A Constrained Diketopiperazine as a New Scaffold for the Synthesis of Peptidomimetics

Article abstract of DOI:10.1002/(SICI)1099-0690(199805)1998:5<853::AID-EJOC853>3.0.CO;2-F

As a new scaffold for peptidomimetic synthesis, a highly constrained bifunctional diketopiperazine, 4, has been prepared by smooth N-alkylation with tert-butyl bromoacetate. As a first application, we describe herein the synthesis of new peptidomimetics of the Arg-Gly-Asp (RGD) sequence. The product 30, which shows a selective platelet-aggregation inhibiting activity, can be used as a lead for the preparation of more potent products.

Full text of DOI:10.1002/(SICI)1099-0690(199805)1998:5<853::AID-EJOC853>3.0.CO;2-F

FULL PAPER
A Constrained Diketopiperazine as a New Scaffold for the Synthesis of
Peptidomimetics
a
b
a
c
a
`
´ ´
´
Jean-Franc¸ois Pons , Jean-Luc Fauchere , Frederic Lamaty , Annie Molla , and Rene Lazaro*
a
´
´
Laboratoire des Aminoacides, Peptides et Proteines CNRS ESA 5075, Universite Montpellier II ,
´
F-34095 Montpellier Cedex 05, France
Institut de Recherches Servierb,
F-92150 Suresnes, France
Laboratoire dЈEtude de lЈAdhesion Cellulaire, CNRS UMR 5538c,
Institut A. Bonniot, F-38000 Grenoble, France
Received October 9, 1997
Keywords: N-Alkylation / Diketopiperazine building block / Peptidomimetics / RGD analogues
As a new scaffold for peptidomimetic synthesis, a highly con- peptidomimetics of the Arg-Gly-Asp (RGD) sequence. The
strained bifunctional diketopiperazine, 4, has been prepared
product 30, which shows a selective platelet-aggregation in-
by smooth N-alkylation with tert-butyl bromoacetate. As a hibiting activity, can be used as a lead for the preparation of
first application, we describe herein the synthesis of new
more potent products.
Introduction
We chose to synthesize derivatives in which the DKP
scaffold and one of these groups are linked by a spacer of
variable structure and length (Figure 1).
2,5-Diketopiperazines (DKP), formed by cyclization of
dipeptides, are interesting compounds because of their bio-
logical properties (stability to proteolysis)[1] and their rigid
backbone, which can mimic a preferential peptide confor-
mation. Moreover, since these molecules are easily synthe-
sized, they have been used as building blocks in combina-
torial chemistry[2][3]. The use of the bicyclic acid, 2-azabicy-
clo[2.2.2]octane-3-carboxylic acid (Abo) introduced an in-
creased rigidity in the molecule c(Asp-Abo) 1, which has
been used to build efficient antagonists of tachykinin that
exhibit antalgic activities comparable to those of mor-
phine[4]. In order to permit the insertion of this building
block in a sequence (and not only at the N-terminal posi-
tion as in the case of tachykinin), we prepared a bifunc-
tional derivative 4 containing an additional carboxylic acid
group. We developed a non-racemizing, smooth alkylation
of the available ring-nitrogen. This new building block was
first used in the preparation of RGD sequence analogues
that show higher specificity than the parent peptide in the
inhibition of integrin-dependent cell aggregation. More
specifically, we studied the inhibition of the interaction of
Figure 1. General scheme of derivatives studied
Results and Discussion
Synthesis of the N-Alkylated Diketopiperazine Scaffold:
The DKP cyclo[(S)Asp-(S)Abo] (1) was used as the starting
material[10]. After esterification of 1 with SOCl2 in MeOH,
the second function was introduced by N-alkylation of the
DKP 2 (Scheme 1). The best results were obtained by ad-
dition of compound 2 to 1.1 equivalent of NaH in THF.
1.1 equivalent of tert-butyl bromoacetate was then added
to afford the N-alkylated DKP 3 in 75% yield without race-
mization, along with 10% of recovered starting material.
When more than 1.1 equivalent of NaH was used, racemiz-
ation occurred and a diastereomeric mixture was detected
α
IIbβ3 integrin and fibrinogen on the one hand, and of that
between α5β1 integrin and fibrinogen or fibronectin on the
1
other.
by H NMR and HPLC. Product 3 was crystallized and
The general features of the synthesized RGD analogues[5] subjected to X-ray analysis, which confirmed the relative
are described below. According to the literature, it is im- stereochemistry of the asymmetric centers of the DKP ring
portant to synthesize products having a carboxylic acid[6] (Figure 3). The tert-butyl ester was then hydrolysed using
and an ammonium[7][8][9] function within a distance of trifluoroacetic acid (TFA) to give 4 in quantitative yield.
11Ϫ15 A[10]. Moreover, it has been shown that the basic This product was used as a building block for preparing the
˚
function can be either a guanidine[7], which is the natural desired derivatives.
function of the RGD sequence, or an amine[8] such as pi-
Synthesis of the Various Peptidomimetic Compounds: The
first designed molecules incorporated a guanidine function
peridine or a benzamidine moiety[9]
.
Eur. J. Org. Chem. 1998, 853Ϫ859
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1434Ϫ193X/98/0505Ϫ0853 $ 17.50ϩ.50/0
853

`
J.-F. Pons, J.-L. Fauchere, F. Lamaty, A. Molla, R. Lazaro
FULL PAPER
Scheme 1. N-Alkylation of the DKP
Synthesis of 10a, b (Scheme 3): The guanidine function
was incorporated into the amines 7d and 7e as described by
Kim and Qian[11]. Thus, by treatment with N,NЈ-bis(tert-
butyloxycarbonyl)thiourea in the presence of mercuric chlo-
ride and triethylamine in DMF at 0°C, the products 8a and
8b were obtained in good yield. Deprotection of the methyl
ester with NaOH in dioxane and hydrolysis of Boc with
TFA in dichloromethane afforded the products 10a and 10b
in 63 and 48% yield, respectively, based on 8a and 8b.
Scheme 3. Introduction of the guanidine function
i) SOCl2, MeOH, 25°C (quantitative yield); ii) NaH,
BrCH2COOtBu, THF, 25°C (75%); iii) TFA, 25°C (quantitative
yield).
Figure 2. X-ray ORTEP of 3
i) Boc-NHϪC(ϭS)ϪNH-Boc, HgCl2, NEt3, DMF (8a 76%, 8b
88%); ii) NaOH (2 ), H2O, dioxane (9a quantitative yield, 9b
85%); iii) TFA, dichloromethane (10a 63%, 10b 56%).
