Novel photosystem involving protonation and deprotonation processes modelled on a PYP photocycle

Article abstract of DOI:10.1039/b807417h

The synthesis of novel ortho-coumaric acid derivatives, with an amide group linked with an olefin moiety, which introduced photoinduced switching of the intramolecular hydrogen bonds is presented. An intramolecular OH · O=C hydrogen bond formed in a Z-phenol compound was switched to an intramolecular NH · O hydrogen bond in Z phenolate state via deprotonation. The pK _a value of the Z-phenol derivative was lower than that of E-phenol, and a novel photocycle system involving protonation and deprotonation processes was achieved.

Full text of DOI:10.1039/b807417h

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Novel photosystem involving protonation and deprotonation processes
modelled on a PYP photocycle†
Takashi Matsuhira, Kazuki Tsuchihashi, Hitoshi Yamamoto,* Taka-aki Okamura and Norikazu Ueyama
Received 1st May 2008, Accepted 30th May 2008
First published as an Advance Article on the web 1st July 2008
DOI: 10.1039/b807417h
The synthesis of novel ortho-coumaric acid derivatives, with an amide group linked with an olefin
moiety, which introduced photoinduced switching of the intramolecular hydrogen bonds is presented.
=
An intramolecular OH · · · O C hydrogen bond formed in a Z-phenol compound was switched to an
intramolecular NH · · · O hydrogen bond in Z phenolate state via deprotonation. The pKa value of the
Z-phenol derivative was lower than that of E-phenol, and a novel photocycle system involving
protonation and deprotonation processes was achieved.
change, temperature change, or photoillumination—resulting in
Introduction
a switching of the hydrogen bond network. We propose that, by
controlling the distance between the hydrogen bond donor and
acceptor, the small molecules that switch their conformation by
external stimulation will achieve switching of the intramolecular
hydrogen bonding artificially (Fig. 2).
Photoactive yellow protein (PYP) is one of the photoreceptor
proteins involved in the negative phototactic response of purple
photosynthetic bacteria.1 The photocycle of PYP around the chro-
mophore indicates that hydrogen bonds between phenolate oxygen
and hydroxyl moieties of Glu 46 or Tyr 42, which were formed in
the ground state, were interrupted by E–Z photoisomerization of
a para-coumaric acid framework, accompanying the protonation
and deprotonation processes of the phenol moiety (Fig. 1).
Rearrangement of the hydrogen bond network around the active
site is believed to play a substantial role in regulating the
reactivity of enzymatic reactions not only in PYP, but also
in other native proteins, such as hydrolytic enzymes.2 These
proteins induce dynamic changes in the overall protein structure—
triggered by external stimulation, such as substance binding, pH
Fig. 2 Switching of the intramolecular distance of hydrogen bond donor
and acceptor, by external stimulation.
Photoisomerization is one of the most promising strategies to
drive these changes, enabling molecular structures to be controlled
in an elegant way. Recently, much attention has been focused
on the isomerization reaction of photochromic compounds as
photoinduced switching devices.3 For example, researchers have
investigated the effect of intramolecular NH · · · N or NH · · · O
hydrogen bonds in Z form on the E–Z photoisomerization of
4
=
the C C double bond, as well as the pKa change of phenol or
carboxylic acid derivatives caused by the switching of conjugation
through photoisomerization.5
Previously, we have proposed that a hydrogen bond between an
amide NH and an oxyanion, such as carboxylate and phenolate,
stabilizes and decreases the nucleophilicity of the anions and
lowers the pKa values of the corresponding acids.6 We reported
carboxylic acid derivatives that could switch the intramolecular
distance between carboxylic oxygen and amide groups through
E–Z photoisomerization, and revealed that the intramolecular
NH · · · O hydrogen bond formed in the carboxylate lowers the
pKa value of the corresponding carboxylic acid.7 In this study,
we designed ortho-coumaric acid derivatives (E-1/Z-1, E-2/Z-2),
both of which have an amide group linked with a photoinduced
olefin moiety (Scheme 1). These compounds are expected to
Fig. 1 Photocycle of the photoactive yellow protein (PYP).
Department of Macromolecular Science, Graduate School of Science, Osaka
University, 1-1 Machikaneyama-cho, Toyonaka, Osaka, 560-0043, Japan.
