Novel NO biosensor based on the surface derivatization of GaAs by hinged iron porphyrins

Article abstract of DOI:10.1002/1521-3773(20001215)39:24<4496::AID-ANIE4496>3.0.CO;2-L

A tailor-made, two-component molecular system bound to a GaAs based electronic device has been used to detect nitric oxide (NO) in physiological buffer solutions down to a concentration of 1 ppm (ca. 3 μM). This is made possible because the current through the GaAs changes when NO binds to an iron(III) porphyrin (see picture).

Full text of DOI:10.1002/1521-3773(20001215)39:24<4496::AID-ANIE4496>3.0.CO;2-L

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Table 1. Selected analytical data for 2 and 9a ± d.
[14] T. Guiberteau, D. Grucker, personal communication.
[15] Ya. S. Lebedev, O. Ya. Grinberg, A. A. Dubinsky, O. G. Poluektov in
Bioactive Spin Labels 7Ed.: R. I. Zhdanov), Springer, Berlin, 1992,
pp. 227± 278.
[16] Spin-labeled spin-traps may be applied to living free radical polymer-
ization: W. Huang, personal communication.
2: red liquid; elemental analysis calcd7%)for C20H34N2O2: C 72.28, H 9.63,
N 8.43; found: C 72.23, H 9.83, N 8.46. 9a: 1H NMR 7400 MHz, CDCl3):
d ˆ 9.2 7s, 1H; CH), 5.1 7s, 1H; CH), 1.5 7s, 9H; CH3); UV/Vis 7EtOH):
lmax[nm] 7e) ˆ 443 71800), 246 716000); high resolution MS 7FAB): m/z
‡
‡
‡
7%): 364.2589 721) [M ‡2H], 363.2536 740) [M ‡H], 362.2450 727) [M ].
9b: 1H NMR 7400 MHz, CDCl3): d ˆ 10.4 7s, 1H; CH), 8.5 7s, 1H; CH), 1.6
7s, 9H; CH3); UV/Vis 7EtOH): lmax[nm] 7e) ˆ 440 74600), 285 7shoulder,
4000), 242 721000); high resolution MS 7FAB): m/z 7%): 363.2528 7100)
[M ‡H], 334.2135 782.6) [M À C2H4]. 9c: 1H NMR 7400 MHz, CDCl3):
‡
‡
d ˆ 9.43 7s, 1H; CH), 8.5 7s, 1H; CH), 5.9 7s, 1H; CH), 1.8 7s, 9H; CH3);
‡
high resolution MS 7FAB): m/z 7%): 364.2594 763) [M ‡2H], 363.2518 760)
‡
‡
[M ‡H], 362.2451 751) [M ], 348.2657737).
9d: 1H NMR 7400 MHz,
Novel NO Biosensor Based on the Surface
Derivatization of GaAs by ªHingedº Iron
porphyrins**
CDCl3): d ˆ 9.8 7s, 1H; CH), 9.1 7s, 1H; CH), 5.6 7s, 1H; CH), 1.8 7s, 9H;
‡
CH3); high resolution MS 7FAB): m/z 7%): 362.2804 712) [M ‡CH4],
‡
‡
348.2655 722) [M ‡2H], 347.2577 744) [M ‡H]
Deng Guo Wu,* Gonen Ashkenasy,* Dmitry Shvarts,
Rachel V. Ussyshkin, Ron Naaman,*
Abraham Shanzer,* and David Cahen*
The use of this spin-trap for the in vivo detection of NO is
more problematic because of the presence of reducing agents:
when 2 was treated with ascorbic acid and the reaction
monitored by EPR spectrocopy, the typical spectrum of 9e
7Scheme 2 where X ˆ OH, Y1 ˆ Y2 ˆ H) immediately ap-
peared and then decayed, but, as expected, at a much lower
rate.[8] However, it is possible to distinguish between the NO
adducts and 9e by combining different analytical methods
Nitric oxide 7NO) plays an important role in biology as a
mediator, for example, of the endothelial-derived relaxing
factor 7EDRF)Ðan agent responsible for the regulation of
blood vessel relaxation and for the maintenance of blood
pressure.[1] Concentrations of 30 to 300 ppm of NO 71 ppm ꢀ
3.3 Â 10À5 m) are sufficient to activate the guanylyl cyclase
signaling cascade.[2] Since NO is a gaseous and highly reactive
species, its direct detection at low concentrations is difficult.