Synthesis of 15 (Scheme 4): The product 7a was also
functionalized with a guanidine group. In this case, an
amide bond was introduced in the spacer. The glycine ethyl
ester was guanidinated as previously described for 8a, to
give 11 in 72% yield, and was saponified with NaOH in
83% yield. The product 12 was coupled with 7a using DCC
and DMAP to afford 13 in 80% yield. Deprotection of the
two functional groups afforded the product 15 in 58% yield.
and a linear spacer such as ϪNHϪ(CH2)nϪNH, n ϭ 2Ϫ6,
or ϪNHϪCH2ϪCONHϪ(CH2)2ϪNHϪ. The monopro-
tected diamines 5a, d, e were coupled with compound 4
using DCC in the presence of DMAP and were deprotected
with TFA in dichloromethane giving the products 7a, d, e
in yields of 90, 70 and 63%, respectively (Scheme 2).
Scheme 2
Scheme 4
i) Boc-NHϪC(ϭS)ϪNH-Boc, HgCl2, NEt3, DMF (72%); ii)
i) Boc2O, CHCl3 (95%); ii) DCC, DMAP, dichloromethane (6a NaOH (2 ), H2O, dioxane (83%); iii) 7a, DCC, DMAP, dichloro-
90%, 6d 70%, 6e 63%,); iii) TFA, dichloromethane (quantitative methane (80%); iv) NaOH (2 ), H2O, dioxane (75%); v) TFA,
yields).
dichloromethane (78%).
854
Eur. J. Org. Chem. 1998, 853Ϫ859

A Constrained Diketopiperazine as a New Scaffold for the Synthesis of Peptidomimetics
FULL PAPER
Synthesis of 19 (Scheme 5): In order to introduce a more 62% yield, respectively, based on 21a, b, c. The deprotection
rigid spacer, 4,4Ј-diaminobenzophenone was converted to of the two functional groups was achieved in a single step
the monoguanidine derivative 16 in the presence of N,NЈ- using NaOH in dioxane, furnishing the products 24a, b, c
bis(tert-butyloxycarbonyl)thiourea, mercuric chloride and in 53, 67 and 65% yield, respectively.
pyridine in DMF at 0°C in 64% yield[12]. Coupling and
Synthesis of 30 (Scheme 7): The latter of the above com-
deprotections afforded compound 19 in 33% yield based pounds is a benzamidine derivative. The amidine function
on 16.
of the 4-aminobenzamidine was first protected by the ac-
tion of NaOH and benzyl chloroformate in THF to afford
25 in 50% yield.[13] This product was reacted with the anhy-
dride of N-tert-butyloxycarbonylglycine in the presence of
DMAP in dichloromethane to give 26 in 42% yield.[14] The
amine was deprotected with TFA in 74% yield and coupled
with 4 to afford 28 in 31% yield. The saponification of the
methyl ester was carried out as described above for 6, giving
a 73% yield, and subsequent hydrogenolysis afforded 30 in
49% yield.
Scheme 5
Scheme 7
i) Boc-NHϪC(ϭS)ϪNH-Boc, HgCl2, pyridine, DMF (64%); ii) 4,
DCC, DMAP, dichloromethane (44%); iii) NaOH (2 ), H2O, di-
oxane (quantitative yield); iv) TFA, dichloromethane (76%).
Synthesis of 24a, b, c (Scheme 6): In order to introduce
a piperidine group instead of a guanidine, we started our
synthesis from N-fluorenylmethyloxycarbonylisonipecotic
acid (20), which was coupled with the monoprotected di-
amines 5a, b, c using DCC in the presence of DMAP in
dichloromethane to afford the products 21a, b, c in 40, 47
and 50% yield, respectively. These compounds were then
treated with TFA in dichloromethane, and coupled with 4
to afford the corresponding products 23a, b, c in 53, 65 and
i) ZCl, NaOH, THF, H2O (50%); ii) (Boc Gly)2O, DMAP, dichlo-
romethane (42%); iii) TFA, dichloromethane (74%); iv) DCC,
DMAP, dichloromethane (31%); v) NaOH, dioxane, H2O (73%);
vi) H2/Pd(OH)2/C, EtOH (49%).
Scheme 6
Biological Tests: Assays of inhibition of platelet aggre-
gation mediated by fibrinogen were performed according
to Zucker.[13] Platelet-rich plasma (PRP) was prepared by
centrifugation (200g, 10 min) of citrated arterial dog blood.
PRP was incubated for 10 min with a known concentration
of the product to be tested. Thereafter, ADP (10 µ) was
added and the aggregating effect was evaluated photo-
metrically in a CHRONOLOG aggregometer (Coulotron-
ics, France). The anti-aggregating activity was compared to
that of the compound BIBU 52[14] (Figure 3 and Table 1),
a highly active non-peptide fibrinogen-receptor antagonist.
Inhibition of the cell adhesion was measured on HEL
(human erythroleukemia) cells (erythroblastic cell line de-
veloped from a patient who contracted leukemia after treat-
ment for a solid tumor[15]). These cells were shown to grow
in suspension, but to become adherent in the presence of
the matrix proteins fibronectin (through α5β1 integrin bind-
ing) or fibrinogen (through αIIbβ3 integrin binding)[16]. The
i) N-Fmoc isonipecotic acid 20, DCC, DMAP, dichloromethane
(21aϪc 40%, 47%, 50%, resp.); ii) TFA, dichloromethane (22aϪc
in quantitative yield, 80%, 92%, resp.); iii) 4, BOP, DIEA, dichloro-
methane (23aϪc 53%, 65%, 62%, resp.); iv) NaOH (2 ), H2O,
dioxane (24aϪc 53%, 67%, 65%, resp.).
Eur. J. Org. Chem. 1998, 853Ϫ859
855

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J.-F. Pons, J.-L. Fauchere, F. Lamaty, A. Molla, R. Lazaro
FULL PAPER
Figure 3. Structure of BIBU 52
gation and of cell adhesion. Compound 30 showed a mod-
est but selective inhibition of fibrinogen binding. This new
structure may be useful as a lead for the synthesis of new,
more potent, selective RGD mimetics. Furthermore, we in-
tend to use this new constrained DKP scaffold to prepare
new mimetics of other biologically active peptides.
The authors wish to thank Dr. T. J. Verbeuren (Institut de Re-
cherches Servier, Suresnes) for performing the dog platelet aggre-
Table 1. Test of inhibition of platelet aggregation
´
gation assays and Dr. M. Pierrot (Universite de Marseille III) for
the X-ray-spectroscopic analyses.
Compound
IC50 (µ)[a]
10a, 10b, 15, 19, 24a, 24b, 24c
>100
18.0 ± 3.5
0.110 ± 0.007
30
Experimental Section
BIBU 52
General. Ϫ Solvents and Reagents: Unless otherwise stated, com-
mercially available solvents and reagents were used. Dichlorometh-
ane, ethyl acetate and tetrahydrofuran were purified prior to use.
