WO2002094803A1

WO2002094803A1 - A process for lactonization to produce highly pure simvastatin

Info

Publication number: WO2002094803A1
Application number: PCT/IN2002/000121
Authority: WO
Inventors: Dandala Ramesh; Sebastian Sonny; Subramanyam Dandala; Sivakumaran Meenakshisunderam
Original assignee: Aurobindo Pharma Limited
Priority date: 2001-05-18
Filing date: 2002-05-16
Publication date: 2002-11-28
Also published as: SK692003A3; SI21234A; US20040077884A1; EP1387835A1; US6825362B2; JP2004520444A; BG107477A

Abstract

There is disclosed, a process for lactonization to produce highly pure simvastatin of Formula (1) which comprises lactonization of a compound of the Formula (II), where Z is H or NH4 in a mixture of acetonitrile and glacial acetic acid to provide anhydrous conditions at a temperature of 65-70 °C and wherein the dimer impurity of formula (III) formed is less tan 0.1, thereafter adding water to the reaction mixture thereby causing simvastatin of formula (I) to precipitate from the reaction mixture.

Description

Title:

A process for lactonization to produce simvastatin

Field of the Invention:

1. A process for lactonization to produce highly pure simvastatin of Formula 1.

Background of the Invention:

This invention relates to a process for lactonization to produce highly pure simvastatin,

Lovastatin, sirwvastatin, pravastatin, atorvastatin and mevastatin are well known potent antihypercholesSerolemic agents that function by limiting cholesterol biosynthesis by inhibiting the enzyme, HMg-COA reductase. This class of compounds referred to generally as statins are produced either by natural fermentation process or through semi-synthetic and totally synthetic means thereof. Two of the most popular compounds in this therapeutic category are simvastatin and atorvastatin. The former is one of the most prescribed drugs in the treatment of primary hypercholesterelemia with minimum side effects and well established safely profile. The use of highly pure sin astatin is exceedingly desirable in preparation of a pharmaceutical product as it would avoid accumulation of impurities during prolonged usage and would reduce the possible side effects during medical treatment.

In most of the synthetic methods known to manufacture simvastatin (Formula 1) shown below, the compound of formula IlKalso shown below, is the common intermediate, which is cyclized to obtain simvastatin and thus lactonization constitutes an essential step of the synthesis.

EσR U fl T F^Qft J fl TTfi

It is of considerable importance to employ an efficient method for the lactonization that can produce simvastatin of high purity in good yield. The process disclosed in the US Patent 4,820,850 involves heating of hydroxyacid ammonium salt in toluene at 100° C under a purge of nitrogen. The lactonization completion requires ^β-8 hours refluxing and results in formation of increased amounts of dimer (Formula III).

formula HI

This dimer impurity is difficult to separate from the desired lactone even with repeated crystallization. Efforts to minimize the formation of the dimer have led to the use of high dilution during lactonization reaction. Nevertheless, this technique results in lower efficiency and is disadvantageous at commercial scale.

US Patent 4,916,239 describes another process where the lactonization reaction has been carried out by treating hydroxyacid ammonium salt in a mbdure of acetic acid and water, and in the presence of a strong acid catalyst. This process requires gradual addition of water in several lots to effect crystallization of the lactonized product from the reaction medium to shift the equilibrium to the lactone side and this drives the lactonization to completion. This process is not amenable to industrial scale due to effluent generation and low purity of simvastatin product even though dimer content obtained is reported to be less than 0.2%.

US Patent 5,917,058 provides an alternate process to lactonize hydroxyacid or its salt by treatment with acetic acid under anhydrous conditions. However, the purity of the final product obtained by this procedure is not more than 99%. Furthermore, in this patent, there is no reference to the level of dimeric impurity produced in the process.

The aim of the present invention is to obtain highly pure simvastatin that contains dimeric impurity less than 0.1 %. An example where simvastatin of greater than 99.5% purity has been achieved is cited in WO 99/42601 wherein the product was purified by successive crystallizations from aqueous acetone and from ethyl acetate. Brief Statement OTthe Invention:

According to this invention, there is provided a process for lactonization to produce highly pure simvastatin of Formula 1

which comprises lactonization of a compound of the Formula II,

p-<^ Λuι_A Λi

where Z is H or NH₄ in a mixture of acetonitrile and gladal acetic acid to provide anhydrous conditions at a temperature of 65-70° C and wherein the dimer impurity of formula III formed is less than 0.1, thereafter adding water to the reaction mixture thereby causing simvastatin of formula I to predpitate from the reaction mixture. ₀

-P jf ^' In this process in Formula II above, preferably Z is NH₄.

The process further comprises adding water to the reaction mixture, thereby causing simvastatin of Formula 1 to precipitate from the reaction mixture.

Detailed Description of the Invention:

The instant invention relates to a novel process for lactonization of simvastatin hydroxyadd or its salt that avoids the use of strong corrosive adds and drastic heat conditions. This process allows lactonization reaction to proceed in a mixture of acetic add and acetonitrille at moderate temperatures and consistently provides simvastatin of greater than 99.5% purity with dimer content less than 0.1%.