E-mail: jin@chem.sci.osaka-u.ac.jp; Fax: +81-6-6850-5474; Tel: +81-6-
6850-5451
† Electronic supplementary information (ESI) available: Cif data of E-1
and Z-1, UV–vis spectrum changes by photoisomerization, and COSY
correlations in the NOESY spectrum. CCDC reference numbers 684897
and 684898. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b807417h
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Results and discussion
Synthesis
The synthetic method is shown in Scheme 2. E-1 was synthesized
through dicyclohexyl carbodiimide (DCC) coupling of ortho-
coumaric acid and tert-butyl amine. Z-1 was isolated from the
photoreaction mixture by recrystallization. E-2 and Z-2 were
prepared through a countercation exchange reaction of the
corresponding phenol derivatives (E-1 and Z-1) with tetraethy-
lammonium hydroxides.
Molecular structures in the solid state
To confirm the molecular structures in the solid state, X-ray
crystallography was used. The crystal structures of E-1 and Z-1
are shown in Fig. 3. The crystal data are shown in the experimental
section. All non-hydrogen atoms were refined anisotropically.
The coordinates of OH and NH protons were refined by using
fixed thermal factors, and the other protons were placed in
Scheme 1 Photoisomerization equilibriums of cinnamic acid derivatives
E-1/Z-1 and E-2/Z-2.
ꢀ
˚
=
have an intramolecular OH · · · O C hydrogen bond in Z-1 and
calculated positions. The intermolecular O01 · · · O 02 (2.645[2] A)
ꢀꢀ
˚
an intramolecular NH · · · O hydrogen bond in Z-2, forming
eight-membered ring structures. And they are expected to con-
struct an artificial cycle that involves protonation and deprotona-
tion processes, as in the PYP photocycle. A tert-butyl moiety was
introduced for the purpose of protecting the amide NH moiety
from intermolecular interaction so as to support the construction
of an intramolecular NH · · · O hydrogen bond.
and O01 · · · N 1 (3.099[3] A) distances of E-1 permitted hydrogen
=
bond formation; these intermolecular NH · · · O and OH · · · O C
hydrogen bonds are thought to stabilize the packing structure of
E-1 [Oꢀ02 indicates an O02 atom at an equivalent position (−x + 1,
y + 1/2, −z + 1/2), and Nꢀꢀ1 indicates an N1 atom at an equivalent
position (x + 1/2, y, −z + 1/2)]. The torsion angles of C5–C6–
C7–C8 (16.5 [4]◦) and C7–C8–C9–O02 (20.3[4]◦) indicate that the
Scheme 2 Synthesis of cinnamic acid derivatives E-1, Z-1, E-2 and Z-2.
Fig. 3 Molecular structures of E-1 (left) and Z-1 (right), ellipsoids set as 50% probability.
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ortho-coumaric frame of E-1 is almost in plane; it can be inferred
that the p-conjugation is extended from the phenol oxygen toward
of Z-1 and Z-2 were 13.0 Hz. This coincides with the typical
values of the trans and cis olefin protons. The configurations of
the compounds before irradiation were confirmed to be the E
form, and the photoproducts were confirmed to be the Z form.
The chemical shifts of the OH signals of the phenol compounds
at 303 K were 7.33 ppm in E-1 and 9.87 ppm in Z-1 (Fig. 4).
The substantial downfield shift (Dd = 2.54 ppm) suggests that Z-1
=
the amide carbonyl oxygen through a C C double bond.
With Z-1, by contrast, the distances of O01 · · · O02 (2.516[2]
˚
˚
A) and H01 · · · O01 (1.63[2] A) were sufficient to permit hydrogen
bond formation (whereas the O01 · · · O02 distance of E-1 was
◦
˚
4.933 A). The O01–H01–O03 angle of Z-1 (164[2] ) is suitable
to cause hydrogen bonding. These results indicate that Z-1 has
=
forms an OH · · · O C hydrogen bond in acetonitrile-d3 solution.
=
an intramolecular OH · · · O C hydrogen bond, forming an eight-
The temperature dependency values of the OH signal chemical
shifts of E-1 and Z-1 are −7.2 and −7.5 ppb K−1, respectively, in
the range of 233 to 303 K. These results indicate a hydrogen bond
formation of the phenol OH moiety in Z-1, including not only an
intramolecular interaction but also an intermolecular interaction.