The methods used to sense NO have generally been based on
following changes in the UV/Vis spectra or electrochemical
properties of the sensing elements.[3] Electron paramagnetic
resonance 7EPR) and NMR image visualization of the
distributions of NO free radicals in vivo were also reported,
but were found to be limited by spatial resolution and sample
size.[4, 5] We report here a novel approach for the direct
detection of low concentrations of NO free radicals in
physiological aqueous solution 7pH ˆ 7.4).
1
such as mass spectrometry, H NMR spectroscopy,[7] 7for 9a
and 9b) and probably by high-field EPR spectroscopy.[15]
Analogously other spin-labeled spin-traps may be used to
study the reactions of a radical RT with reactive radicals.[16]
Received: January 31, 2000
Revised: September 25, 2000 [Z14623]
[1] J. Michon, A. Rassat, J. Am. Chem. Soc. 1974, 96, 335 ± 337.
[2] Because EPR spectra are presented as ªderivative of absorptionº, the
number of spins responsible for an EPR line of peak-height h and
width DH is proportional to h7DH)2.
[3] R. Chiarelli, A. Rassat, Bull. Soc. Chim. Fr. 1993, 130, 299 ± 303.
[4] Typically, a single broad line is observed in fluid solutions when the
average distance between the unpaired spins is smaller than 500 pm.
7See ref. [1].)
The Molecular Controlled Semiconductor Resistor
7MOCSER; see reference [6]) provides an excellent way to
[5] H. Wieland, K. Roth, Chem. Ber. 1920, 53, 210 ± 230.
[6] H. Weber, A. Grzesiok, Pharmazie 1995, 50, 365 ± 366, and references
therein.
[7] R. J. Singh, N. Hogg, H. S. Mchaourab, B. Kalyanaraman, Biochem.
Biophys. Acta 1994, 1201, 437± 444.
[8] L. Marx, R. Chiarelli, T. Guiberteau, A. Rassat, J. Chem. Soc. Perkin
Trans. 1 2000, 1181 ± 1182.
[9] 4: H. J. Waldmann, J. Prakt. Chem. 1930, 126, 65 ± 68; 5: A. M. El-
Sharief, N. E. Hammad, Indian J. Chem. Sect. B 1981, 12, 1039 ± 1042;
6: adapted from K. Heidenbluth, R. Scheffler, J. Prakt. Chem. 1964,
23, 59 ± 70.
[10] In the point-dipole approximation 7N. Hirota, S. I. Weissman, J. Am.
Chem. Soc. 1964, 86, 2538 ± 2545), this interaction corresponds to a
distance d ˆ 580 pm between the two localized spins. It is also the
distance found by molecular mechanics 7Hyperchem software)
between the two nitrogen atoms.
[*] Prof. Dr. D. Cahen, Dr. D. G. Wu
Dept. of Materials and Interfaces
Weizmann Institute of Science
Rehovot 76100 7Israel)
Fax : 7‡972)8-934-4239
E-mail: david.cahen@weizmann.ac.il
Prof. Dr. A. Shanzer, G. Ashkenasy
Dept. of Organic Chemistry
Weizmann Institute of Science
Rehovot 76100 7Israel)
Fax : 7‡972)8-9342917
E-mail: coshanzr@wiccmail.weizmann.ac.il
Dr. D. Shvarts
AMOS Ltd., Rehovot 76100 7Israel)
Prof. Dr. R. Naaman, Dr. R. V. Ussyshkin
Dept. Of Chemical Physics
Weizmann Institute of Science
Rehovot 76100 7Israel)
[11] D. G. Gilles, L. H. Sutcliffe, X. Wu, J. Chem. Soc. Faraday Trans. 1994,
90, 2345 ± 2349.
