Synthesis and Antiviral/Fungicidal/Insecticidal Activities Study of Novel Chiral Indole Diketopiperazine Derivatives Containing Acylhydrazone Moiety

Article abstract of DOI:10.1021/acs.jafc.0c00875

On the basis of the mechanism of acylhydrazone compounds inhibiting the assembly of TMV CP and the unique structural characteristics of diketopiperazine ring, a series of optically pure indole diketopiperazine acylhydrazone were designed and synthesized. In order to systematically study the effect of the spatial configuration of the compounds on the antiviral activity, four compounds with different spatial configurations at C6 and C12a were also prepared. The bioassay results indicated that most of these new compounds displayed moderate to good antiviral activity, among which compounds 23, 25, 27, 28, 31, and 5d showed a significantly higher activity than that of commercial ribavirin. An in-depth structure-activity relationship investigation showed that the spatial conformation was one of the most important factors in adjusting antiviral activity; the research results provided information about the possible optimum configuration for interaction of this molecular with its target protein. At the same time, these new compounds also exhibited broad-spectrum fungicidal activities against 14 kinds of phytopathogenic fungi. What's more, some of these compounds exhibited good insecticidal activity to Plutella xylostella and Culex pipiens pallens.

Full text of DOI:10.1021/acs.jafc.0c00875

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Agricultural and Environmental Chemistry
Synthesis and Antiviral/Fungicidal/Insecticidal Activities Study of Novel
Chiral Indole Diketopiperazine Derivatives Containing Acylhydrazone Moiety
Hongjian Song, Jialin Xie, Wentao Xu, Yuxiu Liu, Jingjing Zhang, and Qingmin Wang
J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.0c00875 • Publication Date (Web): 28 Apr 2020
Downloaded from pubs.acs.org on April 28, 2020
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Synthesis and Antiviral/Fungicidal/Insecticidal Activities Study of Novel Chiral
Indole Diketopiperazine Derivatives Containing Acylhydrazone Moiety
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Jialin Xie, Wentao Xu, Hongjian Song, * Yuxiu Liu, Jingjing Zhang, * and Qingmin Wang *
1State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Collaborative
Innovation Center of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin
300071, People’s Republic of China
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Tianjin Agricultural University, Tianjin 300384, People’s Republic of China
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*To whom correspondence should be addressed. Tel: +86-(0)22-23503952; Fax:
+86-(0)22-23503952; E-mail: songhongjian@nankai.edu.cn, chemzhangjingjing@163.com,
wangqm@nankai.edu.cn.
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ABSTRACT
Based on the mechanism of acylhydrazone compounds inhibiting the assembly
of TMV CP and the unique structural characteristics of diketopiperazine ring, a series
of optically pure indole diketopiperazine acylhydrazone were designed and
synthesized. In order to systematically study the effect of the spatial configuration of
the compounds on the antiviral activity, four compounds with different spatial
configurations at C6 and C12a were also prepared. The bioassay results indicated that
most of these new compounds displayed moderate to good antiviral activity, among
which compounds 23, 25, 27, 28, 31, and 5d showed a significantly higher activity
than that of commercial ribavirin. An indepth structure-activity relationship
investigation showed that the spatial conformation was one of the most important
factors in adjusting antiviral activity; the research results provided the information
about the possible optimum configuration for interaction of this molecular with its
target protein. At the same time, these new compounds also exhibited broad-spectrum
fungicidal activities against 14 kinds of phytopathogenic fungi. What’s more, some of
these compounds exhibited good insecticidal activity to Plutella xylostella and Culex
pipiens pallens.
KEYWORDS: diketopiperazine, acylhydrazone, spatial configuration, antiviral
activity, fungicidal activity
INTRODUCTION
Plant viruses are common and cause serious diseases in agriculture which results
in significant economic losses every year.1,2 Tobacco mosaic virus (TMV) is one of
the most well-studied infectious particles, consisting of nucleic acid packaged in a
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coat protein (CP). Although simple in structure, TMV can infect at least 400
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individual species in 36 plant families. It is also a very tenacious virus that can
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survive for up to 100 years in dry plants. TMV is still difficult to control at present,
even the widely used virus inhibitors ribavirin and ningnanmycin (Figure 1) can
merely reduce the infection degree of plants with a low virus inhibition effect.6
In the search for more effective plant virus inhibitors, natural products are found
to be ideal precursor compounds. Compared with traditional synthetic drug, natural
product-based virus inhibitors have many advantages, such as easy biodegradation,
environmental friendliness, structural diversity, target specificity, and unique mode of
action.7-8 Harmine, β-carboline alkaloid, exhibited good anti-TMV activity, its
antiviral activity against TMV in vitro and inactivation, curative, and protection
activities in vivo were 44±1%, 40±1%, 38±1%, and 42±1%, respectively, at 500
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μg/mL.9
The diketopiperazine is a class of natural privileged structure that can bind to a
wide range of receptors (Figure 1),10 it also has several advantages, such as
constrained conformation, chirally enriched, stable to proteolysis, and it can mimic a
preferential peptide conformation, which makes them attractive scaffolds for drug
discovery. Their three-dimensional molecular skeletons bearing diverse substituents
overcome one of the limitations of conventional planar medicinal chemical reagents.11
As we know, the spatial configuration usually plays an important role in bonding with
the target proteins. Previous work has found that the acylhydrazone moiety is an
important pharmacophore, 12-16 acylhydrazone compounds inhibit TMV virulence by
binding directly to its coat protein discs through hydrogen bonds, this binding leads to
the disassembly of the CP discs into monomers, leading to an almost complete loss of
pathogenicity.17
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On the basis of the mechanism of acylhydrazone compounds inhibiting the
assembly of TMV CP and the unique structural characteristics of diketopiperazine
ring, a series of novel optically pure indole diketopiperazine derivatives containing
acylhydrazone moiety were designed and synthesized (Figure 2). In order to further
systematically study the effect of spatial configuration on the antiviral activity, four
compounds with different spatial configurations at C6 and C12a were prepared. The
antiviral activities of these compounds against TMV were evaluated. In addition, their
anti-phytopathogenic fungus activities and insecticidal activities were also studied.
MATERIALS AND METHODS
Instruments. The hydrazinolysis reaction was carried out in a microwave
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synthesis system (100 ºC, 100 W, Discover S-Class, CEM). H, C and NOE nuclear
magnetic resonance (NMR) spectra were obtained at 400 MHz using a Bruker AC-P
400. Chemical shift values (δ) were given in parts per million (ppm) and were
downfield from internal tetramethylsilane. High resolution mass spectra (HRMS) data
were obtained on an FTICR-MS instrument (Ionspec 7.0 T). The melting points were
determined on an X-4 binocular microscope melting point apparatus and are
uncorrected. Reaction progress was monitored by thin-layer chromatography on silica
gel GF-254 with detection by UV.
General Synthesis. Ribavirin (Shanghai Aladdin Biochemical Technology
Co.,Ltd), ningnanmycin (Alta Scientific Co., Ltd.), chlorothalonil (Shanghai Aladdin
Biochemical Technology Co.,Ltd) and other reagents were purchased from
commercial sources and were used as received. All anhydrous solvents were dried and
purified according to standard techniques just before use. The synthetic routes are
given in Figures 3−6.
Synthesis of methyl (3S)-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-
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3-carboxylate (2). This compound was synthesized by the method reported in 76%
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yield of two-steps: (cis : trans = 9:1); H NMR (400 MHz, CDCl ) δ 8.69 and 8.52 (s,
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1H), 7.46–7.34 (m, 1H), 7.16–7.08 (m, 1H), 7.03 (dd, J = 5.6, 2.8 Hz, 2H), 4.16 and
4.08–3.99 (m, 1H), 3.70 (s, 3H), 3.65 (d, J = 12.8 Hz, 1H), 3.04 (d, J = 12.4 Hz, 1H),
1
3
2.90–2.83 and 2.80–2.69 (m, 1H), 2.43 (s, 1H), 1.32 and 1.26 (d, J = 6.4 Hz, 3H); C
NMR (100 MHz, CDCl ) δ 174.0, 136.8, 136.3, 127.2, 121.6, 119.5, 118.1, 111.3,
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107.0, 56.7, 52.4, 48.6, 26.1, 20.4.
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Synthesis of methyl (3S)-2-(2-chloroacetyl)-1-methyl-2,3,4,9-tetrahydro-1H-
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pyrido[3,4-b] indole-3-carboxylate (3). To a stirred solution of 2 (22.00 g, 90.00
mmol) and NaHCO (9.07 g, 108.00 mmol) in CHCl (500 mL) was added dropwise
3
3
chloroacetyl chloride (16.30 mL, 216.00 mmol) under ice cooling. The mixture was
then stirred at room temperature under a nitrogen atmosphere for 5 h. The mixture
was diluted with CH Cl , washed with a solution of NaHCO , brine, dried over
2
2
3
Na SO , and evaporated under reduced pressure to give 3 as a pale yellow solid
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4
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(25.92 g, 85%); H NMR (400 MHz, CDCl ) δ 8.02 and 7.96 (s, 1H), 7.52 (d, J = 7.6
3
Hz, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.19 (t, J = 6.8 Hz, 1H), 7.14 (q, J = 7.2 Hz, 1H),
5.97 and 5.56 (q, J = 6.4 Hz, 1H), 5.23 and 5.01 (q, J = 6.4 Hz, 1H), 4.39–4.17 (m,
2H), 3.69–3.51 (m, 4H), 3.11 and 3.00 (ddd, J = 15.6, 6.4, 2.0 Hz, 1H), 1.69 and 1.53
1
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(d, J = 6.8 Hz, 3H); C NMR (100 MHz, CDCl ) δ 171.0, 167.2 and 166.9, 136.5 and
3
136.4, 133.0 and 131.8, 128.9 and 126.4, 122.5 and 122.1, 119.9 and 119.7, 118.6 and
118.3, 111.1, 106.3 and 104.5, 54.5 and 52.5, 52.8 and 50.4, 48.8 and 47.2, 42.3 and
+
41.5, 22.5 and 22.4, 21.8 and 19.4; HRMS (ESI) calcd for C H ClN O [M+H]
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18
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321.1000, found 321.1003.