The chemical shifts of the amide NH signals of phenolates at
303 K were 6.11 ppm in E-2 and 9.59 ppm in Z-2 (Fig. 4). The
temperature dependency value of the amide NH chemical shift of
Z-2 is 1.2 ppb K−1 (in the range of 233 to 303 K), whereas that of
E-2 is −5.4 ppb K−1 (263 to 333 K). The substantial downfield shift
(Dd = 3.48 ppm) and the decrease of the temperature coefficient
of the NH proton signal suggest that Z-2 forms an intramolecular
NH · · · O hydrogen bond in acetonitrile-d3 solution.
membered ring structure in the solid state. The intermolecular
ꢀ
˚
O1 · · · N 1 distance (2.971 A) of Z-1 permitted intermolecular
hydrogen bond formation; and was thought to stabilize the pack-
ing structure of Z-1 (Nꢀ1 indicates an N1 atom at an equivalent
position). The torsion angles of C5–C6–C7–C8 (−137.4[3]◦) and
C7–C8–C9–O02 (−27.0 [4]◦) are so large that p-conjugation
extended in E-1 is interrupted in Z-1.
Molecular structures in solution
The molecular structures of isolated isomers in solution were
1
1
determined by H NMR spectroscopy. The H NMR spectra of
E-1, E-2, Z-1, and Z-2 in acetonitrile-d3 at 303 K are shown in
Fig. 4. All signals are assigned by nuclear Overhauser effect (NOE)
and decoupling method. E–Z configurations of these compounds
were confirmed by the 3JHH values of the olefin protons. Generally
speaking, the 3JHH coupling constant of the olefin protons is about
15 to 16 Hz in the trans position, and is about 12 to 13 Hz in
The nuclear Overhauser enhancement spectroscopy (NOESY)
spectra were measured to gain information about the molecular
structure in solution (Fig. 5). A negative NOE correlation between
NH and H1 was observed in E-1, whereas no NOE signal was
observed between NH and H2 (Fig. 5a). Also, the correlation
of H1–H3 was stronger than that of H2–H3. These results
indicate that E-1, in acetonitrile-d3 solution, seems to take the
conformation shown in Fig. 5a, in which the amide carbonyl
3
the cis position. The observed JHH values of the olefin protons
of E-1 and E-2 were 15.8 and 15.5 Hz, respectively, and those
Fig. 4 1H NMR spectra of (a) E-1, (b) Z-1, (c) E-2 and (d) Z-2, 5 mM in acetonitrile-d3 at 303 K.
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Fig. 5 NOESY spectra of (a) E-2 and (b) Z-2, 5 mM in acetonitrile-d3 at 303 K.
orients toward the olefin moiety (s-cis form) and the hydroxyl
moiety orients in the opposite direction of the olefin moiety (s-
trans form). This structure of E-1 is consistent with the solid
structure obtained with X-ray crystallography (Fig. 3). The
characteristic positive–negative correlation patterns of H1–H2
and H5–H3 are predicated to the correlated signal (COSY signal)
caused by spin coupling (ESI†). The correlation of the hydroxyl
OH proton was not observed but exchange signal (EXSY signal)
with water protons was observed. The NOE pattern of E-2 was
almost the same as that of E-1, and E-2 seems to take the structure
shown in Fig. 5b in acetonitrile-d3 solution. The correlation of
H1–H2 in E-2 was the COSY signal as well as that in E-1 (ESI†).
In Z-1, a negative NOE correlation between H1 and H2 was
observed (Fig. 5c). This correlation is characteristically seen in the
cis configuration of the olefin protons; therefore the configuration
of Z-1 is determined to be definitely in the Z form. Correlations
of NH–H1 and H2–H3 were observed, and no NOE signal
was observed around the OH protons. These results indicate
that Z-1 seems to adopt the structure shown in Fig. 5c, with
the hydroxyl proton in close proximity to the amide carbonyl
was characteristically observed in Z-1, was not seen (Fig. 5d).
Additionally, the correlation of H2–H3 was observed. These
results can be ascribed to the flipping of the amide plane by
=
switching of the intramolecular hydrogen bond from OH · · · O C
to NH · · · O−, accompanying the deprotonation of the phenol
moiety (Scheme 3).
Scheme 3 Flipping of the amide plane with the deprotonation of Z-1.
