Process for Producing 20-Dihydro-20-Deoxy-23-Demycinosyltylosin

This invention relates to 20-dihydro-20-deoxy-23-demycinosyltylosin, and to 20-dihydro-20-deoxy-5-O-mycaminosyltylonolide, two new macrolide antibiotics. 20-Dihydro-20-deoxy-23-demycinosyltylosin, which will be called DH-DO-DMT for convenience herein, has structure 1: ##STR1## Although no stereochemical assignments are indicated in the structures given herein, the stereochemistry of the compounds is identical to that of tylosin. The neutral sugar in structure 1 is mycarose, and the amino-sugar in 1 is mycaminose.

20-Dihydro-20-deoxy-5-O-mycaminosyltylonolide, which will be called DH-DO-OMT for convenience herein, has structure 2: ##STR2##

DH-DO-DMT and DH-DO-OMT inhibit the growth of organisms which are pathogenic to animals. More specifically, DH-DO-DMT and DH-DO-OMT are antibacterial agents which are active against gram-positive microorganisms and Mycoplasma species.

DH-DO-DMT can be esterified on the 2', 4", 3", 23 and 3-hydroxyl groups and DH-DO-OMT can be esterified on the 2', 4', 23 and 3-hydroxyl groups to form useful acyl ester derivatives. Esterification of the 2'- and 4'-hydroxyl groups is most facile. Typical esters are those of a monocarboxylic acid or hemi-esters of a dicarboxylic acid having from 2 to 18 carbon atoms.

DH-DO-DMT, DH-DO-OMT and their acyl ester derivatives are basic compounds which, when treated with acids, are converted to acid addition salts. These acid addition salts are also part of this invention.

This invention further relates to a new microorganism which has been classified as a strain of Streptomyces fradiae and to the method of producing DH-DO-DMT or DH-DO-OMT by culturing this strain under submerged aerobic fermentation conditions until a substantial level of antibiotic activity is produced. DH-DO-DMT and DH-DO-OMT can be extracted from basified broth filtrate with polar organic solvents, and can be further purified by extraction, chromatographic and/or crystallization techniques.

This invention also relates to a method of preparing DH-DO-OMT by mild acid hydrolysis of DH-DO-DMT.

The infrared absorption spectra of DH-DO-DMT (free base) and DH-DO-OMT (free base) in chloroform are presented in the accompanying drawings as follows:

FIG. 1--DH-DO-DMT

FIG. 2--DH-DO-OMT

The following paragraphs describe the properties of DH-DO-DMT and DH-DO-OMT.

The structure of DH-DO-DMT is shown in formula 1.

DH-DO-DMT is a white crystalline solid with a melting point of about 198.degree.-200.degree. C. DH-DO-DMT has the following approximate percentage elemental composition: carbon, 63%; hydrogen, 9%; nitrogen, 2%; oxygen, 26%. DH-DO-DMT has an empirical formula of C.sub.38 H.sub.65 NO.sub.12 and a molecular weight of about 728 (727 as determined by field-desorption mass spectrometry).

The infrared absorption spectrum of DH-DO-DMT free base in chloroform is shown in FIG. 1 of the accompanying drawings. Observable absorption maxima occur at the following frequencies (cm.sup.-1): 3676 (small), 3598 (small), 3470 (large broad), 3010 (intense), 2974 (intense), 2938 (intense), 2925 (shoulder), 2880 (intense), 2799 (small), 2457 (small broad), 1715 (intense), 1676 (medium), 1629 (small), 1595 (very intense), 1456 (intense), 1411 (intense), 1380 (intense), 1363 (shoulder), 1315 (intense), 1273 (small), 1263 (shoulder), 1220 (small broad), 1184 (intense), 1162 (intense), 1144 (small), 1117 (medium), 1096 (shoulder), 1076 (intense/shoulder), 1050 (very intense), 1015 (intense), 997 (medium), 986 (medium), 958 (medium), 923 (medium) 905 (medium), 867 (small), 842 (medium), 720 (broad) and 660 (small).

The ultraviolet absorption spectrum of DH-DO-DMT in 95% neutral ethanol exhibits an absorption maximum at 283 nm (.epsilon.21,800).

