From liquid to solid-state fluorescence: Tricyclic lactones based on 4-hydroxy-1,3-thiazoles

Article abstract of DOI:10.1055/s-0033-1340048

This work describes the synthesis of a series of tricyclic lactones based on 4-hydroxy-1,3-thiazoles prepared by the classic Hantzsch synthesis. The tricyclic lactones are more rigid than the parent 4-hydroxythiazoles and are featured not only by fluorescence in solution, but also in the solid state. An extension of the chromophoric system was successfully realized by integration of the benzothiazole substructure, thus resulting in bathochromic shifts of absorption and also fluorescence. The new synthesized lactones additionally show interesting properties in solution, whereby the initial blue fluorescence changes dramatically with a variation of the pH value. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0033-1340048

126▌
PAPER
paper
From Liquid to Solid-State Fluorescence: Tricyclic Lactones Based on
4-Hydroxy-1,3-thiazoles
Fluorescence of Tricyclic Lactones Based on 4-Hydroxy-1,3-thiazoles
Lorena K. Calderón Ortiz,a Hendryk Würfel,a Eric Täuscher,b Dieter Weiß,*a Eckhard Birckner,c Helmar Görls,d
Rainer Beckert*a
a
Institute of Organic and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 10, 07743 Jena, Germany
Fax +49(3641)948212; E-mail: C6bera@uni-jena.de
b
Department of Chemistry and Biotechnology, Technical University of Ilmenau, Weimarer Str. 25, 98693 Ilmenau, Germany
c
Institute of Physical Chemistry, Friedrich-Schiller-University Jena, Lessingstr. 10, 07743 Jena, Germany
d
Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 9, 07743 Jena, Germany
Received: 14.08.2013; Accepted after revision: 30.09.2013
Dedicated to Prof. Dr. W. Kantlehner, Aalen on the occasion of his 70th birthday
of its applicability as an emitter material in organic elec-
Abstract: This work describes the synthesis of a series of tricyclic
troluminescence devices (OLEDs), solid-state dye lasers
lactones based on 4-hydroxy-1,3-thiazoles prepared by the classic
and sensor materials, and the potential use in the construc-
Hantzsch synthesis. The tricyclic lactones are more rigid than the
parent 4-hydroxythiazoles and are featured not only by fluorescence
tion of optoelectronic devices.9,10 It is well known that the
in solution, but also in the solid state. An extension of the chromo- photophysical properties of these compounds depend
phoric system was successfully realized by integration of the ben-
zothiazole substructure, thus resulting in bathochromic shifts of
absorption and also fluorescence. The new synthesized lactones ad-
ditionally show interesting properties in solution, whereby the ini-
strongly on the nature of their conjugated π-system, their
geometry in the solid state, and their packing in the crys-
tal.10c,d
The tricyclic lactones based on 4-hydroxy-1,3-thiazoles
were synthesized according to the classic Hantzsch
synthesis3 in moderate up to good yields (79%). As de-
picted in Scheme 1, different thioamides 2 react with di-
methyl α-bromohomophthalate (1) in DMF in the
presence of triethylamine at 120 °C to furnish the tricyclic
lactones 4. In order to get more information about the in-
fluence of an extended π-system, the benzo[d]thiazole-2-
carbothioamides 3 were used to obtain the lactones 5.
tial blue fluorescence changes dramatically with a variation of the
pH value.
Key words: heterocycles, chromophores, fused-ring systems, thia-
zole, fluorescence
4-Hydroxy-1,3-thiazoles and their derivatives have been
intensively studied in the last few years, because they rep-
resent a new class of functional fluorophores.1,2 In addi-
tion, they form the substructure of several natural
products and were chosen by nature as part of the chemi-
cal compound responsible for the dual luminescence of
the firefly (lampyridae).3 The remarkable spectroscopic
properties of this heterocycle as fluorophore and chromo-
phore, and its easy feasibility of functionalization enable
the development of a variety of novel applications. They
have been used as novel ligands for metal complexes,
emitting polymers, dyes, and sensors.4–8 Furthermore, it is
known that the extension of the π-system attached to the
thiazole ring by substitution with aromatic heterocycles
allows the modification of its photophysical properties.3,7
The new tricyclic lactones 4a–c were isolated as colorless
to beige-colored needles, whereas compound 4d and all
derivatives of type 5 were isolated as yellow crystalline
solids. They have high melting points (from 200 up to
340 °C) and can be purified by recrystallization from
DMSO or DMF. The compounds show a high solubility in
a mixture of CHCl3–CF3CO2H or o-dichlorobenzene,
while they are only slightly soluble in polar organic sol-
vents, such as DMSO, DMF, and EtOH.
All of these new thiazole derivatives were fully character-
ized by NMR, MS, and elemental analysis. In addition,
suitable single crystals of 4d and 5a were obtained for X-
ray analysis. The ORTEP plots of the structures are shown
in Figure 1. Compound 4d shows a bond length of 1.443
(3) Å for C4–C5 connecting the thiophene ring with the
tricyclic lactone, whereas compound 5a shows a bond
length of 1.453 (3) Å for C7–C8 between the benzothia-
zole moiety and the tricyclic lactone. Both compounds
show an almost coplanar structure, due to their torsion an-
gles between the heterocyclic moieties of 176.20 (2)°
around the S1–C4–C5–S2 planes for 4d and 174.42 (1)°
around the S1–C7–C8–S2 planes for 5a.
Consequently, we were interested in the synthesis of a
new class of thiazole-based derivatives containing a ring-
fused π-system. The reaction of dimethyl α-bromoho-
mophthalate with various thioamides should be suitable in
order to obtain annulated thiazoles by intramolecular es-
terification. In contrast to most of the fluorescent dyes de-
scribed in literature,9 these novel thiazole derivatives are
highly fluorescent in solution as well as in the solid state.
Solid-state fluorescence attracts a lot of attention because
SYNTHESIS 2014, 46, 0126–0134
Advanced online publication: 04.11.2013
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DOI: 10.1055/s-0033-1340048; Art ID: SS-2013-T0566-OP
© Georg Thieme Verlag Stuttgart · New York