Ϫ NMR Spectroscopy: NMR spectra were recorded on a Bruker
AC-250 or WM 360 instrument in different solvents such as
CDCl3, CD3OD or [D6]DMSO. Chemical shifts are reported in δ
values with TMS as an internal reference and splitting patterns
are indicated as s (singlet), d (doublet), t (triplet), q (quartet), m
(multiplet). Ϫ Mass Spectrometry: Molecular weights were deter-
mined by fast-atom bombardment mass-spectrometry (FAB MS)
using a matrix of m-nitrobenzyl alcohol (NBA) or thioglycerol
(GT) on Jeol JMS DX100 or DX300 spectrometers. High-resolu-
tion mass-spectrometry (HRMS) was employed for new com-
pounds. Ϫ Other Analytical Methods: Melting points were deter-
mined using a Büchi capillary-tube melting-point apparatus and
are not corrected. TLC was performed on silica gel (MerckTM
60F254) using appropriate solvent systems as eluents. Reaction
products were visualized by UV fluorescence (254 nm) or by expo-
sure to iodine vapour. The purity of products was checked by re-
versed-phase HPLC on a Waters Associates instrument equipped
with two 510 model pumps. The absorbance was measured at 214
nm. The flow rate was 1 ml/min. in a Nucleosil 5-C18 column (10
µm, 25 ϫ 250 mm) for semi-preparative HPLC.
[a]
Inhibition concentration in a dog PRP induced by ADP
cells were incubated with various concentrations of the
products. The cell adhesion was measured after 45 min of
incubation at 37°C in microtiter plates coated with matrix
proteins. The wells were washed with PBS and adherent
´
cells were counted after the Promega reactant had been ad-
ded. The optical density (OD) at 490 nm was measured fol-
lowing the manufacturerЈs instructions and calibrated with
the OD of BSA alone. Experiments were performed at least
in triplicate. A peptide containing the RGD sequence was
taken as a positive standard, another containing RGE as a
negative standard (Table 2). All these tests were performed
in triplicate.
Table 2. Test of inhibition of cell adhesion
Compound
Fibrinogen IC50 (µ) Fibronectin IC50 (µ)
10a, 10b, 15, 19, 24a, inactive
24b, 24c
30
GRGDS
GRGES
inactive
General Procedure for Coupling an Amine and a Carboxylic Acid
Derivative. Ϫ Method A: 1 mmol of the amine and 1 mmol of the
carboxylic acid were dissolved in 10 ml of dichloromethane. At
0°C, 1.1 mmol of DCC and 0.1 mmol of DMAP were added. The
reaction mixture was stirred for 15 h at room temperature. The
solvent was then evaporated, the residue was redissolved in AcOEt,
and the resulting solution was washed sequentially with saturated
NaHCO3 solution, H2O, and 1  HCl. The organic layer was dried
over MgSO4 and the solvent was evaporated. The residue was puri-
fied by column chromatography.
27 ± 7
1.8 ± 0.3
inactive
>1000
2 ± 0.5
inactive
The results show that the compounds bearing a guani-
dine (10a, 10b, 15, 19) or an amine (24aϪc) function have
no inhibitory activity on the fibrinogen or the fibronectin.
On the contrary, the benzamidine derivative (30) exhibits
an inhibitory effect on fibrinogen binding, but not on that
of fibronectin. Thus, this compound has a specific effect on
the interaction between the fibrinogen and its receptor GP
IIb/IIIa located on the membrane surface of both the acti-
vated platelets and the HEL cells. This selectivity may be
related to the presence of a benzamidine instead of a guani-
dine moiety[9] and/or to the higher rigidity of the con-
strained DKP compared to the linear RGDS peptide.
Method B: 1 mmol of the amine and 1 mmol of the carboxylic
acid were dissolved in 10 ml of dichloromethane. At 0°C, 1.1 mmol
of BOP and 3 mmol of DIEA were added. The reaction mixture
was stirred for 15 h at room temperature. The solvents were then
evaporated, the residue was redissolved in 20 ml of AcOEt, and the
resulting solution was washed sequentially with saturated NaHCO3
solution, H2O, and 1  HCl. The organic layer was dried over
MgSO4 and the solvent was evaporated.
Conclusion
General Procedure for the Removal of N-tert-Butyloxycarbonyl: 1
mmol of the protected compound was dissolved in 4 ml of dichloro-
methane. 1 ml of TFA was then added and the solution was stirred
for 6 h at room temperature. The solvents were removed by evapo-
ration.
Smooth alkylation of the single free nitrogen atom of the
diketopiperazine of Asp and Abo allows access to a series
compounds in which the aspartyl residue is constrained in
a heterocyclic ring. As a first application, these compounds
were designed to act as mimetics of the tripeptide RGD.
General Procedure for the Removal of N-Benzyloxycarbonyl: 1
Each analogue was tested as an inhibitor of platelet aggre- mmol of the benzyloxycarbonyl- (Z-)protected product was dis-
856 Eur. J. Org. Chem. 1998, 853Ϫ859

A Constrained Diketopiperazine as a New Scaffold for the Synthesis of Peptidomimetics
FULL PAPER
25
solved in 10 ml of EtOH. 200 mg of Pd(OH)2/C was added and the H]ϩ). Ϫ M.p. 146Ϫ148°C. Ϫ [α]D ϭ Ϫ26.1 (c ϭ 1, MeOH). Ϫ
mixture was stirred for 6 h at room temperature under a hydrogen Rf ϭ 0.75 (dichloromethane/AcOEt, 1:1). Ϫ C19H28O6N2 (380.4):
atmosphere (1 atm). The mixture was subsequently filtered through C 59.99, N 7.36, H 7.42; found C 60.09, N 7.55, H 7.57.
Celite and the filtrate was concentrated to dryness.
(3S,6S)-1,4-Diaza-4-carboxymethyl-7,10-ethano-3-methyl-
General Procedure for the Saponification of a Methyl or Ethyl
Ester: 1 mmol of the methyl or ethyl ester was dissolved in 10 ml
of a mixture of dioxane/water (2:1). 0.6 ml of NaOH (2 ) was
added at 0°C. The reaction mixture was stirred for 6 h at room
temperature, and then acidified to pH 3 with HCl (1 ) and ex-
tracted with AcOEt. The combined organic layers were dried over
MgSO4 and the solvent was evaporated.
carboxymethyl-2,5-dionebicyclo[4.4.0]decane (4): 570 mg (1.5
mmol) of 3 was dissolved in 4 ml of TFA at 0°C. The reaction
mixture was stirred for 1 h at 0°C and then for 3 h at room tem-
perature. The solvents were removed under reduced pressure to af-
ford 490 mg of a white powder (quantitative yield). Ϫ 1H NMR
(CDCl3, 250 MHz): δ ϭ 1.47Ϫ1.85 (m, 8 H), 2.60 (m, 1 H), 2.80
(dd, 1 H, J ϭ 5 Hz, J ϭ 17 Hz), 3.12 (dd, 1 H, J ϭ 7 Hz, J ϭ 17
Hz), 3.57 (s, 3 H), 3.65 (d, 1 H, J ϭ 18 Hz), 4.09 (m, 1 H), 4.41
(m, 1 H), 4.58 (t, 1 H), 4.69 (d, 1 H, J ϭ 18 Hz), 9.45 (m, 1 H). Ϫ
MS (GT): m/z ϭ 325 ([M ϩ H]ϩ). Ϫ m.p. 58Ϫ60°C. Ϫ Rf ϭ 0.6
(dichloromethane/AcOEt, 1:1).
