cysteine methyl ester (Scheme 1).[7]
Under standard peptide coupling conditions, the 6,5-bicy-
clic thiazolidine lactams yield unsaturated products more
readily than the polyhydroxylated 7,5-bicyclic dipeptides
which do not show elimination reactions.[8] Dehydrated
products like the dehydro tripeptide 5 were initially ob-
tained as side products (10% yield) from the ester hydrolysis
of 2 followed by peptide coupling with glycine methyl ester.
Tosylate 6 forms the elimination product 7 in 69% yield.
The elimination reactions are favoured by the pseudo-axial
orientations of 7-OH and 8-OH (Scheme 2).[7] Both elimi-
nations can be combined in one molecule without the neces-
sity of activating 8-OH as shown in Scheme 3. Longer reac-
tion times of the methyl ester hydrolysis of 2 favours the
elimination leading to dehydro dipeptide 8 as the only pro-
duct after several days. The C-6 epimers 2 and 3 are in
slow equilibrium under these reaction conditions. Higher
reaction temperatures accelerate the transformation, yet
with less than quantitative yields. Acidolysis of the Boc
[a] Institut für Organische Chemie, Universität Regensburg,
93040 Regensburg, Germany
Fax: +49-941-943-4627
[b] Fachbereich Chemie, Philipps-Universität Marburg,
35032 Marburg, Germany
Fax: +49-6421-28-22030
E-mail: geyer@staff.uni-marburg.de
Eur. J. Org. Chem. 2005, 3475–3481
DOI: 10.1002/ejoc.200500156
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P. Tremmel, A. Geyer
FULL PAPER
group is accompanied by the elimination of the second
water molecule leading to the hydrochloride of unprotected
dipeptide 1 in excellent overall yield. Fmoc-protected 1 was
used as a building block in solid-phase peptide synthesis of
several bioactive oligopeptides.[9]
Scheme 1.
Scheme 4. a) 1 n LiOH, MeOH; b) HCl·H-Gly-OMe, EDC, HOBT,
DIPEA, DMF (87% both steps); c) HCl in Et2O (93%); d) Boc-
Phe, PyBOP, NMM, DMF (88%); e) PyBOP, NMM, DMF (95%
three steps).
Scheme 2. a) 1 n LiOH, MeOH; b) HCl·H-Gly-OMe, EDC, HOBT,
DIPEA (10% 5, 46% tripeptide without elimination); c) NaN3,
DMF 80° (69%).
Scheme 5. a) HATU, HOAT, collidine, DMF, room temp. (76%).
Synthesis of an octapeptide with a phenylalanine at the
C-terminal position of 1 is shown in Schemes 6 and 7. The
tripeptide 17 (Figure 1) is obtained in 94% yield by coup-
ling of HCl·H-Phe-OMe with the dehydro amino acid
received from the saponification of 2 and 3. Acidolysis
(Ǟ 18) and condensation with Boc-Gly-OH leads to the
Scheme 3. a) 1 n LiOH/MeOH, room temp., 12 d, then adjust pH
to 7 with 1 n HCl (quantitative); b) Et2O/HCl (96%).
Scheme 4 shows how both elimination reactions are im-
plemented in the solution peptide synthesis without the ne-
cessity of isolating unprotected dipeptide 1. Methyl ester
hydrolysis of the diastereomers 2 and 3 together with the
first elimination step is followed by peptide coupling to tri-
peptide 5 (87%) without the necessity of isolating the inter-
mediate 8. Freeing of the amino terminus of 5 with HCl/
Et2O yields the salt 9 which is subsequently acylated by
Boc-Phe-OH. The reduced nucleophilicity of the aromatic
amino group does not cause problems. This condensation
is mediated by PyBOP [benzotriazol-1-yl(oxy)tripyrrolidin-
ylphosphonium hexafluorophosphate] as a coupling reagent
yielding the tetrapeptide 10 in 88% yield. Deprotection of
either the amino terminus or the carboxy terminus yields
the monoprotected tetrapeptides 11 and 12, respectively,
which are combined in the next coupling step to the pro-
tected octapeptide 13. After saponification (Ǟ 14) and aci-
dolysis (Ǟ 15) the cyclisation to 16 (Scheme 5) is ac-
complished under dilution conditions in DMF with HATU
[O-(7-azabenzotriazol-1-yl)-N,N,NЈ,NЈ-tetramethyluronium
hexafluorophosphate] in 76% isolated yield.
Scheme 6. a) 1 n LiOH MeOH; b) HCl·H-Gly-OMe, EDC, HOBT,
DIPEA, DMF (94% both steps); c) HCl in Et2O (87%); d) Boc-
Gly, PyBOP, NMM, DMF (96%); e) PyBOP, NMM, DMF (68%
three steps).
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Pyridone Dipeptides – Synthesis of a Novel Peptide Chromophore
FULL PAPER
tetrapeptide 19, which is selectively deprotected to 20 or 21, 16 and 25 were assembled around pyridone dipeptide 1 to
respectively. The octapeptide 22 obtained from the fragment study its rigidifying influences. Both C2-symmetric cyclic
condensation of tetrapeptides 20 and 21 is deprotected by octapeptides contain two of the rigid dipeptides 1 together
saponification (Ǟ 23) and acidolysis (Ǟ 24). The cyclis- with two Phe-Gly or Gly-Phe dipeptide units, respectively.
ation of octapeptide 24 yields the desired product 25 in only Cyclic octapeptides cannot assume antiparallel β-sheet con-
35% yield, although the reaction conditions were the same formations like cyclic hexapeptides which have an even
as described for 16.
number of antiparallel hydrogen bonds.[3] Therefore, only
kinked structures are possible for cyclic octapeptides and
the glycine residues are expected to form flexible joints be-
tween turn structures stabilized by 1. Indeed, conformation-
3
ally averaged Gly JNH,Hα coupling constants of 5.0 and
3
6.8 Hz and Phe JHα,Hβ coupling constants of 5.5 Hz and
9.5 Hz are observed for 16. A fixed side-chain orientation
is found for the two phenylalanines of the cyclic octapeptide
3
25 in DMSO solution. The JHα,Hβ coupling constants
3
(3JHα,HproS = 3.8, JHα,HproR = 12.6 Hz) together with the
NOE pattern identify a χ1 = –60° orientation as the main
rotamer (Ͼ 80%). NOE and coupling data indicate a type-
I β-turn motif with Phe occupying the i+2 positions. None
of the linear precursors (17, 19, and 22) of the cyclopeptide
25 shows preferred side-chain rotamers for Phe. Thus, the
conformational dynamics of octapeptide 25 is restricted to
the glycine residues. The overall C2-symmetry of both cyclic
octapeptides together with the proton-poor heterocyclic
ring structure yield only few reliable NOEs which are exclu-
sively sequential.
