Substituent effect at the C4-position of 1,3a,6a-triazapentalene

Article abstract of DOI:10.1248/cpb.c16-00196

Various 2,4-disubstituted-1,3a,6a-triazapentalenes possessing methyl and phenyl groups at the C4-position were synthesized. Fluorescence observation of the synthetic 4-methyl- and 4-phenyl-1,3a,6a-triazapentalenes revealed that the introduction of a subst

Full text of DOI:10.1248/cpb.c16-00196

830
Chem. Pharm. Bull. 64, 830–837 (2016)
Vol. 64, No. 7
Special Collection of Papers
This article is dedicated to Professor Satoshi Ōmura in celebration of his 2015 Nobel Prize.
Regular Article
Substituent Effect at the C4-Position of 1,3a,6a-Triazapentalene
Atsushi Nakayama,a Satoshi Nishio,a Akira Otani,a Akane Mera,a
,a
Ayumi Osawa,b Keiji Tanino,c and Kosuke Namba*
a Graduate School of Pharmaceutical Science, Tokushima University; 1–78 Shomachi, Tokushima
b
770–8505, Japan: Graduate School of Chemical Science and Engineering, Hokkaido University;
c
Sapporo 060–0810, Japan: and Department of Chemistry, Faculty of Science,
Hokkaido University; Sapporo 060–0810, Japan.
Received February 27, 2016; accepted April 12, 2016
Various 2,4-disubstituted-1,3a,6a-triazapentalenes possessing methyl and phenyl groups at the C4-posi-
tion were synthesized. Fluorescence observation of the synthetic 4-methyl- and 4-phenyl-1,3a,6a-triazapen-
talenes revealed that the introduction of a substituent at the C4-position allowed a long-wavelength shift of
the fluorescence maximum. Furthermore, the phenyl group at the C4-position was found to induce a substan-
tial increase in the extinction coefficient value.
Key words 1,3a,6a-triazapentalene; substituent effect; longer-wavelength shift; 4-methyl-1,3a,6a-triazapen-
talene; 4-phenyl-1,3a,6a-triazapentalene
Fluorescent organic molecules are an important class of been extended to the red color region, and their molecules
compounds in modern science and technology, and are widely are smaller than the conventional yellow and red fluorescent
used in biological imaging probes, sensors, lasers, and light- molecules.25) The yellow derivatives were proven to be useful
emitting devices.1–3) Thus, the development of useful fluores- fluorescent labeling reagents. On the other hand, the introduc-
cent organic molecules is crucial for the advancement of many tion of an electron-donating substituent at the C5-position
industries, and has been a subject of intensive research.4–15) In substantially increased the fluorescence intensity, whereas the
particular, fluorescent organic molecules have received a great fluorescence wavelength remained nearly unaffected.26) For
deal of attention in a pharmacology field, because the visual- example, the comparison of fluorescence quantum yield (ΦF)
ization of biologically active small compounds by introducing between the 5-methoxy derivative and an unsubstituted analog
fluorophores is one of the most useful methods in mechanistic of 2-(4-cyanophenyl)-1,3a,6a-triazapentalene shows that the
studies.16–22) However, the introductions of fluorescent organic introduction of a methoxy group at the C5-position drastically
molecules sometimes induces a loss of biological activities increases the ΦF from 0.15 to 0.57 with no significant effect
because the physical properties of fluorescent molecules affect on the fluorescence wavelength. Recently, the development
the biological activities of the original compound. Further- of wavelength-tunable and/or quantum yields-tunable fluoro-
more, highly fluorescent organic molecules are usually larger phores has been a subject of great concern for intelligent fluo-
than small biologically active compounds, and the fluorescent rescent probes.27–33) The 1,3a,6a-triazapentalene system also
labeling reagent disturbs the original interactions of the par- provides a novel fluorescent molecule that enables the same
ent compounds with target proteins such as receptors. To fluorescent chromophore to exhibit various fluorescence colors
overcome these problems, there is strong demand for the de- and quantum yields. That is, the fluorescence wavelength and
velopment of small fluorophores. We recently discovered that quantum yield can be controlled by the 2- and 5-substituents,
1,3a,6a-triazapentalene 1 is a compact and highly fluorescent respectively.
chromophore23) (Fig. 1). Since the disclosure of the fluores-
Although we found that the 2- and 5-substitutents respec-
cence properties of 1,3a,6a-triazapentalenes, the 1,3a,6a- tively change the fluorescence properties of 1,3a,6a-triazapen-
triazapentalene system has attracted a great deal of interest talenes in different ways, the effects of other positions, such
as a novel fluorophores, and another group has also reported as the 3-, 4-, and 6-positions, have not been elucidated. In par-
the alternative synthesis of 1,3a,6a-triazapentalenes.24) 1,3a,6a- ticular, although a few 2,4-disubstituted-triazapentalenes have
Triazapentalenes exhibit various useful fluorescence properties already been prepared in previous studies (vide infra),23,25) the
such as intense fluorescence, a large Stokes shift, and a posi- effect of a 4-substituent on fluorescence properties has not
tive fluorescence solvatochromism. More interestingly, the flu- been investigated in detail. Therefore, we herein report the
orescence wavelengths of 1,3a,6a-triazapentalenes vary widely changes in fluorescence properties of 1,3a,6a-triazapentalenes
with 2-substituents. For example, the fluorescence maxima by the introduction of a 4-substituent (Fig. 2).
