Synthesis and evaluation of alkoxy-phenylamides and alkoxy-phenylimidazoles as potent sphingosine-1-phosphate receptor subtype-1 agonists

In the design of potent and selective sphingosine-1-phosphate receptor agonists, we were able to identify two series of molecules based on phenylamide and phenylimidazole analogs of FTY-720. Several designed molecules in these scaffolds have demonstrated selectivity for S1P receptor subtype 1 versus 3 and excellent in vivo activity in mouse. Two molecules PPI-4621 (4b) and PPI-4691 (10a), demonstrated dose responsive lymphopenia, when administered orally.     

Exploring amino acids derivatives as potent,selective, and direct agonists of sphingosine-1-phosphate receptor subtype-1

In the quest to discover a potent and selective class of direct agonists to the sphingosine-1-phosphate receptor, we explored the carboxylate functional group as a replacement to previously reported lead phosphates. This has led to the discovery of potent and selective direct agonists with moderate to substantial in vivo lymphopenia. The previously reported selectivity enhancing moiety (SEM) and selectivity enhancing orientation (SEO) in the phenylamide and phenylimidazole scaffolds were crucial to obtaining selectivity for S1P receptor subtype 1 over 3.     

Exploration of amino alcohol derivatives as novel,potent, and highly selective sphingosine-1-phosphate receptor subtype-1 agonists

In pursuit of a potent and highly selective sphingosine-1-phosphate receptor agonists with an improved in vivo conversion of the precursor to the active phospho-drug, we have utilized previously reported phenylamide and phenylimidazole scaffolds to identify a selectivity enhancing moiety (SEM) and selectivity enhancing orientation (SEO) within both pharmacophores. SEM and SEO have allowed for over 100 to 500-fold improvement in selectivity for S1P receptor subtype 1 over subtype 3. Utility of SEM and SEO and further SAR study allowed for discovery of a potent and selective preclinical candidate PPI-4955 (21b) with an excellent in vivo potency and dose responsiveness and markedly improved overall in vivo pharmacodynamic properties upon oral administration.     

Piperazinyl-oxadiazoles as selective sphingosine-1-phosphate receptor agonists

The discovery of a new series of selective S1P₁ agonists is described. This series of piperazinyl-oxadiazole derivatives was rapidly optimized starting from high-throughput screening hit 1 to afford potent and selective lead compound 10d. Further SAR studies showed that 10d was converted to the active phosphate metabolite 29 in vivo. Oral administration of compound 10d to rats was shown to induce lymphopenia at 3 mg/kg.     

Highly selective and potent agonists of sphingosine-1-phosphate 1 (S1P1) receptor

Novel series of sphingosine-1-phosphate (S1P) receptor agonists were developed through a systematic SAR aimed to achieve high selectivity for a single member of the S1P family of receptors, S1P1. The optimized structure represents a highly S1P1-selective and efficacious agonist: S1P1/S1P2, S1P1/S1P3, S1P1/S1P4>10,000-fold, S1P1/S1P5>600-fold, while EC50 (S1P1) <0.2 nM. In vivo experiments are consistent with S1P1 receptor agonism alone being sufficient for achieving desired lymphocyte-lowering effect.     

2-Piperazinecarboxamides as potent and selective melanocortin subtype-4 receptor agonists

We report the discovery and optimization of substituted 2-piperazinecarboxamides as potent and selective agonists of the melanocortin subtype-4 receptor. The 5- and 6-alkylated piperazine compounds exhibit low bioactivation potential as measured by covalent binding in microsome preparations.     

Nipecotic and iso-nipecotic amides as potent and selective somatostatin subtype-2 receptor agonists

N-Substituted nipecotic and iso-nipecotic amides of beta-methylTrpLys tert-butyl ester were found to be novel, selective and potent agonists of the somatostatin subtype-2 receptor in vitro. For example iso-nipecotic amide 8a showed high hsst2 binding affinity (Ki = 0.5 nM) and good selectivity (h5/h2 = 832).     

