Piperidine Core Research Articles

Ionizable Lipid Nanoparticles for mRNA Delivery

Therapeutics based on messenger RNA (mRNA) have become a promising class of methods for various diseases’ treatments in recent years. The safe and effective delivery of mRNA into target cells is the premise of the clinical translation of mRNA. Due to the protonation of ionizable lipids in acidic conditions, the ionizable lipid nanoparticles (iLNPs) have lower toxicity and higher endosomal escape efficiency than permanent cationic lipid nanoparticles (cLNPs). They not only exhibit excellent delivery ability in commercial COVID‐19 mRNA vaccines but also are highly potential carriers for delivering mRNA drugs. This review summarizes the composition, preparation, stability of mRNA iLNPs, and the recent progress in the mRNA delivery by iLNPs. According to the structure characteristics of ionizable heads, the ionizable lipids are classified into tertiary amine, quaternary amine, imidazole core, piperidine core, piperazine core, and diketopiperazine core‐based head lipids. Their design, optimization, and applications on mRNA delivery are discussed. The current status of representative clinical trials based on mRNA iLNPs delivery is also analyzed. The challenges and prospects of mRNA iLNPs delivery in clinical applications are proposed at the end.

Dual Piperidine-Based Histamine H3 and Sigma-1 Receptor Ligands in the Treatment of Nociceptive and Neuropathic Pain.

In search of new dual-acting histamine H3/sigma-1 receptor ligands, we designed a series of compounds structurally based on highly active in vivo ligands previously studied and described by our team. However, we kept in mind that within the previous series, a pair of closely related compounds, KSK67 and KSK68, differing only in the piperazine/piperidine moiety in the structural core showed a significantly different affinity at sigma-1 receptors (σ1Rs). Therefore, we first focused on an in-depth analysis of the protonation states of piperazine and piperidine derivatives in the studied compounds. In a series of 16 new ligands, mainly based on the piperidine core, we selected three lead structures (3, 7, and 12) for further biological evaluation. Compound 12 showed a broad spectrum of analgesic activity in both nociceptive and neuropathic pain models based on the novel molecular mechanism.

Discovery and In Vivo Efficacy of Trace Amine-Associated Receptor 1 (TAAR1) Agonist 4-(2-Aminoethyl)-N-(3,5-dimethylphenyl)piperidine-1-carboxamide Hydrochloride (AP163) for the Treatment of Psychotic Disorders.

Starting from a screening hit, a set of analogs was synthesized based on a 4-(2-aminoethyl)piperidine core not associated previously with trace amine-associated receptor 1 (TAAR1) modulation in the literature. Several structure–activity relationship generalizations have been drawn from the observed data, some of which were corroborated by molecular modeling against the crystal structure of TAAR1. The four most active compounds (EC50 for TAAR1 agonistic activity ranging from 0.033 to 0.112 μM) were nominated for evaluation in vivo. The dopamine transporter knockout (DAT-KO) rat model of dopamine-dependent hyperlocomotion was used to evaluate compounds’ efficacy in vivo. Out of four compounds, only one compound (AP163) displayed a statistically significant and dose-dependent reduction in hyperlocomotion in DAT-KO rats. As such, compound AP163 represents a viable lead for further preclinical characterization as a potential novel treatment option for disorders associated with increased dopaminergic function, such as schizophrenia.

Collective total synthesis of C4-oxygenated securinine-type alkaloids via stereocontrolled diversifications on the piperidine core

Securinega alkaloids have fascinated the synthetic chemical community for over six decades. Historically, major research foci in securinega alkaloid synthesis have been on the efficient construction of the fused tetracyclic framework that bears a butenolide moiety and tertiary amine-based heterocycles. These “basic” securinega alkaloids have evolved to undergo biosynthetic oxidative diversifications, especially on the piperidine core. However, a general synthetic solution to access these high-oxidation state securinega alkaloids is lacking. In this study, we have completed the total synthesis of various C4-oxygenated securinine-type alkaloids including securingines A, C, D, securitinine, secu’amamine D, phyllanthine, and 4-epi-phyllanthine. Our synthetic strategy features stereocontrolled oxidation, rearrangement, and epimerization at N1 and C2–C4 positions of the piperidine core within (neo)securinane scaffolds. Our discoveries provide a fundamental synthetic solution to all known securinine-type natural products with various oxidative and stereochemical variations around the central piperidine ring.

