Title of Invention

REDUCTIVE ALKYLATION OF GLYCOPEPTIDE ANTIBIOTICS

Abstract

This invention is concerned with improved processes for reductive alkylation of glycopeptide antibiotics. The improvement residing in providing a source of copper which 5 results in the initial production of a copper complex of the glycopeptide antibiotic. Reductive alkylation of this complex favors regioselective alkylation and increased yields. Copper complexes of the glycopeptide antibiotic starting materials and of the alkylated products are also 10 part of the invention.

Full Text

2 The present invention is directed to improved methods for reductively alkylating glycopeptide antibiotics. The invention provides increased regioselectivity of reaction among multiple sites and thereby results in increased yields of the preferred product. In particular, the invention is directed to methods for preferentially conducting a reductive alkylation reaction on an amine on the saccharide of a glycopeptide antibiotic having one or more additional amines. The essence of the invention is the discovery that conducting the reaction in the presence of soluble copper favors preferential reaction with the amine on the saccharide position, and thereby improves the yields of the reductive alkylation at this site. The initial step is the formation of a copper complex of the glycopeptide antibiotic, which subsequently undergoes the reductive alkylation. This invention is also directed to these copper complexes of the starting glycopeptide antibiotics. The alkylated glycopeptide antibiotic products are obtained as copper complexes, which are another embodiment of the present invention. The present invention relates to reductive alkylation of glycopeptide antibiotics. The glycopeptide antibiotics are a large class of substances either produced by microorganisms, or produced by microorganisms and thereafter subsequently modified in part. Two of these, vancomycin and teicoplanin, are sold as antibacterial products, but many others have been discovered and are being considered for development, especially since the emergence in the late 1980s of resistance to various antibiotics, including the glycopeptides themselves. The entire class of glycopeptide antibiotics is well described in "Glycopeptide Antibiotics", edited by Ramakrishnan Nagarajan (Marcel Dekker, Inc., New York, 1994). Among the more recently discovered glycopeptides are those known as A82846A (also called ereomomycin), A82846B (also known as chloroorienticin A), A82846C (also known as orienticin C), and orienticin A. The present invention is preferred for use with vancomycin type glycopeptide antibiotics, including vancomycin, A82846A, A82846B, A82846C, and orienticin A; the invention is especially preferred for use with A82846B. Many modifications of naturally-occurring glycopeptides have been made. Among the modifications are reductive alkylations of reactive amine(s) in glycopeptides. See, for example, U.S. 4,698,327 describing reductive alkylations of vancomycin, and EPO 435 503 Al and EPO 667 353 Al, both of which describe reductive alkylations of a variety of glycopeptides including vancomycin, A82846A, A82846B, A82846C, and orienticin A. These references describe reductive alkylations which introduce into the parent glycopeptides a great variety of alkyl groups. ¦ 4,698,327 describes alkylated vancomycin compounds of the formula: 4 wherein R is hydrogen or methyl; n is 1 or 2; and Rl is hydrogen or methyl; R2 and R3, independently, are hydrogen or a group of the formula: R6R7CH- ; R6 and R7 are independently R5, R5- (C1-C5-alkyl) or R5-(C2-C5-alkenyl) ; R5 is hydrogen, C1-C10-alkyl, C2-C10-alkenyl, C1-C4 alkoxy, C3-C10-cycloalkyl, C5-C12-cycloalkenyl, phenyl, naphthyl, indenyl, tetralinyl, decalinyl, adamantyl, a monocyclic heterocyclic ring system comprising 3 to 8 atoms in the ring or a bicyclic heterocyclic ring system comprising 6 to 11 atoms, provided that at least one atom of the ring system is carbon and at least one atom of the ring system is a heteroatom selected from O, N, and S, and R5 may be substituted with one or more hydroxy, nitro, C1-C10-alkoxy, C1-C10-alkyl, phenyl, C1-C6-alkylthio, nitrile, halo, C2-C4-acyla1rrino, amino, C1-C4-dialkylanuno groups; and R4 is hydrogen, provided that: (1) at least one of R2 and R3 must be other than hydrogen; (2) when n is 2, R must be hydrogen; {3} when R is methyl and R3 is hydrogen, R2 cannot be methyl and (4) when R and R1 are both methyl, then R2 is hydrogen or methyl and n is 1. EPO 435 503 Al is directed to alkylated and acylated glycopeptides of the formula: wherein: R is hydrogen or a (4-epi-vancosaminyl)-O-glucosyl group of formula or the glucosyl group of formula X is hydrogen or chloro; Y is hydrogen or chloro; Rl, R2, and R3 are independently hydrogen; C1-C12 alkyl; C2-C9 alkanoyl; or a group of formula n is 1 to 3; R4 is hydrogen, halo, C1-C8 alkyl, C1-C5 alkoxy, or a group of formula R5 and R6 are independently hydrogen or C1-C3 alkyl; p is 0 to 2; m is 2 or 3, and r = 3 - m; provided that, where R is a (4-epi-vancosaminyl)-O-glucosyl group, R1, R2 and R3 are not all hydrogen, and where R is hydrogen or a glucosyl group, R1 and R3 are not both hydrogen. 