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Fluorescence of Tricyclic Lactones Based on 4-Hydroxy-1,3-thiazoles
127
.
R1
S
N
S
O
O
4a: R1 = pyridin-2-yl (54%)
4b: R1 = pyridin-3-yl (45%)
R1
NH2
4c: R1 = pyrimidin-2-yl (40%)
4d: R1 = thiophen-2-yl (65%)
thioamide
COOMe
Br
2
tricyclic lactones
4a–d
Et3N, DMF
COOMe
N2, 120 °C, 24 h
NH2
S
N
S
R2
5a: R2 = H (49%)
5b: R2 = Me (48%)
5c: R2 = OMe (51%)
5d: R2 = OBn (46%)
5e: R2 = F (79%)
O
O
S
N
N
S
dimethyl α-bromohomophthalate
R2
1
benzo[d]thiazole-2-carbothioamide
tricyclic lactones
3
5a–e
Scheme 1 Synthesis of tricyclic lactones based on 4-hydroxy-1,3-thiazoles
Figure 1 ORTEP plot of the solid-state molecular structure (X-ray
crystallographic analysis) of tricyclic lactones 4d and 5a
The most important feature of tricyclic lactone deriva-
tives, however, is their solid-state fluorescence. With re-
gard to subsequent applications, this type of luminescence
was investigated for derivatives in the series 4 and 5. Un-
der UV radiation, the tricyclic lactones 4a–c are highly
fluorescent in the violet-blue region (450–480 nm),
whereas 4d and the compounds 5a–e fluoresce in the
green-yellow region of the spectrum (490–580 nm). Fig-
ure 2 shows the solid-state fluorescence of the tricyclic
lactones under UV radiation and their spectral profiles are
depicted in Figure 3.
Figure 2 Solid-state fluorescence of 4 and 5 under UV irradiation
The tricyclic lactones 4 and 5 show absorption maxima in
the UVA region (315 to 400 nm) in solution and are highly
fluorescent in the violet-blue region of the visible spec-
trum. However, the fluorescence maxima of these com-
pounds are considerably hypsochromically shifted
compared to their solid-state fluorescence maxima.
The influence of the solvent is reflected in the absorption
and fluorescence data (Table1). The absorption and fluo-
rescence bands of 4a, 4b, and 4c in EtOH, having pyridine
or pyrimidine moieties at R1, are very similar, whereas the
absorption/fluorescence bands of compound 4d with a
thiophene ring are significantly red-shifted. The modifica-
tion of R2 in derivatives 5 influences also the photophysi-
cal properties. The shifts between compounds 5a, 5b, and
5e compared to derivatives 5c and 5d are about λAbs = 10
nm and λFl = 20 nm, hypsochromically. The latter mole-
cules depict the highest Stokes shifts in this group of com-
Comparing compounds 4, the presence of a pyridin-2-yl
(R1) substituent in 4a does not only result in a hypsochro-
mic shift of the solid-state fluorescence, but also in a sig-
nificant increase of the solid-state quantum yield
(λFl = 456 nm; ΦFl = 0.32). The introduction of a substitu-
ent at R2 in the series of compounds 5 results in a decrease
of the quantum yield, where donors have a lower influ-
ence than acceptor groups. Therefore, the introduction of
fluorine strongly reduces the fluorescence intensity (ΦFl:
5a = 0.40: R2 = H; ΦFl: 5e = 0.07: R2 = F).

pounds [5c and 5d: Δν (EtOH) = 3900 cm–1].
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 126–134

128
L. K. Calderón Ortiz et al.
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When the solvent is changed from EtOH to DMSO, the
spectra of all compounds are red-shifted and in most cases
show a slight increase of the Stokes shift, for example, for
5a: (EtOH–DMSO): λAbs = 388/395 nm; λFl = 450/463 nm,

and Δν = 3550/3720 cm–1.
The fluorescence quantum yields of the tricyclic lactones
in DMSO reflect the structural variation of each derivative
measured. Compound 4a containing the pyridin-2-yl moi-
ety (R1) has the highest quantum yield within this first
group of compounds ΦFl (DMSO) = 0.59, which is com-
mon for this kind of substituent, as described in the litera-
ture.1,8
In the second group, compounds 5c, 5d, and 5e with either
a strong donor or acceptor group R2 show the highest
quantum yields: ΦFl (DMSO) = 0.83, 0.61, and 0.61, re-
spectively.
The integration of the benzothiazole substructure in the π-
system of the tricyclic lactones 5 has a significant influ-
ence on the quantum yield of the compounds in both solid
state and solution. In general, compounds of type 5 absorb
bathochromically and their fluorescence is stronger than
those of type 4. Table 1 shows the UV-Vis and fluores-
cence data of the tricyclic lactones 4 and 5 in solution and
solid state.
In addition, the chemical behavior of tricyclic lactones in
basic and acidic media was also investigated. All spectro-
scopic data are shown in Table 2 and the resulting species
in Scheme 2.
Treating solutions of compounds 4 or 5 with inorganic
(NaOH, KOH) or organic bases (tetrabutylammonium hy-
droxide) results in a color change to a deep red and, simul-
Figure 3 Solid-state fluorescence spectra of compounds 4 (λEx = 420
nm) and 5 (λEx = 450 nm).

Table 1 Absorption Maxima (in nm), Fluorescence Maxima (in nm), and Stokes Shift Δν (in cm–1) of 4 and 5 in Polar Solventsa
In EtOH
In DMSO
Solid state


Entry
λAbs
λFl
Δν
λAbs
λFl
Δν
ΦFl ± 0.10b
λFl
ΦFl ± 0.20c
4a
4b
4c
4d
5a
5b
5c
5d
5e
362
360
360
376
388
392
400
400
388
420
420
424
446
450
454
474
474
450
3820
3970
4190
4170
3550
3480
3900
3900
3550
368
362
364
382
395
399
407
408
395
428
428
432
451
463
467
478
479
461
3810
4260
4320
4010
3720
3650
3650
3630
3620
0.59
0.39
0.23
0.47
0.54
0.55
0.83
0.61
0.61
456
479
467
490
518
532
535
552
542
0.32
0.05
0.12
0.07
0.40
0.31
0.27
0.13
0.07
a Quantum yield in DMSO and in solid state.
b Determined using quinine sulfate in 0.1 N aq H2SO4 as standard.
c Determined with an integrating sphere 4 (λEx = 420 nm) and 5 (λEx = 450 nm).
Synthesis 2014, 46, 126–134
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Fluorescence of Tricyclic Lactones Based on 4-Hydroxy-1,3-thiazoles
129
O–
O
O
O
N
S
O
N
S
COO–
N
S
NaOH
HCl
N+
H
N
N
4 protonated*
4 anion
4
*
H
O
O
N
S
N
S
HCl
R2
hν
O–
R2
R2
5 protonated
O
O
S
N
N
S
S
N
S
COO–
NaOH
R2
N
O
O
S
N
S
HCl
5 anion
5
N+
H
5 protonated*
Scheme 2 Treatment of derivatives 4 and 5 with bases or acids