Scheme 7. a) HATU, HOAT, collidine, DMF, room temp. (35%).
Figure 2 shows the spectroscopic data of tetrapeptide 10
which exhibits an intense UV absorption (λmax = 346 nm, ε
= 17000). This absorption is by far more intense than that
of Phe (λmax = 256 nm, ε = 267) and is exclusively caused
by the pyridine dipeptide 1. The peptide backbone chromo-
phore 1 shows fluorescencense at 408 nm.[11] These spectro-
scopic data of 1 do not vary significantly between the dif-
Figure 1. Crystal structure of 17 with disordered tBu group.
Structural Analysis
The amino group (6-NH) and the pyridinone carbonyl
group assume a close to parallel orientation (φ1 = –166°) in
the crystal structure of tripeptide 17 (Figure 1). By this, the
pyridinone ring mimics an extended peptide conformation
which is terminated by the thiazolidine ring (φ2 = –60°; φ2
= –156°). The close to right angle is mainly due to the thi-
azolidine ring mimicking an l-proline in the i+1 position of
a hairpin turn. A fully extended conformation for φ1 and
ψ1 is expected for 1, stabilized by the antiparallel alignment
of the 5-CO and 6-NH dipoles. The benzylic side chain of
17 is found in an extended conformation (χ1 = Nα–Cα–Cβ–
Cγ = 180°) in the crystal structure.
Natural cyclic octapeptides exhibit a complex conforma-
Figure 2. UV and CD spectra of tetrapeptide 10 (c = 0,452 mmol/
tional behaviour[10] and the two cyclic octapeptide models L in MeOH; 0,1 cm cell).
Eur. J. Org. Chem. 2005, 3475–3481
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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P. Tremmel, A. Geyer
FULL PAPER
compound 7 was obtained as a colorless solid. 1H NMR
(600 MHz, [D6]DMSO): δ = 5.20 (d, 3J8,7 = 5.6 Hz, 1 H, 8-H), 5.16
ferent peptides investigated here, thus indicating that the
two pyridone dipeptides in each of the linear or cyclic octa-
peptides behave like independent chromophores and do not
interact with each other due to their close spatial proximity.
3
3
3
(dd, J3,2proS = 1.5, J3,2proR = 7.6 Hz, 1 H, 3-H), 4.68 (t, J7,6/8
=
3
6.5 Hz, 1 H, 7-H), 4.64 (d, J6,7 = 6.8 Hz, 1 H, 6-H), 4.13 (m, 2 H,
3
2
OCH2CH3), 3.53 (dd, J2proR,3 = 7.6, Jgem = 11.4 Hz, 1 H, 2-
3
2
HproR), 3.37 (dd, J2proS,3 = 1.5, Jgem = 11.4 Hz, 1 H, 2-Hh), 1.32
(s, 3 H, CH3Isopr,proR), 1.28 (s, 3 H, CH3Isopr,proS), 1.18 (t,
3JCH2CH3,CH2CH3 = 7.0 Hz, 3 H, OCH2CH3) ppm. 13C NMR: δ =
168.36 (CO2), 166.08 (C-5), 140.41 (C-8a), 108.38 (CqIsopr), 90.77
(C-8), 72.14 (C-6), 71.36 (C-7), 61.51 (OCH2CH3), 59.97 (C-3),
30.52 (C-2), 27.28 (CH3Isopr,proS), 25.89 (CH3Isopr,proR), 13.89
(OCH2CH3) ppm. FAB-MS: m/z = 300 [M + H]+. C13H17NO5S
(299.35): calcd. C 52.16, H 5.72, N 4.68; found C 52.36, H 5.78, N
Conclusions
Two molecules of water are eliminated from a bicyclic
thiazolidine lactam to obtain the pyridone dipeptide 1, thus
transferring a sugar precursor into an amino acid chromo-
phore of the peptide backbone. Two cyclic octapeptides are
described here which prove the feasibility of the synthetic 4.42.
concept and to study their conformational preferences. Cy-
Lithium (3R,8S,8aS)-6,7-Dihydroxy-5-oxo-5H-[1,3]thiazolo[3,2-a]-
clic octapeptides are known to form parallel β-sheets to-
gether with kinked and double-helical “Figure eight” con-
formations.[10] Even the pentacyclic octapeptides 16 and 25
exhibit conformational averaging although the bicyclic di-
pyridine-3-carboxylate (8): 3 mL of 1 n LiOH was added to 700 mg
of 2/3 (1.93 mmol) in 15 mL of MeOH. The reaction mixture was
brought to pH = 6 with 1 n HCl at room temp. after 12 d. The
solvent was removed and the residue dried in high vacuum to ob-
1
peptide 1 stabilizes two reverse turns in 16. The glycines tain analytically pure 8 as a white solid. H NMR (400 MHz, [D6]
3
DMSO): δ = 7.43 (s, 1 H, 6-NH), 6.75 (d, J7,8 = 6.5 Hz, 1 H, 7-
serve as joints where the backbone bends from an antiparal-
lel β-sheet structure to kinked conformations. Within a pep-
tide sequence, 1 can lock an extended dipeptide conforma-
tion. In the context of bioactive peptides, 1 can serve simul-
taneously as a scaffold and as a fluorescence marker to
monitor the fate of the peptide by fluorescence spec-
troscopy in biological testing systems.
3
3
H), 5.10 (d, J8OH,8 = 7.0 Hz, 1 H, 8-OH), 5.01 (d, J8a,8 = 3.4 Hz,
3
3
1 H, 8a-H), 4.71 (dd, J3,2h = 6.7, J3,2t = 2.0 Hz, 1 H, 3-H), 4.03
(m, 1 H, 8-H), 3.17 (dd, J2t,3 = 2.0, Jgem = 9.9 Hz, 1 H, 2-Ht),
3.10 (dd, 3J2h,3 = 6.7, 2Jgem = 9.9 Hz, 1 H, 2-Hh), 1.43 (s, 9 H, CH3
tBu) ppm. 13C NMR δ = 171.46, 157.80, 151.95 (CO2, C-5, CO
tBu), 129.12 (C-6), 113.48 (C-7), 80.13 (Cq tBu), 65.02 (C-8a), 63.95
(C-3), 61.24 (C-8), 33.23 (C-2), 27.92 (CH3 tBu) ppm. ESI-MS:
m/z = 328.9 [M – H]–, 659.2 [2 M – H]–, 665.3 [2 M – 2 H + Li]–.