6 Where R is {4-epi-vancosaminyl)-O-glucosyl, the glycopeptides so defined are X = H, Y = Cl, A82846A X = Y = C1, A82846B X = Y = H, A82846C X = C1, Y = H, orienticin A. Thus, EPO 435 503 Al describes alkyl derivatives of A82846A, A82846B, A82846C, and orienticin A wherein the alkyl group is Preferred groups are C8-C12 alkyl and groups of the formula wherein R4 is hydrogen, halo, C1-C8 alkyl, or C1-C8 alkoxy. EPO 667 353 Al describes alkylated glycopeptide antibiotics of the formula wherein: X and Y are each independently hydrogen or chloro; R is hydrogen, 4-epi-vancosaminyl, actinosaminyl, or ristosaminyl; R1 is hydrogen, or mannose; R2 is -NH2, -NHCH3, or-N(CH3)2; R3 is -CH2CH(CH3)2, [p-OH, m-Cl] phenyl, p-rhamnose-phenyl, or [p-rhamnose-galactose]phenyl, [p-galactose-galactose] phenyl, [p-CH3O-rhamnose]phenyl; R4 is -CH2(CO)NH2, benzyl, [p-OH] phenyl, or [p-OH, m-Cl]phenyl; R5 is hydrogen, or mannose; R6 is vancosaminyl, 4-epi-vancosaminyl, L-acosaminyl, L-ristosaminyl, or L-actinosaminyl; R7 is (C2-C16)alkenyl, (C2-C12) alkynyl, {C1-C12 alkyl}-R8, {C1-C12 alkyl)-halo, (C2-C6 alkenyl)-R8, (C2-C6 alkynyl)-R8, (C1-C12 alkyl)-0-R8, and is attached to the amino group of R8 is selected from the group consisting of: a) multicyclic aryl unsubstituted or substituted with one or more substituents independently selected from the group consisting of: (i) hydroxy, (ii) halo, (iii) nitro, (iv) (C1-C6)alkyl, (v) (C2-C6)alkenyl, (vi) (C2-C6)alkynyl, (vii) (C1-C6)alkoxy, (viii) halo-(C1-C6)alkyl, (ix) halo-(C1-C6)alkoxy, (x) carbo-(C1-C6)alkoxy, (xi) carbobenzyloxy, (xii) carbobenzyloxy substituted with (C1-C6)alkyl, (C1-C6)alkoxy, halo, or nitro, (xiii) a group of the formula -S(0)n'-R9,wherein n' is 0-2 and R9 is (C1-C6) alkyl, phenyl, or phenyl substituted with (C1-C6)alkyl, (C1-C6)alkoxy, halo, or nitro, and (xiv) a group of the formula -C(O)N(R10)2 wherein each R10 substituent is independently hydrogen, (C1-C6)-alkyl, (C1-C6)-alkoxy, phenyl, or phenyl substituted with (C1-C6)-alkyl, (C1-C6)-alkoxy, halo, or nitro; b) heteroaryl unsubstituted or substituted with one or more substituents independently selected from the group consisting of: (i) halo, (ii) (C1-C6)alkyl, (iii) (C1-C6)alkoxy, (iv) halo-(C1-C6)alkyl, (v) halo-(C1-C6)alkoxy, (vi) phenyl, (vii) thiophenyl, (viii) phenyl substituted with halo, (C1-C6)alkyl, (C2 C6)alkenyl, (C2-C6)alkynyl, (C1-C6)alkoxy, or nitro, (ix) carbo-(C1-C6)alkoxy, (x) carbobenzyloxy, (xi) carbobenzyloxy substituted with (C1-C6)alkyl, (Cr C6) alkoxy, halo, or nitro, (xii) a group of the formula -S(0)n'-R9, as defined above, (xiii) a group of the formula -C(0)N(R10)2 as defined above, and wherein M is -OC(A2)2-C(A2)2-0-, -0-C (A2)2-0-,-C (A2)2-0-, or -C(A2)2-C(A2)2-C(A2)2-C(A2)2-, and each A2 substituent (xiv) thienyl; c) a group of the formula: is independently selected from hydrogen, (C1-C6)-alkyl, (Cr C6) alkoxy, and (C4-C10) cycloalkyl; d) a group of the formula: wherein p is from 1 to 5; and R11 is independently selected from the group consisting of: (i) hydrogen, (ii) nitro, (iii) hydroxy, (iv) halo, (v) (C1-C8)alkyl, (vi) (C1-C8)alkoxy, (vii) (C9-C12)alkyl, (viii)(C2-C9)alkynyl, (ix) (C9-C12)alkoxy, (x) (C1-C3)alkoxy substituted with (C1-C3)alkoxy, hydroxy, halo (C1-C3)alkoxy, or (C1-C4)alkylthio, (xi) (C2-C5)alkenyloxy, (xii) (C2-C13)alkynyloxy (xiii) halo- (C1-C6)alkyl, (xiv) halo-(C1-C6)alkoxy, (xv) (C2-C6)alkylthio, (xvi) {C2-C10) alkanoyloxy, (xvii) carboxy-{C2-C4)alkenyl, (xviii) (C1-C3)alkylsulfonyloxy, (xix) carboxy-(C1-C3) alkyl, (xx) N-[di(C1-C3) -alkyl]amino-(C1-C3)alkoxy, (xxi) cyano- (Ci-C6)alkoxy, and (xxii) diphenyl-(C1-C6) alkyl, with the proviso that when R11 is (C1-C6) alkyl, (C1-C8)alkoxy, or halo, p must be greater or equal to 2, or when R7 is (C1-C3 alkyl)-R8 then R11 is not hydrogen, (C1-C8)alkyl, (C1-C8)alkoxy, or halo; e) a group of the formula: wherein q is 0 to 4; R12 is independently selected from the group consisting of: (i) halo, (ii) nitro, (iii) (C1-C6)alkyl, (iv) (C1-C6)alkoxy, (v) halo- (C1-C6)alkyl, (vi) halo-(C1-C6)alkoxy, and (vii) hydroxy, and (vii) (C1-C6)thioalkyl; r is 1 to 5; provided that the sum of q and r is no greater than 5-; Z is selected from the group consisting of: (i) a single bond, (ii) divalent (C1-C6) alkyl unsubstituted or substituted with hydroxy, (C1-C6)alkyl, or (C1-C6)alkoxy, (iii) divalent (C2-C6)alkenyl, (iv) divalent (C2-C6)alkynyl, or (v) a group of the formula -(C(R14) 2)5-R15- or -R15-(C(R14)2)5-, wherein s is 0-6; wherein each R14 substituent is independently selected from hydrogen, (C1-C6) -alkyl, or (C4-C10) cycloalkyl; and R15 is selected from -0-, -S-, -SO-, -S02-, -SO2-O-, -C(O)-, -OC(0}-, -C(0)0-, -NH-, -N(C1-C6 alkyl)-, and -C(0)NH-, -NHC(O)-, N=N; R13 is independently selected from the group consisting of: (i) (C4-C10)heterocyclyl, (ii) heteroaryl, (iii) (C4-C10) cycloalkyl unsubstituted or substituted with (C1-C6)alkyl, or (iv) phenyl unsubstituted or substituted with 1 to 5 substituents independently selected