Synthesis of (6S,12aS)-2-amino-6-methyl-2,3,6,7,12,12a-hexahydropyrazino
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[1',2':1,6] pyrido [3,4-b]indole-1,4-dione (4a). A mixture of 3 (0.96 g, 3.00 mmol)
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and hydrazine hydrate (80%) (0.56g, 9.00 mmol) in ethanol (20 mL) was in a
microwave vessel and heated by microwaves (100 W, 100˚C) for 15 min. Then the
mixture was naturally cooled to room temperature, filtered, washed with a small
amount of alcohol, dried, and gave the pure cis compound 4a as a white solid (0.60 g,
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70%): mp = 246–248 ˚C; H NMR (400 MHz, DMSO-d ) δ 11.05 (s, 1H), 7.54 (d, J =
6
8.0 Hz, 1H), 7.35 (d, J = 8.0 Hz, 1H), 7.08 (t, J = 7.2 Hz, 1H), 7.01 (t, J = 7.6 Hz, 1H),
5.22 (q, J = 6.4 Hz, 1H), 5.09 (s, 2H), 4.31–4.19 (m, 2H), 4.01 (d, J = 17.2 Hz, 1H),
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3.56–3.43 (m, 1H), 2.77 (dd, J = 16.0, 12.0Hz, 1H), 1.43 (d, J = 6.4 Hz, 3H); C
NMR (100 MHz, DMSO-d ) δ 166.8, 165.1, 136.4, 136.0, 126.4, 121.5, 119.3, 118.4,
6
+
111.7, 105.3, 55.7, 53.9, 48.5, 23.7, 23.6; HRMS (ESI) calcd for C H N O [M+H]
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5
17
4
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285.1346, found 285.1349.
Synthesis of (1S,3S)- and (1R,3S)-methyl 1-methyl-2,3,4,9-tetrahydro-1H-
pyrido[3,4-b]indole-3-carboxylate (2a and 2b).21 L-tryptophan methyl ester
hydrochloride (3.83 g, 15.00 mmol) and acetaldehyde 40% solution (2.00 mL, 18.00
mmol) were dissolved in mixture of methanol and water (75/25, v/v). The solution
was then refluxed. After 12 h, TLC analysis showed the complete consumption of
material, the mixture was cooled and the solvent was evaporated under vacuum. The
solid residue was dissolved in aqueous ammonia (14%), extracted with chloroform,
and then dried over anhydrous sodium sulphate. Removing the solvent to give a
1
yellow solid (2.56 g, 70%); cis : trans=(63 : 37), which was determined from H
NMR spectra. The yellow solid was subjected to column chromatography eluted
1
with PE/EA (100:1) to give cis isomer 2a as a pale yellow solid: mp =74–76 ˚C; H
NMR (400 MHz, CDCl ) δ 8.00 (s, 1H), 7.49 (d, J = 7.6 Hz, 1H), 7.30 (d, J = 8.0 Hz,
3
1H), 7.16 (t, J = 7.2 Hz, 1H), 7.12 (t, J = 7.2 Hz, 1H), 4.26 (q, J = 7.0 Hz, 1H),
3.86-3.84 (m, 1H),3.83 (s, 3H), 3.15 (ddd, J = 15.2, 4.4, 2.0 Hz, 1H), 2.85 (ddd, J =
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17.2, 11.2, 2.4 Hz, 1H), 2.05 (s, 1H), 1.50 (d, J = 6.4 Hz, 3H); C NMR (100 MHz,
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CDCl ) δ 173.8, 136.5, 135.9, 127.2, 121.8, 119.7, 118.1, 110.9, 107.5, 56.6, 52.3,
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48.4, 26.0, 20.5.
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Also trans isomer 2b was obtained as a pale yellow solid: mp =169–171 ˚C; H NMR
(400 MHz, CDCl ) δ 7.81 (s, 1H), 7.49 (d, J = 7.6 Hz, 1H), 7.31 (d, J = 8.0 Hz, 1H),
3
7.21 – 7.11 (m, 1H), 7.15 – 7.06 (m, 1H), 4.44 (q, J = 6.8 Hz, 1H), 4.01 (dd, J = 7.2,
5.2 Hz, 1H), 3.75 (s, 3H), 3.14 (dd, J = 15.6, 5.2 Hz, 1H), 3.00 (ddd, J = 15.6, 7.6, 1.6
1
3
Hz, 1H), 2.54 (s, 1H), 1.47 (d, J = 6.4 Hz, 3H). C NMR (100 MHz, CDCl ) δ 174.0,
3
136.1, 135.9, 127.1, 121.8, 119.6, 118.1, 110.8, 106.6, 52.6, 52.2, 45.8, 25.0, 21.6.
Data
for
(1R,3R)-and(1S,3R)-methyl-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-ca
rboxylate (2c and 2d). Compounds 2c and 2d were synthesized using the similar
procedure as compound 2a and 2b from D-tryptophan methyl ester hydrochloride
(3.83 g, 15.00 mmol) as a yellow solid (2.45 g, 67%); cis : trans=(63 : 37), which was
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determined from H NMR spectra. The yellow solid was subjected to column
chromatography eluted with PE/EA (100:1) to give cis isomer 2c as a pale yellow
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solid: mp = 49–51 ˚C; H NMR (400 MHz, CDCl ) δ 7.86 (s, 1H), 7.49 (d, J = 7.6 Hz,
3
1H), 7.32 (d, J = 8.0 Hz, 1H), 7.17 (td, J = 7.2, 1.2 Hz, 1H), 7.12 (td, J = 7.2, 1.2 Hz,
1H), 4.28 (q, J = 6.4 Hz, 1H), 3.86-3.84 (m, 1H), 3.83 (s, 3H), 3.14 (ddd, J = 15.2, 4.4,
2.0 Hz, 1H), 2.84 (ddd, J = 15.2, 11.2, 2.4 Hz, 1H), 1.97 (s, 1H), 1.51 (d, J = 6.8 Hz,
1
3
3H); C NMR (100 MHz, CDCl ) δ 173.7, 136.5, 135.9, 127.1, 121.6, 119.4, 117.9,
3
110.9, 107.2, 56.6, 52.2, 48.4, 25.9, 20.3.
1
Also trans isomer 2d was obtained as a pale yellow solid: mp = 178–180 ˚C; H NMR
(400 MHz, CDCl ) δ 7.78 (s, 1H), 7.49 (d, J = 7.6 Hz, 1H), 7.31 (d, J = 8.0 Hz, 1H),
3
7.20 – 7.11 (m, 1H), 7.11 (t, J = 7.2 Hz, 1H), 4.43 (q, J = 6.8 Hz, 1H), 4.01 (dd, J =
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7.2, 5.2 Hz, 1H), 3.75 (s, 3H), 3.14 (dd, J = 15.2, 5.2 Hz, 1H), 3.00 (dd, J = 15.2, 7.2
1
3
Hz, 1H), 2.48 (s, 1H), 1.47 (d, J = 6.8 Hz, 3H). C NMR (100 MHz, CDCl ) δ 174.1,
3
136.2, 135.9, 127.1, 121.8, 119.6, 118.1, 110.8, 106.7, 52.6, 52.2, 45.8, 25.0, 21.6.
Compounds 4b–4d were synthesized using the similar procedure as compound 4a.
Data for (6R,12aS)- 2-amino-6-methyl-2,3,12,12a-tetrahydropyrazino[1',2':1,6]
pyrido [3,4-b]indole-1,4(6H,7H)-dione (4b). This compound was obtained as a white
1
solid in 93% yield: mp = 277–279 °C; H NMR (400 MHz, DMSO-d ) δ 11.01 (s,
6
1H), 7.44 (d, J = 8.0 Hz, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.08 (t, J = 7.6 Hz, 1H), 6.99
(t, J = 7.6 Hz, 1H), 5.68 (q, J = 6.8 Hz, 1H), 5.10 (s, 2H), 4.43 (dd, J = 11.6, 4.0 Hz,
1H), 4.25 (d, J = 17.2 Hz, 1H), 4.06 (d, J = 17.2 Hz, 1H), 3.26–3.18 (m, 1H), 2.80 (dd,
1
3
J = 15.2, 11.6 Hz, 1H), 1.50–1.42 (m, 3H); C NMR (100 MHz, DMSO-d ) δ 163.4,
6
162.3, 136.4, 134.7, 126.5, 121.7, 119.2, 118.3, 111.6, 105.5, 52.8, 52.6, 45.3, 27.4,
+
19.2. HRMS (ESI) calcd for C H N O [M+H] 285.1346, found 285.1347.
1
5
17
4
2
Data for (6R,12aR)- 2-amino-6-methyl-2,3,12,12a-tetrahydropyrazino[1',2':1,6]
pyrido[3,4-b]indole-1,4(6H,7H)-dione (4c). This compound was obtained as a white
1
solid in 78% yield: mp = 263–265 °C; H NMR (400 MHz, DMSO-d ) δ 11.05 (s,
6
1H), 7.54 (d, J = 7.6 Hz, 1H), 7.34 (d, J = 8.0 Hz, 1H), 7.12–7.03 (m, 1H), 7.05 – 6.96
(m, 1H), 5.21 (q, J = 6.0 Hz, 1H), 5.09 (s, 2H), 4.30–4.20 (m, 2H), 4.00 (d, J = 17.2
Hz, 1H), 3.49 (dd, J = 15.6, 4.4 Hz, 1H), 2.76 (dd, J = 15.6, 11.6 Hz, 1H), 1.43 (d, J =
1
3
6.4 Hz, 3H); C NMR (100 MHz, DMSO-d ) δ 166.8, 165.1, 136.4, 136.1, 126.4,
6
121.5, 119.3, 118.4, 111.7, 105.3, 55.7, 53.8, 48.6, 23.7, 23.6. HRMS (ESI) calcd for
+
C H N O [M+H] 285.1346, found 258.1348.
1
5
17
4
2
Data for (6S,12aR)- 2-amino-6-methyl-2,3,12,12a-tetrahydropyrazino[1',2':1,6]
pyrido[3,4-b]indole-1,4(6H,7H)-dione (4d). This compound was obtained as a white
1
solid in 98% yield: mp = 275–277 °C; H NMR (400 MHz, DMSO-d ) δ 11.04 (s,
6
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1H), 7.44 (d, J = 8.0 Hz, 1H), 7.32 (d, J = 8.0 Hz, 1H), 7.12–7.03 (m, 1H), 7.03–6.94
(m, 1H), 5.68 (q, J = 6.8 Hz, 1H), 5.10 (s, 2H), 4.42 (dd, J = 11.6, 4.0 Hz, 1H), 4.25
(dd, J = 17.6, 1.6 Hz, 1H), 4.05 (d, J = 17.6 Hz, 1H), 3.22 (dd, J = 15.6, 4.4 Hz, 1H),
1
1
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2
2
2
2
2
2
2
2
2
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2
2
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2
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2.79 (ddd, J = 15.2, 11.6, 1.6 Hz, 1H), 1.47 (d, J = 6.8 Hz, 3H); C NMR (100 MHz,
DMSO-d ) δ 163.4, 162.3, 136.4, 134.7, 126.5, 121.7, 119.2, 118.3, 111.6, 105.5, 52.8,
6
+
52.6, 45.3, 27.4, 19.2. HRMS (ESI) calcd for C H N O [M+H] 285.1346, found
1
5
17
4
2
285.1343.