[12] The structures of isomers 9a and 9b were assigned on the basis of the
effect of steric hindrance on their order of elution and on their UV
absorption 7J. N. Murrell, The Theory of the Electronic Spectraof
Organic Molecules, Methuen, London, 1963, p. 242).
[13] D. Grucker, T. Guiberteau, B. Eclancher, J. Chambron, R. Chiarelli,
A. Rassat, G. Subra, B. Gallez, J. Magn. Reson. B 1995, 106, 101 ±
109.
Fax : 7‡972)8-9344123
E-mail: ron.naaman@weizmann.ac.il
[**] We thank Rachel Lazar for her help in the synthesis. This work was
supported by the Israel Ministry of Sciences Tashtyoth program 7D.C.,
R.N., and A.S.), and by a grant from the Fussfeld foundation 7D.C. and
A.S.). A.S. holds the Siegfried and Irma Ullman professorial chair.
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detect NO. Recently we showed that the electrical resistivity
of this device is controlled by the adsorption of molecules on a
GaAs semiconductor surface.[6, 7] Here we present a modified
version of the MOCSER in which the GaAs surface is
derivatized by two-component molecular systems prior to the
experiment. Changes in the MOCSERꢁs current when NO
binds to the outer molecular component are examined to
follow the binding events in situ.
more strongly to the surface.[7] Modification in both elements
relative to 1 were done in ligand 4, which contains the
nonsymmetric binding site for iron porphyrins and a malonic
acid anchor. Devices covered by the iron porphyrin com-
plexes of ligands 2 ± 4 were expected to be more sensitive to
NO than those covered by the corresponding complexes of
the ªparentº ligand 1.
The formation of the expected low-spin ligand ± FeTPPCl
complexes was evidenced in solution by UV/Vis and 1H NMR
measurements, as described earlier for ligand 1.[8] Freshly
formed complexes of the four ligands with FeTPPCl were
adsorbed onto single crystal GaAs and characterized by FT-
IR spectroscopy, using the etched, bare 7but oxidized) GaAs
as a reference. The main absorbance bands 71700 ± 900 cmÀ1)
are listed in Table 1. For comparison, the corresponding bands
of the complexes in KBr are also listed. The typical vibrations
In these systems iron7iii) tetraphenylporphyrin chloride
7FeTPPCl) moieties, the NO binders, are not bound directly
to the GaAs surface, but rather, they are ªhingedº remotely
from the surface by bifunctional ligands 7Scheme 1). These
ligands bind axially, through imidazolyl groups, to the fifth
and sixth coordination sites of the iron7iii) porphyrin, and
simultaneously to the GaAs surface of the MOCSER through
anchoring groupsÐdisulfides or carboxylic acids. A special
feature of such a configuration is that the iron porphyrins will,
on the average, be oriented perpendicular to the surface. The
axial ligation to the metalloporphyrin rings prevents p ± p
interactions between themÐinteractions that are expected to
decrease the porphyrin activity.[8] The imidazole rings of the
ligands are bound to the FeIII center in a kinetically labile
fashion, so that one of them can be replaced by a stronger
binding substrate that approaches near the porphyrin.[9]
Complexes of FeTPPCl with the four bifunctional ligands
shown in Scheme 1 were used to probe the molecular features
that may affect the sensing event. Ligand 1 has a symmetric
bidentate metalloporphyrin binding site made of N-alkylimi-
dazoles and a disulfide as the anchoring group; ligand 2 has
the same anchor, but with a nonsymmetric metalloporphyrin
binding site, in which the NH group of the imidazole ring
imposes a weaker binding of the N-alkylimidazole group at
the opposite face; ligand 3 is symmetric in binding to the iron
porphyrin, but it has a malonic acid as an anchor which binds
Table 1. Main assignments of the vibrations in the transmission FT-IR spectra
7cmÀ1) for complexes of 1 ± 4 on single-crystal GaAs7100) surfaces. The values
obtained in KBr are given in parenthesis.
