* All experimental methods are cited from the reference, please refer to the original source for details. We do not guarantee the accuracy of the content in the reference.
With sodium acetate; In N,N-dimethyl-formamide; at 20℃; for 3.5h;
General procedure: To a solution of catecholamine (5.28 mmol) in DMF (23 mL), was added NaOAc (0.43 g, 5.28 mmol) and Ac2O (500 ml, 5.29 mmol) and the mixture stirred for 3.5h at room temperature. The reaction was followed by thin layer chromatography (CH2Cl2/MeOH, 9:1); the spots were visualized using UV light and also a phosphomolydbic acid solution followed by heating. The solvent was evaporated and the crude mixture purified by flash chromatography on silica (CH2Cl2/MeOH, 9:1)
With hydrogenchloride; potassium chloride electrolysis;
With phenoloxidase from Lucilia cuprina pupae
With 2,3-dicyano-5,6-dichloro-p-benzoquinone In methanol; chloroform-d1
With 2,3-dicyano-5,6-dichloro-p-benzoquinone In d(4)-methanol at 18℃;
With silver(l) oxide In N,N-dimethyl-formamide at 0℃;
With mushroom tyrosinase In aq. phosphate buffer at 20℃; Enzymatic reaction;
2 4.2. General procedure for the enzymatic oxidation of catecholamines, followed by addition of the nitrogen nucleophile
General procedure: Mushroom tyrosinase (0.2 mg, 1074 units) was added to a solution of catecholamine (20 mg) in 1 mL phosphate buffer (pH 7.4, 50 mM) at r.t. The color changed to yellow, indicating the formation of the corresponding o-quinone. The enzyme was removed from the reaction mixture using a 5 mL HitrapTM desalting column (GE Heathcare), eluted with water (20 mL). The yellow solution of catecholamine-quinone was then added dropwise to a solution of NAcHis (10 eq.) or Imid (10 eq.) in phosphate buffer (15 mL, pH 7.4, 50 mM), and the reaction mixture was stirred for 1 h. At the terminus of the reaction 1 mL of 88% formic acid was added, and the reaction mixture was carefully evaporated under reduced pressure. The resulting orange oil was dissolved in water and purified by reverse-phase (RP-18) modified silica gel column chromatography, using water (100 mL) and 50% MeOH (100 mL) as eluent. The fraction containing the product eluted with 50% MeOH and was purified by HPLC (see ESI).
With silver(l) oxide In acetone at 20℃; for 0.5h;
3.1 General procedure for oxidation nucleophilic trapping study
General procedure: 5 equiv of Ag2O were added to a stirred solution of catecholamines in acetone at room temperature. After 30min (10min for NAΔDA), Ag2O was removed from the yellow reaction mixture via filtration. To the filtrate, 5 equiv of ethanethiol were added. Stirring was continued for 1h and then the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (5% MeOH/DCM) and/or semi-preparative reversed-phase HPLC/PDA method. All the purified compounds are brown oil unless specified otherwise
Stage #1: N-acetyldopamine; Kynuramine dihydrobromide With cerium(III) chloride; silver(l) oxide In methanol; acetic acid at 40℃; for 1.5h;
Stage #2: With hydrogenchloride In methanol; acetic acid at 90℃; for 0.5h; Further stages.;
With K2CO3; HCl In water; N,N-dimethyl-formamide N2-atmosphere; refluxing Ru-complex with excess of K2CO3 and acetamide (in DMF, 15 h), addn. of 6 M HCl, stirring with 1 equiv. of aq. NH4PF6 for 15 min; concn., extn. into CH2Cl2, chromy. (Al2O3, CH2Cl2/EtOH=9:1);
Stage #1: N-acetyldopamine With mushroom tyrosinase In aq. phosphate buffer at 20℃; Enzymatic reaction;
Stage #2: N-acetyl-L-histidine In aq. phosphate buffer
2 4.2. General procedure for the enzymatic oxidation of catecholamines, followed by addition of the nitrogen nucleophile
General procedure: Mushroom tyrosinase (0.2 mg, 1074 units) was added to a solution of catecholamine (20 mg) in 1 mL phosphate buffer (pH 7.4, 50 mM) at r.t. The color changed to yellow, indicating the formation of the corresponding o-quinone. The enzyme was removed from the reaction mixture using a 5 mL HitrapTM desalting column (GE Heathcare), eluted with water (20 mL). The yellow solution of catecholamine-quinone was then added dropwise to a solution of NAcHis (10 eq.) or Imid (10 eq.) in phosphate buffer (15 mL, pH 7.4, 50 mM), and the reaction mixture was stirred for 1 h. At the terminus of the reaction 1 mL of 88% formic acid was added, and the reaction mixture was carefully evaporated under reduced pressure. The resulting orange oil was dissolved in water and purified by reverse-phase (RP-18) modified silica gel column chromatography, using water (100 mL) and 50% MeOH (100 mL) as eluent. The fraction containing the product eluted with 50% MeOH and was purified by HPLC (see ESI).
