Intermediates for the preparation of remifentanil hydrochloride
A new intermediate for synthesizing 1-substituted-4-[phenyl(propanoyl)amino]piperidine-4-carbonitrile derivatives is laid open. Specifically set out is a method for use of this intermediate in the preparation of remifentanil. The enclosed shorter process offers a greater yield of products with higher purity as compared to methods reported in the prior art.
1. A compound of formula 20 or a salt thereof:
2. A method for synthesizing Remifentanil (1) or a salt thereof, the method selected from the group consisting of Method A and Method B, wherein Method A comprises reacting the compound of claim 1 or a salt thereof with an acylating agent, optionally in the presence of an acid scavenger, to produce a compound of formula (21), and reacting the compound of formula (21) with methanol under acidic conditions, and Method B comprises hydrolyzing the compound of claim 1 or a salt thereof with an acid, esterifying the hydrolyzed product with an alcohol to produce a compound of formula (12), and reacting the compound of formula (12) with an acylating agent, whereby Remifentanil (1) or a salt thereof is synthesized
3. The method of claim 2 , wherein the compound of formula (20) is first converted to a compound of formula (21)
4. The method of claim 3 , wherein the acylating agent is propionic anhydride or propionyl chloride.
5. The method of claim 4 , wherein the acid scavenger is selected from the group consisting of triethylamine, morpholine, piperidine, and pyridine.
6. A method for preparing a compound of claim 1 , the method comprising reacting a compound of formula (19) with phenylamine in the presence of a cyanide compound to produce a compound of formula (20).
7. The method of claim 6 , wherein the cyanide compound is sodium cyanide.
8. The method of claim 6 , further comprising preparing the compound of formula (19) by alkylating 4-piperidone monohydrate hydrochloride with an appropriate alkylating agent in the presence of a basic catalyst, whereby a compound of formula (19) is prepared.
9. The method of claim 8 , wherein the appropriate alkylating agent is selected from the group consisting of 3-chloropropionitrile, 3-bromopropionitrile, 3-iodopropionitrile, 2-cyanoethyl methanesulfonate, and 2-cyanoethyl 4-methyl benzenesulfonate.
10. The method of claim 9 , wherein the basic catalyst is selected from the group consisting of sodium or potassium carbonate, sodium hydrogen carbonate, sodium or potassium hydroxide, sodium amide, potassium terc-butoxide, and sodium ethoxide.
11. The method of claim 8 , wherein the alkylating is performed in the presence of a solvent, optionally wherein the solvent is selected from the group consisting of acetone, methyl ethyl ketone, isopropanol, acetonitrile, N,N-dimethylacetamide, N,N-dimethylformamide, tetrahydrofuran, and 2-methyl tetrahydrofuran.
12. A method for synthesizing remifentanil hydrochloride, wherein the method is according to the following scheme: