HRP940779A2 - Process for the preparation of n-succinimidylcarbonates - Google Patents

Description

The invention relates to a process for the preparation of N-succinimidyl carbonate with phosgenation of alcohol into the corresponding esters of carbonic acid and subsequent conversion with N-hydroxysuccinimide.

N-succinimidyl carbonates are used in peptide synthesis to introduce appropriate protective groups for the amino function of amino acids. N-succinimidyl carbonates are preferred because of their better selective reaction with the corresponding acid chlorides. A particularly well-suited protecting group is the 9-fluorenylmethyloxy-carbonyl group, because it can be cleaved particularly easily under weakly basic conditions.

Two reaction pathways are generally known for the preparation of N-succinimidylcarbonate.

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

By L.A.Carpino, G.Y-Han, J.Org.Chem. Vol 37, (1972) 3404 ff, phosgenation can also be performed with the addition of alcohol to a solution of phosgene in dichloromethane.

In both procedures, a very high concentration of phosgene is present in the solution, which is disputed due to safety and technical reasons. Excess phosgene must be removed after phosgenation is complete. During phosgenation, as a byproduct, the resulting hydrogen chloride could react in the next conversion with the ester of hydrochloric acid and with the organic amine, used as a neutralizing agent, into the corresponding amine hydrochloride. Therefore, it should also be removed. The resulting amine hydrochlorides are also by-products, which are harmful to the environment and must be taken care of. Furthermore, during the conversion of chlorocarbonic acid ester with N-hydroxysuccinimide in the presence of an organic amine due to the basic lability of the fluorenyl ester, the grafting product dibenzofulvene is often formed, thereby reducing the yield.

According to A. Paquet, Can. J. Chem. 60 (1982), 976ff, the preparation of 9-fluorenylmethylsuccinimidylcarbonate can be carried out with the phosgenation of the cyclohexylamine salt of N-hydroxysuccinimide and in the following conversion of succinimidylchlorocarbonic acid ester with 9-fluorenylmethanol. In this case, liquid phosgene is introduced into the suspension of N-hydroxysuccinimide salt at -30°C, the resulting dicyclohexylamine hydrochloride is separated and the ester of succinimidylchlorocarbonic acid is isolated. The next conversion is carried out in dichloromethane in the presence of pyridine as a neutralizing agent.

In this procedure too, it is necessary to remove the by-products and excess phosgene during phosgenation before the conversion of chlorocarbonic acid ester. During phosgenation, as well as during further conversion of chlorocarbonic acid esters, amine hydrochloride is formed, which needs to be taken care of.

For the preparation of N-hydroxysuccinimidylcarbonate on a technical scale, the known procedures are poorly suited.

Now we have managed to find a process for the preparation of N-succinimidylcarbonate, in which the intermediate does not need to be isolated and the resulting inorganic salts can be separated very easily.

The subject of the invention is a process for the preparation of N-succinimidylcarbonate with formula I

[image]

in which Ar means a 9-fluorenyl radical, a phenyl radical, which in the given example is substituted with halogen, with nitro, with alkyl with 1 to 4 carbon atoms, or trifluoromethyl or a 5- or 6-membered heteroaromatic radical with one or two N- or S-atom, which is characterized by the fact that alcohol with formula II

Ar - CH2OH II

in which Ar has the above meaning, convert with phosgene in the presence of an inert solvent, which is miscible with water, into the carbonic acid ester of formula III

[image]

and convert the reaction mixture without isolating the compound with formula III with an aqueous solution of N-hydroxysuccinimide in the presence of alkaline, alkaline earth or ammonium hydrogencarbonate or carbonate as a neutralizing agent and isolate the compound with formula I from the organic phase.

As starting compounds, we use alcohols with formula II, in which Ar means a fluorenyl radical or a phenyl radical, which in the given example can be substituted one or more times with a halogen, e.g. chlorine, bromine or fluorine, nitro, alkyl with 1 to 4 atoms carbon or trifluoromethyl. Examples of such substituted phenyl radicals are 2-chlorophenyl radical, 4-chlorophenyl radical, 2,4-dichlorophenyl radical, 2-bromophenyl radical, 4-fluorophenyl radical, methylphenyl radical and trifluoromethylphenyl radical. Furthermore, Ar can mean a 5- or 6-membered heteroaromatic ring, which as heteroatoms can contain one or two N- or S-atoms, for example a pyridyl, pyridazinyl, pyrimidyl or thienyl radical.

