NZ204736A - The preparation of the 1-ethoxycarbonyloxyether ester of 6-(d-(-)-alpha-amino-alpha-phenylacetamido)-penicilanic acid - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £04736 "V -- vv < t • 2 047 3 6 Priority Date(s): f. i£/l 2-.

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DBAWENSS NEW ZEALAND THE PATENTS ACT 1953 COMPLETE SPECIFICATION c "IMPROVEMENTS IN THE PREPARATION OF ANTIBIOTICS" We, ASTRA LAKEMEDEL AKTIEBOLAG, a Swedish Company, of S-151 85 Sodertalje, Sweden, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by ^ which it is to be performed, to be particularly described in and by the following statement: 204736 Field_of_the_invention This invention relates to a novel method of manufacturing the 1-ethoxycarbonyloxyethyl ester of the 6-(D-(-)-a-amino-a-phenylacetamido) penicillanic acid of formula I: which is an ampicillin ester of extreme importance from the therapeutic point of view, since it is well absorbed when administered orally and gives much higher blood levels of ampicillin than ampicillin itself.

This ester can be isolated in the form of a hydrochloride and is known as bacampicillin hydrochloride.

On the basis of previous known processes (cf. British Patent Specification 1363506, bacampicillin hydrochloride can be synthesized by the two following methods: A) Reaction of potassium benzylpenicillin with a-chlorodi-ethylcarbonate in organic solvents or in an aqueous solution of 70% dioxane in the presence of sodium bicarbonate. The 1-ethoxycarbonyloxyethyl ester of benzylpenicillin which is obtained is subjected to the reaction of removing the phenyl-acetic chain, via the iminochloride-iminoether, in order to obtain the 1-ethoxycarbonyloxyethyl ester of the 6-amino-penicillanic acid, which is isolated as the hydrochloride. 204736 By subsequent condensation of the latter intermediate with D-(-)-a-phenylglycine, the compound according to formula I is obtained.

B) Esterification reaction of the 6- (D-(-)-a-azido-a-phenyl-acetamido)-pencillanic acid with a-chlorodiethylcarbonate in a polar solvent.

Subsequently, by catalytic hydrogenation of the 1-ethoxycarbonyloxyethyl ester of the 6-(D(-) -a-azido-a-phenyl-acetamido)penicillanic acid,the compound according to formula I is obtained.

As can be seen, these methods are rather complex since they involve the use of numerous raw materials and lengthy processing times.

The_invention A prime object of this invention is to provide a method of preparing the active substance concerned, which is easier to carry out and industrially more advantageous. A more specific object of this invention is to provide a method of preparing bacampicillin using ampicillin as starting material, with considerable simplification of the said method and obtaining a high degree of purity of the desired product.

In accordance with the present invention, the 1-ethoxycarbonyloxyethyl ester of the 6-(D-(-)-a-amino-a-phenylacetamido) pencillanic acid having the following formula: ch — co nk ch—ck (I) ch coo — ch— o -xooc2h5 ✓r-' A \- •\ -<o\ IV mi ch 3 V 2 2 MAY l%6 / " 2 204736 fc5 is prepared by a process which is characterized by the steps of: a) reaction of ampicillin, preferably in the form of an alkaline salt, with, a reactive derivative of acetoacetic acid to form the corresponding enamine having the following formula: ^ CH, ^ ^—ch co nh ch qtc cv (ii) r1 c/xh ch3 n co n ch c00x il r2 c o n h wherein R^" represents an alkyl group containing 1 to 4 carbon atoms, a substituted or unsubstituted aryl group or an aralkyl group; 2 R represents hydrogen, an alkyl group containing 1 to 4 carbon atoms, a substituted or unsubstituted aryl group or an aralkyl group; 3 R represents an alkyl group containing 1 to 4 carbon atoms, 15 a substituted or unsubstituted aryl group, an aralkyl group, an alkoxy group containing 1 to 4 carbon atoms, an aryloxy group, or an amino group; and X represents an alkali metal, an alkaline earth metal, or an organic base; b) reaction of the resulting intermediate with an a-halo-di-ethylcarbonate having,the following formula: z— CH-ocooc2H5 (iii) ch3 22 MAY 1986 wherein Z is bromine, chlorine or iodine to form the / corresponding ester having the following formula: 804736 12 3 where R , R and R have the same significance as above; and c) hydrolysis of said ester in an acid medium to obtain the compound according to formula (I).

Z in reactant III is preferably bromo, since a-bromodiethyl-carbonate is used with great advantage as a reactant in the esterification process. The use of a-bromodiethylcarbonate leads to particularly high yield and high purity of the final product.

When Z in reactant III is bromine, the esterification reaction between the reactants II and III can be carried out with or without an esterification catalyst.present.

The addition of a catalyst at this stage considerably shortens the reaction times and provides higher yields of the product with a greater degree of purity.

