Antibacterial penem esters derivatives

Abstract: Novel antibacterial penem esters are methyl (5R,6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]-penem-3-carboxylates having at the 3-position an ester group of the formula -COOR in which R represents -CH 2 OCO-Y or -CH 2 -Z in which Y is a tetrahydrofuryl group; a tetrahydropyranyl group; a 1,3-dioxolanyl group; a 2-oxo-1,3-dioxolanyl group; or a 1,4-dioxanyl group and Z is a 5-(C 6 -C 10 aryl or C 7 -C 11 aralkyl)-2-oxo-1,3-dioxolen-4-yl group. Other substituted-methyl (5R,6S)-6- [(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]-penem-3-carboxylates are disclosed.

Description: The present invention relates to penem compounds, and more specifically to penem compounds which are expected to find clinical utility as promising antibiotics. The present Inventors previously found that a group of penem compounds represented by the following formula (IV): wherein R 3 is a hydrogen atom or allyl group, -A- represents an oxygen or methylene group, and -B- represents a methylene, ethylene or carbonyl group, and their salts have excellent antibacterial activities on both gram-positive and gram-negative, aerobic or anaerobic bacteria (JP-A-207387/1986, corresponding to EP-A-0199446). High safety of these compounds has been confirmed by a safety test in which laboratory animals were used. Their development as medical drugs is now expected. In the meantime, it has been found by the study on the correlation between structure and antibacterial activities of these compounds [J. Antibiotics, 41, 1685 (1988)] that, among 2-substituents of penem, (R)-2-tetrahydrofuryl group provides the highest antibacterial activities while (S ) -2-tetrahydrofuryl group, a diastereomer at its 2-side chain group, and (R) or (S)-3-tetrahydrofuryl group, a position isomer, provide weaker activities particularly against gram-negative bacteria. From these reasons, compounds represented by the following formula (V): wherein R 4 represents a hydrogen atom or a group capable of forming a pharmaceutically-acceptable salt, have drawn interest as antibiotics. These compounds are also interesting in that they do not require any special chemical modification for oral absorption and they themselves can be developed as both injections and oral drugs. The bioavailability of the above-described compounds per se in laboratory animal (rats) has been found by no means inferior to commercial drugs which are used clinically. However, from the viewpoint of safety and economy, further enhancement of their bioavailability upon oral administration is apparently more advantageous. As far as the above compounds are concerned, there is yet room for further improvement in this regard. Regarding improvements on the absorption upon oral administration, active studies have been conducted on penicillin and cephalosporin antibiotics so that many of these antibiotics are used as curative medicines. There are, however, only a few study reports of this type on penem and carbapenem antibiotics [J. Antibiotics, 36, 938, (1983); JP-A-67287/1990]. There has therefore been interest in determining whether or not the approaches used for penicillin and cephalosporin antibiotics are equally applicable to penem compounds. GB-A-2206578 discloses the preparation of the penem compounds of formula (V) in which R 4 is hydrogen (and salts thereof) by enzymic hydrolysis of a compound corresponding to formula (V) in which R 4 is CHR' 3 OOCR' 4 , wherein R' 3 is hydrogen or C 1- 6 alkyl and R' 4 is hydrogen or C 1-18 alkyl, alkenyl, phenyl or phenylalkyl. EP-A-0295100 discloses that certain esters of [5R, 6S]-6-[(R)-1-hydroxyethyl)-2-methoxymethyl]-penem-3-carboxylic acid are prodrugs which are absorbed from the gastrointestinal tract after oral administration and subsequently hydrolysed in the bloodstream by aspecific serum esterases. Said esters include the 2-oxo-1,3-dioxolan-4-yl, (2-oxo-1,3-dioxolen-4-yl)methyl and 2-oxotetrahydrofuran-5-yl esters in which said dioxolanyl or dioxolenyl ring can be substituted in the 5-position by C 1-4 alkyl or phenyl and said tetrahydrofuryl ring can be substituted at the 4-position by C 1 -C 4 alkyl. The only two exemplified esters tested were the acetoxymethyl and 5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl