The present invention is in the field of the manufacture of mixed anhydrides.
The manufacture of mixed anhydrides is known per se and is based on the reaction of an acid with a reactive acid derivative, for example an acid halide or acid anhydride in the presence of an adjuvant base. The production of mixed anhydrides has been described, for example, by Bodansky in xe2x80x9cPrinciples of Peptide Synthesisxe2x80x9d, 2nd ed., published by Springer Berlin, 1993, pages 21-29 and in xe2x80x9cThe Practice of Peptide Synthesisxe2x80x9d, 2nd ed., published by Springer, Berlin, 1994 as well as by Stelzel in Houben-Weyl, volume XV/2, xe2x80x9cMethoden der organischen Chemie: xe2x80x9cSynthese von Peptidenxe2x80x9d, part II.
Mixed anhydrides play a role primarily in activating and coupling reactions. Thus, Bodansky (loc.cit.) describes the synthesis of mixed anhydrides with pivaloyl chloride for use in the synthesis of peptides. For example, for the production of benzyloxycarbonyl-xcex1-methylalanyl-xcex1-methylalanine methyl ester, acid and adjuvant base are provided and the acid chloride is added. The mixture is stirred at xe2x88x925xc2x0 C. for 2 hours and subsequently at room temperature for 1 hour. The production of benzyloxycarbonyl-Nxcex5-xcex1-p-toluenesulphonyl-L-lysylglycine ethyl ester proceeds analogously.
Stelzel (loc. cit.) describes the synthesis of N-benzyloxycarbonyl-L-prolyl-L-leucylglycine ethyl ester based on the addition of isovaleroyl chloride to a mixture of Z-Pro-OH and triethylamine in toluene.
However, these and other known processes for the production of mixed anhydrides have considerable disadvantages. Thus, the reaction does not proceed quantitatively by a long way. This is primarily due to the formation of byproducts, e.g. by disproportionation to the corresponding symmetrical anhydrides. Consequently, it is necessary to subject the reaction mixture to a costly working-up and purification.
This invention provides a process for producing an anhydride of two different carboxylic acids, comprising forming a mixture of a first carboxylic acid and a reactive acid derivative of a second carboxylic acid other than the first carboxylic acid, and reacting said mixture in the presence of a base to produce said anhydride, said base being added to said mixture to initiate the reaction.
By first mixing a carboxylic acid and the reactive acid derivative of a different carboxylic acid, and only afterwards combining the mixture with the base, it has surprisingly been found that the formation of unwanted byproducts including the symmetrical anhydrides can be largely avoided. Consequently, the yield of the desired mixed anhydride is increased. Because of the increased yield this invention provides a more efficient reaction for producing mixed anhydrides. Additionally, the production of mixed anhydrides is rendered more economical since the reaction product is more pure and therefore requires less post-reaction purification.
This invention provides a process for producing an anhydride of two different carboxylic acids, comprising forming a mixture of a first carboxylic acid and a reactive acid derivative of a second carboxylic acid other than the first carboxylic acid, and reacting said mixture in the presence of a base to produce said anhydride, said base being added to said mixture to initiate the reaction.
In accordance with this invention any of the conventional conditions for forming an anhydride by reacting a carboxylic acid, a reactive acid derivative, and a base, can be used. What is important is that the base is not added until a mixture of the first carboxylic acid and the reactive acid derivative is formed.
Preferably the first carboxylic acid and the reactive acid derivative are present in the mixture in a molar ratio of about 1:1, however either the first carboxylic acid or the reactive acid derivative can be present in excess. Preferably the base is present in the mixture in an amount which is at least about one mole per mole of the first carboxylic acid. More preferably, the base is present in an amount which is from about one mole to about two moles per mole of the first carboxylic acid. Still more preferably the base is present in an amount which is about one mole per mole of the first carboxylic acid. Preferably the base is present in the mixture in an amount which is at least about one mole per mole of the reactive acid derivative. More preferably, the base is present in an amount which is from about one mole to about two moles per mole of the reactive acid derivative. Still more preferably, the base is present in an amount which is about one mole per mole of the reactive acid derivative.
