Browning acetamidation

Preparation of 1 -(/3-D-arabinofuranosyl)-2-thiocytosine A solution of 2.0 g of 1 -(2, 3, 5 -0-triacetyl-/3-D-arabinofuranosyl)-2,4-dithiouracil in 100 ml of methanol is saturated with anhydrous ammonia at 0°C. The mixture, in a glass liner, is heated in a pressure bomb at 100°C for three hours. The reaction mixture is concentrated to a gum in vacuo, and most of the byproduct acetamide is removed by sublimation at 60°C/0.1 mm. The residue is chromatographed on 100 g of silica gel. Elution of the column with methylene chloride-methanol mixtures with methanol concentrationsof 2-25% gives fractions containing acetamide and a series of brown gums. The desired product is eluted with 30% methanol-methylene chloride to give a total yield of 0.386 g (30%), MP 175°-180°C (dec.). Recrystallization from methanol-iso-propanol furnishes an analytical sample, MP 180°-182°C (dec.). 

A mixture of acetamide (30 g. = 0-5 mole) and bromine (80 g. = 26 c.c.) in a half-litre flask is kept well cooled with water while enough of a solution of 50 g. of potassium hydroxide in 350 c.c. of water is added to change the initially red-brown colour into a pale yellow this requires most of the alkali. The solution is now run from a dropping funnel in an unbroken jet into a solution of 80 g. of potassium hydroxide in 150 c.c. of water, maintained at 70°-75° in a litre flask. The operation lasts for several minutes. Until the reaction mixture becomes colourless (one quarter to half an hour) the temperature is maintained at 70°-75°, and then the methylamine is distilled with steam. An adapter is fixed to the lower end of the condenser and dips 1 cm. below the surface of the liquid in the receiver (100 c.c. of approximately 5 N-hydrochloric acid2). As soon as the liquid which forms in the condenser is no longer alkaline the distillation is discontinued and the contents of the receiver are evaporated to dryness in a porcelain basin on the water bath. The last traces of water are removed by allowing the basin to stand over night in a vacuum desiccator. The dried material is boiled with absolute alcohol, which dissolves the methylamine hydrochloride but not the ammonium chloride with which it is mixed. The clear filtrate obtained when the ammonium chloride is removed by filtration is concentrated to a small volume and the methylamine hydrochloride is allowed to crystallise out in the cold. The salt is filtered with suction, washed with a little alcohol, and dried in a desiccator. Yield 15-20 g. 

It can be prepared by reaction of thioacetamide and chloroacetone (Schwarz, 1945) or, using the improvement of Kurkjy and Brown (1952), by reaction of acetamide, phosphorus pentasulfide and bromoacetone (see M.4). 

After a mixture of 1.68 g chloral hydrate (10.2 mmol), 2.03 g hydroxylamine hydrochloride (29.2 mmol), 13.4 g anhydrous Na2S04, and 45 mL water was stirred at 45-50°C for 15 min, a 7.0 mL solution prepared from 1.517 g aniline, 0.75 mL cone. HCl, and water was added. The resulting mixture was heated for 1 h each at 45-50°C, 55-60°C and 65-70°C. An additional 0.45 g chloral hydrate and 4.1 g hydroxylamine hydrochloride were added, and the reaction mixture was heated at 75-80°C for another hour. When the mixture was cooled in ice water, a light brown precipitate formed, which was filtered to afford 1.58 g A-(2,3-dimethoxy-4-methylphenyl)-2-(hydroxyimino)-acetamide of sufficient purity, in a yield of 73%. To 20 mL polyphosphoric acid at 100°C was added 2.0 g M-(2,3-dimethoxy-4-methylphenyl)-2-(hydroxyimino)-acetamide (8.39 mmol) over a period of 5 min. After 20 min, the reaction mixture was cooled, and 40 mL water was carefully added to yield an orange precipitate, which was filtered to give 1.30 g 6,7-dimethoxy-5-methyl-lH-indole-2,3-dione, in a yield of 70%. This compound could be further purified by recrystallization in methanol, m.p. 180.5-181.5°C. 

Powerful amplifiers (potentiators) for both phleomycin and bleomycin have been discovered in Australia (Brown and Grigg, 1982). The potentiators are nitrogen heterocycles of which the most potent seems to be 2-(5, 7 -dimethyl-.y-triazolo[l,5-c]pyrimidin-2 -ylthio)acetamide (Allen et al., 1983). Part of the action of the potentiators seems to be unwinding the DNA helix sufficiently to allow better access of the antibiotic (Grigg, Edwards and Brown, 1971). There is some evidence that they may also stop mitochondrial energy being turned off before destruction of DNA is complete. 

N-(Furan-2-yl(2-hydroxynaphthalen-1 -yl)methyl) acetamide (4a) Brown solid, mp 226-228 °C yield 87%... 

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