N-[2-(4,5-Dihydroxy-2-imidazol-1-yl-phenyl)-ethyl]-acetamide[ No CAS ]
Yield
Reaction Conditions
Operation in experiment
4 mg
Stage #1: N-acetyldopamine With mushroom tyrosinase In aq. phosphate buffer at 20℃; Enzymatic reaction;
Stage #2: 1H-imidazole In aq. phosphate buffer
2 4.2. General procedure for the enzymatic oxidation of catecholamines, followed by addition of the nitrogen nucleophile
General procedure: Mushroom tyrosinase (0.2 mg, 1074 units) was added to a solution of catecholamine (20 mg) in 1 mL phosphate buffer (pH 7.4, 50 mM) at r.t. The color changed to yellow, indicating the formation of the corresponding o-quinone. The enzyme was removed from the reaction mixture using a 5 mL HitrapTM desalting column (GE Heathcare), eluted with water (20 mL). The yellow solution of catecholamine-quinone was then added dropwise to a solution of NAcHis (10 eq.) or Imid (10 eq.) in phosphate buffer (15 mL, pH 7.4, 50 mM), and the reaction mixture was stirred for 1 h. At the terminus of the reaction 1 mL of 88% formic acid was added, and the reaction mixture was carefully evaporated under reduced pressure. The resulting orange oil was dissolved in water and purified by reverse-phase (RP-18) modified silica gel column chromatography, using water (100 mL) and 50% MeOH (100 mL) as eluent. The fraction containing the product eluted with 50% MeOH and was purified by HPLC (see ESI).
Stage #1: N-acetyldopamine With formic acid; sodium sulfate; silver(l) oxide In methanol at 20℃; for 0.25h; Darkness;
Stage #2: L-cysteine methyl ester hydrochloride In methanol
Methyl 6-(2-acetylaminoethyl)-4-hydroxy-benzothiazole-2-carboxylate
General procedure: Silver(I) oxide (256 mg, 1.1 mmol) and sodium sulfate (251 mg, 1.8 mmol) were added to asolution of N-acetyldopamine 8 (60 mg, 0.3 mmol) and formic acid (42 μL, 1.1 mmol) inmethanol (4 mL) and the black suspension was stirred for 15 min in the dark at rt then filteredthrough a pad of Celite. The filter cake was washed with methanol (2 × 6 mL) and thecombined red filtrates were immediately added dropwise to a solution of cysteine methylester hydrochloride (57 mg, 0.3 mmol) in methanol (2 mL). After addition had completed thepale green solution was concentrated to give the cysteine adduct as a pale yellow/green foamthat was used directly without purification; (Found: [M+H+], 329.1160. C14H21N2O5S+requires 329.1166.); The above foam was dissolved in water (0.7mL) and a solution ofiron(III) chloride hexahydrate (442 mg, 1.6 mmol) in water (1.8 mL) was slowly addeddropwise with vigorous stirring. The mixture was stirred for 72 h at rt, then diluted with water(10 ml) and extracted with ethyl acetate (3 × 10 mL). The combined organic extracts werewashed with water (30 mL) and brine (30 mL), dried (Na2SO4) and concentrated. The residuewas subjected to flash column chromatography on silica gel, eluting with ethanol-ethylacetate (1:9) to give the title compound as yellow solid