Sandwich structure of a ruthenium porphyrin and an amino acid hydrazide for probing molecular chirality by circular dichroism

Article abstract of DOI:10.1016/j.tetlet.2011.05.081

Owing to the strong Lewis acidity of ruthenium porphyrins, a commercial carbonyl ruthenium porphyrin and an amino acid hydrazide can assemble into a sandwich structure. The nature of such a structure is diagnostic of the absolute configuration of the amino acid by circular dichroism.

Full text of DOI:10.1016/j.tetlet.2011.05.081

Tetrahedron Letters 52 (2011) 3987–3991
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Tetrahedron Letters
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Sandwich structure of a ruthenium porphyrin and an amino acid hydrazide for
probing molecular chirality by circular dichroism
⇑
Qing-Feng Liang, Juan-Juan Liu, Jian Chen
The Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, 152 Luoyu Road, Wuhan 430079, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Owing to the strong Lewis acidity of ruthenium porphyrins, a commercial carbonyl ruthenium porphyrin
and an amino acid hydrazide can assemble into a sandwich structure. The nature of such a structure is
diagnostic of the absolute configuration of the amino acid by circular dichroism.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 10 January 2011
Revised 8 March 2011
Accepted 17 May 2011
Available online 24 May 2011
Keywords:
Circular Dichroism
Absolute configuration
Amino acid
Porphyrin
Sandwich structure
Porphyrins, a type of unique aromatic macrocyclic compound,
are considered to be natural chromophores. Nakanishi’s group
has utilized a functional porphyrin derivative as a chromophore
in exciton-chirality CD approaches and successfully determined
the absolute configurations of different chiral substrates and some
important natural products.1 They utilized non-covalent (hydrogen
nation. Because there is a carbonyl coordinating at the axial posi-
tion, an amino group could only coordinate at the other axial
position of the Ru porphyrin.5 We presumed that the binding
(ruthenium-amine coordination) was strong enough so that two
Ru porphyrins could significantly coordinate with the two amino
groups of a diamino compound in solution. In that case, two Ru
porphyrins and a chiral diamine will assemble into a sandwich
structure. Such a sandwich structure with a preferential chiral
twist in the porphyrin–porphyrin arrangement would give
an exciton-coupled CD signal, which represents the absolute
configuration of a chiral diamine. Here we describe a new approach
to assemble a sandwich structure with two carbonyl ruthenium
porphyrins and a hydrazide, which is diagnostic of the absolute
configuration of the amino acid by circular dichroism.
bonds,
p–p, or non-bonded) interactions between chiral com-
pounds such as carboxylic acids or amino acids and achiral metal-
lated mono-porphyrins to form a type of mono-porphyrin-based
complex which exhibited a weak to moderate CD response whose
sign is related to the absolute configuration of the substrate.2 To
avoid the inconvenience of derivatizing analytes with Zn and Mg
dimeric porphyrin tweezers have been developed that are capable
of binding to several classes of bifunctional (diamines, amino
alcohols, amino acids) and monofunctional (secondary alcohols,
primary and secondary amines, and carboxylic acids) chiral com-
pounds, including many natural products with complex structures3
through zinc/magnesium-amine coordination. This binding forms
a 1:1 supramolecular host–guest complex with preferred interpo-
rphyrin helicity which represents the chirality of the guest. The in-
tense bisignate CD signals present in the Soret porphyrin region.
This type of CD-active molecular chirality probe requires less mass
We studied the binding properties of Ru porphyrins and amino
compounds. Using excess valine methyl ester (H-L-Val-OMe)
mixed with Ru porphyrin ([RuII(TDCPP)CO], Fig. 1), the free amino
group of Val coordinated to the unoccupied side of the Ru porphy-
rin to form a complex. The complex can be precipitated with meth-
anol from a solution of CH2Cl2. The 1H NMR spectra indicated that
the bonding of the amino group and Ru porphyrin was sufficient
and no dissociation was observed. Moreover, we have tested the
association constant between ruthenium porphyrin and amine
of analytes: about 1–2
lg of tweezer and several micrograms of
substrate.3k
(H-
L
-Val-OMe) by UV titration and determined a Ka of 1.70 Â
We found that ruthenium porphyrins are strong Lewis acids4
and are able to bind amines strongly via ruthenium-amine coordi-
107 MÀ1 (Fig. 2), which is stronger than that of the valine derivative
and Zn porphyrin (0.5–2.5 Â 104 MÀ1 6
)
or Mg porphyrin.7
Amino acids are important biological active small molecules.