shifts to longer wavelengths as the inductive effect of the
We first attempted to introduce a methyl group as the
2-substituents increases. On the basis of this effect, the fluo- simplest substituent into 2-(4-cyanophenyl)-1,3a,6a-triazapen-
rescence wavelength of 1,3a,6a-triazapentalenes has recently talene 1a, which is one of the stablest and highly fluorescent
*To whom correspondence should be addressed. e-mail: namba@tokushima-u.ac.jp
© 2016 The Pharmaceutical Society of Japan

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Fig. 1. Structure of 1,3a,6a-Triazapentalene 1 and Substituent Effects at C2- and C5-Positions
Fig. 2. The Substituent Effects of 1,3a,6a-Triazapentalenes
analog among synthetic triazapentalenes. According to our
previous synthesis of 1,3a,6a-triazapentalenes,23) the azide 2a
having two triflates was treated with alkyne 3a in the pres-
Chart 1. Synthesis of 4-Methyl-2-(4-cyanophenyl)-1,3a,6a-triazapen-
talene 4a
ence of 5mol% of CuI and 5 equiv of triethylamine (TEA) to
induce the following cascade reaction. The click reaction of
2a with 3a proceeded to afford triazole A, which underwent
an intramolecular SN2 reaction to give triazolium ion B. Sub-
sequent reactions of E2 elimination (B→C) and deprotonation
(C→D) produced the desired 4-methyl-2-(4-cyanophenyl)-
1,3a,6a-triazapentalene 4a in 86% yield (Chart 1).
After preparing a 4-methyl analog of 2-(4-cyanophenyl)-
1,3a,6a-triazapentalenes, we compared its fluorescence prop-
erties with 5-methyl analog 5a and unsubstituted analog 1a
in dichloromethane.34) As is the case with 5-methoxy analog
depicted in Fig. 1, the ΦF of 5-methyl analog 5a (ΦF=0.46)
was much higher than that of the unsubstituted analog 1a
(ΦF=0.15), whereas the fluorescence wavelength showed only
a slight shift. In clear contrast, the fluorescence maximum
of 4-methyl analog 4a shifted to a longer-wavelength region
(543nm), and the ΦF value (0.17) was slightly increased. This
suggested that the introduction of the methyl group at the C4-
position induced an approximately 35nm longer shift of the
fluorescence maximum with only a small increase in fluores-
cence quantum yield (Fig. 3).
Fig. 3. Fluorescence Spectra of 1a, 4a, and 5a in Dichloromethane
To investigate the generality of the effect of the methyl a longer-wavelength emission, was also obtained in acceptable
group at the C4-position, various 4-methyl analogs of 1,3a,6a- yield (entry 6), and the corresponding 4-unsubstituted analog
triazapentalenes were next synthesized (Table 1). The similar 1g was also obtained in acceptable yield (entry 6). In the case
click reaction of 2a with methyl propiolate 3b afforded 4b as of 3h possessing two alkynes, the click reaction stopped at the
an aliphatic derivative in 94% yield (entry 1). Although the formation of the first 1,3a,6a-triazapentalene, and the mono-
reaction of ethynylbenzene analogs possessing electron-with- triazapentalene intermediate readily decomposed during silica
drawing groups (3c–e) and another phenyl ring (3f) also pro- gel column chromatography. In contrast, a similar double click
ceeded to give 4c–f in 50, 82, 19, and 28% yields, respectively reaction leading to the corresponding 4-unsubstituted analog
(entries 2–5). The decline in yields of these analogs was due proceeded to give bis-1,3a,6a-triazapentalene 1h in 46% yield.
to the partial decomposition of 4-methyl analogs during silica Finally, the copper-free click reaction of strained alkyne 3i,
gel column chromatography. The stability of 4-methyl analogs reported by Igawa, Tomooka and colleagues,35) was applied to
seems to be poorer than that of 4-unsubstituted analogs. Next, the 1,3a,6a-triazapentalene synthesis. Treatment of 2a with 3i
various alkynes that had never been applied to the synthesis in the presence of TEA without copper salt in tetrahydrofuran
of 1,3a,6a-triazapentalenes were attempted. Thus, 4-unsub- (THF) afforded the desired 4-methyl-1,3a,6a-triazapentalene
stituted-1,3a,6a-triazapentalenes were also synthesized along 4i in 49% yield, and a similar click reaction leading to 4-un-
with 4-methyl analogs. The naphthyl derivative 4g, expecting substiuted analog also proceeded to give 1i in 51% yield. This

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Vol. 64, No. 7 (2016)
Table 1. Click Reaction of 2a with Various Alkynes
analog 1b, whereas the 25nm longer shift of the fluorescence
maximum in 4b was shorter than the 34nm of the 2-phenyl
analog 4a. On the other hand, all other 2-phenyl analogs 4c–f
exhibited around 35nm longer wavelengths of fluorescence
maximum than the corresponding 4-unsubstituted analogs
1c–f. Therefore, the introduction of a methyl group at the
C4-position to 2-phenyl derivatives of 1,3a,6a-triazapentalene
was found to generally induce an approximately 35nm long-
wavelength shift of the fluorescence maximum. In contrast,
a noteworthy regularity was not observed in the effect of
4-methyl group on the ΦF of 4c–f, although the ΦF tended to
decrease in the case of highly electron-deficient phenyl group
at the C2-position. Meanwhile, 2-naphthyl derivative 1g, and
not 2-phenyl derivatives, showed the similar fluorescence
properties as biphenyl derivatives 1f, and the 4-methyl group
of 4g induced a 25nm longer shift of the fluorescence maxi-
mum than 1g as with 2-methoxy carbonyl derivative 4b. Thus,
the approximately 35nm long-wavelength shift induced by the
4-methyl group was found to be a particular shift of 2-phenyl
derivatives. Interestingly, the nine-membered analogs 1i and
4i did not exhibit fluorescence, and we found that the cyclic
analogs at the C2- and C3-positions were non-luminescent
compounds. Therefore, the substituent effect of the methyl
group at the C4-position was found to generally induce the
long-wavelength shift of around 35nm or 25nm in the cases
of 2-phenyl derivatives or other than 2-phenyl derivatives, re-
spectively, whereas the common rule on the ΦF was not found.
