CA1271744A

CA1271744A - Preparation of aminoglycosides

Info

Publication number: CA1271744A
Application number: CA000297395A
Authority: CA
Inventors: Stephen Hanessian
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-02-21
Filing date: 1978-02-21
Publication date: 1990-07-17
Also published as: CA1271744C

Abstract

ABSTRACT OF THE DISCLOSURE

N-Substituted derivatives of aminoglycosides are prepared by (a) complexing an aminoglycoside with divalent metal ion selected from the group consisting of the cations of Fe, CO, Ni, Cu, Pd, Ag and Pt to form a protected species having at least one amino group bound as a metal ion chelate and at least one unbound amino group, (b) reacting the protected species with an N-acylating reagent selected from the group consisting of carboxylic and sulfonic acid anhydrides, halides and active esters to acylate at least one unbound amino group, and (c) removing the amino-protecting chelate groups. Among the aminoglycosides useful are kanamycin A, kanamycin B, kanamycin C, sisomicin, gentamicin B, tobramycin, ribostamycin, butirosin A, butirosin B, neomycin B, paromomycin I, lividomycin A and lividomycin B. The N-substituted derivatives possess utility as antibiotics or as intermediates in the preparation of aminoglycoside antibiotics.

Description

~2717~4 The present invention relates to the preparation of N-substituted derivatives of aminoglycosides which are useful as antibiotics or as intermediates in the preparation of amino-glycoside antibiotics.
Microorganisms are known to frecluently acquire resistance to aminoglycoside antibiotics by a mechanism known in the art as "R~Factors". Very generally an r'R~Factor" is the extrachromosomal genetic capability of biochemically modifying the antibiotics in such a way as to interfere with its antîbacterial action, thereby enabling the organism to grow, The phenomenon of bacterial resistance to amino-glycoside antibiotics has fostered many new developments in the area of semi-synthesis and chemical modification leading to second and third generation aminoglycosides, The latter class comprise .
N-acylated and N-alkylated analogs that exhi~it much broader antibacterial activities than the parent antibiotics~ Improved methods for the selective N~acylation of aminoglycosides are in demand as current procedures are confined mostly to the more accessible sites, or are based on relative basicities, . In a broad aspect the present invention provides a method for the preparati.on of N-substituted derivatives of amino-glycosides which comprises the steps of (a) complexing an am:Lno-glycoside with divalent metal ion ~e1.ected .E~om t~le ~,roup con~q1st:irlg of the cations of F~, Co, Ni., Cu, Pd, Ag and Pt to form a prot:ected species having at least one amino group bound as a meta~ ion chelate and at least one unbound amino gro~lp, (b) reacting the protected species with an N--acylati.rlg reagent selected from the group con-sl~ti.ng of carboxylic and sulfollic acid anhydrides, halides and active esters to acylate at least one unbound amino group, and '~ ' i 1/ -1-~ 71744 (c) removing the amino-protecting chelate groups.
Included among the aminoglycosides useful in the invention are kanamycin A, kanamycin B, kanamycin C, sisomicin, gentamicin B, tobramycin, ribostamycin, butirosin A, butirosin B, neomycin B, paromomycin I~ lividomycin A and lividomycin B.
Broadly speaking, suitable acylating reagents include the anhydrides, halides and active esters of carboxylic and sulfonic acids, The term halide is taken to include azide in view of the pseudo-halide reactivity of the anion _ N3.
Suitable carboxylic acid anhydrides, halides and active esters include those of the formulae (R-CO) 2; R-COX and R-COORl wherein R is r~ _ N ~ ; - N ~ ; ~no ~ Q 2 O O

Preferred N~acylating reagents include the following:

(a) acetic anhydride O O
Il 11 (b~ p-nltrophenylacetate O

Ct~3 - C - O ~ ~ - NO~, (c~ N-acetoxy-5~norbornene-2,3-dicarboxamide O O

o jl/ ~2_ "` 1271744 (d) N-benzyloxycarbonyloxy succinimide O O
CN O C O C H 2 ~

te) N~ benzyloxycarbonylaminobutyroxy) succinimide O O O
CN O C ( CH 2 ) 3 NH I - O CH 2 ~3 Il o (f) benzyl p~nitrophenyl carbonate ~ CH2 O C O ~NO2 (g) N-acetoxy succinimide 1l o (h) N-benzyloxycarbonyloxy-5-norbornene-2, 3-dicarboxamide O O
,- ~. ," 11 ¢~ N o c o C ~1 2 ~

