Synthesis of novel cyclic peptides using a liquid-phase method based on Nα-isophthaloyl sarcosylsarcosine methyl ester

Nα-isophthalic acid 1 or Nα-isophthaloyl dichloride 2 has been coupled with the proper sarcosine methyl esters to create several linear and macrocyclic pentapeptide derivatives. The analogous Nα-isophthaloyl-bis-[sarcosine methyl ester], 3, was obtained by coupling 1 or 2 with sarcosine methyl ester. The equivalent acid 4, Nα-isophthaloyl-bis-[sarcosine], was subsequently obtained by hydrolyzing this with methanolic sodium hydroxide. The corresponding tetrapeptide ester 5, Nα-isophthaloyl-bis [sarcosyl-sarcosine methyl ester], was created by coupling the latter product 4 with another molecule of sarcosine methyl ester. This compound was then hydrolyzed with methanolic sodium hydroxide to obtain the corresponding acid 6, Nα-isophthaloyl-bis [sarcosyl - sarcosine]. The equivalent cyclic pentapeptide methyl ester 7, Nα-isophthaloyl)-bis-[sarcosyl - sarcosine]-L-Lys-OMe, was produced by cyclizing tetrapeptide acids with L-lysine methyl ester. Lastly, the corresponding acids 8 and 9, cyclo-(Nα-isophthaloyl)-bis-[sarcosyl - sarcosine]-L-Ly, and Nα-isophthaloyl)-bis [sarcosyl - sarcosine]-L-Lys-NHNH2, respectively, were obtained by hydrolyzing methyl ester 7 with 1N methanolic sodium hydroxide or hydrazinolyzing it with hydrazine hydrate. KEY WORDS: Nα-isophthaloyl dichloride, Amino acids, Linear peptides, Cyclic pentapeptides Bull. Chem. Soc. Ethiop. 2026, 40(2), 341-351 DOI: https://dx.doi.org/10.4314/bcse.v40i2.6