15N-D-labeled ionic probes for mass spectrometry

Article abstract of DOI:10.1016/j.tet.2011.08.013

An effective ¹⁵N- and deuterium (D)-labeled 2,6-bis(oxazolin-2- yl)pyridine (pybox)-La complex based probe ionization method that produces a distinct isotopic shift was developed. The distinct isotopic shift was detected by using the newly synthesized ¹⁵N-D-labeled pybox complexes. Moreover, O-[3-(tetramethylpybox)-propyl]-hydroxylamine (oxime-TMpybox) was prepared for attachment to the carbonyl group of the target molecule. Distinct isotopic shifts and multiple charged ions were detected for various compounds having amino, thiol, carboxyl, and carbonyl groups and fullerenes, using the TMpybox ionic probe series in cold-spray ionization mass spectrometry.

Full text of DOI:10.1016/j.tet.2011.08.013

Tetrahedron 67 (2011) 8009e8013
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
15N-D-labeled ionic probes for mass spectrometry
*
*
Fumihiro Ito , Shin Ando, Masato Iuchi, Taki Ukari, Momoka Takasaki, Kentaro Yamaguchi
Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan
a r t i c l e i n f o
a b s t r a c t
An effective 15N- and deuterium (D)-labeled 2,6-bis(oxazolin-2-yl)pyridine (pybox)eLa complex based
probe ionization method that produces a distinct isotopic shift was developed. The distinct isotopic shift
was detected by using the newly synthesized 15N-D-labeled pybox complexes. Moreover, O-[3-(tetra-
methylpybox)-propyl]-hydroxylamine (oximeeTMpybox) was prepared for attachment to the carbonyl
group of the target molecule. Distinct isotopic shifts and multiple charged ions were detected for various
compounds having amino, thiol, carboxyl, and carbonyl groups and fullerenes, using the TMpybox ionic
probe series in cold-spray ionization mass spectrometry.
Article history:
Received 19 July 2011
Accepted 6 August 2011
Available online 16 August 2011
Keywords:
Cold-spray ionization mass spectrometry
Isotope shift
Bis(oxazolinyl)pyridine
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
labeling is highly useful for precise structure analysis as well as
trace analysis in MS.4
Bis(oxazolinyl)pyridine tridentate ligands were first developed
by Nishiyama et al. for enantioselective organometallic catalysis,1
and have been used to generate chiral Lewis acid catalysts with
transition metals and lanthanides. Recently, chiral mass spec-
trometry (MS) was reported to be a new approach for stereo-
chemical analysis because of its speed and simplicity.2 In particular,
using an isotope-labeled pyboxemetal complex, Arakawa et al.
reported an excellent method for the determination of hetero-
chirality, which uses electrospray ionization (ESI)-MS.3 Isotope
Previously, we developed MS probes, including NHSeTMpybox
1, MaleTMpybox 2, BrAceTMpybox 3, and SareTMpybox 4. These
probes can donate multiple charges contained in their respective
metal charged sites to the target compound in order to analyze
large complex molecules, including biomolecules,5 and large car-
bon clusters, such as fullerenes,6 in soft ionization conditions
(Fig. 1). These ionic probes enable us to obtain 15N-labeled com-
pounds by complexation with 15N-labeled pyboxeLa complex, as
exemplified by (1þ6), thereby allowing comparison of the isotopic
Fig. 1. Ionic probe attachment ionization mass spectrometry.
shifts between labeled and non-labeled ionic probe attached bio-
molecules and fullerenes.6,7 However, the isotopic shift induced by
15N labeling was not distinct because the difference was only
0.7e1.3 u. Therefore, we prepared 15N2-D4-labeled pyboxeLa
* Corresponding authors. Tel.: þ81 87 894 5111; fax: þ81 87 894 0181; e-mail
addresses: h-itoh@kph.bunri-u.ac.jp (F. Ito), yamaguchi@kph.bunri-u.ac.jp
(K. Yamaguchi).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.08.013

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F. Ito et al. / Tetrahedron 67 (2011) 8009e8013
complex 6 (15N2-D4-6) in an attempt to observe the extended iso-
topic shift clearly. We also prepared a new MS probe, oxi-
meeTMpybox 5, which can react with the carbonyl group of the
target molecule. Various carbonyl compounds are important for
human physiology and a major concern in environmental chemis-
try. Testosterone, an important hormone, shows low ionization
efficiency because of its steroid moiety.8 In this paper, we describe
the preparation of the 15N2-D4-labeled ionic probes, including
oximeeTMpybox 5, which can selectively react with the carbonyl
group, for isotope-labeled MS in soft ionization conditions by using
cold-spray ionization MS (CSI-MS).9.
