Stereocontrolled backbone connection of peptides by C = C-double bonds

Article abstract of DOI:10.1016/S0040-4020(00)00343-4

Treatment of peptides containing an α-chloroglycine residue with triethylamine and catalytic amounts of triphenylphosphine constitutes an efficient method for the stereoselective synthesis of amino acid and peptide dimers bridged by a C = C-double bond. The dimers can be converted into novel peptide structures by standard methods of peptide synthesis. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00343-4

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 4187±4195
Stereocontrolled Backbone Connection of Peptides
by CvC-Double Bonds
*
È
Susanne Schumann, Kirsten Zeitler, Martin Jager, Kurt Polborn and Wolfgang Steglich
È È È
Department Chemie der Ludwig-Maximilians-Universitat Munchen, Butenandtstr. 5-13, D-81377 Munchen, Germany
Dedicated to Professor Rolf Huisgen on the occasion of his 80th birthday
Received 13 April 2000; accepted 18 April 2000
AbstractÐTreatment of peptides containing an a-chloroglycine residue with triethylamine and catalytic amounts of triphenylphosphine
constitutes an ef®cient method for the stereoselective synthesis of amino acid and peptide dimers bridged by a CvC-double bond. The dimers
can be converted into novel peptide structures by standard methods of peptide synthesis. q 2000 Elsevier Science Ltd. All rights reserved.
The disul®de bridge is the most common cross-link found in
proteins formed by oxidative coupling of two cysteine
residues. This reaction is important in stabilising the
three-dimensional folding of the backbone chain in proteins.
Partially rigidi®ed structures can also result from amide
respectively ester linkage of glutamic acid residues with
lysine or serine moieties or by oxidative phenolic coupling
of tyrosine units.1 In addition, bridging by diamino dicarb-
oxylic acids like lanthionine and meso-1,6-diaminopimelic
acid is observed in several biological active peptides.2,3
Recently, a number of bridged peptides have been syn-
thesised to study their importance to conformational
constraints.4,5
amino acids or peptides are connected by a CvC-double
bond.
The reaction relies on the chemistry of a-halogenoglycine
derivatives 1 that are easily available from the correspond-
ing seryl or a-(ethylthio)glycyl compounds.8 Treatment of
an amino acid or peptide derivative of type 1 with triethyl-
amine and catalytic amounts of triphenylphosphine in THF
affords the dimers Z-2 and (or) E-2 in moderate to excellent
yields.9 This mild method allows not only the synthesis of
homomers but also of heteromers containing two different
peptide chains (Scheme 1).
In these cases the triphenylphosphonium salt preformed
from one component is subsequently treated with an acyl-
imine 3 generated from a second a-chloroglycine peptide.
For this procedure stoichiometrical amounts of triphenyl-
phosphine are required.
Much less is known about peptides cross-linked at backbone
positions.6,7 As part of our ongoing investigations on the
modi®cation of oligopeptides,8 we describe now a simple
method for the preparation of dimers 2 in which two
Scheme 1. Dimerisation of a-chloroglycine derivatives 1.
Keywords: peptide analogues; dimerisation; ole®ns; stereoselectivity; phosphines.
* Corresponding author. Tel.: 149-89-2180-7757; fax: 149-89-2180-7756; e-mail: wos@cup.uni-muenchen.de
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00343-4

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S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
Scheme 2. Proposed course for the formation of ole®ns 2.
The catalytic activity of triphenylphosphine can be
explained by the reactions depicted in Scheme 2. We
assume that the triphenylphosphonium salt 4 initially
formed from chloroglycine 1 and triphenylphosphine,
affords both the ylide 6 and the acylimine 5 on treatment
with base. Reaction of the two reactive intermediates 5 and
6 to the diastereomeric betaines 7 followed by b-elimination
yields the dimers Z-2 and E-2, respectively.
Analogous cross-coupling of Boc-Gly(PPh13 Cl2)ValOBn
and Boc-Gly(Cl)-Gly-OMe yielded 63% of E-2l. In the
formation of heteromers the same stereochemical prefer-
ences are observed as for homomeric compounds. The
occurrence of small amounts of homomers as by-products
can be explained through exchange of the triphenyl-
phosphine residues in the pre-equilibrium according to the
reaction sequence proposed in Scheme 2.
For protected di- and tripeptides the ole®nic linkage can be
established at any position of the peptide chain (Table 1).
The stereochemical outcome of the reaction, however,
depends on the position of the activated glycine residue.
The con®gurational assignment of the ole®nic compounds 2
is based on X-ray structure analyses of numerous dimers.10
As an example, the X-ray structure of compound E-2d is
presented in Fig. 2.11 In cases where both stereoisomers are
known, the E-dimers exhibit a greater lmax in their UV
spectra (between 1 to 5 nm) and higher Rf values on silica
gel in chromatographic separations. The conventional
comparison of the 13C NMR shifts of the ole®nic carbons
(cf. maleic and fumaric acid) for determining the stereo-
chemistry is prevented in many cases by a large broadening
of these signals.12
N-Acylamino-a-chloroglycinates or N-acylpeptide esters
with a C-terminal chloroglycine residue afford the cis-
dimers Z-2 with high stereoselectivity. Thus, Boc-Gly-
Gly(Cl)-OBn furnished Z-2c in 61% yield under standard
conditions. The corresponding E-isomer could not been
detected in the reaction mixture. In contrast, peptides with
a chloroglycine residue at the N-terminus yield predomi-
nantly the trans-dimers E-2. For example, Z-Gly(Cl)-Ala-
OMe afforded E-2e in 60% yield in addition to 8% of Z-2e.
The position-dependent control of product stereochemistry
is also observed for tripeptides. Compounds with an acti-
vated glycine residue at the C and N-termini yield preferably
the Z- and E-dimers, respectively (examples 2f and 2g),
whereas an activated glycine residue at the centre of the
peptide chain induces a mixture of both diastereomers
which can be separated by silica gel chromatography.
Like in the case of peptides activated at the N-terminal
position the major product shows trans-con®guration
(examples 2h and 2i).
The peptide dimers 2c±2l are stable against acids and bases
and exhibit high con®gurational stability.13,14 They can
therefore be used for the construction of more complex
compounds by standard methods of peptide synthesis.
This is illustrated by the synthesis of the triple dimeric
peptide structure Z,E,Z-10 (Scheme 3). The carboxylic
acid component E-8 was obtained by hydrogenolysis of
the benzyl esters from the orthogonally protected homo-
meric dimer E-2d. E-8 was then coupled under standard
conditions with two equivalents of the selectively Boc-
deprotected heteromeric amino component Z-9 to yield
the pseudododecapeptide Z,E,Z-10 in which three dimeric
units are connected by peptide bonds.
Dimers with two different peptide chains (heteromers) can
be easily prepared by the two-component procedure
described above (Scheme 1). For example, Boc-Val-
Gly(Cl)-OMe is ®rst converted to the corresponding phos-
phonium salt by treatment with equimolar amounts of
triphenylphosphine and then treated with Z-Gly-Gly(Cl)-
OMe and triethylamine. Chromatography of the products
afforded the dimer Z-2k in 54% yield (Fig. 1).
Some restrictions exist in the use of dimers 2 for further
peptide syntheses. C-terminally bridged homomers 2
(R1ˆR3; R2ˆR4) create problems in carboxyl activation
because of anhydride formation with the neighbouring carb-
oxyl group. Furthermore, deprotection of dimers 2 in direct
neighbourhood to the bridging double bond leads to an
enediamine moiety that is unsuitable for peptide couplings.

S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
4189
Table 1. Symmetrical dimers of type 2 (R1ˆR2ˆR3ˆR4)
a Isolated yields after puri®cation on silica gel.
b Determined through 1H NMR analysis (only one diastereomer detectable).