For this purpose the following substances can be used as catalysts: quaternary ammonium salts, for example tetrabutyl-ammonium bromide, the bromides or iodides of alkali metals ... and cyclic ethers. 204*736 The catalyst may be used in an amount which varies from 0.005 to 0.10 moles per mole of compound III to amounts which are equimolar with the compound III. In a preferred embodiment, tetrabutylammonium bromide is used in an amount of from 0.01 to 0.10 moles per mole of compound III. 12 3 Illustrative examples of the radicals R , R and R are: alkyl: CHj, C2H5' n~C3H7' ^~C3H7' n-C4H9 alkoxy (R3 only): OCH3, OC2H5, OCH2CH2CH3, OCH(CH3)2, o(ch2)3ch3 substituted aryl: phenyl substituted with halogen such as ci and Br The radical X is selected among groups which are well known in the art, for example alkali metal: Na, K alkaline earth metals: Ca, Mg aryloxy: —o — organic base: organic bases which are known in the synthesis of penicillins, e.g. tertiary ammonium groups, triethylamine, ethylpiperidine and methylmorpholine.

In the preferred embodiment of the invention, the group protecting the amino group of the ampicillin is a 1-me.thoxy-carbonyl-propen-2-yl group or a 1-ethoxy-carbonyl-propen-2-yl group for which the preferred intermediate is the sodium or potassium salt of the N-(-1-methoxy-carbonyl-propen-2-yl) penicillanic acid respectively N~(1-ethoxy- carbonylpropen-2-yl penicillanic acid according to formula 12 3 II (R = methyl; R = methyl; R = methoxy or ethoxy and X = Na or K).

The intermediate IV is stable in a neutral or alkaline medium, whereas in an acid medium it is possible to remove the group protecting the amino group simply, quickly and selectively.

The group protecting the amino group of the ampicillin can be selected e.g. from the groups mentioned in the British Patent Specification 991586, and from other groups which are known in the art.

The a-bromodiethylcarbonate, compound III wherein Z is bromine, which is a novel compound, may be prepared by reacting the corresponding a-chlorodiethylcarbonate with sodium bromide as is exemplified in Example 1 below.

More specifically, therefore, the process method according to a preferred embodiment of this invention, comprises the following stages. - transformation of ampicillin trihydrate in a polar solvent, for example N,N-dimethylformamide, into a salt thereof, for example potassium, and subsequent formation of the corresponding enamine (H) by reaction with a derivative of aceto-acetic acid, for example, methyl acetoacetate; 2047&G - addition of an esterification catalyst, preferably tetrabutylammonium bromide ; - addition of ct-bromdi ethyl carbonate to the reaction mixture to form the 1-ethoxycarbonyloxyethyl ester of the ampicillin in the form of the enamine (IV); - hydrolysis of the protective group with HC1 diluted in an organic solvent, for example n-butyl acetate/water; - recovery of the bacampicillin hydrochloride by saturation in the aqueous phase, for example with sodium chloride and extraction with a suitable solvent, -for example n-butyl acetate; and - concentration of the solution at low pressure in n-butyl acetate in order to crystallize the product to a high level of purity, the product then being isolated by filtration.

Among the main advantages of the process according to the invention, the principal one is that, by this process, it is possible to obtain bacampicillin hydrochloride practically in one operation and with a high degree of purity.

In fact the impurities which are present in the product obtained by the process according to the present invention are negligible as compared with the known processes of the previous state of the art. * v Another equally important advantage is that ampicillin trihydrate is ,/£ used as the starting material, this being a known antibiotic which fa is easily obtainable in pure form and at low cost.

The intermediate (II) can be easily prepared as described for example in British Patent Specification 991586 with a yield of over 95% by reaction of ampicillin trihydrate with methyl or ethyl acetoacetate, 204736 O 15 20 C *J to 50% more than the stoichiometric ratio, in the presence of an organic base or an alkali metal carbonate, for example potassium carbonate.

The intermediate (II) can be isolated and added to the esterification reaction in solid form. Or, without isolation of the intermediate (II), the esterification reaction can be effected in the same solvent in which the reaction for the formation of enamine (II) took place.

The reaction for the formation of ampicillin enamine (II) is conducted in an aprotic polar solvent, such as N,N-dimethylacetamide, N,N-dimethylformamide, dimethoxyethane, dimethylsulphoxide, tetrahydrofuran or dioxane.

To complete the reaction, it is sufficient to leave the components of the mixture in contact at a temperature between 0°C and 60°C, preferably between 20°C and 30°C, for 2 to 8 hours, preferably 3 hours.

The compound II can be prepared via acylation of 6-amino-penicillanic acid with a corresponding enamine derivative of phenylglycine for the formation of the compound II which thereafter can be esterified directly and converted to bacampicillin with isolation of the compound II.

The esterification reaction after the addition of the o-halo-diethylcarbonate to the said mixture, takes place at a temperature between 15°C and 80°C, preferably between 45°C and 55°C, for a period of time from 1 hour to 24 hours, preferably from 5 to 10 hours.

The esterification reaction is suitably carried out in an organic solvent such as methylene chloride or acetone, di-methylacetamide, dimethylformamide and dimethylsulfoxide, or in a mixture of organic solvents. It is pos 8 204736 also organic solvent containing water. The use of ester-ification catalyst is desirable when acetone is used as solvent for the esterification reaction.

In the easiest and most suitable conditions fox industrial purposes, the esterified enamine (IV) is isolated by dilution of the reaction mixture with water and subsequent extraction with a suitable solvent which is immiscible with water, for example,n-butyl acetate.

The acetate phase is agitated with a dilute solution (0.2 -0.3N) of HC1 until the protective group is completely hydro-lysed, which requires a contact time of 2 to 8 hours, preferably 4-5 hours, at ordinary temperatures.

By addition of sodium chloride, compound (I) separates out from the aqueous phase in the form of the hydrochloride, which is extracted with a suitable solvent, for example,n-butyl acetate.

