Synthesis of cyclopropanoid analogues of N-acyl-muramyldipeptide as potential immunostimulants

Article abstract of DOI:10.1016/j.tet.2004.01.036

The preparation of diastereomerically pure cyclopropanoid muramyldipeptide analogues from suitable substituted cyclopropylamines is described.

Full text of DOI:10.1016/j.tet.2004.01.036

Tetrahedron 60 (2004) 2201–2211
Synthesis of cyclopropanoid analogues of
N-acyl-muramyldipeptide 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 10 September 2003; revised 9 January 2004; accepted 14 January 2004
Abstract—The preparation of diastereomerically pure cyclopropanoid muramyldipeptide analogues from suitable substituted
cyclopropylamines is described.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
nonspecific immunity against viral and microbial infec-
tions7,8 and against tumors.9 However, MDP also induces
undesirable biological activities such as pyrogenicity,
induction of arthritis, transient leucopenia and sensitiviza-
tion to endotoxin.10–12
Over the past two decades,1 immunopharmacology has
become a viable discipline in its own right. Interest in
immunostimulation has beeen fuelled by advances in bacterial
cell wall chemistry, by the apparent promise of experimental
and clinical tumor immunology, and by the rapidly expanding
knowledge of endogenous regulators and mediators of
lympho-myeloid cell differentiation and cooperation.
Consequently, the MDP structure has undergone extensive
chemical modification in searches for biologically active
analogues having fewer and more tolerable side effects.13,14
As a novel approach toward obtaining glycopeptide
adjuvants that exhibit presumably lower toxicity and/or
pharmacodynamic advantages, we report the synthesis of
several derivatives wherein the carbohydrate part of MDP is
replaced by a cyclopropane moiety (Fig. 1).
Freund’s adjuvant2,3 consisting of mycobacterial cells in a
water-in-oil emulsion containing the antigen in the water phase
has been used for stimulating the production of antibodies
against the antigen used. Degradation of the cell walls and
subjecting these fragments to a lysozyme digestion finally
led to the observation that N-acyl-muramyl dipeptide
(MDP) should be the minimal adjuvant active structure.4,5
2. Results and discussion
In addition, MDP also has been reported6 to enhance
While most of the MDP analogues synthesized so far
Figure 1. Structure of MDP and its cyclopropanoid analogues.
Keywords: Cyclopropanes; Muramyldipeptide; Immunomodulation.
*
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.2004.01.036

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2202
possess an intact carbohydrate-L-Ala-D-Glu-NH2 moiety, is
has been generally accepted that the N-acetyl-D-glucos-
amine fragment is not essential for the immunomodulating
activity of this class10,13,14 of compounds. Thus, replace-
ment of the N-acetyl-muramyl moiety with various acyl
groups represents an approach in the rational design and
synthesis of new immunologically active MDP analogues,
as demonstrated by some carbocyclic MDP analogues,15–17
by the adamantyl substituted MDP analogue LK415,18 by
FK-156,19 pimeloutide,20 7-(oxoacyl)-L-alanyl-D-isoglut-
amine21 and even more recently by the synthesis of new
lipophilic phosphonate and phosphonamidate analogues22
or of acridine-derived compounds.23,24
Treatment of trans-2 with trifluoroacetic acid allowed the
selective cleavage28,29 of the tert-butyl ester without
affecting the isobutyl ester and trans-4 was obtained in
almost quantitative yield. Similarly, from cis-3 the cis-
configurated monoester cis-5 was obtained.
Degradation of the carboxylic group was accomplished by a
modified Curtius degradation30 allowing trans-4 to react
with diphenylphosphoryl azide (DPPA)/tert-butanol in the
presence of triethylamine to yield the Boc-protected amine
trans-6 in 55% isolated yield. Treatment of cis-5 under the
same conditions afforded cis-7 together with 5% of trans-6
that was easily separated by chromatography.
Interestingly enough, even slight structural modifications on
these compounds can lead to molecules with improved or
altered pharmacological activities. Hence, the synthesis of
cyclopropanoid analogues possessing either a N-acetyl or a
N-octanoyl residue was envisaged. Retrosynthetic analysis
revealed that these compounds should be available en route
by a strategy starting from a suitable cyclopropanoid
precursor (Scheme 1).
Cleavage of the ester was performed by treatment of trans-6
with potassium hydroxide in ethanol and the acid trans-8
was obtained as a slowly crystallizing solid that was used for
the next reaction without further purification. In an
analogous way, from cis-7 the acid cis-9 was obtained.
Albeit the rather mild conditions used for this hydrolysis
reaction concomitant epimerization invariably led to some
extend to the formation of trans-8 that had to be separated
by chromatography after the next step (Scheme 2).
Scheme 1. Reactions and conditions: (a) Hg(OAc)2; (b) N2CHCO2tBu,
[(Rh(OAc)2)2]; (c) CF3COOH; (d) DPPA, tBuOH, Et3N; (e) KOH.
The Hg(OAc)2 catalyzed reaction25,26 between isobutyl
(2R)-2-hydroxy-propanoate with ethyl vinyl ether resulted
in the formation of 46% of isobutyl (2R)-2-(vinyloxy)pro-
panoate (1). Although numerous methods are known for the
synthesis of substituted cyclopropanes we decided to apply
the [Rh(OAc)2]2 catalyzed reaction of diazoesters with
olefins.27 Thus, the reaction of 1 with tert-butyl diazoacetate
in the presence of the rhodium catalyst gave a mixture of
trans configurated 2 together with cis configurated 3; both
compounds were easily separated from each other by
chromatography although they were obtained as a mixture
of the corresponding diastereomers differing only in the
absolute configuration at the two stereogenic centers at the
cyclopropane ring.
Scheme 2. Reactions and conditions: (a) ClCO2iBu, NMM, L-Ala-D-
iGln·HCl; (b) HCl in EtOAc then AcCl/Et3N (for 12 and 13) or
C7H15COCl/Et3N (for 16 and 17); (c) Pd/C, H2.
Although there are a quite a number of different methods for
the formation of peptide bonds, preliminary screening
showed the mixed-anhydride method to work best for
these reactions. The reaction of the acid trans-8 with
isobutyl chloroformate/N-methyl-morpholine31 followed by
the addition of L-alanyl-D-iso-glutamine-g-benzyl ester
(that was freshly prepared from commercially available
Boc-L-Ala-D-isoGlnOBn by acidic cleavage of the Boc

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2203
group by reaction with hydrochloric acid in ethyl acetate)
finally afforded the valuable intermediate trans-10 in 86%
yield. Similarly, from cis-9 the protected dipeptide cis-11
was obtained in 60% yield. Treatment of trans-10 with
hydrochloric acid in ethyl acetate followed by acetylation
with acetyl chloride/triethylamine gave the trans configu-
rated diasteromers 12a and 12b. In an analogous way from
cis-11 acetylated cis-13 was obtained. Final deprotection
was achieved by hydrogenolysis. Thus, from trans-12a,b
the cyclopropyl analogues trans-14a,b were obtained and
from cis-13 compound cis-15 was prepared in 88% yield.
in ethylvinyl ether (225 ml, 2.35 mol) was stirred for 7 days
under argon at room temperature, then quenched by the
addition of hexane (225 ml). The organic phase was washed
with 1M KOH (twice 25 ml each), brine (100 ml) and dried
(Na2SO4). The solvents were removed and the residue
subjected to chromatography (silica gel, hexane/ethyl
acetate, 10:1) to afford 1 (5.9 g, 46%) as a colorless oil; Rf
(hexane/ethyl acetate, 3:2) 0.69; [a]2D0 63.68 (c 0.47,
CHCl3); IR (film): n¼3535w, 3120w, 2965s, 2875m,
1760s, 1735s, 1640s, 1620s, 1510w, 1470m, 1395m,
1380m, 1320m, 1280s, 1190s, 1130s, 1095s, 1050s cm21
;
3
1H NMR (400 MHz, CDCl3): d¼6.38 (dd, JH,H¼14.3 Hz,
3
It has been assumed that lipophilic MDP derivatives induce
cellular-specific response and increase non-specific resist-
ance more strongly although these derivatives are often less
good adjuvants for humoral response than MDP itself.32 In
order to prepare more lipophilic compounds the Boc
protecting group in trans-10 was cleaved off followed by
acylation with octanoyl chloride/triethylamine to afford a
mixture of diastereomers trans-16a and trans-16b that were
separated by chromatography. Similaryl, from cis-11 the
products cis-17a and cis-17b were obtained. Hydrogeno-
lysis of 16a,b and 17a,b finally resulted in the formation of
cis-18a, cis-18b, trans-19a and trans-19b, respectively.
3JH,H¼6.8 Hz, 1H, HCvC), 4.39 (q, JH,H¼6.8 Hz, 1H,
3
2
H–C(2)), 4.21 (dd, JH,H¼14.3 Hz, JH,H¼22.5 Hz, 1H,
3
2
H2CvC (trans)), 4.07 (dd, JH,H¼6.8 Hz, JH,H¼22.5 Hz,
1H, H2CvC (cis)), 3.97–3.89 (m, 2H, OCH2), 1.98–1.91
(m, 1H, CH (iBu)), 1.48 (d, JH,H¼6.8 Hz, 3H, Me), 0.92
3
(d, JH,H¼6.6 Hz, 6H, Me (iBu)); 13C NMR (100 MHz,
3
CDCl3): d¼172.1 (s, CvO), 150.4 (d, vCH), 88.6 (t,
vCH2), 72.8 (d, C(2)), 71.1 (t, CH2O), 27.6 (d, CH (iBu)),
18.8 (q, Me (iBu)), 17.9 (q, Me); MS (GC–MS, e.i., 70 eV):
m/z¼172 (2%), 157 (1%), 144 (1%), 129 (1%), 117 (18%),
116 (7%), 99 (2%), 89 (11%), 71 (100%), 57 (31%). Anal.
Calcd for C9H16O3 (172.110): C, 62.77; H, 9.36. Found: C,
62.68; H, 9.32.
Although the absolute configuration of the target molecules
concerning the stereogenic centers at the cyclopropane ring
remains unclear, comparison of the specific rotation values
of these compounds with those reported for carbocyclic nor-
muramyldipeptide analogues as well as with the reported
values for MDP and nor-MDP suggests for 18a a (S,S) and
for 18b a (R,R) configuration at the cyclopropane ring.
3.1.2. Isobutyl trans-(2R)-{[2-(tert-butyloxycarbonyl)-
cyclo-propyl]-oxy}propanoate (2) and isobutyl cis-(2R)-
{[2-(tert-butyloxycarbonyl)cyclopropyl]oxy}propanoate
(3). To a solution containing 1 (5.80 g, 33.7 mmol) in abs.
CH2Cl2 (10 ml) and [(Rh(OAc)2)2] (100 mg) under argon
a solution of tert-butyl-diazoacetate (5.7 g, 40.1 mmol)
in abs. CH2Cl2 (20 ml) was added within 8 h at room
temperature. After the evolution of nitrogen had ceased, the
solvents were removed under reduced pressure and the
residue was purified by chromatography (silica gel, hexane/
ethyl acetate, 16:1) to obtain trans-2 (4.6 g, 48%) and cis-3
(2.6 g, 27%).
The determination of the different biological activities of the
prepared carbocyclic cyclopropanoid MDP analogues is still
in progress and will be reported in due course.