from: halo, hydroxy, nitro, (C1-C10) alkyl, (C1-C10) alkoxy, halo- (C1-C3) alkoxy, halo-(C1-C3)alkyl, (C1-C3)alkoxyphenyl, phenyl, phenyl-(C1-C3)alkyl, (C1-C6)alkoxyphenyl, phenyl-(C2-C3) alkynyl, and (C1-C6)alkylphenyl; f) (C4-C10)cycloalkyl unsubstituted or substituted with one or more substituents independently selected from the group consisting of: (i) (C1-C6)alkyl, (ii) (C1-C6)alkoxy, (iii) (C2-C6)alkenyl, (iv) (C2-C6)alkynyl, (v) (C4-C10)cycloalkyl/ (vi) phenyl, (vii) phenylthio, (viii) phenyl substituted by nitro, halo, (C1-C6)alkanoyloxy, or carbocycloalkoxy, and (ix) a group represented by the formula -Z-R13 wherein Z and R13 are as defined above; and g) a group of the formula: wherein A3 and A4 are each independently selected from (i) a bond, (ii) -0-, (iii) -S(0)t- , wherein t is 0 to 2, (iv) -C(R17)2-' wherein each R17 substituent is independently selected from hydrogen, (C1-C6)alkyl, hydroxy, (C1-C6)alkyl, (C1-C6) alkoxy, or both R17 substituents taken together are O, (v) -N(R18)2-,wherein each R18 substituent is independently selected from hydrogen; (C1-C6)alkyl; (C2-C6)alkenyl; {C2-C6)alkynyl; (C4-C10) cycloalkyl; phenyl; phenyl substituted by nitro, halo, (C1-C6)alkanoyloxy; or both R18 substituents taken together are {C4-C10)cycloalkyl; R16 is R12 or R13 as defined above; and u is 0-4. In this reference, preferred glycopeptide antibiotics are A82846A, A82846B, A82846C, and orienticin A; preferred alkyls are those wherein R7 is CH2-R8; and preferred R8 moieties are those defined as groups "(d)" and "(e)". The present invention can be utilised to make the alkylated glycopeptides described in these references. Preferred alkylated glycopeptides which can be prepared by the present process include the following: N4-n-octylA82 846B N4-n-decylA8284 6B N4-N4-N4-N4-N4-N4-N4-N4-N4-N4-N4-N4- N4-benzylA8284 6B (p-chlorobenzyl)A8284 6B (p-bromobenzyl)A82846B (p-propylbenzyl)A82846B (p-isopropylbenzyl)A82846B (p-butylbenzyl)A82 846B (p-isobutylbenzyl)A82846B (p-pentylbenzyl)A82 846B (p-isohexylbenzyl)A82 846B {p-octylbenzyl)A82 846B (p-propoxybenzyl)A8284 6B (p-isopropoxybenzyl)A82 846B (p-butoxybenzyl)A8284 6B -16- N4-{p-tert-butoxybenzyl)A82846B N4-(p-pentyloxyben2yl)A82846B N4-(p-hexyloxybenzyl)A82846B N4-(o-hexyloxybenzyl)A82 846B N4-(p-heptyloxybenzyl)A82846B N4-(p-octyloxybenzyl)A82846B N4-phenethylA8284 6B N4-(4-phenylbenzyl)A82846B N4-(4-(4-chlorophenyl)benzylA82846B N4-(4-(4-methylbenzyloxy)benzyl)A82846B N4-(4-(4-ethylbenzyloxy)benzyl)A82846B N4-(4-(4-chlorophenethyl)benzyl)A82846B N4-{4-(2~(4-methoxyphenyl)ethynyl)benzyl)A82846B. The references noted above describe the reductive alkylation as comprising a first step, in which the glycopeptide is reacted with the respective aldehyde or ketone to form a Schiff's base, which in a second step is reduced to the desired alkylated product. In one variation of this procedure, EPO 667 353 Al describes a process in which the reducing agent is added simultaneously with the glycopeptide and aldehyde or ketone. The references say that any chemical reducing agent can be employed, but the references also suggest a preference for sodium cyanoborohydride. Essentially all glycopeptides contain multiple reactive sites. Manipulation of these multiple sites is not uniformly advantageous. It is sometimes desired to react -17- the glycopeptide regioselectivity, to have the reaction occur at only one of multiple sites. This is equally true in the case of reductive alkylations of glycopeptides. An example of this is A82846B. While derivatives alkylated on the leucine amine (N1) and/or the monosaccharide (N6) are active as antibacterials, alkylation of the N4 (disaccharide) amine appears to be preferred. Pharmaceutical practices require a relatively pure form, and therefore preferential reaction of the N4 site is desirable in order to achieve a highly pure N4-alkylated product. The present invention provides a technique for obtaining reaction preferentially on the amine on a saccharide at the N4 position in the glycopeptide antibiotic. In the case of vancomycin, A82846A, A82846B, A82846C, and orienticin A, the present process reduces reactivity at sites N1 and N6 and thereby increases reaction selectivity for the N4 (disaccharide) site. The invention requires the initial preparation of a soluble copper complex of the glycopeptide, which is then reductively alkylated. The soluble copper complex is achieved by reacting the glycopeptide antibiotic with copper, typically by adding a source of soluble copper to a reaction mixture containing the glycopeptide antibiotic. The identity of the copper source is not critical, so long as it is at least partially soluble and does not negatively impact the pH. Such a copper salt can be used in anhydrous or hydrated form. A preferred source of copper is copper (II) acetate, most conveniently employed as the hydrate. Supplying copper to the reaction mixture results in the initial production of a copper complex with the glycopeptide antibiotic starting material, typically in a 1:1 ratio. This copper complex of the glycopeptide antibiotic starting material