Bimetallic Iron–Palladium Catalyst System as a Lewis-Acid for the Synthesis of Novel Pharmacophores Based Indole Scaffold as Anticancer Agents

Abstract

The Friedel–Crafts reaction between substituted indoles as nucleophiles with chalcones-based benzofuran and benzothiophene scaffolds was carried out by employing a highly efficient bimetallic iron–palladium catalyst system. This catalytic approach produced the desired bis-heteroaryl products with low catalyst loading, a simple procedure, and with acceptable yield. All synthesized indole scaffolds 3a–3s were initially evaluated for their cytotoxic effect against human fibroblast BJ cell lines and appeared to be non-cytotoxic. All non-cytotoxic compounds 3a–3s were then evaluated for their anticancer activities against cervical cancer HeLa, prostate cancer PC3, and breast cancer MCF-7 cell lines, in comparison to standard drug doxorubicin, with IC₅₀ values 1.9 ± 0.4 µM, 0.9 ± 0.14 µM and 0.79 ± 0.05 µM, respectively, and appeared to be moderate to weak anticancer agents. Fluoro-substituted chalcone moiety-containing compounds, 3b appeared to be the most active member of the series against cervical HeLa (IC₅₀ = 8.2 ± 0.2 µM) and breast MCF-7 cancer cell line (IC₅₀ = 12.3 ± 0.04 µM), whereas 6-fluroindol-4-bromophenyl chalcone-containing compound 3e (IC₅₀ = 7.8 ± 0.4 µM) appeared to be more active against PC3 prostate cancer cell line.

1. Introduction

Nitrogen heterocycles (natural and synthetic) are key components of several biochemical, and therefore possess interesting biological properties. Indoles are one such class of organic heterocyclic compounds that occur frequently as a privileged structural motif in many synthetic and natural products with versatile pharmacological activities [1]. In many cases they have widespread uses as cholesterol lowering agents, antiviral, antibacterial, antifungal, and as anticancer compounds [2]. Some of them regulate cellular signaling and numerous neuropsychological processes. The indole structures have a rich history in chemistry beginning with the study of dyes in the mid-19th century. Despite the reported toxicity of some indole-containing compounds, several of them possess clinically beneficial properties. The natural products vinblastine and vincristine, isolated from C. roseus [3], are active against leukemia, lymphoma, breast, lung and other cancers (Figure 1) [4]. Analogues of these compounds are in use for the treatment of a variety of cancers [5]. Numerous other indole-containing compounds have been shown to possess anti-cancer activity, as well as a myriad of other biological properties [6,7,8]. Because of the prevalence of the indole moiety in biologically active compounds, it is considered a “privileged structure” and that makes it a logical motif to improve biological activity of synthetic compounds [9]. The indole moiety is also found in many natural products and comprises a major subset for the alkaloid class of natural products. For example, ajmalicine is an anti-hypertensive alkaloid [10], asperazine has an unusual profile of cytotoxicity [11,12], and dragmacidin exhibits anti-tumor activity against P-388 cell lines with IC₅₀ value of 15 μg/mL, and IC₅₀ of 1–10 μg/mL against MDAMB (human mammary), HCT-8 (human colon) and A-549 (human lung) cancer cell lines [13,14,15].

Cancer is one of the leading causes of death globally, with almost 10 million deaths worldwide in 2020 [16]. By 2030, it will become the leading cause of death [17]. 70% of cancer deaths occur in middle or low-resource countries, where as 80% of cases are diagnosed too late for effective treatment. Cancer related deaths are increasing globally [17].

The heterogeneity of tumors, the lack of selectivity of drugs, and the development of drug resistance are some of the major obstacles impeding the effective cure of this deadly disease group. The fact of cell-death makes the situation even worse, because anti-cancer drugs follow first-order kinetics; that is, a fixed percentage, rather than a fixed number of cells are killed by a given treatment. Moreover, individual tumors may contain subpopulations of neoplastic cells that differ in terms of crucial features, any one of which could cause recurrence of the disease [17,18].

Although significant progress has been made in cancer research; still urgent need for a new drug with the advantage of less side effect, safe, overcome drug resistance and high efficacy are challenge to the researcher [19].

In this manuscript, we describe the synthesis of the new hits based on indole/benzofuran/benzothiophene analogues, along with the cytotoxities of the newly synthesized compounds against selected cancer cell lines.

2. Results and Discussion

2.1. Chemistry

Michaël-type Friedel–Crafts addition of nucleophiles (especially indoles) with electron-deficient alkenes are fundamentally important chemical transformations [20,21,22,23,24]. These methods have extensive uses in the scientific work on a number of potential nucleophilic species. Stabilized carbanions, organometallic reagents, and heteroatom-based nucleophiles have all been applied to a range of Michael acceptors in previous years [20,21]. The desired chalcones 1a–1l in this study were synthesized by following our previous reported method by Barakat et al [23] (Figure 2). Next, the achiral Friedel–Crafts reaction was explored with the chalcones-based benzofuran or thiophene analogues and the substituted indole by employing Fe-Pd bimetallic catalyst system [23] in MeOH at 60 °C to afford the Friedel–Crafts adducts. To check the productivity and the generality of this approach, the reaction of substituted indoles (indole 2a; 5-bromoindole 2b; 6-fluroroindole 2c) and chalcones based benzofuran or thiophene analogues was carried out under the reaction conditions (10 mol% of FeCl₃, 10 mol% of PdCl₂ and 15 mol% ethyl acetoacetate (EAA), 1.0 equiv. chalcone and 1.1 equiv. substituted indole in CH₃OH at 60 °C; Scheme 1). A range of heteroaryl enone substituents further demonstrated a broad substrate scope. Both electron-deficient and electron-rich heterocycles afforded the Friedel–Crafts products in high yield.

The structures of requisite Friedel–Crafts adducts were determined by using spectroscopic data, including ¹H-, ¹³C-NMR, Mass, and FT-IR spectroscopy.

2.2. Anti-Cancer Activity

All synthesized indoles 3a–3s were first evaluated for their cytotoxic effect against human fibroblast BJ cell line, and appeared to be either non-toxic (3a, 3i–3k, 3r and 3s) or slightly toxic than (30%) 3b–3i, and 3f–3q at a concentration of 30 µM. Based on the largely non-toxic nature of newly synthesized compounds against human fibroblast cell line compounds 3a–3s were further evaluated for their anticancer activities against HeLa, PC3, and MCF-7 cancer cell lines in comparison to standard drug doxorubicin, with IC₅₀ values 1.9 ± 0.4 µM, 0.9 ± 0.14 µM and 0.79 ± 0.05 µM, respectively, and appeared to be moderate to weak anticancer agents. Results of cytotoxic analysis and anti-cancer activities are summarized in Table 1.

Among series of substituted indoles and chalcone-based benzofurans compounds, 3a–3m and 3r–3s, 6-fluoroindol-4-bromophenyl chalcone-containing compound 3e (IC₅₀ = 7.8 ± 0.4 µM) appeared to be the most active anti-cancer agent against prostate PC3 cancer cell line in comparison to non-substituted indoles and chalcone-based benzofuran (3a, IC₅₀ = 11.4 ± 0.2 µM) and drug doxorubicin (IC₅₀ = 1.9 ± 0.4 µM). However, decrease in activity was observed in compounds 3b (IC₅₀ = 22.2 ± 0.4 µM), 3d (IC₅₀ = 26.3 ± 0.8 µM), and 3f (IC₅₀ = 27.0 ± 0.4 µM) having non-fluorinated indole moieties with fluoro-, bromo-, and chloro-substituted chalcone moieties, respectively. Similar pattern of decrease of activity was observed in compounds 3g (IC₅₀ = 20.0 ± 1.3 µM), having chloro substituted phenyl rings of chalcones instead of bromo-substituted chalcone moiety of containing compound 3e (IC₅₀ = 7.8 ± 0.4 µM). A complete loss of anticancer activity against PC3 cells was observed when fluoro-substituted chalcone moieties were replaced by o-nitro phenyl ring of containing 3i. Anti-cancer potential was restored in indole and chalcone-based benzofuran derivative 3j (IC₅₀ = 16.0 ± 0.1 µM) with bromo-substituted indole ring instead of fluorine substituent 3i. Among series of compounds having methoxy-substituted chalcone moiety 3m (IC₅₀ = 19.3 ± 0.1 µM) appeared as weak anti-cancer agents whereas compounds 3r and 3s appeared to be inactive. The pattern of activity of compound 3f (IC₅₀ = 16.3 ± 1.6 µM) and 3r (in active) clearly demonstrated the positional effect of methoxy substituent of the chalcone moiety towards anti-cancer activity. All members of the series of the indole and chalcone-based thiophene derivatives 3n–3q, appeared as weak anti-cancer agents against prostate cancer PC3 cell line in comparison to doxorubicin (IC₅₀ = 1.9 ± 0.4 µM) as standard drug.

