(±)-Nipecotic acid

H-DL-Nip-OH

Synthesis of 4-substituted nipecotic acid derivatives and their evaluation as potential GABA uptake inhibitors.[Pubmed:27039250]

Bioorg Med Chem. 2016 May 1;24(9):2072-96.

In this study, we disclose the design and synthesis of novel 4-susbtituted nipecotic acid derivatives as inhibitors of the GABA transporter mGAT1. Based on molecular modeling studies the compounds are assumed to adopt a binding pose similar to that of the potent mGAT1 inhibitor nipecotic acid. As substitution in 4-position should not cause an energetically unfavorable orientation of nipecotic acid as it is the case for N-substituted derivatives this is expected to lead to highly potent binders. For the synthesis of novel 4-substituted nipecotic acid derivatives a linear synthetic strategy was employed. As a key step, palladium catalyzed cross coupling reactions were used to attach the required biaryl moieties to the omega-position of the alkenyl- or alkynyl spacers of varying length in the 4-position of the nipecotic acid scaffold. The resulting amino acids were characterized with respect to their binding affinities and inhibitory potencies at mGAT1. Though the biological activities found were generally insignificant to poor, two compounds, one of which possesses a reasonable binding affinity for mGAT1, rac-57, the other a notable inhibitory potency at mGAT4, rac-84, both displaying a slight subtype selectivity for the individual transporters, could be identified.

Development of Highly Potent GAT1 Inhibitors: Synthesis of Nipecotic Acid Derivatives with N-Arylalkynyl Substituents.[Pubmed:28125164]

ChemMedChem. 2017 Mar 7;12(5):362-371.

A new scaffold of highly potent and mGAT1-selective inhibitors has been developed. Compounds in this class are characterized by an alkyne-type spacer connecting nipecotic acid with an aromatic moiety. Preliminary evaluations made it apparent that a nipecotic acid derivative with an N-butynyl linker and a terminal 2-biphenyl residue exhibiting a binding affinity (pKi ) of 7.61+/-0.03 to mGAT1 and uptake inhibition (pIC50 ) of 7.00+/-0.06 selective for mGAT1 could serve as a hit compound. Docking calculations for compounds based on this structure in an hGAT1 homology modeling study indicated binding affinities similar to or even higher than that of the well-known mGAT1 inhibitor tiagabine. Synthesis of the designed compounds was readily carried out by two consecutive cross-coupling reactions, giving flexible access to variously substituted biphenyl subunits. With an appropriate substitution pattern of the biphenyl moiety, the binding affinity of enantiopure (R)-nipecotic acid derivatives to mGAT1 increased to pKi =8.33+/-0.01, and the uptake inhibitory potency up to pIC50 =7.72+/-0.02.

CDC20siRNA and paclitaxel co-loaded nanometric liposomes of a nipecotic acid-derived cationic amphiphile inhibit xenografted neuroblastoma.[Pubmed:28045167]

Nanoscale. 2017 Jan 19;9(3):1201-1212.

Despite significant recent progress in the area of translational genomics of neuroblastoma, the overall survival rates for children with high-risk NB continue to be not more than 5 years due to tumor relapse and/or drug-resistant tumors. Herein we report on the development of a neuroblastoma targeting nanometric (130-150 nm) circulation stable liposomal system prepared from a novel nipecotic acid-derived cationic amphiphile (NACA). The size ranges of liposomes (130-150 nm) were confirmed by both dynamic light scattering and transmission electron microscopy. The findings in the gel electrophoresis assay revealed that siRNAs encapsulated within the liposomes of NACA (with 90% entrapment efficiency) are protected from attack by RNase. Cellular uptake experiments using FAM-siRNA loaded liposomes of NACA showed the liposomal entry in human neuroblastoma cells (IMR-32) to be mediated via the GABAA receptor. CDC20siRNA-loaded liposomes of NACA caused significantly higher CDC20 gene silencing efficiency in IMR-32 cells compared to CDC20 gene knockdown efficiency mediated by CDC20siRNA-loaded control non-targeting liposomes (NTL). The findings in the annexin-V binding based flow cytometric apoptosis assay and MTT-based cellular cytotoxicity assay support the notion that pronounced (80%) neuroblastoma cell death upon treatment with CDC20siRNA & PTX co-loaded liposomes of NACA presumably originates from enhanced apoptosis of cells. Importantly, intravenously administered CDC20siRNA & PTX co-loaded liposomes of NACA significantly inhibited growth of xenografted human neuroblastoma in athymic nude mice. The presently disclosed strategy of co-delivering potent anticancer siRNA and small molecule chemotherapeutics using liposomes of NACA opens a new door for combating the dreaded disease of neuroblastoma.

Determination of enantiomeric excess of nipecotic acid as 1-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl) derivatives.[Pubmed:28019695]

Chirality. 2017 Jan;29(1):48-56.

For the enantiopure synthesis of novel chiral GABA uptake inhibitors, nipecotic acid (1) is an important key precursor. To characterize accurately the pharmacological activity of these interesting target compounds, the determination of the correct enantiomeric purity of nipecotic acid as the starting material is indispensable. In this report, a sensitive high-performance liquid chromatography (HPLC) based method for the separation and quantitation of both enantiomers of nipecotic acid as 1-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl) derivatives (5) on a Chiralpak ID-3 column (Daicel, Illkirch, France) was established. UV/Vis-detection at 490 nm was chosen to ensure a selective determination of even highly enantioenriched samples. Reliability was demonstrated by validation of specificity, linearity, lower limit of quantification (LLOQ), accuracy, and precision. By spiking highly enantiopure samples with small amounts of racemic rac-5, it was proven that the established HPLC method is able to detect even slight changes in enantiomeric excess (ee) values. Thus, accurate determination of ee values up to 99.87% ee for (R)-5 and 99.86% ee for (S)-5 over a linear concentration range of 1-1500 muM for (R)-5 and of 1-1455 muM for (S)-5 could be demonstrated.

Tiagabine, SK&F 89976-A, CI-966, and NNC-711 are selective for the cloned GABA transporter GAT-1.[Pubmed:7851497]

Eur J Pharmacol. 1994 Oct 14;269(2):219-24.

gamma-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian brain. The synaptic action of GABA is terminated by rapid uptake into presynaptic terminals and surrounding glial cells. Molecular cloning has revealed the existence of four distinct GABA transporters termed GAT-1, GAT-2, GAT-3, and BGT-1. Pharmacological inhibition of transport provides a mechanism for increasing GABA-ergic transmission, which may be useful in the treatment of various neuropsychiatric disorders. Recently, a number of lipophilic GABA transport inhibitors have been designed and synthesized, which are capable of crossing the blood brain barrier, and which display anticonvulsive activity. We have now determined the potency of four of these compounds, SK&F 89976-A (N-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid), tiagabine ((R)-1-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]-3- piperidencarboxylic acid), CI-966 ([1-[2-[bis 4-(trifluoromethyl)phenyl]methoxy]ethyl]-1,2,5,6-tetrahydro-3- pyridinecarboxylic acid), and NNC-711 (1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,4,6-tetrahydro-3- pyridinecarboxylic acid hydrochloride), at each of the four cloned GABA transporters, and find them to be highly selective for GAT-1. These data suggest that the anticonvulsant activity of these compounds is mediated via inhibition of uptake by GAT-1.