Synthesis of Nα-Z, Nβ-Fmoc or Boc protected α-hydrazinoacids and study of the coupling reaction in solution of Nα-Z-α-hydrazinoesters

Article abstract of DOI:10.1016/j.tet.2006.12.085

The preparation of chiral orthogonally protected N^α-Z, N^β-Fmoc- or Boc-α-hydrazinoacids derivatives, directly suitable for SPPS, is described in six steps with good yields starting from the corresponding α-aminoacids. The coupling reaction assays performed in liquid phase between N^α-Z-hydrazinoesters and N-Fmoc-α-aminoacids demonstrated the low reactivity of the hydrazinoester derivatives. However, we found that the acid fluoride method allowed the formation of hydrazinodipeptides almost quantitatively.

Full text of DOI:10.1016/j.tet.2006.12.085

Tetrahedron 63 (2007) 2223–2234
Synthesis of Na-Z, Nb-Fmoc or Boc protected a-hydrazinoacids
and study of the coupling reaction in solution
of Na-Z-a-hydrazinoesters
*
ꢀ
Isabelle Bouillon, Nicolas Brosse, Regis Vanderesse and Brigitte Jamart-Gregoire
ꢀ
´
Laboratoire de Chimie Physique Macromoleculaire, UMR CNRS-INPL 7568, Nancy-Universite, 1, rue grandville BP 451,
´
54001 Nancy, France
Received 23 October 2006; revised 15 December 2006; accepted 22 December 2006
Available online 4 January 2007
Abstract—The preparation of chiral orthogonally protected Na-Z, Nb-Fmoc- or Boc-a-hydrazinoacids derivatives, directly suitable for SPPS,
is described in six steps with good yields starting from the corresponding a-aminoacids. The coupling reaction assays performed in liquid
phase between Na-Z-hydrazinoesters and N-Fmoc-a-aminoacids demonstrated the low reactivity of the hydrazinoester derivatives. However,
we found that the acid fluoride method allowed the formation of hydrazinodipeptides almost quantitatively.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
possibility to introduce different protecting groups on the
Na and Nb positions, which can lead to the formation of
Na,Nb-orthogonally bisprotected a-hydrazinoesters. In this
paper, we demonstrate that the results previously obtained5,6
can be extended to the preparation of Nb-tert-butyloxy-
carbonyl (Boc) and Nb-fluorenomethyloxycarbonyl (Fmoc)
protected a-hydrazinoacid derivatives, compounds, which
are directly suitable for peptide synthesis on solid support
(SPPS). We also report the first results obtained, involving
Na-Z-a-hydrazinoesters in a coupling process in solution,
which led to the preparation of hydrazinodipeptides.
Hydrazinopeptides are a class of peptide analogues for
which one (or more) peptidic bond(s) has (have) been re-
placed by one (or more) hydrazidic bond(s).1 As recently
demonstrated by Seebach and Lelais,2 the hydrazidic bond
is very resistant to protease and hydrazinopeptides could
be interesting peptidomimetic candidates in drug design.
Moreover, the few investigations concerning the structural
analysis of foldamers constructed starting from a-hydrazino-
acids seem to demonstrate that the presence of supplemen-
tary nitrogen atoms in the backbone leads to new forms
of intramolecular structuration.3 Compared to other pseudo-
peptides, hydrazinopeptides have not received much atten-
tion from the scientific community, the main reason is that
among the numerous described methods,4 few can be applied
generally to provide enantiomerically pure a-hydrazinoacids
directly suitable for oligomerization. Furthermore, the pres-
ence of two reactive nitrogens (Na and Nb) on the a-hydr-
azinoacids leads to a problem of regioselectivity when
performing acylation.
2. Results and discussion
N,N-Triprotected a-hydrazinoesters 4 were prepared via the
Mitsunobu reaction between the acidic partner N-benzyloxy-
carbonylaminophthalimide 3 and the corresponding a-hydr-
oxyesters 2 prepared from 1 via a procedure previously
described in the literature.7 As we demonstrated before, this
reaction proceeds via a total inversion of configuration of the
stereogenic carbon and leads to the formation of enantio-
merically pure compounds 4.6 As R is not too hindered,
this procedure allowed the formation of the corresponding
compounds 4 with good yields (Scheme 1); however, lower
yield (30%) was obtained when R¼CH(CH3)CH2CH3.
A few years ago,5,6 we demonstrated that enantiomerically
pure Na,Nb-bis and triprotected a-hydrazinoesters can be
synthesized by using the Mitsunobu protocol as the key
reaction. One important feature of this strategy is the
As we described in a previous paper,8 the presence of the
phthalimide group is one of the key factors for the success
of the Mitsunobu reaction. Unfortunately, as other authors
reported, we were confronted with the difficulty of finding
Keywords: Pseudopeptide; a-Hydrazinoacid; a-Hydrazinodipeptide; Pro-
tecting group; Mitsunobu reaction.
* Corresponding author. Tel.: +33 3 83 17 52 79; fax: +33 3 83 37 99 77;
e-mail: brigitte.jamart@ensic.inpl-nancy.fr
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.12.085

2224
I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
O
N
NHZ
O
Z
O
3
HO
CO2H
H2N
CO2H
N
N
iii
CO2Me
i, ii
O
R
R
R
1
2
4
4 yields % ( from 2)
R
93
96
97
H
CH3
CH2CH(CH3)2
CH2C6H5
64
64
30
CH(CH3)2
CH(CH3)-CH2CH3
Scheme 1. Reagents, conditions and yields: (i) NaNO2, CH3COOH; (ii) SOCl2, MeOH and (iii) DBAD or DEAD, PPh3, THF.
general and mild conditions to remove the phthaloyl group.9
For this reason, we tried to find conditions that allowed the
conversion of the phthalimide group of compounds 4 into
more convenient protecting groups. The results are given
in (Schemes 2 and 3) Table 1. We first demonstrated that
the phthalimide group could be converted into triprotected
compounds 6 by using a two-step, one-pot protocol10
(Scheme 2).
If we consider the recent work published by Bonnet et al.,11
the preparation of this kind of compounds is of interest, since
the fully protected a-hydrazinoacid derivatives are required
Z
Boc
Z
Z
O
Boc
Boc
O
CO2Me
NH
O
N
CH
R
CO2Me
CO2Me
N
N
N CH
R
N
CH
R
i
ii
4
5
C
C
O
5'
6
MeHN
MeHN
+
6 yields % (from 4)
O
R
H
CH3
97
70
N
Me
CH2CH(CH3)2
38
O
66
CH(CH3)2
Scheme 2. Reagents and conditions: (i) MeNH2/MeOH/THF and (ii) Boc2O/DMAP/THF.
Z
Z
N
CO2H
N
CO2Me
vi
FmocHN
FmocHN
BocHN
R
R
12
11
v
Z
Boc
N
H
N
Z
Z
O
O
N
iii
CO2Me
C
N
CH CO2Me
C
N CH CO2Me
ii
i
4
R
R
R
C
O
C
O
7
8
9
iv
N
N
Z
N
CO2H
BocHN
R
10
Scheme 3. Reagents and conditions: (i) pyrrolidine, THF; (ii) Boc2O, DMAP, THF; (iii) MeNH2, MeOH, THF; (iv) (a) LiOH, H2O, THF; (b) HCl 10%;
(v) (a) HCl, AcOEt; (b) Fmoc-Cl, Na2CO3, dioxane and (vi) NaOH, CaCl2, i-PrOH–H2O.

I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
2225
Table 1. Preparation of Na,Nb-protected hydrazinoacids 10 and 12
12 starting from 11 because of the lability of the Fmoc group
under alkaline conditions. We showed that this problem can
be avoided by using NaOH in the presence of CaCl2 in
Entry
R
7a
8b
9c
10d
11e
12f
14
1
2
3
4
5
6
–CH3
–H
–CH(CH3)CH2CH3
–CH2CH(CH3)2
–CH2Ph
97
99
63
100
79
65
93
96
81
83
76
70
85
96
74
83
72
93
83
98
70
80
81
75
98
75
98
96
nd
nd
nd
nd
a mixture of isopropanol and water, which lead to the forma-
tion of corresponding compounds 12. For two examples
(R¼H and R¼Me) the a-hydrazinoacids 12 were isolated
in pure form. Unfortunately, in other cases, the degradation
of compounds 11 during purification impeded the obtention
of 12 in pure form. However, it is interesting to note that
these crude products 12 can be involved in peptidic synthesis
on solid phase (to be published). To conclude this first part,
we have shown that Na,Nb-orthogonally bisprotected a-
hydrazinoacids 10 and 12 can be obtained starting from
the corresponding a-aminoacids 1 in six or seven steps in
acceptable overall yields.
g
g
g
g
–CH(CH3)2
a
Yields in pure compounds 7 calculated from 4.
Yields in pure compounds 8 calculated from 7.
Yields in pure compounds 9 calculated from 8.
Yields in pure compounds 10 calculated from 9.
Yields in pure compounds 11 calculated from 9.
Yields in pure compounds 12 calculated from 11.
Problem of purification of 11.
b
c
d
e
f
g
to avoid polymerization side reactions in SPPS. Bisprotected
compounds 9 can also be obtained by using a multi-step pro-
tocol (Scheme 3). In fact, the difference between these two
procedures depends on the nature, primary or secondary,
of the nucleophilic amine used to open the phthalimide
ring. In both cases, the fixation of the electron withdrawing
Boc group onto the hydrazide function followed by a nucleo-
philic displacement allowed the dephthaloylation. The
action of MeNH2 on N,N-triprotected a-hydrazinoesters 4
gives rise to the opening of phthaloyl ring leading to com-
pounds 5, which can be isolated if necessary.12 The use of
Boc2O/DMAP allowed the selective protection of the nitro-
gen of the hydrazide group of compound 5, without affecting
the methyl amide. The latter can react with the carbonyl
function of the benzoyl hydrazide leading to the splitting
of the C–N bond with formation of methylphthalimide. An
attack of a second equivalent of Boc2O results in the forma-
tion of the triprotected hydrazinoesters 6. Thus, when meth-
ylamine is used, the C–N bond splitting occurred via an
intramolecular reaction involving the non-isolable interme-
diate 50.5 On the contrary this last step is no more possible
when using a secondary amine like pyrrolidine. In this
case, the Boc protected compound 8 was stable and can be
isolated. The splitting of the C–N bond only occurred in
a supplementary step by the action of methylamine. The
method using the pyrrolidine presents two main advantages:
(1) it avoids the use of Mg(ClO4)2, which was previously de-
scribed13 as the only way to obtain compound 9 from com-
pound 6 and (2) it allows the isolation of intermediated
compounds 7 and 8 with good yields. Unfortunately, in spite
of considerable efforts, the protocol described to obtain
compounds 9 cannot be transposed for the preparation of
Fmoc protected analogues 11. No reaction occurred when
Fmoc–Cl or Fmoc–OSu was used as an electrophile, even
in the presence of DMAP as catalyst. However, we demon-
strated that compounds 11 can be obtained from 9 by
a two-step procedure (see v, Scheme 3).
Very few reactions are reported in the literature describing
the coupling of a-hydrazinoacid derivatives. Collet et al.15
and more recently, Lelais and Seebach2 demonstrated that
Na-benzyl a-hydrazinoacid derivatives, obtained by electro-
philic amination method16 can be linked to a-aminoacids or
oligomerized in solution with fair yields using classical cou-
pling reagents. Collet et al.17 pointed out the problem of the
regioselectivity between the Na and the Nb positions when
unhindered lateral chains were present on the a-hydrazino-
acid, which can be circumvented by the use of Na-benzyl
protected derivatives. As it has been shown above, our
method allowed the preparation of Na-Z protected a-hydr-
azinoacids. This protecting group is very widely employed
as permanent protecting group in SPPS because its removal
can occur simultaneously with the cleavage of the peptide
from the solid support. So, we decided to perform coupling
reactions between a-hydrazinoesters 13 (obtained from 9 us-
ing classical Boc deprotection conditions) and Fmoc pro-
tected a-aminoacids in solution, but keeping in mind the
possibility to use them later in SPPS (Scheme 4 and Table 2).
The first reactions were performed between compound 13
(R¼Me) and N-Fmoc-L-Ala-OH in order to find the best
conditions of coupling (entries 1–7). Surprisingly, using ac-
tivated esters and Leuch’s anhydride (not reported results)
no coupling reaction occurred. Furthermore, the classical
method TBTU/HOBt/DIEA18 leads, in our case, to the
formation of hydrazinodipeptides with a fair yield of 50%
(entry 1). In a same manner, poor results were obtained
when O-(7-azabenzotriazol-yl)-1,1,3,3-tetramethyluronium
hexafluorophosphate (HATU)19 was used as coupling re-
agent (entries 2 and 3), even in the presence of N-methyl-
morpholine (NMM), the conditions described by Lelais
and Seebach.2 This result suggests that Na-Z protected a-hy-
drazinoacids are less reactive than Na-benzyl protected one
and can be explained by the more electron withdrawing abil-
ity of Z group. Fortunately, we demonstrated that the cou-
pling reaction can lead to the desired product with 73%
yield when using HOBt–DCC20 (entry 4). Better results
were obtained with SOCl221 or isobutyl chloroformate22 (en-
tries 5 and 6), however, the use of these reactants necessitate
low temperature conditions (ꢀ20 ꢁC), which are difficultly
compatible with the solid phase synthesis.21 For this reason,
we will prefer the use of the acid fluoride method23 (entry 7),
which can be performed at room temperature. In fact, the
protocol described in the litterature23 suggested the addition
of the acid fluoride to a cold solution (ꢀ20 ꢁC) of
To reach our goal, which was the obtention of Na,Nb-ortho-
gonally bisprotected a-hydrazinoacids directly suitable for
peptidic synthesis on solid phase, the last step to perform
was the conversion of the ester group of compounds 9 and
11 into the corresponding acids 10 and 12. Depending on
the nature of the protection of the hydrazine, two strategies
were used. LiOH was convenient to convert in good yields
compound 9 into the corresponding compounds 10. How-
ever, these conditions cannot be used to obtain compounds