Synthesis of (6S,12aS)- 2-(((E)-benzylidene)amino)-6-methyl- 2,3,6,7,12,12a-
2
2
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (5a). To a solution of
compound 4a (0.43 g, 1.50 mmol) and Amberlyst–15 (40 mg) in toluene (40 mL) was
added dropwise benzaldehyde (0.32 g, 3.00 mmol) at room temperature. Then the
reaction mixture was heated to reflux. After 10 h, TLC analysis showed the complete
consumption of compound 4a. The mixture was concentrated in vacuo, and the crude
product was purified by column chromatography on silica gel (pretreatment with 1%
Et N) eluted with DCM/EA (50:1–20:1) to give 5a as a white solid (0.54 g, yield
3
1
95%): mp = 210–212 ˚C; H NMR (400 MHz, CDCl ) δ 8.72 (s, 1H), 8.61 (s, 1H),
3
7.77 (dd, J = 7.6, 2.0 Hz, 2H), 7.59 (d, J = 7.6 Hz, 1H), 7.48 – 7.36 (m, 4H), 7.22 (td,
J = 7.2, 1.6 Hz, 1H), 7.17 (td, J = 7.6, 1.2 Hz, 1H), 5.49 (q, J = 6.4 Hz, 1H), 4.60 (d, J
= 16.8 Hz, 1H), 4.42 (dd, J = 16.8, 1.2 Hz, 1H), 4.25 (dd, J = 11.6, 4.4 Hz, 1H), 3.73
(dd, J = 15.6, 4.4 Hz, 1H), 3.10 (dd, J = 15.2, 11.6 Hz, 1H), 1.57 (d, J = 6.4 Hz, 3H);
1
3
C NMR (100 MHz, CDCl ) δ 165.7, 164.1, 153.1, 136.1, 134.6, 133.7, 131.2, 128.9,
3
128.01, 126.2, 122.3, 120.1, 118.4, 111.4, 106.1, 56.6, 52.3, 48.8, 23.5, 23.1; HRMS
+
(ESI) calcd for C H N O [M+H] 373.1659, found 373.1658.
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2
21
4
2
Compounds 5b, 5c, 5d, 6-33 were synthesized using the similar procedure as
compound 5a.
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Data
for
(6R,12aS)-
2-(((E)-benzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (5b). This compound was
1
obtained as a pale yellow solid in 95% yield: mp = 214–216 °C; H NMR (400 MHz,
CDCl ) δ 8.55 (s, 1H), 8.06 (s, 1H), 7.81 (dd, J = 7.6, 2.0 Hz, 2H), 7.52–7.41 (m, 4H),
3
7.36 (d, J = 8.0 Hz, 1H), 7.21 (ddd, J = 8.4, 7.2, 1.2 Hz, 1H), 7.14 (td, J = 7.6, 1.2 Hz,
1H), 5.96 (q, J = 6.8 Hz, 1H), 4.57–4.61 (m, 1H), 4.56–4.45 (m, 2H), 3.57 (dd, J =
1
3
15.2, 4.0 Hz, 1H), 2.99 (ddd, J = 15.2, 11.6, 1.6 Hz, 1H), 1.59 (d, J = 6.8 Hz, 3H); C
NMR (100 MHz, CDCl ) δ 162.9, 161.1, 152.5, 136., 133.45, 133.0, 131.3, 128.9,
3
128.2, 126.3, 122.5, 120.1, 118.4, 111.1, 106.5, 53.7, 50.6, 45.7, 28.0, 19.4; HRMS
+
(ESI) calcd for C H N O [M+H] 373.1659, found 373.1654.
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2
21
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2
Data
for
(6R,12aR)-
2-(((E)-benzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (5c). This compound was
1
obtained as a pale yellow solid in 90% yield: mp = 147–149 °C; H NMR (400 MHz,
CDCl ) δ 8.80 (s, 1H), 8.20 (s, 1H), 7.77 (dd, J = 7.6, 2.0 Hz, 2H), 7.61 (d, J = 8.0 Hz,
3
1H), 7.47–7.42 (m, 3H), 7.40 (d, J = 8.0 Hz, 1H), 7.23 (td, J = 7.6, 1.6 Hz, 1H), 7.18
(td, J = 7.2, 1.2 Hz, 1H), 5.49 (q, J = 6. 4 Hz, 1H), 4.63 (d, J = 16.8 Hz, 1H), 4.48 (d,
J = 16.8Hz, 1H), 4.30 (dd, J = 11.2, 4.4 Hz, 1H), 3.75 (dd, J = 15.6, 4.4 Hz, 1H), 3.12
1
3
(dd, J = 15.6, 11.6 Hz, 1H), 1.57 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ
3
165.7, 164.1, 153.1, 136.1, 134.6, 133.7, 131.2, 128.9, 128.01, 126.2, 122.3, 120.1,
118.4, 111.4, 106.1, 56.6, 52.3, 48.8, 23.5, 23.1; HRMS (ESI) calcd for C H N O
2
2
2
21
4
+
[M+H] 373.1659, found 373.1655.
Data for (6S,12aR)- 2-(((E)-benzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (5d). This compound was
1
obtained as a pale yellow solid in 93% yield: mp = 218–220 °C; H NMR (400 MHz,
CDCl ) δ 8.55 (s, 1H), 8.08 (s, 1H), 7.81 (dd, J = 7.6, 2.0 Hz, 2H), 7.52–7.41 (m, 4H),
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7.36 (d, J = 8.4 Hz, 1H), 7.21 (td, J = 8.8, 7.6, 1.6 Hz, 1H), 7.14 (td, J = 7.6, 1.2 Hz,
1H), 5.96 (q, J = 6.8 Hz, 1H), 4.57 – 4.61 (m, 1H), 4.56–4.45 (m, 2H), 3.57 (dd, J =
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15.2, 4.0 Hz, 1H), 2.99 (ddd, J = 15.6, 12.0, 1.6 Hz, 1H), 1.59 (d, J = 6.8 Hz, 3H); C
NMR (100 MHz, CDCl ) δ 162.9, 161.1, 152.5, 136., 133.45, 133.0, 131.3, 128.9,
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128.2, 126.3, 122.5, 120.1, 118.4, 111.1, 106.5, 53.7, 50.6, 45.7, 28.0, 19.4; HRMS
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(ESI) calcd for C H N O [M+H] 373.1659, found 373.1655.
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21
4
2
Data for (6S,12aS)- 2-(((E)-[1,1'-biphenyl]-4-ylmethylene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (6). This
1
compound was obtained as a pale yellow solid in 60% yield: mp = 283–285 °C; H
NMR (400 MHz, DMSO-d ) δ 11.11 (s, 1H), 8.48 (s, 1H), 7.89 (d, J = 8.4 Hz, 2H),
6
7.80 (d, J = 8.0 Hz, 2H), 7.74 (d, J = 7.2 Hz, 2H), 7.58 (d, J = 7.6 Hz, 1H), 7.50 (t, J =
7.6 Hz, 2H), 7.41 (t, J = 7.2 Hz, 1H), 7.37 (d, J = 8.0 Hz, 1H), 7.09 (t, J = 7.2 Hz, 1H),
7.03 (t, J = 7.2 Hz, 1H), 5.33 (q, J = 6.4 Hz, 1H), 4.69 (d, J = 16.8 Hz, 1H), 4.56–4.43
(m, 2H), 3.56 (dd, J = 15.6, 4.4 Hz, 1H), 2.94 (dd, J = 15.6, 11.6 Hz, 1H), 1.48 (d, J =
1
3
6.4 Hz, 3H); C NMR (100 MHz, DMSO) δ 165.9, 164.2, 148.2, 142.4, 139.8, 136.4,
135.9, 133.9, 129.5, 128.6, 128.4, 127.5, 127.2, 126.4, 121.5, 119.3, 118.4, 111.8,
+
105.1, 56.3, 50.3, 48.6, 23.6, 23.4; HRMS (ESI) calcd for C H N O [M+H]
2
8
25
4
2
449.1972, found 449.1969.
Data for (6S,12aS)- 6-methyl-2-(((E)-4-(trifluoromethyl)benzylidene)amino)-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (7). This
1
compound was obtained as a pale yellow solid in 95% yield: mp = 246–248 °C; H
NMR (400 MHz, CDCl ) δ 8.92 (s, 1H), 8.33 (s, 1H), 7.88 (d, J = 8.0 Hz, 2H), 7.69 (d,
3
J = 8.0 Hz, 2H), 7.65–7.57 (m, 1H), 7.40 (d, J = 7.6 Hz, 1H), 7.23 (td, J = 7.6, 1.2 Hz,
1H), 7.18 (td, J = 7.2, 1.2 Hz, 1H), 5.50 (q, J = 6.4 Hz, 1H), 4.65 (d, J = 16.8 Hz, 1H),
4.50 (d, J = 16.8 Hz, 1H), 4.30 (dd, J = 11.2, 4.4 Hz, 1H), 3.74 (dd, J = 15.6, 4.8 Hz,
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1H), 3.12 (dd, J = 15.6, 11.2 Hz, 1H), 1.57 (d, J = 6.4 Hz, 3H); C NMR (100 MHz,
CDCl ) δ 165.6, 164.5, 150.8, 137.3, 136.2, 134.6, 132.6(q, J = 32.0 Hz), 127.0,
3
C-F
126.3, 125.9(q, JC-F = 4.0 Hz), 123.9(JC-F = 271.0 Hz), 122.5, 120.31, 118.46, 111.45,
+
106.1, 56.7, 52.9, 48.9, 23.6, 23.1; HRMS (ESI) calcd for C H F N O [M+H]
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3
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441.1533, found 441.1538.