Table 2 Absorption Maxima (in nm), Fluorescence Maxima (in nm), and Stokes Shift Δν (in cm–1) of 4 and 5 after Addition of NaOH and
HCl in Polar Solvents
In DMSO
In EtOH
+ NaOH
+ NaOH
+ HCl



Entry
λAbs
λFl
Δν
λAbs
λFl
Δν
λAbs
λFl
Δν
4a
4b
4c
4d
5a
5b
5c
5d
5e
496
476
510
490
536
530
530
530
542
620
614
626
622
644
640
636
636
644
4030
4720
3630
4330
3130
3240
3150
3150
2920
442
434
452
434
472
470
466
474
474
598
592
598
592
620
618
616
618
622
5900
6150
5400
6150
5060
5100
5230
4920
5020
364
366
360
378
388
394
402
402
388
476
478
480
448
492
496
504
508
474
6460
6400
6940
4130
5450
5220
5030
5190
4680
taneously, to an orange-red fluorescence. This effect ring-opened compounds was possible (Table 2). The color
could be observed visually in MeCN, EtOH, MeOH, THF, change observed is strongly influenced by the nature of
and especially in DMSO, where the red color is much the solvent as well as of the substituent present in each
stronger. This color change is characteristic for 4-hy- compound.
droxy-1,3-thiazoles in the presence of bases and can be at-
In detail, upon the addition of a base to a solution of 4a in
EtOH, the emission shows a redshift of 178 nm:
λFl (EtOH) 4a/4aanion = 420/598 nm, whereas in DMSO,
tributed to the formation of the thiazol-4-olate anion.2,7,8
Therefore, it is obvious that the compounds reported here
undergo a ring-opening reaction of the lactone, which is
this shift increases to 192 nm: λFl (DMSO) 4a/4aanion
=
common for coumarins under basic conditions.11 This
ring-opening of the lactone ring is an irreversible process
in water and can already be observed at room temperature
at pH 9.97 (see Figure S1, Supporting Information).
428/620 nm. In the case of compounds of type 5, the ben-
zothiazole moiety influences this effect in a way that all
absorption and fluorescence maxima are shifted to the red
region in both solvents compared with types 4. In EtOH,
In an additional experiment performed by the addition of however, the absorption and fluorescence bands of all an-
NaOH (0.01 N) to a solution of 4 and 5 in EtOH and in ions formed are blue-shifted and, additionally, the Stokes
DMSO, the determination of the spectroscopic data of shift is higher than in DMSO.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 126–134

130
L. K. Calderón Ortiz et al.
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The observations made under acidic conditions were only
reproducible in EtOH and, in contrast, no changes in sol-
vents such as DMSO, THF, or MeCN were detected. The
addition of HCl to a solution of 4 or 5 in EtOH at room
temperature resulted in a green fluorescence, which was
measured immediately. After the addition of 2 and 3
equivalents of HCl (0.01 N) to solutions of 4 and 5, re-
spectively, the fluorescence spectra of compounds 4a, 4b,
and 4c exhibited a bathochromic shift of emission of
around 55 nm: λFl (EtOH) 4a/4a + H+ = 420/476 nm,
whereas those of compounds 5 are bathochromically
shifted only about 40 nm: λFl (EtOH) 5a/5a + H+ =
450/492 nm.
This can be explained considering the basicity of the pyr-
idine nitrogen (pKaaH = 5.2)12 present in compounds 4a,
4b, and 4c and its ability to be protonated resulting in pyr-
idinium ions, which strongly modifies the π-system. This
hypothesis was confirmed by adding HCl to a solution of
4d containing a thiophene ring (R1), which does not result
in such a considerable shift.
The reason for the smaller but also significant shift in the
fluorescence spectra of compounds of type 5 might be, on
the one hand, the protonation of the aza atoms of the two
thiazole rings or, on the other hand, a change of geometry.
The crystal structure of 5a (Figure 1) clearly shows a
trans arrangement of the two heterocyclic nitrogens,
while the C–C bond has a partial double bond character
(C7–C8 = 1.453 Å). Considering the excited state, the het-
erocyclic moieties are able to rotate around this bond,
leading to a chelating 1,4-diazadiene substructure. The
latter is now capable of efficiently trapping a proton, thus,
leading to an energy minimized structure13 (Scheme 2).
Figure 4 Color of the species formed from 4a after addition of
NaOH and HCl under daylight and UV radiation and their normalized
fluorescence spectra. 4a = 2 × 10–5 mol L–1; NaOH = 0.01 N,
HCl = 0.01 N. A: in EtOH; B: in DMSO; C: + H+ in EtOH; D:
+ NaOH in EtOH; E: + NaOH in DMSO.
Examples of all resulting species upon treatment of com-
pound 4a with acid/base and their fluorescence spectra are
shown in Figure 4.
additional aza-nitrogen in the neighboring pyridine ring,
show a strong green fluorescence upon the addition of
acids. A geometry change is discussed as a reason for this
unusual shift.
In conclusion, the present work describes the synthesis of
tricyclic lactones based on 4-hydroxy-1,3-thiazoles syn-
thesized by the classic Hantzsch synthesis. This novel
class of thiazole derivatives is featured by fluorescence in
solid state as well as in solution. The solid-state fluores-
cence of these compounds and their spectroscopic proper-
ties in solution have been investigated in detail.
Reagents were purchased from commercial sources and were used
directly. The solvents were of reagent and spectroscopic grade. Re-
actions were monitored by TLC (0.2 mm Merck silica gel plates 60
254). 1H and 13C NMR spectra (in CDCl3 or DMSO-d6 as solvent)
In the crystalline state, the tricyclic lactones of type 4 and
5 are almost coplanar, resulting in an extension of the
chromophore. Compounds 4a, 4b, and 4c show solid-state
fluorescence in the blue region of the visible spectrum,
whereas the donor character of the thiophene ring in 4d
leads to a slight shift to longer wavelengths. The extension
of the π-system in compounds of type 5 resulted in green
to yellow fluorescence in their solid state.
F
were recorded on Bruker Avance 125 and 400 spectrometers. Mass
spectrometry was carried out on a VG Trio-2000 quadrupole mass
spectrometer and elemental analysis (CHNOS) was performed us-
ing a Vario EL III equipment. Melting points (uncorrected) were
measured using a Büchi B-545 apparatus and IR spectra were re-
corded on a JASCO FT/IR 6300 spectrophotometer. UV/Vis and
fluorescence spectra were recorded in solution on a Thermo/
UNICAM UV 500 spectrophotometer and on a JASCO FP-6500
spectrofluorimeter, respectively. Fluorescence spectra of the solid-
state were recorded on a JASCO FP-8300 spectrophotometer. A
PerkinElmer Lambda 750 UV/Vis/NIR spectrophotometer was
used to calculate the Quantum Yield of the compounds in solution
and integrating sphere inserted in the fluorescence spectrometer
CD900FS (Edinburgh Analytical Instruments) was used to calcu-
late the absolute photoluminescence quantum yields of powder
samples.
When a base is added in solution, a drastic change of ab-
sorption and of fluorescence is observed. The lactone
ring-opening process leads to deprotonated 4-hydroxythi-
azoles, which, due to their electronically altered π-sys-
tems, display fluorescence in the orange to red region of
the visible spectrum. Derivatives 4a, 4b, and 4c, which
form pyridinium ions and compounds 5, which contain an
Synthesis 2014, 46, 126–134
© Georg Thieme Verlag Stuttgart · New York