(i) benzyl pentachlorophenyl carbonate C~ ~1 0 Cl ~ O - C - O - C~

Cl Cl and ~ 3-(j) benzyl-2,4-dinitrophenyl carbonate O N ~2 CH2 - O - C ~ O ~ - NO2 Using the readily available kanamycin A as an exemplary substrate because of the clinical importance of its derivatives and the manipulative difficulties associated with selective N-acylations of aminoglycosides eontaining multi amino functions, the following derivatives can be prepared by seleetive N-aeylati.on, according to the following reaction scheme, subsequent to protection of vicinal amino aleohol functions as eopper(II) ehelates by eomplexing kanamycin A with Cu ions:

~ UO
O ~ lating agent ~ ~

~ OH I NHR"

~---~~1~~~-- ~O ~ H

Scheme 1 R = aeetyl; R',R" ~ 11

2 R = benzyloxycarbonyl; R', R" = H

3 R,R',R" = acetyl

4 R,R~,R" - benzyloxycarbonyl R,R" = acetyl; R' ~ H

6 R,R' - aeetyl; R" = H

`` 1~7~744 7 R ~ benzyloxycarbonyl; R',R1' - acetyl 8 R = benzyloxycarbonyl; R',R" = 4-benzyloxycarbonylaminobutyryl 9 R = H; R',R" = 4-aminobutyryl R = H; R',R" = 2-hydroxy~4-benzyloxycarbonyLaminobutyryl - The above derivatives are named as follows:
1 6'-N-acetyl kanamycin A, 2 6'-N-benzyloxycarbonyl kanamycin A, 3 1,3,6'~tri~-acetyl kanamycin A, 4 1,3,6'~tri-N_benzyloxycarbonyl kanamycin A, 1,6'-di~N-acetyl kanamycin A, 6 3,6'-di~N-acetyl kanamycin A, 7 6'-N-benzyloxycarbonyl_1,3~di-N-acetyl kanamycin A, 8 6'-N-benzyloxycarbonyl_1,3-di-N-(4-benzyloxycarbonylaminobutyryl) kanamycin A, _ 1,3-di~N-(4_aminobutyryl) kanamycin A, and L0 6'-N-benzyloxycarbonyl-1,3~di-N-(2-hydroxy-4-benzyloxycarbonyl-aminobutyryl) kanamycin A.
Derivative 2, i,e. 6'~N-benzyloxycarbonyl kanamycin A, is a particularly important species in that it is a key inter-mediate in the preparation of the antibiotic amikacin which is taught in Kawaguchi et al U,S, Patent No. 3,781,268 issued December 25, 1973.
While Scheme 1, above, ilLustratcs chelation of h~ o ~ ~1 A the 3" amino group with the 4" ~ Froul~ :Lt w:Lll be app~rent to those ski.l:led ln t:lle art that all equal:l.y pr:Lmary chelation sit:e ~ ra~ I
is provided by the 3" amino group and the vicinal 2" h~dre:c~
group and that complexing wil:L undo~lbtedly occllr at both sites.
Kanamyc:l.n A has, as menti.oned previously, been used as an exemplary am:inoglycoside both because of its ready availability and the clinical importance of a number of its jl/ _5~

~X~7:1~44 derivatives. It should however be understood that the simple, selective N-acylation afforded by the present invention as a consequence of temporarily protecting certain amino groups as divalent metal ion chelates is applicable to a broad range of aminoglycosides.
The primary chelation site(s) vary dependent on the aminoglycoside, or the type of aminoglycoside, employed.
n the case o~ tobramycin, an aminoglycoside o pseudo trisaccharide of the kanamycin type, the primary chelation sitets) are the same as in kanamycin A, i.e.
the complexing will involve the 3~ amino group with either the 2" or 4~ hydroxyl group.
In the case of pseudotrisaccharides in the 4,5-disubstituted 2-deoxystreptamine series, for example ribostamycin or its 6'-oH analog, butirosin A and butirosin s, the primary chelation sites involve the C-2'/C-3' and C-l/C-6 substituents.
pseudotetrasaccharides of the neomycin type, for example neomycin B and paromomycin I, primarily chelate at the C-2'/C-3' substituents, although chelation is also prevalent in the D ring. The primary chelation site of lividomycin A, another pseudotetrasaccharide of the neomycin type, is at the vicinal amino hydroxyl groups of the D ring.
As will be understood by those skilled in the art, chelation should be carried out with appropriate divalent cation/ligand concentrations. In general a low divalent cation/ligand ratio is preferable to avoid undue complexing of functions which are to be N-acylated. stated differently, selectivity i9 relative to availability, such that chelation will occur at secondary or tertiary etc., sites when the primary sites are chelated.