Data for (6S,12aS)-
2-(((E)-4-(tert-butyl)benzylidene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (8). This
1
compound was obtained as a pale yellow solid in 95% yield: mp = 150–152 °C; H
NMR (400 MHz, CDCl ) δ 8.70 (d, J = 8.0 Hz, 1H), 8.53 (d, J = 50.4 Hz, 1H), 7.69 (d,
3
J = 8.0 Hz, 2H), 7.59 (d, J = 7.6 Hz, 1H), 7.44 (d, J = 8.0 Hz, 2H), 7.39 (d, J = 8.0 Hz,
1H), 7.21 (t, J = 7.6 Hz, 1H), 7.16 (t, J = 7.6 Hz, 1H), 5.49 (q, J = 6.4 Hz, 1H), 4.59
(d, J = 16.8 Hz, 1H), 4.43 (dd, J = 16.8, 6.4 Hz, 1H), 4.28–4.21 (m, 1H), 3.74 (dd, J =
15.6, 4.4 Hz, 1H), 3.10 (dd, J = 16.0, 11.6 Hz, 1H), 1.56 (d, J = 6.0 Hz, 3H), 1.34 (s,
1
3
9H); C NMR (100 MHz, CDCl ) δ 165.8, 164.0, 154.8, 153.7, 136.1, 134.6, 130.9,
3
127.9, 126.2, 125.8, 122.2, 120.1, 118.4, 111.4, 106.2, 56.6, 52.3, 48.8, 35.0, 31.2,
+
23.5, 23.1; HRMS (ESI) calcd for C H N O [M+H] 429.2285, found 429.2291.
2
6
29
4
2
Data for (6S,12aS)- 2-(((E)-4-(dimethylamino)benzylidene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (9). This
1
compound was obtained as an orange solid in 22% yield: mp = 127–129 °C; H NMR
(400 MHz, CDCl ) δ 8.75 (d, J = 53.2 Hz, 1H), 8.47 (d, J = 8.0 Hz, 1H), 7.63 (d, J =
3
8.4 Hz, 2H), 7.58 (d, J = 8.0 Hz, 1H), 7.39 (d, J = 7.6 Hz, 1H), 7.20 (t, J = 7.2 Hz,
1H), 7.15 (t, J = 7.6 Hz, 1H), 6.67 (d, J = 8.8 Hz, 2H), 5.47 (q, J = 6.4 Hz, 1H), 4.53
(d, J = 16.8 Hz, 1H), 4.38 (d, J = 16.8 Hz, 1H), 4.20 (dd, J = 12.0, 4.8 Hz, 1H), 3.73
(dd, J = 15.6, 4.4 Hz, 1H), 3.10 (d, J = 11.6 Hz, 1H), 3.02 (s, 6H), 1.56 (d, J = 6.4 Hz,
1
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3H); C NMR (100 MHz, CDCl ) δ 165.9, 163.6, 155.3, 152.4, 136.2, 134.9, 129.7,
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126.3, 122.0, 120.9, 119.9, 118.3, 111.6, 111.4, 106.1, 56.5, 52.0, 48.8, 40.2, 23.4,
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00
01
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23.2; HRMS (ESI) calcd for C H N O [M+H] 416.2081, found 416.2081.
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Data for (6S,12aS)-6-methyl-2-(((E)-4-nitrobenzylidene)amino)-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (10). This compound was
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obtained as a yellow solid in 98% yield: mp = 263–265 °C; H NMR (400 MHz,
DMSO-d ) δ 11.11 (s, 1H), 8.50 (s, 1H), 8.34 (d, J = 8.4 Hz, 2H), 8.03 (d, J = 8.4 Hz,
6
2H), 7.57 (d, J = 7.6 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.09 (t, J = 7.6 Hz, 1H), 7.02
(t, J = 7.6 Hz, 1H), 5.32 (q, J = 6.0 Hz, 1H), 4.75 (d, J = 16.4 Hz, 1H), 4.56–4.44 (m,
2H), 3.56 (dd, J = 15.6, 4.4 Hz, 1H), 2.94 (dd, J = 15.6, 11.6 Hz, 1H), 1.48 (d, J = 6.4
1
3
Hz, 3H); C NMR (100 MHz, DMSO-d ) δ 165.6, 164.4, 148.5, 145.0, 141.1, 136.4,
6
135.9, 128.9, 126.3, 124.6, 121.5, 119.3, 118.4, 111.8, 105.0, 56.3, 50.0, 48.6, 23.6,
+
23.4; HRMS (ESI) calcd for C H N O [M+H] 418.1510, found 418.1513.
2
2
20
5
4
Data for (6S,12aS)-6-methyl-2-(((E)-3-nitrobenzylidene)amino)-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (11). This compound was
1
obtained as a yellow solid in 87% yield: mp = 240–242 °C; H NMR (400 MHz,
DMSO-d ) δ 11.11 (s, 1H), 8.60 (s, 1H), 8.53 (s, 1H), 8.30 (d, J = 8.0 Hz, 1H), 8.21 (d,
6
J = 7.6 Hz, 1H), 7.78 (t, J = 8.0 Hz, 1H), 7.57 (d, J = 7.6 Hz, 1H), 7.36 (d, J = 8.0 Hz,
1H), 7.09 (t, J = 7.6 Hz, 1H), 7.02 (t, J = 7.6 Hz, 1H), 5.32 (q, J = 6.4 Hz, 1H), 4.72
(d, J = 16.4 Hz, 1H), 4.55–4.44 (m, 2H), 3.56 (dd, J = 15.6, 4.4 Hz, 1H), 2.94 (dd, J =
1
3
15.6, 11.6 Hz, 1H), 1.48 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, DMSO-d ) δ 165.6,
6
164.3, 148.7, 145.4, 136.6, 136.4, 135.9, 134.0, 131.0, 126.3, 125.1, 122.1, 121.5,
119.3, 118.4, 111.8, 105.0, 56.3, 50.0, 48.6, 23.6, 23.4; HRMS (ESI) calcd for
+
C H N O [M+H] 418.1510, found 418.1518.
2
2
20
5
4
Data for (6S,12aS)-2-(((E)-4-chlorobenzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (12). This compound was
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obtained as an orange solid in 60% yield: mp = 136–138 °C; H NMR (400 MHz,
CDCl ) δ 8.79 (s, 1H), 8.37 (s, 1H), 7.70 (d, J = 8.8 Hz, 2H), 7.60 (d, J = 7.6 Hz, 1H),
3
7.40 (d, J = 8.4 Hz, 3H), 7.22 (t, J = 7.6 Hz, 1H), 7.17 (t, J = 7.2 Hz, 1H), 5.48 (q, J =
6.4 Hz, 1H), 4.61 (d, J = 16.8 Hz, 1H), 4.45 (d, J = 16.8 Hz, 1H), 4.28 (dd, J = 11.6,
4.4 Hz, 1H), 3.73 (dd, J = 16.0, 4.4 Hz, 1H), 3.11 (dd, J = 16.0, 11.6 Hz, 1H), 1.56 (d,
1
3
J = 6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ 165.6, 164.2, 151.6, 137.1, 136.1,
3
134.5, 132.3, 129.2, 129.1, 126.2, 122.3, 120.2, 118.4, 111.3, 106.1, 56.6, 52.5, 48.8,
+
23.4, 23.0; HRMS (ESI) calcd for C H ClN O [M+H] 407.1269, found 407.1270.
2
2
20
4
2
Data for (6S,12aS)-2-(((E)-3-chlorobenzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (13). This compound was
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obtained as a pale yellow solid in 80% yield: mp = 217–219 °C; H NMR (400 MHz,
CDCl ) δ 8.81 (s, 1H), 8.69 (s, 1H), 7.76 (s, 1H), 7.58 (t, J = 7.6 Hz, 2H), 7.40 (d, J =
3
7.6 Hz, 2H), 7.33 (t, J = 7.6 Hz, 1H), 7.21 (t, J = 7.2 Hz, 1H), 7.16 (t, J = 7.2 Hz, 1H),
5.48 (q, J = 5.6 Hz, 1H), 4.58 (d, J = 16.8 Hz, 1H), 4.38 (d, J = 16.8 Hz, 1H), 4.22 (dd,
J = 11.2, 4.0 Hz, 1H), 3.70 (dd, J = 16.0, 4.4 Hz, 1H), 3.08 (dd, J = 15.2, 11.6 Hz, 1H),
1
3
1.55 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ 165.6, 164.2, 150.0, 136.2,
3
135.6, 134.9, 134.7, 131.0, 130.1, 127.5, 126.3, 126.2, 122.1, 120.0, 118.4, 111.5,
+
105.7, 56.4, 51.9, 48.9, 23.4, 23.1; HRMS (ESI) calcd for C H ClN O [M+H]
2
2
20
4
2
407.1269, found 407.1263.
Data for (6S,12aS)-2-(((E)-2-chlorobenzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (14). This compound was
1
obtained as a pale yellow solid in 60% yield: mp = 234–236 °C; H NMR (400 MHz,
CDCl ) δ 9.09 (s, 1H), 8.23 (s, 1H), 8.11 (d, J = 7.6 Hz, 1H), 7.60 (d, J = 7.6 Hz, 1H),
3
7.46–7.27 (m, 4H), 7.22 (t, J = 8.0 Hz, 1H), 7.18 (t, J = 7.6 Hz, 1H), 5.49 (q, J = 5.6
Hz, 1H), 4.67 (d, J = 16.8 Hz, 1H), 4.47 (d, J = 16.8 Hz, 1H), 4.31 (dd, J = 12.8, 4.0
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Hz, 1H), 3.77 (dd, J = 15.6, 4.4 Hz, 1H), 3.13 (dd, J = 15.6, 11.6 Hz, 1H), 1.57 (d, J =
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6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ 165.3, 164.1, 148.0, 136.1, 135.2, 134.5,
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131.9, 131.3, 129.9, 127.6, 127.2, 126.2, 122.4, 120.2, 118.4, 111.3, 106.2, 56.6, 52.0,
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48.8, 23.4, 23.1; HRMS (ESI) calcd for C H ClN O [M+H] 407.1269, found
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2
20
4
2
407.1266.
Data
for
(6S,12aS)-
2-(((E)-3,4-dichlorobenzylidene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (15). This
1
compound was obtained as a pale yellow solid in 96% yield: mp = 248–250 °C; H
NMR (400 MHz, CDCl ) δ 8.83 (s, 1H), 8.37 (s, 1H), 7.87 (d, J = 2.0 Hz, 1H),
3
7.63–7.54 (m, 2H), 7.50 (d, J = 8.4 Hz, 1H), 7.39 (d, J = 7.6 Hz, 1H), 7.22 (td, J = 7.2,
1.2 Hz, 1H), 7.18 (td, J = 7.2, 1.2 Hz, 1H), 5.49 (q, J = 6.4 Hz, 1H), 4.61 (d, J = 16.8
Hz, 1H), 4.46 (d, J = 16.8 Hz, 1H), 4.28 (dd, J = 11.6, 4.4 Hz, 1H), 3.72 (dd, J = 16.0,
1
3
4.4 Hz, 1H), 3.11 (dd, J = 15.6, 11.6 Hz, 1H), 1.56 (d, J = 6.4 Hz, 3H); C NMR (100
MHz, CDCl ) δ 165.5, 164.4, 149.9, 136.1, 135.0, 134.5, 133.9, 133.3, 130.9, 129.3,
3
126.9, 126.2, 122.4, 120.2, 118.4, 111.3, 106.0, 56.6, 52.8, 48.8, 23.4, 23.0; HRMS
+
(ESI) calcd for C H Cl N O [M+H] 441.0880, found 441.0877.
