Synthesis of hydrazine and azapeptide derivatives by alkylation of carbazates and semicarbazones

Article abstract of DOI:10.1139/v2012-070

Hydrazine and azapeptide analogs were synthesized effectively by alkylation of alkylidene carbazates and semicarbazones. In comparisons of benzylidene, benzhydrylidene, and fluorenylidene tert-butyl carbazates in alkylations using bases of different pK_b character, superior conversion was obtained using the fluorenone derivative. Mild alkylation conditions were found employing Et₄NOH as base and used to convert fluorenylidene tert-butyl carbazate into 13 different protected hydrazines. Moreover, racemization was avoided during alkylation of fluorenylidene semicarbazide in the synthesis of aza-propargylglycinylphenylalanine tert-butyl ester, the protecting groups from which could be selectively removed.

Full text of DOI:10.1139/v2012-070

985
Synthesis of hydrazine and azapeptide derivatives
by alkylation of carbazates and semicarbazones
Yesica Garcia-Ramos, Caroline Proulx, and William D. Lubell
Abstract: Hydrazine and azapeptide analogs were synthesized effectively by alkylation of alkylidene carbazates and
semicarbazones. In comparisons of benzylidene, benzhydrylidene, and fluorenylidene tert-butyl carbazates in alkylations
using bases of different pKb character, superior conversion was obtained using the fluorenone derivative. Mild alkylation
conditions were found employing Et4NOH as base and used to convert fluorenylidene tert-butyl carbazate into 13 different
protected hydrazines. Moreover, racemization was avoided during alkylation of fluorenylidene semicarbazide in the
synthesis of aza-propargylglycinylphenylalanine tert-butyl ester, the protecting groups from which could be selectively
removed.
Key words: carbazate, tetraethylammonium hydroxide, semicarbazone, alkylation, fluorenone hydrazine.
Résumé : L’alkylation de carbazates et de semicarbazones d’alkylidène permet de réaliser efficacement la synthèse
d’analogues hydrazino- et aza- de peptides. Des comparaisons des réactions d’alkylation des tert-butyl carbazates de
benzylidène, de benzhydrylidène et de fluorénylidène en présence de bases de pKb divers ont permis de montrer que les
meilleures conversions sont obtenues avec le dérivé de la fluorénone. Des conditions d’alkylation douces, faisant appel a
`
Et4NOH comme base, ont été utilisées pour transformer le tert-butyl carbazate de fluorénylidène en 13 hydrazines protégées
différentes. De plus, il a été possible d’éviter la racémisation au cours de l’alkylation du fluorénylidènesemicarbazide dans la
synthèse de l’ester tert-butylique de l’aza-propargylglycinylphénylalanine a partir duquel les groupes protecteurs peuvent être
`
enlevés d’une façon sélective.
Mots-clés : carbazate, hydroxyde de tétraéthylammonium, semicarbazone, alkylation, hydrazone de la fluorénone.
[Traduit par la Rédaction]
a side product from the latter process and removed by chro-
matography.12,13 Combinations of protecting groups have also
been employed in attempts to enhance reactivity and selectivity in
the alkylation of hydrazine. For example, N-tert-butyloxycarbonyl-
and N-benzyloxycarbonyl-aminophthalimides were shown to be
sufficiently reactive acid partners in protocols featuring al-
kylations with alcohols using the Mitsunobu reaction.14 Al-
though a variety of alkylations of such carbamatophthalimides
were successful, attempts to employ ureidophthalimides in
similar Mitsunobu conditions as well as in reactions with alkyl
halides and potassium tert-butoxide as base returned mostly
starting material.15 Considering alkylation of such aza-glycine
amide derivatives is a key step for the diversity-oriented
synthesis of azapeptide and azadiketopiperazine derivatives,
semicarbazones were subsequently explored and shown to
undergo alkylation effectively using alkyl halides and rela-
tively strong bases.15,16 Conditions have also been developed
for the alkylation of tert-butylisopropylidene carbazate;17 in
particular, 77%–93% yields were obtained in reactions with a
set of six primary alkyl bromides using potassium hydroxide
under phase-transfer conditions, albeit at 80 °C.18 In addition,
a set of five tert-butyl arylidene and cyclohexylidene carba-
Introduction
Hydrazine derivatives are employed as pesticides and drugs
for treating depression, Parkinson disease, and tuberculosis.1,2
Substituted hydrazine analogs have also been used as building
blocks for heterocycle and azapeptide synthesis.3,4 The latter
peptidomimetics have evoked particular interest for studying
biologically active peptides because of their potential for ri-
gidifying conformation, increasing metabolic stability, and
improving bioavailability.5,6
Hydrazine synthesis has, however, remained a challenge
owing to the inherent difficulty in differentiating the adjacent
nitrogen atoms. Different ways have been described for func-
tionalizing hydrazine selectively. For example, monoalkylation of
hydrazine, usually in excess, has been achieved using different
alkyl halides, albeit mixtures may ensue from multiple al-
kylation.7,8 Alternatively, alkyl hydrazines have been synthe-
sized by hydrogenation and by hydride reduction of their
corresponding hydrazones.9–11 Issues of overalkylation have
been addressed by employing carbazates in reductive amina-
tion protocols,4 as well as by reactions with reactive alkyl
halides; however, N=,N=-dialkylcarbazate has been observed as
Received 20 June 2012. Accepted 8 August 2012. Published at www.nrcresearchpress.com/cjc on 30 November 2012.
Y. Garcia-Ramos, C. Proulx, and W.D. Lubell. Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville,
Montreal, QC H3C 3J7, Canada.
Corresponding author: William D. Lubell (e-mail: william.lubell@umontreal.ca).
This article is part of a Special Issue dedicated to Professor Derrick Clive.
Can. J. Chem. 90: 985–993 (2012)
doi:10.1139/v2012-070
Published by NRC Research Press

986
Can. J. Chem. Vol. 90, 2012
Scheme 2. Synthesis of carbazates 3 and 4.
Fig. 1. Resonance stabilization of the fluorenylidene hydrazone
anion.
O
H2N
N
H
Ot-Bu
O
AcOH, EtOH,
∆, 16 h
O
R
HN
N
Ot-Bu
R
Boc2O, i-PrOH,
0°C - rt, 16 h
Scheme 1. Synthesis of fluorenylidene tert-butyl carbazate (2).
NH2
H2N-NH2•H2O,
EtOH, ∆, 16 h
N
52%
3: R = Ph (71%)
4: R = H (94%)
O
N
NHR
Boc2O, DMAP,
pyridine, THF,
0°C - rt
1: R = H (87%)
Scheme 3. Propargylation of alkylidene carbazates 2–4.
2: R = Boc (56%)
1. Base, THF, 0°C, 30 min
Ot-Bu
Ot-Bu
2.
Br , 0°C - rt, 16 h
HN
N
O
N
N
O
zates were alkylated with allyl and benzyl bromides, respec-
tively, in a Ͼ85% yield using cesium carbonate in the absence
of solvent with ball milling at 30 Hz.19
R
R
R'
R'
The introduction, alkylation, and deprotection of
semicarbazone-protected aza-glycine residues has given rise to
the submonomer synthesis of azapeptides.16 For the key al-
kylation reaction, aza-glycine has been protected with benzyl-
idene and diphenylmethylidene hydrazones, respectively, on
solid support and in solution, to achieve chemoselective
deprotonation employing KO-t-Bu and tert-butyliminotri
(pyrrolidino)-phosphorane (BTPP) as base.15 In the alkylation
of the azadipeptide ester, aza-Gly-Phe-O-t-Bu, racemization
was, however, detected owing to the competitive removal of
the ester ␣ proton. The influence of the hydrazone structure in
the alkylation of aza-glycine analogs has thus been examined
in pursuit of a means for avoiding racemization without sac-
rificing yield by employment of milder basic conditions. In
early studies, electron-withdrawing groups were considered
for favoring deprotonation by anion stabilization; however,
their inductive effects had modest influence at best during
alkylation. Inspired by the application of fluorenyl imines in
the alkylation of glycine esters,20 the resonance stabilization
of the 14 ␲-electron fluorenyl anion (Fig. 1) has now been
explored for favoring deprotonation of the semicarbazone and
compared with reactions of the benzylidene and diphenylmeth-
ylidene counterparts. The application of this strategy has led to
effective means for selective hydrazine alkylation under mild
conditions and ambient temperature, as well as a racemization-
free method for assembling azadipeptide building blocks for
azapeptide synthesis.
