Short malonyl dehydro peptides as potential scaffolds for peptidomimetics by an efficient Knoevenagel reaction

Article abstract of DOI:10.1007/s00726-009-0462-1

Non-symmetric disubstituted malonamides rAA-mGly-AA;', obtained from Meldrum's acid, were considered as methylene active compounds and a Knoevenagel condensation methodology was developed involving piperidine and activated 4 A molecular sieves as catalysts. The reaction is efficient, broad in scope, and easy to perform and allows access to E/Z mixtures of short malonyl dehydro peptides (MDHPs) rAA-mΔ²AA -AA', partially modified retro peptides characterized by an interesting combination of retro and dehydro modifications in the same structure. Springer-Verlag 2010.

Full text of DOI:10.1007/s00726-009-0462-1

Amino Acids (2010) 39:461–470
DOI 10.1007/s00726-009-0462-1
ORIGINAL ARTICLE
Short malonyl dehydro peptides as potential scaffolds
for peptidomimetics by an efficient Knoevenagel reaction
•
Stefania Fioravanti Simona Gasbarri
•
•
Alberto Morreale Lucio Pellacani
•
•
Federico Ramadori Paolo A. Tardella
Received: 26 October 2009 / Accepted: 22 December 2009 / Published online: 22 January 2010
Ó Springer-Verlag 2010
Abstract Non-symmetric disubstituted malonamides
rAA-mGly-AA0, obtained from Meldrum’s acid, were
considered as methylene active compounds and a Knoeve-
nagel condensation methodology was developed involving
amide bonds, increases the resistance to biodegradation,
without decreasing the receptor binding ability and bio-
logical response of native peptides. Usually, a reverse
amide bond w[NHCO] allows to obtain peptidomimetics
with different conformational structures than the native
residue and that can be incorporated in stable b sheets.
Retro peptide units can be obtained by the introduction of a
gem-diamino moiety and/or a malonyl moiety into the
peptide sequence (Goodman and Chorev 1979; Spatola
1983; Wiley and Rich 1993).
˚
piperidine and activated 4 A molecular sieves as catalysts.
The reaction is efficient, broad in scope, and easy to perform
and allows access to E/Z mixtures of short malonyl dehydro
peptides (MDHPs) rAA-mD2AA00-AA0, partially modified
retro peptides characterized by an interesting combination
of retro and dehydro modifications in the same structure.
In this field, Meldrum’s acid has been recently reported
by us (Fioravanti et al. 2007) as a useful scaffold to obtain
non-symmetric disubstituted malonamides rAA-mGly-AA0
1 as building blocks for the synthesis of retro peptides
(Scheme 1).
Keywords Peptidomimetics ꢀ Amino acids ꢀ
Malonamides ꢀ Knoevenagel reaction
Introduction
Now our attention has turned towards the synthetic
elaboration of 1 with the aim to introduce, into the malo-
namide backbone, the olefinic moiety, interesting potential
site of further synthetic modifications, by a Knoevenagel
condensation.
The structural manipulation of natural peptide backbone is
widely applied to obtain peptidomimetic compounds that
have potential applications in different fields, since the use
of the same natural peptides is limited by their suscepti-
bility to proteolysis and poor bioavailability. Recently,
examples of modifications achieved through the introduc-
tion of small chemical molecule into the natural peptide are
increasing (Qi et al. 2001; Bong and Ghadiri 2001; Ojida
et al. 2005; Lawrence 2005). The introduction of a modi-
fication in a peptide chain, i.e. reversal of direction of the
The Knoevenagel condensation is a very important
reaction that directly provides the synthesis of different
substituted alkenes (Reeves 1966; Jones 1967; Smith and
March 2001; Li 2006). These last compounds are versatile
starting materials to synthesize a great variety of small
molecules and useful scaffolds in the construction of more
complex compounds. During our studies, we have suc-
cessfully tested several Knoevenagel conditions to syn-
thesize different EWG-substituted alkenes by the
condensation of aliphatic or aromatic aldehydes with suit-
able methylene active compounds. Recently, we reported a
synthetic strategy involving an Al2O3 catalyzed Knoeve-
nagel reaction (Texier-Boullet and Foucaud 1982) for the
construction of a library of acrylonitriles carrying L-a-
amino ester residues (Fioravanti et al. 2006), structural
S. Fioravanti ꢀ S. Gasbarri ꢀ A. Morreale ꢀ L. Pellacani (&) ꢀ
F. Ramadori ꢀ P. A. Tardella
`
Dipartimento di Chimica, Universita degli Studi di Roma
‘‘La Sapienza’’, P.le Aldo Moro 5, 00185 Roma, Italy
e-mail: lucio.pellacani@uniroma1.it
S. Fioravanti
e-mail: stefania.fioravanti@uniroma1.it
123

462
S. Fioravanti et al.
O
O
O
O
O
As reported in Table 1, the synthesis of 2a failed using
1
Al2O3 as catalyst. H-NMR and ES Q-TOF analyses, per-
O
O
AA−OR
AA−OR
H−AA−OR
H−AA'−OR'
formed on the crude mixture at regular times, showed only
the presence of both reagents even after 8 h of stirring. A
longer time of reaction (24 h) gave a complex mixture in
which the target compound was not present. The classical
Knoevenagel reaction conditions (Tietze and Beifuss 1993)
at reflux of toluene in the presence of catalytic amount of
piperidine (entry 2) were considered, but 2a was obtained in
low yields (25%) and the starting materials were recovered.
OH
AA'−OR'
1
O
Scheme 1 Synthesis of malonyl peptides
AA-OR
AA-OR
O
O
O
Knoevenagel
R''
reaction
O
˚
Finally, activated 4 A molecular sieves were added at
AA'-OR'
1
rAA-mGly-AA'
AA'-OR'
the reaction mixture and 2a was obtained in nearly quan-
titative yield after 6 h.
2
rAA-mΔ2AA''-AA'
The synthetic procedure was successfully applied to the
construction of an 18 member library of different partially
modified retro peptides 2b–s by the combination of 10 rAA-
mGly-AA0 (1) and 8 different aldehydes (Scheme 4). The
yields and the diastereomeric ratios are reported in Table 2.
As reported in Table 2, the reaction did not seem to
suffer from steric hindrance or to depend on electronic
effects, giving in all cases the expected E and Z malonyl
dehydro peptides in good yields, using both aliphatic and
aromatic aldehydes.
Scheme 2 Synthesis of malonyl dehydro peptides
analogues of tyrphostins, protein tyrosine kinase (PTK)
inhibitors (Levitzki and Gazit 1995).
Starting from these last results, our attention was turned
towards the synthetic elaboration of non-symmetric
disubstituted malonamides rAA-mGly-AA0 1, that can be
regarded not only as building blocks for the synthesis of
retro peptides but also as new potential methylene active
compounds (Scheme 2).
We would like to stress the high stereoselectivity
obtained in the reaction performed on disubstituted
malonamide rPro(OMe)-mGly-Gly(OMe) (entry 16), thus
extending the applicability of the methodology here reported
even starting from a malonamide carrying a tertiary amide
moiety, with respect to the previously reported TMSCl-
promoted Knoevenagel reaction (Ryabukhin et al. 2007).