Direct photoisomerization
Fig. 6 shows the UV–visible (UV–vis) spectra of isolated com-
pounds (E-1, E-2, Z-1, Z-2), in acetonitrile at 303 K. The
wavenumbers of maximum absorbance (k max) in the phenolate
derivatives (E-2, Z-2) were longer than those in the corresponding
phenol derivatives (E-1, Z-1). The red shift of k max can be ascribed
=
oxygen, and is able to form an intramolecular OH · · · O C
hydrogen bond. In Z-2, an NOE correlation of NH–H1, which
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Table 1 E–Z ratios in the photostationary state (PSS) at various irradia-
tion wavelengths
Irradiation wavelength
313 nm
365 nm
405 nm
436 nm
E-1–Z-1
E-2–Z-2
11 : 89
51 : 49
18 : 82
13 : 87
No reaction
16 : 84
No reaction
30 : 70
to electron delocalization in the phenolate derivatives. The UV–
vis spectra in Fig. 6 indicate that the mercury lamp wavelength
emissions for direct photoexcitation are 313 and 365 nm in the
phenol derivatives, and 313, 365, 405, and 436 nm in the phenolate
derivatives, without using any photosensitizer. Following photoir-
radiation, E–Z isomerization progressed without any effective side
reactions (ESI†). The E–Z ratio in the photostationary state (PSS)
depends on the irradiation wavelength. The ratios in PSS at various
wavelengths are shown in Table 1. At 313-nm irradiation, in PSS,
the products were rich in Z configuration phenol derivatives (E-
1–Z-1 = 11 : 89), whereas the amounts of E and Z phenolate
derivatives in PSS were almost equal (E-2–Z-2 = 51 : 49). At 365-
nm irradiation, both phenol and phenolate derivatives generate
Z isomers rather than E isomers (E-1–Z-1 = 18 : 82, E-2–Z-
2 = 13 : 87). The phenolate derivatives generate the Z compound
in PSS with irradiation at 405 nm (E-2–Z-2 = 16 : 84) and at
436 nm (E-2–Z-2 = 30 : 70), whereas no reaction occurs with
the phenol derivatives because E-1 and Z-1 have no absorption
at these wavelengths. The phenolate derivatives progress through
a reversible photoisomerization: E to Z conversion by 405-nm
irradiation, and Z to E reversal by 313-nm irradiation (ESI†).
Fig. 7 UV–vis spectra changes for phenol compounds, by the addition
of aqueous sodium hydroxide solution, (a) E-1 and (b) Z-1, 5 mM in 10%
lauryl ether aqueous micellar solution at 303 K.
Fig. 8 Titration curves of (a) E-1 and (b) Z-1.
Thus the pH value at the intersection of the titration curves
of phenol and phenolate in Fig. 8 stimulates the pKa value of
the corresponding phenol derivatives. The pKa value of Z-1 was
10.24, which has a shift that is 0.13 units lower than that of E-
1 (10.37). We propose that the stabilization of the Z phenolate
derivative (Z-2) by the formation of an intramolecular NH · · · O
hydrogen bond decreases the pKa value of the Z phenol derivative
(Z-1). Fig. 9 shows a comparison of the titration curves of phenol
derivatives. In the pH region around the pKa values of E-1 and
Z-1 (a buffering region), the E compound was protonated and the
Z compound was deprotonated, preferentially. We propose that
photoisomerization of a compound synthesized in this pH region
will achieve control over the protonation and deprotonation of the
phenolic hydroxyl moiety.
Fig. 6 UV–vis spectra of E-1, Z-1 and E-2, Z-2, 1 mM in acetonitrile at
293 K.
Acidity change through photoisomerization
pKa values of E-1 and Z-1 were measured by potentiometric
titration traced with UV–vis spectra in a 10% lauryl ether aqueous
micellar solution at 303 K. UV–vis spectra changes caused by the
addition of aqueous sodium hydroxide solution (0.100 mol L−1)
are shown in Fig. 7. As the pH value increased, the absorbances of
phenol derivatives (323 nm in E-1 and 311 nm in Z-1) decreased,
and those of phenolate derivatives (380 nm in E-2 and 357 nm
in Z-2) increased. The titration curves are shown in Fig. 8.
The Henderson–Hasselbalch equation of acid dissociation in a
buffering region shows that the pKa value is equal to the pH value
when the concentration of phenolate matches that of phenol.
Fig. 9 Comparison of titration curves of E-1 and Z-1; ratios of phenol
components depend on pH.
