NO135985B - - Google Patents

Description

Method of manufacture of

5-fluorouracil derivatives.

This invention relates to a method for manufacturing

of 5-fluorouracil derivs.

It has been shown that 5-fluorouracil, 5-fluorouridine and various related 5-fluorinated pyrimidines have cytotoxic properties which are useful in the treatment of certain types of cancer and certain types of viral infections. In the past, these have been produced by a total synthesis that includes several reaction steps and a relatively low overall yield. It has been found that certain pyrimidines such as uracil can be fluorinated in the 5-position using certain electrophilic fluorinating agents.

This is in contrast to previous attempts at halogenation

of uracil, e.g. chlorination, where further elimination and addition of halogen takes place to give products which are not readily used for the preparation of 5-chlorouracil derivatives.

Although uracil derivatives are practically inert to the known fluorinating agent perchloryl fluoride, we have found that reaction with a hypofluorite, where the fluorooxy group is covalently bound to an inert, electron-withdrawing group, introduces fluorine smoothly in the 5-position. A related agent which has been found suitable is elemental fluorine diluted with an inert gas.

It is assumed that fluorine first adds electrophilically in the 5-position to form a carbonium ion with a positive charge in the 6-position,

which then eliminates hydrogen from the 5-position to form a 5,6-double bond and/or binds to a nucleophile present in the reaction medium to form a 6-substituted 5-fluoro-5,6-dihydro-pyrimidine; this compound can easily be brought to eliminate the 6-substituent together with the 5-hydrogen, e.g. by heating, for

to form the desired 5,6-dihydro product.

According to the invention, a method is thus provided for the preparation of compounds with the formula (where R is an alkyl group, a hydrogen atom or a monosaccharide residue), and the method is characterized by the fact that a compound with the formula:

(where R has the meanings given above) is reacted with a fluoro-alkyl-hypofluorite where. The alkyl part contains at least two fluorine atoms per carbon atom, or reacted with elemental fluorine diluted with an inert gas, to introduce a fluorine atom in the 5-position, followed, when an atom or group is introduced in the 6-position, by elimination of said group together with the hydrogen atom in the 5-position for to form the desired 5,6-double bond.

In the formulas I and II, the alkyl group denoted by R preferably has 1-6 carbon atoms. such as methyl, ethyl, butyl, or hexyl. When R is a monosaccharide residue, it can e.g. be a 1-ribonyl, 1-(2-deoxyribosyl) or arabinosyl residue. The present nucleophile can e.g. include hydroxyl ions from water, alkyl ions from alkanols, carboxylations from a carboxylic acid or halide ions, especially fluoride ions from the fluorinating agent. We have found that such 6-substituted products are relatively stable, and since they do not have a 5,6-double bond, they are relatively little exposed to attack by other agents. It is therefore appropriate to carry out the reaction in the presence of a nucleophile to ensure the formation of 6-substituted-5-fluoro-5,6-dihydrouracil which is usually formed in high yield and can easily be converted to the desired 5-fluorouracil.

The reaction is preferably carried out in a solvent

for the pyrimidine, suitably a polar solvent, so

such as water, a hydrate of a perfluoroketone such as hexafluoroacetone, or trifluoroacetic acid. Water is preferred. With solvents that may be present, e.g. alkanols, preferably C₁-₅₀, such as methanol or ethanol; lower aliphatic acids (preferably C 2 -g ) such as acetic acid or propionic acid; or esters of phosphoric acid or phorsphonic acid. Most of the above-mentioned solvent systems will contain nucleophiles suitable for forming the above-mentioned stable 6-substituted derivatives. In addition, it should be noted that when F is used as a reaction component, F ions will also act as nucleophiles. When a hypofluorite reaction compound is used and this comprises a perfluoroalkyl group such as in trifluoromethyl hypofluorite, cleavage of perfluoroalkoxy anions released by the reaction will also give F . Thus, if the reaction is carried out in water, the first reaction product will usually be mainly a 5-fluoro-6-hydroxy-5,6-dihydrouracil, but it will also contain a smaller amount (e.g. 5-10%) 5 ,6-difluoro-5,6-dihydrouracil. Both of these 6-substituted products which, however, are easily converted to the desired 5-fluorouracil, e.g. by heating, in cases where one has the simpler, heat-stable uracils such as uracil, where heating in a vacuum gives 5-fluorouracil as a sublimate, or in cases where one has

more complex and heat-sensitive starting materials, by heating the first product in a solvent with a hydrogen fluoride and/or water-removing agent, e.g. a molecular sieve, ethylene oxide, sodium or potassium fluoride or sodium or potassium acetate. The formation of approximately the same products with both the hypofluorite reaction component and elemental fluorine suggests that the same reaction mechanism is involved.