N
R
N
N
N
R
2:
=
7a:
=
R'
R'
3: R = R' = Ph
4: R = H, R' = Ph
6: R = R' = Ph
5: R = H, R' = Ph
(Scheme 3 and Table 1).23–28 Conversion was analyzed by
1H NMR spectroscopy. Complete alkylation was consistently
observed using all three carbazates and tert-butoxide as strong
base, and no reaction occurred with triethylamine as the weak-
est base. Significant differences in reactivity were observed
employing 2-tert-butyl-1,1,3,3-tetramethylguanidine and hy-
droxide ion as base. Using such bases, fluorenylidene tert-
butyl carbazate (2) gave superior conversion in comparison
with carbazates 3 and 4. In particular, complete conversion
was achieved in the alkylation of 2 employing the 10% tetraeth-
ylammonium hydroxide in H2O (Table 1, entry 5). For com-
parison, 10% sodium hydroxide in H2O was also employed in
the alkylations of carbazates 2–4 with propargyl bromide
(150 mol%). Although a slight improvement in conversion to
diphenylketamine carbazate (6) was observed using 3 and
aqueous NaOH, yields of carbazates 5–7 were superior with
aqueous tetraethylammonium hydroxide, albeit nearly identi-
cal in the alkylation of 2 with both forms of the aqueous
hydroxide ion. The scope of the alkylation of 2 was thus
examined employing aqueous tetraethylammonium hydroxide.
To examine the scope of the alkylation reaction employing
Et4NOH (150 mol %) as base, 2 (100 mol %) was treated
with different alkylating agents (150 mol %) in tetrahy-
drofuran (THF) at 0 °C and the reactions were allowed to
warm to room temperature over 16 h (Table 2). Yields
varied with the electronic and steric natures of the electrophile.
For example, reactive alkyl halides (Table 2, entries 1–9) gave
62%–89% yields of isolated carbazates 7a–7i. On the other
hand, the reaction with bulky alkyl halides isopropyliodide
and 1-bromoethylbenzene required microwave irradiation
(50–60 °C) to give alkyl branched carbazates 7j and 7k in
55% and 61% yields, respectively. Relative to the ethyl and
butyl counterparts, the longer alkyl chain of 1-iodooctane
Results and discussion
Fluorenylidene tert-butyl carbazate (2) was made by acyla-
tion of fluorenone hydrazone (1),21 using di-tert-butyl dicar-
bonate (Scheme 1). On the other hand, diphenylmethylidene
and benzylidene carbazates (3 and 4) were synthesized
effectively from the condensation of benzophenone and
benzaldehyde, respectively, with tert-butyl carbazate in eth-
anol (Scheme 2).22
With carbazates 2–4 in hand, alkylation was studied using
propargyl bromide (150 mol %) and different bases (150 mol %),
with the pKa of the conjugate acids varying from 19 to 10.7
Published by NRC Research Press

Garcia-Ramos et al.
987
Table 1. Conversions from alkylation of carbazates 2–4 (100 mol %) with propargyl bromide (150 mol %) in tetrahydrofuran (THF).
Entry
Base (150 mol %)
pKa (conjugate acid)a
1
2
KO-t-Bu
EtONa
32.2 (DMSOb)24
29.8 (DMSOb)24
15.9 (H2O)24
100
100
100
100
100
100
3
4
5
6
MeONa
29.0 (DMSOb)24
15.5 (H2O)24
100
50
69
57
NaOH
31.4 (DMSOb)24
15.75 (H2O)24
31.4 (DMSOb)24
15.75 (H2O)24
13.2 (DMSOb)25
13.6 (H2O)25
Tracec
50
90
Et4NOHd
84
100
100
2-tert-Butyl-TMGe
33
Tracec
23.3 (MeCN)27
23.9 (MeCN)26,27
9.0 (DMSOb)28
10.7 (H2O)28
7
8
DBUf
Et3N
SMg
SMg
SMg
SMg
30
SMg
18.5 (MeCN)25
Note: After stirring with base at 0 °C for 30 min, the alkyl halide was added and the reaction was allowed to warm to room temperature for 16 h, before
conversion (%) was ascertained by NMR spectroscopy.
aLiterature for pKa values are cited in refs. 21–25.
bDMSO, dimethyl sulfoxide.
cTrace product was detected.
dAqueous solution (10%).
eTMG, 1,1,3,3-tetramethylguanidine.
fDBU, 1,8-diazabicyclo[5.4.0]undec-7-ene.
gStarting material (SM) was only detected.
Table 2. Alkylation of fluorenylidene tert-butyl carbazate (2) using
Et4NOH.
On the contrary, phenylvinylsulfone reacted with 2 to furnish
carbazate 7m in a 56% yield.
The synthesis and alkylation of aza-Gly-Phe-O-t-Bu dipep-
tides 8 and 11 were subsequently explored using propargyl
bromide and tetraethylammonium hydroxide to examine
effects on yield and racemization. Benzhydrylidene 8 was
synthesized by activation of benzophenone hydrazone with
p-nitrophenyl chloroformate and coupling to L-phenylalanine
tert-butyl ester (Scheme 4).29 From the alkylation of 8 with
propargyl bromide using KO-t-Bu (130 mol %) as base, aza-
propargylglycine 9 was produced as a racemic mixture, as
ascertained by supercritical fluid chromatography (SFC) anal-
ysis on a Chiralpak AD-H column. Removal of the Phe ␣
proton was considered to compete with semicarbazone depro-
tonation during alkylation of 8 using KO-t-Bu as a relatively
strong base. Alkylation of 8 was next performed with the
weaker base Et4NOH and gave 9 without racemization, albeit
in a 43% yield.
Fluorenylidene aza-glycinyl-phenylalanine tert-butyl ester
(11) was synthesized by treatment of L- and D,L-phenylalanine
tert-butyl ester with phosgene to prepare the corresponding
isocyanate, which was reacted with fluorenone hydrazone
(1, Scheme 5).30 Azadipeptide 11 was alkylated as described
above using Et4NOH and furnished aza-propargylglycine 12
without racemization in a 92% yield.
Entry
RX
Product
Yield (%)
1
2
3
4
5
7a
7b
7c
7d
7e
87
85
82
62
89
CH3I
CH3CH2I
CH3CH2CH2CH2I
6
7f
77
7
8
9
CH2ϭCHCH2I
NϵCCH2I
7g
7h
7i
83
71
73
10
11
(CH3)2CHI
CH3(CH2)7I
7j
7k
55
61
12
13
7l
7m
60
56
After alkylation, fluorenylidene aza-propargylglycinyl-D,L-
phenylalanine tert-butyl ester (D,L-12) was selectively con-
verted to amino ester 13 and semicarbazone acid 14 by
respective treatments with NH2OH·HCl in pyridine at 60 °C
reduced the yield of carbazate 7l to a 60% yield. Attempts to
perform Michael reactions using tert-butyl acrylate, acrylamide,
and dimethylvinyl phosphonate provided only recovered starting
material, perhaps because of competitive retro-Michael reactions.
Published by NRC Research Press

988
Can. J. Chem. Vol. 90, 2012
Scheme 4. Synthesis and alkylation of benzhydrylidene aza-Gly-
Phe-O-t-Bu (8).
prior to use. Anhydrous solvents (THF and dichloromethane
(DCM)) were obtained by passage through a solvent filtration
system (GlassContour, Irvine, California). Flash chromatogra-
phy31 was on 230–400 mesh silica gel, and thin-layer chro-
matography was performed on silica gel 60 F254 plates from
Merck. Melting points were determined on a Gallankamp
apparatus. Specific rotations ([␣]D values) were calculated
from optical rotations measured at 20 °C in CHCl3 at the
specified concentrations (c in g/100 mL) using a 1 dm cell (l)
on a PerkinElmer Polarimeter 341, using the general formula
NH2
N
O2N
H
O
CH2Cl2, 0°C - rt, 2 h
N
O
N
O
Cl
O
NO2
L-Phe-Ot-Bu•HCl,
DIEA, CH2Cl2,
0°C - rt, 16 h
[α]2D0 ϭ (100α)/(lcα). Accurate mass measurements were per-
formed on an (LC–MS) instrument from Agilent technologies
in positive electrospray ionization (ESI) mode at the Univer-
sité de Montréal Mass Spectrometry facility. Sodium adducts,
[M ϩ Na]ϩ, were used for empirical formula confirmation. 1H
and 13C NMR spectra were measured in CDCl3 (7.26 and
77.36 ppm, respectively), coupling constant (J) values were
measured in hertz (Hz), and chemical shift values in parts per
million (ppm). IR spectra were recorded neat on an ATR
Bruker apparatus.
