Synthesis of non-proteinogenic phenylalanine derivatives by rhodium-catalyzed [2+2+2] cycloaddition reactions

Article abstract of DOI:10.1039/b910961g

Non-proteinogenic phenylalanine derivatives were efficiently prepared by Rh(I)-catalyzed [2+2+2] cycloaddition reactions between enantiopure and racemic propargylglycine amino acids, with different protective groups, and diynes. Diverse substituents, incl

Full text of DOI:10.1039/b910961g

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of non-proteinogenic phenylalanine derivatives
by rhodium-catalyzed [2+2+2] cycloaddition reactions†
L´ıdia Garcia, Anna Pla-Quintana* and Anna Roglans*
Received 4th June 2009, Accepted 8th September 2009
First published as an Advance Article on the web 30th September 2009
DOI: 10.1039/b910961g
Non-proteinogenic phenylalanine derivatives were efficiently prepared by Rh(I)-catalyzed [2+2+2]
cycloaddition reactions between enantiopure and racemic propargylglycine amino acids, with different
protective groups, and diynes. Diverse substituents, including tags such as dansyl or dabsyl, were
introduced onto the aromatic ring of the amino acid derivatives by selecting the most appropriate diyne
reacting partners.
proteinogenic phenylalanine amino acid derivatives. The synthetic
Introduction
pathway, shown in Scheme 1, is based on [2+2+2] cycloaddition
reactions of several stereochemically pure and racemic protected
propargylglycine derivatives 1 with 1,6-diynes 2. The triple bond in
amino acid 1 offers the possibility of combining the inherent acid
and amine functionalities with a plethora of possible derivatiza-
tions. Compounds 1 with different protective groups at the amino
functionality (Fmoc and acetyl) and at the acid functionality
(methyl and ethyl ester) were selected. The 1,6-diynes 2 provide the
different functionality in the aromatic ring of the phenylalanine
derivatives.
Finding new synthetic processes for the synthesis of complex
amino acids containing different functional groups in their
structure is a major goal as non-proteinogenic amino acids are
important building blocks in drug discovery,1 especially in peptide
pharmacophores.2
Transition-metal-catalyzed [2+2+2] cycloaddition of three
alkynes is a useful and highly atom-economic method for syn-
thesizing polysubstituted benzene derivatives.3 Although this type
of cycloaddition reaction catalyzed by several transition-metal
complexes is efficient, there are only a few examples in the
literature where it has been used for the synthesis of non-natural
amino acids.4-6 Kotha et al. have prepared indane containing
a-amino acids.4 Under Rh(I) or Co(I) catalysis they performed
the [2+2+2] cycloaddition of a protected bispropargyl glycine
and various alkynes. Moderate to good yields of the amino
acids were obtained in a process that had a limited monoalkyne
scope. Additionally, both the groups of Kotha (using Rh(I) or
Co(I) catalysts)5 and Dixneuf (using ruthenium catalysts)6 have
described the preparation of tetrahydroisoquinoline-3-carboxylic
acid derivatives by [2+2+2] cycloaddition. In this case, 1,6- and
1,7-diynes, which incorporate the amino acid functionality in the
tether, were reacted with internal and terminal alkynes.
[2+2+2] cycloaddition can also take place between two alkynes
and various unsaturated substrates.3 When one of these substrates
is an alkene, cyclohexadienes can be obtained, opening the door to
enantioselectivity being achieved. Using this approach, Tanaka7
et al. reacted a diyne with a protected dehydroamino acid with
various non-terminal diynes under Rh(I)/(R)-BINAP catalysis to
yield disubstituted protected a-amino acids with a stereochemi-
cally stable quarternary carbon in excellent enantioselectivities.
Based on our experience in the use of the Wilkinson catalyst
(RhCl(PPh3)3) in [2+2+2] cycloaddition reactions for the synthesis
of fused tetracycles with benzene and cyclohexadiene cores,8 we
present here a highly efficient synthetic approach to new non-
Scheme 1 Retrosynthetic analysis of non-natural amino acids of type 3,
4, and 5.
Results and discussion
Optimization of reaction conditions
Department of Chemistry, University of Girona, Campus de Montilivi, s/n,
17071-Girona, Spain. E-mail: anna.roglans@udg.edu; Fax: +34 972 41 81
50; Web: Web: http://quimica.udg.edu/gr_metso/
† Electronic supplementary information (ESI) available: Experimen-
tal details and NMR spectra for all new compounds. See DOI:
10.1039/b910961g
In a first set of experiments, several reaction conditions were
tested in order to optimize the process. The [2+2+2] cycloaddition
reaction was tested with L,D-Fmoc-propargylglycine, L,D-1a, and
diyne 2a (Scheme 2 and Table 1). The reaction did not succeed
using the Wilkinson catalyst in toluene at 70 ◦C. After 24 h of
5020 | Org. Biomol. Chem., 2009, 7, 5020–5027
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
Table 1 Rh-catalyzed [2+2+2] cycloaddition reaction of L,D-1a and L-1a
with diynes 2a–b
However, when the reaction was performed using the Wilkinson
catalyst in refluxing EtOH, the reaction proceeded in just 30 min-
utes to give the desired cycloaddition product (R,S)-3a exclusively
with a 94% yield (Entry 4, Table 1). Compound (R,S)-3a was
extremely insoluble in common organic solvents preventing its
NMR characterization and only an ESI(-) mass spectrum could
be run to identify the compound. In order to improve solubility, we
decided to methylate the acid functionality in (R,S)-3a to obtain
the more soluble methyl ester derivative (R,S)-4a. Methylation was
readily accomplished with TMSCl in methanol to give a 96% yield
of (R,S)-4a, which could now be fully characterized (Scheme 2).
The same reaction conditions were then applied to the reaction
of L-1a and diyne 2a (Entry 5, Table 1). After methylation of the
acid functionality of (S)-3a, the increased solubility also allowed
an HPLC chiral chromatographic analysis of derivative (S)-4a,
which showed that optically active (S)-4a (>99% ee) was obtained
without any detectable racemization in the cycloaddition step or
in the methylation.10 We then tested the reaction of L,D-1a and
L-1a, with diyne 2b, which has terminal alkynes (Scheme 2, Entries
6 and 7, Table 1). 3b was also an insoluble compound, which
was methylated at the acid functionality to give the more soluble
compound 4b with a yield of over 90%.
Entry Aa, 1
Diyne Solvent/T (◦C) Time (h) Product/Yield (%)
c
1
L,D-1a 2a
Toluene/70
24
96
2
0.5
0.5
2
–
–
–
c
c
2a
3b
4
L,D-1a 2a
L,D-1a 2a
L,D-1a 2a
Toluene/r.t.
CH2Cl2/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
(R,S)-3a/94
(S)-3a/93
(R,S)-3b/93
(S)-3b/92
5
6
7
L-1a
L,D-1a 2b
L-1a 2b
2a
2
The reaction was carried out with 10% molar of Wilkinson catalyst, unless
otherwise stated, and by adding the diyne (1 eq.) slowly over a solution
of the amino acid (1 eq.) and the catalyst.a Reaction carried out with
15% molar of Wilkinson catalyst. b Reaction carried out with 10% molar
of [Rh(COD)2]BF4/BINAP. c Homocoupled product 6 was obtained with
an 83% yield (entry 1), 79% yield (entry 2) and 70% yield (entry 3).
Substrate scope
Since the free carboxylic acid functional group of the starting
amino acid 1a gave problems of insolubility in its derivatives 3,
we decided to methylate 1a both in its racemic and enantiopure10
forms and to perform the [2+2+2] cycloadditions on amino acids
L,D-1b and L-1b (Table 2). We first checked to confirm that the
Table 2 Rh-catalyzed [2+2+2] cycloaddition reactions of L,D-1b and L-1b
with diynes 2
Scheme 2 Rh-catalyzed [2+2+2] cycloaddition reaction of 1a with diynes
2a and 2b.
reaction, only the product derived from the homocoupling of
the diyne, 6, (Fig. 1) was found with an 83% yield (Entry 1,
Table 1). Working at room temperature, the reaction similarly
failed (Entry 2, Table 1). Changing the Rh(I) complex to a mixture
of cationic complex [Rh(COD)2]BF4 and bidentate phosphine
BINAP in CH2Cl2, conditions typically used by Tanaka et al. with
excellent results,9 again only gave the homocoupled product 6 and
no traces of the cycloaddition compound were isolated (Entry 3,
Table 1). All attempts at avoiding dimerization of the diyne by
adding compound 2a slowly over a mixture of propargyl glycine
derivative 1a and rhodium complex failed to improve the results.