3
2
(3R)-6-Amino-5-oxo-5H-[1,3]thiazolo[3,2-a]pyridine-3-carboxylic
Acid Hydrochloride (1·HCl): 950 mg (2.6 mmol) of the protected
dipeptides 2/3 were dissolved in 20 mL of MeOH. 4 mL of 1 n
LiOH was added and the solution was kept at room temp. for two
weeks. A pH of 6 was adjusted by addition of 1 n HCl. The solvent
was removed and 15 mL of Et2O/HCl was added to the dried resi-
due cooled by an ice bath. The mixture was sonicated for 1 h and
stirred at room temp. 2 d. The precipitate was removed by filtration
and dried in high vacuum over KOH. 790 mg (2.5 mmol, 96%) of
hydrochloride 1 was obtained as a black powder. 1H NMR
(400 MHz, [D6]DMSO): δ = 7.11 (d, 3J7,8 = 7.7 Hz, 1 H, 7-H), 6.21
Experimental Section
General Remarks: Solvents were purified according to standard
procedures. Flash chromatography was performed on J. T. Baker
silica gel 60 (0.040–0.063 mm) at a pressure of 0.4 bar. Thin layer
chromatography was performed on Merck silica gel plastic plates,
60F254; compounds were visualized by treatment with a solution of
(NH4)6Mo7O24·4H2O (20 g) and Ce(SO4)2 (0.4 g) in 10% sulfuric
acid (400 mL) and heating at 150 °C. NMR spectra were recorded
with Bruker Avance 400 or 600 spectrometers. TMS, or the reso-
nance of the residual solvent ([D6]DMSO: δ = 2.49 ppm), was used
as internal standard. Diasterotopic proton pairs that could not be
assigned stereochemically are characterized as highfield (h) and
lowfield (l) in the 1H NMR spectroscopic data. The NMR assigne-
ments of the amino-terminal tetrapeptide fragments of the octapep-
tides are labeled “A” and the carboxy-terminal fragments “B”. FAB
mass spectra were acquired with a Finnigan MAT 312 in the posi-
tive mode, using NBA as the matrix. CCDC-263833 (17) contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
Fax: + 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk. Ab-
breviations: DIPEA = N,NЈ-diisopropylethylamine, HATU = O-(7-
azabenzotriazol-1-yl)-N,N,NЈ,NЈ-tetramethyluronium hexafluoro-
3
3
3
(d, J8,7 = 7.5 Hz, 1 H, 8-H), 5.49 (dd, J3,2h = 1.6, J3,2t = 8.6 Hz,
3
2
1 H, 3-H), 3.89 (dd, J2t,3 = 8.7, Jgem = 11.9 Hz, 1 H, 2-Ht), 3.57
(dd, J2h,3 = 1.6, Jgem = 11.8 Hz, 1 H, 2-Hh) ppm. 13C NMR: δ =
3
2
169.12 (CO2), 156.90 (C-5), 125, 123 (br. s, C-6, C-7), 99.18 (C-8),
62.75 (C-3), 32.18 (C-2) ppm. IR (KBr): ν = 3414, 2870, 2597,
˜
1738, 1629, 1536, 1404, 1376, 1233, 760 cm–1. ESI-MS: m/z = 212.7
[M + H]+, 218.7 [M + Li]+, 250.8 [M + K]+.
Tripeptide 5: 4 mL of 1 n LiOH was added to 850 mg (2.35 mmol)
of 2/3 in 30 mL of MeOH. The pH was adjusted to 6 with 1 n HCl
after 20 d and the solvent was removed under high vacuum. The
residue was dissolved in 10 mL of DMF together with 400 mg of
H-GlyOMe·HCl (3.2 mmol, ca. 1.3 equiv.). Then 400 mg of HOBT
(2.96 mmol, ca. 1.2 equiv.), 500 μL of EDCI (442 mg, 2.8 mmol,
ca. 1.2 equiv.) and 550 μL of DIPEA (3.2 mmol) were added. The
reaction mixture was stirred overnight. The solvent was removed
and the tripeptide separated by flash chromatography (ethyl ace-
phosphate, HOAT = 1-hydroxy-7-azabenzotriazole, PyBOP
benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophos-
phate.
=
Ethyl (3R,6S,7S)-6,7-Isopropylidene-5-oxo-5H-[1,3]thiazolo[3,2-a]- tate/toluene, 4:1, Rf = 0.55). 818 mg (2.04 mmol, 87%) of com-
1
pyridine-3-carboxylate (7): 100 mg (1.5 mmol) of NaN3 was added
to 250 mg (0.55 mmol) of compound 6[7] in 15 mL of DMF. The
solution was stirred at room temp. overnight and then the solvent
was removed. The residue was purified by flash chromatography
(ethyl acetate/toluene, 5:4, Rf = 0.55). 112 mg (0.38 mmol, 69%) of
pound 5 was obtained as a colourless solid. H NMR (400 MHz,
3
[D6]DMSO): δ = 8.47 (t, JNH,Hα/HαЈ = 6.0 Hz, 1 H, Gly-NH), 7.51
(s, 1 H, 6-NH), 6.80 (d, J7,8 = 6.7 Hz, 1 H, 7-H), 5.29 (d, J8OH,8
= 7.5 Hz, 1 H, 8-OH), 5.06 (d, J8a,8 = 3.2 Hz, 1 H, 8a-H), 4.97
(dd, J3,2h = 2.7, J3,2t = 6.7 Hz, 1 H, 3-H), 4.08 (m, 1 H, 8-H),
3
3
3
3
3
3478
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Pyridone Dipeptides – Synthesis of a Novel Peptide Chromophore
FULL PAPER
vent was removed and the residue dried over KOH in high vacuum.
