Anti-Mycobacterial N-(2-Arylethyl)quinolin-3-amines Inspired by Marine Sponge-Derived Alkaloid

Abstract

The synthesis and evaluation of simplified analogs of marine sponge-derived alkaloid 3-(phenethylamino)demethyl(oxy)aaptamine were performed to develop novel anti-mycobacterial substances. Ring truncation of the tricyclic benzo[de][1,6]-naphthyridine skeleton effectively weakened the cytotoxicity of the natural product, and the resulting AC-ring analog exhibited good anti-mycobacterial activity. A structure–activity relationship (SAR) study, synthesizing and evaluating some analogs, demonstrated the specificity and importance of the N-(2-arylethyl)quinolin-3-amine skeleton as a promising scaffold for anti-mycobacterial lead compounds.

1. Introduction

Tuberculosis (TB), a bacterial infection caused by Mycobacterium tuberculosis, remains a leading cause of mortality worldwide [1]. According to a World Health Organization report, there are an estimated 10 million new TB cases and 1.5 million deaths annually [2]. Considering the standard regimen, known as directly observed therapy short-course (DOTS), a minimum 6-month TB treatment course is requisite, mainly because most existing anti-TB drugs are effective against M. tuberculosis only during the active state. Therefore, new anti-mycobacterial lead compounds effective against M. tuberculosis are urgently needed to address both active and dormant states. Hypoxic conditions induce the dormant state of Mycobacterium sp., which has a drug susceptibility profile resembling that of latent M. tuberculosis infection, although the physiology of latent M. tuberculosis infection remains unclear [3,4,5].

Marine natural products have garnered considerable attention as rich and promising sources of drug candidates, especially in the field of anti-tubercular drug discovery [6,7]. Based on this background, we have previously established a screening system to isolate anti-dormant mycobacterial substances from marine organisms and marine-derived microorganisms through bioassay-guided separation [8,9]. In a recent study, we discovered 3-(phenethylamino)demethyl(oxy)aaptamine (PDOA, 1) as a promising anti-dormant mycobacterial substance derived from an Indonesian marine sponge of Aaptos sp. (Figure 1). Compound 1 showed potent antimicrobial activity against M. bovis BCG, with a minimum inhibitory concentration (MIC) value of 1.56 µM under both aerobic and hypoxic conditions (Table 1). Remarkably, compound 1 exhibited potent anti-mycobacterial activity against drug-sensitive M. tuberculosis H37Rv, as well as against extensively drug-resistant M. tuberculosis strains, with MIC values ranging between 1.5–6.0 µM [10].

These results imply that compound 1 might be a potential anti-TB drug exerting a novel mechanism of action. However, the scarcity of natural sources has hampered further evaluation. Although the total synthesis of 1 [10,11] can provide a sufficient amount of the compound, lead optimization of the tricyclic benzo[de][1,6]-naphthyridine skeleton might be challenging. In addition, we found that 1 exhibited cytotoxicity against human umbilical vein endothelial cells (HUVECs) with an IC₅₀ value of 1.36 µM, which is comparable with the MIC against M. bovis BCG (Table 1). Cytotoxicity of 1 against some tumor cells has also been reported [12]. To overcome these drawbacks, we engaged in the development of a truncated analog of 1 as a selective anti-TB drug. Herein, we present the synthesis and evaluation of various 3-substituted quinoline derivatives.

2. Results and Discussions

2.1. Synthesis and Evaluation of Truncated Analogs of 1

Generally, natural products have complex chemical structures with various functional groups and exhibit diverse bioactivities by binding to multiple target molecules (proteins). Truncation of some moieties can extract the essential scaffold of the natural product to reduce the number of target proteins without losing specific bioactivity. In addition, a substantial amount of the truncated analog can be easily synthesized owing to its simple structure. Furthermore, downsizing the molecular weight of the compound might improve the absorption, distribution, metabolism, excretion and toxicity (ADMET) profile. Several successful examples of truncated natural product analogs have been reported [13,14,15]. Recently, we developed a simplified analog of cortistatin A, a complex marine-derived anti-angiogenic steroidal alkaloid. The optimized analog, prepared using fewer than 10 steps, was found to exert potent and selective growth inhibitory activity against HUVECs, comparable with that of the natural product, and exhibited potent in vivo antitumor activity [16,17].

Therefore, we simplified the core structure of compound 1 to extract the essential scaffold. An initial structure–activity relationship (SAR) study of 1 and related naturally-occurring congeners 2–4 revealed that the essential functionality of 1 for anti-mycobacterial activity could not be attributed to the tricyclic benzo[de][1,6]-naphthyridine core structure but rather to the 2-phenethylamino side chain [10]. Considering the SAR, we planned to prepare mono- or bicyclic truncated analogs with 2-phenethylamino side chains and evaluate their anti-mycobacterial activity against M. bovis BCG. Figure 2 shows the structures of three bicyclic analogs: AB-ring analog 5, AC-ring analog 6, BC-ring analog 7, and monocyclic analog 8.

First, analog 5 was synthesized, as shown in Scheme 1A. Condensation was performed between homoveratrylamine (9) and Cbz-glycine gave amide 10, which was further converted to dihydroisoquinoline 11 via Bischler–Napieralski cyclization. The following two-step oxidation/aromatization by O₂ yielded isoquinoline 12, and subsequent treatment with 2-phenethyl bromide and NaH afforded the desired AB-ring analog 5 through alkylation and concomitant removal of the Cbz group. Second, AC-ring analog 6 was synthesized as follows (Scheme 1B). The Friedländer reaction [18] with two aldehydes, 13 and 14, and subsequent removal of the Boc group yielded quinolin-3-amine 16. Then, the copper-catalyzed cross-coupling reaction with 2-phenethylboronic acid provided the desired analog 6 [19]. In addition, BC-ring analog 7 was prepared via the C8-bromination of 1,6-naphthyridine (17) and subsequent Buchwald–Hartwig amination with 2-phenethylamine (Scheme 1C). A similar amination reaction toward 3-bromopyridine (19) proceeded smoothly using a BrettPhos-ligated palladium catalyst [20] to provide monocyclic C-ring analog 8 [21] in good yield (Scheme 1D).

Biological evaluation of the synthesized analogs revealed that quinoline analog 6, which mimics the AC ring of 1, exhibited good antibacterial activity against M. bovis BCG under aerobic conditions (Table 1, MIC = 6.25 µM). Conversely, analogs 5 (AB-ring mimic), 7 (BC-ring mimic), and 8 (C-ring mimic) exerted weak anti-mycobacterial activity. Interestingly, analog 6 showed diminished cytotoxicity against HUVECs (IC₅₀ = 18 µM) when compared with analog 1, indicating that the truncation of the B-ring could remove the cytotoxic property of 1. Although analog 6 exhibited weak antibacterial activity against M. bovis BCG under hypoxic conditions (MIC = 50 µM), the initial SAR study revealed that the 3-substituted quinoline skeleton might be a minimal and promising scaffold for anti-mycobacterial drug lead.

