Synthesis and Reactions of New Chiral Linear Dipeptide Candidates Using Nalidixic Acid as Starting Material

A series of dipeptide heterocyclic derivatives 4-15 were synthesized using methyl 2-{[(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridin-3-yl)carbonyl]amino}-3-ethylbutanoate (3) as starting material. Treatment of 3 with L-phenylalanine methyl ester hydrochloride afforded the corresponding dipeptide methyl ester derivative 4, which was treated with hydrazine hydrate to afford the dipeptide acid hydrazide 5. Compound 5 was coupled with aldehyde and acetophenone derivatives to afford the corresponding Schiff bases 6a-f. The hydrazide derivative 5 was reacted with ethyl acetoacetate or acetone to give compounds 7 and 8, respectively. Reaction of 5 with carbon disulfide at different conditions afforded compounds 9 and 10, which were treated with hydrazine hydrate to give the 1-amino-2-dipeptido-1,3,4-triazole derivative 11. In addition, 5 was reacted with phenyl isothiocyanate to give the thiosemicarbazide derivative 12, which was cyclized with sodium hydroxide to the dipeptido 1-phenyl-1,3,4-triazole derivative 13. Finally, treatment of 13 with methyl iodide afforded the S-methyl derivative 14, which was reacted with hydrazine hydrate to give the hydrazine derivative 15.