Study of the reaction between carbamoyl azides of α-N-protected amino acids and hydrazine monohydrate

Article abstract of DOI:10.1002/ejoc.201001385

Two simple and efficient synthetic methods for the preparation of semicarbazide amino acid derivatives are reported. The procedures involve reaction between the carbamoyl azides of α-N-protected amino acids and hydrazine monohydrate: 4-[(alkoxycarbonylamino)(alkyl)methyl]semicarbazides 1 are obtained when hydrazine is added to the separated tetrahydrofuran (THF) solution containing the carbamoyl azide at 0 °C, whereas 1-[(alkoxycarbonylamino)(alkyl)methyl-carbamoyl]-4-[(alkoxycarbonylamino)(alkyl) methyl]semicarbazides 4 are produced by adding hydrazine directly into the final THF/aqueous buffer (KH₂PO₄) biphasic mixture containing the prepared carbamoyl azide at 50 °C, respectively. NMR experimental data obtained from samples dissolved in [D₆]dimethyl sulfoxide suggest a dimeric association for semicarbazides 4 with intermolecular hydrogen bonds. Moreover, the ESI-MS-MS spectra reveal some interesting common features.

Full text of DOI:10.1002/ejoc.201001385

FULL PAPER
DOI: 10.1002/ejoc.201001385
Study of the Reaction between Carbamoyl Azides of α-N-Protected Amino
Acids and Hydrazine Monohydrate
Giancarlo Verardo,*[a] Cesare Daniele Venneri,[a] Gennaro Esposito,[b] and
Paolo Strazzolini[a]
Keywords: Azides / Amino acids / Semicarbazides
Two simple and efficient synthetic methods for the prepara-
tion of semicarbazide amino acid derivatives are reported.
The procedures involve reaction between the carbamoyl az-
ides of α-N-protected amino acids and hydrazine monohy-
drate: 4-[(alkoxycarbonylamino)(alkyl)methyl]semicarbaz-
ides 1 are obtained when hydrazine is added to the separated
tetrahydrofuran (THF) solution containing the carbamoyl az-
ide at 0 °C, whereas 1-[(alkoxycarbonylamino)(alkyl)methyl-
carbamoyl]-4-[(alkoxycarbonylamino)(alkyl)methyl]semicar-
bazides 4 are produced by adding hydrazine directly into the
final THF/aqueous buffer (KH2PO4) biphasic mixture con-
taining the prepared carbamoyl azide at 50 °C, respectively.
NMR experimental data obtained from samples dissolved in
[D6]dimethyl sulfoxide suggest a dimeric association for sem-
icarbazides 4 with intermolecular hydrogen bonds. More-
over, the ESI–MS–MS spectra reveal some interesting com-
mon features.
ingly, the synthesis of semicarbazides of type –NH–*CRH–
NHCONHNH2, bearing the chiral moiety of an α-amino
acid, is not described in the literature.
Introduction
Semicarbazides are useful intermediates in the synthesis
of biologically active compounds containing a heterocyclic
moiety. Representative examples involving these inter-
mediates include pyrazole,[1] pyrazoline,[2] oxazole,[3] 1,2,4-
triazole,[4] 1,3,4-oxadiazole,[5] and 3,4-dihydrophthalazine[6]
moieties. It has been reported that some of these nitrogen-
containing heterocyclic molecules possess antibac-
terial,[1e,2a–2e,3b,5b–5d,5f,6a,6b,7] antimycotic,[1e,2e,5b] or antivi-
ral[1a,4c] activities, as well as exhibiting antiinflamma-
tory,[1b,1d] anticonvulsant,[5a] bronchodilator,[4a] PPAR
alpha agonist,[4b,4f] and antitumor[4b] properties. Moreover,
a number of studies have reported that some semicarb-
azones[8] as well as their Schiff base transition metal com-
plexes[9] also exhibit similar biologically active behavior.
A literature survey revealed a number of different pro-
cedures for the synthesis of semicarbazides using hydraz-
ines[8i,10] or acid hydrazides[3a,5b,5e,7,11] combined with isocy-
anates. Alternative methods involving carbamates and hy-
Recently, we have reported a simple and fast one-pot syn-
thesis of the carbamoyl azides of α-N-protected amino ac-
ids,[18] as well as their use as suitable building blocks in the
preparation of unsymmetrical ureas[19] and ureidopep-
tides.[20] Taking into account the potential biological inter-
est of semicarbazides and their heterocycle derivatives, we
attempted the synthesis of α-amino acid-containing target
compounds starting from the corresponding α-N-protected
carbamoyl azides, which were used as a NCO equivalent.
Results and Discussion
On the basis of our previous experience, two different
protocols were considered for the synthesis of semicarbaz-
ides 1, using α-N-(ethoxycarbonyl)-l-phenylalanine (2db) as
the model substrate. One approach was carried out in a
two-step reaction sequence (Method A):[19] the first step of
the process consisted of the preparation of the carbamoyl
azide of α-N-(ethoxycarbonyl)phenylalanine (3db), which
was readily available through a previously described pro-
cedure.[20] In the second step, hydrazine monohydrate
(6 equiv. with respect to 3db) was slowly added to the cold
(0 °C) separated tetrahydrofuran (THF) solution containing
the carbamoyl azide 3db. The reaction mixture was then
stirred at room temperature for 2 h and, after removal of
THF under reduced pressure, the residue was washed with
water to afford pure 4-[1-(ethoxycarbonylamino)-2-phenyl-
drazine[1b,5b,8h,8i,12] or ethyl carbazate,[13] isocyanates and
[15]
ethyl carbazate,[14] thiosemicarbazides and HIO4
or
KIO3,[16] 1H-imidazole-1-carbohydrazide and amines,[17]
and ureas and hydrazine,[8f,8g,8j] are also known. Interest-
[a] Department of Chemical Sciences and Technologies, University
of Udine,
Via del Cotonificio 108, 33100 Udine (UD), Italy
Fax: +39-0432-558803
E-mail: giancarlo.verardo@uniud.it
[b] Department of Biomedical Sciences and Technologies,
University of Udine,
p.le Kolbe 4, 33100 Udine (UD), Italy
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201001385.
1376
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1376–1384

Semicarbazides from Amino Acids
Scheme 1. Synthesis of semicarbazides 1 and 4. NMM = N-methylmorpholine; IBCF = isobutyl chloroformate.
ethyl]semicarbazide (1db) in 82% overall yield. Alternatively, Table 1. Yields and some properties of semicarbazides 1 and 4.
we tried to perform the reaction in one-pot (Method B)[20]
by simply adding hydrazine monohydrate (6 equiv. with re-
spect to 3db) directly into the final THF/aqueous buffer
(KH2PO4) biphasic mixture containing the previously pre-
pared carbamoyl azide 3db. The ESI-MS analysis of this 1bd
crude reaction mixture showed, after 2 h, the presence of
Product[a] Yield [%][b]
M.p. [°C]
[α]2D0 (c, solvent)
1ab
1ad
1bb
73
87
76
175–177
161–163
107–109
150–152
140–141
141–143
170–172
171–172
185–187
175–177
149–151
214–216
217–219
204–206
210–212
193–195
197–198
203–205
199–201
–32.6 (0.5, DMSO)
+18.0 (0.5, DMSO)
+17.4 (0.5, DMSO)
–15.0 (0.2, DMSO)
–22.3 (0.5, DMSO)
–18.5 (0.5, DMSO)
+16.3 (0.5, DMSO)
–15.6 (0.2, DMSO)
–36.4 (0.5, DMSO)
–30.2 (0.3, DMSO)
–14.0 (0.5, DMSO)
+10.6 (0.3, DMSO)
+20.3 (0.3, DMSO)
–57.2 (0.2, DMSO)
+34.4 (1.0, DMSO)
+7.5 (0.5, DMSO)
–7.8 (0.3, DMSO)
+10.0 (0.3, DMSO)
–26.7 (0.3, DMSO)
78
1cb
83
92
82
74
80
77
74
72
1cd
some unreacted 3db, 1db, and 1-[1-(ethoxycarbonylamino)-
2-phenylethyl-carbamoyl]-4-[1-(ethoxycarbonylamino)-2-
1db
1dc
phenylethyl]semicarbazide (4db) in an approximate 20:40:40
ratio. After 12 h, the carbamoyl azide 3db was fully con-
verted into the corresponding semicarbazides 1db and 4db
in an approximate 35:65 ratio. Under the described experi-
mental conditions, the presence of water in the reaction
mixture greatly reduced the amount of hydrazine dissolved 4cd
in THF, where 3db is soluble and very rapidly reacted with
hydrazine, yielding the semicarbazide 1db. As the reaction
proceeds, the amount of 1db in the THF increases and, al-
though less reactive, begins to compete effectively with hy-
drazine for the carbamoyl azide 3db, producing the semi-
carbazide 4db. On the basis of these experimental findings,
Method A was extended to other α-N-protected amino
acids 2 (Scheme 1, Method A), affording 1 in 73–92% over-
all yield (Table 1).