Let's preferably use such alcohols with formula II, in which Ar means 9-fluorenyl, phenyl or 2-chlorophenyl radical.

The conversion of alcohol with phosgene is carried out in a diluent, which is inert under the reaction conditions and miscible with water, for example as tetrahydrofuran or dioxane, or in an ether with an open chain, such as di-, tri- or tetraethylene glycol diether. We usually use the reaction partners in equivalent quantities. It is convenient to use about 10% excess phosgene to complete the reaction.

When performing the reaction, it is convenient to put alcohol in the diluent and introduce phosgene, because this way we maintain a low concentration of phosgene in the solution. The phosgenation reaction is carried out at temperatures from about 0 to 20°C.

The reaction solution, which is obtained during phosgenation, is then dosed into an aqueous solution, in the given example in a mixture with an inert diluent such as N-hydroxysuccinimide and alkaline, alkaline earth or ammonium hydrogencarbonate or carbonate.

For one mole of alcohol, we usually use one mole of N-hydroxysuccinimide. During the reaction, 2 moles of HCl are formed for 1 mole of phosgene. For neutralization, therefore, two equivalents of the neutralizing agent are necessary. Examples of suitable neutralizing agents are potassium hydrogencarbonate, potassium carbonate, sodium hydrogencarbonate, sodium carbonate, ammonium hydrogencarbonate or ammonium carbonate.

Hydrochloric acid esters are more or less sensitive to hydrolysis depending on the stability of the alcohol component. Hydrochloric acid esters, used in the sense of the invention, when introduced into an aqueous solution do not undergo hydrolysis of the hydrochloric acid ester and after that decarboxylation to alcohol, a complete conversion to N-succinimidylcarbonate occurs. Excess phosgene, which in the given example is present from phosgenation, immediately hydrolyzes. Corresponding alkaline, alkaline earth or ammonium chlorides and, in the given example, CO2 are created as by-products.

Towards the end of the conversion, phase separation occurs, where the water phase contains alkaline, alkaline earth or ammonium chloride.

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

Example 1

Dissolve 98.1 g (0.50 mol) of fluorene-9-methanol in 300 ml of tetrahydrofuran and cool the solution to 15°C.

54.4 g (0.55 mol) of phosgene are introduced during 30 minutes while cooling. Then we mix the solution for another 1.5 hours at 15°C (stage 1). Put 63.3 g (0.55 mol) of N-hydroxysuccinide, 115.1 g (1.15 mol) of potassium hydrogen carbonate, 350 ml and 300 ml of tetrahydrofuran into the second reaction vessel. The reaction solution from the 1st stage is quickly dosed and then stirred for 1 hour.

Towards the end of the reaction, phase separation occurs.

The tetrahydrofuran phase is separated and evaporated.

We obtain 162 g of 9-fluorenylmethylsuccinimidylcarbonate. The gain amounts to 96% of the theoretical considering the used fluorene-9-methanol. Analysis with HPLC gives a content of 98%. A product with a purity of 99.9% can be obtained by digestion with isopropanol.

1H-NMR (CDCl3): delta = 7.77(d.J=7.5Hz; 2H) 7.62(d.J=7.5Hz; 2H), 7.43(t,J=7.5Hz, 2H), 7 .36(t,J=7.5Hz; 2H), 4.56(d.J=7.5Hz; 2H), 4.33(t,J=7.5Hz; 1H), 2.80(s; 4H) ppm.

Example 2

Dissolve 54.1 g (0.50 mol) of benzyl alcohol in 300 ml of tetrahydrofuran. We introduce 49.9 (0.505 mol) phosgene into this solution while cooling for 1 hour and mix for another 30 minutes at 15°C (1st stage).

In the next reaction vessel, put 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. The reaction solution from the 1st stage is quickly dosed and mixed for 20 minutes. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is separated and evaporated.

We get 120 g of benzylsuccinimidylcarbonate. The gain is 96% of the theoretical value for 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

Dissolve 71.3 g (0.50 mol) of 2-chlorobenzylalcohol in 300 ml of tetrahydrofuran. We introduce 54.4 g of phosgene (0.550 moles) into this solution while cooling for 45 minutes and mix for another 1 hour at 15°C (stage 1).