This reaction is generally applicable and can be used for making any mixed anhydride. The first carboxylic acid and the second carboxylic acid can be any carboxylic acid provided that they are different from each other. The term xe2x80x9ccarboxylic acidxe2x80x9d means any compound having a xe2x80x94COOH moiety. These can be e.g. unsubstituted and substituted aliphatic, aromatic, aromatic-aliphatic, heteroaromatic or heteroaromatic-aliphatic carboxylic acids or protected aminocarboxylic acids, e.g. N-acylated aminocarboxylic acids such as natural N-acylated xcex1-amino acids having the L-configuration or corresponding non-natural N-acylated xcex1-amino acids having the D-configuration as well as the corresponding racemates of the L- and D-amino acids. Moreover, homologues of such amino acids can be used, e.g. amino acids in which the amino acid side-chain is lengthened or shortened by one or two methylene groups and/or in which a methyl group is replaced by hydrogen. Furthermore, there can be used substituted aromatic N-acylated xcex1-amino acids, e.g. substituted phenylanine or phenylglycine, which can carry one or more of the following substituentsxe2x80x94independently of one anotherxe2x80x94: alkyl, e.g. methyl, halogen, a protected hydroxy group, alkoxy, e.g. methoxy, alkanoyloxy, e.g. acetoxy, a protected amino or alkylamino group, alkyanoylamino, e.g. acetylamino or pivaloylamino, alkoxycarbonylamino, e.g. t-butoxycarbonylamino, arylmethoxycarbonylamino, e.g. benzyloxycarbonylamino or 9-fluorenylmethoxycarbonyl, and/or nitro. Moreover, benz-fused phenylalanine or phenylglycine, such as xcex1-naphthylamine, or hydrogenated phenylalanine or phenyglycine, such as cyclohexylalanine or cyclohexylglycine, a 5- or 6-membered cyclic benz-fused N-acylated xcex1-amino acid, e.g. indoline-2-carboxylic acid or 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, also come into consideration. Furthermore, natural or homologous N-acylated xcex1-amino acids in which a carboxy group in the side-chain is present in a esterified or amidated form, e.g. as an alkyl ester group, such as methoxycarbonyl or t-butoxycarbonyl, or as a carbamoyl group, an alkylcarbamoyl group, such as methylcarbamoyl, or a dialkylcarbamoyl group, such as dimethylcarbamoyl, and in which the amino group in the side-chain is present in acylated form, e.g. as an alkanoylamino group, such as acetylamino or pivaloylamino, as an alkoxycarbonylamino group, such as t-butoxycarbonylamino, can be used. In addition, amino acids in which a carboxy group in the side-chain is present as an aryl-methoxycarbonylamino group, such as benzyloxycarbonylamino, can be used. A hydroxy group in the side-chain can be present in a etherified or esterified form, e.g. as an alkoxy group, such as methoxy, and also as an arylalkoxy group, such as benzyloxy, or as a lower-alkanoyloxy group, such as acetoxy. Suitable N-acyl groups are alkanoyl, such as acetyl or pivaloyl, alkoxycarbonyl, such as t-butoxycarbonyl and arylalkoxycarbonyl, such as benzyloxycarbonyl.
Examples of suitable unsubstituted and substituted aliphatic, aromatic and aromatic-aliphatic carboxylic acids, which can optionally be used in the form of their protected derivatives, are propionic acid, isobutyric acid, (R)- and (S)-lactic acid as well as the corresponding racemates, 2-phthalimidoxy-isobutyric acid and benzoic acid, 3,4-dihydroxybenzoic acid, salicylic acid, 1-naphthoic acid, 2-naphthoic acid, phenylacetic acid, p-hydroxyphenyl-acetic acid, (S)-xcex1-[(t-butylsulphonyl)methyl]hydrocinnamic acid and (S)-xcex1-[[[1-(morpholinocarbonyl)-1-methylethyl]sulphonyl]methyl]hydrocinnamic acid. 2-Pyridinecarboxylic acid, 3-pyridinecarboxylic acid, 4-pyridinecarboxylic acid, 5-chloro-2-pyridinecarboxylic acid, 2-pyrimidinecarboxylic acid, 4-pyrimidinecarboxylic acid, 2-quinolinecarboxylic acid, 3-quinolinecarboxylic acid, 2-pyridyl-acetic acid, 3-indolylacetic acid, 3-(3-indolyl)propionic acid, isoquinoline-1-carboxylic acid and (4-imidazolyl)acetic acid can be named as examples of suitable heteroaromatic or heteroaromatic-aliphatic carboxylic acid.
