Field of the Invention

This invention, in general relates to a process for producing doxercalciferol. In particular, the present invention provides novel intermediates for producing doxercalciferol, process for producing said intermediates and use thereof in production of doxercalciferol.

Background of Invention

Doxercalciferol is a pharmaceutically active compound used in the regulation of calcium and phosphate metabolism in animal and human. Doxercalciferol is also used in the regulation of bone formation as disclosed in Harrison's principles of internal medicine: Part-II Chapter 335 relating to "Disorders of Bone and mineral metabolism".

There are various prior art methods, which have been tried for synthesizing doxercalciferol.

US 6,90,3083 discloses a method for the synthesis of doxercalciferol, wherein the method comprises tosylating ergocalciferol, converting it to cyclovitamin, followed by hydroxylating cyclovitamin in the lα-position, converting the hydroxylated cyclovitamin to the cis and trans forms and subsequently, irradiating the trans isomer to the cis form and finally recrystallising the cis form. The purity of doxercalciferol so obtained was > 98% and with single impurity of < 0.5%. Similar processes for synthesis of pure doxercalciferol have been disclosed in AU2001278956, US 2003/0045509 and WO2002006218.

Herbert E. Paaren et al. (J. Org. Chem. 1980, 45, 3253-3258) discloses the synthesis of doxercalciferol by separation of cis and trans isomers employing thin layer chromatography (TLC).

US 4554105 discloses the synthesis of doxercalciferol by silyl derivatisation, followed by photoisomerisation and desilylation in tetra butyl ammonium fluoride and Tetrahydrofuran.

WO 9602501 discloses the synthesis of doxercalciferol from vitamin D2 by silylation, Diels-Alder reaction, oxidation with Se02, followed by isomerization, and desilylation. The method requires no separate preparatory procedures prior to the actual hydroxylation step.

However, there still exists a need to develop a method for producing pure doxercalciferol with high purity and yield.

Summary of the Invention

It is an object of the present invention to provide novel intermediates for the production of doxercalciferol.

It is another object of the present invention to provide a process for producing the novel intermediates enabling production of pure doxercalciferol.

It is yet another object of the present invention to provide an improved process for producing doxercalciferol of high purity and yield employing the novel intermediates.

It is yet another object of the present invention to provide an improved process for producing doxercalciferol of formula I of high purity and yield employing the novel intermediates.

The above and other objects of the present invention are further attained and supported by the following embodiments described herein. However, the scope of the invention is not restricted to the described embodiments herein after.

In accordance with an embodiment of the present invention, there are provided novel intermediates of la-alkyloxy doxercalciferol for the production of doxercalciferol, wherein the alkyloxy group is selected from acetoxy, propyloxy, isobutyroxy or pentyloxy group.

In accordance with another embodiment of the present invention, there is provided a process for preparing the novel intermediates of la-alkyloxy doxercalciferol for producing doxercalciferol, the process comprising tosylating vitamin D2 having 3|3-hydroxy group to yield tosylated vit D2, solvolysing tosylated vitamin D2 employing methanol and sodium bicarbonate to obtain cyclo vit D2, subjecting the so formed cyclo vit D2 of formula (III) to allylic oxidation by employing selenium dioxide and t-butyl hydroperoxide to yield hydroxy cyclo vit- D2, subsequently treating the hydroxyl cyclo vit- D2 with an aliphatic acid to yield a mixture of cis and trans la-alkyloxy doxercalciferol.

In accordance with yet another embodiment of the present invention, the cis and trans isomers of la-alkyloxy doxercalciferol are separated by employing column chromatography or TLC.

In accordance with still another embodiment of the present invention, there is provided a process for producing pure doxercalciferol employing the novel intermediates of lα-alkyloxy.

Doxercalciferol, the process comprising hydrolyzing cis la-alkyloxy doxercalciferol, precipitating the resultant employing a solvent to yield doxercalciferol, and recrystallizing the resultant doxercalciferol to yield pure doxercalciferol.

In accordance with yet another embodiment of the present invention, the doxercalciferol so produced is having purity of more than 99% with single impurity of less than 0.2%.