In the next reaction vessel, we put 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.

The reaction solution from step 1 is quickly dosed into it and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is separated and evaporated.

We obtain 138 g of 2-chlorobenzylsuccinimidylcarbonate. The gain is 97% of the theoretical with respect to 2-chlorobenzylalcohol.

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

Example 4

Dissolve 44.3 g (0.25 mol) of 2,4-dichlorobenzylalcohol in 300 ml of tetrahydrofuran. We introduce 27.2 g of phosgene (0.272 mol) into this solution while cooling for 45 minutes and mix for another 1 hour at 15°C (stage 1).

In the next reaction vessel, put a solution of 28.8 g (0.25 mol) of N-hydroxysuccinimide, 57.5 g of potassium hydrogencarbonate (0.575 mol), 350 ml of water and 300 ml of tetrahydrofuran. The reaction solution from step 1 is quickly dosed into it and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is separated and evaporated.

We obtain 75 g of 2,4-dichlorobenzylsuccinimidylcarbonate. The gain is 94% of the theoretical with respect to 2,4-dichlorobenzylalcohol.

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

Example 5

Dissolve 76.6 g (0.50 mol) of 4-nitrobenzylalcohol in 300 ml of tetrahydrofuran. We introduce 54.4 g of phosgene (0.550 moles) into this solution while cooling for 45 minutes and mix for another 1 hour at 15°C (stage 1).

In the next reaction vessel, we put 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.

The reaction solution from step 1 is quickly dosed into it and stirred for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is separated and evaporated.

We get 140 g of 4-nitrobenzylsuccinimidylcarbonate. The gain is 95% of the theoretical with respect to 4-nitrobenzylalcohol.

1H-NMR(CDCl3): delta = 8.27(d.J.=8.7Hz; 2H) 7.58(d.J.=8.7Hz; 2H), 5.42(s, 1H), 2.86(s, 4H) ppm.

Example 6

Dissolve 80.1 g (0.40 mol) of 3-phenoxybenzylalcohol in 300 ml of tetrahydrofuran. 43.5 g of phosgene (0.440 moles) is introduced into this solution while cooling for 45 minutes and stirred for 1 hour at 15°C (1st stage).

In the next reaction vessel, put 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.

The reaction solution from the 1st stage is quickly dosed and mixed for 1 hour. Towards the end of the reaction, phase separation occurs. The tetrahydrofuran phase is separated and evaporated.

We obtain 127 g of 3-phenoxybenzylsuccinimidylcarbonate. The gain is 93% of the theoretical with respect to 3-phenoxybenzylalcohol.

1H-NMR(CDCl3): delta = 7.01-8.38(m; 10H), 5.27(s; 2H), 2.83(s; 4H) ppm.

Claims (4)

1. Procedure for the preparation of N-succinimidyl carbonate with the formula [image] in which Ar means a 9-fluorenyl radical, a phenyl radical, which in the given example is substituted with halogen, with nitro, with alkyl with 1 to 4 carbon atoms, or trifluoromethyl, or a 5- or 6-membered heteroaromatic radical with one or two N - or S-atom, indicated by the fact that the alcohol of the formula Ar - CH2OH II in which Ar has the above meaning, reacts with phosgene in the presence of an inert solvent, which is miscible with water, to give a carbonic acid ester of the formula [image] and the reaction mixture without isolating the compound of formula III reacts with an aqueous solution of N-hydroxysuccinimide in the presence of alkaline, alkaline earth or ammonium hydrogencarbonate or carbonate as a neutralizing agent, and we isolate the compound of formula I from the organic phase. 2. The method according to claim 1, indicated by the fact that as an inert diluent we use a cyclic ether or such, with an open chain. 3. The method according to one of claims 1 or 2, characterized in that we use sodium hydrogencarbonate, sodium carbonate, potassium hydrogencarbonate, potassium carbonate, ammonium hydrogencarbonate or ammonium carbonate as a neutralizing agent. 4. Process according to one of claims 1 to 3, characterized in that we use an alcohol of formula II, in which Ar means 9-fluorenyl radical, phenyl radical or 2-chlorophenyl radical.