Proposed photocycle
The decrease of the pKa value in a Z phenol compound, and the
differences in E–Z ratios between phenol and phenolate deriva-
tives in PSS at 313-nm irradiation, indicate that the novel pho-
tocycle system is probably constructed like the PYP photocycle,
involving protonation and deprotonation processes (Scheme 4).
In this photocycle, E phenol derivatives photoisomerize toward
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Scheme 4 Proposed photocycle.
Z phenols at a UV irradiation wavelength of 313 nm. Then,
deprotonation progresses because of the decrease of the pKa value
in the Z phenol. The Z phenolate photoisomerizes towards the
E isomer at the same UV irradiation wavelength (313 nm), and
the E phenolate returns to the initial state by a protonation
process. Through a series of repetitions of this photocycle,
phenolate was protonated far from the amide moiety, and phenol
was deprotonated near the amide moiety. This indicates proton
transport from the far side to the near side of the amide moiety,
using light energy as a driving force. It represents the achievement
of a light-driven proton pumping system using an artificial small
molecule.
indicate that the artificial photocycle was constructed like the
PYP photocycle, which involves protonation and deprotonation
processes.
Experimental
General procedures
All manipulations involving air- and moisture-sensitive com-
pounds were carried out by the use of a standard Schlenk
technique under an argon atmosphere. E-ortho-coumaric acid,
25% tetraethylammonium bydroxide in methanol solution were
purchased from Tokyo-Kasei Co. Dicyclohexylcarbodiimide was
purchased from Peptide Institute, Inc. Dichloromethane was
distilled over CaH2. Methanol, tetrahydrofuran, diethylether, n-
hexane, and acetonitrile were distilled over CaH2 and dried over
Conclusion
In this work, the authors designed a novel photocycle system,
consisting of phenol E-1/Z-1 and phenolate E-2/Z-2 derivatives,
that was modelled on the PYP photocycle. Z-1 was shown
˚
molecular sieves (3A).
Physical measurements
=
to form an intramolecular OH · · · O C hydrogen bond both
in acetonitrile-d3 solution and in the solid state, and Z-2 was
shown to form an intramolecular NH · · · O hydrogen bond in
acetonitrile-d3 solution. The ortho-coumaric acid moiety has an
extended p-conjugation in phenolate, thus a red shift of the
absorption maximum was observed. Because of the difference in
the absorption wavelength, phenol and phenolate have different
E–Z ratios at the same UV light irradiation wavelength. UV light
irradiation at a wavelength of 313 nm generates the Z form in
phenol and generates the E form in phenolate, preferentially. The
reversion rate led to an almost equal amount of both compounds
(E–Z = 51 : 49). To improve the reversion rate, the substitution
of the conjugated aromatic moiety would be effective to control
the compounds’ absorbance maxima. The pKa value of the phenol
compound was lowered in the Z compound by stabilizing the Z
phenolate with formation of an intramolecular NH · · · O hydrogen
bond. The change of the E–Z ratio in phenol and phenolate,
and the decrease of the pKa value in the Z phenol compound,
1H (270 MHz) NMR spectra were measured on a JEOL JNM-
GSX270 spectrometer. 13C (100, 120 MHz) NMR spectra were
measured on a JEOL JNM-GSX400 spectrometer, and on a
Varian UNITYplus 600 MHz spectrometer. NOESY spectra were
measured on a JEOL JNM-GSX400 spectrometer and Varian
1
UNITYplus 600 MHz spectrometer. The H NMR spectra were
referenced to tetramethylsilane protons at d 0.00. The 13C NMR
spectra were referenced to the methyl carbon of acetonitrile-d3 at
d 1.30. UV–vis spectra was measured on a Shimazu UV-3100PC
and Ocean Optics Inc. TP300-UV/VIS spectrometers. Elemental
analysis was performed at the Elemental Analysis Center, Faculty
of Science, Osaka University. All melting points of the com-
pounds were measured on a micro melting point apparatus from
YANAGIMOTO Co. ESI-MS measurements were performed
on a Finnigan MAT LCQ ion trap mass spectrometer. FT-IR
spectra were measured on a JASCO FT/IR-8300 spectrometer;
the FT-IR measurement was performed in KBr glass cell with
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nujol or with solvent. pKa measurements were performed using
a potentiometric titration in 10 mM micellar solution at 298 K
with a Metrohm 716 DMS titrino combined with a Metrohm
728 stirrer and a saturated calomel LL micro pH glass electrode.