The use of chiral aldehydes (entries 17 and 18) leads to
the multifunctionalized malonyl dehydro peptides 2r and
2s, which can be regarded as the first examples of small
partially modified retro peptide units where a glycosidic or
an amino glycosidic moiety is linked to the malonamidic
residue through a C=C double bond (Taylor 1998; Seitz
et al. 2001; Davis 2002; Galonic et al. 2003). The selective
ring opening reactions (Fioravanti et al. 2009) of the 1,3-
dioxolane (entry 17) and of the 1,3-oxazolidine ring (entry
18), followed by the oxidation of the primary alcoholic
functions, can provide new scaffolds carrying an a-hydroxy
or an a-amino acid moiety.
To the best of our knowledge, only Ryabukhin and co-
workers recently reported a TMSCl-promoted Knoevena-
gel reaction of symmetric malonamides with aromatic
aldehydes. These reactions, carried out for 8–10 h at
100°C, worked for primary or secondary methylene active
amides and failed with tertiary methylene active amides,
due to the decreasing CH acidity and steric effects
(Ryabukhin et al. 2007).
Results and discussion
With the aim to obtain the malonyl dehydro peptides
(MDHPs) 2, characterized by an interesting combination of
retro and dehydro modifications in the same structure
´
´
(Aleman et al. 1998; Aleman 2001), the symmetric
N,N-Boc protected malonamide rGly-mGly-Gly 1a was
synthesized from Meldrum’s acid by reported procedure
and isovaleraldehyde was chosen as aldehyde to test the
condensation reaction conditions (Scheme 3).
All the diastereomeric MDHPs mixtures were separated
by flash chromatography or by HPLC, and the (E)- and (Z)-
2c–p were obtained as pure compounds.
Scheme 3 Knoevenagel
reaction on symmetric malonyl
peptides
O
O
O
O
O
O
t-Bu
N
N
t-Bu
O
O
H
H
O
O
t-Bu
N
N
t-Bu
H
H
O
O
O
1a
rGly(O-t-Bu)-mGly-Gly(O-t-Bu)
2a
rGly(O-t-Bu)-mΔ2Leu-Gly(O-t-Bu)
123

Short malonyl dehydro peptides as potential scaffolds
463
Finally, as a first attempt to test the reactivity of the
synthesized malonyl peptides, 2a was reacted with N-Boc
L-cysteine methyl ester in the molar ratio 2a/amino ester/
NaH = 1:1.5:1.5 (Scheme 5).
Table 1 Optimization of Knoevenagel reaction conditions
Entry Catalyst
Solvent T (°C) Time (h) Yield (%)a
1
2
3
a
Al2O3
CH2Cl2 rt
8
24
6
–
Piperidine
PhCH3 115
25
95
After work-up, the analyses, performed on the crude
mixture purified by a short silica gel column (hexane/ethyl
acetate = 1:9), confirmed the synthesis of the expected
diastereomeric Michael adduct 3 (dr = 1.3:1 by NMR
spectra), suggesting thus the potential cysteine protease
inhibitor activity of the MDHP double bonds like efficient
electrophilic sites (Demarcus et al. 2001; Martina et al.
2005).
˚
Piperidine 4 A MS PhCH3 115
After flash chromatography
AA−OR
AA−OR
O
O
O
°
R''CHO, 4 A MS, piperidine
R''
PhCH3, reflux, 6 h
O
AA'−OR'
AA'−OR'
1
2b-s
rAA-mΔ2AA''-AA'
rAA-mGly-AA'
Conclusion
Scheme 4 Standard Knoevenagel condensation
In conclusion, the Knoevenagel condensation reactions
˚
performed in the presence of 4 A molecular sieves and a
The E/Z isomerism of synthesized MDHP residues is
analogous to that one present in the natural dehydro pep-
tides (DHPs) containing one or more dehydro amino acids
(DHAAs) in which the Ca chirality is replaced by the
double bond stereochemistry.
catalytic amount of piperidine led to the synthesis of
short malonyl dehydro peptides starting from poorly
reactive malonamides. The obtained MDHPs are charac-
terized by an interesting combination of retro and dehy-
dro modifications in the same structure and can be
regarded as important synthetic targets not only for their
potential biological applications, such as the correspond-
ing rAA-mGly-AA0 units, like mimetic compounds (Dolle
et al. 2008) of natural dehydro amino acid residues or
like new optically active alkyl malonyl units by asym-
metric hydrogenation (Kreuzfeld et al. 1998; Kreuzfeld
et al. 1999; Dobler et al. 2002; Drexler et al. 2003;
Au-Yeung et al. 2004; McFarland and Francis, 2005;
Minnaard et al. 2007) for the construction of new pep-
tidomimetic compounds (Davis 2003; Antos and Francis
2004, 2006; Joshi et al. 2004; Tilley and Francis 2006),
but also for their use as scaffolds to synthesize more
complex molecules by further functionalization of the
double bond.
As known, natural dehydro peptides having antibiotic
and phytotoxic activity, play an important role at the active
site of some enzymes (Stammer 1982) and show interesting
features, like the binding abilities towards metal ions
´
(Swia˛tek–Kozłowska et al. 2002), due to the isomerism of
the double bond that determines the peptide conformations.
The same isomerism (Fig. 1) present in MDHPs could
exert a conformational influence when inserted into a
peptidomimetic chain. The choice of the appropriate
aldehyde in the synthesis of some reported MDHPs allows
to introduce in the retro peptide backbone an unsaturated
residue mimetic of natural amino acids. Thus, different (E)-
and (Z)-MDHPs, namely malonyl dehydroleucine (2b, c, i,
j, l–q), dehydroisoleucine (2e), dehydrotyrosine(OMe) (2k)
and dehydrophenylalanine (2f, h) peptides were
synthesized.
Noteworthy, the MDHP 2q functionalized with the
methyl L-prolinate was obtained with a very high diaste-
reomeric purity (entry 16) and the E configuration of the
major isomer was assigned by a NOESY experiment per-
formed on the purified sample.
Experimental
IR spectra were recorded on a Perkin–Elmer 1600 FTIR
spectrophotometer in CHCl3 as the solvent. 1H-NMR
spectra were recorded at 200 and 300 MHz and 13C-NMR
spectra at 50 and 75 MHz with Varian Gemini and Varian
XL instruments. The NOESY experiment was performed at
400 MHz with a Bruker instrument. CDCl3 was used as the
solvent and CHCl3 as the internal standard. HRMS and ES
Q-TOF analyses were performed using a Micromass
Q-TOF spectrometer equipped with an ESI source and a
syringe pump. Anhydrous PhCH3 was used as such.
O
R
O
O
R
H
N
N
N
N
H
H
H
O
dehydro peptide
DHP
malonyl dehydro peptide
MDHP
˚
Type 4 A molecular sieves (Merck, beads, diameter
Fig. 1 Natural and malonyl dehydro peptides
1.7–2.4 mm) were activated by heating at 280°C, 2 h,
123

464
S. Fioravanti et al.
mixtures of HPLC grade hexane and ethyl acetate. NaH
(55–65% suspension in mineral oil) was washed twice with
pentane and dried under nitrogen. Compounds 1 were
synthesized following reported procedures (Fioravanti
et al. 2007).
