Exploitation of a tuned oxidation with N -haloimides in the synthesis of caulibugulones A-D

Article abstract of DOI:10.1021/jo302772t

Marine alkaloids caulibugulones A-D were synthesized in six steps starting from the readily available 2,5-dimethoxybenzaldehyde. Pomeranz-Fritsch reaction of N-(2,5-dimethoxybenzyl)-N-(2,2-dimethoxyethyl)-2-nitrobenzenesulfonamide proceeded smoothly to gi

Full text of DOI:10.1021/jo302772t

Subscriber access provided by UNIV LAVAL
Note
Exploitation of a tuned oxidation with N-
haloimides in the synthesis of caulibugulones A-D
Fabricio Fredo Naciuk, Julio Cesar Milan, Almir Andreão, and Paulo C. M. L. Miranda
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo302772t • Publication Date (Web): 25 Apr 2013
Downloaded from http://pubs.acs.org on April 28, 2013
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
The Journal of Organic Chemistry is published by the American Chemical Society.
1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 19
The Journal of Organic Chemistry
1
2
3
4
5
6
7
Exploitation of a tuned oxidation with N-haloimides in the
synthesis of caulibugulones A-D
8
9
Fabrício F. Naciuk,† Julio C. Milan,† Almir Andreão,‡ and Paulo C. M. L. Miranda†*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
† Institute of Chemistry, State University of Campinas - UNICAMP, P. O. Box 6154,
Campinas, SP, 13083 970, Brazil
‡ IFES, Aracruz, ES, Brazil.
*Corresponding author address:
Institute of Chemistry – State University of Campinas.
Cidade Universitária Zeferino Vaz, Barão Geraldo, Campinas – SP – Brazil
ZIP code: 13083-970
P.O. Box: 6154
e-mail: miranda@iqm.unicamp.br
Phone: +55 19 35213083
Fax: +55 19 35213023
Key words: Isoquinolinedione alkaloids; selective oxidations; Pomeranz-Fritsch reaction
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 19
1
2
3
4
5
Graphical abstract
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Abstract
Marine alkaloids caulibugulones A-D were synthesized in six steps starting from the readily
available 2,5-dimethoxybenzaldehyde. Pomeranz-Fritsch reaction of N-(2,5-
dimethoxybenzyl)-N-(2,2-dimethoxyethyl)-2-nitrobenzenesulfonamide proceeded smoothly
to give 5,8-dimethoxyisoquinoline, which was oxidized to isoquinolinediones by a tunable
oxidation reaction with N-haloimides. Therefore, NBS furnished direct conversion to the
isoquinoline-5,8-dione, alternatively N-haloimides of cyanuric acid provided both oxidation
and halogenation generating 6,7-dihaloisoquinoline-5,8-diones. Aminolyses of these
isoquinolinediones with methylamine or ethanolamine produced the isoquinolinedione
alkaloids caulibugulones A-D in 24-57% overall yield.
ACS Paragon Plus Environment

Page 3 of 19
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Caulibugulones A-D (1-4, Scheme 1) are simple isoquinolinedione alkaloids that were isolated
from the marine bryozoan Caulibugula intermis Harmer (Bugulidae) in 2004, at Palau in the
Indo-Pacific northwest, by Milanowski and coworkers.1 Despite their simplicity and high
activity against tumor cells1 there are only two syntheses, at the same year of their isolation, by
Wipf2 and Alagille3 groups. These compounds attracted our attention because of their high
activity against cdc25 phosphatases,1,4 acting by at least two different mechanisms,4 showing
great potential as a leading compound in the development of new drugs for cancer therapy.5,6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Structures of caulibugulones A-D isolated from the marine bryozoan Caulibugula
intermis Harmer (Bugulidae).
All syntheses exploited the same key intermediate, 5,8-dimethoxyisoquinoline (8), prepared in
four steps in 83% overall yield from the easily accessible 2,5-dimethoxybenzaldehyde (5,
Scheme 2). Using the bespoken oxidation/halogenation step with adequate N-haloimide for
each case, followed by aminolyses with the correspondent amine, the isoquinoline 8 furnished
all four desired caulibugulones in two steps with 29-68% yield (Schemes 3 and 4).