Synthesis, conformational study and DFT analysis of novel nonlinear optically active 2r,6c-diaryl-3t-methylpiperidin-4-one N-(2′-furoyl)hydrazones

A series of nonlinear optical (NLO) active 2-furoic acid hydrazide derivatives, 2r,6c-diaryl-3t-methylpiperidin-4-one N-(2′-furoyl)hydrazones (6–10), were synthesized. The structures of these hydrazones were confirmed unambiguously by Fourier transform infrared spectroscopy, mass spectrometry, elemental analysis, 1H, 13C, HOMO-COSY, HSQC, and HMBC nuclear magnetic resonance spectroscopy. The piperidine core of all the targeted hydrazones (6–10) adopted the chair conformation with the equatorial orientations of all the substituents and the ‘E’ configuration about the C=N bond observed. Density functional theory using the B3LYP/6–31G(d,p) level of theory indicated that all hydrazones favor the ‘E’ isomer state. The Mulliken population, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) surfaces, and reactivity parameters were also evaluated and showed a good correlation with the experimental data. The efficiency of hydrazones (6–10) in terms of the nonlinear optical (NLO) activity was proven, and the hydrazones (6–10) showed higher NLO activity compared to that of the reference molecule, as determined by the molecular hyperpolarizability measurements. The structural, spectral, and electrochemical properties were also determined, and DFT analysis was consistent with the experimental outcomes. The FMO, MEP, and reactivity parameter analyses revealed intramolecular charge transfer and high reactive features, leading to superior NLO property of hydrazones (6–10).

Toxicological and pharmacological characterization of novel cinnamylpiperazine synthetic opioids in humans and in vitro including 2-methyl AP-237 and AP-238.

The recent scheduling actions of fentanyl-related substances in both the United States and China have sparked the emergence and proliferation of other generations of "legal" opioids that are structurally distinct from fentanyl, including the recently emerged class of cinnamylpiperazines. In contrast to fentanyl, which contains a piperidine core and a phenethyl moiety, the primary structural components of cinnamylpiperazines are the piperazine core and a cinnamyl moiety. This manuscript reports on the toxicological profile for antemortem and postmortem cases where a cinnamylpiperazine was detected. Samples were quantitatively confirmed using liquid chromatography tandem mass spectrometry. The cases were received between February 2020 and April 2021. Concentrations of 2-methyl AP-237 from four postmortem cases ranged from 820 to 5800ng/mL, and concentrations of AP-238 from two postmortem cases were 87 and 120ng/mL. µ-Opioid receptor (MOR) activation potential for 2-methyl AP-237, AP-237, para-methyl AP-237, and AP-238 were studied using a βarr2 recruitment assay. Efficacies (Emax, relative to hydromorphone) and potencies (EC50) were derived and of the compounds tested AP-238 was the most potent compound in the panel with an EC50 of 248nM. 2-Methyl AP-237 was found to be the most efficacious drug (Emax = 125%) of the tested cinnamylpiperazines; however, it had substantially less efficacy than fentanyl. The in vitro MOR activation potential of the studied cinnamylpiperazines was lower than that of fentanyl and other novel synthetic opioids (NSOs), in line with the relatively higher concentrations observed in postmortem toxicology samples-an important observational link between in vitro pharmacology and in vivo toxicology.

Experimental and theoretical evaluation of new piperidine and oxaquinuclidine core containing derivatives as an efficient corrosion inhibitor for copper in nitric acid medium

The inhibition efficiency of copper corrosion in 1 M HNO3 by five piperidine and oxaquinuclidine core containing compounds namely 2,4,6,11-tetraphenyl-9-oxa-1,5-diazatricyclo [5.3.1.03.8] undecane (OX1), 2,4,6,11-tetraaryl (4-methoxyphenyl)-9-oxa-1,5-diazatricyclo [5.3.1.03.8] undecane (OX2), 2,4,6,11-tetraaryl (4-chlorophenyl)-9-oxa-1,5-diazatricyclo [5.3.1.03.8] undecane (OX3), 2,4,6,11-tetraaryl-p-tolyl-9-oxa-1,5-diazatricyclo [5.3.1.03.8] undecane (OX4), and 2,4,6,11-tetraaryl (4-fluorophenyl)-9-oxa-1,5-diazatricyclo [5.3.1.03.8] undecane (OX5) has been investigated using gravimetric method, electrochemical studies, FT-IR, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), DFT and Monte Carlo simulation techniques. Inhibitors are chosen based on electron donating and accepting ability to the metal surface. These compounds differentiated in phenyl ring containing electron withdrawing (Cl, F) and electron releasing (OCH3, CH3) substituents. Experimental and computational studies showed that methoxy (OCH3) substituent exhibit more efficiency compared to other compounds and it is due to more electron donating nature of the OCH3 group. The adsorption of the inhibitors on copper surface obeyed Langmuir adsorption isotherm. Polarization results show that OXs are acting as a mixed type of inhibitors. In the surface characterization studies, change in frequency (FT-IR), change in surface roughness (SEM) and appearance of additional element peaks (EDX) before and after film formation confirmed the protective layer formation. Quantum chemical parameters and Monte Carlo simulation studies further evidenced by the inhibitor adsorption of the copper surface.

