Role of N-Methyl-8-(Alkoxy)quinolinium Iodide in Suppression of Protein-Protein Interactions

Bimlesh Ojha, Chirantan Kar and Gopal Das*

Department of Chemistry

Indian Institute of Technology Guwahati, Assam-781039, India

Tel: +91 361 2582313; Fax: +91 361 2582349

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SUPPORTING INFORMATIONS

Materials

8-hydroxyquinoline, alkyl halideswere obtained from Sigma-Aldrich Chemicals, USA.Solvents were purchased from Merck, Mumbai, India and dried following standard protocol. HEPES buffer was procured from Sisco Research Laboratories (SRL), Mumbai, India.

Synthesis of amphiphiles

The amphiphiles synthesized in the present study included 8-alkoxy quinoline (neutral) and N-methyl 8-alkoxy quinolinium iodide (cationic) with varying alkyl chain from butyl, octyl and dodecyl. Neutral amphiphiles were prepared following the literature method.1,2 For N-methylation, methyl iodide was added to a solution of 8-(alkoxy) quinoline in dry acetonitrile, and refluxed for 6 h to complete the reaction. The products obtained were re-crystallized from methanol and characterized by NMR, IR and melting point.

Characterization of Compounds

Melting points of the compounds were recorded using a Type B-540 Buchi melting point apparatus, maintaining the heating rate at 10 oC. The IR spectra of compounds were recorded at 4 per cm resolution with 10 scan using a Perkin Elmer-Spectrum One FT-IR Spectrometer from 4000 to 450 per cm using background spectrum of pure KBr, while 1H and 13C NMR spectra were recorded on a Varian 400 MHz spectrometer using tetramethylsilane (TMS) as internal standard.

Compound 1 [N-methyl-8-(butoxy) quinolinium iodide]

Yield: 65%, IR (KBr): 2921, 1597, 1533, 1467 cm-1; 1H NMR (400 MHz, CDCl3):  1.01 (t, J = 7.2, 3H), 1.51 (m, 2H), 1.95 (m, 2H), 4.23 (t, 2H), 5.063 (s, 3H), 7.47 (d, ArH), 7.79 (m, ArH), 8.09 (m, ArH), 8.90 (m, ArH), 10.15 (d, ArH). 13C NMR (100 MHz, CDCl3):  13.8, 19.6, 30.9, 53.5, 70.9, 109.9, 116.7, 122.5, 122.7, 130.5, 130.9, 130.1, 147.5, 151.0 and 152.0. Light brown solid, Melting point 163 oC, Anal. Calcd C14H18NOI: C, 48.99; H, 5.29; N, 4.08. Found: C, 48.87; H, 5.21; N, 3.99.

Compound 2 [N-methyl-8-(octyloxy) quinolinium iodide]

Yield: 52%, IR (KBr): 2925, 1599, 1530, 1465 cm-1; 1H NMR (400 MHz, CDCl3):  0.90 (t, J = 6.8, 3H), 1.31 (m, 8H), 1.525 (m, 2H), 1.98 (m, 2H), 4.25 (t, J = 6.8, 2H), 5.09 (s, 3H), 7.49 (d, ArH), 7.81 (m, ArH), 8.13 (m, ArH), 8.92 (m, ArH), 10.19 (d, ArH). 13C NMR (100 MHz, CDCl3):  14.2, 22.7, 26.4, 29.0, 29.3, 29.4, 31.9, 53.1, 71.2, 116.5, 122.4, 122.9, 130.9, 132.2, 147.4, 151.1 and 152.3. Light brown solid, Melting point 117 oC, Anal. Calcd C18H26N2: C, 54.14; H, 6.56; N, 3.51. Found: C, 54.09; H, 6.52; N, 3.48.