is one of the features of the present invention. The reducing agent to be employed in the present invention is sodium cyanoborohydride or pyridine.borane complex. The identity of the solvent is important. Straight methanol has given high yields, and it is expected that methanol somewhat diluted as with DMF or DMSO would provide acceptable yields. Other solvents have not produced satisfactory results. Therefore, the reaction solvent is at least predominantly methanol. The reaction should be conducted at a pH of 6-8, and preferably at a pH of 6.3-7.0. The amounts of reactants and reagents to be employed are not critical; amounts to maximize the yield of product will vary somewhat with the identity of the reactants. The reaction consumes the glycopeptide antibiotic and the aldehyde or ketone in equimolar amounts. A slight excess of the aldehyde or ketone, e.g., 1.3 to 1.7:1, is preferred. The amount of the glycopeptide antibiotic to be used must be corrected for its purity. The reaction consumes an equimolar amount of the reducing agent. At least that amount should be employed, and & slight excess is preferred. The amount of soluble copper is not critical when employing sodium cyanoborohydride as reducing agent. When employing pyridine.borane as reducing agent, the amount of soluble copper to be employed is more important, since excess copper will react with the pyridine.borane. Regardless of the identity of the reducing agent, the present process first results in the formation of a 1:1 complex with the glycopeptide antibiotic; therefore, the copper is preferably present in an amount approximately equimolar with the glycopeptide antibiotic. Amounts exceeding one molar equivalent (in the case of pyridine.borane} or two molar equivalents {in the case of sodium cyanoborohydride) are undesirable. Summarizing the foregoing, the ideal amounts to be employed are a ratio of: glycopeptide:aldehyde or ketone:reducing agent:copper salt of: 1:1.3 to 1.5:1.3:1 with the exception that when using pyridine-borane complex as reducing agent, the preferred ratio is: 1:1.3 to 1.7:1.5:0.9 to 1.0. The concentration of the reactants in the solvent has some bearing on the process. Methanol volume relative to mass of glycopeptide antibiotic can vary from 50:1 to 500:1; a 100:1 dilution appears to be a useful, practical ratio, although higher dilutions may give slightly higher yields. The temperature at which the process is carried out is not critical. Reaction mixtures in methanol boil at about 67°C, thereby setting the maximum temperature when employing straight methanol as the solvent. Higher temperatures are of course possible when employing mixtures of methanol or when operating under pressure. Lower temperatures can be tolerated, but preferably not lower than about 450c. The ideal condition for sodium cyanoborohydride as reducing agent is the use of straight methanol and conducting the reaction at reflux; the ideal condition for pyridine.borane as reducing agent is also the use of straight methanol but at temperatures of about 58-63°C. Some product is produced with even short reaction times. Longer reaction times, such as from 6 hours to 48 hours, are preferred. However, the ideal reaction time appears to be approximately 20 to 25 hours. Longer times may increase the yield of products alkylated at undesired sites in the glycopeptide antibiotic. In carrying out the present invention, the glycopeptide antibiotic and copper are preferably mixed in a solvent, creating the soluble copper complex of the glycopeptide antibiotic, and the aldehyde and reducing agents are then added. However, the precise order of addition is not critical. Portionwise addition of the reducing agent is preferred, and is required for good results when employing pyridine.borane complex as reducing agent. The reaction is continued for a period of time, after which the product is produced and can be separated from the reaction mixture. Upon the completion of the reaction period, the reaction mixture is preferably quenched, as by the addition of sodium borohydride. This reagent consumes residual -20-aldehyde or ketone and thereby prevents further undesired reactions. The product is isolated from the reaction mixture as a copper complex of the alkylated glycopeptide. Isolation is achieved by concentration of the reaction mixture and precipitation of the complex by addition of an antisolvent such as ethyl acetate, acetone, 1-propanol, isopropyl alcohol, or preferably acetonitrile. The complex can be broken by aqueous treatment at pH 24, freeing the simple alkylated glycopeptide product, which can, if desired, be purified in conventional manner. The following examples illustrate the present invention and will enable those skilled in the art to practice the same. Reference Example A (no copper) A82846B (6.0 g, 76.5% potency, 4.59 bg, 2.88 mmol), 4'-chloro-4-biphenylcarboxaldehyde (0.86 g, 3.97 mmol), and sodium cyanoborohydride (84 mg, 1.34 mmol} were added to 600 mL methanol and the solution was heated at reflux for 3 hours. An additional portion of sodium cyanoborohydride (84 mg, 