bound TS, doubly charged ions of [Mþacacꢁ]2þ (m/z: 543 and 544)
were detected, respectively (Fig. 2d and e). Similar to CA, the
isotope-labeled ion [Mþacacꢁ]2þ (m/z: 546), together with the
partially exchanged composition from ‘D’ to ‘H’ (m/z: 545.5, 15N2-
H2-D2 and m/z: 546.0, 15N2-H1-D3), was detected. Compared with
14N2-H4- and 15N2-D4-bound carbonyl compounds, the isotopic
shift of m/z ca. 3.0, corresponding to the increase in mass induced
2. Results and discussion
OximeeTMpybox 5 and 15N2-D4-6 were prepared as follows
(Scheme 1). Pybox 9 was obtained by alkylation of 4-hydroxypybox
7,5 which was prepared from chelidamic acid in six steps in 32%
yield, with phthalimide 8.10 Treatment of 9 with hydrazine mono-
hydrate gave oximeeTMpybox 5 in quantitative yield. After ethyl
ester 10, which was prepared from pyridine 2,6-dicarbonyl
dichloride and glycine-15N ethyl ester in 77% yield,5 was reduced
with NaBD4 and LiCl to furnish diol 11 in 79% yield,3 diol 11 con-
taining two hydroxyl groups was converted into dichloride 12 in
76% yield. Finally, 15N2-D4-6 was obtained by construction of an
oxazoline ring and complexation with La. Synthesized probe 5 and
15N2-D4-6 were then introduced to testosterone (TS) and cinna-
maldehyde (CA), and CSI-MS measurement was conducted to
confirm the specific probe attachment of 5 and the 15N and D iso-
tope labeling.11
5-Bound molecules were prepared as follows (method E). After
a pyridine solution of target carbonyl compound and 3 was stirred
at 80 ꢀC, the solution containing the derivative was poured into
a MeCN solution of 14N2-H4- or 15N2-D4-6.
The CSI mass spectra of 14N2-H4-, 15N2-H4-, and 15N2-D4-car-
bonyl compounds are shown in Fig. 2. In the case of (14N2-H4-6þ5)-
and (15N2-H4-6þ5)-bound CA, doubly charged ions of [Mþacacꢁ]2þ
(m/z: 465 and 466) were detected, respectively (Fig. 2a and b).
Similarly, the ion of [Mþacacꢁ]2þ (m/z: 468) was detected in (15N2-
D4-6þ5)-bound CA (Fig. 2c). This isotope-labeled ion was partially
exchanged from ‘D’ to ‘H’ (m/z: 467.4; 15N2-H2-D2 and m/z: 467.9;
15N2-H1-D3). In the case of (14N2-H4-6þ5)- and (15N2-H4-6þ5)-
Fig. 2. CSI mass spectra of (a) (14N2-H4-6þ5)-CA, (b) (15N2-H4-6þ5)-CA, (c) (15N2-D4-
6þ5)-CA, (d) (14N2-H4-6þ5)-TS, (e) (15N2-H4-6þ5)-TS, and (f) (15N2-D4-6þ5)-TS.
Scheme 1. Preparation of oximeeTMpybox 5 and 15N2-D4-6.

F. Ito et al. / Tetrahedron 67 (2011) 8009e8013
8011
by two 15N and four D atoms on an ion with two charges, was
detected. Compared with these mass spectra, extended isotopic
shifts were observed in 15N2-D4-6.
In order to induce multiple charged ions and observe the iso-
topic shift by 15N and D labeling, we applied this method to various
compounds [lysine (Lys), arginine, (Arg), cysteine (Cys), bradykinin
(BK), pepstatin A (PA), and fullerene (C60)].