1dd
1ea
1fb
4ad
4bd
4cb
93
57,[c] 83[d]
93
4db
81
86
72
89
4dc
4ea
4fb
[a] Semicarbazides 1 were synthesized according to Method A; se-
micarbazides 4 according to Method C. [b] Isolated yield. [c] Yield
obtained at 50 °C. [d] Yield obtained at room temperature.
duced to 3 equiv. with respect to 3db and the resulting mix-
Taking into account that semicarbazides 4 are interesting ture was stirred at 50 °C for 5 h. After conventional work-
compounds that possess potential biological activity and up, these experimental conditions (Method C) allowed the
have not been previously described in the literature, we re- pure semicarbazide 4db to be obtained in 82% overall yield.
vised Method B by making the appropriate changes in or- With the exception of α-N-(ethoxycarbonyl)phenylglycine
der to minimize any side reaction, using α-N-(ethoxy- (2cb), the extension of this method to other α-N-protected
carbonyl)-l-phenylalanine (2db) as the model substrate. Ac- amino acids 2 (Scheme 1, Method C) gave 4 in 72–93%
cordingly, the amount of hydrazine monohydrate was re- overall yield (Table 1). Interestingly, when the reaction was
Eur. J. Org. Chem. 2011, 1376–1384
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1377

G. Verardo, C. D. Venneri, G. Esposito, P. Strazzolini
FULL PAPER
carried out with 2cb at 50 °C, ESI-MS analysis of the crude of the diastereoisomeric mixture of semicarbazide diast-4cb
mixture showed, in addition to the semicarbazide 4cb, the obtained from rac-2cb revealed two sets of peaks for each
the presence of 1-benzylidene-4-[(ethoxycarbonylamino)- proton and carbon signal, whereas the corresponding spec-
(phenyl)methyl]semicarbazide (5cb)[21] in an approximate tra of 4cb did not show a similar complexity. The obtained
ratio of 70:30. This by-product arises from the reaction results, as well as some properties of semicarbazides 1 and
of 4-[(ethoxycarbonylamino)(phenyl)methyl]semicarbazide 4, are reported in Table 1.
(1cb) with benzaldehyde produced by the hydrolysis of ethyl
All the 1H NMR spectra of semicarbazides 1, which were
benzylidenecarbamate (6) at 50 °C. As described in recorded in [D6]dimethyl sulfoxide (DMSO), exhibit a
Scheme 2, the presence of water introduced with the buffer broad singlet in the δ = 3.7–4.5 ppm range due to the semi-
mixture and the reaction temperature also proved to be re- carbazide NH2 nuclei, and contain two further common
sponsible for the decomposition of 1cb into 6 and semi- features: (1) a broad doublet (J = 7.3–9.4 Hz) ranging from
1
carbazide.
δ = 6.5 to 7.0 ppm, which were assigned from H–1H de-
coupling experiments to the proton of the semicarbazide
nitrogen linked to the α-carbon of the starting amino acid,
and (2) a sharp singlet at δ = 7.0–7.3 ppm, which was at-
tributed to the other semicarbazide NH signal. These as-
signments were confirmed by analysis of the 2D TOCSY
spectra (see the Supporting Information), which exhibited
a cross-peak between the vicinal hydrogens of semicarbaz-
ide (i.e., the NH2 at δ = 3.7–4.5 ppm and the NH at δ =
7.0–7.3 ppm), which was not connected with the remaining
J-coupling network of the molecule. The NH2–NH connec-
tivity demonstrates that the observed singlet multiplicity for
the two resonances is only apparent because an unresolved
vicinal coupling must exist. Comparison of the correspond-
1
ing signals obtained from the H NMR spectra of semicar-
bazides 4 shows that the semicarbazide doublet NH reso-
nance within the gem-diamino moiety occurs at the same
position (δ = 6.3–6.9 ppm) and exhibits a similar coupling
constant (J = 8.5–9.1 Hz) to those of semicarbazides 1, al-
Scheme 2.
To verify the mechanism outlined in Scheme 2, a THF/ though with a sharper linewidth, whereas the singlet NH
water mixture of 1cb was heated at 50 °C for 5 h: initially, signal (a true singlet because of chemical equivalence) shifts
the ESI-MS analysis of the reaction mixture showed the downfield by about 0.7 ppm (δ = 7.7–8.0 ppm). Moreover,
appearance of an ion at m/z 178 due to the protonated ad- the carbamate NH spin, which is sometimes obscured by
duct of 6.[22] Then, as the reaction proceeds, MS signals overlapping aromatic signals, resonates at δ = 7.2–8.0 ppm
corresponding to this ion and to the sodium cationized mo- as a broad doublet (J = 7.9–8.2 Hz) in semicarbazides 1,
lecule [1cb + Na]+ at m/z 275 decreased, whereas the sodium and in a similar region (δ = 7.2–7.9 ppm) as a barely re-
adduct of 5cb at m/z 363 increased. Surprisingly, the sem- solved doublet in 4.
icarbazide 1cb proved to be stable in hot THF (50 °C) and
The 13C NMR spectra of 1 contained a signal corre-
in a THF/water mixture at room temperature for a long sponding to the semicarbazide C=O carbon in the δ =
time (24 h), and therefore the synthesis of semicarbazide 159.7–160.3 ppm range; in 4, this peak shifted upfield by
4cb was better performed at room temperature (12 h). On about 2 ppm (δ = 157.7–158.3 ppm). This upfield shift of
the other hand, when the reaction was accomplished with the semicarbazide carbonyl and the simultaneous sharpen-
α-N-(benzyloxycarbonyl)phenylglycine (2cd) at 50 °C, ESI- ing of the semicarbazide NH resonance within the gem-di-
MS analysis of the reaction mixture did not indicate the amino moiety in compounds 4 are consistent with a re-
formation of any of the corresponding benzylidene-substi- duced conformational mobility of the molecules. Indeed,
tuted semicarbazone 5cd (sodium adduct at m/z 425) nor of whereas the chemical shift thermal coefficient for the latter
the benzyl benzylidenecarbamate (protonated adduct at m/z NH type resonance in both semicarbazide 4 and 1 models
240), most likely because the steric hindrance of the α-N- (1db and 4db) proved to be significantly smaller than the
benzyloxycarbonyl group prevented the incursion of water. corresponding parameter measured for the carbamate NH
As previously reported,[19,20] we did not observe any ra- (–2.9 vs. –5.0 and –2.3 vs. –5.1 ppb/°C, respectively), the
1
cemization under our experimental conditions: H and 13C result obtained for the other semicarbazide NH resonance
NMR spectra of 1-[(ethoxycarbonylamino)(phenyl)methyl- of model semicarbazides 4 and 1 (the genuine and apparent
carbamoyl]-4-[(ethoxycarbonylamino)(phenyl)methyl]semi- singlet, respectively) were significantly different (i.e., 2.2 and
carbazide (4cb), prepared by reacting N-(ethoxycarbonyl)- 39.3 ppb/°C, respectively). This suggests that a remarkable
l-phenylglycine (2cb) with hydrazine monohydrate, were degree of exchange occurs in semicarbazide 1, which is in
compared with those obtained by employing racemic N- contrast to a possible hydrogen bonded network in semi-
(ethoxycarbonyl)-d,l-phenylglycine (rac-2cb). The spectra carbazide 4. This seems to be consistent with the upfield
1378
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1376–1384

Semicarbazides from Amino Acids
shift of the semicarbazide carbonyl observed for com-
pounds 4, which was interpreted as a reflection of the extent
of hydrogen bonding (as donor) of the NH groups coval-
ently linked to this C=O moiety (in contrast to the direct
carbonyl involvement as acceptor).[23] Further evidence in
favor of this interpretation came from the ROESY and
DOSY experiments (see the Supporting Information). The
2D ROESY maps showed much stronger cross peaks be-
tween either semicarbazide NH groups and the carbamate
NH group in model compound 4 than the corresponding
amplitudes observed with model compound 1. The DOSY
maps enabled
a diffusion coefficient of (2.7Ϯ0.1)ϫ
10–10 m2/s for semicarbazide 1db and (1.8Ϯ0.1)ϫ 10–10 m2/
s for semicarbazide 4db at 30 °C in [D6]DMSO to be esti-
mated. Because, in general, for two closely related molecules
(a and b) under the same conditions, a relationship between
the diffusion coefficient (D) and the molecular weight (M)
can be established according to Equation (1);[24] our data
indicate an effective molecular weight ratio of 3.2Ϯ0.6 for
semicarbazides 4db and 1db, against the expectation of a
ratio of 2 from the chemical structures.