3
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 19
1
2
3
4
5
6
7
8
9
The synthesis of caulibugulones began with the preparation of 8 by reductive amination of
2,5-dimethoxy-benzaldehyde (5) with 2,2-dimethoxy-ethanamine in the presence of NaBH4 to
afford the benzylamine 6, which was activated for the Pomeranz-Fritsch reaction by
derivatization with o-nosyl chloride.7,8 When the nosyl amide 7 was submitted to the
Pomeranz-Fritsch reaction in HCl/dioxane, it consecutively cyclized, underwent methanol
elimination, and 2-nitrobenzenesulfinic acid elimination to furnish 5,8-dimethoxyisoquinoline
(8).7,8 Apparently, the corresponding tosyl amide (9) has a higher SꢀN bond cleavage energy
and stops at the formation of the 2-tosyl-1,2-dihydroisoquinoline intermediate (10, Scheme 2)
under the same conditions.8-11 This result is supported by Miyata and coworker’s findings about
the N-S bond cleavage ability of arylsulfonamides.12 In this case, the velocity of solvolysis is
related not only to the electronic factor as could be supposed at a first glance, but also to a
steric and/or solvent factor.12 It was only possible to generate isoquinoline 8 from 10 after
treatment with t-BuOK/t-BuOH at 80°C for 30 min.10
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 2. Nosylamide-based activation of the Pomeranz-Fritsch reaction for the synthesis of
compound 8.
4
ACS Paragon Plus Environment

Page 5 of 19
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5,8-Dimethoxyisoquinoline (8) was then converted to isoquinoline-5,8-diones (11-13) by
reaction with N-haloimides (Scheme 3). Thereafter, caulibugulones A-D were promptly
prepared from 11-13 after subsequent reaction with the corresponding amines. An interesting
aspect of the oxidation/halogenation step was the chemoselectivity of the process. As shown by
Chi and coworkers in closely related compounds,13 5,8-dimethoxyisoquinoline (8) could be
transformed into isoquinoline-5,8-dione (11) by treatment with NBS/H2O/H2SO4, although in a
much longer time in our case (48h instead of 5min). Nevertheless, 6,7-dibromoisoquinoline-
5,8-dione (12) could not be prepared in this way despite all attempted modifications concerning
reaction time, acid concentration, solvent or temperature.
On the other hand, when N-haloimides derived from isocyanuric acid were applied,14,15 both
oxidation and halogenations at positions 6 and 7 were simultaneously achieved. Thus, the
reaction of 5,8-dimethoxyisoquinoline (8) and trichloroisocyanuric acid (TCCA), in H2O/HCl
at room temperature, furnished 6,7-dichloroisoquinoline-5,8-dione (13). Similarly, the reaction
5
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 19
1
2
3
4
5
of 5,8-dimethoxyisoquinoline (8) and tribromoisocyanuric acid (TBCA), in H2O/HBr at room
temperature, furnished 6,7-dibromoisoquinoline-5,8-dione (12).
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 3. Preparation of isoquinoline-5,8-diones (11-13) by selective oxidation with N-
haloimides,
Unfortunately, all isoquinolinediones (11-13) have insufficient stability to be isolated in
reasonable or reproducible yields and purities using this methodology; thus we proceeded
without their isolation directly toward caulibugulones. This findings corroborate the
experimental data of Wipf and coworkers,2 which also reported difficulties in isolating and
characterizing isoquinoline-5,8-dione (11) using a different reaction condition.2 Therefore, in
all cases, the corresponding isoquinoline-5,8-dione reaction media was treated with the related
amine (methylamine or ethanolamine) and the resulting caulibugulone was isolated without
further problems in 36-86% yield from 8., as a ~4:1 mixture of isomers. In all cases the
caulibugulone/isocaulibugulone mixture was efficiently resolved by PLC.16
6
ACS Paragon Plus Environment

Page 7 of 19
The Journal of Organic Chemistry
1
2
3
In the case of 6,7-dihaloisoquinoline-5,8-diones (12-13), an amine addition followed by
4
5
6
halogen elimination is expected to occur. On the other hand, in the case of the isoquinoline-5,8-
7
8
dione (11), a conjugate addition to the
α,β-unsaturated carbonyl moiety followed by
9
tautomerization of the di-keto derivative to the hydroquinone, and an in situ oxidation probably
take place.17 It is noteworthy to mention that, despite mechanism differences, the presented
regiochemistry of both reactions is quite similar. The observed regioselection for the addition at
position 7 vary within 4:1 and 6:1 for all isoquinoline-5,8-diones. All NMR spectra and high
resolution mass data are in complete accordance with literature.1-3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 4. Aminolysis step for the preparation of caulibugulones A-D (1-4).
