Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with a trans-alkene spacer as potent GABA uptake inhibitors

Our study presents the synthesis and structure-activity relationship (SAR) of novel N-substituted nipecotic acid derivatives closely related to DDPM-1457 [(S)-2a], a chemically stable analog of (S)-SNAP-5114 (1), in the pursuit of finding new and potent mGAT4 selective inhibitors. Iminium ion chemistry served as key step for the preparation of the desired, new N-substituted nipecotic acid derivatives containing a variety of different heterocycles attached to the nipecotic acid moiety via a trans-alkene spacer. The target compounds were characterized with regard to their potency at and subtype selectivity for the GABA transporters mGAT1-mGAT4.     

Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with an alkyne spacer as GABA uptake inhibitors

In this study, we present the synthesis and structure–activity relationships (SAR) of novel N-substituted nipecotic acid derivatives closely related to (S)-SNAP-5114 (2) in the pursuit of finding new and potent mGAT4 selective inhibitors. By the use of iminium ion chemistry, a series of new N-substituted nipecotic acid derivatives containing a variety of heterocycles, and an alkyne spacer were synthesized. Biological evaluation of the prepared compounds showed, how the inhibitory potency and subtype selectivity for the murine GABA transporters (mGATs) were influenced by the performed modifications.     

Generation and screening of pseudostatic hydrazone libraries derived from 5-substituted nipecotic acid derivatives at the GABA transporter mGAT4

The γ-aminobutyric acid (GABA) transporter mGAT4 represents a promising drug target for the treatment of epilepsy and other neurological disorders; however, the lack of highly potent and selective inhibitors for mGAT4 still retards its pharmacological elucidation. Herein, the generation and screening of pseudostatic combinatorial hydrazone libraries at the murine GABA transporter mGAT4 for the search of novel GABA uptake inhibitors is described. The hydrazone libraries contained more than 1100 compounds derived from nipecotic acid derivatives substituted at the 5-position instead, as common, at the 1-position of the core structure. Two hits were found and evaluated, which display potencies in the lower micromolar range at mGAT4 and its human equivalent hGAT3. These compounds possess a lipophilic moiety derived from a biphenyl residue attached to the 5-position of the hydrophilic nipecotic acid moiety via a three-atom spacer. Thus, the novel structures with potencies close to that of the bench mark mGAT4 inhibitor (S)-SNAP-5114 add new insights into the structure–activity relationship of mGAT4 inhibitors and could provide a promising starting point for the development of new mGAT4 inhibitors with even higher potencies.     

Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with a cis-alkene spacer as GABA uptake inhibitors

To discover new, potent, and selective inhibitors for the murine gamma-aminobutyric acid transporter 4 (mGAT4), the structure-activity relationship (SAR) study of a new cis-alkene analog family based on DDPM-1457 [(S)-2], which previously showed promising inhibitory potency at and subtype selectivity for mGAT4, was conducted. To uncover the importance of the differences between the trans- and the cis-alkene moiety in the spacer, the present publication describes the synthesis of the new compounds via catalytic hydrogenation with Lindlar’s catalyst. The biological results collected by the SAR study revealed that analog rac-7j characterized by a four-instead of a three-carbon atom spacer with a cis double bond applying to the majority of the studied compounds displays a surprisingly high potency at mGAT1 (pIC₅₀?=?6.00?±?0.04) and at the same time a reasonable potency at mGAT4 (pIC₅₀?=?4.82).     

Screening oxime libraries by means of mass spectrometry (MS) binding assays: Identification of new highly potent inhibitors to optimized inhibitors γ-aminobutyric acid transporter 1

Generation and screening of oxime libraries by competitive MS Binding Assays represents a powerful tool for the identification of new compounds, with affinity to mGAT1, the most abundant plasma membrane bound GABA transporter in the CNS. By screening a guvacine derived oxime library, new potent inhibitors of mGAT1 had been revealed. In the present study, oxime libraries generated by reaction of a large excess of a rac-nipecotic acid derivative displaying a hydroxylamine functionality in which various aldehydes under suitable conditions, were examined for new potent inhibitors of mGAT1. The pK_i values obtained of the best hits were compared with those of related compounds displaying a guvacine instead of a nipecotic acid subunit as hydrophilic moiety. Amongst the new compounds one of the most affine ligands of mGAT1 known so far (pK_i?=?8.55?±?0.04) was found.     

Synthesis and evaluation of 6-pyrazoylamido-3N-substituted azabicyclo[3,1,0]hexane derivatives as T-type calcium channel inhibitors for treatment of neuropathic pain

A new series of aryls, including benzo[d]imidazole/isoxazole/pyrazole, conjugated to 3N-substituted-azabicyclo[3.1.0]hexane derivatives were designed and synthesized as inhibitors of T-type calcium channels. Among the synthesized compounds, 3N-R-substituted azabicyclo[3.1.0]hexane carboxamide derivatives containing 5-isobutyl-1-phenyl-pyrazole ring exhibited potent and selective T-channel inhibition and good metabolic stability without CYP450 inhibition. Compounds 10d and 10e contained hydrophobic substituents at the 3N-position and exhibited potent in vitro efficacy, as well as neuropathic pain alleviation in rats.     