Scheme 3.
In the case of semicarbazides 4, the fragmentation (MS2)
(1)
of [4 + Na]+ produces, in addition to the most intense
(100% relative intensity) daughter ion corresponding to
[1 + Na]+, four more peaks (30–80% relative intensity)
due to the loss of carbamate (NH2COORЈ), alkylidene-
carbamate (RCH=NCOORЈ), α-aminoalkylcarbamate
[RCH(NH2)NHCOORЈ], and 1-(aminocarbonyl)-4-[1-(alk-
oxycarbonylamino)alkyl]semicarbazide [RCH(NHCOORЈ)-
NHCONHNHCONH2] molecules, respectively (Scheme 4).
As expected, MS3 experiments on the [1 + Na]+ daughter
ions produced fragmentation patterns that were essentially
identical to those observed in the MS2 spectra of the so-
dium-cationized molecule [M + Na]+ of 1.
The occurrence of a dimerization equilibrium of semi-
carbazide 4db with a reduction in the carbamate moiety, the
flexibility and the overall molecular shape anisotropy,
rather than fast association/dissociation kinetics, could be
hypothesized to accommodate both intra- and intermo-
lecular hydrogen bonds and could account for the small
thermal coefficients of the two semicarbazide NH chemical
shifts, as well as for the slower than expected experimental
diffusion coefficient. This interpretation appears more
plausible than resorting to the assumption of a monomeric
rigid conformation for compound 4db with a flat geometry,
which may account for a reduction in the rate of diffusion,
but would require tightly bound solvent molecules to estab-
lish the hydrogen bonds required to account for the experi-
mental data measured for all the semicarbazide NH groups.
Taking into account the importance of ESI-MS-MS
techniques for the elucidation of structures of non-volatile,
thermally labile molecules, we considered it useful to report
The MS2 spectrum of N-Boc derivatives 1dc and 4dc re-
vealed two additional fragment ions corresponding to the
loss of isobutene and CO2.[19]
Conclusions
We have developed two simple and efficient synthetic
some common features that were found in the ESI-MS methods, starting from carbamoyl azides of α-N-protected
spectra of α-N-protected semicarbazides 1 and 4. In detail, amino acids, for the preparation of semicarbazides 1 and 4
with the exception of N-Boc-derivatives 1dc and 4dc, the containing one and two amino acid residues, respectively.
MS2 spectra of sodium-cationized molecule [M + Na]+ for The NMR spectroscopic data suggest that the condensed
1 are characterized by the presence of two intense ions due semicarbazides 4 tend to associate, even in DMSO, into di-
to the loss of semicarbazide (75 Da; 50–100% relative inten- mers, thereby forming intermolecular hydrogen bonds and
sity) and carbamate (NH2COORЈ; 60–100% relative inten- reducing the diffusion rate.
sity) molecules (Scheme 3). Moreover, four additional peaks
Moreover, the ESI-MS-MS spectra revealed some com-
(10–70% relative intensity) corresponding to the imine of mon fragmentation pathways involving the protecting
the α-amino acid side chain, to the carbamate, and to the group of the amino acid and the semicarbazide moiety.
loss of hydrazine (32 Da), and aminoisocyanate (58 Da)
molecules were also observed (Scheme 3).
These compounds may be useful building blocks in the
synthesis of biologically active heterocyclic compounds
Eur. J. Org. Chem. 2011, 1376–1384
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1379

G. Verardo, C. D. Venneri, G. Esposito, P. Strazzolini
FULL PAPER
Scheme 4.
NMR experiments and chemical shift thermal coefficient determi-
nations were performed at 500 MHz, with a Bruker Avance system
equipped with triple-axis pulsed field gradients, at 30 °C and over
the interval 22–30 °C, using a sample concentration of approxi-
mately 30 mg/mL for both semicarbazides 1 and 4. For 2D
TOCSY,[26] a mixing time of 100 ms with a MLEV17[27] train was
employed, with γB2/2π = 8.3 kHz, 500 μs trim pulses and recycling
delay of 1 s. 2D ROESY experiments[28] were obtained using a con-
tinuous-pulse mixing time of 150 ms, at γB2/2π = 2.5 kHz with re-
cycling delay of 1 s. A sweep width of 5 kHz was always selected for
matrices of 2Kϫ256 and 8 (TOCSY) or 16 (ROESY) transients/t1
point were collected; 32 dummy scans were performed only upon
starting acquisition. Quadrature detection in the indirect dimension
was always achieved by time proportional phase incrementation.[29]
Diffusion ordered spectroscopy (DOSY) experiments were con-
ducted with a sequence including bipolar gradients in a double
stimulated echo module and longitudinal eddy current delay for
convection artefact and eddy current suppression.[30] The z-axis
gradient was incremented linearly through 79 increments within the
range 2–95% over a maximum of 65 G/cm. The other relevant pa-
rameters of DOSY were: δ = (2.5ϫ2) ms, Δ ranging from 100 to
400 ms, recycling delay 1 s, 32 transients/gradient increment, and
32 dummy scans. All data were processed using the Bruker routine
software (TOPSPIN) with a squared sine shifted by 90°. Optical
rotations were determined with suitable solutions (g/100 mL) at
20 °C with an AP-300 automatic polarimeter purchased from AT-
AGO (Japan). Elemental analyses were performed with a Carlo–
Erba Mod. 1106 elemental analyzer. Melting points were deter-
mined with an automatic Mettler (Mod. FP61) melting point appa-
ratus.
containing an amino acid moiety. We are currently investi-
gating these semicarbazides to assess whether their capacity
to form intermolecular hydrogen bonds might be exploited
in cross-reactions with amiloidogenic proteins, thus pre-
venting aggregation and fibrillogenesis.
Experimental Section
General: N-Protected amino acids 2 were prepared by reported pro-
cedures.[25] Solvents and reagents were purchased from Aldrich
Chemical Company and used without further purification. Column
chromatography was carried out using silica gel 60 (Merck, 230–
400 mesh) and thin-layer chromatography (TLC) was performed on
Merck 60 F254 0.25 μm silica gel coated aluminum plates. Direct-
inlet mass spectra (DI-MS) were obtained with a Thermo Scientific
Polaris Q ion trap mass spectrometer, working in the positive ion
70 eV electron impact mode. Spectra were recorded in the range
35–450 u, and temperatures between 100 and 250 °C were found to
be suitable to vaporize all the compounds into the ion source. The
reactions were monitored by ESI-MS in the positive ion mode with
a Finnigan LXQ (linear trap) by simply diluting the reaction mix-
ture with MeCN and directly infusing the obtained solution into
the ion source with the aid of a syringe pump. IR spectra were
obtained with a Bruker Vector 22 spectrophotometer using the KBr
disc technique for solids; spectra were recorded in the range 4000–
1
400 cm–1. H and 13C NMR spectra were recorded with a Bruker
AC-F 200 spectrometer operating at 200 and 50 MHz, respectively,
using [D6]DMSO at 40 °C as the solvent. NMR shifts are reported
1
as δ values relative to TMS. Some H multiplets are characterized
by the term app. (apparent): this refers only to their appearance
General Procedure for the Synthesis of Semicarbazides 1 (Method
A): N-Methylmorpholine (NMM; 0.30 mL, 2.73 mmol) was slowly
added to a stirred solution of α-N-protected amino acid 2
(2.50 mmol) in THF (15 mL). After 5 min, isobutyl chloroformate
and may be an oversimplification. To assign the αCHNHCONH
1
proton resonance, H–1H decoupling experiments were performed
by irradiating the αCH proton at the center of its signal. 2D 1H
1380
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1376–1384

Semicarbazides from Amino Acids
(IBCF; 0.36 mL, 2.73 mmol) was slowly added to the previously
cooled (–20 °C) reaction mixture and stirring was continued for
20 min at the same temperature. The reaction mixture was warmed
to 0 °C and a solution of KH2PO4 (0.17 g, 1.25 mmol) in H2O
(1 mL) was added in one portion, followed, after 5 min, by a solu-
tion of KH2PO4 (1.70 g, 12.50 mmol) and NaN3 (0.41 g,
6.25 mmol) in H2O (9 mL). After 30 min at 0 °C, the mixture was
warmed to 40 °C, stirred for 1.5 h, cooled to room temperature,
and the organic phase was separated. The obtained THF solution
containing the carbamoyl azide 3 was cooled to 0 °C and hydrazine
monohydrate (0.73 mL, 15.00 mmol) was slowly added. The mix-
ture was warmed to room temperature whilst stirring and, after
an additional 2 h, THF was removed under reduced pressure. The
obtained crude residue was washed with water to afford, after dry-
ing in vacuo, semicarbazide 1 in a 73–92% overall yield (Table 1).