2
2
19
2
4
2
Data
for
(6S,12aS)-
2-(((E)-2,4-dichlorobenzylidene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (16). This
1
compound was obtained as a pale yellow solid in 90% yield: mp = 163–165 °C; H
NMR (400 MHz, DMSO-d ) δ 11.10 (s, 1H), 8.69 (s, 1H), 8.00 (d, J = 8.4 Hz, 1H),
6
7.77 (d, J = 2.0 Hz, 1H), 7.56 (dd, J = 8.4, 2.0 Hz, 2H), 7.36 (d, J = 8.0 Hz, 1H),
7.12–7.06 (m, 1H), 7.05–7.00 (m, 1H), 5.32 (q, J = 6.4 Hz, 1H), 4.69 (d, J = 16.8 Hz,
1H), 4.57 (d, J = 16.4 Hz, 1H), 4.50 (dd, J = 11.6, 4.4 Hz, 1H), 3.54 (dd, J = 15.6, 4.4
1
3
Hz, 1H), 2.94 (dd, J = 15.6, 11.6 Hz, 1H), 1.47 (d, J = 6.4 Hz, 3H); C NMR (100
MHz, DMSO-d ) δ 165.8, 164.7, 143.5, 136.4, 136.1, 135.9, 135.0, 131.1, 130.0,
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129.0, 128.6, 126.3, 121.5, 119.3, 118.4, 111.8, 104.9, 56.3, 50.9, 48.6, 23.6, 23.2;
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HRMS (ESI) calcd for C H Cl N O [M+H] 441.0880, found 441.0872.
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19
2
4
2
Data for (6S,12aS)-2-(((E)-4-methoxybenzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (17). This compound
1
was obtained as a pale yellow solid in 68% yield: mp = 193–195 °C; H NMR (400
MHz, CDCl ) δ 8.91 (s, 1H), 8.55 (s, 1H), 7.69 (d, J = 8.4 Hz, 2H), 7.57 (d, J = 7.6
3
Hz, 1H), 7.39 (d, J = 7.6 Hz, 1H), 7.20 (t, J = 7.6 Hz, 1H), 7.15 (t, J = 7.2 Hz, 1H),
6.91 (d, J = 8.4 Hz, 2H), 5.46 (q, J = 6.4 Hz, 1H), 4.54 (d, J = 16.8 Hz, 1H), 4.36 (d,
J = 16.8 Hz, 1H), 4.18 (dd, J = 11.6, 4.4 Hz, 1H), 3.84 (s, 3H), 3.71 (dd, J = 15.6, 4.4
1
3
Hz, 1H), 3.07 (dd, J = 15.6, 11.6 Hz, 1H), 1.55 (d, J = 6.4 Hz, 3H); C NMR (100
MHz, CDCl ) δ 165.8, 163.9, 162.1, 153.1, 136.2, 134.8, 130.2, 129.7, 126.2, 122.1,
3
120.0, 118.3, 114.3, 111.5, 105.9, 56.5, 55.5, 51.9, 48.9, 23.4, 23.1. HRMS (ESI)
+
calcd for C H N O [M+H] 403.1765, found 403.1766.
2
3
23
4
3
Data for (6S,12aS)-2-(((E)-3-methoxybenzylidene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (18). This compound was
1
obtained as a pale yellow solid in 93% yield: mp = 210–212 °C; H NMR (400 MHz,
CDCl ) δ 8.74 (s, 1H), 8.48 (s, 1H), 7.60 (d, J = 7.6 Hz, 1H), 7.40 (d, J = 8.0 Hz, 1H),
3
7.37–7.28 (m, 3H), 7.22 (td, J= 7.2, 1.6 Hz, 1H), 7.17 (td, J = 7.5, 1.2 Hz, 1H), 7.00
(ddd, J = 8.0, 2.4, 1.2 Hz, 1H), 5.49 (q, J = 6.4 Hz, 1H), 4.61 (d, J = 16.8 Hz, 1H),
4.45 (d, J = 16.4 Hz, 1H), 4.26 (dd, J = 11.2, 4.4 Hz, 1H), 3.83 (s, 3H), 3.74 (dd, J =
1
3
15.6, 4.4 Hz, 1H), 3.11 (dd, J = 15.6, 11.6 Hz, 1H), 1.57 (d, J = 6.4 Hz, 3H); C
NMR (100 MHz, CDCl ) δ 165.6, 164.1, 159.9, 153.1, 136.1, 135.1, 134.6, 129.8,
3
126.2, 122.3, 121.4, 120.1, 118.4, 117.8, 111.4, 111.3, 106.1, 56.6, 55.4, 52.4, 48.8,
+
23.4, 23.1; HRMS (ESI) calcd for C H N O [M+H] 403.1765, found 403.1767.
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Data for (6S,12aS)-2-(((E)-2-methoxybenzylidene)amino)-6-methyl-2,3,6,7,12,12a-
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95
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hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (19). This compound was
1
obtained as a pale yellow solid in 98% yield: mp = 237–239 °C; H NMR (400 MHz,
CDCl ) δ 8.93 (s, 1H), 8.49 (s, 1H), 8.02 (dd, J = 7.6, 1.6 Hz, 1H), 7.60 (d, J = 7.6 Hz,
3
1H), 7.46–7.36 (m, 2H), 7.21 (td, J =7.6, 1.2 Hz, 1H), 7.16 (td, J = 7.2, 1.2 Hz, 1H),
6.98 (t, J = 7.6 Hz, 1H), 6.93 (d, J = 8.0 Hz, 1H), 5.48 (q, J = 6.4 Hz, 1H), 4.63 (d, J =
16.8 Hz, 1H), 4.40 (dd, J = 16.8, 0.4 Hz, 1H), 4.26 (dd, J = 11.2, 4.0 Hz, 1H), 3.89 (s,
3H), 3.77 (dd, J = 15.6, 4.4 Hz, 1H), 3.11 (dd, J = 15.6, 11.6 Hz, 1H), 1.57 (d, J = 6.4
1
3
Hz, 3H); C NMR (100 MHz, CDCl ) δ 165.5, 163.7, 158.7, 148.0, 136.2, 134.6,
3
132.5, 126.8, 126.2, 122.2, 122.0, 120.9, 120.1, 118.4, 111.3, 111.0, 106.2, 56.5, 55.6,
+
51.4, 48.9, 23.4, 23.2; HRMS (ESI) calcd for C H N O [M+H] 403.1765, found
2
3
23
4
3
403.1768.
Data
for
(6S,12aS)-
2-(((E)-3,4-dimethoxybenzylidene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (20). This
1
compound was obtained as a pale yellow solid in 95% yield: mp = 126–128 °C; H
NMR (400 MHz, CDCl ) δ 8.69 (s, 1H), 8.63 (s, 1H), 7.58 (d, J = 7.6 Hz, 1H), 7.44 (d,
3
J = 2.0 Hz, 1H), 7.39 (d, J = 7.6 Hz, 1H), 7.23–7.12 (m, 3H), 6.89 (d, J = 8.0 Hz, 1H),
5.48 (q, J = 6.4 Hz, 1H), 4.58 (d, J = 16.8 Hz, 1H), 4.43 (dd, J = 16.8, 0.8 Hz, 1H),
4.23 (dd, J = 11.6, 1.0 Hz, 1H), 3.92 (s, 3H), 3.88 (s, 3H), 3.73 (dd, J = 15.6, 4.4 Hz,
1
3
1H), 3.09 (dd, J = 15.6, 11.6 Hz, 1H), 1.56 (d, J = 6.4 Hz, 3H); C NMR (100 MHz,
CDCl ) δ 165.7, 163.9, 154.0, 151.9, 149.5, 136.2, 134.7, 126.5, 126.2, 123.7, 122.2,
3
120.0, 118.3, 111.4, 110.6, 108.2, 106.0, 56.5, 56.0, 55.9, 52.3, 48.8, 23.4, 23.1;
+
HRMS (ESI) calcd for C H N O [M+H] 433.1870, found 433.1869.
2
4
25
4
4
Data for (6S,12aS)-2-(((E)-benzo[d][1,3]dioxol-5-ylmethylene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (21). This
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compound was obtained as a pale yellow solid in 59% yield: mp = 240–242 °C; H
NMR (400 MHz, CDCl ) δ 8.70 (d, J = 4.0 Hz, 1H), 8.30 (d, J = 40.0 Hz, 1H), 7.60 (d,
3
J = 7.2 Hz, 1H), 7.42–7.35 (m, 2H), 7.22 (td, J = 7.6, 1.2 Hz, 1H), 7.17 (td, J = 7.6,
1.2 Hz, 1H), 7.13 (dd, J = 8.0, 1.6 Hz, 1H), 6.84 (d, J = 8.0 Hz, 1H), 6.03 (s, 2H),
5.48 (q, J = 6.4 Hz, 1H), 4.57 (d, J = 16.8 Hz, 1H), 4.50–4.40 (m, 1H), 4.26 (dd, J =
11.6, 4.4 Hz, 1H), 3.73 (dd, J = 15.6, 4.4 Hz, 1H), 3.15–3.05 (m, 1H), 1.56 (d, J = 6.4
1
3
Hz, 3H); C NMR (100 MHz, CDCl ) δ 165.8, 163.9, 153.6, 150.4, 148.5, 136.1,
3
134.6, 128.2, 126.2, 124.9, 122.3, 120.1, 118.4, 111.3, 108.3, 106.2, 106.0, 101.7,
+
56.6, 52.6, 48.8, 23.4, 23.1; HRMS (ESI) calcd for C H N O [M+H] 417.1557,
2
3
21
4
4
found 417.1550.