lX7174~

As stated previously, divalent cations of Fe, Co, Ni, Cu, Pd, Ag and Pt are suitable for complexing with the amino-glycoside to form the protected species which is subsequently N-acylated. The preferred cation is Cu+ , for reasons including availability and cost, although it will be obvious to those skilled in the art that other divalent cations can be used in the invention with equal efficacy.
The diva]ent cations are provided by dissolution of suitable metal salts in a solvent which already contains an aminoglycoside or which may be combined with an aminoglycoside containing solution or to which may be added an amount of an aminoglycoside.
Particularly preferred salts include CuS04.5H20;
Cu(CH3COO) 2 ,H20; Cu(NO3~2 and CuC12.
Deprotection of the aminoglycosides, that is removal of the protective chelate following selective N-acylation~
can be con~eniently accomplished, in the case of product recovery by column chromatography, by utilizing a basic eluent such that deprotection and product recovery are effected in a single step.
The cations removed from the aminoglycoside tend to adsorb at the top of the column. Other procedures for chelate removal will be obvious to those skilled in the art.
The following non-lLTnl~t:Lve ~xalllples Ll:LIl~tra~e the present inverltlorl.

Jl/ -7-~2717~4 E X A M P L E

6'-N-Acetyl Kanamycin A
Kanamycin A free base (484 mg, 1 mmole) was dissolved in 20 ml of distilled water, A solution of cupric acetate monohydrate (150 mg, 0~75 mmole) in 5 ml distilled water was then added dropwise and the resulting purple colored solution was stirred for 5 minutes, p-Nitrophenylacetate (182 mg, 1 mmole) in THF (25 ml) was added to the above solution, which immediately turned green in color. After stirring for 23 h at 25, TH~ was removed under reduced pressure at 25 and the solution poured into acetone (300 ml). The green precipltate thus obtained was filtered, washed with acetone and air~dried, The powdery material was then suspended in 5 ml of ~ CH30H:0.05N ~H40H (1:3.2:2) and 28%
NH40H (0.1 ml) was added to obtain a clear deep blue solution.

This was then applied on a silica gel column (3.5 cm x 8.0 cm).
C J~C~3 The column was first eluted with CHC~,:CH30H:0,05N NH40H (1:3.2:2) ~c/3 (one bed volume) and then with-C~ECL~:CH30H:28% NH40H (1:3:2) (10 ml fractions). The product was found in fractions 26-33, which were combined and coevaporated with ethanol and dried in vacuo to give colorless powder (430 mg, 82%), m,p, 213~215C,[~]D5 +

94.8 (Hzo), The material was analyzed by mass spectrometry and found to have the correct 6tructllrc~.

7~744 E X A M P L E _ _ 6~-N-Benzyloxycarbonyl Kanamycin A
. . .
Kanamycin A free base (250 mg, 0,515 mmole) was dissolved in 5 ml of distilled water. To thls was added, with stirring, a solution of cupric acetate (160 mg, 0.4 mmole~ in