(5þ6).Moreover, we prepared useful ionic probes that can react
with major functionalities in biomolecules, such as amino, car-
boxyl, carbonyl, and thiol groups. The biomolecules to which these
15N2-D4-labeled ionic probes are attached were easily ionized in
soft conditions and exhibited distinct isotopic shifts. We believe
that this method is useful for proteome analysis and isotope trace
experiments as well as the structure determination of large com-
plex molecules by deducing the mass-to-charge ratio in MS.
The CSI mass spectra of 14N2-H4- and 15N2-D4-bound amino
acids (Lys, Arg, and Cys) are shown in Fig. 3. 15N2-D4-amino acids,
which were prepared by method B5 using NHSeTMpybox 1 and
MaleTMpybox 2, exhibited doubly charged ions [Mþacacꢁ]2þ (m/z:
482, 496, and 504) (Fig. 3). The isotopic shift of m/z ca. 3.0, which
corresponded to the increase in mass induced by two 15N and four
D atoms on an ion with two charges, was detected. Next, the CSI
mass spectra of 14N2-H4- and 15N2-D4-bound BK and those of 14N2-
4. Experimental section
4.1. General
All melting points were measured on a Yanaco MP-500D and are
uncorrected. Infrared spectra were recorded on a JASCO FT/IR 6300
Fig. 3. CSI mass spectra of (a) (14N2-H4-6þ1)-Lys, (b) (15N2-D4-6þ1)-Lys, (c) (14N2-H4-6þ1)-Arg, (d) (15N2-D4-6þ1)-Arg, (e) (14N2-H4-6þ2)-Cys, (f) (15N2-D4-6þ2)-Cys.
H4- and 15N2-D4-bound PA are shown in Fig. 4. In the case of 14N2-
H4- and 15N2-D4-PA, which were prepared by method C7 using
BrAceTMpybox 3, doubly charged ions of [Mþacacꢁ]2þ (m/z: 771
and 774) (Fig. 4a and b, respectively) were observed, respectively, in
the CSI mass spectra. For the same reason, the isotopic shift of m/z
ca. 3.0 was detected. In the case of 14N2-H4- and 15N2-D4-BK, which
were prepared by method B5 using NHSeTMpybox 1, triply charged
ions of [Mþacetylacetone]3þ (m/z: 624 and 626) (Fig. 4c and d,
respectively) were observed, respectively, in the CSI mass spectra.
The isotopic shift of m/z ca. 2.0, which corresponded to the increase
in mass induced by two 15N and four D atoms on an ion with three
charges, was detected. Finally, the CSI mass spectra of 14N2-H4- and
15N2-D4-C60, which were prepared by method D6 using SareTM-
pybox 4, are shown in Fig. 5. Using 14N2-H4-6, multiple charged ions
[(14N2-H4-6þ4)-C60þacacꢁ]2þ (m/z: 812) and [2(14N2-H4-6þ4)-
C60þ2acacꢁ]4þ (m/z: 632) were detected (Fig. 5a). In the case of
15N2-D4-6, 15N2-D4-labeled probes attached to C60 were detected as
multiple charged ions [(15N2-D4-6þ4)-C60þacacꢁ]2þ (m/z: 815) and
[2(15N2-D4-6þ4)-C60þ2acacꢁ]4þ (m/z: 635) as observed in the non-
labeled ones with a definite isotopic shift of m/z ca. 3.0 (Fig. 5b).12
spectrophotometer with an ATR (attenuated total reflectance)
system. Unless otherwise stated, 1H, 13C, 15N, and 31P NMR spectra
were recorded in CDCl3 on a JEOL JNM-ECP 400 and a Bruker
400 MHz with tetramethylsilane (TMS) as internal reference. CSI
3. Conclusions
We succeeded in synthesizing 15N2-D4-labeled pyboxeLa com-
plex 6 and oximeeTMpybox 5 to obtain five ionic probes, isotope-
labeled metal complexes (1þ6), (2þ6), (3þ6), (4þ6), and
Fig. 4. CSI mass spectra of (a) (14N2-H4-6þ3)-PA, (b) (15N2-D4-6þ3)-PA, (c) (14N2-H4-
6þ1)-BK, (d) (15N2-D4-6þ1)-BK.