Com-
plex
nÄCONH
nÄCOOH
nÄC
ˆ
C
nÄaromatic
nÄCÀ
O
1
2
3
4
1660 71653)
1651 71652)
1551 71558) 1440 71442) 1100 71096)
1595 71597) 1441 71440) 1093 71094)
1630 ± 1690[a] 71653) 71715) 1546 71539) 1439 71441) 1093 71094)
1626 ± 1683[a] 71670) 71716) 1552 71554) 1441 71440) 1137 71136)
[a] Broad peak overlapping nÄCOOÀ vibration at ꢀ1640 cmÀ1
.
of the carbonyl group of the amide moieties and of the ether
bonds 7in the complexes formed from ligands 1 and 2) were
observed at approximately 1650 and 1100 cmÀ1, respectively.
Strong and broad bands were observed at 1625 ± 1690 cmÀ1 in
the spectra of the complexes formed from 3 and 4 because
Scheme 1.
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bands of the carbonyl group of the amide moieties overlapped
those of the carboxylate groups. The disappearance of the
band corresponding to the carboxylic group in the spectrum
7nÄCOOH 7vibration) 1715 ± 1716 cmÀ1 in KBr) when complexes
derived from 3 or 4 were adsorbed onto the GaAs indicates
consequence of the slight differences in the sensing area and
light conditions, the current was normalized by dividing the
measured current values by the different absolute responses
of the complex-covered MOCSERs to the aqueous medium
without NO.[17, 18] In less than ten minutes following the
introduction of NO no further changes in current were
observed, and the saturation current increases with an
increase of the NO ªsteady stateº concentration.[19]
that their carboxylic groups bind to the GaAs surface.[10] The
as
À
intensities of the absorbance peaks of nÄCONH or nÄCOO were
about 0.5 ± 1.5 Â 10À3, which indicates that a film of about one
monolayer is formed by each of the complexes 7from ligands
1 ± 4) on the GaAs substrate.[11] The ratios of the intensity of
the vibrations corresponding to the ligands to those of the iron
porphyrins remain similar to the ratios obtained from the KBr
measurements, thus eliminating the possibility that the com-
plexes decomposed during the adsorption process.
The experimental system was kept under anaerobic con-
ditions 7N2) for 30 minutes before and during the experiment
to remove practically all the O2 and to prevent formation of
the undesired NO2. No changes in current were observed
when MOCSERs covered by the complexes were exposed to
the unreactive by-product of the proteolysis, that is, N,N-
dimethyl-1,3-propylamine.[14] Only a very slight decrease in
current was observed when bare MOCSER devices were
exposed to various precursor concentrations 70.5 ± 5 ppm).
The changes in current with time for the bare MOCSER with
5 ppm of the precursor are included in Figure 1. The less
stable current obtained in this measurement shows that
adsorption of the complexes stabilizes the device surface.
Figure 2 shows the linear correlation of the saturation
current 7normalized) of MOCSERs covered by complexes of
ligands 2 ± 4 as a function of the NO ªsteady-stateº concen-
tration. To compare the sensitivity of the different MOCSER
types toward NO, we followed the 7interpolated) current
values on exposure of each to 2.0 ppm of NO. This value was
below our signal/noise 7data not shown) for the MOCSER
Contact potential differences 7CPD) were measured under
photosaturation conditions, to reveal the surface band bend-
ing 7BB) of the bare GaAs surface, and of surfaces covered
with monolayers of the complexes formed with ligands 1 ± 4.[12]
Adsorption of the two complexes formed from ligands with
disulfide anchors 71 and 2) resulted in a small decrease in the
BB relative to the bare surfaces. After adsorption of the
complexes formed from ligands 3 or 4, a much more
significant decrease in the BB was observed,[13] which was
ascribed to the stronger binding of their carboxylic groups,
relative to the disulfide groups, to the surface.
