PROCESS FOR PREPARING 4-ACETOXY-3-HYDROXYETHYLAZETIZIN-2-ONE DERIVATIVES

Abstract: A process for preparing 4-acetoxy-3-hydroxyethyl­ azetizin-2-one derivative having the general formula (II): wherein R¹ is a protective group for hydroxy group, which comprises reacting the β-lactam compound having the general formula (I): wherein R¹ is above, R², R³ and R⁴ are a lower alkyl group of C₁ to C₄, phenyl group or aralkyl group and R is a protective group for N, with acetic anhydride in the organic solvent in the presence of base and then removing the protective group for N. 4-Acetoxy-3-hydroxyethylazetin-2-one derivatives are the useful intermediates for preparing carbapenem β-lactam antibiotics such as thienamycin and penem β-­ lactam antibiotics.

Description: PROCESS FOR PREPARING 4-ACETOXY-3 HYDROXYETHYLAZETIZIN-2-ONE DERIVATIVES The present invention relates to a process for preparing 4-acetoxy-3-hydroxyethylazetizin-2-one which has hydroxyethyl group, wherein hydroxy group is protected, at C-3-position and acetoxy group at C-4position. It is known that 4-acetoxy-3-hydroxyethylazetizin-2-one derivatives are the useful intermediates for preparing carbapenem ss-lactam antibiotics such as thienamycin and penem ss-lactam antibiotics (cf., for example, Tetrahedronletters by Laider et al., vol. 23, page 2293, 1982 and Chem. Pharm. Bull. by Yoshida et al., vol. 29, page 2899, 1981). Hitherto, processes for synthesizing 4-acetoxy3-hydroxyethylazetizin-2-one derivatives have been known such as synthesis from 6-aminopenicillanic acid (cf. Chem. Parm. Bull. by Yoshida et al., vol. 29, page 2899, 1981), synthesis from threonine (cf. Tetrahedron by Shiozaki et al, vol. 39, page 2399, 1983), synthesis from aspartic acid (cf. Tetrahedronletters by Laider et al., vol. 23, page 2293, 1982), and the like. However, these processes have a difficult point that industrially unfavourable heavy metals such as mercury acetate and lead tetraacetate are employed in order to introduce acetoxy group at C-4-position of the ss-lactam ring. The inventors have found a process for preparing a novel ss-lactam compound having O-protected hydroxyethyl group at C-3-position and silylether group at C-4-postion by the reaction of enolsilylether with chlorosulfonylisocyanate and this process has already been made patent application. The inventors further found that 4-acetoxy3-hydroxyethylazetizin-2-one could be easily prepared by using the above-mentiond ss-lactam compound and thus the present invention was completed. According to the present invention, there is provided a process for preparing 4-acetoxy-3-hydroxyethylazetizin-2-one having the general formula (11): EMI2.1 wherein R1 is a protective group for hydroxy group, where the ss-lactam compound having the general formula (I): EMI2.2 wherein R1 is a protective group for hydroxy group, R2, R3 and R4 are a lower alkyl group of C1 to C4 phenyl group or aralkyl group and R is a protective group for N, is reacted with acetic anhydride in the organic solvent in the presence of base and then a protective group for N is removed. ss-Lactam compound having the general formula (I) is prepared by introducing substituent group R at N of the ss-lactam compound having the genral formula (I'): EMI2.3 wherein R1, R2, R3 and R4 are as above. As is shown in the application of the inventors (Japanese Unexamined Patent Publication No. 139797/1984), the B-lactam compound having silylether group at C-4-position and having the general formula (I') can be easily obtained by the process of the following reaction scheme: : EMI3.1 The ss-lactam compound having a protective group for N and having the general formula (I) can be obtained by the reaction of the ss-lactam compound having the general formula (I') and the reagent having the genral formula of R-X, wherein R is as above and X is a halogen. The examples of the reagent having the general formula of R-X are, for instance, trialkyl-sily halide such as t-butyldimethylsilyl chloride, isopropyldimethylsilyl