Data for (6S,12aS)-2-(((E)-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)methylene)amino)
-6-methyl-2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione
(22). This compound was obtained as a pale yellow solid in 78% yield: mp = 155–157
1
°C; H NMR (400 MHz, CDCl ) δ 8.63 (s, 1H), 8.47 (s, 1H), 7.59 (d, J = 7.2 Hz, 1H),
3
7.42–7.35 (m, 1H), 7.31 (d, J = 2.0 Hz, 1H), 7.29–7.21 (m, 1H), 7.21 (td, J = 7.6, 1.2
Hz, 1H), 7.16 (td, J = 7.2, 1.2 Hz, 1H), 6.90 (d, J = 8.4 Hz, 1H), 5.48 (q, J = 6.4 Hz,
1H), 4.56 (d, J = 16.8 Hz, 1H), 4.42 (d, J = 16.8 Hz, 1H), 4.33–4.24 (m, 4H),
4.28–4.20 (m, 1H), 3.73 (dd, J = 15.6, 4.4 Hz, 1H), 3.09 (dd, J = 15.6, 11.6 Hz, 1H),
1
3
1.56 (d, J = 6.4 Hz, 3H). C NMR (100 MHz, CDCl ) δ 165.8, 163.9, 153.4, 146.4,
3
143.8, 136.1, 134.7, 127.2, 126.2, 122.2, 122.0, 120.0, 118.3, 117.7, 116.6, 111.4,
106.1, 64.6, 64.2, 56.5, 52.4, 48.8, 23.4, 23.1. HRMS (ESI) calcd for C H N O
4
2
4
23
4
+
[M+H] 431.1714, found 431.1713.
Data for (6S,12aS)- 2-(((E)-3,5-di-tert-butyl-4-hydroxybenzylidene)amino)-
6-methyl-2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione
(23). This compound was obtained as a pale yellow solid in 92% yield: mp = 176–178
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°C; H NMR (400 MHz, CDCl ) δ 8.72 (s, 1H), 8.35 (d, J = 7.6 Hz, 1H), 7.60 (s, 3H),
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44
45
46
47
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7.42–7.35 (m, 1H), 7.25–7.16 (m, 1H), 7.16 (td, J = 7.2, 1.2 Hz, 1H), 5.59 (s, 1H),
5.49 (q, J = 6.4 Hz, 1H), 4.57 (d, J = 17.2 Hz, 1H), 4.49 (dd, J = 16.8, 1.2 Hz, 1H),
4.27 (dd, J = 11.6, 4.4 Hz, 1H), 3.74 (dd, J = 15.6, 4.4 Hz, 1H), 3.10 (ddd, J = 16.0,
1
3
11.6, 0.8 Hz, 1H), 1.57 (d, J = 6.4 Hz, 3H), 1.46 (s, 18H); C NMR (100 MHz,
CDCl ) δ 166.0, 163.7, 157.6, 157.1, 136.4, 136.1, 134.7, 126.2, 125.5, 124.7, 122.2,
3
120.1, 118.3, 111.3, 106.3, 56.6, 52.9, 48.8, 34.4, 30.2, 23.5, 23.1. HRMS (ESI) calcd
+
for C H N O [M+H] 501.2860, found 501.2867.
3
0
37
4
3
Data
(6S,12aS)-2-(((E)-4-bromo-2,6-difluorobenzylidene)amino)-6-methyl-2,3,6,
7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (24).
for
This
1
compound was obtained as a pale yellow solid in 82% yield: mp = 250–252 °C; H
NMR (400 MHz, DMSO-d ) δ 11.10 (s, 1H), 8.38 (s, 1H), 7.62 (d, J = 8.1 Hz, 2H),
6
7.56 (d, J = 7.7 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.08 (t, J = 7.5 Hz, 1H), 7.02 (t, J =
7.3 Hz, 1H), 5.32 (q, J = 6.2 Hz, 1H), 4.66 (d, J = 16.6 Hz, 1H), 4.55–4.45 (m, 2H),
3.53 (dd, J = 15.5, 4.3 Hz, 1H), 2.94 (dd, J = 15.3, 11.7 Hz, 1H), 1.46 (d, J = 6.3 Hz,
1
3
3H); C NMR (100 MHz, DMSO-d ) δ 165.7, 164.5, 160.7 (dd, J = 257.0 Hz, J = 7.0
6
Hz), 138.5, 136.4, 135.9, 126.3, 123.8 (t, J = 13.0 Hz), 121.5, 119.3, 118.4, 116.7 (dd,
J = 27.0 Hz, J = 3.0 Hz), 111.7 (t, J = 14.0Hz), 104.9, 56.2, 55.4, 50.4, 48.5, 23.6,
+
23.2; HRMS (ESI) calcd for C H BrF N O [M+H] 487.0576, found 487.0573.
2
2
18
2
4
2
Data
for
(6S,12aS)-
6-methyl-2-(((E)-naphthalen-2-ylmethylene)amino)-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (25). This
1
compound was obtained as a pale yellow solid in 84% yield: mp = 225–227 °C; H
NMR (400 MHz, CDCl ) δ 9.02 (s, 1H), 8.70 (s, 1H), 8.01 (d, J = 8.8 Hz, 2H),
3
7.87–7.79 (m, 3H), 7.60 (d, J = 7.6 Hz, 1H), 7.57–7.49 (m, 2H), 7.43 (d, J = 8.0 Hz,
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1H), 7.23 (t, J = 7.6 Hz, 1H), 7.18 (t, J = 7.2 Hz, 1H), 5.49 (q, J = 6.4 Hz, 1H), 4.60
(d, J = 16.8 Hz, 1H), 4.33 (d, J = 16.8 Hz, 1H), 4.17 (dd, J = 11.6, 4.4 Hz, 1H), 3.73
(dd, J = 15.6, 4.8 Hz, 1H), 3.10 (dd, J = 15.6, 11.2 Hz, 1H), 1.57 (d, J = 6.4 Hz, 3H);
1
3
C NMR (100 MHz, CDCl ) δ 165.6, 164.1, 151.8, 136.2, 134.8, 134.7, 133.1, 131.4,
3
130.4, 128.8, 128.7, 128.0, 127.6, 126.8, 126.2, 123.0, 122.1, 120.0, 118.4, 111.5,
+
105.9, 56.5, 51.7, 48.9, 23.5, 23.1; HRMS (ESI) calcd for C H N O [M+H]
2
6
23
4
2
423.1816, found 423.1810.
Data for (6S,12aS)-6-methyl-2-(((E)-pyridin-3-ylmethylene)amino)-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (26). This compound was
1
obtained as a pale yellow solid in 91% yield: mp = 248–250 °C; H NMR (400 MHz,
DMSO-d ) δ 11.11 (s, 1H), 8.92 (s, 1H), 8.64 (d, J = 4.0 Hz, 1H), 8.48 (s, 1H), 8.18 (d,
6
J = 8.0 Hz, 1H), 7.57 (d, J = 7.6 Hz, 1H), 7.52 (dd, J = 7.2, 4.8 Hz, 1H), 7.36 (d, J =
8.0 Hz, 1H), 7.09 (t, J = 7.2 Hz, 1H), 7.02 (t, J = 7.2 Hz, 1H), 5.32 (q, J = 6.4 Hz, 1H),
4.70 (d, J = 16.4 Hz, 1H), 4.55–4.44 (m, 2H), 3.56 (dd, J = 15.2, 4.4 Hz, 1H), 2.94
1
3
(dd, J = 15.6, 12.0 Hz, 1H), 1.48 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, DMSO-d )
6
δ 165.8, 164.3, 151.5, 149.7, 145.6, 136.4, 135.9, 134.3, 130.7, 126.4, 124.5, 121.5,
119.3, 118.4, 111.8, 105.0, 56.3, 50.1, 48.6, 23.6, 23.4; HRMS (ESI) calcd for
+
C H N O [M+H] 374.1612, found 374.1619.
2
1
20
5
2
Data
for
(6S,12aS)-
2-(((E)-(1H-pyrrol-2-yl)methylene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (27). This
1
compound was obtained as a pale brown solid in 93% yield: mp = 144–146 °C; H
NMR (400 MHz, CDCl ) δ 9.49 (s, 1H), 8.67 (s, 1H), 8.32 (s, 1H), 7.57 (d, J = 7.6 Hz,
3
1H), 7.38 (d, J = 8.0 Hz, 1H), 7.19 (t, J = 7.2 Hz, 1H), 7.14 (t, J = 7.2 Hz, 1H), 6.90 (s,
1H), 6.59 (s, 1H), 6.27 (q, J = 2.8 Hz, 1H), 5.45 (q, J = 6.4 Hz, 1H), 4.48 (d, J = 16.8
Hz, 1H), 4.32 (d, J = 16.8 Hz, 1H), 4.22 (dd, J = 11.2, 4.4 Hz, 1H), 3.72 (dd, J = 15.6,
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4.4 Hz, 1H), 3.05 (dd, J = 15.6, 11.4 Hz, 1H), 1.54 (d, J = 6.4 Hz, 3H); C NMR (100
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
10
11
12
13
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MHz, CDCl ) δ 165.4, 163.7, 143.8, 136.1, 134.7, 126.8, 126.2, 123.1, 122.2, 120.1,
3
118.4, 116.5, 111.3, 110.5, 106.2, 56.5 51.4, 48.9, 23.4, 23.3; HRMS (ESI) calcd for
+
C H N O [M+H] 362.1612, found 362.1613.
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0
20
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Data for (6S,12aS)-2-(((E)-furan-2-ylmethylene)amino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (28). This compound was
1
obtained as a pale yellow solid in 90% yield: mp = 237–239 °C; H NMR (400 MHz,
DMSO-d ) δ 11.10 (s, 1H), 8.36 (s, 1H), 7.89 (d, J = 1.6 Hz, 1H), 7.57 (d, J = 7.6 Hz,
6
1H), 7.36 (d, J = 8.0 Hz, 1H), 7.13–7.04 (m, 1H), 7.06–6.97 (m, 1H), 6.96 (d, J = 3.6
Hz, 1H), 6.67 (dd, J = 3.2, 1.6 Hz, 1H), 5.29 (q, J = 6.4 Hz, 1H), 4.56 (d, J = 16.8 Hz,
1H), 4.49–4.40 (m, 2H), 3.53 (dd, J = 15.2, 4.4 Hz, 1H), 2.90 (dd, J = 15.2, 12.0 Hz,
1
3
1H), 1.46 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, DMSO-d ) δ 165.9, 164.1, 149.8,
6
146.1, 139.1, 136.4, 135.9, 126.4, 121.5, 119.3, 118.4, 115.7, 112.8, 111.8, 105.1,
+
56.3, 50.5, 48.6, 23.6, 23.4; HRMS (ESI) calcd for C H N O [M+H] 363.1452,
2
0
19
4
3
found 363.1459.