2226
I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
Z
N
Z
N
Z
N
O
O
O
O
O
ii
i
FmocHN
FmocHN
9
or
H2N
OMe
N
H
OMe
N
H
OMe
R
R
R
R'
R'
13
14
15
Scheme 4. Reagents and conditions: (i) HCl 3 N/AcOEt and (ii) FmocNH–CH(R0)–COOH, for coupling conditions, see Table 2.
Table 2. Coupling reactions of a-hydrazinoesters 13 with FmocNH–CH(R0)–COOH
Entry
R
R0
Coupling conditions
T (ꢁC)
Yieldsa in 14 or 15 (%)
1
2
3
4
5
6
7
8
9
10
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
HOBt/TBTU/DIEA18
HATU/HOBt/DIEA19
HATU/NMM2
20
20
20
20
ꢀ20
ꢀ20
20
20
20
50
19
30
73
90
86
98
98
78
68
HOBt/DCC20
21
SOCl2/CH2Cl2
Isobutyl chloroformate/NMM22
N-Fmoc-L-Ala-F23 b
,
N-Fmoc-D-Ala-F23 b
,
N-Fmoc-L-Val-F23 b
,
–CH3
–CH(CH3)CH2CH3
–CH(CH3)2
–CH(CH3)2
N-Fmoc-L-Val-F23 b
20
,
a
Yields in pure 14 or 15 calculated from 13.
Acid fluoride of Fmoc-Ala-OH was previously synthesized and isolated before the coupling reaction. A cold solution (ꢀ10 ꢁC) of Fmoc-Ala-F in DCM is
b
added.
a-aminoester and to perform the reaction at room tempera-
ture. Keeping in mind the possibility to use this protocol in
solid phase synthesis, we decided to add a cold solution of
the acid fluoride (ꢀ10 ꢁC) to the corresponding hydr-
azinoester and to perform the reaction at room temperature.
These conditions led to the formation of the desired products
with 98% yield. The optical purity of compound 14
(R¼R0¼Me) was evaluated up to 95% by comparing its
13C NMR data with those of the corresponding diastereoiso-
mer 15 obtained by coupling N-Fmoc-D-Ala-OH with 13
R¼Me (entry 8). A difference can be observed if we
compare the chemical shift of the corresponding Ca
(dCa(14)¼49.8 ppm and dCa(15)¼49.5 ppm). As it is possi-
ble to check from the Figure 1, both spectra of 14 and 15
exhibit a single signal for the Ca.
68% yields, respectively. These results suggest that this pro-
cedure could be easily extended to the formation of a large
number of hydrazinodipeptides.
3. Conclusion
We have shown that chiral orthogonally protected Na-(Z)-
Nb-(Fmoc or Boc), protected a-hydrazinoacid derivatives,
directly suitable for SPPS, can be prepared in six steps
and in reasonable yields starting from the corresponding
a-aminoacids. The coupling reaction assays performed
between Na-Z-a-hydrazinoesters and N-Fmoc-a-amino-
acids demonstrated the low reactivity of a-hydrazinoester
when the Na is protected by a benzyloxycarbonyl group.
However, we find that the use of the acid fluoride method
allowed the formation of hydrazinodipeptides 14 and 15 in
good yields. The use of these conditions for the synthesis
of hydrazinopeptides in SPPS is under active investigation.
To assess the acid fluoride procedure, we coupled an hin-
dered aminoacid (N-Fmoc-L-Val-F) with an unhindered
hydrazinoester 13 R¼Me or with an hindered hydrazinoester
13 R¼CH(Me)CH2CH3 (entries 9 and 10). In both cases,
the corresponding dipeptides 14 were obtained in 78% and
4. Experimental
4.1. General
Tetrahydrofuran was dried by distillation over sodium
benzophenone ketyl. Unless otherwise stated, reagents were
purchased from chemical companies and used without prior
purification. Reactions were monitored by thin layer chro-
matography (TLC) using aluminium-backed silica gel plates
(Macherey–Nagel ALUGRAMÒ SIL G/UV254). TLC spots
were viewed under ultraviolet light and by heating the plate
after treatment with a staining solution of phosphomolybdic
acid. Product purifications were performed using Geduran
60 H Silica Gel (63–200 mesh). Reagent grade solvents
were used as received. 1H NMR and 13C (300 MHz) spectra
were recorded on a Bruker Advancer 300. Multiplicities
are reported as follow: s¼singlet, t¼triplet, q¼quadruplet,
m¼multiplet. IR spectra were recorded on a Bruker Tensor
Figure 1. Part of 13C NMR spectra of: (a) mixture of 14 (R¼R0¼Me) and 15
(R¼R0¼Me); (b) compound 15 (R¼R0¼Me) and (c) compound 14
(R¼R0¼Me).