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Fluorescence of Tricyclic Lactones Based on 4-Hydroxy-1,3-thiazoles
Pyridine-3-carbothioamide (2b)
131
Determination of Solid-State Fluorescence Quantum Yields: The
absolute photoluminescence quantum yields of powder samples has
been determined with an integrating sphere inserted in the fluores-
cence spectrometer CD900FS (Edinburgh Analytical Instruments).
A custom designed sphere (Mod. 05-105, AMKO) with an inner
diameter of 105 mm, coated inside with BaSO4 was used. The
excitation source was a tungsten lamp of variable intensity in order
to get suitable conditions for the measurement of the
Yield: 8.6 g (6.2 mmol, 62%); yellow crystals; mp 198–200 °C
(DMF).
IR (ATR): 734, 910, 1309, 1587, 2581, 2809, 3023, 3221 cm–1 (N–
H).
1H NMR (250 MHz, DMSO-d6): δ = 10.05 (s, 1 H), 9.69 (s, 1 H),
8.99 (d, J = 2.1 Hz, 1 H), 8.65 (dd, J = 4.8, 1.6 Hz, 1 H), 8.35–8.04
(m, 1 H), 7.59–7.26 (m, 1 H).
fluorescence and scattered
excitation
light. The
measured
13C NMR (63 MHz, DMSO-d6): δ = 198.3, 152.0, 148.0, 135.6,
spectra of scattered excitation light without (S0) and with
(SS) sample and of the sample fluorescence (SS) were corrected re-
garding the spectral sensitivity of the detector and the spectral re-
flectance of the sphere and are to be integrated in the spectral
region of the excitation and the fluorescence. The fluorescence
quantum yield was calculated with Φf = FS/(S0–SS) (see Figure S2,
Supporting Information).
135.2, 123.4.
MS (EI): m/z (%) = 138 (100, [M+]), 105 (24).
Pyrimidin-2-thioamide (2c)
Yield: 10.0 g (7.2 mmol, 72%); yellow brown crystals; mp 192–
194 °C (DMF).
IR (ATR): 742, 910, 1322, 1561, 3115, 3376 cm–1 (N–H).
1H NMR (250 MHz, DMSO-d6): δ = 10.27 (s, 1 H), 9.87 (s, 1 H),
8.89 (d, J = 4.9 Hz, 2 H), 7.61 (dd, J = 4.8 Hz, 1 H).
13C NMR (63 MHz, CDCl3): δ = 196.1, 161.3, 157.8, 122.5.
MS (EI): m/z (%) = 139 (100, [M+]), 106 (65), 80 (52).
Crystal Structure Determination: The intensity data for the com-
pounds were collected on Nonius Kappa CCD diffractometer using
graphite-monochromated MoKα radiation. Data were corrected for
Lorentz and polarization effects but not for absorption effects.14,15
The structures were solved by direct methods (SHELXS) and re-
fined by full-matrix least squares techniques against Fo2 (SHELXL-
97).16 The hydrogen atoms of 5a were located by difference Fourier
synthesis and refined isotropically. The hydrogen atoms of 4d were
included at calculated positions with fixed thermal parameters. All
nondisordered, non-hydrogen atoms were refined anisotropically.16
XP system (Siemens Analytical X-ray Instruments, Inc.) was used
for structure representations.
Thiophene-2-carbothioamide (2d)
Yield: 11.5 g (8.0 mmol, 80%); yellow crystals; mp 94–96 °C
(DMF).
IR (ATR): 680, 1015, 1362, 1517, 1620, 3147, 3267, 3314 cm–1 (N–
H).
1H NMR (250 MHz, DMSO-d6): δ = 9.59 (s, 1 H), 9.41 (s, 1 H),
7.80–7.72 (m, 1 H), 7.68 (dd, J = 3.8, 1.0 Hz, 1 H), 7.13 (dd, J = 5.0,
3.9 Hz, 1 H).
13C NMR (63 MHz, DMSO-d6): δ = 190.2, 147.0, 135.2, 128.8,
125.9.
Dimethyl α-Bromohomophthalate (1)
A mixture of dimethyl homophthalate (33 mmol, 7.0 g) prepared as
described previously17 and NBS (57 mmol, 10.2 g) in anhydrous
CH2Cl2 (170 mL) was stirred under reflux by irradiating with an
UV-light lamp. After 18 h, the solution was filtered off and the fil-
trate was sequentially washed with aq 10% NaHCO3 (50 mL), aq
10% NaHSO3 (50 mL), and brine (50 mL). The solvent was evapo-
rated and the product was purified by column chromatography
(EtOAc–n-heptane, 1:2); yield: 6.6 g (23.1 mmol, 70%); light yel-
low oil.
MS (EI): m/z (%) = 143 (88, [M+]), 45 (100), 60 (84).
Benzo[d]thiazole-2-carbothioamide (3a)
Yield: 17.5 g (9 mmol, 99%); yellow crystals; mp 210–211 °C
(DMF).
IR (ATR): 758, 1011, 1293, 1580 (C=C), 3132, 3224, 3396 cm–1
(N–H).
1H NMR (250 MHz, DMSO-d6): δ = 10.37 (s, 1 H), 10.13 (s, 1 H),
8.11 (m, 2 H), 7.63–7.49 (m, 2 H).
1H NMR (250 MHz, CDCl3): δ = 7.96 (dd, J = 7.8, 1.2 Hz, 1 H),
7.87 (d, J = 8.2 Hz, 1 H), 7.61–7.5 (m, 1 H), 7.43–7.37 (m, 1 H),