Synthesis and biological evaluation of gamma-aminophosphonates as potent, subtype-selective sphingosine 1-phosphate receptor agonists and antagonists

The synthesis of N-arylamide phosphonates and related arylether and arylamine analogues provided potent, subtype-selective agonists and antagonists of the five known sphingosine 1-phosphate (S1P) receptors (S1P(1-5)). To this end, the syntheses of phosphoserine mimetics-selectively protected and optically active phosphonoserines-are described. In vitro binding assays showed that the implementation of phosphonates as phosphate mimetics provided compounds with similar receptor binding affinities as compared to their phosphate precursors. meta-substituted arylamide phosphonates were discovered to be antagonists of the S1P(1) and S1P(3) receptors. When administered to mice, an antagonist blocked the lymphopenia evoked by a S1P receptor agonist and caused capillary leakage in both lung and kidney.     

Synthesis of para-alkyl aryl amide analogues of sphingosine-1-phosphate: discovery of potent S1P receptor agonists

Sphingosine-1-phosphate (S1P) is a biologically active lysophospholipid with the capacity to induce a broad range of cellular responses via its interaction with the S1P family of G-protein coupled receptors. This report describes the synthesis of several potent S1P receptor agonists. For instance, compound 9c displayed an EC(50)=8.6 nM at the S1P(1) receptor using a [gamma-35S]GTP binding assay as compared to an EC(50)=4.5 nM for the endogenous ligand. We also report the effects associated with introduction of a phenyl ring between the 'linker' and 'lipophilic tail' regions of the analogues, for example total loss of activity at S1P(2) and increased agonism at S1P(5).     

Synthesis and biological evaluation of sphingosine kinase substrates as sphingosine-1-phosphate receptor prodrugs

In the search for bioactive sphingosine 1-phosphate (S1P) receptor ligands, a series of 2-amino-2-heterocyclic-propanols were synthesized. These molecules were discovered to be substrates of human-sphingosine kinases 1 and 2 (SPHK1 and SPHK2). When phosphorylated, the resultant phosphates showed varied activities at the five sphingosine-1-phosphate (S1P) receptors (S1P_1–5). Agonism at S1P₁ was displayed in vivo by induction of lymphopenia. A stereochemical preference of the quaternary carbon was crucial for phosphorylation by the kinases and alters binding affinities at the S1P receptors. Oxazole and oxadiazole compounds are superior kinase substrates to FTY720, the prototypical prodrug immunomodulator, fingolimod (FTY720). The oxazole-derived structure was the most active for human SPHK2. Imidazole analogues were less active substrates for SPHKs, but more potent and selective agonists of the S1P₁ receptor; additionally, the imidazole class of compounds rendered mice lymphopenic.     

2,5-Disubstituted pyrrolidine carboxylates as potent, orally active sphingosine-1-phosphate (S1P) receptor agonists

A series of 2,5-cis-disubstituted pyrrolidines were synthesized and evaluated as S1P receptor agonists. Compounds 15-21 were identified with good selectivity over S1P3 which lowered circulating lymphocytes after oral administration in mice.     

Synthesis of benzimidazole based analogues of sphingosine-1-phosphate: discovery of potent, subtype-selective S1P4 receptor agonists

Sphingosine-1-phosphate (S1P) is a biologically active lysophospholipid with the capacity to induce a broad range of cellular responses via its interaction with the S1P family of G-protein coupled receptors. A member of this receptor family, S1P(4), is highly and almost exclusively expressed in the lymphoid system and has been implicated in regulation of cell shape and motility. This report describes the synthesis of several potent benzimidazole based S1P(4) receptor selective agonists. For instance, compound 9b displayed an EC(50)=36 nM at the S1P(4) receptor using a [gamma-(35)S]GTP binding assay as compared to an EC(50)=37 nM for the endogenous ligand. We also report the effects of altering stereochemistry at the C2 position, methylation at the C1 and C2 position, and activity differences between the alcohol and phosphate head groups of the analogues.     

