Development of Highly Potent GAT1 Inhibitors: Synthesis of Nipecotic Acid Derivatives by Suzuki–Miyaura Cross‐Coupling Reactions

Abstract

A new series of potent and selective mGAT1 inhibitors has been identified, featuring a nipecotic acid residue and an N-butenyl linker with a 2-biphenyl residue at the ω-position. Docking, combined with MD calculations, revealed a binding mode for the new compounds similar to that of tiagabine, the only mGAT1 inhibitor currently approved as antiepileptic drug. For the synthesis, a Suzuki-Miyaura cross-coupling reaction was used as a key step by which variously substituted biaryl subunits were assembled. Biological evaluation revealed several compounds that possess binding affinities and inhibitory potencies toward mGAT1, together with subtype selectivities against mGAT2-mGAT4 that were similar to or even higher than those for tiagabine. A derivative carrying the 2',4'-dichloro-2-biphenyl moiety attached to N-but-3-enylnipecotic acid at the terminal position of the linker chain was found to be the most potent binder, with the racemic form of the compound displaying a binding affinity of 8.05±0.13 (pKi ), while the R enantiomer exhibited an affinity value of 8.33±0.06 (pKi ).

Development of Highly Potent GAT1 Inhibitors: Synthesis of Nipecotic Acid Derivatives with N‐Arylalkynyl Substituents

“…With mGAT1 binding affinities being in the range of 8.2–8.3 (p K i ), enantiomers ( R )‐ 17 d , ( R )‐ 17 f , ( R )‐ 17 g , and ( R )‐ 17 i , (Table , entries 4a, 6a, 7a, and 9a) are among the best binders known so far for this target. As compared with the 2′,4′‐dichloro‐substituted derivative of ( R )‐ 4 (p K i =8.33±0.06, pIC 50 =7.43±0.10), which is one of the most active mGAT1 inhibitors, the binding affinity of the most active mGAT1 inhibitors of this study was found to be in the same range, and their inhibitory potencies even somewhat higher. Relative to N ‐substituted derivatives of guvacine with an oxime spacer that are known to be among the most potent mGAT1 inhibitors to date, the best of the nipecotic acid derivatives with an alkyne spacer described in this study generally show inhibitory potencies (pIC 50 ) and binding affinities (p K i ) in a similar range.…”

“…We recently introduced compounds 5 and 6 (Figure ) and related derivatives, the lipophilic part of which is characterized by a biphenylvinyl or a benzylphenylvinyl unit. For the parent compounds 5 and 6 , high binding affinities for GAT1 were observed ( 5 : p K i =7.15±0.07; 6 : p K i =6.16±0.07) . For the biphenyl derivative 5 , docking studies indicated that halogen substitution of the terminal phenyl group might provide compounds with enhanced binding affinities for hGAT1; this was indeed verified, as halogen‐substituted derivatives of 5 were found to exhibit binding affinities of p K i ≥8.…”

“…The building blocks 13 and 14 designed for subsequent Suzuki–Miyaura reactions, via the aryl bromide function present in these molecules, for the construction of the terminal biphenyl residue, were found to be well suited for this purpose. Coupling reactions were performed with a set of phenylboronic acids carrying one to two additional substituents which were either chlorine, fluorine, or methyl, by which a substitution pattern has been gained similar to that studied for analogous systems previously, such as compound 5 (Figure ) . Pd 2 (dba) 3 ⋅CHCl 3 (1 mol %) and S‐Phos (4 mol %) as catalyst systems were found to be well suited to effect the desired coupling reactions, providing coupling products 15 b – l and 16 b – l after heating for 6 h at 60 °C in dioxane/water in the presence of K 3 PO 2 in good yields (87–93 %).…”

“…Previous studies by Wein et al . and Petrera et al . have shown that docking into an hGAT1 model generated by homology modeling from the X‐ray crystallographic structure of the leucine transporter from Aquifex aeolicus (LeuT, PDB ID: 2A65) featuring a “closed” protein conformation provides a solid base for interpretation of various binding modes and biological binding data.…”

“…Because of the lower biological activities of the 2‐benzylphenyl‐residue‐carrying compounds 11 and 12 as compared with the analogous 2‐biphenyl derivatives 17 a and 18 a , only derivatives of the latter were studied next. Because of the results obtained in a study of the structure–activity relationship of 5 , substitution was limited to the ortho (2′) and para (4′) positions of the terminal phenyl residue. In the case of the nipecotic acid derivative 18 a having the C 5 spacer, substitution of the terminal phenyl residue had only minor effects on the already relatively low mGAT1 affinity (p K i =6.16±0.02, Table , entry 12).…”