The response of MOCSERs covered by the complexes
formed from 1 ± 4 to different concentrations of NO was
determined in aqueous buffer solutions 7pH ˆ 7.4) at 258C. A
constant voltage of 100 mV was applied between the ohmic
contacts of the MOCSER during the experiment. Figure 1
shows the changes in the current with time for MOCSERs
covered by complexes derived from 1, when four different
concentrations of the organic NO precursor, 1-hydroxy-3-
methyl-3-7methylaminopropyl)-2-oxo-1-triazene, were re-
leased into the solution. At physiological pH this reagent
releases quantitatively two equivalents of NO with first order
kinetics and t1/2 ˆ 10.1 minutes at room temperature.[14±16] As a
Figure 1. Changes in current over time on exposure of a MOCSER
covered by complexes derived from 1 to different concentrations of
1-hydroxy-3-methyl-3-7methylaminopropyl)-2-oxo-1-triazene that releases
NO. The lower plot refers to reference measurements with
a bare
MOCSER. All measurements were done at room temperature, in pH ˆ
7.4 buffer solution, and under N . Inset: schematic drawing of the sensing
Figure 2. Normalized current of MOCSERs covered by complexes derived
from 2 and 3 7A), or 4 7B), as a function of the NO ªsteady-stateº
concentration.[19] Different MOCSERs were used for each measurement.
2
surface of the MOCSER. S: sensing window 70.3 mm2), E: epoxy, G:
AuGeNi ohmic contacts, W: water level.
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covered by the complex with 1, and the normalized current
values[17] for MOCSERs with complexes formed from 2, 3,
and 4 were 0.07, 0.38, and 0.50, respectively.
type of anchoring group dictate independently the activity of
the entire system.
In recent, preliminary, experiments we observed that dry
devices covered by complexes from 1 or 2 are much more
sensitive to NO7g) than to O27g) or CO7g). This result is
reasonable if one considers the weaker binding of O27g) and
CO7g) to iron7iii) porphyrins.[24] Experiments, designed to
sense NO exclusively in a biological environment of compet-
ing ligands, for example, other NOx species, are under way.
Two methods were used to release NO from the saturated
sample 7complex with 3, 5.0 ± 10.0 ppm NO) and to regenerate
the ability of the MOCSER to detect NO. In the first one, the
NO-saturated sample was taken out of the buffer solution,
dried in a stream of dry N2 for less than 15 seconds, and re-
immersed in a clean buffer solution. A current typical for the
NO-free system could then be measured. In the second
method, the NO-containing solution was replaced by a clean
buffer solution, and the current of the NO-free system was
reached within a few minutes 7t90 ꢀ 120 s). Subsequent ex-
posure of the samples to the same concentration of NO
resulted in the 7saturation) current being 70 ± 85% of the
original change, which demonstrates the system is reasonably
reversible under these conditions.
The system responds to NO mainly through the binding of
NO to the iron7iii) porphyrin moieties,[20] and not by direct
binding to the surface. The increase in current when the NO
binds to the derivatized surfaces results from a decreased
potential drop across the conducting GaAs layer 7of the
device). Such a decrease is explained by a change in the dipole
of the iron porphyrin/ligand complex following the replace-
ment of one coordinated imidazole ring by the NO radical
7stronger positive monopole at the binding group).[21]
Higher sensitivity was obtained for MOCSERs with the
nonsymmetric complex formed from 2 than with the complex
of 1, as deduced from the detection values of 2.0 ppm of NO.
This result can be understood from the greater ease by which
NO replaces the N-alkylimidazolyl ring of ligand 2 relative to
the imidazolyl ring of ligand 1 as a chelator to the FeIII center.
A similar process was observed earlier for replacement of the
coordinated N-alkylimidazole ring by O2.[22] Devices covered
by the complexes formed with ligand 3 are also more sensitive
to NO than those covered by complexes derived from 1. Since
the FeIII binding sites in the two complexes are the same, this
enhancement of the signal with 3 is attributed mainly to a
stronger binding of the dicarboxylate group to the surface,
relative to the binding of the disulfide group.[23] The tighter
mode of binding is expected to improve the electrical
communication between the anchoring site on the GaAs
surface and the NO binding site. Such communication can be
considered as signaling through the ligand skeleton, via its
anchor, to the surface.
