The laboratory glassware in which the chemical reactions were carried out was heated in an oven at 140 °C each time before use. The temperature of the water bath in the rotary evaporator did not exceed the temperature of the reaction in which a particular compound was formed with a maximum of 70 °C for reactions carried out in DMF. The reaction temperature was read from the display of a Heidolph MR Hei-Tec magnetic heating stirrer equipped with an external Pt1000 sensor measuring the temperature of the Heat-On heating jacket. Chemical reagents and solvents of high-grade purity were purchased from commercial suppliers (Sigma Aldrich, Fluorochem, Tokyo Chemical Industry Co., Ltd., and Acros Organics) and used without additional processing. Reactions performed under microwave irradiation were carried out using an Anton Paar Monowave 400 microwave reactor (Anton Paar, Graz, Austria). Thin-layer chromatography (TLC) was performed on precoated TLC plates (SiliaPlate TLC, thickness 200 µm, F-254, SiliCycle Inc., Quebec, Canada) and visualized under a UV lamp (λ = 254 and 365 nm). Chromatographic separations were performed on silica gel columns using the flash method–flash column chromatography (FCC), with the use of silica gel as the stationary phase (SiliaFlash P60, particle size 40–63 µm, SiliCycle Inc., Quebec, Canada). Melting points were determined in open glass capillaries using a Stuart SMP10 apparatus (Bibby Sterilin Ltd., Stone, Staffordshire, UK) and are uncorrected. Nuclear magnetic resonance (NMR) spectra (1D: 1H, 13C; 2D: COSY, HSQC, HMBC) were recorded on an Agilent DD2 800 spectrometer (Agilent Technologies, Santa Clara, California, USA) equipped with a 5 mm 1H probe; data are reported as follows: chemical shift (ppm value), multiplicity (indicated as: br, broad signal; s, singlet; d, doublet; t, triplet; q, quartet; p, quintet; m, multiplet), coupling constants (J) in Hertz (Hz) and integrated intensity. High-resolution mass spectra (HR-MS) were recorded on a Bruker Impact HD apparatus (Bruker Daltonics, Billerica, Massachusetts, USA) operating in electrospray mode (ESI) with positive ionization. Detailed compound data such as NMR spectra, HR-MS spectra and UV-Vis spectra can be found in the Supplementary Information.

Chromatographic purity analysis of compounds was carried out on an Agilent 1260 Infinity II LC System (Agilent Technologies, Bolinem, Germany) equipped with a quaternary pump (model G7111B) and degasser, a vial sampler (model G7129A) set at 20 °C, multicolumn thermostat (model G7116A) set at 35 °C, and detector diode array (DAD) WR, model G7115A. The detection wavelength was adjusted for each tested compound at its absorption maximum. The elution of compounds was achieved on the reverse phase column used as stationary phase (C-18(2) 100 Å Luna, 150 × 4.6 mm ID, 5 µm, Phenomenex®, USA) and a mobile phase with the flow rate 1.0 mL/min based on gradient solvent systems consisting of acetic acid (0.4% in water) (phase A) and acetonitrile (phase B). A sample volume of 10 µL was injected into the column. Gradient conditions for the morpholine-bearing derivatives of curcumin are given in Table S3 (gradient A), and for the other compounds in Table S4 (gradient B) in Supplementary Information.

Reagents used for in vitro experiments, such as Dulbecco’s modified Eagle’s medium (DMEM), fetal bovine serum (FBS), penicillin-streptomycin-L-glutamine solution, phosphate-buffered saline (PBS), trypsin-EDTA, molecular-grade dimethylsulfoxide (DMSO), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), were purchased from Sigma Aldrich (St. Louis, MO, USA). The Roswell Park Memorial Institute 1640 (RPMI) medium and Eagle’s Minimum Essential Medium (EMEM) were purchased from Thermofisher (Waltham, MA, USA). The DMSO for dissolving formazan crystals was obtained from Avantor Performance Materials (Gliwice, Poland).

Synthesis of 2,2-difluoro-6-methyl-4-phenyl-1,3,2-dioxaborinine (3-B) and 2,2‐difluoro‐4,6‐dimethyl‐1,3,2‐dioxaborinine (1-B)

BF2-blocked diketones (acetylacetone and benzoylacetone) were synthesized according to the procedure reported in the literature [24]. For example, benzoylacetone (3, 5.00 g, 30.83 mmol, 1 equiv.) was dissolved in 100 mL of dichloromethane. Then 5.7 mL (6.55 g, 46.25 mmol, 1.5 equiv.) of boron trifluoride diethyl etherate was added and stirred for 24 h at 40 °C under argon. The reaction was cooled to room temperature, and 100 mL of water was added. The organic layer was separated and further extracted with water several times until the pH of the aqueous layer was neutral. Then the organic layer was dried with anhydrous magnesium sulfate and evaporated under reduced pressure to obtain the pure product as a white powder with 85% yield (5.53 g, 26.32 mmol).

Synthesis of morpholine-modified aldehydes

Aldehydes containing a morpholinoethoxy group were synthesized according to the literature and our previous experiments [22, 23]. For example, 3‐methoxy‐4‐[2‐(morpholin‐4‐yl)ethoxy]benzaldehyde (morpholinoethoxyvanillin) was synthesized as follows. First, 750 mg of vanillin (4.93 mmol, 1.0 equiv.), 1.10 g of 4-(2-chloroethyl)morpholine hydrochloride (5.92 mmol, 1.2 equiv.), and 4.08 g of potassium carbonate (29.61 mmol, 6 equiv.) were transferred to a dry round bottom flask. Then, 20 mL of N,N-dimethylformamide (DMF) was added, and the reaction was carried out for 24 h under inert gas at 70 °C with constant stirring. The reaction mixture was cooled to room temperature and filtered to remove potassium carbonate. The filtrate was evaporated to give a yellowish oil which was then purified by column chromatography (DCM: MeOH 20:1), giving a colorless oil with a yield of 91% (1.19 g, 4.49 mmol). The aldehyde was stored in a refrigerator (2−8 °C) for further use.