R
N
O
H
N
N
Ot-Bu
O
Ph
8 : R = H (51%)
9 : R = CH2CCH (43%)
1. Et4NOH, THF, 0°C, 30 min
2.
, 0°C - rt, 16 h
Br
Scheme 5. Synthesis and alkylation of fluorenylidene aza-Gly-Phe-
O-t-Bu (11).
1H and 13C NMR spectra for compounds 2, 5, 6, 7a–7n, and
8–12 and SFC traces for compounds 9 and 12 can be found in
the Supplementary data.
1. pyridine, CH2Cl2,
0°C, 15 min
2. COCl2, 0°C, 2 h
O
L or D,L-Phe-Ot-Bu•HCl
tert-Butyl 3-fluorenylidene carbazate (2)
*
N
Ot-Bu
93%
A solution of fluorenone hydrazone (250 mg, 1.28 mmol,
1 equiv) in THF (10 mL) was treated with pyridine (103 ␮L,
1.28 mmol, 1 equiv) and 4-dimethylaminopyridine (DMAP;
16 mg, 0.13 mmol, 0.2 equiv), cooled with an ice bath,
and treated slowly with di-tert-butyl dicarbonate (419 mg,
1.92 mmol, 1.5 equiv). The ice bath was removed and the
reaction mixture was allowed to warm to room temperature.
After 16 h, CH2Cl2 (50 mL) was added to the mixture, which
was extracted three times with H2O, dried with MgSO4, fil-
tered, and evaporated under vacuum. The residue was purified
by silica gel flash chromatography (100% CH2Cl2). Evapora-
tion of the collected fractions gave a yellow solid (193.7 mg,
51% yield); mp 109.8–111 °C. Rf 0.32 (8:2 hexane/EtOAc).
IR (neat, cm–1) ␯max: 2997, 2968, 1729, 1707, 1507, 1230,
C
O
10
1, DIEA, CH2Cl2,
4Å molecular sieves,
0°C
R
N
O
H
N
*
N
Ot-Bu
O
Ph
1. Et4NOH, THF, 0°C, 30 min
11: R = H (54%)
2.
Br , 0°C - rt, 16 h
12: R = CH2CCH (92%)
for 12 h, and anhydrous acid. In the latter reaction, tert-butyl
ester removal was accomplished more efficiently with HCl gas
in CH2Cl2 than 1:1 TFA/CH2Cl2 (Scheme 6).
1
1150, 768. H NMR (400 MHz, CDCl3) ␦: 8.85 (s, 1H), 7.94
(d, J ϭ 7.5 Hz, 1H), 7.79 (dt, J ϭ 7.7, 0.9 Hz, 1H), 7.74 (dt,
J ϭ 7.5, 0.9 Hz, 1H), 7.61 (dt, J ϭ 7.4, 0.9 Hz, 1H), 7.47 (td,
J ϭ 7.6, 1.0 Hz, 1H), 7.37 (hd, J ϭ 3.9, 1.2 Hz, 2H), 7.31
(td, J ϭ 7.5, 1.1 Hz, 1H), 1.61 (s, 9H). 13C NMR (300 MHz,
CDCl3) ␦: 153.1, 142.7, 139.4, 137.4, 131.3, 130.2, 130.1,
128.6, 128.2, 125.6, 122.7, 121.2, 119.9, 82.7, 28.6. HR-MS
(LC-ESI) m/z calcd for C18H18N2O2Na (M ϩ Na)ϩ: 317.1261;
found: 317.1254.
In summary, milder conditions for the alkylation of
semicarbazones have been achieved by employing fluorenone
derivatives. Tetraethylammonium hydroxide proved an effi-
cient base for the alkylation of fluorenylidene carbazate 2 with
diverse alkyl halides at ambient temperature. Moreover, race-
mization was avoided and a high yield was achieved in the
alkylation of the fluorenylidene azadipeptide 11. In addition,
the orthogonal semicarbazone and carboxylate functions of
aza-propargylglycine 12 were selectively removed. In light of
the potential for subsequent employment of the alkyl deriva-
tives in the synthesis of hydrazines, heterocycles, and longer
azapeptide sequences, this method may find valuable applica-
tions in medicinal chemistry and peptide science.
tert-Butyl N-(propargyl)benzylidene carbazate (5)
tert-Butyl 3-benzylidene carbazate (4; 52.9 mg, 0.24 mmol,
1 equiv) was dissolved in 1 mL of anhydrous THF at 0 °C,
treated with potassium tert-butoxide (39 mg, 0.34 mmol, 1.5
equiv) for 30 min, followed by propargyl bromide (51 ␮L,
0.34 mmol, 1.5 equiv). The ice bath was removed and the
mixture was allowed to warm to room temperature. After
stirring for 16 h, CH2Cl2 was added to the mixture, which was
then extracted twice with H2O, dried with MgSO4, and evap-
orated. The residue was purified by flash chromatography
using 1:9 EtOAc/hexane as the solvent system. Evaporation of
the collected fractions gave carbazate 5 as an oil (27.1 mg,
Experimental section
General method
Unless specified otherwise, fluorenone hydrazone (1),
tert-butyl 3-diphenylmethylene carbazate (3), and tert-butyl
3-benzylidene carbazate (4) were prepared according to the
literature protocols.21,22 Alkyl halides were purchased from
Sigma-Aldrich and filtered through a small plug of silica gel
44% yield). Rf 0.42 (8:2 hexane/EtOAc). IR (neat, cm–1) ␯
:
max
Published by NRC Research Press

Garcia-Ramos et al.
989
Scheme 6. Orthogonal deprotection of fluorenylidene aza-propargylglycinyl-D,L-phenylalanine tert-butyl ester (D,L-12).
O
H2N
O
NH2OH•HCl, pyridine
60°C, 12 h
N
N
H
O
O
(95%)
13
N
O
N
N
O
H
O
N
OH
N
N
H
a) (1:1) TFA/CH2Cl2, 1 h
or
D,L 12
O
b) HCl (g), CH2Cl2, 1 h
a (71%)
b (86%)
14
3292, 3262, 2978, 2931, 1699, 1409, 1348, 1147, 755, 693. 1H
NMR (400 MHz, CDCl3) ␦: 7.94 (s, 1H), 7.73 (dd, J ϭ 7.8,
1.4 Hz, 2H), 7.38 (m, 3H), 4.67 (d, J ϭ 2.0 Hz, 2H), 2.27 (t,
J ϭ 2.4 Hz, 1H), 1.59 (s, 9H). 13C NMR (300 MHz, CDCl3)
␦: 152.9, 141.7, 135.2, 129.9, 128.9, 127.6, 82.8, 77.5, 73.3,
34.3, 28.6. HR-MS (LC-ESI) m/z calcd for C15H18N2O2Na
(M ϩ Na)ϩ: 281.1260; found: 281.1260.
79.7, 72.1, 41.6, 28.4. HR-MS (LC-ESI) m/z calcd for
C21H20N2O2Na (M ϩ Na)ϩ: 355.1417; found: 355.1399.
tert-Butyl N-(methyl)fluorenylidene carbazate (7b)
Employing the procedure to make carbazate 7a, carbazate 2
(52.6 mg, 0.18 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (395 ␮L, 0.27 mmol, 1.5 equiv)
and iodomethane (17 ␮L, 0.27 mmol, 1.5 equiv), and the
product was purified by flash chromatography using 5:95
EtOAc/hexane as the solvent system. Carbazate 7b was ob-
tained as a yellow solid (46.6 mg, 85% yield); mp 66–67.8 °C.