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F. Ito et al. / Tetrahedron 67 (2011) 8009e8013
(12H, s), 2.27 (2H, t, J¼6.0 Hz), 4.20 (4H, s), 4.39 (2H, t, J¼6.0 Hz),
4.41 (2H, t, J¼6.0 Hz), 7.72 (2H, s), 7.75e7.78 (2H, m), 7.82e7.85 (2H,
m). 13C NMR (100 MHz)
: 28.0, 28.4, 64.7, 67.9, 74.6, 79.7, 112.2,
d
123.6, 128.9, 134.6, 148.5, 160.9, 163.6, 165.7. HRESIMS m/z 515.1909
(calcd for C26H28N4NaO6: 515.1907). Anal. Calcd for C26H28N4O6: C,
63.40; H, 5.73; N, 11.38. Found: C, 63.21; H, 5.62; N, 11.38.
4.1.3. Synthesis of O-{3-[2,6-bis-(4,4-dimethyloxazolin-2-yl)-pyr-
idin-4-yloxy]-propyl}-hydroxylamine (5). Hydrazine monohydrate
(0.40 mL, 2.76 mmol) was added to a solution of 9 (300 mg,
0.83 mmol) in CH2Cl2 (10 mL) and the whole mixture was stirred at
room temperature for 30 min and then filtered through a Celite
pad. The filtrate was concentrated in vacuo to give 5 (482 mg, 72%)
as a yellowish powder. This product was used without further
purification. Mp 58e63 ꢀC. IR (ATR, cmꢁ1): 3371, 1643. 1H NMR
(400 MHz)
J¼6.0 Hz), 4.19 (4H, s), 4.20 (2H, t, J¼6.0 Hz), 5.43 (2H, br s), 7.67
(2H, s). 13C NMR (100 MHz)
: 28.0, 28.4, 65.6, 67.9, 71.7, 79.7, 112.1,
d: 1.38 (12H, s), 2.08 (2H, q, J¼6.0 Hz), 3.80 (2H, t,
d
148.4, 161.0, 165.9. HRESIMS m/z 385.1867 (calcd for C18H26N4NaO4:
385.1852).
4.1.4. Synthesis of 15N2,15N6-bis(1,1-dideutero-2-hydroxyethyl)-2,6-
pyridine-dicarboxamide (11). Under Ar, to a dry THF (30 mL) so-
lution of 10 (1.08 g, 3.17 mmol) and LiCl (1.00 g, 23.6 mmol) was
added NaBD4 (846 mg, 20.2 mmol) at room temperature. After the
whole mixture was stirred at room temperature for 12 h, MeOH
and acetone were added at 0 ꢀC and the whole mixture was
evaporated in vacuo. The residue was purified by reversed-phase
flash column chromatography (H2O/MeCN¼100:0 to 50:50) to
obtain colorless powder 11 (647 mg, 79%). Mp 164e168 ꢀC. IR
Fig. 5. CSI mass spectra of (a) (14N2-H4-6þ4)-C60 and (b) (15N2-D4-6þ4)-C60
.
mass spectra were recorded on a JEOL JMS-T100LC mass spec-
trometer equipped with a cold-spray ion source. Silica gel 60 F254
TLC plates (Merck No. 5715) and NH plates (Fuji Silysia Chemical,
Ltd., No. TO80817) were used for TLC. For column chromatography,
silica gel 60 (spherical, particle size 63e210 mm, Kanto Chemical,
(ATR, cmꢁ1): 3386, 3274, 1657, 1519. 1H NMR (400 MHz, CD3OD)
d:
No. 37565-84 for neutral) and NH silica gel (Fuji Silysia Chemical
Ltd., particle size 200e350 mesh, No. HU80502) were used. Com-
biFlash Companion (Teledyne Isco) was used for reversed-phase
flash column chromatography. Eyela FDU-1200 was used as the
vacuum freeze dryer. TS, BK, and all anhydrous solvents were
purchased from Wako Pure Chemical. DMSO was purchased from
Merck. NaBD4 (90%, 98 atm % D) was purchased from Aldrich.
Fullerene C60 was purchased from TCI.
3.58 (4H, s), 8.14 (1H, t, J¼8.2 Hz), 8.27 (2H, d, J¼8.2 Hz). 13C NMR
(100 MHz, CD3OD)
d
: 41.6 (d, JCN¼10 Hz), 59.9 (t, JCD¼22 Hz), 124.3,
139.0, 148.7 (d, JCN¼7 Hz), 164.8 (d, JCN¼18 Hz). 15N NMR (40 MHz,
CD3OD)
d:
102.0. HRCSIMS m/z 282.1110 (calcd for
C111H211H144N15N2NaO4: 282.1152).
