Paul Adrian Wyman

Identification and characterisation of SB-366791, a potent and selective vanilloid receptor (VR1/TRPV1) antagonist

Vanilloid receptor-1 (TRPV1) is a non-selective cation channel, predominantly expressed by peripheral sensory neurones, which is known to play a key role in the detection of noxious painful stimuli, such as capsaicin, acid and heat. To date, a number of antagonists have been used to study the physiological role of TRPV1; however, antagonists such as capsazepine are somewhat compromised by non-selective actions at other receptors and apparent modality-specific properties. SB-366791 is a novel, potent, and selective, cinnamide TRPV1 antagonist isolated via high-throughput screening of a large chemical library. In a FLIPR-based Ca(2+)-assay, SB-366791 produced a concentration-dependent inhibition of the response to capsaicin with an apparent pK(b) of 7.74 +/- 0.08. Schild analysis indicated a competitive mechanism of action with a pA2 of 7.71. In electrophysiological experiments, SB-366791 was demonstrated to be an effective antagonist of hTRPV1 when activated by different modalities, such as capsaicin, acid or noxious heat (50 degrees C). Unlike capsazepine, SB-366791 was also an effective antagonist vs. the acid-mediated activation of rTRPV1. With the aim of defining a useful tool compound, we also profiled SB-366791 in a wide range of selectivity assays. SB-366791 had a good selectivity profile exhibiting little or no effect in a panel of 47 binding assays (containing a wide range of G-protein-coupled receptors and ion channels) and a number of electrophysiological assays including hippocampal synaptic transmission and action potential firing of locus coeruleus or dorsal raphe neurones. Furthermore, unlike capsazepine, SB-366791 had no effect on either the hyperpolarisation-activated current (I(h)) or Voltage-gated Ca(2+)-channels (VGCC) in cultured rodent sensory neurones. In summary, SB-366791 is a new TRPV1 antagonist with high potency and an improved selectivity profile with respect to other commonly used TRPV1 antagonists. SB-366791 may therefore prove to be a useful tool to further study the biology of TRPV1.

New quinoline NK3 receptor antagonists with CNS activity.

Lead optimisation starting from the previously reported selective quinoline NK(3) receptor antagonists talnetant 2 (SB-223412) and 3 (SB-222200) led to the identification of 3-aminoquinoline NK(3) antagonist 10 (GSK172981) with excellent CNS penetration. Investigation of a structurally related series of sulfonamides with reduced lipophilicity led to the discovery of 20 (GSK256471). Both 10 and 20 are high affinity, potent NK(3) receptor antagonists which despite having different degrees of CNS penetration produced excellent NK(3) receptor occupancy in an ex vivo binding study in gerbil cortex.

SB-272183, a selective 5-HT1A, 5-HT1B and 5-HT1D receptor antagonist in native tissue

A novel compound, SB‐272183 (5‐Chloro‐2, 3‐dihydro‐6‐[4‐methylpiperazin‐1‐yl]‐1[4‐pyridin‐4‐yl]napth‐1‐ylaminocarbonyl]‐1H‐indole), has been shown to have high affinity for human 5‐HT1A, 5‐HT1B and 5‐HT1D receptors with pKi values of 8.0, 8.1 and 8.7 respectively and is at least 30 fold selective over a range of other receptors. [35S]‐GTPγS binding studies showed that SB‐272183 acts as a partial agonist at human recombinant 5‐HT1A, 5‐HT1B and 5‐HT1D receptors with intrinsic activities of 0.4, 0.4 and 0.8 respectively, compared to 5‐HT. SB‐272183 inhibited 5‐HT‐induced stimulation of [35S]‐GTPγS binding at human 5‐HT1A and 5‐HT1B receptors to give pA2 values of 8.2 and 8.5 respectively. However, from [35S]‐GTPγS autoradiographic studies in rat and human dorsal raphe nucleus, SB‐272183 did not display intrinsic activity up to 10 μM but did block 5‐HT‐induced stimulation of [35S]‐GTPγS binding. From electrophysiological studies in rat raphe slices in vitro, SB‐272183 did not effect cell firing rate up to 1 μM but was able to attenuate (+)8‐OH‐DPAT‐induced inhibition of cell firing to give an apparent pKb of 7.1. SB‐272183 potentiated electrically‐stimulated [3H]‐5‐HT release from rat and guinea‐pig cortical slices at 100 and 1000 nM, similar to results previously obtained with the 5‐HT1B and 5‐HT1D receptor antagonist, GR127935. Fast cyclic voltammetry studies in rat dorsal raphe nucleus showed that SB‐272183 could block sumatriptan‐induced inhibition of 5‐HT efflux, with an apparent pKb of 7.2, but did not effect basal efflux up to 1 μM. These studies show that, in vitro, SB‐272183 acts as an antagonist at native tissue 5‐HT1A, 5‐HT1B and 5‐HT1D receptors.