Experimental Section
Synthesis: The synthesis of ligands 1 and 2 was described earlier,[8, 22] and
the detailed procedure to make ligands 3 and 4 will be described soon.[25]
Characterization of 3: IR 7KBr): uÄ ˆ 1652 7CONH), 1715 cmÀ1 7COOH);
1H NMR 7CD3OD): d ˆ 8.20 7s, 2H), 7.30 7s, 2H), 7.10 7s, 2H), 4.12 7br,
6H), 3.19 7t, J ˆ 7.0 Hz, 4H), 2.19 7t, J ˆ 6.5 Hz, 4H), 2.12 7t, J ˆ 6.5 Hz,
4H), 1.99 7quint, J ˆ 7.0 Hz, 4H), 1.30 7d, J ˆ 8.0 Hz, 6H); FAB-MS: m/z:
‡
604.8 [M ‡ H] . 4: IR 7KBr): uÄ ˆ 1670 7CONH), 1716 cmÀ1 7COOH);
1H NMR 7CD3OD): d ˆ 7.76 7s, 2H), 7.18 7s, 1H), 6.99 7s, 1H), 6.90 7s, 1H),
4.24 7dq, 2H), 4.06 7t, J ˆ 6.5 Hz, 2H), 3.35 7t, J ˆ 7.0 Hz, 2H), 3.16 7t, J ˆ
7.0 Hz, 2H), 2.79 7t, J ˆ 7.0 Hz, 2H), 2.21 7br, 4H), 2.14 7br, 4H), 1.98
7quint, J ˆ 7.0 Hz, 2H), 1.26 ± 1.34 7dd, 6H); MS 7electrospray): m/z: 591.4
‡
[M ‡ H] .
Complexes of each ligand with FeTPPCl were made by mixing 1/1 solutions
7>15 mm) in DMF 71 or 2), CHCl3/CH3OH 9/1 73), or CHCl3/2,2,2-
trifluoroethanol 7TFE) 8/2 74).
Sample preparation: Etched MOCSERs or GaAs substrates 7NH3/H2O
1/9) were immersed in solutions of freshly prepared ligand ± FeTPPCl
complexes overnight. The substrates were then rinsed by CHCl3/hexane
75% v/v, 1 or 2) or by CHCl3 73 or 4), and dried 7N2). To prevent leakage of
the electrical current through the conducting solution, the device was
encapsulated using epoxy, leaving a ªsensing windowº uncovered 7inset to
Figure 1). The linearity of the I-V characteristics was checked during the
measurements by a Keithley 236 Source Measure Unit.
Sensing NO by the derivatized MOCSERs: The NO-release solution was
prepared by dissolving a weighted amount of commercial 1-hydroxy-3-
methyl-3-7methylaminopropyl)-2-oxo-1-triazene 7Sigma) in a 0.01m solu-
tion of NaOH. These conditions for preparing the NO solution and for NO
injection are very similar to those previously described.[14] At basic pH
values the reagent is stable, and at physiological pH it releases 2.0 equiv-
alents of NO with first order kinetics having t1/2 ˆ 10.1 min at 228C. As
shown in ref. [14] NO is the only nitrosyl compound obtained during
proteolysis.[14] After the MOCSER current had been stabilized in the
7pH ˆ 7.4) phosphate buffer solution, the precursor was injected, and the
saturation current was obtained within 10 min.
Received: May 17, 2000
Revised: September 5, 2000 [Z15136]
[1] L. Packer, Methods in Enzymology, Vol. 301, Academic Press, New
York, 1998.
[2] F. Murad, Angew. Chem. 1999, 38, 1976 ± 1989; Angew. Chem. Int. Ed.
1999, 111, 1856 ± 1868.
[3] See for example: T. Malinski, Z. Taha, Nature 1992, 358, 676 ± 678.
[4] V. Petrouless, B. A. Diner, Biochim. Biophys. Acta 1990, 1015, 131 ±
140.