esters and they are reported to have substantially the same oral bioavailability. Hans Bundgaard in Chapter 2 of "Bioreversible Carriers in Drug Design, Theory and Application (Ed. E.B. Roche, Pergamon Press, 1987, 13-16) discusses the use of esters as prodrugs for drugs having carboxyl, hydroxyl or thiol groups. Reference is made to acyloxyalkyl esters of β-lactam antibiotics, cromoglycic acid, isoguvacine, methyldopa and tyrosine. Reference also is made to the 5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl esters of methyldopa and "a similar ester type of ampicillin". The present Inventors have carried out an extensive investigation on the compounds (V) with a view toward making an improvement in their bioavailability. As a result, it has been found that protection of their carboxyl group with a particular ester-forming group can significantly improve their bioavailability. The present invention provides a penem compound represented by the following formula (I): wherein R represents a group of the general formula (II): -CH 2 OCO-Y in which Y represents a tetrahydrofuryl group. The penem compound (I) of the present invention can be synthesized, for example, by reacting a halogenated alkyl compound (VI) with a penem compound (V') in accordance with the following formula: wherein X represents a halogen atom, R 4 represents a hydrogen or alkali metal atom or an amino residuum, and R has the same meaning as defined above. When R 4 in the compound (V') is an alkali metal atom or an amino residuum in this invention, the target compound can be obtained by stirring the compound (V') and the halogenated alkyl compound (VI) in an organic solvent. When R 4 in the compound (V') is a hydrogen atom, on the other hand, it is first reacted with an alkali metal hydroxide, an alkali metal salt or an amine compound in an organic solvent to form a salt. The halogenated alkyl compound (VI) is then reacted with the reaction mixture, whereby the target compound is synthesized. The halogenated alkyl compound represented by the formula (VI) serves to efficiently esterify the carboxyl group of the compound (V') with the group R so that the target compound of the formula (I) is prepared. Compound (VI) includes those containing, as the group R, a tetrahydrofurylcarbonyloxymethyl group or its optically active isomer such as an (R)-2-tetrahydrofurylcarbonyloxymethyl group or an (S)-2-tetrahydrofurylcarbonyloxymethyl group and, as a halogen X, a chlorine, bromine or iodine atom. No particular limitation is imposed on the alkali metal insofar as it forms a salt with the compound (V'). Examples of the alkali metal include lithium, sodium and potassium. Examples of their hydroxides and salts include sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium carboxylate, potassium bicarbonate and potassium carbonate. Exemplary amine compounds include ammonia, triethylamine, and diisopropyl ethyl amine. No particular limitation is imposed on the reaction solvent. Examples of the reaction solvent include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as pentane and hexane, halogenated alkyls such as methylene chloride and chloroform, halogenated aryls such as chlorobenzenes, ketones such as acetone and methyl ethyl ketone, nitriles such as acetonitrile and propionitrile, amides such as dimethylformamide, sulfoxides such as dimethyl sulfoxide, ethers such as diethyl ether and tetrahydrofuran, and alcohols such as isopropanol and t-butanol. They can be used either singly or in combination. The reaction may be carried out at room temperure or, when desired, under heating at a temperature below 80°C. The reaction time is generally 1-48 hours although it varies depending on the halogenated alkyl compound to be used. As an alternative process for the preparation of the compound of this invention, the compound can also be synthesized by converting the compound of the formula (V) into its chloromethyl or iodomethyl ester in accordance with the process proposed by B. Balzer et al. [J. Antibiotics, 33, 1183 (1980)] and then reacting it with a carboxylate salt represented by the following formula (VII): Y-COOM wherein Y is as defined above and M is an alkali metal or an amino residuum. This reaction is carried out at a temperature in the