43
EXPERIMENTAL SECTION
Materials and Methods.
Melting points were determined using a Reichert Kofler hot-stage apparatus and are uncorrected. Routine nuclear magnetic resonance spectra were recorded in DMSO-d6
solution on a Varian Gemini 200 spectrometer operating at 200 MHz. Optical rotatory power (α) were determined using a Perkin Elmer model 343 polarimeter . Evaporation was performer in vacuo (rotary evaporator). Analytical TLC was carried out on Merck 0.2 mm precoated silica gel aluminium sheet (60 F-254) . Elemental analyses were performed by our analytical laboratory and agree with theoretical values to within ± 0.4% .
All reagent used were obtained from commercial sources. All solvents were of an analytical grade.
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Chemistry.
General procedure for the synthesis of 2-(phenylindol-3-yl)-glyoxyl-chloride (8).
Oxalyl chloride (0.31 mL, 3.6 mmol) in 2 mL of Et2O anhydrous, was added dropwise,
over 10-15 minutes to a cooled (0°C) stirred solution of the 2-phenylindole commercially available (0.500 mg, 2.6 mmol) in 10 mL of freshly distilled Et2O. The mixture was
mainteined at room temperature for 2 hours. A precipitate formed which was collected by vacuum filtration, and it was utilized in the following reaction without any further purification.
General procedure for the synthesis of 2-(phenylindol-3-yl)-glyoxylamide derivatives (1-6).
A solution of the appropriate dipeptides in their methyl ester form ((L)-Phenylalanine-(L)-Leucine; (L)-Valine-(L)-((L)-Phenylalanine-(L)-Leucine; (L)-Leucine-(L)-Valine; (L)-Isoleucine-(L)-Isoleucine; (L)-Isoleucine-(L)-Valine; (L)-Valine-(L)-Isoleucine) (0.7 mmol) in 5 mL of dry toluene was added dropwise to a stirred suspension, cooled at 0°C, of glyoxyl chloride 8 (0.177g, 0.63 mmol), in 15 mL of the same solvent, followed by addition of triethylamine (1.6 mmol, 0.23 mL). The reaction mixture was allowed to warm to room temperature, stirred for 12-24 hours (TLC analysys) and then filtered. The collected precipitate was triturated with a NaHCO3 5% aqueous solution and collected again to give a first portion of crude
product. The toluene solution was removed under reduced pressure, the residue was dissolved with CH2Cl2 and the organic solution was washed with 1) NaHCO3 5% ; 2)
H2O; 3) HCl 10%; and finally 4) H20. After drying with MgSO4 the dichloromethane
solution was evaporated to dryness to yield an additional amount of crude product. Products 1-6 were finally purified by washed with cold diethyl ether.
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2-(phenylindol-3-yl)glyoxyl-(L)-Phenylalanine-(L)-Leucine methyl ester (1). Yield 50%;
mp 95-97°C; α = -36; 1H NMR (200 MHz, DMS-d6 , ppm): 0.84-0.91 (m, 6H, 2CH3);
1.51-1.53 (m, 2H, CH2); 2.72-2.88 (m, 3H, CH2, CH); 3.59 (s, 3H, COOCH3); 4.29-4.32
(m, 2H, 2CH); 7.06-7.49 (m, 11H, Ar-H); 7.77 (d, 1H, Ar-H, J = 8.2 Hz); 8.41 (d, exch. D2O, 1H, NH, J = 6.8 Hz); 8.76 (d, exch. D2O, 1H, NH, J = 8.2 Hz); 12.32 (bs, exch. D2O,
1H, NH).
2-(phenylindol-3-yl)glyoxyl-(L)-Valine-(L)-Leucine methyl ester (2). Yield 50%; mp
107-110°C; α = -32; 1H NMR (200 MHz, DMSO-d6 , ppm): 0.82-0.93 (m, 12H, 4CH3);
1.52-1.57 (m, 3H, CH2, CH); 1.89-1.96 (m, 1H, CH); 3.59 (s, 3H, COOCH3); 3.9-4.2 (m, 1H,
CH ); 4,23-4.31 (m, 1H, CH); 7.17-7.25 (m, 2H, Ar-H); 7.40-7.45 (m, 3H, Ar-H); 7.49-7.63 (m, 2H, Ar-H); 7.97 (d, 1H, Ar-H, J = 7.6 Hz); 8.34 (d, exch. D2O, 1H, NH, J = 7.2
Hz); 8.52 (d, exch. D2O, 1H, NH, J = 8.8 Hz); 12.35 (bs, exch. D2O, 1H, NH).
2-(phenylindol-3-yl)glyoxyl-(L)-Leucine-(L)-Valine methyl ester (3). Yield 50%; mp
93-103°C; α = -34; 1H NMR (200 MHz, DMSO-d6 , ppm): 0.79-0.90 (m, 12H, 4CH3);
1.22-1.34 (m, 4H, 2CH,CH2); 3.59 (s, 1H, COOCH3); 4.12-4.25 (m, 2H, 2CH); 7.13-7.27 (m,
4H, Ar-H); 7.44-7.48 (m, 3H, Ar-H); 7.56-7.60 (m, 1H, Ar-H); 7.97 (d, 1H, Ar-H, J = 7.2 Hz); 8.17 (bs, exch. D2O, 1H, NH).