Next, we attempted to investigate the effect of the
π-extended system at the C4-position. Although two 4-phenyl-
1,3a,6a-triazapentalene derivatives were previously reported,25)
further 4-phenyl analogs were synthesized and investigated to
ensure the generality and trend of the substituent effect of the
4-phenyl group on fluorescence properties (Table 3). The click
reaction of 2b with 3a afforded 4-phenyl-2-(4-cyanophenyl)-
1,3a,6a-triazapentalene 4j in 70% yield (entry 1). Unfortu-
nately, although the 4-phenyl analog was expected to induce a
noteworthy wavelength shift due to the expansion of π–conju-
gation, the fluorescence maximum of 4j (542nm) was similar
to that of the 4-methyl analogs 4a (543nm), suggesting that
the properties of functional groups have no appreciable effect
on the shift value of the fluorescence wavelength. On the other
hand, the ΦF increased to 0.46 from the 0.15 of 4-unsubstitut-
ed analog 1a and the 0.17 of 4-methyl analog 4a. Furthermore,
the extinction coefficient (ε) value of 4j substantially increased
to 6918dm3 mol−1 cm−1 (387nm) from 3020dm3 mol−1 cm−1
(381nm) for 1a and 1000dm3 mol−1 cm−1 (389nm) for 4-methyl
analog 4a (Fig. 4). The expansion of π–conjugation system is
probably responsible for increase in the ε value. In addition, a
new absorption band appeared at 345nm that had never been
observed in various 1,3a,6a-triazapentalenes without a phenyl
group at the C4-position, and its ε value became as high as
27542 dm3 mol−1 cm−1 (Fig. 4). Since the improvement of ε
values has been a remaining goal of 1,3a,6a-triazapentalenes
Entry
Alkyne (3)
4-Methyl-TAP (4)
Yielda) (%)
94
1
2
3
50
82
4
19
5
6
7
28
60
0
8
49
a) Isolated yield.
is the first successful example of the triazapentalene-forming as a practical fluorophore, the 4-phenyl group was expected
reaction with internal alkyne. to have a general effect on the increase in the ε values of
Having prepared various 4-methyl analogs of 1,3a,6a- 1,3a,6a-triazapentalenes. Thus, various 4-phenyl analogs were
triazapentalenes, we compared their fluorescence with those of synthesized and their fluorescence properties were investi-
the corresponding 4-unsubstituted analogs were investigated gated. To compare the ε values with the corresponding 4-un-
in dichloromethane (Table 2). The 2-methoxycarbonyl analog substituted analog, the ε values of synthetic 4-phenyl analogs
4b similarly showed a longer-wavelength fluorescence maxi- were measured at the longer-wavelength absorption that was
mum and a higher ΦF in comparison with the 4-unsubstituted previously assigned as an intramolecular charge transfer (ICT)

Vol. 64, No. 7 (2016)
Chem. Pharm. Bull.
833
Table 2. Comparison of Fluorescence Properties of Synthetic 4-Methyl-1,3a,6a-triazapentalenes 4 with Corresponding 4-Unsubstituted Derivatives 1 in
Dichloromethane
R1
CO2Me
C6H4–SO3Me
C6H4–CO2Me C6H3(CN) CO2Me
C6H4–Ph
Nap
—
R=Me
4b
354
456
0.24
1b
4c
393
558
0.40
1c
4d
380
553
0.56
1d
4e
436
611
0.11
1e
4f
4g
356
485
0.082
1g
4i
0
max
λ
(nm)
360
491
0.40
1f
abs
max
em
λ
(nm)
0
ΦF
0
R=H
1i
0
max
λ
(nm)
(nm)
342
431
0.18
379
525
0.43
376
521
0.44
420
572
0.34
345
456
0.20
358
460
0.35
abs
max
em
λ
0
ΦF
0
Table 3. Click Reaction of 2b with Various Alkynes 3 and Fluorescence Properties of Various 4-Phenyl-1,3a,6a-triazapentalenes in Dichloromethane
max
Entry
Alkyne (3)
Yielda)
λ
(nm)
ΦF
ε dm3 mol−1 cm−1
em
1
3a: R=C6H4CN
4j: 70%
542
0.46
6918 (387nm)
3020 (381nm)d)
10648 (358nm)
2691 (342nm)d)
5497 (378nm)
2542 (358nm)d)
7500 (383nm)
1230 (376nm)d)
4560 (432nm)
631 (420nm)d)
19409 (369nm)
5011 (345nm)d)
19822 (342nm)
4213 (358nm)d)
(509)b)
(0.15)c)
0.086
(0.18)c)
0.21
2
3
3b: R=CO2Me
4k: 87%
4l: 50%
4m: 82%
4n: 88%
4o: 72%
4p: 81%
459
(431)b)
554
3c: R=C6H4SO3Me
3d: R=C6H4CO2Me
3e: R=C6H3(CN)CO2Me
3f: R=C6H4Ph
(525)b)
(0.43)c)
Ref. 6
548
0.36
(521)b)
613
(0.44)c)
0.07
Ref. 6
(572)b)
(0.34)c)
4
5
482
0.10
(456)b)
481
(0.20)c)
0.084
(0.35)c)
3g: R=Naphthyl
(460)b)
a) Isolated yield. b) Fluorescence maximum of corresponding 4-unsubstituted analog. c) Fluorescence quantum yield of corresponding 4-unsubstituted analog. d) The extinc-
tion coefficient value of corresponding 4-unsubstittuted analog.