5 ml distilled water, 3 ml of THF (tetrahydrofuran) was added to the resulting purple solution, followed by the addition of a solution of benzyl p-nitrophenylcarbonate (2.3 mg, 0.778 mmole) dissolved in 13 ml THF, After stirring at room temperature for 12 h, the reaction mixture was slowly poured into acetone ~200 ml) with stirring, The fine blue precipitate was col.lected by filtration, washed with acetone followed by ether and air drled.
This precipitate was dissolved in 2 ml of a solvent mixture (CHClg:CH30H 28~NH40H; 10:7:2.5~, applied on a silica gel column (silicAR~ GF 254) and the product separated using the above solvent system under mild suction from an aspirator, 6'~N-benzyloxy-carbonyl kanamycin A free base (250 mg, 0,406 mmole) was isolated in a 78.8% yield as an amorphous colorless powder; m.p. 204_212 (dec)C (lit:204-212(dec)C)l, [~]D5 + 115.6C (c 0.92, H20) .
(lit: + 116), 1. H, Kawaguch:L, T~ Naito, S. Nalcagaw~ ~nd K. Fu~ saw;.l, J. Anti-biotlcs 25, 695 (.1.972), lZ71744 E _~ M P L E 3 1,3,6'-t _ N ~cetyl Kanamycin ~
Kanamycin free base (242 mg, 0,5 mmole) was dissolved in 10 ml of distilled water. Sodium bicarbonate (420 mg, 10 equivalent) was added followed by copper sulfate pentahydrate (3.75 g, 15 mmole) in 50 ml cf distilled water, Tlle evolution of carbon dioxide was allowed to cease and acetic anhydride (1 ml, 20 equivalent) added. After stirring overnight the mixture was treated with 4 ml of acetylacetone and stirred for five minutes.
The copper acetyl-acetone complex was extracted with chloroform (200 ml), then the aqueous layer treated with two drops of 28%
ammonium hydroxide and the solution extracted with chloroform (100 ml). The inorganic material was precipitated by adding absolute ethanol to the aqueous solution and filtered off. The filtrate was treated with 1:1 ethanol:light petroleum ether (b.p. 30-60C) to give crude 1,3,6'-N~acetyl kanamycin (300 mg3.
This was purified on a silica gel column using CHCL3:CH30H:0,05N
NH40H (1:3.2:2) as the solvent system to give 251 mg (82.5~) of chromatographically pure product, m,p, 235-237C [a]D5 -~ 88,7 (c 1.06, H20); t.i.c, (CHCl3:CH30H:0.05N NH40H, 1:3.2:3), ~f 0 ~9, Mass spectra (as N,0-permethyl derivatives) M~ 778 (molecular ion).
Spectroscopic data (l9Cmr) was in accord with the structure.

~ ~Z7~L744 1,3,6'-tri-N-Acetyl K namycin A
A solution of kanamycin free base (2.00 g, 4.13 mmole) in 200 ml of water was added to a stirred solution of copper sulfate pentahydrate (1,03 g, 4.13 mmole) in 100 ml of water, The resulting complex was treated with acetic anhydride (3.9 ml, 4,22 mmole) and the solution stirred at room temperature f~r five hours. The solution was extracted with ether and the aqueous layer treated with hydrogen sulfide gas. The insoluble black precipitate was filtered off over C,elite~ and the yellow colored filtrate decolorized with activated charcoal, basified with Dowex~ 1 x 8( OH~ resin, coevaporated with ethanol and dried in vacuo (2,37 g), Chromatography of the residue over silica gel with CHel9:CH30H:0.05N NH40H (1:3:1) 'as e].uent solvent afforded ~h~ 60.4~ yield as amorphous powder identical to the material obtained in Example 3.

" 1~7~744 E X A ~ P L_E 5 1,3,6'-tri-N-Benzyloxycarbonyl ~Canamycin A
Cupric acetate (1.0 g, 5 mmole) in 20 ml distilled water was added to a solution of kanamycin A free base (242 mg, 0.5 mmole) and sodium hydrogen bicarbonate (126 mg, 1,5 mmole) in ~rbo~7 d,ox ;1~
10 ml distilled water, The slow evolution of ~Lbv.ldl~xl~e was allowed to cease, the mlxture treated with N-(benzyloxycarbonyl) succinimide (623 mg, 2.5 mmole) in 25 ml tetrahydrofuran and the solution sitrred at room temperature for ten hours. The mixture was concentrated at 25C to 30 ml under reduced pressure and the precipitated material filtered, washed with 100 ml acetone and air dried (605 mg). Chromatography of this green powder over silica ~ o, 7; ~.s gel with CHCl3:CH40H:28%:NH40H (10l ,5-~ -) as eluent gave 1,3,6'-tri-N-benzyloxycarbonyl kanamycin A (393 mg~ 85.8%), m,p.