Table 2 Synthesis of MDHPs
Entry AA–OR
AA0–OR
R00CHO
MDPH Yield Drb
(%)a
1
GlyOMe
Asp(OMe)2
2b
70
1.2/1c
O
H
O
H
di-tert-Butyl 2,20-[(1,3-dioxopropane-1,3-diyl)
diimino]diacetate (1a)
2
3
4
PheOMe
PheOMe
PheOMe
GlyOMe
GlyOMe
GlyOMe
2c
2d
2e
75
62
85
3/1
O
H
1.5/1
2/1
Pale yellow oil, 95%. IR: 3,419, 3,323, 1,736, 1,681 cm-1
.
O
H
HRMS (ES Q-TOF) calcd for C15H26N2NaO6 (M ? Na)?:
353.1689; found: 353.1701. 1H-NMR d 1.37 (s, 18 H), 3.25
(s, 2 H), 3.81–3.88 (m, 4 H), 7.72 (br, 2 H, NH). 13C-NMR
d 27.6 (six), 41.7 (two), 41.9, 81.5 (two), 167.3 (two),
168.3 (two).
O
H
5
PheOMe
GlyOMe
2f
65
1.3/1
O
6
7
PheOMe
PheOMe
GlyOMe
2g
2h
70
83
1.4/1
1.3/1
O
H
Synthesis of malonyl dehydro peptides (2a–s). General
procedure
O
H
GlyO-t-Bu
A solution of 1 (1 mmol) and aldehyde (3 mmol) in
anhydrous toluene (10 ml) was added under Ar in a round-
˚
bottom flask containing previously activated 4 A molecular
O
H
8
9
Phe-OMe GlyO-t-Bu
2i
2j
85
60
1.5/1
2.5/1
O
H
GlyOMe
GlyOMe
b-AlaOMe
b-AlaOMe
sieves (5 g). A catalytic amount of piperidine (0.2 mmol)
was added. The reactions were stirred at reflux and fol-
1
lowed by H-NMR analysis until disappearance of meth-
O
H
10
2k
67
1.3/1
ylene proton signal of 1 (6 h). The crude mixtures were
filtered under Ar through plugs of celite using diethyl ether
as eluent. After solvent removal compounds 2 were
obtained in the yields reported in Table 2. The pure dia-
stereomers were obtained directly by flash chromatography
of the crude or by HPLC-RI with a semipreparative column
(7.8 9 300 mm, flow 3.5 ml/min), using as eluents dif-
ferent mixtures of hexane/ethyl acetate.
O
O
H
11
12
13
14
15
16
GlyOBz
AlaOMe
AlaOMe
ValOMe
PheOMe
ProOMe
b-AlaOMe
Asp(OMe)2
GlyOBz
2l
83
60
68
85
73
56
2/1
O
H
2m
2n
2o
2p
2q
1.5/1
2/1
O
H
O
H
Asp(OMe)2
MetOMe
1/1
O
H
1/1
tert-Butyl 2-[2-(2-tert-butoxy-2-oxoethylcarbamoyl)-
5-methylhex-2-enamido]acetate (2a)
O
H
GlyOMe
19/1
Pale yellow oil, 95%. IR: 3,421, 3,332, 1,732, 1,678,
1,632 cm-1. HRMS (ES Q-TOF) calcd for C20H34N2NaO6
(M ? Na)?: 421.2315; found: 421.2319. 1H-NMR d 0.93 (d,
J = 6.6 Hz, 6 H), 1.45 (s, 9 H), 1.47 (s, 9 H), 1.69–1.88 (m, 1
H), 2.33 (m, 2 H), 3.99 (dd, J = 5.3 Hz, J = 10.0 Hz, 4 H),
6.86 (br, 1 H, NH), 6.96 (t, J = 7.8 Hz, 1 H); 7.62 (br, 1 H,
NH). 13C-NMR 22.3 (two), 27.9 (six), 33.8, 38.2, 42.0 (two),
82.1 (two), 129.1, 145.8, 167.2, 168.5, 169.2, 170.1.
17
GlyO-t-Bu GlyO-t-Bu
GlyO-t-Bu GlyO-t-Bu
2r
2s
78
63
–
–
O
O
O
CHO
18
N
Boc
CHO
a
After flash chromatography
1
Determined by H-NMR and HPLC-UV spectra performed on the
b
crude mixtures
c
Not separated
Dimethyl (2S)-2-[2-(2-methoxy-2-oxoethylcarbamoyl)-
5-methylhex-2-enamido]succinate (2b)
under vacuum and Ar atmosphere. HPLC analyses were
performed with an instrument Varian 9002 equipped with a
Varian 9050 UV detector using an analytical column
(3.9 9 300 mm, flow rate 1.3 ml/min). Eluents were
Orange oil, 70%. IR: 3,426, 3,332, 1,733, 1,685,
1,647 cm-1. HRMS (ES Q-TOF) calcd for C17H26N2NaO8
1
(M ? Na)?: 409.1587; found: 409.1583. H-NMR d 0.94
(major, d, J = 1.8 Hz, 6 H), 0.96 (minor, d, J = 1.8 Hz, 6
123

Short malonyl dehydro peptides as potential scaffolds
465
O
S
O
O
O
O
O
t-Bu
NaH, THF
5h, rt
N
N
t-Bu
H
N
H
H
O
O
O
O
t-Bu
N
N
t-Bu
Boc
SH
H
H
+
H
N
O
O
O
O
Boc
O
O
2a
N-Boc L-cysteine methyl ester
3 (78%)
Scheme 5 Michael addition of a L-cysteine derivative
Methyl (2S)-2-[2-(2-methoxy-2-oxoethylcarbamoyl)
hept-2-enamido]-3-phenylpropanoate (2d)
H), 1.73–1.87 (m, 2 H), 2.32 (major, t, J = 7.6 Hz, 2 H),
2.38 (minor, t, J = 7.6 Hz, 2 H), 2.83–3.14 (m, 4 H), 3.69
(major, s, 3 H), 3.70 (minor, s, 3 H), 3.75 (minor, s, 3 H),
3.76 (major, s, 3 H), 3.77 (major, s, 3 H), 3.78 (minor, s, 3
H), 4.08 (major, d, J = 5.4 Hz, 2 H), 4.14 (minor, d,
J = 5.4 Hz, 2 H), 4.88–4.94 (major, m, 1 H), 4.95–5.00
(minor, m, 1 H), 6.94 (major, t, J = 7.9 Hz, 1 H), 7.05
(minor, t, J = 7.7 Hz, 1 H), 7.05–7.12 (m, 2 H, NH), 7.75–
7.83 (m, 2 H, NH). 13C-NMR d 22.4, 28.4, 35.8 (minor),
36.0 (major), 38.2 (minor), 38.3 (major), 41.3 (major), 41.6
(minor), 48.7 (major), 49.0 (minor), 52.0 (major), 52.1
(minor), 52.2 (minor), 52.4 (major), 52.8 (minor), 52.9
(major), 131.2 (minor), 131.3 (major), 146.5 (major), 147.0
(minor), 164.3 (minor), 165.0 (major), 166.2 (minor), 166.5
(major), 169.9 (major), 170.0 (minor), 170.6 (major), 170.9
(minor), 171.0 (minor), 171.2 (major).