Examples of suitable aforementioned amino acids, which optionally can be used in the form of their protected derivatives, are glycine, alanine, valine, norvaline, leucine, isoleucine, norleucine, serine, homoserine, threonine, methionine, cysteine, proline, trans-3- and trans-4-hydroxyproline, phenylalanine, tyrosine, 4-nitrophenylalanine, 4-aminophenylalanine, 4-chlorophenylalanine, xcex2-phenylserine, phenylglycine, xcex1-naphthylalanine, cyclohexylalanine, cyclohexyl-glycine, tryryptophan, indoline-2-carboxylic acid, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, aspartic acid, asparagine, aminomalonic acid, aminomalonic acid monoamide, glutamic acid, glutamic acid mono-t-butyl ester, glutamine, N-dimethylglutamine, histidine, arginine, lysine, N-t-butoxycarbonyllysine, xcex4-hydroxylysine, ornithine, N-pivaloyl-ornithine, xcex1xcex3-diaminobutyric acid or xcex1,xcex2-diaminopropionic acid and the like. Corresponding peptides which consist e.g of the aforementioned amino acids are also included.
Preferred carboxylic acids are the quinoline-2-carboxylic acids as well as the protected aminocarboxylic acids of formula I 
In which R is an amino protecting group. Especially preferred carboxylic acids are quinolinecarboxylic acids as well as acids of formula I in which R represents the benzyloxycarbonyl or tert.butoxycarbonyl protecting group, for example (S)-2-benzyloxy-carbonylamino-propionic acid or (S)-2-tert.-butoxycarbonylamino-propionic acid.
The described acids are commercially available or can be produced by reaction with reactive derivatives of the amino protecting groups.
The term xe2x80x9calkylxe2x80x9d denotes cyclic, branched or straight-chain alkyl groups with 1-8, preferably 1-4, carbon atoms.
The term xe2x80x9carylxe2x80x9d or xe2x80x9caromaticxe2x80x9d alone or in combination means the phenyl or naphthyl group which can be optionally mono- or multiply-substituted by alkyl, e.g. methyl, halogen, a protected hydroxy group, alkoxy, e.g. methoxy, alkanoyloxy, e.g. acetoxy, a protected amino or alkylamino group, alkanoylamino, e.g. acetylamino or pivaloylamino, alkoxycarbonylamino, e.g. t-butoxycarbonylamino, arylmethoxycarbonylamino, e.g. benzyl-oxycarbonylamino or 9-fluorenylmethoxycarbonyl, and/or nitro. Substitution with akyl or halogen is preferred and substitution with alkyl is especially preferred.
The term xe2x80x9ccycloalkylxe2x80x9d means cyclic alkyl groups with 3 to 8 C atoms.
The term xe2x80x9chalogenxe2x80x9d denotes fluorine, chlorine, bromine and iodine.
The term xe2x80x9cheteroarylxe2x80x9d refers to an aromatic 5- or 6-membered ring which can contain 1 or 2 atoms selected from nitrogen, oxygen or sulphur and which may have a substitution pattern as described earlier in connection with the term xe2x80x9carylxe2x80x9d.
The term xe2x80x9camino protecting groupxe2x80x9d refers to any protecting group conventionally used to replace an acidic proton of an amino group which can be hydrolyzed to yield the amino group containing the acidic proton. Examples of such groups are described in Green, T., Protective Groups in Organic Synthesis, Chapter 7, John Wiley and Sons, Inc. (1981), pp. 218-287, herein incorporated by reference. The benzyloxycarbonyl and the tert.-butoxycarbonyl protecting groups are examples of such amino protecting groups. Other examples include carbamates, e.g. fluorenylmethyl, 2,2,2-trichloroethyl, 2-haloethyl, 2-(trimethylsilyl)ethyl, t-butyl, allyl, benzyl. Further protecting groups are 3,5-dimethoxybenzyl, p-nitro-benzyl, diphenylmethyl, triphenylmethyl, benzyl, formylj, acetyl, trifluoroacetyl, chloro-acetyl, the cyclic imides of N-phthaloyl, N-trimethylsilyl, N-benzenesulfonyl, N-toluenesulfonyl, N-p-methylbenzyl-sulfonyl.