Synthesis of curcuminoids and quasicurcuminoids (aldol condensation)

The synthesis of quasicurcuminoids and curcuminoids followed the aldol condensation mechanism and was performed according to the procedure described earlier in the literature [24]. For example, the synthesis of 4c-B has been described below. Initially, 300 mg of 3-B (1.43 mmol, 1.0 equiv.) and 217 mg of aldehyde (isovanillin, 1.43 mmol, 1 equiv.) were transferred to a dry round bottom flask. Then 10 mL of toluene, 358 µL of tributyl borate (328 mg, 1.43 mmol, 1.0 equiv.), and 14 µL of N-butylamine (10 mg, 0.14 mmol, 0.1 equiv.) were added consecutively. The reaction was carried out for 24 h under inert gas at 70 °C with constant stirring. The reaction was cooled to room temperature, and the resulting colorful precipitate was filtered. The solid was washed several times with toluene and dried in the air, giving 470 mg (1.37 mmol) of 4c-B with 96% yield. In the case of symmetrically substituted curcuminoids, 2.0 equiv. of aldehyde, 2.0 equiv. tributyl borate and 0.2 equiv. of N-butylamine were used. The synthesis and preliminary physicochemical characterization of 2c-B [24], 4f-B [45] was previously reported in the literature.

Detachment of the BF2 moiety

Curcuminoid decomplexation reaction involving cleavage of the BF2 group and release of the diketone moiety was performed in a microwave reactor according to the literature protocol [25]. Briefly, 5 mL of aqueous methanol (methanol: water 4:1, v/v), 200 mg of compound 4c-B (0.6 mmol, 1.0 equiv.), and 156 mg of sodium oxalate (1.2 mmol, 2 equiv.) were mixed in the microwave reaction vial. Then, the sealed vial was placed in a microwave reactor for 8 min at 140 °C. After cooling to ambient temperature, the solvent was evaporated. Afterward, water was added to precipitate the product. The resulting yellow precipitate of 4c was filtered off, washed several times with water, and dried. The reaction yield was 84% (145 mg). The synthesis and preliminary physicochemical characterization of 2c [46], 4a [47], 4b [48], 4c [49], 4d [50], 4e [49], 4f [48], 4g [47] and 4i [47, 48] was previously reported in the literature.

Characterization of the obtained compounds4‐(2‐ethenyl]‐1,3,2‐dioxaborinin‐4‐yl}ethenyl]‐2‐methoxyphenoxy}ethyl)morpholine (2a-B)

Yield: 77%; ESI MS recorded: 643.3009 m/z [M+H]+, expected for C33H41BF2N2O8: 643.2997 m/z [M+H]+; Rf = 0.45 (DCM:MeOH 10:1); MP = 122 °C; λmax (ACN) nm (logε): 502 (5.04); HPLC purity: DAD 96.64%. 1H NMR (800 MHz, acetone-d6) δ 7.97 (d, J = 15.6 Hz, 2H), 7.47 (d, J = 1.9 Hz, 2H), 7.42 (dd, J = 8.3, 2.0 Hz, 1H), 7.11 (d, J = 8.3 Hz, 2H), 6.98 (d, J = 15.6 Hz, 2H), 6.39 (s, 1H), 4.24 (t, J = 5.8 Hz, 4H), 3.91 (s, 6H), 3.61 (t, J = 4.6 Hz, 8H), 2.80 (s, 4H), 2.55 (s, 8H); 13C NMR (201 MHz, acetone-d6) δ 180.8, 153.4, 151.0, 147.4, 128.5, 125.6, 119.8, 113.9, 112.5, 102.2, 68.0, 67.5, 58.2, 56.4, 55.0.

(1E,4Z,6E)‐5‐hydroxy‐1,7‐bis()hepta‐1,4,6‐trien‐3‐one (2a)

Yield: 33%; ESI MS recorded: 595.3012 m/z [M+H]+, expected for C33H42N2O8: 595.3014 m/z [M+H]+; Rf = 0.39 (DCM:MeOH 10:1); MP = 100 °C; λmax (ACN) nm (logε): 421 (4.94); HPLC purity: DAD 96.64%. 1H NMR (800 MHz, acetone-d6) δ 7.61 (d, J = 15.8 Hz, 2H), 7.34 (d, J = 2.0 Hz, 2H), 7.23 (dd, J = 8.4, 1.8 Hz, 2H), 7.04 (d, J = 8.3 Hz, 2H), 6.75 (d, J = 15.8 Hz, 2H), 6.00 (s, 1H), 4.19 (t, J = 5.8 Hz, 4H), 3.89 (s, 6H), 3.62–3.59 (m, 8H), 2.77 (t, J = 5.8 Hz, 4H), 2.54 (s, 8H); 13C NMR (201 MHz, acetone-d6) δ 184.5, 151.8, 150.9, 141.2, 129.2, 123.6, 123.0, 114.1, 111.8, 101.8, 67.9, 67.5, 58.3, 56.3, 55.1.

4‐(2‐ethenyl]‐1,3,2‐dioxaborinin‐4‐yl}ethenyl]‐2‐methoxyphenoxy}ethyl)morpholine (2b-B)

Yield: 50%; ESI MS recorded: 643.3030 m/z [M+H]+, expected for C33H41BF2N2O8: 643.2997 m/z [M+H]+; Rf = 0.45 (DCM:MeOH 10:1); MP = 167 °C; λmax (ACN) nm (logε): 501 (4.99); HPLC purity: DAD 95.43%. 1H NMR (800 MHz, acetone-d6) δ 7.96 (d, J = 15.6 Hz, 2H), 7.49 (d, J = 2.0 Hz, 2H), 7.43 (dd, J = 8.4, 1.8 Hz, 2H), 7.09 (d, J = 8.4 Hz, 2H), 6.97 (d, J = 15.6 Hz, 2H), 6.38 (s, 1H), 4.24 (t, J = 5.9 Hz, 4H), 3.92 (s, 6H), 3.63–3.62 (m, 8H), 2.81–2.80 (m, 11H), 2.57 (s, 8H); 13C NMR (201 MHz, acetone-d6) δ 180.7, 154.4, 150.0, 147.4, 128.4, 125.9, 119.8, 113.7, 112.9, 102.2, 67.9, 67.5, 58.3, 56.4, 55.0.

