NO161120B - INTERMEDIATE SUITABLE FOR PREPARING AN ANTI-BACTERIAL DIHYDRODYRODYROMYCIN DERIVATE. - Google Patents

Description

This invention relates to new intermediates for the production of 11-aza-10-deoxo-10-dihydroerythromycin A which is an antibacterial agent. In particular, the invention relates to N-hydroxy-11-aza-10-deoxo-10-dihydroerythromycin A-N'-oxide, N-methyl-11-aza-10-deoxo-10-dihydroerythromycin A bis-N-oxide and N-methyl -11-aza-10-deoxo-10-dihydroerythromycin A mono-N-oxide. Furthermore, methods for producing the intermediate products are described.

Erythromycin A is a macrolide antibiotic that is produced by fermentation and is described in US patent 2,653,899. Numerous derivatives of erythromycin A have been prepared in an attempt to modify its biological and/or pharmacodynamic properties. Erythromycin-A esters with mono- and dicarboxylic acids are described in Antibiotics Annual, 1953-1954, Proe. Symposium Antibiotics (Washington, DC), pages 500-513 and 514-521. US Patent 3,417,077 describes the cyclic carbonate ester of erythromycin A, the reaction product of erythromycin A and ethylene carbonate, as an active antibacterial agent.

US Patent 4,328,334, issued May 4, 1982, discloses 11-aza-10-deoxo-10-dihydroerythromycin A, and certain N-acyl and N-(4-substituted benzenesulfonyl) derivatives thereof with anti-bacterial properties , and a method for producing them.

The alkylation of primary and/or secondary amine groups in compounds containing a tertiary amine group is usually complicated. However, it is common practice to protect tertiary amine groups in such compounds by converting them to N-oxides prior to alkylation (Greene, "Protective Groups in Organic Synthesis", John Wiley & Sons, Inc., N.Y., 1981, p. 281).

The new compounds according to the invention have the formulas

II, III and III-A:

and represent valuable intermediates for the preparation of N-methyl-11-aza-10-deoxo-10-dihydroerythromycin A of formula I:

The compounds of formula I can be designated as N-methyl-11-aza-4-0-(L-cladinosyl)-6-0-(D-desosaminyl)-15-ethyl-7,13,14-trihydroxy-3,5 ,7,9,12,14-hexamethyloxacyclopentadecan-2-one. For reasons of simplicity, however, it is designated here as the N-methyl derivative of 11-aza-10-deoxo-10-dihydroerythromycin A, according to the nomenclature used in US patent 4,328,334.

The compound of formula II is designated similarly as N-hydroxy-11-aza-10-deoxo-10-dihydroerythromycin A-N<1>oxide,

with the term "N<1->oxide" referring to oxide formation on the dimethylamino group in the desosaminyl part. The alkylated compound of formula III is designated as N-methyl-11-aza-10-deoxo-10-dihydroerythromycin-bis-N-oxide. The stereochemistry of the 11-aza atom in formula II is not yet known. Formula III shall, however, be understood to include the diastereomers.

As an alternative to the above-mentioned nomenclature, the starting compound of formula IV can be designated below as 9-deoxo-9a-aza-9a-homoerythromycin A. Using this system, the compound of formula I is designated as 9-deoxo-9a-methyl-9a- aza-9a-homoerythromycin A.

The compound of formula I and pharmaceutically acceptable acid addition salts thereof are effective antibacterial agents against gram-positive microorganisms, e.g. Staphylococcus aureus and Streptococcus pyogenes, and against gram-negative microorganisms, e.g. Pasturella multocida and Neisseria sicca. Moreover, they exhibit significant activity against Haemophilus in vitro. The N-methyl derivative is superior to erythromycin A and ll-aza-10-deoxo-10-dihydroerythromycin A with regard to in vitro activity against Haemophilus.

The N-methyl derivative (formula I) surprisingly exhibits oral activity against gram-positive and gram-negative microorganisms. The N-methyl derivative of formula I exhibits significant oral in vivo activity, while practical oral in vivo activity is exhibited by 11-aza-10-deoxo-10-dihydroerythromycin A.