In accordance with yet another embodiment of the present invention, there is provided a process for producing pure doxercalciferol comprising tosylating vitamin D2 having 3(3-hydroxy group to yield tosylated vit D2, solvolysing tosylated vitamin D2 employing methanol and sodium bicarbonate to obtain cyclo vit- D2, subjecting cyclo vit D2 to allylic oxidation by employing selenium dioxide and t-butyl hydroperoxide to yield hydroxy cyclo vit- D2, treating the hydroxyl cyclo vit- D2 with an aliphatic acid to yield a mixture of cis and trans la-alkanoyloxy doxercalciferol, separating the cis and trans isomers of la-alkyloxy doxercalciferol to yield pure cis isomer of la-alkyloxy doxercalciferol, by hydrolyzing the cis la-alkyloxy doxercalciferol, precipitating the resultant employing a solvent to obtain doxercalciferol and subsequent recrystallization to obtain pure doxercalciferol.

Detailed Description of the Invention

While this specification concludes with claims particularly pointing out and distinctly claiming that, which is regarded as the invention, it is anticipated that the invention can be more readily understood through reading the following detailed description of the invention and study of the included examples.

The present invention discloses novel intermediates, cis and trans la-alkyloxy doxercalciferol of formula VI and VII for the production of doxercalciferol. In addition, the present invention provides a process for producing said novel intermediates.

wherein, R is an alkyl group.

The alkyloxy group according to the present invention is selected from acetoxy, propyloxy, isobutyroxy or pentyloxy group, preferably propyloxy group.

According to the embodiments of the present invention, the said novel intermediates cis and trans la-alkyloxy doxercalciferol of formula VI and VII are prepared by a process comprising:

(a) tosylating vitamin D2 having 3 β-hydroxy group to yield tosylated vitamin D2 of formula II;

(b) solvolysing tosylated vitamin D2 employing methanol and sodium hydroxide to obtain cyclo vitamin D2 of formula III;

(c) subjecting cyclo vitamin D2 of formula III to allylic oxidation by employing selenium dioxide and t-butyl hydroperoxide to yield hydroxy cyclo vitamin D2 of formula IV;

(d) treating the hydroxyl cyclo vitamin D2 of formula IV with an aliphatic acid to yield a mixture of cis and trans lα-alkyloxy doxercalciferol of formula VI & VII.

According to the further embodiment of the present invention, there is provided a process for producing pure doxercalciferol of formula I, the process comprising:

(a) tosylating vitamin D2 having 3β-hydroxy group to yield tosylated vitamin D2 of Formula II;

(b) solvolysing tosylated vitamin D2 employing methanol and sodium bicarbonate to obtain cyclo vitamin D2 of formula III;

(c) subjecting cyclo vitamin D2 of formula III to allylic oxidation by employing selenium dioxide and t-butyl hydroperoxide to yield hydroxy cyclo vitamin D2 of formula IV;

(d) treating the hydroxyl cyclo vitamin D2 of formula IV with an aliphatic acid to yield a mixture of cis and trans lα-alkyloxy doxercalciferol of formula VI & VII; and

(e) separating the cis and trans isomer of la-alkyloxy doxercalciferol to yield pure cis isomer of la-alkyloxy doxercalciferol of formula VI,

where, R is an alkyl group;

(f) hydrolyzing the cis 1α-alkyloxy doxercalciferol of formula VI;

(g) precipitating the resultant employing a solvent to obtain doxercalciferol offormula I, and

(h) recrystallizing the resultant doxercalciferol to obtain pure doxercalciferol offormula I.

According to another embodiment of the present invention, the novel intermediates cis and trans 1 a-alkyloxy doxercalciferol of formula VI & VII are prepared by a process, which comprises of converting vitamin D2 having 3β-hydroxy group to tosylated vitamin D2 of formula II as detailed below:

Further, solvolysing the tosylated vitamin D2 by methanol and sodium hydroxide/sodium bicarbonate to obtain 3,5- cyclovitamin D2 of formula III,

The cyclo vit D2 of formula III thus obtained is subjected to allylic oxidation employing selenium dioxide and t-butyl hydroperoxide to obtain hydroxy cyclo vitamin D2 offormula IV.