Fig. 4. Absorption and Fluorescence Spectra of 1a, 4a, and j in Dichloromethane
mechanism.25)
fluorophore in fluorescence observation is generally defined
The similar click reaction of 2b with methyl propiolate 3b as the fluorescence brightness, and its intensity is proportional
afforded the desired 4-phenyl-2-methoxycarbonyl-1,3a,6a- to those of both the ΦF and the ε value.36) Therefore, although
triazapentalene 4k in 87% yield (entry 2). The fluores- the ΦF of 4k was slightly decreased, unlike the case with 4j,
cence maximum of 4k showed a long-wavelength shift as the fluorescence brightness of 4k was totally improved by the
with 4j, and the ε value also substantially increased to substantial increase in the ε value (entry 2). The reactions of
10648dm3 mol−1 cm−1 (358nm) from the 2691dm3 mol−1 cm−1 ethynylbenzene derivatives 3c and f also afforded correspond-
(342nm) of the 4-unsubstituted analog. The viewability of ing 4-phenyl analogs 4l and o in acceptable yields (entries 3,

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Chem. Pharm. Bull.
Vol. 64, No. 7 (2016)
4). In addition to previously reported 4m and n as a refer- THF (10mL) was added copper(I) iodide (19mg, 0.10mmol)
ence, the fluorescence properties of 2-phenyl derivatives 4l–o at room temperature. The mixture was stirred until homoge-
were similar to those of 4k such as the approximately 30nm neous. The clear solution of ligand–copper complex should be
long-wavelength shift of the fluorescence maximum, the slight used before it became cloudy.
decrease in ΦF, and the substantial increase in the ε value,
although the 41nm shift of 4n was exceptionally longer than Reaction (Method A) To
Synthesis of 4b as a Typical Procedure of the Click
a
solution of azidoditriflate
those of the other derivatives (entries 3–6). In the case of 2a (36.5mg, 0.092mmol) in THF (9.0mL) were added the
2-naphthyl analog 4p, the long-wavelength shift of the fluo- ligand-copper solution (0.46mL, 0.01M solution in THF),
rescence maximum was 21nm, slightly shorter than the shift Et3N (65µL, 0.46mmol), and alkyne 3b (12 µL, 0.14mmol) at
of the 2-phenyl analogs, and the ΦF and the ε value substan- room temperature, successively. The mixture was stirred at
tially decreased and increased, respectively. Throughout the room temperature for 2.5h and concentrated under reduced
various 4-phenyl analogs, the range of long-wavelength shifts pressure. The residue was purified by flash silica gel column
induced by the phenyl group at the C4-position was similar chromatography (hexane/EtOAc=70/30 to 50/50, 1% Et3N
to that of methyl group, and was insensitive to the properties contained) to give 4b (15.9mg, 0.086mmol, 94%) as green
of the substituent groups. In contrast, ε value was in general amorphous.
substantially higher in all 4-phenyl derivatives and proved to
Synthesis of 4i as a Typical Procedure of the Click Reac-
be a particular effect of the phenyl group, whereas the ΦF of tion (Method B) To a solution of azidoditriflate 2a (27.0mg,
most 4-phenyl analogs tended to decline slightly. Furthermore, 0.069mmol) in THF (4.6mL) were added the ligand–cop-
the synthesized 4-phenyl-1,3a,6a-triazapentalenes exhibited per solution (0.23mL, 0.01M solution in THF), Et3N (32 µL,
strong positive fluorescence solvatochromism as is the case 0.23mmol), and alkyne 3i (20.0mg, 0.046mmol) at room
with 4-unsubstituted analogs, and the similar approximately temperature, successively. The mixture was stirred at room
30nm long-wavelength shifts were also observed in different temperature for 16h and concentrated under reduced pressure.
solvent.37) The mechanistic details of long-wavelength shift The residue was purified by flash silica gel column chroma-
induced by the 4-subustituents is currently investigated in our tography (hexane/EtOAc=90/10 to 70/30, 1% Et3N contained)
laboratory.
to give 4i (11.7mg, 0.023mmol, 49%) as clear amorphous.