4.1.5. Synthesis of 15N2,15N6-bis(1,1-dideutero-2-chloroethyl)-2,6-
pyridine-dicarboxamide (12). Under Ar, a SOCl2 (8 mL) solution of
alcohol 11 (613 mg, 2.36 mmol) was stirred under reflux for 1 h.
After cooling to room temperature, SOCl2 was azeotroped with
toluene. The residue was diluted with CH2Cl2 and the organic layer
was washed with H2O and brine, dried over Na2SO4, and evapo-
rated in vacuo. The residue was purified by column chromatogra-
phy (n-hexane/ethyl acetate¼1:2) to obtain 12 (408 mg, 76%) as
a colorless powder. Mp 145e147 ꢀC. IR (ATR, cmꢁ1): 3344, 3303,
4.1.1. Synthesis of N-3-bromopropyloxy-phthalimide (8). Under Ar,
a solution of N-hydroxyphthalimide (2.01 g, 12.3 mmol), 1,3-
dibromopropane (2.5 mL, 24.5 mmol), and NEt3 (3.3 mL,
23.7 mmol) in dry DMF (30 mL) was stirred at room temperature
for 18 h. The reaction was quenched with H2O and extracted with
ethyl acetate. The organic layer was washed with H2O and brine,
dried over Na2SO4, and evaporated in vacuo. The residue was pu-
rified by SiO2 column chromatography (n-hexane/ethyl
acetate¼5:1) to give 8 (2.30 g, 66%) as a colorless solid. Mp
1650, 1507. 1H NMR (400 MHz)
d
: 3.87 (4H, d, J¼6.0 Hz), 8.07 (1H, t,
J¼8.0 Hz), 8.09 (1H, t, J¼6.0 Hz), 8.32 (1H, t, J¼6.0 Hz), 8.38 (1H, d,
71e72 ꢀC. IR (ATR, cmꢁ1): 1725. 1H NMR (400 MHz)
d
: 2.32 (2H, q,
J¼6.0 Hz), 3.72 (2H, t, J¼6.0 Hz), 4.37 (2H, t, J¼6.0 Hz), 7.75e7.79
(2H, m), 7.83e7.88 (2H, m). 13C NMR (100 MHz)
: 29.3, 31.5, 76.1,
123.6, 128.9, 134.6, 163.6. HRESIMS m/z 305.9704 (calcd for
J¼8.0 Hz). 13C NMR (100 MHz)
: 41.1 (d, JCN¼11 Hz), 43.6 (t,
d
JCD¼21 Hz), 125.3, 139.2, 148.5 (d, JCN¼8.0 Hz), 163.6 (d, JCN¼17 Hz).
15N NMR (40 MHz)
C111H29H345Cl124N15N2NaO2:
d
: 97.6. HRCSIMS m/z 318.0429 (calcd for
d
318.0474),
320.0407
(calcd
for
79
C111H92H435Cl37Cl14N15N2NaO2: 320.0445), 322.0381 (calcd for
C111H29H437Cl124N15N2NaO2: 322.0415).
C11
C11
H
H
BrNNaO3:
305.9742)
and
307.9685
(calcd
for
10
81
10
BrNNaO3: 307.9721). Anal. Calcd for C11H10BrNO3: C, 46.50;
H, 3.55; N, 4.93. Found: C, 46.59; H, 3.28; N, 4.96.
4.1.6. Synthesis of 2,6-bis(5,5-dideutero-oxazolin-2-yl)-15N2-pyridine
(13). Under Ar, to a dry THF (5 mL) solution of dichloride 12
(507 mg, 1.71 mmol) was added NaH (60%, 217 mg, 5.41 mmol) at
room temperature. After the whole mixture was stirred at room
temperature for 1 h, the mixture was filtered. After the filtrate was
evaporated in vacuo, the residue was purified by NH column
chromatography (n-hexane/acetone¼1:1) to obtain 13 (274 g, 72%)
as a brownish powder. Mp 234e236 ꢀC. IR (ATR, cmꢁ1): 1647, 1623,
4.1.2. Synthesis of 2,6-bis(4,4-dimethyloxazolin-2-yl)-4-(3-phthali-
midooxy-propyloxy)pyridine (9). Under Ar, a mixture of 4-hydro-
xypybox
7 (1.44 g, 4.98 mmol), phthalimide 8 (2.24 g,
7.90 mmol), and K2CO3 (2.21 g, 16.0 mmol) in dry DMF (20 mL) was
stirred at room temperature for 15 h. The reaction was quenched
with H2O and extracted with CH2Cl2. The organic layer was washed
with H2O and brine, dried over Na2SO4, and evaporated in vacuo.