The hypofluorite reaction components are fluoroalkyl hypofluorites, which contain at least 2 fluorine atoms per carbon atom in the alkyl part. Preferred reaction components of this type are trifluoromethyl, perfluoropropyl, perfluoroisopropyl, perfluoro-t-butyl, monochlorohexafluoropropyl or perfluoro-t-pentyl hypofluorite or 1,2-difluorooxytetrafluoroethane or 1,1-difluorooxydifluoromethane. The most preferred reaction component is trifluoromethyl hypofluorite.

When the fluorinating agent is a volatile liquid, it can conveniently be introduced into the reaction mixture in gaseous form, or it can be dissolved in an inert liquid, such as chlorotrifluoromethane or other fluorinated hydrocarbons, which conveniently also carry a chlorine substituent.

The reaction temperature is preferably kept relatively low, e.g. in the range -78 to +40°C. The turnover at room temperature is fast and smooth. The turnover can e.g. common by means of nuclear magnetic resonance spectroscopy or thin-layer chromatography.

When elemental fluorine is used as a fluorinating agent, the gas should be diluted with an inert gas, such as nitrogen or argon,

and the concentration of fluorine in the gas is preferably 1 to 50% by volume. In general, lower reaction temperatures are used than those that are optimal for the hypofluorite reaction components, but the conversion can be regulated at room temperature.

The 6-substituted 5-fluoro-5,6-dihydrouracils such as 5,6-difluoro-5,6-dihydrouracils and 5-fluoro-6-hydroxy-5,6-dihydrouracils are new compounds with the general formula:

where R 1 , R 2 and R 3 have the meanings given above, and R 4 is

the rest of. a nucleophile, e.g. a fluorine atom or a hydroxyl group.

The following examples shall serve to further illustrate the invention. All melting points were taken on a Kofler hot plate and are stated uncorrected, PMR spectra were obtained at

6GM Hz using a Varian T-60 spectrometer and are indicated as downshifts from internal tetramethylsilane(s). FMR spectra

was obtained at 56.4M Hz on the above instrument and is indicated

as exchanges from internal CFCl^-CF^OF is a powerful oxidizing agent, and although we have encountered no difficulties in its use, precautions should be taken. All transactions should be carried out with adequate shielding, accumulation of the reaction component in the presence of oxidizable substances should be avoided, material for handling the reaction component should consist of glass, "Teflon", "Kei-F" or passivated metal, and under no circumstances should PVC, rubber, polyethylene or similar substances are used. I.R. spectra were obtained with a Perkin-Elmer model 137 spectrometer. Solutions of CF₂OF were prepared by passing the gaseous reaction component into CFClg at -78°C. Aliquots were treated with an excess of aqueous Kl, and the concentration of CF3OF was calculated by filtering the released I2; CF3OF+2KI+H2O I2+2KF+2HF+CO2.

EXAMPLE 1

Fluorination of uracil with CF^ OF

Uracil (0.336 g, 3 mmol) in a mixture of trifluoroacetic acid

(6 mL) and water (20 mL) were added to a solution of trifluoromethyl hypofluorite (4.5 mmol) in CFCl 3 (50 mL) at -78°C in a pressure vessel.

The precipitated uracil was redissolved in the aqueous layer when the mixture was warmed to room temperature. The mixture was vigorously stirred for 15 hours. Excess CF₂OF was removed under nitrogen, and the solvent was removed under reduced pressure. The solid residue was sublimed at 210 - 230°C under reduced pressure (0.5 mm Hg) to

give impure 5-fluorouracil (0.365 g, 94%) m.p. 260-70°C. Recrystallization from methanol-ether gave pure 5-fluorouracil (0.33 g, 85%) m.p. 282-3°C, mixed m.p. (with authentic 5-fluorouracil) 282-3°C.

PMR, FMR, IR and U.V. spectra were identical to those of authentic 5-fluorouracil.

In a similar fluorination as above, the crude products were not exposed to heat, but were instead separated by preparative thin-layer chromatography (silica gel "GF 254", methanol:chloroform, 20:80) into fractions with Rf 0.5 (5-fluorouracil) and a fraction with R^

0.3 (which on heating was converted quantitatively to 5-fluorouracil): V^fi 3300(s), 1720(s), 1475(m), 1250(m) , 1140(m), 1080(m), 880 (m) ,

cm"

800(m). Proton NMR showed a complex pattern of resonances from 5-6 ppm (AB pattern in an ABX system). FMR had <f> = +207.6 ppm

(broad doublet J=45 Hz). The mass spectrum had molecular ion at m/e 148<+>; exact mass m/e 148.0291 (calculated for C4H5FN2O3, m/e 148.0284). This product was 5-fluoro-6-hydroxy-5,6-dihydrouracil. Analysis: C.H.FH O.

