Complete 1H and 13C NMR spectral assignment of benzo[d]isothiazole derivatives and of an isoindole isoster

Article abstract of DOI:10.1002/mrc.2308

The complete ¹H and ¹³C NMR assignments of the novel compoundmethyl 2-amino-3-(benzo[d]isothiazol-3-yl)propanoate (1), of 3-amino-5-methylbenzo[d]isothiazole (2) and N-(t-butyloxycarbonyl)-2- aminobenzo[d]isothiazol-3(2H)-one (3) and

Full text of DOI:10.1002/mrc.2308

Spectral Assignments and Reference Data
Received: 20 March 2008
Revised: 18 July 2008
Accepted: 22 July 2008
Published online in Wiley Interscience: 13 October 2008
(
www.interscience.com) DOI 10.1002/mrc.2308
1
13
Complete H and C NMR spectral assignment
of benzo[d]isothiazole derivatives and of an
isoindole isoster
a∗
b
a
Matteo Incerti, Domenico Acquotti and Paola Vicini
The complete H and 13C NMR assignments of the novel compound methyl 2-amino-3-(benzo[d]isothiazol-3-yl)propanoate (1),
of 3-amino-5-methylbenzo[d]isothiazole (2) and N-(t-butyloxycarbonyl)-2-aminobenzo[d]isothiazol-3(2H)-one (3) and of the
desulfurated isostere of 3, N-(t-butyloxycarbonyl)-2-aminoisoindolin-1-one (4), using 1D and 2D NMR techniques, including
COSY, INADEQUATE, HSQC, and HMBC experiments are reported. Copyright ꢀc 2008 John Wiley & Sons, Ltd.
1
Keywords: 2D NMR; 1H–13
C long-range coupling; HSQC; HMBC; INADEQUATE, 3-substituted benzo[d]isothiazole; 2-
aminobenzo[d]isothiazol-3-one; 2-aminoisoindolin-1-one
Introduction
(gHSQC). The gCOSY spectra allowed assignment of the aromatic
spin system pattern H4-H5-H6-H7, but the two couples H4–H7
and H5–H6 might be interchanged. In principle, H4 and H7 can be
The benzo[d]isothiazole derivatives are heterocyclic compounds
that have been reported to possess many interesting biolog-
2
discriminated on the basis of C–H correlations governed by JCH
ical activities.[
1,2]
The benzo[d]isothiazole ring can be a sub-
3
and JCH. In gHMBC spectra, H4 proton should show long-distance
stituent of a bioactive scaffold or the pharmacophore of a
bioactive molecule. For a number of years, we have designed,
3
JCH correlations with C6 and with the two quaternary carbons C3
2
and C7a. On the other hand, H7 must show the long-distance JCH
correlations with C6 and C7a and JCH correlations with C3a and
synthetized and tested series of 3-substituted benzisothiazole
3
derivatives[
3–10]
and more recently, we have discovered novel
C5, but not with C3. In fact, supposing H4 at δ = 7.95 ppm, in
2
-aminobenzo[d]isothiazole-3-one derivatives displaying new, in-
2
3
addition to the JCH correlation with C3a, we found, for H4, the JCH
[
11–14]
teresting biological properties.
datahavebeenreportedintheliteratureconcerningthechemistry
Although a lot of structural
correlations with C6 and three quaternary carbons at δ = 162.6,
2
1
34.8, and 152.4 ppm; for H7 we found the JCH correlation with
[
1,2,15]
of the benzofused isothiazoles,
detailed information about
3
C6 and the JCH correlations with C5 and a quaternary carbon at
δ = 134.8 ppm. This suggests that C3, C3a, and C7a should be at
δ = 162.6, 134.8, and 152.4 ppm, respectively. Both H4 and H7
1
13
H and C NMR signals of the class of compounds is still lacking.
