PREPARATION OF 2-(2-TRITYLAMINOTHIAZOL-4-YL)-2-SYN-METHOXYIMINOACETIC ACID

Abstract: The process of the present invention is the conversion of an aminothiazole (I) to the corresponding thiazole acetic acid (IV) which is a precursor in the preparation of cephalosporin antibiotics.

Description: PREPARATION OF 2-(2-TRITYLAMINOTHIAZOL-4-YL)-2-SYN-METHOXYIMINOACETIC ACID BACKGROUND OF THE INVENTION 1. Field of the Invention The process of the present invention is the conversion of an aminothiazole to the corresponding thiazole acetic acid which is a precursor in the preparation of cephalosporin antibiotics. 2. Description of the Related Art 2-(2-Tritylaminothiazol-4-yl)-2-syn-methoxyiminoacetic acid is a known compound (US Patent 4,376,203, Example 3, Step C) useful in the production of a cephalosporin antibiotic, CEFTIOFUR (ceftiofur sodium, US Patent 4,464,367). GB Patent 1,580,621 (Example 21, Stages C-F) and US Patent 4,376,203 (Example 21, Steps C-F) set forth a process the transfor- mation of ethyl 2-(2-aminothiazol-4-yl) -2-syn-hydroxyiroinoacetic acid to 2- (2-tritylaminothiazol-4-yl) -2-syn-methoxyiminoacetic acid, see Stages D-F. Chemical Abstracts 110:57407g of December 15, 1987 reports the conversion of ethyl 2- (2-aminothazol-4-yl)-2-syn-methoxyiminoacetic acid to ethyl 2- (2-tritylaminothiazol-4-yl) -2-syn-methoxyiminoacetic acid by reacting the 2-aminothiazole with 0.8-1.6 mole φ^C- Cl in the presence of a strong inorganic base at room temperature. Chemical Abstracts 110:57653j of December 15, 1987 reports the conversion of ethyl 2- (2-aminothazol-4-yl)-2-syn-methoxyiminoacetic acid to ethyl 2-(2-tritylaminothiazol-4-yl)-2-syn-methoxyiminoacetic acid by reacting the 2-aminothiazole with CICH2-CO-CI in the presence of an inorganic base at room temperature. The process of the present invention is superior to the known methods of producing the thiazole acetic acid (IV) because none of the intermediates are isolated. Up to this time either the thiazole ester (II) or thiazole salt (III) or both were isolated, leading to a long process. The one-pot process of the invention can easily be accomplished, without any solvent changes, in one day giving the product in a higher yield. SUMMARY OF INVENTION Disclosed is a process for the preparation of a thiazole acetic acid of formula (IV) where R2 is -H, C; j _ - C4 alkyl , - CO-NH-CH3 , - CH 2 -C0-CH 2 , 1,2,4-triazol-5-ylmethyl, 1,2,3-triazol-5-ylmethyl, -CH 2 -C0-0CH 3 , -CH 2 -C00H, -C ( R 2 .χ ) R2.2)- c °-°- R 2-3 where R 2-l and R 2-2 are " H or -CH3 and R 2 _3 is C -0 alkyl, -C(R 2 _ i )(R 2 . 2 )-C00H where R 2 -l and 2 -2 are as defined above; R3 is φ^C- and C1 2 CH-C0- which comprises (1) contacting an aminothiazole of formula (I) where R ] _ is C-^-C^ alkyl, benzyl and p-methoxybenzyl and where R 2 is as defined above with a compound of the formula R -X1 where X* j _ is -Cl and -Br and where R3 is as defined above, in the presence of a non-aqueous base, (2) hydrolyzing the product of step (1) with aqueous base and (3) acidifying to a pH < 7, without isolation of any inter¬ mediates. DETAILED DESCRIPTION OF THE INVENTION While there are a number of procedures for the transformation ot ethyl 2-(2-aminothazol-4-yl)-2-syn-methoxyiminoacetic acid to 2-(2- tritylaminothiazol-4-yl)-2-syn-methoxyiminoacetic acid, the process of the present invention is a one-pot process which gives improved yields. The aminothiazole (I) is contacted with the desired alkylating agent R3-X-X in an organic solvent in the presence of a non-aqueous base. The particular R group utilized will be chosen because of the particular R 2 desired in the final product (cephalosporin) of which the thiazole acetic acid (IV) is a portion. For example, if one desires to produce ceftiofur sodium (US Patent 4,464,367) then it is preferred that R2 is methyl. X ] _ is -Cl or -Br. The non-aqueous base can be either an organic base or an inorganic base. Suitable organic bases include pyridine optionally substituted with 1-3 -CH3, DBU, DBN, NX3X X5 where X3, X and X5 are the same or different and are C-^-C^ alkyl and where two of X3, X^ and X5 are taken together with the attached nitrogen atom to form a compound selected from the group consisting of pyrrolidine, piperidine, morpholine or piperazine and the other of X3, X4 and X5 is as t'efined above. Preferred organic bases include pyridine and triethylamine; more preferred is pyridine. The organic base can serve as the solvent for the reaction. Suitable inorganic bases include bicarbonate (HCO3 " - 1 -) and carbonate CO j " -^). Other suitable solvents