By concentrating the organic phase at low pressure at a temperature of 40°C until a small volume remains, crystallization of the product according to formula (I) takes place.

The crystalline product is isolated by filtration, washing and vacuum drying.

The a-bromodiethylcarbonate reactant of the formula III: used in the process of the invention, can be prepared by two novel and inventive processes, herebelow denoted process A and process B.

A: The first of these processes, process A, comprises the Br ch3— ch.o.co.o.c2h5 (III) steps of: 2 2 MAY 1986" ■ * / 9 304736 (a) reacting an aldehyde of the formula CH3CH0 VI with carbonyl bromide C0Br2 VII to give an alpha-bromo-bromoformate of the formula: Br I CH3 CH. Q.CO.Br VIII and; (b) reacting the alpha-bromo-bromoformate of formula VIII with an alcohol of the formula C2H^-0H to yield the desired alpha-bromo-diethylcarbonate of the formula III.

Thus, the process A in accordance with the invention may be summarised by the reaction scheme: Br +C.H OH Br I 2 5 i CH3CH0 + COBr2 > CH3— CH.O.CO.Br > CH3— CH.O.CO.C^ + HBr The alpha-bromo-bromoformate of the formula VIII is, in itself, a new compound.

The reaction between the aldehyde, CH3CHO, and carbonyl bromide is most suitably carried out in the presence of a catalyst which may be, for example, a tertiary amine (for example a tertiary aliphatic amine, a tertiary mixed alkyl/aryl amine or a tertiary aromatic amine), tertiary phosphine, amide, substituted urea or thiourea, phosphoric acid amide, tertiary oxonium or sulphonium salt, or a quaternary ammonium or phosphonium salt. Preferred examples of catalysts for use in the process A include pyridine, dimethylformamide, tetra-n-butyl urea, hexamethyl-phosphoric-tri-amide ayd benzyltri-methyl ammonium bromide. ' The catalyst is suitably used in an amount of from 0.05 to 0.5, preferably from 0.05 to 0.15, moles of catalyst per mole of aldehyde.

The reaction between the aldehyde and the carbonyl bromide is suitably carried out in the presence of a solvent which may be, for example, an aromatic hydrocarbon such as toluene or a halogenated hydrocarbon such as dichloromethane, carbon tetrachloride or chlorobenzene. The reaction between the aldehyde and the carbonyl bromide is suitably carried at a temperature of from -40 to 120°C, preferably 0 - 40°C. The carbonyl bromide will usually be used in molar excess with respect to the aldehyde, suitably in a molar excess of from 10 to 100%, preferably from 20 to 50%.

The intermediate alpha-bromo-bromoformate of formula VIII produced in step (a) of the process A need not be isolated prior to reaction with the alcohol C2H^OH and, indeed, it is generally preferred not to do so. Thus, in accordance with a preferred embodiment, the reaction mixture obtained from step (a) is freed of excess carbonyl bromide, for example by warming under reduced pressure or by purging with nitrogen. The crude alpha-bromo-bromoformate-containing reaction mixture is then reacted with an excess of the alcohol. The reaction may conveniently be effected by heating the mixture under reflux until the evolution of hydrogen bromide ceases or by adding a tertiary base to the mixture and, if necessary, warming it. Any residual catalyst from step (a) or its complex with carbonyl bromide does not appear to interfere with the subsequent reaction and, in some cases, appears beneficial.

The resultant crude alpha-bromocarbonate may conveniently be isolated from the reaction mixture by fractional distillation under reduced pressure.

Process A is illustrated in Examples 7 and 8, which way of illustration only. 11 204736 B: The second process, process B, for the preparation of a-bromodiethylcarbonate, will now be described. Method B is exemplified in Example 9, which is given by way of illustration only.

Process B is concerned with improvements in and relating to the preparation of a-bromodiethylcarbonate by a modification of the Finkelstein reaction, that is, by reaction of an alkyl chloride or arylalkyl(or a compound containing such a group) ^ with an alkali metal bromide or alkali metal iodide to replace ' J the chlorine substituent by a bromine or iodine substituent respectively; or by the reaction of an alkyl bromide or arylalkyl bromide (or a compound containing such a group) with an alkali metal iodide to replace the bromine substituent by an iodine substituent. t The Finkelstein reaction is useful since the resulting iodides are generally more reactive then the bromides which in turn are more reactive then the chlorides. In some cases only catalytic amounts of the alkali metal bromide or iodide are necessary and the resulting more reactive species is allowed 20 to react with the desired substrate regenerating the alkali metal bromide or iodide, thus continuing the reaction.

Not all optionally substituted alkyl chlorides or arylalkyl chlorides undergo the reaction and, in particular, it has been found difficult to carry out the reaction with alpha-chloro 25 esters and alpha-chloro-carbonates, that is,compounds in which the chlorine atom is attached to a carbon atom which is, in ' turn, attached to either end of a group -C(O)-0~. An example of such an. alpha-chlorocarbonate is u-chlorodi-ethylcarbonate, which is a known intermediate in the preparation of ethoxy-30 carbonyloxyethyl esters of 6-aminopenicillanic acid.

' It has now been found, in accordance with the present invention, that this problem may be overcome by carrying out the reaction using a two-phase solvent system, one phase Q^fflFShakis water 204736 and the other is a water-immiscible organic solvent, in the presence of a phase transfer catalyst.

