Method of synthesizing diketopiperazines

1. A method of synthesizing a diketopiperazines of the following formula:

wherein:

R 1 is —CH 2 COR 3 , or —CH 2 CH 2 COR 3 ;

R 2 is the side chain of an amino acid selected from the group consisting of glycine, alanine, valine, leucine, isoleucine, serine, threonine, aspartic acid, asparagine, glutamic acid, glutamine, lysine, hydroxylysine, histidine, arginine, phenylalanine, tyrosine, tryptophan, thyroxine, cysteine, methionine, norvaline and ornithine;

R 3 is —OH, —NH 2 , —OR 4 , —NHR 4 , or —NR 4 R 4 ; and

each R 4 is independently an alkyl, aryl, alkylaryl, or arylalkyl, the method comprising:

(a) reacting a first amino acid selected from the group consisting of glycine, alanine, valine, leucine, isoleucine, serine, threonine, aspartic acid, asparagine, glutamic acid, glutamine, lysine, hydroxylysine, histidine, arginine, phenylalanine, tyrosine, tryptophan, thyroxine, cysteine, methionine, norvaline and ornithine, with a second amino acid derivative having one of the following formulas:

NH 2 CH(CH 2 COOR 5 )COOH or

NH 2 CH(CH 2 CH 2 COOR 5 )COOH, wherein R5 is benzyl, under conditions effective to form a dipeptide; and,

(b) cyclizing the dipeptide at a temperature of between 80° C. and 180° C. in a neutral solvent to form a diketopiperazine having the formula;

wherein:

R 6 is —CH 2 COOR 5 , or —CH 2 CH 2 COOR 5 ; and

(c) hydrogenating the diketopiperazine to remove the R 5 group and form a diketopiperazine having the formula:

wherein:

R 1 is —CH 2 COOH, or —CH 2 CH 2 COOH; and,

R 2 is the side chain of an amino acid selected from the group consisting of glycine, alanine, valine, leucine, isoleucine, serine, threonine, aspartic acid, asparagine, glutamic acid, glutamine, lysine, hydroxylysine, histidine, arginine, phenylalanine, tyrosine, tryptophan, thyroxine, cysteine, methionine, norvaline and ornithine.

2. The method of claim 1 wherein the first amino acid is alanine.

3. The method of claim 1 wherein the first amino acid is protected with one or more protecting groups.

4. The method of claim 1 wherein the amino group or α-carboxyl of the second amino acid derivative is protected with a protecting group.

5. The method of claim 1 wherein the neutral solvent comprises butan-2-ol and toluene.

6. The method of claim 1 wherein hydrogenating step (c) is conducted using a palladium on carbon catalyst.

7. The method of claim 1 further comprising derivatizing the compound formed in step (c) at the carboxylic acid of R 1 to form a derivative selected from the group consisting of an amide and an ester.

8. The method of claim 1 , wherein the first amino acid is attached to a solid support and wherein the dipeptide is removed from the solid support prior to the cyclizing step (b).