6.58 (s, 1 H), 3.91 (s, 3 H), 3.78 (s, 3 H).
13C NMR (63 MHz, CDCl3): δ = 169.2, 167.0, 137.2, 132.9, 131.7,
130.7, 128.8, 128.3, 53.4, 52.5, 44.0.
13C NMR (63 MHz, DMSO-d6): δ = 187.7, 169.2, 153.7, 139.3,
127.6, 127.3, 124.9, 122.9.
MS (EI): m/z (%) = 287 (14, [M+]), 254 (100), 256 (84).
MS (EI): m/z (%) = 194 (100, [M+]), 167 (40), 135 (16).
Carbothioamides 2 and Benzothiazolecarbothioamides 3; Gen-
eral Procedure
The corresponding nitrile (100 mmol) prepared as described
previously18 was dissolved in DMSO (25 mL) and H2S was slowly
bubbled through the solution until no more gas was consumed. The
solution was stirred at r.t. and the reaction progress was monitored
by TLC (acetone). H2O was added to precipitate the product, the
solid formed was collected by filtration, and recrystallized from
DMF.
6-Methylbenzo[d]thiazole-2-carbothioamide (3b)
Yield: 17.5 g (8.4 mmol, 84%); yellow crystals; mp 248–250 °C
(DMF).
IR (ATR): 740, 918, 1211, 1603 (C=C), 3135, 3235, 3339 cm–1 (N–
H).
1H NMR (250 MHz, DMSO-d6): δ = 10.32 (s, 1 H), 10.08 (s, 1 H),
8.10–7.80 (m, 2 H), 7.40 (d, J = 8.4 Hz, 1 H), 3.36 (s, 3 H).
13C NMR (63 MHz, DMSO-d6): δ = 187.8, 168.1, 151.9, 139.5,
Pyridine-2-carbothioamide (2a)
Yield: 11.7 g (8.5 mmol, 85%); yellow crystals; mp 138–140 °C
(DMF).
IR (ATR): 725, 900, 1304, 1579, 3141 cm–1 (N–H).
137.4, 129.3, 124.5, 122.3, 21.6.
MS (EI): m/z (%) = 208 (100, [M+]), 121 (80), 181 (60).
1H NMR (250 MHz, DMSO-d6): δ = 10.13 (s, 1 H), 9.90 (s, 1 H),
8.61–8.56 (m, 1 H), 8.49 (d, J = 8.0 Hz, 1 H), 7.99–7.92 (m, 1 H),
7.60–7.55 (m, 1 H).
6-Methoxybenzo[d]thiazole-2-carbothioamide (3c)
Yield: 18.2 g (8.1 mmol, 81%); yellow crystals; mp 200–202 °C
(DMF).
13C NMR (63 MHz, DMSO-d6): δ = 195.2, 152.2, 148.0, 137.8,
126.7, 124.9.
IR (ATR): 691, 1017, 1224, 1600 (C=C), 3137, 3234, 3399 cm–1
(N–H).
MS (EI): m/z (%) = 138 (100, [M+]), 79 (40), 105 (38).
© Georg Thieme Verlag Stuttgart · New York
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132
L. K. Calderón Ortiz et al.
PAPER
1H NMR (250 MHz, DMSO-d6): δ = 10.24 (s, 1 H), 10.01 (s, 1 H),
7.96 (d, J = 9.0 Hz, 1 H), 7.69 (d, J = 2.5 Hz, 1 H), 7.17 (dd, J = 9.0,
2.5 Hz, 1 H), 3.85 (s, 3 H).
13C NMR (63 MHz, DMSO-d6): δ = 187.7, 166.4, 158.9, 148.1,
141.3, 125.7, 117.8, 104.7, 56.3.
IR (ATR): 743 (C–H), 1019, 1377, 1614 (C=C), 1729 (C=O), 3028
cm–1.
1H NMR (250 MHz, DMSO-d6): δ = 9.18 (d, J = 2.2 Hz, 1 H), 8.73
(dd, J = 4.8, 1.4 Hz, 1 H), 8.39–8.33 (m, 1 H), 8.25 (d, J = 7.9 Hz,
1 H), 7.88 (dd, J = 16.9, 7.1 Hz, 2 H), 7.68–7.56 (m, 2 H).
MS (EI): m/z (%) = 224 (100, [M+]), 191 (96), 165 (78).
13C NMR (63 MHz, DMSO-d6): δ = 162.2, 160.8, 157.8, 152.4,
147.2, 136.6, 134.0, 132.1, 131.1, 129.3, 128.6, 124.9, 124.4, 119.1,
109.8.
6-(Benzyloxy)benzo[d]thiazole-2-carbothioamide (3d)
Yield: 25.5 g (8.5 mmol, 85%); yellow powder; mp 242–244 °C
(DMF).
MS (EI): m/z (%) = 280 (100, [M+]), 176 (40), 120 (28).
IR (ATR): 826, 1014, 1232, 1592 (C=C), 3148, 3237, 3366 cm–1
(NH).
Anal. Calcd for C15H8N2O2S: C, 64.27; H, 2.88; N, 9.99; S, 11.44.
Found: C, 64.30; H, 2.87; N, 10.05; S, 11.40.
1H NMR (250 MHz, DMSO-d6): δ = 10.25 (s, 1 H), 10.02 (s, 1 H),
7.98 (d, J = 9.0 Hz, 1 H), 7.80 (d, J = 2.1 Hz, 1 H), 7.48 (d, J = 6.8
Hz, 2 H), 7.38 (dd, J = 15.4, 7.6 Hz, 3 H), 7.29–7.22 (m, 1 H), 5.19
(s, 2 H).
13C NMR (63 MHz, DMSO-d6): δ = 187.7, 166.6, 158.0, 148.2,
141.2, 136.9, 128.9, 128.5, 128.4, 125.7, 118.2, 105.8, 70.4.
2-(Pyrimidin-2-yl)-5H-isochromeno[3,4-d]thiazol-5-one (4c)
Yield: 0.3 g (1.1 mmol, 35%); off-white fine needles; mp 308–
310 °C (DMF).
IR (ATR): 762 (C–H), 1025, 1610 (C=C), 1748 (C=O), 3092 cm–1.
1H NMR (400 MHz, 70 °C, DMSO-d6): δ = 8.98 (d, J = 4.9 Hz, 2
H), 8.30 (d, J = 7.9 Hz, 1 H), 7.96–7.92 (m, 2 H), 7.73–7.65 (m, 1
H), 7.61 (t, J = 4.9 Hz, 1 H).
MS (EI): m/z (%) = 300 (76, [M+]), 91 (100).
Anal. Calcd for C15H12N2OS2: C, 59.97; H, 4.03; N, 9.33; S, 21. 35.
Found: C, 60.02; H, 4.02; N, 9.40; S, 21.30.
13C NMR (101 MHz, DMSO-d6): δ = 206.3, 163.6, 160.8, 158.7,
158.1, 136.4, 132.2, 131.1, 129.7, 124.7, 122.6, 119.7, 112.9.
MS (EI): m/z (%) = 281 (80, [M+]), 176 (100).