C14H22N4O3 (294.35): calcd. C 57.13, H 7.53, N 19.03; found C
57.17, H 7.50, N 19.00.
Semicarbazide 1cb: White solid (523 mg, 83%). IR (KBr): ν = 3349
˜
(br), 3287 (br), 1686, 1643, 1536, 1496, 1264, 1053, 750, 698 cm–1.
1H NMR: δ = 1.19 (t, J = 7.0 Hz, 3 H, CH3), 4.03 (q, J = 7.0 Hz,
2 H, CH2), 4.26 (br. s, 2 H, NH2), 6.31 (app. t, J = 9.1 Hz, 1 H,
*CH), 7.04 (br. d, J = 7.6 Hz, 1 H, NHCONHNH2), 7.30 (s, 1 H,
NHNH2), 7.31–7.46 (m, 5 H, ArH), 7.93 (br. d, J = 8.2 Hz, 1 H,
NHCOO) ppm. 13C NMR: δ = 15.6, 60.4, 60.9, 126.8, 128.4, 129.3,
142.9, 156.2, 159.7 ppm. DI-MS (EI): m/z (%) = 193 (5) [M –
59]+, 178 (100), 163 (19), 150 (9), 132 (58), 106 (94), 105 (25), 104
(36), 79 (51), 77 (36). MS (ESI+): m/z = 275 [M + Na]+ Ǟ (MS2)
243, 217, 200, 186, 128, 112. C11H16N4O3 (252.27): calcd. C 52.37,
H 6.39, N 22.21; found C 52.40, H 6.34, N 22.17.
Semicarbazide 1cd: White solid (723 mg, 92%). IR (KBr): ν = 3310
˜
(br), 1693, 1653, 1539, 1498, 1324, 1261, 1048, 754, 696 cm–1. H
Semicarbazide 1ab: White solid (398 mg, 73%). IR (KBr): ν = 3306
1
˜
(br), 2980, 2959, 1693, 1635, 1573, 1525, 1308, 1257, 1047 cm–1. 1H
NMR: δ = 0.87 [d, J = 6.8 Hz, 6 H, (CH3)2CH], 1.19 (t, J = 7.0 Hz,
3 H, CH3CH2), 1.86 (app. sextet, J = 7.0 Hz, 1 H, CH), 4.01 (q, J
= 7.0 Hz, 2 H, OCH2), 4.50 (br. s, 2 H, NH2), 4.93 (app. q, J =
8.5 Hz, 1 H, *CH), 6.51 (br. d, J = 9.4 Hz, 1 H, NHCONHNH2),
7.00 (s, 1 H, NHNH2), 7.18 (br. d, J = 7.9 Hz, 1 H, NHCOO) ppm.
13C NMR: δ = 15.4, 19.0, 19.2, 33.7, 60.3, 63.5, 156.1, 159.8 ppm.
DI-MS (EI): m/z (%) = 175 (24) [M – 43]+, 144 (72), 132 (26), 116
(100), 98 (54), 86 (61), 72 (89), 55 (80). MS (ESI+): m/z = 241 [M
+ Na]+ Ǟ (MS2) 209, 183, 166, 152, 112, 94. C8H18N4O3 (218.26):
calcd. C 44.03, H 8.31, N 25.67; found C 44.00, H 8.29, N 25.69.
NMR: δ = 4.25 (br. s, 2 H, NH2), 5.09 (app. s, 2 H, CH2), 6.38
(app. t, J = 8.8 Hz, 1 H, *CH), 7.03 (br. d, J = 7.8 Hz, 1 H,
NHCONHNH2), 7.24 (s, 1 H, NHNH2), 7.28–7.48 (m, 5 H, ArH),
8.02 (br. d, J = 8.0 Hz, 1 H, NHCOO) ppm. 13C NMR: δ = 60.5,
66.3, 126.7, 128.2, 128.5, 128.6, 129.0, 129.1, 137.8, 142.7, 155.8,
159.7 ppm. DI-MS (EI): m/z (%) = 239 (5) [M – 75]+, 238 (29), 196
(13), 194 (26), 132 (70), 108 (51), 107 (37), 91 (100), 79 (74), 77
(62). MS (ESI+): m/z = 337 [M + Na]+ Ǟ (MS2) 305, 279, 262,
186, 174, 128. C16H18N4O3 (314.34): calcd. C 61.14, H 5.77, N
17.82; found C 61.10, H 5.81, N 17.78.
Semicarbazide 1db: White solid (546 mg, 82%). IR (KBr): ν = 3299
˜
(br), 1696, 1650, 1570, 1525, 1305, 1256, 1052, 703 cm–1. 1H NMR:
δ = 1.13 (t, J = 7.0 Hz, 3 H, CH3), 2.92 (app. d, J = 7.0 Hz, 2 H,
PhCH2), 3.95 (q, J = 7.0 Hz, 2 H, OCH2), 4.16 (br. s, 2 H, NH2),
5.29 (app. quintet, J = 8.2 Hz, 1 H, *CH), 6.73 (br. d, J = 9.7 Hz,
1 H, NHCONHNH2), 7.14 (s, 1 H, NHNH2), 7.16–7.38 (m, 5 H,
ArH), 7.46 (br. d, J = 7.9 Hz, 1 H, NHCOO) ppm. 13C NMR: δ =
15.6, 42.3, 60.2, 60.7, 127.3, 129.2, 130.3, 138.8, 156.0, 159.8 ppm.
DI-MS (EI): m/z (%) = 192 (87) [M – 74]+, 191 (37), 178 (25), 175
(35), 148 (17), 132 (22), 120 (100), 91 (27). MS (ESI+): m/z = 289
[M + Na]+ Ǟ (MS2) 257, 231, 214, 200, 142, 112. C12H18N4O3
(266.30): calcd. C 54.12, H 6.81, N 21.04; found C 54.17, H 6.84,
N 21.00.
Semicarbazide 1ad: White solid (610 mg, 87%). IR (KBr): ν = 3318
˜
1
(br), 2960, 1695, 1509, 1309, 1251, 1028, 731, 696 cm–1. H NMR:
δ = 0.89 [d, J = 6.8 Hz, 6 H, (CH3)2CH], 1.89 (app. sextet, J =
7.0 Hz, 1 H, CH), 4.50 (br. s, 2 H, NH2), 5.01 (app. q, J = 8.5 Hz,
1 H, *CH), 5.06 (app. s, 2 H, CH2), 6.54 (br. d, J = 9.4 Hz, 1 H,
NHCONHNH2), 7.02 (s, 1 H, NHNH2), 7.22–7.35 (m, 6 H, 5ϫ
ArH + NHCOO) ppm. 13C NMR: δ = 18.9, 19.2, 33.6, 63.6, 65.9,
128.4, 128.5, 129.1, 138.0, 155.9, 159.8 ppm. DI-MS (EI): m/z (%)
= 237 (7) [M – 43]+, 193 (6), 162 (19), 108 (15), 107 (11), 91 (100),
86 (11), 79 (23), 77 (12), 72 (16). MS (ESI+): m/z = 303 [M +
Na]+ Ǟ (MS2) 271, 245, 228, 174, 152, 94. C13H20N4O3 (280.33):
calcd. C 55.70, H 7.19, N 19.99; found C 55.65, H 7.21, N 19.90.
Semicarbazide 1bb: White solid (441 mg, 76%). IR (KBr): ν = 3346
˜
Semicarbazide 1dc: White solid (545 mg, 74%). IR (KBr): ν = 3390,
˜
(br), 2958, 1686, 1544, 1508, 1256, 1148, 1058 cm–1. 1H NMR: δ =
0.93 [d, J = 5.9 Hz, 6 H, (CH3)2CH], 1.22 (t, J = 7.0 Hz, 3 H,
CH3CH2), 1.55–1.80 (m, 3 H, CHCH2), 4.12 (br. s, 2 H, NH2), 4.09
(q, J = 7.3 Hz, 2 H, OCH2), 5.22 (app. quintet, J = 7.6 Hz, 1 H,
*CH), 6.54 (br. d, J = 8.5 Hz, 1 H, NHCONHNH2), 7.13 (s, 1 H,
NHNH2), 7.35 (br. d, J = 7.9 Hz, 1 H, NHCOO) ppm. 13C NMR:
δ = 14.8, 22.7, 25.1, 44.2, 57.8, 61.1, 156.4, 160.3 ppm. DI-MS (EI):
m/z (%) = 175 (19) [M – 57]+, 158 (64), 143 (21), 132 (15), 117 (19),
102 (70), 86 (100). MS (ESI+): m/z = 255 [M + Na]+ Ǟ (MS2) 223,
197, 180, 166, 112, 108. C13H20N4O3 (232.28): calcd. C 46.54, H
8.68, N 24.12; found C 46.50, H 8.74, N 24.08.