Calyciphylline B-type Alkaloids: Evolution of a Synthetic Strategy to (-)-Daphlongamine H.

We provide a full account of our synthetic studies targeting the hexacyclic calyciphylline B-type alkaloids, a subfamily of the Daphniphyllum natural products. Following an initial set of synthetic strategies focused on constructing the piperidine core of the calyciphylline B-type framework via a 6π-azaelectrocyclization, as well as exploiting the reactivity of underexplored oxazaborinine heterocycles, we ultimately designed a highly functionalized acyclic precursor which underwent carefully orchestrated and efficient cyclizations to forge the architecturally complex natural product scaffold. Our efforts have culminated in the development of the first total synthesis of (-)-daphlongamine H, provided access to its C5-epimer, (-)-isodaphlongamine H, and led to structural revision of deoxyisocalyciphylline B.

Copper-Catalyzed N-F Bond Activation for Uniform Intramolecular C-H Amination Yielding Pyrrolidines and Piperidines.

The dual function of the N-F bond as an effective oxidant and subsequent nitrogen source in intramolecular aliphatic C-H functionalization reactions is explored. Copper catalysis is demonstrated to exercise full regio- and chemoselectivity control, which opens new synthetic avenues to nitrogenated heterocycles with predictable ring sizes. For the first time, a uniform catalysis manifold has been identified for the construction of both pyrrolidine and piperidine cores. The individual steps of this new copper oxidation catalysis were elucidated by control experiments and computational studies, clarifying the singularity of the N-F function and characterizing the catalytic cycle to be based on a copper(I/II) manifold.

Chameleon-like behavior of indolylpiperidines in complex with cholinesterases targets: Potent butyrylcholinesterase inhibitors

Alzheimer's disease (AD) is the most common form of dementia worldwide with an increasing prevalence for the next years. The multifactorial nature of AD precludes the design of new drugs directed to a single target being probably one of the reasons for recent failures. Therefore, dual binding site acetylcholinesterase (AChE) inhibitors have been revealed as cognitive enhancers and β-amyloid modulators offering an alternative in AD therapy field. Based on the dual ligands NP61 and donepezil, the present study reports the synthesis of a series of indolylpiperidines hybrids to optimize the NP61 structure preserving the indole nucleus, but replacing the tacrine moiety of NP61 by benzyl piperidine core found in donepezil. Surprisingly, this new family of indolylpiperidines derivatives showed very potent and selective hBuChE inhibition. Further studies of NMR and molecular dynamics have showed the capacity of these hybrid molecules to change their bioactive conformation depending on the binding site, being capable to inhibit with different shapes BuChE and residually AChE.

An Asymmetric Synthesis of ((3R,6R)‐6‐Methylpiperidine‐3‐yl)methanol; A Piperidine Core Unit of Potent Dual Orexin Receptor Antagonist MK‐6096

AbstractAn asymmetric synthesis of ((3R,6R)‐6‐methylpiperidin‐3‐yl)methanol 2, a potent dual orexin receptor antagonist MK‐6096 1 piperidine core unit, is described. The synthesis utilizes commercial available (S)‐propylene oxide as a starting material and organocatalyzed asymmetric Michael addition reaction as key step.

1‐Substituted 2‐Azaspiro[3.3]heptanes: Overlooked Motifs for Drug Discovery

AbstractThe 2‐substituted piperidine core is found in drugs (18 FDA‐approved drugs), however, their spirocyclic analogues remain unknown. Described here is the synthesis of spirocyclic analogues for 2‐substituted piperidines and a demonstration of their validation in drug discovery.

1-Substituted 2-Azaspiro[3.3]heptanes: Overlooked Motifs for Drug Discovery.

The 2-substituted piperidine core is found in drugs (18 FDA-approved drugs), however, their spirocyclic analogues remain unknown. Described here is the synthesis of spirocyclic analogues for 2-substituted piperidines and a demonstration of their validation in drug discovery.

Towards the total synthesis of keramaphidin B.

The enantio- and diastereoselective Michael addition of a δ-valerolactone-derived pronucleophile to a substituted furanyl nitroolefin catalysed by a bifunctional cinchonine-derived thiourea has been used as the key stereocontrolling step in a new synthetic strategy to the heavily functionalised piperidine core of keramaphidin B.

Synthesis of ((3R,6R)-6-Methylpiperidin-3-yl)methanol via Biocatalytic Transamination and Crystallization-Induced Dynamic Resolution

An asymmetric synthesis of orexin receptor antagonist MK-6096 piperidine core, ((3R,6R)-6-methylpiperidin-3-yl)methanol (3), is described. The target is synthesized in four steps and 40% overall yield from methyl vinyl ketone and diethyl malonate. The key operation is a practical crystallization-induced dynamic resolution for the conversion of a trans/cis mixture of lactam acid 17 into the desired trans-lactam acid salt in >95% de and 91% yield. The substrate lactam acid mixture was prepared via a solvent-free Michael reaction and a practical biocatalytic transamination process.