1.34 mmol) was added and the mixture was heated 3 hours longer at reflux. A final portion of sodium cyanoborohydride (84 mg, 1.34 mmol) was added and heating at reflux was continued an additional 17 hours. The clear colorless solution was cooled to ambient temperature and concentrated to 13 0 mL on a rotary evaporator. The product was precipitated by addition of 200 ml of isopropyl alcohol over 2 hours. After cooling to 0°C and stirring 1 hour, filtration afforded N4-(4-(4-chlorophenyl)benzyl)A82846B as a white solid (5.61 g, 49.3% potency, 2.77 bg, 53.7%). FXAMPLE 1 A82846B(0.50 a 76, % g, 76'3% Potency,o.38 bg, 0.24 mmol) , 4 chloro-4-biphenylcarboxaldehyde(70 mg, 0.32mmol)and cupric acetate monohydrate (51 mg, 0.26 mmol) were stirred in 50 ml methanol. Sodium cyanoborohydride (20 mg, 0.32 mmol) was added and the solution was heated at reflux for 23 hours. The clear purple solution was cooled to ambient temperature and 12% sodium borohydride in aqueous 14 M sodium hydroxide (0.03 ml, 0.14 mmol) was added. One drop of acetic acid was added to pH adjust the solution to 7.3. An additional portion of 12% sodium borohydride in aqueous 14 M sodium hydroxide (0.23 ml, 0.10 mmol) was added followed by one drop of acetic acid to maintain the solution pH at 7.3. The mixture was stirred at ambient temperature for 1 hour and concentrated to 12 ml on a rotary evaporator. The product was precipitated by addition of 25 mL of acetonitrile over 20 min. After stirring 20 min at ambient temperature, filtration afforded the copper complex of N4-(4-(4-chlorophenyl)benzyl)A82846B as a purple solid (0.58 g, potency 59.5%, 0.35 bg, 80.3 %). -23- EXAMPLE 2 A82846B (6.0 g, 78.4% potency, 4.7 bg, 2.95 mmol), was stirred in 600 mL methanol and cupric acetate (0.66 g, 3.6 mmol) was added. After stirring at ambient temperature for 15 rnin, 4' -chloro-4-biphenylcarboxaldehyde (0.95 g, 4.4 mmol), and sodium cyanoborohydride (0.27 g, 4.3 mmol) were added and the mixture was heated at reflux for 24 hours. After cooling to ambient temperature, HPLC analysis of a reaction aliquot afforded a yield of 4.52 g (85.4%) of N4-(4-(4-chlorophenyl)benzyl)A82846B. EXAMPLE 3 A82846B (2.5 g, 78.5% potency, 1.96 bg, 1.23 mmol), was stirred in 250 ml methanol and cupric acetate monohydrate (0.26 g, 1.32 mmol) was added. After stirring at ambient temperature for 10 min, 4'-chloro-4-biphenylcarboxaldehyde (0.35 g, 1.6 mmol), and sodium cyanoborohydride (34 mg, 0.54 mmol) were added and the mixture was heated at reflux for 3 hours. An additional portion of sodium cyanoborohydride (34 mg, 0.54 mmol) was added and the mixture was heated 3 hours longer at reflux. A final portion of sodium cyanoborohydride (34 mg, 0.54 mmol) was added and heating at reflux continued an additional 17 hours. The mixture was cooled to ambient temperature and 12% sodium borohydride in aqueous 14 M sodium hydroxide (0.14 ml, 0.63 mmol) was added. A few drops of acetic acid were added to pH adjust -24- the solution to 7.3. A second portion of 12% sodium borohydride in aqueous 14 M sodium hydroxide (0.13 mL, 0.6 mmol} was added and a few drops of acetic acid were added to adjust the solution pH to 8.1. After stirring at ambient temperature for 2 hours, the reaction mixture was concentrated to 60 mL on a rotary evaporator. Isopropyl alcohol {175 mL) was added dropwise over a period of 1 hour to precipitate the copper complex of N4-(4-(4-chlorophenyl)benzyl)A82846B. Filtration afforded the complex as a purple solid (6.50 g, 2 6.9% potency as wet cake, 1.75 bg, 79.1%). EXAMPLE 4 A82846B (2.5 g, 78.5% potency, 1.96 bg, 1.23 mmol), was stirred in 250 ml methanol and cupric acetate monohydrate (0.26 g, 1.32 mmol) was added. After stirring at ambient temperature for 10 min, 4'-chloro-4-biphenylcarboxaldehyde (0.35 g, 1.6 mmol), and sodium cyanoborohydride (34 mg, 0.54 mmol) were added and the mixture was heated at reflux for 3 hours. An additional portion of sodium cyanoborohydride (34 mg, 0.54 mmol) was added and the mixture was heated 3 hours longer at reflux. A final portion of sodium cyanoborohydride (34 mg, 0.54 mmol) was added and heating at reflux continued an additional 17 hours. The mixture was cooled to ambient temperature and 12% sodium borohydride in aqueous 14 M sodium hydroxide (0.14 mL, 0.63 mmol) was added. A few drops of acetic acid were added to pH adjust the solution to 7.3. A second portion of 12% sodium borohydride in aqueous 14 M sodium hydroxide (0.13 ml, 0.6 mmol) was added and a few drops of acetic acid were added to adjust the solution pH to 8.2. After stirring at ambient temperature for 1.5 hours, the reaction mixture was concentrated to 60 ml on a rotary evaporator. Isopropyl alcohol (175 ml) was added dropwise over a period of 1 hour to precipitate the product. It was filtered and dried in vacuo to afford the copper complex of N4-(4-(4-chlorophenyl)benzyl)A82846B as a purple solid (2.56 g, 62.9% potency, 1.61 bg, 72.9%). EXAMPLE 5 A82846B (6.0 g, 76.1% potency, 4.56 bg, 2.9 mmol), was stirred in 600 mL methanol and cupric acetate monohydrate (0.63 g, 3.15 mmol) was added. After