We tried to form a sandwich structure with Ru porphyrin and ami-
no acids using a convenient protocol to derivatize amino acids with
⇑
Corresponding author.
E-mail address: jianc@mail.ccnu.edu.cn (J. Chen).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.05.081

3988
Q.-F. Liang et al. / Tetrahedron Letters 52 (2011) 3987–3991
Figure 1. (a) 1H NMR of H- -Val-OMe 2. (b) 1H NMR of Ru porphyrin/H- -Val-OMe complex, which shows [RuII(TDCPP)CO]: H-
L L L-Val-OMe = 1: 1 without obvious dissociation
in the solution (CDCl3).
Figure 2. (a) UV–vis spectra with different equivalents of conjugate H-
change in absorption at k = 412 nm leads to the estimation of Ka.
L
-Val-OMe added to [RuII(TDCPP)CO] (4.0 Â 10À6 mol/L in CH2Cl2). (b) Non-linear least square fit of the
hydrazine into diamine structures. As shown in Scheme 1, L-Valine
4 was converted into hydrazide 6 via hydrazinolysis of valine
SOCl2/CH3OH
70 oC, 2 h, 99%
methyl ester. When 1 eq (equivalent) Ru porphyrin was added into
OH
OMe
H2N
H2N
the diamine of
88 were primarily obtained. When another 1 eq of Ru porphyrin
was added, the sandwich structure of -Valine complex 9 was
L
-Valine and monitored by 1H NMR, complex 7 and
4
5
O
O
L
NH2NH2 H2O
MeOH
2 eq
[RuII(TDCPP)CO]
CH2Cl2
NHNH2
H2N
r.t., 12 h, 79%
6
O
NH2
NH
CO
Ru
NH2
H2N
NH
OC
Ru
+
O
H2N
7
8
O
1 eq
H2
N
[RuII(TDCPP)CO]
CH2Cl2
OC Ru
HN
Ru
N
CO
H2
O
9
Figure 3. 1H NMR of the guest of sandwich 9. ⁄signals from impurity. See
Supplementary data for the full spectrum and the analysis of the active hydrogens
of sandwich 9.
Scheme 1. Derivatization of L-valine and assembly of the sandwich structure with
[RuII(TDCPP)CO].

Q.-F. Liang et al. / Tetrahedron Letters 52 (2011) 3987–3991
3989
The sandwich with two achiral porphyrins could be induced
into a chiral twist by a chiral guest and observed by Circular
Dichroism. The solution of complex 9 in CH2Cl2 was diluted to
about 1–10 Â 10À5 mol/L, and CD spectrum was recorded. The
sandwich structure 9 gives rise to a coupled CD in CH2Cl2. The exci-
ton CD couplet was excited in the Soret band of porphyrin, kext
412 nm (
D
e
+8) and 405 nm (
D
e
À7), A À15 (Fig. 4, curve A). The
result indicated that the two porphyrins in the sandwich structure
were arranged into a chiral twist and the preferred chiral confor-
mation of the porphyrins twist reflected the chirality of the guest.
Using the same protocol as for valine, the enantiomers of phenyl-
alanine (Phe) were derivatized and assembled with free porphyrins
into sandwich structures. The symmetric CD curves were obtained
(Fig. 4, curves B and C). The absolute sense of sandwich can be
rationalized with energetically favored conformer (Fig. 4 and
ref.3k,10).
To test the feasibility of this approach, a series of chiral amino
acids were analyzed. The amino acids (including phenylglycine)
were derivatized as L-Val to obtain the diamine compounds. Two
eq Ru porphyrin were added directly, then the hydrazides of the
amino acids were coupled with Ru porphyrin to form the sandwich
structures. The sandwich complexes gave rise to weak to moderate
exciton-coupled CD signals and the signs were in agreement with
the predicted signs3 (Fig. 4, Table 1).
