1-AMINOCYCLOBUTANECARBOXYLIC ACID-DERIVATIVES AS NOVEL STRUCTURAL ELEMENTS IN BIOACTIVE PEPTIDES - APPLICATION TO TUFTSIN ANALOGS

Four novel 2,4-methano amino acids (MAAs, 1-aminocyclobutane-1-carboxy lic acids) were synthesized. These include the basic MAA analogs of ly sine (16), ornithine (5), and arginine (6) and the neutral methanovali ne (22), related to proline. The above MAAs, as well as the MAA analog of homothreonine (7), were incorporated into the peptide chain of the immuno-modulatory peptide tuftsin, Thr-Lys-Pro-Arg, known to enhance several biological activities mediated by phagocytic cells. The synthe tic methano tuftsin analogs were assayed for their ability to stimulat e interleukin-6 (IL-6) secretion by mouse peritoneal macrophages and f or their stability in human serum toward enzymatic degradation. It was found that, at 2 x 10(-7) M, [MThr(1)]tuftsin (24) and an isomer of [ MVal(3)]tuftsin (27a) were considerably more active than the parent pe ptide in augmentation of cytokine release. [MOrn(2)]Tuftsin (25) was e qually potent. The analogs [MThr(1)]tuftsin (24) and [MOrn(2)]tuftsin (25), both pertaining to the proteolytically sensitive Thr-Lys bond of tuftsin, exhibited high resistance to enzymatic hydrolysis as compare d to tuftsin. Using specific rabbit anti-tuftsin antibodies in a compe titive enzyme-linked immunosorbent assay (ELISA) revealed that none of the MAA analogs can crossreact with tuftsin. It may indicate that the peptides assume global structures different than that of tuftsin.