Microwave heating in peptide side chain modification via sulfhydryl reaction E. Calce and S. De Luca* Institute of Biostructures and Bioimaging, National Research Council, 80134 Naples, Italy stefania.deluca@cnr.it Electronic Supplementary Information Table of contents 1. Experimental section S2 2. LC-MS spectra of pure modified peptides S6 3. MW parameters S11 4. NMR spectra of modified peptides S13
1. Experimental section 1.1 Materials Fmoc protected amino acids, Rink Amide MBHA resins (0.7 mmol g -1 ), NovaSyn TGA resin (0.2 mmol g -1 ), N-hydroxybenzotriazole (HOBT), benzotriazol-1-yl-oxy-tris-pyrrolidino-phosphonium (PyBOP) were purchased from Calbiochem-Novabiochem (Laufelfingen, Switzerland); piperidine and diisopropylethylamine (DIPEA) were purchased from Fluka (Milwaukee, WI), all remaining solvents were purchased from Sigma-Aldrich (St Louis, MO) or Fluka (Milwaukee, WI) and were used without further purification, unless otherwise stated. Molecular sieves type 4 Å (beads, diameter 1.6 mm), Fmoc-L-Cys(Mmt)-OH and all remaining alkyl bromides were purchased from Sigma-Aldrich. 1.2 General procedure for the MW-assisted peptide S-alkylation AcGlyCys(Bn)ValAlaNH 2 (1a). HPLC: t R = 5.27 min; ES-MS: calculated [M + H] +, 480.2, found m/z 480.0. 1 H NMR (400 MHz, DMSO), 1.90 (acetyl CH 3 ); 8.17, 3.77 (Gly H N, H -H '); Cys H N, H, H -H '), 7.36, 7.30, 3.80 (Bn); 8.09, 4.20, 2.07, 0.91 (Val H N, H, H, H ); 7.90, 4.24, 1.22, 7.26-7.04 (Ala H N, H, H, CONH 2 ). AcAspGlyCys(Bn)ValAlaNH 2 (2a). Peptide 2a was synthesized, characterized and purified under the experimental conditions described for 1a. The benzyl bromide was employed as alkylating agent (2.1 µl, 0.018 mmol). The final RP-HPLC purification provided compound 2a in 52% yield (5.2 mg). HPLC: t R = 4.33 min; ES-MS: calculated [M + H] +, 595.3, found m/z 595.2. 1 H NMR (400 MHz, DMSO), 1.89 (acetyl CH 3 ); 8.27, 4.57, 2.79-2.50 (Asp H N, H, H -H '); 8.18, 3.76 (Gly H N, H -H '); Cys H N, H, H -H '),, 7.36, 7.28, 3.80 (Bn); 8.08, 4.18, 2.07, 0.90 (Val H N, H, H, H ); 7.92, 4.24, 1.21, 7.27-7.04 (Ala H N, H, H, CONH 2 ). AcArgGlyCys(Bn)ValAlaNH 2 (3a). Peptide 3a was synthesized, characterized and purified under the experimental conditions described for 1a. The benzyl bromide was employed as alkylating agent (1.9 µl, 0.016 mmol). The final RP-HPLC purification provided compound 3a in 49% yield (4.9 mg). HPLC: t R = 5.16 min; ES-MS: calculated [M + H] +, 636.3, found m/z 636.3. 1 H NMR (400 MHz, DMSO), 1.90 (acetyl CH 3 ); 8.16, 4.30, 1.73-1.56, 1.56, 3.14, 7.50 (Arg H N, H, H -H ', H, H ); 8.29, 3.78 (Gly H N, H -H '); Cys H N, H, H - S2
