Biphenyl-derivatives of 2-amino-7-phosphonoheptanoic acid, a novel class of potent competitive N-methyl-D-aspartate receptor antagonist--I. Pharmacological characterization in vitro.

Omega-Phosphono-substituted alpha-amino acids have long been known to be antagonists at the N-methyl-D-aspartate (NMDA) receptor. D-2-Amino-5-phosphonopentanoic (D-AP5) and D-2-amino-7-phosphonoheptanoic (D-AP7) acids are the "prototype" compounds of this kind. Insertion of a biphenyl-moiety in the middle of the AP7 chain results in increased affinity and reverses the enantioselectivity from a D- to an L-form preference (Müller et al., (1992) Helv. Chim. Acta 75: 855-864). We describe here a series of substituted biphenyl-AP7-derivatives, the most potent of which have affinities (in a [3H]CGP-39653 binding assay using native and recombinant receptors) and potencies (antagonism of NMDA-induced depolarizations in a cortical wedge preparation; inhibition of glutamate-stimulated [3H]MK-801 binding under non-equilibrium conditions) in the low nanomolar range. Structure-activity relationships show that hydroxy-substitution at the C5-atom in the AP7-chain as well as substitution in the second phenyl ring with space filling (such as chloro-)groups in the para- and especially the ortho-position (extending the torsion angle of the two rings) increase affinity and potency of these compounds. They have no relevant affinities for the strychnine-insensitive glycine co-agonist site or the MK-801/PCP channel blocking site on the NMDA receptor complex. AMPA- and kainate-induced responses were not affected by biphenyl-analogues. These compounds also do not interact with a number of other neurotransmitter receptor sites, and they do not inhibit the uptake of [3H] glutamate in rat brain synaptosomes. However, they display affinities in the (sub)micromolar range for a non-NMDA, non-AMPA, non-kainate binding site for [3H]glutamate, measured in the presence of calcium chloride, the functional correlate of which has not yet been elucidated.