Entry
Aa
Diyne
Time (h)
Product/Yield (%)
1
2
3
4
5
6
7
8
9
L,D-1b
L,D-1b
L-1b
2a
2b
2a
2c
2c
2d
2e
2g
2h
1
2
1
1.5
1.5
1.5
3
2
7
(R,S)-4a/97
(R,S)-4b/71
(S)-4a/99
(S)-4c/100
(R,S)-4c/100
(R,S)-4d/90
(R,S)-4e/84
(R,S)-4g/76
(R,S)-4h/64
L-1b
L,D-1b
L,D-1b
L,D-1b
L,D-1b
L,D-1b
Reactions were carried out with 10% molar of Wilkinson catalyst in
refluxing ethanol and by adding the diyne (1.5 eq.) slowly over a solution
of the amino acid (1 eq.) and the catalyst when necessary.
Fig. 1 Homocoupled product from diyne 2a.
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 5020–5027 | 5021
©

View Article Online
Table 4 Rh-catalyzed [2+2+2] cycloaddition reactions of 1b with unsym-
metrical 1,6-diynes 7
same previously tested diyne substrates 2a and 2b work with 1b.
Products 4a and 4b were obtained without any significant change
in yields or reaction times (Entries 1–3, Table 2). Terminal diyne
2b needed slow addition of the diyne over the amino acid 1b
and Wilkinson catalyst to suppress homocoupling of the diyne.
Contrarily, no homocoupling was observed with internal diyne
2a. We then explored the scope of this process using the optimized
conditions and employed malonate (2c,d), oxygen-linked (2e) and
carbon tethered (2g) 1,6-diynes (Entries 4–8, Table 2). Also a
nitrogen tethered diyne 2h protected with the easily and readily
removable SES (2-trimethylsilylethanesulfonyl) protecting group
(Entry 9, Table 2) was engaged in the reaction. In all the cases
tested, excellent yields of the cycloaddition compounds 4 were
obtained in a short reaction time. Overall, the various diynes 2a–h
tested proved to be good partners for the cycloaddition reaction
and permitted the introduction of different functionalities in the
fused bicyclic system of phenylalanine derivatives. It should be
noted that the reaction is efficient both with terminal diynes 2b,d,g
and with diynes bearing methyl or ethyl groups at each alkyne
terminus 2a,c,e,h, although in order to avoid homocoupling of
the terminal diynes, this compound was slowly added over a
previously prepared mixture of acetylenic amino acid and the
Wilkinson catalyst. The nature of the group X in the diyne tether
did not affect the efficiency of the reaction. It is interesting to
note that no excess of propargylglycine amino acid was needed to
accomplish the reaction effectively, in contrast to most reported
examples.3 Indeed, an excess of the diyne was used to assure
complete consumption of the more expensive amino acid.
In order to broaden the applicability of the method and extend
it to other protecting groups in the starting amino acid of type 1
we decided to test the acetylpropargylglycine ethyl ester, L,D-1c in
its racemic form (Table 3).
With an acetyl group as a protecting group for the amino
functionality of the amino acid the reactions with several diynes 2
were accomplished even at temperatures lower than reflux. In all
cases, good to excellent yields of the cycloaddition compounds 5
were obtained within short reaction times with several terminal
and alkyl-substituted tethered dialkynes.
We then investigated the case of unsymmetrical 1,6-diynes. Tosyl
(7a,b) and malonate (7c) linked diynes were successfully involved in
the [2+2+2] cycloaddition with protected propargyl glycine amino
acid 1b (Table 4). However, the regioselectivity was poor in all
cases and could only just be raised to 3.1:1 when having a CH2OH
substituent at one of the diyne terminus (7b) and running the
reaction at room temperature instead of reflux.
Entry Diyne Time (h) Temperature
Yield (%)
Ratio of 8:9a
1
2
3
4
7a
7b
7b
7c
2
2
72
1
Reflux
Reflux
r.t.
79
100
100
100
1.4 : 1
1.9 : 1
3.1 : 1
1.3 : 1
Reflux
The reaction was carried out with 10% molar of Wilkinson catalyst
in ethanol and by adding the diyne (1.5 eq.) slowly over a solution
of the amino acid (1 eq.) and the catalyst.a Determined by 1H NMR
spectroscopy.
Labelling of amino acids
The fluorescent labelling of biomolecules11 has drawn special
attention in recent years due to the notable progress made in
detection based on fluorescence techniques. A next step further in
our study consisted in proving that the methodology developed
was applicable to the labelling of amino acids. To this end,
we decided to start from the commercially available dansy-
lamide (5-dimethylamino-1-naphthalenesulfonamide), which is
a common fluorescent probe with strong and environmentally
sensitive fluorescence.12 The dansylamide was bisalkylated with
two equivalents of 1-bromo-2-butyne to yield a 1,6-diyne which
could be submitted to the [2+2+2] cycloaddition. Propargylglycine
amino acid, both in its acid protected and free forms 1b and 1a, was
tested in the reaction. Interestingly, both reactions gave high yields
of soluble products 10a and 10b (Fig. 2 and Table 5). A number of
fluorophores available in their sulfonamide forms may be used
to tag amino acids through this methodology, complementing
the existing techniques to afford the amino acids tagged with
fluorescence groups that are needed for a number of applications.
Table 3 Rh-catalyzed [2+2+2] cycloaddition reactions of 1c with diynes 2
Entry
Diyne
Time (h)
Product/Yield (%)
1
2
3
4
5
6
2a
2b
2c
2d
2e
2f
2
3
1.5
2
3
24
5a/99
5b/64a
5c/100
5d/92
5e/88
5f/48a
The reaction was carried out with 10% molar of Wilkinson catalyst in
ethanol at 60 ◦C and by adding the diyne (1.5 eq.) slowly over a solution
of the amino acid (1 eq.) and the catalyst.a Yield calculated by 1H-NMR
integration.
Fig. 2 Phenylalanine derivatives labelled with dansyl 10 and dabsyl 11
dyes.
5022 | Org. Biomol. Chem., 2009, 7, 5020–5027
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
Table 5 Rh-catalyzed [2+2+2] cycloaddition reactions of 1a and 1b with
diynes 12a–b containing dansyl and dabsyl tags
Experimental
Instrumentation and general materials
Unless otherwise noted, materials were obtained from commercial
suppliers and used without further purification. All reactions
requiring anhydrous conditions were conducted in oven-dried
glassware under a dry nitrogen atmosphere. Dichloromethane was
degassed and dried under nitrogen by passing through solvent
purification columns (MBraun, SPS-800). Toluene was distilled
under nitrogen over sodium as the drying agent. Solvents were
removed under reduced pressure with a rotary evaporator. When
necessary, reaction mixtures were chromatographed in a silica gel
column (230–400 mesh) or alumina gel column (particle size 0.05–
0.15 mm) using a gradient solvent system as the eluent.
Entry
Diyne/X
Aa, 1/R
Time (h)
Product/Yield (%)
1
2
3
4
12a/NDns
12a/NDns
12b/NDbs
12b/NDbs
1a/H
1
2
2
2
10a (R = H)/97
10b (R = Me)/98
11a (R = H)/98
11b (R = Me)/97
1H and 13C NMR spectra were recorded on either a 400 or a
1b/Me
1a/H
300 MHz NMR spectrometer. Chemical shifts (d) for 1H and 13
C
1b/Me
NMR were referenced to internal solvent resonances and reported
The reaction was carried out with 10% molar of Wilkinson catalyst in
refluxing ethanol and by adding the diyne (1.5 eq.) slowly over a solution
of the amino acid (1 eq.) and the catalyst.
relative to SiMe4.
L-Fmoc-Propargylglycine L-1a, L,D-acetylpropargylglycine
ethyl ester L,D-1c, L,D-propargylglycine, dipropargylether 2f, 1,6-
heptadiyne 2g, 2-(trimethylsilyl)ethanesulfonamide, dansylamide
and dabsyl chloride are commercially available.
N,N-Bis(2-butynyl)-(4-methylphenyl)sulfonamide, 2a,18 N,N-
bis(2-propynyl)-(4-methylphenyl)sulfonamide, 2b,19 diethyl 2,2-
dibut-2-ynylpropan-1,3-dioate, 2c,20 diethyl 2,2-diprop-2-ynyl-
propan-1,3-dioate, 2d,21 di-(2-pentynyl)ether, 2e,22 dimethyl 2-but-
2-ynylpropan-1,3-dioate, 7c,23 and N-(2-butynyl)-N-(2-propynyl)-
(4-methylphenyl)sulfonamide, 7a24 were prepared by reported
methods.