Figure 1. Heteromeric peptide structures.

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S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
Figure 2. X-Ray structure of E-2d.11
Scheme 3. Synthesis of a triple dimeric peptide structure Z,E,Z-10.15
Catalytic hydrogenation of the rather inert double bond of
dimers 2 to generate additional peptides, bridged at glycine
residues by a C±C single bond, is also an option. Experi-
ments to study the optimal reaction conditions and the
stereochemistry of these hydrogenations are in progress.
related systems. We found that a-chlorinated a-acylamino-
ketones afford (E)-acylamino ketone dimers of type E-1116
(R1ˆBoc, Bz, Z) in high yields and with excellent stereo-
selectivity. The use of N-arylsulfonyl derivatives instead of
the N-acylamino-a-chloroglycinates yields preferably
trans-dimers like E-12 (Fig. 3).16
Our new dimerisation reaction can also be extended to
In conclusion, the new dimerisation method offers an
ef®cient way for the synthesis of novel peptidic and non-
peptidic structures.
Experimental
General
IR: Perkin±Elmer FTIR spectrophotometer FT 1000 or 1420
IS. UV/Vis: Perkin±Elmer Lambda 16 Spectrophotometer.
Figure 3. Ole®nic bridged a-acylamino ketones 11 and N-sulfonylamino
acid ester 12.

S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
4191
1
NMR: Bruker AMX 600 and ARX 300 with solvent peak as
internal reference. TLC: Silica gel Merck G plates. Column
chromatography: Silica gel Merck 60. Petroleum ether (40±
608C) was used in all cases. FAB MS and ESI MS, HR-FAB
MS and HR-ESI MS were performed on Finnigan MAT 90
and 95 instruments. The X-ray diffraction analyses were
carried out on a Enraf±Nonius CAD4 diffractometer at
(m), 690 (m) cm21. H NMR (CDCl3, 300 MHz): dˆ9.49
(br. s, 2H, NH), 7.84 (d, Jˆ7.2 Hz, 4H, Ph), 7.50±7.30 (m,
6H, Ph), 3.80 (s, 6H, COOCH3). 13C NMR (CDCl3,
75 MHz): dˆ166.0 (COOCH3), 164.7 (CONH), 133.2
(arom. CH), 132.9 (arom. q.C), 129.3 (arom. CH), 128.2
(arom. CH), 123.0 (CvC), 53.6 (COOCH3). ESI MS m/z
(%)ˆ596 7 (3), 596 (17), 407 (1) [MH21Na]1, 406 (16)
[MH1Na]1, 405 (100) [M1Na]1, 262 (1). HR-ESI MS m/z
found 405.1066, Calcd for C20H18N2O6Na [M1Na]1
405.1062.
Ê
296(2) K using Mo Ka (lˆ0.71069 A) radiation. CH2Cl2
was distilled from Sicapentw and THF from potassium/
benzophenone. Sulfuryl chloride was purchased as a 1 M
solution in CH2Cl2 from Aldrich. All reactions were carried
out under an argon atmosphere using oven-dried glassware.
All a-(ethylthio)glycine derivatives were prepared accord-
ing to standard procedures.8 Microanalyses were performed
by the microanalytical laboratory of our department.
2,3-Bis(N,N0-tert-butyloxycarbonyl-glycylamino)maleic
acid dibenzyl ester (Z-2c). Yield 61%, colourless foam.
UV (CH3CN): lmax(e)ˆ276.25 nm (13597). IR(KBr): nˆ
Ä
3420 (m), 2979 (m), 2933 (w), 1711 (s), 1629 (m), 1500
(s), 1456 (m), 1380 (m), 1368 (m), 1328 (m), 1251 (m),
1164 (s), 1052 (m), 1029 (w), 944 (w), 863 (w), 751 (w),
General procedure for the synthesis of a-chloroglycine
derivatives 1
698 (s), 582 (w) cm21. H NMR ([D6]DMSO, 300 MHz):
1
dˆ9.72 (br. s, 2H, NH), 7.47 (s, 10H, Ph), 5.42 (br. t, 2H,
Jˆ5.6 Hz, NH), 4.99 (s, 4H, CH2-Ph), 3.77 (d, Jˆ5.6 Hz,
4H, NH±CH2±CO), 1.39 (s, 18H, C(CH3)3). 13C NMR
([D6]DMSO, 75 MHz): dˆ168.8 (CONH), 163.0
(COOCH2), 155.8 (OCONH), 135.3 (arom. q.C), 128.3
(arom. CH), 128.0 (arom. CH), 123.4 (CvC), 78.1
(C(CH3)3), 66.6 (COOCH2), 42.9 (NH±CH2±CO), 28.2
(C(CH3)3). ESI MS m/z (%)ˆ1319 (6) [2M1K]1, 1305
(8) [2MH1Na]1, 1304 (74) [2M1H1Na]1, 1303 (100)
[2M1Na]1, 983 (6), 925 (5), 679 (12) [M1K]1, 665 (4)
[MH21Na]1, 664 (20) [MH1Na]1, 663 (58) [M1Na]1,
529 (2). HR-ESI MS m/z found 663.2646, calcd for
C29H40N4O10Na [M1Na]1 663.2642. Anal. Calcd for
C29H40N4O10: C, 59.99; N, 8.74; H, 6.29; Found: C, 60.09;
N, 8.76; H, 6.51.
To a solution of the a-(ethylthio)glycyl peptide (1.0 mmol)8
in CH2Cl2 (30 mL) was added a 1 M solution of SO2Cl2
(1.1 mL, 1.1 mmol) in CH2Cl2 at 08C. After 30 min stirring,
the solvent and all volatile by-products were evaporated
(cool trap), and the resulting residue was dried in high
vacuo. The resulting a-chloropeptides were used for the
next step without further puri®cation.
General procedure for the synthesis of homomeric
dimers 2
To a solution of the a-chloroglycyl peptide 1 (1.0 mmol)
and PPh3 (0.2 mmol) in THF (50 mL) was added NEt3 (0.15
mL, 1.1 mmol) in THF (30 mL) dropwise during 5 h. After
continued stirring overnight, petroleum ether (200 mL) was
added and the mixture ®ltered through Celite. Evaporation
of the ®ltrate in vacuo yielded an oily residue which was
puri®ed by column chromatography on silica gel (petroleum
ether/EtOAc).
1,10-[2,3-Bis(N,N0-tert-butyloxycarbonylamino)-maleoyl]-
bis-glycine benzyl ester (Z-2d). Yield 8%, colourless oily
foam. UV (CH3CN):
l
max(e)ˆ267.80 nm (12771).
IR(KBr): n~ ˆ 3409 (s), 2979 (m), 2933 (m), 1740 (s),
1653 (s), 1498 (s), 1456 (m), 1392 (m), 1367 (m), 1249
(m), 1165 (s), 1071 (w), 1017 (w), 740 (m), 697 (m), 578
(w) cm21. 1H NMR (CDCl3, 300 MHz): dˆ7.74 (br. s, 2H,
NH), 7.39±7.16 (m, 12H, NH and Ph), 5.12 (s, 4H, CH2-Ph),
4.10 (d, Jˆ5.3 Hz, 4H, NH±CH2±CO), 1.43 (s, 18H,
C(CH3)3). 13C NMR (CDCl3, 75 MHz): dˆ169.9
(COOCH2), 165.1 (CONH), 153.5 (OCONH), 135.9
(arom. q.C), 129.3 (arom. CH), 129.1 (arom. CH), 129.0
(arom. CH), 124.8 (br., CvC), 82.5 (C(CH3)3), 67.7
(COOCH2), 42.7 (NH±CH2±CO), 28.7 (C(CH3)3). ESI
MS m/z (%)ˆ1305 (15) [2MH1Na]1, 1304 (40)
[2M1H1Na]1, 1303 (54) [2M1Na]1, 981 (1), 806 (4),
679 (13) [M1K]1, 665 (7) [MH21Na]1, 664 (35)
[MH1Na]1, 663 (100) [M1Na]1, 498 (6), 476 (9), 364
(5), 304 (5). HR-ESI MS m/z found 663.2637, calcd for
C29H40N4O10Na [M1Na]1 663.2642. Anal. Calcd for
C29H40N4O10: C, 59.99; N, 8.74; H, 6.29; Found: C, 60.08;
N, 8.77; H, 6.43.