3
3.83 (m, 2 H, Gly-CH2) 3.62 (s, 3 H, OCH3), 3.23 (dd, J2,3 = 6.7,
2Jgem = 11.0 Hz, 1 H, 2-Ht), 3.07 (dd, 3J2h,3 = 2.7, 2Jgem = 11.1 Hz,
c) Peptide Coupling: The selectively deprotected tetrapeptides 11
1 H, 2-Hh), 1.43 (s, 9 H, CH3 tBu) ppm. 13C NMR: δ = 169.86, and 12 were dissolved in 3 mL of DMF together with 150 mg
169.33 (3-CO, Gly-CO), 158.52, 151.94 (C-5, COtBu), 129.33 (C-
6), 114.14 (C-7), 80.06 (Cq, tBu), 65.61 (C-8a), 62.69 (C-3), 61.89
(0.29 mmol) of PyBOP. The pH was adjusted to 8 with NMM and
the reaction mixture was stirred overnight. Then the solvent was
(C-8), 51.67 (OCH3), 40.73 (Gly-CH2), 32.56 (C-2), 27.80 (CH3, removed and the octapeptide purified by flash chromatography
tBu) ppm. ESI-MS: m/z = 402.0 [M + H]+, 424.0 [M + Na]+, 825.3
[2 M + Na]+. C16H23N3O7S (401.44): calcd. C 47.87, H 5.78, N
10.47; found C 51.19, H 6.17, N 7.68.
(ethyl acetate/methanol, 7:1 Rf = 0.4) to obtain 164 mg (0.18 mmol
95%) of 13. 1H NMR (400 MHz, [D6]DMSO): δ = 9.32 (s, 1 H,
3
6B-NH), 9.17 (s, 1 H, 6A-NH), 8.78 (t, JNH,Hα/HαЈ = 5.9 Hz, 1 H,
GlyB-NH), 8.54 (t, 3JNH,Hα/HαЈ = 5.7 Hz, 1 H, GlyA-NH), 8.43 (d,
Tripeptide Hydrochloride 9: 25 mL of Et2O/HCl was added to
550 mg (1.37 mmol) of compound 5. The resulting suspension was
stirred at room temp. overnight and the colorless precipitate was
separated and dried over KOH in high vacuum. 405 mg
3
3JNH,Hα = 8.0 Hz, 1 H, PheB-NH), 8.17 (d, J7,8 = 7.8 Hz, 1 H,
3
3
7A-H), 8.11 (d, J7,8 = 7.8 Hz, 1 H, 7B-H), 7.33 (d, JNH,Hα
=
8.6 Hz, 1 H, Boc-NH), 7.25 (m, 10 H, PheA/B-Harom), 6.25 (d, 3J8,7
= 7.8 Hz, 1 H, 8A-H), 6.23 (d, 3J8,7 = 7.8 Hz, 1 H, 8B-H), 5.52 [m,
(1.27 mmol, 93%) of tripeptide
9
was obtained. 1H NMR
3
2 H, DQF-COSY: 5.53 (3B), 5.51 (3A)], 4.80 (ddd, JHα,Hβh = 9.4,
3
(600 MHz, [D6]DMSO): δ = 9.00 (t, JNH,Hα/HαЈ = 5.9 Hz, 1 H,
3
3JHα,Hβt = 4.9, JHα,NH = 8.0 Hz, 1 H, PheB-αH), 4.33 (ddd,
Gly-NH), 7.52 (d, 3J7¸8 = 7.6 Hz, 1 H, 7-H), 6.30 (d, 3J8,7 = 7.6 Hz,
3
3
3JHα,Hβh = 11.0, JHα,Hβt = 4.1, JHα,NH = 8.4 Hz, 1 H, PheA-αH),
4.0–3.8 [m, 4 H, DQF-COSY: 3.91 (GlyB-CH2), 3.91 (2B-Ht), 3.85
(2A-Ht)], 3.75 (m, 2 H, GlyA-CH2), 3.63 (s, 3 H, OCH3), 3.4 [m, 2
3
3
1 H, 8-H), 5.58 (dd, J3,2h = 1.8, J3,2t = 9.1 Hz, 1 H, 3-H), 3.96
3
2
3
(dd, J2t,3 = 9.1, Jgem = 11.7 Hz, 1 H, 2-Ht), 3.93 (dd, JHαt,NH
=
6.2, 2Jgem = 17.3 Hz, 1 H, Gly-CHt), 3.87 (dd, 3JHαh,NH = 5.6, 2Jgem
H, DQF-COSY: 3.45 (2B-Hh), 3.44 (2A-Hh)], 3.1 (m, 2 H DQF-
= 17.3 Hz, 1 H, Gly-CHh), 3.63 (s, 3 H, OCH3), 3.49 (dd, J2h,3
=
3
COSY: 3.09 (PheA-βHt), 3.08 (PheB-βHt)], 2.83 (dd, JHβh,Hα
=
3
2.0, 2Jgem = 11.7 Hz, 1 H, 2-Hh) ppm. 13C NMR: δ = 169.89, 167.57
(Gly-CO, CO2), 156.87 (C-5), 147 (br. s, C-8a), 130 (br. s, C-7), 119
(br. s, C-6), 98.27 (C-8), 63.44 (C-3), 51.79 (OMe), 40.66 (Gly-
9.7, Jgem = 13.8 Hz, 1 H, PheB-βHh), 2.76 (dd, JHβh,Hα = 11.1,
2
3
2Jgem = 14.0 Hz, 1 H, PheA-βHh), 1.27 (s, 9 H, CH3 tBu) ppm. 13
C
NMR: δ = 170.76, 170.14, 169.93, 168.39, 167.76, 167.34 (PheA/B-
CO, GlyA/B-CO, 3A/B-CO), 156.21, 156.18 (CO-5A/B), 155.38
(CO, tBu), 141.27, 141.09 (C-8aA/B), 138.01, 137.46 (PheA/B-Cq),
129.20, 129.11, 128.05, 128.01, 126.33, 126.19 (PheA/B-CHarom.),
124.88 (C-7B), 123.95 (C-7A) 123.89 (br. s, C-6), 98.69, 98.63 (C-
8A/B), 78.42 (Cq, tBu), 63.72, 63.53 (C-3A/B), 56.70 (PheA-Cα),
54.75 (PheB-Cα), 51.79 (OCH3), 41.69 (GlyA-CH2), 40.67 (GlyB-
CH2), 37.15 (PheB-Cβ), 36.86 (PheA-Cβ), 32.44 32.37 (C-2A/B),
28.04 (3 C, CH3, tBu) ppm. ESI-MS: m/z = 929.4 [M + H]+, 946.5
[M + NH4]+, 951.3 [M + Na]+.