range of from -40°C to room temperature, and is normally completed in 1-48 hours. The penem compound (I) obtained as described above may be used as is but, in general, is purified, as needed, by a method such as column chromatography or recrystallization for use as a medicine. For oral, parenteral or external administration, the compounds according to the present invention can be formulated as antibiotics in a manner known per se in the art. Although the dosage of each penem derivative of the present invention varies depending on many factors, the typical daily dosage ranges from 50 mg to 3 g for standard adults with the administration of 100 mg to 2 g in divided portions being preferred. In general, the above dosage will be administered in the form of a dosage unit which contains an appropriate amount of the active ingredient and a suitable, physiologically-acceptable carrier or extender. For oral administration, tablets or capsules can be used. They may contain- together with the active ingredient - an extender, e.g., lactose, glucose, sucrose, mannitol, sorbitol or cellulose, and a lubricant, e.g., talc, stearic acid or a stearate salt. Tablets may additionally contain a binder, for example, hydroxypropyl cellulose or starch. The compounds according to the present invention can be used not only for men but also for animals. The present invention will hereinafter be described more specifically by the following Examples. Example 1 (Intermediate Compound Preparation) Chloromethyl (5R,6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 5): To a mixture of sodium (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate 2.5 hydrate (Compound 1, 24.7 g), tetrabutylammonium sulfate (2.38 g) and potassium bicarbonate (21.0 g), water (70 ml) and methylene chloride (70 ml) were added. Into the resultant mixture, a solution of chloromethyl chlorosulfate (11.5 g) diluted in methylene chloride (280 ml) was added dropwise over about 10 minutes under ice cooling and stirring. After the reaction mixture was stirred for additional 2.5 hours at room temperature, the organic layer was collected and washed with water. The organic layer was dried and then concentrated. The residue so obtained was purified by passing it through a silica gel column. The title compound was obtained in the amount of 9.92 g. Example 2 (Intermediate Compound Preparation) Iodomethyl (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 6): A mixture of chloromethyl (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 5, 334 mg), sodium iodide (225 mg) and acetone (2 ml) was stirred over night at room temperature, and the reaction mixture was concentrated. Ethyl acetate was added to the residue. The resultant solution was washed with water, dried, and then concentrated, whereby 359 mg of the title compound were obtained. Example 3 (Comparative Compound Preparation) [5-(allyloxy)glutaryl]oxymethyl (5R,6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 2): A mixture of iodomethyl (5R,6S)-6-[(R)-1- hydroxyethyl] -2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 6, 3.4 g), sodium monoallyl-glutarate (3.83 g) and N,N-dimethylformamide (20 ml) was allowed to stand overnight at -20°C. The reaction mixture was then diluted with ethyl ether and washed with water. The organic layer was dried and then concentrated. The residue was purified by passing it through a silica gel column, whereby 0.553 g of the title compound was obtained. Example 4 (R)-2-tetrahydrofurylcarbonyloxymethyl (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl] penem-3-carboxylate (Compound 3): A mixture of iodomethyl (5R, 6S)-6-[(R)-1- hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 6, 3.4 g), (R)-tetrahydro-2-furoic acid sodium salt (1.38 g) and N,N-dimethylformamide (20 ml) was stirred for 2 hours at room temperature. The reaction mixture was diluted with ethyl ether and then washed with water. The organic layer was dried and concentrated. The residue was purified by passing it through a silica gel column, whereby 0.72 g of the title compound was obtained. Example 5 (S)-2-Tetrahydrofurylcarbonyloxymethyl (5R,6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]-penem-3-carboxylate (Compound 4): A mixture of iodomethyl (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 