H '), 7.37, 7.29, 3.80 (Bn); 8.09, 4.21, 2.07, 0.90 (Val H N, H, H, H ); 7.93, 4.24, 1.22, 7.28-7.04 (Ala H N, H, H, CONH 2 ). AcHisGlyCys(Bn)ValAlaNH 2 (4a). Peptide 4a was synthesized, characterized and purified under the experimental conditions described for 1a. The benzyl bromide was employed as alkylating agent (2.0 µl, 0.017 mmol). The final RP-HPLC purification provided compound 4a in 53% yield (5.3 mg). HPLC: t R = 4.30 min; ES-MS: calculated [M + H] +, 617.3, found m/z 617.4. 1 H NMR (400 MHz, DMSO), 1.89 (acetyl CH 3 ); 8.23, 4.64, 3.13-2.97, 7.43, 8.99 (His H N, H H - H ', H ); 8.33, 3.84 (Gly H N, H -H '); Cys H N, H, H -H '), 7.36, 7.28, 3.81 (Bn); 8.13, 4.22, 2.07, 0.90 (Val H N, H, H, H ); 7.94, 4.24, 1.22, 7.27-7.04 (Ala H N, H, H, CONH 2 ). AcTrpGlyCys(Bn)ValAlaNH 2 (5a). Peptide 5a was synthesized, characterized and purified under the experimental conditions described for 1a. The benzyl bromide was employed as alkylating agent (1.8 µl, 0.016 mmol). The final RP-HPLC purification provided compound 5a in 55% yield (5.5 mg). HPLC: t R = 6.65 min; ES-MS: calculated [M + H] +, 666.7, found m/z 666.2. 1 H NMR (400 MHz, DMSO), 1.81 (acetyl CH 3 ); 8.16, 4.53, 3.16-2.94, 7.19, 10.81, 7.01, 7.63, 7.10, 7.37 (Trp H N, H, H -H ', H H 1, H H 3, H 2, H ; 8.39, 3.77 (Gly H N, H -H '); Cys H N, H, H -H '), 7.36, 7.29, 3.81 (Bn); 8.10, 4.20, 2.07, 0.91 (Val H N, H, H, H ); 7.91, 4.24, 1.21, 7.26-7.03 (Ala H N, H, H, CONH 2 ). AcLysGlyCys(Bn)ValAlaNH 2 (6a). Peptide 6a was synthesized, characterized and purified under the experimental conditions described for 1a. The benzyl bromide was employed as alkylating agent (2.1 µl, 0.017 mmol). The final RP-HPLC purification provided compound 6a in 45% yield (4.5 mg). HPLC: t R = 4.19 min; ES-MS: calculated [M + H] +, 608.3, found m/z 608.4. 1 H NMR (400 MHz, DMSO) 1.90 (acetyl CH 3 ); 8.11, 4.27, 1.71-1.55, 1.36, 1.55, 2.81, 7.66 (Lys H N, H, H -H ', H H, H, H ; 8.25, 3.76 (Gly H N, H -H '); Cys H N, H, H -H '); 7.37, 7.29, 3.81 (Bn); 8.09, 4.21, 2.07, 0.90 (Val H N, H, H, H ); 7.92, 4.23, 1.22, 7.28-7.04 (Ala H N, H, H, CONH 2 ). AcGlyTrpCys(Dpm)HisValAlaNH 2 (7b). Peptide 7b was synthesized under the experimental conditions described for 1a. Concerning the alkylation, 1-bromo-2-methylnaphthalene (4.2 mg, 0.017 mmol) was employed as alkylating agent, and the solution was irradiated for 15 min at 40 C in a microwave oven. Then, the mixture was centrifuged in order to eliminate the sieves and the S3
supernatant was concentrated under vacuum. RP-HPLC and mass spectrometry analysis were carried out by using linear gradient from 20 to 90% B in 30 min and from 20 to 90% B in 10 min, respectively. The final RP-HPLC purification provided compound 7b in 55% yield (5.5 mg), as estimated after lyophilization. HPLC: t R = 3.79 min; ES-MS: calculated [M + H] +, 879.5, found m/z 879.6. 