Dansylated non-natural amino acids structurally close to the ones
synthesized here have been incorporated into various positions of
streptavidin and used to probe protein structures.13
In addition, the preparation of dabsyl (dimethylaminoazoben-
zenesulfonyl) dyed amino acids,14 a chromophore extensively used
for the labelling of biomolecules that is an effective quencher15
coupled with various fluorophores including dansyl,16 has been
achieved. In this case, the commercially available sulfonyl chloride
was converted into the corresponding sulfonamide and bisalky-
lated to yield the corresponding 1,6-diyne. Both propargylglycine
amino acids 1a and 1b were reacted with dabsyl containing
1,6-diyne, yielding phenylalanine derivatives 11a and 11b. The
moderate solubility of the carboxylic acid derivative 11a prevented
complete NMR characterization, unlike the methyl ester 11b,
which is freely soluble in common organic solvents.
General procedure for the [2+2+2] cycloaddition reaction of
propargylglycine amino acids 1 and diynes 2
In a 25 mL flask equipped with a pressure compensated addition
funnel, propargylglycine derivative (0.10 mmol) and the Wilkinson
catalyst (0.010 g, 0.01 mmol) were added to absolute ethanol
(8 mL), degassed by bubbling nitrogen and heated to the required
temperature (Tables 1–5). A solution of the diyne (0.15 mmol) in
ethanol (2 mL) was added dropwise over 0.5 h, and the resulting
mixture was stirred at the required temperature for the time
needed to complete the reaction (TLC monitoring, Tables 1–5).
The solvent was removed and the crude was purified by column
chromatography to give the desired phenylalanine derivative.
Both dansyl and dabsyl groups are expected to be stable to
reagents used for deprotection of peptides synthesized using Fmoc
synthesis.17
Conclusions
In conclusion, we have achieved the synthesis of non-natural
phenylalanine derivatives by a convergent and atom-economical
[2+2+2] cycloaddition reaction between different protected
propargylglycine amino acids 1 and diynes 2a–h, 7a–c, and
12a–b. These diynes are suitable for the introduction of diverse
functionalities in various positions of amino acid derivatives 3,
4, 5, 8 and 9, including tags such as dansyl and dabsyl (10 and
11). Furthermore, no excess of the propargylglycine amino acid is
needed to avoid homocoupling, which is interesting for future
applications in peptide chemistry. The reaction is carried out
in an environmentally friendly solvent such as ethanol and the
reaction conditions are mild enough to be compatible with the
acid- and base-labile protecting groups that are normally required
for peptide synthesis and to avoid racemization of the stereogenic
centre of the starting material.
Characterization data of phenylalanine derivatives 3, 4, and 5
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-di-
lmethyl-2-tosylisoindolin-5-yl)propanoic acid, (R,S)-3a, was puri-
fied by column chromatography on alumina gel using mixtures
of dichloromethane/methanol/acetic acid of increasing polarity
(20/1/0 to 0/0/1) as the eluent to afford (R,S)-3a (0.059 g, 94%
yield) as a colourless solid; mp 253–254 ◦C (dec.); IR (ATR)
n (cm-1): 2945, 1561, 1461, 1347, 1163; ESI(-)-MS (m/z) 609
[M - H]-.
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(2-to-
sylisoindolin-5-yl)propanoic acid, (R,S)-3b, was purified by
column chromatography on alumina gel using mixtures of
dichloromethane/methanol/acetic acid of increasing polarity
(20/1/0 to 0/0/1) as the eluent to afford (R,S)-3b (0.054 g,
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 5020–5027 | 5023
©

View Article Online
93% yield) as a colourless solid; mp 271–272 ◦C (dec.); IR (ATR)
n (cm-1): 2970, 1579, 1468, 1342.
4.20 (q, J = 7.2 Hz, 4H), 4.16–4.24 (m, 1H), 4.35 (d, J = 6.4 Hz,
2H), 4.57 (dt, J = 8.4/6.8 Hz, 1H), 5.25 (d, J = 8.4 Hz, 1H), 6.70
(s, 1H), 7.29 (t, J = 7.6 Hz, 2H), 7.39 (t, J = 7.4 Hz, 2H), 7.53 (m,
2H), 7.75 (d, J = 7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3) dC
14.0, 15.3, 35.5, 39.5, 40.1, 47.1, 52.2, 54.4, 59.5, 61.7, 67.0, 119.9,
125.0, 127.0, 127.7, 129.5, 129.9, 130.6, 132.7, 137.6, 139.6, 141.2,
143.7, 143.8, 155.6, 171.8, 171.9, 172.5; ESI-MS (m/z) 614 [M +
H]+; Anal. Calcd. for C36H39NO8·0.5H2O (622.27): C, 69.44; H,
6.47; N, 2.25. Found: C, 69.85; H, 6.14; N, 2.39.
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-di-
methyl-2-tosylisoindolin-5-yl)propanoic acid methyl ester, (R,S)-
4a, was purified by column chromatography on silica gel using
mixtures of dichloromethane/ethyl acetate of increasing polarity
(100/1 to 50/1) as the eluent to afford (R,S)-4a (0.069 g, 97%
◦
yield) as a colourless solid; mp 109–110 C; IR (ATR) n (cm-1):
1
3332, 2920, 1720, 1527, 1448, 1341, 1159; H NMR (400 MHz,
CDCl3) dH 2.07 (s, 6H), 2.38 (s, 3H), 2.95 (dd, J = 13.8/6.6 Hz,
1H), 3.11 (dd, J = 13.8/6.2 Hz, 1H), 3.69 (s, 3H), 4.15 (t, J =
6.8 Hz, 1H), 4.35 (d, J = 6.8 Hz, 2H), 4.49–4.59 (m, 5H), 5.27
(d, J = 8.4 Hz, 1H), 6.73 (s, 1H), 7.23–7.33 (m, 4H), 7.39 (t, J =
7.6 Hz, 2H), 7.52 (m, 2H), 7.74 (d, J = 7.6 Hz, 2H), 7.77 (d, J =
8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3) dC 15.0, 18.1, 21.4,
35.3, 47.0, 52.3, 53.3, 53.7, 54.3, 66.9, 119.9, 124.9, 127.0, 127.5,
127.7, 128.4, 129.5, 129.8, 130.6, 133.7, 133.8, 133.9, 135.8, 141.2,
143.5, 143.6, 143.7, 155.5, 172.1; ESI-MS (m/z) 647 [M + Na]+;
APCI-MS (m/z) 625 [M + H]+; Anal. Calcd. for C36H36N2O6S
(624.75): C, 69.21; H, 5.81; N, 4.47; S, 5.13. Found: C, 68.84; H,
5.95; N, 4.48; S, 5.11.
(S)-5-(2-(Methoxycarbonyl)-2-(((9H -fluoren-9-yl)methoxy)-
carbonylamino)ethyl)-4,7-dimethyl-1H -indene-2,2(3H)-dicar-
boxylic acid diethyl ester, (S)-4c. Colourless solid (0.075 g,
quantitative yield, >99% ee) [a]20 +10.03 (c 0.01, CH2Cl2). The
D
ee was determined with HPLC analysis using a chiral column
(Kromasil 100 TBB column, 4.6 ¥ 250 mm, 5 mm, r.t.; eluent: 95%
hexanes/5% THF, flow rate: 1.0 mL/min over 30 min ; l = 254 nm;
retention time 17.4 min and 19.7 min for (R,S)-4c; retention time
19.7 min for (S)-4c (>99% ee)).
(R,S)-5-(2-(Methoxycarbonyl)-2-(((9H-fluoren-9-yl)methoxy)-
carbonylamino)ethyl)-1H-indene-2,2(3H)-dicarboxylic acid diethyl
ester, (R,S)-4d, was purified by column chromatography on silica
gel using mixtures of dichloromethane/ethyl acetate (50/1) as the
eluent to afford (R,S)-4d (0.056 g, 90% yield) as a colourless solid;
(S)-2-(((9H -Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-
dimethyl-2-tosylisoindolin-5-yl)propanoic acid methyl ester, (S)-4a.
◦
Colourless solid (0.070 g, 99% yield; >99% ee); [a]20 +19.05
mp 57–58 C; IR (ATR) n (cm-1): 3348, 2951, 1722, 1520, 1446;
D
(c 0.01, CH2Cl2). The ee was determined with HPLC analysis
using a chiral column (Kromasil 100 TBB column, 4.6 ¥ 250 mm,
5 mm, r.t.; eluent: 90% hexanes/10% THF, flow rate: 1.0 mL/min
over 40 min; l = 254 nm; retention time 23.8 min and 27.5 min
for (R,S)-4a; retention time 27.5 min for (S)-4a (>99% ee)).
