Synthesis of cyclopropanoid 2-epi-muramyldipeptide analogues as potential immunostimulants

Article abstract of DOI:10.1016/j.tet.2004.01.037

The preparation of cyclopropanoid 2-epi-muramyldipeptide analogues from suitable substituted cyclopropylamines is described.

Full text of DOI:10.1016/j.tet.2004.01.037

Tetrahedron 60 (2004) 2191–2199
Synthesis of cyclopropanoid 2-epi-muramyldipeptide analogues as
potential immunostimulants
*
Rene Csuk and Gunnar Gothe
´
¨
¨ ¨
Institut fur Organische Chemie, Martin-Luther-Universitat Halle-Wittenberg, Kurt-Mothes-Str. 2,
D-06120 Halle (Saale), Germany
Received 29 September 2003; revised 9 January 2004; accepted 14 January 2004
Abstract—The preparation of cyclopropanoid 2-epi-muramyldipeptide analogues from suitable substituted cyclopropylamines is
described.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Over the past two decades intensive investigation of
muramyldipeptide (N-acetylmuramyl-L-alanyl-D-iso-
glutamine, MDP) derivatives revealed their adjuvant
activity and stimulation of non-specific resistance
against bacterial, viral and parasite infections as
well as anticancer properties.1,2 They can also
stimulate tumoricidal activity of monocytes3,4 and of
macrophages.5,6
During ongoing QSAR studies of these compounds we
became interested in derivatives possessing a (S) configur-
ation at the lactic acid residue (Scheme 1).
Although in MDP this stereogenic center is of (R)
configuration it is of interest to note that the chirality at
this center seems to be of minor importance as, e.g., nor-
MDP derivatives where there is no methyl group present at
all at this center, are known to exhibit equal biological
activities and even reduced toxicity.7,8
Many MDP derivatives and analogues have been synthe-
sized and evaluated biologically in order to obtain new
molecules with improved pharmacological properties.1,2,7–19
(Fig. 1)
Our approach to these (2S) configurated cyclopropanoid
analogues started from commercially available isopropyl
Figure 1. Structure of MDP and its 2-epi-cyclopropanoid analogues.
Keywords: Cyclopropanoid 2-epi-muramyldepeptide; Immunostimulant; Pharmacological.
*
Corresponding author. Tel.: þ49-345-5525660; fax: þ49-345-5527030; e-mail address: csuk@chemie.uni-halle.de
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.01.037

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R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2192
Scheme 1. Reagents: (a) Hg(OAc)2; (b) N2CHCO2tBu, [(Rh(OAc)2)2];
(c) CF3COOH; (d) DPPA, tBuOH, Et3N; (e) KOH.
(S)-2-hydroxypropanoate whose Hg(OAc)2 mediated reac-
tion20,21 with ethylvinylether resulted in the formation
of isopropyl (2S)-2-(vinyloxy)propanoate (1) whose
Rh[(OAc)2]2 catalyzed reaction with tert-butyldiazoace-
tate22 yielded a mixture of the cyclopropanes trans-2 and
cis-3 that were easily separated by chromatography.
Hydrolysis of the ester by treatment of trans-2 with
trifluoroacetic acid23,24 gave the acid trans-4; similarly
from the ester cis-3 the cis-configurated acid cis-5 was
obtained.
Scheme 2. Reactions and conditions: (a) ClCO2iBu, NMM, L-Ala-D-iGln-
g-OBn hydrochloride; (b) HCl in EtOAc then AcCl/Et3N (for 12 and 13) or
C7H15COCl/Et3N (for 16 and 17); (c) Pd/C, H2.
Since it has been assumed27 that lipophilic MDP derivatives
induce cellular-specific response and increase non-specific
resistance more strongly, the synthesis of more lipophilic
derivatives was accomplished by deprotection of trans-10
followed by acylation with octanoyl chloride/triethylamine
to afford the corresponding N-octanoyl-derivative trans-16.
Similarly from cis-11 lipophilic cis-17 was obtained in 63%
yield. Hydrogenolysis of trans-16 or cis-17 gave the final
products trans-18 or trans-19 in good yields (Scheme 2).
A modified Curtius degradation25 of the acid 4 using
diphenylphosphoryl azide (DPPA)/tert-butanol/triethyl-
amine gave the N-BOC-protected cyclopropylamine trans-
6. In an analogous manner from the cis-configurated acid 5
the N-BOC-protected amine cis-7 was obtained together
with ca 14% of trans-6 invariably formed by epimerization
during the reaction.
The determination of the different biological activities of
these carbocyclic 2-epi-MDP-derivatives as well as the
determination of the absolute configuration of the stereo-
genic centers of the cyclopropane ring are presently
performed in our labs.
Alkaline saponification of the ester moiety gave the acids
trans-8 and cis-9, respectively. These acids were subjected
to a peptide synthesis using the mixed anhydride method
[isobutyl chloroformate/N-methyl-morpholine (NMM)]26
and H2N-L-Ala-D-iGln-g-OBn as dipeptide. Thus the
products trans-10 and cis-11 were obtained in reasonably
high yields. Treatment of trans-10 with hydrochloric acid
followed by acetylation with acetylchloride/triethylamine
gave a mixture of the corresponding N-acetyl-derivatives
trans-12a/trans-12b that could be separated by chromato-
graphy. In contrast, treatment of cis-11 with hydrochloric
acid followed by acetylation gave a mixture of diastereo-
meric acetates cis-13 that could not be separated under a
variety of different chromatographic conditions.
3. Experimental
3.1. General
Melting points are uncorrected (Leicahot stage microscope),
optical rotations were obtained using a Perkin–Elmer 341
polarimeter (1 cm micro cell), NMR spectra were recorded
using the Varian spectrometers Gemini 200, Gemini 2000 or
Unity 500 (d given in ppm, J in Hz, internal Me4Si, Cp
correspond to the atoms of the cyclopropane), IR spectra
(film or KBr pellet) on a Perkin–Elmer FT-IR spectrometer
Spectrum 1000, MS spectra were taken on a Intectra GmbH
AMD 402 (electron impact, 70 eV) or on a Finnigan MAT
TSQ 7000 (electrospray, voltage 4.5 kV, sheath gas
nitrogen) instrument; for elemental analysis a Foss–
Heraeus Vario EL instrument was used; TLC was
Debenzylation of trans-12a and trans-12b was accom-
plished by hydrogenolysis in the presence of Pd/C to afford
trans-14a and trans-14b, respectively. Under the same
conditions from cis-13 the final target compound cis-15 was
obtained in 95% yield.

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R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2193
performed on silica gel (Merck 5554, detection by UV
absorption or by treatment with either a solution of 10%
sulfuric acid, ammonium molybdate and cerium(IV))
sulfate or a solution of ninhydrine in pyridine followed by
gentle heating. The solvents were dried according to usual
procedures.
(d, C(2), Cp, A), 22.0 (d, C(2), Cp, B),21.7 (q, Me(iPr)),
21.6 (q, Me(iPr)), 18.3 (q, Me), 15.5 (dd, C(3), Cp, A), 14.6
(dd, C(3), Cp, B); MS (GC–MS, e.i., 70 eV): m/z (%)¼216
(5), 199 (10), 185 (20), 174 (35), 157 (16), 145 (16), 133
(29), 129 (27), 101 (27), 91 (73), 84 (100), 73 (25), 57 (33);
Anal. calcd for C14H24O5 (272.16): C, 61.74; H, 8.88;
found: C, 61.63; H, 8.71.
3.1.1. Isopropyl (2S)-2-(vinyloxy)propanoate (1). A
solution of isopropyl (S)-2-hydroxypropanoate (19.8 g,
0.15 mol) and Hg(OAc)2 (47.8 g, 0.15 mol) in ethylvinyl-
ether (450 ml, 4.70 mol) was stirred for 7 days at 25 8C
under argon. The reaction mixture was diluted with hexane
(470 ml) and washed with N aq. KOH solution and brine,
dried (Na2SO4) and the solvents were removed under
diminished pressure. The residue was subjected to
chromatography (silica gel, hexane/ethyl acetate 10:1) to
afford 1 (11.7 g, 49%) as an oil; Rf (hexane/ethyl acetate
3:2) 0.61; [a]D¼268.3 (c 1.01, CHCl3); IR (film):
n¼3120w, 2985s, 2940m, 2880w, 1755s, 1730s, 1640s,
1620s, 1510m, 1455m, 1375s, 1320s, 1280s, 1190s, 1135s,
Data for 3. Oil; Rf (hexane/ethyl acetate 3:2) 0.58; IR (film):
n¼2980s, 2935m, 1730s, 1455m, 1380s, 1370s, 1330m,
1
1280m, 1255m, 1205s, 1145s, 1105s, 1055m, 1020w; H
NMR (400 MHz, CDCl3): d¼5.08 (qq, J¼6.3 Hz, 1H,
3
CH(iPr), A), 5.06 (qq, J¼6.3 Hz, 1H, CH(iPr), B), 3.99
(q, J¼6.9 Hz, 1H, H–C(2), A), 3.82 (q, J¼6.9 Hz, 1H, H–
C(2), B), 3.76 (ddd, J¼6.7, 6.7, 3.9 Hz, 1H, H–C(1), Cp,
A), 3.70 (ddd, J¼6.5, 6.5, 4.7 Hz, 1H, H–C(1), Cp, B), 1.69
(ddd, J¼8.4, 6.8, 6.8 Hz, 1H, H–C(2), Cp, A), 1.58–1.54
(m, 2H, H–C(2), Cp, B and HA–C(3), Cp, A), 1.46 (s, 9H,
tBu, A), 1.43 (s, 9H, tBu, B), 1.42–1.39 (m, 1H, HA–C(3),
Cp, B), 1.34 (d, J¼6.9 Hz, 3H, Me, A), 1.31 (d, J¼6.9 Hz,
3H, Me, B), 1.27 (d, J¼7.2 Hz, 3H, Me(iPr)), 1.25
(d, J¼6.6 Hz, 3H, Me(iPr)), 1.245 (d, J¼6.3 Hz, 3H,
Me(iPr)), 1.24 (d, J¼6.5 Hz, 3H, Me(iPr)), 1.08–1.01
(m, 1H, HB–C(3), Cp, A), 0.87 (ddd, J¼8.6, 6.2, 6.2 Hz,
1H, HB–C(3), Cp, B); 13C NMR (50 MHz, CDCl3):
d¼172.2 (s, CvO), 168.9 (s, CvO, A), 168.4 (s, CvO),
B), 80.3 (s, tBu), 75.6 (d, C(2), A), 74.9 (d, C(2), B), 68.4
(d, CH(iPr), A), 68.2 (d, CH(iPr), B), 58.3 (d, C(1), Cp, A),
56.8 (d, C(1), Cp, B), 28.1 (q, tBu), 22.9 (d, C(2), Cp), 21.7
(q, Me(iPr)), 18.5 (q, Me, A), 17.8 (q, Me, B), 13.5 (dd,
C(3), Cp, A), 11.7 (dd, C(3), Cp, B); MS (GC–MS, e.i.,
70 eV): m/z (%)¼216 (4), 199 (10), 185 (2), 174 (33), 157
(19), 145 (15), 133 (29), 129 (46), 117 (5), 101 (28), 91 (66),
84 (100), 73 (28), 57 (41); Anal. calcd for C14H24O5
(272.16): C, 61.74; H, 8.88; found: C, 61.66; H, 8.74.