Figure 4. Complex 10 can adopt two conformations: conformer I with the L group
projecting out of the sandwich and conformer II with the S group projecting out of
the sandwich. The positive sign of the couple is in agreement with the energetically
favored conformer I.3k CD spectra were presented for sandwich 9 (curve A) and for
Because some Ru porphyrins or base free porphyrins are com-
mercially available,11 including [RuII(TPP)CO], H2TDCPP, H2TMP,
and H2F20-TPP (Fig. 5). Three other Ru porphyrins, [RuII(TPP)CO],
[RuII(TMP)CO], and [RuII(F20-TPP)CO] were investigated using the
derivatives of L-/D-phenylalanine (curves B, C).
same protocol as for [RuII(TDCPP)CO]. The
L-isoleucine derivative
formed (the sandwich structure can assemble directly when 2 eq
Ru porphyrin are mixed with hydrazide 6). The chemical shifts of
the hydrogens of the guest shift up-field significantly and resonate
at d À7 to À0.5 ppm with good resolution (Fig. 3). Because of the
shielding from the porphyrin, the signals of protons in the
sandwich structure present more upfield comparing to those of
monoamine coordinated to Ru porphyrin (Fig. 1).9
was used as the guest and all of the assembled host–guest com-
plexes gave similar exciton-coupled CD spectra (Table 1, entry 6,
9–11).
In summary, we have successfully assembled sandwich struc-
tures with free Ru porphyrins and amino acid hydrazides. Exci-
ton-coupled CD spectra are recorded by testing the sandwich
Table 1
CD data of derivatized amino acids with Ru porphyrins in CH2Cl2
Entry
1
Porphyrins (Host)
Parent amino acids (Guest)
Predicted sign
(+)
k nm (
D
e
)
A
H
H3C
H3C
COOH
[RuII(TDCPP)CO]
410 (+47) 403 (À19)
413 (À29) 400 (+9)
+32
NH2
11
12
H
COOH
NH2
2
3
[RuII(TDCPP)CO]
[RuII(TDCPP)CO]
(À)
À38
H
COOH
COOH
(+)
412 (+8) 405 (À7)
+15
NH2
13
Ph
H
4
5
6
7
[RuII(TDCPP)CO]
[RuII(TDCPP)CO]
[RuII(TDCPP)CO]
[RuII(TDCPP)CO]
(+)
(+)
(+)
(+)
412 (+5) 405 (À7)
413 (+7) 404 (À5)
411 (+12) 406 (À 6)
411 (+18) 407 (À8)
+12
+12
+18
+26
NH2
14
H
COOH
NH2
15
H
COOH
NH2
16
H
COOH
NH2
17
(continued on next page)

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Q.-F. Liang et al. / Tetrahedron Letters 52 (2011) 3987–3991
Table 1 (continued)
Entry
Porphyrins (Host)
[RuII(TDCPP)CO]
Parent amino acids (Guest)
Predicted sign
k nm (
D
e
)
A
H
COOH
8
(À)
412 (À17) 404 (+5)
417 (+ 7) 404 (À6)
413 (+14) 403 (À6)
405 (+ 5) 397 (À3)
À22
NH2
18
H
COOH
9
[RuII(TPP)CO]
(+)
(+)
(+)
+13
+20
+8
NH2
16
H
COOH
10
11
[RuII(TMP)CO]
[RuII(F20-TPP)CO]
NH2
16
H
COOH
NH2
16
References and notes
1. (a) Berova, N.; Pescitelli, G.; Petrovic, A. G.; Proni, G. Chem. Commun. 2009,
5958; (b) Hong, J.; Huang, X.; Nakanishi, K.; Berova, N. Tetrahedron Lett. 1999,
40, 7645; (c) Rickman, B. H.; Matile, S.; Nakanishi, K.; Berova, N. Tetrahedron
1998, 54, 5041; (d) Matile, S.; Berova, N.; Nakanishi, K.; Fleischhauer, J.; Woody,
R. W. J. Am. Chem. Soc. 1996, 118, 5198.
2. (a) Borovkov, V. V.; Inoue, Y. In Supramolecular Chirality ‘‘Topics in Current
Chemistry’’; Crego-Calama, M., Reinhoudt, D. N., Eds.; Springer: Berlin, 2006; pp
89–146. Vol. 265; (b) Tsukube, H.; Shinoda, S. Chem. Rev. 2002, 102, 2389; (c)
Huang, X.; Nakanishi, K.; Berova, N. Chirality 2000, 12, 237; (d) Ogoshi, H.;
Mizutani, T. Acc. Chem. Res. 1998, 31, 81; (e) James, T. D.; Sandanayake, K. R. A.
S.; Shinkai, S. Angew. Chem. Int. Ed. 1996, 35, 1910.