All synthesized substituted indole and chalcone-based benzofurans 3a–3m and 3r–3s were further evaluated for their anticancer activities against cervical cancer HeLa cell lines and appeared to be moderate to weak anticancer agents against standard doxorubicin (IC₅₀ = 0.9 ± 0.14 µM). Non-substituted indole and chalcone-based benzofurans 3a appeared as weak anti-cancer agent with IC₅₀ = 22.5 ± 0.9 µM. However, substitution of fluorine on phenyl ring of chalcone moiety contributed towards drastic increase in anti-cancer potential as observed in 3b (IC₅₀ = 8.2 ± 0.2 µM), followed by gradual decrease in anti-cancer potential by various substituents on chalcone and indole moieties as observed in 6-bromoindol-4-flurophenyl chalcone-containing 3c (IC₅₀ = 10.8 ± 0.1 µM), 4-bromophenyl chalcone-containing 3d (IC₅₀ = 12.6 ± 0.4 µM), 6-fluroindol-4-bromophenyl chalcone-containing 3e (IC₅₀ = 13.6 ± 0.4 µM), 4-chlorophenyl chalcone-containing 3f (IC₅₀ = 11.9 ± 0.2 µM), 6-fluroindol-4-chlorophenyl chalcone-containing 3g (IC₅₀ = 14.7 ± 1.1 µM), 4-aminophenyl chalcone-containing 3h (IC₅₀ = 29.7 ± 0.4 µM), 6-fluroindol-2-nitrophenyl chalcone-containing 3i (IC₅₀ = 15.2 ± 0.6 µM), 5-bromoroindol-2-nitrophenyl chalcone-containing 3j (IC₅₀ = 17.3 ± 0.7 µM), 4-trifluoromethylphenyl chalcone-containing 3k (IC₅₀ = 14.9 ± 0.6 µM), 3-methoxyphenyl chalcone-containing 3l (IC₅₀ = 11.1 ± 0.6 µM), 6-fluoroindol-3-methoxyphenyl chalcone-containing 3m (IC₅₀ = 15.2 ± 0.2 µM), and 5-bromoindol-2-methoxyphenyl chalcone-containing 3s (IC₅₀ = 18.4 ± 0.2 µM). Similar activity pattern was observed in non-substituted indole and chalcone-based thiophene derivative 3n (IC₅₀ = 12.4 ± 0.2 µM), 4-chlorophenyl chalcone-containing compound 3o (IC₅₀ = 13.8 ± 0.3 µM), 4-fluorophenyl chalcone-containing 3p (IC₅₀ = 12.7 ± 0.1 µM), and 4-trifluoromethylphenyl chalcone-containing 3q (IC₅₀ = 18.8 ± 0.2 µM against cervical cancer cell line HeLa in comparison to doxorubicin (IC₅₀ = 1.9 ± 0.4 µM) as standard drug.

Many of the tested compounds appeared to be inactive against MCF-7 breast cancer cell lines, except 3b, 3c, 3f, 3m and 3s. Non-substituted indole and chalcone-based benzofurans 3a, appeared to be inactive against MCF-7 breast cancer cell lines; however, substitution of fluorine on phenyl ring of chalcone moiety contributed towards drastic increase in anti-cancer potential, as observed in 3b (IC₅₀ = 12.37 ± 0.04 µM), followed by gradual decrease in anti-cancer potential due to various substituents on chalcone and indole moieties, as observed in 4-chlorophenyl chalcone-containing 3f (IC₅₀ = 19.28 ± 0.78 µM), 6-fluroindol-3-methoxyphenyl chalcone-containing 3m (IC₅₀ = 22.9 ± 0.43 µM), 6-bromoindol-4-flurophenyl chalcone-containing 3c (IC₅₀ = 25.87 ± 0.8 µM), and 5-bromoindol-2-methoxyphenyl chalcone-containing compound 3s (IC₅₀ = 28.64 ± 0.3 µM) against standard doxorubicin (IC₅₀ = 0.79 ± 0.4 µM). All synthesized indole and chalcone-based thiophene derivatives 3n–3q appeared to be inactive against breast cancer cell line MCF-7.

The comparison of substituted indole and chalcone-based benzofurans (3a, 3b, 3g, and 3k) with substituted indole and chalcone-based thiophenes (3r–3s) disclosed that non-substituted indole and chalcone-based benzofuran 3a (IC₅₀ = 11.4 ± 0.2 µM) and fluoro-, and chloro-substituted chalcone moieties, containing compounds 3b (IC₅₀ = 22.2 ± 0.5 µM) and 3g (IC₅₀ = 22.0 ± 1.3 µM), respectively, appeared to be more active against PC3 prostate cancer cell lines, in comparison to non-substituted indole and chalcone-based thiophene 3r (IC₅₀ = 20.4 ± 0.4 µM) and fluoro-, and chloro-substituted chalcone moieties, containing compounds 3p (IC₅₀ = 27.6 ± 0.5 µM) and 3s (IC₅₀ = 29.7 ± 0.5 µM), respectively, that appeared to have more anti-cancer potential against cervical cancer HeLa cell line 3r (IC₅₀ = 12.4 ± 0.2 µM), 3o (IC₅₀ = 13.8 ± 0.3 µM) and 3p (IC₅₀ = 12.7 ± 0.1 µM)]. Among fluoro-, and chloro-substituted chalcone-containing compounds 3b and 3s, respectively. Whereas trifluoro-substituted chalcone-containing benzofuran 3k (IC₅₀ = 14.9 ± 0.6 µM) showed more activity against cervical cancer HeLa cell line, in comparison to thiophene analogue (3q, IC₅₀ = 18.8 ± 0.2 µM). Among benzofurans (3a, 3b, 3g, and 3k) and thiophene 3r–3s structural analogues, 4-fluorophenyl chalcone-containing 3b (IC₅₀ = 12.37 ± 0.04 µM) appeared to be the only active member against MCF-7 breast cancer cell line. All results are summarized in Table 1.

3. Materials and Methods

3.1. General Procedure (GP1)

Chalcones 1a–1l (0.5 mmol), indoles (0.55 mmol), and dry methanol (20 mL) were charged into a 100 mL round bottom flask, equipped with condenser under inert atmosphere. FeCl₃ (5 mol%), PdCl₂ (5 mol%), and 15 mol% of ethyl-acetoacetate (EAA) were added to the reaction mixture. Then the reaction was heated at 60–80 °C for 2–3 h. The reaction was monitored by TLC until the complete consumption of starting materials. Then the reaction mixture was allowed to cool and 20 mL of distilled water was added. The products were extracted in CH₂Cl₂ (3 × 20 mL) and the organics part were dried over anhydrous Mg₂SO₄. The organic phases were concentrated under reduced pressure and subjected to column chromatography using 100–200 mesh silica gel and 20–30% Ethyl acetate in n-hexane to afford moderate to good yields (60–90%).