(1E,4Z,6E)‐5‐hydroxy‐1,7‐bis()hepta‐1,4,6‐trien‐3‐one (2b)

Yield: 99%; ESI MS recorded: 595.3010 m/z [M+H]+, expected for C33H42N2O8: 595.3014 m/z [M+H]+; Rf = 0.47 (DCM:MeOH 10:1); MP = 195 °C; λmax (ACN) nm (logε): 419 (4.73); HPLC purity: DAD 98.34%. 1H NMR (800 MHz, acetone-d6) δ 7.60 (d, J = 15.8 Hz, 2H), 7.36 (d, J = 1.8 Hz, 2H), 7.24 (dd, J = 8.3, 1.8 Hz, 2H), 7.01 (d, J = 8.3 Hz, 2H), 6.73 (d, J = 15.8 Hz, 2H), 5.99 (s, 1H), 4.20 (t, J = 5.9 Hz, 4H), 3.87 (s, 6H), 3.63–3.61 (m, 8H), 2.78 (t, J = 5.9 Hz, 4H), 2.55 (s, 8H); 13C NMR (201 MHz, acetone-d6) δ 184.5, 152.8, 149.9, 141.2, 129.0, 123.9, 122.9, 113.1, 112.9, 101.8, 67.9, 67.5, 58.4, 56.3, 55.1.

2,2‐difluoro‐4,6‐bis[(1E)‐2‐phenylethenyl]‐1,3,2‐dioxaborinine (2c-B)

Yield: 59%; ESI MS recorded: 347.1034 m/z [M+Na]+, expected for C19H15BF2O2: 347.1026 m/z [M+Na]+; Rf = 0.52 (n-hexane:EtOAc 2:1); MP = 242 °C; λmax (ACN) nm (logε): 422 (4.77); HPLC purity: DAD 99.33%. 1H NMR (800 MHz, acetone-d6) δ 8.08 (d, J = 15.8 Hz, 2H), 7.86 (d, J = 6.1 Hz, 4H), 7.57–7.49 (m, 6H), 7.16 (d, J = 15.7 Hz, 2H), 6.60 (s, 1H); 13C NMR (201 MHz, acetone-d6) δ 181.8, 147.6, 135.3, 132.7, 130.2, 130.1, 122.3, 103.0.

(1E,4Z,6E)‐5‐hydroxy‐1,7‐diphenylhepta‐1,4,6‐trien‐3‐one (2c)

Yield: 79%; ESI MS recorded: 299.1047 m/z [M+Na]+, expected for C19H16O2: 299.1043 m/z [M+Na]+; Rf = 0.83 (n-hexane:EtOAc 2:1); MP = 142 °C; λmax (ACN) nm (logε): 392 (4.76); HPLC purity: DAD 99.57%. 1H NMR (800 MHz, acetone-d6) δ 7.73–7.67 (m, 6H), 7.47–7.40 (m, 6H), 6.89 (d, J = 15.9 Hz, 2H), 6.13 (s, 1H); 13C NMR (201 MHz, acetone-d6) δ 184.5, 141.2, 136.0, 131.0, 129.9, 129.1, 125.2, 102.5.

2,2‐difluoro‐4‐methyl‐6‐phenyl‐1,3,2‐dioxaborinine (3-B)

Yield: 85%; ESI MS recorded: 211.0744 m/z [M + H]+, 233.0570 [M+Na]+, expected for C10H9BF2O2: 211.0736 m/z [M+H]+ 233.0556 [M+Na]+; Rf = 0.27 (n-hexane:EtOAc 2:1); MP = 158 °C; λmax (ACN) nm (logε): 329 (4.47); HPLC purity: DAD 97.45%. 1H NMR (800 MHz, acetone-d6) δ 8.19 (dd, J = 8.5, 1.2 Hz, 2H), 7.80 (t, J = 7.4 Hz, 1H), 7.66–7.63 (m, 2H), 7.11 (s, 1H), 2.48 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 195.2, 183.1, 136.3, 132.3, 130.3, 129.8, 98.7, 24.8.

2,2‐difluoro‐4‐phenyl‐6‐[(1E)‐2‐(3,4,5‐trimethoxyphenyl)ethenyl]‐1,3,2‐dioxaborinine (4a-B)

Yield: 89%; ESI MS recorded: 411.1210 m/z [M+Na]+, expected for C20H19BF2O5: 411.1186 m/z [M+Na]+, Rf = 0.17 (DCM:MeOH 2:1); MP = 235 °C; λmax (ACN) nm (logε): 437 (4.68); HPLC purity: DAD 99.72%. 1H NMR (800 MHz, acetone-d6) δ 8.21 (dd, J = 8.5, 1.2 Hz, 2H), 8.12 (d, J = 15.7 Hz, 1H), 7.79 (t, J = 7.4 Hz, 1H), 7.67–7.64 (m, 2H), 7.24 (s, 2H), 7.19 (d, J = 15.7 Hz, 1H), 7.17 (s, 1H), 3.93 (s, 6H), 3.83 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 183.0, 182.7, 154.9, 149.0, 143.2, 136.1, 133.2, 130.7, 130.4, 129.6, 121.5, 108.2, 98.7, 61.0, 56.8.

(2Z,4E)‐3‐hydroxy‐1‐phenyl‐5‐(3,4,5‐trimethoxyphenyl)penta‐2,4‐dien‐1‐one (4a)

Yield: 90%; ESI MS recorded: 363.1211 m/z [M+Na]+, expected for C20H20O5: 363.1203 m/z [M+Na]+; Rf = 0.58 (n-hexane:EtOAc 2:1); MP = 120 °C; λmax (ACN) nm (logε): 385 (4.66); HPLC purity: DAD 99.04%. 1H NMR (800 MHz, acetone-d6) δ 8.04 (dd, J = 8.3, 1.1 Hz, 2H), 7.67 (d, J = 15.8 Hz, 1H), 7.63 (t, J = 7.3 Hz, 1H), 7.55 (t, J = 7.7 Hz, 2H), 7.06 (s, 2H), 6.90 (d, J = 15.8 Hz, 1H), 6.65 (s, 1H), 3.90 (s, 6H), 3.78 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 189.8, 181.2, 154.7, 141.3, 141.1, 137.1, 133.6, 131.6, 129.6, 128.1, 123.6, 106.6, 98.0, 60.7, 56.5.