The saturated calomel micro glass electrode was calibrated with a
0.05 M KHC8H4O4 buffer (pH = 4.01) and a 0.0025 M KH2PO4
buffer (pH = 6.87) at 303 K. The potentiometric titrations were
performed three times. pKa values were estimated by an average
value of each measurement.
under reduced pressure. The obtained pale yellow powder was
recrystallized from ethyl acetate–n-hexane to obtain colorless
crystals (154.4 mg, 35%). mmax(in acetonitrile solution)/cm−1 3360
=
(NH), and 1645 (C O); dH(270 MHz; acetonitrile-d3) 1.32 (s,
3
9H; tert-butyl), 5.97 (d, J(H,H) = 13.0 Hz, 1H; olefin), 6.72
3
(br s, 1H; NH), 6.77 (d, J(H,H) = 13.0 Hz, 1H; olefin), 6.87
(dt, J(H,H) = 7.5 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 6.89 (dd,
3
3J(H,H) = 7.5 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 7.22 (dt, 3J(H,H) =
7.5 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 7.23 (dd, 3J(H,H) =
7.5 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 9.87 ppm (br s, 1H; OH);
dC(100 MHz; acetonitrile-d3) 28.7, 52.6, 120.0, 120.7, 123.9, 125.8,
131.3, 133.2, 136.7, 156.7, and 168.8 ppm; m/z (ESI) 220.1
([M + H]+ requires 220.1), 460.9 ([2M + Na]+ requires 461.2);
Preparation of (E)-N-tert-butyl-3-(2-hydroxyphenyl) acrylamide
(E-1)
R
To a 1 L tetrahydrofuran solution of E-ortho-coumaric acid
(2.01 g, 12.2 mmol) and tert-butylamine (2.6 mL, 24.4 mmol)
was added dicyclohexylcarbodiimide (DCC, 4.44 g, 24.4 mmol).
The white suspension was stirred at room temperature for 2 days.
The solvent was removed under reduced pressure to obtain a white
solid. The solid was dissolved in 100 mL of 0.8 mol L−1 aqueous
sodium hydroxide solution. The yellow solution was moved to
a dropping funnel and washed with 150 mL of ethyl acetate–
diethyl ether (1 : 1, v/v). The organic layer was extracted again
by 0.8 M aqueous sodium hydroxide solution three times. The
combined aqueous layers were washed with 100 mL of n-hexane.
Whilst cooling in an ice bath, the aqueous layer was acidified
by aqueous sulfuric acid solution (pH 6–7). The orange solution
turned to a white suspension. The mixture was extracted with ethyl
acetate–diethyl ether (1 : 1, v/v) three times. The organic layer was
washed with 4% aqueous sodium bicarbonate solution three times.
The organic layer was dried over anhydrous magnesium sulfate,
and the solvent was removed under reduced pressure. The white
powder was recrystallized from hot acetonitrile to obtain colorless
crystals (1.25 g 46.8%). Mp 229–230 ◦C; (Found: C, 71.14; H,
7.90; N, 6.53. Calc. for C13H17NO2: C, 71.21; H, 7.81; N, 6.39%);
mmax(in nujol mull)/cm−1 3357 (NH), 3130–3047 (OH), and 1657
pKa = 9.70 (10 mM in 10% aqueous micellar solution of Tritonꢀ
X-100).
Preparation of [tetraethyl-ammonium] 2-((E)-2-
(tert-butylcarbamoyl)vinyl) phenolate (E-2)
(E)-N-tert-Butyl-3-(2-hydroxyphenyl) acrylamide (E-1, 100.9 mg,
0.46 mmol) was dissolved in 1 mL of methanol. To the solution was
added 25% tetraethylammonium hydroxide solution in methanol
(0.25 mL, 0.41 mmol). The solution was stirred for 2 hours and
the solvent was removed under reduced pressure. The residue
was washed with 10 mL of diethyl ether twice. The powder
was recrystallized from acetonitrile–diethyl ether to obtain a
yellow crystalline solid. mmax(in acetonitrile solution)/cm−1 3386
=
(NH), and 1661 (C O); dH(270 MHz; acetonitrile-d3) 1.20 (t,
3J(H,H) = 7.3 Hz, 12H; NEt4), 1.35 (s, 9H; tert-butyl), 3.15
(q, 3J(H,H) = 7.3 Hz, 8H; NEt4), 6.11 (s, 1H; NH), 6.31
3
(dt, J(H,H) = 7.3 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 6.67 (dd,
3J(H,H) = 7.3 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 6.88 (d, 3J(H,H) =
15.5 Hz, 1H; olefin), 6.92 (dt, 3J(H,H) = 7.3 Hz,4J(H,H) = 1.2 Hz,
3
1H; aryl), 7.18 (dd, J(H,H) = 7.3 Hz,4J(H,H) = 1.2 Hz, 1H;
aryl), 7.62 ppm (d, 3J(H,H) = 15.5 Hz, 1H; olefin); dC(100 MHz;
acetonitrile-d3) 7.7, 29.3, 51.0, 53.2, 85.0, 89.9, 108.4, 116.0, 122.6,
131.1, 131.7, 141.8, and 169.3 ppm; m/z (ESI) 218.3 ([M − NEt4]−
requires 218.1), 349.3 ([M + H]+ requires 349.3), 335.3 ([M − Me +
2H]+ requires 335.3), 321.5 ([M − Et + 2H]+ requires 321.3).