2,3-Bis(N,N0-tert-butyloxycarbonylamino)maleic
acid
dimethyl ester (Z-2a). Yield 96%, colourless foam. UV
(CH3CN): lmax(e)ˆ270.03 nm (10816). IR(KBr): n~ ˆ
3411 (m, br.), 2981 (m), 1723 (s), 1627 (s), 1494 (m),
1436 (m), 1393 (m), 1369 (s), 1326 (m), 1242 (s), 1154
(s), 1049 (w), 1022 (w), 866 (w), 831 (w), 772 (w), 746
(w), 602 (w) cm21 1H NMR ([D6]DMSO, 300 MHz):
.
dˆ8.85 (br. s, 2H, NH), 3.62 (s, 6H, COOCH3), 1.38 (s,
18H, C(CH3)3). 13C NMR ([D6]DMSO, 75 MHz): dˆ164.3
(COOCH3), 152.5 (OCONH), 123.2 (br., CvC), 79.8
(C(CH3)3), 52.1 (COOCH3), 28.9 (C(CH3)3). ESI MS m/z
(%)ˆ772 (1) [2M1H1Na]1, 771 (4) [2M1Na]1, 399 (3)
[MH21Na]1, 398 (17) [MH1Na]1, 397 (100) [M1Na]1,
341 (12), 303 (8), 285 (4). HR-ESI MS m/z found 397.1599,
calcd for C16H26N2O8Na [M1Na]1 397.1587. Anal. calcd
for C16H26N2O8: C, 51.33; N, 7.48; H, 7.00; Found: C,
50.93; N, 7.39; H, 7.01.
1,10-[2,3-Bis(N,N0-tert-butyloxycarbonylamino)-fumaroyl]-
bis-glycine benzyl ester (E-2d).11 Yield 58%, colourless
oily foam. UV (CH3CN): lmax(e)ˆ270.47 nm (14381).
IR(KBr): n~ ˆ 3412 (s), 2980 (m), 1742 (s), 1703 (s), 1646
(m), 1498 (m), 1455 (m), 1392 (m), 1369 (m), 1248 (m),
1194 (s), 1154 (s), 1051 (w), 753 (w), 699 (w), 577 (w)
2,3-Bis(N,N0-benzoylamino)maleic acid dimethyl ester
(Z-2b). Yield 80%, colourless solid. UV (CH3OH):
lmaxˆ294, 234, 204 nm. IR(KBr): n~ ˆ 3320 (m), 2982
(m), 1730 (s), 1708 (s), 1656 (s), 1613 (m), 1596 (m),
1496 (s), 1472 (s), 1438 (m), 1386 (m), 1362 (m), 1330
(s), 1260 (s), 1113 (m), 1068 (m), 846 (m), 792 (m), 705

4192
S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
cm21. 1H NMR (CDCl3, 300 MHz): dˆ8.39 (br. s, 2H, NH),
7.40±7.24 (m, 10H, Ph), 6.78 (br. t, Jˆ5.8 Hz, 2H, NH),
5.18 (s, 4H, CH2-Ph), 4.13 (d, Jˆ5.8 Hz, 4H, NH±CH2±
CO), 1.41 (s, 18H, C(CH3)3). 13C NMR (CDCl3, 75 MHz):
dˆ169.8 (COOCH2), 165.6 (CONH), 153.8 (OCONH),
135.7 (arom. q.C), 129.3 (arom. CH), 129.2 (arom. CH),
129.0 (arom. CH), 82.4 (C(CH3)3), 67.9 (COOCH2), 42.1
(NH±CH2±CO), 28.7 (C(CH3)3). No CvC-signal was
observable. ESI MS m/z (%)ˆ1319 (18) [2M1K]1, 1305
(29) [2MH1Na]1, 1304 (73) [2M1H1Na]1, 1303 (100)
[2M1Na]1, 999 (2), 743 (9), 742 (23), 697 (22), 681 (60)
[M1Na1H2O]1, 679 (19) [M1K]1, 665 (3) [MH21Na]1,
664 (14) [MH1Na]1, 663 (39) [M1Na]1, 563 (1), 322 (5),
278 (10). HR-ESI MS m/z found 663.2647, Calcd for
C29H40N4O10Na [M1Na]1 663.2642. Anal. Calcd for
C29H40N4O10: C, 59.99; N, 8.74; H, 6.29; Found: C, 59.88;
N, 8.79; H, 6.27.
607.2016. Anal. Calcd for C28H32N4O10: C, 57.53; N,
9.58; H, 5.52; Found: C, 57.42; N, 9.52; H, 5.51.
2,3-Bis-(N,N0-tert-butyloxycarbonyl-l-valyl-l-valylamino)
maleic acid dimethyl ester (Z-2f). Yield 42%, colourless
1
oily foam. UV (CH3CN): lmax(e)ˆ276.08 nm (14016). H
NMR (CDCl3, 300 MHz): dˆ8.69 (br. s, 2H, NH), 6.84 (br.
d, Jˆ5.4 Hz, 2H, NH), 5.37 (br. s, 2H, NH), 4.45±4.28 (m,
2H, CH±CH(CH3)2), 3.86 (ps-t, Jˆ6.9 Hz, 2H, CH±
CH(CH3)2), 3.75 (s, 6H, COOCH3), 2.28±1.78 (m, 4H,
CH±CH(CH3)2), 1.40 (s, 18H, C(CH3)3), 0.99±0.92 (m,
24H, CH±CH(CH3)2). 13C NMR (CDCl3, 75 MHz): dˆ
173.5 (CONH), 170.6 (CONH), 163.9 (COOCH3), 156.9
(OCONH), 124.6 (CvC), 81.0 (C(CH3)3), 61.5 (CH±
CH(CH3)2), 59.4 (CH±CH(CH3)2), 52.3 (COOCH3), 31.3
(CH±CH(CH3)2), 30.9 (CH±CH(CH3)2), 28.9 (C(CH3)3),
20.0, 19.9, 18.9, 18.4 (CH±CH(CH3)2). ESI MS m/z
(%)ˆ1565 (3) [2MH1Na]1, 1564 (6) [2M1H1Na]1,
1563 (8) [2M1Na]1, 1055 (35), 838 (4), 795 (10)
[MH21Na]1, 794 (42) [MH1Na]1, 793 (100) [M1Na]1,
671 (2), 579 (8), 481 (2). HR-ESI MS m/z found 793.4321,
Calcd for C36H62N6O12Na [M1Na]1 793.4323. Anal. Calcd
for C36H62N6O12: C,56.09; N,10.90; H,8.11; Found: C,
56.03; N, 10.67; H, 8.26.
1,10-[2,3-Bis(N,N0-benzyloxycarbonylamino)-maleoyl]-
bis-l-alanine methyl ester (Z-2e). Yield 8%, colourless
oily foam. UV (CH3CN): lmax(e)ˆ264.01 nm (13099).