Rf 0.61 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯: 2998,
2970, 1685, 1366, 1130, 736. 1H NMR (400 MHz, CDCl3) ␦:
7.91 (d, J ϭ 7.3 Hz, 1H), 7.87 (d, J ϭ 7.4, 1H), 7.61 (dd, J ϭ
14.2, 7.4 Hz, 2H), 7.44 (tq, J ϭ 7.5, 1.2 Hz, 2H), 7.30 (m, 2H),
3.42 (s, 3H), 1.41 (s, 9H). 13C NMR (300 MHz, CDCl3) ␦:
165.4, 153.5, 142.6, 141.2, 136.6, 132.0, 131.4, 131.1, 128.3,
128.2, 127.8, 123.1, 120.0, 119.7, 81.4, 38.4, 28.2. HR-MS
(LC-ESI) m/z calcd. for C19H20N2O2Na (M ϩ Na)ϩ: 331.1417;
found: 331.1408.
tert-Butyl N-(propargyl)benzhydrylidene carbazate (6)
Employing the procedure used to make carbazate 5, tert-
butyl 3-diphenylmethylene carbazate (3; 54.7 mg, 0.18 mmol,
1 equiv) was reacted with potassium tert-butoxide (28.4 mg,
0.26 mmol, 1.5 equiv) and propargyl bromide (38 ␮L,
0.26 mmol, 1.5 equiv.), and the product was purified by flash
chromatography using 5:95 EtOAc/hexane as the solvent sys-
tem to afford carbazate 6 as an oil (35.9 mg, 63% yield). Rf
0.64 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯: 3290, 3059,
2976, 1693, 1366, 1237, 1150, 694. 1H NMR (400 MHz,
CDCl3) ␦: 7.61 (m, 2H), 7.44 (m, 3H), 7.37 (m, 5H), 4.40 (d,
J ϭ 1.9 Hz, 2H, CH2), 2.28 (t, J ϭ 2.5 Hz, 1H), 1.25 (s, 9H).
13C NMR (300 MHz, CDCl3) ␦: 173.3, 152.0, 138.2, 135.9,
131.0, 129.6, 129.4, 129.1, 128.4, 128.2, 81.6, 79.6, 72.5, 40.8,
28.3. HR-MS (LC-ESI) m/z calcd for C21H22N2O2Na (M ϩ
Na)ϩ: 357.1574; found: 357.1562.
tert-Butyl N-(ethyl)fluorenylidene carbazate (7c)
Employing the procedure to make carbazate 7a, carbazate 2
(52.9 mg, 0.18 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (397 ␮L, 0.27 mmol, 1.5 equiv)
and iodoethane (22 ␮L, 0.27 mmol, 1.5 equiv), and the product
was purified by flash chromatography using 5:95 EtOAc/hex-
ane as the solvent system. Carbazate 7c was obtained as a
yellow solid (47.6 mg, 82% yield); mp 150.8–153.7 °C. Rf
0.57 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯: 2972, 2925,
1681, 1448, 1363, 1276, 1164, 738. 1H NMR (400 MHz,
CDCl3) ␦: 7.92 (d, J ϭ 7.5 Hz, 1H), 7.88 (d, J ϭ 7.3, 1H), 7.61
(dd, J ϭ 13, 7.4 Hz, 2H), 7.43 (t, J ϭ 7.4 Hz, 2H), 7.33–7.25
(m, 2H), 3.9 (q, J ϭ 7.1 Hz, 2H), 1.38 (s, 9H), 1.3 (t, J ϭ
7.1 Hz, 3H). 13C NMR (300 MHz, CDCl3) ␦: 152.7, 142.9,
141.4, 137.0, 132.1, 131.7, 131.6, 128.5, 128.4, 128.0, 123.3,
120.2, 119.9, 81.5, 46.5, 28.5, 13.8. HR-MS (LC-ESI) m/z
calcd for C20H23N2O2 (M ϩ H)ϩ: 323.1754; found: 323.1764.
tert-Butyl N-(propargyl)fluorenylidene carbazate (7a)
tert-Butyl 3-fluorenylidene carbazate (2; 51.4 mg,
0.17 mmol, 1 equiv) was dissolved in 1 mL of anhydrous THF
at 0 °C, treated with 10% tetraethylammonium hydroxide in
H2O (384 ␮L, 0.27 mmol, 1.5 equiv), stirred for 30 min, and
treated with propargyl bromide (39 ␮L, 0.27 mmol, 1.5 equiv).
The ice bath was removed, and the mixture was allowed to
warm to room temperature, stirred for 16 h, treated with
CH2Cl2, extracted twice with H2O, dried with MgSO4, filtered,
and evaporated. The residue was purified by flash chromatog-
raphy using 5:95 EtOAc/hexane as the solvent system. Evap-
oration of the collected fractions gave carbazate 7a as a yellow
solid (50.2 mg, 87% yield); mp 139.7–140.0 °C. Rf 0.61 (8:2
hexane/EtOAc). IR (thin film, cm–1) ␯: 3314, 1685, 1357,
1339, 1243, 1153, 1140, 738. 1H NMR (400 MHz, CDCl3) ␦:
7.93 (m, 2H), 7.60 (dd, J ϭ 12.8, 7.5 Hz, 2H), 7.44 (t, J ϭ
7.5 Hz, 2H), 7.29 (dt, J ϭ 17.2, 7.5 Hz, 2H), 4.59 (d, J ϭ 2.2,
2H), 2.24 (t, J ϭ 2.2 Hz, 1H), 1.39 (s, 9H). 13C NMR
(300 MHz, CDCl3) ␦: 166.9, 152.6, 143.1, 141.6, 136.8, 132.4,
131.9, 131.8, 128.6, 128.5, 128.3, 123.7, 120.3, 120.0, 82.6,
tert-Butyl N-(n-butyl)fluorenylidene carbazate (7d)
Employing the procedure to make carbazate 7a, 2 (60.6 mg,
0.21 mmol, 1 equiv) was reacted with 10% tetraethylammo-
nium hydroxide in H2O (455 ␮L, 0.31 mmol, 1.5 equiv) and
1-iodobutane (35 ␮L, 0.31 mmol, 1.5 equiv), and the product
was purified by flash chromatography using 1:9 EtOAc/hexane
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990
Can. J. Chem. Vol. 90, 2012
as the solvent system. Carbazate 7d was obtained as a yellow
solid (45.7 mg, 62% yield); mp 80–82 °C. Rf 0.6 (8:2 hexane/
EtOAc). IR (thin film, cm–1) ␯: 2921, 2876, 1682, 1446,
7.29 (m, 2H), 6.01 (m, 1H), 5.30 (dq, J ϭ 17.1, 1.5 Hz, 1H),
5.16 (dq, J ϭ 10.3, 1.2 Hz, 1H), 4.46 (d, J ϭ 6 Hz, 2H), 1.39
(s, 9H). 13C NMR (300 MHz, CDCl3) ␦: 165.4, 152.9, 142.9,
141.4, 138.5, 137.1, 132.1, 131.8, 131.6, 128.6, 128.5, 128.1,
127.5, 123.4, 120.2, 119.9, 82.1, 56.3, 28.5. HR-MS (LC-ESI)
m/z calcd for C21H22N2O2Na (M ϩ Na)ϩ: 357.1573; found:
357.1558.
1
1364, 1245, 1145, 736. H NMR (400 MHz, CDCl3) ␦: 7.90
(m, 2H), 7.61 (dd, J ϭ 13.3, 7.4 Hz, 2H), 7.43 (t, J ϭ 7.3 Hz,
2H), 7.33–7.26 (m, 2H), 3.87 (t, J ϭ 7.3 Hz, 2H), 1.69 (m, 2H),
1.43–1.38 (m, 11H), 0.94 (td, J ϭ 7.3, 2 Hz, 3H). 13C NMR
(300 MHz, CDCl3) ␦: 165.9, 152.9, 142.9, 141.4, 137.1, 132.1,
131.8, 131.6, 128.5, 128.0, 123.4, 120.2, 119.9, 81.6, 51.8,
31.1, 28.5, 20.5, 14.1. HR-MS (LC-ESI) m/z calcd for
C22H27N2O2 (M ϩ H)ϩ: 351.2067; found: 351.2077.
tert-Butyl N-(cyanomethyl)fluorenylidene carbazate (7h)
Employing the procedure to make carbazate 7a, 2 (52.8 mg,
0.18 mmol, 1 equiv) was reacted with 10% tetraethylammo-
nium hydroxide in H2O (396 ␮L, 0.27 mmol, 1.5 equiv) and
iodoacetonitrile (20 ␮L, 0.27 mmol, 1.5 equiv), and the prod-
uct was purified by flash chromatography using 1:9 EtOAc/
hexane as the solvent system. Carbazate 7h was obtained as a
yellow solid (42.7 mg, 71% yield); mp 165–168 °C. Rf 0.32
(8:2 hexane/EtOAc). IR (thin film, cm–1) ␯: 2980, 2187, 1715,
1595, 1345, 1313, 1235, 1144, 726. 1H NMR (400 MHz,
CDCl3) ␦: 7.88 (m, 1H), 7.81 (m, 1H), 7.60 (m, 2H), 7.46 (m,
2H), 7.30 (m, 2H), 4.67 (m, 2H), 1.40 (s, 9H). 13C NMR
(300 MHz, CDCl3) ␦: 167.4, 152.3, 143.3, 141.6, 136.4, 132.9,
132.3, 131.7, 128.7, 128.6, 128.2, 123.8, 120.5, 120.1, 116.0,
84.2, 40.4, 28.3. HR-MS (LC-ESI) m/z calcd for C20H20N3O2 (M ϩ
H)ϩ: 334.1550; found: 334.1566.