Specifically, the process of this invention comprises heating a solution of simvastatin hydroxyacid in its salt form, most preferably the ammonium salt (Formula II) in a mixture of acetic add and acetonitrile under anhydrous conditions at a temperature that vary from 50° C to 80° C and preferably at 65-70° C.

The lactonization reaction is typically accomplished within about 5 to 7 hours. The amount of acetic acid used is at least 3 to 5 parts by volume per part of the starting material. The amount of acetonitrile is 10 to 20 parts by volume per part of the starting material and preferably 15 parts by volume may be used. The lactonized product is isolated after completion of reaction by addition of water.

Major advantage of the present invention as compared to the prior art procedures is the high product purity where the level of dimer impurity has been greatly reduced to less than 0.1%. The addition of water to the reaction mixture directly provides lactone as a homogeneous slurry that makes the filtration operation very easy at large scale and work up involves no solvent concentration or neutralization step prior to proϋuct isolation.

The invention will now be more fully described with reference to the following examples which are only illustrative and are not be construed as any limitation thereof.

Example 1

PREPARATION OF (IS, 3R, 7S, 8S, βaR) -3, 7-DIMETHYL-8- [2- [ (2R, 4R) -4-HYDROXY-6- OXO-3, 4, 5, 6-TETRAHYDRO-2H-PYRAN-2-YL] ETHYL] -1, 2, 3, 7, 8, 8a-HEXAHYDRO NAPHTHALIN-1-YL 2, 2-DI ETHYLBUTANOATE

Lactonization

Ammonium 7- [1 , 2, 6, 7, 8, 8a (R) -hexahydro-2 (S), 6 (R) -dimethyl-8 (S) - (2, 2- dimethylbutyryioxy) -1 (S) -naphthyl] -3 (R), 5 (R)-dihydroxyheptanoate (Formula II) (10 g., 0.022 moles) was dissolved in a mixture of acetonitrile (150 ml.) and gladal acetic add (30 ml.). The solution was then heated to 65-70° C and was maintained at this temperature for 6 hours. At the end of the reaction, HPLC showed simvastatin 97.4%, unreacted starting material 0.69% and dimer 0.07%. The reaction mass was cooled to 15-20° C and water (350 ml.) was added over as period of 30 minutes. The predpitated product was cooled further to 10-15° C and stirring continued for 1 hour. Product was filtered and washed with water (2x10 ml.), 1 :2 v/v acetonitrile- water (2x10 ml.) and dried in vacuo at 45-50° C. The product thus obtained was dissolved in cydohexene (200 ml.) at 80-85° C and then cooled over 1 hourto 10-12° C. Product was filtered and washed with chilled cydohexene (10 ml.) and dried in vacuo at 45-50° C to yield highly pure 8.2 g. (89%) of the title compound with HPLC purity 99.63% and dimer impurity 0.04%.

Example 2

PREPARATION OF (IS, 3R, 7S, 8S, 8aR) -3, 7-DIMETHYL-8- [2- [ (2R, 4R) -4-HYDROXY-6- OXO-3, 4, 5, 6-TETRAHYDRO-2H-PYRAN-2-YL] ETHYL] -1, 2, 3, 7, 8, 8a-HEXAHYDRO NAPHTHALIN-1-YL 2, 2-DIMETHYLBUTANOATE

Lactonization

Ammonium 7- [1 , 2, 6, 7, 8, 8a (R) -hexahydro-2 (S), 6 (R) -dimethyl-8 (S) - (2, 2- dimethylbutyryloxy) -1 (S) -naphthyl] -3 (R), 5 (R) -dihydroxyheptanoate (Formula II) (10 g., 0.022 moles) was dissolved in a mature of acetonitrile (150 ml.) and gladal acetic add (30 ml.). The reaction mixture was heated to 65-70° C under anhydrous conditions for 6 hours. Progress of reaction was checked by HPLC. At the end of the reaction, simvastatin was 97.55%, unreacted starting material 0.66% and dimer impurity 0.07%. Thereafter, reaction mixture was cooled to 10- 15° C and water (350 ml.) was added slowly over as period of 30 minutes and stirring was continued for 30 minutes. The product was filtered, washed with water (2x10 ml.) and dissolved in methanol (90 ml.) at 25-30° C. The solution was cooled to 5-10° C and water (82 ml.) was added in 30 minutes. The produd thus crystallized was stirred at 5-10° C, filtered and washed with cold methanol/water mixture (1:1 v/v, 8 ml.). Produd was dried to constant weight in vacuo at 45-50° C to obtain simvastatin (8.3 g., 90%). Chromatographic purity (HPLC) 99.55% and dimer impurity 0.07%.

Claims

KVe Claim:

1. A process for lactonization to produce highly pure simvastatin of Formula 1.

O^ LR i which comprises lactonization of a compound of the Formulla II

FO MULA IT

where Z is H or NH₄ in a mixture of acetonitrilke and glacial acid to provide anhydrous conditions at a temperature of 65-70° C and wherein the dimer impurity Of formula III formed is less than 0.1%, thereafter adding water to the reaction mixture, thereby causing simvastatin of Formula 1 to predpitate from the readion mixture.

FO Γ\L) R ~_M

2. The process according to Claim 1 wherein Z is NH₄.

3. A process for lactonization to produce highly pure simvastatin of formula I substantially as herein described.