According to process B, therefore, there is provided a process for the preparation of a-bromodiethylcarbonate by reaction of a-chlorodiethylcarbonate with an alkali metal bromide, which process is characterized in that the reaction is carried out in a two-phase solvent system comprising water and a water-immiscible organic solvent in the presence of a phase transfer catalyst.

Suitable water-immiscible organic solvents for use in accordance therewith include halogenated hydrocarbons, for example,halogenated paraffins such as dichloromethane; and aromatic hydrocarbons such as toluene. Suitable phase transfer catalysts include quaternary ammonium salts, for example,tetraalkyl ammonium salts such as cetyltrimethyl ammonium bromide and tetra-n-butyl ammonium hydrogen sulphate. The alkali metal bromide may, for example, be sodium, potassium, or lithium bromide, lithium bromide being preferred.

Thus, in process B, a-chlorodiethylcarbonate of the formula: CI 0 I II CH3 CH — 0 C o C2H5 IX is reacted in a two-phase solvent system, one phase of which is water and the other is a water-immiscible organic solvent, with an alkali metal bromide of the formula: R-Br X in which formula R is an alkali metal such as Na, K and Li, for the formation of the compound of the formula: CH.

Br I CH 0 II c C2H5 III 22MAYJ986 204736 As noted above, the preferred alkali metal R is Li so that LiBr is a preferred reagent of the formula X.

In connection with process B it has been found that lithium bromide may by used with advantage in a conventional Finkelstein reaction (i*e. one employing a single phase organic solvent system), for example to halogenate an alpha-chloro-carbonate. This method is exemplified in Example 10.

Suitable solvents for such a process include lower aliphatic alcohols, lower aliphatic ketones, lower aliphatic ethers and lower aliphatic amides of formic acid.

The following examples illustrate the present aspects of the invention without limiting it in any way.

Example 1: Preparation of g-bromdiethylcarbonate acetone NaBr + Cl-CH-OCOOC^Hc > Br-CH-0C00CoHc+NaCl | Z o | ZD ch3 ch3 Sodium bromide (102.9 g) dissolved in acetone (600 ml) was reacted for 2-3 hours at ambient temperature (20-25°C) with a-chlorodiethylcarbonate (152.6 g) dissolved in 100 ml of acetone. The mixture was then concentrated under vacuum at low temperature, max. 3 5°C, until a semi-solid mass was obtained. The reaction mixture was then partitioned with I^O/ethyl ether. The aqueous phase was separated and was then extracted twice with 400 ml of ethyl ether.

The combined organic phases containing the a-bromdiethyl-carbonate were washed with: ■:> V-N 2 2 MAY 1986' 204736 r> 800 ml of H-0, . 1000 ml of IX sodium metabisulphate aqueous solution,and 1000 ml of.NaCl saturated solution.

The organic phase was dried over Mg sulphate, and then concentrated under vaccum at.low temperature, max. 35°C to give the title product (60%) in the form of a liquid which initially was colourless or slightly yellow-brown.

It was used directly in the esterification step according to Example 2 below.

Example 2- .08 g (0.181 m) of finely ground anhydrous potassium carbonate are suspended in 200 ml of N,N-dimethylacetamide and 32.4 ml (0.3 m) of methyl acetoacetate and 60.4 g (0.15 m) pf ampicillin trihydrate are added.

The mixture is maintained under fast agitation for..5 hours at 20°C - °C; after this time/46.1 g (0.234 m) of bromdiethylcarbonate, 6 g (0.02 m) of tetrabutyl ammonium bromide and 100 ml of N,N-dimethyl-n;etamide are added.

It is heated under agitation for 10 hours at 40°C - 42°C; the reaction 20 mass is poured into a mixture consisting of 1200 ml of .water and 400 mi of n-butyl acetate.

The aqueous phase is collected and extracted with another 100 ml of u . n-butyl acetate.

The reunited organic phases are washed twice with 100 ml of water each 25 time. 150 ml N HC1 and 370 ml of water are added to the organic phase which is subjected to agitation; it is left under agitation at 22°C 23°C for 4 hours. ' - 15 - - ^ 204736 The aqueous phase is collected and the organic phase is extracted with ,y 100 ml of water.

The reunited aqueous phases are brought to pH 4 with a 10% aqueous solution of NagCO^, then bleaching carbon is added to them and they are filtered. 300 ml of n-butyl acetate and 80 g of sodium chloride are added to the aqueous filtrate.

' The organic.phase is separated and the aqueous'phase is extracted with 200 ml of n-butyl acetate. i ' The reunited phase in n-butyl acetate are concentrated at low pressure at 40°C to a volume of approximately 300 ml. The product is left to crystallize for 15 hours at +5°C.

It is filtered, washed with n-butyl acetate (100 ml) and ethyl acetate (100 ml). It is vacuum dried at 40°C for 24 hours.