3. Experimental
3.1. General
Data for 2. Rf (hexane/ethyl acetate, 3:2) 0.68; IR (film):
n¼2970s, 2875m, 1750s, 1720s, 1455m, 1395s, 1370s,
1350m, 1325m, 1275m, 1225s, 1195s, 1155s, 1135s, 1105s,
1050m, 1015m, 985m cm21; 1H NMR (400 MHz, CDCl3):
d¼4.088 (q, JH,H¼6.8 Hz, 1H, H–C(2), A), 4.084 (q,
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 or
internal CCl3F, C0 correspond to the atoms of the
heterocycle), 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 performed on silica gel (Merck 5554,
detection by UV absorption or by treatment with a solution
3
3
3JH,H¼6.8 Hz, 1H, H–C(2), B), 3.941 (virt.-d, JH,H
¼
3
6.4 Hz, 2H, CH2O, A), 3.939 (virt.-d, JH,H¼6.6 Hz, 2H,
CH2O, B), 3.70–3.65 (m, 1H, H–C(1) (Cp)), 2.02–1.90 (m,
1H, CH (iBu)), 1.84–1.79 (m, 1H, H–C(2) (Cp), A), 1.71–
1.67 (m, 1H, H–C(2) (Cp), B), 1.402 (s, 9H, tBu, A), 1.400
(s, 9H, tBu, B), 1.380 (d, 3JH,H¼6.8 Hz, 3H, Me, A), 1.373
3
(d, JH,H¼6.8 Hz, 3H, Me, B), 1.26–1.12 (m, 2H, HA,B
–
C(3) (Cp)), 0.932 (d, 3JH,H¼6.6 Hz, 6H, Me (iBu), A), 0.924
(d, JH,H¼6.8 Hz, 6H, Me (iBu), B); 13C NMR (100 MHz,
3
CDCl3): d¼172.8 (s, CvO, A), 172.7 (s, CvO, B), 171.6
(s, CvO), 80.5 (s, tBu, A), 80.4 (s, tBu, B), 75.4 (d, C(2),
A), 75.3 (d, C(2), B), 71.0 (t, CH2O, A), 70.9 (t, CH2O, B),
59.6 (d, C(1) (Cp), A), 59.5 (d, C(1) (Cp), B), 28.0 (q, tBu),
27.60 (d, CH (iBu), A), 27.57 (d, CH (iBu), B), 22.3 (d, C(2)
(Cp), A), 21.9 (d, C(2) (Cp), B), 18.9 (q, Me (iBu), A), 18.8
(q, Me (iBu), B), 18.4 (q, Me, A), 18.3 (q, Me, B), 15.4 (dd,
C(3) (Cp), A), 14.5 (dd, C(3) (Cp), B); MS (GC–MS, e.i.,
70 eV): m/z¼271 (1%), 230 (1%), 213 (2%), 201 (1%), 185
(7%), 174 (2%), 147 (10%), 129 (9%), 101 (8%), 91 (25%),
of 10% sulfuric acid, ammonium molybdate and cerium(IV)
sulfate followed by gentle heating. The solvents were dried
according to usual procedures.
)
3.1.1. (1R) 1-(Vinyloxy)ethyl-3-methyl butanoate (1).
A solution of (1R) 1-hydroxyethyl-3-methyl-butanoate
(10.96 g, 0.075 mol) and Hg(OAc)2 (23.90 g, 0.075 mol)

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R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2204
84 (30%), 57 (100%). Anal. Calcd for C15H26O5 (286.178):
C, 62.91; H, 9.15. Found: C, 62.70; H, 9.05.
3.1.4. cis-2-{[(1R)-2-Isobutoxy-1-methyl-2-oxoethyl]-
oxy}-1-cyclopropanecarboxylic acid (5). Following the
synthesis of 4 starting from 3 (2.40 g, 8.4 mmol) in abs.
CH2Cl2 (30 ml) and CF3COOH (5.70 g, 50.0 mmol) in abs.
CH2Cl2 (5 ml) compound 5 (1.90 g, 100%) was obtained
as a slightly brown oil that was used without further
purification in the next step. IR (film): n¼2965s, 2875m,
2690w, 1745s, 1705s, 1455s, 1370m, 1350m, 1280m,
Data for 3. Rf (hexane/ethyl acetate, 3:2) 0.64; IR (film):
n¼3440w, 2970s, 1730s, 1455m, 1380s, 1205s, 1145s,
1055m, 985m cm21; 1H NMR (400 MHz, CDCl3): d¼4.05
3
(q, JH,H¼6.8 Hz, 1H, H–C(2), A), 4.00–3.90 (m, 2H,
CH2O), 3.88 (q, 3JH,H¼6.8 Hz, 1H, H–C(2), B), 3.79–3.75
(m, 1H, H–C(1) (Cp), A), 3.75–3.70 (m, 1H, H–C(1) (Cp),
B), 2.00–1.90 (m, 1H, CH (iBu)), 1.71–1.67 (m, 1H,
H–C(2) (Cp), A), 1.59–1.56 (m, 1Hþ1H, H–C(2) (Cp), B,
1210s, 1135s, 1050m, 965s cm21 1H NMR (400 MHz,
;
3
CDCl3): d¼9.15 (br, 1H, COOH), 4.10 (q, JH,H¼7.0 Hz,
1H, H–C(2), A), 4.00–3.84 (m, 1Hþ2Hþ1H, H–C(2), B,
CH2O, H–C(1) (Cp)), 2.00–1.88 (m, 1H, CH (iBu)), 1.82–
1.76 (m, 1H, H–C(2) (Cp), A), 1.72–1.62 (m, 1H, H–C(2)
(Cp), B), 1.52–1.48 (m, 1H, HA–C(3) (Cp), A), 1.44–1.39
(m, 1H, HA–C(3) (Cp), B), 1.38 (d, 3JH,H¼6.8 Hz, 3H, Me,
HA–C(3) (Cp), A), 1.46 (s, 9H, tBu, A), 1.43 (s, 9H, tBu, B),
3
1.41–1.36 (m, 1H, HA–C(3) (Cp), B), 1.36 (d, JH,H
3
¼
7.0 Hz, 3H, Me, A), 1.34 (d, JH,H¼7.0 Hz, 3H, Me, B),
3
1.09–1.01 (m, 1H, HB–C(3) (Cp), A), 0.93 (d, JH,H
¼
3
3
6.8 Hz, 6H, Me (iBu), A), 0.92 (d, JH,H¼6.6 Hz, 6H, Me
(iBu), B), 0.90–0.85 (m, 1H, HB–C(3) (Cp), B); 13C NMR
(100 MHz, CDCl3): d¼172.8 (s, CvO), 169.0 (s, CvO, A),
168.5 (s, CvO, B), 80.27 (s, tBu, A), 80.24 (s, tBu, B), 75.4
(d, C(2), A), 74.7 (d, C(2), B), 70.8 (t, CH2O, A), 70.7 (t,
CH2O, B), 58.3 (d, C(1) (Cp), A), 56.8 (d, C(1) (Cp), B),
27.89 (q, tBu, A), 27.86 (q, tBu, B), 27.5 (d, CH (iBu)), 22.7
(d, C(2) (Cp), A), 21.4 (d, C(2) (Cp), B), 18.78 (q, Me (iBu),
A), 18.77 (q, Me (iBu), B), 18.4 (q, Me, A), 17.8 (q, Me, B),
13.3 (dd, C(3) (Cp), A), 11.5 (dd, C(3) (Cp), B); MS (GC–
MS, e.i., 70 eV): m/z¼230 (1%), 213 (2%), 201 (1%), 185
(1%), 174 (2%), 156 (3%), 147 (6%), 129 (18%), 117 (2%),
101 (8%), 91 (20%), 84 (25%), 73 (10%), 57 (100%). Anal.
Calcd for C15H26O5 (286.178): C, 62.91; H, 9.15. Found: C,
62.87; H, 9.08.
A), 1.36 (d, JH,H¼7.0 Hz, 3H, Me, B), 1.24–1.18 (m, 1H,
HB–C(3) (Cp), A), 1.11–1.04 (m, 1H, HB–C(3) (Cp), B),
3
0.917 (d, JH,H¼6.6 Hz, 6H, Me (iBu), A, B), 0.913 (d,
3JH,H¼6.6 Hz, 6H, Me (iBu), A, B), 0.911 (d, 3JH,H¼6.8 Hz,
6H, Me (iBu), A, B); 13C NMR (50 MHz, CDCl3): d¼178.1
(s, CvO), 172.6 (s, CvO), 172.5 (s, CvO), 75.7 (d, C(2),
A), 75.4 (d, C(2), B), 71.2 (t, CH2O, A), 71.1 (t, CH2O, B),
59.3 (d, C(1) (Cp), A), 58.2 (d, C(1) (Cp), B), 27.7 (d, CH
(iBu)), 21.4 (d, C(2) (Cp), A), 20.2 (d, C(2) (Cp), B), 18.9
(q, Me (iBu)), 18.6 (q, Me, A), 18.0 (q, Me, B), 14.9 (dd,
C(3) (Cp), A), 13.3 (dd, C(3) (Cp), B); MS (e.i., 70 eV):
m/z¼231 (1%), 212 (2%), 201 (1%), 186 (2%), 175 (2%),
156 (6%), 145 (8%), 129 (43%), 117 (4%), 101 (18%), 91
(33%), 85 (81%), 73 (33%), 57 (100%); HRMS Calcd for
C11H18O5: 230.1154. Found: 230.1154.
3.1.3. trans-2-{[(1R)-2-Isobutoxy-1-methyl-2-oxoethyl]-
oxy}-1-cyclopropanecarboxylic acid (4). To a solution of
2 (4.07 g, 14.2 mmol) in abs. CH2Cl2 (40 ml) at 0 8C under
argon a solution of CF3COOH (8.10 g, 71.0 mmol) in abs.
CH2Cl2 (7 ml) was added slowly and stirring continued
for another 18 h, then the solvents were removed under
diminished pressure, toluene (twice 50 ml) was added, and
again the solvent was removed. Compound 4 (3.3 g, 100%)
was obtained as a slightly brown oil that was used without
any further purification for the next step; IR (film):
n¼2965s, 2875m, 1750s, 1695s, 1450s, 1370m, 1310m,
3.1.5. trans-Isobutyl (2R)-2-({2-[tert-butoxycarbonyl)-
amino] cyclopropyl}oxy)propanoate (6). To a solution
of
4 (2.70 g, 11.7 mmol) in triethylamine (1.78 g,
17.6 mmol) and tert-butanol (4.33 g, 58.5 mmol) under
argon diphenylphosphorylazide (3.85 g, 14.0 mmol) was
added and the mixture stirred at 80 8C for 3 h; the solvents
were removed and the residue was subjected to chroma-
tography (hexane/ethyl acetate, 5:1) to afford 6 (1.9 g, 55%)
as an oil; Rf (hexane/ethyl acetate, 3:2) 0.49; IR (film):
n¼3370m, 2975s, 2875m, 1715s, 1505s, 1455m, 1390m,
1365s, 1255s, 1165s, 1135s, 1055m, 1020m, 990m,
1285m, 1200s, 1175s, 1135s, 1050m cm21
;
1H NMR
945w cm21
;
1H NMR (400 MHz, CDCl3): d¼4.46 (br,
3
(400 MHz, CDCl3): d¼8.35 (br, 1H, COOH), 4.11 (q,
3JH,H¼6.8 Hz, 1H, H–C(2), A), 4.09 (q, 3JH,H¼6.8 Hz, 1H,
H–C(2), B), 3.98–3.90 (m, 2H, CH2O), 3.83–3.80 (m, 1H,
H–C(1) (Cp), A),), 3.77–3.74 (m, 1H, H–C(1) (Cp), B),
2.00–1.90 (m, 1H, CH (iBu)), 1.92–1.88 (m, 1H, H–C(2)
(Cp), A), 1.78–1.73 (m, 1H, H–C(2) (Cp), B), 1.43–1.23
1H, NH), 4.23 (q, JH,H¼7.0 Hz, 1H, H–C(2), A), 3.96–
3.92 (m, 1H, H–C(2), B), 3.921 (virt.-d, 3JH,H¼6.8 Hz, 2H,
3
CH2O, A), 3.915 (virt.-d, JH,H¼6.6 Hz, 2H, CH2O, B),
3.45–3.39 (m, 1H, H–C(1) (Cp)), 2.71–2.67 (m, 1H,
H–C(2) (Cp), A), 2.57–2.53 (m, 1H, H–C(2) (Cp), B),
2.00–1.90 (m, 1H, CH (iBu)), 1.41 (s, 9H, tBu), 1.40 (d,
3
(m, 2H, HA,B–C(3) (Cp)), 1.39 (d, JH,H¼6.8 Hz, 3H, Me,
3JH,H¼6.8 Hz, 3H, Me, A), 1.37 (d, 3JH,H¼7.0 Hz, 3H, Me,
3
3
3
A), 1.37 (d, JH,H¼7.0 Hz, 3H, Me, B), 0.92 (d, JH,H
¼
B), 1.15–1.05 (m, 1H, HA–C(3) (Cp)), 0.933 (d, JH,H
¼
6.6 Hz, 6H, Me (iBu)); 13C NMR (100 MHz, CDCl3):
d¼178.6 (s, CvO), 172.67 (s, CvO, A), 172.58 (s, CvO,
B), 75.6 (d, C(2), A), 75.4 (d, C(2), B), 71.2 (t, CH2O, A),
71.1 (t, CH2O, B), 60.6 (d, C(1) (Cp), A), 60.4 (d, C(1) (Cp),
B), 27.6 (d, CH (iBu), A), 27.5 (d, CH (iBu), B), 21.1 (d,
C(2) (Cp), A), 20.9 (d, C(2) (Cp), B), 18.82 (q, Me (iBu), A),
18.80 (q, Me (iBu), B), 18.4 (q, Me, A), 18.1 (q, Me, B),
16.5 (dd, C(3) (Cp), A), 15.6 (dd, C(3) (Cp), B); MS (e.i.,
70 eV): m/z¼230 (1%), 213 (2%), 201 (2%), 185 (4%), 174
(3%), 156 (3%), 147 (7%), 129 (12%), 117 (5%), 101 (9%),
91 (20%), 85 (16%), 69 (21%), 57 (100%); HRMS Calcd for
C11H18O5: 230.1154. Found: 230.1155.