3.2. Synthesis of 3-(Benzofuran-2-yl)-3-(1H-indol-3-yl)-1-phenylpropan-1-one (3a)

Following the general procedure (GP1) chalcone 1a (124 mg, 0.5 mmol) and indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3a (yield 159 mg, 87%); m.p. 114–115 °C; ¹H-NMR (500 MHz, DMSO-d₆) δ 10.97 (d, J = 2.4 Hz, 1H, NH), 8.08–8.02 (m, 2H, Ar-H), 7.66–7.60 (m, 2H, Ar-H), 7.55–7.48 (m, 3H, Ar-H), 7.44–7.40 (m, 1H, Ar-H), 7.38–7.32 (m, 2H, Ar-H), 7.16 (pd, J = 7.3, 1.5 Hz, 2H, Ar-H), 7.06 (ddd, J = 8.1, 7.0, 1.2 Hz, 1H, Ar-H), 6.96 (ddd, J = 7.9, 6.9, 1.0 Hz, 1H, Ar-H), 6.70 (d, J = 1.0 Hz, 1H, Ar-H), 5.12 (t, J = 7.2 Hz, 1H, CH), 4.07 (dd, J = 17.5, 7.6 Hz, 1H, CH_2(a)), 3.93 (dd, J = 17.5, 7.0 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 197.7 (CO), 161.0, 153.9, 136.6, 136.3, 133.3, 128.7, 128.4, 128.1, 126.1, 123.3, 122.9, 122.6, 121.1, 120.5, 118.7, 118.6, 114.3, 111.6, 110.7, 101.8, 41.9 (CH), 31.8 (CH₂); IR (KBr, cm⁻¹) ν_max = 3404, 3056, 29.04,2848, 1678, 1589, 1450, 1415, 1334, 1253; [Anal. Calcd. for C₂₅H₁₉NO₂: C, 82.17; H, 5.24; N, 3.83; Found: C, 82.29; H, 5.12; N, 3.65]; LC/MS (ESI, m/z): 366.15 [M + H]⁺, exact mass 365.14 for C₂₅H₁₉NO₂.

3.3. Synthesis of 3-(Benzofuran-2-yl)-1-(4-fluorophenyl)-3-(1H-indol-3-yl)propan-1-one (3b)

Following the general procedure (GP1) chalcone 1b (133 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3b (yield 174 mg, 91%); m.p. 157–158 ^oC; ¹H-NMR (500 MHz, DMSO-d₆) δ 10.98 (d, J = 2.4 Hz, 1H, NH), 8.16−8.10 (m, 2H, Ar-H), 7.64 (d, J = 7.9 Hz, 1H, Ar-H), 7.50 (dd, J = 6.8, 2.2 Hz, 1H, Ar-H), 7.44−7.40 (m, 1H, Ar-H), 7.38–7.32 (m, 4H, Ar-H), 7.16 (td, J = 7.0, 1.6 Hz, 2H, Ar-H), 7.06 (ddd, J = 8.1, 6.9, 1.2 Hz, 1H, Ar-H), 6.98–6.93 (m, 1H, Ar-H), 6.70 (d, J = 1.0 Hz, 1H, Ar-H), 5.11 (t, J = 7.2 Hz, 1H, CH), 4.07 (dd, J = 17.5, 7.5 Hz, 1H, CH_2(a)), 3.92 (dd, J = 17.5, 6.9 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 196.9 (CO), 166.6 & 164.6 (C₁-F, J_C-F = 200.3 Hz), 161.5, 154.4, 136.9, 133.9, 133.9, 131.7 & 131.6 (C₄-F, J_C-F = 7.4 Hz), 128.9, 126.6, 123.9, 123.5, 123.10, 121.6, 121.1, 119.2 &119.1 (C₃-F, J_C-F = 11.1 Hz), 116.3 & 116.2 (C₂-F, J_C-F = 17.4 Hz), 114.8, 112.1, 111.3, 102.4, 42.4 (CH), 32.3(CH₂); IR (KBr, cm⁻¹) ν_max = 3331, 3055, 2904, 1677, 1591, 1502, 1452, 1363, 1340, 1234, 1225; [Anal. Calcd. for C₂₅H₁₈FNO₂: C, 78.31; H, 4.73; N, 3.65; Found: C, 78.19; H, 4.65; N, 3.52]; LC/MS (ESI, m/z): 384.14 [M + H]⁺, exact mass 383.13 for C₂₅H₁₈FNO₂.

3.4. Synthesis of 3-(Benzofuran-2-yl)-3-(5-bromo-1H-indol-3-yl)-1-(4-fluorophenyl)propan-1-one (3c)

The general procedure (GP1) chalcone 1b (133 mg, 0.5 mmol) 5-bromoindole 2b (108 mg, 0.55 mmol) produces Friedel–Crafts product-3c (yield 191 mg, 83%); m.p. 167–168 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 11.21 (d, J = 2.4 Hz, 1H, NH), 8.13 (dd, J = 8.7, 5.8 Hz, 2H, Ar-H), 7.82 (d, J = 2.0 Hz, 1H, Ar-H), 7.54–7.50 (m, 1H, Ar-H), 7.47–7.41 (m, 2H, Ar-H), 7.34 (t, J = 8.9 Hz, 3H, Ar-H), 7.22–7.12 (m, 3H, Ar-H), 6.73 (s, 1H, Ar-H), 5.10 (t, J = 7.1 Hz, 1H, CH), 4.06 (dd, J = 17.7, 7.3 Hz, 1H, CH_2(a)), 3.93 (dd, J = 17.7, 7.2 Hz, 1H, CH_2(b)); ¹³C-NMR (101 MHz, DMSO-d₆) δ 196.2 (CO), 166.4 & 163.9 (C₁-F, J_C-F = 250.7 Hz), 160.6, 153.9, 134.9, 133.3, 131.2 & 131.1 (C₄-F, J_C-F = 9.6 Hz), 128.4, 127.9, 124.8, 123.6, 123.4, 122.6, 120.9, 120.6, 115.8 & 115.6 (C₂-F, J_C-F = 22.2 Hz), 114.2, 113.6, 111.3, 110.7, 101.9, 41.9 (CH), 31.4 (CH₂); IR (KBr, cm⁻¹) ν_max = 3396, 3066, 2921, 1675, 1591, 1504, 1452, 1413, 1226; [Anal. Calcd. for C₂₅H₁₇BrFNO₂: C, 64.95; H, 3.71; N, 3.03; Found: C, 65.17; H, 3.62; N, 2.93]; LC/MS (ESI, m/z): 462.05 [M + H] ⁺, exact mass 461.04 for C₂₅H₁₇BrFNO₂.

3.5. Synthesis of 3-(Benzofuran-2-yl)-1-(4-bromophenyl)-3-(1H-indol-3-yl)propan-1-one (3d)

Following the general procedure (GP1) chalcone 1c (164 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3d (yield 189 mg, 85%); m.p. 108–109 °C; ¹H-NMR (500 MHz, DMSO-d₆) δ 10.99–10.93 (m, 1H, NH), 8.00–7.94 (m, 2H, Ar-H), 7.73 (d, J = 8.5 Hz, 2H, Ar-H), 7.62 (d, J = 8.0 Hz, 1H, Ar-H), 7.51–7.47 (m, 1H, Ar-H), 7.41 (d, J = 7.6 Hz, 1H, Ar-H), 7.37–7.31 (m, 2H, Ar-H), 7.16 (td, J = 7.1, 1.7 Hz, 2H, Ar-H), 7.05 (t, J = 7.6 Hz, 1H, Ar-H), 6.95 (t, J = 7.5 Hz, 1H, Ar-H), 6.70 (s, 1H, Ar-H), 5.08 (t, J = 7.3 Hz, 1H, CH), 4.06 (dd, J = 17.5, 7.5 Hz, 1H, CH_2(a)), 3.91 (dd, J = 17.5, 6.8 Hz, 1H CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 197.0 (CO), 160.9, 153.9, 136.3, 135.5, 131.8, 130.2, 128.4, 127.4, 126.1, 123.4, 123.0, 122.6, 121.1, 120.5, 118.7, 118.6, 114.2, 111.6, 110.7, 101.9, 41.9 (CH), 31.7 (CH₂); IR (KBr, cm⁻¹) ν_max = 3323, 3057, 2920, 2852, 1678, 1580, 1452, 1394, 1363, 1338, 1252, 1197; [Anal. Calcd. for C₂₅H₁₈BrNO₂: C, 67.58; H, 4.08; N, 3.15; Found: C, 67.45; H, 4.19; N, 3.01]; LC/MS (ESI, m/z): 444.06 [M + H] ⁺, exact mass 443.05 for C₂₅H₁₈BrNO₂.

