Field of the invention:

The present invention relates to a process for the manufacture of D Penicillamine (DEPEN) of formula I, in good yield and purity. D Penicillamine is a valuable therapeutic compound useful in the treatment of rhuematoid arthritis, chronic hepatitis and multiple sclerosis.

Background and prior art:

D-Penicillamine, having the following formula I is known to be useful in the treatment of rhuematoid arthritis, chronic hepatitis and multiple sclerosis, which produces less serious side-effects than the L(+)-penicillamine.

Formula 1

There is ample literature available for the manufacture of D-penicillamine from penicillins. Such processes generally proceed via penilloic acids as intermediates which may subsequently be converted into penicillamines. The penicillamines are precipitated from the reaction mixture as heavy metal complex. Subsequently, the penicillamines are regenerated from the heavy metal complexes by treatment with sulphur compound, such as hydrogen sulphide. Since the use of heavy metal compounds being a necessity in the reaction, produces poisonous contaminants in the final product. Therefore these processes results in poor yields of the desired product and thus render such processes commercially unattractive (see British Specification No. 854,339).

Subsequently, US3888923 (Degussa) discloses process for preparation of Penicillamine which comprises the reaction of 2- isopropyl-S,S-dimethyl- thiazolidine with a carbonyl reagent (such as hydrazine, phenylhydrazine, 2,4- dinitrophenylhydrazine, semicarbazide, Thiosemicarbazide and hydroxylamine) in the presence of water and a water immiscible inert solvent. The DL-penicillamine or its derivative or salts thus obtained are isolated from the aqueous phase in conventional manner, for instance, by evaporation to dryness or by solvent extraction, etc. and further separated into its optical antipodes by first converting into an acyl derivative of the penicillamine, separating the desired antipode and then deprotecting to obtain D- penicillamine. The process reported in this patent is also very elaborate, lengthy, equipment intensive and involves several stages and intermediates and resolution steps. Moreover, the process involves non asymmetric synthesis approach and involves several intermediates and purification procedures. The process is shown below as scheme 1.

Schem

US3960940 discloses another process, wherein, D(-)-Penicillamine and its salts are prepared by reacting a 6-amino or blocked 6-amino penicillin e.g. penicillin G or penicillin V, or a salt thereof, with a hydrazine having two -- NH-groups, or a salt or solvate thereof in presence of a mineral acid. In this method, the reaction takes place in two stages; firstly, the hydrazine compound reacts with the penicillin compound to cleave the β-lactam ring to yield penicilloic acid hydrazide. Subsequently the hydrazide undergoes cleavage to yield the desired D- penicillamine and a pyrazolinone by-product. This process also suffers from disadvantages such as nitrogen environment, employment of different temperatures at different stages; isolation of the byproducts formed, precipitation of Penicillamine as an acid addition salt, and the recovery of the D-penicillamine by re-precipitation with the addition of a base such as triethylamine. US3281461 discloses a process for preparing penicillamine by degradation of a penicillin, such as penicillin G. US'461 discloses a process for converting penicillins to penicillamine by hydrolysis of penicillin to penicilloic acid, decarboxylating the penicilloic acid to penilloic acid, treating the penilloic acid with a mercuric salt to yield a solution of penicillamine-mercuric salt complex and a byproduct penilloaldehyde, and converting said complex to penicillamine. The process further comprises separating the by-product penilloaldehyde from the penicillamine mercuric salt complex by acidifying said solution to a pH within the range of about 1.3 to about 1.8 and precipitating the by-product penilloaldehyde from this acidified solution with a reagent selected from the group consisting of hydroxylamine, semicarbazide, thiosemicarbazide, benzohydrazide, phenylhydrazine and substituted phenylhydrazine, wherein the substituent is a member of the group consisting of nitro, dinitro, halo and dihalo.

As is evident from the above, the reported processes are cumbersome, lengthy, involve multiple process steps, necessitate additional equipment and further suffer from poor yields. Therefore, there is a need in the art for a provision of commercially attractive process for preparing D-penicillamine, as the known processes are not commercially viable for the reasons mentioned above.