6.8 Hz, 6H, Me (iBu), A), 0.926 (d, JH,H¼6.6 Hz, 6H, Me
(iBu), B), 0.80–0.74 (m, 1H, HB–C(3) (Cp)); 13C NMR
(100 MHz, CDCl3): d¼173.3 (s, CvO, A), 173.1 (s, CvO,
B), 156.2 (s, CvO (Boc)), 79.5 (s, tBu), 74.61 (d, C(2), A),
74.55 (d, C(2), B), 70.86 (t, CH2O, A), 70.77 (t, CH2O, B),
59.1 (d, C(1) (Cp), A), 58.8 (d, C(1) (Cp), B), 29.5 (d, C(2)
(Cp)), 28.19 (q, tBu, A), 28.17 (q, tBu, B), 27.62 (d, CH
(iBu), A), 27.58 (d, CH(iBu), B), 18.89 (q, Me (iBu), A),
18.87 (q, Me (iBu), B), 18.6 (q, Me, A), 18.1 (q, Me, B),
15.0 (dd, C(3) (Cp)); MS (e.i., 70 eV): m/z¼245 (4%), 228
(1%), 200 (6%), 172 (4%), 144 (6%), 130 (11%), 116
(48%), 100 (19%), 72 (100%), 57 (100%). Anal. Calcd for
3

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2205
C15H27O5N (301.189): C, 59.78; H, 9.03; N, 4.65. Found: C,
59.86; H, 9.18; N, 4.52.
(Cp)); MS (e.i., 70 eV): m/z¼245 (1%), 230 (1%), 189 (7%),
172 (1%), 144 (5%), 128 (1%), 116 (79%), 100 (9%), 72
(79%), 57 (100%); HRMS Calcd for C11H19O5N: 245.1263.
Found: 245.1262.
3.1.6. cis-Isobutyl (2R)-2-({2-[tert-butoxycarbonyl)amino]-
cyclo-propyl}oxy)propanoate (7). To a solution of 5
(1.90 g, 8.25 mmol) in triethylamine (1.26 g, 12.48 mmol)
and tert-butanol (3.07 g, 41.49 mmol) under argon
diphenylphosphorylazide (2.75 g, 9.99 mmol) was added
and stirring at 70 8C was continued for another 2 h, then the
solvents were removed and the residue was subjected to
chromatography (silica gel, hexane/ethyl acetate, 6:1) to
afford 7 (0.5 g, 20%) and 6 (0.13 g, 5%, for data: vide supra)
as an oil; Rf (hexane/ethyl acetate, 3:2) 0.46; IR (film):
n¼3375m, 2970s, 2875m, 2150w, 1790w, 1715s, 1505s,
1470m, 1455m, 1390m, 1365s, 1255s, 1175s, 1135s,
3.1.8. cis-(2R)-2-({2-[(tert-Butoxycarbonyl)amino]cyclo-
propyl}oxy)propanoic acid (9). Following the synthesis of
8 from 7 (480 mg, 1.59 mmol) in ethanol (5 ml) and KOH
(280 mg, 5.00 mmol) in ethanol (7 ml) 9 (400 mg, 100%)
was obtained as a brown oil that was used direct for the next
step; IR (KBr): n¼3360s, 2980s, 2935m, 1720s, 1680s,
1520s, 1460m, 1395m, 1370s, 1325m, 1285s, 1250s, 1170s,
1
1135s, 1105m, 1085s, 1055m, 1035m, 1005m cm21; H
NMR (400 MHz, CDCl3): d¼5.04 (br, 1H, NH, A), 4.80 (br,
3
1H, NH, B), 4.23 (q, JH,H¼6.5 Hz, 1H, H–C(2)), 3.47–
1075m, 1055m, 985m cm21
;
1H NMR (400 MHz,
3.39 (m, 1H, H–C(1) (Cp)), 2.70–2.59 (m, 1H, H–C(2)
3
CDCl3): d¼5.32 (br, 1H, NH, A), 4.78 (br, 1H, NH, B),
(Cp)), 1.45 (d, JH,H¼6.6 Hz, 3H, Me), 1.448 (s, 9H, tBu),
3
3
4.19 (q, JH,H¼6.7 Hz, 1H, H–C(2), A),), 4.11 (q, JH,H
¼
1.00–0.95 (m, 1H, HA–C(3) (Cp)), 0.69–0.60 (m, 1H, HB–
C(3) (Cp)); 13C NMR (100 MHz, CDCl3): d¼176.3 (s,
CvO), 155.8 (s, CvO (Boc)), 79.9 (s, tBu), 75.3 (d, C(2),
A), 75.0 (d, C(2), B), 54.9 (d, C(1) (Cp)), 28.4 (q, tBu), 27.4
(d, C(2) (Cp)), 18.3 (q, Me, A), 18.0 (q, Me, B), 13.5 (dd,
C(3) (Cp), A), 12.5 (dd, C(3) (Cp), B); MS (e.i., 70 eV): m/
z¼189 (4%), 172 (3%), 144 (4%), 126 (3%), 116 (57%), 100
(5%), 72 (49%), 57 (100%); HRMS Calcd for C11H19O5N:
245.1263. Found: 245.1262.
6.8 Hz, 1H, H–C(2), B), 3.99–3.87 (m, 2H, CH2O),
3.43–3.39 (m, 1H, H–C(1) (Cp)), 2.70–2.65 (m, 1H,
H–C(2) (Cp)), 2.00–1.90 (m, 1H, CH (iBu)), 1.44 (s, 9H,
3
tBu, A), 1.43 (s, 9H, tBu, B), 1.40 (d, JH,H¼6.8 Hz, 3H,
3
Me), 0.925 (d, JH,H¼6.6 Hz, 6H, Me (iBu), A), 0.923
3
(d, JH,H¼6.6 Hz, 6H, Me (iBu), B), 0.89–0.76 (m, 1H,
HA–C(3) (Cp)), 0.64–0.54 (m, 1H, HB–C(3) (Cp)); 13C
NMR (50 MHz, CDCl3): d¼172.9 (s, CvO), 156.8 (s,
CvO (Boc)), 79.2 (s, tBu), 75.5 (d, C(2), A), 75.2 (d, C(2),
B), 71.0 (t, CH2O, A), 70.8 (t, CH2O, B), 54.7 (d, C(1)
(Cp)), 28.3 (q, tBu, A), 28.2 (q, tBu, B), 27.6 (d, CH (iBu)),
27.4 (d, C(2) (Cp)), 18.9 (q, Me (iBu)), 18.5 (q, Me, A), 18.4
(q, Me, B), 13.5 (dd, C(3) (Cp), A), 12.4 (dd, C(3) (Cp), B);
MS (e.i., 70 eV): m/z¼245 (4%), 228 (1%), 200 (3%), 172
(3%), 144 (12%), 130 (9%), 116 (25%), 100 (9%), 85 (5%),
72 (90%), 57 (100%). Anal. Calcd for C15H27O5N
(301.189): C, 59.78; H, 9.03; N, 4.65. Found: C, 59.88; H,
9.16; N, 4.69.
3.1.9. Benzyl N-{trans-(2R)-2[2(tert-butoxycarbonyl-
amino)cyclopropyloxy]propionyl}-L-alanyl-D-isogluta-
minate (10). To a solution of Boc-L-alanyl-D-isoglutamin-
g-benzylester (40 mg, 1.57 mmol, Bachem) in abs. ethyl
acetate (4 ml) a solution of hydrochloric acid in abs. ethyl
acetate (ca. 3.6 N by titration, 2.7 ml, 9.7 mmol) was added
and stirred at ambient temperature for 2 h, the volatiles were
removed under reduced pressure and the semi-solid residue
used in the next step without any further purification. To a
solution of 8 (350 mg, 1.43 mmol) in abs. ethyl acetate
(6 ml) and abs. DMF (6 ml) under argon at 0 8C N-methyl-
morpholine (NMM, 159 mg, 1.57 mmol) was added, the
mixture cooled to 215 8C and isobutyl chloroformate
(214 mg, 1.57 mmol) was added. Stirring at this temperature
was continued for another 5 min and then a solution of L-
alanyl-D-isoglutamine-g-benzylester hydro-chloride (vide
supra, 539 mg, 1.57 mmol) in NMM (318 mg, 3.14 mmol),
ethyl acetate (4 ml) and DMF (2 ml) was added. Stirring
was continued for another 18 h at room temperature, the
solvents were removed under reduced pressure, water
(20 ml) was added and the aq. phase extracted with ethyl
acetate (4£40 ml). The combined organic phases were dried
(Na2SO4), the solvents were removed and the residue was
subjected to chromatography (silica gel, ethyl acetate/
methanol, 12:1) and 10 (660 mg, 86%) was obtained as a
white amorphous solid; Rf (ethyl acetate/methanol 10:1)
0.4; IR (KBr): n¼3410m, 2980w, 1665s, 1520s, 1455m,
1365m, 1255m, 1165s cm21; 1H NMR (400 MHz, CDCl3):
d¼7.52 (br, 1H, NH), 7.37–7.28 (m, 5H, Ph), 7.10 (d,
3JH,H¼7.0 Hz, 1H, NH, A), 7.09 (d, 3JH,H¼8.0 Hz, 1H, NH,
B), 6.82 (br, 1H, CONH2), 5.41 (br, 1H, CONH2), 5.11 (AB
3.1.7. trans-(2R)-2-({2-[(tert-Butoxycarbonyl)amino]-
cyclo-propyl}oxy)propanoic acid (8). To a solution of 6
(0.5 g, 1.66 mmol) in ethanol (8 ml) at 0 8C a solution of
KOH (0.3 g, 5.36 mmol) in ethanol (8 ml) was added, and
the mixture stirred for 2 h at room temperature. The solvents
were removed in vacuo, water (15 ml) was added to the oily
residue and the pH adjusted to 3 by the careful addition of
10% aq. hydrochloric acid. The aq. phase was extracted with
diethyl ether (2£20 ml) and ethyl acetate (2£20 ml), the
combined organic phases were dried (Na2SO4), and the
solvents removed to afford 8 (0.42 g, 100%) as a solid that
was used in the next step without any further purification; IR
(film): n¼3340m, 2980s, 2935m, 2360w, 1715s, 1515s,
1455s, 1395s, 1370s, 1255s, 1220s, 1165s, 1135s, 1055s,
950w cm21; 1H NMR (400 MHz, CDCl3): d¼4.63 (br, 1H,
NH), 4.48–4.40 (m, 1H, H–C(2), A), 4.36–4.28 (m, 1H,
H–C(2), B), 3.47–3.39 (m, 1H, H–C(1) (Cp)), 2.72–2.68
(m, 1H, H–C(2) (Cp), A), 2.61–2.58 (m, 1H, H–C(2) (Cp),
3
B), 1.45 (d, JH,H¼7.0 Hz, 3H, Me, A), 1.431 (s, 9H, tBu,
3
A), 1.426 (s, 9H, tBu, B), 1.42 (d, JH,H¼6.8 Hz, 3H, Me,
B), 1.19–1.07 (m, 1H, HA–C(3) (Cp)), 0.84–0.78 (m, 1H,
HB–C(3) (Cp)); 13C NMR (125 MHz, CDCl3): d¼176.8 (s,
CvO, A), 176.4 (s, CvO, B), 156.3 (s, CvO (Boc)), 80.0
(s, tBu), 74.5 (d, C(2)), 59.1 (d, C(1) (Cp), A), 58.9 (d, C(1)
(Cp), B), 29.5 (d, C(2) (Cp), A), 29.3 (d, C(2) (Cp), B), 28.3
(q, tBu), 18.5 (q, Me, A), 18.0 (q, Me, B), 15.1 (dd, C(3)
2
system, JH,H¼12.3 Hz, 2H, CH2Ph), 4.70 (br, 1H, NH
(Boc), A), 4.63 (br, 1H, NH (Boc), B), 4.46–4.39 (m, 1H,
CH (iGln)), 4.30–4.15 (m, 1Hþ1H, CH (Lac), CH (Ala)),
3.40–3.36 (m, 1H, H–C(1) (Cp), A), 3.36–3.32 (m, 1H, H–
C(1) (Cp), B), 2.71–2.66 (m, 1H, H–C(2) (Cp), A), 2.61–

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2206
2.54 (m, 1Hþ1H, HA–C(4) (iGln), H–C(2) (Cp), B), 2.48–
2.41 (m, 1H, HB–C(4) (iGln)), 2.26–2.18 (m, 1H, HA–C(3)
(iGln)), 2.06–1.99 (m, 1H, HB–C(3) (iGln)), 1.41 (s, 9H,
(4%), 270 (4%), 255 (23%), 237 (20%), 192 (39%), 127
(100%). Anal. Calcd for C26H38O8N4 (534.269): C, 58.41;
H, 7.16; N, 10.48. Found: C, 58.38; H, 6.98; N, 10.69.