3.6. Synthesis of 3-(Benzofuran-2-yl)-1-(4-bromophenyl)-3-(6-fluoro-1H-indol-3-yl)propan-1-one (3e)

Following the general procedure (GP1) chalcone 1c (164 mg, 0.5 mmol) 6-fluoroindole 2c (74 mg, 0.55 mmol) produces Friedel–Crafts product-3e (yield 166 mg, 72%); m.p. 123–124 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 11.05 (d, J = 2.5 Hz, 1H, NH), 7.97 (d, J = 8.1 Hz, 2H, Ar-H), 7.72 (d, J = 8.1 Hz, 2H, Ar-H), 7.62 (dd, J = 8.8, 5.3 Hz, 1H, Ar-H), 7.50 (d, J = 7.1 Hz, 1H, Ar-H), 7.41 (d, J = 7.5 Hz, 1H, Ar-H), 7.37 (d, J = 2.6 Hz, 1H, Ar-H), 7.22–7.08 (m, 3H, Ar-H), 6.82 (td, J = 9.4, 2.5 Hz, 1H, Ar-H), 6.71 (s, 1H, Ar-H), 5.08 (t, J = 7.2 Hz, 1H, CH), 4.06 (dd, J = 17.6, 7.4 Hz, 1H, CH_2(a)), 3.90 (dd, J = 17.6, 6.8 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 196.9 (CO), 160.7, 159.8 & 157.9 (C₁-F, J_C-F = 186.3 Hz), 153.9, 136.2 & 136.1 (C₃-F, J_C-F = 10.3 Hz), 135.5, 131.8, 130.2, 128.4, 127.5, 123.6 & 123.6 (C₄-F, J_C-F = 2.6 Hz), 123.4, 122.9, 122.6, 120.6, 119.7 & 119.7 (C₅-F, J_C-F = 8.2 Hz), 114.5, 110.7, 107.2 & 106.9 (C₂-F, J_C-F = 19.5 Hz), 101.9, 97.6 & 97.4 (C₆-F, J_C-F = 20.2 Hz), 41.9 (CH), 31.6 (CH₂); IR (KBr, cm⁻¹) ν_max = 3359, 2918, 2850, 1678, 1624, 1581, 1454, 1394, 1336, 1250; [Anal. Calcd. for C₂₅H₁₇BrFNO₂: C, 64.95; H, 3.71; N, 3.03; Found: C, 64.84; H, 3.66; N, 3.21]; LC/MS (ESI, m/z): 462.05 [M + H], exact mass 461.04 for C₂₅H₁₇BrFNO₂.

3.7. Synthesis of 3-(Benzofuran-2-yl)-1-(4-chlorophenyl)-3-(1H-indol-3-yl)propan-1-one (3f)

Following the general procedure (GP1) chalcone 1d (141 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3f (yield 158 mg, 79%); m.p. 126–127 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.98 (d, J = 2.4 Hz, 1H, NH), 8.05 (d, J = 8.2 Hz, 2H, Ar-H), 7.63 (d, J = 8.0 Hz, 1H, Ar-H), 7.58 (d, J = 8.6 Hz, 2H, Ar-H), 7.52–7.47 (m, 1H, Ar-H), 7.44–7.40 (m, 1H, Ar-H), 7.38–7.33 (m, 2H, Ar-H), 7.16 (t, J = 5.6 Hz, 2H, Ar-H), 7.06 (t, J = 7.7 Hz, 1H, Ar-H), 6.96 (t, J = 7.4 Hz, 1H, Ar-H), 6.70 (s, 1H, Ar-H), 5.10 (t, J = 7.2 Hz, 1H, CH), 4.07 (dd, J = 17.6, 7.4 Hz, 1H, CH_2(a)), 3.93 (dd, J = 17.6, 7.1 Hz, 1H, CH_2(b)); ¹³C-NMR (101 MHz, DMSO-d₆) δ 197.4 (CO), 161.5, 154.5, 138.8, 136.9, 135.8, 130.6, 129.4, 128.9, 126.7, 123.9, 123.6, 123.2, 121.7, 121.1, 119.3, 119.1, 114.8, 112.1, 111.3, 102.5, 42.6 (CH), 32.3 (CH₂); IR (KBr, cm⁻¹) ν_max = 3323, 2935, 2918, 2854, 1680, 1585, 1456, 1396, 1362, 1340, 1250; [Anal. Calcd. for C₂₅H₁₈ClNO₂: C, 75.09; H, 4.54; N, 3.50; Found: C, 75.23; H, 4.46; N, 3.39]; LC/MS (ESI, m/z): 400.14 [M + H] ⁺, exact mass 399.10 for C₂₅H₁₈ClNO₂.

3.8. Synthesis of 3-(Benzofuran-2-yl)-1-(4-chlorophenyl)-3-(6-fluoro-1H-indol-3-yl)propan-1-one (3g)

Following the general procedure (GP1) chalcone 1d (141 mg, 0.5 mmol) 6-fluoroindole 2c (74 mg, 0.55 mmol) produces Friedel–Crafts product-3g (yield 146 mg, 70%); m.p. 112–113 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 11.08 (d, J = 2.4 Hz, 1H, NH), 8.05 (d, J = 8.6 Hz, 2H, Ar-H), 7.64 (dd, J = 8.8, 5.6 Hz, 1H, Ar-H), 7.57 (d, J = 8.3 Hz, 2H, Ar-H), 7.50 (d, J = 7.4 Hz, 1H, Ar-H), 7.44–7.36 (m, 2H, Ar-H), 7.21–7.10 (m, 3H, Ar-H), 6.84 (td, J = 9.2, 2.6 Hz, 1H, Ar-H), 6.71 (s, 1H, Ar-H), 5.11 (t, J = 7.2 Hz, 1H, CH), 4.07 (dd, J = 17.6, 7.7 Hz, 1H, CH_2(a)), 3.92 (dd, J = 17.6, 7.1 Hz, 1H, CH_2(b)); ¹³C-NMR (101 MHz, DMSO-d₆) δ 196.7 (CO), 160.7, 160.0 & 157.7 (C₁-F, J_C-F = 233.3 Hz), 153.9, 138.3, 136.3 & 136.1 (C₃-F, J_C-F = 12.6 Hz), 135.2, 130.0, 128.8, 128.4, 123.6 & 123.4 (C₄-F, J_C-F = 2.4 Hz), 122.9, 122.6, 120.6, 119.8 & 119.7 (C₅-F, J_C-F = 10.1 Hz), 114.5, 110.7, 107.2 & 106.9 (C₂-F, J_C-F = 24.3 Hz), 101.9, 97.6 & 97.4 (C₆-F, J_C-F = 25.2 Hz), 41.9 (CH), 31.7 (CH₂); IR (KBr, cm⁻¹) ν_max = 3304, 3028, 2910, 2850, 1665, 1554, 1450, 1394, 1363, 1338, 1252; [Anal. Calcd. for C₂₅H₁₇ClFNO₂: C, 71.86; H, 4.10; N, 3.35; Found: C, 71.69; H, 4.25; N, 3.19]; LC/MS (ESI, m/z): 418.10 [M + H] ⁺, exact mass 417.09 for C₂₅H₁₇ClFNO₂.