include THF, N-methylpyrrolidinone, DMAC and acetone. The reaction is operable in a temperature range of about 20-100°, preferably at about 20-50°. The tritylation step is complete within about 1 hr at about 60-70° using 1.1 equivalents of trityl chloride and 5 ml of pyridine/g of reactants. During the tritylation reaction about 1-2% of the anti oxime is formed. At about 40° the reaction is still complete and no anti oxime is detected. The product of the above step is then hydrolyzed with aqueous base. Any aqueous base which will cleave the ester is operable. Suitable aqueous bases include hydroxides, alkoxides of the formula 0-X 2 where X 2 is C-^-C^ alkyl, and equivalents thereof. Preferred aqueous bases include hydroxides; more preferred are sodium or potassium hydroxide. About 3-4 equivalents of the aqueous base is preferred. If less is used the reaction rate is slowed, if more is used no advantage is observed. The hydrolysis is complete in about 3 hr at about SC° and in about 2 hr at about 70° . The temperature is not important to the yield, it only affects the rate of the reaction. Operable temperatures are from about 20-100°, preferably from about 50 to about 80° . The temperature used is affected by the amount of solvent present. With pyridine, the more solvent used the faster the reaction rate at a given temperature. Following hydrolysis, the reaction mixture is acidified to a pH of about 2 to form the free acid. Any acid sufficiently strong is operable as is well known to those in the art. Operable acids include sulfuric, hydrochloric, phosphoric, nitric, trifluoroacetic, perchloric and equivalents thereof; preferred are sulfuric or hydrochloric. Prior to acidifying it is preferred to dilute the reaction mixture somewhat with an organic solvent such as methylene chloride. If this step is performed in less than one hr, very little of the anti oxime is formed. However, if this two phase system (organic solvent/water) is stirred for a long time at elevated temperatures the anti oxime forms in increasing amounts. Therefore, it is preferred to cool the thiazole salt (III) prior to acidifying and allowing the heat of neutralization bring the reaction tempera¬ ture to about 30-35° . At this time the layers are separated. The organic layer is washed to remove the salt of the amine base and is then worked up by known means. For purposes of work-up the reaction mixture can be diluted with water or an organic solvent (depending on the method of work-up desired) and the thiazole acetic acid (IV) either extracted or filtered. The anti oxime is efficiently removed by crystallization from methylene chloride or a methylene chloride/hexane mixture. It is desired to remove the anti oxime because it is very poorly active in the cephalosporin antibiotics of which the thiazole acetic acid (IV) is a part. The thiazole acetic acids (IV) are useful intermediates in the production of cephalosporin antibiotics. More particularly, 2-(2- tritylaminothiazol-4-yl)-2-syn-methoxyiminoacetic acid (IV) is useful in the production of ceftiofur sodium (US Patent 4,464,367). DEFINITIONS AND CONVENTIONS The definitions and explanations below are for the terms as used throughout this entire document including both the specification and the claims. I. CONVENTIONS FOR FORMULAS AND DEFINITIONS OF VARIABLES The chemical formulas representing various compounds or molecu¬ lar fragments in the specification and claims may contain variable substituents in addition to expressljr defined structural features. These variable substituents are identified by a letter or a letter followed by a numerical subscript, for example, "Z ] _ n or "R^" or "R^" where "i" is an integer. Chemical formulas or portions thereof drawn in a linear fashion represent atoms in a linear chain. The symbol "-" in general represents a bond between two atoms in the chain. Thus CH3-O-CH2- CH(R^)-CH represents a 2-substituted-1-methoxypropane compound. In a similar fashion, the symbol "=" represents a double bond, e.g., CH2=C(R )-O-CH3, and the symbol "≡" represents a triple bond, e.g., HC≡C-CH(R^)-CH2-CH3. Carbonyl groups are represented in either one of two ways: -CO- or -C(=0) - , with the former being preferred for simplicity. II. DEFINITIONS All temperatures are in degrees Centigrade. TLC refers to thin-layer chromatography. THF refers to tetrahydrofuran. DBU refers to 1,8-diazabicyclo[5.4.0]undec-7-ene. DBN refers to 1,5-diazabicyclo[4.3.Ojnon-5-ene. DMAC refers to dimethylacetamide. φ refers to phenyl ( ^ ^ . M includes lithium, sodium and potassium. EXAMPLES EXAMPLE 1 2- (Trityla