2.2. SAR Study of N-(2-Arylethyl)quinolin-3-amine Analog

Next, we prepared congeners of 6 to examine the SAR around the quinoline ring, as depicted in Scheme 2. p-Quinone-type analogs 25 and 32, mimicking the A-ring of 1, were obtained by oxidation of the corresponding quinolinols 24 and 31, respectively, using Fremy’s salt [22]. Compound 23 was prepared from 3-bromoquinolin-5-ol (21) [23], with the side chain attached through Buchwald–Hartwig amination. The synthetic method for 30 was the same as that for 6 (Scheme 2B), starting from isovanillin (26). Thus, 26 was converted to 27 according to the literature [24], and the Friedländer reaction with aldehyde 14 afforded isoquinoline 28. Subsequent removal of the Boc group and a cross-coupling reaction with 2-phenethylboronic acid yielded 30. Selective cleavage of the 8-OCH₃ ether bond from 30 to 31 was achieved by treatment with 48% HBr aq and subsequent oxidation using Fremy’s salt provided 32.

4-Quinolones and related compounds are important core structures of broad-spectrum antibiotics that inhibit DNA gyrase [25]. We also prepared quinolone-type analog 35 anticipating potent and selective anti-mycobacterial activity through bromination of quinolin-4(1H)-one (33) and copper-catalyzed amination [26] with phenethylamine (Scheme 2C).

Analogs 25 and 32 exhibited weakened anti-mycobacterial activity and enhanced cytotoxicity, undoubtedly owing to the quinone structure (Table 1). In contrast, quinolone-type analog 35 exhibited no anti-mycobacterial or cytotoxic activity. These results indicated the uniqueness of the quinoline core structure in the scaffold, and the electron density of the aromatic ring might be pivotal for anti-mycobacterial activity.

We further explored the SAR of the side chains (Scheme 3). To explore the importance of the secondary amine moiety, phenacyl analog 36, N-alkyl analog 37/38, and ether analog 40 were prepared. Compound 36 was obtained through the acylation of quinolin-3-amine (16), and treatment of 6 or quinolin-3-ol (39) with the corresponding alkyl halide yielded 37, 38, and 40, respectively. Moreover, analogs 42–46 were synthesized to examine the appropriate structure of the alkyl chain. Notably, analogs 42–45 were obtained by Buchwald–Hartwig amination between 3-bromoquinoline (41) and the corresponding primary amines, and the alkynyl analog 46 was prepared through the alkylation of 16.

Phenacyl amide analog 36, ether analog 40, and N-propargyl analog 38 exhibited significantly weakened anti-mycobacterial activity, whereas N-methyl analog 37 exhibited antibacterial activity comparable to that of 6 (Table 1). These findings indicate that basic nitrogen at that position is essential for binding to the target molecule responsible for the anti-mycobacterial activity, and the steric hindrance around the nitrogen might interrupt binding. In addition, on comparing the anti-mycobacterial activities of analogs 42–46, we observed that the presence of an aromatic ring at the side chain terminal was indispensable, and the 2-naphthyl analog 44 exhibited the most potent antibacterial activity under hypoxic conditions (MIC 12.5 µM). Conversely, the markedly reduced anti-mycobacterial activity of 1-naphthyl analog 43 further confirmed the importance of the side chain, probably through precise structure recognition by the target molecule.

Table 1. Anti-mycobacterial activity and cytotoxicity of PDOA analogs.

Compound	MIC (Aerobic) 1	MIC (Hypoxic) 1	Cytotoxicity 2
1	1.56	1.56	1.36
5	100	200	11.9
6	6.25	50	18
7	100	50	8.1
8	200	200	>100
25	100	>200	<1.0
32	25	50	<1.0
35	>200	>200	>100
36	100	100	4.9
37	6.25	50	16
38	100	100	18
40	50	100	11
42	50	100	15
43	100	>200	11
44	6.25	12.5	13
45	6.25	50	14
46	>200	>200	53
isoniazid	0.39	>200	—

¹ MIC against M. bovis BCG (µM) under respective conditions. ² IC₅₀ against HUVECs (µM).

Table 1. Anti-mycobacterial activity and cytotoxicity of PDOA analogs.

Compound	MIC (Aerobic) 1	MIC (Hypoxic) 1	Cytotoxicity 2
1	1.56	1.56	1.36
5	100	200	11.9
6	6.25	50	18
7	100	50	8.1
8	200	200	>100
25	100	>200	<1.0
32	25	50	<1.0
35	>200	>200	>100
36	100	100	4.9
37	6.25	50	16
38	100	100	18
40	50	100	11
42	50	100	15
43	100	>200	11
44	6.25	12.5	13
45	6.25	50	14
46	>200	>200	53
isoniazid	0.39	>200	—

¹ MIC against M. bovis BCG (µM) under respective conditions. ² IC₅₀ against HUVECs (µM).

In summary, ring truncation of the marine-derived alkaloid PDOA (1) resulted in the development of N-(2-arylethyl)quinolin-3-amine as a promising scaffold for generating novel anti-mycobacterial substances. The SAR study revealed the specificity and importance of the side chain structure, and the 2-naphthyl analog 44 exhibited good anti-mycobacterial activity under aerobic and hypoxic conditions. Although it remains unclear whether the target molecule of the compound developed in the present study is the same as that of 1, further synthesis and evaluation of various analogs would lead to the development of potent and selective anti-mycobacterial drug candidates. Structural optimization for anti-TB activity/selectivity over cytotoxicity and mechanistic analysis will be undertaken in due course.

3. Materials and Methods

3.1. General

The following instruments were used to obtain physical data: JEOL (Tokyo, Japan) ECS-300 (¹H-NMR: 300 MHz, ¹³C-NMR: 75 MHz), JEOL ECS-400 (¹H-NMR: 400 MHz, ¹³C-NMR: 100 MHz), JEOL ECA-500 (¹H-NMR: 500 MHz, ¹³C-NMR: 125 MHz), and an Agilent (Santa Clara, CA, USA) NMR system (¹H-NMR: 600 MHz, ¹³C-NMR: 150 MHz) spectrometer for ¹H and ¹³C NMR data (Supplementary materials), using tetramethylsilane as an internal standard; a JASCO (Tokyo, Japan) FT/IR-5300 infrared spectrometer for IR spectra; a Waters (Milford, CT, USA) Q-Tof Ultima API mass spectrometer for ESI-TOF MS; and a Hitachi (Tokyo, Japan) L-6000 pump equipped with Hitachi L-4000H UV detector for HPLC. Silica gel (Kanto (Tokyo, Japan) 40–100 μm, Nacalai (Kyoto, Japan) COSMOSIL 75C18-OPN) and pre-coated thin layer chromatography (TLC) plates (Merck 60F₂₅₄, Merck (Darmstadt, Germany) 60RP-18 WF₂₅₄S) were used for column chromatography and TLC, respectively. Spots on the TLC plates were detected by spraying with an acidic p-anisaldehyde solution (p-anisaldehyde: 25 mL, c-H₂SO₄: 25 mL, AcOH: 5 mL, EtOH: 425 mL) or with a phosphomolybdic acid solution (phosphomolybdic acid: 25 g, EtOH: 500 mL) with subsequent heating. Unless otherwise noted, all of the reactions were performed under a N₂ atmosphere. After the workup, the organic layers were dried over anhydrous Na₂SO₄.