stirring at ambient temperature for 15 min, 4'-chloro-4-biphenylcarboxaldehyde (0.85 g, 3.9 mmol), and sodium cyanoborohydride (84 mg, 1.3 mmol) were added and the mixture was heated at reflux for 3 hours. An additional portion of sodium cyanoborohydride (84 mg, 1.3 mmol) was added and the mixture was heated 3 hours longer at reflux. A final portion of sodium cyanoborohydride (84 mg, 1.3 mmol) was added and heating at reflux continued an additional 16 hours. The mixture was cooled to ambient temperature and 50% aqueous sodium hydroxide solution was added to adjust the pH of the reaction mixture to 7.6. Sodium borohydride (0.11 g, 2.9 mmol) was added and the solution was stirred 3.5 hours at ambient temperature. The reaction mixture was concentrated to 110 ml on a rotary evaporator and isopropyl alcohol (250 ml) was added dropwise over a period of 4 hours to precipitate the product. After cooling the purple slurry to 0°C for 1 hour, filtration afforded the purple complex of N4-(4-(4-chlorophenyl)benzyl)A82846B (11.03 g, 36.2% potency as wet cake, 3.99 bg, 77.6%. Reference Example B (no copper) A82846B (0.50 q, 84.3% potency, 0.42 bg, 0.26 mmol} was stirred in 50 mL methanol and 4'-chloro 4-biphenylcarboxaldehyde (72 mg, 0.33 mmol) and pyridine.borane complex (0.033 mL, 0.33 mmol) were added. The mixture was heated at reflux for 6 hours before being cooled to ambient temperature. HPLC analysis of a reaction aliquot afforded a yield of 0.25 g (53.2%) of N4-(4-(4-chlorophenyl)benzyl)A82 846B. EXAMPLE 6 A82846B {0.50 g, 84.3% potency, 0.42 bg, 0.26 mmol ) was stirred in 50 mL methanol and cupric acetate (45 mg, 0.25 mmol) was added. After stirring at ambient temperature for 10 min, 4'-chloro-4-biphenylcarboxaldehyde (84 mg, 0.39 mmol) and pyridine-borane complex (0.03 9 ml, 0.3 9 mmol) were added. The mixture was heated at 57° C for 24 hours before -27- being cooled to ambient temperature. HPLC analysis of a reaction aliquot afforded a yield of 0.34 g (72.3%) of N4-(4-(4-chlorophenyl)benzyl}A82 846B. EXAMPLE 7 A82846B (0.50 g, 76.3% potency, 0.38 bg, 0.24 mmol , and cupric acetate monohydrate (43 mg, 0.216 mmol) were stirred in 50 ml methanol and 4'-chloro-4-biphenylcarbox-aldehyde (84.5 mg, 0.3 9 mmol) and pyridine.borane complex (0.011 ml, 0.11 mmol) were added. The mixture was heated at 63°C for 2 hours and an additional portion of pyridine.borane was added (0.01 ml, 0.1 mmol). After 2 hours more at 63°C a third portion of pyridine.borane (0.005 ml, 0.05 mmol} was added. A fourth portion of pyridine.borane (0.005 ml, 0.05 mmol) was added 2 hours later followed by a fifth portion of pyridine.borane (0.005 ml, 0.05'mmol) after another 5 hours at 63°C. The mixture was heated at 63 °C for another 11 hours before being cooled to ambient temperature. HPLC analysis of a reaction aliquot afforded a yield of 0.34 g (79.2%) of N4-(4-(4-chlorophenyl)benzyl)A82846B. The reactions reported in Reference Examples A and B and Examples 1-7 were also evaluated (1) for the amount of the remaining starting glycopeptide, (2) for the amount of products alkylated on amine sites other than the N4position, and (3) for the amount of multiply-alkylated products. The results are set forth in the following table 28 and are expressed as a percentage relative to the intended product monoalkylated on the N4-amine; yields of the intended product are actual yields as recited in the foregoing examples. TABLE I Ex. % Mono- % % Mono- % Mono- % Di- % Di- % Tri- No. alkyl- A82846B alkyl- alkyl- alkylated alkylated alkylated ated ated ated at both at both at N4 at N6 at N1 N4 and N6 N1 and N4 RE A 53.7 14.1 3.5 2.4 24.4 15.9 3.4 1 80.3 7.6 1.0 0.4 9.7 5.6 0.7 2 85.4 13.0 2.4 0.7 8.2 5.9 0.9 3 79.1 9.8 1.1 0.5 8.1 6.4 0.6 4 72.9 10.1 1.0 0.4 5.8 4.7 0.3 5 77.6 9.3 1.0 0.4 7.1 5.4 0.5 RE B 53.2 47.6 9.9 1.3 21.7 7.8 1.8 6 72.3 17.8 2.1 0.7 6.2 2.5 0.4 7 79.2 9.2 1.4 0.3 7.4 3.4 0.3 These data show that the present invention provides several advantages. First, the yield of the product alkylated on N4 is increased. Second, the yields of products alkylated on N1 and/or N6 are decreased. Therefore, the present invention provides significant improvement in reaction regioselectivity. EXAMPLE 8 N4-- (4-(4-chlorophenyl)benzyl)A82846B Copper Complex A82846B (0.50 g, 75.6 - 78.8 % potency, 0.24 - 0.25 mmol) was stirred in 50 ml methanol and cupric acetate (53 - -29- 56 mg, 0.2 9 - 0.31 mmol} was added followed by 4' -chloro-4-biphenylcarboxaldehyde (7 0 - 73 mg, 0.32 - 0.34 mmol) and sodium cyanoborohydride (20 - 22 mg, 0.32 - 0.35 mmol). The reaction mixture was heated at reflux for 24 hours and cooled to ambient temperature. The pH was adjusted to 9.0 -9.3 by addition of 1 M NaOH solution. The reaction mixture was concentrated to 10 - 2 0 ml on a rotary evaporator and isopropyl alcohol (13 - 20 ml) was added dropwise to precipitate the purple glycopeptide copper complex which was isolated by suction filtration. Drying in vacuo at 60°C afforded the glycopeptide copper complex as a purple powder. After four repetitions of the process the combined glycopeptide complex was assayed for