DH-DO-DMT (free base) has the following specific rotation: [.alpha.].sub.D.sup.25 =46.3.degree. (c 3.3, CH.sub.3 OH).

DH-DO-OMT is a white crystalline solid with a melting point of about 214.degree.-217.degree. C. DH-DO-OMT has the following approximate percentage elemental composition: carbon, 64%; hydrogen, 9%; nitrogen, 2.5%; oxygen, 24.5%. DH-DO-OMT has an empirical formula of C.sub.31 H.sub.53 NO.sub.9 and a molecular weight of about 584 (583 by field-desorption mass spectrometry).

The infrared absorption spectrum of DH-DO-OMT free base in chloroform is shown in FIG. 2 of the accompanying drawings. Observable absorption maxima occur at the following frequencies (cm.sup.-1): 3677 (very small), 3601 (small), 3422 (broad), 3006 (intense), 2971 (intense), 2937 (intense), 2879 (intense), 2798 (small), 1714 (intense), 1677 (intense), 1627 (small), 1593 (very intense), 1457 (intense), 1407 (small), 1382 (medium), 1362 (shoulder), 1315 (medium), 1269 (small), 1181 (very intense), 1141 (small), 1115 (small), 1181 (very intense), 1141 (small), 1115 (small), 1079 and 1058 (intense, doublet), 1008 (medium), 983 (medium), 923 (small), 903 (small), 865 (small), 835 (small), 712 (broad), 658 (small) and 629 (small).

The ultraviolet absorption spectrum of DH-DO-OMT in 95% neutral ethanol exhibits an absorption maximum at 282 nm (.epsilon.22,400).

DH-DO-OMT (free base) has the following specific rotation: [.alpha.].sub.D.sup.25 -7.35 (c 6, CH.sub.3 OH).

The .sup.1 H nuclear magnetic resonance (NMR) data at 360 MHz for DH-DO-OMT (free base) in CDCl.sub.3 are summarized in Table 1.

DH-DO-DMT and DH-DO-OMT as free bases are soluble in water and in most polar organic solvents such as acetone, methanol, ethanol, chloroform, dimethylformamide and dimethyl sulfoxide. Acid addition salts of DH-DO-DMT and DH-DO-OMT are more soluble in water than are the free bases.

DH-DO-DMT and DH-DO-OMT can be distinguished by thin-layer chromatography (TLC). The approximate Rf values of DH-DO-DMT and DH-DO-OMT in one TLC system are summarized in Table 2. Ultraviolet absorption was used for detection.

This invention also relates to a method of preparing DH-DO-OMT by mild acid hydrolysis of DH-DO-DMT. Mild acid hydrolysis conditions are known in the art. Appropriate solutions having a pH of about four or below can be used to accomplish the hydrolysis. Temperatures of about 20.degree. to about 100.degree. C. can be used in this method. The reaction time needed to carry out the hydrolysis varies, depending upon the pH of the reaction mixture and the temperature used. At higher pH levels the reaction rate is slower, and at higher temperatures the reaction rate is faster. The reaction is carried out by treating DH-DO-DMT with a mild acid solution for a time sufficient to effect removal of the mycarosyl group to give DH-DO-OMT.

Alternatively, and sometimes preferably, DH-DO-OMT can be prepared by treating DH-DO-DMT in the fermentation broth in which it is produced, using mild acidic conditions as described above for a time sufficient to convert the DH-DO-DMT to DH-DO-OMT. DH-DO-OMT thus prepared can be isolated from the fermentation broth using techniques herein described.

DH-DO-DMT can be esterified on the 2', 4", 3", 23 and 3-hydroxyl groups to give acyl ester derivatives by treatment with acylating agents using methods known in the art. DH-DO-OMT can be esterified on the 2', 4', 23 and 3-hydroxyl groups. Typical acylating agents include anhydrides, halides (usually in combination with a base or other acid scavenger) and active esters of organic acids. Acylation can also be achieved by using a mixture of an organic acid and a dehydrating agent such as N,N'-dicyclohexylcarbodiimide. Acylations can also be carried out enzymatically as described by Okamoto et al. in U.S. Pat. No. 4,092,473. Once formed, the acyl derivatives can be separated and purified by known techniques.