Therefore, it is an object of the present invention to provide a feasible and cost effective process for the manufacture of D - penicillamine in high yield and purity that can be easily scaled for industrial production.

Another object of the invention is to employ a chiral moiety containing multiple acid functional groups to convert them into multiple oxazolones containing molecule as a precursor for making amino acids in general sulphur containing amino acids in particular and more particularly D - penicillamine. Summary of the invention:

In line with the above objective, the present invention provides substantially pure D - penicillamine, compound of formula 1, and the process for its preparation and purification.

Accordingly, the process for the preparation of substantially pure D-penicillamine comprising;

a) a) reacting D- camphoric acid with Glycine methyl ester in the presence of dehydrating agent to obtain the corresponding amido ester of formula 2; b) hydrolyzing the amido ester compound of formula 2 with a base in hydroxylic solvent to obtain the corresponding acid compound of formula

3;

c) cyclizing the acid compound of formula 3 by employing dehydrating agent in presence of a base under reflux to obtain oxazolones compound of formula 4;

d) condensing the oxazolones compound of formula 4 with acetone in the presence of a base to obtain compound of formula 5 which is reacted with sulfur transfer reagent followed by acid hydrolysis to obtain D - penicillamine and

e) optionally purifying the D - penicillamine by salting out the product or by employing suitable organic solvents to precipitate the product from water.

The process of the present invention has been found to be advantageous in that the reactions involved are highly reproducible and the product, viz. D - penicillamine (formula 1) can be obtained in high yields and in substantially pure form.

As referred to herein 'substantially pure D - penicillamine' is D - penicillamine of purity greater than 99 %.

The inventiveness of the present invention lies in the employment of a chiral acid for the preparation of the D - penicillamine in high yields by employing mild and simple procedures. The novel process converts the starting material to the intended product in an efficient manner and the starting material can be recovered and recycled for use in subsequent batches.

Detailed description of the invention:

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

The present invention discloses novel chiral acid based oxazolones which has been designed for asymmetric synthesis of D-penicillamine. Oxazolones are well known chiral auxiliaries and are well documented in chemical literature. The novel chiral acid moiety as used in the invention hosts two to three oxazolones which in fact leads to doubling or tripling the yields and thus boost the economics of the synthesis. The salient features of present invention involves elegant chemistry, asymmetric synthesis with well- known oxazolone systems but on a new molecular system, which facilitates the process with versatile chiral auxiliaries, low effluent load, excellent economics thereby opens up new vista for amino acid synthesis.

The chiral auxiliary as designed in the present invention is novel. The process of the present invention is more chemistry intensive and less equipment intensive. The effluent loads are very high in the existing Degussa process. By virtue of having two oxazolone rings on the same molecule the yields can get doubled and the lead time also gets halved. The process is economically viable as there are two oxazolones on the same template. The same auxiliary or similar bis and tri carboxylic acid containing chiral auxiliaries from the chiral pool can be employed for the synthesis of unnatural D amino acid.

None of the methods disclosed in the prior art employ oxazolones based on a chiral acid auxiliary, especially chiral acids containing two to three acid functional groups. The intermediates and the methods of their preparation or a process to obtain high conversions are also not reported. The chiral acids that can be used in the process of the present invention may be selected from the group consisting of:

However, in one preferred embodiment, the chiral acid is D- camphoric acid.

Accordingly, the invention provides a process for the preparation of substantially pure D - penicillamine which comprises;

a) reacting D- camphoric acid with Glycine methyl ester in the presence of dehydrating agent to obtain the corresponding amido ester of formula 2;

Formula 2

b) hydrolyzing the amido ester compound of formula 2 with a base in hydroxylic solvent to obtain the corresponding acid compound of formula

Formula 3

c) cyclizing the acid compound of formula 3 by employing dehydrating agent in presence of a base under reflux to obtain oxazolones compound of formula 4;

Formula 4 d) condensing the oxazolones compound of formula 4 with acetone in the presence of a base to obtain compound of formula 5 which is reacted with sulfur transfer reagent followed by acid hydrolysis to obtain D - penicillamine and

Formula 5 e) optionally purifying the D - penicillamine of formula 1 by salting out the product or by employing suitable organic solvents to precipitate the product from water.