Cl
Cl
Cl
Cl
N
HN
N
N
N
N
Ru
NH
N
CO
Cl
Cl
Cl
Cl
3. (a) Chen, Y.; Petrovic, A. G.; Roje, M.; Pescitelli, G.; Kayser, M. M.; Yang, Y.;
Berova, N.; Proni, G. Chirality 2010, 22, 140; (b) Petrovic, A. G.; Chen, Y.;
Pescitelli, G.; Berova, N.; Proni, G. Chirality 2010, 22, 129; (c) Ishii, H.; Chen, Y.;
Miller, R. A.; Karady, S.; Nakanishi, K.; Berova, N. Chirality 2005, 17, 305; (d) Van
Klink, J. W.; Baek, S.-H.; Barlow, A. J.; Ishii, H.; Nakanishi, K.; Berova, N.; Perry,
N. B.; Weavers, R. T. Chirality 2004, 16, 549; (e) Huang, X.; Fujioka, N.; Pescitelli,
G.; Koehn, F. E.; Williamson, R. T.; Nakanishi, K.; Berova, N. J. Am. Chem. Soc.
2002, 124, 10320; (f) Yang, Q.; Olmsted, C.; Borhan, B. Org. Lett. 2002, 4, 3423;
(g) Proni, G.; Pescitelli, G.; Huang, X.; Quraishi, N. Q.; Nakanishi, K.; Berova, N.
Chem. Commun. 2002, 1590; (h) Kurtán, T.; Nesnas, N.; Li, Y.-Q.; Huang, X.;
Nakanishi, K.; Berova, N. J. Am. Chem. Soc. 2001, 123, 5962; (i) Borovkov, V. V.;
Yamamoto, N.; Lintuluoto, J. M.; Tanaka, T.; Inoue, Y. Chirality 2001, 13, 329; (j)
Huang, X. F.; Borhan, B.; Rickman, B. H.; Nakanishi, K.; Berova, N. Chem. Eur. J.
2000, 6, 216; (k) Huang, X.; Rickman, B. H.; Borhan, B.; Berova, N.; Nakanishi, K.
J. Am. Chem. Soc. 1998, 120, 6185.
20
19
H2TDCPP
[RuII(TPP)CO]
F
F
F
F
F
F
F
F
F
F
F
F
F
N
HN
N
N
HN
N
F
F
NH
NH
F
F
F
F
4. Chen, J.; Che, C.-M. Angew. Chem. Int. Ed. 2004, 43, 4950.
5. (a) Samachetty, H. D.; Branda, N. R. Chem. Commun. 2005, 2840; (b) Fantauzzi,
S.; Gallo, E.; Caselli, A.; Ragaini, F.; Macchi, P.; Casati, N.; Cenini, S.
Organometallics 2005, 24, 4710; (c) McCleverty, J. A.; Navas Badiola, J. A.;
Ward, M. D. J. Chem. Soc., Dalton Trans. 1994, 2415.
6. (a) Kuroda, Y.; Kato, Y.; Higashioji, T.; Hasegawa, J.; Kawanami, S.; Takahashi,
M.; Shiraishi, N.; Tanabe, K.; Ogosh, H. J. Am. Chem. Soc. 1995, 117, 10950; (b)
Mizutani, T.; Ema, T.; Tomita, T.; Kuroda, Y.; Ogoshi, H. J. Am. Chem. Soc. 1994,
116, 4240.
F
21
H2TMP
22
H2F20-TPP
Figure 5. Commercial porphyrins and Ru porphyrin.
7. Based on bidentate coordinating, the association constant of amino and Mg
dimeric porphyrin tweezers is about 1.13 Â 106 MÀ1
. Ref.: Proni, G.;
Pescitelli, G.; Huang, X.; Nakanishi, K.; Berova, N. J. Am. Chem. Soc. 2003,
125, 12914.
structure and can be used to analyze the absolute configuration of
the amino acid.12 The advantage of this approach is that commer-
cial Ru porphyrins/base free porphyrins can be used as hosts/host
precursors directly.
8. The N of amide is almost neutral, so the Ru porphyrin is prior to coordinate
basic amino.
9. Morice, C.; Maux, P. L.; Simonneaux, G.; Toupet, L. J. Chem. Soc., Dalton trans.
1998, 4165.
10. Gonnella, N. C.; Nakanishi, K.; Martin, V. S; Sharpless, K. B. J. Am. Chem. Soc.
1982, 104, 3775.