IR(KBr): n~ ˆ 3279 (s), 2991 (m), 2952 (m), 1741 (s),
1648 (s), 1512 (s), 1454 (m), 1217 (s), 1148 (m), 1091
(m), 1056 (m), 1002 (w), 898 (w), 844 (w), 748 (m), 697
1
(m), 579 (w) cm21. H NMR (CDCl3, 300 MHz): dˆ7.66
(br. s, 2H, NH), 7.59 (br. d, Jˆ7.0 Hz, 2H, NH), 7.47±6.97
(m, 10H, Ph), 5.07 (s, 4H, COOCH2), 4.52 (psq, Jˆ7.0 Hz,
2H, CH±CH3), 3.64 (s, 6H, COOCH3), 1.32 (d, Jˆ7.0 Hz,
6H, CH±CH3). 13C NMR (CDCl3, 75 MHz): dˆ173.5
(COOCH3), 164.0 (CONH), 154.3 (OCONH), 136.2
(arom. q.C), 129.1 (arom. CH), 128.9 (arom. CH), 128.8
(arom. CH), 125.3 (CvC), 68.4 (CH2-Ph), 52.9
(COOCH3), 49.4 (CH±CH3), 18.0 (CH±CH3). ESI MS
m/z (%)ˆ1776 (29) [3M1H1Na]1, 1207 (22), 1193 (18)
[2MH1Na]1, 1192 (58) [2M1H1Na]1, 1191 (100)
[2M1Na]1, 688 (17), 623 (9), 609 (1) [MH21Na]1, 608
(3) [MH1Na]1, 607 (36) [M1Na]1, 423 (2), 331 (7), 304
(12). HR-ESI MS m/z found 607.2027, Calcd for
C28H32N4O10Na [M1Na]1 607.2016. Anal. Calcd for
C28H32N4O10: C, 57.53; N, 9.58; H, 5.52; Found: C, 57.61;
N, 9.53; H, 5.73.
2,3-Bis-(N,N0-tert-butyloxycarbonyl-l-valyl-l-valylamino)
fumaric acid dimethyl ester (E-2f). Yield 7%, colourless
oily foam. UV (CH3CN): lmax(e)ˆ277.52 nm (17144).
IR(KBr): n~ ˆ 3341 (m), 2967 (m), 2934 (m), 1734 (s),
1657 (s), 1506 (s), 1392 (m), 1369 (m), 1239 (m), 1154
(s), 1047 (w), 1021 (w), 889 (w), 814 (w), 769 (w), 605
1
(w) cm21. H NMR (CDCl3, 300 MHz): dˆ8.17 (br. s,
2H, NH), 6.89 (br. d, Jˆ8.2 Hz, 2H, NH), 6.06 (br. d,
Jˆ6.9 Hz, 2H, NH), 4.36 (dd, Jˆ8.2 Hz; Jˆ5.6 Hz, 2H,
CH±CH(CH3)2), 4.32 (ps-t, Jˆ7.0 Hz, 2H, CH±
CH(CH3)2), 3.79 (s, 6H, COOCH3), 2.45±2.25 (m, 2H,
CH±CH(CH3)2), 2.16±2.03 (m, 2H, CH±CH(CH3)2), 1.39
(s, 18H, C(CH3)3), 1.09±0.90 (m, 24H, CH±CH(CH3)2). 13
C
NMR (CDCl3, 75 MHz): dˆ174.1 (CONH), 170.7
(CONH), 164.0 (COOCH3), 157.5 (OCONH), 124.3
(CvC), 80.9 (C(CH3)3), 61.3 (CH±CH(CH3)2), 60.3
(CH±CH(CH3)2), 53.4 (COOCH3), 31.8 (CH±CH(CH3)2),
31.1 (CH±CH(CH3)2), 29.0 (C(CH3)3), 19.5, 19.3, 18.2,
17.7 (CH±CH(CH3)2). ESI MS m/z (%)ˆ1565 (5)
[2MH1Na]1, 1564 (10) [2M1H1Na]1, 1563 (12)
[2M1Na]1, 844 (1), 795 (11) [MH21Na]1, 794 (43)
[MH1Na]1, 793 (100) [M1Na]1, 693 (1), 481 (1). HR-
ESI MS m/z found 793.4321, Calcd for C36H62N6O12Na
[M1Na]1 793.4323. Anal. Calcd for C36H62N6O12: C,
56.09; N, 10.90; H, 8.11; Found: C, 55.79; N, 10.60; H,
8.48.
1,10-[2,3-Bis(N,N0-benzyloxycarbonylamino)-fumaroyl]-
bis-l-alanine methyl ester (E-2e). Yield 60%, colourless
oily foam. UV (CH3CN): lmax(e)ˆ267.54 nm (17419).
IR(KBr): n~ ˆ 3338 (s), 2954 (m), 1747 (s), 1671 (s), 1647
(s), 1499 (s), 1451 (s), 1375 (m), 1308 (m), 1207 (s), 1158
(m), 1044 (m), 982 (w), 890 (w), 850 (w), 801 (w), 743 (m),
697 (m), 579 (w), 470 (w) cm21 1H NMR (CDCl3,
.
300 MHz): dˆ8.75 (br. s, 2H, NH), 7.39±7.16 (m, 10H,
Ph), 6.82 (br. d, Jˆ7.2 Hz, 2H, NH), 5.16±5.07 (m, 4H,
COOCH2), 4.55 (ps-q, Jˆ7.2 Hz, 2H, CH±CH3), 3.68 (s,
6H, COOCH3), 1.35 (d, Jˆ7.2 Hz, 6H, CH-CH3). 13C
NMR (CDCl3, 75 MHz): dˆ173.4 (COOCH3), 164.6
(CONH), 154.6 (OCONH), 136.1 (arom. q.C), 129.1
(arom. CH), 129.0 (arom. CH), 128.8 (arom. CH), 68.5
(CH2Ph), 53.1 (COOCH3), 48.8 (CH±CH3), 18.4 (CH±
CH3). No CvC-signal was observable. ESI MS m/z
(%)ˆ1777 (28) [3M12H1Na]1, 1481 (2), 1207 (4), 1193
(20) [2MH1Na]1, 1192 (61) [2M1H1Na]1, 1191 (100)
[2M1Na]1, 1152 (13), 862 (1), 688 (1), 644 (9), 608 (2)
[MH1Na]1, 607 (13) [M1Na]1, 412 (9). HR-ESI MS m/z
found 607.2003, Calcd for C28H32N4O10Na [M1Na]1
1,10-[2,3-Bis-(N,N0-tert-butyloxycarbonylamino)-maleoyl]-
bis-l-valyl-l-valine methyl ester (Z-2g). Yield 17%,
colourless oily foam. UV (CH3CN): lmax(e)ˆ 267.49 nm
(10330). IR(KBr): n~ ˆ 3351 (m), 2967 (m), 2876 (m),
1735 (s), 1663 (s), 1497 (s), 1393 (m), 1369 (m), 1314
(m), 1248 (s), 1156 (s), 1049 (w), 1020 (w), 890 (w), 772
1
(w), 605 (w) cm21. H NMR (CDCl3, 300 MHz): dˆ7.73
(br. d, Jˆ8.2 Hz, 2H, NH), 7.12 (br. d, Jˆ8.3 Hz, 2H, NH),
7.01 (br. s, 2H, NH), 4.51 (dd, Jˆ8.3 Hz; Jˆ5.7 Hz, 2H,
CH±CH(CH3)2), 4.42 (dd, Jˆ8.2 Hz; Jˆ5.4 Hz, 2H,
CH±CH(CH3)2), 3.72 (s, 6H, COOCH3), 2.33±2.16 (m,

S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
4193
4H, CH±CH(CH3)2), 1.42 (s, 18H, C(CH3)3), 0.97±0.93 (m,
24H, CH±CH(CH3)2). 13C NMR (CDCl3, 75 MHz): dˆ
173.1 (CO), 171.5 (CO), 164.9 (CONH), 153.6 (OCONH),
126.2 (CvC), 82.4 (C(CH3)3), 60.2 (CH±CH(CH3)2), 58.2
(CH±CH(CH3)2), 52.7 (COOCH3), 31.5 (CH±CH(CH3)2),
31.2 (CH±CH(CH3)2), 28.7 (C(CH3)3), 19.8, 19.7, 18.9,
18.5 (CH±CH(CH3)2). FAB MS m/z (%)ˆ793 (100)
[M1Na]1, 737 (3), 634 (2), 619 (3), 593 (26), 541 (31),
485 (12), 429 (63), 385 (10), 226 (24). HR-ESI MS m/z
found 793.4344, Calcd for C36H62N6O12Na [M1Na]1
793.4323. Anal. Calcd for C36H62N6O12: C, 56.09; N,
10.90; H, 8.11; Found: C, 55.98; N, 10.60; H, 8.51.