3353, 3314, 1682, 1542, 1499, 1391, 1251, 1169, 1015, 753 cm–1. 1H
NMR: δ = 1.35 [s, 9 H, (CH3)3C], 2.90 (app. d, J = 7.0 Hz, 2 H,
CH2), 4.15 (br. s, 2 H, NH2), 5.25 (app. quintet, J = 8.2 Hz, 1 H,
*CH), 6.68 (br. d, J = 8.5 Hz, 1 H, NHCONHNH2), 7.12 (s, 1 H,
NHNH2), 7.15–7.38 (m, 6 H, 5ϫ ArH + NHCOO) ppm. 13C
NMR: δ = 29.2, 42.5, 59.8, 78.9, 127.1, 129.1, 130.2, 138.8, 155.8,
159.7 ppm. DI-MS (EI): m/z (%) = 203 (5) [M – 91]+, 178 (13), 177
(25), 164 (22), 163 (17), 147 (33), 128 (15), 120 (100), 119 (27), 118
(30), 91 (44). MS (ESI+): m/z = 317 [M + Na]+ Ǟ (MS2) 285, 261,
259, 242, 217, 200, 142. C14H22N4O3 (294.35): calcd. C 57.13, H
7.53, N 19.03; found C 57.08, H 7.55, N 19.06.
Semicarbazide 1bd: White solid (574 mg, 78%). IR (KBr): ν = 3345
Semicarbazide 1dd: White solid (657 mg, 80%). IR (KBr): ν = 3355,
˜
˜
(br), 3281 (br), 2958, 1690, 1545, 1507, 1255, 1225, 1160, 1028, 3275, 1691, 1655, 1542, 1504, 1326, 1247, 1049, 756, 733, 702 cm–1.
730 cm–1. 1H NMR: δ = 0.85 [d, J = 5.9 Hz, 6 H, (CH3)2CH], 1.37–
1.62 (m, 3 H, CHCH2), 4.12 (br. s, 2 H, NH2), 5.00 (app. s, 2 H,
1H NMR: δ = 2.95 (app. d, J = 6.8 Hz, 2 H, *CHCH2), 4.18 (br.
s, 2 H, NH2), 5.01 (app. s, 2 H, OCH2), 5.34 (app. quintet, J =
OCH2), 5.21 (app. quintet, J = 7.3 Hz, 1 H, *CH), 6.54 (br. d, J = 7.3 Hz, 1 H, *CH), 6.75 (br. d, J = 8.5 Hz, 1 H, NHCONHNH2),
8.5 Hz, 1 H, NHCONHNH2), 7.08 (s, 1 H, NHNH2), 7.22–7.43 7.17 (s, 1 H, NHNH2), 7.18–7.47 (m, 10 H, ArH), 7.66 (br. d, J =
(m, 5 H, ArH), 7.49 (br. d, J = 7.9 Hz, 1 H, NHCOO) ppm. 13C
NMR: δ = 23.3, 25.4, 45.6, 57.4, 66.2, 128.8, 129.3, 129.4, 138.1,
7.9 Hz, 1 H, NHCOO) ppm. 13C NMR: δ = 42.2, 60.3, 66.1, 127.3,
128.6, 128.8, 129.2, 129.3, 130.2, 138.1, 138.7, 155.9, 159.7 ppm.
156.0, 159.8 ppm. DI-MS (EI): m/z (%) = 237 (6) [M – 57]+, 193 DI-MS (EI): m/z (%) = 254 (4) [M – 74]+, 253 (7), 237 (25), 210
(4), 176 (22), 143 (6), 108 (14), 91 (100), 86 (29), 79 (15). MS (ESI+):
(22), 193 (19), 177 (13), 120 (27), 108 (14), 91 (100). MS (ESI+):
m/z = 317 [M + Na]+ Ǟ (MS2) 285, 259, 242, 174, 166, 108.
m/z = 351 [M + Na]+ Ǟ (MS2) 319, 293, 276, 200, 174, 142.
Eur. J. Org. Chem. 2011, 1376–1384
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1381

G. Verardo, C. D. Venneri, G. Esposito, P. Strazzolini
FULL PAPER
C17H20N4O3 (328.37): calcd. C 62.18, H 6.14, N 17.06; found C
62.13, H 6.18, N 17.10.
(ESI+): m/z = 551 [M + Na]+ Ǟ (MS2) 400, 346, 329, 303, 228.
C26H36N6O6 (528.61): calcd. C 59.08, H 6.86, N 15.90; found C
59.14, H 6.81, N 15.94.
Semicarbazide 1ea: White solid (561 mg, 77%). IR (KBr): ν = 3337
˜
(br), 1694, 1666, 1601, 1559, 1531, 1498, 1454, 1443, 1347, 1308,
Semicarbazide 4bd: White solid (647 mg, 93%). IR (KBr): ν = 3330,
˜
1251, 1100, 733 cm–1. 1H NMR: δ = 3.03 (app. d; J = 6.5 Hz, 2 H, 3279, 1699, 1655, 1504, 1255, 1156, 1127, 1049, 698 cm–1. 1H
CH2), 3.49 (s, 3 H, CH3), 4.07 (br. s, 2 H, NH2), 5.37 (app. quintet,
7.9 Hz, H, *CH), 6.65 (br. d, 8.2 Hz, H,
NMR: δ = 0.86 [d, J = 6.2 Hz, 12 H, 2ϫ (CH3)2CH], 1.38–1.64
(m, 6 H, 2ϫ CHCH2), 5.01 (app. s, 4 H, 2ϫ OCH2), 5.22 (app.
J
=
1
J
=
1
NHCONHNH2), 6.92–7.15 (m, 4 H, 3ϫ ArH + NHNH2), 7.24– quintet, J = 8.2 Hz, 2 H, 2ϫ *CH), 6.34 (d, J = 8.8 Hz, 2 H, 2ϫ
7.42 (m, 2 H, ArH + NHCOO), 7.58 (app. d, J = 7.3 Hz, 1 H,
NHCONHNH), 7.25–7.43 [m, 12 H, 2ϫ (5ϫ ArH + NHCOO)],
ArH), 10.74 (s, 1 H, ArNH) ppm. 13C NMR: δ = 32.3, 51.9, 59.6,
7.70 (s, 2 H, NHNH) ppm. 13C NMR: δ = 23.1, 23.2, 25.0, 45.2,
111.1, 112.1, 119.1, 119.2, 121.7, 124.1, 128.4, 136.9, 156.0, 57.6, 66.1, 128.5, 129.1, 137.9, 155.7, 157.7 ppm. DI-MS (EI): m/z
159.7 ppm. DI-MS (EI): m/z (%) = 217 (19) [M – 74]+, 216 (93),
185 (27), 184 (43), 157 (23), 156 (33), 155 (18), 130 (100). MS
(ESI+): m/z = 314 [M + Na]+ Ǟ (MS2) 282, 256, 239, 181, 98.
C13H17N5O3 (291.31): calcd. C 53.60, H 5.88, N 24.04; found C
53.64, H 5.82, N 24.09.
(%) = 220 (3) [M – 336]+, 176 (5), 158 (6), 143 (8), 108 (38), 107
(27), 91 (100), 86 (27), 79 (51), 65 (18). MS (ESI+): m/z = 579 [M
+ Na]+ Ǟ (MS2) 428, 360, 343, 317, 242. C26H36N6O6 (556.66):
calcd. C 60.42, H 7.24, N 15.10; found C 60.40, H 7.24, N 15.13.