1
1110s, 1045s; H NMR (200 MHz, CDCl3): d¼6.38 (dd,
J¼14.3, 6.8 Hz, 1H, HCvC), 5.07 (qq, J¼6.3 Hz, 1H,
CH(iPr)), 4.33 (q, J¼6.8 Hz, 1H, H–C(2)), 4.19 (dd,
J¼14.3, 22.5 Hz, 1H, H2CvC(trans)), 4.06 (dd, J¼6.8,
22.5 Hz, 1H, H2CvC(cis)), 1.45 (d, J¼6.8 Hz, 3H, Me),
1.25 (d, J¼6.3 Hz, 3H, MeA(iPr)), 1.23 (d, J¼6.3 Hz, 3H,
MeB(iPr)); 13C NMR (100 MHz, CDCl3): d¼171.5
(s, CvO), 150.3 (d, vCH), 88.4 (t, vCH2), 72.7
(d, C(2)), 68.6 (d, CH(iPr)), 21.5 (q, MeA(iPr)), 21.4
(q, MeB(iPr)), 17.7 (q, Me); MS (GC–MS, e.i., 70 eV): m/z
(%)¼158 (15), 144 (1), 130 (1), 116 (20), 99 (1), 89 (1), 71
(80), 43 (100); Anal. calcd for C8H14O3 (158.19): C, 60.74;
H, 8.92; found: C, 60.88; H, 9.03.
3.1.2. Isopropyl trans-(2S)-2-[2-(tert-butoxycarbonyl)
cyclopropyl]-oxypropanoate (trans-2) and isopropyl cis-
(2S)-2-[2-(tert-butoxycarbonyl)cyclopropyl]oxy-pro-
panoate (cis-3). To solution of 1 (8.7 g, 55.0 mmol) in dry
CH2Cl2 (15 ml) containing [Rh[OAc)2)2] (100 mg) a
solution of tert-butyl diazoacetate (9.4 g, 66.1 mmol) in
abs. CH2Cl2 (30 ml) was slowly added within 8 h keeping
the temperature at 25 8C. Then the solvents were removed
under diminished pressure and the residue was subjected to
chromatography (silica gel, hexane/ethyl acetate 16:1) to
afford trans-2 (7.4 g, 49%) and cis-3 (4.2 g, 28%).
3.1.3. trans-2-[(1S)-2-Isopropoxy-1-methyl-2-oxoethyl]
oxy-1-cyclopropanecarboxylic acid (trans-4). To a solution
of 2 (3.70 g, 13.6 mmol) in dry CH2Cl2 (30 ml) a solution of
CF3COOH (9.30 g, 81.6 mmol) in dry CH2Cl2 (6 ml) was
added at 0 8C and stirring was continued for another 18 h.
The solvents were removed under reduced pressure and the
residue was dissolved in toluene, the solvent removed and
the crude acid trans-4 (2.90 g, 99%) was obtained as a
slightly brown oil that was used for the next step without
any further purification; IR (film): n¼2985s, 2940m, 2645m,
1730s, 1695s, 1455s, 1375s, 1285s, 1205s, 1180s, 1140s,
1105s, 1045m, 1015m; 1H NMR (400 MHz, CDCl3):
d¼5.08 (qq, J¼6.3 Hz, 1H, CH(iPr), A), 5.07 (qq,
J¼6.3 Hz, 1H, CH(iPr), B), 4.05 (q, J¼6.8 Hz, 1H, H–
C(2), A), 4.04 (q, J¼6.8 Hz, 1H, H–C(2), B), 3.80 (ddd,
J¼6.5, 4.4, 2.1 Hz, 1H, H–C(1), Cp, A), 3.74 (ddd, J¼6.5,
4.4, 2.1 Hz, 1H, H–C(1), Cp, B), 1.92 (dd, J¼9.6, 6.2,
2.0 Hz, 1H, H–C(2), Cp, A), 1.76 (ddd, J¼9.6, 6.1, 2.0 Hz,
1H, H–C(2), Cp, B), 1.43–1.23 (m, 2H, HA,B–C(3), Cp),
1.37 (d, J¼6.8 Hz, 3H, Me, A), 1.35 (d, J¼7.0 Hz, 3H, Me,
B), 1.259 (d, J¼6.3 Hz, 6H, 2£Me(iPr)), 1.256 (d, J¼
6.3 Hz, 3H, Me(iPr)), 1.250 (d, J¼6.1 Hz, 3H, Me(iPr)); 13C
NMR (50 MHz, CDCl3): d¼178.5 (s, COOH), 172.0
(s, CvO, A), 171.8 (s, CvO, B), 75.8 (d, C(2), A), 75.5
(d, C(2), B), 68.8 (d, CH(iPr)), 60.5 (d, C(1), Cp), 21.6
(q, Me(iPr)), 21.2 (d, C(2), Cp, A), 20.9 (d, C(2), Cp, B),
18.4 (q, Me, A), 18.2 (q, Me, B), 16.6 (dd, C(3), Cp, A), 15.7
Data for 2. Oil; Rf (hexane/ethyl acetate 3:2) 0.64; IR (film):
n¼2980s, 2935m, 1750s, 1720s, 1450s, 1395s, 1375s,
1345s, 1275s, 1205s, 1155s,1105s, 1045s; 1H NMR
(400 MHz, CDCl3): d¼5.07 (qq, J¼6.3 Hz, 1H, CH(iPr)),
4.03 (q, J¼6.8 Hz, 1H, H–C(2)), 3.66 (ddd, J¼6.4, 4.2,
2.3 Hz, 1H, H–C(1) Cp, A), 3.64 (ddd, J¼6.4, 4.7, 2.0 Hz,
1H, H–C(1), Cp, B), 1.83 (ddd, J¼9.0, 6.8, 2.1 Hz, 1H, H–
C(2), Cp, A), 1.69 (ddd, J¼9.7, 6.2, 2.1 Hz, 1H, H–C(2),
Cp, B), 1.401 (s, 9H, tBu, A), 1.396 (s, 9H, tBu, B), 1.35
(d, J¼6.8 Hz, 3H, Me, A), 1.34 (d, J¼6.8 Hz, 3H, Me, B),
1.27 (d, J¼6.3 Hz, 3H, Me (iPr)), 1.26 (d, J¼6.3 Hz, 3H,
Me(iPr)), 1.25 (d, J¼6.3 Hz, 3H, Me(iPr)), 1.24
(d, J¼6.3 Hz, 3H, Me(iPr)), 1.22–1.16 (m, 1H, HA–C(3)
Cp), 1.15–1.10 (m, 1H, HB–C(3) Cp)); 13C NMR (50 MHz,
CDCl3): d¼172.1 (s, CvO), 171.4 (s, CvO), 80.43 (s, tBu,
A), 80.39 (s, tBu, B), 75.6 (d, C(2), A), 75.4 (d, C(2), B),
68.5 (d, CH(iPr)), 59.6 (d, C(1) Cp)), 28.0 (q, tBu), 22.3

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R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2194
(dd, C(3), Cp, B); MS (e.i., 70 eV): m/z (%)¼217 (1), 199
(1), 174 (2), 156 (9), 145 (6), 129 (43), 117 (5), 102 (22), 91
(42), 84 (100), 73 (87), 55 (44); HRMS calcd for C10H16O5:
216.0998; found: 216.0998.
CDCl3): d¼172.5 (s, CvO, A), 172.4 (s, CvO, B), 156.0
(s, CvO, BOC, A), 155.9 (s, CvO, BOC, B), 79.4 (s, tBu),
74.6 (d, C(2)), 68.2 (d, CH(iPr), A), 68.1 (d, CH(iPr), B),
58.7 (d, C(1), Cp), 29.6 (d, C(2), Cp, A), 29.1 (d, C(2), Cp,
B), 28.3 (q, tBu, A), 28.2 (q, tBu, B), 21.7 (q, Me(iPr)), 21.3
(q, Me(iPr)), 18.6 (q, Me, A), 18.1 (q, Me, B), 15.2 (dd, C(3),
Cp);MS(GC–MS, e.i., 70 eV):m/z(%)¼231(1), 214(1), 200
(1), 186 (1), 172 (1), 144 (3), 126 (1), 116 (22), 100 (10), 72
(51), 57 (100); Anal. calcd for C15H29NO5 (303.39): C, 59.38;
H, 9.63; N, 4.62; found: 59.27; H, 9.91; N, 4.59.