Acknowledgments
11. The porphyrins can be purchased from Acros, Alfa Aesar, Aldrich, and TCI, et al.
12. Experimental procedure. Preparation of [RuII(TDCPP)CO], [RuII(TMP)CO] and
[RuII(F20-TPP)CO]: 0.3 mmol Ru3(CO)12
, 0.2 mmol base free porphyrin, and
We are grateful for financial support by the National Natural
Science Foundation of China (No. 20802023), Specialized
Research Fund for the Doctoral Program of Higher Education
(200805111015) and in part by the Program for Changjiang Schol-
ars and Innovative Research Team in University (No. IRT0953).
25 mL 1,2,4-trichlorobenzene were mixed in 50 mL flask. After degassed in
vacuum and protected with Ar, the mixture was heated at 195–200 °C (the
temperature of oil bath) for 4–7 h. The reaction solution was diluted with
75 mL petroleum ether (PE) and was loaded on
a neutral Al2O3 flash
chromatographer column. Washed with PE and CH2Cl2, 1,2,4-trichloro-
benzene and product were collected respectively.
[RuII(TDCPP)CO] 1. Yield: 99%; 1H NMR (300 MHz, CDCl3): d 8.49 (s, 8H), 7.74–
7.79 (m, 8H), 7.66 (dd, 4H, J = 7.8, 7.8 Hz). IR (KBr): 1951 cmÀ1; MS (FAB) m/z:
1018 [M+1]+, 990 [M+1ÀCO]+.
Supplementary data
[RuII(TMP)CO] 27. Yield: 66%; 1H NMR (300 MHz, CDCl3): d 8.50 (s, 8H), 7.26 (m,
8H), 2.61 (s, 12H), 1.89 (s, 12H), 1.86 (s, 12H); IR (KBr): 1945 cmÀ1; MS (FAB)
m/z: 911 [M+1]+, 883 [M+1ÀCO]+.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.05.081.

Q.-F. Liang et al. / Tetrahedron Letters 52 (2011) 3987–3991
3991
[RuII(F20-TPP)CO] 28. Yield: 86%; 1H NMR (300 MHz, CDCl3): d 8.72 (s, 8H); IR
(KBr): 1977 cmÀ1; MS (MALDI-TOF) m/z: 1074 [MÀCO]+.
1H), 7.31–7.39 (m, 5H), 4.55 (s, 1H); 13C NMR (100 MHz, CDCl3): d 173.08,
140.41, 128.49, 127.73, 126.56, 58.37; IR (KBr): 3314, 1668; MS (CI) m/z: 163
[M-2H]+.
Preparation of the complex of Ru porphyrin/H-L
-Val-OMe 3: [RuII(TDCPP)CO]
(20 mg, 0.02 mmol) was dissolved in 25 mL CH2Cl2, and then valine methyl
ester (10 mg, 0.076 mmol) was added, and the mixture was stirred at room
temperature for 5 min. Then 10 mL MeOH was added. The solution was
concentrated by rotary evaporation to an about 10 mL volume on an about 0–
10 °C water bath. Red solid was precipitated and collected, affording 21 mg 3,
yield 93%. 1H NMR (300 MHz, CDCl3): d 8.45 (s, 8H), 7.61–7.78 (m, 12H), 2.72
(s, 3H), –0.85 (d, J = 6.9 Hz, 3H), –1.44 (d, J = 6.9 Hz, 3H), –2.07 to –2.05 (m, 1H),
L
-Leucine derivative 15: yield, 77%. 1H NMR (400 MHz, CDCl3): d 8.44 (s, 1H),
3.44 (m, 1H), 1.65–1.76 (m, 2H), 1.34–1.40 (m, 1H), 0.92–0.97 (m, 6H); 13C
NMR (100 MHz, CDCl3): d 175.61, 52.38, 43.94, 24.42, 22.95, 21.35; IR (KBr):
3199, 1679; MS (CI) m/z: 145 M+.
L
-Isoleucine derivative 16: yield, 83%. 1H NMR (400 MHz, CDCl3): d 8.27 (s, 1H),
3.32 (d, 1H, J.3.6 Hz), 1.97–2.01 (m, 1H), 1.35–1.41 (m, 1H), 1.07–1.15 (m, 1H),
0.89–1.00 (m, 6H); 13C NMR (100 MHz, CDCl3): d 174.53, 59.06, 37.92, 23.59,
15.69, 11.55; IR (KBr): 3339, 3305, 3175, 1637; MS (CI) m/z: 145 M+.