Semicarbazide 4cb: White solid (490 mg, 83%). IR (KBr): ν = 3252
˜
1
Semicarbazide 1fb: White solid (463 mg, 74%). IR (KBr): ν = 3336
(br), 1696, 1672, 1509, 1254, 1108, 1056, 616 cm–1. H NMR: δ =
˜
(br), 2980, 2916, 1696, 1636, 1559, 1522, 1447, 1257, 1055 cm–1. 1H 1.20 (t, J = 7.0 Hz, 6 H, 2ϫ CH3), 4.05 (q, J = 7.0 Hz, 4 H, 2ϫ
NMR: δ = 1.19 (t, J = 7.0 Hz, 3 H, CH3CH2), 1.81–1.97 (m, 2 H, CH2), 6.32 (app. t, J = 8.5 Hz, 2 H, 2ϫ *CH), 6.94 (d, J = 9.1 Hz,
*CHCH2), 2.07 (s, 3 H, SCH3), 2.34–2.50 (m, 2 H, SCH2), 3.68 (br. 2 H, 2ϫ NHCONHNH), 7.26–7.42 (m, 10 H, 5ϫ ArH), 7.73 (br.
s, 2 H, NH2), 4.01 (q, J = 7.0 Hz, 2 H, OCH2), 5.20 (app. quintet, s, 2 H, 2 ϫ NHCOO), 8.01 (s, 2 H, NHNH) ppm. 13C NMR: δ =
J
=
8.4 Hz,
1
H, *CH), 6.62 (br. d,
J
=
8.9 Hz,
1
H,
15.4, 60.6, 126.7, 128.2, 129.0, 142.2, 155.9, 158.1 ppm. DI-MS
(EI): m/z (%) = 251 (8) [M – 221]+, 178 (49), 163 (18), 132 (100),
120 (18), 106 (38), 105 (57), 104 (93), 91 (23), 77 (56). MS (ESI+):
m/z = 495 [M + Na]+ Ǟ (MS2) 406, 318, 301, 275, 200.
NHCONHNH2), 7.01 (s, 1 H, NHNH2), 7.29 (br. d, J = 8.0 Hz, 1
H, NHCOO) ppm. 13C NMR: δ = 15.4, 15.6, 30.2, 35.9, 58.2, 60.5,
156.0, 159.8 ppm. DI-MS (EI): m/z (%) = 176 (27) [M – 74]+, 175
(7), 128 (100), 114 (25), 86 (79), 61 (51), 56 (66). MS (ESI+): m/z = C22H28N6O6 (472.50): calcd. C 55.92, H 5.97, N 17.79; found C
273 [M + Na]+ Ǟ (MS2) 241, 215, 198, 184, 126, 112. C8H18N4O3S
(250.32): calcd. C 38.39, H 7.25, N 22.38; found C 38.34, H 7.22,
N 22.40.
55.96, H 5.96, N 17.76.
Semicarbazide 4cd: White solid (694 mg, 93%). IR (KBr): ν = 3307
˜
(br), 1701, 1655, 1558, 1543, 1508, 1347, 1310, 1236, 1055,
1
General Procedure for the Synthesis of Semicarbazides 4 (Method
C): NMM (0.30 mL, 2.73 mmol) was slowly and dropwise added
into a stirred solution of α-N-protected amino acid 2 (2.50 mmol)
in THF (15 mL). After 5 min, IBCF (0.36 mL, 2.73 mmol) was
slowly added into the reaction mixture, which was cooled to –20 °C
and stirring was continued for 20 min at the same temperature. The
reaction mixture was subsequently warmed to 0 °C and a solution
of KH2PO4 (0.17 g, 1.25 mmol) in H2O (1 mL) was added in one
portion, followed, after 5 min, by a solution of KH2PO4 (1.70 g,
12.50 mmol) and NaN3 (0.41 g, 6.25 mmol) in H2O (9 mL). After
stirring 30 min at 0 °C, the mixture was warmed to 40 °C for 1.5 h,
hydrazine monohydrate (0.73 mL, 7.50 mmol) was slowly added
and the resulting mixture was warmed to 50 °C and stirred for 5 h.
THF was finally removed under reduced pressure, water was fil-
tered off, and the obtained crude residue was washed with water
and EtOAc affording, after drying in vacuo, semicarbazide 4 as a
white solid in 57–93% overall yield (Table 1).
755 cm–1. H NMR: δ = 5.09 (app. s, 4 H, 2ϫ OCH2), 6.38 (app.
t, J = 8.9 Hz, 2 H, 2ϫ *CH), 6.98 (d, J = 8.9 Hz, 2 H, 2ϫ
NHCONHNH), 7.24–7.59 (m, 20 H, ArH), 7.90 (br. s, 2 H, 2ϫ
NHCOO), 8.01 (s, 2 H, NHNH) ppm. 13C NMR: δ = 60.8, 66.4,
126.8, 128.3, 128.6, 128.7, 129.1, 129.2, 137.7, 142.1, 155.9,
158.1 ppm. DI-MS (EI): m/z (%) = 239 (34) [M – 357]+, 238 (57),
194 (45), 132 (98), 108 (60), 107 (56), 91 (96), 79 (100), 77 (75). MS
(ESI+): m/z = 619 [M + Na]+ Ǟ (MS2) 468, 380, 363, 337, 262.
C32H32N6O6 (596.64): calcd. C 64.42, H 5.41, N 14.09; found C
64.36, H 5.46, N 14.03.
Semicarbazide 4db: White solid (507 mg, 81%). IR (KBr): ν = 3307
˜
1
(br), 1698, 1672, 1547, 1512, 1323, 1298, 1253, 1054, 701 cm–1. H
NMR: δ = 1.14 (t, J = 7.3 Hz, 6 H, 2ϫ CH3), 2.91 (app. d, J =
7.1 Hz, 4 H, 2ϫ PhCH2), 3.97 (q, J = 7.1 Hz, 4 H, 2ϫ OCH2),
5.30 (app. quintet, J = 8.2 Hz, 2 H, 2ϫ *CH), 6.53 (d, J = 8.5 Hz,
2 H, 2ϫ NHCONHNH), 7.16–7.39 [m, 12 H, 2ϫ (5ϫ ArH +
NHCOO)], 7.76 (s, 2 H, NHNH) ppm. 13C NMR: δ = 15.3, 41.9,
60.4, 60.5, 127.0, 128.9, 130.0, 138.4, 155.8, 157.7 ppm. DI-MS
(EI): m/z (%) = 192 (40) [M – 308]+, 191 (72), 175 (20), 163 (41),
145 (51), 120 (52), 119 (63), 118 (79), 117 (67), 91 (100), 65 (26).
MS (ESI+): m/z = 523 [M + Na]+ Ǟ (MS2) 434, 332, 315, 289, 214.
C24H32N6O6 (500.55): calcd. C 57.59, H 6.44, N 16.79; found C
57.55, H 6.46, N 16.84.
To optimize the yield of semicarbazide 4cb by avoiding the forma-
tion of the semicarbazide 5cb,[21] the addition of hydrazine mono-
hydrate (0.73 mL, 7.50 mmol) into the reaction mixture containing
the synthesized carbamoyl azide 3cb was carried out at room tem-
perature and stirring was continued for 12 h at the same tempera-
ture. Under these conditions, after usual work-up, semicarbazide
4cb was obtained in 83% yield (Table 1).
Semicarbazide 4dc: White solid (598 mg, 86%). IR (KBr): ν = 3349
˜
Semicarbazide 4ad: White solid (476 mg, 72%). IR (KBr): ν = 3320
(br), 1698, 1656, 1568, 1500, 1367, 1250, 1171, 1120, 1049,
˜
1
1
(br), 1698, 1655, 1570, 1508, 1265, 1244, 1125, 1036, 697 cm–1. H 700 cm–1. H NMR: δ = 1.13 [s, 18 H, 2ϫ (CH3)3C], 2.88 (app. d,
NMR: δ = 0.88 [d, J = 6.8 Hz, 12 H, 2ϫ (CH3)2CH], 1.87 (app.
sextet, J = 7.0 Hz, 2 H, 2ϫ CH), 4.99 (app. q, J = 8.5 Hz, 2 H,
J = 6.8 Hz, 4 H, 2ϫ CH2), 5.22 (app. quintet, J = 8.5 Hz, 2 H, 2ϫ
*CH), 6.46 (d, J = 8.5 Hz, 2 H, 2ϫ NHCONHNH), 7.12–7.33 [m,
2ϫ *CH), 5.05 (app. s, 4 H, 2ϫ CH2), 7.28–7.46 [m, 12 H, 2ϫ 12 H, 2ϫ (5ϫ ArH + NHCOO)], 7.74 (s, 2 H, NHNH) ppm. 13C
(5ϫ ArH + NHCOO)], 7.79 (s, 2 H, NHNH) ppm. 13C NMR: δ
= 19.0, 19.1, 33.6, 63.9, 6.1, 128.5, 128.6, 129.1, 137.9, 155.9,
158.3 ppm. DI-MS (EI): m/z (%) = 206 (7) [M – 322]+, 162 (25),
NMR: δ = 28.9, 42.0, 60.2, 78.8, 126.9, 128.8, 130.0, 138.5, 155.6,
157.7 ppm. DI-MS (EI): m/z (%) = 220 (6) [M – 336]+, 203 (11),
177 (16), 163 (41), 146 (33), 145 (54), 119 (56), 118 (97), 117 (43),
140 (9), 108 (19), 107 (21), 91 (100), 86 (20), 79 (35), 77 (15). MS 91 (100), 86 (28). MS (ESI+): m/z = 573 [M + Na]+ Ǟ (MS2) 498,
1382
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1376–1384

Semicarbazides from Amino Acids
J. T. Vicenzi, J. G. Wei, J. A. Werner, Org. Process Res. Dev.
2009, 13, 131–143.