6-Fluorobenzo[d]thiazole-2-carbothioamide (3e)
Yield: 16.9 g (8.0 mmol, 80%); yellow needles; mp 252–254 °C
(DMF).
Anal. Calcd for C14H7N3O2S: C, 59.78; H, 2.51; N, 14.94; S, 11.40.
Found: C, 59.70; H, 2.50; N, 14.99; S, 11.38.
IR (ATR): 854, 1044, 1230, 1584 (C=C), 3135, 3226, 3395 cm–1
(N–H).
1H NMR (250 MHz, DMSO-d6): δ = 10.39 (s, 1 H), 10.13 (s, 1 H),
2-(Thiophen-2-yl)-5H-isochromeno[3,4-d]thiazol-5-one (4d)
Yield: 0.6 g (1.95 mmol, 65%); yellow needles; mp 210–212 °C
(DMF).
8.13–8.02 (m, 2 H), 7.49–7.41 (m, 1 H).
IR (ATR): 694 (C–H), 1003, 1383, 1601 (C=C), 1727 (C=O), 3107
cm–1.
1H NMR (250 MHz, DMSO-d6): δ = 8.21 (d, J = 7.9 Hz, 1 H), 7.93–
7.81 (m, 3 H), 7.76 (d, J = 7.7 Hz, 1 H), 7.61 (dd, J = 11.2, 4.0 Hz,
1 H), 7.23 (dd, J = 4.9, 3.9 Hz, 1 H).
13C NMR (63 MHz, DMSO-d6): δ = 187.4, 169.3 (d, J = 3.5 Hz),
161.0 (d, J = 246 Hz), 150.6 (d, J = 1.3 Hz), 140.7 (d, J = 11.8 Hz),
126.6 (d, J = 9.8 Hz), 116.5 (d, J = 25.3 Hz), 109.1 (d, J = 27.2 Hz).
MS (EI): m/z (%) = 212 (100, [M+]), 60 (50) 185 (40).
Anal. Calcd for C8H5FN2S2: C, 45.27; H, 2.37; N, 13.20; S, 30.21.
Found: C, 45.33; H, 2.35; N, 13.21; S, 30.15.
13C NMR (63 MHz, DMSO-d6): δ = 160.9, 159.1, 157.1, 136.5,
135.9, 132.3, 131.6, 131.0, 129.4, 129.2, 128.9, 124.0, 118.9, 108.0.
MS (EI): m/z (%) = 285 (100, [M+]), 176 (28), 120 (36).
Tricyclic Lactones 4 and 5 Based on 4-Hydroxy-1,3-thiazoles;
General Procedure
Anal. Calcd for C14H7NO2S2: C, 58.93; H, 2.47; N, 4.91; S, 22.47.
Found: C, 58.93; H, 2.30; N, 4.99; S, 22.43.
Under an inert atmosphere, the corresponding thioamide 2 or 3
(3 mmol) was dissolved in DMF (3–5 mL) and Et3N (3 mmol) was
added. The solution was stirred for 20 min at 30 °C and dimethyl α-
bromohomophthalate (1; 1.148 g, 4 mmol) was added. The temper-
ature of the stirred reaction was slowly increased up to 120 °C. Af-
ter 24 h, the solid formed was collected by filtration, washed with
EtOH (10 mL), and recrystallized from DMF.
Crystal Data for 4d19
C14H7NO2S2, Mr = 285.33
g
mol–1, colorless prism, size
21,
0.07 × 0.03 × 0.03 mm3, monoclinic, space group
P
a = 3.8212(2), b = 14.0344(9), c = 11.2879(8) Å, β = 95.856(3)°,
V = 602.19(7) Å3, T = –140 °C, Z = 2, ρcalcd = 1.574 gcm–3, μ
(MoKα) = 4.36 cm–1, F(000) = 292, 3482 reflections in h(–4/4),
k(–18/15), l(–14/10), measured in the range 3.63° ≤ Θ ≤ 27.44°,
completeness Θmax = 98.9%, 2382 independent reflections,
2-(Pyridin-2-yl)-5H-isochromeno[3,4-d]thiazol-5-one (4a)
Yield: 0.6 g (2.1 mmol, 70%); colorless needles; mp 270–272 °C
(DMF).
IR (ATR): 805 (C–H), 1038, 1613 (C=C), 1740 (C=O), 2950 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.64 (d, J = 4.2 Hz, 1 H), 8.42 (d,
J = 7.9 Hz, 1 H), 8.25 (d, J = 7.9 Hz, 1 H), 7.86–7.77 (m, 2 H), 7.65
(d, J = 7.7 Hz, 1 H), 7.55 (t, J = 7.6 Hz, 1 H), 7.41–7.35 (m, 1 H).
R
int = 0.0243, 2283 reflections with Fo > 4ρ(Fo), 191 parameters, 1
restraints, R1obs = 0.0352, wR2obs = 0.0777, R1all = 0.0386,
wR2all = 0.0806, GOOF = 1.143, Flack-parameter 0.10(9), largest
difference peak and hole: 0.244/–0.194 e Å–3.
Selected bond lengths (Å): C4–C5 1.443 (3); C6–C7 1.367 (4); C9–
C14 1.411 (3); C8–O2 1.204 (4); C5–N1 1.314 (4); C5–S2 1.745
(3); C4–S1 1.718 (4); torsion angle [°] S1–C4–C5–S2 176.20 (2).
13C NMR (101 MHz, CDCl3): δ = 166.4, 160.8, 158.0, 150.6, 149.5,
137.0, 135.3, 132.8, 131.4, 128.2, 125.2, 123.3, 120.0, 119.5, 110.9.
MS (EI): m/z (%) = 280 (48, [M+]), 120 (100), 148 (16).
2-(Benzo[d]thiazol-2-yl)-5H-isochromeno[3,4-d]thiazol-5-one
(5a)
Anal. Calcd for C15H8N2O2S: C, 64.27; H, 2.88; N, 9.99; S, 11.44.
Found: C, 64.30; H, 2.61; N, 9.95; S, 11.16.
Yield: 0.5 g (1.5 mmol, 49%); yellow needles; mp 190–192 °C
(DMF).
IR (ATR): 760 (C–H), 917, 1480, 1600 (C=C), 1737 (C=O) cm–1.
2-(Pyridin-3-yl)-5H-isochromeno[3,4-d]thiazol-5-one (4b)
Yield: 0.4 g (1.4 mmol, 45%); beige powder; mp 220–222 °C
(DMF).
1H NMR (400 MHz, 70 °C, DMSO-d6): δ = 8.32 (d, J = 8.4 Hz, 1
H), 8.23 (d, J = 7.4 Hz, 1 H), 8.16 (d, J = 8.3 Hz, 1 H), 7.99 (s, 2 H),
7.73 (s, 1 H), 7.65 (s, 1 H), 7.59 (s, 1 H).
Synthesis 2014, 46, 126–134
© Georg Thieme Verlag Stuttgart · New York

