ABSTRACT
Four novel 2,4-methano amino acids (MAAs, 1-aminocyclobutane-1-carboxylic acids) were synthesized. These include the basic MAA analogs of lysine (16), ornithine (5), and arginine (6) and the neutral methanovaline (22), related to proline. The above MAAs, as well as the MAA analog of homothreonine (7), were incorporated into the peptide chain of the immunomodulatory peptide tuftsin, Thr-Lys-Pro-Arg, known to enhance several biological activities mediated by phagocytic cells. The synthetic methano tuftsin analogs were assayed for their ability to stimulate interleukin-6 (IL-6) secretion by mouse peritoneal macrophages and for their stability in human serum toward enzymatic degradation. It was found that, at 2 x 10(-7) M, [MThr1]tuftsin (24) and an isomer of [MVal3]tuftsin (27a) were considerably more active than the parent peptide in augmentation of cytokine release. [MOrn2]Tuftsin (25) was equally potent. The analogs [MThr1]tuftsin (24) and [MOrn2]tuftsin (25), both pertaining to the proteolytically sensitive Thr-Lys bond of tuftsin, exhibited high resistance to enzymatic hydrolysis as compared to tuftsin. Using specific rabbit anti-tuftsin antibodies in a competitive enzyme-linked immunosorbent assay (ELISA) revealed that none of the MAA analogs can cross-react with tuftsin. It may indicate that the peptides assume global structures different than that of tuftsin.
Subject(s)
Amino Acids, Cyclic , Amino Acids , Peptides/chemical synthesis , Peptides/pharmacology , Tuftsin/analogs & derivatives , Amino Acids/chemistry , Animals , Antibodies/immunology , Antibodies/metabolism , Circular Dichroism , Endopeptidases/blood , Endopeptidases/metabolism , Enzyme-Linked Immunosorbent Assay , Humans , Interleukin-6/metabolism , Macrophages, Peritoneal/drug effects , Macrophages, Peritoneal/metabolism , Magnetic Resonance Spectroscopy , Mass Spectrometry , Mice , Molecular Structure , Peptides/immunology , Peptides/metabolism , Tuftsin/analysis , Tuftsin/pharmacologyABSTRACT
A range of cis- and trans-3-substituted 1-aminocyclobutane-1-carboxylic acids has been synthesized and evaluated for antagonism at excitatory amino acid receptor sites and for anticonvulsant activity. Potent and selective antagonist activity at N-methyl-D-aspartate (NMDA) receptor sites in neonatal rat motoneurones was shown by compounds in which the 3-substituent was, or contained, a 2'-carboxyethyl or 2'-phosphonoethyl moiety. Substances 4b, 24, 35, and 40 were more potent than the standard NMDA receptor antagonist, D-2-amino-5-phosphonopentanoate (D-AP5) as NMDA antagonists in this preparation, and about equipotent with [3-(+/-)-2-carboxypiperazin-4-yl)-1-propyl]phosphonate (CPP). Anticonvulsant activity, as assessed following intracerebroventricular injection into audiogenic DBA/2 mice, generally paralleled NMDA receptor antagonist activity.
Subject(s)
Amino Acids, Cyclic , Amino Acids/chemistry , Anticonvulsants/chemical synthesis , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Acoustic Stimulation , Amino Acids/pharmacology , Amino Acids/therapeutic use , Animals , Animals, Newborn , Anticonvulsants/therapeutic use , Binding Sites , Computer Simulation , Mice , Mice, Inbred DBA , Models, Molecular , Molecular Conformation , Molecular Structure , Motor Neurons/metabolism , Rats , Seizures/etiology , Seizures/prevention & control , Spinal Cord/metabolism , Structure-Activity RelationshipABSTRACT
Cis- and trans-2,4-methanoglutamate were compared with L-glutamate as acidic amino acid ligands. Cis-2,4-methanoglutamate had a Ki of 0.052 microM against N-methyl-D-aspartate (NMDA)-specific L-[3H]glutamate binding compared with 0.050 microM for L-glutamate. Cis-2,4-methanoglutamate exhibited no significant affinity against [3H]kainate or [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate ([3H]AMPA) binding. Trans-2,4-methanoglutamate had no significant affinity for any of these sites. Cis-2,4-methanoglutamate increased [3H]N-1[2-thienyl]cyclohexyl-3,4-piperidine [( 3H]TCP) binding with EC50 of 0.35 +/- 0.14 microM. It produced an inward current in rat brain mRNA-injected Xenopus oocytes which was blocked by the NMDA antagonist, D-2-amino-7-phosphonoheptanoate (D-AP7). Cis-2,4-methanoglutamate (EC50 = 15.9 microM) was 100-fold more potent than L-glutamate (EC50 = 1,584 microM) in reducing the excitatory postsynaptic potential in CA1 of hippocampal slices. Cis-2,4-methanoglutamate is the most potent, selective NMDA agonist known.