2-(phenylindol-3-yl)glyoxyl-(L)-Isoleucine-(L)-Isoleucine methyl ester (4). Yield 50%;
mp 95-100°C; α = -30; 1H NMR (200 MHz, DMSO-d6 , ppm): 0.79-0.89 (m, 12H, 4CH3);
1.19-1.21 (m, 3H, CH, CH2); 1.74-1.76 (m, 3H, CH,CH2); 1.74-1.76 (m, 3H, CH, CH2);
3.59 (s, 3H, COOCH3); 4.14-4.19 (m, 2H, 2CH); 7.16-7.24 (m, 2H, Ar-H); 7.42-7.58 (m,
4H, Ar-H); 7.58-7.62 (m, 2H, Ar-H); 7.94 (d, 1H, Ar-H, J = 7.6 Hz); 8.24 (d, 1H, NH, exch. D2O, J = 7.6 Hz); 8.56 (d, exch. D2O, 1H, NH, J = 8.8 Hz); 12.35 (bs, exch. D2O,
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2-(phenylindol-3-yl)glyoxyl-(L)-Isoleucine-(L)-Valine methyl ester (5). Yield 50%; mp
106-110°C; α =-31; 1H NMR (200 MHz, DMSO-d6, ppm): 0.81-0.94 (m, 14H, 6CH3,CH2);
1.41-1.44 (m, 1H, CH); 1.63-1.66 (m, 1H, CH); 3.61 (s, 3H, COOCH3); 4.13-4.20 (m, 2H,
2CH); 7.14-7.29 (m, 2H, Ar-H); 7.44-7.46 (M, 4H, Ar-H ; 7.60-7.64 (m, 2H, Ar-H); 7.96 (d, 1H, Ar-H, J = 7.6 Hz); 8.23 (d, exch D2O, 1H, NH, J = 7.4 Hz); 5.58 (d, exch D2O, 1H,
NH, J = 9.2 Hz); 12.36 (bs, exch D2O, 1H, NH).
2-(phenylindol-3-yl)glyoxyl-(L)-Valine-(L)-Isoleucine methyl ester (6). Yield 65.8%; mp
90-94°C; α = -27; 1H NMR (200 MHz, DMSO-d6, ppm): 0.81-0.84 (m, 12H, 4CH3);
1.21-1.43 (m, 2H, CH2 ; 1.76-1.85 (m, 2H, 2CH); 3.59 (s, 3H, COOCH3); 4.05-4.24 (m, 2H,
2CH); 7.18-7.59 (m, 8H, Ar-H); 7.97 (d, 1H, Ar-H, J = 7.4 Hz); 8.24 (d, 1H, exch. D2O,
NH, J = 7 Hz); 8.56 (d, exch D2O, 1H, NH, J = 8.8 Hz); 12.36 (bs, exch. D2O, 1H, NH).
Procedure for the Synthesis of 5-nitro-2-phenylindole (9).
A solution of sodium nitrate (1.40 g, 16.5 mmol) in concentrated sulphuric acid (50 mL) was added to an ice-cooled solution of 2-phenylindole (3.00 g, 15.5 mmol) in concentrated sulphuric acid (100 mL). The reaction was mantained under stirring for 5 minutes and then was diluited with water and ice, the formed precipitate was collected by filtration and purified by recristallization from dichloromethane.
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Procedure for the synthesis of 5-nitro-(2-phenylindole-3-yl)-glyoxyl-chloride (10).
Oxalyl chloride (11.2 mmol , 0.97 mL) in 2 mL of Et2O anhydrous was added dropwise
over 10-15 minutes to a cooled (0°C) stirred solution of 5-nitro-2-phenylindole (9) (0.658 g, 2.8 mmol) in freshly distilled diethyl ether (10 mL). The mixture was mantained at room temperature for 2 hours. A precipitate formed which was collected by vacuum filtration and it was utilized in the following reaction without any further purification.
Procedure for the synthesis of 5-nitro-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (11).
A solution of L-Phenylalanine ethyl ester (0.39 g, 1.6 mmol) in 5 mL of dry toluene was added dropwise to a stirred suspension, cooled at 0°C, of the 5-nitro-(2-phenylindol-3-yl)-glyoxyl chloride (10) (0.500 g, 1.5mmol) in 15 mL of the same solvent, followed by addition of triethylamine (1.9 mmol, 0.27 mL) . The reaction mixture was allowed to warm to room temperature, stirred for 12-24 hours (TLC analysis with appropriate eluent), and then filtered. The collected precipitate was triturated with a NaHCO3 5% aqueous solution
and collected again to give a first portion of crude product. The toluene solution was removed under reduced pressure and the residue obtained was dissolved with Cl2CH2 and
the organic solution was washed with: 1. NaHCO3 5%
2. H2O
3. HCl 10% 4. H2O
After drying with MgSO4, the dichloromethane solution was evaporated to dryness to yield
an additional amount of crude product. Product 10 was finally purified by washed with cold diethyl ether .