CH ), 32.82 (C-2). IR (KBr): ν = 3297, 3027, 2795, 2525, 1753,
˜
2
1661, 1512, 1376, 1203, 760 cm–1. ESI-MS: m/z = 283.8 [M + H]+.
Tetrapeptide 10: 320 mg (1.0 mmol) of hydrochloride 9 and 400 mg
(1.5 mmol) BocPheOH were dissolved in 8 mL of DMF. 1 g
(1.9 mmol) of PyBOP and 1 mL of NMM were added and the reac-
tion mixture was stirred overnight. The solvent was evaporated and
the product purified by flash chromatography (ethyl acetate/tolu-
ene, 5:1, Rf = 0.55). The combined fractions which contained pro-
duct were concentrated and hexane was added until a white precipi-
tate was observed. The suspension was kept at 4 °C overnight, the
precipitate separated and washed with Et2O to obtain 469 mg
(0.88 mmol, 88%) of tetrapeptide 10 as a yellowish powder. 1H
NMR (400 MHz, [D6]DMSO): δ = 9.18 (s, 1 H, 6-NH), 8.76 (t,
Cyclic Octapeptide 16: 4 equiv. of 1 n LiOH were added over 5 h
to a solution of 50 mg (0.054 mmol) of octapeptide 13 in 15 mL of
MeOH and 5 mL of DCM. The solution was neutralized with 1 n
HCl and the solvent was removed. The dry residue was taken up
in 8 mL of Et2O/HCl and sonicated for 30 min. The Suspension
was stirred overnight. The solvent was removend and the reaction
mixture dried over KOH in high vacuum. The deprotected peptide
was dissolved in 500 mL of DMF. 25 mg (0.066 mmol) of HATU,
10 mg (0.073 mmol) of HOAT, and 75 mL of collidine (0.69 mmol)
were added and the solution was stirred overnight. The solvent
was removed and the residue was purified by flash chromatography
3
3JNH,Hα/HαЈ = 5.9 Hz, 1 H, Gly-NH), 8.18 (d, J7,8 = 7.8 Hz, 1 H,
7-H), 7.3 [m, 6 H, PheH/Boc-NH, (DQF-COSY: 7.35)], 6.26 (d,
3J8,7 = 7.8 Hz, 1 H, 8-H), 5.54 (dd, 3J3,2proS = 2.1, 3J3,2proR = 8.6 Hz,
3
3
3
1 H, 3-H), 4.35 (dd, JHα,HβproR = 11.0, JHα,HβproS = 4.1, JHα,NH
= 8.4 Hz, 1 H, Pheα-H), 3.9 (m, 3 H, GlyCH2/ 2-HproR), 3.64 (s, 3
H, OCH3), 3.46 (dd, 3J2proS,3 = 2.1, Jgem = 11.8 Hz, 1 H, 2-HproS),
2
3.10 (dd, JHβproS,Hα = 4.1, Jgem = 13.8, 1 H, Pheβ-HproS), 2.77
3
2
(dd, JHβproR,Hα = 11.0, Jgem = 13.8, 1 H, Pheβ-HproR), 1.28 (s, 9
H, CH3, tBu) ppm. 13C NMR: δ = 170.78, 169.93, 167.70 (CO2,
Phe-CO, Gly-CO), 156.18, 155.39, (C-5, CO, tBu) 140.92 (C-8a),
138.04 (Phe-Cq), 129.13, 128.02, 126.20 (Phe-CHarom.), 124.03,
123.88 (C-7/C-6), 98.75 (C-8), 78.42 (Cq, tBu), 63.56 (C-3), 56.68
(Phe-Cα), 51.78 (OCH3), 40.68 (Gly-CH2), 36.83 (Phe-Cβ), 32.41
3
2
[CHCl3/MeOH, 5:1, Rf(CHCl3/MeOH, 7:1)
= 0.15]. 33 mg
(0.041 mmol, 76%) of the cyclic octapeptide 16 was obtained as a
1
white solid. H NMR (400 MHz, [D6]DMSO): δ = 9.18 (s, 2 H, 6-
3
NH), 8.59 (br. s, 2 H, Gly-NH), 8.36 (d, JNH,Hα = 9.5 Hz, 2 H,
Phe-NH), 8.10 (d, 3J7,8 = 7.9 Hz, 2 H, 7-H), 7.1–7.2 (m, 10 H, Phe-
3
3
Harom.), 6.28 (d, J8,7 = 7.9 Hz, 2 H, 8-H), 5.49 (dd, J3,2t = 8.4,
3J3,2h = 2.2 Hz, 2 H, 3-H), 4.86 (m, 2 H, Pheα-H), 3.85–3.75 (m, 4
H, Gly-CHt, 2-Ht), 3.54–3.44 (m, 4 H, GlyCHh, 2-Hh), 2.99 (dd,
(C-2), 28.05 (3C, CH tBu) ppm. IR (KBr): ν = 3339, 2977, 1753,
˜
3
1678, 1649, 1512, 1239, 1170, 767, 702 cm–1. ESI-ESI: m/z = 531.2
[M + H]+, 548.2 [M + NH4]+, 553.2 [M + Na]+, 1078.5 [2 M +
NH4]+. C25H30N4O7S (530.60) calcd. C 56.59, H 5.70, N 10.56;
found C 55.84, H 5.62, N 10.37.
3JHβt,Hα = 5.5, Jgem = 13.8 Hz, 2 H, Pheβ-Ht), 2.81 (dd, JHβh,Hα
2
3
= 9.5, Jgem = 13.6 Hz, 2 H, Pheβ-Hh) ppm. 13C NMR: δ = 128.2,
2
127.6, 125.9 (Phe-CHarom.), 125.4 (C-7), 99.3 (C-8), 63.9 (C-3), 54.5
(Phe-Cα), 41.4 (Gly-CH2), 37.1 (Phe-Cβ), 32.3 (C-2) ppm. ESI-MS:
m/z = 797.4 [M + H]+, 803.4 [M + Li]+.