1 H NMR (400 MHz, DMSO) 1.86 (acetyl CH 3 ); 8.13, 3.79-3.60, (Gly H N, H -H '); 8.08, 4.62, 3.18-2.97, 7.17, 10.86, 7.01, 7.61, 7.10, 7.35 (Trp H N, H, H -H ', H H 1, H H 3, H 2, H Cys H N, H, H -H '), 7.47-7.35-7.26, 5.42 (Dpm) ; 8.39, 4.72, 3.12-3.04, 7.42, 8.94 (His H N, H, H -H ', H H 1); 7.88, 4.19, 2.02, 0.85 (Val H N, H, H, H ); 8.14, 4.26, 1.26, 7.28-7.00 (Ala H N, H, H, CONH 2 ). AcGlyTrpCys(Far)HisValAlaNH 2 (7c). Peptide 7c was synthesized, characterized and purified under the experimental conditions above described for peptide 7b. The trans, trans farnesyl bromide (4.6 µl, 0.017 mmol) was employed as alkylating agent. The final RP-HPLC purification provided compound 7c in 50% yield (5.0 mg), as estimated after lyophilization. HPLC: t R = 8.66 min; ES-MS: calculated [M + H] +, 917.6, found m/z 917.6. 1 H NMR (400 MHz, DMSO) 1.85 (acetyl CH 3 ); 8.13, 3.78-3.61, (Gly H N, H -H '); 8.08, 4.59, 3.19-3.01, 7.19, 10.86, 7.02, 7.62, 7.09, 7.37 (Trp H N, H, H -H ', H H 1, H H 3, H 2, H Cys H N, H, H -H '), 5.23, 5.13, 5.11, 3.21, 2.08, 2.03, 1.97, 1.68, 1.67, 1.60 (farnesyl); 8.32, 4.72, 3.13-2.99, 7.36, 8.98 (His H N, H, H -H ', H H 1); 7.85, 4.21, 2.08, 0.90 (Val H N, H, H, H ); 8.14, 4.26, 1.27, 7.29-7.02 (Ala H N, H, H, CONH 2 ). AcGlyTrpCys(HD)HisValAlaNH 2 (7d). Peptide 7d was synthesized, characterized and purified under the experimental conditions above described for peptide 7b. The hexadecyl bromide was employed as alkylating agent (5.2 µl, 0.017 mmol). The final RP-HPLC purification provided compound 7d in 42% yield (4.2 mg). HPLC: t R = 8.32 min; ES-MS: calculated [M + H] +, 937.7, found m/z 937.8. 1 H NMR (400 MHz, DMSO) 1.86 (acetyl CH3); 8.13, 3.79-3.61 (Gly H N, H -H ',); 8.07, 4.58, 3.17-2.98, 7.18, 10.86, 7.02, 7.62, 7.10, 7.37 (Trp H N, H, H -H ', H, H 1, H 3 H 3, H 2, H 2 8.27, 4.41, 2.85-2.73 (Cys H N, H, H -H '), 2.55, 1.53, 1.36, 1.29, 0.90 (HD); 8.38, 4.72, 3.12-3.04, 7.38, 8.93 (His H N, H, H -H ', H 2, H 1); 7.82, 4.20, 2.06, 0.91 (Val H N, H, H, H ); 8.14, 4.26, 1.26, 7.29-7.01 (Ala H N,+ H, H, CONH 2 ). 1.3 General procedure for the MW-assisted peptide solid-phase S-alkylation S4
For the synthesis of compound 1, appropriate Fmoc-amino acid derivatives [Fmoc-Gly-OH, Fmoc- Cys(Mmt)-OH, Fmoc-Val-OH, Fmoc-Ala-OH] were employed and the Rink Amide MBHA resin (0.7 mmol g -1 substitution; 50 µmol scale) was used as solid support. The removal of the Mmt group was performed by washing the peptidyl-resin with TFA-TIS-CH 2 Cl 2 (1:5:94) (10 3 min) and then with CH 2 Cl 2 (5 1 min). Then, the peptidyl resin, acetylated at the N-terminus, was placed in a 0.5-2 ml microwave vial, and suspended in ~3 ml of DMF under argon atmosphere. Subsequently, benzyl bromide (5 equiv) was added by a syringe and, as final step, 4 Å molecular sieves (3-3.5 g), previously activated at 