(C O); mmax(in acetonitrile solution)/cm−1 3380 (NH), and 1672
=
=
(C O); dH(270 MHz; acetonitrile-d3) 1.36 (s, 9H; tert-butyl), 6.26
3
(br s, 1H; NH), 6.58 (d, J(H,H) = 15.8 Hz, 1H; olefin), 6.87
3
4
(dd, J(H,H) = 8.2 Hz, J(H,H) = 1.2 Hz, 1H; aryl), 6.88 (dt,
3J(H,H) = 8.2 Hz, 4J(H,H) = 1.2 Hz, 1H; aryl), 7.18 (dt, 3J(H,H) =
8.2 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 7.33 (br s, 1H; OH), 7.44
Preparation of [tetraethyl-ammonium] 2-((Z)-2-
(tert-butylcarbamoyl)vinyl) phenolate (Z-2)
(dd, J(H,H) = 8.2 Hz,4J(H,H) = 1.2 Hz, 1H; aryl), 7.63 ppm
3
(d, 3J(H,H) = 15.8 Hz, 1H; olefin); dC(100 MHz; acetonitrile-d3)
29.0, 51.7, 117.0, 121.2, 123.4, 124.2, 129.5, 131.4, 135.1, 156.6,
and 166.5 ppm; m/z (ESI) 218.3 ([M − H]− requires 218.1), 220.1
([M + H]+ requires 220.1), 242.2 ([M + Na]+ requires 242.1), 461.0
([2M + Na]+ requires 461.2); pKa = 9.84 (10 mM in 10% aqueous
(Z)-N-tert-Butyl-3-(2-hydroxyphenyl) acrylamide (Z-1, 100.9 mg,
0.46 mmol) was dissolved in 1 mL of methanol. To the solution was
added 25% tetraethylammonium hydroxide solution in methanol
(0.25 mL, 0.41 mmol). The solution was stirred for 2 hours and
the solvent was removed under reduced pressure. The residue
was washed with 10 mL of diethyl ether twice. The powder was
recrystallized from acetonitrile–diethyl ether to obtain a yellow
R
micellar solution of Tritonꢀ X-100).
Preparation of (Z)-N-tert-butyl-3-(2-hydroxyphenyl) acrylamide
(Z-1)
crystalline solid. mmax(in acetonitrile solution)/cm−1 1635 (C O);
=
3
dH(270 MHz; acetonitrile-d3) 1.21 (t, J(H,H) = 7.4 Hz, 12H;
3
(E)-N-tert-Butyl-3-(2-hydroxyphenyl) acrylamide (E-1, 441.2 mg,
2.01 mmol) was dissolved in 50 mL of acetonitrile. UV-light
was irradiated on the solution for 400 minutes. The solvent
was removed under reduced pressure. The residue was repre-
cipitated from diethyl ether–n-hexane. A white precipitate was
collected by filtration and was suspended in ice-cooled chloroform.
