Synthesis and characterization of aminoacidic pro-drugs of valproic acid

Some new derivatives of valproic acid (1) have been synthesized by condensation reaction of L-phenylalanine ethyl ester (2), L-tryptophan methyl ester (3), L-leucine methyl ester (4), L-methionine methyl ester (5) or L-histidine methyl ester (6) with 1 in the presence of dicyclohexylcarbodiimide (DCC). The reaction afforded in good yield prodrugs containing an amino acidic moiety. The structure of the new compounds was determined with the aid of spectroscopic and analytical data. To evaluate the stability following p.o. administration, the synthesized molecules were tested for gastro-intestinal hydrolysis. No significant general acid-base hydrolysis for the peptide bond was observed. The molecules offer a potentially useful mean to obtain highly selective drug release to the brain.