The term xe2x80x9creactive acid derivativesxe2x80x9d means acid halide, acid anhydride or alkyl haloformate derivatives of carboxylic acids. Acid halide derivatives are preferred. The corresponding carboxylic acid chlorides and the corresponding protected aminocarboxylic acid chlorides, for example alkanecarboxylic acid chlorides, are also preferred. Especially preferred are reactive derivatives such as anhydrides or acid halides which are derived from an acid R1xe2x80x94COOH in which R1 is alkyl, cycloalkyl, heteroaryl or aryl. Compounds in which R1 is alkyl or aryl are preferred; compounds in which R1 is alkyl are especially preferred. Thus, the corresponding acid halides (R1xe2x80x94C(O)Hal), especially the chlorides (the acid chlorides R1xe2x80x94C(O)Cl), are preferred. Branched aliphatic carboxylic acid halides, such as e.g. 2-ethylbutyryl chloride, cyclohexanecarboxylic acid chloride, 2,2-dimethyl-propionyl chloride (pivaloyl chloride) and isovaleroyl chloride, are preferably used because of the steric and positive inductive effects. Furthermore, corresponding anhydrides can also be used the process in accordance with the invention. Moreover, alkyl chloroformates, e.g. ethyl chloroformate, can be used. The especially preferred reactive acid derivatives are pivaloyl chloride, isovaleroyl chloride and ethyl chloroformate. The corresponding halides are commercially available or can be produced according to known methods. For example, the corresponding acid chlorides can be produced by reacting the acid with thionyl chloride, phosphorus trichloride or phosphorus pentachloride. Anhydrides can be produced according to the process described in the Application. The aforementioned alkyl chloroformates are commercially available or can be produced according to known methods.
In accordance with this invention any conventional base utilized in anhydride formation reactions can be used in the reaction of this invention. Among the bases which can be utilized are the organic bases such as the tertiary amines (both aliphatic and aromatic), or the alkali and alkaline earth salts of the carboxylic acids used in the respective reaction. Examples of tertiary amines include pyridine, N-alkylmorpholines, e.g. N-methyl- and N-ethylmorpholine, and dialkylanilines, such as dimethylaniline. Triethylamine is preferred. In the case of alkali and alkaline earth salts of the carboxylic acids, the sodium and potassium salts are preferred. The by far most preferred bases are tertiary amines, such as N-ethylmorpholine, dimethylaniline, triethylamine and N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, especially triethylamine.
As used herein the term xe2x80x9cpharmaceutically suitable saltsxe2x80x9d means salts derived from metals, the ammonium salt, quaternary ammonium salts derived from organic bases and amino acid salts. Examples of metal salts are those derived from the alkali metals, for example lithium (Li+), sodium (Na+) and potassium (K+). Examples of quaternary ammonium salts derived from organic bases include tetramethylammonium (N+(CH3)4), tetraethylammonium (N+(CH2CH3)4), benzyltrimethylammonium (N+(C6H5CH2)(CH3)3), phenyltriethylammonium (N+(C6H5)(CH2CH3)3), and the like. Those salts derived from amines include salts with N-ethylpiperidine, procaine, dibenzylamine, N,Nxe2x80x2-dibenzylethylenediamine, alkylamines or dialkylamines as well as salts with amino acids such as, for example, salts with arginine or lysine. Other examples include hydrochlorides, sulfates, phosphates, lactates, and mesylates.
Any conventional inert solvent can be used as the solvent. Examples of such inert solvents include tetrahydrofuran, toluene, hexane, acetone, dioxan, preferably lower carboxylic acid esters such as alkyl acetates, primarily methyl, ethyl and isopropyl acetate.
Advantageously, the reaction is carried out with temperature control at between xe2x88x9225 and +25xc2x0 C., preferably between 0 and +5xc2x0 C.
Anhydrides which can be manufactured according to the process in accordance with the invention are likewise an object of the present invention. Thus, the present invention also embraces anhydrides of the formula 
in which R is an amino protecting group and R1 is alkyl, cycloalkyl, heteroaryl or aryl. Compounds in which R1 is alkyl or aryl are preferred; compounds in which R1is alkyl are especially preferred. (S)-2-Benzyloxycarbonylaminopropionic acid-2,2-dimethylpropionic acid anhydride, (S)-2-tert.-butoxycarbonylamino-propionic acid-2,2-dimethylpropionic acid-anhydride and 2,2-dimethylpropionic acid quinoline-2-carboxylic acid anhydride are examples of these compounds.
The process described above is suitable, for example, for use in peptide synthesis and/or for the manufacture of pharmaceutically active substances or corresponding starting materials or intermediates.
Thus, the present invention embraces a process for the manufacture of a mixed quinoline-2-carboxylic acid anhydride of the formula 
wherein R1 is as defined above, in accordance with the described process. Quinoline-2-carboxylic acid is thereby reacted with the corresponding reactive acid derivative, e.g. an anhydride or preferably an acid halide which is derived from the corresponding acid R1xe2x80x94COOH. The corresponding acid chloride is preferred.