3.2. Bacterial Culture

Mycobacterium bovis BCG Pasteur was grown in Middlebrook 7H9 broth (BD, Franklin lakes, NJ, USA) containing 10% OADC (BD), 0.5% glycerol, and 0.05% Tween 80, or on Middlebrook 7H10 agar (BD) containing 10% OADC and 0.5% glycerol.

3.3. Antimicrobial Activity of the Compounds under Aerobic and Hypoxic Conditions

The minimum inhibitory concentrations (MICs) against M. bovis BCG Pasteur were determined using the established MTT method [27]. All of the testing samples were purified with reversed-phase HPLC, and the purity of >99% was confirmed by ¹H-NMR and HPLC. The samples were dissolved in DMSO, and the activity of the samples was evaluated by preparing samples in 2-fold dilution series from 200 µM (final concentration). The mid-log phase of M. bovis BCG (1 × 10⁵ CFU/0.1 mL) was inoculated in a 96-well plate, and the serially diluted sample was added to the 96-well plate. In case of aerobic conditions, bacteria were incubated at 37 °C for 7 days. Alternatively, the hypoxic model was established based on the protocol of Rustad et al., with minor modifications [28]. The mycobacterial bacilli were grown in Middlebrook 7H9 broth at 37 °C under a nitrogen atmosphere containing 0.2% oxygen until the optical density at 600 nm reached 0.8. Subsequently, the bacilli were inoculated in a 96-well plate at the same density under aerobic conditions and incubated at 37 °C under a nitrogen atmosphere containing 0.2% oxygen for 14 days. After incubation, an aliquot (50 µL) of MTT solution (5.0 mg/mL) was added to each well and incubated at 37 °C for an additional 12 h under aerobic or hypoxic condition. The optical density at 560 nm was then measured to determine the MIC value. The reproducibility of the data was confirmed by three independent experiments.

3.4. Assay for Cytotoxicity of Compounds against HUVECs

HUVECs (5 × 10⁵ cells/vial) was purchased from Kurabo Inc. and grown in HuMedia-EG2 medium with growth supplements (Kurabo Inc., Osaka, Japan). HUVECs in the culture medium was plated into each well of 96-well plates (2 × 10³ cells/well/100 µL). After 24 h, the serially diluted compounds, which were dissolved in the medium containing no more than 0.5% EtOH, were added, and then the plates were incubated for an additional 72 h in a humidified atmosphere of 5% CO₂ at 37 °C. The cell proliferation was detected by WST-8 colorimetric reagent (Nacalai Tesque, Inc., Kyoto, Japan). The IC₅₀ value was determined by linear interpolation from the growth inhibition curve.

3.5. Synthesis

3.5.1. Benzyl (2-((3,4-Dimethoxyphenethyl)amino)-2-oxoethyl)carbamate (10)

EDCI·HCl (9.2 g, 48.1 mmol) and HOBt (3.8 g, 25.1 mmol) were added to a solution of homoveratrylamine (9, 4.6 g, 25.4 mmol) and Cbz-glycine (5.0 g, 23.9 mmol) in DMF (100 mL) and the whole mixture was stirred at rt for 2 h. AcOEt (30 mL) and 1 N HCl aq. were added to the mixture at 0 °C and the whole mixture was extracted with AcOEt. The organic phase was successively washed with sat. NaHCO₃ aq. and brine. Removal of the solvent from the organic phase under reduced pressure gave 10 (7.93 g, 89%).

All the spectral data were identical to the reported ones [29].

3.5.2. Benzyl ((6,7-Dimethoxy-3,4-dihydroisoquinolin-1-yl)methyl)carbamate (11)

POCl₃ (11.9 mL, 128 mmol) was added to a solution of 10 (7.93 g, 21.3 mmol) in CH₂Cl₂ (210 mL), preheated at 45 °C. The mixture was stirred with reflux for 27 h. 28% NH₃ aq. was added to the mixture at 0 °C and the whole mixture was extracted with CH₂Cl₂. Removal of the solvent from the organic phase under reduced pressure gave crude 11 (4.07 g, 54%), which was almost pure and was used for the next reaction without further purification.

All the spectral data were identical to the reported ones [29].

3.5.3. Benzyl (6,7-Dimethoxyisoquinoline-1-carbonyl)carbamate (12)

A solution of 11 (10.7 mg, 0.030 mmol) in CHCl₃ (0.5 mL) was stirred for 3 days under air. Removal of the solvent from the mixture under reduced pressure gave a crude product, which was used for the next reaction without further purification.

¹H NMR (400 MHz, CDCl₃) δ: 10.03 (1H, brs), 8.01 (1H, s), 7.63–7.31 (5H, m), 6.68 (1H, s), 5.25 (2H, s), 3.92 (3H, s), 3.91 (3H, s), 3.78 (1H, t, J = 7.8 Hz), 2.66 (2H, t, J = 7.8 Hz). ¹³C NMR (150 MHz, CDCl₃) δ: 161.6, 156.5, 151.6, 150.5, 147.3, 135.1, 131.9, 128.62, 128.58, 118.3, 111.4, 109.8, 67.5, 56.0, 55.9, 47.1, 25.3. IR (KBr): 3020, 1782, 1479, 1216, 1045, 758, 669 cm⁻¹. ESI MS: m/z 369 [M + H]⁺. HR-ESI MS: m/z 369.1450, calcd for C₂₀H₂₁N₂O₅. Found: 369.1461.

Activated carbon (20.5 mg, 100 wt%) was added to a solution of the above product (20.0 mg, 0.054 mmol) in xylene (2.0 mL), and the whole mixture was stirred under an O₂ atmosphere at 120 °C for 10 h. After cooling to rt, the mixture was filtered through a Celite pad. Removal of the solvent from the filtrate under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (n-Hexane/AcOEt = 2:1) to give 12 (5.8 mg, 29%) as a yellow solid.

¹H NMR (300 MHz, CDCl₃) δ: 10.85 (1H, brs), 9.08 (1H, s), 8.33 (1H, d, J = 5.3 Hz), 7.73 (1H, d, J = 5.3 Hz), 7.56–7.33 (5H, m), 7.09 (1H, s), 5.31 (2H, s), 4.08 (3H, s), 4.04 (3H, s). ¹³C NMR (150 MHz, CDCl₃) δ: 164.2, 153.3, 152.2, 151.0, 142.1, 139.1, 135.4, 135.3, 128.7, 128.5, 124.7, 124.3, 105.1, 104.6, 67.6, 56.4, 56.1. IR (KBr): 3020, 1777, 1471, 1216, 1050, 757, 669 cm⁻¹. ESI MS: m/z 389 [M + Na]⁺. HR-ESI MS: m/z 389.1113, calcd for C₂₀H₁₈N₂O₅Na. Found: 389.1117.