General Procedure for Guanidination of an Amine[11]: 2.5 mmol
of thiourea was dissolved in 50 ml of THF. At 0°C, 11.3 mmol of
NaH was added and the mixture was stirred at this temperature
for 5 min, then for 10 min at room temperature, and then again
cooled to 0°C. 5.5 mmol of Boc2O was added and the mixture was
stirred for 30 min at 0°C and for 2 h at room temperature. After
cooling to 0°C once more, the reaction was quenched by the ad-
dition of saturated NaHCO3 solution, the organic phase was sepa-
rated, and washed with brine. The aqueous phase was extracted
with AcOEt. The combined organic layers were dried over MgSO4
and the solvent was evaporated. The product was crystallized from
diethyl ether to afford 550 mg of N,NЈ-bis(tert-butyloxycarbonyl)-
General Synthesis of the N-tert-Butyloxycarbonyldiamines 5: 22
mmol of diamine was stirred in 100 ml of CHCl3. 960 mg of
(Boc)2O (4.4 mmol) dissolved in 50 ml of CHCl3 was added drop-
wise at 0°C. The reaction mixture was stirred for 2 h at room tem-
perature. The solution was filtered and the filtrate was concen-
trated. The oily residue was diluted with AcOEt and washed with
brine. The aqueous layer was extracted with AcOEt. The organic
layers were dried over MgSO4 and the solvent was evaporated.
1
thiourea (80%). Ϫ H NMR (CDCl3, 250 MHz): δ ϭ 1.60 (s). Ϫ
1,2-Diamino-N-tert-butyloxycarbonylethane (5a): 600 mg of 5a
MS (NBA): m/z ϭ 277 ([M ϩ H]ϩ). Ϫ M.p. 120Ϫ122°C (ref.[11]
124Ϫ127°C). Ϫ Rf ϭ 0.92 (dichloromethane/AcOEt, 4:1).
1
was obtained as a colourless oil (85%). Ϫ H NMR (CDCl3, 250
MHz): δ ϭ 1.38 (s, 9 H), 1.60 (m, 2 H), 2.75 (t, 2 H, J ϭ 6.5 Hz),
3.09 (q, 2 H, J ϭ 6.5 Hz), 5.13 (m, 1 H). Ϫ MS (GT): m/z ϭ 161
([M ϩ H]ϩ). Ϫ Rf ϭ 0.45 (MeOH/NH4OH, 99:1).
The amine (1.2 mmol) was then treated with this reagent (1.2
mmol) in 2 ml of DMF. The solution was cooled to Ϫ10°C and
0.6 ml of NEt3 and 1.2 mmol of HgCl2 were added. The reaction
mixture was stirred for 2 h at Ϫ10°C and for 1 h at room tempera-
ture. Then, 20 ml of AcOEt was added and the mixture was filtered
through Celite. The filtrate was washed with brine then with 0.5
 HCl. The organic layer was dried over MgSO4 and the solvent
was evaporated.
1,3-Diamino-N-tert-butyloxycarbonylpropane (5b): 660 mg of 5b
1
was obtained as a colourless oil (86%). Ϫ H NMR (CDCl3, 250
MHz): δ ϭ 1.36 (s, 9 H), 1.56 (q, 2 H, J ϭ 6.5 Hz), 2.26 (m, 2 H),
2.71 (t, 2 H, J ϭ 6.5 Hz), 3.14 (q, 2 H, J ϭ 6 Hz), 5.09 (m, 1
H). Ϫ MS (GT): m/z ϭ 175 ([M ϩ H]ϩ). Ϫ Rf ϭ 0.25 (MeOH/
NH4OH, 99:1).
(3S,6S)-1,4-Diaza-7,10-ethano-3-methylcarboxymethyl-2,5-
dionebicyclo[4.4.0]decane (2): To a suspension of 1 (500 mg, 2
mmol) in 5 ml of MeOH, 0.29 ml (4 mmol) of thionyl chloride was
slowly added at Ϫ10°C. The mixture was stirred for 3 h at room
temperature. The solvents were then removed to give 530 mg of a
white solid (quantitative yield). Ϫ 1H NMR (CDCl3, 250 MHz):
δ ϭ 1.40Ϫ1.75 (m, 8 H), 2.49 (m, 1 H), 2.57 (dd, 1 H, J ϭ 9 Hz,
J ϭ 17 Hz), 3.19 (dd, 1 H, J ϭ 4 Hz, J ϭ 17 Hz), 3.68 (s, 3 H),
1,4-Diamino-N-tert-butyloxycarbonylbutane (5c): 750 mg of 5c
was obtained as a colourless oil (90%). Ϫ H NMR (CDCl3, 250
MHz): δ ϭ 1.32 (m, 13 H), 2.78 (m, 2 H), 2.95 (m, 2 H), 3.76 (m,
1 H), 4.55 (m, 2 H). Ϫ MS (NBA): m/z ϭ 189 ([M ϩ H]ϩ). Ϫ Rf ϭ
0.35 (MeOH/NH4OH, 9:1).
1
1,5-Diamino-N-tert-butyloxycarbonylpentane (5d): 870 mg of 5d
1
was obtained as a colourless oil (98%). Ϫ H NMR (CDCl3, 250
3.98 (m, 1 H), 4.26 (m, 1 H), 4.40 (m, 1 H), 6.38 (m, 1 H). Ϫ MS
MHz): δ ϭ 1.37 (m, 15 H), 2.62 (m, 2 H), 3.03 (m, 2 H), 3.67 (m,
1 H), 4.54 (m, 2 H). Ϫ MS (NBA): m/z ϭ 203 ([M ϩ H]ϩ). Ϫ Rf ϭ
0.41 (MeOH/NH4OH, 9:1).
25
(NBA): m/z ϭ 267 ([M ϩ H]ϩ). Ϫ M.p. 112Ϫ114°C. Ϫ [α]D
ϭ
Ϫ16 (c ϭ 2, MeOH). Ϫ Rf ϭ 0.37 (dichloromethane/AcOEt, 1:1).