tert-Butyl N-(benzyl)fluorenylidene carbazate (7e)
Employing the procedure to make carbazate 7a, 2 (200 mg,
0.68 mmol, 1 equiv) was reacted with 10% tetraethylammo-
nium hydroxide in H2O (1.5 mL, 1.02 mmol, 1.5 equiv) and
benzyl bromide (122 ␮L, 1.02 mmol, 1.5 equiv), and the
product was purified by flash chromatography using 1:9
EtOAc/hexane as the solvent system. Carbazate 7e was ob-
tained as a yellow solid (232.3 mg, 89% yield); mp 106.7–
109.1 °C. Rf 0.47 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯:
2980, 2918, 1685, 1321, 1242, 1148, 730. 1H NMR (400 MHz,
CDCl3) ␦: 7.90 (d, J ϭ 7 Hz, 1H), 7.79 (d, J ϭ 7.1, 1H), 7.59
(dd, J ϭ 10.9, 7.7 Hz, 2H), 7.42 (m, 4H), 7.30 (t, J ϭ 7.3, 3H),
7.23 (m, 2H), 5.05 (s, 2H), 1.37 (s, 9H). 13C NMR (300 MHz,
CDCl3) ␦: 165.4, 152.9, 142.9, 141.4, 138.5, 137.1, 132.1,
131.8, 131.6, 128.6, 128.48, 128.46, 128.45, 128.1, 127.5,
123.4, 120.2, 119.9, 82.1, 56.3, 28.5. HR-MS (LC-ESI) m/z
calcd for C25H24N2O2Na (M ϩ Na)ϩ: 407.173; found:
407.1725.
tert-Butyl N-(tert-butylacetyl)fluorenylidene carbazate (7i)
Employing the procedure to make carbazate 7a, carbazate 2
(50 mg, 0.17 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (368 ␮L, 0.25 mmol, 1.5 equiv)
and tert-butyl bromoacetate (38 ␮L, 0.25 mmol, 1.5 equiv),
and the product was purified by flash chromatography using
1:9 EtOAc/hexane as the solvent system. Carbazate 7i was
obtained as a yellow solid (50.6 mg, 73% yield); mp 135.5–
136.7 °C. Rf 0.39 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯:
tert-Butyl N-(cinnamyl)fluorenylidene carbazate (7f)
Employing the procedure to make carbazate 7a, carbazate 2
(50 mg, 0.17 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (376 ␮L, 0.26 mmol, 1.5 equiv)
and cinnamyl bromide (52 mg, 0.26 mmol, 1.5 equiv), and the
product was purified by flash chromatography using 1:9
EtOAc/hexane as the solvent system. Carbazate 7f was ob-
tained as an oil (53.4 mg, 77% yield). Rf 0.4 (8:2 hexane/
EtOAc). IR (thin film, cm–1) ␯: 2973, 2928, 1687, 1448, 1366,
1226, 1142, 729. 1H NMR (400 MHz, CDCl3) ␦: 7.90 (m, 2H),
7.60 (dd, J ϭ 15.8, 7.5 Hz, 2H), 7.42 (hd, J ϭ 3.8, 1 Hz, 2H),
7.37–7.2 (m, 7H), 6.64 (d, J ϭ 15.8 Hz, 1H), 6.40 (dt, J ϭ
15.8, 6.4 Hz, 1H), 4.61 (dd, J ϭ 6.3, 1 Hz, 2H), 1.40 (s, 9H).
13C NMR (300 MHz, CDCl3) ␦: 165.4, 152.4, 142.4, 140.9,
136.6, 136.4, 132.4, 131.7, 131.2, 131.1, 128.2, 128.0, 127.9,
127.6, 127.2, 126.2, 124.8, 122.9, 119.7, 119.4, 81.4, 53.8,
28.0. HR-MS (LC-ESI) m/z calcd for C27H26N2O2Na (M ϩ
Na)ϩ: 433.1886; found: 433.1885.
1
2978, 2929, 1745, 1692, 1365, 1224, 1147, 752. H NMR
(400 MHz, CDCl3) ␦: 7.86 (d, J ϭ 7.5 Hz, 2H), 7.61 (d, J ϭ
7.5 Hz, 1H), 7.58 (d, J ϭ 7.6 Hz, 1H), 7.42 (td, J ϭ 7.6 Hz,
2H), 7.28 (m, 2H), 4.46 (s, 2H), 1.47 (s, 18H). 13C NMR
(300 MHz, CDCl3) ␦: 168.8, 153.0, 142.9, 141.5, 137.1, 132.1,
131.9, 131.6, 128.8, 128.4, 128.3, 123.5, 120.1, 119.9, 82.4,
82.0, 54.7, 28.4. HR-MS (LC-ESI) m/z calcd for C24H29N2O4
(M ϩ H)ϩ: 409.2122; found: 409.2104.
tert-Butyl N-(isopropyl)fluorenylidene carbazate (7j)
Employing the procedure to make carbazate 7a, carbazate 2
(51.9 mg, 0.18 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (383 ␮L, 0.26 mmol, 1.5 equiv)
and isopropyl iodide (26 ␮L, 0.26 mmol, 1.5 equiv), and
stirred at 50 °C under microwave irradiation in a 300 MW
Biotage apparatus on the high absorption level with automated
temperature monitoring for 12 h. The product was purified by
flash chromatography using 5:95 EtOAc/hexane as the solvent
system. Carbazate 7j was obtained as a yellow solid (32.4 mg,
55% yield); mp 119.7–120.8 °C. Rf 0.75 (8:2 hexane/EtOAc).
IR (thin film, cm–1) ␯: 2965, 2919, 2850, 1683, 1302, 1088,
737. 1H NMR (400 MHz, CDCl3) ␦: 7.92 (d, J ϭ 7.5 Hz, 1H),
7.87 (d, J ϭ 7.5, 1H), 7.60 (dd, J ϭ 12.6, 7.5 Hz, 2H), 7.41 (m,
2H), 7.30 (t, J ϭ 7.5 Hz, 1H), 7.24 (t, J ϭ 7.3 Hz, 1H), 4.71
(q, J ϭ 6.6 Hz, 1H), 1.34 (s, 15H). 13C NMR (300 MHz,
CDCl3) ␦: 166.5, 152.2, 143.0, 141.4, 137.2, 132.0, 131.9,
131.5, 128.5, 128.4, 128.0, 123.4, 120.2, 119.9, 81.4, 51.5,
tert-Butyl N-(allyl)fluorenylidene carbazate (7g)
Employing the procedure to make carbazate 7a, carbazate 2
(50 mg, 0.17 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (376 ␮L, 0.25 mmol, 1.5 equiv)
and allyl iodide (24 ␮L, 0.25 mmol, 1.5 equiv), and the
product was purified by flash chromatography using 1:9
EtOAc/hexane as the solvent system. Carbazate 7g was ob-
tained as a yellow solid (47.3 mg, 83% yield); mp 109.2–
111.4 °C. Rf 0.47 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯:
1
2956, 2921, 2852, 1676, 1374, 1251, 1142, 738. H NMR
(400 MHz, CDCl3) ␦: 7.90 (d, J ϭ 7.6 Hz, 1H), 7.88 (d, 1H),
7.61 (dd, J ϭ 14.9, 7.5 Hz, 2H), 7.43 (td, J ϭ 7.5, 1.0 Hz, 2H),
Published by NRC Research Press

Garcia-Ramos et al.
991
28.5, 20.3. HR-MS (LC-ESI) m/z calcd for C21H24N2O2Na (M ϩ
Benzhydrylidene aza-glycinyl-L-phenylalanine tert-butyl
ester (8)
Na)ϩ: 359.173; found: 359.1727.