The N-methyl derivative of 11-aza-10-deoxo-10-dihydroerythromycin A (formula I) is prepared from 11-aza-10-deoxo-10-dihydroerythromycin A (formula IV) by the following reaction sequence, where the intermediates of formula II - III and III-A are utilized:

The oxidation of 11-aza-10-deoxo-10-dihydroerythromycin A is carried out in a reaction-inert solvent, i.e. one that does not react with reaction components or products to form unwanted substances, under the reaction conditions, using hydrogen peroxide or a peracid as oxidizing agent1

such as peracetic acid, perbenzoic acid, m-chloro-perbenzoic acid,

permaleic acid and perphthalic acid.

The choice of solvent will partly depend on

oxidizing agent used. When a water-soluble oxidizing agent such as hydrogen peroxide or peracetic acid is used,

a water-miscible solvent should be used. When oxidizing agents with low water solubility are used, e.g. perbenzoic acid or m-chloro-perbenzoic acid, an aqueous reaction mixture is usually avoided in order to maintain a reaction

mixture with a single phase.

Suitable solvents for use with the latter oxidizing agents are methylene chloride, chloroform, ethers, e.g.

dioxane, tetrahydrofuran.

The oxidation is carried out at ambient temperature, i.e. from approx. 18-25°C, for reaction periods of up to 24 hours. Excess oxidizing agent is used to ensure maximum conversion of 11-aza-10-deoxo-10-dihydroerythromycin A, the limiting reaction component. Usually used from approx. 1.0 mol to approx. 35 mol oxidizing agent per moles of said limiting reaction component. In practice, for economic reasons, from approx. 5 to approx. 15 mol oxidizing agent per moles of the limiting reaction component. Hydrogen peroxide is preferred as an oxidizing agent due to its availability. The amine oxide of formula II is isolated by extraction, followed by removal or destruction of excess oxidizing agent.

The thus prepared amine oxide of formula II is then alkylated by reaction with a suitable alkylating agent such as methyl iodide or bromide in a reaction-inert solvent

and in the presence of an acid acceptor. Representative reaction-inert solvents suitable for this step are methylene chloride, chloroform, tetrahydrofuran and toluene. Suitable acid acceptors

are inorganic bases such as alkali metal hydroxides and carbonates,

and organic amines such as hindered amine bases, e.g. 2,6-lutidine, the said substances being used in at least a stoichiometric amount based on the alkylating agent used.

The alkylating agents are generally used in amounts based on the amine oxide reaction component from equimolar to up to 100% excess.

When methyl iodide is used as alkylating agent, the alkylation reaction is suitably carried out at ambient temperature. Alkylation using methyl bromide is slow at ambient temperature and requires longer reaction times of several days.

When methyl bromide is used, elevated temperatures are preferred, e.g. up to 120°C, to accelerate the reaction.

An alternative alkylation method includes the use of

an inorganic base such as those mentioned above. The reaction conditions when dimethyl sulfate is used correspond to those mentioned above for the methyl halides.

The intermediates formed by alkylation of the compounds

with formula II is optionally isolated by standard methods such as evaporation of the reaction mixture followed by washing with water to remove inorganic salts. The reduction products (formula I) from these intermediates are also isolated by standard methods such as extraction.

It has been found that alkylation of the crude product from the oxidn

of IV leads to two products, namely the compound of formula III identified here as N-methyl-11-aza-10-deoxo-10-dihydroerythromycin A-bis-N-oxide (III), and the mono-oxide (III- A) where the oxide formation is on the desosaminyl nitrogen. Said compound is designated here as N-raethyl-11-aza-10-deoxo-10-dihydroerythromycin A-desosaminyl-N-oxide.

It is not necessary to purify the intermediate products described above before they are used in the subsequent steps of the process. They can be used in impure form, i.e. as they are after separation from the respective reaction mixtures. For practical and economic reasons, the intermediate products are usually not purified before they are used in the method according to the invention.

The third and last step of the reaction process, the reduction step, is carried out either catalytically or chemically on the crude product from the alkylation reaction, or on the individual, pure alkylated mono- and bis-oxides (HIA and III). Catalytic reduction is carried out at ambient temperature (e.g. 18-25°C),

at hydrogen pressure from approx. 1 to approx. 70 atmospheres in a reaction-inert solvent. Higher temperatures and pressures can be used, but offer no advantages.