Yield 58%, colourless oily foam. UV (CH3OH):
lmaxˆ276, 238 nm. IR(KBr): n~ ˆ 3400 (s, br.), 3065 (m)
3034 (m), 2957 (m), 2871 (w), 1736 (vs, sh.), 1646 (s), 1524
(s), 1498 (s), 1455 (s), 1388 (m), 1333 (m), 1260 (s), 1215
1
(s), 1168 (s), 1123 (m), 1081 (w), 697 (s) cm21. H NMR
(CDCl3, 600 MHz): dˆ9.76 (br. s, 2H, NH), 7.36±7.26 (m,
30H, Ph), 7.12±7.08 (m, br., 2H, NH), 5.21 (br. s, 2H, NH),
5.18±5.00 (m, 12H, CH2±Ph), 4.66±4.63 (br. m, 2H, CH±
CH2CH2), 4.15 (br. s, 2H, CH±CH2±CH(CH3)2), 2.46±2.42
(br. m, 4H, CH2CH2CO2Bn), 2.24±2.23, 2.08±2.06 (m, 4H,
CH(NH)CH2), 1.67±1.62 (m, 4H, CH2±CH(CH3)2), 1.52±
1.51 (m, 2H, CH2±CH(CH3)2), 0.89 (d, Jˆ6.0 Hz, 12H,
CH(CH3)2). 13C NMR (CDCl3, 75 MHz): dˆ173.1 (CO),
173.0 (CO), 172.5 (CO), 165.0 (CONH), 156.9 (OCONH),
136.5, 136.2, 135.7 (arom. q.C) 129.0, 128.9, 128.8, 128.6,
128.5 (arom. CH), 125.3 (CvC), 67.8, 66.8 (OCH2Ph),
54.6, 52.6 (NH±CH±CH), 40.5 (CH2±CH(CH3)2), 30.6,
27.0 (CH2±CH2COOBn), 25.1 (CH(CH3)2), 23.4, 21.9
(CH(CH3)2). FAB MS m/z (%)ˆ1259 (2) [M1H]1,775(1),
685 (1), 328 (5), 181 (4), 105 (2), 91 (100), 77 (3), 55 (3).
HR-FAB MS m/z found 1259.5552, Calcd for C70H79N6O16
[M1H]1 1259.5621. Anal. Calcd for C70H79N6O16: C,
66.76; N, 6.67; H, 6.24; Found: C, 66.59; N, 6.47; H, 6.17.
1,10-[2,3-Bis-(N,N0-tert-butyloxycarbonylamino)-fumar-
oyl]-bis-l-valyl-l-valine methyl ester (E-2g). Yield 61%,
colourless oily foam. UV (CH3CN): lmax(e)ˆ273.28 nm
(13820). IR (KBr): n~ ˆ 3341 (m), 2967 (m), 2934 (m),
1734 (s), 1657 (s), 1506 (s), 1392 (m), 1369 (m), 1239
(m), 1154 (s), 1047 (w), 1021 (w), 889 (w), 814 (w), 769
1
(w), 605 (w) cm21. H NMR (CDCl3, 300 MHz): dˆ8.57
(br. s, 2H, NH), 6.67 (br. d, Jˆ8.1 Hz, 2H, NH), 6.58 (br. d,
Jˆ8.4 Hz, 2H, NH), 4.50 (dd, Jˆ8.4 Hz; Jˆ5.3 Hz, 2H,
CH±CH(CH3)2), 4.32 (dd, Jˆ8.1 Hz; Jˆ5.8 Hz, 2H, CH±
CH(CH3)2), 3.74 (s, 6H, COOCH3), 2.28±2.16 (m, 4H, CH±
CH(CH3)2), 1.42 (s, 18H, C(CH3)3), 1.01±0.91 (m, 24H,
CH±CH(CH3)2). 13C NMR (CDCl3, 75 MHz): dˆ172.7
(CO), 171.0 (CO), 165.3 (CONH), 153.9 (OCONH), 82.4
(C(CH3)3), 59.5 (CH±CH(CH3)2), 58.1 (CH±CH(CH3)2),
52.7 (COOCH3), 31.7 (CH±CH(CH3)2), 31.5 (CH±
CH(CH3)2), 28.7 (C(CH3)3), 19.8, 19.6, 18.7, 18.6 (CH±
CH(CH3)2). No CvC-signal was observable. ESI MS m/z
(%)ˆ1565 (40) [2MH1Na]1, 1564 (84) [2M1H1Na]1,
1563 (100) [2M1Na]1, 1541 (3), 1241 (4), 1001 (2), 811
(9), 795 (3) [MH21Na]1, 794 (16) [MH1Na]1, 793 (39)
[M1Na]1, 671 (2), 571 (1), 441 (1). HR-ESI MS m/z found
793.4334, Calcd for C36H62N6O12Na [M1Na]1 793.4323.
Anal. Calcd for C36H62N6O12: C, 56.09; N, 10.90; H, 8.11;
Found: C, 55.83; N, 10.82; H, 8.40.
1,10-[2,3-Bis-(N,N0-tert-butyloxycarbonyl-O-tert-butyl-l-
tyrosylamino)-maleoyl]-bis-O-tert-butyl-l-serine
tert-
butyl ester (Z-2i). Yield 12%, colourless oily foam. UV
(CH3CN): lmax(e)ˆ221.26 nm (22975), 273.42 (10270)
nm. IR(KBr): n~ ˆ 3432 (s, br.), 2933 (s), 1716 (s, sh.),
1507 (s, sh.), 1392 (m), 1366 (s), 1247 (m),1240 (m),
1165 (vs), 1101 (w), 1051 (w), 1027 (w), 900 (w), 848
1
(w) 765 (w), 568 (w) cm21. H NMR (CDCl3, 300 MHz):
dˆ9.92 (br. s, 2H, NH), 7.09 (d, Jˆ8.4 Hz, 4H, Ph), 6.95
(br. s, 2H, NH), 6.88 (d, Jˆ8.4 Hz, 4H, Ph), 5.48 (br. s, 2H,
NH), 4.58±4.55 (m, 4H, NH±CH±CH), 3.79 (dd, Jˆ2.9,
8.8 Hz, 2H, CH2OtBu), 3.57 (br. d, Jˆ6.6 Hz, 2H,
CH2OtBu), 3.30 (br. d, Jˆ12.2 Hz, 2H, CH2Ph), 2.86 (br.
p-t, Jˆ11.5 Hz, 2H, CH2Ph), 1.49 (s, 18H, C(CH3)3), 1.32
(s, 18H, C(CH3)3), 1.30 (s, 18H, C(CH3)3), 1.13 (s, 18H,
C(CH3)3). 13C NMR (CDCl3, 75 MHz): dˆ172.3, 170.0
(CO), 164.6 (CONH), 156.1 (OCONH), 154.7, 132.5
(arom. q.C), 130.5 (arom. CH), 125.5 (CvC), 124.8
(arom. CH), 82.9, 80.4, 78.9, 74.1 (C(CH3)3), 62.4
(OCH2), 56.4, 54.3 (NH±CH±CH), 37.8 (CH2Ph), 29.5,
28.9, 28.8, 28.0 (C(CH3)3). ESI MS m/z (%)ˆ1205 (14)
[M1Na]1, 1200 (3) [M1NH4]1, 1183 (45) [M1H]1, 966
(100), 910 (3). HR-ESI MS m/z found 1183.7082 Calcd for
C62H99N6O16 [M1H]1 1183.7117.