Data for
(6S,12aS)-
6-methyl-2-(((E)-thiophen-2-ylmethylene)amino)-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (29). This
1
compound was obtained as a pale yellow solid in 90% yield: mp = 242–244 °C; H
NMR (400 MHz, CDCl ) δ 9.16 (s, 1H), 8.60 (s, 1H), 7.58 (d, J = 7.6 Hz, 1H),
3
7.47–7.44 (m, 1H), 7.42–7.36 (m, 2H), 7.21 (td, J = 7.6, 1.2 Hz, 1H), 7.16 (td, J = 7.6,
1.2 Hz, 1H), 7.10 (dd, J = 4.8, 3.6 Hz, 1H), 5.49 (q, J = 6.4 Hz, 1H), 4.55 (d, J = 17.2
Hz, 1H), 4.45 (dd, J = 16.8, 0.8 Hz, 1H), 4.23 (dd, J = 11.6, 4.0 Hz, 1H), 3.69 (dd, J =
1
3
15.6, 4.8 Hz, 1H), 3.08 (dd, J = 15.2, 11.6 Hz, 1H), 1.55 (d, J = 6.4 Hz, 3H); C
NMR (100 MHz, CDCl ) δ 165.9, 164.2, 149.3, 138.8, 136.1, 134.7, 132.0, 129.8,
3
2
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525
526
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528
529
530
531
532
533
534
535
536
537
538
539
540
127.7, 126.2, 122.2, 120.0, 118.3, 111.4, 105.9, 56.6, 53.4, 48.7, 23.5, 22.9; HRMS
+
(ESI) calcd for C H N O S [M+H] 379.1223, found 379.1231.
2
0
19
4
2
Data for (6S,12aS)- 2-(((E)-(1H-imidazol-2-yl)methylene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (30). This
1
compound was obtained as a pale yellow solid in 95% yield: mp = 203–205 °C; H
NMR (400 MHz, DMSO-d ) δ 12.79 (s, 1H), 11.10 (s, 1H), 8.34 (s, 1H), 7.57 (d, J =
6
7.6 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.26 (s, 1H), 7.14 (s, 1H), 7.13–7.04 (m, 1H),
7.02 (t, J = 7.6 Hz, 1H), 5.30 (q, J = 6.4 Hz, 1H), 4.61 (d, J = 16.4 Hz, 1H), 4.52 (d, J
= 17.2 Hz, 1H), 4.50–4.45 (m, 1H), 3.55 (dd, J = 15.6, 4.4 Hz, 1H), 2.92 (dd, J = 15.6,
1
3
11.6 Hz, 1H), 1.47 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, DMSO-d ) δ 165.9,
6
164.2, 142.9, 140.8, 136.4, 135.9, 126.3, 121.5, 119.3, 118.4, 111.8, 105.0, 56.3, 50.7,
+
48.6, 23.6, 23.4; HRMS (ESI) calcd for C H N O [M+H] 363.1564, found
1
9
19
6
2
363.1572.
Data for (6S,12aS)- 6-methyl-2-(((E)-1-phenylethylidene)amino)-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (31). This compound was
1
obtained as a pale red solid in 54% yield: mp = 262–264 °C; H NMR (400 MHz,
CDCl ) δ 8.50 (s, 1H), 7.88 (d, J = 7.2 Hz, 2H), 7.57 (d, J = 7.6 Hz, 1H), 7.51–7.40
3
(m, 3H), 7.37 (d, J = 7.6 Hz, 1H), 7.20 (t, J = 7.2 Hz, 1H), 7.15 (t, J = 7.2 Hz, 1H),
5.48 (q, J = 6.4 Hz, 1H), 4.58 (d, J = 16.8 Hz, 1H), 4.31 (d, J = 17.2 Hz, 1H), 4.25 (dd,
J = 11.6, 4.4 Hz, 1H), 3.75 (dd, J = 15.6, 4.4 Hz, 1H), 3.03 (dd, J = 15.6, 11.6 Hz, 1H),
1
3
2.32 (s, 3H), 1.60 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ 172.0, 166.3,
3
161.8, 136.5, 136.1, 134.8, 131.2, 128.6, 127.3, 126.2, 122.2, 120.0, 118.3, 111.3,
+
106.3, 56.5, 53.4, 48.9, 23.7, 23.5, 17.8; HRMS (ESI) calcd for C H N O [M+H]
2
3
23
4
2
387.1816, found 387.1808.
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5
5
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5
5
5
5
5
41
Data for (6S,12aS)- 2-(((E)-3,3-dimethylbutan-2-ylidene)amino)-6-methyl-
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (32). This
1
compound was obtained as a pale yellow solid in 65% yield: mp = 141–143 °C; H
NMR (400 MHz, CDCl ) δ 8.46 (s, 1H), 7.55 (d, J = 7.6 Hz, 1H), 7.38 (d, J = 8.0 Hz,
3
1H), 7.20 (t, J = 7.6 Hz, 1H), 7.15 (t, J = 7.2 Hz, 1H), 5.46 (q, J = 6.4 Hz, 1H), 4.43
(d, J = 17.2 Hz, 1H), 4.24–4.10 (m, 2H), 3.70 (dd, J = 15.6, 4.4 Hz, 1H), 2.99 (dd, J =
1
3
16.0, 11.6 Hz, 1H), 1.91 (s, 3H), 1.58 (d, J = 6.4 Hz, 3H), 1.24 (s, 9H); C NMR (100
MHz, CDCl ) δ 184.4, 166.3, 161.2, 136.1, 134.8, 126.2, 122.2, 120.0, 118.3, 111.3
3
106.4, 56.4, 52.8, 48.8, 39.5, 27.9, 26.4, 23.5, 15.2; HRMS (ESI) calcd for
+
C H N O [M+H] 367.2129, found 367.2123.
2
1
27
4
2
Data
for
(6S,12aS)-
2-(cyclohexylideneamino)-6-methyl-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (33). This compound was
1
obtained as a pale yellow solid in 68% yield: mp = 122–124 °C; H NMR (400 MHz,
CDCl ) δ 8.37 (s, 1H), 7.56 (d, J = 8.0 Hz, 1H), 7.38 (d, J = 8.0 Hz, 1H), 7.20 (td, J =
3
7.6, 1.2 Hz, 1H), 7.15 (td, J = 7.2, 0.8 Hz, 1H), 5.44 (q, J = 6.4 Hz, 1H), 4.44 (dd, J =
16.8, 1.6 Hz, 1H), 4.24–4.14 (m, 2H), 3.71 (dd, J = 15.6, 4.4 Hz, 1H), 2.97 (ddd, J =
15.6, 11.6 Hz, 1H), 2.49 (t, J = 6.4 Hz, 2H), 2.38–2.20 (m, 2H), 1.91–1.77 (m, 3H),
1
3
1.76–1.63 (m, 3H), 1.58 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ 180.8,
3
166.2, 162.1, 136.1, 134.7, 126.2, 122.2, 120.1, 118.3, 111.3, 106.4, 56.4, 52.9, 48.9,
+
35.5, 30.8, 27.3, 26.3, 25.5, 23.7, 23.5; HRMS (ESI) calcd for C H N O [M+H]
2
1
25
4
2
365.1972, found 365.1969.
Synthesis of (6S,12aS)- 2-(((E)-2,2-dimethylpropylidene)amino)-6-methyl-
2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (34).23
To a solution of compound 4a (0.426 g, 1.5 mmol), Amberlyst–15 (40 mg) in toluene
(40 mL) was added dropwise trimethylacetaldehyde (0.26 g, 3.0 mmol) at room
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582
583
584
585
586
587
588
589
590
temperature. Then the reaction mixture was stir overnight at room temperature. When
TLC analysis showed the complete consumption of compound 4a, the mixture was
raised the temperature to 100 C for 3 h. Then the mixture was concentrated in vacuo,
and the crude product was purified by column chromatography on silica gel
(pretreatment with 1% Et N) eluted with DCM/EA (50:1–20:1) to give 34 as a pale
3
1
yellow solid (0.493 g, yield 93%): Mp = 222–224 ˚C; H NMR (400 MHz, CDCl ) δ
3
8.45 (s, 1H), 7.97 (s, 1H), 7.57 (d, J = 7.6 Hz, 1H), 7.42–7.35 (m, 1H), 7.25–7.16 (m,
1H), 7.16 (td, J = 7.2, 1.2 Hz, 1H), 5.47 (q, J = 6.4 Hz, 1H), 4.41 (d, J = 16.8 Hz, 1H),
4.32 (d, J = 17.2 Hz, 1H), 4.19 (dd, J = 11.2, 4.4 Hz, 1H), 3.69 (dd, J = 15.6, 4.4 Hz,
1
3
1H), 3.06 (dd, J = 15.6, 11.6 Hz, 1H), 1.55 (d, J = 6.4 Hz, 3H), 1.19 (s, 9H); C NMR
(100 MHz, CDCl ) δ 168.0, 166.0, 163.8, 136.1, 134.7, 126.2, 122.2, 120.0, 118.3,
3
111.4, 106.0, 56.4, 52.0, 48.8, 35.9, 27.1, 23.4, 23.0; HRMS (ESI) calcd for
+
C H N O [M+H] 353.1972, found 353.1976.
2
0
25
4
2
Compounds 35–36 were synthesized using the similar procedure as compound 34.
Data for (6S,12aS)- 6-methyl-2-(((E)-octylidene)amino)-2,3,6,7,12,12a-
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (35). This compound was
1
obtained as a pale yellow solid in 47% yield: mp = 64–66 °C; H NMR (400 MHz,
CDCl ) δ 8.66 (d, J = 11.6 Hz, 1H), 7.87 (d, J = 5.6 Hz, 1H), 7.57 (d, J = 7.6 Hz, 1H),
3
7.37 (d, J = 8.0 Hz, 1H), 7.20 (t, J = 7.6 Hz, 1H), 7.15 (t, J = 7.2 Hz, 1H), 5.44 (q, J =
6.4 Hz, 1H), 4.39 (d, J = 16.8 Hz, 1H), 4.26 (d, J = 16.8 Hz, 1H), 4.17 (d, J = 8.8 Hz,
1H), 3.71 (dd, J = 15.6, 2.8 Hz, 1H), 3.04 (dd, J = 15.6, 11.2 Hz, 1H), 2.43 (q, J = 7.2
1
3
Hz, 2H), 1.63–1.49 (m, 5H), 1.41–1.26 (m, 8H), 0.89 (t, J = 6.4 Hz, 3H); C NMR
(100 MHz, CDCl ) δ 165.6, 163.7, 159.0, 136.2 134.7, 126.2, 122.0, 119.9, 118.3,
3
111.4, 105.9, 56.3, 51.0, 48.9, 33.3, 31.7, 29.2, 29.1, 26.5, 23.4, 23.2, 22.7, 14.1.
+
HRMS (ESI) calcd for C H N O [M+H] 395.2442, found 395.2447.