357, 340, 314, 239 C28H40N6O6 (556.66): calcd. C 60.42, H 7.24, N
15.10; found C 60.45, H 7.20, N 15.15.
[5]
a) R. P. Archana, K. Bajaj, V. K. Srivastava, R. Chandre, A.
Kumar, Arzneim.-Forsch. 2003, 53, 301–306; b) D. Ramesh, B.
Sreenivasulu, Indian J. Heterocycl. Chem. 2003, 13, 163–164; c)
R. Severinsen, J. P. Kilburn, J. F. Lau, Tetrahedron 2005, 61,
5565–5575; d) U. C. Mashelkar, A. A. Audi, Indian J. Chem.
Sect. B: Org. Chem. Incl. Med. Chem. 2006, 45, 1463–1469; e)
A. Demirbas, S. Ceylan, N. Demirbas, J. Heterocycl. Chem.
2007, 44, 1271–1280; f) I. Tumosiene, K. Kantminiene, A. Pavi-
lonis, Z. Mazeliene, Z. J. Beresnevicius, Heterocycles 2009, 78,
59–70.
a) M. C. Cardia, S. Distinto, E. Maccioni, L. Bonsignore, A.
Delogu, J. Heterocycl. Chem. 2003, 40, 1011–1015; b) D. Hab-
ibi, O. Marvi, Catal. Commun. 2007, 8, 127–130.
V. V. Dabholkar, F. Y. Ansari, Acta Pol. Pharm. 2008, 65, 521–
526.
For selected examples of semicarbazones with antimicrobial
properties, see: a) N. C. Kasuga, K. Sekino, C. Kaumo, N. Shi-
mada, M. Ishikawa, N. Nomiya, J. Inorg. Biochem. 2001, 84,
55–65; b) H. S. B. Naik, M. S. Ramesha, B. V. Swetha, T. R.
Roopa, Phosphorus Sulfur Silicon Relat. Elem. 2006, 181, 533–
541; c) P. Valentina, K. Ilango, P. Prashad, D. K. Basedia,
Asian J. Chem. 2009, 21, 6116–6120; d) for semicarbazones
with anti-inflammatory properties, see: A. Rineh, N. Mah-
moodi, M. Abdollahi, A. Foroumadi, M. Sorkhi, A. Shafiee,
Arch. Pharm. 2007, 340, 409–415; e) I. M. I. Fakhr, M. A. A.
Radwan, S. El-Batran, O. M. E. Abd El-Salam, S. M. El-Shen-
awy, Eur. J. Med. Chem. 2009, 44, 1718–1725; for semicarb-
azones with anticonvulsant properties, see: f) P. Yogeeswari, R.
Thirumurugan, R. Kavya, J. S. Samuel, J. Stables, D. Sriram,
Eur. J. Med. Chem. 2004, 39, 729–734; g) N. Siddiqui, A. Rana,
S. A. Khan, M. A. Bhata, S. E. Haqueb, Bioorg. Med. Chem.
Lett. 2007, 17, 4178–4182; h) F. Azam, I. A. Alkskas, S. L.
Khokra, O. Prakash, Eur. J. Med. Chem. 2009, 44, 203–211;
i) A. Shafiee, A. Rineh, A. Kebriaeezadeh, A. Foroumadi, V.
Sheibani, M. R. Afarinesh, Med. Chem. Res. 2009, 18, 758–
769; j) for semicarbazones with antitumor properties, see: S. E.
Asis, A. M. Bruno, A. R. Martinez, M. V. Sevilla, C. H.
Gaozza, A. M. Romano, J. D. Coussio, G. Ciccia, Farmaco
1999, 54, 517–523.
Semicarbazide 4ea: White solid (496 mg, 72%). IR (KBr): ν = 3330
˜
1
(br), 1703, 1667, 1511, 1458, 1343, 1248, 1101, 1052, 743 cm–1. H
NMR: δ = 3.07 (app. d, J = 6.7 Hz, 4 H, 2ϫ CH2), 3.52 (s, 6 H,
2ϫ CH3), 5.38 (app. quintet, J = 7.4 Hz, 2 H, 2ϫ *CH), 6.55 (d,
J = 8.6 Hz, 2 H, 2ϫ NHCONHNH), 6.94–7.22 (m, 6 H, ArH),
7.25–7.46 [m, 4 H, 2ϫ (ArH + NHCOO)], 7.62 (app. d, J = 7.0 Hz,
2 H, ArH), 7.77 (s, 2 H, NHNH), 10.78 (s, 2 H, 2ϫ ArNH) ppm.
13C NMR: δ = 36.2, 52.0, 60.0, 110.9, 112.1, 119.0, 119.1, 121.7,
124.3, 128.3, 136.9, 155.9, 158.1 ppm. DI-MS (EI): m/z (%) = 217
(15) [M – 333]+, 216 (98), 184 (100), 157 (26), 156 (48), 155 (21),
130 (70). MS (ESI+): m/z = 579 [M + Na]+ Ǟ (MS2) 523, 479, 462,
360, 343, 317, 242. C26H30N8O6 (550.57): calcd. C 56.72, H 5.49,
N 20.35; found C 56.70, H 5.52, N 20.30.
[6]
[7]
[8]
Semicarbazide 4fb: White solid (521 mg, 89%). IR (KBr): ν = 3315
˜
1
(br), 1695, 1656, 1561, 1527, 1509, 1263, 1226, 1059, 977 cm–1. H
NMR: δ = 1.19 (t, J = 7.2 Hz, 6 H, 2ϫ CH3CH2), 1.80–1.98 (m,
4 H, 2ϫ *CHCH2), 2.07 (s, 6 H, 2ϫ SCH3), 2.35–2.52 (m, 4 H,
2ϫ SCH2), 4.02 (q, J = 7.1 Hz, 4 H, 2ϫ OCH2), 5.20 (app. quintet,
J = 8.4 Hz, 2 H, 2ϫ *CH), 6.49 (d, J = 8.8 Hz, 2 H, 2ϫ
NHCONHNH), 7.24 (br. s, 2 H, 2ϫ NHCOO), 7.74 (s, 2 H,
NHNH) ppm. 13C NMR: δ = 15.4, 15.6, 30.1, 35.7, 58.4, 60.6,
155.9, 159.1 ppm. DI-MS (EI): m/z (%) = 176 (18) [M – 292]+, 175
(10), 128 (100), 114 (14), 102 (14), 86 (48), 61 (52), 56 (74). MS
(ESI+): m/z = 523 [M + Na]+ Ǟ (MS2) 402, 316, 299, 273, 198.
C16H32N6O6S2 (468.59): calcd. C 41.01, H 6.88, N 17.93; found C
41.00, H 6.91, N 17.90.
Supporting Information (see footnote on the first page of this arti-
cle): 2D TOCSY, 2D ROESY, and DOSY NMR spectra of 1db and
4db.
Acknowledgments
1
The authors are grateful to Dr. S. Turco for recording H and 13C
NMR spectra and to Dr. I. Duse for MS measurements.
[9]
For selected examples of semicarbazone transition-metal com-
plexes with antimicrobial properties, see: a) A. Gulea, D. Poir-
ier, J. Roy, V. Stavila, I. Bulimestru, V. Tapcov, M. Birca, L.
Popovschi, J. Enzyme Inhib. Med. Chem. 2008, 23, 806–818;
b) N. Thilagavathi, A. Manimaran, N. P. Priya, N. Sathya, C.
Jayabalakrishnan, Trans. Met. Chem. 2009, 34, 725–732; c) N.
Nishat, R. Ud-Din, S. Dhyani, J. Coord. Chem. 2009, 62, 996–
1004; d) for semicarbazone transition-metal complexes with
antitumor properties, see: N. S. Youssef, E. A. Zahany, M. M.
Anwar, S. A. Hassan, Phosphorus Sulfur Silicon Relat. Elem.
2009, 184, 103–125.
a) A. M. Hussein, A. A. Atalla, A. M. K. ElDean, Pharmazie
1995, 50, 788–791; b) C. W. Phoon, M. M. Sim, Synlett 2001,
697–699; c) V. Novikovaite, Z. J. Beresnevicius, Chem. Hetero-
cycl. Compd. 2009, 45, 786–792; d) A. O. Omran, Chin. J.
Chem. 2009, 27, 1937–1941.
a) S. V. Andurkar, C. Beguin, J. P. Stables, H. Kohn, J. Med.