5-nitro-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (10). Yield 72%; mp
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2.80-2,86 (m, 2H, CH2); 3.94-4.079 (m, 3H, CH, CH2); 7.18-7.36 (m, 8H, Ar-H); 7.55-7.62
(m, 3H, Ar-H); 8.01 (d, 1H, Ar-H , J = 8.6 Hz); 8.84 (s, 1H, Ar-H); 9.26 (d, exch. D2O,
1H, NH, J = 7 Hz).
Procedure for the synthesis of 5-amino-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (12).
A mixture of the 5-nitro-(2-phenylindole-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (11) (0.300 g, 0.62 mmol) and 10% Pd/C (0.03 g) in 150 mL of absolute ethanol was hydrogenated at room temperature and pressure. Once hydrogen absorption ceased (4-6 hours), the catalyst was filtered off and the solution was evaporated to dryness at reduce pressure. The product 12 obtained was purified by flash-chromatography (AcOEt/Ether petrol 60°-80° C= 3/7 as eluent).
5-amino-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (12). Yield 73%; mp =
95°C α = -12; 1H NMR (200 MHz , DMSO-d6 , ppm): 0.97 (t, 3H, CH3, J = 7.2 Hz);
2.73-2.79 (m, 2H, CH2); 3.85-3.94 (m, 3H, CH2, CH); 4.89 (bs , exch. D2O, 2H, NH2); 6.65 (d,
1H, Ar-H, J = 8.6 Hz ); 7.13-7.47 (m, 12H, Ar-H); 8.94 (d, 1H, exch. D2O, NH, J = 7 Hz);
11.96 (bs, 1H, exch. D2O, NH ).
Procedure for the synthesis of 5-Boc-(L)-Leucine-amino-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (13)
N-Boc-L-Leucine (0.269 g, 1.2 mmol) was solubilized in dry DMF (10mL); N,N’-carbonyldiimidazole (0.195 g, 1.2 mmol) was added and the solution was stirred for 2 hours at room temperature. Then N-5-amino-2-phenylindole-3-yl-glyoxyl-phenylalanine
(12) (0.265 g, 0.58 mmol) in 5 mL of the same solvent was added dropwise. The reaction
was mantained under stirring for 12 hours and then was diluited with water and ice. The solution obtained was extracted with ethylacetate. After drying with MgSO4 the
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ethylacetate solution was evaporated to dryness to yield the crude product 13 that was purified by flash-chromatography (AcOEt/Ether petrol 60°-80°C C= 4/6 as eluent).
5-Boc-(L)-Leucine-amino-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (13).
Yield 55%; mp = 101-103; α = -18; 1H NMR (200 MHz , DMSO-d6 , ppm): 0.89-0.99 (m,
9H, 3 CH3); 1.27-1.39 (m, 12H, 3 CH3, CH2, CH); 2.774 (d, 2H, CH2, J = 7); 3.86-3.97 (m,
3H, CH2, CH); 4.01-4.1 (m, 1H, CH); 6.93 (d, 1H, exch. D2O, NH, J = 8); 7.15-7.53 (m,
11H, Ar-H); 7.66 (d, 1H, Ar-H, J = 8); 8.34 (s, 1H, Ar-H); 9.05 (d, 1H, exch. D2O, NH, J
= 6.8); 9.99 (bs, 1H, exch. D2O, NH); 12.34 (bs, 1H, exch. D2O, NH).
Procedure for the synthesis of 5-(L)-Leucine-amino-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (7)
Trifluoroacetic acid (0.15 mL, 2 mmol). was added dropwise to a stirred solution of derivative 13 (0.107 g, 0.2 mmol) in 10 mL of CH2Cl2, cooled at 0 °C. The mixture was
stirred at room temperature for 4-5 h (TLC analysis). Then the reaction mixture was concentrated under reduce pressure. The resulting solid residue was taken up with NaHCO3 5%, and was extracted with ethylacetate. After drying with MgSO4 the
ethylacetate solution was evaporated to dryness to yield the crude product 7 that was purified by washed with cold diethyl ether .
5-(L)-Leucine-amino-(2-phenylindol-3-yl)-glyoxyl-(L)-phenylalanine ethyl ester (7). Yield
55%; mp = 110-112; α = -20; 1H NMR (200 MHz , DMSO-d6 , ppm): 0.88-1.00 (m, 9H,
3CH3); 1.28-1.49 (m, 3H, CH2, CH); 1.52-1.75 (m, 1H, CH); 2.77-2.81 (m, 2H, CH2);
3.91-3.94 (m, 3H, CH2, CH); 7.16-7.66 (m, 14H, Ar-H, NH2); 8.36 (s, 1H, Ar-H); 9.06 (d,