Lead-oriented synthesis: Investigation of organolithium-mediated routes to 3-D scaffolds and 3-D shape analysis of a virtual lead-like library

Synthetic routes to six 3-D scaffolds containing piperazine, pyrrolidine and piperidine cores have been developed. The synthetic methodology focused on the use of N-Boc α-lithiation-trapping chemistry. Notably, suitably protected and/or functionalised medicinal chemistry building blocks were synthesised via concise, connective methodology. This represents a rare example of lead-oriented synthesis. A virtual library of 190 compounds was then enumerated from the six scaffolds. Of these, 92 compounds (48%) fit the lead-like criteria of: (i) −1⩽AlogP⩽3; (ii) 14⩽number of heavy atoms⩽26; (iii) total polar surface area⩾50Å2. The 3-D shapes of the 190 compounds were analysed using a triangular plot of normalised principal moments of inertia (PMI). From this, 46 compounds were identified which had lead-like properties and possessed 3-D shapes in under-represented areas of pharmaceutical space. Thus, the PMI analysis of the 190 member virtual library showed that whilst scaffolds which may appear on paper to be 3-D in shape, only 24% of the compounds actually had 3-D structures in the more interesting areas of 3-D drug space.

3,5-Disubstituted Piperidine Derivatives—A Scalable Route to All Four Stereoisomers

3,5-Disubstituted piperidines are versatile building blocks that find broad application in medicinal chemistry programs. Here we describe how all four diastereoisomers of a 5-aryl-substituted nipecotic acid derivative were prepared on preparative scale in high enantiomeric purity. The piperidine core structure was formed by catalytic hydrogenation of the corresponding pyridine derivatives. After Boc-protection, the resulting cis/trans mixture was separated by preparative normal phase chromatography into the pure cis and pure trans racemates. Subsequent preparative separation of those racemates by Simulated Moving Bed chromatography (SMB) allowed us to obtain all four enantiopure isomers in amounts between 80 and 140 g. The absolute configuration of all compounds was determined by crystallization and X-ray spectroscopy of suitable derivatives.

Core modification of substituted piperidines as Novel inhibitors of HDM2–p53 protein–protein interaction

The discovery of 3,3-disubstituted piperidine 1 as novel p53–HDM2 inhibitors prompted us to implement subsequent SAR follow up directed towards piperidine core modifications. Conformational restrictions and further functionalization of the piperidine core were investigated as a strategy to gain additional interactions with HDM2. Substitutions at positions 4, 5 and 6 of the piperidine ring were explored. Although some substitutions were tolerated, no significant improvement in potency was observed compared to 1. Incorporation of an allyl side chain at position 2 provided a drastic improvement in binding potency.

Enantioselective Synthesis and Physicochemical Properties of Libraries of 3‐Amino‐ and 3‐Amidofluoropiperidines

The enantioselective syntheses of 3-amino-5-fluoropiperidines and 3-amino-5,5-difluoropiperidines were developed using the ring enlargement of prolinols to access libraries of 3-amino- and 3-amidofluoropiperidines. The study of the physicochemical properties revealed that fluorine atom(s) decrease(s) the pKa and modulate(s) the lipophilicity of 3-aminopiperidines. The relative stereochemistry of the fluorine atoms with the amino groups at C3 on the piperidine core has a small effect on the pKa due to conformationnal modifications induced by fluorine atom(s). In the protonated forms, the C-F bond is in an axial position due to a dipole-dipole interaction between the N-H(+) and C-F bonds. Predictions of the physicochemical properties using common software appeared to be limited to determine correct values of pKa and/or differences of pKa between cis- and trans-3-amino-5-fluoropiperidines.

Synthesis of Alkaloid (−)-205B via Stereoselective Reductive Cross-Coupling and Intramolecular [3+2] Cycloaddition

An asymmetric synthesis of alkaloid (-)-205B, a tricyclic member of the architecturally diverse family of natural products isolated from the skin of neotropical poison frogs, is described that proceeds through two recently developed stereoselective synthetic methods: (1) Ti-mediated allylic alcohol-imine reductive cross-coupling and (2) intramolecular [3+2] cycloaddition of a glyoxylate-based homoallylic nitrone. The utility of this latter cycloaddition process for the assembly of the stereochemically dense piperidine core of 205B is noteworthy, as this method enables direct [3+2] cycloaddition of an intermediate homoallylic (E)-nitrone via a pathway that is stereochemically unscathed by competitive [3,3]-sigmatropic rearrangement processes. Overall, the synthesis is asymmetric, concise, and highly stereoselective-features which point to the potential future utility of these chemical methods in natural product synthesis and medicinal chemistry.