The discovery of a series of N-substituted 3-(4-piperidinyl)-1,3-benzoxazolinones and oxindoles as highly brain penetrant, selective muscarinic M1 agonists.

A series of N-substituted 3-(4-piperidinyl)-1,3-benzoxazolinones and oxindoles are reported which were found to be potent and selective muscarinic M1 agonists. By control of the physicochemical characteristics of the series, particularly the lipophilicity, compounds with good metabolic stability and excellent brain penetration were identified. An exemplar of the series was shown to be pro-cognitive in the novel object recognition rat model of temporal induced memory deficit.

Azabicyclic indole esters as potent 5-HT4 receptor antagonists.

The synthesis of a series of azabicyclic indole esters is described and their potency reported as 5-HT4 receptor antagonists. Optimization of the most potent compound (19) by preparing the corresponding oxazino[3,2-a]indole ester afforded 34, which had a pIC50 of 9.5 in the guinea pig distal colon longitudinal muscle myenteric plexus preparation.

5-HT4receptor antagonists : oxazolo, oxazino and oxazepino[3,2-a]indole derivatives

Abstract The identification of oxazolo, oxazino and oxazepino[3,2-a]indoles as new structural classes of highly potent 5-HT4 receptor antagonists is described. Compounds (4) (5) and (6) are among the most potent 5-HT4 receptor antagonists reported to date.

Synthesis of ethyl 1-azabicyclo[2.2.1]hept-4-yl carboxylate

Abstract The dipolar cycloaddition reaction of α-methylene butyrolactone and N-benzyl azomethine ylid (5) affords the spirolactone (2) which rearranges to give ethyl 1-zabicyclo[2.2.1]hept-4-yl carboxylate (1) in excellent overall yield.

SB-616234-A (1-[6-(cis-3,5-dimethylpiperazin-1-yl)-2,3-dihydro-5-methoxyindol-1-yl]-1-[2′methyl-4′-(5-methyl-1,2,3-oxadiazol-3-yl)biphenyl-4-yl]methanone hydrochloride): A novel, potent and selective 5-HT1B receptor antagonist

SB-616234-A possesses high affinity for human 5-HT1B receptors stably expressed in Chinese hamster ovary (CHO) cells (pKi 8.3+/-0.2), and is over 100-fold selective for a range of molecular targets except h5-HT1) receptors (pKi 6.6+/-0.1). Similarly, affinity (pKi) for rat and guinea pig striatal 5-HT1B receptors is 9.2+/-0.1. In [35S]-GTPgammaS binding studies in the human recombinant cell line, SB-616234-A acted as a high affinity antagonist with a pA2 value of 8.6+/-0.2 whilst providing no evidence of agonist activity in this system. In [35S]-GTPgammaS binding studies in rat striatal membranes, SB-616234-A acted as a high affinity antagonist with an apparent pKB of 8.4+/-0.5, again whilst providing no evidence of agonist activity in this system. SB-616234-A (1 microM) potentiated electrically stimulated [3H]-5-HT release from guinea pig and rat cortical slices (S2/S1) ratios of 1.8 and 1.6, respectively). SB-616234-A (0.3-30 mg kg(-1) p.o.) caused a dose-dependent inhibition of ex vivo [3H]-GR125743 binding to rat striatal 5-HT1B receptors with an ED50 of 2.83+/-0.39 mg kg(-1) p.o. Taken together these data suggest that SB-616234-A is a potent and selective 5-HT(1B) autoreceptor antagonist that occupies central 5-HT1B receptors in vivo following oral administration.

Acylglycinamides as inhibitors of glycine transporter type 1.

A screening hit was used as the basis for the core structure of a new series of acylglycinamide GlyT-1 inhibitors. Investigation of the SAR around four areas of diversity used facile chemistry to prepare compounds quickly. By focussing on reducing the lipophilicity and improving the aqueous solubility in the series we were able to prepare a compound (17e) with a good level of activity at GlyT-1, selectivity over GlyT-2 and moderate oral bioavailability.

The Discovery and Development of 5-HT-terminal Autoreceptor Antagonists

Publisher Summary The chapter illustrates the changes that have taken place within the pharmaceutical industry over the past few years. The first compounds were identified from experiments in animal tissue in which the nature of the receptors involved was poorly characterized. Receptor subtypes were subsequently identified, and for some time, species differences caused confusion that was subsequently resolved with the use of recombinant receptors expressed in cell lines and careful pharmacological analysis. The use of human recombinant receptors led to the identification of selective agents that were used to define the receptor subtypes present in native tissue preparations. Thus, in the brain, the terminal 5-hydroxytryptamine (HT) autoreceptor was identified as being of the 5-HT 1B subtype. However, the use of highly expressed recombinant receptors in functional assays led to the further complication that antagonists in tissue were shown to be partial agonists in the cell-based functional assays where the recombinant receptor was expressed. Using the latter technology, selective inverse agonists were identified but many of the compounds identified as partial agonists in the recombinant cell lines have been shown to be antagonists in native tissue.