3.1.4. cis-2-[(1S)-2-Isopropoxy-1-methyl-2-oxoethyl]oxy-
1-cyclopropanecarboxylic acid (cis-5). Following the
procedure given for the synthesis of 4 a solution of 3
(2.55 g, 9.4 mmol) in CH2Cl2 (30 ml) was treated with
CF3COOH (6.4 g, 56.1 mmol) in CH2Cl2 (5 ml) to afford
cis-5 (2.00 g, 99%) as a slightly brown oil that was used in
the next step without any further purification; IR (film):
n¼2985s, 2940s, 2670m, 1740s, 1700s, 1450s, 1375s,
3.1.6. Isopropyl cis-(2S)-2-(2-[(tert-butoxycarbonyl) amino]
cyclo-propyloxy)propanoate (cis-7). Following the pro-
cedure for the synthesis of 6 from 5 (3.3 g, 15.3 mmol),
triethylamine (2.3 g, 23.0 mmol), tert-butanol (4.5 g,
61.2 mmol) and DPPA (5.1 g, 18.4 mmol) followed by
chromatography (silica gel, hexane/ethyl acetate 6:1) cis-7
(1.0 g, 23%) was obtained as an oil; in addition, trans-6
(0.6 g, 14%) was isolated. Rf (hexane/ethyl acetate 3:2)
0.41; IR (film): n¼3370m, 2980s, 2935m, 1715s, 1505s,
1455m, 1365s, 1275s, 1210s, 1175s, 1105s; 1H NMR
(400 MHz, CDCl3): d¼5.34 (br, 1H, NH, A), 5.07 (qq,
J¼6.3 Hz, 1H, CH(iPr), A), 5.05 (qq, J¼6.3 Hz, 1H,
CH(iPr), B), 4.80 (br, 1H, NH, B), 4.12 (q, J¼6.8 Hz, 1H,
H–C(2), A), 4.04 (q, J¼6.8 Hz, 1H, H–C(2), B), 3.45–3.36
(m, 1H, H–C(1), Cp), 2.70–2.61 (m, 1H, H–C(2), Cp), 1.43
(s, 9H, tBu), 1.36 (d, J¼6.8 Hz, 3H, Me), 1.26 (d, J¼6.3 Hz.
3H, Me(iPr)), 1.25 (d, J¼6.3 Hz, 6H, Me(iPr)), 1.23
(d, J¼6.3 Hz, 3H, Me(iPr)), 0.95–0.89 (m, 1H, HA–C(3),
Cp), 0.63–0.55 (m, 1H, HB–C(3), Cp); 13C NMR
(100 MHz, CDCl3): d¼172.4 (s, CvO), 156.8 (s, CvO,
BOC, A), 156.6 (s, CvO, BOC, B), 79.4 (s, tBu, A), 79.2
(s, tBu, B), 75.8 (d, C(2), A), 75.4 (d, C(2), B), 68.7
(d, CH(iPr), A), 68.4 (d, CH(iPr), B), 54.7 (d, C(1), Cp),
28.4 (q, tBu, A), 28.3 (q, tBu, B), 27.4 (d, C(2), Cp), 21.73
(q, Me(iPr)), 21.71 (q, Me(iPr)), 21.68 (q, Me(iPr)), 21.65
(q, Me(iPr)), 18.4 (q, Me), 13.6 (dd, C(3), Cp, A), 12.6 (dd,
C(3), Cp, B); MS (e.i. 70 eV): m/z (%)¼231 (1), 214 (1),
188 (1), 172 (5), 144 (17), 116 (21), 100 (9), 72 (100), 57
(91); Anal. calcd for: C15H29NO5 (303.39): C, 59.38; H,
9.63; N, 4.62; found: C, 59.21; H, 9.79; N, 4.65.
1
1330m, 1280m, 1215s, 1140s, 1105s, 1050s, 1015m; H
NMR (400 MHz, CDCl3): d¼5.08 (qq, J¼6.3 Hz, 1H,
CH(iPr), A), 5.07 (qq, J¼6.3 Hz, 1H, CH(iPr), B), 4.08
(q, J¼6.9 Hz, 1H, H–C(2), A), 3.97 (q, J¼6.9 Hz, 1H, H–
C(2), B), 3.862 (ddd, J¼6.6, 6.6, 4.6 Hz, 1H, H–C(1), Cp,
A), 3.857 (ddd, J¼6.5, 6.5, 4.6 Hz, 1H, H–C(1), Cp, B),
1.80 (ddd, J¼9.0, 6.7, 6.7 Hz, 1H, H–C(2), Cp, A), 1.74
(ddd, J¼9.1, 6.5, 6.5 Hz, 1H, H–C(2), Cp, B), 1.59 (ddd,
J¼6.5, 6.5, 4.7 Hz, 1H, HA–C(3), Cp, A), 1.46 (ddd, J¼6.4,
6.4, 4.9 Hz, 1H, HA–C(3), Cp, B), 1.39 (d, J¼6.9, 3H, Me,
A), 1.37 (d, J¼6.9, 3H, Me, B), 1.269 (d, J¼6.3 Hz, 3H,
Me(iPr)), 1.260 (d, J¼6.3 Hz, 3H, Me(iPr)), 1.253
(d, J¼6.3 Hz, 3H, Me(iPr)), 1.248 (d, J¼6.3 Hz, 3H,
Me(iPr)), 1.21 (ddd, J¼9.1, 6.5, 6.5 Hz, 1H, HB–C(3),
Cp, A), 1.11 (ddd, J¼9.1, 6.3, 6.3 Hz, 1H, HB–C(3), Cp, B);
13C NMR (100 MHz, CDCl3): d¼178.3 (s, COOH), 172.3
(s, CvO), 172.1 (s, CvO), 75.7 (d, C(2), A), 75.4 (d, C(2),
B), 68.8 (d, CH(iPr), A), 68.6 (d, CH(iPr), B), 59.2 (d, C(1),
Cp, A), 57.9 (d, C(1), Cp, B), 21.61 (q, Me(iPr)), 21.57
(q, Me(iPr)), 21.3 (d, C(2), Cp, A), 20.1 (d, C(2), Cp, B),
18.4 (q, Me, A), 17.8 (q, Me, B), 14.7 (dd, C(3), Cp, A), 13.1
(dd, C(3), Cp, B); MS (e.i., 70 eV): m/z (%)¼217 (1), 199
(1), 174 (2), 156 (6), 145 (7), 129 (19), 119 (2), 101 (16), 91
(19), 85 (100), 73 (25), 55 (21); HRMS calcd for C10H16O5:
216.0998; found: 216.0997.
3.1.5. Isopropyl trans-(2S)-2-(2-[(tert-butoxycarbonyl)
amino]cyclo-propyloxy)propanoate (trans-6). To a solu-
tion containing 4 (3.80 g, 17.6 mmol), triethylamine
(2.67 g, 26.4 mmol) and tert-butanol (6.5 g, 87.7 mmol)
under argon DPPA (5.81 g, 21.1 mmol) was carefully
added. The mixture was heated at 80 8C for 3 h, then the
solvents were removed under reduced pressure, and the
residue was subjected to chromatography (silica gel,
hexane/ethyl acetate 5:1) to afford oily 6 (1.9 g, 55%); Rf
(hexane/ethyl acetate 3:2) 0.49; IR (film): n¼3365m, 2980s,
2935m, 1715s, 1505s, 1455s, 1390s, 1365s, 1255 s, 1165s,
1110s, 1055s, 1020m; 1H NMR (400 MHz, CDCl3): d¼5.08
(qq, J¼6.3 Hz, 1H, CH(iPr), A), 5.06 (qq, J¼6.3 Hz, 1H,
CH(iPr), B), 4.52 (br, 1H, NH), 4.36 (q, J¼7.0 Hz, 1H, H–
C(2), A), 4.16 (q, J¼7.0 Hz, 1H, H–C(2), B), 3.44–3.40
(m, 1H, H–C(1), Cp, A), 3.38 (ddd, J¼7.1, 3.9, 1.4 Hz, 1H,
H–C(1), Cp, B), 2.71–2.67 (m, 1H, H–C(2), Cp, A), 2.56–
252 (m, 1H, H–C(2), Cp, B), 1.41 (s, 9H, tBu), 1.37
(d, J¼7.0 Hz, 3H, Me, A), 1.34 (d, J¼7.0 Hz, 3H, Me, B),
1.27 (d, J¼6.3 Hz, 3H, Me(iPr)), 1.254 (d, J¼6.3 Hz, 3H,
Me(iPr)), 1.245 (d, J¼6.3 Hz, 3H, Me(iPr)), 1.238
(d, J¼6.3 Hz, 3H, Me(iPr)), 1.12 (ddd, J¼8.8, 6.9, 3.9 Hz,
1H, HA–C(3), Cp, A), 1.09–1.05 (m, 1H, HA–C(3), Cp, B),
0.89–0.75 (m, 1H, HB–C(3), Cp); 13C NMR (50 MHz,
3.1.7. trans-(2S)-2-(2-[(tert-Butoxycarbonyl)amino]
cyclo-propyloxy)propanoic acid (trans-8). To an ice-cold
solution of 6 (0.58 g, 1.93 mmol) in ethanol (6 ml) a
solution of KOH (0.34 g, 6.0 mmol) in ethanol (10 ml) was
slowly added; the mixture is allowed to warm to 25 8C and
stirred at this temperature for 3 h, then the solvents were
removed under reduced pressure, and water (15 ml) was
added and the pH adjusted to 3. The aqueous phase was
extracted with ethyl acetate (4£40 ml), the combined
organic phases were dried (Na2SO4), and the solvents
were evaporated to afford trans-8 (0.45 g, 95%) that was
used in the next step without any further purification; IR
(film): n¼3340m, 2980s, 2935m, 2625w, 1715s, 1515s,
1455s, 1395s, 1370s, 1255s, 1220s, 1165s, 1135s, 1055m,
1021m; 1H NMR (400 MHz, CDCl3): d¼4.64 (br, 1H, NH),
4.49–4.41 (m, 1H, H–C(2), A), 4.35–4.27 (m, 1H, H–C(2),
B), 3.47–3.41 (m, 1H, H–C(1), Cp), 2.72–2.68 (m, 1H, H–
C(2), Cp, A), 2.60–2.57 (m, 1H, H–C(2), Cp, B), 1.432
(s, 9H, tBu, A), 1.429 (d, J¼7.2 Hz, 3H, Me, A), 1.425
(s, 9H, tBu, B), 1.417 (d, J¼7.2 Hz, 3H, Me, B), 1.17–1.09
(m, 1H, HA–C(3), Cp), 0.84–0.78 (m, 1H, HB–C(3), Cp);

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2195
13C NMR (50 MHz, CDCl3): d¼176.9 (s, CvO, A), 176.5
(s, CvO, B), 156.0 (s, CvO, BOC), 80.0 (s, tBu), 74.4
(d, C(2)), 59.1 (d, C(1), Cp, A), 58.9 (d, C(1), Cp, B), 29.4
(d, C(2), Cp), 28.3 (q, tBu), 18.5 (q, Me, A), 18.0 (q, Me, B),
15.1 (dd, C(3), Cp); MS (e.i., 70 eV): m/z (%)¼261 (1), 245
(1), 230 (1), 189 (1), 144 (8), 128 (1), 116 (26), 100 (4), 72
(45), 57 (100); HRMS calcd for C12H23NO5: 261.1576;
found: 261.1577.