Further, propylating /treating so produced hydroxyl cyclo vitamin D2 of formula IV with an aliphatic acid to obtain a mixture of cis and trans la-alkyloxy doxercalciferol of formulae VI and VII,

where R= Ethyl, isopropyl or n-butyl.
wherein, propylation is done by treating with aliphatic acid, preferably acetic acid, isobutyric acid and pentanoic acid or propionic acid, more preferably propionic acid.

According to the embodiments of the present invention, the pure doxercalciferol is obtained by first separating the cis and trans isomers of formula VI and VII, to yield pure cis isomer of lα-alkyloxy doxercalciferol (VI), wherein the separation of cis and trans isomers is performed on TLC plate employing chloroform and methanol as mobile phase.
The isomers may be further separated employing column chromatography or thin layer to obtain pure form of the two isomers, preferably the cis isomer of formula VI,


Further, hydrolysing the cis isomer and precipitating the resultant in hexane followed by recrystallization of the resultant to yield doxercalciferol, having purity > 99% and single impurity of less than 0.2%

According to one embodiment of the present invention, there is formation of an impurity 1-oxo cyclo vitamin D2 of formula V due to over oxidation of hydroxyl group during the reaction, which is purified by column chromatography.

The following non-limiting examples illustrate specific embodiments of the present invention. They are not intended to be limiting the scope of present invention in any way.

Example 1

Preparation of Tosylated vitamin-D2 (Formula ID

A solution of 100 gm of Vitamm-D2 in 340 ml of Dichloro methane (MDC) and 100ml of pyridine with 3 gm of Dimethylaminopyridine (DMAP) as catalyst is treated with 120 gm of tosyl chloride at 0°C. The reaction is carried out in dark room at 10°C for 30 hrs. After the reaction, the reaction mass is quenched with saturated solution of sodium bicarbonate and the product is extracted in Methyl tertiary-butyl ether (MTBE), dried over anhydrous sodium sulfate and concentrated to residue. The crude Tosylated vitamin-D2 is precipitated in methanol and the white solid is isolated by filtration and dried at 40°C under vacuum for 8hrs. Thus, 120 gm of product of purity > 99% is obtained.

Example 2

Preparation of Cvclo vitamin-D2 (Formula IIP

100 gm of compound of formula II is slurried in 1:10 ratio of MDC and anhydrous methanol. 350 gm of finely powdered sodium bicarbonate is added to the mixture and the reaction mass is heated to 55-60°C for 18hrs. After the reaction, the inorganic mass is filtered and the filtrate is concentrated to residue. The residue is extracted in MTBE to yield the compound of formula III.

Example 3

Preparation of la-Hvdroxy Cvclo vitamin-D2(Formula IV)

A mixture of 13.5 g of selenium dioxide, 2800 ml of methylenedichloride and 98 ml of 5M solution of t-butyl hydro peroxide in decane is stirred at 0°C for 3 hrs. 20 ml of pyridine is added and stirred for 15 minutes. At 0°C, 100 gm of compound of formula III is added in MDC. The reaction is maintained at 10-15°C and after 2-3 hrs 200 ml of 20% sodium hydroxide solution is added. Subsequently, the MDC layer is separated and the resultant product is extracted from aqueous layer with MDC. To the MDC layer, brine wash is given and the organic layer is dried by employing anhydrous sodium sulfate and is concentrated. The crude la-Hydroxy cyclo vitamin-D2 is purified by column chromatography to remove the impurity 1-Oxo cyclo vitamin-D2 of formula V formed due to over oxidation.

Example 4

Preparation of Cis lct-Propyloxy doxercalciferol (Formula VI)

100 gm of compound of formula IV is heated to 50-55°C in 2 L of propionic acid for 30 minutes. After the completion of the reaction, the reaction mass is cooled to 20°C and quenched with saturated sodium bicarbonate solution at 20°C. The product is extracted in MTBE and the crude contains both cis (VI) and trans (VII) isomers. The cis isomer is separated by column chromatography using ethyl acetate and hexane solvents starting from 1% ethyl acetate upto 5% in hexane.