2-(4-(Methoxysulfonyl)phenyl)pyrazolo[1,2-a][1,2,3]triazol-
In conclusion, the substituent effect at the C4-position of
1,3a,6a-triazapentalenes was elucidated. Various 4-methyl- 8-ium-1-ide (1c) (Method B)
and 4-phenyl-1,3a,6a-triazapentalene derivatives were synthe-
1H-NMR (400MHz, CDCl3) δ: 7.91 (1H, d, J=8.8Hz), 7.78
sized by the click-cyclization-aromatization cascade reaction (1H, d, J=8.5Hz), 7.06 (1H, dd, J=1.5Hz, 0.8Hz), 6.53 (1H,
of various alkynes with azidoditriflate possessing a methyl or d, J=1.2Hz), 6.42 (1H, dd, J=3.0Hz, 0.5Hz), 6.13 (1H, t,
phenyl group. The introduction of a methyl group at the C4- J=2.8Hz), 3.22 (3H, s). 13C-NMR (125MHz, C6D6) δ: 146.0,
position induced a long-wavelength shift of the fluorescence 137.7, 135.5, 129.0, 126.6, 109.5, 102.3, 101.0, 94.5, 55.8. IR
maximum and an irregular change in the fluorescence quan- (KBr) cm−1: 3154, 2954, 1600, 1353, 1175. High resolution
tum yield. Among the various 4-methyl-1,3a,6a-triazapen- (HR)-MS electrospray ionization (ESI) m/z [M+H]+ Calcd
talenes, 2-phenyl derivatives showed an approximately 35nm for [C12H12N3O3S]+ 278.0599. Found 278.0606. UV/Vis
shift of the fluorescence maximum and other derivatives (CH2Cl2): λmax (logε)=379 (3.41), 283 (4.45) nm. FL (CH2Cl2):
without a phenyl group at the C2-position exhibited a smaller λmax=525nm; ΦF=0.43 (reference to 9,10-diphenylanthracene
(25nm) shift. Additionally, the introduction of a phenyl group (9,10-DPA); excited at 370nm).
at the C4-position also showed a similar long-wavelength shift
2-(Naphthalen-2-yl)pyrazolo[1,2-a][1,2,3]triazol-8-ium-1-
of the fluorescence maximum, and the range of shift was only ide) (1g) (Method B)
slightly affected by the properties of the substituents. On the
1H-NMR (500MHz, CDCl3) δ: 8.30 (1H, s), 7.87 (4H, dq,
other hand, the ε value was substantially increased by the J=7.8Hz, 1.5Hz), 7.52–7.47 (4H, m), 7.15 (1H, d, J=3.0Hz),
phenyl substituents at the C4-position, although the ΦF of the 6.64 (1H, t, J=2.8Hz). 13C-NMR (125MHz, CDCl3) δ:
most 4-phenyl derivatives decreased. Therefore, the brightness 147.7, 133.5, 133.4, 128.8, 128.4, 127.8, 126.4, 126.2, 124.6,
of all 4-phenyl derivatives was totally enhanced due to the 123.9, 108.9, 102.4, 100.9, 93.7. IR (KBr) cm−1: 3141, 3047,
substantial increases in the ε values. Throughout the various 2921, 1380, 1141, 862, 747, 661. HR-MS (ESI) m/z [M+Na]+
4-methyl and 4-phenyl derivatives of 1,3a,6a-triazapentalenes, Calcd for [C15H11N3Na]+ 256.0851. Found 256.0849. UV/Vis
we successfully elucidated the substituent effect on the fluo- (CH2Cl2): λmax (logε)=358 (3.62), 329 (3.56), 290 (4.47) nm.
rescence properties at the C4-position following the C2- and FL (CH2Cl2): λmax=460nm; ΦF=0.35 (reference to 9,10-DPA;
C5-positions. That is, in addition to the control of fluorescence excited at 370nm).
wavelength and quantum yield by the 2- and 5-substituents,
a further long-wavelength shift and enhancement of bright- ium-1-ide) (1h) (Method A)
ness can be induced by the 4-substituent. Since the 4-phenyl
2,2′-(1,4-Phenylene)bis(pyrazolo[1,2-a][1,2,3]triazol-8-
1H-NMR (400MHz, C6D6) δ: 8.02 (4H, s), 7.04 (2H, d,
derivatives were relatively unstable compared with the cor- J=2.8Hz), 6.66 (2H, d, J=1.2Hz), 6.35 (2H, d, J=2.8Hz),
responding 4-unsubstituted analogs, the improvement of their 6.06 (2H, t, J=2.8Hz). 13C-NMR (125MHz, C6D6) δ: 147.7,
stability for the practical fluorophores is currently underway 132.3, 128.4, 126.5, 108.6, 101.6, 100.0, 93.4. IR (KBr) cm−1:
in our laboratory.
3153, 2926, 2107, 946, 848. HR-MS (ESI) m/z [M+Na]+
Calcd for [C16H12N6Na]+ 311.1021. Found 311.1031. UV/Vis
(CH2Cl2): λmax (logε)=356 (3.87), 292 (4.58) nm. FL (CH2Cl2):
Experimental
Preparation of Ligand-Copper Solution To a solution of λmax=455nm; ΦF=0.22 (reference to 9,10-DPA; excited at
bis[2-(N,N-dimethylaminoethyl)]ether (19.0µL, 0.10mmol) in 370 nm).

Vol. 64, No. 7 (2016)
Chem. Pharm. Bull.