3.35–3.32 (m, 1H, H–C(1), Cp, B), 2.69–2.62 (m, 1H, H–
C(2), Cp, A), 2.61–2.53 (m, 2H, HA–C(4) of iGln and
H–C(2), Cp, B), 2.49–2.40 (m, 1H, HB–C(4) iGln), 2.24–
2.16 (m, 1H, HA–C(3), iGln), 2.04–1.97 (m, 1H, HB–C(3)
iGln), 1.40 (s, 9H, tBu), 1.37 (d, J¼7.0 Hz, 3H, Me), 1.35
(d, J¼7.2 Hz, 3H, Me), 1.12–1.05 (m, 1H, HA–C(3), Cp),
0.82–0.77 (m, 1H, HB–C(3), Cp); 13C NMR (100 MHz,
CD3OD): d¼176.3 (s, CvO), 175.8 (s, CvO), 175.2
(s, CvO), 174.4 (s, CvO), 159.0 (s, CvO, BOC), 137.7
(s, Ph), 129.7 (d, Ph), 129.4 (d, Ph), 129.3 (d, Ph), 80.0
(s, tBu), 77.3 (d, C(2), Lac), 67.5 (t, CH2–Ph), 59.8 (d, C(1),
Cp), 53.6 (d, C(2) iGln), 50.4 (d, C(2), Ala), 31.4 (t, C(4)
iGln), 30.3 (d, C(2), Cp), 28.7 (q, tBu), 27.9 (t, C(3) iGln),
18.5 (q, Me), 18.0 (q, Me), 17.9 (q, Me), 15.0 (dd, C(3), Cp);
MS (e.i., 70 eV): m/z (%)¼478 (11), 461 (30), 444 (6), 435
(6), 390 (3), 378 (4), 370 (6), 363 (9), 346 (13), 299 (4), 255
(34), 243 (4), 237 (13), 215 (11), 192 (21), 127 (100); Anal.
calcd for C29H43N3O8 (549.66): C, 62.01; H, 7.72; N, 7.48;
found: 61.97; H, 7.89; N, 7.49.
3.1.8. cis-(2S)-2-(2-[(tert-Butoxycarbonyl)amino]cyclo-
propyloxy)propanoic acid (cis-9). Following the pro-
cedure given for the synthesis of trans-8 from 7 (0.8 g,
2.79 mmol), KOH (0.45 g, 8.0 mmol) and ethanol (20 ml)
the acid cis-9 (600 mg, 90%) was obtained as an oil that was
used without any further purification in the next step; IR
(film): n¼3335m, 2980s, 2935s, 1715s, 1520s, 1455s,
1
1395s, 1370s, 1165s, 1055s; H NMR (400 MHz, CDCl3):
d¼5.60–4.90 (br, 2H, COOH, NH), 4.25–4.19 (m, 1H, H–
C(2), A), 4.15–4.08 (m, 1H, H–C(2), B), 3.47–3.40 (m, 1H,
H–C(1), Cp), 2.71–2.61 (m, 1H, H–C(2), Cp), 1.46–1.41
(m, 12H, tBu, Me), 1.00–0.95 (m, 1H, HA–C(3), Cp), 0.68–
0.59 (m, 1H, HB–C(3), Cp); 13C NMR (100 MHz, CDCl3):
d¼176.5 (s, CvO, A), 176.1 (s, CvO, B), 155.8 (s, CO,
BOC), 79.9 (s, tBu), 75.3 (d, C(2), A), 75.0 (d, C(2), B), 55.0
(d, C(1), Cp), 28.4 (q, t Bu), 27.6 (d, C(2), Cp), 18.4 (q, Me,
A), 18.1 (q, Me, B), 13.6 (dd, C(3), Cp, A), 12.7 (dd, C(3),
Cp, B); MS (e.i. 70 eV): m/z (%)¼261 (1), 189 (1), 171 (1),
144 (6), 126 (2), 116 (36), 100 (7), 72 (79), 57 (100); HRMS
calcd for C12H23NO5: 261.1576; found: 261.1577.
3.1.10. Benzyl N-{cis(2S)-2-[2-(tert-butoxycarbonyl amino)
cyclo-propyloxy]propionyl-L-alanyl-D-iso-glutaminate
(cis-11). Following the procedure given for the synthesis of
10 from 9 (550 mg, 2.24 mmol), isobutyl chloroformate
(336 mg, 2.46 mmol) and NMM (248 mg, 2.46 mmol) in
ethyl acetate (5 ml) and DMF (5 ml) followed by the
addition of the deprotected dipeptide (845 mg, 2.46 mmol;
obtained by deprotection of the Boc-protected dipeptide
(1.0 g, 2.46 mmol in abs. ethyl acetate (8 ml) with
hydrochloric acid in ethyl acetate (3.6 N by titration,
4.1 ml, 14.8 mmol)) and NMM (497 mg, 4.92 mmol) in
ethyl acetate (6 ml) and DMF (4 ml) followed by chromato-
graphy (silica gel, ethyl acetate/methanol 20:1) gave cis-11
(536 mg, 45%) as a white amorphous solid; Rf (ethyl
acetate/methanol 10:1) 0.34; IR (KBr): n¼3395s, 3285s,
2980m, 2935w, 1710s, 1685s, 1650s, 1525s, 1455m, 1365m,
1320m, 1260m, 1170s, 1125m, 1085m; 1H NMR (400 MHz,
CDCl3): d¼7.37–7.28 (m, 5H, Ph), 7.13 (d, J¼8.0 Hz, 1H,
NH), 6.98 (d, J¼7.4 Hz, 1H, NH), 6.72 (br, 1H, NH), 5.52
(br, 1H, NH), 5.24 (br, 1H, NH), 5.11 (AB system,
J¼12.3 Hz, 2H, CH2–Ph), 4.48–4.38 (m, 2H, CH(iGln),
CH(Ala), A), 4.29 (qd, J¼6.9 Hz, 1H, CH(Ala), B), 4.02
(q, J¼6.9 Hz, 1H, CH(Lac)), 3.46–3.42 (m, 1H, H–C(1),
Cp), 2.71–2.65 (m, 1H, H–C(2), Cp), 2.64–2.56 (m, 1H,
HA–C(4) iGln), 2.49– 2.41 (m, 1H, HB–C(4) iGln), 2.23–
2.15 (m, 1H, HA–C(3) iGln), 2.06–1.97 (m, 1H, HB–C(3)
iGln), 1.44 (s, 9H, tBu), 1.39 (d, J¼6.8 Hz, 3H, Me), 1.36
(d, J¼7.2 Hz, 3H, Me), 0.92–0.89 (m, 1H, HA–C(3) Cp),
0.69–0.65 (m, 1H, HB–C(3) Cp); 13C NMR (125 MHz,
CDCl3): d¼173.7 (s, CvO), 173.6 (s, CvO), 172.9
(s, CvO), 172.8 s, CvO), 172.7 (s, CvO), 157.2
(s, CvO, Boc, A), 156.8 (s, CvO, BOC, B), 135.6
(s, Ph), 128.4 (d, Ph), 128.1 (d, Ph), 128.05 (d, Ph), 79.5
(s, tBu), 76.9 (d, C(2) Lac), 66.4 (t, CH2–Ph), 55.2 (d, C(1)
Cp, A), 54.9 (d, C(1) Cp, B), 52.3 (d, C(2) iGln, A), 52.2
(d, C(2) iGln, B), 48.6 (d, C(2) Ala), 30.45 (t, C(4) iGln, A),
30.41 (t, C(4) iGln, B), 28.2 (q, tBu), 28.7 (d, C(2) Cp), 26.8
(t, C(3) iGln), 18.4 (q, Me, A), 18.0 (q, Me, B), 17.8 (q, Me),
12.8 (dd, C(3) Cp, A), 11.2 (dd, C(3) Cp, B); MS (e.i.,
70 eV): m/z (%)¼534 (1), 461 (2%), 416 (1), 378 (1), 370
(4), 363 (6), 346 (9), 299 (1), 270 (6), 255 (41), 237 (9), 192
(12), 127 (100); Anal. calcd for C29H43N3O8 (549.66): C,
62.01; H, 7.72; N, 7.48; found: 61.88; H, 7.82; N, 7.51.
3.1.9. Benzyl N-{trans-(2S)-2-[2-(tert-butoxycarbonyl-
amino)cyclopropyloxy]propionyl-L-alanyl-D-isogluta-
minate
(trans-10).