Deep orange oil, 62%. IR: 3,415, 3,342, 1,736, 1,672,
1,631 cm-1 HRMS (ES Q-TOF) calcd for C21H28N2NaO6
(M ? Na)?: 427.1845; found: 427.1840. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 35:65).
Major: 1H-NMR d 0.84 (t, J = 6.6 Hz, 3 H), 1.05–1.36 (m,
4 H), 1.85–2.08 (m, 2 H), 2.85–3.18 (m, 2 H), 3.62 (s, 3 H),
3.65 (s, 3 H), 4.05–4.32 (m, 2 H), 4.63–4.89 (m, 1 H), 6.58
(t, J = 7.8 Hz, 1 H), 6.80 (br, 1 NH), 7.20–7.25 (m, 5 H),
7.48 (br, 1 NH). 13C-NMR d 22.3, 34.1, 35.4 (two), 37.6,
42.1, 52.1 (two), 53.5, 126.8, 128.3 (two), 129.0 (two),
131.3, 135.8, 145.6, 167.0, 167.3, 169.8, 171.5. Minor: 1H-
NMR d 0.81 (t, J = 6.6 Hz, 3 H), 1.06–1.30 (m, 4 H),
1.88–2.07 (m, 2 H), 2.85–3.09 (m, 2 H), 3.60 (s, 3 H), 3.69
(s, 3 H), 4.12–4.29 (m, 2 H), 4.70–4.85 (m, 1 H), 6.77 (t,
J = 7.8 Hz, 1 H), 7.01–7.19 (m, 5 H), 7.40 (br, 1 NH), 7.56
(br, 1 NH). 13C-NMR d 22.4, 34.2, 36.4 (two), 38.0, 41.9,
51.9 (two), 53.5, 126.3, 128.3 (two), 128.8 (two), 131.8,
135.7, 146.7, 166.9, 167.8, 170.1, 171.9.
Methyl (2S)-2-[2-(2-methoxy-2-oxoethylcarbamoyl)-
5-methylhex-2-enamido]-3-phenylpropanoate (2c)
Deep orange oil, 75%. IR: 3,426, 3,335, 1,742, 1,678,
1,631 cm-1 HRMS (ES Q-TOF) calcd for C21H28N2NaO6
(M ? Na)?: 427.1845; found: 427.1856. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 65:35).
Methyl (2S)-2-[2-(2-methoxy-2-oxoethylcarbamoyl)-
4-methylhex-2-enamido]-3-phenylpropanoate (2e)
1
Major: H-NMR d 0.83 (d, J = 6.6 Hz, 6 H), 1.64–1.81
Deep orange oil, 85%. IR: 3,412, 3,342, 1,742, 1,672,
1,637 cm-1. HRMS (ES Q-TOF) calcd for C21H28N2NaO6
(M ? Na)?: 427.1845; found: 427.1853. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 65:35).
Major: 1H-NMR d 0.91 (t, J = 6.5 Hz, 3 H), 1.03 (d,
J = 6.5 Hz, 3 H), 1.22–1.49 (m, 2 H), 2.67–2.90 (m, 1 H),
3.02–3.38 (m, 2 H), 3.76 (s, 3 H), 3.79 (s, 3 H), 4.04–4.21
(m, 2 H), 4.78–4.99 (m, 1 H), 6.68 (d, J = 8.4 Hz, 1 H),
6.88 (br, 1 H, NH), 7.10–7.46 (m, 5 H), 7.58 (br, 1 H, NH).
13C-NMR d 21.9, 22.2, 28.3, 32.7, 38.0, 41.2, 52.2 (two),
53.5, 126.9, 128.3 (two), 129.2 (two), 131.3, 135.6, 145.9,
164.6, 166.5, 169.8, 171.9. Minor: 1H-NMR d 0.72 (t,
J = 6.5 Hz, 3 H), 1.05 (d, J = 6.5 Hz, 3 H), 1.21–1.48 (m,
2 H), 2.35–2.51 (m, 1 H), 3.02–3.38 (m, 2 H), 3.71 (s, 3 H),
(m, 1 H), 2.27 (t, J = 7.4 Hz, 2 H), 3.08–3.34 (m, 2 H),
3.75 (s, 3 H), 3.80 (s, 3 H), 4.04–4.12 (m, 2 H), 4.83–5.02
(m, 1 H), 6.58 (br, 1 H, NH), 6.95 (t, J = 7.8 Hz, 1 H),
7.10–7.14 (m, 5 H), 7.62 (br, 1 H, NH). 13C-NMR d 22.3
(two), 28.2, 37.2, 38.1, 41.3, 52.2 (two), 53.5, 127.0, 128.4
(two), 129.1 (two), 131.1, 135.7, 146.0, 164.6, 166.5,
169.8, 171.6. Minor: 1H-NMR d 0.87 (d, J = 6.5 Hz, 6 H),
1.56–1.78 (m, 1 H), 2.28 (t, J = 6.9 Hz, 2 H), 2.96–3.22
(m, 2 H), 3.68 (s, 3 H), 3.72 (s, 3 H), 4.02–4.13 (m, 2 H),
4.73–4.88 (m, 1 H), 6.78 (t, J = 7.7 Hz, 1 H), 6.88 (br, 1
H, NH), 7.04–7.25 (m, 5 H), 7.33 (br, 1 H, NH). 13C-NMR
d 22.3 (two), 28.2, 37.4, 38.2, 43.1, 52.8 (two), 54.1, 127.0,
128.4 (two), 129.2 (two), 131.0, 135.8, 146.0, 164.8, 165.9,
169.8, 171.6.
123

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S. Fioravanti et al.
3.78 (s, 3 H), 4.04–4.23 (m, 2 H), 4.80–5.00 (m, 1 H), 6.59
(d, J = 8.4 Hz, 1 H), 7.10–7.44 (m, 5 H), 7.57 (br, 1 H,
NH), 7.79 (br, 1 H, NH). 13C-NMR d 21.9, 22.2, 28.3, 32.4,
38.0, 41.2, 52.4 (two), 53.5, 126.9, 128.3 (two), 129.2
(two), 131.1, 135.6, 146.2, 164.6, 166.5, 170.0, 171.6.
semi-preparative column (eluent hexane/ethyl acetate
1
70:30). Major: H-NMR d 1.48 (s, 9 H), 2.96–3.00 (m, 2
H), 3.64 (s, 3 H), 3.98–4.02 (m, 2 H), 4.85–4.94 (m, 1 H),
7.15–7.43 (m, 10 H), 7.70 (br, 2 H, NH), 7.88 (s, 1 H, CH).
13C-NMR d 27.8 (three), 37.7, 42.4, 52.1, 53.4, 82.2, 127.1
(two), 127.2 (two), 128.4 (four), 128.7, 129.0, 129.3, 133.1,
136.1, 140.3, 167.4, 168.2, 171.2, 171.5. Minor: 1H-NMR d
1.43 (s, 9 H), 3.13–3.22 (m, 2 H), 3.74 (s, 3 H), 3.87–3.94
(m, 2 H,), 4.83–4.94 (m, 1 H), 7.16–7.45 (m, 10 H), 7.83 (s,
1 H), 7.95 (br, 2 H, NH). 13C-NMR d 27.7 (three), 37.6,
42.4, 52.0, 53.5, 82.2, 127.2 (two), 127.5 (two), 128.3
(four), 128.8, 129.0, 129.4, 134.2, 136.3, 139.1, 167.6,
168.4, 171.0, 171.9.