Esterification of the 2'- and 4'-hydroxyl groups is most facile. Thus, esterification of DH-DO-DMT gives 2'-monoester derivatives by selective esterification techniques generally known in the art, such as, for example, treatment of the antibiotic with a stoichiometric quantity (or a slight excess) of an acylating agent, such as an acyl anhydride, at about room temperature for from about 1 to about 24 hours until esterification is substantially complete. These derivatives can be isolated from the reaction mixture by standard procedures such as extraction, chromatography and crystallization. Esterification of DH-DO-OMT under similar conditions gives 2',4'-diester derivatives. 2'-Monoesters of DH-DO-OMT are prepared by hydrolyzing the corresponding 2'-monoesters of DH-DO-DMT, using mildly acidic conditions as described above. Mixed 2',4'-diesters of DH-DO-OMT are then prepared by esterification of the 2'-monoesters of DH-DO-OMT as described above.

Useful esters are those of organic acids including aliphatic, cycloaliphatic, aryl, aralkyl, heterocyclic carboxylic, sulfonic and alkoxycarbonic acids of from 2 to 18 carbon atoms, and of inorganic acids, such as sulfuric and phosphoric acids.

Representative suitable esters include those derived from acids such as acetic, chloroacetic, propionic, butyric, isovaleric, alkoxycarbonic, stearic, cyclopropanecarboxylic, cyclohexanecarboxylic, .beta.-cyclohexylpropionic, 1-adamantanecarboxylic, benzoic phenylacetic, phenoxyacetic, mandelic and 2-thienylacetic acids, and alkyl-, aryl-, and aralkyl-sulfonic acids. The aryl- and aralkyl-acids optionally possess substituents such as halogen, nitro, lower alkoxy and the like on the aromatic moiety. Suitable esters also include hemi-esters derived from dicarboxylic acids such as succinic, maleic, fumaric, malonic and phthalic acids.

Pharmaceutically acceptable ester derivatives are a preferred group. Other ester derivatives are useful, however, as intermediates.

DH-DO-DMT, DH-DO-OMT and their specified derivatives form acid addition salts. The acid addition salts of DH-DO-DMT and DH-DO-OMT and of their acyl derivatives are also part of this invention. Such salts are useful, for example, for separating, purifying and crystallizing DH-DO-DMT, DH-DO-OMT and their acyl derivatives. In addition, the salts have an improved solubility in water.

Representative suitable salts include those salts formed by standard reactions with both organic and inorganic acids such as, for example, sulfuric, hydrochloric, phosphoric, acetic, succinic, citric, lactic, maleic, fumaric, palmitic, cholic, pamoic, mucic, D-glutamic, d-camphoric, glutaric, glycolic, phthalic, tartaric, formic, lauric, stearic, salicylic, methanesulfonic, benzenesulfonic, sorbic, picric, benzoic, cinnamic and the like acids.

Pharmaceutically acceptable acid addition salts are an especially preferred group of salts of this invention. "Pharmaceutically acceptable" salts are those which may be administered safely and effectively to warm-blooded animals.

DH-DO-DMT and DH-DO-OMT are prepared by culturing a strain of Streptomyces fradiae, such as S. fradiae ATCC 31733, which produces these compounds under submerged aerobic conditions in a suitable culture medium until substantial antibiotic activity is produced. The culture medium used to grow Streptomyces fradiae ATCC 31733 can be any one of a number of media. For economy in production, optimal yield, and ease of product isolation, however, certain culture media are preferred. Thus, for example, preferred carbon sources in large-scale fermentation include carbohydrates such as dextrin, glucose, starch, and corn meal, and oils such as soybean oil. Preferred nitrogen sources include corn meal, soybean meal, fish meal, amino acids and the like. Among the nutrient inorganic salts which can be incorporated in the culture media are the customary soluble salts capable of yielding iron, potassium, sodium, magnesium, calcium, ammonium, chloride, carbonate, sulfate, nitrate, and like ions.

Essential trace elements necessary for the growth and development of the organism should also be included in the culture medium. Such trace elements commonly occur as impurities in other constituents of the medium in amounts sufficient to meet the growth requirements of the organism. It may be necessary to add small amounts (i.e. 0.2 ml/L) of an antifoam agent such as polypropylene glycol (M.W. about 2000) to large-scale fermentation media if foaming becomes a problem.