In a flame-dried round-bottom flask, at 0 °C, a solution of
4-nitrophenylchloroformate (1.12 g, 5.58 mmol, 1.1 equiv) in
dry CH2Cl2 (40 mL) was treated dropwise by cannula with a
0 °C solution of benzophenone hydrazone (1 g, 5.07 mmol,
1 equiv) in dry CH2Cl2 (40 mL). The ice bath was removed and
the reaction mixture was allowed to warm to room tempera-
ture. After stirring for 1 h, the mixture was cooled to 0 °C, and
treated dropwise by cannula with a premixed 0 °C solution of
L-Phe-O-t-Bu·HCl (1.44 g, 5.60 mmol, 1.1 equiv) and N,
N-diisopropylethylamine (DIEA; 1.80 mL, 10.14 mmol, 2 equiv)
in CH2Cl2 (13 mL). The ice bath was removed. The reaction
mixture was allowed to warm to room temperature and stirred
for 16 h. The volatiles were evaporated and the residue was
purified on a column of silica gel using flash chromatography
with 30% diethyl ether in petroleum ether as the solvent
system. Ester 8 was obtained as an oil (1.15 g, 51% yield).
tert-Butyl N-(1-(R,S)-ethylbenzyl)fluorenylidene carbazate
(7k)
Employing the procedure to make carbazate 7a, carbazate 2
(57.6 mg, 0.2 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (432 ␮L, 0.29 mmol, 1.5 equiv)
and 1-bromoethylbenzene (40 ␮L, 0.29 mmol, 1.5 equiv), and
stirred at 60 °C under microwave irradiation in a 300 MW
Biotage apparatus on the high absorption level with automated
temperature monitoring for 12 h. The product was purified by
flash chromatography using 1:9 diethyl ether/petroleum ether
as the solvent system. Carbazate 7k was obtained as a yellow
oil (47 mg, 61% yield). Rf 0.57 (8:2 hexane/EtOAc). IR (thin
film, cm–1) ␯: 2973, 2939, 1682, 1448, 1366, 1290, 1154, 729.
1H NMR (400 MHz, CDCl3) ␦: 7.91 (d, J ϭ 7.5 Hz, 1H), 7.83
(m, 1H), 7.62–7.55 (m, 4H), 7.44–7.40 (m, 2H), 7.33–7.23 (m,
5H), 5.71 (m, 1H), 1.73 (s, 3H), 1.32 (s, 9H). 13C NMR
(300 MHz, CDCl3) ␦: 165.7, 152.4, 142.9, 142.6, 141.3, 137.3,
132.0, 131.9, 131.4, 128.5, 128.45, 128.44, 128.4, 127.9,
127.8, 127.4, 123.4, 120.2, 119.9, 81.8, 59.0, 28.5. HR-MS
(LC-ESI) m/z calcd for C26H27N2O2 (M ϩ H)ϩ: 399.2067;
found: 399.2059.
[α]2D0 14.2 (c 1.02, CHCl3). Rf 0.21 (8:2 hexane/EtOAc). IR
(thin film, cm–1) ␯: 2974, 2931, 1662, 1590, 1515, 1333, 1109,
692. 1H NMR (400 MHz, CDCl3) ␦: 8.08 (d, J ϭ 9.2 Hz, 1H),
7.24–7.67 (m, 15H), 6.80–6.91 (m, 1H), 4.77–4.82 (m, 1H),
3.17–3.30 (m, 2H), 1.48 (s, 9H). 13C NMR (300 MHz, CDCl3)
␦: 170.5, 162.9, 154.7, 148.4, 136.4, 135.8, 131.2, 129.5,
129.4, 129.2, 128.2, 128.0, 127.0, 126.9, 126.7, 125.7, 115.2,
81.9, 53.6, 38.3, 27.6. HR-MS (LC-ESI) m/z calcd for
C27H29N3O3Na (M ϩ Na)ϩ: 466.2101; found: 466.2082.
tert-Butyl N-(octanyl)fluorenylidene carbazate (7l)
Employing the procedure to make carbazate 7a, 2 (54.3 mg,
0.18 mmol, 1 equiv) was reacted with 10% tetraethylammo-
nium hydroxide in H2O (407 ␮L, 0.28 mmol, 1.5 equiv) and
1-iodooctane (51 ␮L, 0.28 mmol, 1.5 equiv), and the product
was purified by flash chromatography using 1:9 EtOAc/hexane
as the solvent system. Carbazate 7l was obtained as a yellow
oil (45.2 mg, 60% yield). Rf 0.39 (8:2 hexane/EtOAc). IR (thin
film, cm–1) ␯: 2924, 2853, 1689, 1449, 1365, 1142, 731.
1H NMR (400 MHz, CDCl3) ␦: 7.91 (d, J ϭ 7.5 Hz, 1H), 7.85 (m,
1H), 7.61 (dd, J ϭ 13.4, 7.5 Hz, 2H), 7.43 (t, J ϭ 7.5 Hz, 2H),
7.33–7.25 (m, 2H), 3.86 (t, J ϭ 7.4 Hz, 2H), 1.71 (m, 2H),
1.38 (s, 9H), 1.32–1.24 (m, 10H), 0.87 (m, 3H). 13C NMR
(300 MHz, CDCl3) ␦: 165.8, 152.9, 142.9, 141.4, 137.1, 132.1,
131.8, 131.6, 128.5, 128.1, 123.4, 120.2, 119.9, 81.6, 52.1,
32.1, 29.6, 29.5, 28.9, 28.5, 27.2. HR-MS (LC-ESI) m/z calcd
for C26H34N2O2Na (M ϩ Na)ϩ: 429.2512; found: 429.2498.
Benzhydrylidene aza-propargylglycinyl-L-phenylalanine
tert-butyl ester (9)
Employing the procedure to make carbazate 7a, 8 (50 mg,
0.11 mmol, 1 equiv) was reacted with 10% tetraethylammo-
nium hydroxide in H2O (243 ␮L, 0.16 mmol, 1.5 equiv) and
propargyl bromide (25 ␮L, 0.16 mmol, 1.5 equiv), and the
product was purified by flash chromatography eluting with 1:9
EtOAc/hexane. Ester 9 was obtained as a white oil (21.1 mg,
43% yield). [α]2D0 –1.8 (c 1.24, CHCl3). Rf 0.33 (8:2 hexane/
EtOAc). IR (thin film, cm–1) ␯: 3227, 2967, 2920, 1734, 1671,
1505, 1150, 694. 1H NMR (400 MHz, CDCl3) ␦: 7.45 (m, 6H),
7.36 (m, 4H), 7.27 (m, 5H), 7.08 (d, J ϭ 8.2 Hz, 1H), 4.77 (m,
1H), 4.21 (dd, J ϭ 17.9, 2.4 Hz, 1H), 3.91 (dd, J ϭ 17.9,
2.4 Hz, 1H), 3.20 (d, J ϭ 5.9 Hz, 2H), 2.08 (t, J ϭ 2.4 Hz, 1H),
1.43 (s, 9H). 13C NMR (300 MHz, CDCl3) ␦: 171.1, 158.3,
158.0, 138.8, 136.8, 135.8, 130.3, 130.0, 129.5, 129.0, 128.9,
128.7, 128.4, 127.1, 82.2, 79.0, 72.2, 55.3, 38.8, 35.4, 28.3.
HR-MS (LC-ESI) m/z calcd for C30H31N3O3Na (M ϩ Na)ϩ:
504.2258; found: 504.2234. The degree of racemization
(enantiomeric excess, 98.9%) was determined by SFC analysis on
a chiral stationary phase (Chiralcel AD-H 25 cm, 15% i-PrOH,
3 mL/min, 35 °C, 150 bar (1 bar ϭ 100 kPa), tr (major): 3.33 min,
tr (minor): 5.29 min).
tert-Butyl N-(phenylethylsulfone)fluorenylidene carbazate
(7m)
Employing the procedure to make carbazate 7a, carbazate 2
(51.4 mg, 0.17 mmol, 1 equiv) was reacted with 10% tetraeth-
ylammonium hydroxide in H2O (386 ␮L, 0.26 mmol, 1.5 equiv)
and phenyl vinyl sulfone (44 mg, 0.26 mmol, 1.5 equiv),
and the product was purified by flash chromatography using
1:9 EtOAc/hexane as the solvent system. Carbazate 7m was
obtained as a yellow oil (45.4 mg, 56% yield). Rf 0.18
(8:2 hexane/EtOAc). IR (thin film, cm–1) ␯: 2974, 2923, 1693,
1446, 1307, 1279, 1141, 728. 1H NMR (400 MHz, CDCl3) ␦:
7.96 (d, J ϭ 7.7 Hz, 2H), 7.80 (d, J ϭ 7.3 Hz, 1H), 7.67–7.54
(m, 6H), 7.43 (m, 2H), 7.30 (m, 1H), 7.23 (t, J ϭ 7.5 Hz, 1H),
4.18 (t, J ϭ 7.5 Hz, 2H), 3.61 (t, J ϭ 7.4 Hz, 2H), 1.34 (s, 9H).
13C NMR (300 MHz, CDCl3) ␦: 166.1, 152.1, 142.8, 141.1,
139.0, 136.3, 133.9, 132.2, 131.7, 131.2, 129.4, 128.3, 128.2,
128.1, 127.8, 123.2, 120.1, 119.7, 82.5, 54.0, 45.6, 28.0.
HR-MS (LC-ESI) m/z calcd for C26H26N2O4SNa (M ϩ Na)ϩ:
485.1505; found: 485.1518.
Fluorenylidene aza-glycinyl-L-phenylalanine tert-butyl
ester (11)
In a flame-dried flask under N2, L-Phe-O-t-Bu·HCl (500 mg,
1.95 mmol, 1 equiv) was suspended in CH2Cl2 (8 mL), treated
with pyridine (629 ␮L, 7.8 mmol, 4 equiv), cooled to 0 °C for
15 min, and treated with a 20% solution of phosgene in toluene
(1.45 mL, 2.93 mmol, 1.5 equiv). (Caution: Phosgene is ex-
tremely toxic and should be employed in a well-ventilated
hood.) After stirring for 2 h at 0 °C, the mixture was washed
twice with ice cold 0.5 mol/L HCl. The combined aqueous
Published by NRC Research Press

992
Can. J. Chem. Vol. 90, 2012
fractions were extracted with cold CH2Cl2. The combined
organic phases were washed with ice cold NaCl, dried with
MgSO4, filtered, and evaporated. The resulting isocyanate 10
was obtained as an oil (375.7 mg, 74% yield), which was used
directly in the next reaction without further purification.
1H NMR (400 MHz, CDCl3) ␦: 7.33 (m, 3H), 7.26 (m, 2H), 4.16
(dd, J ϭ 5.0, 7.5 Hz, 1H), 3.14 (dd, J ϭ 4.8, 13.8 Hz, 1H), 3.04
(dd, J ϭ 7.5, 13.7 Hz, 1H), 1.50 (s, 9H). Under inert atmo-
sphere, to fluorenone hydrazone (195 mg, 1 mmol, 1 equiv) in
CH2Cl2 (8 mL) containing molecular sieves at 0 °C, DIEA
(174 ␮L, 1 mmol, 1 equiv) was added. The mixture was stirred
for 15 min and treated with a solution of isocyanate 10
(375.7 mg, 1.5 mmol, 1.5 equiv) in CH2Cl2 (2 mL). The ice
bath was removed. The reaction was allowed to warm to room
temperature, stirred for 16 h, and evaporated. The residue was
purified by flash chromatography eluting with 2:8 EtOAc/
hexane. Azadipeptide 11 was isolated as a yellow solid (261.5 mg,
54% yield); mp 65.6–67.6 °C. Rf 0.18 (8:2 hexane/EtOAc).
Aza-propargylglycinyl-D,L-phenylalanine tert-butyl ester
(13)
Fluorenylidene aza-propargylglycinyl-D,L-phenylalanine tert-
butyl ester (D,L-12; 54.4 mg, 0.11 mmol, 1 equiv) was treated
with a solution of NH2OH·HCl (28 mg, 0.44 mmol, 4 equiv)
in pyridine (12 mL) at 60 °C for 12 h. The volatiles were
evaporated and the residue was purified by flash chromatog-
raphy eluting with 4:6 EtOAc/hexane. Ester 13 was obtained
as a white oil (34.3 mg, 95% yield). Rf 0.1 (8:2 hexane/
EtOAc). IR (thin film, cm–1) ␯: 3285, 2982, 2936, 1726, 1658,
1
1498, 1368, 1152. H NMR (400 MHz, CDCl3) ␦: 7.31–7.20
(m, 5H), 6.91 (d, J ϭ 8.3 Hz, 1H), 4.64 (m, 1H), 4.40 (dd,
J ϭ 2.4, 17.5 Hz, 1H), 4.31 (dd, J ϭ 2.4, 17.5 Hz, 1H), 3.72
(s, 2H), 3.09 (m, 2H), 2.30 (t, J ϭ 2.4 Hz, 1H), 1.41 (s, 9H). 13
C
NMR (300 MHz, CDCl3) ␦: 170.7, 157.1, 136.0, 128.9, 127.6,
126.1, 81.1, 77.3, 72.7, 53.9, 39.0, 38.0, 27.3. HR-MS
(LC-ESI) m/z calcd for C17H23N3O3Na (M ϩ Na)ϩ: 340.1632;
found: 340.1620.
[α]2D0 25.9 (c 1.04, CHCl3). IR (thin film, cm–1) ␯: 2966, 2919,
1673, 1508, 1149, 1115, 1077, 727. 1H NMR (400 MHz,
CDCl3) ␦: 8.73 (s, 1H), 7.87 (d, J ϭ 7.7 Hz, 1H), 7.76 (d, J ϭ
7.5 Hz, 1H), 7.67 (dd, J ϭ 17.0, 7.5 Hz, 2H), 7.49 (td, J ϭ 7.5,
0.7 Hz, 1H), 7.40 (m, 2H), 7.36–7.28 (m, 6H), 7.03 (d, J ϭ
8.2 Hz, 1H), 4.85 (m, 1H), 3.25 (m, 2H), 1.47 (s, 9H). 13C
NMR (300 MHz, CDCl3) ␦: 171.0, 155.4, 143.7, 142.5, 139.5,
137.2, 136.6, 131.2, 130.2, 130.1, 130.0, 128.8, 128.4, 128.3,
127.3, 125.7, 121.8, 121.2, 120.0, 82.6, 54.4, 39.1, 28.3.
HR-MS (LC-ESI) m/z calcd for C27H27N3O3Na (M ϩ Na)ϩ:
464.1945; found: 464.1943.
Fluorenylidene aza-propargylglycinyl-D,L-phenylalanine
acid (14)
tert-Butyl ester D,L-12 (48.6 mg, 0.1 mmol, 1 equiv) in dry
CH2Cl2 (10 mL) was treated with bubbles of HCl for 1 h. The
volatiles were evaporated and the residue was purified by flash
chromatography eluting with 1:20 MeOH/CH2Cl2. Acid 14
was obtained as a yellow solid (37 mg, 86% yield): decom-
position was observed after 98.1 °C. Rf 0.2 (9:1 CH2Cl2/
MeOH). IR (thin film, cm–1) ␯: 3265, 1709, 1663, 1506, 1447,
1314, 1230, 1154, 1083, 931, 730. 1H NMR (400 MHz,
CDCl3) ␦: 10.49 (s, 1H), 7.85 (d, J ϭ 7.6 Hz, 1H), 7.75 (d,
J ϭ 6.9 Hz, 1H), 7.59 (dd, J ϭ 7.4, 13.1 Hz, 2H), 7.44 (t, J ϭ
6.7 Hz, 2H), 7.27 (m, 2H), 7.16 (m, 5H), 6.45 (d, J ϭ 5.6 Hz,
1H), 4.83 (m, 1H), 4.55 (m, 2H), 3.22 (m, 2H), 2.19 (m, 1H).
13C NMR (300 MHz, CDCl3) ␦: 163.8, 158.1, 142.6, 140.6,
135.5, 135.2, 132.1, 131.3, 128.8, 128.6, 128.1, 127.9, 127.8,
127.6, 126.3, 122.7, 119.7, 119.2, 77.8, 71.9, 39.6, 36.8.
HR-MS (LC-ESI) m/z calcd for C26H21N3O3Na (M ϩ Na)ϩ:
446.1475; found: 446.1481.
Fluorenylidene aza-glycinyl-D,L-phenylalanine tert-butyl
ester (D,L-11)
D,L-11 was synthesized employing the same procedure de-
scribed for 11 using D,L-Phe-O-t-Bu·HCl and was obtained as
a yellow solid (236.2 mg, 54% yield).
Fluorenylidene aza-propargylglycinyl-L-phenylalanine
tert-butyl ester (12)
Using the procedure to make carbazate 7a, ester 11 (50 mg,
0.11 mmol, 1 equiv) was reacted with 10% tetraethylammo-
nium hydroxide in H2O (250 ␮L, 0.17 mmol, 1.5 equiv) and
propargyl bromide (33 ␮L, 0.22 mmol, 1.5 equiv), and the
product was purified by flash chromatography eluting with 1:9
EtOAc/hexane. Ester 12 was obtained as a yellow solid
Supplementary data
Supplementary data are available with the article through
the journal Web site http://nrcresearchpress.com/doi/suppl/
10.1139/v2012-070.