The residue was washed with a mixed solvent of n-hexane/ethyl
acetate¼1:1 to give 9 (1.78 g, 73%) as a colorless solid. Mp
1567. 1H NMR (400 MHz)
d
: 4.12 (4H, s), 7.89 (1H, t, J¼8.0 Hz), 8.17
(2H, d, J¼8.0 Hz). 13C NMR (100 MHz)
: 54.9 (d, JCN¼4 Hz), 68.0 (t,
d
191e192 ꢀC. IR (ATR, cmꢁ1): 1725, 1641. 1H NMR (400 MHz)
d: 1.39
JCD¼22 Hz), 125.5 (d, JCN¼1 Hz), 137.4, 146.7 (d, JCN¼8 Hz), 163.5. 15
N

F. Ito et al. / Tetrahedron 67 (2011) 8009e8013
8013
NMR (40 MHz)
d
: 221.0. HRCSIMS m/z 246.0904 (calcd for
Supplementary data
C111H27H144N15N2NaO2: 246.0941).
1H and 13C NMR spectra of 5, 8, 9, 11, 12,13, 14 and mass spec-
4.1.7. Synthesis of tris(acetylacetonato)[2,6-bis(5,5-dideutero-ox-
azolin-2-yl)-15N2-pyridine]lanthanum (III) (14). Under Ar, after
a mixture of 13 (103 mg, 0.46 mmol) and La(acac)3 (353 mg,
0.81 mmol) in THF (5 mL) was stirred at room temperature for 24 h,
it was filtered to give 14 (282 mg, 93%) as a colorless powder. This
product was used without further purification. Mp 223e225 ꢀC. IR
trometry of [3(15N2-D4-6þ5)þC60þ3acacꢁ
]
6þ, [3(14N2-H4-6þ5)þ
C60þ3acacꢁ]6þ. Supplementary data associated with this article can
be found in online version at doi:10.1016/j.tet.2011.08.013.
References and notes
(ATR, cmꢁ1): 1645, 1591, 1575, 1509. 1H NMR (400 MHz, CD2Cl2)
d:
1. (a) Nishiyama, H.; Kondo, M.; Nakamura, T.; Itoh, K. Organometallics 1991, 10,
500e508; (b) Motoyama, Y.; Kurihara, O.; Murata, K.; Aoki, K.; Nishiyama, H.
Organometallics 2000, 19, 1025e1034.
2. (a) Speranza, M. Int. J. Mass Spectrom. 2004, 232, 277e317; (b) Filippi, A.;
Giardini, A.; Piccirillo, S.; Speranza, M. Int. J. Mass Spectrom. 2000, 198, 137e163;
(c) Sawada, M. Mass Spectrom. Rev. 1997, 16, 73e90; (d) Tao, W. A.; Cooks, R. G.
Anal. Chem. 2003, 75, 25Ae31A.
1.66 (18H, s), 4.32 (4H, s), 5.15 (3H, s), 7.89 (2H, d, J¼8.0 Hz), 8.00
(1H, t, J¼8.0 Hz). 13C NMR (100 MHz, CD2Cl2)
d: 27.5, 53.7, 69.9, 99.7,
124.9, 139.3, 145.1, 163.7, 187.8. 15N NMR (40 MHz, CD2Cl2)
d: 224.4.
HRCSIMS m/z 560.0973 (calcd for C126H228H1439La14N15N2O8ꢁacac:
560.0999).
3. Sato, H.; Suzuki, Y.; Takai, Y.; Kawasaki, H.; Arakawa, R.; Shizuma, M. Chem. Lett.
2010, 39, 564e566.