[5] H. Fujii, X. Wan, J. Zhong, L. J. Berliner, K. Yoshikawa, Magn. Reson.
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[6] K. Gartsman, D. Cahen, A. Kadyshevitch, J. Libman, T. Moav, R.
Naaman, A. Shanzer, V. Umansky, A. Vilan, Chem. Phys. lett. 1998,
283, 301 ± 306.
[7] A. Vilan, R. Ussyshkin, K. Gartsman, D. Cahen, R. Naaman, A.
Shanzer, J. Phys. chem. B 1998, 102, 3307± 3309.
[8] G. Ashkenasy, G. Kalyuzhny, J. Libman, I. Rubinstein, A. Shanzer,
Angew. Chem. 1999, 111, 1333 ± 1336; Angew. Chem. Int. Ed. 1999, 38,
1257± 1261.
Devices covered by the complexes of 4 were found to be the
most sensitive to NO. By utilizing the complex formed with 4
we demonstrated simultaneously: a) a better NO binding to
FeTPPCl, relative to the complex with 3, occurs with the
nonsymmetric metalloporphyrin binding site, and b) an en-
hanced signaling to the GaAs surface via the dicarboxylic
anchors occurs, relative to that found in devices covered by
the complexes formed with 2. We note that the currents
obtained when MOCSERs covered by complexes derived
from 4 were exposed to NO are similar to the summation in
current obtained in the two separate measurements with
devices covered by the complexes derived from 2 or 3 7for
example, for 2.0 ppm of NO). This phenomenon suggests that
the symmetry of the metalloporphyrin binding site and the
[9] Very recently another hybrid system was reported for detecting
gaseous NO. The binding of NO to MIII porphyrins which had been
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adsorbed directly onto CdSe surfaces was monitored by following
changes in the CdSe photoluminesence: A. Ivanisevic, M. F. Reynolds,
J. N. Burstyn, A. B. Ellis, J. Am. Chem. Soc. 2000, 122, 3731 ± 3738.
[10] M. Bruening, E. Moons, D. Yaron-Marcovich, D. Cahen, J. Libman, A.
Shanzer, J. Am. Chem. Soc. 1994, 116, 2972 ± 2977.
spite potentially useful carbon ± carbon bond forming reac-
tions, however, synthetic application of this rearrangement
still remains severely limited, mainly because of the rather low
yields and the restricted range of substrates. To this end, we
have recently developed the acetal [1,2] Wittig rearrangement
protocol which provides C-glycosides from primary-alcohol-
derived O-glycosides in a highly diastereoselective manner
[Eq. 71)].[2, 3]
[11] R. Cohen, S. Bastide, D. Cahen, J. Libman, A. Shanzer, Y. Rosenwaks,
Adv. Mater. 1997, 9, 746 ± 749.
[12] R. Cohen, L. Kronik, A. Shanzer, D. Cahen, A. Liu, Y. Rosenwaks,
J. K. Lorenz, A. B. Ellis, J. Am. Chem. Soc. 1999, 121, 10545 ± 10553.
[13] BB values 7Æ5 mV) as derived from the CPD measurements: bare
surface À265 mV, GaAs derivatized by: 1: À210, 2: À255, 3: À115,
and 4: À125 mV.
[14] J. A. Harbie, J. R. Klose, D. A. Wink, L. K. Keefer, J. Org. Chem.
1993, 58, 1472 ± 1476.
[15] C. M. Maragos, D. Morley, D. A. Wink, T. M. Dunams, J. E. Saavedra,
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Keefer, Cancer Res. 1993, 53, 564 ± 568.
[17] The normalized current was calculated from In7t) ˆ Im7t)/DI, where
In7t) is the normalized current, Im7t) is the measured current, and DI is
the difference between the currents measured in the buffer solution
and dry under N2.
[18] Y. Rudich, I. Benjamin, R. Naaman, E. Thomas, S. Trakhtenberg, R.
Ussyshkin, J. Phys. Chem. A 2000, 104, 5238 ± 5245.