258-263(dec~C*, [~]D5 + 83.9C (60%aq, THF); M. 1054 (on the corresponding per-N,O-methyl derivative), * T. Naito, S. Nakagawa, Y~ Abe, S, Toda, K. Fuiisawa, T~ ~iyaki, fs'~,z) Q9~C~,`
H, }Coshigawa, H. Ohkuma and H, Ka~7agu~1i-a, J. Antibiotics 26, 297 (1973)-" ~27~7~4 1,3,6'_tri~N-Benzyloxycarb =
A solution containing 6'-N-benzyloxycarbonyl kanamycin A (205,5 mg, 0.33 mmole), from Example 2, in 10 ml of distilled water was treated with cupric acetate monohydrate (200 mg, 1 mmole) in 5 ml distilled water, To -this was added, over thirty minutes, N-(benzyloxycarbonyloxy)-succinimide(164.5 mg, 0.66 mmole) in 10 ml tetrahydrofuran and the solution stirred at room temperature for ten hours. Tetrahydrofuran was removed by evaporation at 25C under reduced pressure and the mixture filtered, washed with distilled water, acetone and finally with ether.
1,3,6'-tri~N-benzyloxycarbonyl kanamycin A (2~0 mg, 92.6%) was isolated by silica gel column chromatography using CHCl3:CH30H:25%
NH40H (10:3:0.5) as eluent solvent. The physical properties proved identical to those of the 1,3,6'-tri_N-benzyloxycarbonyl kanamycin A of Example 5, ~27~744 E_AMPLE 7 Synthesis of 1,3,6'-tri-N-Acetyl Kanamycin A:1,6'-di-N
Acetyl_Kanamycin A and 3,6' -dl-N-Acetyl Kanamycin ~

A solution of copper sulfate pentahydrate (75.2 mg, 0.3 mmole) in 2 ml of water was added to a stirred solution of kanamycin A free base (192 mg, 0.4 mmole) in 8 ml water The resulting purple chelate was treated with a solution of N-acetoxy-5-norbornene-2~3 dicarbo~amide (353.6 mg, 1.6 mmole) in water:
tetrahydrofuran (4:1, 4 ml) and the solution stirred at room temperature for 1 1/2 hours. The copper chelate was precipitated with acetone (100 ml) and filtered to give a green solid. chromatography of this over silica get with CHC13 : CH3OH : 0.05N NH40H (1:3.2:2) isolated the following products:
Tetra-N-acetyl kanamycin A (14 mg, 6.2%), m p. 222-225 (dec)C, Rf 0.71*;
1,3,6'-tri-N-acetyl kanamycin A (108 mg, 44.2~), m~p. 235-237(de c)C, Rf 49* [~q 25 88 H2O);
1,6'-di-N-acetyl kanamycin A (56 mg, 24.6%), m.p.
228-231C, ~C]D + 92.1 (c 1.06" H20), Rf 0.37*
3l6~-di-N-acetyl kanamycin ~ (43 mg, 18.9%), m.p.
25206-208C, [C]D + 91.8 (c 0.98, H20), Rf 0.25*

The structures of these products were proved by mass spectrometry and 13Cnmr spectrometry *CHC13:MeOH:0.05N NH40H (1:3.2:2) X

127:174~

6'-N-Benzyloxycarbonyl-1,3-d_-N-Acetyl Ka amycin A
A solution of copper sulfate pentahydrate (2.475 g, 9.9 mmole) in 30 ml of distilled water was added to a stirred solution containing 6'~N-benzyloxycarbonyl kanamycin A (205.5 mg, 0.33 mmole), from Example 2, and sodiumbicarbonate (277,2 mg, 3.3 mmole) in 15 ml distilled water. The resulting slow evolution of carbon dioxide was allowed to cease and the mixture heated with acetic anhydride (0.66 ml, 6.6 mmole) and stirred at room temper-ature for ten hours. The insoluble matter was filtered and dis~
carded and the filtrate evaporated to dryness under reduced pressure. Chromatography of the residue on silica gel using CHCl3:CH30H:0.05N NH40H (1:3,2:2) as eluting solvent afforded A 189 mg (81,7~o) of 6'-N-benzyloxycarbonyl~1,3-di-N-acetyl kanamycin A, m.p. 173-177(dec)C. The structure of the compound was confirmed, using 13 Cmr spectroscopy, by the diagnostic ~-protonation shifts.