7
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 19
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Interestingly, despite the spectroscopic conditions described in the literature,1 all
caulibugulones were sufficiently soluble in CDCl3 to perform all NMR experiments furnishing
adequate spectra (Table 1). The structures of caulibugulones B (2) and C (3) were also
unambiguously assigned by X-ray crystallography (Figure 1).16 Thus, the regiochemistry of the
nucleophilic addition of the amines was confirmed concurrently by 2D-NMR data and XRD
experiments. Crystals of both compounds, and also of caulibugulone A (1),16 were obtained by
slow evaporation of dichloromethane solutions. The ORTEP drawings of caulibugulone B (2)
and caulibugulone C (3) are shown in Figure 1 and fully corroborate all 2D-NMR data.16
8
ACS Paragon Plus Environment

Page 9 of 19
The Journal of Organic Chemistry
1
2
3
4
5
6
Table 1. 13C-NMR chemical shift (in ppm) comparison among natural caulibugulones (I)1 and
7
8
9
synthesized in this work (II).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Caulibugulone
A
IIa
B
IIb
C
IIb
D
IIc
Ia
IId
Ib
IId
Ib
IId
Ic
IId
Position
1
3
147.4 148.0 147.9 148.1 148.4 148.5 148.4 148.6 148.4 148.3 148.4 148.1
155.5 156.3 156.3 156.1 156.1 156.3 156.1 156.7 156.1 156.9 157.1 156.5
120.1 119.9 119.0 118.8 119.2 119.5 119.2 119.4 119.3 119.3 119.4 119.6
141.0 140.7 139.3 138.4 138.2 138.0 138.2 139.0 138.4 140.1 140.2 139.2
181.1 181.3 180.9 174.8 174.5 174.8 173.4 175.3 175.3 181.5 181.7 181.2
4
4a
5
6
100.7 100.8 101.2
e
e
e
e
e
e
e
101.0 101.6 101.7
7
150.7 150.7 148.8 146.4
146.9 148.4 146.9 144.9 149.6 149.7
e
e
8
181.0 181.5 181.2 180.5 180.1 179.8 180.1 180.9 179.9 182.2 182.5
8a
9
125.8 125.6 124.3 124.4 123.1 123.6 123.8 123.9 123.5 125.6 125.7 124.4
29.3 29.4 29.2 32.5 33.0 33.3 33.0 32.9 32.7 45.2 45.5 44.5
10
-
-
-
-
-
-
-
-
-
59.7 60.0 60.1
Spectral data were acquired in (a) CD3OD/CDCl3 (1:1), (b) pyridine-d5, (c) CD3CN or (d) CDCl3. (e) Signal not observed.
Figure 1. ORTEP representations of caulibugulone B (2), at the left; and caulibugulone C (3),
at the right. Ellipsoids displayed at 50% probability.16
In summary, the synthesis of the naturally occurring caulibugulones A–D was accomplished in
six steps with 25-57% overall yield, and provided sufficient material for further biological
testing. Conditions for selective oxidation, or oxidation/halogenations of dialkoxyisoquinolines
9
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 19
1
2
3
4
5
6
7
8
were also described. Structure assignments were in full agreement with the literature (Table 1).
X-ray diffraction and 2D-NMR data unequivocally prove the regiochemistry of isoquinoline-
5,8-diones aminolyses.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental section
General methods
Flash column chromatography was performed as described by W. C. Still et al 18
.
employing
silica gel 60 (spherical), 40-100 m. Analytical thin-layer chromatography (TLC) was
ꢁ
performed on analytical plates pre-coated with silica gel 60 F254 (0.25 mm thick). TLC plates
were visualized by exposure to ultraviolet light (UV) and/or stained with iodine vapor.
Preparative thin-layer chromatography (PLC) was performed on pre-coated glass plates (20 x
20 cm) with silica gel 60 F254 (1 mm thick). Tribromoisocyanuric acid (TBCA) was prepared
according to the literature.19 Other reagents were obtained from commercial sources and used
without previous purifications. Tetrahydrofuran was distilled from sodium/benzophenone under
argon and methanol was distilled from calcium hydride. Melting points were obtained in open
1
capillary tubes and are uncorrected. Chemical shifts for H-NMR were reported in parts per
million (δ scale) downfield from tetramethylsilane as the internal standard and coupling
constants were in hertz (Hz). The following abbreviations were used for spin multiplicity: s =
13
singlet, d = doublet, t = triplet, m = multiplet, br = broad. Chemical shifts for C NMR were
reported in parts per million (δ scale) relative to the tetramethylsilane signal. High resolution
mass spectrometry (HRMS) analyses were obtained by ESI/TOF at positive mode, and low-
resolution MS data were obtained using EI at 70 eV.