(R,S)-2-(((9H -Fluoren-9-yl)methoxy)carbonylamino)-3-(2-
tosylisoindolin-5-yl)propanoic acid methyl ester, (R,S)-4b, was
purified by column chromatography on silica gel using mixtures
of dichloromethane/ethyl acetate of increasing polarity (100/1 to
50/1) as the eluent to afford◦(R,S)-4b (0.043 g, 71% yield) as a
colourless solid; mp 158–159 C; IR (ATR) n (cm-1): 3314, 2923,
1733, 1691, 1545, 1437, 1340, 1154; 1H NMR (400 MHz, CDCl3)
dH 2.38 (s, 3H), 3.01 (dd, J = 14.0/5.6 Hz, 1H), 3.08 (dd, J =
14.0/5.6 Hz, 1H), 3.71 (s, 3H), 4.18 (t, J = 6.8 Hz, 1H), 4.35 (dd,
J = 10.4/6.8 Hz, 1H), 4.45 (dd, J = 10.4/6.8 Hz, 1H), 4.53 (s, 2H),
4.56 (s, 2H), 4.60 (dt, J = 8.0/5.6 Hz, 1H), 5.18 (d, J = 8.0 Hz,
1H), 6.85 (s, 1H), 6.93 (d, J = 7.8 Hz, 1H), 7.05 (d, J = 7.8 Hz,
1H), 7.26–7.33 (m, 4H), 7.37–7.44 (m, 2H), 7.51–7.57 (m, 2H),
7.74 (d, J = 8.4 Hz, 2H), 7.75–7.80 (m, 2H); 13C NMR (100 MHz,
CDCl3) dC 21.4, 37.9, 47.1, 52.3, 53.4, 53.5, 54.7, 66.7, 119.95,
120.0, 122.7, 123.3, 124.8, 124.9, 126.9, 127.0, 127.5, 127.7, 128.7,
129.8, 133.7, 135.0, 135.6, 136.5, 141.2, 141.3, 143.5, 143.6, 143.7,
155.5, 171.6; ESI-MS (m/z) 597 [M + H]+, 619 [M + Na]+; Anal.
Calcd. for C34H32N2O6S·AcOEt (684.25): C, 66.65; H, 5.89; N,
4.09; S, 4.68. Found: C, 67.03; H, 5.62; N, 4.37; S, 4.91; HRMS
calcd. for [C34H32N2O6S + Na]+: 619.1873. Found: 619.1885.
(R,S)-5-(2-Methoxycarbonyl)-2-(((9H-fluoren-9-yl)methoxy)-
carbonylamino)-4,7-dimethyl-1H -indene-2,2(3H)-dicarboxylic
acid diethyl ester, (R,S)-4c, was purified by column chromatogra-
phy on silica gel using mixtures of dichloromethane/ethyl acetate
(50/1) as the eluent to afford (R,S)-4c (0.072 g, quantitative yield)
as a colourless solid; mp 59–60 ◦C; IR (ATR) n (cm-1): 3341, 2922,
1H NMR (400 MHz, CDCl3) dH 1.25 (t, J = 7.2 Hz, 6H), 3.07 (d,
J = 6.0 Hz, 2H), 3.55 (s, 4H), 3.72 (s, 3H), 4.19 (q, J = 7.2 Hz,
4H), 4.15–4.24 (m, 1H), 4.35 (dd, J = 7.0/10.4 Hz, 1H), 4.43 (dd,
J = 7.4/10.4 Hz, 1H), 4.64 (dt, J = 6.0/8.0 Hz, 1H), 5.24 (d, J =
8.0 Hz, 1H), 6.88 (d, J = 7.6 Hz, 1H), 6.93 (s, 1H), 7.10 (d, J =
7.6 Hz, 1H), 7.31 (m, 2H), 7.40 (t, J = 7.4 Hz, 2H), 7.57 (m, 2H),
7.76 (d, J = 7.4 Hz, 2H); 13C NMR (100 MHz, CDCl3) dC 14.0,
38.0, 40.1, 40.3, 47.1, 52.3, 54.8, 60.3, 61.7, 66.9, 119.9, 124.3,
125.0, 125.1, 127.0, 127.7, 128.0, 134.4, 138.9, 140.5, 141.2, 143.7,
143.8, 155.5, 171.5, 171.9; ESI-MS (m/z) 586 [M + H]+, 603 [M +
NH4]+, 608 [M + Na]+; Anal. Calcd. for C34H35NO8·0.5AcOEt
(629.26): C, 68.67; H, 6.24; N, 2.22. Found: C, 68.47; H, 5.83;
N, 2.44; HRMS calcd. for [C34H35NO8 + Na]+: 608.2255. Found:
608.2263.
(R,S)-3-(4,7-Diethyl-1,3-dihydroisobenzofuran-5-yl)-2-(((9H-
fluoren-9-yl)methoxy)carbonylamino)propanoic acid methyl ester,
(R,S)-4e, was purified by column chromatography on silica gel
using mixtures of dichloromethane/ethyl acetate (50/1) as the
eluent to afford (R,S)-4e (0.051 g, 84% yield) as a colourless solid;
mp 100–101 ◦C; IR (ATR) n (cm-1): 3317, 2959, 2360, 1749, 1686,
1533, 1448; 1H NMR (400 MHz, CDCl3) dH 1.10 (t, J = 7.4 Hz,
3H), 1.16 (t, J = 7.6 Hz, 3H), 2.45 (q, J = 7.6 Hz, 2H), 2.41–2.58
(m, 2H), 3.06 (dd, J = 14.0/6.8 Hz, 1H), 3.16 (dd, J = 14.0/6.8 Hz,
1H), 3.72 (s, 3H), 4.18 (t, J = 7.2 Hz, 1H), 4.36 (d, J = 7.2 Hz,
2H), 4.62 (dt, J = 8.2/6.8 Hz, 1H), 5.09 (s, 2H), 5.11 (s, 2H),
5.26 (d, J = 8.2 Hz, 1H), 6.80 (s, 1H), 7.29 (t, J = 7.4 Hz, 2H),
7.39 (t, J = 7.4 Hz, 2H), 7.55 (m, 2H), 7.75 (d, J = 7.4 Hz, 2H);
13C NMR (100 MHz, CDCl3) dC 14.2, 14.5, 23.0, 26.0, 34.6, 47.1,
52.3, 54.9, 67.0, 73.1, 73.2, 119.9, 124.9, 125.0, 127.0, 127.7, 128.6,
132.7, 133.7, 134.8, 136.5, 138.3, 141.2, 143.6, 143.7, 155.6, 172.4;
ESI-MS (m/z) 500 [M + H]+, 522 [M + Na]+; HRMS calcd. for
[C31H33NO5 + Na]+: 522.2251. Found: 522.2259.
1
1723, 1517, 1447; H NMR (400 MHz, CDCl3) dH 1.26 (t, J =
(R,S)-2-(((9H -Fluoren-9-yl)methoxy)carbonylamino)-3-(2,3-
dihydro-1H-inden-6-yl)propanoic acid methyl ester, (R,S)-4g, was
purified by column chromatography on silica gel using mixtures
7.2 Hz, 6H), 2.16 (s, 6H), 2.99 (dd, J = 14.0/6.8 Hz, 1H), 3.12
(dd, J = 14.0/6.6 Hz, 1H), 3.49 (s, 2H), 3.53 (s, 2H), 3.69 (s, 3H),
5024 | Org. Biomol. Chem., 2009, 7, 5020–5027
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
of hexanes/ethyl acetate of increasing polarity (9/1 to 6/4) as the
128.9, 129.8, 133.8, 135.0, 135.9, 136.5, 143.7, 169.5, 171.4; ESI-
MS (m/z) 431 [M + H]+; HRMS calcd. for [C22H26N2O5S + Na]+:
453.1455. Found: 453.1451.
eluent to afford (R,S)-4g (0.097 g, 76% yield) as a yellow solid;
◦
mp 58–59 C; IR (ATR) n (cm-1): 2948, 2924, 1720, 1511, 1447,
1
1208; H NMR (400 MHz, CDCl3) dH 2.04 (quint, J = 7.2 Hz,
5-(2-(Ethoxycarbonyl)-2-acetamidoethyl)-4,7-dimethyl-1H -
indene-2,2(3H)-dicarboxylic acid diethyl ester, 5c, was purified
by column chromatography on silica gel using mixtures of
dichloromethane/ethyl acetate (50/1) as the eluent to afford 5c
(0.076 g, quantitative yield) as a colourless oil; IR (ATR) n (cm-1):
3275, 2932, 1728, 1654, 1535, 1444; 1H NMR (400 MHz, CDCl3)
dH 1.17 (t, J = 7.2 Hz, 3H), 1.26 (t, J = 7.2 Hz, 3H), 1.27 (t, J =
7.2 Hz, 3H), 1.97 (s, 3H), 2.16 (s, 3H), 2.17 (s, 3H), 3.01 (dd, J =
10.5/6.8 Hz, 1H), 3.07 (dd, J = 10.5/6.8 Hz, 1H), 3.50 (s, 2H),
3.53 (s, 2H), 4.06–4.17 (m, 2H), 4.21 (q, J = 7.2 Hz, 2H), 4.22
(q, J = 7.2 Hz, 2H), 4.76 (dt, J = 7.6/6.8 Hz, 1H), 5.99 (d, J =
7.6 Hz, 1H), 6.69 (s, 1H); 13C NMR (100 MHz, CDCl3) dC 13.9,
14.0, 15.3, 23.1, 35.2, 39.4, 40.1, 52.7, 59.4, 61.3, 61.7, 129.5, 129.9,
130.5, 132.8, 137.4, 139.4, 169.6, 171.8, 172.1; ESI-MS (m/z) 448
[M + H]+; HRMS calcd. for [C24H33NO7 + Na]+: 470.2149. Found:
470.2165.