copper content and was found to contain 3.0% copper, confirming a 1:1 copper complex with N4-(4-(4-chlorophenyl)benzyl}A82 846B. Reference Example C & EXAMPLE 9-19 Various copper salts were evaluated in a standardized procedure. A82846B (1 equivalent as potency adjusted free base) was stirred in 50 ml methanol and a divalent metal salt (MX2, 0.63 equivalent) or a monovalent metal salt (MX, 1.25 equivalent) was added followed by 4'-chloro-4-biphenylcarboxaldehyde (1.25 equivalent) and sodium cyanoborohydride (1.25 equivalent). The mixture was heated -30- at reflux for 24 hours. After cooling to ambient temperature, an aliquot was removed for HPLC analysis. The following HPLC System was used for in situ reaction monitoring and yield calculation: HPLC system Waters 600E with HP3395 integrator and Applied Biosystems 757 detector set at 230 nm, sensitivity 0.1 absorption units, 1 sec. filter rise time. Column: DuPont Zorbax SB-Phenyl, 4.6 mm x 25 cm. Eluant A: 10% acetonitrile, 90% buffer (0.2% triethylamine, 0.25% H3PO4). Eluant B: 60% acetonitrile, 40% buffer (0.2% triethylamine, 0.25% H3PO4). Gradient profile at 1 mL/min: initialize 100% A, gradient to 80% A, 20% B over 5 minutes, hold 5 minutes, gradient to 100% B over 2 0 minutes, gradient to 100% A over 5 minutes, hold 2 0 minutes. Sample preparation: 0.5 - 1.0 g of reaction mixture diluted to 25 ml in acetonitrile - buffer. Hold at ambient temperature about 30 minutes until the purple color of the copper complex is discharged. The desired glycopeptide alkylation product elutes at 16-18 minutes, the starting glycopeptide nucleus at 3-4 minutes, the site N6 (monosugar) alkylation product at 18-19 minutes, the site N1 (methyl leucine) alkylation product at 19-21 minutes, dialkylated impurities at 24-26 minutes, and aldehyde at 35-36 minutes. In situ yield is determined by correlation to standards prepared with a reference sample of the product. The results are shown in the following table. Results for alkylated byproducts are expressed as percentage relative to the desired N4 alkylation product. -31- TABLE II % Relative to Mono Salt Yield pH on N4 nucleus mono mono Ex. No. (%) on N6 on N1 Ref Ex C none 63.5 7.2 25.6 7.8 1.8 9 CuF2 57.8 7.2 33.3 6.2 6.1 10 Cu(OH)2 62.0 7.0 21.3 4.1 1.6 11 . Cu(OAc)2 71.7 6.4 16.9 3.6 1.8 12 Cu(O2CCF3)2 64.0 6.2 17.9 4.0 2.1 13 Cu(cyc ilohexanebutyrate)2 69.0 6.4 15.6 2.3 1.2 14 Cu(2 -ethylhexanoate)2 69.0 6.5 20.8 3.1 1.4 15 CuCl2 66.9 6.2 28.6 4.7 3.3 16 CuBr2 67.5 6.1 18.5 3.9 2.4 17 18 CuCl CuS04.5H20 67.4 33.9 52.1 6*8 5-8 6.9 23.8 >100 32.2 4.1 4.6 7.1 2.4 1.9 8.8 * r\ CUSO4 The same copper salts were further evaluated for their solubility in methanol and for the solubility of the starting glycopeptide antibiotic in their presence. The procedure was as follows: the copper salt (0.165 mmol) was added to 50 mL methanol and stirred at ambient temperature for 15 min. Solubility data was recorded as well as the pH. Glycopeptide nucleus (0.55 g, 74.7% potency, 0.41 bg, 0.26 mmol) was added and stirring continued 15 min. Solubility and pH data was recorded. 32 TABLE III Salt Salt Solubility in MeOH pH nucleus solubility pH in presence of salt CuF2 low, cloudy white soln. 5. ,9 slightly, cloudy pink 7. .0 Cu(0H)2 low, cloudy lite blue soln 6. ,2 slightly, cloudy lite blue 7. ,0 Cu(0Ac)2 soluble, clear blue-green 6. .5 soluble, clear purple 6. .7 Cu{02CCF3)2 soluble, clear lite blue 4. .4 soluble, clear purple 6. 2 Cu(cyclohexane- faint cloudiness, 6. .0 soluble, clear 6. .7 butyrate)2 lite blue-green purple Cu(2-ethyl- soluble, clear blue- 6. .5 soluble, clear 6. ,7 hexanoate)2 CuCl2 CuBr2 green soluble, clear colorless soluble, clear yellow 3 2 .2 .8 purple slightly, cloudy purple soluble, clear purple 6 5 .6 .9 CuS04.5H20 soluble, clear colorless 3 .7 slightly, cloudy purple 6 .2 The foregoing examples illustrate several facets of the present invention. First, copper must be supplied to the reaction mixture in a form which is at least partially soluble: Copper salts such as CuF2 and Cu(OH)2, which are nearly insoluble in methanol, are not effective. Further, the copper salt preferably should allow full solubility of the starting glycopeptide antibiotic, and ideally at the preferred pH. The salts which work the best (Cu 33 at about pH 6.7. The salts which afford improvements over no additive but are not optimal (Cu (O2CCF3)2, CuCl2, CuBr2) either afford solubility of nucleus but at less than optimal pH (CuBr2 and Cu(02CCF3)2) or are at optimal pH but do not afford complete nucleus solubility (CuCl2). In summary, the copper must be in a form which is at least partially soluble, and should allow or maintain full solubility of the starting glycopeptide antibiotic at an acceptable pH, typically 6.3-7. Also, these experiments were conducted with suboptimal amounts of the copper; further advantage from the present invention is obtained at higher copper concentration. Reference Example D (no cooper) & EXAMPLE 20 Two reactions were conducted with the glycopeptide antibiotic A82846A, one without copper {Reference Example D) and one with cupric acetate