3.5.4. 6,7-Dimethoxy-N-phenethylisoquinoline-1-carboxamide (5)

NaH (5.2 mg, 0.11 mmol) was added to a solution of 12 (5.0 mg, 0.014 mmol) in DMF (0.5 mL) at 0 °C and the whole mixture was stirred for 5 min. Phenethyl bromide (20 µL, 0.16 mmol) was added to the mixture and the whole mixture was stirred for 24 h at rt, 48 at 60 °C, and 9 h at 90 °C. After cooling to rt, H₂O (1 mL) was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with preparative TLC (n-Hexane/AcOEt = 2:1) to give 5 (3.3 mg, 72%) as a yellow solid.

¹H NMR (400 MHz, CDCl₃) δ: 9.36 (1H, s), 8.73 (1H, t-like), 8.49 (1H, d, J = 5.4 Hz), 7.83 (1H, d, J = 5.4 Hz), 7.65–7.40 (5H, m), 4.29 (3H, s), 4.23 (3H, s), 4.00–3.91 (2H, m), 3.19 (2H, t, J = 7.3 Hz). ¹³C NMR (150 MHz, CDCl₃) δ: 166.7, 152.8, 151.1, 144.9, 139.1, 139.0, 134.9, 128.8, 128.6, 126.4, 122.9, 105.7, 104.4, 56.2, 56.0, 40.8, 36.0. IR (KBr): 3382, 2972, 1662, 1480, 1216, 760 cm⁻¹. ESI MS: m/z 337 [M + H]⁺. HR-ESI MS: m/z 337.1552, calcd for C₂₀H₂₁N₂O₃. Found: 337.1544.

3.5.5. tert-Butyl quinolin-3-ylcarbamate (15)

4 N NaOH aq. (49 µL, 0.20 mmol) was added dropwise to a solution of 2-aminobenzaldehyde (13, 28.8 mg, 0.18 mmol) and tert-butyl (2-oxoethyl)carbamate (14, 7.9 mg, 0.065 mmol) in MeOH (0.5 mL) and the whole mixture was stirred at rt for 18 h. Removal of the solvent from the mixture under reduced pressure gave a crude product, which was diluted with AcOEt and was then washed with H₂O. Removal of the solvent from the AcOEt phase under reduced pressure gave a crude product, which was purified with preparative TLC (PTLC, CHCl₃/MeOH = 60:1) to give 15 (10.4 mg, 52%) as a white solid.

All the spectral data were identical to the reported ones [30].

3.5.6. Quinolin-3-amine (16)

TFA (120 µL) was added to a solution of 15 (6.4 mg, 0.026 mmol) in CH₂Cl₂ (1.0 mL) at 0 °C and the whole mixture was stirred at rt for 24 h. Sat. NaHCO₃ aq. was added to the mixture and the whole mixture was extracted with CH₂Cl₂. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (CH₂Cl₂/MeOH = 80:1, 1% Et₃N) to give 16 (3.6 mg, 95%)

All the spectral data were identical to the reported ones [31].

3.5.7. N-Phenethylquinolin-3-amine (6)

6 was prepared through the reported method [19]. All the spectral data were identical to the reported ones.

3.5.8. 8-Bromo-1,6-naphthyridine (18)

18 was prepared through the reported method [32]. All the spectral data were identical to the reported ones.

3.5.9. N-Phenethyl-1,6-naphthyridin-8-amine (7)

Pd₂(dba)₃ (0.4 mg, 0.44 µmol) was added to a solution of rac-BINAP (0.6 mg, 0.96 µmol) in toluene (0.4 mL). After stirring at rt for 5 min, 18 (1.7 mg, 0.0081 mmol), 2-phenethylamine (1.1 µL, 0.0089 mmol) and t-BuONa (1.3 mg, 0.014 mmol) were successively added to the mixture and the whole mixture was stirred at 90 °C for 3 h. Removal of the solvent from the mixture under reduced pressure gave a crude product, which was purified with PTLC (CHCl₃/MeOH = 30:1) to give 7 (0.9 mg, 45%) as a tan solid.

¹H NMR (500 MHz, CDCl₃) δ: 8.88 (1H, dd, J = 4.3, 1.7 Hz), 8.59 (1H, s), 8.18 (1H, dd, J = 8.3, 1.7 Hz), 8.04 (1H, s), 7.49 (1H, dd, J = 8.3, 4.3 Hz), 7.39–7.29 (5H, m), 5.91 (1H, brs), 3.71–3.58 (2H, m), 3.09 (2H, t, J = 7.3 Hz). ¹³C NMR (150 MHz, CDCl₃) δ 150.2, 138.1, 138.0, 134.4, 127.8, 127.6, 125.5, 123.6, 121.6, 43.6, 34.4. IR (KBr): 3020, 2927, 1216, 1028, 762 cm⁻¹. MS (ESI-TOF) m/z: 250 [M + H]⁺. HRMS (ESI-TOF) m/z: 250.1344, calcd for C₁₆H₁₆N₃. Found: 250.1344.

3.5.10. N-Phenethylpyridin-3-amine (8)

The flask containing BrettPhos/BrettPhos precatalyst (1:1, 13.2 mg, 0.02 mmol) and K₂CO₃ (331 mg, 2.4 mmol) was evacuated and was filled by Ar. 1,4-Dioxane (2.0 mL) was added to the flask and the whole mixture was stirred at rt for 10 min. 3-Bromopyridine (19, 96 µL, 1.0 mmol) and 2-phenethylamine (0.15 mL, 1.2 mmol) were then added to the mixture, and the whole mixture was stirred at reflux (oil bath temp. 110 °C) for 24 h. H₂O was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the AcOEt phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (n-Hexane/AcOEt = 1:1) to give 8 (148 mg, 71%) as a colorless solid.

All the spectral data were identical to the reported ones [21].

3.5.11. 3-Bromoquinolin-5-ol (21)

21 was prepared from commercially available 5-nitroquinoline (20) through the reported method [23]. All the spectral data were identical to the reported ones.

3.5.12. 3-Bromo-5-(methoxymethoxy)quinoline (22)

Chloromethyl methyl ether (84 μL, 1.10 mmol) and K₂CO₃ (408 mg, 2.95 mmol) were added to a solution of 21 (225 mg, 1.00 mmol) in acetone (5 mL) and the whole mixture was stirred at rt for 2 h. H₂O was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the AcOEt phase under reduced pressure gave a crude product containing 22, which was used for the next reaction without further purification.