3.9. Synthesis of 3-(Benzo[b]thiophen-2-yl)-1-(4-bromophenyl)-3-(1H-indol-3-yl)propan-1-one (3h)

Following the general procedure (GP1) chalcone 1i (172 mg, 0.5 mmol), indole 2a (108 mg, 0.55 mmol) produces Friedel–Crafts product-3h (yield 156 mg, 68%); m.p. 121–122 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.97 (s, 1H, NH), 7.98 (d, J = 8.2 Hz, 2H, Ar-H), 7.72 (dt, J = 18.7, 9.0 Hz, 4H, Ar-H), 7.54 (d, J = 8.0 Hz, 1H, Ar-H), 7.41 (d, J = 2.5 Hz, 1H, Ar-H), 7.35–7.19 (m, 4H, Ar-H), 7.05 (t, J = 7.6 Hz, 1H, Ar-H), 6.92 (t, J = 7.4 Hz, 1H, Ar-H), 5.23 (t, J = 7.3 Hz, 1H, CH), 4.01 (dd, J = 10.8, 7.1 Hz, 2H, CH₂); ¹³C-NMR (126 MHz, DMSO-d₆) δ 197.0 (CO), 150.76, 139.5, 138.5, 136.4, 135.6, 131.8, 130.2, 127.5, 126.1, 124.1, 123.6, 123.0, 122.5, 122.2, 121.2, 120.2, 118.7, 118.5, 116.8, 111.5, 44.5 (CH), 33.4 (CH₂); IR (KBr, cm⁻¹) ν_max = 3335, 3038, 2907, 2852, 1678, 1580, 1455, 1440, 1360, 1348, 1255; [Anal. Calcd. for C₂₅H₁₈BrNOS: C, 65.22; H, 3.94; N, 3.04; Found: C, 65.04; H, 3.86; N, 2.91]; LC/MS (ESI, m/z): 460.04 [M + H] ⁺, exact mass 459.03 for C₂₅H₁₈BrNOS.

3.10. Synthesis of 3-(Benzofuran-2-yl)-3-(6-fluoro-1H-indol-3-yl)-1-(2-nitrophenyl)propan-1-one (3i)

Following the general procedure (GP1) chalcone 1e (147 mg, 0.5 mmol) and 6-fluoroindole 2c (74 mg, 0.55 mmol) produces Friedel–Crafts product-3i (yield 146 mg, 68%); m.p. 139–140 °C; ¹H-NMR (500 MHz, DMSO-d₆) δ 11.10 (d, J = 2.5 Hz, 1H, NH), 8.06 (dd, J = 8.0, 1.2 Hz, 1H, Ar-H), 7.78 (td, J = 7.5, 1.2 Hz, 1H, Ar-H), 7.71 (ddd, J = 12.9, 7.5, 1.6 Hz, 2H, Ar-H), 7.61 (dd, J = 8.8, 5.4 Hz, 1H, Ar-H), 7.54–7.50 (m, 1H, Ar-H), 7.44 (dt, J = 7.2, 1.3 Hz, 1H, Ar-H), 7.40 (d, J = 2.5 Hz, 1H, Ar-H), 7.22–7.12 (m, 3H, Ar-H), 6.83 (ddd, J = 9.7, 8.7, 2.4 Hz, 1H, Ar-H), 6.78–6.74 (m, 1H, Ar-H), 5.05 (t, J = 7.1 Hz, 1H, CH), 4.01 (dd, J = 17.9, 7.6 Hz, 1H, CH_2(a)), 3.82 (dd, J = 18.0, 6.6 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 199.5 (CO), 160.1, 159.8 &157.9 (C₁-F, J_C-F = 186.4 Hz), 154.0, 146.2, 136.3 & 136.2 (C₃-F, J_C-F = 10.0 Hz), 135.4, 134.1, 131.8, 128.4 & 128.4 (C₄-F, J_C-F = 3.8 Hz), 124.3, 123.9, 123.8, 123.5, 122.9, 122.7, 120.7, 119.7 & 119.6(C₅-F, J_C-F = 8.0 Hz), 114.1, 110.8, 107.3 & 107.1 (C₂-F, J_C-F = 19.5 Hz), 102.3, 97.7 & 97.5 (C₆-F, J_C-F = 20.0 Hz), 45.2 (CH), 31.6 (CH₂); IR (KBr, cm⁻¹) ν_max = 3305, 3062,2915, 2858, 1699, 1621, 1527, 1452, 1338, 1255, 1144, 798, 748, 696; [Anal. Calcd. for C₂₅H₁₇FN₂O₄: C, 70.09; H, 4.00; N, 6.54; Found: C, 69.89; H, 4.11; N, 6.45]; LC/MS (ESI, m/z): 429.13 [M + H] ⁺, exact mass 428.12 for C₂₅H₁₇FN₂O₄.

3.11. Synthesis of 3-(Benzofuran-2-yl)-3-(5-bromo-1H-indol-3-yl)-1-(2-nitrophenyl)propan-1-one (3j)

Following the general procedure (GP1) chalcone 1e (147 mg, 0.5 mmol) 5-bromoindole 2b (108 mg, 0.55 mmol) produces Friedel–Crafts product-3j (yield 154 mg, 63%); m.p. 173–174 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 11.25 (d, J = 2.6 Hz, 1H, NH), 8.06 (d, J = 7.9 Hz, 1H, Ar-H), 7.84–7.76 (m, 2H, Ar-H), 7.73 (d, J = 7.6 Hz, 2H, Ar-H), 7.54 (d, J = 6.8 Hz, 1H, Ar-H), 7.50–7.40 (m, 2H, Ar-H), 7.33 (d, J = 8.7 Hz, 1H, Ar-H), 7.17 (q, J = 7.3, 6.7 Hz, 3H, Ar-H), 6.77 (s, 1H, Ar-H), 5.06 (t, J = 6.9 Hz, 1H, CH), 4.02 (dd, J = 18.0, 7.5 Hz, 1H, CH_2(a)), 3.83 (dd, J = 17.8, 6.7 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 199.4 (CO), 159.9, 153.9, 146.1, 135.3, 134.9, 133.9, 131.7, 128.4, 128.4, 127.8, 124.9, 124.2, 123.7, 123.5, 122.6, 120.8, 120.6, 113.7, 113.6, 111.3, 110.7, 102.2, 45.1 (CH), 31.2 (CH₂); IR (KBr, cm⁻¹) ν_max = 3324, 3062, 2918, 2850, 1695, 1570, 1519, 1452, 1334, 1245, 1099, 879, 854, 791, 746, 694, 604; [Anal. Calcd. for C₂₅H₁₇BrN₂O₄: C, 61.36; H, 3.50; N, 5.72; Found: C, 61.21; H, 3.63; N, 5.62]; LC/MS (ESI, m/z): 489.05 [M + H], exact mass 488.04 for C₂₅H₁₇BrN₂O₄.

3.12. Synthesis of 3-(Benzofuran-2-yl)-3-(1H-indol-3-yl)-1-(2-nitrophenyl)propan-1-one (3k)

Following the general procedure (GP1) chalcone 1e (147 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3k (yield 135 mg, 66%); m.p. 154–155 °C; ¹H-NMR (500 MHz, DMSO-d₆) δ 11.01 (d, J = 2.5 Hz, 1H, NH), 8.06 (dd, J = 8.0, 1.2 Hz, 1H, Ar-H), 7.78 (td, J = 7.5, 1.2 Hz, 1H, Ar-H), 7.74–7.68 (m, 2H, Ar-H), 7.60 (d, J = 7.9 Hz, 1H, Ar-H), 7.54–7.50 (m, 1H, Ar-H), 7.45–7.41 (m, 1H, Ar-H), 7.39–7.33 (m, 2H, Ar-H), 7.17 (pd, J = 7.2, 1.4 Hz, 2H, Ar-H), 7.08–7.03 (m, 1H, Ar-H), 6.95 (t, J = 7.4 Hz, 1H, Ar-H), 6.75 (s, 1H, Ar-H), 5.05 (t, J = 7.1 Hz, 1H, CH), 4.01 (dd, J = 17.9, 7.8 Hz, 1H, CH_2(a)), 3.82 (dd, J = 17.9, 6.4 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 199.6 (CO), 160.3, 153.9, 146.2, 136.4, 135.4, 134.1, 131.8, 128.5, 128.4, 126.0, 124.3, 123.5, 123.2, 122.7, 121.2, 120.7, 118.7, 118.6, 113.8, 111.7, 110.8, 102.2, 45.3 (CH), 31.6 (CH₂); IR (KBr, cm⁻¹) ν_max = 3310, 3055, 2901, 2850, 1684, 1625, 1530, 145, 1331, 1253; [Anal. Calcd. for C₂₅H₁₈N₂O₄: C, 73.16; H, 4.42; N, 6.83; Found: C, 73.10; H, 4.38; N, 6.79]; LC/MS (ESI, m/z): 411.13 [M + H] ⁺, exact mass 410.13 for C₂₅H₁₈N₂O₄.