5-(2-(Ethoxycarbonyl)-2-acetamidoethyl)-1H-indene-2,2(3H)-
dicarboxylic acid diethyl ester, 5d, was purified by column chro-
matography on silica gel using mixtures of dichloromethane/ethyl
acetate (20/1) as the eluent to afford 5c (0.065 g, 92% yield) as a
colourless oil; IR (ATR) n (cm-1): 3262, 2929, 1724, 1635, 1551;
1H NMR (400 MHz, CDCl3) dH 1.23 (t, J = 7.2 Hz, 3H), 1.25 (t,
J = 7.2 Hz, 3H), 1.26 (t, J = 7.2 Hz, 3H), 1.98 (s, 3H), 3.07 (d, J =
6.0 Hz, 2H), 3.54 (s, 2H), 3.55 (s, 2H), 4.12–4.24 (m, 6H), 4.82 (dt,
J = 7.8/6.0 Hz, 1H), 5.99 (d, J = 7.8 Hz, 1H), 6.90 (d, J = 7.6 Hz,
1H), 6.93 (s, 1H), 7.10 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz,
CDCl3) dC 13.9, 14.1, 23.1, 37.7, 40.1, 40.3, 53.2, 60.4, 61.4, 61.7,
124.2, 125.1, 127.9, 134.6, 138.9, 140.4, 169.5, 171.5, 171.6; ESI-
MS (m/z) 442 [M + Na]+; HRMS calcd. for [C22H29NO7 + Na]+:
442.1836. Found: 442.1843.
2H), 2.85 (t, J = 7.2 Hz, 4H), 3.02–3.15 (m, 2H), 3.74 (s, 3H),
4.20 (t, J = 7.2 Hz, 1H), 4.32 (dd, J = 7.2/10.4 Hz, 1H), 4.43
(dd, J = 7.2/10.4 Hz, 1H), 4.65 (dt, J = 5.6/8.4 Hz, 1H), 5.27
(d, J = 8.4 Hz, 1H), 6.85 (d, J = 7.6 Hz, 1H), 6.96 (s, 1H), 7.13
(d, J = 7.6 Hz, 1H), 7.22–7.34 (m, 2H), 7.39 (t, J = 7.6 Hz, 2H),
7.52–7.59 (m, 2H), 7.75 (d, J = 7.6 Hz, 2H); 13C NMR (100 MHz,
CDCl3) dC 25.4, 32.4, 32.7, 37.9, 47.1, 52.3, 54.8, 66.9, 119.9,
124.4, 125.0, 125.1, 125.2, 127.0, 127.6, 133.3, 141.2, 143.1, 143.7,
143.8, 144.7, 155.5, 172.0; HRMS calcd. for [C28H27NO4 + Na]+:
464.1832. Found: 464.1827.
(R,S)-2-(((9H -Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-
dimethyl-2-trimethylsilylethylisoindolin-5-yl)propanoic acid methyl
ester, (R,S)-4h, was purified by column chromatography on silica
gel using mixtures of dichloromethane/hexanes (20/1) as the
eluent to afford (R,S)-4h (0.114 g, 64% yield) as a colourless solid;
mp 87–88 ◦C; IR (ATR) n (cm-1): 2921, 1721, 1331, 1143; 1H NMR
(400 MHz, CDCl3) dH 0.05 (s, 9H), 1.05–1.12 (m, 2H), 2.14 (s, 6H),
2.98–3.07 (m, 3H), 3.16 (dd, J = 14.0/6.4 Hz, 1H), 3.73 (s, 3H),
4.18 (t, J = 6.8 Hz, 1H), 4.39 (d, J = 6.8 Hz, 2H), 4.56–4.69 (m,
5H), 5.27 (d, J = 8.4 Hz, 1H), 6.81 (s, 1H), 7.27–7.33 (m, 2H),
7.40 (t, J = 7.6 Hz, 2H), 7.55 (t, J = 6.6 Hz, 2H), 7.76 (d, J =
7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3) dC -2.0, 10.1, 15.1,
18.2, 35.5, 46.3, 47.1, 52.4, 53.6, 54.0, 54.4, 67.0, 120.0, 124.9,
127.0, 127.7, 128.6, 129.7, 130.8, 134.1, 136.1, 141.3, 143.6, 143.7,
155.6, 172.2; HRMS calcd. for [C34H42N2O6SSi + Na]+: 657.2425.
Found: 657.2446.
2-(Acetamido)-3-(4,7-dimethyl-2-tosylisoindolin-5-yl)propanoic
acid ethyl ester, 5a, was purified by column chromatography on
silica gel using mixtures of dichloromethane/ethyl acetate (20/1)
as the eluent◦to afford 5a (0.061 g, 99% yield) as a colourless solid;
mp 169–170 C; IR (ATR) n (cm-1): 2924, 1738, 1656, 1537, 1342,
2-(Acetamido)-3-(4,7-diethyl-1,3-dihydroisobenzofuran-5-yl)-
propanoic acid ethyl ester, 5e, was purified by column chromatogra-
phy on silica gel using mixtures of dichloromethane/ethyl acetate
(50/1) as the eluent to afford 5e (0.064 g, 88% yield) as a colourless
solid; mp 154–155 ◦C; IR (ATR) n (cm-1): 3321, 2968, 2836, 1753,
1
1161; H NMR (400 MHz, CDCl3) dH 1.17 (t, J = 7.2 Hz, 3H),
1.95 (s, 3H), 2.11 (s, 6H), 2.42 (s, 3H), 2.98 (dd, J = 14.0/6.8 Hz,
1H), 3.07 (dd, J = 14.0/6.8 Hz, 1H), 4.05–4.19 (m, 2H), 4.45 (dt,
J = 8.0/6.8 Hz, 1H), 4.54 (m, 4H), 5.92 (d, J = 8.0 Hz, 1H), 6.73 (s,
1H), 7.33 (d, J = 8.0 Hz, 2H), 7.78 (d, J = 8.0 Hz, 2H); 13C NMR
(100 MHz, CDCl3) dC 14.0, 15.1, 18.1, 21.5, 23.1, 35.2, 52.7, 53.3,
53.7, 61.5, 127.5, 128.5, 129.4, 129.8, 130.7, 133.7, 133.9, 134.1,
135.8, 143.6, 169.6, 171.9; ESI-MS (m/z) 459 [M + H]+; Anal.
Calcd. for C24H30N2O5S·0.5H2O (467.19): C, 61.65; H, 6.68; N,
5.99; S, 6.86. Found: C, 61.95; H, 6.62; N, 5.91; S, 6.82; HRMS
calcd. for [C24H30N2O5S + Na]+: 481.1768. Found: 481.1767.
2-(Acetamido)-3-(2-tosylisoindolin-5-yl)propanoic acid ethyl es-
ter, 5b, was purified by column chromatography on silica gel using
mixtures of dichloromethane/ethyl acetate (20/1) as the eluent to
afford 5b with traces of triphenylphosphine oxide (0.028 g, 64%
1
1650, 1539, 1176; H NMR (400 MHz, CDCl3) dH 1.11 (t, J =
7.2 Hz, 3H), 1.17 (t, J = 8.0 Hz, 3H), 1.19 (t, J = 7.6 Hz, 3H),
1.98 (s, 3H), 2.47 (q, J = 8.0 Hz, 2H), 2.50–2.59 (m, 2H), 3.07 (dd,
J = 14.0/6.6 Hz, 1H), 3.12 (dd, J = 14.0/6.6 Hz, 1H), 4.08–4.22
(m, 2H), 4.82 (dt, J = 8.0/6.6 Hz, 1H), 5.10 (d, J = 8.2 Hz, 2H),
5.11 (d, J = 8.2 Hz, 2H), 5.92 (d, J = 8.0 Hz, 1H), 6.80 (s, 1H);
13C NMR (100 MHz, CDCl3) dC 13.9, 14.2, 14.5, 22.9, 23.1, 26.0,
34.4, 53.2, 61.4, 73.1, 73.2, 128.7, 132.9, 133.8, 134.7, 136.4, 138.3,
169.5, 172.1; ESI-MS (m/z) 356 [M + Na]+; HRMS calcd. for
[C19H27NO4 + Na]+: 356.1832. Found: 356.1826.