3.5.13. 5-(Methoxymethoxy)-N-phenethylquinolin-3-amine (23)

An aliquot of 22 (53.6 mg, 0.20 mmol), 2-phenethylamine (63 μL, 0.399 mmol), Pd₂(dba)₃ (19.2 mg, 21.0 μmol), rac-BINAP (23.5 mg, 37.7 μmol), and t-BuONa (43.5 mg, 0.453 mmol) were dissolved in toluene (2 mL) and the whole mixture was stirred at 80 °C for 17 h. After cooling to rt, the reaction mixture was filtered through a Celite pad. The filtrate was concentrated under reduced pressure to give a crude product, which was used for the next reaction without further purification.

3.5.14. 3-(Phenethylamino)quinolin-5-ol (24)

Conc. HCl aq. (0.3 mL) was added to a solution of 23 (49.2 mg, 0.160 mmol) in MeOH (0.9 mL) and the whole mixture was stirred at rt for 3 h. The reaction mixture was neutralized with sat. NaHCO₃ aq. And the whole mixture was extracted with CHCl₃ containing 10% MeOH. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (CHCl₃/MeOH = 10:1) to give 24 (29.9 mg, 70% in 3 steps) as a yellow solid.

¹H NMR (500 MHz, CDCl₃) δ: 9.30 (brs, 1H), 8.39 (d, J = 2.9 Hz, 1H), 7.61 (d, J = 2.7 Hz, 1H), 7.59 (d, J = 8.5 Hz, 1H), 7.33 (t, J = 7.3 Hz, 2H), 7.26–7.23 (m, 3H), 7.20 (d, J = 8.0 Hz, 1H), 6.86 (dd, J = 7.6, 0.6 Hz, 1H), 3.99 (brs, 1H), 3.52 (t, J = 6.9 Hz, 2H), 2.99 (t, J = 6.9 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ: 151.4, 142.6, 142.4, 140.8, 138.8, 128.8 (2C), 128.7 (2C), 126.6, 125.2, 121.5, 119.8, 109.5, 106.9, 44.7, 34.9. IR (KBr): 3413, 3019, 1608, 1476 cm^–1. ESI MS: m/z 265 (M + H)⁺. HR-ESI MS: m/z 265.1341, calcd for C₁₇H₁₇N₂O. Found: 265.1342.

3.5.15. 3-(Phenethylamino)quinoline-5,8-dione (25)

Fremy’s salt (60%, 76.2 mg, ca. 0.170 mmol) was dissolved to a solution of KH₂PO₄ (204 mg, 1.50 mmol) in H₂O (30 mL), and a solution of 24 (15.0 mg, 56.7 μmol) in acetone (8 mL) was added dropwise to the mixture. After stirring the whole mixture at rt for 1 h, acetone was removed from the mixture under reduced pressure, and the resulting aqueous phase was extracted with CH₂Cl₂. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with PTLC (CHCl₃/MeOH = 50:1) to give 25 (4.6 mg, 29%) as a red-purple solid.

¹H NMR (600 MHz, CDCl₃) δ: 8.28 (d, J = 2.9 Hz, 1H), 7.34 (t, J = 7.5 Hz, 2H), 7.32 (d, J = 2.9 Hz, 1H), 7.27 (t, J = 7.2 Hz, 1H), 7.22 (d, J = 7.3 Hz, 2H), 7.00 (d, J = 10.3 Hz, 1H), 6.91 (d, J = 10.3 Hz, 1H), 4.70 (brs, 1H), 3.59 (q, J = 6.5 Hz, 2H), 2.99 (t, J = 6.9 Hz, 2H). ¹³C NMR (150 MHz, CDCl₃) δ: 185.8, 182.2, 147.0, 140.9, 139.7, 137.8, 137.3, 137.0, 130.5, 128.9 (2C), 128.7 (2C), 127.0, 111.7, 44.1, 34.9. IR (KBr): 3619, 3020, 1672, 1579 cm^–1. ESI MS: m/z 279 (M + H)⁺. HR-ESI MS: m/z 279.1134, calcd for C₁₇H₁₅N₂O₂. Found: 279.1127.

3.5.16. N-Phenethylquinolin-3-amine (27)

27 was prepared from isovanillin (26) through the reported method [24]. All the spectral data were identical to the reported ones.

3.5.17. tert-Butyl (7,8-dimethoxyquinolin-3-yl)carbamate (28)

4 N NaOH aq. (124 µL, 2.4 mmol) was added dropwise to a solution of 27 (25.1 mg, 0.21 mmol) and 14 (149 mg, 0.93 mmol) in MeOH (1.0 mL), and the whole mixture was stirred at rt for 30 h. MeOH was removed from the mixture under reduced pressure, and the resulting aqueous phase was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (n-hexane/AcOEt = 1:1) to give 28 (19.2 mg, 30%) as a tan oil.

¹H NMR (300 MHz, CDCl₃) δ: 8.63 (1H, s), 8.50 (1H, br), 7.49 (1H, d, J = 9.0 Hz), 7.32 (1H, d, J = 9.0 Hz), 7.08 (1H, s), 4.07 (3H, s), 3.99 (3H, s), 1.52 (9H, s). ¹³C NMR (151 MHz, CDCl₃) δ 153.1, 150.3, 143.8, 143.0, 139.4, 130.9, 124.4, 122.9, 122.0, 116.2, 61.7, 56.9, 28.3. IR (KBr): 3433, 3020, 2401, 1712, 1525, 1370, 1216, 758 cm⁻¹. ESI MS: m/z 327 [M + Na]⁺. HR-ESI MS: m/z 327.1321, calcd for C₁₆H₂₀N₂O₄Na. Found: 327.1305.

3.5.18. 7,8-Dimethoxyquinolin-3-amine (29)

TFA (0.17 mL, 2.2 mmol) was added to a solution of 28 (34.8 mg, 0.11 mmol) in CH₂Cl₂ (1.0 mL) at 0 °C, and the whole mixture was stirred at rt for 3 h. Sat. NaHCO₃ aq. was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with PTLC (CHCl₃/MeOH = 30:1) to give 29 (14.0 mg, 60%) as a tan oil.

¹H NMR (500 MHz, CDCl₃) δ: 8.54 (1H, d, J = 2.7 Hz), 7.32 (1H, d, J = 9.1 Hz), 7.27 (1H, d, J = 9.1 Hz), 7.21 (1H, d, J = 2.7 Hz), 4.10 (3H, s), 3.98 (3H, s), 3.83 (2H, brs). ¹³C NMR (151 MHz, CDCl₃) δ 148.3, 143.7, 143.4, 138.5, 137.8, 125.4, 121.1, 116.5, 115.3, 61.8, 57.2. IR (KBr): 3394, 3019, 2400, 1626, 1484, 1347, 1216, 1109, 768 cm⁻¹. MS (ESI-TOF) m/z: 205 [M + H]⁺. HRMS (ESI-TOF) m/z: 205.0977, calcd for C₁₁H₁₃N₂O₂. Found: 205.0986.