In pursuing studies on this class of benzisothiazole derivatives,
structural elucidation is a significant part of our work. So, we de-
cided to perform the complete H and C NMR assignment of a
2
showed a mutual weak correlation. H5 showed the expected JCH
1
13
3
and JCH correlations with C3a, C4, C6, and C7 together with two
JCH correlations with C3 and C7a. H6 showed exactly the expected
novel 3-substituted derivative (1) and of the previously described
4
3
-amino-5-methylbenzo[d]isothiazole (2), the parent compound
correlations with C4, C5, C7, and C7a.
of 5-methyl substituted benzo[d]isothiazoles extensively investi-
gated by us (Table 1).[
plete spectral assignment of the key intermediate (3) used for the
synthesis of 2-aminobenzo[d]isothiazol-3-one derivatives[
andofitsdesulfuratedisoster, the2-aminoisoindolin-1-oneanalog
The assignment of 2 was easier (Table 1); the signal of H4 was a
3,7–9,16]
Moreover, we report here the com-
2
singlet, which showed a JCH coupling with C3a and a number of
3
long-range JCH correlations with C3, C6, C7a, and with the methyl
11–14]
carbon C8.
For compound 3 (Table 2), the protons and carbon atoms 4, 5, 6,
(4) (Table 2).
7
1
, and 10 were assigned using the same strategy as described for
; the HMBC experiment showed that H4 had strong correlations
with C6, and with three quaternary carbons at δ = 122.0, 140.4,
3
Results and Discussion
and 164.9 ppm, while H7 showed the expected JCH correlations
1
13
All H and C chemical shifts and coupling constants are given
1
3
1
in Tables 1 and 2 along with the HMBC C– H correlations on
which the unambiguous assignments of all carbons and protons
were made. The structures of the compounds 1–4 were assigned
by analysis of one- and two-dimensional NMR experiments.
In the case of 1 (Table 1), the amino protons and the protons on
thecarbons4, 5, 6, 7, 8, 9, and11, whichwereeasilyassignedonthe
basis of chemical shift and multiplicity, allowed the assignment
of the carbons they are directly attached to, by C–H correlation
∗
Correspondenceto:Matteo Incerti,DipartimentoFarmaceuticoUniversit a` degli
Studi di Parma, Viale G. P. Usberti 27/A, Parma 43100, Italy.
E-mail: matteo.incerti@unipr.it
a Dipartimento Farmaceutico, Universit a` degli Studi di Parma, Viale G. P. Usberti
27/A, Parma 43100, Italy
b Centro Interdipartimentale Misure ‘Giuseppe Casnati’, Universit a` degli Studi di
Parma, Viale G.P. Usberti 23/A, Parma 43100, Italy
Magn. Reson. Chem. 2008, 46, 1175–1179
Copyright ꢀc 2008 John Wiley & Sons, Ltd.

M. Incerti, D. Acquotti and P. Vicini
Table 1. 1H and 13C chemical shifts and HMBC correlations of 1 and 2
a
b
1
1
NH2
4
O
8
5
3a
3
5
4
1
0
8
O
9
N
3
a
3
6
6
7a
S
1
7
NH2
7
7a
N
S
1
1
2
Position
3
1H
13C
HMBC
Position
1H
13C
HMBC
–
–
162.6
134.8
123.1
124.7
127.7
119.9
152.4
36.1
–
–
–
3
3a
4
–
158.3
126.7
121.3
134.0
129.9
120.0
149.1
21.2
–
–
3
a
4
5
6
7
a
a
b
9
0
1
–
7.45(s)
–
–
7.95 (d, J = 8.3)
7.42 (t, J = 8.3)
7.50 (t, J = 8.3)
7.90 (d, J = 8.3)
–
3,3a,6,7,7a
3,3a,4,6,7,7a
4,5,7,7a
3a,4,5,6
–
3,3a,6,7a,8
5
–
6
7.30 (d, J = 8.2)
4,5,7,7a,8
7
7.65 (d, J = 8.2)
3a,4,5,6
7
8
8
7a
8
–
–
3.41 (dd, J8a–9 = 7.8, J8a–8b = 15.4)
3,3a,9,10
3,3a,9,10
3,8,10
–
2.45 (s)
4,5,6
3.54 (dd, J8b–9 = 4.7, J8a–8b = 15.4)
NH2
–
4.81 (b)
–
–
–
–
–
4.14 (dd, J9–8a = 7.8, J9–8b = 4.7)
53.3
175.1
52.2
–
–
–
–
–
–
1
1
–
–
–
3.69 (s)
1.87 (s)
10
–
–
NH2
–
–
–
a
Chemical shifts in ppm (multiplicity, J in Hz).