4‐[(1E)‐2‐(2,2‐difluoro‐6‐phenyl‐1,3,2‐dioxaborinin‐4‐yl)ethenyl]‐2‐methoxyphenol (4b-B)

Yield: 96%; ESI MS recorded: 367.0920 m/z [M+Na]+, expected for C18H15BF2O4: 367.0924 m/z [M+Na]+; Rf = 0.20 (DCM); MP = 211 °C; λmax (ACN) nm (logε): 446 (4.75); HPLC purity: DAD 100.0%. 1H NMR (800 MHz, acetone-d6) δ 8.66 (s, 1H), 8.18 (dd, J = 8.5, 1.2 Hz, 2H), 8.13 (d, J = 15.6 Hz, 1H), 7.76 (t, J = 7.4 Hz, 1H), 7.65–7.62 (m, 2H), 7.52 (d, J = 2.0 Hz, 1H), 7.41 (dd, J = 8.2, 1.6 Hz, 1H), 7.13 (s, 1H), 7.06 (d, J = 15.6 Hz, 1H), 6.97 (d, J = 8.2 Hz, 1H), 3.96 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 183.1, 181.4, 152.4, 149.5, 149.1, 135.6, 133.3, 130.1, 129.3, 127.5, 126.3, 119.0, 116.7, 112.7, 98.1, 56.4.

(2Z,4E)‐3‐hydroxy‐5‐(4‐hydroxy‐3‐methoxyphenyl)‐1‐phenylpenta‐2,4‐dien‐1‐one (4b)

Yield: 78%; ESI MS recorded: 319.0941 m/z [M+Na]+, expected for C18H16O4: 319.0941 m/z [M+Na]+; Rf = 0.42 (n-hexane:EtOAc 2:1); MP = 158 °C; λmax (ACN) nm (logε): 393 (4.60); HPLC purity: DAD 98.66%. 1H NMR (800 MHz, acetone-d6) δ 8.19 (s, 1H), 8.03 (dd, J = 8.2, 1.1 Hz, 2H), 7.68 (d, J = 15.8 Hz, 1H), 7.61 (t, J = 7.3 Hz, 1H), 7.54 (t, J = 7.7 Hz, 2H), 7.36 (d, J = 1.8 Hz, 1H), 7.20 (dd, J = 8.1, 1.9 Hz, 1H), 6.90 (d, J = 8.1 Hz, 1H), 6.79 (d, J = 15.8 Hz, 1H), 6.62 (s, 1H), 3.93 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 189.0, 182.2, 150.1, 148.8, 141.5, 137.1, 133.4, 129.6, 128.2, 128.0, 123.9, 121.5, 116.3, 111.5, 97.6, 56.3.

5‐[(1E)‐2‐(2,2‐difluoro‐6‐phenyl‐1,3,2‐dioxaborinin‐4‐yl)ethenyl]‐2‐methoxyphenol (4c-B)

Yield: 96%; ESI MS recorded: 367.0927 m/z [M+Na]+, expected for C18H15BF2O4: 367.0924 m/z [M+Na]+; Rf = 0.20 (DCM); MP = 203 °C; λmax (ACN) nm (logε): 446 (4.73); HPLC purity: DAD 100.0%. 1H NMR (800 MHz, acetone-d6) δ 8.19 (dd, J = 8.5, 1.2 Hz, 2H), 8.09 (d, J = 15.6 Hz, 1H), 8.06 (s, 1H), 7.77 (t, J = 7.4 Hz, 1H), 7.66–7.63 (m, 2H), 7.40–7.33 (m, 2H), 7.17 (s, 1H), 7.10 (d, J = 8.9 Hz, 1H), 7.03 (d, J = 15.6 Hz, 1H), 3.95 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 183.0, 181.8, 152.6, 149.1, 148.1, 135.7, 133.2, 130.2, 129.4, 128.5, 125.1, 119.7, 115.2, 112.5, 98.4, 56.5.

(2Z,4E)‐3‐hydroxy‐5‐(3‐hydroxy‐4‐methoxyphenyl)‐1‐phenylpenta‐2,4‐dien‐1‐one (4c)

Yield: 84%; ESI MS recorded: 319.0954 m/z [M+Na]+, expected for C18H16O4: 319.0941 m/z [M+Na]+; Rf = 0.38 (n-hexane:EtOAc 2:1); MP = 136 °C; λmax (ACN) nm (logε): 390 (4.65); HPLC purity: DAD 99.40%. 1H NMR (800 MHz, acetone-d6) δ 8.04 (d, J = 7.2 Hz, 2H), 7.84 (s, 1H), 7.64 (d, J = 15.8 Hz, 1H), 7.61 (t, J = 7.3 Hz, 1H), 7.54 (t, J = 7.7 Hz, 2H), 7.23 (d, J = 2.1 Hz, 1H), 7.16 (d, J = 8.3 Hz, 1H), 7.01 (d, J = 8.3 Hz, 1H), 6.76 (d, J = 15.8 Hz, 1H), 6.65 (s, 1H), 3.90 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 189.3, 181.8, 150.6, 147.9, 141.1, 137.1, 133.4, 129.6, 129.4, 128.1, 122.5, 122.1, 114.4, 112.4, 97.8, 56.3.

4‐[(1E)‐2‐(2,2‐difluoro‐6‐phenyl‐1,3,2‐dioxaborinin‐4‐yl)ethenyl]‐2‐ethoxyphenol (4d-B)

Yield: 80%; ESI MS recorded: 381.1083 m/z [M+Na]+, expected for C19H17BF2O4: 381.1080 m/z [M+Na]+; Rf = 0.68 (n-hexane:EtOAc 1:2); MP = 197 °C; λmax (ACN) nm (logε): 452 (4.47); HPLC purity: DAD 100.0%. 1H NMR (800 MHz, acetone-d6) δ 8.64 (s, 1H), 8.18 (dd, J = 8.5, 1.2 Hz, 2H), 8.12 (d, J = 15.6 Hz, 1H), 7.76 (t, J = 7.4, Hz, 1H), 7.65–7.62 (m, 2H), 7.50 (d, J = 2.0 Hz, 1H), 7.40 (dd, J = 8.2, 2.0 Hz, 1H), 7.12 (s, 1H), 7.05 (d, J = 15.6 Hz, 1H), 6.97 (d, J = 8.2 Hz, 1H), 4.23 (q, J = 7.0 Hz, 2H), 1.42 (t, J = 7.0 Hz, 3H); 13C NMR (201 MHz, acetone-d6) δ 183.1, 181.4, 152.5, 149.6, 148.2, 135.6, 133.3, 130.1, 129.3, 127.4, 126.2, 118.9, 116.7, 113.6, 98.1, 65.3, 14.9.