3.5.19. 7,8-Dimethoxy-N-phenethylquinolin-3-amine (30)

Pyridine (6.3 µL, 0.078 mmol) and Cu(OAc)₂ (6.1 mg, 0.034 mmol) were added to a solution of 29 (5.3 mg, 0.026 mmol) in 1,4-dioxane (2.0 mL) and the whole mixture was stirred under reflux for 15 min. 2-Phenethylboronic acid (5.1 mg, 0.034 mmol) was added to the mixture and the whole mixture was further stirred under reflux for 14 h. After cooling to rt, H₂O was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with PTLC (CHCl₃/MeOH = 30:1) to give 30 (3.0 mg, 38%) as a red-purple solid.

¹H NMR (500 MHz, CDCl₃) δ: 8.42 (1H, d, J = 2.8 Hz), 7.36–7.32 (3H, m), 7.28–7.20 (4H, m), 7.02 (1H, d, J = 2.8 Hz), 4.10 (3H, s), 3.98 (3H, s), 3.91 (1H, t, J = 5.5 Hz), 3.49 (2H, dd, J = 12.9, 6.8 Hz), 3.00 (2H, t, J = 7.0 Hz). ¹³C NMR (150 MHz, CDCl₃) δ 148.5, 143.9, 143.7, 140.1, 138.8, 137.2, 128.8, 126.7, 125.7, 121.1, 116.5, 110.7, 61.8, 57.3, 44.8, 35.1. IR (KBr): 3413, 3020, 2400, 1610, 1511, 1382, 1216, 773 cm⁻¹. MS (ESI-TOF) m/z: 309 [M + H]⁺. HRMS (ESI-TOF) m/z: 309.1603, calcd for C₁₉H₂₁N₂O₂. Found: 309.1618.

3.5.20. 7-Methoxy-3-(phenethylamino)quinolin-8-ol (31)

A solution of 30 (30.5 mg, 98.9 μmol) in 48% HBr aq. (2.5 mL) was stirred at 100 °C for 3 h. Sat. NaHCO₃ aq. was added to the mixture and the whole mixture was extracted with CH₂Cl₂. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with PTLC (CHCl₃/MeOH = 20:1) to give 31 (19.8 mg, 68%) as a red-purple solid.

¹H NMR (500 MHz, CDCl₃) δ: 8.28 (s, 1H), 7.37 (t, J = 7.2 Hz, 2H), 7.31–7.24 (m, 4H), 7.13 (d, J = 9.2 Hz, 1H), 7.06 (s, 1H), 4.02 (s, 3H), 3.51 (t, J = 6.3 Hz, 2H), 3.02 (t, J = 6.3 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ: 142.8, 141.8, 141.1, 140.7, 138.8, 132.7, 128.8 (4C), 126.7, 124.8, 117.4, 115.5, 110.9, 57.6, 44.8, 35.0. IR (KBr): 3154, 2932, 2253, 1791, 1609, 1469, 1383 cm⁻¹. MS (ESI-TOF) m/z: 295 [M + H]⁺. HRMS (ESI-TOF) m/z: 295.1441, calcd for C₁₈H₁₉N₂O₂. Found: 295.1452.

3.5.21. 7-Methoxy-3-(phenethylamino)quinoline-5,8-dione (32)

Using the same synthetic procedure as that of 25, 31 (12.0 mg, 40.7 μmol) was converted to 32 (6.0 mg, 47%) as a red-purple solid.

¹H NMR (600 MHz, CDCl₃) δ 8.24 (d, J = 2.7 Hz, 1H), 7.35 (t, J = 7.0 Hz, 3H), 7.28 (d, J = 7.3 Hz, 1H), 7.22 (d, J = 7.5 Hz, 2H), 6.11 (s, 1H), 4.64 (s, 1H), 3.91 (s, 3H), 3.60 (q, J = 6.5 Hz, 2H), 2.99 (t, J = 6.8 Hz, 2H). ¹³C NMR (150 MHz, CDCl₃) δ: 184.7, 176.9, 161.5, 147.3, 140.4, 137.7, 136.4, 130.9, 128.9 (4C), 128.7, 127.0, 111.7, 108.4, 56.6, 44.0, 34.9. IR (KBr): 2253, 1672, 1646, 1579, 1260, 1231, 1073 cm⁻¹. ESI MS: m/z 331 (M + Na)⁺. HR-ESI MS: m/z 331.1059, calcd for C₁₈H₁₆N₂O₃Na. Found: 331.1047.

3.5.22. 3-Bromoquinolin-4(1H)-one (34)

Bromine (52 μL, 1.00 mmol) was added to a solution of quinolin-4(1H)-one (33, 147 mg, 1.01 mmol) in AcOH (2 mL) and the whole mixture was stirred at reflux (oil bath temp. 120 °C) for 2 h. After cooling to rt, ice water (8 mL) and 1 N Na₂S₂O₃ aq. (2 mL) were added to the mixture, and the whole mixture was vigorously stirred for 15 min. Suction filtration of the precipitated white solid gave 34 (198 mg, 88%).

All the spectral data were identical to the reported ones [33].

3.5.23. 3-(Phenethylamino)quinolin-4(1H)-one (35)

CuSO₄ (0.3 mg, 1.88 μmol) was added to a solution of 34 (44.8 mg, 0.200 mmol) in 2-phenethylamine (200 μL, 1.71 mmol) and the whole mixture was stirred at 150 °C for 56 h. H₂O was added to the mixture and the whole mixture was extracted with CH₂Cl₂. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (hexane/AcOEt = 1:1 then CHCl₃/MeOH = 10:1) to give 35 (34.3 mg, 27%) as a yellow solid.

¹H NMR (600 MHz, CDCl₃) δ: 11.66 (brs, 1H), 8.38 (d, J = 8.3 Hz, 1H), 7.53 (d, J = 8.5 Hz, 1H), 7.43 (td, J = 8.4, 1.5 Hz, 1H), 7.33 (d, J = 5.2 Hz, 1H), 7.22–7.19 (m, 3H), 7.17–7.12 (m, 3H), 4.66 (brs, 1H), 3.30 (t, J = 7.2 Hz, 2H), 2.94 (t, J = 7.2 Hz, 2H).¹³C NMR (150 MHz, CDCl₃) δ: 170.4, 139.1, 137.5, 133.1, 130.1, 128.6 (2C), 128.5 (2C), 126.4, 125.0, 122.2, 121.6, 118.4, 117.5, 46.8, 35.5. IR (KBr): 3063, 2939, 1633, 1559, 1497, 1460, 754, 699 cm^–1. ESI MS: m/z 265 (M + H)⁺. HR-ESI MS: m/z 265.1341, calcd for C₁₇H₁₇N₂O. Found: 265.1341.

3.5.24. 2-Phenyl-N-(quinolin-3-yl)acetamide (36)

A solution of phenacyl chloride (93 μL, 0.704 mmol) in CH₂Cl₂ (2 mL) was added dropwise to a solution of 16 (68.4 mg, 0.474 mmol) and pyridine (402 μL, 4.99 mmol) in CH₂Cl₂ (3 mL) and the whole mixture was stirred at rt for 7 h. Sat. NH₄Cl aq. was added to the mixture and the whole mixture was extracted with CH₂Cl₂. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (hexane/AcOEt = 1:1) to give 36 (82.5 mg, 66%) as a white solid.

