NOVEL PROCESS FOR PREPARING 4-SUBSTITUTED-1H-PYRROLE-3-CARBOXYLIC ACID ESTER

Abstract: The present invention relates to a novel process for preparing pyrrole ester compounds, which are key intermediates in the preparation of farnesyl transferase inhibitors, an anti-cancer agent. Horner-Emmons reaction of aldehyde compounds provides the corresponding alpha , beta -unsaturated esters, which without any separation and/or purification steps, are treated with toluenesulfonylmethylisocyanate in the presence of base to give pyrrole esters in one-pot fashion.

Description: NOVEL PROCESS FOR PREPARING 4-SUBSTITUTED-1H- PYRROLE-3-CARBOXYLIC ACID ESTER TECHNICAL FIELD The present invention relates to a novel process for preparing pyrrole ester compounds which are key intermediate in the preparation of farnesyl transferase inhibitors, an anti-cancer agent (see Ko, J S et al , WO 9928315) Horner-Emmons reaction of aldehyde compounds provides the corresponding α,β-unsaturated esters, which without any separation and/or purification steps, are treated with toluenesulfonylmefhylisocyanate (TosMIC hereinafter referred to as 'TosMIC') in the presence of base to give pyrrole esters in one-pot fashion BACKGROUND ART The most typical method for the synthesis of 3-substituted-4-pyrrole ester compound is through the cyclization reaction of an isonitrile compound with an electrophilic α,β-unsaturated compound, as depicted in the following Reaction Scheme 1 As isonitrile part, TosMIC is the most well known reagent (van Leusen, A M et al Tetahedron Lett 1972, 52, 5337 ) Reaction Scheme 1 TosCH 2 NC in which Ri and R 2 independently of one another represent Cι-C 4 -alkyl Recently BetMIC (Katrizky, A.R et al Heterocycles, 1997, 44, 67 ) of the following formula showing a similar reactivity to TosMIC has been developed Thereafter, the same researcher has developed a new method as depicted in the following Reaction Scheme 2 TosMIC is reacted with a carbonyl compound in the presence of a base and POCl 3 (phosphorous oxychloride) in sequence to give an α ,β - unsaturated isonitrile compound, which is then reacted with an activated nucleophile to give a pyrrole compound (van Leusen, A M et al J. Org. Chem 1992, 57, 2245 ) Reaction Scheme 2 RCHO + TosMIC in which R represents alkyl, allyl, or aryl, and E represents an electron-withdrawing group As known in the previous arts, the general synthesis of 3-substituted-4-pyrrole ester contains two discrete stages The first stage is the preparation and purification of ,β-unsaturated compound and the second stage is the cyclization reaction of the purified ,β-unsaturated compound with TosMIC in the presence of base However, since the conventional method requires purification step after the preparation of α,β-unsaturated compound, it is inevitable to efflux the reaction solvent as waste unless it is recycled To remove the efflux of waste solvent and increase the efficiency of the process, it is proposed to run the two reactions in the same solvent as one-pot fashion. DISCLOSURE OF INVENTION Under the technical background as explained above, the present inventors have investigated extensively on the eradication of the waste solvent problem and the increase of the efficiency of the process for the purpose of mass production of pyrrole ester As a result, we have come up with the present invention by combining the two stages of the pyrrole synthesis into one-pot/one stage process Therefore, the pyrrole ester is obtained in high purity and in environmentally friendly manner The object of the present invention is to provide a process for preparing a desired pyrrole ester derivative represented by the following formula (1) in which R represents alkyl, allyl, or aryl, and R 1 represents Cι-C -alkyl, by reacting an aldehyde compound represented by the following formula (2) O (2) R^H in which R is defined as previously described, with a trialkylphosphonoacetate represented by the following formula (3) (R 1 O) 2 PO ^ / C0 2 R 1 (3) in which R 1 is defined as previously described, in an inert solvent in the presence of an alkali metal alkoxide base in an amount of 1 to 1 5 molar equivalent with respect to the compound of formula (2) to give an α,β-unsaturated ester compound represented by the following formula (4) R /^ / Cθ Rl (4) in which R and R 1 are defined as previously described, and subsequently by adding TosMIC and the same base as used in the previous step in an amount of 1 to 1 5 molar equivalent with respect to the compound of formula (2) BEST MODE FOR CARRYING OUT THE INVENTION The process according to the present invention is depicted in the following Reaction Scheme 3 Reaction Scheme 3 (1) In the process of the present invention, it is very important to use the alkali metal alkoxide base in an amount of 1 to 1 5 molar equivalents with respect to the compound of formula (2) If the amount of base is