Yield: 54.2 g (72%) of the 1-ethoxycarbonyloxyethyl ester of the 6-(D(-)-a-amino-a-phenylacetamido) penicillanic acid with m.p. 160-2°C. (d) and characteristics conforming to the authentic hydrochloride sample. /22MAYt9«7 Example 3: ^ f - .20 36.4 g (0.075 m) of potassium N-(l-methoxycarbonyl-propen-2-yl)-6-I U D(-)-a-amino-a-phenylacetamido) penicillate are added to a solution >. -of 17.8 g (0.116 m) of a-chlorodiethylcarbonate and 3 g (0.01 m) of tetrabutylammonium bromide in 150 ml of N,N-dimethylformamide. Under agitation the temperature is raised to 45°C and maintained at 45°C -50°C for 5 hours. , When heating is completed, the reaction mixture is poured into a mixture comprising 300 ml of a 14% aqueous sodium chloride solution and 600 ml of n-butyl acetate. The mixture is agitated for 10 minutes, then the 204736 n organic phase is separated and the aqueous phase is extracted with 100 ml of n-butyl. acetate. The reunited organic phases, after two washings with 75 ml of .14% sodium chloride aqueous solution, are concentrat-* ed at low pressure until an oil is obtained.

The oil is mixed with 200 ml of tetrahydrofuran and 100 ml of water; the solution obtained (pH 4.8) is brought under agitation to pH 1.5 by adding, in all, 12 ml of 6N HC1 in 1 hour.

. • After leaving the solution to stand for another hour at ordinary temperature, the tetrahydrofuran is removed at low pressure at 40°C, 150 10 ml of n-butyl acetate are added to the remaining aqueous phase (150 ml) and then 15 g of sodium chloride are added.

The organic phase is separated and the aqueous phase is extracted with 100 ml of n-butyl acetate.

The reunited organic phases are concentrated under vacuum at 40°C to 15 a volume of 120 ml.

The product is left to crystallize for 15 hours at 5°C.

It is thenTfiltered,,>/ashed_with n-tiutyl acetate.(50,ml) :and ethyl acetate (50 ml).

It is vacuum dried at. 40°C.

^J0 The following is obtained: 25.2 g (66.9%) of the 1-ethoxycarbonyloxyethyl ester of the 6-(D-(-)-a-amino-Q-phenylacetamido)-penicillanic * acid hydrochloride'with m.p". 160-2°C.

Analytical determinations: ^ Titre: 97.82% Rotatory power: +166.3° (c=l, EtOH95°) pH: 4.05 (2% aqueous solution) Moisture content: 0.82% Residual solvents: ethyl acetate 0.45; n-butyl acetate 0.98% IR and NMR spectra are standard Residual ampicillin: 0.06% Example 4: 204736 I 16.2 ml (0.15 m) of methyl acetoacetate and 30.2 g (0.075 m) of ampicillin trihydrate are added to a suspension of 12.54 g (0.0907)m) of finely pulverized anhydrous potassium carbonate in 100 ml of N,N-dimethylformamide.

It is maintained with agitation at 22°C-23°C for 3 hours and after this time, considerable fluidization of the mass can be observed. 17.8 g (0.117 m) of a-chloro-diethylcarbonate, 3 g (0.01 m) of tetrabutylammoniumbromide and 50 ml of N,N-dimethylformamide are now added in that order. f) The mixture is heated under agitation for 5 hours at 45 C -50°C, then left to stand at +5°C for 15 hours.

The reaction mass is poured into a mixture consisting of 600 ml of water and 200 ml of n-butyl acetate, and it is agitated until a complete solution is obtained, the aqueous phase is collected and extracted with another 50 ml of n-butyl acetate.

The reunited organic phases are washed twice with 50 ml of water each time. 75 ml of N HC1 and 185 ml of water are added to the organic phase subjected to agitation; it is left under agitation at 22°C - 23°C for 4 hours.

The aqueous phase is collected and the organic phase is extracted with 50 ml of water. The reunited aqueous phases are brought to pH4 with a 10% aqueous solution of Na^CO^, then bleaching carbon is added to them and they are filtered. 150 ml of n-butyl acetate and 40 g sodium chloride are added to the aqueous filtrate.

The organic phase is separated and the aqueous phase is extracted with 100 ml of n-butyl acetate. z > The reunited phases in butyl acetate are concentrated at low pressure at 40°C to a volume of approximately 150 ml.

The product is left to crystallize for 15 hours at +5°C. 209736 n It is filtered, washed with n-butyl acetate (50 ml) and ethyl acetate (50 ml).

It is dried under a vacuum of 10 mm Hg in the presence of moisture at 25°C for 24 hours.

Yield: 20.8 g (55%) of the 1-ethoxycarbonyloxyethyl ester of the 6-(D-(-)-a-amino-o-phenylacetamide) penicillanic acid hydrochloride with m.p. 159-161°C and characteristics conforming to an authentic sample.

When tested for esterification of amphicillin dane salt with ethyl acetoacetate, the results were: Obtained: M.P. : IR/TLC: K.F. : pH: Assay to: 16.1 grams of white crystalline product 144-148°C (Tottoli apparatus) Conform 0.35% 3.55 (2% water solution) 95.2% Total residual solvents: 3.5% Example 4A: Example 4 was repeated except that the addition of a-chlorodiethylcarbonate was carried out in two phases. In the first phase, 9 gms was added immediately,, and in the second phase another 9 gm was added after 2 hours, whereupon the mixture was heated for 3 hours at 45°C.

When tested for esterification of amphicillin dane salt with ethyl acetoacetate, the results were: _ 30 Obtained: M.P.: .