I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
2227
1
27. Electron impact mass spectra were performed on a Pro-
MALDI/FTMS apparatus in the ‘Laboratoire de Spectro-
1717; H NMR (300 MHz, CDCl3) d 7.46–7.13 (m, 5H,
arom), 5.29–5.07 (m, 2H, CH2 Z), 4.37–4.15 (m, 2H,
aCH2), 3.81–3.55 (m, 3H, O–CH3), 1.64–1.33 (m, 18H,
Boc); 13C NMR (CDCl3) d 171.5, 168.5, 168.4 (COOCH3),
155.5, 154.9 (COOCH2Ph), 150.7, 150.5 (COOt-Bu), 136.2,
136.1 (C arom), 128.9, 128.7, 128.6, 128.4 (CH arom), 84.6,
84.5 (CBoc), 69.0, 68.8 (CH2 Z), 53.9 (O–CH3), 52.4
(aCH2), 28.2, 27.9 (CH3 Boc); HRMS calcd for
C21H30N2O8 [M+Na+] m/z 461.18944, found 461.1894.
ꢀ
metrie de Masse et de Chimie Laser—Universite de Metz—
France’.
ꢀ
4.2. General procedure for the preparation of
compounds 4
To a solution of N-benzyloxycarbonylaminophthalimide 3
(5 mmol), PPh3 (2 g, 7.5 mmol) and a-hydroxyester
(RCH(OH)COOMe, 5 mmol) 2 in dry THF (50 mL) and un-
der nitrogen was added in one portion diethylazodicarb-
oxylate (DEAD) or di-tert-butylazodicarboxylate (DBAD)
(7.5 mmol) with stirring at 0–5 ꢁC. The resulting solution
was stirred at room temperature for 0.5 h (monitored by
TLC until completion) or 3 h in the special case of
R¼CH2CH(CH3)2, CH(CH3)CH2CH3 and concentrated in
vacuo. The residue was triturated in AcOEt, and the most
of triphenylphosphine oxide and diethyl (or di-tert-butyl)
hydrazinedicarboxylate was removed by filtration. The fil-
trate was evaporated and the residue was chromatographied
on silica gel.
4.3.2. Na-(Benzyloxycarbonyl)-Nb,Nb-[bis(tert-butyloxy-
carbonyl)]-hydrazinoalanine methyl ester (6, R¼CH3).
Oil; IR (NaCl) nmax/cmꢀ1: 1800, 1764, 1734; 1H NMR
(300 MHz, CDCl3) d 7.38–7.26 (m, 5H, arom), 5.29–5.17
(m, 2H, CH2 Z), 4.58 (q, J¼7 Hz, 1H, aCH), 3.68 (s, 3H,
O–CH3), 1.48, 1.47, 1.40 (3s, 18H, Boc), 1.26 (d, J¼7 Hz,
3H, bCH3); 13C NMR (CDCl3) d 173.1 (COOCH3), 155.5
(COOCH2Ph), 150.3 (COOt-Bu), 136.3, 135.4, 130.6,
130.2 (CH arom), 128.8, 128.7, 128.6, 128.4 (CH arom),
84.0 (CBoc), 68.7 (CH2 Z), 54.9 (aCH), 53.9 (O–CH3),
28.1 (CH3 Boc), 14.7 (bCH3); HRMS calcd for
C22H32N2O8 [M+Na+] m/z 475.20509, found 475.2052.
The spectroscopic data of compounds 4, R¼H, CH3,
CH(CH3)2, CH2CH(CH3)2, CH2C6H5 were described else-
where.6
4.3.3. Na-(Benzyloxycarbonyl)-Nb,Nb-[bis (tert-butyloxy-
carbonyl)]-hydrazinovaline methyl ester (6, R¼
CH(CH3)2). Oil; IR (NaCl) nmax/cmꢀ1: 3332, 1748, 1733,
1
1717; H NMR (300 MHz, CDCl3) d 7.49–7.14 (m, 5H, H
4.2.1. Na-Benzyloxycarbonyl-Nb-phthalimidohydrazino-
isoleucine methyl ester (4, R¼CH(CH3)CH2CH3). Oil;
arom), 5.25–5.05 (m, 2H, O–CH2), 4.56–4.23 (m, 1H, N–
CH), 3.75–3.48 (m, 3H, O–CH3), 1.51–1.34 (m, 19H,
2(CH3)3, CH), 1.13–0.97 (m, 3H, CH3), 0.94–0.77 (m, 3H,
CH3); 13C NMR (CDCl3) d 171.7, 169.9 (COOCH3), 156.0
(COOCH2Ph), 151.8, 151.7 (COOt-Bu), 136.3 (C arom),
129.0, 128.9, 128.8, 128.7, 128.5 (CH arom), 84.6, 84.5,
84.2 (C(CH3)3), 69.3 (O–CH2), 67.0 (N–CH), 52.3 (O–
CH3), 29.1 (CH), 28.4, 28.3, 28.2 (C(CH3)3), 21.0, 19.3
(2CH3); HRMS calcd for C24H36N2O8 [M+Na+] m/z
503.23639, found 503.2364.
1
IR (NaCl) nmax/cmꢀ1: 1800, 1739; H NMR (300 MHz,
CDCl3): d 7.89–7.85 (m, 2H, arom Pht), 7.81–7.72 (m, 2H,
arom Pht), 7.39–7.33 (m, 2H, arom Ph), 7.20–7.12 (m, 3H,
arom Ph), 5.32–5.00 (m, 2H, CH2 Z), 4.87 (d, 0.6H,
J¼11.2 Hz, aCH), 4.65 (d, 0.4H, J¼12 Hz, aCH), 3.71 (s,
3H, O–CH3), 2.04–1.72 (m, 2H, gCH2), 1.42–1.22 (m, 4H,
bCH and gCH3), 1.00–0.74 (m, 3H, dCH3); 13C NMR
(CDCl3) d 169.9, 169.7 (COOCH3), 166.7, 116.3, 166.2,
165.8 (O]C–Pht), 154.9, 154.7 (N–COOCH2C6H5), 136.0
(C arom), 135.5, 135.4 (CH arom Pht), 130.7, 130.3 (CH
arom Pht), 129.3, 129.1, 129.0, 128.8, 128.7, 127.7 (CH
arom), 124.6 (CH arom Pht), 70.1, 69.4 (CH2 Z), 66.9,
65.6 (aCH), 53.5 (O–CH3), 35.4 (bCH), 26.3 (gCH2), 15.3
(bCH), 12.0 (dCH3); HRMS calcd for C23H24N2O6
[M+Na+] m/z 447.15266, found 447.1527.
4.3.4. Na-(Benzyloxycarbonyl)-Nb,Nb-[bis(tert-butyloxy-
carbonyl)]-hydrazinoleucine methyl ester (6, R¼
CH2CH(CH3)2). Oil; IR (NaCl) nmax/cmꢀ1: 3361, 1762,
1
1745, 1733; H NMR (300 MHz, CDCl3) d 7.43–7.17 (m,
5H, H arom), 5.25–5.07 (m, 3H, O–CH2), 3.84–3.52
(m, 1H, N–CH), 3.84–3.52 (m, 3H, O–CH3), 1.66–1.27
(m, 21H, CH, CH2 and 2(CH3)3), 1.06–0.80 (m, 6H,
2CH3); 13C NMR (CDCl3) d 171.2 (COOCH3), 155.6
(COOCH2Ph), 151.5 (COOt-Bu), 136.4 (C arom), 129.1,
128.8, 128.6 (CH arom), 84.6 (C(CH3)3), 69.2 (O–CH2),
60.4, 59.6 (N–CH), 52.7 (O–CH3), 38.4 (CH2), 28.7
(CH(CH3)2), 28.4 (C(CH3)3), 23.7, 22.5, 22.4 (2CH3);
HRMS calcd for C25H38N2O8 [M+Na+] m/z 517.25204,
found 517.2523.
4.3. General procedure for the preparation of
compounds 6
To a solution of compounds 3 (3 mmol) in THF (20 mL) was
added at room temperature 3 equiv of methylamine
(9 mmol, 2 M in MeOH). The mixture was stirred at room
temperature until completion (about 5 h, monitored by
TLC). The solvent and the excess of amine were removed
in vacuo. The residue was dissolved in THF (20 mL),
Boc2O (3 equiv, 9 mmol) and a catalytic amount of DMAP
were added. The mixture was stirred at room temperature
until completion (about 6 h, monitored by TLC). Then, the
solvent and the excess of amine were removed in vacuo
and compounds 6 were purified by column chromatography.
4.4. General procedure for the preparation of
compounds 7
To a solution of compound 4 (3 mmol) in THF (20 mL) was
added at room temperature 3 equiv of pyrrolidine (9 mmol).
The mixture was stirred at room temperature during 3 h for
R¼H and CH3 (monitored by TLC until completion) or 5 h
for the other compounds. The solvent and the excess of
amine were removed in vacuo and the residue was chro-
matographied on silica gel.
4.3.1. Na-(Benzyloxycarbonyl)-Nb,Nb-[bis(tert-butyloxy-
carbonyl)]-hydrazinoglycine methyl ester (6, R¼H).
White solid; IR (NaCl) nmax/cmꢀ1: 3325, 1770, 1733,

2228
I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
4.4.1. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-hydrazinoglycine methyl ester (7, R¼H).
Oil; IR (NaCl) nmax/cmꢀ1: 3277, 1795, 1771, 1746; 1H NMR
(300 MHz, CDCl3) d 9.03–8.93 (m, 1H, bNH), 7.95–7.70
(m, 1H, arom), 7.61–7.20 (m, 8H, arom), 5.30–5.14 (m,
2H, CH2 Z), 4.44–4.31 (m, 2H, aCH2), 3.83–3.46 (m, 5H,
O–CH3, pyrro), 3.19–3.07 (m, 2H, pyrro), 2.04–1.82 (m,
4H, pyrro); 13C NMR (CDCl3) d 170.3, 170.1 (COOCH3),
167.3 (OC-pyrro), 166.8 (N–COC6H4), 156.4, 155.6
(COOCH2Ph), 137.7, 137.5, 136.8, 136.3 (C arom), 135.5
(CH arom), 132.4, 132.3 (C arom), 130.8, 130.5, 130.3,
129.9, 129.2, 129.0, 128.8, 128.2, 127.3, 124.7 (CH arom),
69.6, 69.2, 69.0 (CH2 Z), 53.1 (O–CH3), 54.1, 53.1
(aCH2), 49.7, 46.7, 46.4, 45.8, 26.5, 25.1 (CH2 pyrro);
HRMS calcd for C23H25N3O6 [M+Na+] m/z 462.16356,
found 462.1635.
(2CH2 pyrro), 38.1, 37.8 (CH2), 26.1, 24.8 (2CH2 pyrro),
24.7 (gCH), 23.6, 21.7 (dCH3); HRMS calcd for
C27H33N3O6 [M+Na+] m/z 518.22616, found 518.2265.
4.4.5. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-hydrazinoisoleucine methyl ester (7,
R¼CH(CH3)CH2CH3). Oil; IR (NaCl) nmax/cmꢀ1: 3245,
1772, 1741, 1717, 1696; 1H NMR (300 MHz, CDCl3)
d 9.22–8.91 (m, 1H, bNH), 7.97–7.65 (m, 1H, arom),
7.56–7.22 (m, 8H, arom), 5.30–5.05 (m, 2H, CH2 Z),
4.98–4.48 (m, 1H, aCH), 3.88–3.41 (m, 5H, O–CH3, pyrro),
3.29–2.89 (m, 2H, pyrro), 2.05–1.70 (m, 4H, pyrro), 1.60–
1.40 (m, 1H, bCH), 1.33–1.16 (m, 2H, gCH2), 1.05–0.72
(m, 2H, dCH3); 13C NMR (CDCl3) d 171.0 (COOCH3),
169.7 (OC-pyrro), 166.9 (N–COC6H4), 156.2 (COOCH2Ph),
136.5 (C arom), 131.7 (CH arom), 130.5, 130.2 (C arom),
129.3, 128.7, 128.3, 127.8, 126.6 (CH arom), 68.6 (CH2
Z), 63.8 (aCH), 60.5 (gCH2), 52.4 (O–CH3), 49.3, 46.1
(2CH2 pyrro), 34.7 (bCH), 26.1, 24.8 (2CH2 pyrro), 15.7
(bCH3), 11.6 (dCH3); HRMS calcd for C27H33N3O6
[M+Na+] m/z 518.22616, found 518.2263.
4.4.2. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-hydrazinoalanine methyl ester (7,
R¼CH3). Oil; IR (NaCl) nmax/cmꢀ1: 3247, 1786, 1742,
1
1716; H NMR (300 MHz, CDCl3) d 9.19–8.43 (m, 1H,
bNH), 7.90–7.06 (m, 9H, arom Phe), 5.29–4.74 (m, 3H,
CH2 Z, aCH), 3.81–3.34 (m, 5H, O–CH3, CH2 pyrro),
3.17–2.92 (m, 2H, CH2 pyrro), 2.02–1.54 (m, 4H, 2CH2
pyrro), 1.43 (d, J¼7 Hz, 3H, bCH3); 13C NMR (CDCl3)
d 172.6 (COOCH3), 169.8, 169.5 (OC-pyrro), 168.6, 168.1
(N–COC6H4), 160.0, 155.7 (COOCH2Ph), 137.5 (C arom),
136.8, 136.3 (C arom), 130.8, 129.6, 128.8, 128.0 (CH
arom), 68.6, 68.5 (CH2 Z), 56.5 (aCH), 52.9 (O–CH3),
49.3, 46.1, 26.1, 24.8 (N–(CH2)4), 14.6 (bCH3); HRMS
calcd for C24H27N3O6 [M+Na+] m/z 476.17921, found
476.1793.
4.4.6. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-hydrazinophenylalanine methyl ester (7,
R¼CH2C6H5). Oil; IR (NaCl) nmax/cmꢀ1: 3289, 1792,
1
1743, 1718; H NMR (300 MHz, CDCl3) d 8.83–8.92 (m,
1H, bNH), 8.00–7.08 (m, 14H, arom), 5.37–4.90 (m, 3H,
CH2 Z and aCH), 3.83–3.47 (m, 5H, O–CH3 et pyrro), 3.40–
2.93 (m, 4H, pyrro et bCH2), 2.04–1.63 (m, 4H, pyrro); 13
C
NMR (CDCl3) d 171.7 (COOCH3), 170.1 (OC-pyrro), 167.9
(N–COC6H4), 156.6 (COOCH2Ph), 137.8 (C arom), 137.0,
136.4 (C arom), 135.3, 134.4, 132.7, 132.6, 132.2, 131.2
(CH arom), 131.0, 130.4, 128.7, 128.2, 126.8, 124.5, 124.1,
122.2 (CH arom), 69.0 (CH2 Z), 53.1 (O–CH3), 49.7, 46.6
(2CH2 pyrro), 35.5 (bCH2), 26.1, 24.8 (2CH2 pyrro);
HRMS calcd for C30H31N3O6 [M+Na+] m/z 552.21051,
found 552.2103.
4.4.3. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-hydrazinovaline methyl ester (7,
R¼CH(CH3)2). Oil; IR (NaCl) nmax/cmꢀ1: 3275, 1741,
1
1734, 1717; H NMR (300 MHz, CDCl3) d 9.20–8.90 (m,
1H, bNH), 7.89–7.70 (m, 1H, arom), 7.62–7.26 (m, 8H,
arom), 5.30–5.10 (m, 2H, CH2 Z), 4.93–4.36 (m, 1H,
aCH), 3.86–3.51 (m, 5H, O–CH3, pyrro), 3.35–2.93 (m,
2H, pyrro), 2.47–2.14 (m, 1H, bCH), 2.04–1.60 (m, 4H,
pyrro), 1.11–0.89 (m, 6H, gCH3); 13C NMR (CDCl3)
4.5. General procedure for the synthesis of
compound 8
Compound 7 (3 mmol) was dissolved in THF (20 mL) and
1.5 equiv of Boc2O and a catalytic amount of DMAP were
added. The mixture was stirred at room temperature for
6 h until completion (monitored by TLC). The solvent was
removed in vacuo, and the residue was chromatographied
on silica gel.
d
171.4 (COOCH3), 170.1 (OC-pyrro), 167.2 (N–
COC6H4), 160.0, 155.7 (COOCH2Ph), 137.5 (C arom),
136.8, 136.3 (C arom), 130.9, 130.6, 129.8, 129.0, 128.7,
128.2, 126.9 (CH arom), 69.0 (CH2 Z), 65.6 (aCH), 52.8
(O–CH3), 49.7, 46.5 (CH2 pyrro), 28.6 (bCH), 26.3, 25.0
(2CH2 pyrro), 20.1, 19.7 (gCH3); HRMS calcd for
C26H31N3O6 [M+Na+] m/z 504.21051, found 504.2109.
4.5.1. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-Nb, tert-butyloxycarbonyl-hydrazino-
4.4.4. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-hydrazinoleucine methyl ester (7,
R¼CH2CH(CH3)2). Oil; IR (NaCl) nmax/cmꢀ1: 3171,
glycine methyl ester (8, R¼H). Oil; IR (NaCl) nmax/cmꢀ1
:
1
1810, 1735, 1680; H NMR (300 MHz, CDCl3) d 7.23–
7.09 (m, 9H, arom), 5.28–5.15 (m, 2H, CH2 Z), 4.27–4.01
(m, 2H, aCH2), 3.80–3.33 (m, 7H, O–CH3 et pyrro), 1.88–
1.75 (m, 4H, pyrro), 1.31–1.85 (m, 9H, Boc); 13C NMR
(CDCl3) d 169.9, 169.5 (COOCH3), 169.0, 168.6 (OC-
pyrro), 168.4 (N–COC6H4), 155.8, 155.5 (COOCH2Ph),
151.0 (COOt-Bu), 136.7 (C arom Z), 136.3, 135.8 (C arom
C4H6), 129.4, 129.2, 128.9, 128.6, 128.1, 127.8, 127.2, 127.0
(CH arom), 85.5 (CBoc), 69.4 (CH2 Z), 54.1, 53.1 (aCH2),
52.6, 52.5 (O–CH3), 49.7, 46.5 (2CH2 pyrro), 28.2, 28.1
(CH3 Boc) et 26.7, 25.1 (2CH2 pyrro); HRMS calcd for
C28H33N3O8 [M+Na+] m/z 562.21599, found 562.2163.
1
1772, 1743, 1718; H NMR (300 MHz, CDCl3) d 8.68 (s,
1H, bNH), 7.76–7.48 (m, 1H, arom), 7.44–7.07 (m, 8H,
arom), 5.25–4.82 (m, 3H, CH2 Z, aCH), 3.65 (s, 3H, O–
CH3), 3.54–3.46 (m, 2H, pyrro), 3.05–2.90 (m, 2H, pyrro),
1.98–1.49 (m, 7H, pyrro, bCH2 and gCH), 0.91–0.75 (m,
6H, dCH3); 13C NMR (CDCl3) d 172.3 (COOCH3), 169.5
(OC-pyrro), 167.2 (N–COC6H4), 156.3 (COOCH2Ph),
136.8, 136.5 (C arom), 132.1 (CH arom), 130.9 (C arom),
130.0, 129.7, 129.5, 128.8, 128.4, 127.8, 126.6 (CH arom),
68.7 (CH2 Z), 60.0, 59.0 (aCH), 52.9 (O–CH3), 49.3, 46.1