(2Z,4E)‐5‐(3‐ethoxy‐4‐hydroxyphenyl)‐3‐hydroxy‐1‐phenylpenta‐2,4‐dien‐1‐one (4d)

Yield: 90%; ESI MS recorded: 333.1099 m/z [M+Na]+, expected for C19H18O4: 333.1098 m/z [M+Na]+; Rf = 0.62 (n-hexane:EtOAc 2:1); MP = 75 °C; λmax (ACN) nm (logε): 394 (4.61); HPLC purity: DAD 98.12%. 1H NMR (800 MHz, acetone-d6) δ 8.17 (s, 1H), 8.03 (d, J = 7.1 Hz, 2H), 7.67 (d, J = 15.8 Hz, 1H), 7.61 (t, J = 7.3 Hz, 1H), 7.53 (t, J = 11.5, 4.1 Hz, 2H), 7.34 (d, J = 1.9 Hz, 1H), 7.20 (d, J = 6.3 Hz, 1H), 6.90 (d, J = 8.1 Hz, 1H), 6.78 (d, J = 15.8 Hz, 1H), 6.61 (s, 1H), 4.19 (q, J = 7.0 Hz, 2H), 1.41 (t, J = 7.0 Hz, 3H); 13C NMR (201 MHz, acetone-d6) δ 189.0, 182.2, 150.3, 148.0, 141.6, 137.1, 133.4, 129.6, 128.1, 128.0, 123.8, 121.4, 116.3, 112.4, 97.6, 65.2, 15.0.

4‐[(1E)‐2‐(2,2‐difluoro‐6‐phenyl‐1,3,2‐dioxaborinin‐4‐yl)ethenyl]‐2,6‐dimethoxyphenol (4e-B)

Yield: 97%; ESI MS recorded: 397.1035 m/z [M+Na]+, expected for C19H17BF2O5: 397.1030 m/z [M+Na]+; Rf = 0.56 (DCM:MeOH 50:1); MP = 170 °C; λmax (ACN) nm (logε): 461 (4.67); HPLC purity: DAD 100.0%. 1H NMR (800 MHz, acetone-d6) δ 8.18 (dd, J = 8.5, 1.2 Hz, 1H), 8.12 (d, J = 15.5 Hz, 1H), 7.76 (t, J = 7.4, Hz, 1H), 7.65–7.61 (m, 1H), 7.25 (s, 2H), 7.11 (s, 1H), 7.09 (d, J = 15.5 Hz, 1H), 3.93 (s, 6H); 13C NMR (201 MHz, acetone-d6) δ 182.9, 181.4, 149.9, 149.2, 141.9, 135.6, 133.3, 130.1, 129.3, 126.1, 119.2, 108.5, 98.2, 56.8.

(2Z,4E)‐3‐hydroxy‐5‐(4‐hydroxy‐3,5‐dimethoxyphenyl)‐1‐phenylpenta‐2,4‐dien‐1‐one (4e)

Yield: 91%; ESI MS recorded: 349.1050 m/z [M+Na]+, expected for C19H18O5: 349.1047 m/z [M+Na]+; Rf = 0.27 (n-hexane:EtOAc 2:1); MP = 133 °C; λmax (ACN) nm (logε): 399 (4.59); HPLC purity: DAD 99.37%. 1H NMR (800 MHz, acetone-d6) δ 8.03 (d, J = 7.1 Hz, 2H), 7.82 (s, 1H), 7.67 (d, J = 15.7 Hz, 1H), 7.61 (t, J = 7.3 Hz, 1H), 7.53 (t, J = 7.9, 7.4 Hz, 2H), 7.06 (s, 2H), 6.82 (d, J = 15.8 Hz, 1H), 6.61 (s, 1H), 3.90 (s, 6H); 13C NMR (201 MHz, acetone-d6) δ 189.1, 182.0, 149.0, 141.8, 139.6, 137.1, 133.4, 129.6, 128.0, 126.9, 121.7, 106.9, 97.6, 56.7.

2,2‐difluoro‐4‐phenyl‐6‐[(1E)‐2‐phenylethenyl]‐1,3,2‐dioxaborinine (4f-B)

Yield: 57%; ESI MS recorded: 321.0881 m/z [M+Na]+, expected for C17H13BF2O2: 321.0869 m/z [M+Na]+; Rf = 0.40 (n-hexane:EtOAc 2:1); MP = 184 °C; λmax (ACN) nm (logε): 396 (4.77); HPLC purity: DAD 99.34%. 1H NMR (800 MHz, acetone-d6) δ 8.22 (dd, J = 8.5, 1.2 Hz, 2H), 8.18 (d, J = 15.8 Hz, 1H), 7.87 (dd, J = 7.8, 1.2 Hz, 2H), 7.80 (t, J = 7.4, Hz, 1H), 7.66 (t, J = 7.9 Hz, 2H), 7.55–7.52 (m, 3H), 7.27 (s, 1H), 7.24 (d, J = 15.8 Hz, 1H); 13C NMR (201 MHz, acetone-d6) δ 183.2, 182.8, 148.2, 136.2, 135.2, 133.0, 132.8, 130.3, 130.3, 130.2, 129.6, 122.4, 98.8.

