FORM 2
THE PATENTS ACT, 19?o
{39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13]


TITLE OF THE INVENTION
"A PROCESS FOR THE PREPARATION OF CIS-
DIAMMINEDIlODO PLATINIUM (II) AND THEIR USE IN THE
SYNTHESIS OF CARBOPLATIN"

We, CADILA HEALTHCARE LIMITED, a company incorporated under the Companies Act, 1956, of Zydus Research Centre, "Zydus Tower", Satellite Cross Roads, Gandhinagar-Sarkhej Highway, Ahmedabad-380 015, Gujarat, India
The following specification particularly describes the nature of the invention and the manner in
which it is to be performed.


ZRC_Onco_01_comp
Field of the Invention
The present invention relates to a novel process for the synthesis of cis-diamminediiodo platinum (II) of formula (1), which is a key intermediate for the preparation of Carboplatin.

Background and Prior art:
cis-Diamminediiodo platinum, [Pt(NH212] is an analogue of the known antitumor drug Cisplatin ie. cis-[Pt(NH3)2Cl2]- It is soluble in DMF and in excess of acetone but very sparingly soluble in water and insoluble in ethanol and diethyl ether. The compound is a key raw material for synthesis of Carboplatin. Carboplatin is a second-generation antitumor platinum drug.

o
Carboplatin
Cisplatin i.e., cis-diamminedichloro platinum (II), an antitumor platinum based drug
and was the first member of its class which now also includes Carboplatin. Oxaliplatin etc.
H3N CI
\ /
Pt
H3N CI
Cisplatin
Cisplatin, has a number of side effects like nephrotoxicity & neurotoxicity, accessibility to hydrolysis at neutral pH creating a new species including toxic bridged dimers & other oligomers & also low solubility in water, all of which limits its use.
Carboplatin, Platinum diammine(l,l-cyclobutane dicarboxylato-0,0'), a second-generation platinum based antineoplastic drug differs from Cisplatin as it has a bidentate cyclobutane dicarboxylate moiety. Replacement of the Chloro ligands by dicarboxylate group reduces the toxicity and increases solubility in water. Due to these advantages this drug has gained importance in clinical treatment compared to its parent compound Cisplatin. Its

ZRC_Onco_001_comp
dosage is higher than Cisplatin due to delayed formation of aquated metabolites but produces equally strong antitumor effect.
cis-Diamminediiodoplatinum of formula (1) may be used as key raw material for most of the known Platinum analogue drugs and therefore a valuable intermediate. There are a number of processes known for preparing cis-diamminediiodoplatinum, many of the conventional processes uses Potassium tetrachloroplatinate (II), K2PtC14.
According to S. C. Dhara as per Indian J Chem. Vol. 8 Feb. 1970, K2PtCI4 is reacted with Potassium Iodide to form K2Pt14 which is further made to react with (1:1)NH3 and water to generate cis-diamminediiodoplatinum and then used further to obtain Cisplatin.
Underestimating the pH of the reaction mixture makes the formation of impurity tetraamminediiodo Platinum.
US Patent 4.335,087 uses H2PtC16 (Chloroplatinic acid) to form cisplatin and cis-diamminediiodoplatinum is synthesized as an intermediate. K2PtC14 is reacted with 10 molar potassium iodide, which further is reacted with dil. ammonium hydroxide solution under controlled condition of pH 7 to give cis-diamminediiodoplatinum. The disadvantage of the process is the total reaction time that is 6-7 h and temperature required from 40°C and elevating it to 60°C as well as 85°C. Also, the pH of the reaction mixture is to be maintained at 7 is difficult as very diluted NH4OH is to be utilized that increases the volume and its low dilution makes the pH hike to basic condition very fast i.e. pH>7.
According to the WO 98/49174, K2PtC14 is reacted with 6 molar Potassium Iodide at 80°C and addition of cone. Ammonium Hydroxide (liq. NH3). Keeping pH<7 is not favorable because at high temperature till 80°C creates hassle in large size batches.
US patent no. 4,140,707 by Cleare et al discloses the process for synthesis of Carboplatin using key raw material Cisplatin. Cisplatin is converted to cis-diamminediaquo platinum (II) nitrate [Pt(NH3)2(H2O)2]NO3; by reacting it with AgNO3 that is slightly less than stoichiometric amount in aqueous medium at 60°C with continuous stirring. The precipitate of silver chloride is filtered and Potassium 1,1-cyclobutanedicarboxylate solution was added to mother layer to form Carboplatin. The product was filtered and concentrated and cooled the mother liquor again for collection of another crop of Carboplatin.
HVN OH?