chloride, isobutyldimethylsilyl chloride, trimethylsilyl chloride, and the like, alkyloxyoxalyl chloride, aralkyloxyoxalyl chloride or allyloxyoxalyl chloride EMI3.2 EMI3.3 and the like. t-Butyldimethylsilyl chloride is particularly preferable and t-butyldimethylsilyl group can be introduced as a protecting group. The compound having the general formula (I) can be obtained by conducting an elimination of hydrogen chloride in the reaction of the ss-lactam compound (I') with the reagent having the general formula of R-X in the solvent such as DMF or methylene chloride in the presence of base such as triethylamine and imidazole, followed by distilling away a solvent, extracting and distilling away the extraction solvent. The examples of the O-protective group of R1 for hydroxy group at C-3-position of the B-lactam compound having the general formula (I) are, for instance, trialkylsilyl group having the general formula (III): EMI4.1 wherein R5, R6 and R7 are a lower alkyl group of C1 to C4 such as tert-butyldimethylsilyl group, triisopropylsilyl group, isopropyldimethylsilyl group, and isobutyldimethylsilyl group, t-butyl group, benzyl group, trichloroethoxycarbonyl group, tert-butoxycarbonyl group, p-nitrobenzyloxycarbonyl group and the like. tert-Butyldimethylsilyl group or isopropyldimethylsilyl group, which are stable during the reaction and can be selectively deprotected by acid treatment, are particularly preferable. Though R2, R3 and R4 of the ss-lactam compound having the general formula (I) can be the same or different from each other and selected from a lower alkyl group of C1 to C4 such as methyl, ethyl, isopropyl, isobutyl and tert-butyl group, phenyl group, benzyl group or aralkyl group such as p-nitrobenzyl group, preferably all of Rê, R and R4 are methyl group. Base, solvent and reaction temperature are the factors which affect the yield when the ss-lactam compound prepared as mentioned above and having the general formula (I): EMI4.2 wherein R1, R2, R3, R4 and R are as above, is reacted with acetic anhydride in the organic solvent in the presence of base to convert the said ss-lactam compound into the desired 4-acetoxy-3-hydroxyethylazetizin-2-one derivative having the general formula (II'): EMI5.1 wherein R1 and R are as above. Halogenated hydrocarbon or aromatic hydrocarbon, preferably halogenated hydrocarbon such as methylene chloride can be employed as a reaction solvent. Most preferable base is dimethylaminopyridine and it can also be used in combination with other bases such as pyridine, lutidine and picoline. The amount of the base employed is 1 to 5 times moles, preferably 1 to 3 times moles of the B-lactam compound having the general formula (I) and the amount of acetic anhydride employed as the reagent for introducing acetoxy is 1 to 20 times moles, preferably 3 to 15 times moles of the ss-lactam compound having the general formula (I). The reaction is carried out in the organic solvent such as methylene chloride by adding dimethylaminopyridine and acetic anhydride to the ss-lactam compound having the general formula (I) and stirring the mixture at a temperature of -50 C to room temperature, preferably at a temperature of -30 to 5 0C until the compound having the general formula (I) disappears. When another base such as pyridine or picoline is added in addition to dimethylaminopyridine, the yield can be improved. After the reaction is completed, extraction solvent such as methylene chloride or hexane is added to the reaction mixture, followed by addition of aqueous sodium bicarbonate, separation of the organic layer, washing the organic layer, dehydration and distilling away the organic solvent to give N-protected ss-lactam compound having acetoxy group at C-4-position. The obtained compound having the general formula (II') can be subjected to the next reaction where N-protective group is removed. However, if desired, this compound can be purified by silica-gel column-chromatography. When