deviated from the defined range, the reaction to prepare the unsaturated ester compound of formula (4) is not proceeded cleanly As a result, the object of the present invention to react the unsaturated ester compound directly in the next step in the same reaction system without being separated cannot be achieved As the base which can be used for such a purpose, alkali metal methoxide, -ethoxide, -t- butoxide, -t-pentoxide, etc , preferably sodium- or potassium-t-butoxide or -t-pentoxide can be used Though the reaction is well proceeded by using the base in an amount of 1 to 1 5 molar equivalents, however, 1 to 1 3 molar equivalent thereof may be sufficient to exhaust the aldehyde compound Further, an excess base may cause hydrolysis in the subsequent separation step of layers, it is preferable to use the base in an amount of 1 to 1 3 molar equivalent in order to minimize such a hydrolysis reaction Any inert solvent which does not adversely affect to the reaction can be used in the process according to the present invention, but tetrahydrofuran, dimethoxyethane, toluene or mixtures thereof is preferably used After the process for preparing the compound of formula (4) is completed, TosMIC and the same base as used in the previous reaction step were added and stirred until the α,β-unsaturated ester is completely removed to produce the pyrrole ester compound of formula (1) In this reaction, TosMIC is added in an amount of 1 to 1 3 molar equivalent with respect to the compound of formula (2) and the base is added in an amount fallen under the same range as mentioned in the previous step of preparing the compound of formula (4) Then, the reaction solution is quenched with water and extracted with a suitable extracting solvent which is not miscible with water at temperature of 40 to 90°C (if a high yield is desired, 60 to 90°C is preferable) The organic layer was separated and stirred at room temperature, and the formed precipitate is filtered to give the desired compound of formula (1) in a pure state The solvent is not always required to remove before carrying out the extraction. But, in case of tetrahydrofuran or dimethoxyethane is used as the reaction solvent, since they are well miscible with water, it is required to be removed by distillation Therefore, the increase of yield can be expected if the solvent is removed in advance by distillation under reduced pressure before the extraction As the extracting solvent for this purpose, toluene or «-butyl acetate can be preferably used Particularly, when sodium-t-pentoxide is used as the base, since this base is well soluble in the preferable extracting solvent toluene, the trouble to have to use an extracting solvent different from the reaction solvent may be saved The reaction for preparing the compound of formula (4) is proceeded at temperature ranging from -20 to 40°C, preferably 10 to 25°C on a satisfactory level Also, the process for producing the desired pyrrole ester derivative of formula (1) from the compound of formula (4) thus obtained is suitably carried out at temperature ranging from 0 to 40°C Contrary to the prior arts, after the unsaturated ester compound of formula (4) is produced, it directly reacts with TosMIC without any separation or purification, in the present invention to afford the pyrrole ester Thus, reduction of the waste solvent and enhancement of the efficiency of the process is obvious and provides great advantage particularly when the process is applied on an industrial production The present invention will be more specifically explained in the following examples However, it should be understood that they are intended to illustrate the present invention but not in any manner to limit the scope of the present invention Example 1 Synthesis of ethyl 4-(naphthalen-l-yl)-lH-pyrrole-3-carboxylic acid ester 1-Naphthaldehyde(35g, 0 224mol) and triethylphosphonoacetate(50g, 0 224mol) were mixed under nitrogen atmosphere, 180^ of dimethoxyethane(DME) was added, and the resulting mixture was cooled to 0 ° C under a thorough stirring To this solution was added slowly potassium-t-butoxide(30g, 1 2molar equivalent) while maintaining reaction temperature below 20 ° C After confirming the complete removal of 1-naphthaldehyde by HPLC, TosMIC(52 5g, 1 2molar equivalent) and potassium-t-butoxide(32g, 1 3molar equivalent) were added slowly in sequence maintaining the reaction temperature below 20 °C After confirming the exhaustion of α ,β -unsaturated ester by HPLC, 70^ of distilled water was added and DME was removed therefrom by distillation under reduced pressure 200 πτ2 of toluene was added to this concentrate The mixture was warmed and extracted with 350 ^ of distilled water The separated organic layer was subjected to azeotropic distillation to remove the residual moisture The concentrate was cooled with slow stirring to room temperature and the formed