SI9110628A - Process for the preparation of n-succinimidyl carbonates - Google Patents

Abstract

Procedure for the preparation of N-succinimidylcarbonates with formula I in which Ar stands for 9-fluorenyl, phenyl, which can in the given case be substituted with halogen, nitro, C1-4-alkyl or trifluormethyl, or 5- or 6-membered heteroaromatic with one or two N or S, with the alcohol reaction formula II in which Ar has the above-mentioned meaning, with phosgene in the presence of an inert diluent which mixes with water into the ester of chlorcarbonic acid with formula III and a reaction mixture without the isolation of the compound III is transformed with water solution of N-hydroxysuccinimide in the presence of alkaline, alkaline earth or ammonium hydrogencarbonate or carbonate and the compound I is isolated from the organic phase.

Description

Chemie Linz Gesellschaft m.b.H.

Process for the preparation of N-succinimidyl carbonates

The invention relates to a process for the preparation of N-succinimidyl carbonates by phosgeneation of alcohols into the corresponding hydrochloric acid esters and subsequent conversion with N-hydroxysuccinimide.

N-succinimidyl carbonate is used in peptide synthesis to introduce suitable protecting groups for the amino function of amino acids. Due to their more selective reaction, N-succinimidyl carbonates are favored over the corresponding acid chlorides. A particularly well-protected protecting group is the 9-fluorenylmethyloxycarbonyl group because it can be easily cleaved under weakly basic conditions.

Two reaction routes are generally known for the preparation of N-succinimidyl carbonates.

In Ten Kortenaar et al., Int. Peptide Protein Research 27 (1986), 398ff describes the preparation of 9-fluorenylmethylsuccinimidyl carbonate by phosgeneation of 9-fluorenylmethanol and subsequent conversion with N-hydroxysuccinimide. Phosphenation is performed by dosing alcohol into liquid phosgene at -78 ° C. The resulting hydrochloric acid ester is isolated, dissolved in dioxane and converted with N-hydroxysuccinimide in the presence of triethylamine as a neutralizing agent at 10 to 15 ° C.

According to L.A. Carpino, G.Y-Han, J. Org. Chem. Vol 37, (1972) 3404 ff. fo-sgenation can also be carried out by adding alcohol to a solution of phosgene in dichloromethane.

In both processes, a very high concentration of phosgene is present in the solution, which is arguable for safety and technical reasons. The excess phosgene should be removed after the phosgeneation is complete. In phosgeneation as a by-product, the resulting hydrochloride could, in the following conversion, react in addition to the hydrochloric acid ester with an organic amine used as a neutralizing agent, to the corresponding aminhydrochloride. Therefore, it should also be removed. Emerging aminhydrochlorides are, moreover, environmental byproducts that need to be taken care of. Furthermore, the conversion of chlorocarboxylic acid ester with N-hydroxysuccinimide in the presence of an organic amine due to the basic lability of fluorenyl ester results in an easily cleavable product of dibenzofulven, thereby reducing the yield.

According to A. Paquet, Can. J. Chem 60 (1982), 976ff may be used to prepare 9-fluorenylmethylsuccinimidyl carbonate also by phosgeneation of the cyclohexylamine salt of N-hydroxysuccinimide and subsequent conversion of the succinimidyl hydrochloric acid ester with 9-fluorenylmethanol. Liquid phosgene is introduced to the suspension of the N-hydroxysuccinimide salt at -30 ° C, the resulting dicyclohexylaminhydrochloride is determined and the succinimidyl hydrochloric acid ester isolated. Subsequent conversion with 9-fluorenylmethanol takes place in dichloromethane in the presence of pyridine as a neutralizing agent.

In this process, too, prior to the conversion of the hydrochloric acid ester, the emerging by-products as well as excess phosgene must be removed from the phosgeneation. The phosgeneation as well as the subsequent conversion of the hydrochloric acid ester produces the aminhydrochloride to be taken care of.

For the preparation of N-hydroxysuccinimidyl carbonates on a technical scale, known methods are poorly suited for this purpose.

However, we have now been able to identify a process for the preparation of N-succinimidylcarbonates, in which the intermediate does not need to be isolated and the resulting inorganic salts are easily decided.

The subject of the invention is therefore a process for the preparation of N-succinimidyl carbonates of formula I

Ar

in which Ar represents a 9-fluorenyl radical, a phenyl radical optionally substituted by halogen, nitro, alkyl of 1 to 4 carbon atoms, or trifluoromethyl, or a 5 or 6 membered heteroaromatic radical of one or two N- or S- atoms, characterized in that the alcohol of formula II

Ar - CH ₂ OH jj in which Ar has the above meaning, is converted by phosgene in the presence of a water miscible inert diluent to the hydrochloric acid ester of formula III

Ar - CH ₂ - O - C - Cl

III and the reaction mixture without isolation of the compound of formula III is converted to an aqueous solution of N-hydroxysuccinimide in the presence of alkali, alkaline earth metal or ammonium hydrogen carbonate or carbonate as a neutralizing agent, and the compound of formula I is isolated from the organic phase.