Suitable catalysts are noble metal catalysts, preferably on a support, and certain salts thereof such as the oxides. Representative catalysts are Pd/C, Rh/C, PtO 2 and Raney nickel. The ratio between catalyst and substrate is not critical, but is usually in the range from 1:1 to 1:2.

Typical solvents for the reduction step are <C>j_4-alcohols, especially ethanol, ethyl acetate and ethers, e.g. tetrahydrofuran and dioxane.

In addition to the above-mentioned heterogeneous catalytic reduction, homogeneous catalysis can be used by e.g.

uses tris(triphenylphosphine)chlororhodium (I), known as the Wilkinson catalyst. Suitable solvents for this reaction are those mentioned above in connection with the heterogeneous catalysis process, and in which the homogeneous catalyst is soluble. The concentration of homogeneous catalyst is not critical, but for economic reasons is usually kept at amounts from approx. 0.01 mol% to approx. 10 mol% based on the substrate.

The hydrogen pressure is not critical, but for practical reasons

is usually in the range from approx. 1 to approx. 70 atmospheres.

Although the amounts of catalyst used are generally not considered "catalytic" in the normal sense of the word, in the above discussions of heterogeneous and homogeneous catalysis they are considered catalytic since little or no reaction would take place if they were absent.

The temperature during the catalytic reductions, heterogeneous or homogeneous, is not critical, but can vary from approx. 20 to approx. 100°C. The preferred temperature range is from 20 to 80°C.

Chemical reduction of the alkylated amine oxides (III-A and III) is achieved by means of metal hydrides such as sodium borohydride, sodium cyanoborohydride, pyridine-SO 3 /potassium iodide or zinc/glacial acetic acid.

Any further transformation of the compound with formula I as well as its effect and use is described in the parent application, 83.2616.

In the following examples, no attempt has been made to extract the maximum amount of the manufactured product or to optimize the yield of a given product. The examples only serve to illustrate the method and the products that can be obtained with it.

Example 1

N- hydroxy- ll- aza- 10- deoxo- 10- dlhydroerythromycin A- N'- oxide

(Formula II)

To a solution of 11-aza-10-deoxo-10-dihydroerythromycin A (10.0 g) in 40 ml of methanol, a total of 50 ml of 30% aqueous hydrogen peroxide was added dropwise with stirring over a period of 5-10 minutes. After stirring overnight at ambient temperature, the reaction mixture was poured onto a slurry of ice (200 g), ethyl acetate (200 ml) and water (100 ml). Excess hydrogen peroxide was eliminated by careful, dropwise addition of saturated aqueous sodium sulfite until a negative starch-iodine test was demonstrated. The layers were separated and the aqueous layer was washed twice with 200 mL portions of ethyl acetate. The three organic extracts were combined, dried over anhydrous sodium sulfate and evaporated to give crude N-hydroxy-11-aza-10-deoxo-10-dihydroerythromycin A-N'-oxide as a colorless foam (8.6 g). .

The crude product proved satisfactory for use by the preparative method described below, but purification could easily be accomplished by silica gel chromatography eluting with a methylene chloride:methanol:concentrated ammonium hydroxide system (12:1:0.1). The evolution of the column was followed by thin-screen chromatography on silica gel plates using the system methylene chloride:methanol:concentrated ammonium hydroxide (9:1:0.1). The plates were developed with a vanillin spray [ethanol (50 mL): 85% H 3 PO 4 (50 mL): vanillin (1.0 g)] indicator with heat.

1 H NMR (CDCl 3 ) 6 : 3.21 [6H, s, (CH 3 ) 2 N->O], 3.39 (3H, s,

cladinose CH30-).

MS: main peaks at m/e 576 (ion from desosamine cleavage),

418 (aglycon ion minus both sugars). Both peaks show

-N-OH part in aglycone.

in

In the same way, but by replacing hydrogen peroxide with an equivalent amount of peracetic acid, the same compound was prepared.