[19] The term ªsteady-stateº concentration refers to NO concentrations
when t > t1/2, and the precursor decomposition is slow.
[20] M. Hoshino, L. Laverman, P. C. Ford, Coord. Chem. Rev. 1999, 187,
75 ± 102.
[21] A small change in the opposite direction explains the small decrease in
current seen for bare devices. The interaction of NO with the surface
of the bare device, which follows a release of surface-bound water
molecules, leaves the surface more negative than before.
[22] G. Ashkenasy, A. Ivanisevic, R. Cohen, C. E. Felder, D. Cahen, A. B.
Ellis, A. Shanzer, J. Am. Chem. Soc. 2000, 122, 1116 ± 1122.
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To extend this protocol we envisioned that the rearrange-
ment of a more functionalized O-glycoside system with a
secondary-alcohol-derived migrating terminus might afford
the C-glycoside with a tertiary alcohol side chain.[4] A key
feature for the success of the rearrangement is a rational
design of a migrating terminus. Thus, we selected the
ethynylvinylmethanol system as the migrating terminus with
a view that the ethynyl and vinyl substituent not only
enhances the [1,2] Wittig reactivity, as a result of the large
radical stabilizing effect, but also imparts unique multifunc-
tionality to the products 7Scheme 1, path A). Here we report a
stereoselective entry to the highly functionalized C-glycosides
based on an acetal [1,2] Wittig rearrangement and also a novel
[25] A. Ivanisevic, A. B. Ellis, G. Ashkenasy, A. Shanz-
er, Y. Rosenwaks, Langmuir 2000, 16, 7852 ± 7858.
HO ★
H3O+
O
path A
4'
X
3'
★
R'
[1,2] shift
H
Li
1'
OPG
2'
O
O
O
nBuLi
O
X
X
Stereoselective Synthesis of Highly
Functionalized C-Glycosides based
on Acetal [1,2] and [1,4] Wittig
Rearrangements**
X
E
R'
R'
1
★
OPG
E+
path B
O
O
[1,4] shift
★
R'
OPG
Katsuhiko Tomooka,*
Hiroshi Yamamoto, and Takeshi Nakai
Scheme 1. [1,2] and [1,4] Wittig rearrangement approach to the multi functionalized C-glycosides.
The [1,2] Wittig rearrangement is a classic class of carban-
ion rearrangements which is now well recognized to proceed
by a radical dissociation ± recombination mechanism.[1] De-
[1,4] Wittig rearrangement of an acetal system 7Scheme 1,
path B), which was discovered by chance in the [1,2] rear-
rangement study.
At the outset we studied the rearrangement of acetal b-3
which was prepared from 7À)-dihydro-3-hydroxy-4,4-dimeth-
yl-273H)-furanone 77À)-pantolactone) as a 1:1 epimeric
mixture at the C1' position in three steps: protection of the
hydroxyl groups, addition of lithium acetylide, and a mont-
morillonite K 10 clay catalyzed acetalization[5] with the
[*] Prof. Dr. K. Tomooka, Dr. H. Yamamoto, Prof. Dr. T. Nakai
Department of Applied Chemistry
Graduate School of Science and Engineering
Tokyo Institute of Technology
Meguro-ku, Tokyo 152 ± 8552 7Japan)
Fax : 7‡81)3-5734-3931
E-mail: ktomooka@o.cc.titech.ac.jp
protected ethynylvinylmethanol
2 7racemate) [Eq. 72);
[**] This work was supported by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Science, Sports, and Culture, Japan,
and by the Research for the Future Program, administered by the
Japan Society for the Promotion of Science.
TBDPS ˆ tert-butyldiphenylsilyl]. Two epimers of b-3 were
separable by chromatography on silica gel and their stereo-
chemistries were determined by X-ray crystallography and by
chemical conversion.[6] The reaction of b-7R)-3 with nBuLi
73 equiv) in THF at À788C afforded 7<10 min) the [1,2] re-
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Angew. Chem. Int. Ed. 2000, 39, No. 24