IR/TLC: K.F. : pH: Assay to: Residual solvents: 13.7 grams of crystalline beige product 143-146°C (Tottali apparatus) Conform 0.2% 3.43 (2% water solution) 94.8% 2.6% 7V f22MIOT$S 1 _19 _ ) 204736 Example 5 A mixture of/J 60 ml acetone, 22.6 g (0.075 mol) of the potassium salt of D(-)-N-methcxicarbonylpropen-2-yl-aminophenylacetic acid, 6.9 ml (0.088 mol) ethyl chloroformate and 3 drops of N-methylmorpholine, is . 5 stirred fori5 minutes at a temperature of -20 - -30°C. To this reaction mixture a solution of 16.2 g 6-aminopenicillanic acid, dissolved in 35 ml water through the gentle addition of 7.6 g (0.075 mol) triethyl-, amine with agitation, is added in one portion, after which the mixture is diluted with 90 ml acetone and chilled to -20°C.

After stirring for 45 minutes, without any additional cooling, 23.4 g (0.117 mol) of a-bromodiethylcarbonate, 3 g (0.01 mol) or tetrabutyl-ammonium bromide and 250 ml .of N,N-dimethylformamide are added in that 0W .. order. The mixture is stirred for 18 hours at 25°C..After that time the reaction mass is poured into a mixture consisting of 600 ml of water and 200 ml of n-butyl acetate and it is agitated until a complete solution is obtained. The aqueous phase is collected and extracted with another 50 ml of n-butyl acetate.

The reunited organic phases are washed twice with 50 ml of water each time. 185 ml of water is added to the organic phase and 1 N HC1 is added 2-0 . . dropwise .with agitation to a pH -of -1.9. . The mixture is left under agitation at 22-23cC for 4 hours..

The aqueous phase is collected and the organic phase is extracted with 50 ml of water. The reunited aqueous phases are brought to pH 4 with .... ^ a 10% aqueous solution of ^CO^, active carbon is added to them and *"^5 they are filtered. 150 ml of n-butyl acetate and 40 g of sodium chloride are added to-the,aqueous filtrate.

The organic phase is separated and the aqueous phase is extracted with 100 ml of n-butyl acetate. The reunited phases in butyl acetate are concentrated at low pressure at 40°C to a volume of approximately 150 ml. 30 The product is left to crystallize for 15 hours at +5°C.

It is filtered, washed with n-butyl acetate (25 ml) and ethyl acetate . (25 ml). It is dried.under a vacuum of 10 mm Hg at 25°C for 24 hoursf : 20 - '• v 204736 Yield: 1.17 g of the l-etho^ycarbonylo^yethyl ester of 6-(D(-)-a-amino--a-phenylacetamidopenicillanic acid hydrochloride with m.p. 159-161°C and characteristics (NMR, TLC) conforming to an authentic sample.' Example 5a : * The procedure of example 5 was repeated with the difference that the 6-aminopenicillanic acid was dissolved in 20 ml water instead of in 35.

Yield: 1.05 g of the ettioxycarbonyloxyethyl ester of 6-*(0(-)-a-amino-a-phenylacetamidopenici11anic acid hydrochloride as a white crystalline powder with m.p. 148-151°C, with decomposition, and characteristics (TLC, 1R) conforming to an authentic sample.

Example 6: 6.25 g (0.045 m) of finely ground anhydrous potassium carbonate are suspended in 50 ml of dimethyl sulphoxide and 8.1 ml (0.075 m) of methyl acetoacetate and 15.1 g (0.0375 m) of ampicillin trihydrate are added.

The mixture is maintained under fast agitation for 5 hours at °C - 25°C; after this time 11.5 g (0.059 mj of bromodiethylcarbonate and 25 ml of dimethyl sulplioxide are added.

It is heated under agitation for 17 hours at 35-37°C; the reaction mass is poured into a mixture consisting of 300 jnl of water and 100 ml of n-butyl acetate.

: • - ' * ' \ The aqueous phase is collected and extracted with another 100 ml of - \\ 22MAY n-butyl acetate.

... H The reunited organic phases are washed twice with 25 ml of water each time. ~ • 92.5 ml of water and NHC1 (7.0 ml) to a pH of 1.9 are added to the organic phase which is subjected to agitation; it is left under agitation at 22°C - 23°C for 2.5 hours.' .

S0473< The aqueous phase is collected and the organic phase is extracted with 25 ml water.

The reunited aqueous phases are brought to pH 4 with 10% aqueous solution of Na2C03f then active carbon is added to them and they are filtered. 75 ml of n-butyl acetate and 37 g of sodium chloride are added to the aqueous filtrate.

The organic phase is separated and the aqueous phase is extracted with 50 ml of n-butyl acetate.

The reunited phases in n-butyl acetate are concentrated at low pressure at 40°C to a volume of approximately 75 ml. The product is left to crystallize for 15 hours at +5°C.

It is filtered, washed with n-butyl acetate (25 ml) and ethyl acetate (25 ml). It is vacuum dried at 40°C for 3 hours.

Yield: 1.9 g :(10%) of the 1-ethoxycarbonyloxyethyl ester of the 6-(D(-)-a-amino-a-phenylacetamido) penicillanic acid with m.p. 160-162°C and characteristics conforming to an authentic sample of the hydrochloride (e.g. IR:V 1790.cm \ B-lactam carbonyl).

Example 7: A mixture of acetaldehyde (44 g, 1 mole), carbon tetrachloride (300 ml) and freshly distilled carbonyl bromide (235 g, 1.25 mole) was cooled to 0°C and maintained at this temperature by external cooling during^ the addition over a period of 1 hour of pyridine (11.9 gf 0.15 mole).