Carbons coupled to the corresponding H atom.
b
with C5 and with the quaternary carbon at δ = 122.0 ppm. Both Experimental
4
H4 and H7 showed mutual correlations due to JCH; moreover,
4
Synthesis
H7 showed a weak JCH correlation at δ = 164.9. This suggests
that the signals at δ = 164.9 and 122.0 ppm belong to C3 and
The synthesis of methyl 2-amino-3-(benzo[d]isothiazol-3-
yl)propanoate (1) was accomplished as reported in Fig. 2. Accord-
ingtoUnoandKurokawa, 3-(bromomethyl)benzo[d]isothiazole
2
C3a, respectively. So, H4 showed a JCH correlation with C3a but
2
[17]
a very weak coupling with C5; also, H7 showed only one JCH
correlation with C6, but H7–C7a coupling was missing. Moreover,
was obtained from 2-(benzo[d]isothiazol-3-yl)acetic acid
through bromination under suitable conditions, followed
by decarboxylation. It was converted, by reaction with
diethyl 2-acetamidomalonate, to diethyl 2-acetamido-2-
2
3
4
H5 and H6, besides the expected JCH and JCH, showed the JCH
couplings: H5–C3, H5–C7a, and H6–C3a. These anomalies in the
intensities of the cross-peaks suggested us to run an INADEQUATE
experiment to build a reliable C–C correlation map. This is a
very powerful experiment; however, it is not very sensitive and
needs a very concentrated sample solution to provide a C–C
connectivity map.
[(benzo[d]isothiazol-3-yl)methyl]malonate.Hydrolysisofthelatter,
in 6 M hydrochloric acid, afforded the hydrochloride salt of 2-
amino-3-(benzo[d]isothiazol-3-yl)propanoic acid, which was easily
converted to target 1.
The synthesis of 3-amino-5-methylbenzo[d]isothiazole (2)[16] as
Starting from the unambiguous C3 (Fig. 1), the only carbonyl
group without proton correlation, it is easy to trace the aromatic
ring correlation net; C3a correlates with C4, but has another
connection with a carbon at δ = 140.4 ppm, which cannot be
other than C7a. This spectrum allows discriminating C3a from C7a.
The same approach was used for compound 4 (Table 2): the
protons and carbon atoms 1, 4, 5, 6, 7, and 10 were assigned
using the same strategy as described for 1. Both gHMBC and
INADEQUATE were used to assign all carbon atoms. In particular
in gHMBC spectrum, the correlations of H1 with C7a and C7
are diagnostic to discriminate H4 from H7. So, starting from the
unambiguous C4, it is easy to trace the aromatic ring correlation
net; C3a has a second connection with a carbon at δ = 167.6 ppm,
which can be only C3.
well as that of N-(t-butyloxycarbonyl)-2-aminobenzo[d]isothiazol-
3
new N-(t-butyloxycarbonyl)-2-aminoisoindolin-1-one (4) was per-
(2H)-one (3)[ was described earlier. The preparation of the
11]
formed starting phthalide from which, according to Burton and
[18]
Koppes,
was initially heated with dibromotriphenylphospho-
rane, to give 2-(bromomethyl)benzoylbromide, which was then
treated with tert-butyl carbazate in anhydrous dioxane in the
presence of triethylamine (TEA) to yield 4 (Fig. 3).
Allreactionswerecarriedoutusingflame-driedglasswareunder
an atmosphere of nitrogen. Anhydrous dichloromethane was
obtained by its distillation from dried granular calcium chloride.
Melting points were measured on a Buchi 512 apparatus and
are uncorrected. Flash chromatography was performed using
Merck silica gel 60 (Si 60, 40–63 µm, 230–400 mesh ASTM).