10
ACS Paragon Plus Environment

Page 11 of 19
The Journal of Organic Chemistry
1
2
3
4
Nꢀ(2,5ꢀDimethoxybenzyl)ꢀ2,2ꢀdimethoxyethanamine (6)
5
6
7
8
9
To a stirred solution of 2,5-dimethoxybenzaldehyde (5, 216.0 mg; 1.3 mmol) in 5 mL of dry
toluene, 1.0 mmol (105.0 mg) of 2,2-dimethoxyethanamine was added. The solution was boiled
under reflux in a Dean-Stark apparatus until no further water was evolved (4 h). The removal of
solvent under vacuum gave the required Schiff's base in a virtually quantitative yield. The
isolated benzylideneamino-acetal was used without further purification in the following step.
Thus, the isolated intermediate (253.0 mg, 1.0 mmol) was dissolved in 5 mL of methanol and
189.0 mg (5.0 mmol) of sodium borohydride was added to the mixture at room temperature.
The mixture was stirred at room temperature for 3 h and after this period the organic solvent
was evaporated in vacuum. Addition of saturated NaHCO3 solution and CH2Cl2 followed by
separation, drying, and evaporation of the organic phase under reduced pressure gave a yellow
oil. The residue obtained was purified by column chromatography in silica gel with
AcOEt/MeOH (90:10, rf = 0.44) as eluent to yield 6 (95%) as a pale yellow oil. 1H-NMR (250
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
MHz, CDCl3),
δ(ppm),
J(Hz): 6.81 (d,
J
= 1.6, 1H); 6.73 (m, 2H); 4.48 (t,
J = 5.3, 1H); 3.78 (s,
3H); 3.76 (s, 2H) 3.75 (s, 3H); 3.34 (s, 6H); 2.72 (d,
J
= 5.3, 2H). 13C-NMR (62.5 MHz,
CDCl3), δ(ppm): 153.4; 151.8; 128.7; 116.1; 112.4; 111.1; 103.7; 55.8; 55.7; 53.8; 50.1; 49.2.
MS (EI, 70eV), (m/z, relative abundance): 255 (7%); 180 (30%); 151 (100%).
Nꢀ(2,5ꢀDimethoxybenzyl)ꢀNꢀ(2,2ꢀdimethoxyethyl)ꢀ2ꢀnitrobenzenesulfonamide (7)
To 8.0 mL of a dichloromethane solution of 6 (255.0 mg; 1.0 mmol) an aqueous solution of
sodium carbonate (10%, 5.0 mL), and 215.0 mg (0.97 mmol) of 2-nitrobenzenesulfonyl
chloride were added. The resulting emulsion was stirred at room temperature for 6 h. Hereafter,
the organic layer was separated, dried over MgSO4, filtered and evaporated. The residue
11
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 19
1
2
3
obtained was purified by column chromatography in silica gel using hexane/AcOEt (70:30, rf =
4
5
6
1
0.33) as eluent to yield 7 (>99%) as a yellowish oil. H-NMR (250 MHz, CDCl3),
δ(ppm),
7
8
J(Hz): 7.87 (d, J = 7.6, 1H); 7.66-7.49 (m, 3H); 6.87-6.79 (m, 1H); 6.74-6.65 (m, 2H); 4.65 (s,
9
2H); 4.47 (t,
J
= 5.4, 1H); 3.68 (s, 3H); 3.67 (s, 3H); 3.45 (d,
J
= 5.4, 2H); 3.31 (s, 6H).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13C-NMR (62.5 MHz, CDCl3),
δ
(ppm): 153.7; 151.8; 148.0; 134.5; 133.1; 131.5; 130.8; 124.4;
123.9; 115.5; 114.0; 111.3; 103.9; 55.7; 54.9; 53.5, 49.4; 47.5; 41.9. HRMS: Found: 479.0891,
calc. for [C19H25N2O8S + K]+: 479.0917; and also found: 463.1151, calc. for [C19H25N2O8S +
Na]+: 463.1172.
5,8ꢀDimethoxyisoquinoline (8, from 7)
A stirred solution of 7 (440.0 mg; 1.0 mmol) in 25 mL of dioxane/HCl 6 M (4:1), in the dark
and under argon atmosphere, was kept under reflux in a round-bottom flask for 7 h. After
completion of the reaction as indicated by TLC, the pH of the reaction mixture was adjusted to
8 with Na2CO3 and extracted with 3 X 50 mL of dichloromethane. The combined extracts were
dried over MgSO4, filtered, and evaporated to yield brownish oil. Purification of this oil by
column chromatography in silica gel with hexane/AcOEt (60:40, rf = 0.33) as eluent furnished
5,8 dimethoxyisoquinoline (8) in 88 % yield as a pale brown solid. Mp: 59-61 °C; (lit. m.p.
