Chemistry: natural resins or derivatives; peptides or proteins; – Peptides of 3 to 100 amino acid residues – Peptides containing saccharide radicals – e.g. – bleomycins – etc.
Reexamination Certificate
2001-05-01
2004-12-14
Carlson, Karen Cochrane (Department: 1653)
Chemistry: natural resins or derivatives; peptides or proteins;
Peptides of 3 to 100 amino acid residues
Peptides containing saccharide radicals, e.g., bleomycins, etc.
C530S317000, C530S333000, C530S345000, C514S008100, C514S009100
Reexamination Certificate
active
06831150
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to an improved method for reductively alkylating a saccharide-amine of a glycopeptide antibiotic. Specifically, the method of the invention allows for selective alkylation at a saccharide-amine over other amine sites in the glycopeptide (e.g. a leucinyl nitrogen).
2. Background
Glycopeptides are a well-known class of antibiotics produced by various microorganisms (see
Glycopeptide Antibiotics,
edited by R. Nagarajan, Marcel Dekker, Inc. New York (1994)). These complex multi-ring peptide compounds are effective antibacterial agents against a majority of Gram-positive bacteria. Although potent antibacterial agents, the glycopeptides antibiotics are not used in the treatment of bacterial diseases as often as other classes of antibiotics, such as the semi-synthetic penicillins, cephalosporins and lincomycins, due to concerns regarding toxicity.
In recent years, however, bacterial resistance to many of the commonly-used antibiotics has developed (see J. E. Geraci et al.,
Mayo Clin. Proc.
1983, 58, 88-91; and M. Foldes,
J. Antimicrob. Chemother.
1983, 11, 21-26). Since glycopeptide antibiotics are often effective against these resistant strains of bacteria, glycopeptides such as vancomycin have become the drugs of last resort for treating infections caused by these organisms. Recently, however, resistance to vancomycin has appeared in various microorganisms, such as vancomycin-resistant enterococci (VRE), leading to increasing concerns about the ability to effectively treat bacterial infections in the future (see Hospital Infection Control Practices Advisory Committee,
Infection Control Hospital Epidemiology,
1995, 17, 364-369; A. P. Johnson et al.,
Clinical Microbiology Rev.,
1990, 3, 280-291; G. M. Eliopoulos,
European J. Clinical Microbiol., Infection Disease,
1993, 12, 409-412; and P. Courvalin,
Antimicrob. Agents Chemother,
1990, 34, 2291-2296).
In an attempt to identify agents with improved antibacterial properties, or to identify agents that are effective against resistant bacterial strains, numerous derivatives of vancomycin and other glycopeptides have been prepared. For example, see U.S. Pat. Nos. 4,639,433; 4,643,987; 4,497,802; 5,840,684; and 5,843,889. Other derivatives are disclosed in EP 0 802 199; EP 0 801 075; WO 97/28812; WO 97/38702; WO 98/52589; WO 98/52592; and in
J. Amer. Chem. Soc.,
1996, 118, 13107-13108;
J. Amer. Chem. Soc.,
1997, 119, 12041-12047; and
J. Amer. Chem. Soc.,
1994, 116, 4573-4590.
One group of glycopeptide derivatives that has been reported to have useful antibiotic properties includes glycopeptide compounds that are alkylated at a nitrogen on a saccharide of the glycopeptide. See for example, U.S. Pat. Nos. 5,919,756; 5,843,889; 5,916,873; 4,698,327; and 5,591,714; and European Patent Application Publication Nos. EP 435 503A1; and EP 667 353A1. One difficulty that is encountered in preparing such alkylated derivatives is the non-selective alkylation at multiple amine sights within the glycopeptide compound. For example, vancomycin has a vancosamine amino group, and a leucinyl amino group. Thus, alkylation under standard conditions typically provides a mixture of mono- and di-alkylated compounds.
U.S. Pat. Nos. 5,952,466 and 5,998,581 disclose a method for the reductive alkylation of a copper complex of a glycopeptide antibiotic such as vancomycin or A82846B, which favors alkylation at the saccharide amino group. In spite of this disclosure, there is currently a need for additional methods that are useful for the selective alkylation of glycopeptide antibiotics at a saccharide-amino group. In particular, there is a need for highly selective methods that are simple and efficient to carry out.