I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
2229
4.5.2. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-Nb, tert-butyloxycarbonyl-hydrazino-
4.5.5. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-Nb, tert-butyloxycarbonyl-hydrazino-
isoleucine methyl ester (8, R¼CH(CH3)CH2CH3). Oil; IR
(NaCl) nmax/cmꢀ1: 1749, 1732, 1717, 1684, 1670; 1H
NMR (300 MHz, CDCl3) d 7.99–7.15 (m, 9H, arom),
5.36–5.08 (m, 2H, CH2 Z), 4.89–4.68 (m, 0.77H, aCH),
4.63–4.45 (m, 0.23H, aCH), 3.79–3.05 (m, 7H, O–CH3 et
pyrro), 2.04–1.57 (m, 4H, pyrro) et 1.45–0.71 (m, 18H,
bCH, gCH2, gCH3, Boc); 13C NMR (CDCl3) d 170.7,
170.5, 170.3 (COOCH3), 169.8 (OC-pyrro), 168.6 (N–
COC6H4), 156.0 (COOCH2Ph), 151.7 (COOt-Bu), 138.6,
138.4 (C arom Z), 136.3, 136.2, 134.4, 134.3 (C arom
C6H4), 131.7, 131.3, 129.4, 129.2, 129.1, 129.0, 128.9,
128.7, 128.6, 128.5, 128.4, 127.7, 127.2 (CH arom), 85.5,
85.4 (CBoc), 69.4, 69.2 (CH2 Z), 66.3 (aCH), 61.1
(gCH2), 52.6, 52.5 (O–CH3), 49.2, 49.1, 46.1, 46.0 (CH2
pyrro), 35.6, 35.4 (bCH), 28.1, 27.9, 27.8 (CH3 Boc), 26.2,
26.1 (CH2 pyrro), 16.1, 11.5 (b, dCH3); HRMS calcd for
C32H41N3O8 [M+Na+] m/z 618.27859, found 618.2785.
alanine methyl ester (8, R¼CH3). Oil; IR (NaCl) nmax
/
cmꢀ1: 1825, 1733, 1684; 1H NMR (300 MHz, CDCl3)
d 7.69–7.12 (m, 9H, arom), 5.22–5.01 (m, 2H, CH2 Z),
4.92 (q, J¼7 Hz, 0.26H, aCH), 4.84 (q, J¼7 Hz, 0.20H,
aCH), 4.71 (q, J¼7 Hz, 0.33H, aCH), 4.62 (q, J¼7 Hz,
0.24H, aCH), 3.66–3.52 (m, 5H, O–CH3 et pyrro), 3.39–
3.19 (m, 2H, pyrro), 2.01–1.73 (m, 4H, pyrro) et 1.55–1.35
(m, 12H, bCH3 et Boc); 13C NMR (CDCl3) d 171.5, 171.3,
171.2 (COOCH3), 171.1, 170.0, 169.7, 169.5 (OC-pyrro),
168.2, 168.1, 168.0 (N–COC6H4), 154.9, 154.8, 154.7
(COOCH2Ph), 151.4, 151.2, 151.1 (COOt-Bu), 137.3,
137.1, 136.9, 136.0, 135.8, 134.8 (C arom), 128.7, 128.5,
128.3, 127.6, 127.3, 126.9 (CH arom), 85.0, 84.9, 84.8
(CBoc), 68.9, 68.8 (CH2 Z), 58.8, 58.1, 57.7, 56.7 (aCH),
52.6, 52.5 (O–CH3), 49.2, 45.9, 26.3, 24.8 (N–(CH2)4),
27.7, 27.6, 27.5 (CBoc), 14.5, 14.4 (CH3); HRMS
calcd for C29H35N3O8 [M+Na+] m/z 576.23164, found
576.2316.
4.5.6. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-Nb, tert-butyloxycarbonyl-hydrazino-
phenylalanine methyl ester (8, R¼CH2C6H5). Oil; IR
4.5.3. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-Nb, tert-butyloxycarbonyl-hydrazino-
1
valine methyl ester (8, R¼CH(CH3)2). Oil; IR (NaCl) nmax
/
(NaCl) nmax/cmꢀ1: 1806, 1754, 1727, 1638, 7.81–7.07; H
cmꢀ1: 1786, 1740, 1723; 1H NMR (300 MHz, CDCl3)
d 8.03–7.18 (m, 9H, arom), 5.41–4.87 (m, 2.5H, 2CH2 Z,
0.5H, aCH), 4.84–4.37 (m, 0.5H, aCH), 3.92–3.55 (m,
5H, O–CH3 et pyrro), 3.26–2.97 (m, 2H, pyrro), 2.04–1.58
NMR (300 MHz, CDCl3) d 7.81–7.07 (m, 14H, arom),
5.35–4.82 (m, 3H, CH2 Z, aCH), 3.62–2.98 (m, 9H, O–
CH3, bCH2 et pyrro), 1.97–1.66 (m, 4H, pyrro), 1.31–0.95
(m, 9H, Boc); 13C NMR (CDCl3) d 170.3, 170.1, 170.0
(COOCH3), 169.8, 169.7 (OC-pyrro), 168.4, 168.3 (N–
COC6H4), 155.1, 154.6 (COOCH2Ph), 151.8, 151.7, 151.5,
151.3 (COOt-Bu), 138.1, 138.0, 137.3, 137.1, 137.0,
136.8, 136.1, 136.0, 134.6, 134.5 (C arom), 131.3, 131.2,
131.1, 130.1, 130.0, 129.9, 129.1, 129.0, 128.9, 128.8,
128.7, 128.5, 128.4, 128.2, 127.5, 127.3 (CH arom), 85.6,
85.5, 85.3 (CBoc), 69.8, 69.4, 69.3 (CH2 Z), 63.9, 63.7,
63.5, 62.5, 61.8 (aCH), 52.6, 52.4 (O–CH3), 49.3, 49.2,
46.3, 46.1, 46.0 (CH2 pyrro), 36.2, 36.1 (bCH2), 28.3,
27.9, 27.7 (CH3 Boc) et 26.5, 26.4, 25.0 (CH2 pyrro);
HRMS calcd for C35H39N3O8 629.27 [M+Na+] m/z
652.26294, found 652.2632.
(m, 4H, pyrro), 1.48–0.83 (m, 16H, gCH3, bCH, Boc); 13
C
NMR (CDCl3) d 170.1, 170.0, 169.9 (COOCH3), 169.6,
169.5, 169.4 (OC-pyrro), 168.2, 168.1, 168.0 (N–
COC6H4), 155.7, 155.6, 155.0, 154.9 (COOCH2Ph), 151.9,
151.8, 151.5, 151.4 (COOt-Bu), 138.3, 138.0, 137.7 (C
arom Z), 136.0, 135.9, 135.8, 134.0, 133.8, 133.7 (C arom
C6H4), 131.4, 131.0, 128.9, 128.8, 128.7, 128.6, 128.5,
128.4, 128.3, 128.2, 128.1, 128.0, 127.4, 127.2, 126.9 (CH
arom), 85.2, 85.1 (CBoc), 69.1, 69.0, 68.8 (CH2 Z), 66.8
(aCH), 52.2, 52.1 (O–CH3), 49.8, 46.0, 45.7 (CH2 pyrro),
29.1, 29.0 (bCH), 27.7, 27.6, 27.5, 27.4 (CH3 Boc), 26.1,
24.8, 24.7 (CH2 pyrro), 20.0, 19.4, 19.3, 19.2 (gCH3);
HRMS calcd for C31H39N3O8 [M+Na+] m/z 604.26294,
found 604.2630.
4.6. General procedure for the preparation of
compound 9
4.5.4. Na-(Benzyloxycarbonyl)-Nb, [2-(pyrrolidine-1-car-
bonyl)-benzoyl]-Nb, tert-butyloxycarbonyl-hydrazino-
leucine methyl ester (8, R¼CH2CH(CH3)2). Oil; IR
(NaCl) nmax/cmꢀ1: 1792, 1756, 1733, 1718, 1669; 1H
NMR (300 MHz, CDCl3) d 7.72–7.13 (m, 9H, arom),
5.33–4.68 (m, 3H, CH2 Z, aCH), 3.63–2.99 (m, 7H, O–
CH3 et pyrro), 1.84–1.32 (m, 7H, pyrro, gCH and bCH2),
1.22–0.81 (m, 15H, dCH3 et Boc); 13C NMR (CDCl3)
d 171.1, 171.0 (COOCH3), 170.1, 169.8 (OC-pyrro),
168.4, 168.2 (N–COC6H4), 155.4, 155.3, 154.8
(COOCH2Ph), 151.8, 151.5 (COOt-Bu), 138.2, 138.1,
137.9, 137.8 (C arom Z), 136.2, 136.1, 134.4, 134.3 (C
arom C6H4), 131.3, 131.1, 128.9, 128.7, 128.6, 128.5,
128.4, 127.7, 127.5, 127.2 (CH arom), 85.3 (CBoc), 69.2,
69.1 (CH2 Z), 60.6, 60.1, 59.3, 58.4 (aCH), 52.7, 52.6,
52.5 (O–CH3), 49.1, 46.2, 46.0, 45.9 (CH2 pyrro), 38.9,
38.6, 38.5, 38.4 (bCH2), 27.9, 27.7 (CH3 Boc), 26.4 (CH2
pyrro), 25.3, 25.2 (gCH), 25.0 (CH2 pyrro), 23.5, 23.4,
22.7, 22.6, 22.4 (dCH3); HRMS calcd for C32H41N3O8
[M+H+] m/z 596.2972, found 596.2979.
Compound 8 (3 mmol) was dissolved in THF (20 mL) and
a solution of methylamine (4.5 mmol, 2 M in MeOH) was
added at room temperature. After 3 h (R¼H, CH3, CH2Ph)
or 5 h (until completion monitored by TLC), the solvent
and the excess of amine were removed in vacuo and 9 was
purified by column chromatography.
4.6.1. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinoglycine methyl ester (9, R¼H). White
1
solid; IR (NaCl) nmax/cmꢀ1: 3325, 1733, 1717; H NMR
(300 MHz, CDCl3) d 7.50–7.18 (m, 5H, arom), 6.88–6.37
(m, 1H, bNH), 5.25–5.06 (m, 2H, CH2 Z), 4.46–4.24 (m,
2H, aCH2), 3.82–3.61 (m, 3H, O–CH3) et 1.61–1.31 (m,
9H, Boc); 13C NMR (CDCl3) d 170.6 (COOCH3), 156.6
(COOCH2Ph), 155.6 (COOt-Bu), 136.3 (C arom), 129.1,
129.0, 128.8, 128.7, 128.4 (CH arom), 82.5 (CBoc), 69.2,
69.0 (CH2 Z), 52.9 (O–CH3), 51.9 (aCH2) et 28.7 (CH3
Boc); HRMS calcd for C16H22N2O6 [M+Na+] m/z
361.13701, found 361.1372.