The mixture was allowed to warm up to ambient temperature and then heated to 50°C and maintained at this temperature for a period of 3 hours during which time a precipitate formed.

Evaporation of the reaction mixture under reduced pressure,^, 0 t 50 C gave a semi-solid oily mass which readily dissolved in 2 2^^ ethanol (92 g, 2 mole) on warming and heating under reflux. After heating under reflux for a further 2 hours, excess ethanol was removed in vacuo and the residue triturated with water (100 ml) and methylene dichloride (200 ml).

Separation of the organic layer and fractional distillation afforded pure ethyl alpha-bromo-ethyl-carbonate (130 g, 66% yield) having a boiling point of 90-92°C at 45 mms of mercury pressure and identical in all respect with an authentic specimen.

Example 8: A mixture of acetaldehyde (44 g, 1 mole), dichloromethane (300 ml) and hexamethylphosphoric-tri-amide (17.9 g, 0.1 mole) was cooled to -10°C and freshly distilled carbonyl bromide (207 g, 1.1 mole) was gradually added over a period of 4 hours during which time the temperature was allowed to rise to 10°C.

The mixture was then heated under gentle reflux (ca. 40°C) for 4 hours. While still under reflux, ethanol (69 g, 1.5 mole) was carefully added over a period of 1 hour and heating under reflux continued for a further 1 hour.

Fractional distillation of the resulting mixture afforded pure ethyl alpha-bromoethyl-carbonate directly (114 g, 58% yield).

The authenticity of the ethyl alpha-bromoethyl carbonate formed was confirmed by analysis and independent synthesis as follows: Diethylcarbonate (118 g, 1.0 mole) was stirred and heated to between 110°C and 120°C and illuminated by a 150 watt tungsten filament lamp. Bromine (96 g, 0.6 mole) was added dropwsie over a period of 3 to 4 hours and at such a rate that the j_ mixture did not deepen beyond a pale orange colour.. ' v>^ _ 23 nefc 204736 After addition of bromine was complete, the mixture was cooled to ambient temperature and sodium bicarbonate (20 g) added.

Distillation and fractionation of the resulting mixture gave authentic ethyl alpha-brorao-ethyl carbonate (84.2 g, 70% yield) having a boiling point of 87-88°C at 40 nuns of mercury pressure.

Example 9: A mixture of lithium bromide (43 g, 0.5 m), ethyl alphachloro-ethyl-carbonate (15.3 g, 0.1 m), water (100 ml), dichloro-methane (100 ml) and cetyl trimethyl ammonium bromide (1.5 g) was stirred at ambient temperature for 24 hours. The aqueous layer was removed and replaced by a fresh solution of lithium bromide (26 g, 0.3 m) in water (4 0 ml) containing cetyl trimethyl ammonium bromide (1 g). After stirring for a further 24 hours during which time the temperature was raised to 35°C, the organic layer was separated, dried and vacuum distilled to afford after repeated fractionation the new compound, ethyl alpha-bromoethyl carbonate (15.0 g, 76% yield) having a boiling point of 90-92°C at 35 nuns of mercury pressure.

Found: Calculated: C 30.7; C 30.5; H 4.8 Br 40.1% H 4.6 Br 40.6% The NMR spectrum exhibited peaks as follows 1.2 - 1.6 (3H, triplet) -ch2.ch3 2.0 - 2.2 C3H, doublet) - CH.CH 3 4.1 - 4.5 (2H, Quartet) ch2.ch3 6.5 - 6.8 (1H, Quartet) CH. CH 3 24

Claims (24)

204736 Example 10: Lithium bromide (17.4 g, 0.2 m) was dissolved in dimethyl formamide (150 ml) and the mixture cooled to ambient temperature. Ethyl alphachloroethyl carbonate (30.5 g, 0.2 m) was added and the mixture stirred at ambient temperature for 24 hours. The precipitated lithium chloride was filtered off and the filtrate vacuum distilled to afford after careful re-fractionation, ethyl alpha-bromoethyl carbonate in 76% yield based upon recovered ethyl alphachloroethyl carbonate. Example 11: The authenticity of the foregoing new compound ethyl alpha-bromoethyl carbonate was confirmed by independent synthesis as follows:- A mixture of diethyl carbonate (35 g, 0.3 m) in carbon tetrachloride (50 ml) and alpha-azo-isobutyronitrile (AIBN) (O.lg) was heated to gentle reflux and dibromodimethyl hydantoin (28.6 g, 0.1 m) was added in small aliquotes over a period of 8 hours together with further additions of AIBN (8x0.05g); care being taken to ensure that free bromine did not accumulate in the reaction mixture. At the end of the : reaction, the mixture was subjected to vacuum fractional distillation to afford pure ethyl alpha-bromoethyl carbonate (32.3 g, 82% yield) identical in all respects with the product of Examples 9 and 10. - 25 - 204736 What we claim is:

1. A process for the preparation of the 1—ethoxycarbonyloxyether ester of the 6— (D- (—) -a —amino-a—phenylacetamido) penicillanic acid with the formula: /r\ / CH3 y- ch - co - nh - ch - ch c (i) CH3 nh2 co - n ch - coo - ch - 0 - c00c„hc i 25 ch3 characterized by the steps of: a) reacting ampicillin with a reactive derivative of acetoacetic acid to form the corresponding enamine with the formula: V ch - co - nh - ch - ch c S\ ^H3 ■ , , . , ch3 1 / \ co - n ch - coox (ii) r1— c h ««-? 6 Y l3 R wherein R"*" represents an alkyl group containing 1-4 carbon atoms, a substituted or non-substituted aryl group or an 2 aralkyl group; R represents hydrogen, an alkyl group containing 1-4 carbon atoms, a substituted or non-substituted ' . 3 aryl group or.'an'aralkyl group;. :R represents an alkyl group 204736 containing 1-4 carbon atoms, a substituted or non—substituted aryl group, an aralkyl group, an alkoxy group containing 1-4 carbon atoms, an aryloxy group or an amine group, and X represents an alkali metal, an alkaline earth metal, or an organic base; b) reacting the resulting intermediate with a-bromo-diethyl carbonate with the1formula: Br-CH-O-COO C-H,- (iii) I CH3 to form the corresponding ester with the formula: ^ 5 \ /CH3 0 ^— ch - co - nh - ch - ch c | "CH3 nch. N 1 1 ' , / \ CO - N CH - COO - CH - 0 - C00C?Hr r1— c h i o ii • ch- R CO V ' 3 R (IV) • 12 3 wherein R , R and R have the means specified above; and c) mild hydrolysis in an acid medium to obtain the compouhd of formula (I). - -

2. A process according to claim 1, characterized in that the ampicillin is in the form of an alkaline salt^ - 27 - ^22MAYI984^ 20473* n

3. A process according to claim 2, characterized in that the said alkaline salt of ampicillin is obtained by transforming ampicillin trihydrate by a per se known method in a polar solvent.

4. A process according to claim 3, characterized in that the polar solvent is N,N-dimethylformamide.

5. A process according to any one of claims 2 to 4, characterized in that the said formation of the enamine (II) is carried out by means of reacting the alkaline salt of ampicillin with methyl or ethyl acetoacetate in an aprotic polar solvent at a temperature between 0°C and 60°C and for a time between 2 and 8 hours.

6. A process according to claim 5, charaterized in that the said reaction of forming the enamine (II) is carried out in the presence of an organic base or an alkali metal carbonate.

7. A process according to claim 5 or 6, characterized in that the methyl or ethyl acetoacetate is in an amount 10-50% more than the stoichiometric ratio.

8. A process according to any one of claims 5.to 7, characterized in that the said aprotic polar solvent is selected from N,N-dimethylacetamide, N,N-dimethylformamide, dimethoxyethane, dimethylsulphoxide, tetrahydrofuran and dioxane.

9. A process according to any one of claims 5 to 8, characterized in that the said reaction of formation of enamine is carried out at a temperature between 20°C and 30°C.

10. A process according to any one of claims 5 to 9, characterized in that the said reaction is carried out in a time of 3 hours.

11. A process according to any one of claims 1 to 10, chara^, _ cterized in that -the esterification reaction of the enamin^p^7*" <2^ - 28 - 1 (II) is carried out by addition to the reaction mixture of a-broraodiethyl carbonate, the reaction being carried out at a temperature of 15 to 80°C and for a time of 1 to 24 hours.

12. A process according to claim 11, characterized in that the esterification is carried out in the presence of a catalyst.

13. A process according to claim 11 or 12, characterized in

14. A process according to any one of claims 11 to 13, characterized in that the said esterification reaction is carried out in a time of 5 to 10 hours.

15. A process according to any one of claims 12 to 14, characterized in that the said catalyst is selected from quaternary ammonium salts, alkali metal bromides, alkali metal iodides and cyclic ethers.

16. A process according to claim 15, characterized in that the said catalyst is tetrabutylammonium bromide.

17. A process according to any one of claims 1 to 16, characterized in that the said hydrolysis is carried out with dilute hydrochloric acid after isolating the ester (IV).

18. A modification of the process according to any one of -claims 1 to 10, characterized in that: a) the enamine II is reacted with a compound of the formula Z - CH - O - COO - C_H i 2 (V) wherein Z is CI or I, and 29 204736 b) the reaction between the compounds II and y is carried out in the presence of a catalyst.

19. A process according to claim 18, characterized in that the said catalyst is selected from quaternary ammonium salts, alkali metal bromides and iodides and cyclic ethers.

20. A process according to claim 19, characterized in that the catalyst is tetrabutylammonium bromide.

21. A process according to any one of claims 12 to 16 and 18 to 20, characterized in that the catalyst, is present in an amount of from 0.005 to 0.10 mole per mole of the compound III and V, respectively.

22. A process according to claim 21, characterized in that the catalyst is present in an amount of from 0.01 to 0.10 mole per mole of the compound III and V, respectively.

23. A process according to claim 1 substantially as described herein.

24. The 1-ethoxycarbonyloxyethyl ester of the 6-(D-(-)-a-amino-a-phenylacetamido) penicillanic acid with the formula: yS CH0 / \ / \.^ 3 // VV- CH- CO— NH -CH -CH K ,T. W| | I |\CH3 (I) CO— N—: CH COO— CH — O — COOC-Ht- I 2 5 CH3 when obtained by the process according to any one of claims 1 to 23. e* T DATKgV this day of M ->»* V'XUJ ) AiD. 1086 ASTRA LAKEMEDEL AKTIEBOLAG, By its Patent Attorney HENRY HUGHES LIMITED - so - &,■