(3S,6S)-1,4-Diaza-4-tert-butylcarboxymethyl-7,10-ethano-3-
methylcarboxymethyl-2,5-dionebicyclo[4.4.0]decane (3): To a stirred
suspension of NaH (53 mg, 2.2 mmol) in 15 ml of THF at Ϫ10°C
under argon atmosphere, was added 530 mg of 2 (2 mmol). The
solution was stirred for 10 min at Ϫ10°C, and then 0.36 ml of tert-
butyl bromoacetate (2.2 mmol) was added. The reaction mixture
was stirred for 8 h at room temperature and then acidified with 5
ml of 1  HCl. The phases were separated and the aqueous layer
was extracted with AcOEt. The combined organic layers were dried
over MgSO4 and the solvent was evaporated. The residue was puri-
fied by column chromatography (dichloromethane/AcOEt, 1:1)
yielding 570 mg (75%) of a white powder, which could be crys-
tallized from AcOEt. Ϫ 1H NMR (CDCl3, 250 MHz): δ ϭ 1.43
(m, 9 H), 1.55Ϫ1.79 (m, 8 H), 2.59 (m, 1 H), 2.80 (dd, 1 H, J ϭ 5
Hz, 16 Hz), 3.00 (dd, 1 H, J ϭ 7 Hz, J ϭ 16 Hz), 3.64 (d, 1 H,
J ϭ 18 Hz), 3.70 (s, 3 H), 4.07 (m, 1 H), 4.41 (m, 1 H), 4.55 (d, 1
1,6-Diamino-N-tert-butyloxycarbonylhexane (5e): 950 mg of 5e
was obtained as a slightly coloured oil (quantitative yield). Ϫ 1H
NMR (CDCl3, 250 MHz): δ ϭ 1.30Ϫ1.55 (m, 17 H), 2.58 (m, 2
H), 3.15 (m, 2 H), 3.42 (m, 1 H), 4.58 (m, 2 H). Ϫ MS (NBA):
m/z ϭ 217 ([M ϩ H]ϩ). Ϫ Rf ϭ 0.68 (MeOH/NH4OH, 9:1).
8a: According to general coupling procedure A, 6d was obtained
in 70% yield from 5d and 4, and was then deprotected to afford 7d
in quantitative yield. 7d was guanidinated following the general
procedure to afford 8a in 76% yield as a light-yellow oil. Ϫ 1H
NMR (CDCl3, 250 MHz): δ ϭ 1.42Ϫ1.73 (m, 32 H), 2.55 (m, 1
H), 2.89Ϫ3.18 (m, 6 H), 3.64 (s, 3 H), 3.74Ϫ3.80 (d, 1 H, J ϭ 16
Hz), 4.00Ϫ4.01 (m, 2 H), 4.19Ϫ4.26 (d, 1 H, J ϭ 16 Hz), 4.39 (m,
1 H), 6.26 (m, 1 H), 8.24 (m, 1 H), 11.42 (m, 1 H). Ϫ MS (GT):
m/z ϭ 651 ([M ϩ H]ϩ). Ϫ Rf ϭ 0.24 (dichloromethane/AcOEt, 1:1).
8b: According to general coupling procedure A, 6e was obtained
H, J ϭ 18 Hz), 4.59 (m, 1 H). Ϫ MS (NBA): m/z ϭ 381 ([M ϩ in 63% yield from 5e and 4, and was then deprotected to afford
Eur. J. Org. Chem. 1998, 853Ϫ859 857

`
J.-F. Pons, J.-L. Fauchere, F. Lamaty, A. Molla, R. Lazaro
FULL PAPER
7e in quantitative yield. 7e was guanidinated following the general
procedure to afford 8b in 88% yield as a light-yellow oil. Ϫ 1H
250 MHz): δ ϭ 1.46 (s, 18 H), 4.21 (m, 2 H), 6.58 (d, 2 H, J ϭ 8
Hz), 7.60 (d, 2 H, J ϭ 8 Hz), 7.63 (m, 4 H), 10.45 (m, 1 H), 11.59
NMR (CDCl3, 250 MHz): δ ϭ 1.10Ϫ1.73 (m, 34 H), 2.55 (m, 1 (m, 1 H). Ϫ MS (NBA): m/z ϭ 455 ([M ϩ H]ϩ). Ϫ M.p. 96Ϫ98°C.
H), 2.94Ϫ3.45 (m, 6 H), 3.66 (s, 3 H), 3.74Ϫ3.80 (d, 1 H, J ϭ 16 Ϫ Rf ϭ 0.73 (dichloromethane/AcOEt, 4:1).
Hz), 4.03Ϫ4.05 (m, 1 H), 4.19Ϫ4.26 (d, 1 H, J ϭ 16 Hz), 4.38 (m,
17: According to standard procedure A, compound 16 was cou-
1 H), 4.46 (m, 1 H), 6.25 (m, 1 H), 8.24 (m, 1 H), 11.42 (m, 1 H). Ϫ
pled with 4 to afford 17 in 44% yield as a yellow oil after purifi-
MS (NBA): m/z ϭ 665 ([M ϩ H]ϩ). Ϫ Rf ϭ 0.43 (dichloromethane/
cation by column chromatography (dichloromethane/AcOEt, 4:1).
AcOEt, 1:1).
1
Ϫ H NMR (CDCl3, 250 MHz): δ ϭ 1.47 (s, 9 H), 1.49 (s, 9 H),
1.58Ϫ1.66 (m, 8 H), 2.25 (m, 1 H), 2.83Ϫ3.00 (m, 2 H), 3.56 (s, 3
H), 3.95 (d, 1 H, J ϭ 16.5 Hz), 4.12 (m, 1 H), 4.36Ϫ4.51 (m, 2 H),
4.62 (m, 1 H), 7.58Ϫ7.70 (m, 8 H), 8.90 (m, 1 H), 10.59 (m, 1 H),
11.61 (m, 1 H). Ϫ MS (NBA): m/z ϭ 761 ([M ϩ H]ϩ). Ϫ Rf ϭ
0.45 (dichloromethane/AcOEt, 4:1)
10a: Deprotection of 8a followed by purification by HPLC af-
forded 10a as a light-yellow powder in 63% overall yield. ؊ 1H
NMR (CD3OD, 250 MHz): δ ϭ 1.27Ϫ1.83 (m, 14 H), 2.48 (m, 1
H), 2.79 (dd, 1 H, J ϭ 4 Hz, J ϭ 16 Hz), 2.97 (dd, 1 H, J ϭ 7 Hz,
J ϭ 16 Hz), 3.12Ϫ3.18 (m, 4 H), 4.02 (dd, 1 H, J ϭ 4 Hz, J ϭ 7
Hz), 4.24Ϫ4.34 (m, 4 H). Ϫ (C20H33N6O5): HRMS (NBA): m/z ϭ
437.2525 (for 437.2512). Ϫ M.p. 166Ϫ168°C. Ϫ HPLC: Rt ϭ 6.3
19: Deprotection of 17 followed by purification by HPLC af-
forded 19 as a yellow powder in 76% overall yield. Ϫ 1H NMR
(CD3OD, 250 MHz): δ ϭ 1.64Ϫ1.95 (m, 8 H), 2.53 (m, 1 H), 2.88
(m, 1 H), 3.08 (m, 1 H), 4.10 (m, 1 H), 4.45 (m, 4 H), 7.44 (d, 2
H, J ϭ 8 Hz), 7.73 (m, 3 H), 7.86 (m, 3 H). Ϫ (C28H31N6O6):
HRMS ϭ 547.2328 (for 547.2305). Ϫ M.p. 195Ϫ197°C. Ϫ HPLC:
25
min (H2O/CH3CN, 4:1). Ϫ [α]D ϭ ϩ9.1 (c ϭ 1, MeOH).