3.13. Synthesis of 3-(Benzofuran-2-yl)-3-(1H-indol-3-yl)-1-(3-methoxyphenyl)propan-1-one (3l)

Following the general procedure (GP1) chalcone 1g (139 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3l (yield 162 mg, 82%); m.p. 162–163 °C; ¹H-NMR (500 MHz, DMSO-d₆) δ 10.97 (d, J = 2.5 Hz, 1H, NH), 7.68–7.61 (m, 2H, Ar-H), 7.52–7.47 (m, 2H, Ar-H), 7.46–7.40 (m, 2H, Ar-H), 7.37–7.33 (m, 2H, Ar-H), 7.21–7.14 (m, 3H, Ar-H), 7.05 (ddd, J = 8.2, 7.0, 1.2 Hz, 1H, Ar-H), 6.95 (ddd, J = 8.0, 7.0, 1.0 Hz, 1H, Ar-H), 6.70 (d, J = 1.0 Hz, 1H, Ar-H), 5.10 (t, J = 7.2 Hz, 1H, CH), 4.04 (dd, J = 17.5, 7.5 Hz, 1H, CH_2(a)), 3.93 (dd, J = 17.5, 7.0 Hz, 1H, CH_2(b)), 3.79 (s, 3H, OCH₃); ¹³C-NMR (126 MHz, DMSO-d₆) δ 197.5 (CO), 161.0, 159.4, 153.9, 138.0, 136.3, 129.9, 128.4, 126.1, 123.3, 123.0, 122.5, 121.1, 120.6, 120.5, 119.4, 118.7, 118.5, 114.2, 112.4, 111.6, 110.7, 101.8, 55.3 (OCH₃), 42.0 (CH), 31.8 (CH₂); IR (KBr, cm⁻¹) ν_max = 3392, 3055, 2960, 2916, 2852, 1674, 1591, 1452,1423, 1333, 1265, 1190, 1161, 1095, 1008, 813, 790, 744, 609, 544; [Anal. Calcd. for C₂₆H₂₁NO₃: C, 78.97; H, 5.35; N, 3.54; Found: C, 79.13; H, 5.25; N, 3.44]; LC/MS (ESI, m/z): 396.16 [M + H], exact mass 395.15 for C₂₆H₂₁NO₃.

3.14. Synthesis of 3-(Benzofuran-2-yl)-3-(6-fluoro-1H-indol-3-yl)-1-(3-methoxyphenyl)propan-1-one (3m)

Following the general procedure (GP1) chalcone 1g (139 mg, 0.5 mmol) 6- fluoroindole 2c (74 mg, 0.55 mmol) produces Friedel–Crafts product-3m (yield 153 mg, 74%); m.p. 154–155 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 11.04 (d, J = 2.4 Hz, 1H, NH), 7.67–7.58 (m, 2H, Ar-H), 7.53–7.46 (m, 2H, Ar-H), 7.46–7.40 (m, 2H, Ar-H), 7.36 (d, J = 2.5 Hz, 1H, Ar-H), 7.22–7.09 (m, 4H, Ar-H), 6.82 (td, J = 9.4, 2.5 Hz, 1H, Ar-H), 6.71 (s, 1H, Ar-H), 5.08 (t, J = 7.1 Hz, 1H, CH), 4.03 (dd, J = 17.5, 7.5 Hz, 1H, CH_2(a)), 3.95–3.87 (m, 1H, CH_2(b)), 3.79 (s, 3H, CH₃); ¹³C-NMR (126 MHz, DMSO-d₆) δ 197.5 (CO), 160.8, 159.4, 159.78 &157.9(C₁-F, J_C-F = 186.0 Hz), 153.9, 137.9, 136.2 & 136.1 (C₃-F, J_C-F = 10.1 Hz), 129.9, 128.4, 123.7, 123.4, 123.0, 122.6, 120.6 & 120.6 (C₄-F, J_C-F = 7.4 Hz), 119.7 & 119.6 (C₅-F, J_C-F = 8.1 Hz), 119.5, 114.5, 112.5, 110.7, 107.2 & 106.9 (C₂-F, J_C-F = 19.4 Hz), 101.9, 97.6 & 97.4 (C₆-F, J_C-F = 20.3 Hz), 55.3 (OCH₃), 42.0 (CH), 31.7 (CH₂); IR (KBr, cm⁻¹) ν_max = 3409, 3053, 2922, 2836, 1666, 1513, 1483, 1454, 1430, 1286, 1244, 1163, 1101, 1016, 806, 740, 586; [Anal. Calcd. for C₂₆H₂₀FNO₃: C, 75.53; H, 4.88; N, 3.39; Found: C, 75.41; H, 4.99; N, 3.27]; LC/MS (ESI, m/z): 414.15 [M + H] ⁺, exact mass 413.14 for C₂₆H₂₀FNO₃.

3.15. Synthesis of 3-(Benzo[b]thiophen-2-yl)-3-(1H-indol-3-yl)-1-phenylpropan-1-one (3n)

Following the general procedure (GP1) chalcone 1h (132 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3n (yield 164 mg, 86%); m.p. 159–160 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.90 (s, 1H, NH), 7.97 (d, J = 7.7 Hz, 2H, Ar-H), 7.68 (d, J = 8.1 Hz, 1H, Ar-H), 7.60 (d, J = 8.0 Hz, 1H, Ar-H), 7.54 (t, J = 7.4 Hz, 1H, Ar-H), 7.50–7.40 (m, 3H, Ar-H), 7.35 (s, 1H, Ar-H), 7.30–7.22 (m, 2H, Ar-H), 7.19 (t, J = 7.5 Hz, 1H, Ar-H), 7.13 (t, J = 7.6 Hz, 1H, Ar-H), 6.98 (t, J = 7.7 Hz, 1H, Ar-H), 6.86 (t, J = 7.5 Hz, 1H, Ar-H), 5.19 (t, J = 7.2 Hz, 1H, CH), 4.02–3.87 (m, 2H, CH₂); ¹³C-NMR (101 MHz, DMSO-d₆) δ 197.8 (CO), 150.9, 139.6, 138.6, 136.7, 136.475, 133.4, 128.7, 128.1, 126.2, 124.1, 123.7, 122.9, 122.4, 122.1, 121.1, 120.2, 118.8, 118.6, 116.9, 111.5, 44.6 (CH), 33.4 (CH₂); IR (KBr, cm⁻¹) ν_max = 3427, 3394, 3053, 2885, 1668, 1597, 1450, 1334, 1265, 1194; [Anal. Calcd. for C₂₅H₁₉NOS: C, 78.71; H, 5.02; N, 3.67; Found: C, 78.62; H, 5.17; N, 3.61]; LC/MS (ESI, m/z): 382.13 [M + H] ⁺, exact mass 381.12 for C₂₅H₁₉NOS.