The resulting anhydride of formula II above can then be converted, for example, into N-(2-quinolylcarbonyl)-L-asparagine (quinargine) by reaction with asparagine. Quinargine is known per se and is described, for example, in European Patent Application No. 611774. It is a valuable intermediate for the manufacture of pharmacologically active compounds. Thus, quinargine can be converted as described in Example 7 of the aforementioned European Patent Application into pharmacologically active compounds which are suitable primarily for the treatment of viral infections, especially such infections which are caused by HIV or other retroviruses.
For the manufacture of quinargine according to the process described above, quinoline-2-carboxylic acid can be reacted with a reactive derivative of an acid R1xe2x80x94COOH, in which R1 is defined above, for example with pivaloyl chloride, and an adjuvant base, e.g. triethylamine. This reaction, which is described in detail in Example 1, yields the corresponding mixed anhydride, here e.g. 2,2-dimethylpropionic acid-quinoline-2-carboxylic acid anhydride, which, after isolation or even directly without further purification, can be reacted with asparagine in an aqueous, alkaline solution to give quinargine. The reaction with asparagine preferably takes place in an aqueous NaOH/NaHCO3 solution. With this process N-(2-quinolylcarbonyl)-L-asparagine (S-quinargine) can be manufactured directly from the educts in high yield without the isolation of an intermediate.
Furthermore, the present invention embraces the manufacture of pharmaceutically active substances. For example, the aforementioned N-(2-quinolylcarbonyl)-L-asparagine can be converted by reaction with 2-[3(S)-amino-2(R)-hydroxy-4-phenylbutyl]-N-tert.butyl-decahydro-(4aS,8aS)-isoquinoline-3(S)carboxamide, which is known from European Patent Application No. 635,493, in the presence of a coupling reagent such as e.g. a carbodiimide and a N-hydroxy compound, with the N-hydroxy compound being present in a catalytic amount. As described in Example 7 of European Patent Application No. 611774, the aforementioned substances can be converted in the presence of dicyclo-hexylcarbodiimide using a catalytic amount of 1 -hydroxy-2(1 H)-pyridone in an inert solvent or solvent mixture such as ethyl acetate/tetrahydrofuran into N-t-butyl-decahydro-2-[2(R)-hydroxy-4-phenyl-3(S)-[[N-(2-quinolylcarbonyl)-L-asparaginyl]-amino]butyl]-(4aS,8aS)-isoquinoline-3(S)-carboxamide or into pharmaceutically suitable salts or corresponding esters derived therefrom.
Accordingly, the present invention also includes a process for the manufacture of these compounds. Such a process embraces in a first step the manufacture of a mixed anhydride and its conversion into quinargine as described above. The mixed anhydride, e.g. 2,2-dimethylpropionic acid-quinoline-2-carboxylic acid anhydride, can be obtained by adding an adjuvant base, e.g. triethylamine, to a mixture of quinoline-2-carboxylic acid and a reactive acid derivative, preferably pivaloyl chloride. The resulting mixed anhydride is subsequently reacted with asparagine in alkaline solution to give N-(2-quinolylcarbonyl)-L-asparagine. This substance is then converted in a subsequent step with 2-[3(S)-amino-2(R)-hydroxy-4-phenylbutyl]-N-tert.butyl-decahydro-(4aS,8aS)-isoquinoline-3(S)carboxamide into N-t-butyl-decahydro-2-[2(R)-hydroxy-4-phenyl-3(S)-[[N-(2-quinolylcarbonyl)-L-asparaginyl]-amino]butyl]-(4aS,8aS)-isoquinoline-3(S)-carboxamide as described above or optionally into a corresponding salt, preferably the methanesulphonic acid salt, or into an ester.
Furthermore, by means of the process in accordance with a invention it is possible to convert an acid of formula I 
with a reactive derivative of an acid R1xe2x80x94COOH into an anhydride of formula III 
wherein R is an amino protecting group as defined above and R1 is alkyl, cycloalkyl, heteroaryl or aryl. Preferred processes are those in which compounds are used in which R1 is alkyl or aryl; compounds in which R1 is alkyl are especially preferred. The amino protecting group can be a protecting group known from the state of the art, such as, for example, as used in peptide chemistry. The benzyl-oxycarbonyl and tert.-butoxycarbonyl protecting groups are examples of such amino protecting groups.