For production of substantial quantities of DH-DO-DMT or DH-DO-OMT, submerged aerobic fermentation in tanks is preferred. Small quantities of DH-DO-DMT or DH-DO-OMT may be obtained by shake-flask culture. Because of the time lag in antibiotic production commonly associated with inoculation of large tanks with the spore form of the organism, it is preferable to use a vegetative inoculum. The vegetative inoculum is prepared by inoculating a small volume of culture medium with the spore form or mycelial fragments of the organism to obtain a fresh, actively growing culture of the organism. The vegetative inoculum is then transferred to a larger tank. The medium used for the vegetative inoculum can be the same as that used for larger fermentations, but other media can also be used.

S. fradiae ATCC 31733 can be grown at temperatures between about 10.degree. and about 40.degree. C. Optimum antibiotic production appears to occur at temperatures of about 28.degree. C.

As is customary in aerobic submerged culture processes, sterile air is bubbled through the culture medium. For efficient antibiotic production the percent of air saturation for tank production should be about 30% or above (at 28.degree. C. and one atmosphere of pressure).

Antibiotic production can be followed during the fermentation by testing samples of the broth against organisms known to be sensitive to these antibiotics. One useful assay organism is Staphylococcus aureus ATCC 9144. The bioassay is conveniently performed by an automated turbidometric method. In addition, antibiotic production can be readily monitored by high-performance liquid chromatography with UV detection.

Following its production under submerged aerobic fermentation conditions, DH-DO-DMT or DH-DO-OMT can be recovered from the fermentation medium by methods used in the art. Recovery of DH-DO-DMT or DH-DO-OMT is accomplished by an initial filtration of the fermentation broth. The filtered broth can then be further purified to give the desired antibiotic. A variety of techniques may be used in this purification. A preferred technique for purification of the filtered broth involves adjusting the broth to about pH 9; extracting the broth with a suitable solvent such as ethyl acetate, amyl acetate, or methyl isobutyl ketone; extracting the organic phase with an aqueous acidic solution; and precipitating the antibiotic by making the aqueous extract basic. Further purification involves the use of extraction, chromatographic and/or precipitation techniques.

The new microorganism which produces DH-DO-DMT and DH-DO-OMT was obtained by chemical mutagenesis of a Streptomyces fradiae strain which produced tylosin. The new microorganism produces only minimal amounts of tylosin, but produces DH-DO-DMT and DH-DO-OMT in approximately equal amounts as major components.

The new DH-DO-DMT- and DH-DO-OMT-producing microorganism is also classified as Streptomyces fradiae. A culture of the new microorganism has been deposited and made part of the stock culture collection of The American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md., 20852, from which it is available to the public under the accession number ATCC 31733.

As is the case with other organisms, the characteristics of Streptomyces fradiae ATCC 31733 are subject to variation. For example, artificial variants and mutants of the ATCC 31733 strain may be obtained by treatment with various known physical and chemical mutagens, such as ultraviolet rays, X-rays, gamma rays, and N-methyl-N'-nitro-N-nitrosoguanidine. All natural and artificial variants, mutants and recombinants of Streptomyces fradiae ATCC 31733 which retain the characteristic of production of DH-DO-DMT and/or DH-DO-OMT may be used in this invention.

DH-DO-DMT and DH-DO-OMT inhibit the growth of pathogenic bacteria, especially gram-positive bacteria and Mycoplasma species. Table 3 summarizes the minimal inhibitory concentrations (MIC), as measured by standard agar-dilution assays, at which DH-DO-DMT and DH-DO-OMT (as free bases) inhibit certain bacteria.

DH-DO-OMT also inhibits certain anaerobic bacteria. Table 4 summarizes the MIC's at which DH-DO-OMT inhibits these bacteria. The MIC's were determined using a standard agar-dilution assay and reading the end point after 24 hours.

DH-DO-OMT also inhibits Chlamydia trachomatis grown in cell culture with an MIC of 0.5 .mu.g/ml. In addition, DH-DO-OMT inhibits Mycoplasma species. For example, DH-DO-OMT had an MIC value of 12.5 .mu.g/ml against both M. gallisepticum and M. synoviae.

DH-DO-OMT has shown in vivo antimicrobial activity against experimental bacterial infections. When two doses of test compound were administered to mice in experimental infections, the activity observed was measured as an ED.sub.50 value [effective dose in mg/kg to protect 50% of the test animals: see Warren Wick, et al., J. Bacteriol. 81, 233-235 (1961)]. The ED.sub.50 values observed for DH-DO-OMT (free base) are given in Table 5.

Although DH-DO-DMT and its derivatives have some antibacterial activity, these compounds are best used as intermediates to the corresponding DH-DO-OMT compounds.

DH-DO-OMT, the acyl ester derivatives of DH-DO-OMT and their acid addition salts can also be used as surface disinfectants. Solutions containing as little as 0.01% by weight are useful for disinfecting purposes. Such solutions, preferably also containing a detergent or other cleansing agent, are useful for disinfecting objects and surfaces where maintenance of sterile conditions is important.

In order to illustrate more fully the operation of this invention, the following examples are provided:

A lyophilized pellet of Streptomyces fradiae ATCC 31733 is dispersed in 1-2 ml of sterilized water. A portion of this solution (0.5 ml) is used to inoculate a vegetative medium (150 ml) having the following composition:

Alternatively, a vegetative culture of S. fradiae ATCC 31733 preserved, in 1-ml volumes, in liquid nitrogen is rapidly thawed and used to inoculate the vegetative medium. The inoculated vegetative medium is incubated in a 500-ml Erlenmeyer flask at 29.degree. C. for about 48 hours on a closed-box shaker at 300 rpm.

This incubated vegetative medium (0.5 ml) is used to inoculate 7 ml of a production medium having the following composition:

The inoculated fermentation medium is incubated in a 50-ml bottle at 29.degree. C. for about 6 days on a closed-box shaker at 300 rpm.

In order to provide a larger volume of inoculum, 1200 ml of incubated vegetative medium, prepared in a manner similar to that described in section A, is used to inoculate 250 gallons of a second-stage vegetative growth medium having the following composition:

Adjust pH to 8.5 with 50% NaOH solution.

This second-stage vegetative medium is incubated in a 350-gallon tank for about 48 hours at 28.degree. C., with adequate aeration and agitation.

Incubated second-stage medium (144 gallons) thus prepared is used to inoculate 1000 gallons of sterile production medium having the following composition:

Adjust pH to 7.2 with 50% NaOH solution.

The inoculated production medium is allowed to ferment in a 1600-gallon tank for 8 to 9 days at a temperature of 28.degree. C. The fermentation medium is aerated with sterile air to keep the dissolved oxygen level between about 30% and 50% and is stirred with conventional agitators at about 250 rpm.

Whole broth (38 L), prepared as described in Example 1, section B, is filtered using a filtration aid. The mycelial cake is washed with water; and the filtrate and wash solution (30 L) is adjusted to pH 9.1 with 10% sodium hydroxide. The resulting solution is extracted twice with ethyl acetate (15 L and 5.5 L). The ethyl acetate extracts are combined and extracted with 9 L and then 3 L of a dilute phosphoric acid solution (water phase adjusted to pH 4.1 by the addition of 28% H.sub.3 PO.sub.4). The combined aqueous extracts (8.8 L), adjusted to pH 9.2 with sodium hydroxide, are extracted twice with chloroform (2 L each). The chloroform extracts are dried to give 32 g of solid material.

A portion of this material (5 g) is dissolved in ethyl acetate and treated, using a six-stage countercurrent distribution procedure, with ethyl acetate and 0.5 M phosphate buffer at pH 6.1 to give 2.5 g of DH-DO-OMT. A second six-stage procedure at pH 5.5 gives an additional 0.1 g of DH-DO-OMT. DH-DO-OMT is crystallized from dry acetone.

These procedures also give 1.42 g of impure DH-DO-DMT. In order to purify DH-DO-DMT a countercurrent system consisting of an organic phase of ethyl acetate:heptane (1:2) and an aqueous phase of 0.5 M phosphate buffer at pH 6.2 is used. Six stages give partial separation of DH-DO-DMT. DH-DO-DMT is crystallized from aqueous methanol. From 1 g of crude material, 400 mg of purified DH-DO-DMT is obtained.