The suspension was filtered and the filtrate was concentrated
NEt4), 1.23 (s, 9H; tert-butyl), 3.16 (q, J(H,H) = 7.4 Hz, 8H;
NEt4), 5.57 (d, 3J(H,H) = 13.0 Hz, 1H; olefin), 6.21 (dt, 3J(H,H) =
7.6 Hz,4J(H,H) = 1.8 Hz, 1H; aryl), 6.50 (dd, 3J(H,H) =
7.6 Hz,4J(H,H) = 1.8 Hz, 1H; aryl), 6.61 (d, 3J(H,H) = 13.0 Hz,
3
1H; olefin), 6.89 (dt, J(H,H) = 7.6 Hz,4J(H,H) = 1.8 Hz, 1H;
3
aryl), 6.98 (dd, J(H,H) = 7.6 Hz,4J(H,H) = 1.8 Hz, 1H; aryl),
9.58 ppm (br s, 1H; NH); dC(120 MHz; acetonitrile-d3) 7.7, 15.6,
3124 | Org. Biomol. Chem., 2008, 6, 3118–3126
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29.0, 53.1, 96.6, 123.6, 125.6, 130.1, 131.1, 131.3, 135.0, 161.8, and
168.1 ppm; m/z (ESI) 218.5 ([M − NEt4]− requires 218.1), 349.3
([M + H]+ requires 349.3), 335.3 ([M − Me + 2H]+ requires 335.3),
321.5 ([M − Et + 2H]+ requires 321.3).
Acknowledgements
One of the authors (T. Matsuhira) express his special thanks for
the Global Education and Research Center for Bio-Environmental
Chemistry (GCOE) program of Osaka University.
Crystallographic data collection and structure determination of
E-1 and Z-1
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Suitable single crystals of E-1 and Z-1 were mounted on a
fine nylon loop with nujol and immediately frozen at 200
1 K. All measurements were performed on a Rigaku RAXIS-
RAPID Imaging Plate diffractometer with graphite monochro-
˚
mated MoKa radiation (k = 0.71075 A). The structures were
solved by direct method (SIR 92)8 and the following refinements
were performed using the SHELXL-979 and teXsan crystallo-
graphic software packages. All non-hydrogen atoms were refined
anisotropically. The coordinates of OH and NH protons were
refined by using fixed thermal factors, and the other protons were
placed in calculated positions. Crystal data for C13H17NO2 (E-1):
0.35 × 0.30 × 0.02 mm3, orthorhombic, Pbca (#61), a = 12.940(5)
3
˚
˚
˚
˚
A, b = 9.252(5) A, c = 20.60(1) A, V = 2466(3) A , Z = 8,
qcalcd = 1.181 g cm−3, l (MoKa) = 0.79 cm−1, Mw = 219.28. Total
number of reflections measured 23376, unique reflections 21726
(Rint = 0.174), final R indices: R1 = 0.058, wR2 = 0.128 for all
data. GOF (F2) = 1.03. Crystal data for C13H17NO2 (Z-1): 0.40 ×
3
˚
3
0.35 × 0.08 mm , monoclinic, P21/c (#14), a = 11.000(6) A, b =
◦
˚
˚
˚
12.346(16) A, c = 9.398(7) A, b = 103.58(2) , V = 1240(1) A , Z =
4, qcalcd = 1.174 g cm−3, l (MoKa) = 0.79 cm−1, Mw = 219.28. Total
number of reflections measured 11695, unique reflections 11384
(Rint = 0.089), final R indices: R1 = 0.070, wR2 = 0.129 for all data.
GOF (F2) = 1.04.†
UV-light irradiation technique for UV–vis and 1H NMR spectrum
measurements
A Xe/Hg lamp (MUV-202U, Moritex Co.) was used for 313 nm
UV-light irradiation. UV-light was filtered through 6784-t01.uv1
(Asahi tech.) to select the 313-nm emission line of Hg gas. For 365-,
405-, and 436-nm irradiation, filters of #43–155 FILTER INT
365NM 50.8 mm SQ, #43–156 FILTER INT 405NM 50.8 mm
SQ, and #43–161 FILTER INT 436NM 50.8 mm SQ (Edmund
Optics Inc.) were used respectively. The sample was dissolved in
distilled solvent under an argon atmosphere and sealed in an NMR
tube or a UV cell. The spectrum was measured before and after
irradiation. During irradiation and spectrum measurements, the
sample was always kept at the desired temperature.
Potentiometric titration traced by a UV–vis spectrum
To a solution of a phenol derivative dissolved in distilled THF
was added lauryl ether, and the solution was stirred for several
minutes. THF was removed under reduced pressure, and the
residue was added to aqueous sodium perchlorate solution. The
UV–vis spectrum and the pH value were measured at the same
time, by using the reaction tracking system (ESI†). During each
measurement, the sample was kept at 303 K in a temperature
controlled bath.
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