Roger M. Freidinger

Orally Efficacious NR2B-Selective NMDA Receptor Antagonists

A novel series of benzamidines was synthesized and shown to exhibit NR2B-subtype selective NMDA antagonist activity. Compound 31 is orally active in a carrageenan-induced rat hyperalgesia model of pain and shows no motor coordination side effects.

Nonpeptidic ligands for peptide and protein receptors.

The first potent nonpeptidic ligands for somatostatin, luteinizing hormone-releasing hormone, glucagon and bradykinin receptors have been reported. Nonpeptidic clinical candidates have been identified or are currently under study for substance P, bradykinin, endothelin, growth hormone secretagogue, angiotensin, vasopressin, motilin and cholecystokinin. Design, screening, combinatorial chemistry and classical medicinal chemistry all played important roles in these advances.

Synthesis, evaluation, and crystallographic analysis of L-371,912: A potent and selective active-site thrombin inhibitor.

Abstract Removal of the β-ketoamide functionality from L-370,518 (Ki = 0.09 nM) provided a 5 nM Ki inhibitor of thrombin: L-371,912. Comparison of the enzyme-inhibitor crystal structures suggests a possible explanation for the relatively small change in affinity for thrombin. L-371,912 is selective for thrombin over related serine proteases and is efficacious in an animal model of arterial thrombosis.

Approaches to peptidomimetics which serve as surrogates for the cis amide bond: novel disulfide-constrained bicyclic hexapeptide analogs of somatostatic.

Abstract In testing and refining our model of the receptor-bound conformation of the potent small-ring somatostatin analog cyclo-(Pro6-Phe7-D-Trp8-Lys9-Thr10-Phe11), we have investigated structures constrained within bicyclic systems. Specifically, we have incorporated the 8-membered -C ys-Cy s- unit in place of the -Phe11-Pro6-segment, thus achieving two aims: 1) constraint of the 11- > 6 amide bond to the cis geometry established for the cyclic hexapeptide; 2) positioning of the disulfide in place of the position-11 phenyl group, to act as surrogate for phenyl in receptor binding. Synthetic methodology which provides ready access to this class of compounds is presented, along with results of NMR spectral studies of the bicyclic systems. Biological assays show retention of high potency, in confirmation of our view of cyclo-cystine as a good mimetic for cis amide. Other reported mimetics for the cis amide bond are reviewed from the perspectives of comparative ease of accessibility and approximation of various amide bond parameters.

Discovery of a nonpeptidic small molecule antagonist of the human platelet thrombin receptor (PAR-1)

The synthesis and biological evaluation of a series of nonpeptidic small molecule antagonists of the human platelet thrombin receptor (PAR-1) are described. Optimization of the 5-amino-3-arylisoxazole lead resulted in an approximate 100-fold increase in potency. The most potent of these compounds (54) inhibits platelet activation with IC(50)s of 90 nM against the thrombin receptor agonist peptide (TRAP) and 510 nM against thrombin as the agonist. Further, antagonist 54 fully blocks platelet aggregation stimulated by 1 nM thrombin for 10 min.

Discovery and initial structure-activity relationships of trisubstituted ureas as thrombin receptor (PAR-1) antagonists.

Thrombin is the most potent agonist of platelet activation, and its effects are predominantly mediated by platelet thrombin receptors. Therefore, antagonists of the thrombin receptor have potential utility for the treatment of thrombotic disorders. Screening of combinatorial libraries revealed 2 to be a potent antagonist of the thrombin receptor. Modifications of this structure produced 11k, which inhibits thrombin receptor stimulated secretion and aggregation of platelets.

In vitro studies on L-771,688 (SNAP 6383), a new potent and selective α1A-adrenoceptor antagonist

L-771,688 (SNAP 6383, methyl(4S)-4-(3, 4-difluorophenyl)-6-[(methyloxy)methyl]-2-oxo-3-[(¿3-[4-(2-pyridin yl)-1-piperidinyl]propyl¿amino)carbonyl]-1,2,3, 4-tetrahydro-5-pyrimidine carboxylate) had high affinity (Ki less than or = 1 nM) for [3H]prazosin binding to cloned human, rat and dog alpha1A-adrenoceptors and high selectivity (>500-fold) over alpha1B and alpha1D-adrenoceptors. [3H]Prazosin / (+/-)-beta-[125I]-4-hydroxy-phenyl)-ethyl-aminomethylteralone ([125I]HEAT) binding studies in human and animal tissues known to contain alpha1A and non-alpha1A-adrenoceptors further demonstrated the potency and alpha1A-subtype selectivity of L-771,688. [3H]L-771,688 binding studies at the cloned human alpha1A-adrenoceptors and in rat tissues indicated that specific [3H]L-771,688 binding was saturable and of high affinity (Kd=43-90 pM) and represented binding to the pharmacologically relevant alpha1A-adrenoceptors. L-771,688 antagonized norepinephrine-induced inositol-phosphate responses in cloned human alpha1A-adrenoceptors, as well as phenylephrine or A-61603 (N-[5-4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7, 8-terahydro-naphthlen-1-yl] methanesulfonamide hydrobromide) induced contraction in isolated rat, dog and human prostate, human and monkey bladder neck and rat caudal artery with apparent Kb values of 0.02-0.28 nM. In contrast, the contraction of rat aorta induced by norepinephrine was resistant to L-771,688. These data indicate that L-771,688 is a highly selective alpha1A-adrenoceptor antagonist.

Preparation and evaluation of 1,3-diaminocyclopentane-linked dihydropyrimidinone derivatives as selective α1a-receptor antagonists

Abstract Several 1,3-diaminocyclopentane linked α 1a -receptor antagonists were prepared using a divergent chemical strategy that allows for rapid analysis of all stereochemical permutations for their effect on α 1 -receptor binding.

Nonpeptide oxytocin antagonists: Analogs of L-371,257 with improved potency

Structure-activity studies on the oxytocin antagonist 1 (L-371,257; Ki = 9.3 nM) have led to the identification of a related series of compounds containing an ortho-trifluoroethoxyphenylacetyl core which are orally bioavailable and have significantly improved potency in vitro and in vivo, e.g., compound 8 (L-374,943; Ki = 1.4 nM).

Identification of a series of CCK-2 receptor nonpeptide agonists: Sensitivity to stereochemistry and a receptor point mutation

The search for small-molecule drugs that act at peptide hormone receptors has resulted in the identification of a wide variety of antagonists. In contrast, the discovery of nonpeptide agonists has been far more elusive. We have used a constitutively active mutant of the cholecystokinin 2 receptor (CCK-2R) as a sensitive screen to detect ligand activity. Functional assessment of structural analogs of the prototype CCK-2R antagonist, L-365,260 [3R-N- (2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin-3-yl)-N′-(3-methylphenyl)urea], resulted in the identification of a series of agonists. Each of the active molecules is an S enantiomer, whereas the corresponding R stereoisomers have little or no activity. Further in vitro and in vivo assessment at the wild-type receptor indicated that efficacy of the two most active ligands approached that of the endogenous hormone. The function of selected R and S enantiomers was differentially sensitive to a point mutation, N353L, within the putative CCK-2R ligand pocket. The results of this study highlight the potential of constitutively active receptors as drug screening tools and the interdependence of ligand stereochemistry and receptor conformation in defining drug efficacy.