Methyl (2S)-2-[2-(2-methoxy-2-oxoethylcarbamoyl)-
3-phenylprop-2-enamido]-3-phenylpropanoate (2f)
Deep orange oil, 65%. IR: 3,413, 3,331, 1,743, 1,672,
1,645 cm-1 HRMS (ES Q-TOF) calcd for C23H24N2NaO6
(M ? Na)?: 447.1532; found: 447.1528. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 60:40).
Major: 1H-NMR d 2.95–3.21 (m, 2 H), 3.60 (s, 6 H), 3.87–
3.96 (m, 2 H), 4.71–4.88 (m, 1 H), 6.29 (br, 2 H, NH),
7.09–7.41 (m, 10 H), 7.71 (s, 1 H). 13C-NMR d 37.2, 41.6,
52.3 (two), 53.5, 127.0 (four), 128.6 (two), 128.9 (two),
129.4 (two), 129.8 (two), 133.1, 141.0, 163.6, 167.5, 169.7,
171.5. Minor: 1H-NMR d 3.05–3.15 (m, 2 H), 3.65 (s, 6 H),
3.94 (d, J = 5.5 Hz, 2 H), 4.73–4.85 (m, 1 H), 6.48 (br, 2
H, NH), 7.09–7.43 (m, 10 H), 7.75 (s, 1 H).13C-NMR d
37.8, 41.3, 52.1 (two), 53.3, 126.9 (four), 128.4 (two),
129.2 (two), 129.5 (two), 129.8 (two), 135.4, 140.9, 163.2,
167.7, 169.3, 171.1.
Methyl (2S)-2-[2-(2-tert-butoxy-2-oxoethylcarbamoyl)-
5-methylhex-2-enamido]-3-phenylpropanoate (2i)
Deep orange oil, 85%. IR: 3,422, 3,333, 1,739, 1,678,
1,641 cm-1. HRMS (ES Q-TOF) calcd for C24H34N2NaO6
(M ? Na)?: 469.2315; found: 469.2309. HPLC-RI with a
semi-preparative column (eluent hexane/ethyl acetate
1
70:30). Major: H-NMR d 0.83 (d, J = 6.2 Hz, 6 H), 1.47
(s, 9 H), 1.64–1.90 (m, 1 H), 2.00–2.19 (m, 2 H), 2.99–3.26
(m, 2 H), 3.71 (s, 3 H), 3.89–4.07 (m, 2 H), 4.80–5.00 (m, 1
H), 6.79 (br,1 H, NH), 6.90 (t, J = 7.7 Hz, 1 H), 7.08–7.32
(m, 5 H), 7.52 (br, 1 H, NH). 13C-NMR d 22.4 (two), 27.7
(three), 28.1, 37.2, 38.2, 41.3, 52.2, 53.4, 82.1, 127.1, 128.4
(two), 129.1 (two), 131.1, 135.7, 146.0, 164.6, 166.6,
169.9, 171.2. Minor: 1H-NMR d 0.90 (d, J = 6.2 Hz, 6 H),
1.48 (s, 9 H), 1.69–1.89 (m, 1 H), 1.96–2.11 (m, 2 H),
2.98–3.22 (m, 2 H), 3.63 (s, 3 H), 3.68–3.95 (m, 2 H),
4.69–4.92 (m, 1 H), 6.77 (br, 1 H, 1 NH), 6.84 (t,
J = 7.7 Hz, 1 H), 6.99–7.27 (m, 5 H), 7.50 (br, 1 H, NH).
13C-NMR d 22.4 (two), 27.6 (three), 28.1, 37.2, 38.2, 41.3,
52.2, 53.4, 82.1, 127.3, 128.3 (two), 128.9 (two), 131.3,
135.7, 145.8, 164.6, 166.6, 170.0, 171.3.
Methyl (2S)-2-{3-(furan-2-yl)-2-[(2-methoxy-2-
oxoethyl)carbamoyl]acrylamido}-3-phenylpropanoate
(2g)
Deep orange oil, 70%. IR: 3,419, 3,323, 1,736, 1,681,
1,645 cm-1 HRMS (ES Q-TOF) calcd for C21H22N2NaO7
(M ? Na)?: 437.1325; found: 437.1329. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 60:40).
1
Major: H-NMR d 2.92–3.47 (m, 2 H), 3.68 (s, 6 H), 4.17
(d, J = 5.5 Hz, 2 H), 4.69–4.82 (m, 1 H), 6.42–6.50 (m, 1
H), 6.81–6.89 (m, 2 H), 7.12–7.36 (m, 5 H), 7.50 (s, 1 H),
7.65 (br, 2 H, NH). 13C-NMR d 37.6, 41.2, 51.9 (two),
54.0, 112.3, 117.5, 124.7, 126.1 (two), 128.2 (two), 129.1,
136.0, 145.3, 149.1, 152.3, 163.5, 167.2, 169.7, 171.3.
Methyl 3-[2-(2-methoxy-2-oxoethylcarbamoyl)-
5-methylhex-2-enamido]propanoate (2j)
1
Minor: H-NMR d 2.94–3.28 (m, 2 H), 3.68 (s, 3 H), 3.71
(s, 3 H), 3.93 (d, J = 5.5 Hz, 2 H), 4.90–5.04 (m, 1 H),
6.27–6.32 (m, 1 H), 6.53–6.61 (m, 2 H), 6.99–7.28 (m, 5
H), 7.39 (s, 1 H), 7.53 (br, 2 H, NH). 13C-NMR d 37.1,
41.5, 53.3 (two), 53.9, 112.1, 117.3, 124.5, 126.0 (two),
128.4 (two), 129.0, 136.2, 145.2, 148.8, 153.1, 164.1,
167.1, 169.5, 171.7.
Yellow oil, 67%. IR: 3,426, 33,358, 1,742, 1,678,
1,636 cm-1. HRMS (ES Q-TOF) calcd for C15H24N2NaO6
(M ? Na)?: 351.1532; found: 351.1538. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 40:60).
1
Major: H-NMR d 0.93 (d, J = 6.2 Hz, 6 H), 1.51–1.77
(m, 1 H), 2.02–2.31 (m, 2 H), 2.47–2.65 (m, 2 H), 3.39–
3.58 (m, 2 H), 3.66 (s, 3 H), 3.72 (s, 3 H), 3.98–4.10 (m, 2
H), 6.82 (t, J = 7.7 Hz, 1 H), 6.90 (br, 1 H, NH), 7.83 (br,
1 H, NH). 13C-NMR d 22.3 (two), 28.3, 33.6, 35.1, 38.2,
41.3, 51.7 (two), 132.3, 143.8, 165.0, 166.6, 169.3, 172.5.