As the starting compounds, alcohols of formula II are used, in which Ar represents a fluorenyl residue or a phenyl residue which may optionally be substituted one or more times with halogen, e.g. chlorine, bromine or fluorine, nitro, alkyl of 1 to 4 carbon atoms or trifluoromethyl. Examples of such substituted phenyl moieties are 2-chlorophenyl moiety, 4-chlorophenyl moiety, 2,4-dichlorophenyl moiety, 2-bromophenyl moiety, 4-fluorophenyl moiety, methylphenyl moiety and trifluoromethylphenyl moiety.

Further, Ar may be a 5- or 6-membered heteroaromatic ring which, as heteroatoms, may contain one or two N- or S-atoms, e.g. pyridyl, pyridazinyl, pyrimidyl or thienyl radicals.

Preferably, such alcohols of formula II are used, in which Ar represents a 9-fluorenyl, phenyl or 2-chlorophenyl residue.

The conversion of alcohol to phosgene takes place in a diluent which is inert under reaction conditions and miscible with water, e.g. in cyclic ether as tetrahydrofuran or dioxane, or in open chain ether as diethyl di-, tri- or tetraethylene glycol. Usually, reaction participants are used in equivalents. It may be convenient to use about 10% excess phosgene to complete the reaction.

In carrying out the reaction, it is convenient to present the alcohol in the diluent and introduce phosgene, as this maintains a low concentration of phosgene in the solution. The phosgenation reaction is carried out at temperatures from 0 to 20 ° C.

The reaction solution obtained from the phosgeneation is then dosed to an aqueous solution, optionally in admixture with an inert diluent such as N-hydroxysuccinimide and alkali, alkaline earth or ammonium hydrogen carbonate or carbonate.

Usually 1 mole of N-hydroxysuccinimide is used per 1 mole of alcohol. The reaction produces 1 mol of phosgene and 2 moles of HCl. Therefore, two equivalents of neutralizing agent are required for neutralization. Examples of suitable neutralizing agents are potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate, ammonium hydrogen carbonate, or ammonium carbonate.

The hydrochloric acid esters are more or less sensitive to hydrolysis, depending on the stability of the alcohol component. However, for the hydrochloric acid esters used in the invention, hydrolysis of the hydrochloric acid ester and subsequent decarboxylation to the alcohol does not result in the introduction into the aqueous solution, since virtually complete conversion to N-succinimidyl carbonate occurs. The excess phosgene, which is presently present from the phosgeneation, immediately hydrolyzes. As a by-product, the corresponding alkali, alkaline earth or ammonium chlorides and, where appropriate, CO ₂ are formed.

Towards the end of the conversion, a phase separation occurs, with the aqueous phase containing alkali, alkaline earth or ammonium chloride.

The organic phase contains N-succinimidyl carbonate, which can be easily isolated by solvent evaporation.

EXAMPLE 1:

98.1 g (0.50 mol) of fluoren-9-methanol were dissolved in 300 ml of tetrahydrofuran and the solution was cooled to 15 ° C.

54.4 g (0.55 mol) of phosgene were introduced under cooling for 30 minutes. The solution was then stirred for 1.5 hours at 15 ° C (stage 1). In the second reaction vessel, 63.3 g (0.55 mol) of N-hydroxysuccinimide, 115.1 g (1.15 mol) of potassium hydrogen carbonate, 350 ml of water and 300 ml of tetrahydrofuran are provided. The reaction solution from step 1 was rapidly injected and then stirred for 1 hour.

Towards the end of the reaction, phase separation occurs.

The tetrahydrofuran phase is decided and evaporated.

162 g of 9-fluorenylmethylsuccinimidyl carbonate are obtained. The yield is 96% of theory, based on the fluoren-9-methanol used. Analysis by HPLC gave a content of 98%. Digerization with isopropanol yields a product of purity

99.9%.

Ή-NMR (CDCl ₃ ): delta = 7.77 (d. J = 7.5 Hz; 2H) 7.62 (d. J = 7.5 Hz; 2H), 7.43 (t, J = 7 , 5 Hz, 2H), 7.36 (t, J = 7.5 Hz; 2H), 4.56 (d. J = 7.5 Hz; 2H), 4.33 (t.

J = 7.5 Hz; 1H), 2.80 (s; 4H) ppm.

EXAMPLE 2:

54.1 g (0.50 mol) of benzyl alcohol are dissolved in 300 ml of tetrahydrofuran. 49.9 g (0.505 mol) of phosgene are introduced into this solution under cooling for 1 hour and stirred for a further 30 minutes at 15 ° C (stage 1).

A solution of 57.5 g (0.5 mol) of N-hydroxysuccinimide, 105.1 g of potassium hydrogen carbonate (1.05 mol), 350 ml of water and 300 ml of tetrahydrofuran is added to the further reaction vessel. Stage 1 reaction solution was rapidly injected and stirred for 20 minutes. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is decided and evaporated.

120 g of benzylsuccinimidyl carbonate are obtained. The yield is 96% of theory, based on the benzyl alcohol used.

¹ H-NMR (CDCl ₃ ): delta = 7.40 (s; 5H), 5.32 (s; 2H), 2.82 (s; 4H) ppm.