2230
I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
4.6.2. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinoalanine methyl ester (9, R¼CH3). Oil;
IR (NaCl) nmax/cmꢀ1: 3320, 1743, 1717; 1H NMR
(300 MHz, CDCl3) d 7.58–7.17 (m, 5H, arom), 6.88–6.35
(m, 1H, bNH), 5.47–4.66 (m, 3H, CH2 Z et aCH), 3.96–
3.56 (m, 3H, O–CH3), 1.60–1.32 (m, 12H, Boc et bCH3),
173.1 (COOCH3), 156.5 (COOCH2Ph), 155.7 (COOt-Bu),
136.2 (C arom), 128.9, 128.6, 128.4, 128.3 (CH arom),
81.6 (CBoc), 68.7 (CH2 Z), 57.6, 56.4 (aCH), 52.8 (O–
CH3), 28.5 (CH3 Boc) et 14.7 (bCH3); HRMS calcd for
C17H24N2O6 [M+Na+] m/z 375.15266, found 375.1528.
127.9, 127.8, 127.3, 127.1 (CH arom), 81.9 (CBoc), 68.8
(CH2 Z), 62.2 (aCH), 52.8 (O–CH3), 35.5 (bCH2), 28.5
(CH3 Boc); HRMS calcd for C23H28N2O6 [M+Na+] m/z
451.18396, found 451.1840.
4.7. General procedure for the preparation of
compound 10
a-Hydrazinoester 9 (1 mmol) was dissolved in 10 mL of
THF and LiOH (10 mL, 2.5 M) was added. The mixture
was stirred at room temperature for 1 h until completion
(monitored by TLC). The mixture was poured into water
and extracted three times with chloroform. The aqueous
layer was then acidified to pH 1 and extracted eight times
with EtOAc. The combined organic layers were dried over
MgSO4 and evaporated to give the desired a-hydrazino-
acid 10.
4.6.3. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinovaline methyl ester (9, R¼CH(CH3)2).
Oil; IR (NaCl) nmax/cmꢀ1: 3332, 1747, 1717; 1H NMR
(300 MHz, CDCl3) d 7.51–7.20 (m, 5H, arom), 6.80–6.34
(m, 1H, bNH), 5.29–5.05 (m, 2H, CH2 Z), 4.82–4.38 (m,
1H, aCH), 3.81–3.56 (m, 3H, O–CH3), 2.34–2.01 (m, 1H,
bCH), 1.53–1.30 (m, 9H, Boc), 1.16–0.80 (m, 6H, gCH3);
13C NMR (CDCl3) d 171.8 (COOCH3), 157.2 (COOCH2Ph),
155.2 (COOt-Bu), 136.3 (C arom), 129.1, 128.8, 128.5 (CH
arom), 81.9 (CBoc), 69.1 (CH2 Z), 65.9 (aCH), 52.7 (O–
CH3), 29.1 (bCH), 28.7 (CH3 Boc) et 20.3, 19.6 (2CH3);
HRMS calcd for C19H28N2O6 [M+Na+] m/z 403.18396,
found 403.1838.
4.7.1. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinoglycine (10, R¼H). Oil; IR (NaCl) nmax
/
cmꢀ1: 3466–3126, 1734, 1718; 1H NMR (300 MHz,
DMSO) d 9.83–8.91 (m, 1H, COOH), 7.39–7.27 (m, 5H,
arom), 5.76–5.73 (m, 1H, bNH), 5.24–4.48 (m, 2H, CH2
Z), 4.33–3.72 (m, 2H, aCH2) et 1.61–1.10 (m, 9H, Boc);
13C NMR (CDCl3) d 156.6 (COOCH2Ph), 155.6 (COOt-
Bu), 136.3 (C arom), 129.1, 129.0, 128.8, 128.7, 128.4
(CH arom), 82.5 (CBoc), 69.2, 69.0 (CH2 Z), 51.9 (aCH2),
28.7 (CH3 Boc).
4.6.4. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxy-
carbonyl)-hydrazinoleucine methyl ester (9, R¼
CH2CH(CH3)2). Oil; IR (NaCl) nmax/cmꢀ1: 3334, 1740,
1
1684; H NMR (300 MHz, CDCl3) d 7.49–7.17 (m, 5H,
4.7.2. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinoalanine (10, R¼CH3). Oil; IR (NaCl)
arom), 6.70–6.23 (m, 1H, bNH), 5.35–4.67 (m, 3H, CH2
Z, aCH), 3.84–3.54 (m, 3H, O–CH3), 1.88–1.24 (m, 12H,
bCH2, gCH, Boc) et 1.05–0.79 (m, 6H, dCH3); 13C NMR
(CDCl3) d 173.5 (COOCH3), 157.3 (COOCH2Ph), 155.4
(COOt-Bu), 136.3 (C arom), 129.1, 128.8, 128.5 (CH
arom), 81.8 (CBoc), 69.1 (CH2 Z), 60.4, 59.4 (aCH), 53.0
(O–CH3), 38.2 (bCH2), 29.1 (gCH), 28.7 (CH3 Boc), et
23.1, 21.9 (dCH3); HRMS calcd for C20H30N2O6 [M+Na+]
m/z 417.19961, found 417.1995.
1
nmax/cmꢀ1: 3500–3000, 1743, 1717; H NMR (300 MHz,
CDCl3) d 9.34–9.12 (m, 1H, COOH), 7.68–6.98 (m, 6H,
arom, bNH), 5.20–4.66 (m, 3H, CH2 Z, aCH), 1.45–1.28
(m, 12H, Boc, bCH3); 13C NMR (CDCl3) d 175.4, 175.0
(COOH), 157.4 (COOCH2Ph), 156.4 (COOt-Bu), 136.0 (C
arom), 128.9, 128.8, 128.7, 128.5, 128.3, 127.9, 127.5 (CH
arom), 82.9, 82.5 (CBoc), 69.2, 69.0, 68.6 (CH2 Z), 58.6
(aCH), 28.6, 28.5, 28.0 (CH3 Boc), 15.0, 14.6 (bCH3);
HRMS calcd for C16H22N2O6 [M+Na+] m/z 361.13701,
found 361.1372.
4.6.5. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxy-
carbonyl)-hydrazinoisoleucine methyl ester (9, R¼
CH(CH3)CH2CH3). Oil; IR (NaCl) nmax/cmꢀ1: 3333,
4.7.3. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinovaline (10, R¼CH(CH3)2). Oil; IR
(NaCl) nmax/cmꢀ1: 3490–3170, 1736, 1715; 1H NMR
(300 MHz, CDCl3) d 10.92–9.67 (m, 1H, COOH), 7.70–
6.59 (m, 6H, 5 arom, bNH), 5.35–4.93 (m, 2H, CH2 Z),
4.81–3.88 (m, 1H, aCH), 2.56–2.16 (m, 1H, bCH), 1.58–
0.90 (m, 15H, Boc, gCH3); 13C NMR (CDCl3) d 177.6,
176.9 (COOH), 156.8 (COOCH2Ph), 136.0 (C arom),
129.1, 128.9, 128.6 (CH arom), 83.4 (CBoc), 69.3, 69.1
(CH2 Z), 67.1 (aCH), 30.3 (bCH), 28.7 (CH3 Boc) et 20.9,
17.9 (gCH3); HRMS calcd for C18H26N2O6 [M+Na+] m/z
389.16831, found 389.1682.
1
1747, 1716; H NMR (300 MHz, CDCl3) d 7.43–7.12 (m,
5H, arom), 6.83–6.32 (m, 1H, bNH), 5.27–4.50 (m, 3H,
CH2 Z, aCH), 3.86–3.56 (m, 3H, O–CH3), 1.70–1.15 (m,
12H, Boc, bCH, gCH2) et 1.13–0.76 (m, 6H, dCH3); 13C
NMR (CDCl3) d 172.6 (COOCH3), 157.6 (COOCH2Ph),
136.3 (C arom), 129.1, 128.8, 128.5 (CH arom), 81.8
(CBoc), 69.2 (CH2 Z), 64.4 (aCH), 52.7 (O–CH3), 35.9
(bCH), 28.7 (CH3 Boc), 26.5 (gCH2), 16.3, 12.3 (b,
dCH3); HRMS calcd for C20H30N2O6 [M+Na+] m/z
417.19961, found 417.1993.
4.6.6. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinophenylalanine methyl ester (9, R¼
CH2C6H5). Oil; IR (NaCl) nmax/cmꢀ1: 3313, 1794, 1744,
4.7.4. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinoleucine (10, R¼CH2CH(CH3)2). Oil; IR
1
1
1717; H NMR (300 MHz, CDCl3) d 7.38–7.09 (m, 10H,
(NaCl) nmax/cmꢀ1: 3400–3186, 1718; H NMR (300 MHz,
arom), 6.86–6.35 (m, 1H, bNH), 5.35–4.77 (m, 3H, CH2
Z, aCH), 3.75–3.41 (m, 3H, O–CH3), 3.26–3.03 (m, 2H,
bCH2), 1.49–1.27 (m, 9H, Boc); 13C NMR (CDCl3)
d 171.5 (COOCH3), 156.4 (COOCH2Ph), 155.4 (COOt-
Bu), 137.2, 136.1 (C arom), 129.6, 128.9, 128.6, 128.4,
CDCl3) d 10.47–8.94 (m, 1H, COOH), 7.61–7.06 (m, 6H,
5 arom, bNH), 5.47–4.34 (m, 3H, CH2 Z, aCH), 1.94–1.05
(m, 12H, gCH, bCH2, Boc), 1.02–0.55 (m, 6H, dCH3); 13
C
NMR (CDCl3) d 156.7 (COOCH2Ph), 136.3 (C arom),
129.2, 128.9, 128.6 (CH arom), 85.8 (CBoc), 69.8, 69.3