PAPER
Fluorescence of Tricyclic Lactones Based on 4-Hydroxy-1,3-thiazoles
133
MS (EI): m/z (%) = 336 (100, [M+]), 176 (44), 120 (32).
IR (ATR): 757 (C–H), 837, 1604 (C=C), 1741 (C=O), 3064 cm–1.
Anal. Calcd for C17H8N2O2S2: C, 60.70; H, 2.40; N, 8.33; S, 19.06.
Found: C, 60.65; H, 2.26; N, 8.56; S, 19.14.
1H NMR (400 MHz, 70 °C, DMSO-d6): δ = 8.31 (d, J = 7.8 Hz, 1
H), 8.18 (dd, J = 9.0, 5.1 Hz, 1 H), 8.11 (dd, J = 8.7, 2.6 Hz, 1 H),
7.98 (d, J = 3.0 Hz, 2 H), 7.74–7.70 (m, 1 H), 7.49 (dd, J = 10.3, 7.6
Hz, 1 H).
Crystal Data for 5a19
C17H8N2O2S2, Mr = 336.37 gmol–1, yellow prism, size
0.06 × 0.06 × 0.05 mm3, orthorhombic, space group P bca, a =
7.0319(2), b = 14.3660(3), c = 27.3922(9) Å, V = 2767.17(13) Å3,
T = –140 °C, Z = 8, ρcalcd = 1.615 gcm–3, μ (MoKα) = 3.96 cm–1,
F(000) = 1376, 16319 reflections in h(–9/8), k(–18/18), l(–35/33),
measured in the range 2.84° ≤ Θ ≤ 27.50°, completeness
MS (EI): m/z (%) = 354 (94, [M+]), 120 (100), 148 (70).
Anal. Calcd for C17H7FN2O2S2: C, 57.62; H, 1.99; N, 7.90; S, 18.10.
Found: C, 57.60; H, 1.95; N, 7.95; S, 18.15.
Acknowledgment
Θ
max = 99.7%, 3169 independent reflections, Rint = 0.0486, 2795 re-
flections with Fo 4ρ(Fo), 240 parameters, restraints,
>
0
We are very grateful for the financial support by DAAD (grant for
Lorena Calderón Ortiz). Our special thanks go to Prof. Uwe Ritter
for the provision of the equipments and assistance in solid-state
fluorescence measurements.
R1obs = 0.0389, wR2obs = 0.0851, R1all = 0.0472, wR2all = 0.0892,
GOOF = 1.096, largest difference peak and hole: 0.385/–0.269 e Å–3.
Selected bond lengths (Å): C7–C8 1.453 (3); C9–C17 1.363 (2);
C11–C16 1.410 (3); C10–O2 1.201 (2); C7–S1 1.742 (2); C8–S2
1.728 (2); C7–N1 1.302 (2); C8–N2 1.314 (2); C1–C6 1.411 (3);
torsion angle [°]S1–C7–C8–S2 174.42 (1).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
m
tgioSrantnugIifoop
r
itmnatr
2-(6-Methylbenzo[d]thiazol-2-yl)-5H-isochromeno[3,4-d]thia-
zol-5-one (5b)
Yield: 0.5 g (1.44 mmol, 48%); yellow needles; mp >340 °C
(DMF).
References
(1) Stippich, K.; Weiß, D.; Güther, A.; Görls, H.; Beckert, R.
J. Sulfur Chem. 2009, 30, 109.
IR (ATR): 760 (C–H), 807, 917, 1600 (C=C), 1733 (C=O), 3061
cm–1.
(2) Täuscher, E.; Weiß, D.; Beckert, R.; Fabian, R.; Assumpsao,
A.; Görls, H. Tetrahedron Lett. 2011, 52, 2292.
(3) Täuscher, E.; Weiß, D.; Beckert, R.; Görls, H. Synthesis
2010, 1603.
(4) Menzel, R.; Täuscher, E.; Weiß, D.; Beckert, R.; Görls, H. Z.
Anorg. Allg. Chem. 2010, 636, 1380.
(5) Menzel, R.; Breul, A.; Pietsch, C.; Schäfer, J.; Friebe, C.;
Täuscher, E.; Weiß, D.; Dietzek, B.; Popp, J.; Beckert, R.;
Schubert, U. S. Macromol. Chem. Phys. 2011, 212, 840.
(6) Menzel, R.; Kupfer, S.; Mede, R.; Weiß, D.; Görls, H.;
González, L.; Beckert, R. Eur. J. Org. Chem. 2012, 27, 5231.
(7) Täuscher, E.; Weiß, D.; Beckert, R.; Görls, H. Synthesis
2011, 2334.
1H NMR (400 MHz, 70 °C, DMSO-d6): δ = 8.32 (d, J = 7.2 Hz, 1
H), 8.02 (s, 2 H), 7.97 (s, 2 H), 7.73 (s, 1 H), 7.48 (s, 1 H), 2.33 (s,
3 H).
MS (EI): m/z (%) = 350 (46, [M+]), 120 (100), 176 (56).