DH-DO-DMT, prepared as described in Example 2, is dissolved in a dilute hydrochloric acid solution (HCl added to the water solution until the pH of the solution is 1.8). The resulting solution is allowed to stand for 24 hours at room temperature and then is adjusted to pH 9.0 by the addition of sodium hydroxide. This basic solution is extracted with ethyl acetate, dichloromethane or chloroform. The extract is dried and evaporated under vacuum to give DH-DO-OMT.

DH-DO-OMT is prepared from DH-DO-DMT by treating the DH-DO-DMT in the fermentation broth in which it is produced with mild acid as described in Example 3. Isolation of the DH-DO-OMT is accomplished by a procedure similar to that described in Example 2.

DH-DO-DMT is dissolved in acetone and treated with 1.2 equivalents of propionic anhydride at room temperature for about six hours to give 2'-O-propionyl-DH-DO-DMT.

2'-O-Isovaleryl-DH-DO-DMT, prepared according to the procedure of Example 5, but using isovaleric anhydride.

2'-O-Benzoyl-DH-DO-DMT, prepared according to the procedure of Example 5 but using benzoic anhydride.

2'-O-(n-Butyryl)DH-DO-DMT, prepared according to the procedure of Example 5, but using n-butyric anhydride.

2'-O-Acetyl-DH-DO-DMT, prepared according to the procedure of Example 5 but using acetic anhydride.

2'-O-Propionyl-DH-DO-OMT, prepared by hydrolyzing 2'-O-propionyl-DH-DO-DMT of Example 5 using the procedure of Example 3.

2'-O-Isovaleryl-DH-DO-OMT, prepared according to the procedure of Example 10, but using 2'-O-isovaleryl-DH-DO-DMT.

2'-O-Benzoyl-DH-DO-OMT, prepared according to the procedure of Example 10, but using 2'-O-benzoyl-DH-DO-DMT.

2'-O-(n-Butyryl)-DH-DO-OMT, prepared according to the procedure of Example 10, but using 2'-O-(n-butyryl)DH-DO-DMT.

2'-O-Acetyl-DH-DO-OMT, prepared according to the procedure of Example 10, but using 2'-O-acetyl-DH-DO-DMT.

2',4'-Di-O-acetyl-DH-DO-OMT, prepared by the procedure described in Example 5, but using about 2 to 2.5 equivalents of acetic anhydride and DH-DO-OMT as the starting material.

2',4'-Di-O-propionyl-DH-DO-OMT, prepared according to the procedure of Example 15, but using propionic anhydride.

2',4'-Di-O-isovaleryl-DH-DO-OMT, prepared according to the procedure of Example 15, but using isovaleric anhydride.

2',4'-Di-O-benzoyl-DH-DO-OMT, prepared according to the procedure of Example 15, but using benzoic anhydride.

2',4'-Di-O-(n-butyryl)-DH-DO-OMT, prepared according to the procedure of Example 15, but using n-butyric anhydride.

2'-O-Acetyl-4'-O-isovaleryl-DH-DO-OMT, prepared by treating 2'-O-acetyl-DH-DO-OMT of Example 14 with isovaleric anhydride, using the procedure of Example 5.

2'-O-Acetyl-4'-O-propionyl-DH-DO-OMT, prepared by treating the 2'-O-acetyl-DH-DO-OMT of Example 14 with propionic anhydride, using the procedure of Example 5.

2'-O-Propionyl-4'-O-isovaleryl-DH-DO-OMT, prepared by treating the 2'-O-propionyl-DH-DO-OMT of Example 10 with isovaleric anhydride, using the procedure of Example 5.

2'-O-Isovaleryl-4'-O-acetyl-DH-DO-OMT, prepared by treating 2'-O-isovaleryl-DH-DO-OMT of Example 11 with acetic anhydride, using the procedure of Example 5.

2'-O-Benzoyl-4'-O-acetyl-DH-DO-OMT, prepared by treating 2'-O-benzoyl-DH-DO-OMT of Example 12 with acetic anhydride using the procedure of Example 5.