Process for producing amino acid N-carboxyanhydride
The present invention provides a process for producing an amino acid N-carboxyanhydride, which comprises reacting an amino acid or a derivative thereof with a compound represented by the following formula (1): wherein R 1 and R 2 represent the same or different electron-withdrawing substituents and each independently are an optionally substituted acyl group, an optionally substituted alkyloxycarbonyl group, an optionally substituted perfluoroalkyl group, an optionally substituted perchloroalkyl group, a cyano group, a halogen atom, or a nitro group; and a and b are the same or different and each are an integer of 1-5.
1. A process for producing an amino acid N-carboxyanhydride having the following formula (5):
which comprises reacting an amino acid with a compound represented by the following formula (1):
wherein R 1 and R 2 represent the same or different electron-withdrawing substituents and each independently are an optionally substituted perfluoroalkyl group, an optionally substituted perchloroalkyl group, a halogen atom, or a nitro group; and a and b are the same or different and each are an integer of 1, 2, 3, 4 or 5, and wherein R 3 and R 4 each independently is a hydrogen atom or an optionally substituted alkyl group.
2. The process for producing an amino acid N-carboxyanhydride according to claim 1 , which comprises:
reacting the compound represented by formula (1) with an amino acid ester represented by the following formula (2):
wherein R 3 and R 4 are the same as the R 3 and R 4 , respectively, in formula (5); and R 5 and R 6 are independently an optionally substituted alkyl group, to obtain an amino acid ester carbamate compound represented by the following formula (3):
wherein R 1 and a respectively are the same as the R 1 and a in formula (1), provided that they may respectively be the R 2 and b in formula (1); and R 3 , R 4 , R 5 , and R 6 respectively are the same as the R 3 , R 4 , R 5 , and R 6 in formula (2);
adding an ester-deprotecting agent to the amino acid ester carbamate compound;
to thereby obtain an amino acid carbamate compound represented by the following formula (4):
wherein R 1 and a respectively are the same as the R 1 and a in formula (1), provided that they may respectively be the R 2 and b in formula (1); and R 3 , R 4 , and R 6 respectively are the same as the R 3 , R 4 , and R 6 in formula (2); and
heating the amino acid carbamate compound to thereby obtain the amino acid N-carboxyanhydride.
3. The process for producing an amino acid N-carboxyanhydride of claim 1 , wherein the reaction is conducted in the presence of a reaction promoter, wherein the reaction promoter is at least one member selected from the group consisting of an ion-exchange resin, a solid basic compound, a zeolite, an aluminosilicate, a molecular sieve, a diatomaceous earth and a silica gel.
4. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein the compound represented by formula (1) is selected from the group consisting of bis(4-nitrophenyl) carbonate, bis(2-nitrophenyl) carbonate, bis(2,4-dinitrophenyl) carbonate, bis(2,4,6-trinitrophenyl)carbonate, bis(pentafluorophenyl) carbonate, bis(4-chlorophenyl) carbonate, bis(2,4-dichlorophenyl) carbonate, and bis(2,4,6-trichlorophenyl) carbonate.
5. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein the compound represented by formula (1) is used in an amount of 0.1-10 mol per mol of the amino acid.
6. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein the compound represented by formula (1) is used in an amount of 0.5-5 mol per mol of the amino acid.
7. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein the compound represented by formula (1) is used in an amount of 0.8-1.5 mol per mol of the amino acid.
8. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein said reacting is carried out in an inert atmosphere.
9. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein said reacting is carried out at a reaction temperature in the range of −78° C. to 120° C.
10. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein said reacting is carried out at a reaction temperature in the range of −10° C. to 100° C.
11. The process for producing an amino acid N-carboxyanhydride according to claim 3 , wherein the reaction promoter is present in an amount of 1-1,000 parts by weight per 100 parts by weight of the amino acid.
12. The process for producing an amino acid N-carboxyanhydride according to claim 3 , wherein the reaction promoter is present in an amount of 10-200 parts by weight per 100 parts by weight of the amino acid.
13. The process for producing an amino acid N-carboxyanhydride according to claim 1 , wherein said reacting is carried out in the presence of a Lewis acid selected from the group consisting of titanium tetraisoproxide, lanthanum trifluoromethanesulfonate and tris(pentafluorophenyl) borane.
14. The process for producing an amino acid N-carboxyanhydride of claim 2 , wherein the reaction is conducted in the presence of a reaction promoter, wherein the reaction promoter is at least one member selected from the group consisting of an ion-exchange resin, a solid basic compound, a zeolite, an aluminosilicate, a molecular sieve, a diatomaceous earth and a silica gel.