solid was filtered The filter cake was washed twice with 30m of cold toluene, twice with 50"^ of distilled water, and dried to give 37g (HPLC Purity 95 2%, Yield 61%) of the title compound as a white powder 1H NMR(CDC1 3 , ppm) δ 8 65(1H, br, s), 7 80(3H, m), 7 59(1H, dd, Jl=3 2Hz, J2=2 3Hz), 7 41(4H, m), 6 79(1 H, t, J=2 3Hz), 3 91(2H, q, J=6 9Hz), 0 71(3H, t, J=6 9Hz) 13C NMR(CDC13, ppm) δ 165 2, 133 8, 133 51, 133 50, 128 0, 127 5, 127 3, 126 7, 125 5, 125 4, 125 2, 124 7, 123 9, 119 3, 115 9, 59 5, 13 7 m p (not calibrated) 164-165 ° C Example 2 Synthesis of ethyl 4-(naphthalen-l-yl)-lH-pyrrole-3-carboxylic acid ester 1-Naphthaldehyde(28g, 0 18mol) and triethylphosphonoacetate(40 35g, 0 18mol) were introduced into 500mL round bottom flask and diluted with 180m^ of toluene The reaction misture was cooled to about 0 to 5 ° C and sodium-t-pentoxide (23 8g, 0 216mol) was added slowly in order to maintain the reaction temperature below 20 °C After the addition was completed, the reaction mixture was stirred for 1 to 2 hours at room temperature and cooled again to 0 to 5 ° C TosMIC(36 9g, 0 189mol) and sodium-t- penroxide(23 8g, 0 216mol) were added slowly in sequence maintaining the reaction temperature below 20 ° C After the addition was completed, the reaction mixture was stirred for 3 to 6 hours at room temperature and 250m^ of distilled water was added The resulting mixture was heated at about 70 ° C and the organic layer was separated, washed once again with 250^ of distilled water at the same temperature The separated organic layer was subjected to azeotropic distillation to remove the residual moisture Then, the concentrate was cooled to about 50 ° C with slow stirring After the crystal was precipitated, the reaction temperature was lowered to 0 to 5 ° C and further stirred The formed solid was filtered, washed twice with 30π^ of toluene and dried under nitrogen to give 29 6g (HPLC Purity 96%PAR, Yield 62%) of the title compound as a white powder INDUSTRIAL APPLICABILITY According to the process of the present invention, the pyrrole ester compounds of formula (1), key intermediates for preparing farnesyl transferase inhibitors, an anti-cancer agent, can be prepared with a high purity and yield on an industrial scale

Claims: CLAIMS A process for preparing a pyrrole ester derivative represented by the following formula (1) in which R represents alkyl, allyl, or aryl, and R 1 represents Cι-C 4 -alkyl, characterized by reacting an aldehyde compound represented by the following formula (2) in which R is defined as previously described, with a trialkylphosphonoacetate represented by the following formula (3) (R'O^PO ^^ ^CC^R 1 (3) in which R 1 is defined as previously described, in an inert solvent in the presence of an alkali metal alkoxide base in an amount of 1 to 1 5 molar equivalent with respect to the compound of formula (2) to give an α,β-unsaturated ester compound represented by the following formula (4) R ^^∞2R l (4) in which R and R 1 are defined as previously described, and subsequently by adding TosMIC and the same base as used in the previous step in an amount of 1 to 1 5 molar equivalent with respect to the compound of formula (2) The process of claim 1 wherein the alkali metal alkoxide base is used in an amount of 1 to 1.3 molar equivalent with respect to the compound of formula (2). The process of claim 1 or 2 wherein the alkali metal alkoxide base is sodium- or potassium-t-butoxide or -t-pentoxide. The process of claim 1 wherein the inert solvent is tetrahydrofuran, dimethoxyethane, toluene or mixtures thereof. The process of claim 1 wherein TosMIC is used in an amount of 1 to 1 3 molar equivalent with respect to the compound of formula (2) The process of claim 1 wherein the process for preparing the compound of formula (4) is carried out at temperature ranging from -20 to 40°C, and the process for preparing the compound of formula (1) is carried out at temperature ranging from 0 to 40°C The process of claim 6 wherein the process for preparing the compound of formula (4) is carried out at temperature ranging from 10 to 25°C The process of claim 1 wherein the compound of formula (1) is prepared and extracted with an organic solvent further added, the organic layer is separated, and the compound of formula (1) is recrystallized therefrom The process of claim 8 wherein the organic solvent is toluene or «-butyl acetate The process of claim 8 or 9 wherein the extraction is carried out at temperature ranging from 40 to 90°C

Inventors: CHANG JAY HYOK, LEE KYOO WOONG, OH SUNG TAK, SHIN HYUN IK, CHANG, JAY, HYOK, LEE, KYOO, WOONG, OH, SUNG, TAK, SHIN, HYUN, IK
Applicants: CHANG JAY HYOK, LEE KYOO WOONG, LG CHEMICAL LTD, OH SUNG TAK, SHIN HYUN IK, CHANG, JAY, HYOK, LEE, KYOO, WOONG, LG CHEMICAL LTD., OH, SUNG, TAK, SHIN, HYUN, IK
Application year: 2001
Main classification: C07D207
IPC codes: C07D207