NO173654B - ANALOGUE PROCEDURE FOR THE PREPARATION OF THERAPEUTIC ACTIVE DIASTEREOMERS 5R, 6S-6- (1R-HYDROXYTHYL) -2- (CIS-1-OXO-3-THIOLANYLTIO) -2-PENEM-3-CARBOXYL ACID - Google Patents

Description

Background for the invention

The present invention relates to a method for the preparation of antibacterial compounds which are diastereomeric 5R,6S-6-(1R-hydroxyethyl)-2-(cis-1-oxo-3-thiolanylthio)-2-penem-3-carboxylic acids, i.e. 2 -(1R-oxo-3S-thiolanylthio)-variant of the formula (II) indicated below; and the pharmaceutically acceptable salts and in vivo hydrolyzable esters thereof.

Antibacterial 5R,6S-6-(1R-hydroxyethyl)-2-(cis-1-oxo-3-thiolanylthio)-2-penem-3-carboxylic acid which is a diastereomeric mixture of two compounds, has previously been discussed as a valuable antibacterial substance, by Hamanaka, US Patent 4,619,924 and European Patent Application 130,025. Although they have been able to be detected analytically, the pure diastereomeric compounds with the given structure have so far not been available. Disclosure of an improved process for the preparation of the diastereomeric mixture from racemic cis-3-(acetylthio)thiolane-1-oxide, which makes use of mixed diastereomeric intermediates which are otherwise analogous to those now used, will be found in a European patent application by Volkmann et al., calculated published on May 27, 1987 under No. 223,397.

With respect to the present optically active precursors, Brown et al., J. Am. Chem. Soc., vol. 108, pp. 2049-2054

(1986) described the synthesis of (S)-3-hydroxythiolane [mistakenly shown as the (R)-isomer, but in reality with the reverse configuration of the present (R)-3-hydroxythiolane of formula (XI) below] by asymmetric hydroboration of 2,3-dihydrothiophene. Partial Enzymatic Oxidation of Racemic 3-Hydroxythiolane by Jones et al., Can. J. Chem., vol. 59, pp. 1574-1579 (1981) made it possible to recover 3-hydroxythiolane containing a slight excess of the (R)-isomer. Present optically active precursor (R)-(2-methanesulfonyloxyethyl)oxirane [with the formula (XIII) indicated below where R<9> = CH3] and (S)-2-bromo-1,4-di-(methanesulfonyloxy)butane [with the formula Xa given below, where R<8> = CH3] are known compounds both of which can be prepared according to Shibata et al., Heterocycles, vol. 24, pp. 1331-1346 (1986); the former also according to Boger et al., J. Org. Chem., vol. 46, pp. 1208-1210 (1981).

According to the invention, a method is provided for the preparation of the diastereomeric penem compound 5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-3-carboxylates with the absolute stereochemical formula

where R is hydrogen or pivaloyloxymethyl; and the pharmaceutically acceptable cationic salts thereof when R is hydrogen.

Said pharmaceutically acceptable cationic salts include, but are not limited to, salts of sodium, potassium, calcium, N,N'-dibenzylethylenediamine, N-methylglycamine (meglumine) and diethanolamine. Preferred are cationic salts of potassium and sodium.

The method according to the present invention is characterized by

(a) when R is hydrogen, reaction of a compound of formula

where X is hydrogen or chlorine, with at least one equivalent of an alkali metal salt of 2-ethylhexanoic acid in a reaction-inert solvent in the presence of triphenylphosphine and tetrakis(tri-

phenylphosphine) palladium, and optionally converting the compound produced into a salt; or

(b) when R is pivaloyloxymethyl, reaction with a cationic salt of a compound of formula

where R<6> is a silyl hydroxy protecting group, with an organic chloride or bromide derivative of the radical R, and removal of the protecting group R<6> in a known manner.

In this context, the term "reaction-inert solvent" refers to a solvent that does not react with starting materials, reagents, intermediates or products in a manner that adversely affects the yield of the desired product.