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Copyright ꢀc 2008 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2008, 46, 1175–1179

Spectral Assignments and Reference data
Table 2. 1H and 13C chemical shifts and HMBC correlations of 3 and 4
a
b
1
0
10
1
0
10
O
4
O
9
10
4
O
O
3
a
9
5
O
3
a
10
8
5
6
O
3
8
N
NH
3
N
NH
6
S
1
7
a
7
7a
1
7
3
4
Position
1H
13C
HMBC
Position
1H
13C
HMBC
1
3
–
–
–
–
–
–
–
1
3
4.57 (s)
51.7
167.6
130.3
124.2
128.0
132.2
122.9
140.3
154.7
82.0
3,3a,6,7,7a
164.9
122.0
127.3
125.5
132.8
120.4
140.4
153.8
83.0
–
–
–
–
3
a
4
5
6
7
a
8
9
0
3a
4
8.02 (d, J = 8.2)
3,3a,5,6,7a,7
7.82 (d, J = 7.7)
3,3a,6,7,7a
7.35 (t, J = 8.2)
3,3a,4,6,7,7a
5
7.41 (t, J = 7.7)
3,3a,4,6,7,7a
7.60 (t, J = 8.2)
3a,4,5,7,7a
6
7.53 (t, J = 7.7)
3a,4,5,7,7a
7.44 (d, J = 8.2)
3,3a,4,5,6
7
7.37 (d, J = 7.7)
1,3a,4,5,6,7a
7
1
–
–
–
–
–
9
–
7a
8
–
–
–
–
–
9
–
–
9
–
1.45 (s)
7.29 (b)
28.0
10
NH
1.44 (s)
7.17 (b)
28.1
NH
–
–
a
Chemical shifts in ppm (multiplicity, J in Hz).
Carbons coupled to the corresponding H atom.
b
Methyl 2-amino-3-(benzo[d]isothiazol-3-yl)propanoate (1)
To an ethanolic suspension of sodium diethyl 2-
acetamidomalonate[
(
19]
(10 mmol),
a
solution
of
3-
in
bromomethyl)benzo[d]isothiazole
(1.94 g,
8.5 mmol)
anhydrous CH2Cl2 was added dropwise and the reaction
◦
mixture was heated at 90 C for 15 min. The solvent was then
evaporated under reduced pressure and the residue, poured into
water, was extracted with CH2Cl2. From the organic extract, dried
over Na2SO4 and evaporated, a yellowish oil was obtained, which
solidified slowly, and was collected after elution on silica gel, by
flash chromatography (methylene chloride-ethanol: 98/2), to yield
1
3
.62 g (1.7 mmol) of diethyl 2-acetamido-2-[(benzo[d]isothiazol-
-yl)methyl]malonate. Then, it was used as such, for the following
reaction step; it was suspended in 6 N HCl (10 ml) and refluxed
for 12 h. After cooling and evaporation of the solution under
reduced pressure, the reddish solid residue, consisting of
2
-amino-3-(benzo[d]isothiazol-3-yl)propanoic acid hydrochloride,
was carefully dried and used as a crude compound for the
following chlorination/esterification. To a cooled methanolic
solution (20 ml) of the above amino acid hydrochloride (0.5 g,
1
0
.9 mmol), SOCl2 (0.8 ml, 11 mmol) was added. After 15 min at
C, under stirring, the reaction mixture was warmed up to room
Figure 1. Compound3:INADEQUATEspectrumandcarbonconnectivities.
◦
temperature and then refluxed for 30 min. The residue, obtained
by concentration of the solution in vacuo, was subjected to silica
gel flash chromatography with CH2Cl2/MeOH/NH3 (98 : 2 : 0.1) and
CH2Cl2/MeOH/NH3 (95 : 5 : 0.25), when the expected pure product
was obtained as a pale yellow viscous oil, which became solid
slowly and was recrystallized from ethanol/water. Yield 75%; mp
Elemental analyses for C, H, N, and S were performed using a
ThermoQuest Flash 1112 Elemental Analyzer. IR spectra were
recorded on a Jasco FT-IR 300E spectrometer. Mass spectra were
recorded on an Applied Biosystem, API 150 EX LC/MS system
spectrometer. NMR spectra were run on a Varian INOVA 600
spectrometer.
◦
−1
223–225 C; IR (KBr) (νmax cm ): 3230 and 3185 (NH2), 3068 (CH
−
1
+
Ar), 2937 (CH3), 1677 (CO). MS (APCI) m z = 237, (M + 1) . Calc.
Magn. Reson. Chem. 2008, 46, 1175–1179
Copyright ꢀc 2008 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/mrc

M. Incerti, D. Acquotti and P. Vicini
Br
Br
O
O
O
O
O
P(Ph) Br2
NH -NH Boc
2
2
3
O
N
NH
-
P(Ph) O
3
4
Figure 2. Synthesis of compound 1.
Br
O
O
HN
O
COOH
O
1
) Br , AcOH
2
O
2) H SO , reflux
N
Na, EtOH
N
2
4
+
S
S
O
O
HO
MeO
O
O
O
HCl
MeOH, SOCl2
O
NH2
NH2
HN
N
N
.