¹H NMR (600 MHz, CDCl₃) δ: 8.71 (d, J = 2.5 Hz, 1H), 8.60 (d, J = 2.6 Hz, 1H), 8.18 (s, 1H), 7.98 (d, J = 8.4 Hz, 1H), 7.73 (d, J = 8.2 Hz, 1H), 7.59 (t, J = 7.6 Hz, 1H), 7.50 (t, J = 7.5 Hz, 1H), 7.37 (t, J = 7.4 Hz, 1H), 7.34–7.30 (m, 3H), 3.79 (s, 2H). ¹³C NMR (150 MHz, CDCl₃) δ: 170.1, 145.0, 143.8, 134.0, 131.4, 129.4 (2C), 129.2 (2C), 128.6, 128.4, 128.1, 127.7 (2C), 127.3, 124.1, 44.5. IR (KBr): 3019, 1689, 1530 cm⁻¹. ESI MS: m/z 263 (M + H)⁺. HR-ESI MS: m/z 263.1179, calcd for C₁₇H₁₅N₂O. Found: 263.1170.

3.5.25. N-Methyl-N-phenethylquinolin-3-amine (37)

A solution of 6 (25.0 mg, 0.101 mmol) in 2,2,2-trifluoroethanol (TFE, 0.25 mL) was added to a solution of HCHO aq. (18 μL, 0.500 mmol) in TFE (0.25 mL) and the whole mixture was stirred at rt for 5 min. NaBH₄ (7.6 mg, 0.201 mmol) was added to the mixture and the whole mixture was stirred at rt for 13 h. The reaction was quenched by the addition of H₂O, and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (CHCl₃/MeOH = 20:1) to give 37 (20.4 mg, 77%) as a pale yellow oil.

¹H NMR (600 MHz, CDCl₃) δ: 8.69 (d, J = 3.0 Hz, 1H), 7.96 (dd, J = 6.3, 2.6 Hz, 1H), 7.64 (dd, J = 7.5, 2.1 Hz, 1H), 7.45–7.40 (m, 2H), 7.31 (t, J = 7.5 Hz, 2H), 7.25–7.21 (m, 3H), 7.11 (d, J = 3.0 Hz, 1H), 3.73 (t, J = 7.5 Hz, 2H), 3.00 (s, 3H), 2.90 (t, J = 7.6 Hz, 2H). ¹³C NMR (150 MHz, CDCl₃) δ: 142.3, 141.2, 140.9, 139.1, 129.3, 128.8 (4C), 128.6, 126.8, 126.4, 126.0, 124.9, 112.2, 54.6, 38.5, 33.2. IR (KBr): 3019, 2957, 1599 cm⁻¹. ESI MS: m/z 263 (M + H)⁺. HR-ESI MS: m/z 263.1543, calcd for C₁₈H₁₉N₂. Found: 263.1550.

3.5.26. N-Phenethyl-N-(prop-2-yn-1-yl)quinolin-3-amine (38)

K₂CO₃ (2.2 mg, 15.9 μmol) and propargyl bromide (52 μL, 0.480 mmol) were added to a solution of 6 (40.0 mg, 0.161 mmol) in acetone (2.4 mL) and the whole mixture was stirred at 60 °C for 32 h. After cooling to rt, H₂O was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (hexane/AcOEt = 2:1) to give 38 (7.0 mg, 15%) as a pale yellow oil.

¹H NMR (500 MHz, CDCl₃) δ: 8.71 (d, J = 2.9 Hz, 1H), 7.97 (dd, J = 6.3, 2.9 Hz, 1H), 7.69–7.67 (m, 1H), 7.49–7.44 (m, 2H), 7.34–7.31 (m, 3H), 7.25–7.23 (m, 2H), 4.09 (t, J = 2.3 Hz, 2H), 3.76 (t, J = 7.4 Hz, 2H), 3.01 (t, J = 7.4 Hz, 2H), 2.27 (t, J = 5.2 Hz, 1H). ¹³C NMR (125 MHz, CDCl₃) δ: 142.2, 142.1, 141.3, 139.1, 129.1, 129.0, 128.9 (2C), 128.8 (2C), 127.0, 126.7, 126.4, 125.8, 114.8, 79.2, 73.0, 53.5, 40.5, 34.1. IR (KBr): 3155, 2253, 1217 cm⁻¹. ESI MS: m/z 287 (M + H)⁺. HR-ESI MS: m/z 287.1543, calcd for C₂₀H₁₉N₂. Found: 287.1539.

3.5.27. 3-Phenethoxyquinoline (40)

NaH (60.0 mg, ca. 1.50 mmol) and 2-phenethyl bromide (205 μL, 1.52 mmol) were added to a solution of quinolin-3-ol (39) (149 mg, 1.03 mmol) in DMF (2 mL) and the whole mixture was stirred at rt for 18 h. Sat. NaHCO₃ aq. was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (hexane/EtOAc = 1:1) to give 40 (108 mg, 42%) as a pale yellow oil.

¹H NMR (600 MHz, CDCl₃) δ: 8.69 (d, J = 2.9 Hz, 1H), 8.05 (d, J = 8.4 Hz, 1H), 7.69 (dd, J = 8,2, 1.5 Hz, 1H), 7.55 (td, J = 8.3, 1.5 Hz, 1H), 7.50 (td, J = 8.2, 1.3 Hz, 1H), 7.37–7.32 (m, 5H), 7.28 (tt, J = 6.9, 1.9 Hz, 1H), 4.30 (t, J = 7.1 Hz, 2H), 3.20 (t, J = 7.1 Hz, 2H). ¹³C NMR (150 MHz, CDCl₃) δ: 152.2, 144.7, 143.4, 137.7, 129.1, 129.0 (2C), 128.7, 128.6 (2C), 127.0, 126.7, 126.6 (2C), 112.9, 68.9, 35.5. IR (KBr): 3019, 2953, 1604, 1346, 1216 cm⁻¹. ESI MS: m/z 250 (M + H)⁺. HR-ESI MS: m/z 250.1232, calcd for C₁₇H₁₆NO. Found: 250.1241.

3.5.28. N-(2-Cyclohexylethyl)quinolin-3-amine (42)

With the same synthetic procedure as that of 7, 3-bromoquinoline (41, 61 μL, 0.454 mmol) was converted to 42 (102.1 mg, 88%) using 2-(cyclohexyl)ethylamine (72 μL, 0.500 mmol) as a colorless oil.