The process of the present invention is depicted in scheme II.

Scheme II:

5

Formula 1 The stepwise preparation of D - penicillamine according to the current invention includes novel intermediates and its preparation.

Accordingly the invention further encompasses the following novel intermediates viz.,;

a) dimethyl 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane-l,3- diyl]bis(carbonylazanediyl)}diacetate(2)

Formula 2

b) 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane- l,3diyl]bis(carbonylazanediyl)}diacetic acid (3)

Formula 3 c) 2,2'-[(lR,3R)-2,2-dimethylcyclopentane-l,3-diyl]di(l,3-oxazo l-5(4H)- one) 4)

Formula 4

d) intermediate compound of formula (5)

Formula 5

According to a preferred embodiment, the preparation of dimethyl 2,2'-{[(lR,3R)- l,2,2-trimethylcyclopentane-l,3-diyl]bis(carbonylazanediyl)} diacetate, which comprises reaction of D-camphoric acid with Glycine methyl ester hydrochloride in the presence of a dehydrating agent and a base in methylene dichloride as a solvent. After the completion of the reaction, the aqueous work up followed by concentration of methylene dichloride furnished the product, viz., dimethyl 2,2'- {[(lR,3R)-l,2,2-trimethylcyclopentane-l,3- diyl]bis(carbonylazanediyl)}diacetate(2).

According to the invention, the dehydrating reagents used in the preparation of amido ester (2) are selected from the group consisting of EDC HC1, DCC and HOBt.

In the second stage, the dimethyl 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane-l,3- diyl]bis(carbonylazanediyl)}diacetate(2) is hydrolyzed by treating with a base in a hydroxylic solvent at room temperature for about 10 to 14 hrs to afford 2,2'- {[(lR,3R)-l,2,2-trimethylcyclopentane-l,3diyl]bis(carbonylaz anediyl)}diacetic acid (3).

According to the invention, the base employed for the hydrolysis of amido ester(2) may be an inorganic base selected from sodium hydroxide, potassium hydroxide, and other alkaline earth hydroxides, or an organic base selected from triethylamine or diisopropylethylamine. The hydroxylic solvent may be selected from the group consisting of methanol, ethanol, isopropanol and water or a combination thereof. A preferable hydroxylic solvent may be a mixture of water and methanol or ethanol or isopropanol.

In the third stage, the 2,2'-{ [(lR,3R)-l,2,2-trimethylcyclopentane- l,3diyl]bis(carbonylazanediyl)}diacetic acid(3) thus obtained in acetic acid is reacted with a dehydrating agent in presence of a base at a temperature of 65 ^° C for 12 hours. The product bis - oxazolone (4) is isolated by extracting into methylene dichloride. The dehydrating agents used in the preparation of compound of formula 4 (Oxazolones) is selected from the group consisting of phosphoric acid, polyphosphoric acid, sodium sulphate, and organic anhydrides. The base is selected from sodium acetate or potassium acetate.

In the last stage, D - penicillamine is prepared by condensing the bis-oxazolone (4) thus obtained with acetone in the presence of a base to obtain intermediate compound of formula 5. The condensed product (formula 5) thus obtained is either isolated or insitu reacted with a sulphur transfer agent to open the oxazolone rings followed by acid hydrolysis to obtain the product, D - penicillamine.

The sulphur transfer reagents employed in the preparation of D - penicillamine of formula 1 is selected from the group consisting of sodium thioacetate, potassium thioacetate, benzyl triethylammonium tetrathiomolybdate, hydrogen sulphide and phosphorous penta sulphide. The base is selected from sodium acetate or potassium acetate and the acid employed in the hydrolysis are selected from HC1, acetic acid, sulphuric acid.