835
2,6-Ditosyl-2,3,4,5,6,7-hexahydro-1H-pyrazolo[1′,2′:1,2]- 2.44 (3H, s). 13C-NMR (125MHz, CDCl3) δ: 147.4, 141.0,
[1,2,3]triazolo[4,5-g][1,5]diazonin-9-ium-8-ide (1i) (Method B) 140.7, 130.7, 128.8, 127.4, 127.0, 126.2, 109.9, 107.4, 102.3,
1H-NMR (500MHz, CDCl3) δ: 7.73 (2H, d, J=8.0Hz), 7.68 90.4, 11.3. IR (KBr) cm−1: 3151, 2923, 1471, 1445, 1412, 1393,
(2H, d, J=8.0Hz), 7.54 (1H, d, J=3.0Hz), 7.36–7.34 (5H, m), 1236, 1112, 1034, 1006, 947, 843, 766, 728, 575. HR-MS
6.62 (1H, t, J=3.0Hz), 4.81 (2H, s), 4.34 (2H, s), 3.53–3.51 (ESI) m/z [M+Na]+ Calcd for [C18H15N3Na]+ 296.1164. Found
(2H, m), 3.03 (2H, t, J=6.0Hz), 2.45 (6H, d, J=3.5Hz), 296.1161. UV/Vis (CH2Cl2): λmax (logε)=360 (3.71), 290
1.92–1.88 (2H, m). 13C-NMR (125MHz, CDCl3) δ: 143.7, (4.69) nm. FL (CH2Cl2): λmax=491nm; ΦF=0.40 (reference to
141.7, 130.0, 127.6, 127.0, 108.5, 103.9, 103.2, 102.6, 48.3, 9,10-DPA; excited at 370nm).
48.06, 48.02, 43.4, 29.5, 21.5. IR (KBr) cm−1: 3155, 2925, 2857,
5-Methyl-2-(naphthalen-2-yl)pyrazolo[1,2-a][1,2,3]triazol-8-
1449, 1335, 1160, 548. HR-MS (ESI) m/z [M+Na]+ Calcd for ium-1-ide (4g) (Method A)
[C24H27N5O4S2Na]+ 536.1402. Found 536.1385.
1H-NMR (500MHz, CDCl3) δ: 8.33 (1H, s), 7.97–7.88 (4H,
2-(Methoxycarbonyl)-5-methylpyrazolo[1,2-a][1,2,3]- m), 7.55–7.49 (3H, m), 7.47 (1H, br-s), 6.46 (1H, s), 2.43 (3H,
triazol-8-ium-1-ide (4b) (Method A)
d, J=3.5Hz). 13C-NMR (125MHz, CDCl3) δ: 147.4, 134.5,
1H-NMR (400MHz, CDCl3) δ: 7.46 (1H, d, J=1.0Hz), 7.41 134.2, 129.2, 128.6, 127.44, 127.37, 127.1, 125.04, 125.03124.8,
(1H, dd, J=2.8Hz, 1.0Hz), 6.48 (1H, dd, J=2.6Hz, 0.6Hz), 123.6, 110.0, 108.5, 11.2. IR (KBr) cm−1: 2925. HR-MS (ESI)
3.95 (3H, s), 2.43 (3H, s). 13C-NMR (100MHz, C6D6) δ: m/z [M+H]+ Calcd for [C16H14N3]+ 248.1188. Found 248.1181.
162.4, 140.1, 109.8, 109.0, 102.0, 97.6, 51.5, 10.3. IR (KBr) UV/Vis (CH2Cl2): λmax (logε)=356 (3.88), 291 (4.53) nm. FL
cm−1: 3133, 2949, 1717, 1557, 1516, 1266, 1003. HR-MS (ESI) (CH2Cl2): λmax=485nm; ΦF=0.082 (reference to 9,10-DPA;
m/z [M+Na]+ Calcd for [C8H9N3O2Na]+ 202.0592. Found excited at 360nm).
202.0586. UV/Vis (CH2Cl2): λmax (logε)=354 (3.44) nm. FL
(CH2Cl2): λmax=456nm; ΦF=0.24 (reference to 9,10-DPA; ex- [1′,2′:1,2][1,2,3]triazolo[4,5-g][1,5]diazonin-9-ium-8-ide
cited at 370nm).
2-(4-(Methoxysulfonyl)phenyl)-5-methylpyrazolo[1,2-a]-
[1,2,3]triazol-8-ium-1-ide (4c) (Method B)
12-Methyl-2,6-ditosyl-2,3,4,5,6,7-hexahydro-1H-pyrazolo-
(4i)
(Method B)
1H-NMR (500MHz, CDCl3) δ: 7.84 (2H, d, J=8.3Hz),
7.69 (2H, d, J=8.3Hz), 7.45 (2H, d, J=7.5Hz), 7.37 (2H, d,
1H-NMR (500MHz, CDCl3) δ: 7.96 (2H, d, J=8.8Hz), J=8.3Hz), 6.37 (1H, d, J=1.7Hz), 5.09 (3H, s), 4.26 (2H,
7.94 (2H, d, J=8.8Hz), 7.42 (1H, d, J=2.2Hz), 7.27 (1H, s), s), 3.30–3.26 (2H, m), 2.87–2.83 (2H, m), 2.72 (3H, s), 2.52
6.40 (1H, d, J=2.2Hz), 3.79 (3H, s), 2.44 (3H, s). 13C-NMR (3H, s), 2.48 (3H, s). 13C-NMR (125MHz, C6D6) δ: 143.2,
(125MHz, CDCl3) δ: 145.4, 137.5, 134.0, 128.5, 126.3, 110.7, 138.2, 134.7, 130.2, 129.7, 113.6, 108.1, 102.6, 101.3, 49.6,
108.0, 102.7, 91.5, 56.4, 11.2. HR-MS (ESI) m/z [M+H]+ 48.7, 44.7, 40.3, 30.0, 21.0, 11.2. IR (KBr) cm−1: 2924, 2865,
Calcd for [C13H14N3O3S]+ 292.0756. Found 292.0757. UV/Vis 1335, 1159, 814, 547. HR-MS (ESI) m/z [M+Na]+ Calcd for
(CH2Cl2): λmax (logε)=393 (2.99), 284 (4.08) nm. FL (CH2Cl2): [C25H30N5O4S2Na]+ 528.1739. Found 528.1742.