Identifying structural features on 1,1-diphenyl-hexahydro-oxazolo[3,4-a]pyrazin-3-ones critical for Neuropeptide S antagonist activity

A series of 7-substituted 1,1-diphenyl-hexahydro-oxazolo[3,4-a]pyrazin-3-ones were synthesized and tested for Neuropeptide S (NPS) antagonist activity. A concise synthetic route was developed, which features a DMAP catalyzed carbamate formation. 4-Fluorobenzyl urea (1c) and benzyl urea (1d) were identified as the most potent antagonists among the compounds examined. Structure-activity relationships (SARs) demonstrate that a 7-position urea functionality is required for potent antagonist activity and alkylation of the urea nitrogen (1e) or replacement with carbon or oxygen (5a) results in reduced potency. In addition, compounds with alpha-methyl substitution (1b) or elongated alkyl chains (1h and 1j) had reduced potency, indicating a limited tolerance for 7-position substituents.     

Synthesis and antiproliferative activity of pyrrolo[3,2-b]pyridine derivatives against melanoma

Synthesis of a new series of diarylureas and amides having pyrrolo[3,2-b]pyridine scaffold is described. Their in vitro antiproliferative activity against human melanoma cell line A375 and HS 27 human fibroblast cell line was tested and the effect of substituents on the pyrrolo[3,2-b]pyridine was investigated. The newly synthesized compounds, except meta-substituted derivatives (Ij–k and Iv–w), generally showed superior or similar activity against A375 to Sorafenib. Among all of these derivatives, compounds Ir and It having 5-benzylamide substituted 4′-amide moieties showed the most potent antiproliferative activity against A375.     

Discovery of 3,6-diaryl-1H-pyrazolo[3,4-b]pyridines as potent anaplastic lymphoma kinase (ALK) inhibitors

A new series of 3,6-diaryl-1H-pyrazolo[3,4-b]pyridine compounds have been discovered as potent anaplastic lymphoma kinase (ALK) inhibitors. The 4-hydroxyphenyl in the 6-position of 1H-pyrazolo[3,4-b]pyridine were crucial and a fluorine atom substitution could give promising inhibitory activity. The IC₅₀ of compound 9v against ALK was up to 1.58?nM and a binding mechanism was proposed.     

Synthesis and biological activity of 1,4-dihydrobenzothiopyrano[4,3-c]pyrazole derivatives,novel pro-apoptotic mitochondrial targeted agents

This study reports the synthesis of a number of 1- and 2-phenyl derivatives of the 1,4-dihydrobenzothiopyrano[4,3-c]pyrazole nucleus, which were obtained by the reaction of the versatile 7-substituted 2,3-dihydro-3-hydroxymethylene-4H-1-benzothiopyran-4-ones with hydrazine and substituted phenylhydrazines. The antiproliferative activity of the synthesized compounds was evaluated by an in vitro assay on human tumor cell lines (HL-60 and HeLa) and showed a significant capacity of the 7-methoxy-substituted benzothiopyrano[4,3-c]pyrazoles 3b–d, carrying the pendant phenyl group in the 1-position, to inhibit cell growth. Investigation of the mechanism of action indicated the induction of the mitochondrial permeability transition (MPT) as the molecular event responsible for the inhibition of cell growth. This phenomenon is related to the ability of the test compounds to cause a rapid Ca²⁺-dependent and cyclosporin A-sensitive collapse of the transmembrane potential (ΔΨ) and matrix swelling. All this leads to the release of caspase activators, such as cytochrome c (cyt c) and apoptosis-inducing factor (AIF), which trigger the pro-apoptotic pathway leading to DNA fragmentation.     