Methyl (2S)-2-[2-(2-tert-butoxy-2-oxoethylcarbamoyl)-
3-phenylacrylamido]-3-phenylpropanoate (2h)
1
Deep orange oil, 83%. IR: 3,412, 3,342, 1,736, 1,672,
1,642 cm-1 HRMS (ES Q-TOF) calcd for C26H30N2NaO6
(M ? Na)?: 489.2002; found: 489.1996. HPLC-RI with a
Minor: H-NMR d 0.93 (d, J = 6.2 Hz, 6 H), 1.49–1.53
(m, 1 H), 2.01–2.33 (m, 2 H), 2.47–2.72 (m, 2 H), 3.43–
3.61 (m, 2 H), 3.70 (s, 3 H), 3.78 (s, 3 H), 3.98–4.15 (m, 2
123

Short malonyl dehydro peptides as potential scaffolds
467
H), 6.80 (t, J = 7.7 Hz, 1 H), 7.66 (br, 1 H, NH), 7.80 (br,
1 H, NH). 13C-NMR d 21.3 (two), 28.5, 33.4, 35.1, 38.2,
41.5, 51.8 (two), 131.8, 143.8, 165.0, 166.7, 169.3, 172.4.
Major: 1H-NMR d 0.92 (d, J = 6.6 Hz, 6 H), 1.41 (d,
J = 7.2 Hz, 3 H), 1.72–1.81 (m, 1 H), 2.25–2.33 (m, 2 H),
2.80–2.91 (m, 2 H), 3.66 (s, 3 H), 3.71 (s, 3 H), 3.75 (s, 3
H), 4.51–4.65 (m, 1 H), 5.58–5.75 (m, 1 H), 6.98 (t,
J = 7.9 Hz, 1 H), 7.18 (d, J = 7.8 Hz, 1 H, NH), 7.86 (d,
J = 7.9 Hz, 1 H, NH). 13C-NMR d 17.7, 22.2 (two), 28.3,
35.6, 38.1, 48.2, 48.4, 51.9, 52.3, 52.7, 131.4, 146.2, 164.6,
165.6, 170.9, 171.0, 173.0. Minor: 1H-NMR d 0.92 (d,
J = 6.6 Hz, 6 H), 1.44 (d, J = 7.2 Hz, 3 H), 1.72–1.81 (m,
1 H), 2.25–2.33 (m, 2 H), 2.95–3.10 (m, 2 H), 3.67 (s, 3 H),
3.73 (s, 3 H), 3.74 (s, 3 H), 4.85–4.97 (m, 1 H), 5.56–5.64
(m, 1 H), 6.90 (t, J = 7.8 Hz, 1 H), 7.02 (d, J = 7.8 Hz, 1
H, NH), 7.85 (d, J = 7.0 Hz, 1 H, NH). 13C-NMR d 17.5,
22.3 (two), 28.3, 35.2, 38.4, 48.4, 48.9, 52.0, 52.4, 52.8,
131.2, 146.4, 164.0, 164.2, 170.6, 170.9, 172.9.
Methyl 3-[2-(2-methoxy-2-oxoethylcarbamoyl)-3-(4-
methoxyphenyl)acrylamido]propanoate (2k)
Yellow oil, 67%. IR: 3,430, 3,351, 1,735, 1,673,
1,639 cm-1. HRMS (ES Q-TOF) calcd for C18H22N2NaO7
(M ? Na)?: 401.1325; found: 401.1329. Flash chroma-
tography on silica gel using (hexane/ethyl acetate 50:50).
Major: 1H-NMR d 2.48–2.52 (m, 2 H), 3.46–3.59 (m, 2 H),
3.67 (s, 3 H), 3.75 (s, 3 H), 3.80 (s, 3 H), 3.97–4.20 (m, 2
H), 7.19 (br, 1 H, NH), 7.25–7.42 (m, 4 H), 7.75 (s, 1 H),
7.92 (br, 1 H, NH). 13C-NMR d 32.9, 35.0, 41.3, 51.5, 52.2,
55.2, 114.1 (two), 126.6, 127.4 (two), 128.2, 131.1, 140.4,
168.7, 169.8, 172.2 (two). Minor: 1H-NMR d 2.48-2.52 (m,
2 H), 3.46–3.59 (m, 2 H), 3.67 (s, 3 H), 3.75 (s, 3 H), 3.80
(s, 3 H), 3.97–4.20 (m, 2 H), 7.25–7.42 (m, 4 H), 7.59 (s, 1
H), 7.92 (br, 1 H, NH), 8.11 (br, 1 H, NH). 13C-NMR d
33.5, 35.7, 41.5, 51.6, 52.3, 55.2, 114.1 (two), 125.7, 127.4
(two), 128.2, 131.5, 140.0, 168.1, 169.6, 172.0 (two).
Methyl (2S)-2-{2-[2-(benzyloxy)-2-
oxoethylcarbamoyl]-5-methylhex-2-
enamido}propanoate (2n)
Orange oil, 68%. IR: 3,435, 3,339, 1,741, 1,678,
1,637 cm-1. HRMS (ES Q-TOF) calcd for C21H28N2NaO6
(M ? Na)?: 427.1845; found: 427.1839. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 60:40).
Major: 1H-NMR d 0.90 (d, J = 6.6 Hz, 6 H), 1.49 (d,
J = 4.6 Hz, 3 H), 1.88–1.97 (m, 1 H), 2.30 (t, J = 7.2 Hz, 2
H), 3.70 (s, 3 H), 4.02–4.17 (m, 2 H), 4.46–4.65 (m, 1 H),
5.15 (s, 2 H), 7.06 (t, J = 7.6 Hz, 1 H), 7.32–7.34 (m, 5 H),
7.67–7.78 (m, 2 H, NH). 13C-NMR d 17.7, 22.9 (two), 24.8,
33.7, 41.3, 42.3, 48.2, 52.3, 52.7, 67.1, 128.2, 128.4 (two),
Methyl 3-{2-[2-(benzyloxy)-2-oxoethylcarbamoyl]-
5-methylhex-2-enamido}propanoate (2l)
Yellow oil, 83%. IR: 3,436, 3,342, 1,741, 1,678,
1,637 cm-1. HRMS (ES Q-TOF) calcd for C21H28N2NaO6
(M ? Na)?: 427.1845; found: 427.1849. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 65:35).
1
1
Major: H-NMR d 0.90 (d, J = 6.6 Hz, 6 H), 1.19–1.28
128.5 (two), 135.1, 166.8, 167.6, 169.4, 172.9. Minor: H-
(m, 2 H), 1.35–1.46 (m, 1 H), 2.29 (t, J = 7.2 Hz, 2 H),
3.27–3-48 (m, 2 H), 3.70 (s, 3 H), 4.02–4.17 (m, 2 H), 5.15
(s, 2 H), 6.93 (t, J = 7.6 Hz, 1 H), 7.32–7.34 (m, 5 H),
7.67–7.78 (m, 2 H, NH). 13C-NMR d 22.3 (two), 28.3,
33.6, 35.3, 38.2, 41.4, 51.7, 67.0, 128.2, 128.5 (two), 128.8
(two), 131.8, 135.9, 146.5, 165.0, 166.6, 169.3, 172.4.