1,10-[2,3-Bis-(N,N0-benzyloxycarbonyl-l-leucylamino)-
maleoyl]-bis-l-glutaminic acid dibenzylester (Z-2h).
Yield 8%, colourless oily foam. 1H NMR (CDCl3,
300 MHz): dˆ8.67 (br. s, 2H, NH), 8.09 (br. d, Jˆ6.8 Hz,
2H, NH), 7.29±7.26 (m, 30H, Ph), 5.49 (br. d, Jˆ6.5 Hz,
2H, NH), 5.14±4.95 (m, 12H, CH2-Ph), 4.67±4.62 (br. m,
2H, CH±CH2CH2), 4.22 (br. s, 2H, CH±CH2±CH(CH3)2),
2.44±2.38 (br. m, 4H, CH2CH2CO2Bn), 2.25±2.21, 2.07±
1.96 (m, 4H, CH(NH)CH2), 1.67±1.60 (m, 4H, CH2±
CH(CH3)2), 1.54±1.51 (m, 2H, CH2±CH(CH3)2), 0.92 (d,
Jˆ4.9 Hz, 12H, CH(CH3)2). 13C NMR (CDCl3, 150 MHz):
dˆ173.3 (CO), 172.3 (CO), 171.5 (CO), 164.1 (CONH),
157.2 (OCONH), 136.7, 136.5, 136.0 (arom. q.C) 129.2,
129.1, 129.0, 128.9, 128.8, 128.7 (arom. CH), 126.8
(CvC), 67.9, 66.9 (OCH2Ph), 54.8, 53.1 (NH±CH±CH),
41.0 (CH2±CH(CH3)2), 30.6, 27.3 (CH2±CH2COOBn),
25.4 (CH(CH3)2), 23.7, 22.2 (CH(CH3)2). ESI MS m/z
(%)ˆ2559 (13) [2M1K]1, 2541 (37) [2M1Na]1, 2053
(6), 1395 (24), 1299 (33) [M1K]1, 1282 (100) [M1Na]1,
933 (4), 653 (8). HR-ESI MS m/z found 1281.5380, Calcd
for C70H78N6O16Na [M1Na]1 1281.5372.
1,10-[2,3-Bis-(N,N0-tert-butyloxycarbonyl-O-tert-butyl-l-
tyrosylamino)-fumaroyl]-bis-O-tert-butyl-l-serine tert-
butyl ester (E-2i). Yield 58%, colourless oily foam. UV
(CH3CN): lmax(e)ˆ222.01 nm (25715), 275.87 (20420).
IR(KBr): n~ ˆ 3432 (m), 2977 (s), 2932 (m), 1720 (s, sh),
1646 (m), 1507 (s), 1476 (m), 1457 (m), 1392 (m), 1366 (s),
1238 (s), 1164 (s), 1101 (w), 1052 (w), 1022 (w), 900 (w)
849 (m) cm21. 1H NMR (CDCl3, 300 MHz): dˆ8.74 (br. s,
2H, NH), 7.90 (br. s, 2H, NH), 7.09 (d, Jˆ8.4 Hz, 4H, Ph),
6.90 (d, Jˆ8.4 Hz, 4H, Ph), 5.48 (br. d, Jˆ8.0 Hz, 2H, NH),
4.60±4.58 (m, 2H, NH±CH±CH), 4.37 (s, 2H, NH±CH±
CH), 3.74 (dd, Jˆ3.3, 8.6 Hz, 2H, CH2OtBu), 3.59 (d d,
Jˆ3.3, 4.3 Hz, 2H, CH2OtBu), 3.20 (br. dd, Jˆ4.9, 14 Hz,
2H, CH2Ph), 2.83±2.91 (br. m, Jˆ11.5 Hz, 2H, CH2Ph),
1,10-[2,3-Bis-(N,N0-benzyloxycarbonyl-l-leucylamino)-
fumaroyl]-bis-l-glutamic acid dibenzyl ester (E-2h).

4194
S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
1.45 (s, 18H, C(CH3)3), 1.35 (s, 18H, C(CH3)3), 1.31 (s,
18H, C(CH3)3), 1.14 (s, 18H, C(CH3)3). 13C NMR (CDCl3,
75 MHz): dˆ171.2, 169.4 (CO), 163.7 (CONH), 156.0
(OCONH), 154.8, 132.1 (arom. q.C), 130.4 (arom. CH),
126.5 (CvC), 125.0 (arom. CH), 82.5, 80.9, 79.1, 73.7
(C(CH3)3), 62.5 (OCH2), 56.9, 55.0 (NH±CH±CH), 37.6
(CH2Ph), 29.5, 28.9, 28.7, 28.0 (C(CH3)3). FAB MS m/z
(%)ˆ1205 (37) [M1Na]1, 1200 (61) [M1NH4]1, 1183
(100), [M1H]1, 1127 (16). HR-ESI MS m/z found
1183.7130, Calcd for C62H99N6O16 [M1H]1 1183.7117.
3-(N-Benzyloxycarbonyl-glycylamino)-2-(N-tert-butyloxy-
carbonyl-l-valyl-amino)-maleic acid dimethyl ester
(Z-2k). Yield 58%, colourless oily foam. UV (CH3CN):
l
max(e)ˆ275.32 nm (15526). IR(KBr): n~ ˆ 3407 (m),
2968 (m), 1702 (s), 1630 (m), 1511 (s), 1456 (m), 1436
(m), 1392 (m), 1367 (m), 1335 (m), 1210 (m), 1162 (m),
1051 (w), 1016 (w), 977 (w), 871 (w), 839 (w), 740 (w), 698
(w), 577 (w) cm21 1H NMR ([D6]DMSO, 300 MHz):
.
dˆ9.69 (br. s, 1H, NH), 9.63 (br. s, 1H, NH), 7.51 (t,
Jˆ5.7 Hz, 1H, NH), 7.43±7.24 (m, 5H, Ph), 6.68 (d,
Jˆ9.1 Hz, 1H, NH), 5.04 (s, 2H, CH2±Ph), 4.13±4.08 (m,
1H, CH±CH(CH3)2), 3.91±3.78 (m, 2H, NH±CH2±CO),
3.63 (s, 3H, COOCH3), 3.61 (s, 3H, COOCH3), 2.12±2.00
(m, 1H, CH±CH(CH3)2), 1.39 (s, 9H, C(CH3)3), 0.97, 0.92
(2d, Jˆ6.6 Hz, 6H, CH±CH(CH3)2). 13C NMR ([D6]DMSO,
75 MHz): dˆ171.0 (COOCH3), 168.4 (COOCH3), 163.4 (2
CONH), 156.5 (OCONH), 155.6 (OCONH), 136.9 (arom.
q.C), 128.3 (arom. CH), 127.7 (arom. CH), 123.6 (CvC),
123.4 (CvC), 78.2 (C(CH3)3), 65.6 (CH2-Ph), 58.7 (CH±
CH(CH3)2), 52.2 (COOCH3), 52.1 (COOCH3), 43.2 (NH±
CH2±CO), 30.7 (CH±CH(CH3)2), 28.1 (C(CH3)3), 19.1,
17.2 (CH±CH(CH3)2). ESI MS m/z (%)ˆ1153 (1)
[2MH1Na]1, 1152 (3) [2M1H1Na]1, 1151 (5) [2M1
Na]1, 953 (2), 952 (5), 866 (2), 865 (2), 773 (2), 623 (1),
603 (5), 589 (5) [MH21Na]1, 588 (29) [MH1Na]1, 587
(100) [M1Na]1, 584 (2), 531 (4), 487 (9), 484 (3), 465
(4). HR-ESI MS m/z found 587.2331, Calcd for
C26H36N4O10Na [M1Na]1 587.2329.