EXAMPLE 3:

71.3 g (0.50 mol) of 2-chlorobenzyl alcohol are dissolved in 300 ml of tetrahydrofuran. 54.4 g of phosgene (0.550 moles) were introduced into this solution under cooling for 45 minutes and stirred for another 1 hour at 15 ° C (stage 1).

A solution of 57.5 g (0.5 mol) of N-hydroxysuccinimide, 115.1 g of potassium hydrogen carbonate (1,150 mol), 350 ml of water and 300 ml of tetrahydrofuran is added to the further reaction vessel.

Stage 1 reaction solution was rapidly injected and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is decided and evaporated.

138 g of 2-chlorobenzylsuccinimidyl carbonate are obtained. The yield is 97% of theory, with respect to 2-chlorobenzyl alcohol.

1 H-NMR (CDCl ₃ ): delta = 7.3-7.5 (m; 4H), 5.43 (s; 2H), 2.80 (s; 4H) ppm.

EXAMPLE 4:

44.3 g (0.25 mol) of 2,4-dichlorobenzyl alcohol are dissolved in 300 ml of tetrahydrofuran. 27.2 g of phosgene (0.272 moles) were introduced into this solution under cooling for 45 minutes and stirred at 15 ° C for 1 hour (step 1).

A solution of 28.8 g (0.25 mol) of N-hydroxysuccinimide, 57.5 g of potassium hydrogen carbonate (0.575 mol), 350 ml of water and 300 ml of tetrahydrofuran is added to the further reaction vessel. Stage 1 reaction solution was rapidly injected and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is decided and evaporated.

75 g of 2,4-dichlorobenzylsuccinimidyl carbonate are obtained. The yield is 94% of theory, with respect to 2,4-dichlorobenzyl alcohol.

1 H-NMR (CDCl ₃ ): delta = 7.27-7.45 (m; 3H), 5.40 (s; 2H), 2.84 (s; 4H) ppm.

EXAMPLE 5:

76.6 g (0.50 mol) of 4-nitrobenzyl alcohol are dissolved in 300 ml of tetrahydrofuran. Into this solution, 54.4 g of phosgene (0.550 mol) were introduced under cooling for 45 minutes and stirred at 15 ° C for 1 hour (step 1).

In a further reaction vessel, a solution of 57.5 g (0.5 mol) of N-hydroxysuccinimide, 115.1 g of potassium hydrogen carbonate (1,150 mol), 350 ml of water and 300 ml of tetrahydrofuran is presented.

Stage 1 reaction solution was rapidly injected and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is decided and evaporated.

140 g of 4-nitrobenzylsuccinimidyl carbonate are obtained. The yield is 95% of theory, with respect to 4-nitrobenzyl alcohol.

1 H-NMR (CDCl ₃ ): delta = 8.27 (d. = 8.7 Hz; 2H) 7.58 (d. J = 8.7 Hz; 2H), 5.42 (s, 1H) , 2.86 (s, 4H) ppm.

EXAMPLE 6:

80.1 g (0.40 mol) of 3-phenoxybenzylalcohol are dissolved in 300 ml of tetrahydrofuran. 43.5 g of phosgene (0.440 moles) were introduced into this solution under cooling for 45 minutes and stirred at 15 ° C for 1 hour (step 1).

A solution of 46.0 g (0.4 mol) of N-hydroxysuccinimide, 92.1 g of potassium hydrogen carbonate (0.92 mol), 350 ml of water and 300 ml of tetrahydrofuran is added to the further reaction vessel. Stage 1 reaction solution was rapidly injected and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is decided and evaporated.

127 g of 3-phenoxybenzylsuccinimidyl carbonate are obtained. The yield is 93% of theory, with respect to 3-phenoxybenzyl alcohol.

Claims (4)

PATENT APPLICATIONS A process for the preparation of N-succinimidyl carbonates of formula I in which Ar represents a 9-fluorenyl residue, a phenyl residue optionally substituted by halogen, nitro, alkyl of 1 to 4 carbon atoms, or trifluoromethyl, or 5 or 6 membered heteroaromatic residue having one or two N or S atoms, characterized in that the alcohol of formula II Ar - CH2 OH U in which Ar has the above meaning is converted by phosgene in the presence of a water miscible inert diluent to the hydrochloric acid ester of formula III Ar III and the reaction mixture without isolation of the compound of formula III is converted to an aqueous solution of N-hydroxysuccinimide in the presence of alkali, alkaline earth metal or ammonium hydrogen carbonate or carbonate as a neutralizing agent, and the compound of formula I is isolated from the organic phase. A process according to claim 1, characterized in that a cyclic ether or an open-chain ether is used as the inert diluent. Process according to one of Claims 1 or 2, characterized in that sodium hydrogen carbonate, sodium carbonate, potassium hydrogen carbonate, potassium carbonate, ammonium hydrogen carbonate or ammonium carbonate are used as the neutralizing agent. Process according to one of Claims 1 to 3, characterized in that an alcohol of formula II is used in which A; means a 9-fluorenyl radical, a phenyl radical or a 2-chlorophenyl radical.