NMR d 0.90 (d, J = 6.6 Hz, 6 H), 1.49 (d, J = 4.6 Hz, 3
H), 1.88–1.97 (m, 1 H), 2.30 (t, J = 7.2 Hz, 2 H), 3.73 (s, 3
H), 4.02–4.17 (m, 2 H), 4.46–4.65 (m, 1 H), 5.17 (s, 2 H),
6.90 (t, J = 7.6 Hz, 1 H), 7.12 (d, J = 7.5 Hz, 1 H, NH),
7.32–7.34 (m, 5 H), 7.73–7.78 (m, 1 H, NH). 13C-NMR d
18.3, 22.9 (two), 25.5, 33.7, 41.3, 42.3, 47.9, 52.3, 52.5,
68.0, 128.2, 128.4 (two), 128.5 (two), 135.0, 166.8, 167.8,
170.0, 173.6.
1
Minor: H-NMR d 0.90 (d, J = 6.6 Hz, 6 H), 1.20–1.29
(m, 2 H), 1.35–1.46 (m, 1 H), 2.29 (t, J = 7.2 Hz, 2 H),
3.27–3.48 (m, 2 H), 3.73 (s, 3 H), 4.02–4.21 (m, 2 H), 5.17
(s, 2 H), 6.87 (t, J = 7.6 Hz, 1 H), 7,09–7.17 (m, 1 H, NH),
7.32–7.34 (m, 5 H), 7.73–7.78 (m, 1 H, NH). 13C-NMR d
22.1 (two), 28.3, 33.5, 35.0, 38.1, 41.6, 51.8, 67.2, 128.2,
128.5 (two), 128.8 (two), 131.2, 135.9, 146.5, 164.9, 166.9,
169.3, 172.6.
Dimethyl (R)-2-{[2-(1S)-1-methoxy-3-methyl-1-
oxobutan-2-ylcarbamoyl]-5-methylhex-2-enamido}
succinate (2o)
Deep orange oil, 85%. IR: 3,448, 3,354, 1,736, 1,672,
1,637 cm-1. HRMS (ES Q-TOF) calcd for C20H32N2NaO8
(M ? Na)?: 451.2056; found: 451.2051. Flash chromatog-
raphy on silica gel (eluent: hexane/ethyl acetate 65:35).
Major: 1H-NMR d 0.86–0.98 (m, 12 H), 1.72–1.86 (m, 1 H),
2.30 (t, J = 7.2 Hz, 2 H), 2.78–3.14 (m, 3 H), 3.68 (s, 3 H),
3.72 (s, 3 H), 3.74 (s, 3 H), 4.47–4.55 (m, 1 H), 4.76–4.98 (m,
1 H), 7.01 (t, J = 8.0 Hz, 1 H), 7.15 (d, J = 8.0 Hz, 1
H, NH), 7.85 (d, J = 8.0 Hz, 1 H, NH). 13C-NMR d 18.3
Dimethyl (2S)-2-{2-[(1S)-1-methoxy-1-oxopropan-2-
ylcarbamoyl]-5-methylhex-2-enamido}succinate (2m)
Yellow oil, 60%. IR: 3,426, 3,332, 1,746, 1,674,
1,637 cm-1. HRMS (ES Q-TOF) calcd for C18H28N2NaO8
(M ? Na)?: 423.1743; found: 423.1751. Flash chroma-
tography on silica gel (eluent: hexane/ethyl acetate 55:45).
123

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S. Fioravanti et al.
tert-Butyl (R)-[2-(2-tert-butoxy-2-oxoethylcarbamoyl)-
3-(2,2-dimethyl-1,3-dioxolan-4-yl)acrylamido]acetate
(2r)
(two), 25.6 (two), 29.7, 31.4, 37.3, 38.9, 49.5, 53.2, 53.6
(two), 56.2, 133.2, 145.2, 168.4 (two), 174.3 (two), 179.1.
Minor: 1H-NMR d 0.86–0.98 (m, 12 H), 1.72–1.86 (m, 1 H),
2.30 (t, J = 7.2 Hz, 2 H), 2.78–3.14 (m, 3 H), 3.66 (s, 3 H),
3.72 (s, 3 H), 3.77 (s, 3 H), 4.58–4.66 (m, 1 H), 5.64–5.74 (m,
1 H), 6.85–6.92 (m, 1 H, NH), 6.93 (t, J = 7.9 Hz, 1 H), 7.72
(d, J = 8.0 Hz, 1 H, NH). 13C-NMR d 18.5 (two), 25.9 (two),
29.7, 31.4, 37.3, 39.1, 49.5, 53.3, 53.9 (two), 56.2, 133.4,
145.5, 168.4 (two), 175.2 (two), 178.9.
Pale yellow oil, 78%. IR: 3,428, 3,334, 1,735, 1,682,
1,648 cm-1. HRMS (ES Q-TOF) calcd for C21H34N2NaO8
(M ? Na)?: 465.2213; found: 465.2207. 1H-NMR d 1.28–
1.52 (m, 24 H), 3.69–4.42 (m, 6 H), 5.14–5.29 (m, 1 H),
6.87 (d, J = 7.3 Hz, 1 H), 7.34 (br, 1 H, NH), 7.93 (br, 1 H,
NH). 13C-NMR d 24.9 (two), 28.0 (six), 42.2, 42.3, 69.6,
82.3 (two), 82.5, 110.1, 132.2, 145.3, 164.6 (two), 168.3
(two).
Methyl (2S)-2-{2-[(1S)-1-methoxy-1-oxo-3-phenylpro-
pan-2-ylcarbamoyl]-5-methylhex-2-enamido}-4-
(methylthio)butanoate (2p)
tert-Butyl (R)-5-[3-(2-tert-butoxy-2-oxoethylamino)-2-
(2-tert-butoxy-2-oxoethylcarbamoyl)-3-oxoprop-1-
enyl]-2,2-dimethyloxazolidine-3-carboxylate (2s)
Deep orange oil, 73%. IR: 3,418, 3,330, 1,736, 1,678,
1,632 cm-1. HRMS (ES Q-TOF) calcd for C24H34N2
NaO6S (M ? Na)?: 501.2035; found: 501.2041. Flash
chromatography on silica gel (eluent: hexane/ethyl acetate
35:65). Major: 1H-NMR d 0.88 (d, J = 6.2 Hz, 6 H), 1.57–
1.75 (m, 1 H), 1.92–2.41 (m, 4 H), 2.05 (s, 3 H), 2.45–2.51
(m, 2 H), 3.00–3.28 (m, 2 H), 3.67 (s, 3 H), 3.70 (s, 3 H),
Yellow oil, 63%. IR: 3,430, 3,338, 1,737, 1,645,
1,643 cm-1. HRMS (ES Q-TOF) calcd for C26H43N3NaO9
(M ? Na)?: 564.2897; found: 564.2882. 1H-NMR d 1.18–
1.59 (m, 33 H), 3.68–3.85 (m, 2 H), 3.91–4.08 (m, 1 H),
4.10 (dd, J = 6.0, 9.4 Hz, 2 H), 4.22 (dd, J = 6.9, 17.3 Hz,
2 H), 6.92 (d, J = 11.3 Hz, 1 H), 8.41 (br, 1 H, NH), 9.72
(br, 1 H, NH). 13C-NMR d 24.5, 27.3, 27.9 (three), 28.0
(three), 28.3 (three), 42.2, 42.4, 55.1, 67.6, 81.6, 81.7
(two), 94.3, 131.4, 140.6, 153.1, 163.3 (two), 166.7, 168.4.