3
tBu), 1.37 (d, JH,H¼6.8 Hz, 3H, Me), 1.36 (d,
3
3JH,H¼7.0 Hz, 3H, Me), 1.35 (d, JH,H¼7.0 Hz, 3H, Me),
3.1.11. Benzyl N-{trans-(2R)-2[2-acetylamino-cyclopro-
pyloxy]propionyl}-L-alanyl-D-isoglutaminate (12). A sol-
ution of 10 (600 mg, 1.12 mmol) in ethyl acetate (7 ml) was
treated with a solution of hydrochloric acid in ethyl acetate
(ca. 3.6 N by titration, 5 ml, 18 mmol). After stirring for 3 h
at room temperature all volatiles were removed under
diminished pressure. The residue was suspended in a
mixture of triethylamine (963 mg, 9.5 mmol) and CH2Cl2
(9 ml), cooled to 0 8C and a cold solution of acetyl chloride
(264 mg, 3.4 mmol) in CH2Cl2 (3 ml) was added dropwise,
stirring was continued for 14 h at room temperature, the
solvents were removed and water (30 ml) was added to
the residue. The solution was extracted with ethyl acetate
(4£40 ml), the combined organic phases were dried
(Na2SO4), the solvents removed, and the residue was
subjected to chromatography (silica gel, ethyl acetate/
methanol, 10:1) to afford diastereomers 12a (125 mg, 23%)
and 12b (165 mg, 31%) together with a mixture of 12a/12b
(118 mg, 22%).
3
1.33 (d, JH,H¼6.6 Hz, 3H, Me), 1.10–1.02 (m, 1H, HA–
C(3) (Cp)), 0.81–0.74 (m, 1H, HB–C(3) (Cp)); 13C NMR
(100 MHz, CDCl3): d¼173.8 (s, CvO), 173.5 (s, CvO),
173.4 (s, CvO), 172.8 (s, CvO), 156.8 (s, CvO (Boc), A),
156.6 (s, CvO (Boc), B), 135.8 (s, Ph), 128.6 (d, Ph),
128.34 (d, Ph), 128.29 (d, Ph), 79.9 (s, tBu), 76.2 (d, C(2)
(Lac), A), 75.9 (d, C(2) (Lac), B), 66.5 (t, CH2Ph), 59.2 (d,
C(1) (Cp)), 52.3 (d, C(2) (iGln)), 49.3 (d, C(2) (Ala)), 30.5
(t, C(4) (iGln)), 29.4 (d, C(2) (Cp)), 28.3 (q, tBu, A), 28.2 (q,
tBu, B), 26.6 (t, C(3) (iGln)), 17.7 (q, Me), 17.3 (q, Me),
14.9 (dd, C(3) (Cp)); MS (e.i., 70 eV): m/z¼535 (3%), 478
(4%), 461 (2%), 390 (6%), 378 (4%), 363 (31%), 346
(34%), 299 (16%), 255 (36%), 243 (17%), 237 (27%), 215
(16%), 192 (56%), 127 (100%). Anal. Calcd for:
C26H38O8N4 (534.269): C, 58.41; H, 7.16; N, 10.48.
Found: C, 58.49; H, 7.01; N, 10.32.
3.1.10. Benzyl N-{cis-(2R)-2[2(tert-butoxycarbonyl-ami-
no)cyclopropyloxy]propionyl}-L-alanyl-D-isoglutami-
nate (11). Following the procedure given for the preparation
of 10 from 9 (390 mg, 1.59 mmol) in abs. ethyl acetate
(6 ml) and abs. DMF (6 ml) and NMM (177 mg,
1.75 mmol), isobutyl chloroformate (239 mg, 1.75 mmol)
and L-alanyl-D-isoglutamin-g-benzylester hydrochloride
[601 mg, 1.75 mmol, obtained from the deprotection of
Data for 12a. White solid; mp: 125–130 8C; Rf (ethyl
acetate/methanol, 3:1) 0.39; [a]D 33.48 (c 0.62, MeOH); IR
(KBr): n¼3405s, 3280s, 3070w, 2930w, 1735m, 1645s,
1545s, 1450m, 1370m, 1295m, 1245m, 1165m, 1095m,
1040w cm21
;
1H NMR (400 MHz, CDCl3): d¼7.74 (d,
3JH,H¼6.6 Hz, 1H, NH), 7.34–7.30 (m, 5H, Ph), 7.25 (br,
1H, NH), 7.00 (br, 1H, NH), 5.93 (br, 1H, NH), 5.67 (br, 1H,
NH), 5.10 (AB system, 2JH,H¼12.3 Hz, 2H, CH2Ph), 4.37–
Boc-L-alanyl-D-isoglutamin-g-benzylester
(712 mg,
1.75 mmol) in abs. ethyl acetate (4 ml) and HCl/ethyl
acetate (ca. 3.6 N by titration, 2.9 ml, 10.0 mmol)] in NMM
(354 mg, 3.5 mmol), ethyl acetate (4 ml) and DMF (4 ml)
followed by chromatography (silica gel, ethyl acetate/
methanol, 12:1) 11 (500 mg, 60%) was obtained as a white
solid; Rf (ethyl acetate/methanol, 10:1) 0.32. In addition,
compound 10 (90 mg, 11%) was isolated; IR (KBr):
n¼3405m, 2980w, 1675s, 1520s, 1455m, 1365m, 1255m,
3
4.34 (m, 1H, CH (iGln)), 4.34 (q, JH,H¼6.6 Hz, 1H, CH
3
(Lac)), 4.16 (qd, JH,H¼6.9 Hz, 1H, CH (Ala)), 3.30–3.26
(m, 1H, H–C(1) (Cp)), 2.67–2.62 (m, 1H, H–C(2) (Cp)),
2.59–2.52 (m, 1H, HA–C(4) (iGln)), 2.49–2.41 (m, 1H,
HB–C(4) (iGln)), 2.25–2.18 (m, 1H, HA–C(3) (iGln)),
2.09–1.99 (m, 1H, HB–C(3) (iGln)), 1.93 (s, 3H, Ac), 1.33
3
3
(d, JH,H¼7.0 Hz, 3H, Me (Ala)), 1.30 (d, JH,H¼6.6 Hz,
3H, Me (Lac)), 1.16–1.10 (m, 1H, HA–C(3) (Cp)), 0.90–
0.82 (m, 1H, HB –C(3) (Cp)); 13C NMR (100 MHz,
CD3OD): d¼176.3 (s, CvO), 175.6 (s, CvO), 175.4 (s,
CvO), 175.0 (s, CvO), 174.3 (s, CvO), 137.7 (s, Ph),
129.7 (d, Ph), 129.3 (d, Ph), 77.0 (d, C(2) (Lac)), 67.4 (t,
CH2Ph), 59.0 (d, C(1) (Cp)), 53.6 (d, C(2) (iGln)), 50.7 (d,
C(2) (Ala)), 31.4 (t, C(4) (iGln)), 29.7 (d, C(2) (Cp)), 27.9 (t,
C(3) (iGln)), 22.5 (q, Ac), 18.7 (q, Me), 17.7 (q, Me), 15.0
(dd, C(3) (Cp)); MS (e.i., 70 eV): m/z¼476 (3%), 459 (1%),
432 (3%), 368 (1%), 363 (7%), 346 (17%), 328 (1%), 300
(1%), 292 (1%), 275 (1%), 255 (20%), 241 (32%), 237
(23%), 213 (46%), 192 (41%), 127 (100%). Anal. Calcd for
C23H32O7N4 (476.227): C, 57.97; H, 6.77; N, 11.76. Found:
C, 57.76; H, 6.70; N, 11.55.
1
1170s cm21; H NMR (500 MHz, CDCl3): d¼7.47–7.42
(m, 1Hþ1H, NH (iGln), NH (Ala), A), 7.34–7.26 (m,
5Hþ1H, Ph, NH (Ala), B), 6.79 (br, 1H, CONH2), 5.96 (br,
2
1H, CONH2), 5.08 (AB system, JH,H¼12.3 Hz, 2H,
CH2Ph), 5.03 (br, 1H, NH), 4.46–4.42 (m, 1H, CH
(iGln)), 4.38–4.35 (m, 1H, CH (Ala)), 4.06 (q,
3
3JH,H¼7.0 Hz, 1H, CH (Lac), A), 4.02 (q, JH,H¼7.0 Hz,
1H, CH (Lac), B), 3.34–3.31 (m, 1H, H–C(1) (Cp)), 2.63–
2.60 (m, 1H, H–C(2) (Cp)), 2.60–2.48 (m, 1H, HA–C(4)
(iGln)), 2.45–2.39 (m, 1H, HB–C(4) (iGln)), 2.21–2.16 (m,
1H, HA–C(3) (iGln)), 2.01–1.95 (m, 1H, HB–C(3) (iGln)),
1.42 (s, 9H, tBu, A), 1.41 (s, 9H, tBu, B), 1.38–1.34 (m, 6H,
Me (Ala), Me (Lac)), 0.95–0.91 (m, 1H, HA–C(3) (Cp)),
0.62–0.59 (m, 1H, HB–C(3) (Cp)); 13C NMR (100 MHz,
CDCl3): d¼173.8 (s, CvO), 173.5 (s, CvO), 172.8 (s,
CvO), 157.1 (s, CvO (Boc)), 135.8 (s, Ph), 128.7 (d, Ph),
128.4 (d, Ph), 128.3 (d, Ph), 79.8 (s, tBu), 76.9 (d, C(2)
(Lac)), 66.58 (t, CH2Ph, A), 66.57 (t, CH2Ph, B), 54.64 (d,
C(1) (Cp), A), 54.60 (d, C(1) (Cp), B), 52.3 (d, C(2) (iGln)),
49.1 (d, C(2) (Ala), A), 49.0 (d, C(2) (Ala), B), 30.5 (t, C(4)
(iGln)), 28.2 (q, tBu), 26.8 (t, C(3) (iGln)), 18.0 (q, Me),
17.4 (q, Me), 12.9 (dd, C(3) (Cp), A), 12.4 (dd, C(3) (Cp),
B); MS (e.i., 70 eV): m/z¼535 (1%), 514 (8%), 488 (1%),
435 (1%), 390 (3%), 370 (4%), 363 (6%), 346 (12%), 299
Data for 12b. Mp: 172.5–175.5 8C; Rf (ethyl acetate/
methanol 3:1) 0.35; [a]D 13.38 (c 0.63, MeOH); IR (KBr):
n¼3405s, 3280s, 3070w, 2930w, 1735m, 1645s, 1545s,
1450m, 1370m, 1295m, 1245m, 1165m, 1095m,
1040w cm21
;
1H NMR (400 MHz, CDCl3): d¼7.69 (d,
3JH,H¼6.4 Hz, 1H, NH), 7.36–7.30 (m, 5Hþ1H, Ph, NH),
6.91 (br, 1H, NH), 5.83 (br, 1H, NH), 5.68 (br, 1H, NH),
5.09 (AB system, JH,H¼12.4 Hz, 2H, CH2Ph), 4.43–4.38
2
(m, 1H, CH (iGln)), 4.25–4.19 (m, 1Hþ1H, CH (Ala), CH

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2207
(Lac)), 3.31–3.28 (m, 1H, H–C(1) (Cp)), 2.78–2.75 (m,
1H, H–C(2) (Cp)), 2.58–2.50 (m, 1H, HA–C(4) (iGln)),
2.48–2.40 (m, 1H, HB–C(4) (iGln)), 2.26–2.19 (m, 1H,
HA–C(3) (iGln)), 2.05–1.95 (m, 1H, HB–C(3) (iGln)), 1.90
(s, 3H, Ac), 1.34 (d, 3JH,H¼6.8 Hz, 3Hþ3H, Me (Ala), Me
(Lac)), 1.11–1.06 (m, 1H, HA–C(3) (Cp)), 0.80–0.75 (m,
1H, HB–C(3) (Cp)); 13C NMR (100 MHz, CD3OD): d¼
176.3 (s, CvO), 175.9 (s, CvO), 175.3 (s, CvO), 174.9 (s,
CvO), 174.4 (s, CvO), 137.7 (s, Ph), 129.7 (d, Ph), 129.3
(d, Ph), 77.3 (d, C(2) (Lac)), 67.4 (t, CH2Ph), 59.5 (d, C(1)
(Cp)), 53.6 (d, C(2) (iGln)), 50.7 (d, C(2) (Ala)), 31.4 (t,
C(4) (iGln)), 29.7 (d, C(2) (Cp)), 27.9 (t, C(3) (iGln)), 22.4
(q, Ac), 18.5 (q, Me), 17.8 (q, Me), 14.6 (dd, C(3) (Cp)); MS
(e.i., 70 eV): m/z¼476 (3%), 459 (1%), 432 (3%), 368 (1%),
363 (7%), 346 (17%), 328 (1%), 300 (1%), 292 (1%), 275
(1%), 255 (20%), 241 (32%), 237 (23%), 213 (46%), 192
(41%), 127 (100%). Anal. Calcd for C23H32O7N4 (476.227):
C, 57.97; H, 6.77; N, 11.76. Found: C, 57.84; H, 6.85; N,
11.61.