(2Z,4E)‐3‐hydroxy‐1,5‐diphenylpenta‐2,4‐dien‐1‐one (4f)

Yield: 79%; ESI MS recorded: 273.0893 m/z [M+Na]+, expected for C17H14O2: 273.0886 m/z [M+Na]+; Rf = 0.85 (n-hexane:EtOAc 2:1); MP = 110 °C; λmax (ACN) nm (logε): 363 (4.58); HPLC purity: DAD 99.88%. 1H NMR (800 MHz, acetone-d6) δ 8.06 (d, J = 7.2 Hz, 2H), 7.73 (d, J = 16.0 Hz, 1H), 7.71 (d, J = 7.3 Hz, 2H), 7.63 (t, J = 7.3 Hz, 1H), 7.55 (t, J = 7.8 Hz, 2H), 7.46 (t, J = 7.3 Hz, 2H), 7.42 (t, J = 7.2 Hz, 1H), 6.95 (d, J = 15.9 Hz, 1H), 6.72 (s, 1H); 13C NMR (201 MHz, acetone-d6) δ 190.3, 180.7, 140.6, 137.0, 136.1, 133.7, 130.9, 129.9, 129.7, 129.0, 128.2, 124.5, 98.3.

4‐[(1E)‐2‐(3,5‐dimethoxyphenyl)ethenyl]‐2,2‐difluoro‐6‐phenyl‐1,3,2‐dioxaborinine (4g-B)

Yield: 86%; ESI MS recorded: 381.1093 m/z [M+Na]+, expected for C19H17BF2O4: 381.1080 m/z [M+Na]+; Rf = 0.38 (n-hexane:EtOAc 2:1); MP = 205 °C; λmax (ACN) nm (logε): 402 (4.74); HPLC purity: DAD 99.72%. 1H NMR (800 MHz, acetone-d6) δ 8.21 (dd, J = 8.4, 1.1 Hz, 2H), 8.09 (d, J = 15.8 Hz, 1H), 7.80 (t, J = 7.4 Hz, 1H), 7.67–7.64 (m, 2H), 7.23 (t, J = 7.9 Hz, 2H), 7.04 (d, J = 2.2 Hz, 2H), 6.66 (t, J = 2.2 Hz, 1H), 3.87 (s, 6H); 13C NMR (201 MHz, acetone-d6) δ 183.2, 182.8, 162.3, 148.3, 137.1, 136.2, 132.9, 130.3, 129.6, 122.9, 107.9, 105.1, 98.8, 55.9.

(2Z,4E)‐5‐(3,5‐dimethoxyphenyl)‐3‐hydroxy‐1‐phenylpenta‐2,4‐dien‐1‐one (4g)

Yield: 86%; ESI MS recorded: 333.1102 m/z [M+Na]+, expected for C19H18O4: 333.1098 m/z [M+Na]+; Rf = 0.69 (n-hexane:EtOAc 2:1); MP = 104 °C; λmax (ACN) nm (logε): 374 (4.64); HPLC purity: DAD 99.61%. 1H NMR (800 MHz, acetone-d6) δ 8.05 (dd, J = 8.2, 1.1 Hz, 1H), 7.68–7.61 (m, J = 19.3, 11.8 Hz, 2H), 7.55 (t, J = 7.8 Hz, 2H), 6.95 (d, J = 15.9 Hz, 1H), 6.88 (d, J = 2.2 Hz, 1H), 6.69 (s, 1H), 6.55 (t, J = 2.2 Hz, 1H), 3.84 (s, 6H); 13C NMR (201 MHz, acetone-d6) δ 190.4, 180.6, 162.2, 140.7, 138.0, 137.1, 133.7, 129.7, 128.2, 124.9, 106.8, 103.2, 98.4, 55.8.

2,2‐difluoro‐4‐phenyl‐6‐[(1E)‐2‐(2,4,6‐trimethoxyphenyl)ethenyl]‐1,3,2‐dioxaborinine (4h-B)

Yield: 99%; ESI MS recorded: 411.1188 m/z [M+Na]+, expected for C20H19BF2O5: 411.1186 m/z [M+Na]+; Rf = 0.10 (n-hexane:EtOAc 2:1); MP = 210 °C; λmax (ACN) nm (logε): 472 (4.63); HPLC purity: DAD 98.48%. 1H NMR (800 MHz, acetone-d6) δ 8.60 (d, J = 15.6 Hz, 1H), 8.16 (dd, J = 8.3, 1.1 Hz, 2H), 7.73 (t, J = 7.4 Hz, 1H), 7.62 (t, J = 7.8 Hz, 2H), 7.41 (d, J = 15.6 Hz, 1H), 7.02 (s, 1H), 6.36 (s, 2H), 4.01 (s, 6H), 3.95 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 184.2, 179.9, 167.1, 164.0, 140.5, 135.1, 133.6, 130.0, 129.1, 120.1, 107.0, 98.7, 91.9, 56.7, 56.3.

(2Z,4E)‐3‐hydroxy‐1‐phenyl‐5‐(2,4,6‐trimethoxyphenyl)penta‐2,4‐dien‐1‐one (4h)

Yield: 51%; ESI MS recorded: 363.1206 m/z [M+Na]+, expected for C20H20O5: 363.1203 m/z [M+Na]+; Rf = 0.48 (n-hexane:EtOAc 2:1); MP = 143 °C; λmax (ACN) nm (logε): 405 (4.67); HPLC purity: DAD 98.55%. 1H NMR (800 MHz, acetone-d6) δ 8.17 (d, J = 16.0 Hz, 1H), 8.02 (dd, J = 8.3, 1.1 Hz, 1H), 7.59 (t, J = 7.3 Hz, 1H), 7.52 (t, J = 7.7 Hz, 1H), 7.16 (d, J = 16.0 Hz, 1H), 6.52 (s, 1H), 6.31 (s, 2H), 3.95 (s, 6H), 3.89 (s, 3H); 13C NMR (201 MHz, acetone-d6) δ 188.5, 183.9, 164.4, 162.4, 137.3, 133.1, 132.6, 129.5, 128.0, 123.5, 106.8, 97.8, 91.7, 56.3, 55.9.

4‐[(1E)‐2‐(2,2‐difluoro‐6‐phenyl‐1,3,2‐dioxaborinin‐4‐yl)ethenyl]phenol (4i-B)

Yield: 93%; ESI MS recorded: 337.0825 m/z [M+Na]+, expected for C17H13BF2O3: 337.0818 m/z [M+Na]+; Rf = 0.59 (n-hexane:EtOAc 1:2); MP = 179 °C; λmax (ACN) nm (logε): 440 (4.87); HPLC purity: DAD 97.63%. 1H NMR (800 MHz, acetone-d6) δ 9.36 (s, 1H), 8.18 (d, J = 7.3 Hz, 2H), 8.14 (d, J = 15.6 Hz, 1H), 7.79–7.74 (m, 3H), 7.63 (t, J = 7.9 Hz, 2H), 7.15 (s, 1H), 7.02 (d, J = 15.6 Hz, 1H), 6.99 (d, J = 8.6 Hz, 2H); 13C NMR (201 MHz, acetone-d6) δ 183.2, 181.5, 162.6, 149.1, 135.6, 133.2, 132.9, 130.1, 129.3, 127.0, 118.8, 117.3, 98.2.