2-(Acetamido)-3-(1,3-dihydroisobenzofuran-5-yl)propanoic acid
ethyl ester, 5f, was purified by column chromatography on silica
gel using mixtures of dichloromethane/ethyl acetate (20/1) as
the eluent to afford 5f with traces of triphenylphosphane oxide
(0.032 g, 48% yield calculated by 1H NMR integration) as a
colourless oil; IR (ATR) n (cm-1): 3292, 2863, 1741, 1677, 1552;
1H NMR (400 MHz, CDCl3) dH 1.25 (t, J = 7.2 Hz, 3H), 1.99 (s,
3H), 3.10 (dd, J = 14.0/6.0 Hz, 1H), 3.16 (dd, J = 14.0/6.0 Hz,
1H), 4.17 (q, J = 7.2 Hz, 2H), 4.85 (dt, J = 8.0/6.0 Hz, 1H), 5.06
(s, 4H), 6.12 (d, J = 8.0 Hz, 1H), 6.99 (s, 1H), 7.01 (d, J = 7.6 Hz,
1H), 7.14 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) dC
1
yield as calculated by H NMR integration) as a colourless oil;
IR (ATR) n (cm-1): 3355, 2931, 1739, 1666, 1346, 1162; 1H NMR
(300 MHz, CDCl3) dH 1.23 (ap t, J = 7.2 Hz, 3H), 1.97 (s, 3H), 2.41
(s, 3H), 3.04 (dd, J = 13.8/5.8 Hz, 1H), 3.12 (dd, J = 13.8/5.8 Hz,
1H), 4.15 (ap dq, J = 7.2/1.2 Hz, 2H), 4.57 (s, 4H), 4.80 (dt, J =
7.5/5.8 Hz, 1H), 5.90 (d, J = 7.5 Hz, 1H), 6.92 (s, 1H), 6.97 (d,
J = 7.8 Hz, 1H), 7.08 (d, J = 7.8 Hz, 1H), 7.32 (d, J = 8.1 Hz,
2H), 7.76 (d, J = 8.1 Hz, 2H); 13C NMR (75 MHz, CDCl3) dC
14.1, 21.5, 23.1, 37.7, 53.2, 53.4, 53.5, 61.6, 122.6, 123.4, 127.6,
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 5020–5027 | 5025
©

View Article Online
14.1, 23.3, 38.7, 53.2, 61.4, 73.3, 120.9, 121.7, 128.3, 135.2, 137.9,
139.5, 169.5, 171.6; ESI-MS (m/z) 278 [M + H]+; HRMS calcd.
for [C15H19NO4 + Na]+: 300.1206. Found: 300.1217.
2H), 7.46–7.52 (m, 2H), 7.72–7.78 (m, 4H); 13C NMR (100 MHz,
CDCl3) dC 18.4, 21.5, 34.9, 47.0, 52.5, 53.0, 53.2, 55.2, 59.1, 67.0,
119.9, 124.9, 125.0, 127.0, 127.1, 127.5, 127.7, 127.8, 129.8, 130.6,
131.2, 132.6, 133.8, 134.6, 135.0, 136.5, 141.2, 141.3, 143.6, 156.0,
172.4; HRMS calcd. for [C36H36N2O7S + Na]+: 663.2135. Found:
663.2126.
Characterization data of phenylalanine derivatives 8 and 9
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(7-methyl-
2-tosylisoindolin-5-yl)propanoic acid methyl ester, (R,S)-8a and
(R,S)-2-(((9H-fluoren-9-yl)methoxy)carbonylamino)-3-(4-methyl-
2-tosylisoindolin-5-yl)propanoic acid methyl ester, (R,S)-9a, [(R,S)-
8a/(R,S)-9a = 1.4:1] were purified by column chromatography
on silica gel using mixtures of dichloromethane/hexanes (9/1)
as the eluent to afford an inseparable mixture of (R,S)-8a and
(R,S)-9a (0.139 g, 79% yield) as a colourless solid; IR (ATR) n
(R,S)-5-(2-Methoxycarbonyl)-2-(((9H-fluoren-9-yl)methoxy)-
carbonylamino)-7-methyl-1H-indene-2,2(3H)-dicarboxylic
acid
dimethyl ester, (R,S)-8c and (R,S)-5-(2-methoxycarbonyl)-2-
(((9H-fluoren-9-yl)methoxy)carbonylamino)-4-methyl-1H-indene-
2,2(3H)-dicarboxylic acid dimethyl ester, (R,S)-9c, [(R,S)-
8c/(R,S)-9c = 1.3:1] were purified by column chromatography
on silica gel using mixtures of dichloromethane/ethyl acetate
(50/1) as the eluent to afford an inseparable mixture of (R,S)-8c
and (R,S)-9c (0.162 g, quantitative yield) as a colourless solid; IR
1
(cm-1): 2922, 1720, 1342, 1160; H NMR (400 MHz, CDCl3) dH
1
2.11 (s, 3H, 9a), 2.12 (s, 3H, 8a), 2.38 (s, 6H, 8a + 9a), 2.96–3.10
(m, 2H, 8a), 3.01–3.10 (m, 1H, 9a), 3.13 (dd, J = 14.0/6.2 Hz,
1H, 9a), 3.68 (s, 3H, 9a), 3.71 (s, 3H, 8a), 4.17 (t, J = 7.2 Hz, 2H,
8a + 9a), 4.31–4.45 (m, 4H, 8a + 9a), 4.46–4.64 (m, 10H, 8a + 9a),
5.22–5.30 (m, 2H, 8a + 9a), 6.68 (s, 1H, 8a), 6.75 (s, 1H, 8a), 6.88
(d, J = 8.0 Hz, 1H, 9a), 6.91 (d, J = 8.0 Hz, 1H, 9a), 7.25–7.33
(m, 8H, 8a + 9a), 7.36–7.43 (m, 4H, 8a + 9a), 7.50–7.57 (m,
4H, 8a + 9a), 7.73–7.79 (m, 8H, 8a + 9a); 13C NMR (100 MHz,
CDCl3) dC 15.3, 18.6, 21.4, 35.4, 37.9, 47.0, 47.1, 52.3, 52.4, 52.8,
53.4, 53.8, 53.9, 54.2, 54.7, 66.8, 66.9, 119.8, 119.9, 120.6, 124.9,
127.0, 127.5, 127.7, 127.8, 129.5, 129.8, 130.8, 132.8, 133.5, 133.6,
133.7, 134.7, 135.9, 136.1, 136.2, 141.2, 143.6, 143.7, 155.4, 155.5,
171.8, 172.1; HRMS calcd. for [C35H34N2O6S + Na]+: 633.2030.
Found: 633.2004
(ATR) n (cm-1): 2952, 1728, 1247; H NMR (400 MHz, CDCl3)
dH 2.20 (s, 6H, 8c + 9c), 2.97–3.08 (m, 2H 8c + 1H 9c), 3.14 (dd,
J = 14.0/6.4 Hz, 1H, 9c), 3.48 (s, 2H, 8c), 3.53 (s, 2H, 9c), 3.56
(s, 2H, 8c), 3.57 (s, 2H, 9c), 3.69 (s, 3H, 9c), 3.72 (s, 3H, 8c), 3.74
(s, 12H, 8c + 9c), 4.18 (t, J = 7.2 Hz, 1H, 9c), 4.21 (t, J = 7.2 Hz,
1H, 8c), 4.30–4.45 (m, 4H, 8c + 9c), 4.55–4.67 (m, 2H, 8c + 9c),
5.24–5.29 (m, 2H, 8c + 9c), 6.73 (s, 1H, 8c), 6.76 (s, 1H, 8c), 6.87
(d, J = 7.6 Hz, 1H, 9c), 6.93 (d, J = 7.6 Hz, 1H, 9c), 7.27–7.33
(m, 4H, 8c + 9c), 7.39 (t, J = 7.6 Hz, 4H, 8c + 9c), 7.53–7.60
(m, 4H, 8c + 9c), 7.75 (d, J = 7.6 Hz, 4H, 8c + 9c); 13C NMR
(100 MHz, CDCl3) dC 15.5, 19.0, 35.6, 38.0, 39.1, 40.0, 40.6,
47.0, 47.1, 52.2, 52.3, 52.9, 54.2, 54.8, 59.7, 67.0, 119.9, 121.4,
122.3, 125.0, 127.0, 127.7, 128.9, 129.1, 132.5, 132.6, 133.8, 134.8,
137.7, 138.5, 139.7, 140.1, 141.2, 143.7, 143.8, 155.6, 172.0, 172.1,
172.2, 172.4; ESI-MS (m/z) 594 [M + Na]+; HRMS calcd. for
[C33H33NO8 + Na]+: 594.2098. Found: 594.2097.