Chem. 2001, 44, 1475–1478; b) I. Bélai, Tetrahedron Lett. 2003,
44, 7475–7477; c) A. G. E. Amr, Z. Naturforsch., Teil B 2005,
60, 990–998; d) X. C. Wang, L. Q. Chai, M. G. Wang, Z. Q.
Quan, Z. Li, Synth. Commun. 2006, 36, 645–652; e) O. I. El-
Sabbagh, H. M. Rady, Eur. J. Med. Chem. 2009, 44, 3680–3686;
f) M. Pitucha, P. Borowski, Z. Karczmarzyk, A. Fruzinski, J.
Mol. Struct. 2009, 919, 170–177.
a) H. Cerecetto, R. Di Maio, M. González, M. Risso, G. Sag-
rera, G. Seoane, A. Denicola, G. Peluffo, C. Quijano, A. O. M.
Stoppani, M. Paulino, C. Olea-Azar, M. A. Basombrío, Eur. J.
Med. Chem. 2000, 35, 343–350; b) M. K. Abdel-Hamid, A. A.
[1] a) N. Nishimura, M. Banno, A. Maki, Y. Nishiyama, I. Maeba,
Carbohydr. Res. 1998, 307, 211–215; b) V. N. Sonar, M. B. Had-
imani, Indian J. Heterocycl. Chem. 1998, 8, 125–128; c) J. Quir-
oga, J. Portilla, R. Abonía, B. Insuasty, M. Nogueras, J. Cobo,
Tetrahedron Lett. 2008, 49, 5943–5945; d) F. F. Barsoum, A. S.
Girgis, Eur. J. Med. Chem. 2009, 44, 2172–2177; e) J. Nayak,
K. S. Girish, M. Babu, B. Kalluraya, Indian J. Heterocycl.
Chem. 2009, 19, 105–108.
[2] a) R. M. Kedar, Asian J. Chem. 2001, 13, 477–480; b) D. Azari-
far, M. Shaebanzadeh, Molecules 2002, 7, 885–895; c) M. D.
Desai, K. K. Desai, Asian J. Chem. 2002, 14, 995–998; d) V. S.
Jamode, H. S. Chandak, P. R. Bhagat, Asian J. Chem. 2004, 16,
233–238; e) S. S. Khan, A. Hasan, Heterocycl. Commun. 2007,
13, 131–138.
[3] a) M. Kidwai, R. Kumar, Gazz. Chim. Ital. 1997, 127, 263–267;
b) S. A. Khan, Eur. J. Med. Chem. 2008, 43, 2040–2044.
[4] a) K. S. Rajan, A. R. R. Rao, K. Mogilaiah, M. R. Prasad, J.
Chem. Res., Synop. 2002, 10, 490–492; b) E. Pomarnacka, M.
Gdaniec, Bioorg. Med. Chem. 2003, 11, 1259–1267; c) A.
Bishnoi, R. Saxena, K. Srivastav, M. N. Joshi, S. K. Bajpai,
Indian J. Heterocycl. Chem. 2006, 15, 307–308; d) O. I. El-Sab-
bagh, H. M. Rady, Eur. J. Med. Chem. 2009, 44, 3680–3686; e)
M. Pitucha, P. Borowski, Z. Karczmarzyk, A. Fruzinski, J.
Mol. Struct. 2009, 919, 170–177; f) M. D. Argentine, T. M.
Braden, J. Czarnik, E. W. Conder, S. E. Dunlap, J. W. Fennell,
M. A. LaPack, R. R. Rothhaar, R. B. Scherer, C. R. Schmid,
[10]
[11]
[12]
Eur. J. Org. Chem. 2011, 1376–1384
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1383

G. Verardo, C. D. Venneri, G. Esposito, P. Strazzolini
FULL PAPER
Abdel-Hafez, N. A. El-Koussi, N. M. Mahfouz, A. Innocenti,
C. T. Supuran, Bioorg. Med. Chem. 2007, 15, 6975–6984.
[13] S. Mallakpour, Z. Rafiee, Synth. Commun. 2007, 37, 1927–
1934.
[14] S. Mallakpour, A. R. Hajipour, H. A. Taghizadeh, Monatsh.
Chem. 2003, 134, 1015–1017.
[15] Z. J. Quan, Z. Zhang, X. C. Wang, Z. Li, Phosphorus Sulfur
Silicon Relat. Elem. 2006, 181, 1397–1402.
[16] Z. Li, Z. J. Quan, X. C. Wang, Chin. J. Org. Chem. 2003, 23,
822–826.
(s, 1 H, HC=N), 10.62 (br. s, 1 H, NHN=CH) ppm. 13C NMR:
δ = 15.5, 60.4, 61.1, 126.7, 127.4, 128.5, 129.3, 129.6, 130.3,
135.3, 141.4, 142.5, 155.2, 156.1 ppm. DI-MS (EI): m/z (%) =
252 (5) [M – 88]+, 251 (8), 178 (100), 163 (19), 147 (46), 132
(76), 119 (31), 106 (39), 105 (58), 104 (90), 90 (28), 77 (55), 51
(35). MS (ESI+): m/z = 363 [M + Na]+ Ǟ (MS2) 274, 200, 186,
128. C18H20N4O3 (340.38): calcd. C 63.52, H 5.92, N 16.46;
found C 63.49, H 5.95, N 16.41.
2
The ESI-MS spectrum of [6 + H]+ revealed the presence of
[22]
three ions at m/z 150, 134, and 106 due to the loss of ethene
(28 Da), ethylene oxide (44 Da), and β-propiolactone (72 Da),
respectively.
M. Llinas, D. M. Wilson, M. P. Klein, J. Am. Chem. Soc. 1977,
99, 6846–6850.
A. R. Waldeck, P. W. Kuchel, A. J. Lennon, B. E. Chapman,
Prog. Nucl. Magn. Reson. 1997, 30, 39–68.
a) F. M. F. Chen, N. L. Benoiton, Can. J. Chem. 1987, 65, 1224;
b) A. Vogel, in: Vogel’s Textbook of Practical Organic Chemis-
try, 5th ed., Longman Scientific and Technical, New York,
1989, p. 762 and 786.
[17] A. S. Ali, J. S. Wilkie, K. N. Winzenberg, Aust. J. Chem. 1996,
49, 927–930.
[18] G. Verardo, E. Bombardella, P. Geatti, P. Strazzolini, Synthesis
2008, 438–444.
[19] G. Verardo, E. Bombardella, C. D. Venneri, P. Strazzolini, Eur.
J. Org. Chem. 2009, 6239–6244.
[20] C. D. Venneri, G. Verardo, P. Strazzolini, Synth. Commun.
2011, in press.
[21] When the synthesis of 4cb was carried out following Method C
at 50 °C, the H2O/EtOAc mixture used to wash the final
crude residue contained the 1-benzylidene-4-[(ethoxycarbonyl-
amino)(phenyl)methyl]semicarbazide (5cb). At this point, the
organic layer was separated, dried with Na2SO4, filtered, and
concentrated in vacuo. The obtained residue was purified by
column chromatography on silica gel (CH2Cl2/acetone gradient
elution) to afford 5cb (0.18 g, 21%) as a white solid; Rf = 0.71
(CH2Cl2/acetone, 1:1); m.p. 189–191 °C. [α]2D0 = –25.7 (c = 0.2,
[23]
[24]
[25]
[26]
L. Braunschweiler, R. R. Ernst, J. Magn. Reson. 1983, 53, 521–
528.
[27]
[28]
A. Bax, D. G. Davis, J. Magn. Reson. 1985, 65, 355–360.
A. A. Bothner-By, R. L. Stephens, J.-M. Lee, C. D. Warren,
R. W. Jeanholz, J. Am. Chem. Soc. 1984, 106, 811–813.
D. Marion, K. Wüthrich, Biochem. Biophys. Res. Commun.
1983, 113, 967–974.
[29]
[30]
DMSO). IR (KBr): ν = 3381, 3082, 2974, 1699, 1672, 1542,
˜
1
1497, 1364, 1312, 1240, 1054, 697 cm–1. H NMR: δ = 1.22 (t,
A. Jerschow, N. Müller, J. Magn. Reson., Ser. A 1996, 123, 222–
225.
J = 7.00 Hz, 3 H, CH3), 4.09 (q, J = 7.00 Hz, 2 H, CH2), 6.51
(app. t, J = 8.9 Hz, 1 H, *CH), 7.28–7.54 (m, 9 H, 8ϫ ArH +
*CHNHCON), 7.64–7.58 (m, 3 H, 2ϫ ArH + NHCOO), 7.97
Received: October 8, 2010
Published Online: January 18, 2011
1384
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1376–1384