Example 2

N- methyl- ll- aza- 10- deoxo- 10- dihydroerythromycin- A- bls- N- oxide

(Formula III)

To a stirred mixture of N-hydroxy-11-aza-10-deoxo-10-dihydroerythromycin A-N'-oxide (4.83 g), methylene chloride (100 ml)

and solid anhydrous potassium carbonate (69.7 g) was added dropwise 15.7 ml (35.8 g) of iodomethane under nitrogen over 2 minutes. The mixture was stirred under nitrogen at ambient temperature

for 3.5 hours, and the solid that formed was collected by filtration. The filter cake was washed with methylene chloride (250 mL), the filtrate and washings were combined, water (300 mL) was added, and the pH of the vigorously stirred mixture was adjusted to 11. The organic phase was separated, dried over anhydrous sodium sulfate, and concentrated to give give the crude product as a colorless foam (4.36 g).

The crude product proved satisfactory for use in the reduction reaction described below, but purification could be readily accomplished by the technique well known as "flash" silica gel chromatography [W. Clark Still, et al., J. Org. Chem. 4_3, 2923

(1978)] using 230-400 mesh silica gel (silica gel/raw material approx. 45/1 by weight), elution being carried out by "flash" technique with acetone/methanol = 4/1 by volume. The 10 ml collected fractions which were shown to be pure bis-N-oxide by thin layer chromatography (TLC elution system: methylene chloride: methanol: concentrated ammonium hydroxide = 6:1:0.1; vanillin: 85% H3PO4: ethanol spray indicator applied with heat on silica gel plates) were collected. From 1 gram of crude product, 128 mg of pure bis oxide was obtained. <X>H NMR (CDC13) 6: 3.20 [9H, broad s, aglycone CH3-N->0 and (CH3)2-N->0], 3.39 (3H, s, cladinose CH30-) ;

MS: m/e 461 and 431, 415 (these two peaks show aglycone N-oxide),

159 (cladinos-derived fragment), 115 (desosamine-N-oxide-derived fragment).

The chromatographic method described above also gave a

second, less polar product from the crude product: N-methyl-11-aza-10-deoxo-10-dihydroerythromycin-A-desosaminyl-N-oxide (246 mg).

hi NMR (CDCl 3 ) 6 : 2.30 (3H, s, aglycone CH3~N-), 3.18 [6H, s, (CH3)2-N->0], 3.37 (3H, s, cladinos CH-jO-) ;

MS: main peaks at m/e 461, 156, 115.

Example 3 (Conversion to the compound of formula I)

N-methyl-II-aza-10-deoxo-10-dihydroerythromycin. A

A solution of the crude product from Example 2, comprising N-methyl-11-aza-10-deoxo-10-dihydroerythromycin A-desosarainyl-N-oxide and N-methyl-11-aza-10-deoxo-10-dihydroerythromycin A-bis -N-oxide (4.36 g) in 150 mL absolute ethanol was hydrogenated on a Parr apparatus (3.52 kg/m 2 , 8.0 g 10% palladium-on-charcoal catalyst; ambient temperature) in 1 1 /4 hours. The catalyst was filtered off and the resulting filtrate was evaporated to dryness to give a colorless foam (4.3 g). The crude product was taken up in methylene chloride (100 ml) and was then stirred with water (100 ml) while the pH of the mixture was adjusted to 8.8. The organic and aqueous layers were separated. The aqueous layer was then extracted twice with 50 mL portions of methylene chloride. The three organic extracts were combined, dried over anhydrous sodium sulfate and evaporated to give a colorless foam (3.0 g). The entire sample was dissolved in 11 ml of hot ethanol, and water was added until the solution became slightly cloudy. After standing overnight, 1.6 g of the title product crystallized from the solution;

sm.p. 136°C, decomposition. Recrystallization by the same method raised the melting point to 142°C, dec.

<1>H NMR (CDCl3 ) 6 2.31 [6H, s, (CH^N-], 2.34 (3H, s, aglycone

CH, -N-);

XJC NMR [CDC13, (CH3)4Si internal standard] ppm: 178.3 (lactone, C=0), 102.9 and 94.8 (C-3, C-5), 41.6 (aglycone CH3~N -), 40.3

t(CH3)2-N-];

MS: m/e 590, 432, 158.

Claims (1)

New compound, characterized by the formula: where or where n is 1 (III) or 0 (HIA).