propionyl-L-alanyl-D-isoglutamine (14a). Hydrogenolysis
of 12a (90 mg, 0.19 mmol) in ethanol (15 ml) with Pd/C
(10%, 20 mg) was performed for 6 h at 3 bar pressure. After
the completion of the reaction the catalyst was filtered off,
the solvent removed and the residue purified by chroma-
tography (silica gel, chloro-form/methanol/acetic acid,
70:25:5) to afford 14a (62 mg, 85%) as a white solid; mp:
200–208 8C (decomp.); Rf (CHCl3/MeOH/AcOH, 70:25:5)
0.30; [a]D 30.68 (c 0.64, MeOH); IR (KBr): n¼3410s,
1660s, 1540s, 1430s, 1300m, 1180w, 1130w, 1100w,
1050w, 1020w cm21 1H NMR (400 MHz, DMSO-d6):
;
3
d¼8.51 (br, 1H, NH), 8.15 (br, 1H, NH), 8.01 (d, JH,H
¼
7.4 Hz, 1H, NH), 7.29 (br, 1H, NH), 7.03 (br, 1H, NH), 4.23
(qd, 3JH,H¼7.1 Hz, 1H, CH (Ala)), 4.14 (q, 3JH,H¼6.64 Hz,
1H, CH (Lac)), 4.11–4.05 (m, 1H, CH (iGln)), 3.38–3.33
(m, 1H, H–C(1) (Cp)), 2.60–2.57 (m, 1H, H–C(2) (Cp)),
2.10–2.04 (m, 2H, H–C(4) (iGln)), 1.91–1.65 (m, 2H,
3
HA–C(3) (iGln)), 1.75 (s, 3H, Ac), 1.23 (d, JH,H¼7.0 Hz,
3
3H, Me), 1.19 (d, JH,H¼6.8 Hz, 3H, Me), 0.99–0.94 (m,
1H, HA–C(3) (Cp)), 0.72–0.68 (m, 1H, HB–C(3) (Cp)); 13
C
3.1.12. Benzyl N-{cis-(2R)-2[2-acetylamino-cyclopropyl-
oxy] propionyl}-L-alanyl-D-isoglutaminate (13). Follow-
ing the procedure for the synthesis of 12 from 11 (265 mg,
0.56 mmol) in abs. ethyl acetate (3 ml), HCl in ethyl acetate
(ca. 3.6 N, 0.6 ml, ca. 2.0 mmol) and CH2Cl2 (5 ml),
triethylamine (505 mg, 5.0 mmol) and a solution of acetyl
chloride (79 mg, 1 mmol) in CH2Cl2 (2 ml) followed by
chromatography (silica gel, ethyl acetate/methanol, 10:1) 13
(171 mg, 65%) was obtained as a white solid; Rf (ethyl
acetate/methanol, 10:1) 0.12; IR (KBr): n¼3415m, 3065w,
2930w, 1730m, 1660s, 1535m, 1450m, 1385m, 1260m,
NMR (100 MHz, CD3OD): d¼176.9 (s, CvO), 175.7 (s,
CvO), 175.1 (s, CvO), 174.9 (s, CvO), 77.0 (d, C(2)
(Lac)), 59.0 (d, C(1) (Cp)), 54.5 (d, C(2) (iGln)), 50.8
(d, C(2) (Ala)), 34.0 (t, C(4) (iGln)), 29.8 (d, C(2) (Cp)),
29.1 (t, C(3) (iGln)), 22.5 (q, Ac), 18.9 (q, Me), 17.6
(q, Me), 15.1 (dd, C(3)); HPLC-MS (ESI, 4.1 kV, 8 ml/min,
N2, methanol): m/z¼849.2 [M2K22H]þ (31%), 425.5
[MK]þ (100%); HRMS Calcd for C16H26O7N4: 386.1801.
Found: 386.1802. Anal. Calcd for C16H26O7N4 (386.180):
C, 49.73; H, 6.78; N, 14.50. Found: C, 49.55; H, 6.50;
N, 14.36.
1170m cm21
;
1H NMR (400 MHz, CDCl3): d¼7.47 (d,
3JH,H¼8.0 Hz, 1H, NH, A), 7.43 (d, 3JH,H¼7.0 Hz, 1H, NH),
7.36–7.28 (m, 5Hþ1H, Ph, NH, B), 6.89 (br, 1H, NH, A),
6.81 (br, 1H, NH, B), 6.33 (br, 1H, NH), 5.98 (br, 1H, NH,
A), 5.95 (br, 1H, NH, B), 5.09 (AB system, 2JH,H¼12.5 Hz,
2H, CH2Ph), 4.45–4.34 (m, 1Hþ1H, CH (iGln), CH (Ala)),
3.1.14. trans-(2R)-2-[2-(Acetylamino)cyclopropyloxy]-
propionyl-L-alanyl-D-isoglutamine (14b). Hydrogenolysis
of 12b (140 mg, 0.29 mmol) in ethanol (15 ml) in the
presence of Pd/C (10%, 20 mg) afforded after chromato-
graphy (silica gel, chloroform/methanol/acetic acid,
70:25:5) 14b (100 mg, 88%) as a white solid; mp: 200–
210 8C (decomp.); Rf (CHCl3/MeOH/AcOH, 70:25:5) 0.30;
[a]D 13.88 (c 0.56, MeOH); IR (KBr): n¼3430s, 2935w,
3
3
4.07 (q, JH,H¼6.7 Hz, 1H, CH (Lac), A), 4.01 (q, JH,H
¼
6.9 Hz, 1H, CH (Lac), B), 3.41–3.37 (m, 1H, H–C(1) (Cp),
A), 3.34–3.32 (m, 1H, H–C(1) (Cp), B), 2.87–2.81 (m, 1H,
H–C(2) (Cp), A), 2.79–2.74 (m, 1H, H–C(2) (Cp), B),
2.58–2.50 (m, 1H, HA–C(4) (iGln)), 2.48–2.40 (m, 1H,
HB–C(4) (iGln)), 2.23–2.14 (m, 1H, HA–C(3) (iGln)),
2.03–1.93 (m, 1H, HB–C(3) (iGln)), 1.98 (s, 3H, Ac, A),
1.96 (s, 3H, Ac, B), 1.38 (d, 3JH,H¼6.8 Hz 3H, Me), 1.35 (d,
3JH,H¼6.4 Hz, 3H, Me), 1.02–0.96 (m, 1H, HA–C(3) (Cp)),
0.65–0.60 (m, 1H, HB–C(3) (Cp)); 13C NMR (100 MHz,
CD3OD): d¼176.0 (s, CvO), 175.5 (s, CvO), 175.4 (s,
CvO), 175.04 (s, CvO), 174.96 (s, CvO), 174.87 (s,
CvO), 174.1 (s, CvO), 137.4 (s, Ph), 129.5 (d, Ph), 129.2
(d, Ph), 77.9 (d, C(2) (Lac), A), 77.8 (d, C(2) (Lac), B), 67.4
(t, CH2Ph), 55.8 (d, C(1) (Cp), A), 55.5 (d, C(1) (Cp), B),
53.6 (d, C(2) (iGln)), 50.5 (d, C(2) (Ala)), 31.4 (t, C(4)
(iGln)), 28.4 (d, C(2) (Cp)), 28.0 (t, C(3) (iGln)), 22.44 (q,
Ac, A), 22.40 (q, Ac, B), 18.9 (q, Me, A), 18.6 (q, Me, B),
18.0 (q, Me), 12.6 (dd, C(3) (Cp), A), 12.0 (dd, C(3) (Cp),
B); MS (e.i., 70 eV): m/z¼476 (1%), 432 (1%), 363 (3%),
346 (5%), 255 (18%), 241 (11%), 213 (20%), 200 (4%), 192
(16%), 127 (100%). Anal. Calcd for: C23H32O7N4
(476.227): C, 57.97; H, 6.77; N, 11.76. Found: C, 57.76;
H, 6.78; N, 11.93.
1655s, 1560s, 1440w, 1300w, 1165w, 1045w cm21 1H
;
NMR (400 MHz, DMSO-d6): d¼8.50 (br, 1H, NH), 8.04
(br, 1H, NH), 7.96 (d, 3JH,H¼7.0 Hz, 1H, NH), 7.35 (br, 1H,
3
NH), 6.99 (br, 1H, NH), 4.25 (qd, JH,H¼6.9 Hz, 1H, CH
(Ala)), 4.10–4.04 (m, 1H, CH (iGln)), 4.09 (q,
3JH,H¼6.64 Hz, 1H, CH (Lac)), 3.34–3.31 (m, 1H,
H–C(1) (Cp), from the measurement in CD3OD), 2.70–
3
2.66 (m, 1H, H–C(2) (Cp)), 1.99 (t, JH,H¼7.2 Hz, 2H,
H–C(4) (iGln)), 1.91–1.82 (m, 1H, HA–C(3) (iGln)),
1.75–1.66 (m, 1H, HB–C(3) (iGln)), 1.74 (s, 3H, Ac),
1.21 (d, 3JH,H¼6.6 Hz, 3Hþ3H, Me (Ala), Me (Lac)), 0.99–
0.95 (m, 1H, HA–C(3) (Cp)), 0.72–0.68 (m, 1H, HB–C(3)
(Cp)); 13C NMR (100 MHz, CD3OD): d¼177.3 (s, CvO),
176.2 (s, CvO), 175.3 (s, CvO), 175.1 (s, CvO), 77.4 (d,
C(2) (Lac)), 59.7 (d, C(1) (Cp)), 54.5 (d, C(2) (iGln)), 50.7
(d, C(2) (Ala)), 34.4 (t, C(4) (iGln)), 29.7 (d, C(2) (Cp)),
29.2 (t, C(3) (iGln)), 22.4 (q, Ac), 18.6 (q, Me), 17.6 (q,
Me), 14.5 (dd, C(3)); HPLC-MS (ESI, 4.1 kV, 8 ml/min, N2,
methanol): m/z¼811.0 [M2K]þ (77%), 425.1 [MK]þ
(100%), 409.4 [MNa]þ (15%), 393.3 [MLi]þ (16%);
HRMS Calcd for C16H26O7N4: 386.1801. Found:
386.1802. Anal. Calcd for C16H26O7N4 (386.180): C,
49.73; H, 6.78; N, 14.50. Found: C, 49.53; H, 6.59; N, 14.68.