Example 5

Preparation of Doxercalciferol (Formula I):

The compound of formula VI is taken in methanol and treated with sodium hydroxide solution in methanol at 50-55°C for 30 minutes. After the completion of reaction, methanol is distilled out, the product is extracted in MTBE and concentrated to residue.
The residue is titrated with hexane to yield white solid which on recrystallization in ethyl format gives the product of formula I of purity > 99% with single impurity < 0.2%.
While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments rather, in view of the present disclosure, which describes the current best mode for practicing the invention, many modifications and variations, would present themselves to those skilled in the art without departing from the scope and spirit of this invention. This invention is susceptible to considerable variation in its practice within the spirit and scope of the appended claims.

We Claim:

1. Novel intermediates cis and trans lα-alkyloxy doxercalciferol for the production of doxercalciferol having the formula (VI) and (VII),

where, R is an alkyl group.

2. The novel intermediates cis and trans lα-alkyloxy doxercalciferol according to claim 1, wherein the alkyloxy group is acetoxy, propyloxy, isobutyroxy or pentyloxy group.

3. A process for preparing a novel intermediate la-alkyloxy doxercalciferol of formula VI and VII for production of doxercalciferol,

where, R is an alkyl group, the process comprising:

(a) tosylating vitamin D2 having 3β-hydroxy group to yield tosylated vitamin D2 of formula II;

(b) solvolysing tosylated vitamin D2 employing methanol and sodium hydroxide to obtain cyclo vitamin D2 of formula III;

(c) subjecting cyclo vitamin D2 of formula III to allylic oxidation by employing selenium dioxide and t-butyl hydroperoxide to yield hydroxy cyclo vitamin D2 of formula IV;

(d) treating the hydroxyl cyclo vitamin D2 of formula IV with an aliphatic acid to yield a mixture of cis and trans la-alkyloxy doxercalciferol of formula VI and VII.

4. The process according to claim 3, wherein the aliphatic acid is selected from acetic acid, propionic acid, isobutyric acid and pentanoic acid.

5. A process for producing pure doxercalciferol, the process comprising:

(a) separating the cis and trans isomer of la-alkyloxy doxercalciferol of formula VI and VII as claimed in claim 1 to yield pure cis isomer of lα-alkyloxy doxercalciferol;

(b) hydrolyzing the cis lα-alkyloxy doxercalciferol;

(c) precipitating the resultant employing a solvent to yield doxercalciferol; and

(d) recrystallizing the resultant doxercalciferol to yield pure doxercalciferol.

6. The process according to claim 5, wherein the step of separating the cis and trans isomer of la-alkyloxy doxercalciferol is performed employing column chromatography, thin layer chromatography.

7. The process according to claim 5, wherein the doxercalciferol is having purity of more than 99% with single impurity of less than 0.2%.

8. A process for producing pure doxercalciferol of formula I,

the process comprising:

(a) tosylating vitamin D2 having 3β-hydroxy group to yield tosylated vitamin D2 of Formula II;

(b) solvolysing tosylated vitamin D2 employing methanol and sodium hydroxide to obtain cyclo vitamin D2 of formula III;

(c) subjecting cyclo vitamin D2 of formula III to allylic oxidation by employing selenium dioxide and t-butyl hydro peroxide to yield hydroxy cyclo vitamin D2 of formula IV;

(d) treating the hydroxyl cyclo vitamin D2 of formula IV with an aliphatic acid to yield a mixture of cis and trans lα-alkyloxy doxercalciferol; and

(e) separating the cis and trans isomer of la-alkyloxy doxercalciferol to yield pure cis isomer of la-alkyloxy doxercalciferol of formula VI,

where, R is an alkyl group;

(f) hydrolyzing the cis 1α-alkyloxy doxercalciferol of formula VI;

(g) precipitating the resultant employing a solvent to obtain doxercalciferol of formula I, and

(h) recrystallizing the resultant doxercalciferol to obtain pure doxercalciferol of formula I.

9. The process according to claim 8, wherein the alkyloxy group is acetoxy,
propyloxy, isobutyroxy or pentyloxy group.

10. The process according to claim 8, wherein the aliphatic acid is selected from acetic acid, propionic acid, isobutyric acid and pentanoic acid.

11. The process according to claim 8, wherein the doxercalciferol is having purity of more than 99% with single impurity of less than 0.2%.

12. The process according to claim 8, wherein the step of separating the cis isomer of 1 a-alkyloxy doxercalciferol is performed employing column chromatography or thin layer chromatography.