3.16. Synthesis of 3-(Benzo[b]thiophen-2-yl)-1-(4-chlorophenyl)-3-(1H-indol-3-yl)propan-1-one (3o)

Following the general procedure (GP1) chalcone 1j (149 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3o (yield 160 mg, 77%); m.p. 150–151 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.99 (d, J = 2.5 Hz, 1H, NH), 8.09–8.03 (m, 2H, Ar-H), 7.76 (d, J = 8.0 Hz, 1H, Ar-H), 7.69 (d, J = 7.9 Hz, 1H, Ar-H), 7.57 (dd, J = 11.7, 8.4 Hz, 3H, Ar-H), 7.43 (d, J = 2.7 Hz, 1H, Ar-H), 7.35 (d, J = 8.2 Hz, 1H, Ar-H), 7.32 (s, 1H, Ar-H), 7.26 (d, J = 7.9 Hz, 1H, Ar-H), 7.22 (d, J = 7.4 Hz, 1H, Ar-H), 7.06 (t, J = 7.6 Hz, 1H, Ar-H), 6.94 (t, J = 7.5 Hz, 1H, Ar-H), 5.25 (t, J = 7.1 Hz, 1H, CH), 4.11–3.95 (m, 2H, CH₂); ¹³C-NMR (101 MHz, DMSO-d₆) δ 196.8 (CO), 150.8, 139.6, 138.5, 138.2, 136.4, 135.3, 130.1, 128.8, 126.1, 124.1, 123.5, 123.1, 122.6, 122.2, 121.1, 120.3, 118.7, 118.6, 116.8, 111.6, 44.6 (CH), 33.4 (CH₂).; IR (KBr, cm⁻¹) ν_max = 3383, 3055, 2954, 2921, 2852, 1676, 1583, 1483, 1454, 1402, 1356, 1328, 1261, 1194; [Anal. Calcd. for C₂₅H₁₈ClNOS: C, 72.19; H, 4.36; N, 3.37; Found: C, 72.05; H, 4.24; N, 3.33]; LC/MS (ESI, m/z): 416.10 [M + H] ⁺, exact mass 415.08 for C₂₅H₁₈ClNOS.

3.17. Synthesis of 3-(Benzo[b]thiophen-2-yl)-1-(4-fluorophenyl)-3-(1H-indol-3-yl)propan-1-one (3p)

Following the general procedure (GP1) chalcone 1k (141 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3p (yield 164 mg, 82%); m.p. 142–143 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.98 (s, 1H, NH), 8.14 (dd, J = 8.5, 5.6 Hz, 2H, Ar-H), 7.76 (d, J = 8.0 Hz, 1H, Ar-H), 7.68 (d, J = 7.9 Hz, 1H, Ar-H), 7.55 (d, J = 8.0 Hz, 1H, Ar-H), 7.43 (s, 1H, Ar-H), 7.40–7.30 (m, 4H, Ar-H), 7.30–7.24 (m, 1H, Ar-H), 7.21 (t, J = 7.6 Hz, 1H, Ar-H), 7.06 (t, J = 7.6 Hz, 1H, Ar-H), 6.93 (t, J = 7.5 Hz, 1H, Ar-H), 5.25 (t, J = 7.2 Hz, 1H, CH), 4.02 (dd, J = 11.1, 7.2 Hz, 2H, CH₂); ¹³C-NMR (101 MHz, DMSO-d₆) δ 196.4 (CO), 166.3 & 163.8 (C₁-F, J_C-F = 250.2 Hz), 150.8, 139.6, 138.5, 136.4, 133.4 & 133.4 (C₄-F, J_C-F = 2.9 Hz), 131.2, 126.1, 124.1, 123.6, 123.0, 122.5, 122.5, 122.2, 121.1, 120.2 & 120.2 (C₃-F, J_C-F = 6.3 Hz), 118.5, 116.9, 115.8 & 115.6 (C₂-F, J_C-F = 22.0 Hz), 111.5, 44.5 (CH), 33.5(CH₂); IR (KBr, cm⁻¹) ν_max = 3400, 3059, 2904, 1670, 1591, 1502, 1454, 1411, 1356, 1335, 1226, 1153; [Anal. Calcd. for C₂₅H₁₈FNOS: C, 75.16; H, 4.54; N, 3.51; Found: C, 75.26; H, 4.43; N, 3.47]; LC/MS (ESI, m/z): 400.13 [M + H] ⁺, exact mass 399.11 for C₂₅H₁₈FNOS.

3.18. Synthesis of 3-(Benzo[b]thiophen-2-yl)-3-(1H-indol-3-yl)-1-(4-(trifluoromethyl)phenyl)propan-1-one (3q)

Following the general procedure (GP1) chalcone 1l (162 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3q (yield 171 mg, 76%); m.p. 165–166 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.98 (d, J = 2.5 Hz, 1H, NH), 8.23 (d, J = 8.1 Hz, 2H, Ar-H), 7.89 (d, J = 8.3 Hz, 2H, Ar-H), 7.77 (d, J = 8.0 Hz, 1H, Ar-H), 7.69 (d, J = 7.9 Hz, 1H, Ar-H), 7.56 (d, J = 8.0 Hz, 1H, Ar-H), 7.43 (d, J = 2.6 Hz, 1H, Ar-H), 7.35 (d, J = 8.6 Hz, 2H, Ar-H), 7.30–7.19 (m, 2H, Ar-H), 7.06 (t, J = 7.6 Hz, 1H, Ar-H), 6.94 (t, J = 7.4 Hz, 1H, Ar-H), 5.26 (t, J = 7.1 Hz, 1H, CH), 4.10 (t, J = 7.4 Hz, 2H, CH₂); ¹³C-NMR (101 MHz, DMSO-d₆) δ 197.3 (CO), 150.6, 139.7, 139.5, 138.5, 136.4, 132.7, 132.4, 128.9, 126.1, 125.70, 124.1, 123.6, 123.0, 122.5, 122.1, 121.2, 120.2, 118.6, 116.7, 111.5, 44.9 (CH), 33.4 (CH₂); IR (KBr, cm⁻¹) ν_max = 3458, 3415, 3050, 2960, 2902, 1689, 1454, 1409, 1319, 1261, 1166; [Anal. Calcd. for C₂₆H₁₈F₃NOS: C, 69.47; H, 4.04; N, 3.12; Found: C, 69.59; H, 3.97; N, 3.07]; LC/MS (ESI, m/z): 450.11 [M + H] ⁺, exact mass 449.11 for C₂₆H₁₈F₃NOS.

3.19. Synthesis of 3-(Benzofuran-2-yl)-3-(1H-indol-3-yl)-1-(2-methoxyphenyl)propan-1-one (3r):

Following the general procedure (GP1) chalcone 1f (139 mg, 0.5 mmol) indole 2a (64 mg, 0.55 mmol) produces Friedel–Crafts product-3r (yield 158 mg, 80%); m.p. 67–68 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 10.96 (d, J = 2.5 Hz, 1H, NH), 7.56–7.48 (m, 3H, Ar-H), 7.47–7.40 (m, 2H, Ar-H), 7.35 (d, J = 8.1 Hz, 1H, Ar-H), 7.26 (d, J = 2.6 Hz, 1H, Ar-H), 7.16 (dd, J = 8.1, 4.9 Hz, 3H, Ar-H), 7.06 (t, J = 7.4 Hz, 1H, Ar-H), 6.96 (dt, J = 14.9, 7.2 Hz, 2H, Ar-H), 6.62 (s, 1H, Ar-H), 5.06 (t, J = 7.2 Hz, 1H, CH), 3.94 (dd, J = 17.1, 7.6 Hz, 1H, CH_2(a)), 3.86 (s, 3H, OCH₃), 3.78 (dd, J = 17.0, 7.1 Hz, 1H, CH_2(b)); ¹³C-NMR (101 MHz, DMSO-d₆) δ 199.5 (CO), 160.9, 158.0, 153.9, 136.3, 133.6, 129.6, 129.4, 128.4, 127.7, 126.0, 122.9, 122.7, 121.1, 120.6, 120.4, 118.6, 118.4, 114.2, 112.5, 111.7, 110.6, 101.9, 55.8 (OCH₃), 47.1 (CH), 31.9 (CH₂); IR (KBr, cm⁻¹) ν_max = 3408, 3051, 2918, 2837, 1666, 1599, 1483, 1454, 1430, 1340, 1286, 1244, 1161; [Anal. Calcd. for C₂₆H₂₁NO₃: C, 78.97; H, 5.35; N, 3.54; Found: C, 78.81; H, 5.19; N, 3.39]; LC/MS (ESI, m/z): 396.16 [M + H] ⁺, exact mass 395.15 for C₂₆H₂₁NO_3.