56.5-57.0 °C).8 1H-NMR (250 MHz, CDCl3),
δ
(ppm),
= 9.0, 1H); 6.74 (d,
(ppm): 150.0; 148.1; 147.2; 143.4; 129.1; 121.0; 114.5; 107.5;
J(Hz): 9.57 (s, 1H); 8.56 (d,
J = 5.6, 1H);
7.92 (d,
J
= 5.6, 1H); 6.86 (d,
J
J = 9.0, 1H); 3.97 (s, 3H); 3.94 (s, 3H).
13C-NMR (62.5 MHz, CDCl3),
δ
104.3; 55.8; 55.7. HRMS: Found: 190.0877, calc. for [C11H11NO2 + H]+ 190.0868.
Nꢀ(2,5ꢀdimethoxybenzyl)ꢀNꢀ(2,2ꢀdimethoxyethyl)ꢀ4ꢀmethylbenzenesulfonamide (9)
12
ACS Paragon Plus Environment

Page 13 of 19
The Journal of Organic Chemistry
1
2
3
To 9.0 mL of a dichloromethane/ether (3:1) solution of 6 (255.3 mg; 1.0 mmol) an aqueous
4
5
6
solution of sodium carbonate (10%, 5.0 mL), and 228.8 mg (1.2 mmol) of p-toluenesulfonyl
7
8
9
chloride were added. The resulting emulsion was stirred at room temperature for 2 h. Hereafter,
the organic layer was separated, dried over MgSO4, filtered and evaporated. The residue
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
obtained was purified by column chromatography in silica gel using hexane/AcOEt (70:30, rf =
1
0.50) as eluent to yield 7 (>99%) as a yellowish oil. H-NMR (250 MHz, CDCl3),
δ
(ppm),
= 2.6, 1H); 6.74-6.65 (m, 2H); 4.46
= 5.4, 2H); 3.24 (s, 6H); 2.38
(ppm): 157.6; 151.4; 143.0; 137.5; 129.4; 127.2;
J
(Hz): 7.65 (d, J = 8.5, 2H); 7.23 (d, J = 8.5, 2H); 6.86 (d, J
(s, 2H); 4.42 (t,
J = 5.4, 1H); 3.68 (s, 3H); 3.64 (s, 3H); 3.29 (d, J
(s, 3H). 13C-NMR (62.5 MHz, CDCl3),
δ
125.5; 113.5; 111.2; 103.7; 77.3; 55.7; 54.4; 49.9; 47.6; 21.5. HRMS: Found: 410.1663, calc.
for [C20H28NO6S + H]+ 410.1637.
5,8ꢀDimethoxyꢀ3ꢀmethylꢀ2ꢀtosylꢀ1,2ꢀdihydroisoquinoline (10)
A stirred suspension of 9 (409.5 mg; 1.0 mmol) in 10 mL of dioxane/HCl 6M (4:1), in the dark
and under argon atmosphere, was kept under reflux in a round-bottom flask for 7 h. After
completion of the reaction as indicated by TLC, the pH of the reaction mixture was adjusted to
8 with Na2CO3 and extracted with 3 X 50 mL of dichloromethane. The combined extracts were
dried over MgSO4, filtered, and evaporated to yield brownish oil. Purification of this oil by
column chromatography in silica gel with hexane/AcOEt (60:40, rf = 0.50) as eluent furnished
5,8-dimethoxy-3-methyl-2-tosyl-1,2-dihydroisoquinoline (10) in 62% yield as a yellow solid.
Mp: 128-130 °C, dec; (lit. m.p. 130-133 °C).8 1H-NMR (250 MHz, CDCl3),
7.71 (d, = 8.5, 2H); 7.26 (d, = 8.5, 2H); 6.75 (d, = 8.0, 1H); 6.65-6.54 (m, 2H); 6.11 (d, J =
δ(ppm), J(Hz):
J
J
J
8.0, 1H); 4.59 (s, 2H); 3.73 (s, 6H); 2.38 (s, 3H). 13C-NMR (62.5 MHz, CDCl3),
δ(ppm): 149.4;
13
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 19
1
2
3
4
5
148.2; 144.1; 134.9; 129.9; 127.4; 126.0; 120.8; 117.1; 110.3; 109.8; 104.1; 56.3; 55.9; 41.9;
21.7. HRMS: Found: 346.1139, calc. for [C18H19NO4S + H]+ 346.1113.
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5,8ꢀDimethoxyisoquinoline (8, from 10)
To a solution of 10 (345.4 mg; 1.0 mmol) in 3.5 mL of t-BuOH was added t-BuOK (224.4 mg;
2.0 mmol) and the mixture was stirred and kept at 80 °C in a round-bottom flask for 30 min.