I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
2231
(CH2 Z), 60.5 (aCH), 38.5, 38.1 (bCH2), 29.1 (gCH), 28.6
(CH3 Boc), et 23.8, 21.9 (dCH3); HRMS calcd for
C19H28N2O6 [M+Na+] m/z 403.18396, found 403.1839.
61.9, 61.5 (CH2 Fmoc), 56.3 (aCH), 52.5, 52.3 (O–CH3),
47.3 (CH Fmoc) et 14.3 (bCH3); HRMS calcd for
C27H26N2O6 [M+Na+] m/z 497.16831, found 497.1682.
4.7.5. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinoisoleucine (10, R¼CH(CH3)CH2CH3).
Oil; IR (NaCl) nmax/cmꢀ1: 3500–3124, 1733, 1716; 1H
NMR (300 MHz, CDCl3) d 10.13–9.31 (m, 1H, COOH),
7.49–6.55 (m, 6H, 5 arom, bNH), 5.56–4.05 (m, 3H, CH2
Z, aCH), 2.23–1.16 (m, 12H, Boc, gCH2, bCH), 1.09–
0.72 (m, 6H, bCH3, dCH3); 13C NMR (CDCl3) d 177.7,
177.2 (COOH), 157.1 (COOCH2Ph), 136.0 (C arom),
129.1, 128.9, 128.5 (CH arom), 82.3 (CBoc), 69.3, 69.0
(CH2 Z), 68.1 (aCH), 37.1 (bCH), 28.8, 28.6 (CH3 Boc),
26.8, 26.6, 26.3 (gCH2), 16.6, 16.1, 12.4, 12.2 (b, dCH3);
HRMS calcd for C19H28N2O6 [M+Na+] m/z 403.18396,
found 403.1837.
4.8.2. Na-(Benzyloxycarbonyl)-Nb (9H-fluoren-9-yl-
methoxycarbonyl)-hydrazinoglycine methyl ester (11,
R¼H). Oil; IR (NaCl) nmax/cmꢀ1: 3383, 1771, 1747, 1734,
1716; 1H NMR (300 MHz, CDCl3) d 8.01–6.72 (m,
14H, arom, bNH), 5.37–4.95 (m, 2H, CH2 Z), 4.58–
4.02 (m, 5H, aCH2, CH2 Fmoc, CH Fmoc), 3.80–3.63 (m,
3H, O–CH3); 13C NMR (CDCl3) d 170.5 (COOCH3),
156.4 (COOCH2Ph), 155.8 (CO Fmoc), 144.0, 141.9,
136.1 (C arom), 129.4, 129.1, 128.9, 128.6, 128.4,
127.9, 127.7 (CH arom), 69.4 (CH2 Z), 68.4 (CH2 Fmoc),
53.0 (O–CH3), 52.8 (aCH2), 47.6 (CH Fmoc); HRMS
calcd for C26H24N2O6 [M+Na+] m/z 483.15266, found
483.1530.
4.7.6. Na-(Benzyloxycarbonyl)-Nb (tert-butyloxycar-
bonyl)-hydrazinophenylalanine (10, R¼CH2C6H5). Oil;
4.9. General procedure for the preparation of
compound 12
1
IR (NaCl) nmax/cmꢀ1: 3601–3225, 1734, 1717; H NMR
(300 MHz, DMSO) d 9.98–6.72 (m, 13H, arom, bNH,
COOH), 5.49–4.60 (m, 3H, CH2 Z, aCH), 3.07–2.68 (m,
1H, bCH2), 2.67–2.53 (m, 1H, bCH2) 1.68–1.22 (m, 9H,
Boc); 13C NMR (DMSO) d 157.1, 156.8 (COOCH2Ph),
155.6 (COOt-Bu), 142.5, 140.8, 137.2, 136.2 (C arom),
129.0, 128.3, 128.1, 127.9, 127.8, 127.3, 127.0 (CH arom),
81.9 (CBoc), 66.5 (CH2 Z), 64.2, 62.8 (aCH2), 28.0 (CH3
Boc); HRMS calcd for C22H26N2O6 [M+Na+] m/z
437.16831, found 437.1685.
a-Hydrazinoester 11 (1 mmol) was dissolved in 2.25 mL of
CaCl2 (0.8 M) in i-PrOH–H2O, 7:3, at room temperature.
NaOH (1.2 equiv) was added and the mixture was stirred
for 7 h at room temperature. The mixture was poured into
water, acidified and extracted five times with EtOAc. The
combined organic layers were dried over MgSO4 and evap-
orated to give the desired a-hydrazinoacid 12.
4.9.1. Na-(Benzyloxycarbonyl)-Nb (9H-fluoren-9-yl-
methoxycarbonyl)-hydrazinoglycine (12, R¼H). Oil; IR
(NaCl) nmax/cmꢀ1: 3682–3085, 1734, 1717, 1653; 1H
NMR (300 MHz, CDCl3) d 10.38–9.70 (m, 1H, COOH),
8.29–6.93 (m, 14H, arom, bNH), 5.44–4.67 (m, 2H, CH2
Z), 4.60–4.12 (m, 5H, aCH2, CH2 Fmoc, CH Fmoc); 13C
NMR (CDCl3) d 157.1 (COOCH2Ph), 143.5, 140.8, 136.3
(C arom), 128.9, 128.4, 128.3, 127.9, 127.8, 127.7, 127.4,
125.3, 121.4, 120.1 (CH arom), 67.4, 67.2 (CH2 Z), 66.7,
66.6 (CH2 Fmoc), 59.8 (aCH2), 51.9 (CH Fmoc); HRMS
calcd for C25H22N2O6 [M+Na+] m/z 469.13701, found
469.1370.
4.8. General procedure for the preparation of
compound 11
A solution of dry hydrochloric acid in EtOAc (3 N, 3 mL)
was added to compound 9 (3 mmol). The mixture was stirred
at room temperature for 1 h until completion (monitored by
TLC). The mixture was poured into saturated solution of
NaHCO3 (pH 7–8) and extracted three times with EtOAc.
The combined organic layers were dried over MgSO4 and
evaporated. The residue was dissolved in a 10% solution of
Na2CO3 in water (7.95 mL, 7.5 mmol). Dioxane (4.5 mL) is
added and the mixture is stirred in an ice-water bath. 9-Fluor-
enylmethyl chlorocarbonate (1.16 g, 4.5 mmol) is added in
small portions and stirring is continued at an ice-water bath
temperature for 30 min and then at room temperature for
12 h. The reaction mixture is poured into water (180 mL),
the solution is acidified to pH 1, and then extracted with
diethyl ether. The combined organic layers were dried over
MgSO4 and evaporated in vacuo. The residue was chroma-
tographied on silica gel.
4.9.2. Na-(Benzyloxycarbonyl)-Nb (9H-fluoren-9-yl-
methoxycarbonyl)-hydrazinoalanine (12, R¼CH3). Oil;
1
IR (NaCl) nmax/cmꢀ1: 3447–3133, 1743, 1718; H NMR
(300 MHz, CDCl3) d 10.74–9.67 (m, 1H, COOH), 8.11–
6.73 (m, 14H, arom, bNH), 5.29–4.63 (m, 3H, CH2 Z,
aCH), 4.57–3.96 (m, 3H, CH Fmoc, CH2 Fmoc), 1.77–
1.35 (m, 3H, bCH3); 13C NMR (CDCl3) d 177.9 (COOH),
156.4 (COOCH2Ph), 144.2, 143.8, 141.9, 136.0 (C arom),
129.1, 128.9, 128.5, 127.8, 125.6, 120.7 (CH arom), 69.3,
68.6 (CH2 Z), 61.1 (CH2 Fmoc), 56.9 (aCH), 47.6 (CH
Fmoc), 14.8 (bCH3); HRMS calcd for C26H24N2O6
[M+Na+] m/z 483.15266, found 483.1527.
4.8.1. Na-(Benzyloxycarbonyl)-Nb (9H-fluoren-9-yl-
methoxycarbonyl)-hydrazinoalanine methyl ester (11,
R¼CH3). Oil; IR (NaCl) nmax/cmꢀ1: 3311, 1741, 1717; 1H
NMR (300 MHz, CDCl3) d 8.03–7.09 (m, 14H, arom),
7.02–6.24 (m, 1H, bNH), 5.52–4.65 (m, 3H, CH2 Z, aCH),
4.73–4.09 (m, 3H, CH Fmoc et CH2 Fmoc), 3.85–3.56
(m, 3H, O–CH3), 1.70–1.32 (m, 3H, bCH3); 13C NMR
4.10. General procedure for the preparation of
compound 13
A solution of dry hydrochloric acid in EtOAc (3 N, 3 mL)
was added to compound 9 (3 mmol). The mixture was stirred
at room temperature for 1 h until completion (monitored by
TLC). The mixture was poured into saturated solution of
NaHCO3 (pH 7–8) and extracted three times with EtOAc.
(CDCl3)
d 172.7, 171.1 (COOCH3), 157.2, 157.0
(COOCH2Ph), 156.9, 156.7, 156.1 (COOFmoc), 144.0,
143.7, 141.6, 136.0 (C arom), 128.6, 128.4, 128.3, 128.0,
127.3, 125.3, 120.2 (CH arom), 68.5, 68.1, 67.9 (CH2 Z),