ino)-α-(methoxyimino) -4-thiazoleacetic acid (IV) A mixture of ethyl 2-amino-α- (me hoxyimino) -4-thiazoleacetate (10.0 g) , trityl chloride (13.99 g) , and pryidine (20.0 ml) is stirred under nitrogen at 40° . After stirring for 1 hr the reaction is checked by TLC. When the tritylation is complete, water (20.0 ml) and aqueous sodium hydroxide (50%, 8.14 ml) are added and the mixture heated at 65° for 4-5 hr. When the hydrolysis is complete (TLC) the resulting slurry is cooled to 20° and methylene chloride (100 ml) is added. This mixture is then acidified by the addition of con- centrated aqueous hydrochloric acid. The layers are separated. The organic layer is washed with water (2 x 70 ml). Heptane (150 ml) is added to the organic phase with stirring. The resulting slurry is cooled to 0° and filtered. The solids are washed with heptane/- methylene chloride mixture (60/40, 200 ml) and dried under vacuum at 55° to give the title compound. EXAMPLE 2 2- (Tritylamino)-α(methoxyimino) -4-thiazoleacetic acid (IV) A mixture of ethyl 2-amino-α- (methoxyimino)-4-thiazoleacetate (10.0 g) , dimethylacetamide (50 ml), trityl chloride (14.59 g) , and triethylamine (9.12 ml) are stirred under nitrogen at 40°. When the tritylation is complete by TLC, water (20 ml) and aqueous sodium hydroxide (50%, 8 ml) are added. This mixture is heated at 65° for 2 to 2.5 hours. When the hydrolysis is complete (TLC) the resulting slurry is cooled in an ice bath and diluted with water (50 ml) . This mixture is then acidified by the addition of concentrated aqueous hydrochloric acid. This slurry is filtered. The solids are washed with water and dried under vacuum. The crude solids are stirred with a mixture of heptane/ ethylene chloride (70/30, 77 ml). After stirring for 30 min the slurry is filtered. The solids are washed with a mixture of heptane/methylene chloride (70/30, 150 ml) and dried under vacuum at 55° to give the title compound. \ OR, 10 20 30 35

Claims: CLAIMS 1. A process for the preparation of a thiazole acetic acid of formula (IV) where R2 is -H, C-χ-C alkyl, -C0-NH-CH 3 ,- -CH 2 -CO-CH 2 , l,2,4-triazol-5-ylmethyl, 1,2, 3-triazol-5-ylmethyl, -CH 2 -CO-OCH 3 , -CH 2 -C00H, -C(R 2 .ι) 2 .2 - co -°- R 2-3 where R 2-l and R 2-2 are "H or "CH 3 and R 2 _3 is 0-^-0 alkyl, -C(R 2 .χy R2-2)" C00H where .χ and 2 -2 are as defined above; R3 is φ-^C- and CI2CH-CO- which comprises (1) contacting an aminothiazole of formula (I) where R-χ is C_-C^ alkyl, benzyl and p-methoxybenzyl and where R 2 is as defined above with a compound of the formula R3-X where X*χ is -Cl and -Br and where R3 is as defined above, in the presence of a non- aqueous base, (2) hydrolyzing the product of step (1) with aqueous base and (3) acidifying to a pH < 7, without isolation of any inter¬ mediates. 2. A process for the preparation of thiazole acetic acid (IV) according to claim 1 where the non-aqueous base is an organic or inorganic base. 3. A process for the preparation of thiazole acetic acid (IV) according to claim 2 where the organic base is selected from the group consisting of pyridine optionally substituted with 1-3 -CH3, DBU, DBN, NX3X4X5 where X3, X4 and X5 are the same or different and are C -C alkyl and where two of X3. X and X5 are taken together with the attached nitrogen atom to form a compound selected from the group consisting of pyrrolidine, piperidine, morpholine or piperazine and the other of X , X and X5 is as defined above. 4. A process for the preparation of thiazole acetic acid (IV) according to claim 3 where the organic base is pyridine or triethyl- amine. 5. A process for the preparation of thiazole acetic acid (IV) according to claim 2 where the inorganic base is HCO3 and CO3 " . 6. A process for the preparation of thiazole acetic acid (IV) according to claim 1 where the aqueous base is selected from the group consisting of hydroxide and O-X2 where X2 is C*ι_-C alkyl. 7. A process for the preparation of thiazole acetic acid (IV) according to claim 1 where the acid is selected from the group consisting of sulfuric, hydrochloric, phosphoric, nitric, tri- fluoracetic and perchloric. 8. A process for the preparation of thiazole acetic acid (IV) according to claim 7 where the acid is sulfuric or hyrochloric. 9. A process for the preparation of thiazole acetic acid (IV) according to claim 1 where the thiazole acetic acid is 2-(trityl¬ amino) - - (methoxyimino) -4-thiazoleacetic acid.

Inventors: SHEPHARD KENNETH PAUL, SHEPHARD, KENNETH, PAUL
Applicants: UPJOHN CO, THE UPJOHN COMPANY
Application year: 1990
Main classification: C07D277
IPC codes: C07D277