In another process variant, the intermediate 5 can also be prepared directly by treating the compound of formula 3 by employing acetone as solvent in the presence of dehydrating agents selected from phosphoric acid, polyphosphoric acid, sodium sulphate, organic anhydrides and the base selected from sodium acetate or potassium acetate.

The final product, D - penicillamine is purified by employing organic solvents selected from the group consisting of methanol, ethanol, isopropanol, acetic acid and mixture thereof or a combination of toluene with ethers selected from DIPE or MTBE.

Thus the present invention provides a process for synthesis of D - penicillamine (formula 1) involving the following novel intermediates; a) dimethyl 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane-l,3- diyl]bis(carbon lazanediyl)}diacetate (amido ester of formula 2);

Formula 2

b) 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane- l,3diyl]bis(carbonylazanediyl)}diacetic acid (amido acid of formula 3);

Formula 3

c) 2,2'-[(lR,3R)-2,2-dimethylcyclopentane-l,3-diyl]di(l,3-oxazo l-5(4H)- one) (oxazolones compound of formula 4) and

Formula 4

d) Intermediate (formula 5)

Further details of the process of the present invention will be apparent from the examples presented below. The examples presented are purely illustrative and are not limited to the particular embodiments illustrated herein but include the permutations, which are obvious as set forth in the description.

EXAMPLES Example 1:

Preparation of dimethyl 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane-l,3- diyl]bis(carbonylazanediyl)}diacetate) (compound of formula 2)

D-Camphoric acid (70 grams) was reacted with 2.5 mol. equiv of EDC. HC1; 2.5 mol equiv. of glycine methyl ester HC1 and 2.5 mol. eqiv. of TEA in 700 ml MDC and stirred for 12 hours at room temperature and pressure. The Reaction mass was washed with 100 ml of water two times and concentrated to obtain the crude mass which was pure enough to carry out the next reactions.

Yield: 60 %

Example 2

Preparation of 2,2'-{[(lR,3R)-l,2,2-trimethylcyclopentane- l,3diyl]bis(carbonylazanediyl)}diacetic acid: (compound of formula 3)

25 grams of the amido ester(compound of formula 2) was dissolved in 25 ml each of methanol and water and reacted with 2.5 moles of NaOH under stirring at room temperature and pressure for 12 hours. After completion of the reaction, the solvent was distilled off and the product extracted into MDC which was repeatedly washed with IN HC1 to obtain the product in good yields and purity.

Yield: 99 %

Example 3

Preparation of 2,2'-[(lR,3R)-2,2-dimethylcyclopentane-l,3-diyl]di(l,3-oxazo l- 5(4H)-one) (compound of formula 4)

3.5 grams of the amido acid (compound of formula 3) was dissolved in 20 ml acetic acid and reacted with 2 mol equiv. sodium acetate and 2 mol equiv. polyphosphoric acid and heated at 65°C for 12 hours. Water was added (50 ml) and the product extracted into MDC (50 ml *3). The MDC layer was washed with NaHC03 followed by brine and concentrated to obtain the oxazolones (1.8 grams)

Yield = 58 %

Purity: 99 % Example 4

Preparation of the D - penicillamine (compound of formula 1)

15 grams of the oxazolone was heated with 100 ml acetone in the presence of sodium acetate for 24 hours at 60°C. Acetone was distilled off. The residue (intermediate compound of formula 5) was taken in acetonitrile and heated in the presence of phosphorous pentasulphide (P4S10) for 12 hours. The acetonitrile layer was distilled off. The residue was taken in methylene dichloride (MDC) and washed successively with water and brine. The MDC layer was concentrated and heated with 25 ml, 5 N HC1 for 12 hours. The HC1 layer was neutralized to obtain a solid. The solid was filtered and a slurry wash was performed employing acetic acid and methanol (1 : 1). The product was dried at 50°C for 6 hours.

Yield = 6.9 grams (81.4 %)

Purity: 99.5%

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

This work has been done with the financial support from Biotechnology Industry Research Assistance Council-DBT(Govt. of India).