(R,S)-2-(((9H -Fluoren-9-yl)methoxy)carbonylamino)-3-(7-
methyl-4-(2-propyne-4-ol)-2-tosylisoindolin-5-yl)propanoic
acid
methyl ester (R,S)-8b, and (R,S)-2-(((9H-fluoren-9-yl)methoxy)-
carbonylamino)-3-(4-methyl-7-(2-propyne-4-ol)-2-tosylisoindolin-
5-yl)propanoic acid methyl ester, (R,S)-9b, [(R,S)-8b/(R,S)-
9b = 1.9:1 at reflux and (R,S)-8b/(R,S)-9b = 3.1:1 at room
temperature] were purified by column chromatography on silica
gel using mixtures of hexanes/ethyl acetate of increasing polarity
(9/1 to 7/3) as the eluent to afford (R,S)-8b and (R,S)-9b (0.110 g,
100% yield) as a colourless solid. Regioisomers (R,S)-8b and
(R,S)-9b could be separated by column chromatography on silica
gel using mixtures of hexanes/ethyl acetate of increasing polarity
(9/1 to 7/3) as the eluent. (R,S)-8b: mp 69–70 ◦C; IR (ATR)
n (cm-1): 3366, 2952, 1719, 1340, 1160; 1H NMR (400 MHz,
CDCl3) dH 2.09 (s, 3H), 2.38 (s, 3H), 2.74 (br abs, 1H), 2.97 (dd,
J = 14.0/6.8 Hz, 1H), 3.14 (dd, J = 14.0/6.2 Hz, 1H), 3.70 (s,
3H), 4.10–4.15 (m, 1H), 4.32 (d, J = 6.8 Hz, 2H), 4.45 (s, 2H),
4.49 (s, 2H), 4.52–4.60 (m, 3H), 5.42 (d, J = 8.4 Hz, 1H), 6.94 (s,
1H), 7.24–7.31 (m, 4H), 7.36–7.42 (m, 2H), 7.50–7.54 (m, 2H),
7.72–7.78 (m, 4H); 13C NMR (100 MHz, CDCl3) dC 15.2, 21.4,
35.2, 46.9, 52.4, 52.8, 53.2, 54.3, 62.5, 66.9, 119.9, 124.8, 124.9,
126.9, 127.5, 127.7, 128.4, 129.8, 130.6, 132.6, 132.9, 133.6, 134.1,
136.5, 141.1, 141.2, 143.6, 143.7, 155.6, 172.1; HRMS calcd. for
[C36H36N2O7S + Na]+: 663.2135. Found: 663.2126.; (R,S)-9b:
Characterization data of dansyl- and dabsyl-containing amino
acids 10 and 11
(R,S)-2-(((9H -Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-
dimethyl-2-(5-(dimethylamino)naphthalene-1-sulfonyl)indolin-5-
yl)propanoic acid, (R,S)-10a, was purified by column chromatogra-
phy on silica gel using mixtures of dichloromethane/ethyl acetate
(20/1) as the eluent to affor◦d (R,S)-10a (0.040 g, 97% yield) as
a yellow solid; mp 112–113 C; IR (ATR) n (cm-1): 3344, 2921,
1
1719, 1327, 1145; H NMR (400 MHz, CDCl3) dH 2.03 (s, 3H),
2.04 (s, 3H), 2.86 (s, 6H), 2.94 (dd, J = 14.0/6.8 Hz, 1H), 3.18
(dd, J = 14.0/6.8 Hz, 1H), 4.08–4.16 (m, 1H), 4.30–4.34 (m, 2H),
4.54 (dt, J = 8.4/6.8 Hz, 1H), 4.64 (s, 4H), 5.26 (d, J = 8.4 Hz,
1H), 6.80 (s, 1H), 7.16 (d, J = 7.6 Hz, 1H), 7.20–7.27 (m, 2H),
7.29–7.38 (m, 2H), 7.46–7.57 (m, 4H), 7.67–7.73 (m, 2H), 8.22 (d,
J = 7.2 Hz, 1H), 8.51–8.57 (m, 2H); 13C NMR (100 MHz, CDCl3)
dC 15.1, 18.2, 34.9, 45.4, 47.0, 53.2, 53.6, 54.6, 67.2, 115.4, 119.8,
120.0, 123.3, 124.9, 127.0, 127.8, 128.2, 129.4, 129.7, 130.2, 130.5,
130.7, 130.9, 133.9, 134.0, 135.9, 141.2, 143.6, 143.7, 151.6, 155.9,
175.4; HRMS calcd. for [C40H39N3O6S + H]+: 690.2632. Found:
690.2650.
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-
dimethyl-2-(5-(dimethylamino)naphthalene-1-sulfonyl)indolin-5-
yl)propanoic acid methyl ester, (R,S)-10b, was purified by
column chromatography on silica gel using mixtures of
dichloromethane/hexanes (3/1 to 5/1) as the eluent to afford
(R,S)-10b (0.080 g, 98% yield) as a bright yellow solid; mp
◦
mp 88–89 C; IR (ATR) n (cm-1): 3366, 2952, 1719, 1340, 1160;
1H NMR (400 MHz, CDCl3) dH 2.10 (s, 3H), 2.37 (s, 3H), 2.61
(br abs, 1H), 2.97 (dd, J = 13.8/8.8 Hz, 1H), 3.18 (dd, J =
13.8/5.2 Hz, 1H), 3.74 (s, 3H), 4.04–4.10 (m, 1H), 4.24–4.28 (m,
2H), 4.48 (s, 2H), 4.54–4.59 (m, 3H), 4.71 (s, 2H), 6.01 (d, J =
8.0 Hz, 1H), 6.84 (s, 1H), 7.24–7.31 (m, 4H), 7.39 (t, J = 7.4 Hz,
5026 | Org. Biomol. Chem., 2009, 7, 5020–5027
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
128–129 ◦C; IR (ATR) n (cm-1): 2922, 1720, 1328, 1145; 1H NMR
(400 MHz, CDCl3) dH 2.05 (s, 3H), 2.08 (s, 3H), 2.87 (s, 6H), 2.96
(dd, J = 14.0/6.4 Hz, 1H), 3.10 (dd, J = 14.0/6.4 Hz, 1H), 3.68
(s, 3H), 4.15 (t, J = 6.8 Hz, 1H), 4.35 (d, J = 6.8 Hz, 2H), 4.54 (dt,
J = 8.4/6.4 Hz, 1H), 4.66 (s, 4H), 5.23 (d, J = 8.4 Hz, 1H), 6.74
(s, 1H), 7.16 (d, J = 7.6 Hz, 1H), 7.23–7.30 (m, 2H), 7.33–7.40 (m,
2H), 7.48–7.59 (m, 4H), 7.70–7.75 (m, 2H), 8.23 (d, J = 7.6 Hz,
1H), 8.52–8.58 (m, 2H); 13C NMR (100 MHz, CDCl3) dC 15.0,
18.2, 35.4, 45.4, 47.1, 52.4, 53.2, 53.6, 54.4, 67.0, 115.3, 119.7,
120.0, 123.2, 125.0, 127.0, 127.7, 128.2, 129.4, 129.7, 130.2, 130.5,
130.6, 130.7, 133.9, 134.1, 135.9, 141.3, 143.6, 143.7, 151.7, 155.6,
172.2; HRMS calcd. for [C41H41N3O6S + H]+: 704.2789. Found:
704.2755.
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-
dimethyl-2-(4-dimethylaminoazobenzene-4¢-sulfonyl)isoindolin-5-
yl))propanoic acid, (R,S)-11a, was purified by column chro-
matography on silica gel using mixtures of dichloromethane/
hexanes/ethyl acetate of increasing polarity (5/1/0 to 2/0/1) as
the eluent to◦afford (R,S)-11a (0.091 g, 98% yield) as a red solid;
mp 218–219 C; IR (ATR) n (cm-1): 3380, 2923, 1707, 1587, 1339,
1155; 1H NMR (400 MHz, CDCl3) dH 2.04 (br s, 6H), 2.95–3.02
(m, 1H), 3.08–3.18 (m, 1H), 3.10 (s, 6H), 4.10–4.16 (m, 1H), 4.31–
4.35 (m, 2H), 4.48–4.58 (m, 4H), 5.09–5.13 (m, 1H), 5.28 (d, J =
8.4 Hz, 1H), 6.69 (d, J = 9.0 Hz, 2H), 6.78 (s, 1H), 7.23–7.30 (m,
2H), 7.34–7.40 (m, 2H), 7.48–7.54 (m, 2H), 7.70–7.75 (m, 2H),
7.84–7.90 (m, 4H), 7.96 (d, J = 8.4 Hz, 2H); HRMS calcd. for
[C42H41N5O6S + H]+: 744.2850. Found: 744.2827.
Esseveldt, F.L. van Delft, H.E. Schoemaker, R.H. Blaauw and F.P.J.T.