The pure diastereomeric, antibacterial compounds of formula (II) are tested, formulated and used according to methods described in more detail in the above-mentioned US patent 4,619,924 (Hamanaka). Within the human medical dosage ranges described there, the preferred dosage range for the new compounds (II) is 10-80 mg/kg/day both orally and parenterally. The figures only serve as an illustration, as treating physicians will sometimes find it more advantageous to use dosages outside these ranges. In vivo hydrolyzable esters, especially the pivaloyloxymethyl and 1-(ethoxycarbonyloxy)ethyl esters are preferred for oral use, while sodium- or the potassium salts are particularly preferred for parenteral use.

The following examples are given by way of illustration.

Example 1

a) Sodium- 3S-( thio( thiocarbonyl) thio) thiolane- 1R- oxide ( Villa, M<* >= Na<+>)

In a flame-dried flask, a solution of 1.78 g

(10 mmol) 3S-(acetylthio)thiolane-1R-oxide in 6 ml of ethanol under nitrogen cooled to -5°C. Sodium ethoxide (21% by weight in ethanol, 3.73 mL, 10 mmol) was added and the mixture stirred at

-5°C for 30 minutes, then cooled to -20°C, whereupon 3.0 mL (50 mmol) of carbon disulfide was added and stirring continued for 30 minutes. To this was added 75 ml of anhydrous tetrahydrofuran. The resulting mixture was stirred for a few minutes, seeded with crystals of the title compound, cooled and kept at 15°C and stirred until crystallization was complete. The mixture was filtered, washed with cold tetrahydrofuran and then with ethyl ether. The resulting crystals were air-dried under nitrogen to give 2.10 g of the title product solvated with 0.5 molar equivalents of tetrahydrofuran. A further 592 mg was recovered by working up the mother liquor; m.p. 120-121°C (decomp.), blackens at 155-156°C; [o]D = -79.52° (c = 0.05, in H 2 O). b) 3S,4R-3-[1R-1-(dimethyl-t-butylsilyloxy)ethyl]-4-[1R-oxo-3S-thiolanylthio(thiocarbonvl)thiol-2-azetidinone (VI. R<7>=H ,

R<6>=Me2tBuSi)

In a flame-dried flask, a solution of 3R,4R-4-acetoxy-3-[IR-(dimethyl-t-butylsilyloxy)ethyl]-2-azetidinone [1.87 g, 6.5 mmol; Leanza et al., Tetrahedron 39, pp. 2505-2513

(1983)] in 20 mL of isopropyl alcohol and CS2 (0.15 mL, 2.5 mmol) combined under nitrogen and cooled to 3°C. The product from step a) (1.36 g, 5 mmol) was added portionwise during which the temperature was kept at 3°C. After 0.5 hours at 3°C, the reaction was quenched with 40 ml of saturated ammonium chloride solution and the mixture then added with 50 ml of ethyl acetate. The organic layer was separated and the aqueous layer extracted with an additional 2 x 25 mL of ethyl acetate. The combined ethyl acetate layers were washed 2 x 20 mL H 2 O and 2 x 20 mL 20% CaCl 2 , dried over MgSOA, filtered and concentrated in vacuo to give the crude title product, 3.04 g. The latter was dissolved in ca. 2 ml of acetone and isopropyl ether added dropwise until precipitation of solids started, after which the mixture was stirred for 1 hour and then, while stirring, quickly added 120 ml of petroleum ether. The resulting solid was filtered off, air dried, then dried in vacuo and finally chromatographed on silica gel using 19:1 ethyl acetate:methanol as eluent to give 1.35 g (61%) of purified title product. Recrystallization from 4 ml of acetone following the same procedure gave 1.15 g of product; [a]D = +109.36°