(3E)-3,4-Bis(N,N0-tert-butyloxycarbonylamino)hexene-
2,5-dione (E-11).16 Yield 70%, colourless solid. UV
(CH3CN): lmax(e)ˆ289.17 nm (13055). IR(KBr): n~ ˆ
3327 (s), 2976 (m), 2932 (w), 1737 (s), 1725 (s), 1654
(m), 1587 (s), 1497 (s), 1442 (s), 1393 (w), 1370 (m),
1360 (m), 1265 (s), 1250 (s), 1048 (w), 1033 (w), 991
1
(w), 875 (w), 784 (w), 762 (w), 581 (w) cm21. H NMR
(CDCl3, 300 MHz): dˆ8.38 (br. s, 1H, NH), 2.29 (s, 6H,
COCH3), 1.45 (s, 9H, C(CH3)3). 13C NMR (CDCl3,
75 MHz): dˆ200.4 (CO), 154.2 (OCONH), 82.9
(C(CH3)3), 29.2 (COCH3), 28.8 (C(CH3)3). No CvC signal
was observable. ESI MS m/z (%)ˆ365 (15) [M1Na]1, 333
(11), 297 (12), 265 (44), 197 (50), 165 (100). HR-ESI MS
m/z found 381.1401, Calcd for C16H26N2O6K [M1K]1
381.1428. Anal. Calcd for C16H26N2O6: C, 56.13; N, 8.18;
H, 7.65. Found: C, 55.68; N, 7.98; H, 7.82.
2,3-Bis(N,N0benzenesulfonylamino)fumaric acid dimethyl
ester (E-12).16 Yield 57%, colourless foam. UV (CH3CN):
[2,3-Bis(N,N0-tert-butyloxycarbonylamino)-fumaroyl]-1-
l-valine-benzylester-4-glycine methyl ester (E-2l). Yield
63%, colourless oily foam. IR(KBr): n~ ˆ 3422 (s), 2967
(m), 2931 (m), 1736 (s), 1669 (s), 1497 (m), 1392 (m),
1368 (m), 1312 (w), 1248 (m), 1154 (s), 1051 (w), 889
l
max(e)ˆ217.84 (1495), 272.88 (923) nm. IR(KBr): n~ ˆ
3436 (s), 2926 (w), 1740 (m), 1711 (m), 1624 (m),
1448 (m), 1439 (m), 1345 (w), 1276 (s), 1163 (s), 1090
(m), 1018 (w), 849 (w), 789 (m), 757 (m), 725 (m), 688
(m), 593 (m, sh.) cm21
.
1H NMR (CDCl3, 300 MHz):
(w), 822 (w), 750 (m), 698 (m), 583 (w) cm21. H NMR
1
dˆ7.90±7.43 (m, 10H, Ph), 7.15 (br. s, 2H, NH), 3.56 (s,
6H, OCH3). 13C NMR ([D6]Acetone, 150 MHz): dˆ164.0
(CO), 141.4 (arom. q. C), 134.8, 130.7, 128.9 (arom. CH),
126.5 (CvC). ESI MS m/z (%)ˆ477 (100) [M1Na]1, 393
(4).
(CDCl3, 300 MHz): dˆ8.98 (br. s, 1H, NH), 8.52 (br. s, 1H,
NH), 7.41±7.18 (m, 5H, Ph), 6.94 (br. s, 1H, NH), 5.30±
4.86 (m, 3H, NH; CH2-Ph), 4.27±3.89 (m, 3H, CH±
CH(CH3)2; NH±CH2±CO), 3.73 (s, 3H, COCH3), 2.23±
1.92 (m, 1H, CH±CH(CH3)2), 1.42 (s, 9H, C(CH3)3), 1.40
(s, 9H, C(CH3)3), 0.86, 0.75 (2d, Jˆ6.8 Hz, 6H, CH±
CH(CH3)2). 13C NMR (CDCl3, 75 MHz): dˆ172.7 (COO),
169.7 (COO), 165.2 (CONH), 163.1 (CONH), 155.7
(OCONH), 151.3 (OCONH), 134.9 (arom. q.C), 128.6
(arom. CH), 128.5 (arom. CH), 128.3 (arom. CH), 82.3
(C(CH3)3), 79.9 (C(CH3)3), 67.4 (CH2Ph), 59.6 (CH±
CH(CH3)2), 52.3 (COOCH3), 41.4 (NH±CH2±CO), 30.5
(CH±CH(CH3)2), 28.2 (C(CH3)3), 27.9 (C(CH3)3), 19.1,
17.2 (CH±CH(CH3)2). No CvC signals were observable.
ESI MS m/z (%)ˆ1238 (21) [2MH1Na]1, 1237 (63)
[2M1H1Na]1, 1236 (100) [2M1Na]1, 1234 (24),
1214 (5), 1128 (8), 885 (1), 666 (5), 630 (1)
[MH1Na]1, 629 (3) [M1Na]1, 607 (1), 403 (1). HR-ESI
MS m/z found 629.2820, Calcd for C29H42N4O10Na
[M1Na]1 629.2799.
General procedure for the synthesis of heteromeric
dimers 2
To a solution of an a-chloroglycyl peptide (1.0 mmol) in
CH2Cl2 (40 mL) was added PPh3 (1.0 mmol) and the
mixture stirred at room temperature overnight. Removal
of the solvent afforded the phosphonium salt in quantitative
yield. The salt was dissolved in THF (100 mL) and cooled to
2788C (solution I).
A solution of the second a-chloroglycyl peptide (1.5 mmol)
in THF (50 mL) was transferred to an addition funnel with
cooling (CO2/acetone) and NEt3 (2.5 mmol) was added at
2788C (solution II).
a0
Tetramethyl-2,20-(Na,N -{N,N0-[2,3-bis(tert-butyloxy-
Solution II was added dropwise at 2788C to the stirred
solution I, and the mixture was allowed to rise to room
temperature overnight. After addition of petroleum ether
and ®ltration through Celite the ®ltrate was concentrated
in vacuo. The residue was puri®ed by column chroma-
tography on silica gel (petroleum ether/EtOAc).
carbonylamino)fumaroyl]diglycyl}bis-l-valine amido)-
bis{3-[1-(benzyloxycarbonyl)-l-proline amido]-maleate}
(Z,E,Z-10). N-terminal deprotection of 2(N-benzyloxycar-
bonyl-l-prolylamino)-3(N-tert-butyloxycarbonyl-l-valyl-
amino)-maleic acid dimethylester (Z-9) (108 mg, 0.18
mmol) was achieved by treatment with a 2 M solution of

S. Schumann et al. / Tetrahedron 56 (2000) 4187±4195
4195
2. Williams, R. M.; Fegley, G. J.; Gallegos, R.; Schaefer, F.;
Pruess, D. L. Tetrahedron 1996, 52, 1149±1164.
HCl in ethyl acetate (4 mL). The amino compound of Z-9
was isolated as hydrochloride.
3. Jung, G. Angew. Chem. 1991, 103, 1067±1084; Angew. Chem.,
Int. Ed. Engl. 1991, 30, 1051±1068.
C-terminal deprotection of E-2d (41 mg, 0.09 mmol) was
carried out in dry ethanol (10 mL) with 1,4-cyclohexadiene
(0.85 mL, 1.80 mmol) and palladium on charcoal (90 mg) to
yield the acid E-8.