2
3
31
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6
91
Data for (6S,12aS)-2-(((E)-cyclohexylmethylene)amino)-6-methyl-2,3,6,7,12,12a-
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
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08
09
10
11
12
13
14
15
hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione (36). This compound was
1
obtained as a pale yellow solid in 61% yield: mp = 129–131 °C; H NMR (400 MHz,
CDCl ) δ 8.36 (s, 1H), 7.75 (d, J = 6.0 Hz, 1H), 7.58 (d, J = 7.6 Hz, 1H), 7.38 (d, J =
3
8.0 Hz, 1H), 7.25–7.16 (m, 1H), 7.16 (td, J = 7.2, 1.2 Hz, 1H), 5.45 (q, J = 6.4 Hz,
1H), 4.41 (d, J = 16.8 Hz, 1H), 4.28 (dd, J = 16.8, 1.2 Hz, 1H), 4.20 (ddd, J = 11.6,
4.0 Hz, 1H), 3.72 (dd, J = 15.6, 4.4 Hz, 1H), 3.06 (ddd, J = 15.6, 11.6, 0.8 Hz, 1H),
2.49–2.39 (m, 1H), 1.91–1.66 (m, 6H), 1.55 (d, J = 6.4 Hz, 3H), 1.40–1.28 (m, 4H);
1
3
C NMR (100 MHz, CDCl ) δ 165.6, 163.7, 162.8, 136.1, 134.6, 126.2, 122.2, 120.1,
3
118.4, 111.3, 106.3, 56.4, 51.3, 48.8, 41.6, 30.1, 30.0, 25.8, 25.3, 25.3, 23.4, 23.1.
+
HRMS (ESI) calcd for C H N O [M+H] 379.2129, found 379.2126.
2
2
27
4
2
Synthesis
of
(6S,12aS)-
2-(benzylamino)-6-methyl-2,3,6,7,12,12a-
2
4
hexahydropyrazino [1',2':1,6]pyrido[3,4-b]indole-1,4-dione (37). Acylhydrazone
compound 5a (0.45 g, 1.20 mmol) and 30 mL anhydrous methanol were added to a
round-bottomed flask and cooled to 0 C̊ . NaCNBH (0.19 g, 3.00 mmol) was added,
3
and then 15 mL of anhydrous methanol solution containing 1 mL of concentrated
hydrochloric acid was added dropwise. Then the reaction mixture was stirred
overnight at room temperature. When TLC analysis showed the complete
consumption of compound 5a, the mixture was successively washed with a solution
of NaHCO and brine, dried over Na SO , and evaporated under reduced pressure.
3
2
4
The crude product was purified by column chromatography on silica gel eluted with
DCM/MeOH (200:1) to give 37 as a white solid (0.32 g, yield 70%): mp = 94–97 ˚C;
1
H NMR (400 MHz, CDCl ) δ 8.15 (s, 1H), 7.57 (d, J = 7.6 Hz, 1H), 7.43–7.29 (m,
3
6H), 7.21 (t, J = 7.2 Hz, 1H), 7.16 (t, J = 7.2 Hz, 1H), 5.37 (q, J = 6.4 Hz, 1H),
4.14–4.03 (m, 5H), 3.69 (dd, J = 15.6, 4.0 Hz, 1H), 2.94 (dd, J = 15.6, 11.6 Hz, 1H),
2
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3
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
1.53 (d, J = 6.4 Hz, 3H); C NMR (100 MHz, CDCl ) δ 166.1, 165.9, 136.3, 136.1,
3
134.7, 129.3, 128.7, 128.2, 126.2, 122.3, 120.1, 118.3, 111.3, 106.4, 55.8, 53.9, 53.0,
+
48.8, 23.5, 23.2; HRMS (ESI) calcd for C H N O [M+H] 375.1816, found
2
2
23
4
2
375.1811.
Biological Assay.
Each bioassay was repeated three times at 25 ± 1 °C. Activity results were
estimated according to a percentage scale of 0−100 (0, no activity; 100, total kill). The
anti-TMV, fungicidal, and insecticidal activities of the synthesized compounds were
tested using our previously reported methods,25-26 The results are presented as means
± standard errors. The detail biological assays methods were given in Supporting
Information.
RESULTS AND DISCUSSION
Synthesis. The synthesis of the compound 4a was depicted in Figure 3.
1-Methyl-tetrahydro-β-carboline 1 was obtained through the Pictet-Spengler
cyclization reaction by using L-tryptophan as the raw material. Compound 1 reacted
with thionyl chloride and methanol to give methyl ester 2 which subsequently reacted
with chloroacetyl chloride to give the diastereomeric diketone intermediate 3. As a
key step, a rigid diketopiperazine ring was obtained by the microwave-assisted
hydrazinolysis reaction with hydrazine hydrate. Due to the poor solubility of the cis
configuration, the (6S,12aS)-configured indole diketopiperazine hydrazide compound
4a could be obtained by crystallization in a satisfactory yield. Then 4a was reacted
with aromatic aldehydes, aliphatic aldehydes, or ketones to produce the corresponding
(6S,12aS)-configured products 6–36 (Figure 4).
To further investigate the effects of the chirality at the C6 and C12a positions
and in-depth discuss the SARs, the diastereomers (6S, 12aS)-, (6R, 12aS)-, (6R,
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6
6
6
6
6
6
41
12aR)- and (6S, 12aR)-configured indole diketopiperazine acylhydrazone compounds
5a–5d were prepared in a new route (Figure 5). The traditional Pictet-Spengler
cyclization reaction condition generated a large proportion of the cis isomers. In order
to get the more trans products, we changed the conditions. By using tryptophan
42
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65
methyl ester hydrochloride as a raw material and MeOH:H O = 3:1 as a solvent under
2
reflux condition, the trans-methyl ester intermediate could be obtained at a relatively
high ratio. The diastereoisomers were then separated by column chromatography, and
the acylhydrazone compounds 5a–5d were generated via chlorination, hydrazinolysis
and condensation reaction. We further reduced the acylhydrazone compound 5a with
NaCNBH /HCl to give N-benzylamino substituted hydrazide compound 37. Note to
3
mention that, in this reduction reaction, if NaBH was used as the reducing agent, it
4
mainly acted as a base; we could not obtain the reduction product but compound 5d.
Configuration. As mentioned above, using optically pure L-tryptophan methyl
ester as the starting material, the Pictet-Spengler reaction generated an additional
chiral center; therefore a pair of diastereomers 2a and 2b were obtained in a ratio of
63:37 (Figure 5). The two diastereomers was separated by column chromatography
and then transformed to corresponding target compounds 5a and 5b. In order to assign
1
the exact configuration to each other, compound 5a was conducted H NMR and
nuclear overhauser enhancement spectroscopy (NOESY) experiment. In the NOESY
spectrum (Figure 7), the hydrogen of methyl group on the C was observed as a
a
doublet at δ 1.55 ppm, and a quartet at δ 5.49 ppm to H ; there is a NOE effect
a
between them. The quartet peak at δ 4.25 ppm was assigned to H which was split by
b
H and H . The intense nuclear overhauser NOE enhancement observed for H
a
and H
b
c
d
suggests that these two protons were in a cis configuration, the absolute configuration
of compound 5a was definitely assigned as (6S, 12aS), and by extension, that of
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689
690
diastereomer 5b was assigned as (6R, 12aS). The absolute configuration of 5b was
306 confirmed by analysis of its NOESY spectrum.
1
The difference in the H NMR spectra for this diastereoisomers could be easily
seen: due to the different chemical environments, the chemical shifts of H and H in
a
b
the trans configuration were 0.46 and 0.34 ppm higher than that of the cis isomer.
When using optically pure D-tryptophan as the starting material, the absolute
1
stereochemistry of compound 4 was also assigned by analyzing H NMR and NOE
data. In the NOESY experiment (Figure 7), we could find an intense NOE effects
between the H and H , and this information suggested that the H and H was in a cis
a
b
a
b
configuration, so the absolute configuration of compound 4 was (6R, 12aR). In
comparison, in the NOESY experiment of compound 5 (Figure 7), we could not
observe a NOE effects between the H and H . This information suggested that the H
a
b
a
and H was in a trans configuration, so the absolute configuration of compound 5 was
b
(6S, 12aR).
Antiviral Activities. The results of anti-TMV activity of compound 4a, 6–37
were shown in Table 1, and the results of anti-TMV activity of compound 5a–5d were
shown in Table 2. In order to make the antiviral activity results of the synthetic
compounds more reliable, we took the commercial plant virus inhibitor ribavirin and
ningnanmycin as the control.
In Vitro Anti-TMV Activity. The results shown in Table 1 indicated that most of
the target compounds displayed moderate to good inhibitory activity against TMV in
vitro at 500 μg/mL, the activities of part of these compounds, such as compounds 31,
23, 25, 27, 28 was significantly higher than that of ribavirin (36±2%).
It was worth noting that the substituents of the acylhydrazone moiety had a
significant impact on anti-TMV activity. The anti-TMV data of aromatic-aldehyde
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91
hydrazones 6 – 30 indicated that the type, position, and number of substituents on the
benzene ring had a crucial influence on activity. First, the electronic effect of the
benzene ring had a certain influence on anti-TMV activity. As a whole, the anti-TMV
activity of introducing an electron withdrawing group on the benzene ring was higher
than that of the compound with an electron donating group. For example, when the
substituent was at the para position, the trifluoromethyl substituted 7 (37±2%) was
better than the dimethylamino substituted 9 (19±2%); when in the ortho position, the
chlorine substituted 14 (40±1%) was better than the methoxy substituted 19 (29±2%).
In addition, the position and number of substituents on the benzene ring also had a
certain relationship with the antiviral activity. When it was alkoxy substituent, it
manifested as the meta > ortho > para; meanwhile, compared to the bisalkoxy
substitution compounds 20 – 22, the antiviral activities of the monoalkoxy
substitution compounds 17 – 19 were relatively higher. It was noteworthy that the
antiviral activity of the benzo[d][1,3]dioxolane 21 (31±2%) was significantly better
than those of the 3,4-methoxyphenyl compound 20 (0) and benzo[d][1,4]dioxane 22
(18±1%). We speculated that the main reason was that the tension of five-membered
ring made the lone pair electrons of the oxygen atoms unable to conjugate with the
benzene ring, so that the oxygen atoms only exhibited the induced
electron-withdrawing effect. That is, it was the electron-withdrawing group that could
facilitate antiviral activity. Surprisingly, the antiviral activity was significantly
increased when the phenyl ring with a tert-butyl or the benzene ring was replaced by a
naphthyl, example by 8 (41±2%), 23 (53±2%) and 25 (47±3%). Furthermore,
compound 23 exhibited the best antiviral activity in vitro, the introduction of these
large lipophilic groups greatly increased the lipid solubility of the molecule which
availed to the activity. As to the aromatic heterocyclic compounds 26 – 30, the
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