Thus, using the process in accordance with the invention it is possible to manufacture ethyl (S)-[1-(2-benzyloxycarbonylamino-propionyl)-piperidin-4-yloxy]-acetate and ethyl (S)-[1-(2-tert.butoxycarbonylamino-propionyl)-piperidin-4-yloxy]-acetate, which are also important pharmaceutical intermediates. As described in Examples 2 and 3, the corresponding intermediates can be obtained also in these cases in very good yields even without isolation of the corresponding mixed anhydrides. In particular, the reaction is effected by reacting a protected aminopropionic acid, e.g. (S)-2-benzyloxycarbonylamino-propionic acid or, respectively, (S)-2-tert.butoxycarbonylamino-propionic acid, with a reactive acid derivative as described above, here in both cases with pivaloyl chloride, using a tertiary amine, here triethylamine, as the adjuvant base. The amino protecting group of the aminopropionic acid can be any suitable amino protecting group, with the benzyloxycarbonyl and tert.butoxycarbonyl protecting groups being preferred. The resulting mixed anhydrides (S)-2-benzyloxycarbonylaminopropionic acid-2,2-dimethylpropionic acid anhydride and (S)-2-tert.butoxycarbonylamino-propionic acid-2,2-dimethylpropionic acid anhydride can be reacted with ethyl (piperidin-4-yloxy)-acetate, e.g. in a potassium phosphate-buffered, aqueous ethyl acetate suspension, to give the aforementioned intermediates. These intermediates can be processed further to give pharmaceutically active substances.
For example, with the process in accordance with the invention it is possible to use these intermediates for the manufacture of ethyl [Z]-(S)-[[1-[2-[[4-(amino-hydroximino-methyl)-benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]acetate, a fibrinogen receptor antagonist (Alig et al. (1992) J. Med. Chem. 35, 4393-4407; Weller et al. (1996) J. Med. Chem. 39, 3139-3147). The process described above can be performed as follows for the manufacture of this substance: The protecting groups can be cleaved off from the aforementioned intermediates and the amine obtained can be converted with a corresponding acid chloride and subsequent reaction with hydroxylamine into the desired substance. In particular, the benzyloxycarbonyl protecting group can be cleaved off by hydrogenation and the tert.-butoxycarbonyl protecting group can be cleaved off by acid from, respectively, ethyl (S)-[1-(2-benzyloxycarbonylamino-propionyl)-piperidin-4-yloxy]-acetate and ethyl (S)-[1-(2-tert.-butoxycarbonylamino-propionyl)-piperidin-4-yloxy]-acetate. The liberated amine can then reacted with 4-cyanobenzoyl chloride, which can be prepared from thionyl chloride and 4-cyanobenzoic acid, and subsequently converted by reaction with hydroxylamine hydrochloride and triethylamine and working-up in acidic medium into ethyl [Z]-(S)-[[1-[2-[[4-(amino-hydroximino-methyl)-benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]acetate in accordance with Example 4.
Accordingly, the process in accordance with the invention also relates to the manufacture of ethyl [Z]-(S)-[[1-[2-[[4-(amino-hydroximino-methyl)-benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]acetate by producing a mixed anhydride in a first step as described above and converting it by reaction with a compound of formula IV 
wherein R2 represents an alkyl group, preferably ethyl or tert.-butyl, into an ester or formula V 
wherein R and R2 are as defined above. Subsequently, the amino protecting group R can be cleaved off and optionally the R2 group can be trans-esterified to the ethyl ester, with the cleavage of the amino protecting group and the trans-esterification to the ethyl ester being optionally carried out simultaneously depending on the protecting group used, e.g. in the case of the tert.-butyl protecting group by reaction with H2SO4/ethanol. Subsequently, the resulting amine of formula VI 
wherein R2 is as defined above, can be reacted with 4-cyano-benzoyl chloride to give the compound of formula VII 
wherein R2 is as defined above. Alternatively, when e.g. the benzyloxycarbonyl protecting group is used, the cleavage of the protecting group can be effected by hydrogenation, followed by reaction with 4-cyanobenzoyl chloride and trans-esterification to the corresponding ethyl ester (R2=ethyl). Of course, the corresponding ethyl ester may be introduced simultaneously as described in Example 4 via compound IV with R2=ethyl. Subsequently, ethyl [Z]-(S)-[[1-[2-[[4-(amino-hydroximino-methyl)-benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]acetate can be obtained by reacting hydroxylamine hydrochloride with the compound of formula VII. If desired, the compound obtained can be converted into a pharmaceutically suitable salt.
The following Examples illustrate the invention and do not have any limiting character.
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