3.20. Synthesis of 3-(Benzofuran-2-yl)-3-(5-bromo-1H-indol-3-yl)-1-(2-methoxyphenyl)propan-1-one (3s)

Following the general procedure (GP1) chalcone 1f (139 mg, 0.5 mmol) 5-bromoindole 2b (108 mg, 0.55 mmol) produces Friedel–Crafts product-3s (yield 180 mg, 76%); m.p. 60–61 °C; ¹H-NMR (400 MHz, DMSO-d₆) δ 11.20 (d, J = 2.3 Hz, 1H, NH), 7.72 (s, 1H, Ar-H), 7.51 (t, J = 7.5 Hz, 2H, Ar-H), 7.47–7.41 (m, 2H, Ar-H), 7.37–7.31 (m, 2H, Ar-H), 7.17 (dd, J = 11.8, 7.6 Hz, 4H, Ar-H), 6.98 (t, J = 7.4 Hz, 1H, Ar-H), 6.65 (s, 1H, Ar-H), 5.05 (t, J = 7.3 Hz, 1H, CH), 3.91 (dd, J = 17.3, 7.4 Hz, 1H, CH_2(a)), 3.87 (s, 3H, OCH₃), 3.81 (dd, J = 17.1, 7.3 Hz, 1H, CH_2(b)); ¹³C-NMR (126 MHz, DMSO-d₆) δ 199.4, 160.6, 158.1, 153.9, 135.0, 133.7, 129.6, 128.3, 127.9, 127.6, 124.7, 123.6, 123.5, 122.6, 120.8, 120.6, 120.5, 114.0, 113.6, 112.4, 111.2, 110.7, 101.9, 55.8, 47.0, 31.8; IR (KBr, cm⁻¹) ν_max = 3320, 3045, 2915, 2857, 1668, 1575, 1452, 1395, 1365, 1338, 1252; [Anal. Calcd. for C₂₆H₂₀BrNO₃: C, 65.83; H, 4.25; N, 2.95; Found: C, 66.02; H, 4.11; N, 2.86]; LC/MS (ESI, m/z): 474.07 [M + H] ⁺, exact mass 473.06 for C₂₆H₂₀BrNO₃

3.21. The Biological Activity Assays Protocols

Cytotoxicity against BJ Human fibroblast cells, and anti-cancer activity against PC3, HeLa and MCF-7 cancer cell lines were evaluated by following the procedure as described in the literature [25,26,27,28,29] (Supplementary Materials).

4. Conclusions

We have successfully synthesized multi-scaffold-based indoles, benzofurans and benzothiophenes. The anti-cancer activity showed promising results which make them candidates for further research. Fluorine atoms apparently play a crucial role in the bioactivity of this class of compounds with 3b appearing to be the most active member of the series against cervical cancer HeLa (IC₅₀ = 8.2 ± 0.2 µM) and breast cancer MCF-7 cell lines (IC₅₀ = 12.3 ± 0.04 µM), whereas hit 3e (IC₅₀ = 7.8 ± 0.4 µM) appeared more active against PC3 prostate cancer cell line. The mechanism of action and in vivo study are required to further validate results of in vitro status.

Supplementary Materials

The following are available online, ¹H-NMR and ¹³C-NMR for compounds 3a–3s along with the biological activity assays protocols are provided in the Supplementary Materials.

Author Contributions

Conceptualization, A.B. and M.I.C.; methodology, M.S.I.; M.A.; A.M.A.-M.; A.S.A.; S.A.; validation, M.S.I.; M.A.; A.M.A.-M.; A.S.A.; S.A.; formal analysis, M.S.I.; M.A.; A.M.M.A.-M.; A.S.A.; S.A.; investigation, M.S.I.; M.A.; A.M.A.-M.; A.S.A.; S.A.; resources, A.B.; data curation, M.S.I.; M.A.; A.M.A.-M.; A.S.A.; writing—original draft preparation, A.B.; and S.Y.; writing—review and editing, M.I.C.; visualization, A.B. and M.I.C.; project administration, M.A.; funding acquisition, A.B. All authors have read and agreed to the published version of the manuscript.

Funding

King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia, Award Number (14-BIO128-02).

Data Availability Statement

The data presented in this study are available in Supplementary Materials.

Acknowledgments

This Project was funded by the National Plan for Science, Technology and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia, Award Number (14-BIO128-02).

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of the compounds 3a–3s are available from the authors.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures, Scheme and Table

Figure 1. Bioactive compounds incorporating indole skeleton.

Scheme 1. Synthetic routes to 3a–3s. The reaction carried out with optimum reaction conditions as reported by Barakat et al. [23].

Figure 2. List of synthesized chalcones and substituted indoles utilized in this study.

Table 1

The IC₅₀ results of the synthesized against 4 cancer cell lines.

Compound	Structure3a–3s	Cancer Type/Cell Line (IC50, µM)
		Human fibroblastBJ	PC3	HeLa	MCF-7
3a	[Image omitted. Please see PDF.]	NA	11.4 ± 0.2	22.5 ± 0.9	NA
3b	[Image omitted. Please see PDF.]	>30	22.2 ± 0.5	8.2 ± 0.2	12.37 ± 0.04
3c	[Image omitted. Please see PDF.]	>30	21.9 ± 1.5	10.8 ± 0.1	25.87 ± 0.80
3d	[Image omitted. Please see PDF.]	>30	26.3 ± 0.8	12.6 ± 0.4	NA
3e	[Image omitted. Please see PDF.]	>30	7.8 ± 0.4	13.6 ± 0.4	NA
3f	[Image omitted. Please see PDF.]	>30	27.0 ± 0.4	11.9 ± 0.2	19.28 ± 0.78
3g	[Image omitted. Please see PDF.]	>30	20.0 ± 1.3	14.7 ± 1.1	NA
3h	[Image omitted. Please see PDF.]	>30	29.7 ± 0.4	13.8 ± 0.3	NA
3i	[Image omitted. Please see PDF.]	NA	NA	15.2 ± 0.6	NA
3j	[Image omitted. Please see PDF.]	NA	16.0 ± 0.1	17.3 ± 0.7	NA
3k	[Image omitted. Please see PDF.]	NA	NA	14.9 ± 0.6	NA
3l	[Image omitted. Please see PDF.]	>30	16.3 ± 1.6	11.1 ± 0.6	NA
3m	[Image omitted. Please see PDF.]	>50	19.3 ± 0.1	15.2 ± 0.2	22.93 ± 0.43
3n	[Image omitted. Please see PDF.]	>50	20.4 ± 0.4	12.4 ± 0.2	NA
3o	[Image omitted. Please see PDF.]	>50	29.7 ± 0.1	13.8 ± 0.3	NA
3p	[Image omitted. Please see PDF.]	>50	27.6 ± 0.1	12.7 ± 0.1	NA
3q	[Image omitted. Please see PDF.]	>50	18.0 ± 0.3	18.8 ± 0.2	NA
3r	[Image omitted. Please see PDF.]	NA	NA	NA	NA
3s	[Image omitted. Please see PDF.]	NA	NA	18.4 ± 0.2	28.64 ± 0.33
	STD. Doxorubicin	NA	1.9 ± 0.4	0.9 ± 0.14	0.79 ± 0.05

IC₅₀ (μM) was evaluated using MTT assay and ± is the standard deviation from three independent experiments. NA: means that the tested compound did not show anticancer activity at 30 µM.