Synthesis of 4(5)-phenylimidazole-based analogues of sphingosine-1-phosphate and FTY720: discovery of potent S1P1 receptor agonists

The novel immunosuppressant FTY720 has been demonstrated to elicit immunomodulating effects via interaction with the G-protein coupled receptor S1P(1). FTY720 induced agonism at the S1P(3) receptor, however, has been shown to result in mild bradycardia, a minor side-effect of initial FTY720 therapy. This report describes the synthesis of several potent 4(5)-phenylimidazole-based S1P(1) receptor agonists that are accompanied by poor agonist activity at S1P(3). For instance, compound 20 displayed an EC(50)=4.7+/-1.3 nM at the S1P(1) receptor and EC(50)=780+/-1.3 nM at the S1P(3) receptor using a [gamma-(35)S]GTP-binding assay as compared to phospho-FTY720 (S1P(1): EC(50)=1.3+/-1.3nM, S1P(3): EC(50)=2.0+/-2.4 nM).     

Synthesis of fluorinated agonist of sphingosine-1-phosphate receptor 1

The bioactive metabolite sphingosine-1-phosphate (S1P), a product of sphingosine kinases (SphKs), mediates diverse biological processes such as cell differentiation, proliferation, survival and angiogenesis. A fluorinated analogue of S1P receptor agonist has been synthesized by utilizing a ring opening reaction of oxacycles by a lithiated difluoromethylphosphonate anion as the key reaction. In vitro activity of this S1P analogue is also reported.     

Discovery of pyrimidine carboxamides as potent and selective CCK1 receptor agonists

A series of six-membered heterocycle carboxamides were synthesized and evaluated as cholecystokinin 1 receptor (CCK1R) agonists. A pyrimidine core proved to be the best heterocycle, and SAR studies resulted in the discovery of analog 5, a potent and structurally diverse CCK1R agonist.     

SAR studies of 3-arylpropionic acids as potent and selective agonists of sphingosine-1-phosphate receptor-1 (S1P1) with enhanced pharmacokinetic properties

Structure-activity relationship (SAR) studies of 3-arylpropionic acids-a class of novel S1P(1) selective agonists-by introducing substitution to the propionic acid chain and replacing the adjacent phenyl ring with pyridine led to a series of modified 3-arylpropionic acids with enhanced half-life in rat. These analogs (e.g., cyclopropanecarboxylic acids) exhibited longer half-life in rat than did unmodified 3-arylpropionic acids. This result suggests that metabolic oxidation at the propionic acid chain, particularly at the C3 benzylic position of 3-arylpropionic acids, is probably responsible for their short half-life in rodent.     

Pyrazole derived from (+)-3-carene; a novel potent,selective scaffold for sphingosine-1-phosphate (S1P1) receptor agonists

High throughput screening and hit to lead optimization led to the identification of ‘carene’ as a promising scaffold showing selective S1P₁ receptor agonism. In parallel to this work we have established a pharmacophore model for the S1P₁ receptor highlighting the minimal structural requirement necessary for potent receptor agonism.     

Indole-propionic acid derivatives as potent, S1P3-sparing and EAE efficacious sphingosine-1-phosphate 1 (S1P1) receptor agonists

Novel indole-propionic acid derivatives were developed as sphingosine-1-phosphate (S1P) receptor agonists through a systematic SAR study. The optimized and S1P(3) selective S1P(1) agonist 9f induced peripheral blood lymphocyte reduction in vivo and has an excellent efficacy in mouse experimental autoimmune encephalomyelitis (EAE).     

New potent and selective A1 adenosine receptor agonists

Thiirane analogs of ENAdo have been synthesised and found to be extremely potent and selective A(1) adenosine receptor agonists.     

Discovery of substituted biphenyl imidazoles as potent,bioavailable bombesin receptor subtype-3 agonists

We report SAR studies on a novel non-peptidic bombesin receptor subtype-3 (BRS-3) agonist lead series derived from high-throughput screening hit RY-337. This effort led to the discovery of compound 22e with significantly improved potency at both rodent and human BRS-3.