- l5 -127~ 7d~

6'-N-Benzyloxycarbonyl~1,3-di-N-(4-Benzyloxycarbonylaminobutyryl) Kanamycin A
A solution of 6~-N-benzyloxycarbonyl kanamycin A
(789.2 mg, 1,28 mmole), from Examp]e 2, in 10 ml o~ distilled water was treated with cupric acetate monohydrate (255,5 mg, 1.28 mmole) in 25 ml of distilled water and then diluted with 10 ml of -tetra-hydrofuran. To this was added, over thirty minutes, N-hydroxy-succinimide ester of 4-benzyloxycarbonylaminobutyric acid (479 g, 1.28 mmole) in 15 ml tetrahydrofuran and the solution stirred at room temperature for ten hours. Ammonium hydroxide ~28%) was added dropwise to the reaction mixture until a clear blue colored solution was obtained. The product (Rf 0.44) was separated by /0,,~ '~
A thick layer chromatography using CHCl3:CH30H:28% NH40H (~ }-~) as solvent system. 6'-N-benzyloxycarbonyl-1,3-di-N-(4-benzyloxy-carbonylaminobutyryl) kanamycin A was isolated (213 mg, 15.6%) as an amorphous powder, m.p. 192 195(dec)C, M. 1252 (on corresponding N,0-permethyl derivatives), The structure was further confirmed from mass spectral and 13 Cmr spectroscopic studies.

~.~7~744 1,3-di-N-(4-Amino _t~ Kanamycin _ 6'~N-ben7yloxycarbonyl 1,3-di-N-(4-ben~yloxy carbonylaminobutyryl)kanamycin A (168 mg, 0.16 mmole), from Example 9, in 20 ml of 60%aq tetrahydrofuran was brought to pH 4 with 3%aq hydrochloric acid. To this, 10% palladised charcoal (100 mg) was added and the mixture hydrogenated at room temperature for three hours. The mixture was filtered, concentrated under reduced pressure and applied on a Dowex~ 1 x 8 ( OH) column.
/yo~ t'~
A The product was eluted with water and cyophiliscd'(97 mg, 91.0%), m.p. 168-74C. The product was a chromatographically homogeneous amorphous solid, ~:7~7~

E X A M P L_E 11 6'-N-Benzyloxycarbonyl-1,3-di-N-~2~Hydroxy-4~Benzyloxycarbonyl-aminobutyryl) Kanamycin A _ _ _ _ Using the procedure of Example.9, but employing N-hydroxysuccinimide ester of 2~hydroxy~4_benzyloxycarbonyl_ aminobutyric acid in place of N-hydroxysuccinimide ester of 4-benæyloxycarbonylaminobutyric acid, there is obtained 6'~N-benzyloxycarbonyl-1,3-di-N-(2-hydroxy-4-benzyloxycarbonylamino-butyryl) kanamycin A.

Modifications within the true broad spirit and scope of the invention will be obvious to those skilled in the art~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED
AS FOLLOWS:

1. A method for the preparation of N-substituted derivatives of aminoglycosides which comprises the steps of (a) complexing an aminoglycoside with a divalent metal ion selected from the group consisting of the cations of Fe, Pd, Ag and Pt to form a protected species having at least one unbound amino group, (b) reacting the protected species with an N-acylating reagent and (c) removing the amino-protecting groups.

2. A method according to Claim 1 wherein the aminoglycoside is selected from the group consisting of kanamycin A, kanamycin B, kanamycin C, sisomicin, gentamicin B, tobramycin, ribostamycin, butirosin A, butirosin B, neomycin B, paromomycin I, lividomycin A
and lividomycin B.

3. A method according to Claim 1 or 2 wherein the N-acylating reagent is selected from the group consisting of R-COX; (R-CO)2O and R-COOR1, wherein R is lower alkyl, aryl, aralkyl or aralkyloxy, X is chloride, bromide or azide, and R1 is

4. A method for the preparation of 6'-N-substituted derivatives of aminoglycosides which comprises the steps of (a) complexing an aminoglycoside with divalent metal ion selected from the group consisting of the cations of Fe, Pd, Ag and Pt to form a protected species having at least one amino group bound as a metal ion chelate and at least one unbound amino group, (b) reacting the protected species with an N-acylating reagent selected from the group consisting of R-COX; (R-CO)2O and R-COOR1, wherein R is lower alkyl, aryl, aralkyl or aralkyloxy, X is chloride, bromide or azide, and R1 is

5. A method according to Claim 4, in which the aminoglycoside is kanamycin A and the N-acylating reagent is P-nitrophenylacetate.