(c = 0.20, CHCl3) , pnmr (CDC13) (delta) (ppm) 300 MHz: 0.05 (s, 3H) , 0.86 (s, 9H) , 1.18 (s, 3H) , 1.74 (s, 2H), 2.68 (m, 3H), 2.82 (m, 1H), 3.17 (m, 2H), 3.74 (q, 1H), 4.25 (t , 1H), 4.52 (t, 1H), 5.61 (s, 1H), 6.52 (s, 1H), 7.20 (s, 1H).

c) 3S,4R-N-[(2-chloroallyloxy)oxalyl]-3-[1R-(dimethyl-t-butylsilyl-oxy)ethyl]-4-[1R-oxo-3S-thiolanylthio(thiocarbonyl)-thiol- 2- azetidinone (VI. R6=Me, tBuSi, R7=C0C00CH, CC1CH,)

To a flame-dried, three-necked flask fitted with a dropping funnel and a low-temperature thermometer was added, under a N2 atmosphere, the product from step b) (878 mg, 2 mmol) and 15 mL of dry methylene chloride (passed through neutral

aluminum oxide). The reaction mixture was cooled to -50° more

-55°C internal temperature and added N,N-diisopropylethylamine (0.45 ml, 2.6 mmol), during which the temperature was kept lower than 50°C. Then 2-chloroallyl oxalofluoride (0.34 mL, 2.6 mmol) was added as quickly as possible, during which the temperature was again kept below 50°C, and the reaction mixture was stirred for another 50 min at -50° to - 55°C. The reaction was quenched with 15 ml of H 2 O, after which the mixture was allowed to warm to 0°C and was diluted with 20 ml of fresh CH 2 Cl 2 . The organic layer was separated, washed 1 x 15 ml H2O, 1 x 20 ml pH 7 buffer and 1 x 25 ml saturated NaCl, dried over MgSOA, filtered and concentrated in

vacuum to give 1.05 g of the title product as a yellow foam, which was used in its entirety directly in the next step.

d) 2-chloroallyl-5R,6S-6-[1R-(dimethyl-t-butylsilyloxy)ethyl]-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylate

(IV, RA=Me, tBuSi, R5=CH, CC1CH-,)

To a flame-dried, three-necked flask fitted with a condenser and an equalizing dropping funnel, under a N 2 atmosphere, was added the product from tin (c) (1.05 g, 2 mmol) and 80 mL of ethanol-free chloroform. The reaction mixture was heated to gentle reflux and triethyl phosphite (0.74 mL, 48 mmol) in 10 mL of ethanol-free chloroform was added dropwise over 10 h. The mixture was kept under gentle reflux for another 10 hours. The reaction mixture was cooled to room temperature and concentrated in vacuo. The residue was dissolved in 5 ml of ethyl acetate. Isopropyl ether (40 ml) was added dropwise with stirring from the start of crystallization. Finally, 40 ml of petroleum ether was added dropwise, the mixture filtered and the solid dried to give 0.47 g (44%) of product; m.p. 140-141°C; [α]D = +36.78° (c = 0.5, CHCl 3 ).

e) 2-chloroallyl-5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxvlate ( IV, R<4>=H, R5=CH , CC1CH,')

To a flame-dried three-necked flask fitted with a thermometer and two dropping funnels under N 2 atmosphere was added the product from step d) (0.25 g, 0.46 mmol) and 0.5 mL of dry tetrahydrofuran. To the stirred reaction mixture was added glacial acetic acid (0.26 mL, 4.6 mmol), followed by tetrabutylammonium fluoride in tetrahydrofuran (1 M, 1.38 mL). The resulting solution was stirred for 16 hours at room temperature, diluted with 15 ml of ethyl acetate and 4 ml of water, pH adjusted to 6.4 with potassium acetate, the layers separated and the organic layer washed 3 x 3 ml of water. The latter were combined and extracted 3 x 3 mL CH 2 Cl 2 . The combined organic layers (ethyl acetate and CH 2 Cl 2 ) were dried over Na 2 SO 4 , filtered and concentrated in vacuo to give a crude product, 0.46 g. The crude product was taken up in 25 mL ethyl acetate and washed 3 x 6 mL H 2 O. The organic layer was dried over Na 2 SO 4 , filtered and evaporated to give purified title product, 88 mg; m.p. 177-178°C; [a]D = +45.28° (c = 0.25 in dimethylsulfoxide).

