Native State Mass Spectrometry, Surface Plasmon Resonance, and X-ray Crystallography Correlate Strongly as a Fragment Screening Combination

Fragment-based drug discovery (FBDD) is contingent on the development of analytical methods to identify weak protein-fragment noncovalent interactions. Herein we have combined an underutilized fragment screening method, native state mass spectrometry, together with two proven and popular fragment screening methods, surface plasmon resonance and X-ray crystallography, in a fragment screening campaign against human carbonic anhydrase II (CA II). In an initial fragment screen against a 720-member fragment library (the "CSIRO Fragment Library") seven CA II binding fragments, including a selection of nonclassical CA II binding chemotypes, were identified. A further 70 compounds that comprised the initial hit chemotypes were subsequently sourced from the full CSIRO compound collection and screened. The fragment results were extremely well correlated across the three methods. Our findings demonstrate that there is a tremendous opportunity to apply native state mass spectrometry as a complementary fragment screening method to accelerate drug discovery.

GABA(B)-agonistic activity of certain baclofen homologues

Baclofen (1) is a potent and selective agonist for bicuculline-insensitive GABA(B) receptors and is used clinically as an antispastic and muscle relaxant agent. In the search for new bioactive chemical entities that bind specifically to GABA(B) receptors, we report here the synthesis of certain baclofen homologues, namely (R,S)-5-amino-3-arylpentanoic acid hydrochlorides (R,S)-1a-h as well as (R,S)-5-amino-3-methylpentanoic acid [(RS)-1i] to be evaluated as GABA(B)R agonists. Compound 1a is an agonist to GABA(B) receptors with an EC₅₀ value of 46 μM on tsA201 cells transfected with GABA(B1b)/GABA(B2)/Gqz5, being the most active congener among all the synthesized compounds.

GABAB receptors

GABAB receptors are a distinct subclass of receptors for the major inhibitory transmitter 4-aminobutanoic acid (GABA) that mediate depression of synaptic transmission and contribute to the inhibition controlling neuronal excitability. The development of specific agonists and antagonists for these receptors has led to a better understanding of their physiology and pharmacology, highlighting their diverse coupling to different intracellular effectors through Gi/G(o) proteins. This review emphasises our current knowledge of the neurophysiology and neurochemistry of GABAB receptors, including their heterogeneity, as well as the therapeutic potential of drugs acting at these sites.

Synthesis and binding properties to GABA receptors of 3-hydroxypyridinyl- and 3-hydroxypiperidinyl-analogues of baclofen

The synthesis of 3-(3-hydroxy-2-pyridinyl)propanoic acid, 3-(3-hydroxy-2-pyridinyl)-4-aminobutanoic acid, their corresponding piperidine compounds, and of some cyclized derivatives is described. In in vitro assays none of the new compounds shows any noteworthy affinity for GABAA or GABAB receptors; only (R,S)-3-(3-hydroxy-2-pyridinyl)-4-aminobutanoic acid and its lactam inhibited in some degree [3H]GABA binding, at 10(-4) M concentration, with low specificity as regards the two receptors.

Resolution of the stereoisomers of baclofen by high performance liquid chromatography

The GABA analogue baclofen [3-(p-chlorophenyl)-4-aminobutanoic acid] has stereospecific actions on the peripheral and central nervous systems. This paper describes the resolution of tritium-labelled baclofen by high performance liquid chromatography on a reverse-phase C18 column using a chiral mobile phase. The method, which may have general application to certain other GABA analogues, affords optically pure (+)- and (-)-baclofen labelled with tritium to high specific activity suitable for ligand binding and other neurochemical studies.