Acknowledgments
(42 mg, 83% yield); mp 82.5–85.4 °C. [α]2D0 –50.8 (c 1.04,
CHCl3). Rf 0.3 (8:2 hexane/EtOAc). IR (thin film, cm–1) ␯:
3208, 2958, 2921, 2854, 1750, 1742, 1674, 1497, 1217, 1144,
736. 1H NMR (400 MHz, CDCl3) ␦: 7.93 (d, J ϭ 7.6 Hz, 1H),
7.83 (d, J ϭ 7.5 Hz, 1H), 7.65 (d, J ϭ 7.4 Hz, 1H), 7.60 (d,
J ϭ 7.5 Hz, 1H), 7.47 (m, 2H), 7.31 (m, 2H), 7.21 (s, 5H), 6.54
(d, J ϭ 7.9 Hz, 1H), 4.80 (m, 1H), 4.68 (dd, J ϭ 17.4, 2.3 Hz,
1H), 4.54 (dd, J ϭ 17.4, 2.3 Hz, 1H), 3.18 (m, 2H), 2.21 (t,
J ϭ 2.3 Hz, 1H), 1.40 (s, 9H). 13C NMR (300 MHz, CDCl3) ␦:
170.8, 164.2, 158.4, 143.6, 141.6, 136.8, 136.6, 133.0, 132.1,
130.1, 129.8, 129.0, 128.8, 128.6, 127.1, 123.6, 120.7, 120.2,
82.3, 79.1, 72.6, 55.1, 40.5, 38.9, 28.3. HR-MS (LC-ESI) m/z
calcd for C30H29N3O3Na (M ϩ Na)ϩ: 502.2101; found:
502.2079. The degree of racemization (enantiomeric excess,
99.8%) was determined by SFC analysis on a chiral stationary
phase (Chiralcel AD-H 25 cm, 15% i-PrOH, 3 mL/min, 35 °C,
150 bar, tr (major): 8.26 min, tr (minor): 21.32 min).
This research was supported by the Natural Sciences and
Engineering Research Council of Canada (NSERC) and the
Canadian Institutes of Health Research (CIHR; grant No.
TGC-114046). C.P. is grateful to NSERC and Boehringer
Ingelheim for graduate student fellowships. The authors thank
Dr. A. Fürtös, K. Venne, and M.-C. Tang for assistance with
mass spectrometry as well as V.N.G. Lindsay and C. Camy for
SFC analyses.
References
(1) Alizadeh, A.; Babaki, M.; Zohreh, N. Synthesis 2008, (20),
3295. doi:10.1055/s-0028-1083142.
(2) Ragnarsson, U. Chem. Soc. Rev. 2001, 30 (4), 205. doi:10.1039/
b010091a.
(3) Melendez, R. E.; Lubell, W. D. J. Am. Chem. Soc. 2004, 126
(21), 6759. doi:10.1021/ja039643f.
Published by NRC Research Press

Garcia-Ramos et al.
993
(4) Boeglin, D.; Lubell, W. D. J. Comb. Chem. 2005, 7 (6), 864.
doi:10.1021/cc050043h.
(18) Meyer, K. G. Synlett 2004, 13 (13), 2355. doi:10.1055/s-2004-
831336.
(5) Gante, J. Synthesis 1989, (6), 405. doi:10.1055/s-1989-27269.
(6) Proulx, C.; Sabatino, D.; Hopewell, R.; Jochen, S.; Garcia-
Ramos, Y.; Lubell, W. D. Future Med. Chem. 2011, 3, 1139.
doi:10.4155/fmc.11.74.
(7) Biel, J. H.; Drukker, A. E.; Mitchell, T. F.; Sprengeler, E. P.;
Nuhfer, P. A.; Conway, A. C.; Horita, A. J. Am. Chem. Soc.
1959, 81 (11), 2805. doi:10.1021/ja01520a048.
(8) Han, H.; Janda, K. D. J. Am. Chem. Soc. 1996, 118 (11), 2539.
doi:10.1021/ja9535470.
(9) Kline, G. B.; Cox, S. H. J. Org. Chem. 1961, 26 (6), 1854.
doi:10.1021/jo01065a040.
(10) Braden, T. M.; Coffey, D. S.; Doecke, C. W.; LeTourneau,
M. E.; Martinelli, M. J.; Meyer, C. L.; Miller, R. D.; Pawlak,
J. M.; Pedersen, S. W.; Schmid, C. R.; Shaw, B. W.; Staszak,
M. A.; Vicenzi, J. T. Org. Process Res. Dev. 2007, 11 (3), 431.
doi:10.1021/op700040v.
(11) Licandro, E.; Perdicchia, D. Eur. J. Org. Chem. 2004, (4), 665.
doi:10.1002/ejoc.200300416.
(12) Bonnet, D.; Margathe, J.-F.; Radford, S.; Pflimlin, E.; Riche, S.;
Doman, P.; Hibert, M.; Ganesan, A. ACS Comb. Sci. 2012, 14
(5), 323. doi:10.1021/co300015k.
(19) Nun, P.; Martin, C.; Martinez, J.; Lamaty, F. Tetrahedron 2011,
67 (42), 8187. doi:10.1016/j.tet.2011.07.056.
(20) Kobayashi, S.; Yazaki, R.; Seki, K.; Yamashita, Y. Angew.
Chem. Int. Ed. 2008, 47 (30), 5613. doi:10.1002/
anie.200801322.
(21) Minabe, M.; Takabayashi, Y.; Setta, Y.; Nakamura, H.; Kimura,
T.; Tsubota, M. Bull. Chem. Soc. Jpn. 1996, 69 (12), 3633.
doi:10.1246/bcsj.69.3633.
(22) Lawton, G.; Moody, C. J.; Pearson, C. J.; Williams, D. J.
J. Chem. Soc. Perkin Trans. 1 1987, 885. doi:10.1039/
p19870000885.
(23) McEwen, W. K. J. Am. Chem. Soc. 1936, 58 (7), 1124. doi:
10.1021/ja01298a017.
(24) Olmstead, W. L.; Margolin, Z.; Bordwell, F. G. J. Org. Chem.
1980, 45 (16), 3295. doi:10.1021/jo01304a032.
(25) Kolthoff, I. M.; Chantooni, M. K.; Bhowmik, S. J. Am. Chem.
Soc. 1968, 90 (1), 23. doi:10.1021/ja01003a005.
(26) Galezowski, W.; Jarczewski, A.; Stanczyk, M.; Brzezinski, B.;
Bartl, F.; Zundel, G. J. Chem. Soc., Faraday Trans. 1997, 93
(15), 2515. doi:10.1039/a700668c.
(27) Leffek, K.T.; Pruszynski, P.; Thanapaalasingham, K. Can. J.
Chem. 1989, 67 (4), 590. doi:10.1139/v89-089.
(28) Crampton, M. R.; Robotham, I. A. J. Chem. Res. (S) 1997, 22.
doi:10.1039/a606020j.
(29) Bourguet, C. B.; Sabatino, D.; Lubell, W. D. Pept. Sci. 2008, 90
(6), 824. doi:10.1002/bip.21103.
(30) Nowick, J. S.; Powell, N. A.; Nguyen, T. M.; Noronha, G.
J. Org. Chem. 1992, 57 (26), 7364. doi:10.1021/jo00052a069.
(31) Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43 (14),
2923. doi:10.1021/jo00408a041.
(13) Spiegel, J.; Mas-Moruno, C.; Kessler, H.; Lubell, W. D. J. Org.
Chem. 2012, 77 (12), 5271.
(14) Brosse, N.; Pinto, M. F.; Bodiguel, J.; Jamart-Gregoire, B.
J. Org. Chem. 2001, 66 (8), 2869. doi:10.1021/jo005696t.
(15) Bourguet, C. B.; Proulx, C.; Klocek, S.; Sabatino, D.; Lubell,
W. D. J. Pept. Sci. 2010, 16 (6), 284. doi:10.1002/psc.1235.
(16) Sabatino, D.; Proulx, C.; Klocek, S.; Bourguet, C. B.; Boeglin,
D.; Ong, H.; Lubell, W. D. Org. Lett. 2009, 11 (16), 3650.
doi:10.1021/ol901423c.
(17) Zawadzki, S.; Zwierzak, A. Pol. J. Chem. 2003, 77, 315.
Published by NRC Research Press