2232
I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
The combined organic layers were dried over MgSO4 and
evaporated.
mixture was allowed to warm to room temperature and
stirred overnight. Saturated aqueous NaHCO3 solution was
added, and the mixture was stirred for another 10 min. The
mixture was diluted with H2O and extracted with Et2O
(3ꢂ). The combined organic layer were dried over MgSO4
and concentrated under reduced pressure. Then the residue
was purified by column chromatography (30%).
4.10.1. Na-(Benzyloxycarbonyl)-hydrazinoalanine
methyl ester (13, R¼CH3). Oil; IR (NaCl) nmax/cmꢀ1
:
1
3404, 1744, 1706; H NMR (300 MHz, CDCl3) 7.53–7.17
(m, 5H, H arom), 5.25–5.03 (m, 2H, CH2 Z), 4.99–4.62 (m,
1H, bNH), 4.12–3.81 (m, 2H, bNH, aCH), 3.80–3.54 (m,
3H, O–CH3), 1.61–1.30 (m, 3H, bCH3); 13C NMR
(CDCl3) d 172.7 (COOCH3), 156.5 (COOCH2Ph), 136.2
(C arom), 129.1, 128.8, 128.5 (CH arom), 68.5 (CH2 Z),
57.1 (aCH), 52.8 (O–CH3), 15.3 (bCH3); HRMS calcd for
C11H14N2O4 [M+Na+] m/z 253.1183, found 253.1169.
4.11.5. SOCl2 (entry 5, Table 2). A solution of N-Fmoc-
L-Ala-OH (3 mmol) in 17 mL of dry CH2Cl2 was treated
with SOCl2 (30 mmol) and the mixture refluxed for 2 h un-
der nitrogen. Solvent and excess of SOCl2 were removed in
vacuo and the residue was dissolved in 3.4 mL of CH2Cl2.
Addition of 34 mL of hexane allowed pure N-Fmoc-L-Ala-
Cl to precipitate. To a stirred solution of 13 (1.77 mmol)
in a solution of NaHCO3 (3.76 mmol) in 6.3 mL of dry
CH2Cl2 was added at ꢀ10 ꢁC dropwise N-Fmoc-L-Ala-Cl
in 2.5 mL of CH2Cl2. The mixture was allowed to warm to
0 ꢁC for 1 h, then 10 h more at room temperature. NaCl
was filtered and the solvent was evaporated. The residue
was chromatographied on silica gel (90%).
4.10.2. Na-(Benzyloxycarbonyl)-hydrazinoisoleucine
methyl ester (13, R¼CH(CH3)–CH2–CH3). Oil; IR
1
(NaCl) nmax/cmꢀ1: 3352, 1743, 1705; H NMR (300 MHz,
CDCl3) 7.56–7.16 (m, 5H, H arom), 5.25–5.07 (m, 2H,
CH2 Z), 4.82–4.29 (m, 1H, bNH), 4.22–3.81 (m, 2H, bNH,
aCH), 3.77–3.51 (m, 3H, O–CH3), 2.34–2.09 (m, 1H,
bCH), 1.63–1.38 (m, 1H, gCH2), 1.32–1.08 (m, 1H,
gCH2), 1.10–0.73 (m, 6H, bCH3 et gCH3); 13C NMR
(CDCl3) d 172.1 (COOCH3), 158.6 (COOCH2Ph), 136.7
(C arom), 129.1, 128.8, 128.5 (CH arom), 68.6 (CH2 Z),
64.9 (aCH), 52.4 (O–CH3), 35.3, 34.6 (bCH); 26.8, 26.5
(gCH2), 16.7, 16.4 (bCH3), 11.9, 11.4 (gCH3); HRMS calcd
for C14H20N2O4 [M+Na+] m/z 295.1652, found 295.1652.
4.11.6. Mixte anhydride (entry 6, Table 2). To a solution of
N-Fmoc-L-Ala-OH (5 mmol), NMM (5 mmol) in 5 mL of
THF was added at ꢀ10 ꢁC successively, isobutyl chlorofor-
mate (5 mmol) and a solution of 13 (5 mmol) in 5 mL of
THF. After half an hour at ꢀ10 ꢁC and 2 h at room tem-
perature, the mixture was filtered and the solvent was
evaporated. Then the residue was purified by column chro-
matography (86%).
4.11. Procedures for coupling reactions (see Table 2)
4.11.1. TBTU/HOBt/DIEA (entry 1, Table 2). To a stirred
solution of N-Fmoc-L-Ala-OH (1.35 mmol) in 3 mL of dry
THF was added at 0 ꢁC successively HOBt (1.35 mmol),
TBTU (1.35 mmol), a cold solution of 13 (0.45 mmol) in
5 mL of dry THF and DIEA (4.5 mmol). After 15 min at
0 ꢁC, the mixture was allowed to warm to room temperature
and stirred overnight. The solvent was evaporated and the
residue was chromatographied on silica gel (50%).
4.11.7. Acid fluoride (entries 7–10, Table 2). To a stirred
solution of the Fmoc aminoacid (2 mmol) in dry CH2Cl2
(10 mL) and pyridine (2 mmol, 2 mL) kept under nitrogen
atmosphere was added cyanuric fluoride (4 mmol,
0.33 mL) at ꢀ20 ꢁC. After stirring at room temperature for
3 h, crushed ice was added along with 10 mL of additional
CH2Cl2. The organic layer was separated and the aqueous
layer extracted once with 5 mL of CH2Cl2. The combined or-
ganic layers were extracted with 10 mL of ice-cold water
and dried (MgSO4), and the solvent was removed with a ro-
tary evaporator at room temperature to give the pure acid
fluoride. A cold solution (ꢀ10 ꢁC) of N-Fmoc-Xaa-F in
2.5 mL of CH2Cl2 is added dropwise to a stirred solution
of 13 (1.77 mmol) and NaHCO3 (3.76 mmol) in 6.3 mL of
dry CH2Cl2. The mixture was allowed to warm to 20 ꢁC
(room temperature) and stirred for 10 h. NaF was filtered
and the solvent was evaporated. The residue was chromato-
graphied on silica gel (98%).
4.11.2. DCC/HOBt (entry 4, Table 2). To a stirred solution
of 13 (1 equiv), N-Fmoc-L-Ala-OH (1 equiv) and HOBt
(1.5 equiv) in dry THF (0.5 M) was added at 0 ꢁC DCC
(1 equiv). After 1 h at 0 ꢁC, the mixture was allowed to
warm to room temperature and stirred overnight. The DCHU
was filtered, the solvent was evaporated and the residue was
dissolved in EtOAc. The mixture was stirred for 2 h at
ꢀ20 ꢁC and filtered. The solvent was evaporated and the
residue was chromatographied on silica gel (73%).
4.11.3. HATU/HOBt/DIEA (entry 2, Table 2). To a stirred
solution 13 (0.7 mmol), N-Fmoc-L-Ala-OH (0.7 mmol) and
HOBt (2.1 mmol) in 3 mL of dry THF was added at 0 ꢁC
successively HATU (0.7 mmol) and DIEA (2.1 mmol). After
15 min at 0 ꢁC, the mixture was allowed to warm to room
temperature and stirred overnight. The solvent was evapo-
rated and the residue was chromatographied on silica gel
(19%).
4.11.8. N-Fmoc-(S)-Ala-(R)-h(Z)Ala-OMe (14, R0¼
1
R¼Me). Wax solid; IR (NaCl) nmax/cmꢀ1: 3309, 1718; H
NMR (300 MHz, CDCl3) d 8.34–7.14 (m, 15H, arom,
bNH), 5.59–4.72 (m, 4H, CH2 Z, aCH hAla, NH Ala),
4.54–4.05 (m, 4H, CH Fmoc, CH2 Fmoc, aCH Ala), 3.89–
3.48 (m, 3H, O–CH3), 1.70–1.35 (m, 6H, CH3 Ala, CH3
hAla); 13C NMR (CDCl3) d 173.4 (COOCH3), 156.6 (CO
Fmoc), 155.9 (CO Z), 144.5, 144.4, 142.0, 136.3 (C arom),
129.1, 128.9, 128.4, 127.9, 125.7, 120.7 (CH arom), 69.1
(CH2 Z), 68.0 (CH2 Fmoc), 56.6 (aCH hAla), 53.1 (O–
CH3), 49.8 (aCH hAla), 47.8 (CH Fmoc), 18.6, 15.1 (CH3
Ala, CH3 hAla); HRMS calcd for C30H31N3O7 [M+Na+]
m/z 568.20542, found 568.2052.
4.11.4. HATU/NMM (entry 3, Table 2). Compound 13
(5 mmol) was dissolved in 2.5 mL of CH2Cl2 and cooled
in an ice bath. To the mixture was successively added,
NMM (15 mmol), a solution of N-Fmoc-L-Ala-OH
(5 mmol) in 1.3 mL of CH2Cl2 and HATU (5 mmol). The