λmax=558nm; ΦF=0.40 (reference to rhodamine B; excited at
370 nm).
2-(4-(Methoxycarbonyl)phenyl)-5-methylpyrazolo[1,2-a]-
[1,2,3]triazol-8-ium-1-ide (4d) (Method B)
2-(Methoxycarbonyl)-5-phenylpyrazolo[1,2-a][1,2,3]-
triazol-8-ium-1-ide (4k) (Method A)
1H-NMR (400MHz, CDCl3) δ: 8.08(1H, s), 7.59–7.57 (3H,
overlapped), 7.49 (2H, dd, J=8.3Hz, 7.5Hz), 7.30 (1H, t,
1H-NMR (400MHz, C6D6) δ: 8.25 (1H, d, J=8.5Hz), 7.92 J=7.5Hz), 6.99 (1H, d, J=2.5Hz), 3.99 (3H, s). 13C-NMR
(1H, d, J=8.8Hz), 7.05 (1H, d, J=2.5Hz), 6.53 (1H, br s), 5.81 (100MHz, C6D6) δ: 162.0, 140.4, 129.7, 129.3, 126.3, 123.6,
(1H, dd, J=2.8Hz, 0.8Hz), 3.52 (3H, s), 1.76 (3H, s). 13C-NMR 115.5, 108.1, 104.1, 101.1, 51.6. IR (KBr) cm−1: 3151, 2951,
(125MHz, C6D6) δ: 166.4, 146.8, 136.9, 130.3, 128.4, 125.9, 1733, 1522, 1396, 1223, 1008. HR-MS (ESI) m/z [M+H]+
109.2, 107.5, 101.7, 91.2, 51.5, 10.6. HR-MS (ESI) m/z [M+H]+ Calcd for [C13H12N3O2]+ 242.0930. Found 242.0937. UV/
Calcd for [C14H14N3O2]+ 256.1086. Found 256.1095. UV/Vis Vis (CH2Cl2): λmax (logε)=358 (4.03) nm. FL (CH2Cl2):
(CH2Cl2): λmax (logε)=380 (3.50), 288 (4.61) nm. FL (CH2Cl2): λmax=459nm; ΦF=0.086 (reference to 9,10-DPA; excited at
λmax=553nm; ΦF=0.56 (reference to rhodamine B; excited at 370 nm).
420nm).
2-(4-(Methoxysulfonyl)phenyl)-5-phenylpyrazolo[1,2-a]-
2-(2-Cyano-4-(methoxycarbonyl)phenyl)-5-methyl- [1,2,3]triazol-8-ium-1-ide (4l) (Method B)
pyrazolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4e) (Method B)
1H-NMR (500MHz, CDCl3) δ: 8.03 (2H, d, J=8.5Hz),
1H-NMR (400MHz, C6D6) δ: 8.29 (1H, d, J=8.3Hz), 7.98 (2H, d, J=9.0Hz), 7.90 (1H, d, J=1.0Hz), 7.62 (1H,
8.18 (1H, d, J=1.8Hz), 8.00 (1H, dd, J=8.3Hz, 1.8Hz), 7.70 dd, J=11.5Hz, 1.0Hz), 7.61 (1H, d, J=0.5Hz), 7.51 (2H, t,
(1H, d, J=1.0Hz), 6.99 (1H, dd, J=2.5Hz, 1.0Hz), 5.75 (1H, J=7.5Hz), 7.31 (1H, d, J=7.5Hz), 6.92 (1H, d, J=3.0Hz), 3.81
dd, J=2.5Hz, 0.7Hz), 3.41 (3H, s), 1.63 (3H, s). 13C-NMR (3H, s). 13C-NMR (125MHz, CDCl3) δ: 146.0, 137.0, 134.5,
(125MHz, C6D6) δ: 164.8, 143.1, 139.0, 135.6, 133.8, 130.2, 129.6, 129.3, 128.6, 126.6, 126.4, 123.7, 116.0, 107.1, 104.7,
128.9, 119.1, 110.8, 109.5, 108.5, 102.1, 94.1, 52.1, 10.5. HR-MS 94.7, 56.4. IR (KBr) cm−1: 2924, 2851, 1729, 1601, 1362, 1176,
(ESI) m/z [M+Na]+ Calcd for [C15H12N4O2Na]+ 303.0858. 988. HR-MS (ESI) m/z [M+H]+ Calcd for [C18H16N3O3S]+
Found 303.0854. UV/Vis (CH2Cl2): λmax (logε)=436 (3.05), 354.0912. Found 354.0912. UV/Vis (CH2Cl2): λmax (logε)=378
287 (4.23) nm. FL (CH2Cl2): λmax=611nm; ΦF=0.11 (reference (3.74) nm, 345 (4.29) nm, 277 (4.31) nm. FL (CH2Cl2):
to rhodamine B; excited at 420nm).