N-protective group is removed, it is required that only N-protective group is selectively removed without removal of O-protective group of hydroxyethyl at C-3-position. For example, tetrabutylammonium fluoride is preferably used in case that N-protective group is alkylsilyl group such as tert-butyldimethylsilyl group. A combination of quarternary ammonium halide such as, for example, tetrabutylammonium chloride, tetrabutylammonium bromide, tetramethylammonium chloride, trimethylbenzylammonium chloride with potassium fluoride can provide a equivalent effect to tetrabutylammonium fluoride, and also potassium fluoride alone can be available when methanol is used as the solvent. The solvent used in the elimination reaction is preferably tetrahydrofuran, acetonitrile or methylene chloride and the reaction is smoothly proceeded by stirring at room temprature. Employing acetic acid in the removal of the protective group results in the improvement of the yield. After the reaction is completed, the extraction solvent such as ethyl acetate is added to the reaction mixture, followed by the addition of the dilute alkali solution. Then, the organic layer is extracted, washed with water, dehydrated and dire, and finally the organic solvent is distilled away to give the desired compound of 4-acetoxy-3hydroxyethylazetizin-2-one derivatives. 4-Acetoxy-3hydroxyethylazetizin-2-one derivatives can be purified by crystallization from n-hexane or petroleum ether or silica-gel column-chromatography. The present invention is more particularly explained by the following non-limiting examples. However, it is to be understood that any modification or development can be made without departing from the scope and spirit of the present invention. Example 1 [Preparation of (3R,4R)-4-acetoxy-3-[(R)-l-tert-butyldimethylsilyloxyethyl]-azetizin-2-one] There was dissolved 1.0 g of (3R,5R)-3-(1-tert- butyldimethylsilyloxyethyl)-4-trimethylsilyloxyazetizin2-one in 10 ml of DMF, to which 0.89 g of triethylamine and 0.61 g of tert-butyldimethylsilyl chloride were added and the mixture was stirred for 9 hours at room temperature. After the reaction was completed, DMF was distilled away under reduced pressure and thereto 30 ml of hexane was added. After the solution was washed successively with 2.5 % aqueous solution of NaHC03, aqueous solution of hydrochloric acid of pH 3 and saturated solution of salt and dried with magnesium sulfate, the solvent was distilled away to give 1.24 g of the liquid of the crude product. To 5 ml of methylene chloride was added 1.0 g of the liquid, thereto further 0.85 g of dimethylaminopyridine and 1.1 ml of acetic anhydride was added and the mixture was reacted for 6 hours at room temperature. After the reaction mixture was washed successively with 5 % aqueous solution of NaHC03, aqueous solution of hydrochloric acid of pH 3 and saturated solution of salt and dried with magnesium sulfate, the solvent was distilled away to give 0.8 g of the liquid of the crude product. The liquid was purified by a silica-gel column-chromatography (benzene : hexane = 2 : 1) to give 0.5 g of (3R,4R,5R)-4-acetoxy-1-(tert-butyldimethylsilyl)- 3-(l-tert-butyldimethylsilyloxyethyl)-azetizin-2-one as a liquid. There was added 0.5 g of the liquid to 2 ml of THF, to which 0.4 g of tetrabutylammonium fluoride and 0.17 g of acetic acid in 2 ml of THF solution was added and the mixture was stirred for 30 minutes at room temperature. After adding 20 ml of ethyl acetate to the reaction mixture, the resultant was washed successively with 5 % aqueous solution of NaHCO3 and saturated solution of salt and dried with magnesium sulfate. The solvent was distilled away to give 0.30 g of the desired compound as a crystal. The obtained crystal was purified by a silica-gel column-chromatography (benzene : ethyl acetate = 6 : 1) to give 0.27 g of the desired ss-lactam as a solid. mp: 1070 to 108 0C [al 25 = +500 (C=0.5 CHCl3) HNMR (90 MHz, CDCQ3)8 , (ppm) 0.08 (6H, s), 0.84 (9H, s), 1.20 (3H, d), 2.01 (3H, s), 3.04 (1H, dd), 4.12 (1H, m), 5.76 (1H, d) and 6.73 (NH) Example 2 (preparation of (3R,4R)-4-acetoxy-3-[(R)-l-tert-butyl- dimethylsilyloxyethyl]-azetizin-2-one] There was dissolved 1 g of (3R,4R)-l-tert butyldimethylsilyl-3-t(R)-l-tert-butyldimethylsilylOxy- ethyl]-4-trimethylsilyloxyazetizin-2-one into 10 ml of methylene chloride, thereto 0.85 g of dimethylaminopyridine and 0.71 g of acetic anhydride were added and the mixture was reacted for one day at 0 0C. After the reaction mixture was diluted with hexane and washed successively with 5 % aqueous solution of NaHCO3, aqueous solution of hydrochloric acid of pH 4 and saturated solution of salt, the resultant was dried with magnesium sulfate and the solvent was distilled away to give 0.85 of the liquid of the crude product. The obtained liquid was purified by a silica-gel column-chromatography (hexane : ether = 30 : 1) to give 0.40 g of (3R,4R)-4 acetoxy-l-tert-butyldimethylsilyl)-3-[(R)-l-tert- butyldimethylsilyloxyethyl)azetizin-2-one as a colorless liquid. There was added 2 ml of THF to the obtained liquid, thereto 0.26 g of tetrabutylammonium fluoride and 0.12 g of acetic acid in 2 ml of THF were added and the mixture was stirred for 30 minutes at room temperature. After adding 20 ml of ethyl acetate to the reaction mixture, the resultant was washed successively with 5 % aqueous solution of NaHCO3 and saturated solution of salt, and dried with magnesium sulfate. The solvent was distilled away to give 0.29 g of the solid. The obtained solid was recrystallized from hexane to give 0.20 g of the desired ss-lactam as colorless needles. The properties of the obtained B-lactam were agreed with the values shown in Example 1. Example 3 {Preparation of (3R,4R)-4-acetoxy-3-[(R)-l-tert-butyl- dimethylsilyloxyethyl]-azetizin-2-one] There was dissolved 1 g of (3R,4R)-l-tert butyldimethylsilyl-3-t(R)-l-tert-butyldimethylsilylOxy- ethyl)-4-trimethylsilyloxyazetizin-2-one into 10 ml of methylene chloride, thereto 0.85 g of dimethylaminopyridine, 0.75 g of 2,6-lutidine and 1.42 g of acetic anhydride were added and the mixture was reacted for 44 hours at -150C. After the reaction mixture was diluted with ether and washed successively with 5 % aqueous solution of NaHCO3, aqueous solution of hydrochloric acid of pH 4 and saturated solution of salt, the resultant was dried with magnesium sulfate. The solvent was distilled away to give 0.88 g of the liquid of the crude product. The obtained liquid was purified by a silica-gel columnchromatography (hexane : ethyl acetate = 100 : 1) to give 0.58 g of (3R,4R)-4-acetoxy-tert-butyldimethylsilyl)-3- [(R)-l-tert-butyldimethylsilyloxyethyl)azetizin-2-one as a liquid. There was dissolved the obtained liquid into 2 ml of THF, thereto 0.38 g of tetrabutylammonium fluoride and 0.17 g of acetic acid in 2 ml of THF was added and the mixture was stirred for 30 minutes at room temperature After adding 20 ml of ethyl acetate to the reaction mixture, the resultant was washed successively with 5 % aqueous solution of NaHCO3 and saturated solution of salt, and dried with magnesium sulfate. The solvent was distilled away to give 0.42 g of a solid. The obtained solid was purified by a silica-gel columnchromatography (hexane : ether = 10 : 3) to give 0.39 g of the desired ss-lactam as colorless needles. The properties of the obtained ss-lactam were agreed with the values shown in Example 1. Example 4 (Preparation of (3R,4R)-4-acetoxy-3-[(R)-l-isopropyl dimethylsilyloxyethy13-azetizin-2-one] There was dissolved 1.2 g of 3-((R)-l- isopropyldimethylsilyloxyethyl ]-4-trimethylsilyloxy- azetizin-2-one ((3R,4R,5R)-form : (3S,4S,5R)-form = 5 : 1) into 12 ml of DMF, thereto 0.52 g of triethylamine and 0.79 g of tert-butyldimethylsilyl chloride were added and the mixture was stirred for 9 hours at room temperature. After the reaction was completed, DMF was distilled away under reduced pressure and thereto 30 ml of hexane was added. After the reaction mxiture was