3.1.13. trans-(2R)-2-[2-(Acetylamino)cyclopropyloxy]-

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2208
3
3
3.1.15. cis-(2R)-2-[2-(Acetylamino)cyclopropyloxy]pro-
pionyl-L-alanyl-D-isoglutamine (15). Hydrogenolysis of
13 (95 mg, 0.29 mmol) in ethanol (15 ml) in the presence of
Pd/C (10%, 20 mg) followed by chromatography (silica gel,
chloroform/methanol/acetic acid, 70:25:5) afforded 15
(100 mg, 88%) as an amorphous solid; Rf (CHCl3/MeOH/
AcOH, 70:25:5) 0.30; IR (KBr): n¼3425s, 3075w, 2995w,
(q, JH,H¼6.4 Hz, 1H, CH (Lac)), 4.12 (qd, JH,H¼6.9 Hz,
1H, CH (Ala)), 3.30–3.28 (m, 1H, H–C(1) (Cp)), 2.64–
2.60 (m, 1H, H–C(2) (Cp)), 2.58–2.39 (m, 2H, H–C(4)
(iGln)), 2.25–2.17 (m, 1H, HA–C(3) (iGln)), 2.13–2.08 (m,
2H, H–C(2) (Oct)), 2.06–1.95 (m, 1H, HB–C(3) (iGln)),
3
1.59–1.53 (m, 2H, H–C(3) (Oct)), 1.32 (d, JH,H¼7.0 Hz,
3
3H, Me), 1.28 (d, JH,H¼6.6 Hz, 3H, Me), 1.28–1.22 (m,
1655s, 1540m, 1450w, 1375w, 1320s, 1235w, 1170w cm21
;
8H, Oct), 1.13–1.08 (m, 1H, HA–C(3) (Cp)), 0.89–0.79 (m,
3Hþ1H, Me (Oct), HB–C(3) (Cp)); 13C NMR (100 MHz,
CD3OD): d¼178.1 (s, CvO), 176.3 (s, CvO), 175.7 (s,
CvO), 175.4 (s, CvO), 174.4 (s, CvO), 137.7 (s, Ph),
129.7 (d, Ph), 129.3 (d, Ph), 77.0 (d, C(2) (Lac)), 67.5 (t,
CH2Ph), 59.1 (d, C(1) (Cp)), 53.6 (d, C(2) (iGln)), 50.8 (d,
C(2) (Ala)), 36.9 (t, C(2) (Oct)), 32.8 (t, C(3) (Oct)), 31.4 (t,
C(4) (iGln)), 30.2 (t, Oct), 30.0 (t, Oct), 29.7 (d, C(2) (Cp)),
27.9 (t, C(3) (iGln)), 26.8 (t, Oct), 23.6 (t, Oct), 18.7 (q, Me),
17.7 (q, Me), 15.1 (dd, C(3) (Cp)), 14.3 (q, Me (Oct)). Anal.
Calcd for C29H44O7N4 (560.321): C, 62.12; H, 7.91; N,
9.99. Found: C, 62.02; H, 7.71; N, 10.11.
1H NMR (400 MHz, DMSO-d6): d¼13.0–11.0 (very br,
3
1H, COOH), 8.10 (d, JH,H¼7.8 Hz, 1H, NH, A), 8.08 (d,
3JH,H¼8.2 Hz, 1H, NH, B), 7.91 (d, 3JH,H¼4.5 Hz, 1H, NH),
3
7.87–7.85 (m, 1H, NH), 7.70 (d, JH,H¼7.2 Hz, 1H, NH),
3
7.33 (br, 1H, NH), 7.08 (br, 1H, NH), 4.29 (qd, JH,H
¼
6.9 Hz, 1H, CH (Ala), A), 4.28 (qd, 3JH,H¼6.9 Hz, 1H, CH
3
(Ala), B), 4.18–4.14 (m, 1H, CH (iGln)), 3.91 (q, JH,H
¼
3
6.6 Hz, 1H, CH (Lac), A), 3.85 (q, JH,H¼6.8 Hz, 1H, CH
(Lac), B), 3.46–3.41 (m, 1H, H–C(1) (Cp), determined in
CD3OD), 2.62–2.57 (m, 1H, H–C(2) (Cp)), 2.18 (virt.-t,
3JH,H¼7.8 Hz, 2H, H–C(4) (iGln)), 1.98–1.94 (m, 1H,
HA–C(3) (iGln)), 1.84 (s, 3H, Ac, A), 1.78 (s, 3H, Ac, B),
1.74–1.67 (m, 1H, HB–C(3) (iGln)), 1.25 (d, 3JH,H¼6.4 Hz,
Data for 16b. White solid; mp: 135–140 8C; Rf (EtOAc/
MeOH, 10:1) 0.26; [a]D 15.28 (c 1.07, MeOH); IR (KBr):
n¼3395s, 3270s, 3070m, 2930s, 2855m, 1740s, 1650s,
1545s, 1455m, 1375m, 1310m, 1250s, 1165s, 1095m,
3
3
3H, Me), 1.23 (d, JH,H¼6.8 Hz, 3H, Me), 1.18 (d, JH,H
¼
6.8 Hz, 3H, Me), 0.94–0.86 (m, 1H, HA–C(3) (Cp)), 0.68–
0.64 (m, 1H, HB–C(3) (Cp)); 13C NMR (100 MHz,
CD3OD): d¼176.0 (s, CvO), 175.3 (s, CvO), 174.8 (s,
CvO), 77.9 (d, C(2) (Lac), A), 77.8 (d, C(2) (Lac), B), 55.8
(d, C(1) (Cp), A), 55.6 (d, C(1) (Cp), B), 53.8 (d, C(2)
(iGln)), 50.6 (d, C(2) (Ala)), 31.3 (t, C(4) (iGln)), 28.5
(d, C(2) (Cp), A), 28.2 (t, C(3) (iGln)), 28.1 (d, C(2) (Cp),
B), 22.4 (q, Ac), 18.9 (q, Me), 18.6 (q, Me), 18.1 (q, Me),
12.6 (dd, C(3), A), 12.0 (dd, C(3), B); MS (e.i., 70 eV):
m/z¼386 (3%), 369 (1%), 342 (1%), 255 (9%), 241 (6%),
213 (9%), 200 (3%), 184 (4%), 169 (4%), 145 (12%),
127 (100%); HRMS Calcd for C16H26O7N4: 386.1801.
Found: 386.1802. Anal. Calcd for: C16H26O7N4 (386.180):
C, 49.73; H, 6.78; N, 14.50. Found: C, 49.69; H, 6.55;
N, 14.72.
1040m cm21
;
1H NMR (400 MHz, CDCl3): d¼7.81 (d,
3JH,H¼6.3 Hz, 1H, NH), 7.36–7.29 (m, 5H, Ph), 7.14 (d,
3JH,H¼8.0 Hz, 1H, NH), 6.90 (br, 1H, NH), 5.57 (br, 1H,
2
NH), 5.41 (br, 1H, NH), 5.10 (AB system, JH,H¼12.3 Hz,
2H, CH2Ph), 4.44–4.38 (m, 1H, CH (iGln)), 4.27 (q, 3JH,H
¼
3
6.7 Hz, 1H, CH (Lac)), 4.16 (qd, JH,H¼6.7 Hz, 1H, CH
(Ala)), 3.31–3.28 (m, 1H, H–C(1) (Cp)), 2.82–2.79 (m,
1H, H–C(2) (Cp)), 2.60–2.52 (m, 1H, HA–C(4) (iGln)),
2.48–2.40 (m, 1H, HB–C(4) (iGln)), 2.26–2.18 (m, 1H,
3
HA–C(3) (iGln)), 2.09 (virt.-t, JH,H¼7.6 Hz, 2H, H–C(2)
(Oct)), 2.06–1.97 (m, 1H, HB–C(3) (iGln)), 1.59–1.54 (m,
3
2H, H–C(3) (Oct)), 1.35 (d, JH,H¼6.5 Hz, 3H, Me), 1.33
(d, 3JH,H¼6.2 Hz, 3H, Me), 1.28–1.22 (m, 8H, Oct), 1.11–
1.06 (m, 1H, HA–C(3) (Cp)), 0.85 (t, 3JH,H¼6.8 Hz, 3H, Me
(Oct)), 0.78–0.74 (m, 1H, HB–C(3) (Cp)); 13C NMR
(100 MHz, CD3OD): d¼177.5 (s, CvO), 175.9 (s, CvO),
175.4 (s, CvO), 174.9 (s, CvO), 173.9 (s, CvO), 137.3 (s,
Ph), 129.2 (d, Ph), 128.91 (d, Ph), 128.89 (d, Ph), 76.9 (d,
C(2) (Lac)), 67.0 (t, CH2Ph), 59.2 (d, C(1) (Cp)), 53.2 (d,
C(2) (iGln)), 50.2 (d, C(2) (Ala)), 36.4 (t, C(2) (Oct)), 32.4
(t, C(3) (Oct)), 31.0 (t, C(4) (iGln)), 29.7 (t, Oct), 29.6 (t,
Oct), 29.2 (d, C(2) (Cp)), 27.5 (t, C(3) (iGln)), 26.4 (t, Oct),
23.1 (t, Oct), 18.1 (q, Me), 17.3 (q, Me), 14.3 (dd, C(3)
(Cp)), 13.9 (q, Me (Oct)); MS (e.i., 70 eV): m/z¼560 (4%),
543 (19%), 516 (4%), 453 (1%), 363 (1%), 346 (4%), 325
(4%), 297 (21%), 282 (2%), 255 (29%), 237 (4%), 198
(5%), 183 (12%), 127 (100%). Anal. Calcd for C29H44O7N4
(560.321): C, 62.12; H, 7.91; N, 9.99. Found: C, 61.99; H,
7.82; N, 9.76.
3.1.16. Benzyl N-{trans-(2R)-2[2-octanoylamino-cyclo-
propyl-oxy]propionyl}-L-alanyl-D-isoglutaminate (16).
As described for the synthesis of 12 treatment of a solution
of 10 (250 mg, 0.47 mmol) in abs. ethyl acetate (3 ml) with
hydrochloric acid in ethyl acetate (ca. 3.6 N, 1.0 ml, ca.
3.6 mmol) followed by the reaction of the intermediary
hydrochloride in CH2Cl2 (3 ml) with triethylamine (404 mg,
4.0 mmol) and a solution of octanoyl chloride (100 mg,
0.62 mmol) in CH2Cl2 (2 ml) gave after chromatography
(silica gel, ethyl acetate/methanol, 9:1) the diastereomers
16a (70 mg, 27%) and 16b (40 mg, 15%) together with a
mixture 16a/16b (130 mg, 49%).
Data for 16a. White solid; mp: 151–153 8C; Rf (EtOAc/
MeOH 10:1) 0.27; [a]D 34.98 (c 1.07, MeOH); IR (KBr):
n¼3395s, 3270s, 3070m, 2930s, 2855m, 1740s, 1650s,
1545s, 1455m, 1375m, 1310m, 1250s, 1165s, 1095m,
1040m cm21; MS (e.i., 70 eV): m/z¼560 (4%), 543
(19%), 516 (4%), 453 (1%), 363 (1%), 346 (4%), 325
(4%), 297 (21%), 282 (2%), 255 (29%), 237 (4%), 198
(5%), 183 (12%), 127 (100%); 1H NMR (400 MHz, CDCl3):
d¼7.86 (d, 3JH,H¼6.5 Hz, 1H, NH), 7.39 (d, 3JH,H¼8.0 Hz,
3.1.17. Benzyl N-{cis-(2R)-2[2-octanoylamino-cyclopro-
pyloxy]-propionyl}-L-alanyl-D-isoglutaminate (17). Fol-
lowing the procedure given for the synthesis of 12 from 11
(210 mg, 0.39 mmol) in abs. ethyl acetate (3 ml), hydro-
chloric acid in ethyl acetate (ca. 3.6 N, 0.7 ml, ca.
2.5 mmol), triethylamine (394 mg, 3.9 mmol) in CH2Cl2
(3 ml), and a solution of octanoyl chloride (96 mg,
0.59 mmol) in CH2Cl2 (1 ml) followed by chromatography
(silica gel, ethyl acetate/methanol, 16:1!10:1) 17a (60 mg,
1H, NH), 7.35–7.26 (m, 5H, Ph), 6.99 (br, 1H, NH), 6.02
2
(br, 1H, NH), 5.94 (br, 1H, NH), 5.09 (AB system, JH,H
12.4 Hz, 2H, CH2Ph), 4.40–4.33 (m, 1H, CH (iGln)), 4.36
¼

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2209
27%) and 17b (40 mg, 18%) together with a mixture 17a/
17b (95 mg, 43%) were obtained.
226 (4%), 198 (6%), 192 (4%), 181 (4%), 127 (100%). Anal.