f) Sodium 5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylate (II, R=Na)

To a flame-dried flask wrapped in aluminum foil, under N2 was added the product from step e) (3.60 g, 8.5 mmol) in 115 mL of degassed CH2Cl2, whereupon triphenylphosphine (0.72 g, 2.75 mmol), sodium-2- ethyl hexanoate (6.72 mL of 1.39M in ethyl acetate,

9.34 mmol) and tetrakis(triphenylphosphine)palladium (0.72 g,

0.62 mmol) was added. The reaction mixture was stirred at room temperature for 50 minutes, after which 72 mg each of triphenylphosphine and tetrakis(triphenylphosphine)palladium were added and the reaction mixture stirred at room temperature for another 20 minutes. HPLC grade ethyl acetate (150 mL) was added to the reaction mixture over 15 minutes. The reaction mixture was filtered and the solid air dried to give the crude product, 4.97 g. The latter was slurried with 45 ml of ethyl acetate for 45 minutes, filtered and dried to give 3.96 g of the still crude product. The latter was taken up in 70 ml of water, treated with activated charcoal, filtered and the filtrate freeze-dried to give the title product, 2.63 g.

Example 2

5R,6S-6-(1R-1-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylic acid ( II. R = H)

The sodium salt from the previous example (2.63 g) was dissolved in 8 ml of H 2 O and cooled to 0-5°C. The pH was adjusted to 2.45 with IN HCl as the product began to crystallize. The mixture was stirred at 0-5°C for 45 minutes, filtered, washed with a little H 2 O and dried to give 2.16 g of the title product as a white solid; m.p. 135°C (decomp.); [a]D = +366.01° (c =

1 in dimethylsulfoxide).

Example 3

Sterile sodium 5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylate (II. R = Na)

The product from the previous example (1.95 g) was suspended in 60 ml of H 2 O and cooled to 0-5°C. Maintaining the same temperature range and with vigorous stirring, the pH was adjusted from 2.98 to a constant pH of 6.00 by dropwise addition of NaOH (4.2 mL of IN, then 10.75 mL of 0.1N). The solution was millipore-filtered into a sterile flask and lyophilized (if desired, lyophilized after aliquoting to obtain the desired dosage in sterile vials) to obtain the sterile title product, 1.926 g, which, if not already aliquoted, can be dispensed into ampoules of the desired dosage level. This purified product has m.p. 158°C (decomp.); [a]D = +81.31° (c =1

in H2O).

For parenteral dosing, dissolve the sterile sodium salt in sterile water for injection.

Example 4

a) Tetrabutylammonium-5R,6S-6-[IR-(dimethyl-t-butylsilyloxy)-ethyl]-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylate ( IV . R4=Me, tBuSi.R5=TBA- salt)

The product from Example ld) (0.80 g, 1.5 mmol) was reacted according to the procedure in Example lf) to form the intermediate sodium salt in situ. The reaction mixture was diluted with 35 ml ethyl acetate and 4 ml ether, washed 3 x 10 ml H 2 O, and the organic layer was further diluted with 35 ml hexane, and finally washed 3 x 20 ml H 2 O. The 6 aqueous layers were combined and then tetrabutylammonium hydrogen sulfate (0.51 g, 1.5 mmol) and NaHCO 3 ) (0.25 g, 3 mmol) in 5 mL H 2 O were added. After stirring for 15 minutes and salting out with Na 2 SO 4 , the desired product was extracted into CH 2 Cl 2 (3 x 90 mL), dried (Na 2 SO 2 , treated with activated carbon, filtered and concentrated in vacuo to give the title product, 0.80 g; pnmr (CDC13) delta (ppm) 300 MHz: 0.05 (s, 6H), 0.85 (s, 9H), 0.99 (t, 12H), 1.28 (d, 3H), 1.30 -1.50 (m, 8H), 1.50-1.70 (m, 8H), 2.50-2.82 (m, 4H), 2.96-3.10 (m, 1H), 3 .05-3.42 (t, 8H), 3.45-3.62 (m, 2H), 3.80-3.92 (m, 1H), 4.05-4.18 (m, 1H) , 5.42 (s, 1H) .