I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
2233
4.11.9. N-Fmoc-(S)-Val-(R)-h(Z)Ala-OMe (14, R0¼i-Pr,
2. Lelais, G.; Seebach, D. Helv. Chim. Acta 2003, 86, 4152–4168.
ꢀ
R¼Me). Wax solid; IR (NaCl) nmax/cmꢀ1
:
1H NMR
3. (a) Aubry, A.; Bayeul, D.; Mangeot, J.-P.; Vidal, J.; Sterin, S.;
Collet, A.; Lecoq, A.; Marraud, M. Biopolymers 1991, 31, 793–
801; (b) G€unther, R.; Hofmann, H.-J. J. Am. Chem. Soc. 2001,
123, 247–255.
(300 MHz, CDCl3) d 8.47–7.97 (m, 1H, bNH), 7.94–6.99
(m, 13H, arom), 5.77–5.28 (m, 1H, aNH), 5.18–4.91 (m,
2H, CH2 Z), 4.85–4.28 (m, 2H, CH Fmoc, aCH hAla),
4.28–3.99 (m, 3H, CH2 Fmoc, aCH Val), 3.77–3.46 (m,
3H, O–CH3), 2.46–1.94 (m, 1H, bCH Val), 1.60–1.32 (m,
3H, CH3 hAla), 1.11–0.63 (gCH3 Val); 13C NMR (CDCl3)
4. (a) Achiwa, K.; Yamada, S.-I. Tetrahedron Lett. 1975, 16,
2701–2704; (b) Andreae, S.; Schmitz, E. Chem. Abstr. 1986,
107, 198926; (c) Andreae, S.; Schmitz, E. Synthesis 1991,
327–341; (d) Burk, M. J.; Martinez, J. P.; Feaster, J. E.;
Cosford, N. Tetrahedron 1994, 50, 4399–4428; (e) Carmi, A.;
Pollak, G.; Yellin, H. J. Org. Chem. 1960, 25, 44–46; (f) Di
Grandi, M. J.; Tilley, J. W. Tetrahedron Lett. 1996, 37, 4327–
4330; (g) Evans, D. A.; Britton, T. C.; Dorow, R. L.; Dellaria,
J. F. J. Am. Chem. Soc. 1986, 108, 6395–6397; (h) Evans,
D. A.; Britton, T. C.; Dorow, R. L.; Dellaria, J. F., Jr.
Tetrahedron 1988, 44, 5525–5540; (i) Gennari, C.; Colombo,
L.; Bertolini, G. J. Am. Chem. Soc. 1986, 108, 6394–6395; (j)
Gustafsson, H.; Ragnarsson, U. Acta Pharm. Suec. 1974, 11,
493–494; (k) Hoffman, R. V.; Kim, H. O. Tetrahedron Lett.
1990, 31, 2953–2956; (l) Karady, S.; Ly, M. G.; Pines, S. H.;
Sletzinger, M. J. Org. Chem. 1971, 36, 1949–1951; (m)
Klosterman, H. J.; Lamoureux, G. L.; Parsons, J. L.
Biochemistry 1976, 6, 170–177; (n) Oppolzer, W.; Moretti, R.
Tetrahedron 1988, 44, 5541–5552; (o) Schmitz, E.; Andreae,
S.; Schramm, S.; Albert, F. M.; Lohamm, D. German (East)
Patent DD 230865, 1985; Chem. Abstr. 1985, 105, 227301j;
(p) Schmitz, E.; Andreae, S.; Schramm, S.; Albert, F. M.;
Lohamm, D. German (East) Patent DD 240818, 1986;
Chem. Abstr. Ger. 1987, 198926a; (q) Schestakov, P.
Z. Angew. Chem. 1903, 16, 1061–1062; (r) Trimble, L. A.;
Vederas, J. C. J. Am. Chem. Soc. 1986, 108, 6397–6399; (s)
Viret, J.; Gabard, J.; Collet, A. Tetrahedron 1987, 43, 891–894.
d
175.3, 175.4 (CONH), 171.9 (COOCH3), 157.1
(COOCH2Ph), 155.9 (COOFmoc), 144.5, 144.3 (C arom
Fmoc), 136.2 (C arom Z), 129.1, 128.9, 128.6, 128.4,
127.8, 125.8, 120.6 (CH arom), 68.7, 67.9, 67.7 (CH2 Z),
61.1 (CH2 Fmoc), 59.8 (aCH Val), 56.7 (aCH hAla), 53.1
(O–CH3), 47.9, 47.8 (CH Fmoc), 31.9, 31.2 (bCH Val),
21.7, 19.9, 19.7, 18.3 (gCH3 Val), 15.3, 14.9 (bCH3 hAla);
HRMS calcd for C32H35N3O7 [M+Na+] m/z 596.23672,
found 596.2367.
4.11.10. N-Fmoc-(S)-Val-(R)-h(Z)Ile-OMe (14, R0¼i-Pr,
R¼CH(CH3)CH2CH3). Wax solid; IR (NaCl) nmax/cmꢀ1
:
1
3310, 1772, 1717; H NMR (300 MHz, CDCl3) d 8.50–
8.14 (m, 1H, bNH), 7.83–7.12 (m, 14H, arom), 5.81–5.27
(m, 1H, NH), 5.24–4.97 (m, 2H, CH2 Z), 4.92–4.56 (m,
1H, aCH hIle), 4.50–3.83 (m, 4H, CH Fmoc, CH2 Fmoc,
aCH Val), 3.81–3.49 (m, 3H, O–CH3), 2.42–1.76 (m, 2H,
bCH hIle, bCH Val), 1.64–0.37 (m, 19H, bCH3 hIle,
2gCH3 Val, gCH2 hIle, gCH3 hIle); 13C NMR (CDCl3)
d 175.7 (CONH), 172.5 (COOCH3), 157.2 (COOCH2Ph),
156.9 (COOFmoc), 144.6, 144.4, 144.3, 141.9 (C arom
Fmoc), 136.1 (C arom Z), 129.1, 129.0, 128.8, 128.5,
128.4, 127.7, 125.7, 120.6 (CH arom), 69.3 (CH2 Z), 68.0
(CH2 Fmoc), 59.7 (aCH Val), 59.4 (aCH hIle), 52.8 (O–
CH3), 47.7 (CH Fmoc), 35.4 (bCH hIle), 30.9 (bCH Val),
26.3 (gCH2 hIle), 19.8 (gCH3 Val), 18.1 (gCH3 Val), 16.6
(bCH3 hIle), 11.9 (gCH3 hIle); HRMS calcd for
C34H39N3O7 [M+Na+] m/z 616.3017, found 616.3033.
ꢀ
5. Bouillon, I.; Brosse, N.; Vanderesse, R.; Jamart-Gregoire, B.
Tetrahedron Lett. 2004, 45, 3569–3572.
6. Brosse, N.; Pinto, M.-F.; Bodiguel, J.; Jamart-Gregoire, B.
ꢀ
J. Org. Chem. 2001, 66, 2869–2873.
7. Kolasa, T.; Miller, M. J. J. Org. Chem. 1987, 52, 4978–4984.
ꢀ
8. Brosse, N.; Pinto, M.-F.; Jamart-Gregoire, B. J. Org. Chem.
2000, 65, 4370–4374.
9. (a) Osby, J. O.; Martin, M. G.; Ganem, B. Tetrahedron Lett.
1984, 25, 2093–2096; (b) Stocksdale, M. G.; Ramurthy, S.;
Miller, M. J. J. Org. Chem. 1998, 63, 1221–1225.
4.11.11. N-Fmoc-(R)-Ala-(R)-h(Z)Ala-OMe (15). Wax
solid; IR (NaCl) nmax/cmꢀ1: 3292, 1717; 1H NMR
(300 MHz, CDCl3) d 8.21 (s, 1H, bNH), 7.82–7.21 (m,
14H, arom), 5.56 (s, 1H, NH Ala), 5.26–4.78 (m, 3H, CH2
Z, aCH hAla), 4.54–4.05 (m, 4H, CH Fmoc, CH2 Fmoc,
aCH Ala), 3.79–3.48 (m, 3H, O–CH3), 1.60–1.10 (m, 6H,
CH3 Ala, CH3 hAla); 13C NMR (CDCl3) d 173.5 (COOCH3),
156.6 (CO Fmoc), 155.9 (CO Z), 144.4, 144.3, 141.9, 136.0
(C arom), 129.1, 128.9, 128.7, 128.4, 127.7, 125.7, 120.6
(CH arom), 69.2 (CH2 Z), 67.8 (CH2 Fmoc), 56.5 (aCH
hAla), 53.1 (O–CH3), 49.5 (aCH hAla), 47.7 (CH Fmoc),
18.9, 14.9 (CH3 Ala, CH3 hAla); HRMS calcd for
C30H31N3O7 [M+Na+] m/z 568.20542, found 568.2053.
ꢀ
10. Brosse, N.; Jamart-Gregoire, B. Tetrahedron Lett. 2002, 43,
249–251.
11. Bonnet, D.; Rommens, C.; Gras Masse, H.; Melnyk, O.
Tetrahedron Lett. 2000, 41, 45–48.
1
12. Compound 5 R¼CH3: H NMR (300 MHz, CDCl3): d 8.97–
7.91 (m, 1H, NH), 7.82–7.05 (m, 9H, arom), 6.10–6.08 (m,
1H, NH–Me), 5.25–4.75 (m, 3H, CH2 Z, aCH), 3.75–3.26
(m, 3H, O–CH3), 2.87–2.40 (m, 3H, NH–CH3), 1.50–0.90
(m, 3H, bCH3).
ꢀ
13. Brosse, N.; Grandeury, A.; Jamart-Gregoire, B. Tetrahedron
Lett. 2002, 43, 2009–2011.
14. Pascal, R.; Sola, R.; Labeguere, F.; Jouin, P. Eur. J. Org. Chem.
2000, 22, 3755–3761.
15. Guy, L.; Vidal, J.; Collet, A. J. Med. Chem. 1998, 41, 4833–
4843.
Acknowledgements
We thank Graduiertenkolleg 532 for a grant and Research
National Agency (ANR) for financial support (N
NT05_4_42848).
16. Vidal, J.; Damestoy, S.; Guy, L.; Hannachi, J. C.; Aubry, A.;
Collet, A. Chem.—Eur. J. 1997, 3, 1691–1709.
17. Hannachi, J.-C.; Vidal, J.; Mulatier, J.-C.; Collet, A. J. Org.
Chem. 2004, 69, 2367–2373.
References and notes
18. Huisgen, R.; Li, X.; Mloston, G.; Knorr, R.; Huber, H.;
Stephenson, D. S. Tetrahedron 1999, 55, 12793–12796.
1. Marraud, M.; Vanderesse, R. In Houben–Weyl; Goodman, M.,
Ed.; Thieme Stuttgart: New York, NY, 2003; pp 423–457.

2234
I. Bouillon et al. / Tetrahedron 63 (2007) 2223–2234
19. (a) Carpino, L. A.; Manssour, E.-S. M. E.; Ayman, E.-F. J. Org.
Chem. 1993, 58, 4162–4164; (b) Albericio, F.; Botfill, J. M.;
El-Faham, A.; Kates, S. A. J. Org. Chem. 1998, 63, 9678–9683.
20. Kholer, R.; Fanghanel, J.; Konig, B.; Luneberg, E.; Frosch, M.;
Rahfeld, J.-U.; Hilgenfeld, R.; Fischer, G.; Hacker, J.; Steinert,
M. Infect. Immun. 2003, 71, 4389–4397.
22. (a) Stavropoulos, G.; Karagiannis, K.; Anagnostides, S.;
Ministrouski, I.; Selinger, Z.; Chorev, M. Int. J. Protein Res.
1995, 45, 508–513; (b) Vaughan, J. R. J. Am. Chem. Soc.
1951, 73, 3547.
23. (a) Carpino, L. A.; Mansour, E.-S. M. E.; Sadat-Aalsee, D.
J. Org. Chem. 1991, 56, 2611–2614; (b) Carpino, L. A.;
Sadat-Aalaee, D.; Chao, H. G.; DeSelms, R. H. J. Am. Chem.
Soc. 1990, 112, 9651–9652.
21. Carpino, L. A.; Cohen, B. J.; Stephens, K. E.; Sadat-Aalaee, D.;
Tien, J. H.;Langridge, D. C. J. Org. Chem. 1986, 51, 3732–3734.