EXAMPLE 2

Fluorination of uracil with fluorine

Fluorine gas liberally diluted with nitrogen was introduced at room temperature into a vigorously stirred solution of uracil (150 mg, 1.34 mmol) in water (50 mL). After the starting material had disappeared (NMR control, ca. 2.5 mmol F 2 ), the solvent was removed under reduced pressure and the residue sublimed to give 5-fluorouracil (95 mg, 0.74 mmol, 55% yield ) identified by comparison with authentic 5-fluorouracil.

EXAMPLE 3

A solution of uridine triacetate (0.25 g) in methanol

(50 mL) was added to a solution of trifluoromethyl hypofluorite (1.2 mmol) in CFCl 3 (25 mL) at -78°C, and the mixture was vigorously stirred for 5 min at -78°C and then purged with nitrogen.

The resulting solution was concentrated to give a waxy, white solid, from which methanol could only be completely removed by vacuum treatment at 3 mm Hg overnight.

The crude fluorinated product was dissolved in a 10% v/v solution of triethylamine in 50% v/v aqueous methanol, and the solution was stirred for 48 hours at room temperature and then concentrated to give a white solid. Crystallization of this solid from ethanol gave 5-fluorouridine (0.15 g), m.p. 178 - 181 C.

EXAMPLE 4

The procedure according to example 3 was repeated, except that uracil-2'-deoxyriboside diacetate was treated instead of uridine triacetate. The resulting 5-fluorouracil-2'-dioxy-riboside had m.p. 150 - 152°C.

EXAMPLE 5

Uridine (1 g) was dissolved in acetic acid (25 ml) which was kept at about 5°C and was treated with elemental fluorine (3% in nitrogen) with vigorous stirring. The fluorine was introduced into the solution until the reaction was complete (NMR control). Excess fluorine was removed by flushing the solution with nitrogen. A strongly basic ion exchange resin in formate form (Dowex 1) (3 g) was added. The solution was heated at 80°C for 15 minutes, filtered and the acetic acid was removed under reduced pressure. Crystallization from ethanol/ether gave 5-fluorouridine, identical to an authentic sample.

EXAMPLE 6

A solution of uridine triacetate (1g) in acetonitrile (25 mL) and CFCl3 (15 mL) kept at -78°C was treated

with elemental fluorine (3% in nitrogen) under vigorous stirring. After completion of the reaction and removal of excess fluorine as in Example 5, the reaction mixture was treated with triethylamine

Claims (6)

1. Process for the preparation of 5-fluorouracil derivatives with the formula (where R is an alkyl group, a hydrogen atom or a monosaccharide residue), characterized in that a compound with (where R has the meanings given above) is reacted with a fluoro-alkyl-hypofluorite where the alkyl part contains at least two fluorine atoms per carbon atom, or is reacted with elemental fluorine diluted with an inert gas, to introduce a fluorine atom into the 5-position, followed, when an atom or a group is introduced into the 6-position by one of the aforementioned reactions, by elimination of said group together with the hydrogen atom in the 5-position to form the desired 5,6-double bond. (2 mL) and methanol (10 mL) and was then stored overnight at room temperature. The solvents were removed under reduced pressure. The crude product was dissolved in water and treated with a strongly acidic ion exchange resin (Dowex 50) in hydrogen form. The product was filtered, the solvent was removed and the residue was recrystallized from ethanol/ether to give 5-fluorouridine, identical to the product of Example 5. 2. Procedure as stated in claim 1, characterized in that trifluoromethyl hypofluorite is used as the hypofluorite reaction component. 3. Method as stated in claims 1 and 2, characterized in that the elimination of said 6-substituent is carried out by heating. 4. Method as stated in one of the preceding claims, characterized in that the fluorination is carried out in the presence of a polar solvent. 5. Method as stated in one of the preceding claims, characterized in that the fluorination is carried out in the presence of a nucleophile, whereby fluorine is added in the 5-position and the nucleophile is added in the 6-position. 6. Method as set forth in claim 5, characterized in that the nucleophile used is a hydroxyl ion, alkoxy ion, carboxylation or halide ion.