Methods of making amidino compounds useful as nitric oxide synthase inhibitors

1. A method for the preparation of an alpha-amino acid compound having the structure of Formula 32:

or a salt, an enantiomer, or a racemate thereof, wherein:

R 2 is selected from the group consisting of C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 5 alkoxy-C 1 alkyl, and C 1 -C 5 alkylthio-C 1 alkyl;

R 1 , R 5 , R 6 , and R 7 independently are selected from the group consisting of —H, halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, and C 1 -C 5 alkoxy-C 1 alkyl;

R 9 and R 10 independently are selected from the group consisting of —H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, and C 1 -C 5 alkoxy-C 1 alkyl; and

when any of R 1 , R 2 , R 5 , R 6 , R 7 , R 9 , and R 10 independently is a moiety selected from the group consisting of alkyl, alkenyl, and alkynyl, then the moiety is optionally substituted by one or more substituent selected from the group consisting of —OH, alkoxy, and halogen;

wherein the method comprises hydrolyzing a hydantoin compound having the structure of Formula 33:

 or a salt, an enantiomer, or a racemate thereof, thereby forming the alpha-amino acid compound.

2. The method of claim 1 wherein the hydrolyzing conditions comprise contacting the hydantoin compound with an acid to produce an acid hydrolyzate.

3. The method of claim 2 wherein the acid is selected from the group consisting of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, trifluoroacetic acid, and phosphoric acid.

4. The method of claim 2 wherein the method further comprises treating the acid hydrolyzate with an ion exchange resin.

5. The method of claim 1 wherein the hydrolyzing conditions comprise contacting the hydantoin compound with a base to produce a base hydrolyzate.

6. The method of claim 5 wherein the base is selected from the group consisting of a hydrazine, a metal sulfide, a metal hydroxide, and a metal alkoxide.

7. The method of claim 1 wherein R 1 , R 5 , R 6 , and R 7 each is —H.

8. The method of claim 1 wherein R 9 and R 10 each is —H.

9. The method of claim 1 where the alpha-amino acid compound has the structure of Formula 34:

or a salt, an enantiomer, or a racemate thereof.

10. A method for the preparation of a hydantoin compound having the structure of Formula 35:

or a salt, an enantiomer, or a racemate thereof, wherein:

R 2 is selected from the group consisting of C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 5 alkoxy-C 1 alkyl, and C 1 -C 5 alkylthio-C 1 alkyl;

R 1 , R 5 , R 6 , and R 7 independently are selected from the group consisting of —H, halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, and C 1 -C 5 alkoxy-C 1 alkyl;

R 9 and R 10 independently are selected from the group consisting of —H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, and C 1 -C 5 alkoxy-C 1 alkyl; and

when any of R 1 , R 2 , R 5 , R 6 , R 7 , R 9 , and R 10 independently is a moiety selected from the group consisting of alkyl, alkenyl, and alkynyl, then the moiety is optionally substituted by one or more substituent selected from the group consisting of —OH, alkoxy, and halogen;

wherein the method comprises contacting an alpha-sulfo ketone compound having the structure of Formula 36:

 with a source of cyanide in the presence of a source of ammonium carbonate and water, thereby producing the hydantoin compound.

11. The method of claim 10 wherein the source of cyanide is hydrogen cyanide.

12. The method of claim 10 wherein the source of cyanide is a metal cyanide salt.

13. The method of claim 12 wherein the metal cyanide salt is selected from the group consisting of sodium cyanide, potassium cyanide, and lithium cyanide.

14. The method of claim 13 wherein the metal cyanide salt is sodium cyanide.

15. The method of claim 10 wherein R 1 , R 5 , R 6 , and R 7 each is —H.

16. The method of claim 10 wherein R 9 and R 10 each is —H.

17. The method of claim 10 further comprising a chiral separation step.

18. The method of claim 17 wherein the hydantoin compound has the structure of Formula 33:

or a salt or an enantiomer thereof.