10b: Deprotection of 8b followed by purification by HPLC af-
forded 10b as a light-yellow powder in 48% overall yield. ؊ 1H
NMR (CD3OD, 250 MHz): δ ϭ 1.26Ϫ2.03 (m, 16 H), 2.51 (m, 1
H), 2.7 (m, 2 H), 3.19Ϫ3.33 (m, 5 H), 4.10Ϫ4.17 (m, 1 H),
4.33Ϫ4.41 (m, 3 H). Ϫ (C21H35N6O5): HRMS (NBA): m/z ϭ
451.2702 (for 451.2669). Ϫ M.p. 96Ϫ98°C. Ϫ HPLC: Rt ϭ 20.2
25
Rt ϭ 10.1 min (H2O/CH3CN/TFA, 75:25:0.1). Ϫ [α]D ϭ ϩ 8.5
(c ϭ 1, MeOH).
N-(Fluorenylmethyloxycarbonyl)isonipecotic Acid 20: 2 mmol of
isonipecotic acid was dissolved in 14 ml of a 1:1 water/acetone mix-
ture. The pH was adjusted to 8.5 with a saturated solution of
NaHCO3. A solution of 2 mmol of FmocOSu in 7 ml of acetone
was added dropwise while the pH was kept constant by the addition
of NaHCO3. The reaction mixture was stirred for 3 h at room tem-
perature and then 35 ml of AcOEt was added at 0°C. The resulting
solution was acidified with KHSO4 (1 ) and the aqueous layer
was extracted with AcOEt. The combined organic phases were
dried over MgSO4 and the solvent was evaporated to afford 700
mg of a white powder (quantitative yield). Ϫ 1H NMR (CDCl3,
250 MHz): δ ϭ 1.66Ϫ1.94 (m, 4 H), 2.53 (m, 1 H), 2.95 (m, 2 H),
4.11 (m, 2 H), 4.14 (m, 1 H), 4.43 (m, 2 H), 7.26Ϫ7.78 (m, 8 H).
Ϫ MS (NBA): m/z ϭ 352 ([M ϩ H]ϩ). Ϫ M.p. 168Ϫ170°C. Ϫ Rf ϭ
0.4 (MeOH/NH4OH, 99:1).
25
min (H2O/CH3CN, 9:1). Ϫ [α]D ϭ ϩ9.7 (c ϭ 1, MeOH).
Ethyl
2-[N,NЈ-Bis(tert-butyloxycarbonyl)guanidino]ethanoate
(11): 170 mg of glycine ethyl ester hydrochloride (1.2 mmol) was
guanidinated according to the general procedure to afford 250 mg
of 11 (72%) as white crystals. Ϫ 1H NMR (CDCl3, 250 MHz): δ ϭ
1.12 (t, 3 H, J ϭ 7 Hz), 1.43 (s, 9 H), 1.47 (s, 9 H), 4.15 (m, 2 H),
4.20 (m, 2 H), 8.83 (m, 1 H), 11.40 (m, 1 H). Ϫ MS (NBA): m/z ϭ
346 ([M ϩ H]ϩ). Ϫ M.p. 96Ϫ98°C. Ϫ Rf ϭ 0.45 (dichloromethane/
AcOEt, 1:1).
13: Compound 11 was saponified to give 12 (83%), which was
coupled with 7a according to the coupling procedure B to afford
13 in 80% yield as a white foam, which was not further purified.
1
Ϫ H NMR (CDCl3, 250 MHz): δ ϭ 1.44 (s, 9 H), 1.46 (s, 9 H),
1.52Ϫ1.76 (m, 8 H), 2.56 (m, 1 H), 3.00 (m, 2 H), 3.04Ϫ3.30 (m,
4 H), 3.66 (s, 3 H), 3.70 (m, 1 H), 3.99 (m, 1 H), 4.17 (m, 2 H),
4.37 (m, 2 H), 4.40 (m, 1 H), 4.53 (m, 1 H), 6.86 (m, 1 H), 8.85
(m, 1 H), 11.31 (m, 1 H). Ϫ MS (NBA): m/z ϭ 666 ([M ϩ H]ϩ).
Ϫ M.p. 112Ϫ114°C. Ϫ Rf ϭ 0.35 (dichloromethane/AcOEt, 1:1).
23: According to general procedure A, 20 was coupled with the
monoprotected diamines 5a, b and c to afford 21a, b and c in yields
of 40, 47 and 50%, respectively. After removal of Boc in 80% yield,
the deprotected compounds 22a, b and c were coupled with 4 ac-
cording to general procedure B to afford 23a, b and c in respective
yields of 53, 65 and 62%, based on 21a, b and c.
23a: 1H NMR (CDCl3, 250 MHz): δ ϭ 1.52Ϫ1.92 (m, 12 H),
2.50 (m, 2 H), 2.70Ϫ2.96 (m, 4 H), 3.45Ϫ3.53 (m, 6 H), 3.70 (s, 3
H), 3.87 (d, 1 H, J ϭ 16 Hz), 4.08Ϫ4.26 (m, 6 H), 4.60Ϫ4.71 (m,
3 H), 7.27Ϫ7.78 (m, 8 H). Ϫ MS (NBA): m/z ϭ 700 ([M ϩ H]ϩ).
Ϫ Rf ϭ 0.4 (AcOEt/MeOH, 8:2).
23b: 1H NMR (CDCl3, 250 MHz): δ ϭ 1.24 (m, 4 H), 1.38Ϫ1.62
(m, 10 H), 2.25 (m, 1 H), 2.57 (m, 1 H), 2.81 (m, 2 H), 3.06 (m, 2
H), 3.18 (m, 4 H), 3.67 (s, 3 H), 3.76 (d, 1 H, J ϭ 19 Hz), 4.03Ϫ4.22
(m, 5 H), 4.40 (m, 4 H), 6.17 (m, 1 H), 6.90 (m, 1 H), 7.31Ϫ7.71
(m, 8 H). Ϫ MS (GT): m/z ϭ 714 ([M ϩ H]ϩ). Ϫ Rf ϭ 0.52 (AcOEt/
MeOH, 8:2).
23c: 1H NMR (CDCl3, 250 MHz): δ ϭ 1.18Ϫ1.34 (m, 4 H),
1.51Ϫ1.86 (m, 12 H), 2.25 (m, 1 H), 2.60 (m, 1 H), 2.69 (m, 2 H),
2.86 (m, 2 H), 3.05Ϫ3.25 (m, 4 H), 3.69 (s, 3 H), 3.86 (d, 1 H, J ϭ
16 Hz), 4.13Ϫ4.40 (m, 6 H), 4.55 (m, 3 H), 6.36 (m, 1 H), 6.86 (m,
1 H). 7.21Ϫ7.65 (m, 8 H). Ϫ MS (NBA): m/z ϭ 728 ([M ϩ H]ϩ).
Ϫ Rf ϭ 0.68 (AcOEt/dichloromethane, 8:2).
15: Compound 13 was saponified to give 14 in 75% yield, which
was then N-deprotected. The product 15 was crystallized from Ac-
OEt (58% based on 13). Ϫ 1H NMR (CD3OD, 250 MHz): δ ϭ
1.49Ϫ1.75 (m, 8 H), 2.40 (m, 1 H), 2.49Ϫ2.84 (m, 6 H), 3.50 (m, 2
H), 3.66 (d, 1 H), 3.70 (m, 2 H), 3.96 (m, 1 H), 4.21 (m, 1 H). Ϫ
MS (NBA): m/z ϭ 452 ([M ϩ H]ϩ). Ϫ HRMS (C19H30N7O6):
452.2253 (for 452.2258). Ϫ M.p. 136Ϫ138°C. Ϫ HPLC: Rt ϭ 8.8
25
min (H2O/CH3CN/TFA, 4:1:0.1). Ϫ [α]D ϭ ϩ10.2 (c ϭ 1,
MeOH).
4-Amino-4Ј-[N,NЈ-bis(tert-butyloxycarbonyl)guanidino]-
benzophenone (16): 1060 mg of diaminobenzophenone (5 mmol)
and 280 mg of N,NЈ-bis(tert-butyloxycarbonyl)thiourea (1 mmol)
were dissolved in 5 ml of DMF. The solution was cooled to Ϫ10°C,
and 0.6 ml of pyridine and 1.2 mmol of HgCl2 were added. The
reaction mixture was stirred for 2 h at Ϫ10°C and for 1 h at room
temperature. Then, 20 ml of AcOEt was added and the resulting
solution was filtered through Celite. The filtrate was washed with
brine and then with 0.5  HCl. The organic layer was dried over
MgSO4 and the solvent was evaporated. The oily residue was puri-
fied by column chromatography (dichloromethane/AcOEt, 4:1)
Compounds 24: 0.3 mmol of one of the above products 23a, b or
c was dissolved in 4 ml of MeOH and 0.7 ml of NaOH (1 ) was
1
yielding 290 mg (64%) of a yellow powder. Ϫ H NMR (CDCl3,
858
Eur. J. Org. Chem. 1998, 853Ϫ859

A Constrained Diketopiperazine as a New Scaffold for the Synthesis of Peptidomimetics
FULL PAPER
added. The solution was stirred for 15 h at room temperature. The 1.26 mmol of 27 were coupled to give, after purification by column
mixture was then neutralized with HCl (1 ) and the solvents were chromatography (AcOEt/dichloromethane, 1:1), 28 as a yellow
evaporated. The residue was purified by reversed-phase HPLC.
powder in 31% yield. Ϫ 1H NMR (CDCl3, 250 MHz): δ ϭ
1.51Ϫ1.86 (m, 8 H), 2.48 (m, 1 H), 2.94 (m, 2 H), 3.63 (s, 3 H),
3.68Ϫ3.79 (m, 4 H), 4.03 (m, 1 H), 4.37 (m, 2 H), 4.54 (m, 1 H),
5.18 (s, 2 H), 7.32Ϫ7.87 (m, 9 H), 8.23 (m, 1 H), 9.08 (m, 1 H),
9.47 (m, 1 H). Ϫ MS (NBA): m/z ϭ 633 ([M ϩ H]ϩ). Ϫ M.p.
132Ϫ134°C. Ϫ Rf ϭ 0.4 (AcOEt/dichloromethane, 1:1).
70 mg (53%) of 24a was obtained as a white powder. Ϫ 1H NMR
(CD3OD, 250 MHz): δ ϭ 1.54Ϫ2.04 (m, 12 H), 2.50 (m, 2 H), 2.84
(dd, 1 H, J ϭ 12 Hz, J ϭ 4 Hz), 2.95Ϫ3.06 (m, 3 H), 3.22Ϫ3.50
(m, 6 H), 4.04 (d, 1 H, J ϭ 16 Hz), 4.27Ϫ4.36 (m, 4 H). Ϫ MS
(GT): m/z ϭ 464 ([M ϩ H]ϩ). Ϫ HRMS (C22H34N5O6): 464.2536
(for 464.2509). Ϫ M.p. 198Ϫ200°C. Ϫ HPLC: Rt ϭ 6.8 min (H2O/
30: Saponification and subsequent hydrogenolysis of 250 mg of
28 afforded 70 mg of 30 as a yellow powder after purification by
HPLC (36%). Ϫ 1H NMR (CD3OD, 250 MHz): δ ϭ 1.39Ϫ1.81
(m, 8 H), 2.47 (m, 1 H), 2.77 (dd, 1 H, J ϭ 4 Hz, J ϭ 16 Hz), 3.09
(dd, 1 H, J ϭ 4 Hz, J ϭ 16 Hz), 3.95 (d, 1 H, J ϭ 16 Hz), 4.00
(m, 1 H), 4.12 (d, 1 H, J ϭ 16 Hz), 4.32 (m, 4 H), 7.74 (d, 2 H,
J ϭ 9 Hz), 7.87 (d, 2 H, J ϭ 9 Hz). Ϫ C23H39N6O6: HRMS (NBA):
m/z ϭ 485.2162 (485.2149). Ϫ M.p. 108Ϫ110°C. Ϫ HPLC: Rt ϭ
11.1 min (H2O/CH3CN/TFA, 85:15:0.1). Ϫ Rf ϭ 0.40 (MeOH). Ϫ
25
CH3CN, 9:1). Ϫ [α]D ϭ ϩ10.2 (c ϭ 1, MeOH).
90 mg (67%) of 24b was obtained as a white powder after purifi-
cation. Ϫ 1H NMR (CD3OD, 250 MHz): δ ϭ 1.56Ϫ1.74 (m, 6 H),
1.80Ϫ2.03 (m, 8 H), 2.50 (m, 1 H), 2.54 (m, 1 H), 2.62Ϫ2.72 (m,
2 H), 3.02 (td, 2 H, J ϭ 12 Hz, J ϭ 3 Hz), 3.22 (m, 4 H), 3.40 (m,
2 H), 4.18 (d, 1 H, J ϭ 16 Hz), 4.24 (d, 1 H, J ϭ 16 Hz), 4.36 (m,
3 H). Ϫ (C23H36N5O6): HRMS (GT): m/z ϭ 478.2654 (for
478.2666). Ϫ M.p. 192Ϫ194°C. Ϫ HPLC: Rt ϭ 6.3 min (H2O/
25
25
[α]D ϭ ϩ8.8 (c ϭ 1, MeOH).
CH3CN, 1:1). Ϫ [α]D ϭ ϩ8.8 (c ϭ 1, MeOH).
90 mg (65%) of 24c was obtained as a white powder after purifi-
cation. Ϫ 1H NMR (CD3OD, 250 MHz): δ ϭ 1.47Ϫ1.92 (m, 16
H), 2.45 (m, 2 H), 2.93Ϫ3.15 (m, 6 H), 3.36Ϫ3.49 (m, 4 H), 4.00
(d, 1 H, J ϭ 16 Hz), 4.22 (d, 1 H, J ϭ 16 Hz), 4.27 (m, 3 H). Ϫ
(C24H38N5O6): HRMS (NBA): m/z ϭ 492.2820 (492.2822). Ϫ M.p.
90Ϫ92°C. HPLC: Rt ϭ 12.1 min (H2O/CH3CN/TFA, 85:15:0.1).
[1]
C. Prasad, Peptides 1995, 16, 155.
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D. W. Gordon, J. Steele, Bioorg. Med. Chem. Lett. 1995, 5, 47.
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B. O. Scott, A. C. Siegmund, C. K. Marlowe, Y. Pei, K. L.
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N. Kucharczyk, C. Thurieau, J. Paladino, A. D. Morris, J. Bon-
net, E. Canet, J. E. Krause, D. Regoli, R. Couture, J. L. Fau-
25
`
chere, J. Med. Chem. 1993, 36, 1654.
Ϫ [α]D ϭ ϩ9.3 (c ϭ 1, MeOH).
[5]
For reviews on analogues and mimetics of RGD see: I. Ojima,
Q. Dong, S. Chakravarty, E. Peerschke, S. M. Hwang, A. S.
Wong, Bioorg. Med. Chem. 1995, 5, 1941; J. A. Zablocki, M.
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Feigen, J. Med. Chem. 1992, 35, 4914; V. Austel, F. Him-
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ture see: J. Lefkovits, E. Plow, E. J. Topol, New Engl. J. Med.
1995, 332, 1553.
4-[N-(Benzyloxycarbonyl)aminoiminomethyl]aniline 25: To
a
solution of 850 mg of aminobenzamidine dihydrochloride in 20 ml
of THF and 4 ml of H2O, was added 2.5 ml of 5  NaOH. Then,
0.5 ml of benzyloxycarbonyl chloride in 13 ml of THF was slowly
added dropwise at 0°C. The reaction mixture was stirred for 1 h at
room temperature. The phases were then separated and the organic
layer was concentrated to dryness. The residue was taken up in
AcOEt and the resulting solution was washed with water. The or-
ganic layer was dried and the solvent was evaporated. The residue
was crystallized from CHCl3, affording 550 mg of 25 as a yellow
powder (50% yield). Ϫ 1H NMR ([D6]DMSO, 250 MHz): δ ϭ 5.03
(s, 2 H), 5.82 (s, 2 H), 6.51 (d, 2 H, J ϭ 8 Hz), 7.33 (m, 5 H), 7.73
(d, 2 H, J ϭ 8 Hz), 8.66 (m, 1 H), 9.11 (m, 1 H). Ϫ MS (NBA):
m/z ϭ 270 ([M ϩ H]ϩ). Ϫ M.p. 140Ϫ142°C (ref.[12] 147Ϫ148°C).
Ϫ HPLC: Rt ϭ 8.4 min (H2O/CH3CN/TFA, 85:15:0.1). Ϫ Rf ϭ
0.55 (AcOEt/dichloromethane, 1:1).
[6]
[7]
G. Marguerie, French Patent 1988, 2, 608, 160; G. Marguerie,
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G. D. Hartman, M. S. Egbertson, W. Halczenko, W. L. Laswell,
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[8]
J. A. Zablocki, M. Miyano, R. B. Garland, D. Pireh, L. Schretz-
man, N. R. Shashidhar, S. N. Rao, R. J. Lindmark, S. Panzer-
Knodle, N. Nicholson, B. B. Taite, A. K. Salyers, L. W. King,
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I. Ojima, Q. Dong, M. Eguchi, Y. I. Oh, C. M. Amman, B. S.
Coller, Bioorg. Med. Chem. Lett. 1994, 4, 1749.
26: 480 mg of Boc-Gly-OH (2.7 mmol) was dissolved in 10 ml
of dichloromethane. At 0°C, 280 mg of DCC (1.35 mmol) was
added. The reaction mixture was stirred for 1 h at 0°C and then
filtered. The filtrate was added to a solution of 540 mg (2 mmol)
of 25 in 10 ml of dichloromethane, and then 30 mg of DMAP and
0.3 ml of NEt3 were added. The resulting mixture was stirred for
15 h at room temperature. The solvents were then evaporated, the
residue was taken up in AcOEt, and the resulting solution was
washed with 1  HCl. The combined organic layers were dried and
the solvent was evaporated. The residue was purified by column
chromatography (AcOEt/dichloromethane, 1:1), affording 360 mg
of a white powder (42% yield). Ϫ 1H NMR (CDCl3, 250 MHz):
δ ϭ 1.46 (s, 9 H), 3.88 (m, 2 H), 5.32 (s, 2 H), 5.98 (m, 1 H), 6.62
(m, 1 H), 7.30Ϫ7.58 (m, 9 H), 9.19 (m, 2 H). Ϫ MS (NBA): m/z ϭ
427 ([M ϩ H]ϩ). Ϫ M.p. 124Ϫ126°C. Ϫ Rf ϭ 0.60 (AcOEt/di-
chloromethane, 1:1).
[9]
[10]
D. Ben-Ishai, E. Goldstein, Tetrahedron 1971, 27, 3119; M.
´
Vincent, C. Pascard, M. Cesario, G. Remond, J. P. Bouchet, Y.
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W. E. Bondinell, R. M. Keenan, W. H. Miller, F. E. Ali, A. C.
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Haltiwanger, W. F. Huffman, S. M. Hwang, D. R. Jakas, P. F.
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[11]
[12]
[13]
[14]
V. Austel, W. G. Eiser, F. Himmelsbach, G. Linz, T. H. Miller,
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[15]
[16]
28: Compound 26 was deprotected (Boc removal) to afford 27 in
74% yield. According to general procedure A, 1.26 mmol of 4 and
[97320]
Eur. J. Org. Chem. 1998, 853Ϫ859
859