4.59–4.91 (m,
1 H), 5.49–5.69 (m, 1 H), 6.86
(t, J = 7.8 Hz, 1 H), 7.05–7.27 (m, 5 H), 7.55 (d, J = 7.5 Hz,
1 H, NH), 7.77 (d, J = 7.8 Hz, 1 H, NH). 13C-NMR d 15.2,
22.1, 22.2, 28.0, 29.9 (two), 37.0, 37.5, 51.6, 52.1, 52.2, 53.5,
127.1, 128.3 (two), 128.5 (two), 131.2, 135.6, 146.2, 164.3,
166.1, 171.6, 171.9. Minor: 1H-NMR d 0.90 (d, J = 6.2 Hz, 6
H), 1.57–1.75 (m, 1 H), 1.92–2.29 (m, 4 H), 2.05 (s, 3 H),
2.45–2.51 (m, 2 H), 3.00–3.28 (m, 2 H), 3.71(s, 3 H), 3.73(s, 3
H), 4.59–4.91 (m, 1 H), 5.44–5.63 (m, 1 H), 6.77
(t, J = 7.7 Hz, 1H), 6.92(d, J = 7.6 Hz, 1H, NH), 7.05–7.27
(m, 5 H), 7.40 (d, J = 7.8 Hz, 1 H, NH). 13C-NMR d 15.2,
22.1, 22.2, 28.1, 31.2 (two), 37.8, 38.8, 51.8, 52.2, 52.3, 53.8,
126.9, 128.8 (two), 129.0 (two), 131.2, 135.9, 146.2, 164.5,
166.5, 171.7, 172.0.
tert-Butyl (6RS,9R)-5-(2-tert-butoxy-2-
oxoethylcarbamoyl)-6-isobutyl-9-(methoxycarbonyl)-
13,13-dimethyl-4,11-dioxo-12-oxa-7-thia-3,10-
diazatetradecanoate (3)
N-tert-(Butoxycarbonyl)-L-cysteine methyl ester (1.5 mmol)
wasaddedunder Ar toastirredsuspensionofNaH(1.5 mmol)
in dry THF (2.5 ml). After 5 min. a THF solution (0.5 ml) of
2a (1 mmol) was added. After stirring at room temperature
(5 h), the solvent was removed in vacuo and the residue
dissolved in EtOAc (10 ml) and washed with saturated
ammonium chloride solution (2 9 10 ml) and with H2O
(2 9 10 ml) then dried on MgSO4. The solvent was removed
in vacuo and the crude mixture was purified by a short silica
gel column (hexane/ethyl acetate = 1:9) to afford diastereo-
meric 3 as a deep orange oil (78%).
Methyl (E)-(2S)-1-[2-(2-methoxy-2-oxoethylcarba-
moyl)-5-methylhex-2-enoyl]pyrrolidine-2-carboxylate
(2q)
Yellow oil, 56%. IR: 3,422, 3,334, 1,735, 1,659,
1,640 cm-1. HRMS (ES Q-TOF) calcd for C17H26N2NaO6
1
(M ? Na)?: 377.1689; found: 377.1695. H-NMR d 0.92
IR: 3,424, 3,318, 1,737, 1,713, 1,678 cm-1. HRMS (ES
Q-TOF) calcd for C29H51N3NaO10S (M ? Na)?:
656.3193; found: 656.3201. 1H-NMR d 0.88 (major, d,
J = 6.8 Hz, 6 H), 0.90 (minor, d, J = 6.8 Hz, 6 H), 1.42
(major, s, 18 H), 1.43 (minor, s, 18 H), 1.44 (s, 18 H), 1.77–
1.94 (m, 4 H), 2.23–2.35 (m, 2 H), 2.89–3.32 (m, 6 H),
3.44–3.53 (m, 2 H), 3.72 (minor, s, 3 H), 3.73 (major, s, 3
(dd, J = 3.3, 6.6 Hz, 6 H), 1.69–1.85 (m, 1 H), 1.87–2.15
(m, 6 H), 2.22–2.41 (m, 1 H), 3.30–3.45 (m, 1 H) 3.70 (s, 3
H), 3.76 (s, 3 H), 3.85 (dd, J = 5.0, 17.8 Hz, 1 H), 4.30
(dd, J = 6.6, 17.8 Hz, 1 H), 4.61–4.66 (m, 1 H), 6.97
(t, J = 7.9 Hz, 1 H), 7.48 (br, 1 H, NH). 13C-NMR d 22.4
(two), 24.7, 28.1, 29.3, 38.4, 41.3, 48.0, 52.1, 52.6, 58.3,
132.3, 143.0, 163.1, 166.7, 170.1, 173.1.
123

Short malonyl dehydro peptides as potential scaffolds
469
carrying L-a-amino acidic or D-glycosyl residues. J Comb Chem
8:808–811. doi:10.1021/cc060029k
Fioravanti S, Morreale A, Pellacani L, Ramadori F, Tardella PA
(2007) Solution-phase parallel synthesis of dissymmetric disub-
stituted malonamides carrying amino ester residues. Synlett:
2759–2761. doi:10.1055/s-2007-986659
Fioravanti S, Morea S, Morreale A, Pellacani L, Tardella PA (2009)
One-pot synthesis of chiral multifunctionalized aziridines. Tet-
rahedron 65:484–488. doi:10.1016/j.tet.2008.11.017
Galonic DP, van der Donk WA, Gin DY (2003) Oligosaccharide-
peptide ligation of glycosyl thiolates with dehydropeptides:
synthesis of S-linked mucin-related glycopeptide conjugates.
Chem Eur J 9:5997–6006. doi:10.1002/chem.200305290
Goodman M, Chorev M (1979) On the concept of linear modified
retro-peptide structures. Acc Chem Res 12:1–7. doi:10.1021/
ar50133a001
H), 3.86–4.02 (m, 8 H), 4.38–4.67 (m, 2 H), 6.95 (major,
br, 1 NH), 7.21 (minor, br, 1 H, NH), 7.47 (minor, t,
J = 5.5 Hz, 1 H, NH), 7.52 (major, t, J = 5.2 Hz, 1 H,
NH), 7.67 (br, 2 H, NH). 13C-NMR d 20.9 (major, two),
21.0 (minor, two), 23.4 (minor), 23.5 (major), 28.0
(twelve), 28.2 (major, three), 28.3 (minor, three), 29.6
(two), 30.3 (two), 35.1 (major), 35.2 (minor), 42.0 (two),
42.1 (minor), 42.2 (major), 52.5 (two), 59.5 (two), 60.2
(two), 82.0 (major), 82.1 (minor), 82.2 (two), 82.3 (two),
155.1 (two), 168.2 (minor), 168.3 (major), 168.4 (two),
169.2 (two), 171.1 (major), 171.2 (minor), 171.4 (two).
`
Acknowledgments Italian MIUR and Universita degli Studi di
Roma ‘‘La Sapienza’’ are gratefully acknowledged for financial
support (PRIN 2007FJC4SF_005).
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Mannich-Type Reaction for selective tyrosine bioconjugation. J
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