After completion of the reaction as indicated by TLC, was added H2O (10 mL) and the reaction
mixture was extracted with 3 X 10 mL of AcOEt. The combined extracts were dried over
MgSO4, filtered, and evaporated furnished 5,8-dimethoxyisoquinoline (8) in 60% yield as a
pale brown solid without purification process. Mp: 59-61 °C; (lit. m.p. 56.5-57.0 °C).8
1H-NMR (250MHz, CDCl3),
1H); 6.86 (d, = 9.0, 1H); 6.74 (d,
MHz, CDCl3),
δ
(ppm),
J
(Hz): 9.57 (s, 1H); 8.56 (d,
J
= 5.6, 1H); 7.92 (d, J = 5.6,
13
J
J
= 9.0, 1H); 3.97 (s, 3H); 3.94 (s, 3H). C-NMR (62.5
δ
(ppm): 150.0; 148.1; 147.2; 143.4; 129.1; 121.0; 114.5; 107.5; 104.3; 55.8;
55.7. HRMS: Found: 190.0877, calc. for [C11H11NO2 + H]+ 190.0868.
Caulibugulone A (1)
5,8-Dimethoxyisoquinoline (8, 189.0 mg, 1.0 mmol) was added to a well-stirred mixture of
NBS (196.0 mg, 1.1 mmol) in a solution of THF (15 mL), water (5 mL), and sulfuric acid (0.05
mL) at room temperature. The reaction mixture was stirred for 48 h, and afterward 493.0 mg of
CeCl3 (2 mmol) and 346.0 ꢀL of 40% aqueous methylamine (4 mmol) and stirred for additional
20 h at room temperature. Then the suspension was concentrated under reduced pressure and
the crude residue was diluted with EtOAc (50 mL) and washed with brine (3 X 20 mL). The
organic layer was dried over MgSO4 and concentrated under reduced pressure. The residue
14
ACS Paragon Plus Environment

Page 15 of 19
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
obtained was purified by column chromatography in silica gel with AcOEt/hexane (80:20, rf =
0.37) as eluent to yield a mixture of caulibugulone A (1) and its regioisomer (69%, ~4:1 ratio
by 1H-NMR). Further purification in PLC silica gel plate (CH2Cl2/MeOH 199:1, rf = 0.03) gave
caulibugulone A (1) as red needles. Ten consecutive runs were necessary to separate the
regioisomers. The spectroscopic data obtained for this compound were consistent with those
reported in the literature.1-3 M.p. 218-220 °C, dec.; (lit. m.p. 228 230 °C).2 1H-NMR (500 MHz,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CDCl3),
δ
(ppm),
J
(Hz): 9.19 (s, 1H), 8.94 (d,
J
= 5.0 Hz, 1H), 7.85 (d,
J
= 5 Hz, 1H), 6.05 (br
(ppm): 181.2,
13
s, 1H), 5.75 (s, 1H), 2.90 (d,
J
= 5.0 Hz, 3H). C-NMR (125 MHz, CDCl3),
δ
180.9, 156.3, 148.5, 147.9, 139.3, 124.3, 119.0, 101.2, 29.3. HRMS: Found: 189.0667, calc. for
[C10H9N2O2 + H]+ 189.0664.
Caulibugulone B (2)
5,8-Dimethoxyisoquinoline (8, 189.0 mg, 1.0 mmol) was solubilized in HBr 8.84 M (22 mL).
After the cooling in an ice bath (0 ºC) was added TBCA (475.4 mg, 1.3 mmol). The reaction
mixture was stirred for 48 h at room temperature, after this time a liquid-liquid extraction was
performed by addition of aqueous sodium carbonate (97 mmol in 20 mL of water) and three
portions if CH2Cl2 (20 mL). The organic phase was dried with anhydrous MgSO4 and the
solvent was removed on a rotary evaporator. To the flask containing a solution of 6,7-
dibromoisoquinolino-5,8-dione (12) in ethanol (10 mL) a second solution of 86.7 ꢀL of 40%
aqueous methylamine (1.0 mmol) in ethanol (5.0 mL) was added and the resulting mixture was
stirred for additional 24 h at room temperature. Then the reaction was concentrated under
reduced pressure, and the residue obtained was purified by column chromatography in silica gel
with AcOEt (rf = 0.66) as eluent to yield a mixture of caulibugulone B (2) and its regioisomer
1
(44%, ~4:1 ratio by H-NMR). After eight consecutive elutions in a PLC silica gel plate
15
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 19
1
2
3
4
5
6
7
8
(CH2Cl2/MeOH 199:1, rf = 0.06) caulibugulone B (2) was isolated as dark red needles. The
spectroscopic data obtained for this compound were consistent with those reported in the
literature.1-3 M.p. 198 200 °C, dec; (lit. m.p. 182 184 °C).2 1H-NMR (500 MHz, CDCl3),
9
δ(ppm),
J
(Hz): 9.19 (s, 1H), 8.93 (d, 1H, = 5.0 Hz), 6.21 (br s, 1H),
J
= 5.0 Hz), 7.89 (d, 1H,
J
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3.42 (d, 3H,
J
= 5.0 Hz). 13C-NMR (125 MHz, CDCl3),
δ(ppm): 179.6, 174.9, 156.3, 148.5,
146.8, 138.2, 124.0, 119.5, 33,3. HRMS: Found: 266.9754, calc. for [C10H9N2O2 + H]+
266.9769.