Pt
/ HUN OH,
.(NO3)2
c/.y-diamminediaquo platinum (II) Nitrate
j

ZRC_Onco_001_comp
This process as per Cleare et al needs some improvement. The solubility of Carboplatin (14mg/ml, as per RX list) in water tends to decrease the overall yield of Carboplatin as more than one filtration is required to isolate it. Also, it is very difficult to evaluate the extent of the reaction, since all the reactants, products and byproducts are soluble in water. Furthermore, the separation of the Platinum complexes from potassium nitrate is quite difficult
Allesandro Pasini and Cristina Caldirola discloses in Inorganica Chimica Acta, 15 (1988) 19-20. process for the preparation of Carboplatin comprising the simultaneous use of DMF in aqueous medium. Cisplatin is dissolved in N,N-dimethyl formamide (DMF) and was added 1,1-Cyclobutanedicarboxylic acid and 0.1N KOH at a temperature of 60°C for 20 h to give Carboplatin in 70% yield. The drying of Carboplatin for removing DMF solvent is difficult as the boiling point of DMF is very high (152-154°C) and requires high temperature drying. Alternatively, DMF can be removed by washing or slurring Carboplatin in water, which eventually affects the yield of Carboplatin. It is also reported that the use of cis-diamminediiodoplatinum instead of cisplatin as a key raw material also decreases the yield considerably to only 40%.
R.C. Harrison and C.A. McAuliffe in Inorganica Chimica Acta, 46 (1980), L15-L16 provided a process for generation of Carboplatin wherein cis-diamminediiodo platinum is reacted with silver sulfate that is less than stoichiometric amount in aqueous medium in dim light to form [cis-diamminediaquo platinum(II)]sulphate; [Pt(NH3)2(H2O)2]SO4 (diaquo complex). Filtered the precipitated silver iodide and concentrate the mother liquor containing diaquo complex to 2/3 volumes and further treated with aqueous solution of Barium salt of 1,1-cyclobutane dicarboxylic acid (CBDCA). After filtration of precipitated barium sulfate, concentrated the filtrate till a white crystalline residue is obtained. This was washed with ethanol and ether and dried in vaccuo to give Carboplatin.
The major drawback of the process includes the concentration of intermediate diaquo complex. As the scale up of the batch begins, the evaporation of water from the reaction medium is extremely difficult. Temperature is to be provided to the reaction mixture along with vacuum, this cause an extra load. Also it hinders the stability of diaquo complex of this moiety as evaporation of water takes long time at elevated temperature. Another important drawback is that the process gives no information regarding the purity of Carboplatin which plays major role for drug development.
Thus, though several processes for the preparation of the intermediate of formula (1) as well as preparation of Carboplatin either using the intermediate formula (1) or other routes are know, known processes for preparing both the compounds have several limitations and
4

ZRC_Onco_001 comp
inadequacies. Therefore, there exists a need for further improvement of one or more of these processes in a way as to improve the yield as well as process conditions. We herein disclose one such process. Summary of the Invention
The present invention provides a process for the preparation of cis-diamminediiodoplatmum (II) of formula (1) as a key intermediate and its use to get highly pure Carboplatin by using suitable buffer(s) makes the reaction to proceed till completion at ambient temperature in faster means with a better yield.
According to the embodiment of the present invention, there is provided a process for the preparation of cz's-diamminediiodoplatinum (II) of formula (1)

cis- diamminediiodo platinum(ll)
which comprises the reaction of potassium tetrachloroplatinate (II) with suitable ammonium buffer.
According to the embodiment of the present invention, there is provided a process for the preparation of Carboplatin, which comprises the reaction of potassium tetrachloro platinate (II) with ammonium buffer to provide m-diamminediiodoplatinum (II) of formula (1) and converting to Carboplatin, by making use of silver sulphate or silver nitrate for diaquo complex generation and Barium or potassium salt of 1,1-cyclobutane dicarboxylic acid for substitution of ligands. Detailed description of the invention
The present invention provides a process for the preparation of cis-diamminediiodoplatinum (II) of formula (1)

cis- diamminediiodo platinum(Il) which comprises the reaction of potassium tetrachloro platinate (II) with suitable ammonium buffer which also acts as a iodine donor reagent.
The suitable ammonium buffer is prepared from ammonium iodide (NH4I) and ammonium hydroxide (NH4OH). The used buffer maintains the pH while reacting with Potassium tetrachloroplatinate (II) K2PtC14 and makes the substitutions of the ligands very
5