Octapeptide 13. a) Saponification of 10: Within 5 min, 400 μL of
1 n LiOH was added to 100 mg (0.19 mmol) of tetrapeptide 10,
suspended in 5 mL of MeOH. Another 5 mL of MeOH was added,
until the peptide was fully dissolved. After 2 h 40 min, an ad-
ditional 1 mL of 0.1 n LiOH was added. After 3 h 15 min, the reac-
tion mixture was adjusted to pH = 6 with 1 n HCl and then the
solvent was removed. b) Acidolysis of 10: 100 mg of 10 was sus-
pended in 6 mL of Et2O/HCl and stirred overnight. Then the sol-
Tripeptide 17 (CCDC-263833): 2.5 mL of 1 n LiOH was added to
a solution of 620 mg (1.7 mmol) of 2/3 in 15 mL of MeOH. The
reaction mixture was stirred for 17 d at room temp. and neutralized
with 1 n HCl. The solvent was removed and the residue dried in
high vacuum and dissolved in 10 mL of DMF together with 500 mg
(2.3 mmol) of LPhe-OMe, 400 mg (2.1 mmol) of EDCI·HCl, and
Eur. J. Org. Chem. 2005, 3475–3481
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3479

P. Tremmel, A. Geyer
FULL PAPER
300 mg of HOBT. The solution was brought to pH = 7 with DI-
PEA and stirred at room temp. overnight. After removal of the
solvent, the residue was purified by flash chromatography (ethyl
acetate/toluene, 9:1, Rf = 0.7) to obtain 780 mg (1.6 mmol, 94%)
[M + NH4]+, 553.3 [M + Na]+. C25H30N4O7S (530.60) calcd. C
56.59, H 5.70, N 10.56; found C 55.96, H 5.59, N 10.43.
Octapeptide 22. a) Saponification of 19: 60 mg (0.11 mmol) of tetra-
peptide 19 was dissolved in 2 mL of MeOH. Aliquots of 1 n LiOH
were added starting with 250 μL, 50 μL after 1 h, 50 μL after 1 h
30 min. The reaction mixture was brought to pH = 6 with 1 n HCl
after 2 h and then the solvent was removed and dried. b) Acidolysis
of 19: 60 mg (0.11 mmol) of 19 was dissolved in 3 mL of MeOH.
1 mL of TFA was added and another 3 mL after 15 min. The solu-
tion was stirred at room temp. for 3 h and another 2 h at 45 °C.
The solvent was removed by coevaporation. c) Peptide coupling:
Both selectively deprotected tetrapeptides 20 and 21 were dissolved
in 4 mL of DMF. Then, 100 mg (0.19 mmol) of PyBOP was added
and the pH adjusted to 8 with NMM. After 16 h of stirring at
room temp., the solvent was removed and the raw product purified
by flash chromatography (CHCl3/MeOH, 10:1, Rf = 0.25) and
dried in high vacuum to obtain 70 mg (0.075 mmol, 68%) of octa-
peptide 22 as a colourless foam. 1H NMR (600 MHz, [D6]DMSO):
1
of 17 as a white solid. H NMR (400 MHz, [D6]DMSO): δ = 8.38
3
(d, JNH,Hα = 7.7 Hz, 1 H, Phe-NH), 7.50 (s, 1 H, 6-NH), 7.17–7.3
3
(m, 5 H, Phe-Harom.), 6.81 (d, J7,8 = 6.8 Hz, 1 H, 7-H), 5.26 (d,
3
3J8–OH,8 = 7.3 Hz, 1 H, 8-OH), 5.00, (d, J8a,8 = 3.3 Hz, 1 H, 8a-
3
3
H), 4.94 (dd, J3,2h = 3.1, J3,2t = 6.8 Hz, 1 H, 3-H), 4.5 (m, 1 H,
Pheα-H), 4.09 (m, 1 H, 8-H), 3.59 (s, 3 H, OCH3), 3.21 (dd, 1 H,
2
3
3J2t,3 = 6.8, Jgem = 11.0 Hz, 1 H, 2-Ht), 3.04 (dd, 1 H, JHβt,Hα
=
5.9, 2Jgem = 13.9 Hz, 1 H, Pheβ-Ht), 2.96 (m, 2 H, 2-Hh, Pheβ-Hh),
1.44 (s, 9 H, CH3 tBu) ppm. 13C NMR: δ = 171.45, 168.92 (C3-
CO, Phe-CO), 158.40, 151.89 (CO-5, CO tBu) 136.93 (Phe-Cq),
129.08 (C-6), 129.05, 128.18, 126.49 (Phe-CHarom.), 114.35 (C-7),
80.06 (Cq, tBu), 65.91 (C-8a), 62.49 (C-3), 61.64 (C-8), 53,67 (Phe-
Cα), 51.83 (OCH3), 36.40 (Phe-Cβ), 32.43 (C-2), 27.79 (3C, CH3
tBu) ppm. IR (KBr): ν = 3442, 3387, 3278, 2988, 1743, 1701, 1662,
˜
1633, 1518, 1434, 1157, 697 cm–1. ESI-MS: m/z = 492.2 [M + H]+,
509.2 [M + NH4]+. C23H29N3O7S (491.57): calcd. C 56.20, H 5.95,
N 8.55; found C 56.05, H 5.77, N 8.40.