washed successively with 2.5 % aqueous solution of NaHCO3, aqueous solution of hydrochloric acid of pH 5 and saturated solution of salt, and was dried with magnesium sulfate, the solvent was distilled away to give 1.13 g of the liquid of the crude product. There was added 0.90 g of the obtained liquid to 10 ml of methylene chloride, thereto 0.79 g of dimethylaminopyridine and 0.61 ml of acetic anhydride were added and the mixture was reacted for 16 hours at 4 C. After the reaction mixture was washed successively with 5 % aqueous solution of NaHCO3, aqueous solution of hydrochloric acid of pH 5 and saturated solution of salt, and dried with magnesium sulfate, the solvent was distilled away to give 0.70 g of the liquid of the crude product. The obtained liquid was purified by a silicagel column-chromatography (hexane : ether = 100 : 3) to give 0.20 g of 4-acetoxy-l-tert-butyldimethylsilyl)-3 (1-isopropyldimethylsilyloxyethyl)azetizin-2-one as a liquid. There was added 0.20 g of the obtained liquid to 2 ml of THF, thereto 0.13 g of tetrabutylammonium fluoride and 0.03 g of acetic acid in 2 ml of THF was added and the mixture was stirred for 30 minutes at room temperature. There was added 60 ml of ethyl acetate to the reaction mixture and the mixture was washed successively with 5 % aqueous solution of NaHCO3 and saturated solution of salt, and dried with magnesium sulfate. The solvent was distilled away to give 0.14 g of the desired crude product ((3R,4R,5R)-form (3S,4S,SR)-form = 5 : 1). Recrystallization of the product from hexane gave 0.58 g of (3R,4R,5R)-form as white crystals. 1HNMR (90 MHz, CDC13) ((3R,4R,5R)-form) 8 (ppm): 0.04 (6H, s), 0.90 (7H), 1.23 C3H, d), 2.06 (3H, s), 3.13 (1H, dd), 4.13 (1H, m), 5.76 (lH, d) and 6.40 (NH) 25 o [a3D = +54.2 (C=0.5, CHCi3) mp: 920 to 940C

Claims: WHAT WE CLAIM IS: 1. A process for preparing 4-acetoxy-3hydroxyethylazetizin-2-one derivative having the general formula (II): EMI12.1 wherein R1 is a protective group for hydroxy group, which comprises reacting the ss-lactam compound having the general formula (I): EMI12.2 wherein RÚ is above, Rê, R and R4 are a lower alkyl group of C1 to C4, phenyl group or aralkyl group and R is a protective group for N, with acetic anhydride in the organic solvent in the presence of base and then removing the protective group for N. 2. The process of Claim 1, wherein R1 is the general formula (III): EMI12.3 wherein R5, R and R7 are a lower alkyl group of C1 to c4. 3. The process of Claim 1, wherein R1is t-butylmethylsilyl group. 4. The process of Claim 1, wherein R is isopropyldimethylsilyl group. 5. The process of Claim 1, wherein R is t-butylmethylsilyl group. 6. The process of Claim 1, wherein R2, R3 and R4 are methyl groups. 7. The process of Claim 1, wherein the base is dimethylaminopyridine. 8. The process of Claim 1, wherein the base comprises dimethylaminopyridine and other base. 9. The process of Claim 8, wherein the other base is pyridine, picoline or lutidine. 10. The process of Claim 1, wherein the organic solvent is halogenated hydrocarbon. 11. A process for preparing 4-acetoxy-3hydroxyethylazetizin-2-one having the general formula (II): EMI13.1 wherein R1 is a protective group for hydroxy group, which comprises reacting the compound having the general formula (I'): EMI13.2 wherein R1 is as above, R2, R3 and R4 are a lower alkyl group of C1 to C4, phenyl group or aralkyl group, with the reagent having the general formula R-X, wherein R is a protective group for N and X is a halogen atom, to form the compound having the general formula (I): EMI14.1 wherein R1, R2, R3 and R4 are as above, which is reacted with acetic anhydride in the organic solvent and in the presence of base, and then a protective group for N is removed.

Inventors: KAZUNORI, KAN, MIYAMA, AKIMASA, OHASHI, TAKEHISA, SADA, ISAO, WATANABE, KIYOSHI
Applicants: KANEGAFUCHI KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1985
Main classification: C07D205
IPC codes: C07D205, C07F7