ZRC_Onco_001_comp
fast. Preferably, reaction of Potassium tetrachloroplatinate (II) K2PtC14 with ammonium buffer is carried out at pH of about 7 to 11.
Thus, the buffer is prepared from ammonium iodide (NH4I) and ammonium hydroxide (NH4OH) such that it provides pH of reaction mass about 7 to 11 during reaction. The preferred molar ratio of ammonium iodide (NH4I) relative to ammonium hydroxide (NH4OH) is about !: 1 molar equivalent to about 1:5 molar equivalents. The preferred range is about 1:1 to about 1:2.5 molar equivalents. The reaction is carried out at ambient temperature in suitable solvent. The preferred solvent is water or suitable polar organic solvent or mixtures thereof. Preferably, reaction is carried out in aqueous medium. The higher trans effect of co-ordinated iodide isomer ensures the exclusive cis-configuration of formula (1). This stereochemistry is retained by the subsequent reaction, which is confirmed by the formation of crude Carboplatin in 100% yield.
The present invention further provides a process for the preparation of Carboplatin of formula (2), which
o

o

(2) comprises the reaction of potassium tetrachloro platinate (II) with suitable ammonium buffer to provide cis-diamminediiodoplatinum (II) of formula (1) which is further converted to Carboplatin.
Pt
/ H3N I
(1) cis- diamminediiodo platinum(ll)
The product c/s-diamminediiodo platinum (II) formed is converted to Carboplatin by making use of silver sulphate or silver nitrate for diaquo complex generation and Barium or potassium salt of 1.1-cyclobutane dicarboxylic acid for substitution of diaquo ligand.
6
The present invention further provides a process for the preparation of Carboplatin of formula (2)


ZRC_Onco_001_comp

(2) which comprises
(i) reaction of potassium tetrachloro platinate (II) with suitable ammonium buffer to provide m-diamminediiodoplatinum (II) of formula (1)

Pt
/ \.

cis- diamminediiodo platinumfll)
(ii) treating m-diamminediiodoplatinum (II) of formula (1) with salt of silver to provide cis-Diaquodiammine platinum (II) of formula (3) and
H3N OH2
\ /
Pt
X
/ H3N OH2
(3)
X = SO4, (NO3)2. (iii) treating cis-Diaquodiammine platinum (II) formula (3) with barium hydroxide or potassium hydroxide in presence of 1,1-cyclobutanedicarboxyIate to provide Carboplatin.
Preferably, formation of cis-Diaquodiammine platinum (II) of formula (3) and its conversion to Carboplatin is carried out in suitable polar solvent. The preferable solvent is water.
Preferably, The conversion of K2PtCl4 into formula (I) is carried out by using the buffer of NH4I and NH4OH, maintaining the pH between 6 to 9.5, preferably 7.5 to 9.
The product cis-diamminediiodo platinum (II) formed is converted to Carboplatin by making use of silver salt for diaquo complex generation and Barium or potassium salt of 1,1-cyclobutane dicarboxylic acid for substitution of diaquo ligand.
Unlike the classical methods, no formation of an intermediate Potassium tetraiodo platinate (II), K2PtI4 is required and the product is achieved straightly that saves time and precious chemicals. Also, the unreacted buffer is easy to remove as it remains in less quantity after the reaction completion so its removal by use of water and ethanol is highly effective.
The varying pH is obtained by applying different molar quantity of NH4I and NH4OH is shown in Table-1.
cis-Diamminediiodo platinum obtained above is converted to the diaquo complex by treating with silver sulphate or silver nitrate in dim light It is preferable to perform the reaction with silver sulphate. Upon completion of the reaction, the precipitates of silver iodide (Agl) are filtered. The mother layer is treated with salt solution of Barium or
7