Rutjes, Org. Biomol. Chem., 2005, 3, 3435; R. Galeazzi, G. Mobbili and
M. Orena, Curr. Org. Chem., 2004, 8, 1799; F.P.J.T. Rutjes, L.B. Wolf
and H.E. Schoemaker, J. Chem. Soc., Perkin Trans. 1, 2000, 4197; F.J.
Sardina and H. Rapoport, Chem. Rev., 1996, 96, 1825; R.M. Williams
in Synthesis of Optically Active a-Amino Acids, Pergamon, Oxford,
1989.
2 G. Lelais and D. Seebach, Biopolymers (Pept. Sci.), 2004, 76, 206;
H. Ishida, M. Kyakuno and S. Oishi, Biopolymers (Pept. Sci.), 2004,
76, 69; A.J. Souers and J.A. Ellman, Tetrahedron, 2001, 57, 7431; V.J.
Hruby, G. Li, C. Haskell-Luevano and M. Shenderovich, Biopolymers,
1997, 43, 219; S. Hanessian, G. McNaughton-Smith, H.-G. Lombart
and W.D. Lubell, Tetrahedron, 1997, 53, 12789.
3 For recent reviews, see: S. Saito and Y. Yamamoto, Chem. Rev., 2000,
100, 2901; J.A. Varela and C. Saa´, Chem. Rev., 2003, 103, 3787; Y.
Yamamoto, Curr. Org. Chem., 2005, 9, 503; S. Kotha, E. Brahmachary
and K. Lahiri, Eur. J. Org. Chem., 2005, 4741; P.R. Chopade and J.
Louie, Adv. Synth. Catal., 2006, 348, 2307; V. Gandon, C. Aubert and
M. Malacria, Chem. Commun., 2006, 2209; B. Heller and M. Hapke,
Chem. Soc. Rev., 2007, 36, 1085; N. Agenet, O. Buisine, F. Slowinski,
V. Gandon, C. Aubert and M. Malacria, Org. React., 2007, 68, 1; J.A.
Varela and C. Saa´, Synlett, 2008, 2571; T. Shibata and K. Tsuchikama,
Org. Biomol. Chem., 2008, 6, 1317; B.R. Galan and T. Rovis, Angew.
Chem., Int. Ed., 2009, 48, 2830.
4 S. Kotha and E. Brahmachary, Tetrahedron Lett., 1997, 38, 3561;
S. Kotha, K. Mohanraja and S. Durani, Chem. Commun., 2000,
1909; S. Kotha and E. Brahmachary, Bioorg. Med. Chem., 2002, 10,
2291.
5 S. Kotha and N. Sreenivasachary, Bioorg. Med. Chem. Lett., 2000, 10,
1413; S. Kotha and N. Sreenivasachary, Eur. J. Org. Chem., 2001, 3375;
S. Kotha and S. Banerjee, Synthesis, 2007, 1015.
6 G. Shchetnikov, S.N. Osipov, C. Bruneau and P.H. Dixneuf, Synlett,
2008, 578.
7 K. Tanaka, M. Takahashi, H Imase, T. Osaka, K. Noguchi and
M Hirano, Tetrahedron, 2008, 64, 6289.
(R,S)-2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-3-(4,7-
dimethyl-2-(4-dimethylaminoazobenzene-4¢-sulfonyl)isoindolin-5-
yl))propanoic acid methyl ester, (R,S)-11b, was purified by
column chromatography on silica gel using mixtures of
dichloromethane/hexanes of increasing polarity (3/1 to 5/1) as
the eluent to afford (R,S)-11b (0.085 g, 97% yield) as an orange
solid; mp 206–207 ◦C; IR (ATR) n (cm-1): 2922, 1605, 1344, 1138;
1H NMR (300 MHz, CDCl3) dH 2.07 (s, 3H), 2.08 (s, 3H), 2.96 (dd,
J = 14.1/6.6 Hz, 1H), 3.05–3.14 (m, 1H), 3.09 (s, 6H), 3.67 (s, 3H),
4.14 (t, J = 7.0 Hz, 1H), 4.35 (d, J = 7.0 Hz, 2H), 4.49–4.61 (m,
5H), 5.27 (d, J = 8.1 Hz, 1H), 6.69–6.76 (m, 3H), 7.23–7.30 (m,
2H), 7.34–7.42 (m, 2H), 7.49–7.56 (m, 2H), 7.73 (d, J = 7.5 Hz,
2H), 7.86 (d, J = 9.0 Hz, 2H), 7.92 (d, J = 8.7 Hz, 2H), 7.99 (d, J =
8.7 Hz, 2H); 13C NMR (75 MHz, CDCl3) dC 15.0, 18.1, 35.2, 40.2,
46.9, 52.3, 53.4, 53.7, 54.3, 66.8, 111.3, 119.9, 122.6, 124.9, 125.6,
126.9, 127.6, 128.3, 128.4, 129.5, 130.6, 133.6, 133.9, 135.6, 136.0,
141.2, 143.4, 143.5, 143.6, 153.0, 155.5, 155.7, 172.1; HRMS calcd.
for [C43H43N5O6S + H]+: 758.3007. Found: 758.2999.
8 A. Pla-Quintana, A. Roglans, A. Torrent, M. Moreno-Man˜as and
J. Benet-Buchholz, Organometallics, 2004, 23, 2762; A. Torrent, I.
Gonza´lez, A. Pla-Quintana, A. Roglans, M. Moreno-Man˜as, T. Parella
and J. Benet-Buchholz, J. Org. Chem., 2005, 70, 2033; I. Gonza´lez,
S. Bouquillon, A. Roglans and J. Muzart, Tetrahedron Lett., 2007,
48, 6425; S. Brun, L. Garcia, I. Gonza´lez, A. Torrent, A. Dachs,
A. Pla-Quintana, T. Parella and A. Roglans, Chem. Commun., 2008,
4339.
9 K. Tanaka, Synlett, 2007, 1977.
10 No racemization occurred in the methylation reaction as seen by HPLC
analysis: B.-C. Chen, A.P. Skoumbourdis, P. Guo, M.S. Bednarz, O.R.
Kocy, J.E. Sundeen and G.D. Vite, J. Org. Chem., 1999, 64, 9294.
11 M.S.T. Gonc¸alves, Chem. Rev., 2009, 109, 190.
12 Y.-H. Li, L.-M. Chan, L. Tyer, R.T. Moody, C.M. Himel and D.M.
Hercules, J. Am. Chem. Soc., 1975, 97, 3118.
13 T. Hohsaka, N. Muranaka, C. Komiyama, K. Matsui, S. Takaura, R.
Abe, H. Murakami and M Sisido, FEBS Lett., 2004, 560, 173.
14 J.-K. Lin and J.-Y. Chan, Anal. Chem., 1975, 47, 1634.
15 X. Tang and I.J. Dmochowski, Org. Lett., 2005, 7, 279.
16 M. Ternon, J.J. D´ıaz-Mocho´n, A. Belsom and M. Bradley, Tetrahedron,
2004, 60, 8721.
17 R.P. Haugland, M.T.Z. Spence, I.D. Johnson and A. Basey, The
Handbook: A Guide to Fluorescent Probes and Labeling Technologies,
2005, 10th ed., Molecular Probes, Eugene, OR.
18 M. Nishida, H. Shiga and M. Mori, J. Org. Chem., 1998, 63,
Acknowledgements
8606.
19 P. Nova´k, R. Pohl, M. Kotora and M. Hocek, Org. Lett., 2006, 8,
2051.
20 I.M. Wyzlic, W. Tjarks, A.H. Soloway, D.J. Perkins, M. Burgos and
K.P. O’Reilly, Inorg. Chem., 1996, 35, 4541.
Financial support from MEC (CTQ2005-04968) and MICINN
(CTQ2008-05409) of Spain, “Generalitat de Catalunya” (2009-
SGR-637) and University of Girona (grant to L.G.) is acknowl-
edged. We also thank the Research Technical Services of the UdG
for analytical data and Johnson and Matthey for a loan of RhCl3.
21 S. Bhar, S.K. Chandhuri, S.G. Sahu and C. Panja, Tetrahedron, 2001,
57, 9011.
22 K. Tanaka, K. Takeishi and K. Noguchi, J. Am. Chem. Soc., 2006, 128,
4586.
23 S. Apte, B. Radetich, S. Shin and T.V. RajanBabu, Org. Lett., 2004, 6,
4053.
Notes and references
24 S. Kezuka, S. Tanaka, T. Ohe, Y. Nakaya and R. Takeuchi, J. Org.
1 D. Haldar, Curr. Org. Synth., 2008, 5, 61; A. Perdih and M.S. Dolenc,
Curr. Org. Chem., 2007, 11, 801; J. Kaiser, S.S. Kinderman, B.C.J. van
Chem., 2006, 71, 543.
This journal is
The Royal Society of Chemistry 2009
Org. Biomol. Chem., 2009, 7, 5020–5027 | 5027
©