New ventures in the chemistry of avermectins

An overview is given on recent work towards new avermectin derivatives of extremely high insecticidal and acaricidal activity. These compounds were prepared from commercially available abamectin (avermectin B1) 1. For the synthesis, many novel entries have been opened up, making use of modern synthetic methods and applying them, for the first time, to the chemistry of avermectins. Several types of avermectin derivatives can be regarded as key innovations in the field. These are, in particular, 4″-deoxy-4″-(S)-amino avermectins 3, 4′-O-alkoxyalkyl avermectin monosaccharides 5, 4″-deoxy-4″-C-substituted 4″-amino avermectins 6 and 2″-substituted avermectins 7. 4″-Deoxy-4″-(S)-amino avermectins 3 were obtained by the consecutive application of the Staudinger and Aza-Wittig reaction. 4′-O-Alkoxyalkyl avermectin monosaccharides 5 were prepared by alkoxyalkylation of 5-O-protected avermectin monosaccharide. For the synthesis of 4″-deoxy-4″-C-substituted 4″-amino avermectins 6, several methods were used to construct the fully substituted 4″-carbon centre, such as a modified Strecker synthesis, the addition of organometallics to a 4″-sulfinimine and a modified Ugi approach. In order to prepare 2″-substituted avermectins 7, 5-O-protected avermectin monosaccharide was coupled with carbohydrate building blocks. An alternative synthesis involved the hitherto unknown enol ether chemistry of 4″-oxo-avermectin and the conjugate addition of a cuprate to an avermectin 2″,3″-en-4″-one. In addition, a number of other highly potent derivatives were synthesised. Examples are 4″-O-amino avermectins 8, as well as products arising from intramolecular rhodium catalysed amidations and carbene insertions. A radical cyclisation led to an intriguing rearrangement of the avermectin skeleton. Many of the new avermectins surpassed the activity of abamectin 1 against insects and mites.     

Synthesis and structure–activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: Part 3

In an effort to develop potent and selective inhibitors toward ACAT2, structure–activity relationship studies were carried out using derivatives based on pyripyropene A (PPPA, 1). In particular, we investigated the possibility of introducing appropriate 1,11-O-benzylidene and 7-O-substituted benzoyl moieties into PPPA (1). The new o-substituted benzylidene derivatives showed higher selectivity for ACAT2 than PPPA (1). Among them, 1,11-O-o-methylbenzylidene-7-O-p-cyanobenzoyl PPPA derivative 7q and 1,11-O-o,o-dimethylbenzylidene-7-O-p-cyanobenzoyl PPPA derivative 7z proved to be potent ACAT2 inhibitors with unprecedented high isozyme selectivity.     

Synthesis of new antimicrobial pyrrolo[2,1-a]isoquinolin-3-ones

The attractive structure of the pyrroloisoquinoline moiety, together with its potential antimicrobial activity, encouraged us to prepare six 8-substituted and seven 8,9-disubstituted-1,2,3,5,6,10b-hexahydropyrrolo[2,1-a]isoquinolin-3-ones in a few steps with good yields. We applied a convenient methodology via double intramolecular cyclization conducted by a Bischler-Napieralski cyclodehydration-imine reduction sequence, which is widely employed in the synthesis of isoquinoline alkaloids. Therefore, we synthesized three series of these pyrrolo[2,1-a]isoquinolin-3-ones characterized by the substituent at the 8-position or 8,9-positions of the aromatic ring: (a) different side chains are attached to an 8-OH group (series 1); (b) a chlorine atom is attached to the 8-position (series 2); and (c) 8- and 9-carbons are bearing an identical group (series 3). The compounds bearing a benzylic moiety at the 8-position, for example, 8-benzyloxy-pyrrolo[2,1-a]isoquinolin-3-one (1a) and 8-(4-fluorobenzyloxy)-pyrrolo[2,1-a]isoquinolin-3-one (1e), as well as, a 8-chloro-9-methoxy moiety including the 8-chloro-9-methoxy-pyrrolo[2,1-a]isoquinolin-3-one (2a), provided the most fungicide and bactericide agents, respectively.     

Identification of pyrrolo[2,3-g]indazoles as new Pim kinase inhibitors

The synthesis and Pim kinase inhibition potency of a new series of pyrrolo[2,3-g]indazole derivatives is described. The results obtained in this preliminary structure–activity relationship study pointed out that sub-micromolar Pim-1 and Pim-3 inhibitory potencies could be obtained in this series, more particularly for compounds 10 and 20, showing that pyrrolo[2,3-g]indazole scaffold could be used for the development of new potent Pim kinase inhibitors. Molecular modeling experiments were also performed to study the binding mode of these compounds in Pim-3 ATP-binding pocket.     

Evaluation of benzoic acid derivatives as sirtuin inhibitors

Employing a genetically modified yeast strain as a screening tool, 4-dimethylaminobenzoic acid (5) was isolated from the marine sediment-derived Streptomyces sp. CP27-53 as a weak yeast sirtuin (Sir2p) inhibitor. Using this compound as a scaffold, a series of disubstituted benzene derivatives were evaluated to elucidate the structure activity relationships for Sir2p inhibition. The results suggested that 4-alkyl or 4-alkylaminobenzoic acid is the key structure motif for Sir2p inhibitory activity. The most potent Sir2p inhibitor, 4-tert-butylbenzoic acid (20), among the tested compounds in this study turned out to be a weak but selective SIRT1 inhibitor. The calculated binding free energies between the selected compounds and the catalytic domain of SIRT1 were well correlated to their measured SIRT1 inhibitory activities.     