ZRC_Onco_00 Icomp
potassium 1.1-cyclobutane dicarboxylate at ambient temperature. When using silver sulfate, Barium hydroxide is used, as Barium sulphate immediately gets precipitated, simultaneously transforming diaquo complex into Carboplatin. Insolubility of barium sulphate in aqueous medium (lg/400L water, as per Merck Index) always favours the forward reaction and the product is much easier to purify. The aqueous condition enables the substitution of diaquo ligand by bidentate carboxylate ligand in homogenous phase to give Carboplatin having good quality and yield. The crystallization of crude compound provides Carboplatin in pure form with HPLC purity 99.9%.
According the preferred embodiment of the invention, the preparation of Carboplatin involves reacting potassium tetrachloro platinate in aqueous medium with a buffering agent consisting of ammonium iodide and ammonium hydroxide provides cis-diamminediiodo platinum. The dropwise addition of buffer initiates the reaction simultaneously and quantitative amount of product is seen visible immediately by the yellow colour of the compound. Rate of reaction is very fast and the reaction proceeds at RT. The substitution of chloride ligands by iodides and ammines ligands begins immediately on addition of buffer.
The formation of the product can be monitored quite readily by thin layer chromatography. The pH factor is maintained by addition of different molar quantity of buffer.
Jn the next step, iodo ligands were substituted by the bidentate dicarboxylate group, cis-diamminediiodo platinum is reacted with silver sulfate to formation of diaquo complex. Thereafter bidentate ligand 1,1 -cyclobutane dicarboxylate is introduced substituting diaquo group by salt solution of barium hydroxide octahydrate and cyclobutane dicarboxylic acid in stoichiometric amount. Precipitation of barium sulphate is observed immediately which is later filtered. Evaporation of the mother layer to dryness provides crude Carboplatin in quantitative yield. The crystallization of crude product by using water provides the pure Carboplatin with purity of 99.9% having an assay of 99.9% analyzed by HPLC. The results of Atomic Absorption Spectroscopy showed that, this process also limits the silver and barium content in Carboplatin below 10 ppm.
The synthesis of Carboplatin according to the present invention is schematically shown below, which should not be considered as limiting the scope of the invention.
8


ZRC_Onco_00l_comp
Having thus described the invention with reference to particular preferred embodiments and illustrative examples, those in the art would appreciate modifications to the invention as described and illustrated that do not depart from the spirit and scope of the invention as disclosed in the specification. The examples are set forth to aid in understanding the invention but are not intended to, and should not be construed to, limit its scope in any way. The examples do not include detailed descriptions of conventional methods. Such methods are well known to those of ordinary skill in the art and are described in numerous publications. Example 1
To a solution of l0g (24.1mmol) Potassium tetrachloro platinate (II) dissolved in 50ml water was added aqueous buffer of ammonium iodide (70.35 mmol) and ammonium hydroxide (54.16mmol) for an hour with the pH of reaction mixture maintained at 8.64 and stirred the reaction mass for 4 hr. Filtered the precipitate of cis-diamminediiodo platinum and suspended it in 150ml warm water, filtered, washed with 15ml ethanol and ether to give 10.94g cis-diamminediiodo platinum with 94% yield.
Experiments for synthesis of cis-[Pt(NH3) 2I2] were performed using buffer of NH4I and NH4OH and K2PtC14 by controlling the pH factor at various level.
Tablc-1

K2PtCl4 NH4I NH4OH cis-[Pt (NH3)2I2] pH Colour
9

ZRC_Onco_01_comp

G mmol g mmol g Mmo 1 g Yield %
0.2 0.48 0.262 1.80 0.028 0.80 0.194 83.6 7.58 Pale yellow
0.2 0.48 0.28 1.93 0.030 0.85 0.180 77.6 8.05 Yellowish green
0.2 0.48 0.25 1.72 0.026 1.57 0.190 81.6 8.54 Yellow
0.5 1.20 1.40 9.66 0.207 5.91 0.428 73.7 8.94 Yellowish green
0.3 0.72 0.419 2.89 0.050 1.43 0.292 83.7 9.5 Yellowish green
10 24.10 10.2 70.35 1.89 54.16 10.94 94 8.64 Yellow
Example 2
cis-Diamminediiodo platinum (5g, 10.35mmol) was added to a clear aqueous solution containing slightly less than the stoichiometric amount of silver sulphate (3.15g,10.10mmol) in 420ml distilled water at ambient temperature. The reaction mixture was stirred for 2.5 h in dim light and the precipitated silver iodide was filtered. To this filtrate was added salt solution of Barium-1,l-cyclobutane dicarboxylate [Barium hydroxide octahydrate (3.2g, 10.14 mmol) in 170 ml water and 1,1-CBDCA (1.675g, 11.62 mmol)] with continuous agitation till completion of reaction. Treated the reaction mixture with 0.75g activated charcoal, filtered and concentrated the filtrate U/V provided crude Carboplatin of 3.80g with 98.9% yield. Example 3
Added 15ml distilled water to the lg crude Carboplatin and heated at 90 °C under stirring for 15-30 min. The clear solution obtained was treated with 50 mg charcoal and stirred for 30 min. After Filtration of charcoal, cooled the mother liquor to RT and then in ice bath at 3-5 °C for 1 h for complete crystallization. Filtered the product and washed with 3 ml ethanol for two times, 3ml ether and dried to get 0.72g pure Carboplatin. Spectral data: 1H NMR (DMSO-d6): ppm: 1.63 q, 2.66 t 4.05(NH3); l3C NMR (DMSO-d6): ppm: 14.91, 30.28, 55.52, 177.46:
IR (cm'1): 3254s, 3107w, 2952w, 1618s, 1500w; 1379s, 1294w, 1221br: 1119m, 1042w,
893m, 766w, 696w, 567w, 470m;
HPLC Data: Purity: 99.9%, Assay: 99.9.
Atomic Absorption Spectroscopy Data:
Silver : < 10 ppm.
10