Calcd for C29H44O7N4 (560.321): C, 62.12; H, 7.91; N,
9.99. Found: C, 61.98; H, 7.89; N, 10.10.
Data for 17a. White solid; mp: 166–169 8C; Rf (EtOAc/
MeOH, 10:1) 0.27; [a]D 213.38 (c 0.36, MeOH); IR (KBr):
n¼3430s, 3300m, 2930m, 2855w, 1725m, 1650s, 1540m,
1450w, 1385w, 1240w, 1175m cm21; 1H NMR (400 MHz,
CDCl3): d¼7.45 (d, 3JH,H¼7.8 Hz, 1H, NH), 7.35–7.28 (m,
5Hþ1H, Ph, NH), 6.81 (br, 1H, NH), 6.07 (br, 1H, NH),
3.1.18. trans-(2R)-2-[2-(Octanoylamino)cyclopropyloxy]
propionyl-L-alanyl-D-isoglutamine (18a). Hydrogenolysis
of 16a (45 mg, 0.08 mmol) in ethanol (10 ml) in the
presence of Pd/C (10%, 20 mg) followed by chroma-
tography (silica gel, chloroform/methanol/acetic acid,
85:10:5) gave 18a (33 mg, 86%) as a white solid; mp:
200–210 8C (decomp.); Rf (CHCl3/MeOH/AcOH, 85:10:5)
0.35; [a]D 31.88 (c 1.02, MeOH); IR (KBr): n¼3430s,
2930m, 2860w, 1655m, 1615s, 1570s, 1555s, 1420s,
2
5.94 (br, 1H, NH), 5.09 (AB system, JH,H¼12.3 Hz, 2H,
3
CH2Ph), 4.45–4.40 (m, 1H, CH (iGln)), 4.38 (qd, JH,H
¼
3
7.0 Hz, 1H, CH (Ala)), 4.00 (q, JH,H¼6.8 Hz, 1H, CH
(Lac)), 3.40–3.36 (m, 1H, H–C(1) (Cp)), 2.88–2.82 (m,
1H, H–C(2) (Cp)), 2.58–2.50 (m, 1H, HA–C(4) (iGln)),
2.50–2.40 (m, 1H, HB –C(4) (iGln)), 2.23–2.16 (m,
1Hþ2H, HA–C(3) (iGln), H–C(2) (Oct)), 2.03–1.94 (m,
1H, HB–C(3) (iGln)), 1.61–1.58 (m, 2H, H–C(3) (Oct)),
1.36 (d, 3JH,H¼6.8 Hz, 3H, Me), 1.34 (d, 3JH,H¼6.6 Hz, 3H,
Me), 1.29–1.22 (m, 8H, Oct), 1.03–0.98 (m, 1H, HA–C(3)
(Cp)), 0.84 (t, 3JH,H¼6.8 Hz, 3H, Me (Oct)), 0.64–0.59 (m,
1H, HB –C(3) (Cp)); 13C NMR (100 MHz, CD3OD):
d¼178.0 (s, CvO), 176.0 (s, CvO), 175.6 (s, CvO),
175.0 (s, CvO), 174.1 (s, CvO), 137.5 (s, Ph), 129.5 (d,
Ph), 129.2 (d, Ph), 77.7 (d, C(2) (Lac)), 67.5 (t, CH2Ph),
55.7 (d, C(1) (Cp)), 53.6 (d, C(2) (iGln)), 50.6 (d, C(2)
(Ala)), 36.8 (t, C(2) (Oct)), 32.8 (t, C(3) (Oct)), 31.4 (t, C(4)
(iGln)), 30.4 (t, Oct), 30.1 (t, Oct), 28.4 (t, C(3) (iGln)), 28.0
(d, C(2) (Cp)), 27.0 (t, Oct), 23.6 (t, Oct), 19.0 (q, Me), 18.0
(q, Me), 14.4 (q, Me (Oct)), 11.9 (dd, C(3) (Cp)); MS (e.i.,
70 eV): m/z¼560 (5%), 452 (1%), 363 (1%), 346 (3%), 325
(1%), 297 (4%), 282 (1%), 255 (11%), 237 (4%), 226 (4%),
198 (6%), 192 (4%), 181 (4%), 127 (100%). Anal. Calcd for
C29H44O7N4 (560.321): C, 62.12; H, 7.91; N, 9.99. Found:
C, 61.90; H, 7.87; N, 9.74.
1280m, 1050m, 1020m cm21
;
1H NMR (400 MHz,
DMSO-d6): d¼8.67 (br, 1H, NH), 8.12 (br, 1H, NH), 8.02
3
(d, JH,H¼6.6 Hz, 1H, NH), 7.31 (br, 1H, NH), 7.00 (br,
3
1H, NH), 4.22 (qd, JH,H¼6.8 Hz, 1H, CH (Ala)), 4.17 (q,
3JH,H¼6.6 Hz, 1H, CH (Lac)), 4.07–4.02 (m, 1H, CH
(iGln)), 3.38–3.33 (m, 1H, H–C(1) (Cp)), 2.61–2.56 (m,
1H, H–C(2) (Cp)), 2.04–1.97 (m, 2Hþ2H, H–C(4) (iGln),
H–C(2) (Oct)), 1.90–1.70 (m, 2H, H–C(3) (iGln)),
2.11–1.97 (m, 2Hþ1H, H–C(2) (Oct), 1.47–1.42 (m, 2H,
H–C(3) (Oct)), 1.23–1.18 (m, 3Hþ3Hþ8H, Me, Me, Oct),
3
0.99–0.94 (m, 1H, HA–C(3) (Cp)), 0.84 (t, JH,H¼6.6 Hz,
3H, Me (Oct)), 0.71–0.66 (m, 1H, HB–C(3) (Cp)); 13C
NMR (100 MHz, CD3OD): d¼177.8 (s, CvO), 176.9 (s,
CvO), 175.5 (s, CvO), 175.0 (s, CvO), 77.1 (d, C(2)
(Lac)), 59.1 (d, C(1) (Cp)), 54.6 (d, C(2) (iGln)), 50.8
(d, C(2) (Ala)), 36.9 (t, C(2) (Oct)), 32.9 (t, C(3) (Oct)), 32.1
(t, C(4) (iGln)), 30.3 (t, Oct), 30.1 (t, Oct), 29.8 (d, C(2)
(Cp)), 29.2 (t, C(3) (iGln)), 26.9 (t, Oct), 23.7 (t, Oct), 18.8
(q, Me), 17.6 (q, Me), 15.2 (dd, C(3) (Cp)), 14.4 (q, Me
(Oct)); HPLC-MS (ESI, 4.1 kV, 8 ml/min, N2, methanol):
m/z¼509.5 [MK]þ (100%), 493.5 [MNa]þ (2.5%); HRMS
Calcd for C22H38O7N4: 470.2740. Found: 470.2741. Anal.
Calcd for C22H38O7N4 (470.274): C, 56.15; H, 8.14; N,
11.91. Found: C, 55.93; H, 7.95; N, 11.79.
Data for 17b. White solid; mp: 174–175 8C; Rf (EtOAc/
MeOH, 10:1) 0.27; [a]D 29.38 (c 0.48, MeOH); IR (KBr):
n¼3430s, 3300m, 2930m, 2855w, 1725m, 1650s, 1540m,
1450w, 1385w, 1240w, 1175m cm21; 1H NMR (400 MHz,
CDCl3): d¼7.35–7.30 (m, 5Hþ1H, Ph, NH), 7.14 (d,
3JH,H¼7.8 Hz, 1H, NH), 6.79 (br, 1H, NH), 5.87 (br, 1H,
3.1.19. trans-(2R)-2-[2-(Octanoylamino)cyclopropyloxy]
propionyl-L-alanyl-D-isoglutamine (18b). Hydrogenolysis
of 16b (75 mg, 0.13 mmol) in ethanol (10 ml) in the
presence of Pd/C (10%, 20 mg) followed by chromato-
graphy (silica gel, chloroform/methanol/acetic acid,
85:10:5) gave 18b (55 mg, 87%) as a white solid; mp: ca.
200–209 8C (decomp.); Rf (CHCl3/MeOH/AcOH, 85:10:5)
0.35; [a]D 12.58 (c 1.03, MeOH); IR (KBr): n¼3405s,
3070w, 2930m, 2855w, 1740m, 1645s, 1545m, 1450m,
2
NH), 5.44 (br, 1H, NH), 5.10 (AB system, JH,H¼12.3 Hz,
2H, CH2Ph), 4.45–4.41 (m, 1H, CH (iGln)), 4.34 (qd,
3
3JH,H¼7.0 Hz, 1H, CH (Ala)), 4.06 (q, JH,H¼6.7 Hz, 1H,
CH (Lac)), 3.38–3.34 (m, 1H, H–C(1) (Cp)), 2.83–2.77
(m, 1H, H–C(2) (Cp)), 2.62–2.56 (m, 1H, HA–C(4) (iGln)),
2.49–2.40 (m, 1H, HB –C(4) (iGln)), 2.21–2.15 (m,
1Hþ2H, HA–C(3) (iGln), H–C(2) (Oct)), 2.04–1.96 (m,
1H, HB–C(3) (iGln)), 1.62–1.58 (m, 2H, H–C(3) (Oct)),
1.40 (d, 3JH,H¼7.0 Hz, 3H, Me), 1.37 (d, 3JH,H¼6.8 Hz, 3H,
Me), 1.28–1.22 (m, 8H, Oct), 1.03–0.98 (m, 1H, HA–C(3)
(Cp)), 0.85 (t, 3JH,H¼6.9 Hz, 3H, Me (Oct)), 0.61–0.58 (m,
1H, HB –C(3) (Cp)); 13C NMR (100 MHz, CD3OD):
d¼178.5 (s, CvO), 176.3 (s, CvO), 175.8 (s, CvO),
175.2 (s, CvO), 174.4 (s, CvO), 137.7 (s, Ph), 129.7 (d,
Ph), 129.4 (d, Ph), 77.9 (d, C(2) (Lac)), 67.5 (t, CH2Ph),
55.5 (d, C(1) (Cp)), 53.6 (d, C(2) (iGln)), 50.6 (d, C(2)
(Ala)), 36.8 (t, C(2) (Oct)), 32.8 (t, C(3) (Oct)), 31.4 (t, C(4)
(iGln)), 30.2 (t, Oct), 30.1 (t, Oct), 28.02 (t, C(3) (iGln)),
27.98 (d, C(2) (Cp)), 27.0 (t, Oct), 23.6 (t, Oct), 18.6 (q,
Me), 17.9 (q, Me), 14.3 (q, Me (Oct)), 12.5 (dd, C(3) (Cp));
MS (e.i., 70 eV): m/z¼560 (5%), 452 (1%), 363 (1%), 346
(3%), 325 (1%), 297 (4%), 282 (1%), 255 (11%), 237 (4%),
1375w, 1310w, 1245w, 1170w, 1090w cm21 1H NMR
;
3
(400 MHz, CDCl3): d¼7.83 (d, JH,H¼6.3 Hz, 1H, NH),
7.15 (d, 3JH,H¼7.2 Hz, 1H, NH), 6.93 (br, 1H, NH), 5.55 (br,
1H, NH), 5.47 (br, 1H, NH), 4.43–4.39 (m, 1H, CH (iGln)),
3
4.28 (q, JH,H¼6.4 Hz, 1H, CH (Lac)), 4.21 (qd,
3JH,H¼6.7 Hz, 1H, CH (Ala)), 3.32–3.27 (m, 1H, H–C(1)
(Cp)), 2.84–2.79 (m, 1H, H–C(2) (Cp)), 2.55–2.48 (m, 1H,
HA–C(4) (iGln)), 2.44–2.38 (m, 1H, HB–C(4) (iGln)),
2.24–2.16 (m, 1H, HA–C(3) (iGln)), 2.11–1.97 (m,
2Hþ1H, H–C(2) (Oct), HB–C(3) (iGln)), 1.62–1.55 (m,
3
2H, H–C(3) (Oct)), 1.38 (d, JH,H¼6.8 Hz, 3H, Me), 1.36
(d, 3JH,H¼6.6 Hz, 3H, Me), 1.28–1.22 (m, 8H, Oct), 1.12–
1.07 (m, 1H, HA–C(3) (Cp)), 0.85 (t, 3JH,H¼6.8 Hz, 3H, Me
(Oct)), 0.79–0.74 (m, 1H, HB–C(3) (Cp)); 13C NMR
(100 MHz, CD3OD): d¼ 178.0 (s, CvO), 176.4 (s, CvO),
175.9 (s, CvO), 175.4 (s, CvO), 175.1 (s, CvO), 77.4 (d,

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2210
C(2) (Lac)), 59.6 (d, C(1) (Cp)), 53.6 (d, C(2) (iGln)), 50.7
(d, C(2) (Ala)), 36.8 (t, C(2) (Oct)), 32.8 (t, C(3) (Oct)), 31.1
(t, C(4) (iGln)), 30.2 (t, Oct), 30.0 (t, Oct), 29.6 (d, C(2)
(Cp)), 28.0 (t, C(3) (iGln)), 26.8 (t, Oct), 23.6 (t, Oct), 18.5
(q, Me), 17.7 (q, Me), 14.7 (dd, C(3) (Cp)), 14.3 (q, Me
(Oct)); MS (e.i., 70 eV): m/z¼452 (1%), 342 (2%), 325
(3%), 297 (14%), 273 (1%), 255 (14%), 226 (2%), 198
(8%), 183 (9%), 144 (21%), 127 (100%); HRMS Calcd for
C22H38O7N4: 470.2740. Found: 470.2741. Anal. Calcd for
C22H38O7N4 (470.274): C, 56.15; H, 8.14; N, 11.91. Found:
C, 55.97; H, 8.09; N, 11.74.