λmax=554nm; ΦF=0.21 (reference to rhodamine B; excited at
2-([1,1′-Biphenyl]-4-yl)-5-methylpyrazolo[1,2-a][1,2,3]- 400 nm).
triazol-8-ium-1-ide (4f) (Method A)
2-(4-(Methoxycarbonyl)phenyl)-5-phenylpyrazolo[1,2-a]-
1H-NMR (500MHz, CDCl3) δ: 7.86 (2H, d, J=8.5Hz), 7.65 [1,2,3]triazol-8-ium-1-ide (4m) (Method B)
(4H, t, J=8.3Hz), 7.46 (2H, brt, J=7.8Hz), 7.42 (1H, brd,
1H-NMR (400MHz, CDCl3) δ: 8.11 (2H, d, J=8.3Hz), 7.90
J=2.5Hz), 7.36 (1H, brt, J=7.3Hz), 6.36 (1H, brd, J=2.0Hz), (2H, d, J=8.6Hz), 7.86 (1H, s), 7.60 (2H, d, J=7.5Hz), 7.58

836
Chem. Pharm. Bull.
Vol. 64, No. 7 (2016)
(1H, d, J=2.5Hz), 7.49 (2H, t, J=7.5Hz), 7.31–7.24 (1H, m), a Research Fund. A.N. is grateful to the Uehara Memorial
6.88 (1H, d, J=2.5Hz), 3.94 (3H, s). 13C-NMR (125MHz, Foundation for support through a Research Fund for Young
CDCl3) δ: 166.7, 147.0, 135.6, 130.0, 129.8, 129.7, 129.2, Researcher.
125.6, 123.4, 115.5, 106.7, 104.4, 94.5, 52.1. IR (neat) cm−1:
3155, 1950, 1715, 1277. HR-MS (ESI) m/z [M+Na]+ Calcd
Conflict of Interest The authors declare no conflict of
for [C19H15N3O2Na]+ 340.1062. Found 340.1064. UV/Vis interest.
(CH2Cl2): λmax (logε)=345 (4.35), 279 (4.44) nm. FL (CH2Cl2):
λmax=548nm; ΦF=0.36 (reference to rhodamine B; excited at
400 nm).
References and Notes
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2-(2-Cyano-4-(methoxycarbonyl)phenyl)-5-phenylpyra-
zolo[1,2-a][1,2,3]triazol-8-ium-1-ide (4n) (Method B)
1H-NMR (400MHz, CDCl3) δ: 8.44 (1H, s), 8.39 (1H, s),
8.31 (1H, d, J=8.0Hz), 8.24 (1H, d, J=8.0Hz), 7.66–7.59 (3H,
m), 7.50 (2H, t, J=7.6Hz), 7.30 (1H, t, J=7.6Hz), 6.95 (1H,
d, J=2.8Hz), 3.98 (3H, s). 13C-NMR (125MHz, CDCl3) δ:
164.9, 143.1, 138.0, 135.3, 133.8, 130.2, 129.4, 129.4, 128.7,
126.8, 123.7, 118.3, 116.3, 109.3, 107.6, 104.5, 96.9, 52.7. IR
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(4.48) nm. FL (CH2Cl2): λmax=613nm; ΦF=0.070 (reference to
rhodamine B; excited at 400nm).
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2-([1,1′-Biphenyl]-4-yl)-5-phenylpyrazolo[1,2-a][1,2,3]-
triazol-8-ium-1-ide (4o) (Method A)
1H-NMR (500MHz, CDCl3) δ: 7.92 (2H, d, J=8.3Hz), 7.85
(1H, d, J=1.0Hz), 7.71–7.62 (5H, m), 7.59 (1H, dd, J=2.9Hz,
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(4.57) nm. FL (CH2Cl2): λmax=482nm; ΦF=0.10 (reference to
9,10-DPA; excited at 370nm).
2-(Naphthalen-2-yl)-5-phenylpyrazolo[1,2-a][1,2,3]triazol-8-
ium-1-ide (4p) (Method A)
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d, J=0.8Hz), 8.06–7.94 (4H, m), 7.78 (2H, d, J=7.2Hz), 7.71
(1H, brdd, J=3.0Hz, 1.0Hz), 7.60–7.53 (4H, m), 7.32 (1H,
t, J=7.4Hz), 7.10 (1H, d, J=3.2Hz). 13C-NMR (125MHz,
CDCl3) δ: 148.3, 133.54, 133.45, 130.0, 129.3, 128.6, 128.5,
128.3, 127.8, 126.5, 126.3, 126.2, 124.82, 123.9, 123.5, 115.4,
106.6, 104.4, 94.3. IR (neat) cm−1: 3152, 3055, 2924, 1205,
1599, 1522, 1389, 1239, 1029, 751. HR-MS (ESI) m/z [M+Na]+
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(CH2Cl2): λmax (logε)=342 (4.30), 283 (4.24), 259 (4.67), 251
(4.69). FL (CH2Cl2): λmax=481nm; ΦF=0.084 (reference to rho-
damine B; excited at 360nm).
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Acknowledgments The authors thank Professors Igawa
and Tomooka for the useful advice and discussion about the
strained alkyne 3i. This work was partially supported by
Grants-in-Aid for Scientific Research (Nos. 26560449 and
15K18830), and by a Grant-in-Aid for Scientific Research
on Innovative Areas (Project No. 2301: Chemical Biology of
Natural Products) from the Ministry of Education, Culture,
Sports, Science and Technology of Japan. K.N. is grateful to
the Naito Foundation, the Yamada Science Foundation, the
Kurata Memorial Hitachi Science and Technology Founda-
tion, and the Uehara Memorial Foundation for support through

Vol. 64, No. 7 (2016)
Chem. Pharm. Bull.
837
Chem. Sci., 6, 1083–1093 (2015).
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ε=10648), acetone (λem=460nm, ΦF=0.042, ε=12095), aceto-
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