b) Pivaloyloxymethyl-5R,6S-6-[1R-(dimethyl-t-butylsilyloxy)-ethyl]-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylate

(IV, RA=Me2 tBuSi , R5=CH,- C— CO- C f CH,),

In flame-dried glass equipment, the product from step a)

(0.80 g, 1.13 mmol) dissolved under N2 in 11 mL of acetone. Chloromethyl pivalate (0.25 mL, 1.71 mmol) was added and the mixture stirred for 16 h at room temperature, evaporated in vacuo, and finally

under high vacuum, to give the title product, 1.05 g; pnmr (CDC13) delta (ppm) 300 MHz: 0.05 (s, 6H), 0.88 (s, 9H), 1.20 (s, 9H), 1.24 (d, 3H), 2.4 -2.6 (m, 4H), 3.05-3.12 (m, 1H), 3.6-3.90 (m, 3H), 4.15-4.28 (m, 1H), 5 .59 (s, 1H) , 5.81 (q, 2H, Jab =

12.5 Hz).

Alternatively, the title product can be prepared stepwise according to the procedures in Example lc-e) using equivalent amounts of pivaloyloxymethyl oxalofluoride instead of 2-chloroallyl oxalofluoride in Example lc).

c) Pivaloyloxymethyl-5R,6S-6-[(1R-hydroxyethyl-2-(1R-oxo-3S- thiolanylthio)- 2- penem- 3- carboxyvlate ( II, R=CH,- 0- CC— C ( CH ,) 3)

Following the procedure in Example le), the product from the preceding step b) (0.40 g, 0.69 mmol) was converted into the present title product. For isolation, the reaction mixture was diluted with 45 mL of ethyl acetate and washed with 4 x 9 mL of H 2 O. The washings were combined and extracted with 3 x 9 ml of ethyl acetate. The organic layers were combined, washed with 2 x 9 ml saturated NaCl, dried, filtered and concentrated in vacuo, finally under high vacuum, to give the crude product > 0.28 g. The latter was flash chromatographed on a 40 mm x 25 cm column of silica gel, first eluting with 1:9 ethyl acetate:tetrahydrofuran (50 ml fractions 1-10) and then with 50 ml fractions tetrahydrofuran. Fractions 18-44 were combined, evaporated to dryness and the residue stirred with 70 ml of ethyl acetate and filtered to give purified title product, 0.193 g; pnmr (CDC13) delta (ppm) 300 MHz: 1.18 (s, 9H), 1.29 (d, 3H, J=6.3Hz), 2.12 (bs, 1H), 2.6-2, 9 (m, 4Hz), 3.1-3.2 (m, 1H), 3.6-3.90 (m, 3H), 4.20-4.32 (m, 1H), 5.64 ( s, 1H), 5.76 (q, 2H, JAB=12 , 5Hz).

Claims (1)

Analogy method for the preparation of a therapeutic active penem with the absolute stereochemical formula where R is hydrogen or pivaloyloxymethyl; or a pharmaceutically acceptable cationic salt thereof when R is hydrogen, characterized by (a) when R is hydrogen, reacting a compound with formula where X is hydrogen or chlorine, with at least one equivalent of an alkali metal salt of 2-ethylhexanoic acid in a reaction-inert solvent in the presence of triphenylphosphine and tetrakis(triphenylphosphine)palladium, and optionally converting the compound produced into a salt; or (b) when R is pivaloyloxymethyl, reaction of et > .icionic salt of a compound of formula where R<6> is a silyl hydroxy protecting group, with an organic chloride or bromide derivative of the radical R, and removal of the protecting group R<6> in a known manner.