ZRC_Onco_001_comp
Barium: < 10 ppm.
Advantages of the present process:
(1) Present invention involves novel process for the synthesis of cis-diamminediiodo platinum (II) Formula (1).
(2) Present process does not require formation of Potassium tetraiodo Platinate (II) an intermediate, for the synthesis of Formula (1).
(3) Present process for the synthesis of formula (1) is free from impurity tetraammine diiodo platinum.

(3) Present process does not require any elevation in temperature for the synthesis of Formula I.
(4) Present process does not require any concentration of aqueous solution of diaquo complex during formation of Carboplatin.
(5) Carboplatin obtained by this process is of high purity of 99.9% and 99.9% assay (by HPLC).
(6) Carboplatin formed by this process has Silver and Barium content below the 10 ppm level (by AAS).
11

ZRC_Onco_001_comp
We Claim:
1. A process for the preparation of m-diamminediiodoplatinum (II) of formula (1)

cis- diamminediiodo platinum(ll)
which comprises reacting potassium tetrachloro platinate (II) with ammonium buffer of ammonium iodide (NH4I) and ammonium hydroxide (NH4OH).

2. A process as claimed in claim 1, wherein the pH maintained by buffer solution is ranging from 7 to 11.
3. A process as claimed in claim 1, where ammonium iodide (NH4I) and ammonium hydroxide (NH4OH) used in molar ratio of about 1:1 molar equivalent to about 1:5 molar equivalents, more particularly, in the range of about 1:1 to about 1:2.5 molar equivalents.
4. A process as claimed in claim 1, wherein the reaction is carried out in aqueous medium.
5. A process as claimed in claim 1, wherein the synthesis of Formula (1) is free from impurity tetraammine diiodo platinum.
6. A process for converting compound of formula (1) to Carboplatin of formula (2)
(2)
which comprises
i) preparing the compound of formula (1) as per the process of claim 1,
ii) converting the compound (1) to Carboplatin of formula (2) by making use of silver salt for diaquo complex generation and Barium or potassium salt of 1.1-cyclobutane dicarboxylic acid for substitution of diaquo ligand.
7. The process for the preparation of Carboplatin of formula (2) as claimed in claim 6

(2) which comprises
(i) reacting potassium tetrachloro platinate (II) with ammonium buffer to provide cis-diamminediiodoplatinum (II) of formula (1)
12

ZRC_OncoJ)01 comp

cis- diamminediiodo platinum(ll)
(ii) treating m-diamminediiodoplatinum (II) of formula (1) with silver sulfate or silver nitrate to provide cis-Diaquodiammine platinum (II) of formula (3) and

X = SO4; (NO3)2.
(iii) treating cis-Diaquodiammine platinum (II) of formula (3) with barium hydroxide or potassium hydroxide in presence of 1.1-cyclobutanedicarboxylate to provide Carboplatin.
8. A process as claimed in claim 6 & 7, wherein formation of cis-Diaquodiammine platinum (II) of formula (3) and its conversion to Carboplatin is carried out insitu in suitable solvent.
9. A process as claimed in claim 8, wherein suitable solvent is water.
10. A process as claimed in claim 9, wherein said carboplatin is having > 98% purity and having > 98% assay by HPLC.
11. Carboplatin substantially free of 1,1-Cyclobutanedicarboxylic acid, produced in accordance with the process of claim 6 and 7.
12. Substantially pure Carboplatin containing less than 10 ppm of Silver and Barium content, which is produced in accordance with the process of claim 6.
13. A process for preparing Carboplatin such as here in described in accompanying text, description and examples.
Dated this the 9lh day of September 2008
H. SUBRAMANIAM Of Subramaniam, Nataraj & Associates Attorneys for the Applicants
13