SUMMARY OF THE INVENTION
Previously, the reductive alkylation of glycopeptide antibiotics was carried out by combining an aldehyde, a glycopeptide antibiotic, and a suitable base to form an imine and/or hemiaminal; subsequently adding a suitable reducing agent (e.g. sodium cyanoborohydride); and then adding a suitable acid (e.g. trifluoroacetic acid).
Applicant has unexpectedly discovered that by contacting the glycopeptide and the aldehyde to form the imine and/or hemiaminal in the presence of a suitable base, and then acidifying the mixture before contact with the reducing agent, the selectivity for the reductive alkylation at a saccharide-amine is significantly improved, i.e. reductive alkylation at a saccharide-amino group (e.g. a vancosamine amino group) in vancomycin is favored over reductive alkylation at other amino groups (e.g. a leucinyl amino group) in vancomycin.
Accordingly, the present invention provides a method for alkylating a glycopeptide that comprises a saccharide-amine comprising:
combining an aldehyde or ketone, a suitable base, and the glycopeptide or a salt thereof, to provide a reaction mixture;
acidifying the reaction mixture; and
combining the reaction mixture with a suitable reducing agent, to provide a glycopeptide that is alkylated at the saccharide-amine.
Preferably, the glycopeptide comprises at least one amino group other than the saccharide-amine. More preferably, the glycopeptide is vancomycin or A82846B.
Preferably, the reductive alkylation at the saccharide-amine is favored over reductive alkylation at another amino group of the glycopeptide by at least about 10:1; and more preferably, by at least about 15:1 or about 20:1.
The reductive alkylation is typically carried out in the presence of a suitable solvent or combination of solvents, such as, for example, a halogenated hydrocarbon (e.g. methylene chloride), a linear or branched ether (e.g. diethyl ether, tetrahydrofuran), an aromatic hydrocarbon (e.g. benzene or toluene), an alcohol (methanol, ethanol, or isopropanol), dimethylsulfoxide (DMSO), N,N-dimethylformamide, acetonitrile, water, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidone, tetramethyl urea, N,N-dimethylacetamide, diethylformamide (DMF), 1-methyl-2-pyrrolidinone, tetramethylenesulfoxide, glycerol, ethyl acetate, isopropyl acetate, N,N-dimethylpropylene urea (DMPU) or dioxane. Preferably the alkylation is carried out in acetonitrile/water, or DMF/methanol.
Preferably the reduction (i.e. treatment with the reducing agent) is carried out in the presence of a protic solvent, such as, for example, an alcohol (e.g. methanol, ethanol, propanol, isopropanol, or butanol), water, or the like.
The reductive alkylation can be carried out at any suitable temperature from the freezing point to the reflux temperature of the reaction mixture. Preferably the reaction is carried out at a temperature in the range of about 0° C. to about 100° C. More preferably at a temperature in a range of about 0° C. to about 50° C., or in a range of about 20° C. to about 30° C.
Any suitable base can be employed in the reductive alkylation. Preferred bases include tertiary amines (e.g. diisopropylethylamine, N-methylmorpholine or triethylamine) and the like.
Any suitable acid can be used to acidify the reaction mixture. Suitable acids include carboxylic acids (e.g. acetic acid, trichloroacetic acid, citric acid, formic acid, or trifluoroacetic acid), mineral acids (e.g. hydrochloric acid, sulfuric acid, or phosphoric acid), and the like. A preferred acid is trifluoroacetic acid.
Suitable reducing agents for carrying out reductive alkylations are known in the art. Any suitable reducing agent can be employed in the methods of the invention, provided it is compatible with the functionality present in the glycopeptide. For example, suitable reducing agents include sodium cyanoborohydride, sodium triacetoxyborohydride, pyridine/borane, sodium borohydride, and zinc borohydride. The reduction can also be carried out in the presence of a transition metal catalyst (e.g. palladium or platinum) in the presence of a hydrogen source (e.g. hydrogen gas or cycloheadiene). See for example,
Advanced Organic Chemistry,
Fourth Edition, John Wiley & Sons, New York (1992), 899-900.
Upon completion of the reductive alkylation, the alkylated glycopeptide can
Boone David E.
Carlson Karen Cochrane
Desai Anand U
Hagenah Jeffrey A.
Theravance Inc.
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