4.1.8. Synthesis of acetylacetonato(dihexafluorophosphine)[2,6-
bis(5,5-dideutero-oxazolin-2-yl)-15N2-pyridine]lanthanum (III) (6).
Under Ar, a suspension of 14 (245 mg, 0.34 mmol) and NH4PF6
(376 mg, 2.31 mmol) in CH2Cl2 (5 mL) was stirred at room tem-
perature for 24 h. The reaction mixture was filtered to give 15N2-
D4-6 (435.7 mg, quant.) as a colorless powder. This product was
used without further purification. Mp >300 ꢀC. IR (ATR, cmꢁ1):
4. (a) Sawada, M.; Takai, Y.; Yamada, H.; Yamaoka, H.; Azuma, T.; Fujioka, T.; Ka-
wai, Y.; Tanaka, T. Chem. Commun. 1998, 1569e1570; (b) Shizuma, M.; Imamura,
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Sawada, M.; Takai, Y.; Yamada, H.; Hirayama, S.; Kaneda, T.; Tanaka, T.; Kamada,
K.; Mizooku, T.; Takeuchi, S.; Ueno, K.; Hirose, K.; Tobe, Y.; Naemura, K. J. Am.
Chem. Soc. 1995, 117, 7726e7736.
5. (a) Ito, F.; Nakamura, T.; Yorita, S.; Danjo, H.; Yamaguchi, K. Tetrahedron Lett.
2009, 50, 6252e6255; (b) Ito, F.; Yamaguchi, K. Heterocycles 2010, 81, 895e990.
6. Ito, F.; Yamaguchi, K. Org. Biomol. Chem. 2011, 9, 2674e2679.
7. Ito, F.; Ando, S.; Iuchi, M.; Nakamura, T.; Yorita, S.; Yamaguchi, K. Org. Biomol.
Chem. 2010, 8, 4408e4413.
1644, 1575, 1508, 1409. 1H NMR (400 MHz, DMSO-d6)
s), 3.97 (4H, s), 5.35 (1H, s), 8.08 (3H, s). 13C NMR (100 MHz,
DMSO-d6) : 27.9, 54.6, 68.7, 94.8, 126.4, 140.0, 145.6, 162.8, 188.8.
d: 1.77 (6H,
d
31P{1H} NMR (162 MHz, DMSO-d6)
d
: ꢁ143.6 (heptet, J¼711 Hz).
8. Suzuki, Y.; Taniji, N.; Ikeda, C.; Honda, A.; Ookubo, K.; Citterio, D.; Suzuki, K.
Anal. Sci. 2004, 20, 475e482.
15N NMR (40 MHz, DMSO-d6)
d: 224.2. HRCSIMS m/z 342.0766
9. CSI condition is suited for the analysis of biomolecules and metal complexes;
(a) Sakamoto, S.; Fujita, M.; Kim, K.; Yamaguchi, K. Tetrahedron 2000, 56,
955e964; (b) Yamaguchi, K. J. Mass Spectrom. 2003, 38, 473e490.
10. Rathore, K.; Vyas, R.; Talesara, G. L. Indian J. Chem., Sect. B: Org. Chem. Incl. Med.
Chem. 2005, 44B, 2166e2170.
139
(calcd for C16H18
342.0798).
F
12
LaN15N2O4P2þ13 (C111H27H144N15N2O2)ꢁ2PF6:
11. CSI mass spectra were recorded on a JEOL JMS-T100LC time of flight mass
spectrometer equipped with a cold-spray ion source. This setup makes it pos-
sible to conduct measurements at low temperatures. Measurement conditions
were as follows: sprayer temperature: ꢁ20 to 20 ꢀC; needle voltage: þ1500 to
2500 V; ring lens voltage: þ5 to 10 V; orifice 1 voltage: þ20 to 50 V; orifice 2
Acknowledgements
This work was supported by JST and a Grant-in-Aid for Scientific
Research on Innovation Areas ‘Emergence in Chemistry’ (20111007)
from the Japanese Ministry of Education, Culture, Sports, Science
and Technology (MEXT).
voltage: þ5 to 10 V; concn ca. 0.5 mM.
12. Although [3(15N2-D4-6þ5)þC60þ3acacꢁ
]
(m/z 575) was detected, the ion
6þ
intensity was as small as a noise (see Supplementary data).