Caulibugulone C (3)
5,8-Dimethoxyisoquinoline (8, 189.0 mg, 1.0 mmol) was solubilized in HCl 12 M (17 mL).
After the cooling in an ice bath (0 °C) was added TCCA (302.0 mg, 1.3 mmol). The reaction
mixture was stirred for 3 h at room temperature, after this time a liquid-liquid extraction was
performed by addition of aqueous sodium carbonate (97 mmol in 20 mL of water) and three
portions if CH2Cl2 (20 mL). The organic phase was dried with anhydrous MgSO4 and the
solvent was removed on a rotary evaporator. To the flask containing a solution of extracted 6,7-
dichloroisoquinolino-5,8-dione (13) in ethanol (10 mL) a second solution of 86.7 ꢀL of 40%
aqueous methylamine (1.0 mmol) in ethanol (5.0 mL) was added and the resulting mixture was
stirred for additional 24 h at room temperature. Then the suspension was concentrated under
reduced pressure. The residue obtained was purified by column chromatography in silica gel
with AcOEt (rf = 0.64) as eluent to yield a mixture of caulibugulone C (3) and its regioisomer
1
(85%, ~4:1 ratio by H-NMR). After eight consecutive elutions in a PLC silica gel plate
(CH2Cl2/MeOH 199:1, rf = 0.05) caulibugulone C (3) was isolated as dark red needles. The
spectroscopic data obtained for this compound were consistent with those reported in the
literature.1-3 M.p. 225-227 °C, dec.; (lit. m.p. 219 221 °C).2 1H-NMR (500 MHz, CDCl3),
16
ACS Paragon Plus Environment

Page 17 of 19
The Journal of Organic Chemistry
1
2
3
4
δ(ppm),
J
(Hz): 9.18 (s, 1H), 8.94 (d, 1H, = 5.0 Hz), 6.15 (br s, 1H),
J
= 5.0 Hz), 7.89 (d, 1H,
J
3.41 (d, 3H,
J
= 5.0 Hz). 13C-NMR (125 MHz, CDCl3),
δ(ppm): 180.0, 175.3, 156.5, 148.4,
5
6
7
8
9
144.9, 138.4, 123.5, 119.3, 32.7 HRMS: Found: 223.0257, calc. for [C10H9N2O2 + H]+
223.0274.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Caulibugulone D (4)
5,8-Dimethoxyisoquinoline (8, 189.0 mg, 1.0 mmol) was added to a well-stirred mixture of
NBS (196.0 mg, 1.1 mmol) in a solution of THF (15 mL), water (5 mL), and sulfuric acid (0.05
mL) at room temperature. The reaction mixture was stirred for 48 h, afterward 493.0 mg of
CeCl3 (2 mmol) and 241.0 ꢀL of ethanolamine (4 mmol) and stirred for additional 20 h at room
temperature. Then the suspension was concentrated under reduced pressure and the crude
residue was diluted with EtOAc (50 mL) and washed with brine (3 X 20 mL). The organic
layer was dried over MgSO4 and concentrated under reduced pressure. The residue obtained
was purified by column chromatography in silica gel with AcOEt/MeOH (95:05, rf = 0.42) as
eluent to yield a mixture of caulibugulone D (4) and its regioisomer (36%, ~4:1 ratio by
1H-NMR). After eight sequential elutions in a PLC silica gel plate (CHCl3/MeOH 97:3, rf =
0.07) caulibugulone D (4) was isolated as a dark orange solid. The spectroscopic data obtained
for this compound were consistent with those reported in the literature.1-3 M.p. 180-182 °C,
dec.; (lit. m.p. 189-191 °C).2 1H-NMR (500 MHz, CDCl3),
δ(ppm), J(Hz): 9.20 (s, 1H), 8.94 (d,
1H,
2H,
J
= 5.0 Hz), 7.84 (d, 1H,
J = 5.0 Hz), 6.28 (br s, 1H), 5.80 (s, 1H), 3.88 (m, 2H), 3.32 (q,
J
= 5.0 Hz). 13C-NMR (125 MHz, CDCl3),
δ(ppm): 181.2, 156.5, 148.1, 139.3, 124.4,
119.1, 101.7, 60.1, 44.5. HRMS: Found: 219.0768, calc. for [C10H9N2O2 + H]+ 219.0770.