BOC-L-alanyl-D-isoglutamine-g-
benzylester (696 mg, 1.71 mmol) was deprotected in ethyl
acetate (4 ml) by the addition of a solution of dry
hydrochloric acid in ethyl acetate (3.6 N by titration,
2.9 ml, 10 mmol) for 2 h, then the volatiles were removed
and the residue was used as obtained. To a solution of 8
(380 mg, 1.55 mmol) in dry ethyl acetate (6 ml) and dry
DMF (6 ml) under argon at 0 8C NMM (173 mg,
1.71 mmol) was added. The mixture was cooled to
215 8C and isobutyl chloroformate (233 mg, 1.71) was
added dropwise through a syringe. After stirring for 5 min at
this temperature, a solution of the deprotected dipeptide
(587 mg, 1.71 mmol, vide supra) in a mixture of ethyl
acetate (4 ml), DMF (2 ml) and NMM (345 mg, 3.42 mmol)
was added and the reaction mixture stirred at ambient
temperature for 18 h. The solvents were removed under
diminished pressure, the residue suspended in water (20 ml)
and extracted with ethyl acetate (4£40 ml), the combined
organic phases were dried (Na2SO4), and the solvents were
removed. The residue was purified by chromatography
(silica gel, ethyl acetate/methanol 12:1) to afford 10
(740 mg, 90%) as a white amorphous solid. Rf (ethyl
acetate/methanol 10:1) 0.42; IR (KBr): n¼3410s, 3285s,
3070w, 2980m, 2935w, 1730s, 1690s, 1640s, 1520s, 1455m,
1390m, 1365m, 1255m, 1170s; 1H NMR (400 MHz,
CDCl3): d¼7.36–7.28 (m, 5H, Ph), 7.26–7.22 (br, 1H,
NH), 7.10 (br, 1H, NH), 6.74 (br, 1H, NH), 5.63 (br, 1H,
NH), 5.11 (AB system, J¼12.3 Hz, 2H, CH2–Ph), 4.93 (br,
1H, NH, BOC, A), 4.83 (br, 1H, NH, BOC, B), 4.46–4.40
(m, 1H, CH(iGln)), 4.33–4.26 (m, 1H, CH(Lac)), 4.21–4.18
(m, 1H, CH(Ala)), 3.40–3.37 (m, 1H, H–C(1), Cp, A),

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2196
3.1.11. Benzyl N-{trans-(2S)-2-(acetylamino)cyclopropyl-
oxy]-propionyl}-L-alanyl-D-isoglutaminate (trans-12). To
a solution of 10 (850 mg, 1.59 mmol) in ethyl acetate
(10 ml) a solution of hydrochloric acid in ethyl acetate
(3.6 N by titration, 6.5 ml, 24 mmol) was added and stirring
was continued for another 3 h, then all the volatiles were
removed under diminished pressure. The residue was
dissolved in CH2Cl2 (15 ml) and triethylamine (1.62 mg,
16 mmol) was added. After cooling to 0 8C a solution of
acetylchloride (188 mg, 2.4 mmol) in CH2Cl2 (5 ml) was
added and stirring was continued at 25 8C for 14 h. The
solvents were removed under reduced pressure, water
(40 ml) was added and extracted with ethyl acetate
(4£50 ml); the combined organic phases were dried
(Na2SO4), the solvent was removed and the residue
subjected to chromatography (silica gel, ethyl acetate/
methanol 16:1!10:1) to afford 12a (210 mg, 27%), 12b
(90 mg, 12%) and a mixture of 12a/12b (310 mg, 41%).
77.3 (d, C(2) Lac), 67.4 (t, CH2–Ph), 59.4 (d, C(1) Cp), 53.6
(d, C(2) iGln), 50.5 (d, C(2) Ala), 31.5 (t, C(4) iGln), 30.0
(d, C(2) Cp), 28.0 (t, C(3) iGln), 22.5 (q, Ac), 19.0 (q, Me),
18.0 (q, Me), 14.7 (dd, C(3) Cp); MS (e.i., 70 eV): m/z
(%)¼476 (1), 459 (1), 433 (1), 363 (3), 346 (4), 255 (16),
241 (11), 237 (8), 213 (24), 192 (22), 127 (100); Anal. calcd
for C23H32N4O7 (476.53): C, 57.97; H, 6.77; N, 11.76;
found: 57.70; H, 6.61; N, 11.68.
3.1.12. Benzyl N-{cis-(2S)-2-(acetylamino)cyclopropyl-
oxy]-propionyl}-L-alanyl-D-isoglutaminate (cis-13). Fol-
lowing the procedure given for the synthesis of 12 a solution
of 11 (190 mg, 0.36 mmol) in ethyl acetate (3 ml) was
treated with hydrochloric acid in ethyl acetate (3.6 N,
0.7 ml, 2.5 mmol) followed by acetylation (acetylchloride
(71 mg, 0.9 mmol), triethylamine (364 mg, 3.6 mmol in
CH2Cl2 (5 ml)) to afford after chromatography (silica gel,
ethyl acetate/methanol 16:1!10:1) 13 (94 mg, 55%) as an
amorphous white solid; Rf (ethyl acetate/methanol 10:1)
0.12; IR (KBr): n¼3405s, 3065w, 2985w, 2935w, 1735m,
Data for12a. Amorphous white solid; Rf (ethyl acetate/
methanol 3:1) 0.36; [a]D 223.1 (c, 0.51 MeOH); IR (KBr):
n¼3410s, 3280s, 3070w, 2980w, 2930w, 1735s, 1640s,
1545s, 1450m, 1370m, 1295m, 1235m, 1165m, 1095m,
1040w; 1H NMR (400 MHz, CDCl3): d¼7.40 (d, J¼7.7 Hz,
1H, NH), 7.36–7.28 (m, 5H, Ph), 7.15 (d, J¼7.3 Hz, 1H,
NH), 6.88 (br, 1H, NH), 5.81 (br, 1H, NH), 5.10 (AB system,
J¼12.3 Hz, 2H, CH2–Ph), 4.44–4.36 (m, 2H, CH(iGln),
CH(Ala)), 4.19 (q, J¼6.8 Hz, 1H, CH(Lac)), 3.38–3.36
(m, 1H, H–C(1) Cp), 2.79–2.75 (m, 1H, H–C(2) Cp),
2.60–2.52 (m, 1H, HA–C(4) iGln), 2.49–2.41 (m, 1H, HB–
C(4) iGln), 2.24–2.18 (m, 1H, HA–C(3) iGln), 2.04–1.95
(m, 1H, HB –C(3) iGln), 1.89 (s, 3H, Ac), 1.365
(d, J¼6.9 Hz, 3H, Me), 1.359 (d, J¼6.9 Hz, 3H, Me),
1.15–1.10 (m, 1H, HA–C(3) Cp), 0.84–0.79 (m, 1H, HB–
C(3) Cp); 13C NMR (100 MHz, CDCl3): d¼176.0 (s, CvO),
175.5 (s, CvO), 174.9 (s, CvO), 174.5 (s, CvO), 174.1
(s, CvO), 137.4 (s, Ph), 129.4 (d, Ph), 129.12 (d, Ph),
129.10 (d, Ph), 77.3 (d, C(2) Lac), 67.4 (t, CH2–Ph), 59.4
(d, C(1) Cp), 53.7 (d, C(2) iGln), 50.5 (d, C(2) Ala), 31.5
(t, C(4) iGln), 29.8 (d, C(2) Cp), 28.0 (t, C(3) iGln), 22.4
(q, Ac), 18.7 (q, Me), 17.9 (q, Me), 14.9 (dd, C(3) Cp); MS
(e.i., 70 eV): m/z (%)¼476 (1), 459 (1), 433 (1), 363 (3), 346
(4), 255 (16), 241 (11), 237 (8), 213 (24), 192 (22), 127
(100); Anal. calcd for C23H32N4O7 (476.53): C, 57.97; H,
6.77; N, 11.76; found: 57.63; H, 6.63; N, 11.70.
1
1655s, 1535s, 1455m, 1375m, 1320m, 1255m, 1170m; H
NMR (400 MHz, CDCl3): d¼7.68 (br, 1H, NH), 7.36
(d, J¼8.2 Hz, 1H, NH, A), 7.33–7.28 (m, 5H, Ph), 7.24
(d, J¼7.8 Hz, 1H, NH, B), 6.95 (br, 1H, NH, A), 6.89 (br,
1H, NH, B), 6.80 (d, J¼4.9 Hz, 1H, NH, A), 6.58
(d, J¼4.1 Hz, 1H, NH, B), 6.33 (br, 1H, NH, A), 6.28 (br,
1H, NH, B), 5.08 (AB system, J¼12.5 Hz, 2H, CH2–Ph),
4.52 (qd, J¼7.3 Hz, 1H, CH(Ala), A), 4.48 (qd, J¼7.3 Hz,
1H, CH(Ala), B), 4.43–4.38 (m, 1H, CH (iGln)), 4.02
(q, J¼6.7 Hz, 1H, CH(Lac), A), 3.95 (q, J¼6.8 Hz, 1H,
CH(Lac), B), 3.47–3.42 (m, 1H, H–C(1) Cp), 2.92–2.88
(m, 1H, H–C(2) Cp, A), 2.77–2.71 (m, 1H, H–C(2) Cp, B),
2.53–2.39 (m, 2H, H–C(4) iGln), 2.21–2.14 (m, 1H, HA–
C(3) iGln), 2.01–1.92 (m, 1H, HB–C(3) iGln), 1.98 (S, 3H,
Ac, A), 1.88 (s, 3H, Ac, B), 1.35 (d, J¼6.8 Hz, 3H, Me),
1.34 (d, J¼6.8 Hz, 3H, Me), 1.32 (d, J¼7.0 Hz, 3H, Me),
1.05–0.99 (m, 1H, HA–C(3) Cp, A), 0.90–0.84 (m, 1H,
HA–C(3) Cp, B), 0.70–0.68 (m, 1H, HB–C(3) Cp, A),
0.65–0.61 (m, 1H, HB–C(3) Cp, B); 13C NMR (125 MHz,
CDCl3): d¼173.7 (s, CvO), 173.6 (s, CvO), 173.4
(s, CvO), 173.33 (s, CvO), 173.30 (s, CvO), 173.05
(s, CvO), 173.00 (s, CvO), 172.5 (s, CvO), 172.1
(s, CvO), 135.6 (s, Ph), 128.6 (d, Ph), 128.3 (d, Ph), 128.2
(d, Ph), 76.9 (d, C(2) Lac), 66.7 (t, CH2–Ph), 54.7 (d, C(1)
Cp, A), 54.6 (d, C(1) Cp, B), 52.6 (d, C(2) iGln, A), 52.5
(d, C(2) iGln, B), 48.7 (d, C(2) Ala, A), 48.4 (d, C(2) Ala,
B), 30.7 (t, C(4) iGln, A), 30.6 (t, C(4) iGln, B), 28.0 (d, C(2)
Cp, A), 27.1 (d, C(2) Cp, B), 27.08 (t, C(3) iGln, A), 26.9
(t, C(3) iGln, B), 22.83 (q, Ac, A), 22.80 (q, Ac, B), 18.5
(q, Me), 18.3 (q, Me), 18.2 (q, Me), 18.1 (q, Me), 12.8 (dd,
C(3) Cp, A), 11.3 (dd, C(3) Cp, B); MS (e.i. 70 eV): m/z
(%)¼476 (1), 432 (1), 369 (2), 346 (2), 255 (16), 241 (8),
213 (18), 200 (6), 192 (12), 127 (100); Anal. calcd for
C23H32N4O7 (476.23): C, 57.97; H, 6.77; N, 11.76; found:
C, 57.79; H, 6.86; N, 11.52.