monohydrate. The aldehyde was 4'-chloro-4-biphenylcarboxaldehyde. The reactions were conducted in the essentially same procedures as reported in the foregoing examples. Results were as set forth in the following table: 34 TABLE IV Reaction HPLC % Mono- % Mono- % Di- % Di- Area % alkylated alkylated alkylated on alkylated on Yield on N6 on N1 N4 and N6 N1 and N4 Ref Ex D 52.4 4.7 2.6 15.8 9.0 Example 20 71.4 1.1 0.9 6.6 6.0 EXAMPLE 21 A82846B Copper Complex A82846B (3.0 g, 78.7% potency, 2.4 bg, 1.5 mmol) was stirred in 300 ml methanol at ambient temperature and cupric acetate monohydrate (0.31 g, 1.6 mmol) was added. After stirring at ambient temperature for 2 0 minutes, the purple mixture was heated to 35 to 40oC and stirred an additional 30 minutes. the solution was concentrated to 45 mL on a rotary evaporator and 100 mL or isopropyl alcohol was added dropwise over 2 hours. The slurry was cooled to 0oC and filtered. Drying in vacuo at 35oC afforded 2.6 g of the A82846B copper complex as a purple solid. Mass spectroscopic analysis showed the expected ions for the complex, including a series of peaks around 1653, not seen in the analysis of a reference sample of A82846B, and indicative of the A82846B-copper complex. Another sample of A82846B copper complex was prepared in like manner and analyzed by UV-visible spectroscopy, which showed an absorbance maxima at about 540 mm, not seen in the spectra of a reference standard of A82846B or of cupric acetate and indicative of the A82846B copper complex 35 We Claim: 1. A method for reductively alkylating a glycopeptide antibiotic comprising an amine-containing saccharide at N4 and one or more other amines, wherein the reaction alkylates the amine on said N4 saccharide selectively over said one or more other amines, said method comprises of: a) reacting a soluble copper complex of the glycopeptide antibiotic with a slight molar excess of a ketone or aldehyde, in the presence of a solvent and a reducing agent, such as herein described, and heating at reflux and at a pH of 6-8, to obtain a reaction mixture, b) Isolating a copper complex of alkylated glycopeptide from the reaction mixture of step (a) by adding an antisolvent such as herein described to obtain a copper complex of an alkylated glycopeptide, optionally breaking the copper complex by aqueous treatment at pH 4 to obtain an alkylated glycopeptide product. 2. A method as claimed in claim 1, wherein the reducing agent is selected from sodium cyanoborohydride or pyridine.borane complex. 3. A method as claimed in claim 2, wherein the soluble copper complex of the glycopeptide antibiotic is prepared in situ from the glycopeptide antibiotic and a soluble form of copper. 4. A method as claimed in claim 3, wherein the glycopeptide antibiotic is a vancomycin type glycopeptide antibiotic. 5. A method as claimed in claim 4, wherein the glycopeptide antibiotic is A82846B. 6. A method as claimed in claim 1, wherein the pH is in a range of 6.3 - 7.0. 7. A method as claimed in claimed 1, wherein the solvent is selected from a group of methanol, Dimethyl Formamide and Dimethyl sulfoxide. 8. A method as claimed in claim 1, wherein the solvent is selected from methanol. 36 9. A method as claimed in claim l, wherein the aldehyde is 4'-chloro-4-biphenylcarboxaldehyde. 10. A method as claimed in any of the claims 1-6, which further comprises recovering a copper complex of the alkylating glycopeptide antibiotic. 11. A method as claimed in any of the claims 1-7, which further comprises recovering the alkylated glycopeptide antibiotic. 12. A method as claimed in claim 1, wherein in step (b) the antisolvent is selected from a group of ethyl acetate, acetonitrile, acetone, 1-propanol, isopropyl alcohol. 13. A method as claimed in claim 10, wherein the antisolvent is acetonitrile. 14. A copper complex of an alkylated glycopeptide antibiotic wherein the glycopeptide antibiotic is selected from A82846A and A82846B. 15. The copper complex as claimed in claim 12, said complex is a 1:1 copper complex with A82846B. 16. The complex of copper with a reductively. alkylated glycopeptide antibiotic, which is produced by the method as claimed in the claims 1-11. 17. The complex as claimed in claim 14, said complex is of a reductively alkylated A82846B. 18. The complex as claimed in claim 15, in which the reductively aklylated A82846B is N4 - (4-(4-(4-chlorophenyl) benzyl) A82846B. 19 . A method as claimed in claim 1 ,wherein the soluble copper complex of the glycopeptide antibiotic is in a molar ratio with the ketone or aldehyde of 1:1.3to1.7. This invention is concerned with improved processes for reductive alkylation of glycopeptide antibiotics. The improvement residing in providing a source of copper which 5 results in the initial production of a copper complex of the glycopeptide antibiotic. Reductive alkylation of this complex favors regioselective alkylation and increased yields. Copper complexes of the glycopeptide antibiotic starting materials and of the alkylated products are also 10 part of the invention.

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