6, 3.4 g), (S)-tetrahydro-2-furoic acid sodium salt (1.38 g) and N,N-dimethylformamide (20 ml) was stirred for 2 hours at room temperature. The reaction mixture was diluted with ethyl ether, followed by washing with water. The organic layer was dried and then concentrated. The residue was purified by passing it through a silica gel column, whereby 0.92 g of the title compound was obtained. Physical properties of the compounds synthesized in Examples 2-6 are summarized in Table 1. Example 6 The bioavailability of Compounds 3 and 4 of the present invention was compared with that of Compound 2 and with sodium [5R, 6S]-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]penem-3-carboxylate (Compound 1) relying upon their recovery rates in urine. Each test compound (30 µmole/kg) was orally administered to SD strain rats (three male rats per group). Urine was collected over 6 hours from the administration, and the recovery rate of the corresponding compound present in the urine was determined by bioassay. The results are shown below. As is apparent from the results, the Compounds 3 and 4 of the present invention showed a higher urinary recovery rate, in other words, a higher bioavailability, compared with the Compounds 1 and 2. Preparation Examples Preparation 1 Capsules Ingredient No. Ingredient mg/capsule 1 Invention compound 150 2 Lactose 20 3 Magnesium stearate 4 (Total) 174 mg (Production procedures) Ingredients 1 and 2 were combined together in a suitable mixer, to which Ingredient 3 was added, followed by further mixing. The resultant mixture was filled into capsules by a capsule filling machine. Preparation 2 Tablets Inqredient No. Ingredient mg/tablet 1 Invention compound 150 2 Crystalline cellulose 50 3 Calcium carboxymethylcellulose 10 4 Magnesium stearate 4 (Total) 214 mg (Production procedures) Ingredients 1-3 were combined together in a suitable mixer, to which Ingredient 4 was added, followed by mixing for additional several minutes. The resultant mixture was compressed into tablets of a predetermined size and weight by a tableting machine.

Claims: A penem compound represented by the following formula (I): wherein R represents a group of the general formula (II): -CH 2 OCO-Y in which Y represents a tetrahydrofuryl group. A compound according to Claim 1, wherein Y represents an (R)-2(R)-2-tetrahydrofuryl group. A compound according to Claim 1, wherein Y represents a (S)-2(S)-2-tetrahydrofuryl group. A compound according to Claim 1, wherein R is an optically active group. The compound of Claim 1, which is (R)-2-tetrahydrofurylcarbonyloxymethyl (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]-penem-3-carboxylate. The compound of Claim 1, which is (S)-2-tetrahydrofurylcarbonyloxymethyl (5R, 6S)-6-[(R)-1-hydroxyethyl]-2-[(R)-2-tetrahydrofuryl]-penem-3-carboxylate. An antibiotic composition, comprising an effective amount of a compound of formula (I) as defined in Claim 1 and a pharmaceutically-acceptable carrier. A composition according to Claim 7, wherein said compound is as defined in any one of Claims 2 to 6. A composition according to Claim 7 or Claim 8 for oral administration. A penem compound according to any one of Claims 1 to 6 for use in the treatment of bacterial infections in the human or animal body. The use of a penem compound according to any one of Claims 1 to 6 in the manufacture of an antibiotic medicament. A method of preparing a penem compound as defined in Claim 1 which comprises: (a) reacting a penem compound of the following formula (V') wherein R 4 represents an alkali metal atom or an amino residuum with an halogenated compound of the following formula (VI) RX wherein R is as defined in Claim 1 and X is halogen. or (b) reacting a penem compound of the following formula (V") wherein R 4 ' represents -CH 2 X' in which X' is chloride or iodine with a salt of the following formula (VII) Y - COOM wherein Y is as defined in Claim 1 and M is an alkali metal atom or an amino residuum.

Inventors: ISHIGURO MASAJI, IWATA HIROMITSU, NAKATSUKA TAKASHI, TANAKA RIE, ISHIGURO, MASAJI, IWATA, HIROMITSU, NAKATSUKA, TAKASHI, TANAKA, RIE
Applicants: DAIICHI SUNTORY PHARMA CO LTD, DAIICHI SUNTORY PHARMA CO., LTD.
Application year: 1991
Main classification: C07D499
IPC codes: C07D499, A61K31, A61P31