(2Z,4E)‐3‐hydroxy‐5‐(4‐methoxyphenyl)‐1‐phenylpenta‐2,4‐dien‐1‐one (4i)

Yield: 58%; ESI MS recorded: 289.0837 m/z [M+Na]+, expected for C17H14O3: 289.0835 m/z [M+Na]+; Rf = 0.41 (n-hexane:EtOAc 2:1); MP = 173 °C; λmax (ACN) nm (logε): 419 (4.66); HPLC purity: DAD 98.34%. 1H NMR (800 MHz, acetone-d6) δ 8.93 (s, 1H), 8.03 (d, J = 7.0 Hz, 2H), 7.69 (d, J = 15.8 Hz, 1H), 7.61 (t, J = 7.4 Hz, 1H), 7.59 (d, J = 8.6 Hz, 2H), 7.54 (t, J = 7.8 Hz, 2H), 6.92 (d, J = 8.6 Hz, 2H), 6.75 (d, J = 15.8 Hz, 1H), 6.64 (s, 1H); 13C NMR (201 MHz, acetone-d6) δ 189.0, 182.2, 160.6, 141.1, 137.1, 133.4, 131.0, 129.6, 128.1, 127.7, 121.3, 116.8, 97.6.

4‐(2‐ethyl)morpholine (4j-B)

Yield: 99%; ESI MS recorded: 458.1952 m/z [M + H]+, expected for C24H26BF2NO5: 458.1945 m/z [M + H]+; Rf = 0.40 (DCM:MeOH 20:1); MP = 210 °C; λmax (ACN) nm (logε): 451 (4.76); HPLC purity: DAD 99.28%. 1H NMR (800 MHz, acetone-d6) δ 8.19 (dd, J = 8.4, 1.1 Hz, 2H), 8.13 (d, J = 15.7 Hz, 1H), 7.77 (t, J = 7.4 Hz, 1H), 7.64 (t, J = 7.9 Hz, 2H), 7.53 (d, J = 2.0 Hz, 1H), 7.48 (dd, J = 8.3, 2.0 Hz, 1H), 7.13 (s, 1H), 7.12 (d, J = 8.3 Hz, 1H), 7.08 (d, J = 15.6 Hz, 1H), 4.26 (t, J = 5.8 Hz, 2H), 3.94 (s, 3H), 3.65–3.62 (m, 4H), 2.83 (t, J = 5.8 Hz, 2H), 2.59 (s, 4H); 13C NMR (201 MHz, acetone-d6) δ 183.2, 182.0, 154.9, 150.2, 149.1, 135.7, 133.4, 130.2, 129.4, 128.3, 126.3, 119.9, 114.3, 113.2, 98.3, 68.1, 67.5, 58.4, 56.6, 55.1.

4‐(2‐ethyl)morpholine (4k-B)

Yield: 73%; ESI MS recorded: 458.1959 m/z [M + H]+, expected for C24H26BF2NO5: 458.1945 m/z [M + H]+; Rf = 0.34 (DCM:MeOH 20:1); MP = 110 °C; λmax (ACN) nm (logε): 452 (4.62); HPLC purity: DAD 99.24%. 1H NMR (800 MHz, acetone-d6) δ 8.19 (dd, J = 8.3, 1.0 Hz, 2H), 8.14 (d, J = 15.6 Hz, 1H), 7.77 (t, J = 7.4 Hz, 1H), 7.65 (t, J = 7.9 Hz, 2H), 7.51 (d, J = 1.9 Hz, 1H), 7.46 (dd, J = 8.3, 2.0 Hz, 1H), 7.15 (s, 1H), 7.14 (d, J = 8.3 Hz, 1H), 7.11 (d, J = 15.6 Hz, 1H), 4.32 (t, J = 5.6 Hz, 2H), 3.93 (s, 3H), 3.69 (t, J = 4.5 Hz, 4H), 2.97 (s, 2H), 2.73 (s, 4H); 13C NMR (201 MHz, acetone-d6) δ 183.0, 181.8, 153.4, 151.0, 149.0, 135.8, 133.2, 130.2, 129.4, 128.5, 126.0, 119.8, 114.1, 112.5, 98.3, 67.5, 67.0, 58.0, 56.4, 54.9.

4‐(2‐ethyl)morpholine (4l-B)

Yield: 79%; ESI MS recorded: 428.1850 m/z [M + H]+, expected for C23H24BF2NO4: 428.1839 m/z [M + H]+; Rf = 0.18 (DCM:MeOH 35:1); MP = 154 °C; λmax (ACN) nm (logε): 440 (4.72); HPLC purity: DAD 98.02%. 1H NMR (800 MHz, acetone-d6) δ 8.19 (dd, J = 8.5, 1.2 Hz, 2H), 8.15 (d, J = 15.7 Hz, 1H), 7.84 (d, J = 8.6 Hz, 2H), 7.77 (t, J = 7.4 Hz, 1H), 7.66–7.63 (m, 2H), 7.17 (s, 1H), 7.10 (d, J = 8.8 Hz, 2H), 7.08 (d, J = 15.7 Hz, 1H), 4.30 (t, J = 5.7 Hz, 2H), 3.66 (t, J = 4.6 Hz, 4H), 2.90 (t, J = 5.4 Hz, 2H), 2.65 (s, 4H); 13C NMR (201 MHz, acetone-d6) δ 183.1, 181.9, 163.3, 148.6, 135.8, 133.2, 132.6, 130.2, 129.4, 128.1, 119.6, 116.3, 98.4, 67.1, 66.7, 58.1, 54.8.