Nature-inspired pyrrolo[2,3-d]pyrimidines targeting the histamine H3 receptor

Inspired by marine compounds the derivatization of the natural pyrrolo[2,3-d]pyrimidine lead scaffold led to a series of novel compounds targeting the histamine H₃ receptor. The focus was set on improved binding towards the receptor and to establish an initial structure-activity relationship for this compound class based on the lead structure (compound V, K_i value of 126 nM). As highest binding affinities were found with 1,4-bipiperidines as basic part of the ligands, further optimization was focused on 4-([1,4′-bipiperidin]-1′-yl)-pyrrolo[2,3-d]pyrimidines. Related pyrrolo[2,3-d]pyrimidines that were isolated from marine sponges like 4-amino-5-bromopyrrolo[2,3-d]pyrimidine (compound III), showed variations in halogenation pattern, though in a next step the impact of halogenation at 2-position was evaluated. The chloro variations did not improve the affinity compared to the dehalogenated compounds. However, the simultaneous introduction of lipophilic cores with electron-withdrawing substitution patterns in 7-position and dehalogenation at 2-position (11b, 12b) resulted in compounds with significantly higher binding affinities (K_i values of 7 nM and 6 nM, respectively) than the initial lead structure compound V. The presented structures allow for a reasonable structure-activity relationship of pyrrolo[2,3-d]pyrimidines as histamine H₃ receptor ligands and yielded novel lead structures within the natural compound library against this target.     

Synthesis and structure–activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: Part 1

In an effort to develop potent and selective inhibitors toward ACAT2, structure–activity relationship studies were carried out using derivatives based on pyripyropene A (PPPA, 1). We have successfully developed novel PPPA derivatives with a 7-O-substituted benzoyl substituent that significantly exhibit more potent ACAT2 inhibitory activity and higher ACAT2 isozyme selectivity than 1.     

]Hexitol derivatives containing a 1,4-oxathiane ring

The synthesis of 2,5-anhydro-3-O-methylsulfonyl-6-thio-1,4-thioanhydro-D-galactitol (4; type A structure) and 2,5-anhydro-3,4-di-O-methylsulfonyl-1,6-thioanhydro-D-glucitol (10, type B structure), starting from 2,5-anhydro-1,6-dibromo-1,6-dideoxy-3,4-di-O-methylsulfonyl-D-glucitol (1) is described. The 4-O-methyl-sulfonyl group of 10 can be displaced by nucleophiles with retention of configuration. In this reaction, a cyclic sulfonium intermediate 21 is involved, which, depending on the nucleophilicity of the anion, leads to different ratios of type A and B compounds. Introduction of a three-membered ring into the 3,4-position of type B compounds yielded tricyclic derivatives of allitol.     

Synthesis of 2-substituted 17β-hydroxy/17-methylene estratrienes and their in vitro cytotoxicity in human cancer cell cultures

Synthesis of various types of 2-(alkylaminomethyl) and 2-(aroyl) 17β-estradiol analogs are reported. The synthesis of similar types of 2-substituted 17-methylene estratriene analogs was also achieved. Synthesis of chalcone derivatives of 17β-estradiol and 17-methylene estratriene were also realized. All these 2-substituted estratrienes were tested for their antiproliferative activity by using four different cell lines from colon, lung, glioma and breast cancers. Among the various 2-substituted estratrienes, the compounds 10d, 14a-h and 17e were found to have in vitro antiproliferative activity comparable to that of parent analogs 1-4. Comparison of the SAR pattern of these 2-susbtituted estratriene derivatives confirmed that relatively, 17-methylene estratrienes are more active than that of 17β-estradiol analogs.     

Design and synthesis of novel pyrimido[4,5-b]azepine derivatives as HER2/EGFR dual inhibitors

A novel 7,6 fused bicyclic scaffold, pyrimido[4,5-b]azepine was designed to fit into the ATP binding site of the HER2/EGFR proteins. The synthesis of this scaffold was accomplished by an intramolecular Claisen-type condensation. As the results of optimization lead us to 4-anilino and 6-functional groups, we discovered 6-substituted amide derivative 19b, which has a 1-benzothiophen-4-yloxy group attached to the 4-anilino group. An X-ray co-crystal structure of 19b with EGFR demonstrated that the N-1 and N-3 nitrogens of the pyrimido[4,5-b]azepine scaffold make hydrogen-bonding interactions with the main chain NH of Met793 and the side chain of Thr854 via a water-mediated hydrogen bond network, respectively. In addition, the NH proton at the 9-position makes an additional hydrogen bond with the carbonyl group of Met793, as we expected. Compound 19b revealed potent HER2/EGFR kinase (IC₅₀: 24/36 nM) and BT474 cell growth (GI₅₀: 18 nM) inhibitory activities based on its pseudo-irreversible (PI) profile.