4. (a) Lange, M.; Undheim, K. Tetrahedron 1998, 54, 5337±5344.
(b) Undheim, K. Lett. Peptide Sci. 1998, 103, 227±233. (c)
Efskind, J.; Benneche, T.; Undheim, K. Acta Chem. Scand. 1997,
103, 942±952. (d) Rodbotten, S.; Benneche, T.; Undheim, K. Acta
Chem. Scand. 1997, 51, 873±880.
To a suspension of Z-9 and E-8 in THF (10 mL) were added
triethylamine (0.05 mL, 0.36 mmol), HOBt (32 mg, 0.24
mmol) and EDC£HCl (35 mg, 0.18 mmol) at 08C. After
stirring overnight, the solvent was removed in vacuo and
the resulting oil suspended in EtOAc. The solution was
washed successively with 1 M KHSO4, saturated aqueous
NaHCO3, water and brine. The organic layer was dried over
Na2SO4, ®ltered and concentrated in vacuo. The resulting
oily residue was puri®ed by column chromatography on
silica gel with CHCl3/MeOH 15:1 as eluent. Yield 25%,
colourless solid. IR(KBr): n~ ˆ 3412 (s), 2980 (m), 1742
(s), 1703 (s), 1646 (m), 1498 (m), 1455 (m), 1392 (m),
1369 (m), 1248 (m), 1194 (s), 1154 (s), 1051 (w), 753
5. Crisp, G. T.; Jiang, Y.-L.; Pullman, P. J.; De Savi, C.
Tetrahedron 1997, 51, 17489±17500.
6. For the formation of non-ole®nic amino acid dimers by
coupling of two identical glycine units see: (a) Easton, C. J.; Peters,
S. C. Aust. J. Chem. 1994, 47, 859±868. (b) Alvarez-Ibarra, C.;
Csaky, A. G.; Colmenero, B.; Quiroga, M. L. J. Org. Chem. 1997,
62, 2478±2482.
7. A backbone bridge towards the NH group of a tryptophan resi-
due occurs in the cyclopeptide lyciumin A: Yahara, S.; Shigeyama,
C.; Nohara, T.; Okuda, H.; Wakamatsu, K.; Yashuhara, T.;
Tetrahedron Lett. 1989, 30, 6041±6042.
8. (a) Apitz, G.; Steglich, W. Tetrahedron Lett. 1991, 32, 3163±
È È
3166. (b) Apitz, G.; Jager, M.; Jaroch, S.; Kratzel, M.; Schaffeler,
(w), 699 (w), 577 (w) cm21 1H NMR ([D6]DMSO,
.
600 MHz): dˆ9.73 (d, Jˆ10.3 Hz, 4H, NH), 9.57 (d,
Jˆ11.7 Hz, 2H, NH), 9.37 (s, br., 2H, NH), 8.15 (s, br.,
2H, NH), 7.88 (d, Jˆ7.0 Hz, 2H, NH), 7.36±7.30 (m,
10H, Ph), 5.13±4.96 (m, 4H, OCH2-Ph), 4.52±4.40 (m,
4H, 2 CH±CH(CH3)2, 2 CH-Pro), 3.91±3.70 (m, 4H, NH±
CH2±CO), 3.61 (s, 12H, COOCH3), 3.43±3.31 (m, 4H,
CH2-Pro), 2.13±1.81 (m, 10H, 2 CH±CH(CH3)2, 4 CH2-
Pro), 1.37 (s, 18H, C(CH3)3), 0.89 (ps-t, Jˆ6.5 Hz, 12H,
CH±CH(CH3)2). 13C NMR ([D6]DMSO, 150 MHz):
dˆ168.7, 168.5, 168.4 (CONH), 164.7, 163.5, 163.3 (2
COOCH3, CONH), 154.1, 152.6 (OCONH), 136.8 (arom.
q.C), 128.4 (arom. CH), 127.0 (arom. CH), 126.5 (arom.
CH), 125.0, 122.5, 121.1 (CvC), 80.1 (C(CH3)3), 66.0
(CH2-Ph), 59.5 (CH-Pro), 57.5 (CH±CH(CH3)2), 52.2
(COOCH3), 52.0 (COOCH3), 47.0 (NCH2-Pro), 42.4
(NH±CH2±CO), 31.0 (CH±CH(CH3)2), 29.8 (CH2-Pro),
27.8 (C(CH3)3), 23.7 (CH2-Pro), 19.0, 17.7 (CH±
CH(CH3)2). For the proline sidechain doubling of signals
is observed. ESI MS m/z (%)ˆ1456 (100) [M1Na]1,
1377 (4), 1321 (5), 1299 (7), 1039 (6), 856 (7), 780 (5),
771 (6), 755 (19), 617 (7), 406 (4). HR-ESI MS m/z found
1455.5926, Calcd for C66H88N12O24Na [M1Na]1
1455.5932.
L.; Steglich, W. Tetrahedron 1993, 49, 8223±8232. (c) Steglich,
È
W.; Jager, M.; Jaroch, S.; Zistler, P. Pure Appl. Chem. 1994, 66,
2167±2170.
9. Kober, R.; Steglich, W. Liebigs Ann. Chem. 1983, 599±609.
È
È
10. Schumann, S. Dissertation, Universitat Munchen, 1998.
11. (a) Crystal data for E-2d: C29H40N4O10, Mˆ640.69;
Ê
Ê
2.96,u,24.97; triclinic, P-1; aˆ5.676 (2) A, bˆ12.308 (3) A,
Ê
cˆ13.975 (3) A, aˆ63.58 (2)8, bˆ78.22 (2)8, gˆ82.87 (3)8; Vˆ
Ê 3
Ê
855.3 (4) A ;
l
0.71069 A; Zˆ1; Dcˆ1.244 Mg/m3; mˆ
0.093 mm21
;
crystal size: 0.57£0.40£0.27 mm3; full-matrix
least-squares, R1ˆ0.0444, wR2ˆ0.1014 for observed 3016 re¯ec-
tions [I.2s(I)] (CCDC 143354); the structure was solved with
shelxs 86 and re®ned by shelxl 93 program.17 (b) Further details
of the X-ray analyses (see also Ref. 16) are available on request
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK (deposit@ccdc.cam.ac.uk).
12. Details concerning the unusual NMR phenomena exhibited by
the dimers 2 will be published elsewhere.
13. (a) Eliel, E. L. Stereochemistry of Carbon Compounds;
McGraw-Hill: New York, 1962. (b) Crombie, L. Q. Rev. Chem.
Soc. 1952, 6, 101±104. (c) Sonnet, P. E. Tetrahedron 1980, 36,
557±604.
14. In contrast, the amino acid dimers 2a and 2b are equilibrated
with bases to yield mixtures of both diastereomers in a ratio of
about 1:1 (Ref. 10).
Acknowledgements
15. Compound Z-9 was prepared according to the general
procedure for heteromers from Boc-Val-Gly(Cl)-OMe and
Z-ProGly(PPh13 Cl2)-OMe; for details concerning deprotection
and peptide coupling see Experimental.
We thank the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for ®nancial support. The
help of Dr Gustav Penzlin in the nomenclature of the dimers
is gratefully acknowledged.
16. The con®guration of the compounds E-11 and E-12 was
con®rmed by X-ray structure analyses (CCDC 143355 and
CCDC 143356).11b
References
È È
17. (a) Sheldrick, G. M. shelxs 86; Universitat Gottingen, 1986.
È È
(b) Sheldrick, G. M. shelxs 93; Universitat Gottingen, 1993.
1. Hardy, P. M. Chemistry and Biochemistry of the Amino Acids;
Barett, G. C., Ed.; Chapman and Hall: New York, 1985.