4‐(2‐ethyl)morpholine (4m-B)

Yield: 32%; ESI MS recorded: 428.1843 m/z [M + H]+, expected for C23H24BF2NO4: 428.1839 m/z [M + H]+; Rf = 0.18 (DCM:MeOH 35:1); MP = 192 °C; λmax (ACN) nm (logε): 418 (4.53); HPLC purity: DAD 96.52%. 1H NMR (800 MHz, acetone-d6) δ 8.44 (d, J = 15.9 Hz, 1H), 8.23 (dd, J = 8.5, 1.2 Hz, 2H), 7.88 (dd, J = 7.7, 1.6 Hz, 1H), 7.80 (t, J = 7.4 Hz, 1H), 7.68–7.65 (m, 2H), 7.55 (t, J = 8.7 Hz, 1H), 7.30 (d, J = 15.9 Hz, 1H), 7.26–7.24 (m, 2H), 7.15 (t, J = 7.5 Hz, 1H), 4.73 (t, 2H), 4.03 (s, 4H), 3.94 (s, 2H), 3.65 (s, 4H); 13C NMR (201 MHz, acetone-d6) δ 183.1, 182.8, 158.5, 142.7, 136.2, 134.7, 132.9, 130.3, 130.2, 129.7, 124.1, 122.9, 122.8, 113.9, 99.1, 65.1, 64.7, 57.7, 54.5.

The absorbance scan

The compounds 2a-B and 2a were dissolved in DMSO to a final concentration of 10 µM. The absorbance and emission scans were done using the Infinite® M Plex microplate reader (Tecan Trading AG, Männedorf, Switzerland).

Microtox assay

Acute toxicity of the prepared compounds was assessed on Modern Water Microtox Model 500 apparatus equipped with Modern Water MicrotoxOmni 4.2 software, according to the 81.9% Screening test procedure provided by the supplier. The change of the bioluminescence of the bacterial suspension was monitored upon adding the sample solution compared to the negative control. For all the experiments, the solutions of appropriate concentrations were prepared using DMSO and deionized water. The concentration of DMSO was ≤1% v/v. Each compound was tested at three concentrations (1, 10, and 100 µM) at two-time points: 5 min and 15 min.

Cell culture

The human bladder cancer cell lines 5637 (human bladder grade II carcinoma) and SCaBER (human bladder squamous cell carcinoma) were obtained from the American Type Culture Collection (ATCC, Manassas, VA, USA). The MRC-5 cell line (normal human lung fibroblasts) was obtained from the European Collection of Authenticated Cell Cultures (ECACC) distributed by Sigma-Aldrich. SCaBER cells were cultured in EMEM, 5637 cells were maintained in RPMI 1640 medium, and MRC-5 were grown in DMEM. All media were supplemented with 10% (v/v) FBS, 2 mM L-glutamine, 100 U/mL penicillin, and 10 mg/mL streptomycin. Cells were incubated in a humidified atmosphere containing 5% CO2 at 37 °C. Tested compounds were dissolved in DMSO at a concentration of 10 mM and stored at −20 °C in dark conditions. The final concentration of DMSO in the cell culture medium did not exceed 0.1%.

MTT assay

The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was performed to evaluate the cytotoxic activity of tested derivatives. The cells were seeded at a density of 15 × 103 cells/well (5637 cells), 10 × 103 cells/well (SCaBER cells), and 20 × 103 cells/well (MRC-5 cells) on a 96-well plate. Screening experiments were performed for 5637 and SCaBER cells treated with tested compounds at a concentration of 1, and 10 µM. The most active compounds were selected for further studies employing 5637, SCaBER, and MRC-5 cells. Cells were seeded and incubated overnight at standard cell culture conditions. Cells were treated with a series of different concentrations (0.3, 0.6, 1.2, 2.5, 5, and 10 µM) of each compound. DMSO at a concentration of 0.1% was used as a control. Cells were incubated with tested compounds for 24 and 48 h. Then, cells were washed twice with PBS (100 µL), and MTT solution at a final concentration of 0.59 mg/mL in a cell culture medium was added to each well. After incubation lasting 1.5 h, the formazan crystals were solubilized by adding 200 μL of DMSO. The absorbance was measured at 570 nm using a microplate reader (Biotek Instruments, Elx-800, Winooski, VT, USA). The relative cell viability was expressed as the mean percentage of viable cells relative to the untreated cells. The IC50 values were calculated using GraphPad Prism 8 software. The results were presented as mean ± standard deviation from three independent experiments.

The intracellular uptakeQuantitative method

The 5637 cells were seeded at a density of 100 × 103 cells/well on a 24-well plate and incubated overnight under standard cell culture conditions. Then, the cells were treated with 2a-B and 2a at 2 and 8 µM concentrations. The cells were incubated with tested compounds for 0.5, 1, 2, 4, 6, and 8 h. DMSO was used as a control, and the concentration did not exceed 0.1% in the cell culture medium. After incubation, cells were washed twice with PBS. Cells were lysed in 80 µL of RIPA buffer (Thermofisher, Waltham, MA, USA). Standard curves were prepared in RIPA buffer for both compounds. Lysates were then transferred to a 96-well black microplate, and fluorescence intensity was measured at an excitation of 520 nm and emission of 605 nm for 2a-B, and 430 nm and 520 nm for compound 2a using Infinite® M Plex microplate reader (Tecan Trading AG, Männedorf, Switzerland). Additionally, the total protein concentration of each sample was measured using the Pierce™ BCA Protein Assay Kit (Thermofisher, Waltham, MA, USA). Data were presented as mean values for at least two experiments.

Fluorescence microscopy

The 5637 cells were seeded at a density of 45 × 103 cells/well on a Falcon® 8-well culture glass slide (Corning, New York, USA) and incubated overnight under standard cell culture conditions. Then, the cells were treated with 2a-B and 2a at a concentration of 8 µM for 0.5, 2, and 4 h. DMSO was used as a control, and the concentration did not exceed 0.1% in the cell culture medium. After incubation, cells were washed three times with PBS and fixed with 4% paraformaldehyde. Then, cells were washed three times with PBS, and stained with 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI, at a concentration of 0.5 µg/mL). The slides were mounted with Dako mounting medium (Agilent, Santa Clara, CA, USA) and images were captured using the Leica model DM4 B Fluorescence Microscope.