6. A method according to Claim 4, in which the aminoglycoside is kanamycin A and the N-acylating reagent is benzyl p-nitrophenyl carbonate.

7. A method according to Claim 4, in which the aminoglycoside is kanamycin A and the N-acylating reagent is acetic anhydride.

8. A method according to Claim 4, in which the aminoglycoside is kanamycin A and the N-acylating reagent is N-(benzyloxycarbonyl) succinimide.

9. A method according to Claim 4, in which the aminoglycoside is kanamycin A and the N-acylating reagent is N-(benzyloxycarbonyloxy) succinimide.

10. A method according to Claim 4, in which the aminoglycoside is kanamycin A and the N-acylating reagent is N-acetoxy-5-norbornene-2,3-dicarboxamide.

11. A method according to Claim 4, in which the aminoglycoside is 6'-N-benzyloxycarbonyl kanamycin A and the N-acylating reagent is acetic anhydride.

12. A method according to Claim 4, in which the aminoglycoside is 6'-N-benzyloxycarbonyl kanamycin A and the N-acylating reagent is N-hydroxysuccinimide ester of 4-benzyloxycarbonylaminobutyric acid.

13. A method according to Claim 12, including the further step of hydrogenating the product obtained.

14. A method according to Claim 4, in which the aminoglycoside is 6'-N-benzyloxycarbonyl kanamycin A and the N-acylating reagent is N-hydroxysuccinimide ester of 2-hydroxy-4-benzyloxycarbonyl amino butyric acid.

15. Novel N-substituted aminoglycosides, except for 6'-N-acetyl Kanamycin A.

16. The compound of Claim 15, wherein the substituent is chosen from acetyl, benzyloxycarbonyl, and hydroxy-benzyloxycarbonyl groups.

17. 1,3,6'-tri-N-acetyl kanamycin A.

18. 1,3,6'-tri-N-benzyloxycarbonyl kanamycin A.

19. 1,6'-di-N-acetyl kanamycin A.

20. 3,6'-di-N-acetyl kanamycin A.

21. 6'-N-benzyloxycarbonyl-1,3-di-N-acetyl kanamycin A,

22. 6'-N-benzyloxycarbonyl-1,3-di-N-(4-benzyloxy-carbonylaminobutyryl) kanamycin.

23. 1,3-di-N-(4-aminobutyryl) kanamycin A.

24. 6'-N-benzyloxycarbonyl-1,3-di-N-(2-hydroxy-4-benzyloxycarbonyl-aminobutyryl) kanamycin A.

25. A method according to Claim 1, wherein said N-acylating reagent is selected from the group consisting of carboxylic and sulfonic acid anhydrides, halides and active esters to acylate at least one unbound amino group.

26. A method for the preparation of 3,6'-di-N-acetyl Kanamycin A which comprises the steps of (a) complexing Kanamycin A with a divalent metal ion selected from the group consisting of the cations of Co, Ni and Cu to form a protected species having at least one unbound amino group, (b) reacting the protected species with an N-acylating reagent and (c) removing the amino-protecting groups to form said diacetyl Kanamycin A.

27. A method according to Claim 26 wherein the metal cation is Cu++ ion.

28. A method according to Claim 26 or 27 wherein the N-acylating reagent is selected from the group consisting of R-COX; (R-CO)2O and R-COOR1, wherein R is methyl, X is chloride, bromide or azide, and R1 is

29. A method according to Claim 26, in which the aminoglycoside is kanamycin A, the cation is Cu++, and the N-acylating reagent is N-acetoxy-5-norbornene-2,3-dicarboxamide.

30. A composition comprising a compound of Claims 16, 17 or 18, together with a pharmaceutically acceptable carrier therefor.

31. A composition comprising a compound of Claim 19, 20 or 21, together with a pharmaceutically acceptable carrier therefor.

32. A composition comprising a compound of Claim 22, 23 or 24, together with a pharmaceutically acceptable carrier therefor.