¹H NMR (500 MHz, CDCl₃) δ: 8.42 (d, J = 2.8 Hz, 1H), 7.92 (dd, J = 7.3, 1.6 Hz, 1H), 7.60 (dd, J = 7.8, 1.7 Hz, 1H), 7.45–7.35 (m, 2H), 6.98 (d, J = 2.8 Hz, 1H), 3.92 (s, 1H), 3.21 (td, J = 7.3, 4.3 Hz, 2H), 2.60 (d, J = 1.4 Hz, 1H), 1.82–1.63 (m, 3H), 1.63–1.54 (m, 2H), 1.49–1.37 (m, 1H), 1.33–1.11 (m, 3H), 0.98 (qd, J = 11.9, 3.1 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ: 143.4, 141.9, 141.8, 129.6, 129.0, 126.8, 125.8, 124.6, 109.6, 41.3, 36.7, 35.5, 33.3, 26.5, 26.2. IR (KBr): 3423, 3019, 2925, 2853, 1611 cm⁻¹. ESI MS: m/z 255 (M + H)⁺. HR-ESI MS: m/z 255.1856, calcd for C₁₇H₂₃N₂. Found: 255.1866.

3.5.29. N-(2-(Naphthalen-1-yl)ethyl)quinolin-3-amine (43)

With the same synthetic procedure as that of 7, 41 (9.4 μL, 70 µmol) was converted to 43 (13.5 mg, 64%) using 2-(naphthalen-1-yl)ethylamine (17.1 mg, 0.10 mmol) as a yellow solid.

¹H NMR (600 MHz, CDCl₃) δ: 8.37 (d, J = 2.8 Hz, 1H), 8.07 (d, J = 8.2 Hz, 1H), 7.95 (dd, J = 6.6, 2.5 Hz, 1H), 7.90 (dd, J = 7.8, 1.6 Hz, 1H), 7.79 (d, J = 8.2 Hz, 1H), 7.61–7.59 (m, 1H), 7.56–7.51 (m, 2H), 7.45–7.40 (m, 3H), 7.38 (d, J = 6.9 Hz, 1H), 7.05 (d, J = 8.2 Hz, 1H), 4.06 (brs, 1H), 3.65 (q, J = 6.5 Hz, 2H), 3.47 (t, J = 6.9 Hz, 2H). ¹³C NMR (150 MHz, CDCl₃) δ: 143.4, 142.1, 141.2, 134.8, 134.0, 131.8, 129.4, 129.0 (2C), 127.5, 126.9, 126.8, 126.2, 125.9, 125.8, 125.5, 124.9, 123.3, 110.2, 43.9, 32.1. IR (KBr): 3049, 1610, 1510, 1390, 1220, 778 cm⁻¹. ESI MS: m/z 299 (M + H)⁺. HR-ESI MS: m/z 299.1548, calcd for C₂₁H₁₉N₂. Found: 299.1537.

3.5.30. N-(2-(Naphthalen-2-yl)ethyl)quinolin-3-amine (44)

With the same synthetic procedure as that of 7, 41 (46 μL, 0.35 mmol) was converted to 44 (97.5 mg, 92%) using 2-(naphthalen-2-yl)ethylamine (66.4 mg, 0.39 mmol) as a yellow solid.

¹H NMR (500 MHz, CDCl₃) δ 8.39 (d, J = 2.8 Hz, 1H), 7.97–7.91 (m, 1H), 7.87–7.78 (m, 3H), 7.72–7.68 (m, 1H), 7.67–7.59 (m, 1H), 7.53–7.36 (m, 5H), 7.10 (d, J = 2.8 Hz, 1H), 4.03 (brs, 1H), 3.61 (t, J = 6.9 Hz, 2H), 3.18 (t, J = 6.9 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ 143.4, 142.1, 141.2, 136.2, 133.6, 132.3, 129.5, 128.9, 128.5, 127.7, 127.5, 127.2, 127.0 (2C), 126.3, 125.9, 125.7, 125.0, 110.4, 44.5, 35.1. IR (KBr): 3413, 3019, 1611, 1516, 1030 cm⁻¹. ESI MS: m/z 299 (M + H)⁺. HR-ESI MS: m/z 299.1548, calcd for C₂₁H₁₉N₂. Found: 299.1548.

3.5.31. N-(2-(Thiophen-2-yl)ethyl)quinolin-3-amine (45)

With the same synthetic procedure as that of 7, 41 (67 μL, 0.50 mmol) was converted to 45 (114 mg, 90%) using 2-(thiophen-2-yl)ethylamine (117 mg, 1.0 mmol) as a yellow solid.

¹H NMR (500 MHz, CDCl₃) δ 8.38 (d, J = 2.9 Hz, 1H), 7.99–7.92 (m, 1H), 7.66–7.58 (m, 1H), 7.49–7.37 (m, 2H), 7.18 (dd, J = 5.1, 1.2 Hz, 1H), 7.03 (d, J = 2.8 Hz, 1H), 6.97 (dd, J = 5.1, 3.4 Hz, 1H), 6.88 (dd, J = 3.4, 1.1 Hz, 1H), 4.25 (brs, 1H), 3.50 (t, J = 8.3 Hz, 2H), 3.19 (t, J = 6.7 Hz, 2H). ¹³C NMR (125 MHz, CDCl₃) δ: 143.3, 142.0, 141.1, 141.0, 129.4, 128.8, 127.0, 126.9, 125.8, 125.4, 124.9, 124.0, 110.2, 44.7, 29.1. IR (KBr): 3405, 3256, 3054, 2927, 2849, 1613, 1517, 1222, 700 cm⁻¹. ESI MS: m/z 255 (M + H)⁺. HR-ESI MS: m/z 255.0956, calcd for C₁₅H₁₅N₂S. Found: 255.0946.

3.5.32. N-(But-3-yn-1-yl)quinolin-3-amine (46)

4-Bromobut-1-yne (92 μL, 0.997 mmol) was added to a solution of 16 (145 mg, 1.00 mmol) K₂CO₃ (153 mg, 1.11 mmol) in DMF (6 mL) and the whole mixture was stirred at 85 °C for 11 h. After cooling to rt, H₂O was added to the mixture and the whole mixture was extracted with AcOEt. Removal of the solvent from the organic phase under reduced pressure gave a crude product, which was purified with SiO₂ column chromatography (hexane/AcOEt = 1:1) to give 46 (14.8 mg, 7%) as a yellow solid.

¹H NMR (600 MHz, CDCl₃) δ: 8.47 (d, J = 2.9 Hz, 1H), 7.95–7.93 (m, 1H), 7.64–7.61 (m, 1H), 7.45–7.41 (m, 2H), 7.05 (d, J = 2.8 Hz, 1H), 4.28 (brs, 1H), 3.43 (q, J = 6.3 Hz, 2H), 2.60 (td, J = 6.6, 2.7 Hz, 2H), 2.09 (t, J = 2.6 Hz, 1H). ¹³C NMR (150 MHz, CDCl₃) δ: 143.4, 142.3, 140.9, 129.3, 129.0, 127.0, 125.9, 125.1, 110.5, 81.2, 70.5, 42.0, 18.8. IR (KBr): 3409, 3307, 3154, 3056, 1793, 1614, 1515, 1483 cm⁻¹. ESI MS: m/z 197 (M + H)⁺. HR-ESI MS: m/z 197.1079, calcd for C₁₃H₁₃N₂. Found: 197.1070.