Compound 3 [N-methyl-8-(dodecyloxy) quinolinium iodide]

Yield: 45%, IR (KBr): 2930, 1595, 1535, 1470 cm-1; 1H NMR (400 MHz, CDCl3): 0.88 (t, J = 7.2, 3H), 1.27 (m, 16H), 1.53 (m, 2H), 2.01 (m, 2H), 4.25 (t, J = 6.4, 2H), 5.09 (s, 3H), 7.50 (d, ArH), 7.82 (m, ArH), 8.13 (m, ArH), 8.96 (m, ArH), 10.19 (d, ArH). 13C NMR (100 MHz, CDCl3):  14.2, 22.7, 26.4, 29.1, 29.4, 29.5, 29.6, 29.7, 31.1, 53.1, 71.21, 116.6, 122.5, 122.874, 123.1, 130.9, 132.2, 147.5, 151.1 and 152.3. Light brown solid, Melting point 110 oC, Anal. Calcd C22H34N2: C, 58.02; H, 7.52; N, 3.08. Found: C, 57.97; H, 7.48; N, 2.99.

References

1. Vudumula U, Adhikari M D, Ojha B, Goswami S, Das G, Ramesh A, 2012 RSC Adv.23864.

2. Andree L, Jean S, Farchid V Z 1987 Bull. Soc. Chim. Fr. 6 1027.

Figure S1. CR absorbance spectra in presence of HEWL under different experimental conditions: (A) CR with HEWL in absence (solid line) and in presence of the compound 1 (dotted line) and (B) CR with HEWL in absence (solid line) and in presence of the compound 2 (dotted line).

Figure S2.(A) Change in absorbance maxima wavelength of CR in presence of HEWL under different experimental conditions as a function of incubation time. HEWL without compound at pH 12.2 (●), HEWL at pH 12.2 with compound 1 (▀), compound 2 (▲) and compound 3(♦) and (B) Effect of DMSO on the emission spectra of CR in presence of HEWL at pH 12.2. Where, solid line represents without DMSO and dashed line with DMSO.

Figure S3. Emission spectra of (A)Congo red (CR) and (B) Thioflavin T(ThT) in presence ofthe compounds at pH 12.2. Dyes without compound at 0 hrs (black solid line) and after 24 hrs (black dotted line), with compound 1 at 0 hrs (red solid line) and after 24 hrs (red dotted line),with compound 2 at 0 hrs (blue solid line) and after 24 hrs (blue dotted line), with compound 3 at 0 hrs (green solid line) and after 24 hrs (green dotted line).

Figure S4. Emission spectra of CR in presence of HEWL under different experimental conditions with increasing time: (A) CR with HEWL in absence (solid line) and in presence of the compound 1 (dotted line) and (B) CR with HEWL in absence (solid line) and in presence of the compound 2 (dotted line).

Figure S5. Emission spectra ofThT in presence of HEWL under different experimental conditions with increasing time: (A) ThT with HEWL in absence (solid line) and in presence of the compound 1 (dotted line) and (B) ThT with HEWL in absence (solid line) and in presence of the compound 2 (dotted line).

Figure S6. (A) Emission spectra of CR with HEWL at pH 7.0 in absence of the compounds and (B) Intensity of CR fluorescence in presence of non-amphiphilic compound i.e. the parent compound (8-hydroxyquinoline) and the neutral counterpart of the cationic amphiphilic compound [8-(alkoxy)quinoline]. HEWL alone at pH 12.2 (●), HEWL at pH 12.2 with 8-hydroxyquinoline(♦) and 8-(alkoxy)quinoline (▲).

Figure S7. AFM images of HEWL different scanning modes like amplitude, phase and topograph at specified times under different experimental conditions: (A) Native lysozyme at pH 7.0, (B) Lysozyme incubated at pH 12.2, (C) Lysozyme incubated at pH 12.2.

Figure S8. AFM images of HEWL different scanning modes like amplitude, phase and topograph at specified times under different experimental conditions: (A) Lysozyme incubated with compound 1 at pH 12.2, (B) Lysozyme incubated with compound 2 at pH 12.2, (C) Lysozyme incubated with compound 3 at pH 12.2.

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