2.09–1.99 (m, 4H, H–C(4) (iGln), H–C(2) (Oct)), 1.88–
1.82 (m, 1H, HA–C(3) (iGln)), 1.74–1.68 (m, 1H, HB–C(3)
(iGln)), 1.48–1.40 (m, 2H, H–C(3) (Oct)), 1.25–1.21 (m,
6Hþ8H, 2£MeþOct), 0.92–0.87 (m, 1H, HA–C(3) (Cp)),
3
0.84 (t, JH,H¼6.7 Hz, 3H, Me (Oct)), 0.72–0.68 (m, 1H,
HB–C(3) (Cp)); 13C NMR (125 MHz, CD3OD): d¼178.2
(s, CvO), 175.7 (s, CvO), 175.0 (s, CvO), 169.6 (s,
CvO), 77.8 (d, C(2) (Lac)), 55.5 (d, C(1) (Cp)), 54.5 (d,
C(2) (iGln)), 50.6 (d, C(2) (Ala)), 36.9 (t, C(2) (Oct)), 32.9
(t, C(3) (Oct)), 30.3 (t, Oct, C(4) (iGln)), 30.1 (t, Oct), 29.3
(t, C(3) (iGln)), 28.1 (d, C(2) (Cp)), 27.0 (t, Oct), 23.6 (t,
Oct), 18.7 (q, Me), 17.9 (q, Me), 14.4 (q, Me (Oct)), 12.5
(dd, C(3) (Cp)); HPLC-MS (ESI, 4.1 kV, 8 ml/min, N2,
methanol): m/z¼509.3 [MK]þ (n100%); HRMS Calcd for
C22H38O7N4: 470.2740. Found: 470.2741. Anal. Calcd for
C22H38O7N4 (470.274): C, 56.15; H, 8.14; N, 11.91. Found:
C, 56.10; H, 8.24; N, 11.73.
3.1.20. cis-(2R)-2-[2-(Octanoylamino)cyclopropyloxy]
propionyl-L-alanyl-D-isoglutamine (19a). Hydrogenolysis
of 17a (80 mg, 0.14 mmol) in ethanol (20 ml) in the
presence of Pd/C (10%, 20 mg) followed by chromato-
graphy (silica gel, chloroform/methanol/acetic acid,
85:10:5) gave 19a (66 mg, 100%) as a white solid; mp:
198–209 8C (decomp.); Rf (CHCl3/MeOH/AcOH, 85:10:5)
0.20; [a]D 215.58 (c 0.57, MeOH); IR (KBr): n¼3425s,
2930m, 2860w, 1655s, 1545s, 1420s, 1175w, 1025w cm21
;
References and notes
1H NMR (400 MHz, DMSO-d6): d¼8.64 (br, 1H, NH), 8.00
(br, 1H, NH), 7.99 (br, 1H, NH), 7.35 (br, 1H, NH), 6.98 (br,
1H, NH), 4.25 (qd, JH,H¼7.1 Hz, 1H, CH (Ala)), 4.08–
1. Dukor, P.; Tarcsay, L.; Baschang, G. Ann. Rep. Med. Chem.
1979, 14, 146–167.
3
3
4.03 (m, 1H, CH (iGln)), 3.85 (q, JH,H¼6.7 Hz, 1H, CH
2. Lefrancier, P. Fortschr. Chem. Org. Naturstoffe 1982, 40,
1–47.
(Lac)), 3.28–3.24 (m, 1H, H–C(1) (Cp)), 2.66–2.60 (m,
1H, H–C(2) (Cp)), 2.09 (t, JH,H¼7.4 Hz, 2H, H–C(2)
3
3. Freund, J. Adv. Tuberc. Res. 1956, 7, 130–148.
4. Ellouz, F.; Adam, A.; Ciorbaru, R.; Lederer, E. Biochem.
Biophys. Res. Commun. 1974, 59, 1317–1325.
5. Kotani, S.; Watanabe, Y.; Kinoshita, F.; Shimano, T.;
Marisaki, I.; Siba, T.; Kusumoto, S.; Tarumi, Y.; Ikenaka,
K. Biken J. 1975, 18, 105–111.
3
(Oct)), 2.02 (t, JH,H¼7.1 Hz, 2H, H–C(4) (iGln)), 1.90–
1.82 (m, 1H, HA–C(3) (iGln)), 1.74–1.68 (m, 1H, HB–C(3)
(iGln)), 1.51–1.46 (m, 2H, H–C(3) (Oct)), 1.28–1.22 (m,
3Hþ8H, MeþOct), 1.17 (d, 3JH,H¼6.6 Hz, 3H, Me), 0.91–
0.85 (m, 1H, HA–C(3) (Cp)), 0.84 (t, 3JH,H¼6.8 Hz, 3H, Me
(Oct)), 0.72–0.68 (m, 1H, HB–C(3) (Cp)); 13C NMR
(100 MHz, CD3OD): d¼178.2 (s, CvO), 176.5 (s, CvO),
175.8 (s, CvO), 175.2 (s, CvO), 169.6 (s, CvO), 77.8 (d,
C(2) (Lac)), 55.8 (d, C(1) (Cp)), 53.8 (d, C(2) (iGln)), 50.6
(d, C(2) (Ala)), 36.8 (t, C(2) (Oct)), 32.8 (t, C(3) (Oct)), 31.3
(t, C(4) (iGln)), 30.3 (t, Oct), 30.1 (t, Oct), 28.3 (d, C(2)
(Cp)), 28.1 (t, C(3) (iGln)), 27.0 (t, Oct), 23.6 (t, Oct), 18.9
(q, Me), 17.9 (q, Me), 14.3 (q, Me (Oct)), 11.8 (dd, C(3)
(Cp)); HPLC-MS (ESI, 4.1 kV, 8 ml/min, N2, methanol):
m/z¼1487.2 [M3K22H]þ (61%),1017.2 [M2K22H]þ
(28%), 979.3 [M2K]þ (100%), 509.3 [MK]þ (95%), 471.4
[MH]þ (10%); HRMS Calcd for C22H38O7N4: 470.2740.
Found: 470.2741. Anal. Calcd for C22H38O7N4 (470.274):
C, 56.15; H, 8.14; N, 11.91. Found: C, 56.00; H, 8.10; N,
11.99.
6. Parant, M. Springer Semin. Immunopathol. 1979, 2, 101–118.
7. Fraser-Smith, E. B.; Matthews, T. R. Infect. Immun. 1981, 34,
676–683.
8. Krahenbuhl, J. L.; Sharma, S. D.; Ferraresi, R. W.; Remington,
J. S. Infect. Immun. 1981, 31, 716–722.
9. Fidler, I. J. Cancer Res. 1985, 45, 4714–4726.
10. Lefrancier, P.; Lederer, E. Pure Appl. Chem. 1987, 59,
449–454.
11. Masek, K. Methods Find Exp. Clin. Pharmacol. 1986, 8,
97–99.
12. Bahr, G. M.; Chedid, L. Fed. Proc. 1986, 45, 2541–2544.
13. Adam, A.; Lederer, E. Med. Res. Rev. 1984, 4, 111–152.
14. Baschang, G. Tetrahedron 1989, 45, 6331–6360.
15. Hasegawa, A.; Okumura, H.; Kiso, M. Res. Bull. Fac. Agric.
Gifu University 1979, 42, 169–175.
16. Barton, D. H. R.; Camar, J.; Dalko, P.; Gero, S. D.; Quiclet-
Sire, B.; Stu¨tz, P. J. Org. Chem. 1989, 54, 3764–3766.
17. Kikelj, D.; Pecar, S.; Kotnik, V.; Stalc, A.; Wraber-Herzog, B.;
Simcic, S. S.; Ihan, A.; Klamfer, L.; Pavsic, L.; Grahek, R.;
3.1.21. cis-(2R)-2-(2-(Octanoylamino)cyclopropyloxy)
propionyl-L-alanyl-D-isoglutamine (19b). Hydrogenolysis
of 17b (53 mg, 0.095 mmol) in ethanol (40 ml) in the
presence of Pd/C (10%, 20 mg) followed by chroma-
tography (silica gel, chloroform/methanol/acetic acid,
85:10:5) afforded 19b (38 mg, 85%) as a white solid; mp:
196–204 8C (decomp.); Rf (CHCl3/MeOH/AcOH, 85:10:5)
0.20; [a]D 17.48 (c 0.95, MeOH); IR (KBr): n¼3430s,
¨
Suhadolc, E.; Hocevar, M.; Honig, H.; Rogi-Kohlenprath, R.
J. Med. Chem. 1998, 41, 530–539.
18. Gobec, S.; Urleb, U.; Simcic, S.; Wraber, B. Pharmazie 2001,
56, 523–526.
19. Hemmi, K.; Takeno, H.; Okada, S.; Nakaguchi, O.; Kitaura,
Y.; Hashimoto, M. J. Am. Chem. Soc. 1981, 103, 7026–7028.
20. Migliore-Samour, D.; Bouchaudon, J.; Floc’h, F.; Zerial, A.;
Ninet, L.; Werner, G. W.; Jolles, P. A. Life Sci. 1980, 26,
883–888.
2930w, 2855w, 1655s, 1550s, 1420s, 1175w, 1020w cm21
;
1H NMR (400 MHz, DMSO-d6): d¼8.71 (br, 1H, NH), 7.98
(br, 1H, NH), 7.80 (d, 3JH,H¼7.5 Hz, 1H, NH), 7.33 (br, 1H,
3
NH), 6.98 (br, 1H, NH), 4.24 (qd, JH,H¼6.7 Hz, 1H, CH
3
(Ala)), 4.08–4.02 (m, 1H, CH (iGln)), 3.91 (q, JH,H
6.6 Hz, 1H, CH (Lac)), 3.47–3.43 (m, 1H, H–C(1) (Cp),
determined in CD3OD), 2.60–2.55 (m, 1H, H–C(2) (Cp)),
¼
21. Sollner, M.; Pecar, S.; Stalc, A. Eur. J. Med. Chem. 1996, 31,
927–933.
22. Gobec, S.; Urleb, U. Molecules 2002, 7, 394–404.

¨
R. Csuk, G. Gothe / Tetrahedron 60 (2004) 2201–2211
2211
23. Dzierzbicka, K.; Kolodziejczyk, A. M.; Wysocka-Skrzela, B.;
Mysliwski, A.; Sosnowska, D. J. Med. Chem. 2001, 44,
3606–3615.
28. Miki, Y.; Nakamura, N.; Yamakowa, R.; Hachikem, H.;
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Trans. 2 2000, 1819–1831.
24. Dzierzbicka, K.; Kolodziejczyk, A. M. J. Med. Chem. 2003,
46, 183–189.
30. Csuk, R.; von Scholz, Y. Tetrahedron 1994, 50,
10431–10442.
25. Dujardin, G.; Molato, S.; Brown, E. Tetrahedron: Asymmetry
1993, 4, 193–196.
31. Dick, F.; Jenny, T. A. Helv. Chim. Acta 1993, 76, 2951–2957.
32. Kobayashi, S.; Fukuda, T.; Yukimasa, H.; Fujino, M.; Azuma,
I.; Yamamura, Y. Bull. Chem. Soc. Jpn 1984, 57, 3182–3196.
26. Dujardin, G.; Rossignol, S.; Molato, S.; Brown, E.
Tetrahedron 1994, 50, 9037–9050.
27. Dowd, P.; Garner, P.; Schappert, R.; Irngartinger, H.;
Goldman, A. J. Org. Chem. 1982, 47, 4240–4246.