3
δ = 9.13 (s, 1 H, 6B-NH), 9.03 (s, 1 H, 6A-NH), 8.78 (d, JNH,Hα
= 7.1 Hz, 1 H, PheB-NH), 8.56 [m, 2 H, DQF-COSY: 8.56 (PheA-
3
NH), 8.57 (GlyB-NH)], 8.16 (d, J7,8 = 7.9 Hz, 1 H, 7A-H), 8.15
3
3
Tripeptide Hydrochloride 18: 1.5 g (3.1 mmol) of 17 was dissolved
in 3 mL of MeOH and cooled with an ice bath. Then, 20 mL of
Et2O/HCl was added and a colorless precipitate formed after
1 min. The suspension was sonicated for 2 h and then stirred at
room temp. overnight. The precipitate was separated by filtration
(d, J7,8 = 7.9 Hz, 1 H, 7B-H), 7.29 (t, JNH,Hα/HαЈ = 6.0 Hz, 1 H,
3
Boc-NH), 7.3–7.1 (m, 10 H, PheA/B-Harom.), 6.24 (d, J8,7
=
3
7.9 Hz, 1 H, 8B-H), 6.22 (d, J8,7 = 7.9 Hz, 1 H, 8A-H), 5.52 (dd,
3J3,2proR = 8.5, J3,2proS = 1.9 Hz, 1 H, 3B-H), 5.51 (dd, J3,2proR
=
3
3
3
8.5, J3,2proS = 1.9 Hz, 1 H, 3A-H), 4.55 (m, 1 H, PheA-αH), 4.49
(m, 1 H, PheB-αH), 3.9–3.85 [m, 3 H, DQF-COSY: 3.92 (GlyB-
and dried over KOH to obtain 1.1 g (2.7 mmol, 87%) of 18. 1H
3
3
2
NMR (400 MHz, [D6]DMSO): δ = 8.94 (d, JNH,Hα = 7.7 Hz, 1 H, CH2), 3.88 (2 B-HproR)], 3.75 (dd, J2proR,3 = 8.8, Jgem = 11.8 Hz,
Phe-NH), 7.5 (m, 1 H, 7-H), 7.3–7.2 (m, 5 H, Phe-Harom.), 6.30 (d, 1 H, 2A-HproR), 3.71 (m, 2 H, GlyA-CH2), 3.59 (s, 3 H, OCH3),
3J8,7 = 7.7 Hz, 1 H, 8-H), 5.56 (dd, J3,2h = 2.2, J3,2t = 9.2 Hz, 1 3.53 (dd, J2proS,3 = 1.9, Jgem = 11.8 Hz, 1 H, 2A-HproS), 3.40 (dd,
3
3
3
2
3
2
2
3
H, 3-H), 4.49 (m, 1 H, Pheα-H), 3.93 (dd, J2t,3 = 9.2, Jgem
=
3J2proS,3 = 1.9, Jgem = 11.8 Hz, 1 H, 2 B-HproS), 3.07 (dd, JHβt,Hα
11.9 Hz, 1 H, 2-Ht), 3.60 (s, 3 H, OCH3), 3.42 (dd, J2h,3 = 2.0, = 5.2, Jgem = 14.0 Hz, 1 H, PheA-βHt), 3.02 (dd, JHβt,Hα = 5.8,
3
2
3
2Jgem = 11.9 Hz, 1 H, 2-Hh), 3.01 (m, 2 H, Pheβ-H) ppm. 13C 2Jgem = 14.0 Hz, 1 H, PheB-βHt), 2.95 (dd, JHβh,Hα = 8.2, Jgem
=
3
2
3
2
NMR: δ = 171.36 (Phe-CO), 167.09 (3-CO), 156.85 (CO-5), 148
(br. s, C-8a), 136.65 (Phe-Cq), 131 (br. s, C-7), 129.07, 128.27,
14 Hz, 1 H, PheB-βHh), 2.83 (dd, JHβh,Hα = 8.5, Jgem = 14.0 Hz,
1 H, PheA-βHh), 1.38 (s, 9 H, CH3, tBu) ppm. 13C NMR: δ =
126.63 (Phe-CHarom.), 119 (br. s, C-6), 98.18 (C-8), 63.42 (C-3), 171.44 (PheB-CO), 171.20 (PheA-CO), 168.53 (GlyA-CO) 167.81
53.94 (Phe-Cα), 51.94 (OCH3), 36.43 (Phe-Cβ), 32.63 (C-2) ppm.
(GlyB-CO), 167.29 (3B-CO), 167.00 (3A-CO), 156.19, 156.16 (C-
5A, C-5B), 155.88 (CO tBu), 140.92, 140.84 (C-8aA, C-8aB),
137.28 (PheA-Cq), 136.61 (PheB-Cq), 129.15, 129.01, 128.25,
128.05, 126.60, 126.23 (PheA/B-CHarom.),124.26 (C-7B), 124.06
(6A/B-C), 123.70 (C-7A), 98.75, 98.68 (C-8A, C-8B), 78.39 (Cq,
tBu), 63.64 (C-3B), 63.43 (C-3A), 54.15 (PheA-Cα), 53.97 (PheB-
Cα), 51.92 (OCH3), 44.25 (GlyB-CH2), 43.01 (GlyA-CH2), 37.59
(PheA-Cβ), 36.51 (PheB-Cβ), 32.27 (C-2B), 32.22 (C-2A), 28.11
CI-MS (NH3): m/z
=
374.1 [MH]+, 391.2 [M NH4]+.
+
C18H20ClN3O4S (409.89): calcd. C 52.77, H 4.92, N 10.25; found
C 52.44, H 5.14, N 9.94.
Tetrapeptide 19: 850 mg (2.07 mmol) of hydrochloride 18 and
500 mg (2.85 mmol) of BocNH-Gly-OH were dissolved in 20 mL
of DMF. 1.25 g (2.54 mmol) of PyBOP and 2 mL of NMM were
added and the reaction misture was stirred at room temp. over-
night. The solvent was removed and the residue purified by flash
chromatography [ethyl acetate/toluene, 5:1 Ǟ 9:1, Rf(EtOAc/tolu-
ene, 9:1) = 0.55] to obtain 1.05 g (1.98 mmol, 96%) of tetrapeptide
19. 1H NMR (600 MHz, [D6]DMSO): δ = 9.00 (s, 1 H, 6-NH), 8.75
(CH3, tBu) ppm. ESI-MS: m/z
= 929.5 [M +
H]+, 946.5
[M + NH4]+. C44H48N8O11S2 (929.05): calcd. C 56.89, H 5.21, N
12.06; found C 56.06, H 5.29, N 11.73.