17
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 19
1
2
3
4
Associated content
5
6
7
Supporting information
8
9
Additional analytical and spectroscopic data of all compounds, and X-ray crystallographic
information files (CIF) are available free of charge via the Internet at http://pubs.acs.org.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Author information
Corresponding author
* E-mail: miranda@iqm.unicamp.br
Notes
The authors declare no competing financial interest.
Acknowledgments
This work was supported by a grant from the State of São Paulo Research Foundation, Fapesp
(grant number 09/51602-5). Authors want to thank Prof. Bob Bolland for kindly providing us
with the Caulibugula sp. image used in the abstract. The Chemistry Institute of Unicamp is
deeply acknowledged for the provided analytical facilities. Authors are also in debt with Jason
G. Taylor for insightful discussion and for reviewing the manuscript for its English usage. J. C.
M. and F. F. N. thank SAE/UNICAMP and CNPq for fellowships.
18
ACS Paragon Plus Environment

Page 19 of 19
The Journal of Organic Chemistry
1
2
3
4
References
5
6
7
8
1. Milanowski, D. J.; Gustafson, K. R.; Kelley, J. A.; McMahon, J. B. J. Nat. Prod. 2004,
67, 70.
9
2. Wipf, P.; Joo, B.; Nguyen, T.; Lazo, J. S. Org. Biomol. Chem. 2004, 2, 2173.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3. Alagille, D.; Baldwin, R. M.; Tamagnan, G. D. Tetrahedron Lett. 2004, 45, 6179.
4. Brisson, M.; Foster, C.; Wipf, P.; Joo, B.; Tomko Jr., R. J.; Nguyen, T.; Lazo, J. S. Mol
Pharmacol. 2007, 71, 184.
5. Vintonyak, V. V.; Antonchick, A. P.; Rauh, D.; Waldmann, H. Curr. Opin. Chem. Biol
2009, 13, 272.
.
6. Contour-Galcera, M. O.; Sidhu, A.; Prévost, G.; Bigg, D.; Ducommun, B. Pharmacol.
Therapeut. 2007, 115, 1.
7. Konakahara, T.; Kiran, Y. B.; Okuno, Y.; Ikeda, R.; Sakai, N. Tetrahedron Lett. 2010,
51, 2335.
8. Birch, A. J.; Jackson, A. H.; Shannon, P. V. R. J. Chem. Soc. Perkin Soc. I 1974, 2185.
9. Song, Y.; Shao, Z.; Dexheimer, T. S.; Scher, E. S.; Pommier, Y.; Cushman, M. J. Med.
Chem. 2010, 53, 1979.
10. Bracca, A. B. J.; Kaufman, T. S. Eur. J. Org. Chem. 2007
, 5284.
11. Silveira, C. C.; Bernardi, C. R.; Braga, A. L.; Kaufman, T. S. Synlett 2002
,
907.
12. Aizawa, K.; Nakagawa, H.; Matsuo, K.; Kawai, K.; Ieda, N.; Suzuki, T.; Miyata, N.
Bioorg. Med. Chem. Lett. 2013, 23, 2340.
13. Kim, D. W.; Choi, H. Y.; Lee, K. J.; Chi, D. Y. Org. Lett. 2001, 3, 445.
14. Tozetti, S. D. F.; Almeida, L. S.; Esteves, P. M.; Mattos, M. C. S. J. Braz. Chem. Soc
2007, 18, 675.
.
15. Almeida, L. S.; Esteves, P. M.; Mattos, M. C. S. Synthesis 2006, 221.
16. See supplemental material for further details.
17. Lisboa, C. D.; Santos, V. G.; Vaz, B. G.; Lucas, N. C.; Eberlin, M. N.; Garden, S. J. J.
Org. Chem. 2011, 76, 5264.
18. Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923.
19. Almeida, L. S.; Esteves, P. M.; Mattos, M. C. S. Synlett 2006, 10, 1515.
19
ACS Paragon Plus Environment