Anal. Calcd for C18H10N2O2S2: C, 61.70; H, 2.88; N, 7.99; S, 18.30.
Found: C, 61.68; H, 2.86; N, 7.95; S, 18.35.
2-(6-Methoxybenzo[d]thiazol-2-yl)-5H-isochromeno[3,4-d]thia-
zol-5-one (5c)
Yield: 0.6 g (1.5 mmol, 51%); yellow powder; mp 200–202 °C
(DMF).
IR (ATR): 751 (C–H), 1017, 1050, 1600 (C=C), 1723 cm–1 (C=O).
(8) Calderón-Ortiz, L. K.; Täuscher, E.; Leite-Bastos, E.; Görls,
H.; Weiß, D.; Beckert, R. Eur. J. Org. Chem. 2012, 2535.
(9) Dong, B.; Wang, M.; Xu, C.; Feng, Q.; Wang, Y. Cryst.
Growth Des. 2012, 12, 5986.
(10) (a) Park, S. Y.; Ebihara, M.; Kubota, Y.; Funabiki, K.;
Masaki, K.; Matsui, M. Dyes Pigments 2009, 82, 258.
(b) Matsui, M.; Fukuschima, M.; Kubota, Y.; Funabiki, K.;
Schiro, M. Tetrahedron 2012, 68, 1932. (c) Gupta, R.;
Thomas, R.; Kulkarni, G. J. Mater. Chem. 1012, 22, 19139.
(11) Delalande, Z. Justus Liebigs Ann. Chem. 1843, 45, 332.
(12) (a) Linnell, R. J. Org. Chem. 1960, 25, 290. (b) Bordwell, F.
G. Acc. Chem. Res. 1988, 21, 456.
1H NMR (400 MHz, 70 °C, DMSO-d6): δ = 8.31 (s, 1 H), 8.08–8.01
(m, 1 H), 7.97 (s, 2 H), 7.79 (s, 1 H), 7.76–7.67 (m, 1 H), 7.28–7.22
(m, 1 H), 3.92 (s, 3 H).
MS (EI): m/z (%) = 366 (86, [M+]), 120 (100), 148 (44).
Anal. Calcd for C18H10N2O3S2: C, 59.00; H, 2.75; N, 7.65; S, 17.50.
Found: C, 59.05; H, 2.70; N, 7.69; S, 17.52.
2-(6-Benzyloxybenzo[d]thiazol-2-yl)-5H-isochromeno[3,4-
d]thiazol-5-one (5d)
Yield: 0.6 g (1.4 mmol, 46%); yellow powder; mp 272–274 °C
(DMF).
IR (ATR): 759 (C–H), 1217, 1368, 1598 (C=C), 1740 (C=O), 3030
cm–1.
(13) Öğretir, C.; Görgün, K.; Özkütük, M.; Sakarya, H. C.
ARKIVOC 2009, (vii), 197.
1H NMR (400 MHz, 70 °C, DMSO-d6): δ = 8.30 (s, 1 H), 8.06 (d,
J = 8.4 Hz, 1 H), 7.97 (s, 2 H), 7.88 (s, 1 H), 7.71 (s, 1 H), 7.50 (s,
2 H), 7.42 (s, 2 H), 7.33 (s, 2 H), 5.26 (s, 2 H).
(14) COLLECT, Data Collection Software; Nonius B.V.: Delft,
The Netherlands, 1998.
(15) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276,
307.
(16) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 46, 112.
(17) Billamboz, M.; Bailly, F.; Cotelle, P. J. Heterocycl. Chem.
2009, 46, 392.
MS (EI): m/z (%) = 442 (24, [M+]), 91 (100), 120 (88).
Anal. Calcd for C24H14N2O3S2: C, 65.14; H, 3.19; N, 6.33; S, 14.49.
Found: C, 65.16; H, 3.17; N, 6.38; S, 14.45.
(18) (a) Würfel, H.; Weiß, D.; Beckert, R.; Güther, A. J. Sulfur
Chem. 2012, 33, 9. (b) Würfel, H. Ph.D. Thesis; Friedrich
Schiller Universität: Germany, 2012.
(19) Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data
2-(6-Fluorobenzo[d]thiazol-2-yl)-5H-isochromeno[3,4-d]thia-
zol-5-one (5e)
Yield: 0.8 g (2.3 mmol, 78%); yellow powder; mp 340–342 °C
(DMF).
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2014, 46, 126–134

134
L. K. Calderón Ortiz et al.
PAPER
the Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: +44(1223)336033;
E-mail: deposit@ccdc.cam.ac.uk
Centre as supplementary publication CCDC-936840 for 4d
and CCDC-936841 for 5a. These data can be obtained free
of charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif or by writing to
Synthesis 2014, 46, 126–134
© Georg Thieme Verlag Stuttgart · New York