280 C for 4 h under vacuum (10-4 mbar), cooled at r.t., were quickly added. The mixture was irradiated for 5-15 min at 40 C in a microwave oven and stirred at 320 rpm. Afterwards, the peptidyl-resin, suspended in abundant DMF, was firstly isolated from the molecular sieves and, then, from the reaction mixture by filtration. After cleavage procedure, the crude product was isolated by precipitation in cold diethyl ether, purified by preparative RP-HPLC, analyzed and characterized by mass spectrometry. S5
2. LC-MS spectra of pure modified peptides AcGlyCys(Bn)ValAlaNH 2 (1a) AcAspGlyCys(Bn)ValAlaNH 2 (2a) S6
AcArgGlyCys(Bn)ValAlaNH 2 (3a) AcHisGlyCys(Bn)ValAlaNH 2 (4a) S7
AcTrpGlyCys(Bn)ValAlaNH 2 (5a) AcLysGlyCys(Bn)ValAlaNH 2 (6a) S8
AcGlyTrpCys(Dpm)HisValAlaNH 2 (7b) AcGlyTrpCys(Far)HisValAlaNH 2 (7c) S9
AcGlyTrpCys(HD)HisValAlaNH 2 (7d) S10
3. MW parameters AcGlyCys(Bn)ValAlaNH 2 (1a) Status: OK Absorption level: Normal Vial type: 2.0-5.0 ml Pre-stirring: 0 Initial power: 0 Dynamic deflector optimization: On Temperature ( C) Pressure (bar) Power (W) S11
AcGlyTrpCys(Dpm)HisValAlaNH 2 (7b) Status: OK Absorption level: Normal Vial type: 2.0-5.0 ml Pre-stirring: 0 Initial power: 0 Dynamic deflector optimization: On Temperature ( C) Pressure (bar) Power (W) S12
4. NMR spectra of modified peptides 0.91 1,22 1.90 2.07 2.79-2.64 3.80; 3.77 4.24; 4.20 4.66 7.36; 7.30 7.04 7.26 8.19; 8.17; 8.09 7.90 S13
0.90 1.21 1.89 2.07 2.82; 2.79; 2.69; 2.50 3.80; 3.76 4.24; 4.18 4.64; 4.57 7.36; 7.28 7.04 7.27 7.92 8.27; 8.18; 8.08; 8.07 S14
0.90 1.22 1.90 1.56 1.73 2.07 2.79; 2.65 3.14 3.80; 3.78 4.30; 4.24; 4.21 4.65 7.37; 7.29 7.28 7.04 7.50 7.93 8.29; 8.16; 8.14; 8.09 S15
0.90 1.22 1.89 2.07 2.80; 2.65 3.13; 2.97 3.84; 3.81 4.24; 4.22 4.67; 4.64 7.04 7.43; 7.36; 7.28 7.29 8.33; 8.26; 8.23; 8.13 7.94 8.99 S16
0.91 1.21 1.81 2.07 2.83; 2.66 3.16; 2.94 3.77; 3.81 4.24; 4.20 4.67; 4.53 7.37; 7.36; 7.29; 7.26; 7.19; 7.10; 7.03; 7.01 7.63 7.91 8.39; 8.16; 8.10 10.81 S17
0.90 1.22 1.71; 1.55; 1.36 1.90 2.07 2.81; 2.79; 2.65 3.81; 3.76 4.27; 4.23; 4.21 4.65 7.04 7.37; 7.29 7.28 7.66 7.92 8.25; 8.11; 8.10; 8.09 S18
0.85 1.26 1.86 2.02 2.73; 2.60 3.18; 3.12; 3.04; 2.97 3.79; 3.60 4.26; 4.19 4.72; 4.62; 4.51 5.42 7.47; 7.42; 7.35; 7.28; 7.26; 7.17; 7.10; 7.01; 7.00 7.61 7.88 8.39; 8.33; 8.14; 8.13; 8.08 8.94 10.86 S19
0.90 1.27 1.68; 1.67; 1.60 1.86 2.08; 2.03; 1.97 3.21; 3.19; 3.13; 3.01; 2.99; 2.82; 2.70 3.78; 3.61 4.72; 4.59; 4.44; 4.26; 4.21 5.23; 5.13; 5.11 7.37; 7.36; 7.29; 7.19; 7.09; 7.02 8.32; 8.14; 8.13; 8.08 7.62 7.85 8.98 10.86 S20
1.30; 1.29; 1.26 0.91; 0.90 1.86 1.53 2.06 3.17; 3.12; 3.04; 2.98; 2.85; 2.73; 2.70 3.79; 3.61 4.72; 4.58; 4.41; 4.26; 4.20 7.38; 7.37; 7.29; 7.18; 7.10; 7.02; 7.01 7.62 7.82 8.38; 8.27; 8.14; 8.13; 8.07 8.93 10.86 S21