–2.62 to –2.60 (m, 1H), –4.53 (m, 1H), –5.43 (m, 1H); IR: 1957 cmÀ1
Preparation of the amino acid derivatives 11–18, A general procedure:
.
L
-amino
L
-Phenylalanine derivative 17: yield, 78%. 1H NMR (400 MHz, CDCl3): d 8.23 (s,
acid (5.6 mmol) was added into 10 mL mixed solution of SOCl2/CH3OH (1:10)
and refluxed at 70 °C for 2 h. The solution was concentrated in vacuo and
added hydrazine (27.2 mL, 561 mmol) and CH3OH (50 mL), and then stirred at
rt for 12 h. The solution was concentrated in vacuo, and finally purified by
1H), 7.21–7.35 (m, 5H), 3.66 (q, 1H, J = 4.4 Hz), 3.26 (dd, 1H, J = 10.0, 4.0 Hz),
2.72 (dd, 1H, J = 9.6, 4.0 Hz); 13C NMR (100 MHz, CDCl3): d 174.18, 137.38,
129.10, 128.56, 126.74, 55.68, 40.93; IR (KBr): 3319, 3349, 3289, 3180, 1672;
MS (CI) m/z: 179 M+.
column chromatography (10:1 CH2Cl2/CH3OH), affording
derivative as white solid.
L
-amino acid
D
-Phenylalanine derivative 18: yield, 75%. 1H NMR (400 MHz, CDCl3): d 8.26 (s,
1H), 7.21–7.34 (m, 5H), 3.65 (q, 1H, J = 4.5 Hz), 3.26 (dd, 1H, J = 9.6, 4.4 Hz),
2.71 (dd, 1H, J = 9.0, 4.8 Hz); 13C NMR (100 MHz, CDCl3): d 173.77, 137.17,
129.04, 128.35, 126.53, 55.22, 40.72; IR (KBr): 3348, 3286, 1671; MS (CI) m/z:
179 M+.
L
-Alanine derivative 11: yield, 85%. 1H NMR (400 MHz, CDCl3): d 8.25 (s, 1H),
3.57 (q, 1H, J = 7.2 Hz), 1.36 (d, 3H, J = 7.6 Hz); 13C NMR (100 MHz, CDCl3): d
175.75, 50.02, 21.67; IR (KBr): 3332, 1668; MS (CI) m/z: 103 [M+H]+.
D
-Alanine derivative 12: yield, 92%. 1H NMR (400 MHz, CDCl3): d 8.27 (s, 1H),
Preparation of the complex 9: [RuII(TDCPP)CO] (1.0 mg, 1.0
lmol) was dissolved
3.56 (q, 1H, J = 7.2 Hz), 1.37 (d, 3H, J = 6.0 Hz); 13C NMR (100 MHz, CDCl3): d
with 1.0 mL CH2Cl2. 0.04 mg hydrazide 6 (about 0.3 eq) was added in the
solution of Ru porphyrin. The mixture was shaken at room temperature for 10
minutes. Then the solution was dried in vacuo, red solid affording. 1H NMR
(600 MHz, CDCl3): d 8.26 (m, 8H), 8.08 (s, 8H), 7.55–7.70 (m, 24H), À0.77 (d,
J = 5.4 Hz, 1H), À2.40 (d, J = 6.6 Hz, 3H), À2.54 (d, J = 6.6 Hz, 3H), À2.77 to
À2.74 (m, 2H), À3.77 (d, J = 12.0 Hz, 1H), À4.06 to À4.08 (m, 1H), À5.42 (dd,
J = 3.6, 13.2 Hz, 1H), À6.33 (dd, 6.0, 13.2 Hz, 1H).
175.78, 49.65, 21.34; IR (KBr): 3310, 1668; MS (CI) m/z: 103 [M+H]+.
L
-Valine derivative 13: yield, 79%. 1H NMR (400 MHz, CDCl3): d 8.33 (s, 1H), 3.28
(d, 1H, J = 4.0 Hz), 2.28 (m, 1H), 0.98 (d, 3H, J = 6.8 Hz), 0.84 (d, 3H, J = 6.8 Hz);
13C NMR (100 MHz, CDCl3): d 174.39, 59.43, 31.16, 19.15, 16.57; IR (KBr): 3292,
1658; MS (ESI) m/z: 132 [M+H]+.
L
-Phenylglycine derivative 14: yield, 82%. 1H NMR (400 MHz, CDCl3): d 8.19 (s,