Data for12b: Amorphous white solid. Rf (ethyl acetate/
methanol 3:1) 0.36; [a]D 241.2 (c, 0.51 MeOH); IR (KBr):
n¼3410s, 3280s, 3070w, 2980w, 2930w, 1735s, 1640s,
1545s, 1450m, 1370m, 1295m, 1235m, 1165m, 1095m,
1040w; 1H NMR (400 MHz, CDCl3): d¼7.37–7.28 (m, 6H,
Ph, NH), 7.09 (d, J¼6.2 Hz, 1H, NH), 5.92 (br, 1H, NH),
5.59 (br, 1H, NH), 5.11 (AB system, J¼12.2 Hz, 2H, CH2–
Ph), 4.45–4.40 (m, 1H, CH(iGln)), 4.33 (qd, J¼7.0 Hz, 1H,
CH(Ala)), 4.26 (q, J¼6.8 Hz, 1H, CH(Lac)), 3.37–3.34
(m, 1H, H–C(1) Cp), 2.72–2.69 (m, 1H, H–C(2) Cp),
2.62–2.54 (m, 1H, HA–C(4) iGln), 2.50–2.43 (m, 1H, HB–
C(4) iGln), 2.23–2.18 (m, 1H, HA–C(3) iGln), 2.06–1.97
(m, 1H, HB–C(3) iGln), 1.90 (s, 3H, Ac), 1.36 (d, J¼6.8 Hz,
3H, Me), 1.35 (d, J¼6.6 Hz, 3H, Me), 1.20–1.16 (m, 1H,
HA–C(3) Cp), 0.84–0.79 (m, 1H, HB–C(3) Cp); 13C NMR
(100 MHz, CD3OD): d¼175.3 (s, CvO), 174.8 (s, CvO),
174.0 (s, CvO), 137.4 (s, Ph), 129.4 (d, Ph), 129.1 (d, Ph),
3.1.13. trans-(2S)-2-[2-(Acetylamino)cyclopropyloxy]-
propionyl-L-alanyl-D-isoglutamine (trans-14a). A sol-
ution of 12a (155 mg, 0.33 mmol) in ethanol (35 ml) was
hydrogenated for 8 h at 3 bar in the presence of Pd/C
(10%, 30 mg). The catalyst was filtered off, the solvent
removed, and the residue was subjected to chromatography
(silica gel, chloroform/methanol/acetic acid 70:25:5) to

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2197
yield 14a (110 mg, 87%) as an amorphous white solid. Rf
(CHCl3/MeOH/AcOH 70:25:5) 0.30; [a]D 227.2 (c 0.53,
MeOH); IR (KBr): n¼3415s, 2935w, 1655s, 1560s, 1450m,
1290w, 1160w, 1125w, 1040w; 1H NMR (400 MHz,
DMSO-d6): d¼8.61 (br, 1H, NH), 8.18 (br, 1H, NH), 7.87
(d, J¼7.0 Hz, 1H, NH), 7.32 (br, 1H, NH), 7.02 (br, 1H,
NH), 4.28 (qd, J¼7.0 Hz, 1H, CH(Ala)), 4.14–4.07 (m, 1H,
CH(iGln)), 4.07 (q, J¼6.6 Hz, 1H, CH(Lac)), 3.48–3.44
(m, 1H, H–C(1) Cp), 2.68–2.66 (m, 1H, H–C(2) Cp), 2.08
(t, J¼7.3 Hz, 2H, H–C(4) iGln), 1.94–1.84 (m, 1H, HA–
C(3) iGln), 1.73 (s, 3H, Ac), 1.73–1.69 (m, 1H, HB–C(3)
iGln), 1.22 (d, J¼6.6 Hz, 3H, Me), 1.21 (d, J¼6.8, 3H, Me),
0.99–0.94 (m, 1H, HA–C(3) Cp), 0.69–065 (m, 1H, HB–
C(3) Cp); 13C NMR (100 MHz, CD3OD): d¼176.9
(s, CvO), 176.0 (s, CvO), 174.8 (s, CvO), 174.7
(s, CvO), 77.4 (d, C(2) Lac), 59.5 (d, C(1) Cp), 54.3
(d, C(2) iGln), 50.4 (d, C(2) Ala), 31.6 (t, C(4) iGln), 29.8
(d, C(2) Cp), 28.8 (t, C(3) iGln), 22.5 (q, Ac), 18.7 (q, Me),
17.9 (q, Me), 14.8 (dd, C(3)); HPLC–MS (ESI, 4.1 kV,
8 ml/min, N2, methanol): m/z¼849.3 [(M22H)K2]þ (14%),
833.3 [(M22H)NaK]þ (37%), 811.3 [M2K]þ (54%), 425.3
[MK]þ (96%), 409.7 [MNa]þ (100%); HRMS calcd for
C16H26N4O7: 386.1801; found: 386.1800; Anal. calcd for
C16H26N4O7 (386.41): C, 49.73; H, 6.78; N, 14.50; found:
C, 49.52; H, 6.85; N, 14.47.
(CHCl3/MeOH/AcOH 70:25:5) 0.30; IR (KBr): n¼3415s,
2930m, 1655s, 1555s, 1445s, 1315m, 1170m, 1125m,
1045w; H NMR (400 MHz, DMSO-d6): d¼8.99 (br, 1H,
1
NH), 8.43 (br, 1H, NH, A), 8.20 (br, 1H, NH, B), 7.83
(d, J¼7.7 Hz, 1H, NH, A), 7.79 (d, J¼7.3 Hz, 1H, NH, B),
7.33 (br, 1H, NH, A), 7.29 (br, 1H, NH, B), 6.95 (br, 1H,
NH), 4.27 (qd, J¼7.3 Hz, 1H, CH(Ala), A), 4.24 (qd,
J¼6.8 Hz, 1H, CH(Ala), B), 4.05–3.96 (m, 1H, CH(iGln),
3.94 (q, J¼6.5 Hz, 1H, CH(Lac), A), 3.87 (q, J¼7.1 Hz,
CH(Lac), B), 3.52–3.48 (m, 1H, H–C(1), Cp determined in
CD3OD), 2.70–2.64 (m, 1H, H–C(2), Cp, A), 2.63–2.58
(m, 1H, H–C(2), Cp, B), 2.03–1.97 (m, 2H, H–C(4) iGln),
1.87–1.69 (m, 2H, H–C(3) iGln), 1.84 (s, 3H, Ac, A), 1.77
(s, 3H, Ac, B), 1.26 (d, J¼6.9 Hz, 3H, Me), 1.23
(d, J¼6.6 Hz, 3H, Me), 1.21 (d, J¼6.0 Hz, 3H, Me), 1.20
(d, J¼6.4, 3H, Me), 0.90–0.75 (m, 2H, H–C(3), Cp); 13C
NMR (100 MHz, CD3OD): d¼176.8 (s, CvO), 175.6
(s, CvO), 175.4 (s, CvO), 175.2 (s, CvO), 174.8
(s, CvO), 174.7 (s, CvO), 77.9 (d, C(2) Lac), 55.8
(d, C(1) Cp, A), 55.6 (d, C(1) Cp, B), 54.7 (d, C(2) iGln),
50.4 (d, C(2) Ala, A), 50.3 (d, C(2) Ala, B), 30.7 (t, C(4)
iGln), 29.3 (t, C(3) iGln), 28.7 (d, C(2) Cp, A), 28.2 (d, C(2)
Cp, B), 22.5 (q, Ac, A), 22.4 (q, Ac, B), 18.9 (q, Me), 18.7
(q, Me), 18.1 (q, Me), 18.0 (q, Me), 12.5 (dd, C(3), A), 11.9
(dd, C(3), B); HPLC–MS (ESI, 4.1 kV, 8 ml/min, N2,
methanol): m/z¼1253.3 [(M32H)K2]þ (46%), 849.4
[(M22H)K2]þ (61%), 833.5 [(M22H)NaK]þ (30%), 425
[MK]þ (100%), 409.7 [MNa]þ (11%); HRMS calcd for
C16H26N4O7: 386.1801; found: 386.1802; Anal. calcd for
C16H26N4O7 (386.41): C, 49.73; H, 6.78; N, 14.50.