Cyclic Octapeptide 25: 100 mg (0.11 mmol) of 22 was dissolved in
3
3
(d, JNH,Hα = 7.5 Hz, 1 H, Phe-NH), 8.15 (d, J7,8 = 7.8 Hz, 1 H, 3 mL of CH2Cl2/MeOH, 1:1. 0.22 mL, 0.1 mL, and 0.1 mL of 1 n
7-H), 7.2 (m, 6 H, Phe-Harom./Boc-NH, DQF-COSY: 7.27), 6.23 LiOH were added at room temp. within 5 h. The solution was neu-
3
3
3
(d, J8,7 = 7.8 Hz, 1 H, 8-H), 5.53 (dd, J3,2proS = 2.0, J3,2proR
=
tralized with 1 n HCl. The solvent was removed and the dry residue
was suspended in 10 mL of Et2O/HCl and sonicated in an ice bath
for 3 h and then stirred overnight at room temp. 24 was separated
by filtration and dried over KOH in high vacuum. The deprotected
3
9.0 Hz, 1 H, 3-H), 4.51 (m, 1 H, Pheα-H), 3.87 (dd, J2proR,3 = 9.0,
2Jgem = 11.9 Hz, 1 H, 2-HproR), 3.71 (m, 2 H, Gly-CH2), 3.60 (s, 3
H, OCH3), 3.38 (dd, 3J2proS,3 = 2.0, Jgem = 11.7 Hz, 1 H, 2-HproS),
2
3.03 (dd, JHβt,Hα = 5.9, Jgem = 13.9 Hz, 1 H, Pheβ-Ht), 2.96 (dd, peptide was dissolved in 600 mL of DMF. Then, 50 mg
3
2
3JHβh,Hα = 7.9, 2Jgem = 13.9, 1 H, Pheβ-Hh), 1.38 (s, 9 H, CH3, tBu) (0.13 mmol) of HATU, and 15 mg (0.11 mmol) of HOAT, and
ppm. 13C NMR: δ = 171.37 (Phe-CO), 168.51 (Gly-CO), 167.21 (3-
CO), 156.12 (CO-5), 155.86 (CO, tBu), 140.72 (C-8a), 136.61 (Phe-
Cq), 129.05, 128.25, 126.59 (Phe-CHarom), 124.02 (C-6), 123.69 (C-
7), 98.67 (C-8), 78.38 (Cq, tBu), 63.45 (C-3), 53.83 (Phe-Cα), 51.90
0.2 mL (1.5 mmol) of collidine were added. After 3 d at room
temp., the solvent was removed and the raw product purified by
flash chromatography [CHCl3/MeOH, 7:1 Ǟ 4:1, Rf(CHCl3/
MeOH, 4:1) = 0.7] to obtain 31 mg (0.39 mmol, 35%) of cyclic
(OCH3), 44.23 (Gly-CH2), 36.50 (Phe-Cβ), 32.17 (C-2), 28.08 (CH3 octapeptide 25 as a white solid. 1H NMR (600 MHz, [D6]DMSO):
tBu) ppm. IR (KBr): ν =˜ = 3277, 2979, 1752, 1672, 1636, 1501,
δ = 9.12 (s, 2 H, 6-NH), 8.58 (br. s, 2 H, Gly-NH), 8.55 (d, 3JNH,Hα
˜
1240, 1164, 768, 738 cm–1. ESI-MS: m/z = 531.3 [M + H]+, 548.3 = 9.1 Hz, 2 H, Phe-NH), 8.10 (d, J7,8 = 7.9 Hz, 2 H, 7-H), 7.1–
3
3480
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3475–3481

Pyridone Dipeptides – Synthesis of a Novel Peptide Chromophore
FULL PAPER
[3] P. Tremmel, A. Geyer, Angew. Chem. 2004, 116, 5913–5915;
Angew. Chem. Int. Ed. 2004, 43, 5789–5791.
[4] P. K. C. Paul, P. A. Burney, M. M. Campbell, D. J. Osguthorpe,
J. Computer-Aided Mol. Design 1990, 4, 239–253.
[5] F. W. Lichtenthaler, Carbohydrates as Organic Raw Materials
(Ed.: F. W. Lichtenthaler), VCH Publishers, Weinheim, New
York, 1991, p. 1–32.
[6] a) P. S. Dragovich, T. J. Prins, R. Zhou, E. L. Brown, F. C. Mal-
donado, S. A. Fuhrmann, L. S. Zalman, T. Tuntland, C. A.
Lee, A. K. Patick, D. A. Matthews, T. F. Hendrickson, M. B.
Kosa, B. Liu, M. R. Batugo, J.-P. R. Gleeson, S. K. Sakata,
L. Chen, M. C. Guzman, J. W. Meador III, R. A. Ferre, S. T.
Worland, J. Med. Chem. 2002, 45, 1607–1623; b) X. Zhang,
A. C. Schmitt, C. P. Decicco, Tetrahedron Lett. 2002, 43, 9663–
9666; c) N. Pemberton, V. Aberg, H. Almstedt, A. Westermark,
F. Almqvist, J. Org. Chem. 2004, 69, 7830–7835.
[7] P. Tremmel, J. Brand, V. Knapp, A. Geyer, Eur. J. Org. Chem.
2003, 878–884.
[8] P. Tremmel, A. Geyer, J. Am. Chem. Soc. 2002, 124, 8548–8549.
[9] M. Haack, A. Geyer, P. Tremmel, A. Beck-Sickinger, J. Peptide
Sci. 2005, 10, 225.
3
6.9 (m, 10 H, Phe-Harom.), 6.34 (d, J8,7 = 7.9 Hz, 1 H, 8-H), 5.47
(dd, 3J3,2t = 8.2, 3J3,2h = 3.6 Hz, 2 H, 3-H), 4.54 (m, 2 H, Pheα-H),
3
2
3.98 (m, 4 H, Gly-CH2), 3.68 (dd, J2t,3 = 8.5, Jgem = 11.3 Hz, 2
H, 2-Ht), 3.46 (m, 2 H, 2-Hh), 3.26 (dd, JHβt,Hα = 3.8, Jgem
=
3
2
13.7 Hz, 2 H, Pheβ-Ht), 2.67 (t, JHβh,Hα/Hβt = 12.6 Hz, 2 H, Pheβ-
Hh) ppm. 13C NMR (HMQC): δ = 128.1, 127.6, 125.9 (Phe-
CHarom.), 125.0 (C-7), 100.2 (C-8), 64.8 (C-3), 53.8 (Phe-Cα), 43.4
(Gly-CH2), 36.9 (Phe-Cβ), 29.9 (C-2) ppm. ESI-MS: m/z = 797.3
[M + H]+, 814.2 [M + NH4]+.
3
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie is gratefully acknowledged.
The authors thank Dr. M. Zabel (Fakultät für Chemie und Pharm-
azie, Universität Regensburg) for the crystal structure analysis of 17
and Nikola Kastner-Pustet for measuring the UV/Vis-spectroscopic
data.
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Received: March 4, 2005
Published Online: June 30, 2005
Eur. J. Org. Chem. 2005, 3475–3481
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