S
S
HCl
N
S
O
1
Figure 3. Synthesis of compound 4.
for C11H12N2O3S : mz 1 = 236.29; C, 57.58; H, 5.64; N, 11,19; S,
−
(50 mg ml ). INADEQUATE spectra were obtained from samples
−1
−
1
1
2.81%. Found: C, 57.80; H, 5.27; N, 11.27, S, 12.65%.
as DMSO solutions (500 mg ml ) and calibrated setting the DMSO
residual signal at δ = 2.49 ppm.
1
13
3
-Amino-5-methylbenzo[d]isothiazole (2) was prepared and
The H and C NMR spectra (at δ = 599.74 and 150.82 MHz,
[
16]
◦
purified as described elsewhere.
respectively) were measured at 25 C in 5 mm o.d. tubes. Chemical
shifts are reported as δ (ppm); coupling constants (J) are expressed
in Hz. Spectra were referenced to residual CHCl3 at δ = 7.24 ppm.
N-(t-Butyloxycarbonyl)-2-aminobenzo[d]isothiazol-3(2H)-one
[
11]
1
(
3) was prepared and purified as described earlier.
In 1D H NMR analysis, 16 transients were acquired with a 1.5 s
relaxation delay using 32K data points and zero-filled to a digital
1
3
resolution of 0.17 Hz. The C NMR spectra were run operating
N-(t-Butyloxycarbonyl)-2-aminoisoindolin-1-one (4)
◦
typically with a 45 pulse flip angle, a relaxation delay time of
To a magnetically stirred solution, containing triethylamine
3
–5 s and a spectral width of 25 000 Hz with 64K data points and
(2.5 ml) and 2-(bromomethyl)benzoylbromide (1.12 g, 4 mmol) in
zero-filled to a digital resolution of 0.4 Hz.
anhydrous dioxane (5 ml), tert-butylcarbazate (2.00 g, 15.2 mmol),
dissolved in the same solvent (10 ml), was added dropwise. After
refluxing for 2 h, the reaction mixture was cooled, and then the
solvent was removed under reduced pressure. The residue was
extracted with CH2Cl2, washed with 2 N HCl, and then dried over
Na2SO4. The crude product was obtained after concentration
under reduced pressure. By silica gel flash chromatography
with CH2Cl2/MeOH/NH3 (98 : 2 : 0.1), the expected pure product
was separated and further purified by recrystallization from
The data for the gCOSY, gHSQC, and gHMBC spectra were
collected with 2K data points for F2 and 128–256 increments for
F1 with pulse sequences that allowed gradient selection; spectral
1
windows were 5500–6000 and 27 000–37 000 Hz in the F2 ( H)
13
and F1 ( C) dimensions, respectively. The relaxation delay was set
to 1.5 s and evolution time was varied between 60 and 100 ms.
Once acquired, the data were processed using sine-bell weighting
functions in both dimensions; 2K data points were zero-filled to
4
K in F2 and 256 data were linear predicted to 768 data points in
◦
−1
ethanol/water. Yield 27%; mp 173–175 C; IR (KBr) (νmax cm ):
274 (NH), 2975 and 2929 (CH3), 1731 and 1693 (CO). Anal. Calcd.
for C13H16N2O3 (248.12): C, 62.89; H, 6.50; N, 11.28%. Found C,
3.01; H, 6.49; N, 11.06%.
F1. INADEQUATE was recorded with a recycle time of 3 s, a spectral
width of 9050 Hz in F2 and 18 100 in F1, and 2K data points for 128
3
13 13
increments of 256 transients. J( C, C) was set to 55 Hz.
6
NMR measurements
Acknowledgements
The structural and spectroscopic assignments were made through
the combined use of 1 and 2D homonuclear NMR experiments,
such as COSY and INADEQUATE, and heteronuclear HSQC and
HMBC correlation techniques. H and C NMR, gCOSY, gHSQC,
gHMBC spectra were obtained from samples as CDCl3 solutions
The authors acknowledge the financial support of the Ministero
dell’Universit a` e della Ricerca (MUR), Italy, and are grateful to the
Centro Interdipartimentale Misure (CIM), University of Parma, for
the use of NMR instruments.
1
13
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Copyright ꢀc 2008 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2008, 46, 1175–1179

Spectral Assignments and Reference data
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Copyright ꢀc 2008 John Wiley & Sons, Ltd.
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