3.1.14. trans-(2S)-2-[2-(Acetylamino)cyclopropyloxy]-
propionyl-L-alanyl-D-isoglutamine (trans-14b). Hydro-
genolysis of 12b (57 mg, 0.12 mmol) in ethanol (20 ml)
with Pd/C (10%, 20 mg) as described above followed by
chromatography (silica gel, chloroform/methanol/acetic
acid 70:25:5) gave 14b (40 mg, 86%) as an amorphous
white solid; Rf (CHCl3/MeOH/AcOH 70.25:5) 0.30;
[a]D¼242.0 (c, 0.36 MeOH); IR (KBr): n¼3410s,
2930m, 1660s, 1555s, 1415s, 1300m, 1160w, 1100m,
3.1.16. Benzyl {trans-(2S)-2-[2-(octanoylamino)cyclopro-
pyloxy]-propionyl}-L-alanyl-D-isoglutaminate (trans-
16). According to the procedure given for the synthesis of
12 from 10 (600 mg, 1.12 mmol), hydrochloric acid in ethyl
acetate (3.6 N, 2.0 ml, 7.2 mmol) in ethyl acetate (7 ml)
followed by acylation with octanoyl chloride (237 mg,
1.46 mmol) and triethylamine (1.13 g, 11.2 mmol) in
dichloromethane (9 ml) and chromatographic work-up
(silica gel, ethyl acetate/methanol 20:1!15:1) gave 16
(500 mg, 79%) as a white amorphous solid. Rf (ethyl
acetate/methanol 10:1) 0.29; IR (KBr): n¼3410m, 3280s,
3070w, 2955w, 2930m, 2855w, 1735m, 1680s, 1635s,
1550s, 1455m, 1385w, 1275m, 1235m, 1170m, 1100w,
1040w; 1H NMR (400 MHz, CDCl3): d¼7.47 (d, J¼6.6 Hz,
1H, NH, A), 7.45 (d, J¼7.8 Hz, 1H, NH, B), 7.35–7.27
(m, 5H, Ph), 7.24 (d, J¼6.4 Hz, 1H, NH, A), 7.20
(d, J¼7.0 Hz, 1H, NH, B), 6.86 (br, 1H, NH, A), 6.82 (br,
1H, NH, B), 6.04 (br, 1H, NH, A), 5.95 (br, 1H, NH, B),
5.89 (br, 1H, NH, A), 5.87 (br, 1H, NH, B), 5.10 (AB system,
J¼12.4 Hz, 2H, CH2–Ph), 4.46–4.34 (m, 2H, CH (Ala),
CH(iGln)), 4.25 (q, J¼6.7 Hz, 1H, CH(Lac), A), 4.20
(q, J¼6.8 Hz, 1H, CH(Lac), B), 3.36–3.31 (m, 1H, C(1)
Cp), 2.75–2.70 (m, 1H, H–C(2) Cp), 2.58–2.40 (m, 2H, H–
C(4) iGln), 2.25–2.14 (m, 1H, HA–C(3) iGln), 2.07
(t, J¼7.5 Hz, 2H, H–C(2) Oct), 2.03–1.96 (m, 1H, HB–
C(3) iGln), 1.57–1.51 (m, 2H, H–C(3) Oct), 1.35
(d, J¼6.5 Hz, 3H, Me), 1.34 (d, J¼7.0 Hz, 3H, Me), 1.33
(d, J¼6.6 Hz, 3H, Me), 1.29–1.23 (m, 8H, Oct), 1.17–1.10
(m, 1H, HA–C(3) Cp), 0.84 (t, J¼6.6 Hz, 3H, Me (Oct)),
0.79–0.75 (m, 1H, HB–C(3) Cp); 13C NMR (100 MHz,
CD3OD): d¼178.0 (s, CvO), 177.9 (s, CvO), 176.4
(s, CvO), 175.9 (s, CvO), 175.8 (s, CvO), 175.4 (s, CvO),
1
1050m; H NMR (400 MHz, DMSO-d6): d¼8.96 (br, 1H,
NH), 8.42 (br, 1H, NH), 7.94 (d, J¼7.3 Hz, 1H, NH), 7.34
(br, 1H, NH), 6.98 (br, 1H, NH), 4.28 (qd, J¼7.0 Hz, 1H,
CH(Ala)), 4.14 (q, J¼6.7 Hz, 1H, CH(Lac)), 4.08–4.01
(m, 1H, CH(iGln)), 3.42–3.40 (m, 1H, H–C(1) Cp deter-
mined in CD3OD), 2.65–2.63 (m, 1H, H–C(2) Cp), 2.01
(t, J¼6.9 Hz, 2H, H–C(4) iGln), 1.90–1.81 (m, 1H, HA–
C(3) iGln), 1.78–1.72 (m, 1H, HB–C(3) iGln), 1.74 (s, 3H,
Ac), 1.22 (d, J¼6.8 Hz, 3H, Me), 1.21 (d, J¼6.8 Hz, 3H,
Me), 1.01–0.96 (m, 1H, HA–C(3) Cp), 0.69–0.65 (m, 1H,
HB–C(3) Cp); 13C NMR (100 MHz, CD3OD): d¼176.8
(s, CvO), 175.9 (s, CvO), 174.7 (s, CvO), 77.4 (d, C(2)
Lac), 59.4 (d, C(1) Cp), 54.6 (d, C(2) iGln), 50.4 (d, C(2)
Ala), 31.7 (t, C(4) iGln), 29.9 (d, C(2) Cp), 29.0 (t, C(3)
iGln), 22.5 (q, Ac), 19.1 (q, Me), 17.7 (q, Me), 14.9 (dd,
C(3) Cp); HPLC–MS (ESI, 4.1 kV, 8 ml/min, N2, methanol):
m/z¼849.4 [(M22H)K2]þ (38%), 833.5 [(M22H)NaK]þ
(27%), 425.5 [MK]þ (100%); HRMS calcd For
C16H26N4O7: 386.1801; found: 386.1802; Anal. calcd for
C16H26N4O7 (386.41): C, 49.73; H, 6.78; N, 14.50; found:
C, 49.61; H, 6.95; N, 14.45.
3.1.15. cis-(2S)-2-[2-(Acetylamino)cyclopropyloxy]pro-
pionyl-L-alanyl-D-isoglutamine (cis-15). Hydrogenolysis
of 13 (33 mg, 0.07 mmol) in ethanol (20 ml) with Pd/C
(10%, 10 mg) as described above followed by chromato-
graphy (silica gel, chloroform/methanol/acetic acid 70:25:5)
yielded 15 (25 mg, 95%) as a white amorphous solid. Rf

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2198
174.4 (s, CvO), 137.7 (s, Ph), 129.7 (d, Ph), 129.4 (d, Ph),
129.3 (d, Ph), 77.4 (d, C(2) Lac), 67.5 (t, CH2–Ph), 59.5
(d, C(1) Cp), 53.8 (d, C(2) iGln, A), 53.7 (d, C(2) iGln, B),
50.60 (d, C(2) Ala, A), 50.57 (d, C(2) Ala, B), 36.84 (t, C(2)
Oct, A), 36.79 (t, C(2) Oct, B), 32.8 (t, Oct), 31.4 (t, C(4)
iGln), 30.2 (t, Oct), 30.0 (t, Oct), 29.8 (d, C(2) Cp, A), 29.7
(d, C(2) Cp, B), 27.9 (t, C(3) iGln), 26.8 (t, Oct), 23.6
(t, Oct), 18.9 (q, Me), 18.5 (q, Me), 17.9 (q, Me), 14.8 (dd,
C(3) Cp, A), 14.6 (dd, C(3) Cp, B), 14.3 (q, Me, Oct); MS
(e.i. 70 eV): m/z (%)¼560 (4), 543 (3), 517 (2), 453 (2), 363
(2), 346 (3), 325 (4), 297 (12), 282 (2), 255 (26), 237 (4),
192 (7), 183 (10), 127 (100); Anal. calcd for C29H44N4O7
(560.70): C, 62.12; H, 7.91; N, 9.99; found: C, 61.96; H,
7.95; N, 9.83.
(silica gel, chloroform/methanol/acetic acid 85:10:5) gave
18 (120 mg, 95%) as an amorphous white solid. Rf
(chloroform/methanol/acetic acid 85:10:5) 0.35; IR (KBr):
n¼3410s, 2930m, 2860m, 1650s, 1550s, 1450s, 1305m,
1
1210m, 1165m, 1100m; H NMR (400 MHz, DMSO-d6):
d¼8.69 (br, 1H, NH), 8.24 (br, 1H, NH, A), 8.10 (br, 1H,
NH, B), 7.90 (d, J¼7.7 Hz, 1H, NH), 7.32 (br, 1H, NH),
6.98 (br, 1H, NH), 4.27 (qd, J¼7.1 Hz, 1H, CH(Ala)), 4.14
(q, J¼6.9 Hz, 1H, CH(Lac) A), 4.09–4.02 (m, 1H, CH(iGln)),
4.07 (q, J¼6.9 Hz, 1H, CH(Lac) B), 3.42–3.39 (m, 1H, H–
C(1) Cp, A determined in CD3OD), 3.39–3.35 (m, 1H, H–
C(1) Cp, B determined in CD3OD), 2.70–2.61 (m, 1H, H–
C(2), Cp), 2.02–1.96 (m, 4H, H–C(4) iGln, H–C(2) Oct),
1.91–1.82 (m, 1H, HA–C(3) iGln), 1.76–1.70 (m, 1H, HB–
C(3) iGln), 1.47–1.42 (m, 2H, H–C(3) Oct), 1.28–1.14
(m, 14H, 2£Me, Oct), 0.99–0.92 (m, 1H, HA–C(3) Cp),
0.84 (t, J¼6.7 Hz, 3H, Me(Oct)), 0.68–0.64 (m, 1H, HB–
C(3) Cp); 13C NMR (100 MHz, CD3OD): d¼177.6
(s, CvO), 177.5 (s, CvO), 176.8 (s, CvO), 175.6
(s, CvO), 174.8 (s, CvO), 174.7 (s, CvO), 77.3 (d, C(2)
Lac, A), 77.2 (d, C(2) Lac, B), 59.5 (d, C(1) Cp, A), 59.4
(d, C(1) Cp, B), 54.6 (d, C(2) iGln), 50.5 (d, C(2) Ala, A),
50.4 (d, C(2) Ala, B), 36.9 (t, C(2) Oct), 32.8 (t, Oct), 30.3
(t, C(4) iGln), 30.2 (t, Oct), 30.1 (t, Oct), 30.0 (d, C(2) Cp,
A), 29.7 (d, C(2) Cp, B), 29.1 (t, C(3) iGln), 26.9 (t, Oct),
23.6 (t, Oct), 19.0 (q, Me, A), 18.6 (q, Me, B), 17.9 (q, Me),
15.0 (dd, C(3) Cp, A), 14.8 (dd, C(3) Cp, B), 14.3 (q, Me
(Oct)); HPLC–MS (ESI, 4.1 kV, 8 ml/min, N2, methanol):
m/z¼1487.5 [(M32H)K2]þ (45%), 1017.5 [(M22H)K2]þ
(10%), 1001.5 [(M22H)NaK]þ (38%), 979.5 [M2K]þ (79%),
963.5 [(M22H)NaK]þ (65%), 509.6 [MK]þ (82%), 493.7
[MNa]þ (100%); HRMS calcd for C22H38N4O7: 470.2740;
found: 470.2741; Anal. calcd for C16H26N4O7 (470.57): C,
56.15; H, 8.14; N, 11.91; found: C, 56.02; H, 8.29; N, 11.82.
3.1.17. Benzyl {cis-(2S)-2-[2-(octanoylamino)cyclopropyl-
(cis-17).
oxy]propionyl}-L-alanyl-D-isoglutaminate
According to the procedure given for the synthesis of 12
from 11 (170 mg, 0.32 mmol), hydrochloric acid in ethyl
acetate (3.6 N, 0.7 ml, 2.5 mmol) in ethyl acetate (3 ml)
followed by acylation with octanoyl chloride (78 mg,
0.48 mmol) and triethylamine (323 mg, 3.2 mmol) in
dichloromethane (3 ml) and chromatographic work-up
(silica gel, ethyl acetate/methanol 20:1!10:1) gave 17
(112 mg, 63%) as a white amorphous solid. Rf (ethyl
acetate/methanol 10:1) 0.27; IR (KBr): n¼3395m, 3280m,
3065w, 2930m, 2855w, 1710s, 1680m, 1650s, 1540m,
1
1460m, 1420w, 1380w, 1325m, 1260m, 1175w; H NMR
(400 MHz, CDCl3): d¼7.43 (d, J¼7.6 Hz, 1H, NH, A), 7.41
(d, J¼6.8 Hz, 1H, NH, B), 7.38 (d, J¼8.0 Hz, 1H, NH, A),
7.34–7.29 (m, 5H, Ph), 7.07 (d, J¼7.6 Hz, 1H, NH, B), 6.91
(br, 1H, NH, B), 6.70 (br, 1H, NH, B), 6.38 (d, J¼4.9 Hz,
1H, NH, A), 6.07 (d, J¼3.5 Hz, 1H, NH, B), 5.87 (br, 1H,
NH, A), 5.71 (br, 1H, NH, B), 5.10 (AB system, J¼12.3 Hz,
2H, CH2–Ph), 4.50–4.39 (m, 2H, CH(iGln), CH(Ala)), 4.07
(q, J¼6.8 Hz, 1H, CH(Lac) A), 3.98 (q, J¼6.8 Hz, CH(Lac),
B), 3.50–3.45 (m, 1H, H–C(1) Cp), 2.95–2.91 (m, 1H, H–
C(2) Cp, A), 2.77–2.72 (m, 1H, H–C(2) Cp, B), 2.60–2.52
(m, 1H, HA–C(4) iGln), 2.48–2.39 (m, 1H, HB–C(4) iGln),
2.23–2.12 (m, 3H, HA–C(3) iGln, H–C(2) Oct), 2.02–1.93
(m, 1H, HB–C(3) iGln), 1.63–1.55 (m, 2H, H–C(3) Oct),
1.39 (d, J¼7.2 Hz, 3H, Me), 1.37 (d, J¼7.4 Hz, 3H, Me),
1.34 (d, J¼6.8 Hz, 3H, Me), 1.33 (d, J¼7.0 Hz, 3H, Me),
1.30–1.23 (m, 8H, Oct), 1.04–0.98 (m, 1H, HA–C(3) Cp),
0.84 (t, J¼6.6 Hz, 3H, Me (Oct)), 0.66–0.60 (m, 1H, HB–
C(3) Cp); 13C NMR (100 MHz, CDCl3): d¼175.3 (CvO),
173.9 (s, CvO), 173.7 (s, CvO), 173.3 (s, CvO), 173.2
(s, CvO), 135.7 (s, Ph), 128.7 (d, Ph), 128.4 (d, Ph), 128.3
(d, Ph), 77.0 (d, C(2) Lac), 66.6 (t, CH2–Ph), 54.8 (d, C(1)
Cp), 52.4 (d, C(2) iGln), 48.4 (d, C(2) Ala), 36.2 (t, C(2)
Oct), 31.6 (t, Oct), 30.5 (t, C(4) iGln), 29.2 (t, Oct), 28.9
(t, Oct), 28.8 (t, C(3) iGln), 27.7 (d, C(2) Cp), 25.7 (t, Oct),
22.4 (t, Oct), 18.3 (q, Me), 13.9 (q, Me (Oct)), 11.1 (dd, C(3)
Cp); MS (e.i., 70 eV): m/z (%)¼560 (1), 453 (1), 346 (1),
325 (1), 297 (6), 282 (1), 255 (14), 237 (2), 226 (4), 198 (8),
192 (3), 183 (6), 127 (100); Anal. calcd for C29H44N4O7
(560.70): C, 62.12; H, 7.91; N, 9.99; found: C, 61.96; H,
7.98; N, 9.87.
3.1.19. cis-(2S)-2-[2-(Octanoylamino)cyclopropyloxy]-
propionyl-L-alanyl-D-isoglutamine (cis-19). Hydrogeno-
lysis of 17 (95 mg, 0.17 mmol) in ethanol (20 ml) with Pd/C
(10%, 20 mg) followed by chromatography (silica gel,
chloroform/methanol/acetic acid 85:10:5) afforded 19
(65 mg, 81%) as a white amorphous solid. Rf (chloroform/
methanol/ acetic acid 85:10:5) 0.20; IR (KBr): n¼3405s,
2930m, 2855w, 1655s, 1550s, 1450m, 1320m, 1170m,
1
1105m; H NMR (400 MHz, DMSO-d6): d¼9.02 (br, 1H,
NH), 8.10 (br, 1H, NH), 7.82 (d, J¼6.8 Hz, 1H, NH), 7.31
(br, 1H, NH, A), 7.27 (br, 1H, NH, B), 6.96 (br, 1H, NH),
4.24 (qd, J¼7.2 Hz, 1H, CH(Ala)), 4.03–3.99 (m, 1H,
CH(iGln)), 3.93 (q, J¼6.6 Hz, 1H, CH(Lac), A) 3.83
(q, J¼6.7 Hz, 1H, CH(Lac), B), 3.56–3.52 (m, 1H, H–
C(1) Cp, A determined in CD3OD), 3.48–3.44 (m, 1H, H–
C(1) Cp, B determined in CD3OD), 2.70–2.61 (m, 1H, H–
C(2) Cp), 2.10 (t, J¼7.4 Hz, 2H, H–C(2) Oct), 2.05–1.98
(m, 2H, H–C(4) iGln), 1.88–1.80 (m, 1H, HA–C(3) iGln),
1.78–1.70 (m, 1H, HB–C(3) iGln), 1.50–1.45 (m, 2H, H–
C(3) Oct), 1.28–1.20 (m, 11H, Me, Oct), 1.18 (d, J¼6.6 Hz,
3H, Me), o.88–0.80 (m, 2H, H–C(3) Cp), 0.84 (t, J¼7.0 Hz,
3H, Me(Oct)); 13C NMR (100 MHz, CD3OD): d¼178.1
(s, CvO), 177.7 (s, CvO), 176.7 (s, CvO), 175.5
(s, CvO), 174.7 (s, CvO), 77.9 (d, C(2) Lac, A), 77.8
(d, C(2) Lac, B), 55.9 (d, C(1) Cp, A), 55.7 (d, C(1) Cp, B),
54.7 (d, C(2) iGln), 50.3 (d, C(2) Ala), 36.9 (t, C(2) Oct),
32.9 (t, Oct), 30.4 (t, Oct), 30.2 (t, C(4) iGln), 30.1 (t, Oct),
29.2 (t, C(3) iGln), 28.6 (d, C(2) Cp, A), 28.0 (d, C(2) Cp,
3.1.18. trans-(2S)-2-[2-(Octanoylamino)cyclopropyloxy]-
propionyl-L-alanyl-D-isoglutamine (trans-18). Hydro-
genolysis of 16 (150 mg, 0.27 mmol) in ethanol (30 ml)
with Pd/C (10%, 30 mg) followed by chromatography

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2191–2199
2199
11. Barton, D. H. R.; Camara, J.; Dalko, P.; Gero, S. D.; Sire-
Quiclet, B.; Stu¨tz, P. J. Org. Chem. 1989, 54, 3764–3766.
12. Kikelj, D.; Pecar, S.; Kotnik, V.; Stalc, A.; Wraber-Herzog, B.;
Simcic, S. S.; Ihan, A.; Klamfer, L.; Pavsic, L.; Grahek, R.;
B), 27.1 (t, Oct), 23.7 (t, Oct), 19.1 (q, Me, A), 19.0 (q, Me,
B), 18.0 (q, Me), 14.4 (q, Me (Oct)), 12.7 (dd, C(3) Cp, A),
11.8 (dd, C(3) Cp, B); HPLC–MS (ESI, 4.1 kV, 8 ml/min,
N2, methanol): m/z¼1487.5 [(M32H)K2]þ (95%), 1017.3
[(M22H)K2]þ (16%), 979.3 [(M2K]þ (100%), 509.5 [MK]þ
(82%), 493.7 [MNa]þ (37%); Anal. calcd for C22H38N4O7
(470.57): C, 56.15; H, 8.14; N, 11.91; found: C, 55.96; H,
8.28; N, 11.82.
¨
Suhadolc, E.; Hocevar, M.; Honig, H.; Rogi-Kohlenprath, R.
J. Med. Chem. 1998, 41, 530–539.
13. Gobec, S.; Urleb, U.; Simcic, S.; Wraber, B. Pharmazie 2001,
56, 523–526.
14. Sollner, M.; Pecar, S.; Stalc, A. Eur. J. Med. Chem. 1996, 31,
927–933.
15. Gobec, S.; Urleb, U. Molecules 2002, 7, 394–404.
16. Dzierzbicka, K.; Kolodziejczyk, A. M.; Wysocka-Skrzela, B.;
Mysliwski, A.; Sosnowska, D. J. Med. Chem. 2001, 44,
3606–3615.
Acknowledgements
Financial support by the Fonds der Chemischen Industrie is
gratefully acknowledged. We like to thank Dr. R. Kluge for
¨
the MS spectra and Dr. D. Strohl for numerous NMR
spectra.
17. Dzierzbicka, K.; Kolodziejczyk, A. M. J. Med. Chem. 2003,
46, 183–189.
18. Lefrancier, P.; Lederer, E. Pure Appl. Chem. 1987, 59,
449–454.
19. Danijel Kikelj, D.; Kidric, J.; Pristovsek, P.; Pecar, S.; Urleb,
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U.; Krbavcic, A.; Honig, H. Tetrahedron 1992, 48,
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