In-Cell Quantification of Drugs by Magic-Angle Spinning Dynamic Nuclear Polarization NMR.

The determination of intracellular drug concentrations can provide a better understanding of the drug function and efficacy. Ideally, this should be performed nondestructively, with no modification of either the drug or the target, and with the capability to detect low amounts of the molecule of interest, in many cases in the µM to nM range (pmol to fmol per million cells). Unfortunately, it is currently challenging to have an experimental technique that provides direct quantitative measurements of intracellular drug concentrations that simultaneously satisfies these requirements. Here, we show that magic-angle spinning dynamic nuclear polarization (MAS DNP) can be used to fulfill these requirements. We apply a quantitative 15N MAS DNP approach in combination with 15N labeling to quantify the intracellular amount of the drug [15N]CHIR-98014, an activator of the Wingless and Int-1 signaling pathway, determining intracellular drug amounts in the range of tens to hundreds of picomoles per million cells. This is, to our knowledge, the first time that MAS DNP has been used to successfully estimate intracellular drug amounts.

Synthesis, 3 H-labelling and in vitro evaluation of a substituted dipiperidine alcohol as a potential ligand for chemokine receptor 2.

The immune system is implicated in the pathology of neurodegenerative disorders. The C-C chemokine receptor 2 (CCR2) is one of the key targets involved in the activation of the immune system. A suitable ligand for CCR2 could be a useful tool to study immune activation in central nervous system (CNS) disorders. Herein, we describe the synthesis, tritium radiolabelling, and preliminary in vitro evaluation in post-mortem human brain tissue of a known potent small molecule antagonist for CCR2. The preparation of a tritium-labelled analogue for the autoradiography (ARG) study gave rise to an intriguing and unexpected side reaction profile through a novel amination of ethanol and methanol in the presence of tritium. After successful preparation of the tritiated radioligand, in vitro ARG measurements on human brain sections revealed nonspecific binding properties of the selected antagonist in the CNS.

Late-occurring and Long-circulating Metabolites of GABAAα2,3 Receptor Modulator AZD7325 Involving Metabolic Cyclization and Aromatization: Relevance to MIST Analysis and Application for Patient Compliance.

AZD7325 [4-amino-8-(2-fluoro-6-methoxyphenyl)-N-propylcinnoline-3-carboxamide] is a selective GABAAα2,3 receptor modulator intended for the treatment of anxiety disorders through oral administration. An interesting metabolic cyclization and aromatization pathway led to the tricyclic core of M9, i.e., 2-ethyl-7-(2-fluoro-6-methoxyphenyl)pyrimido[5,4-c]cinnolin-4(3H)-one. Further oxidative metabolism generated M10 via O-demethylation and M42 via hydroxylation. An authentic standard of M9 was synthesized to confirm the novel structure of M9 and that of M10 and M42 by liver microsomal incubation of the M9 standard. Metabolites M9, M10, and M42 were either minor or absent in plasma samples after a single dose; however, all became major metabolites in human and preclinical animal plasma after repeated doses and circulated in humans longer than 48 hours after the end of seven repeated doses. The absence of these long circulating metabolites from selected patients' plasma samples was used to demonstrate patient noncompliance as the cause of unexpected lack of drug exposure in some patients during a Phase IIb outpatient clinical study. The observation of late-occurring and long-circulating metabolites demonstrates the need to collect plasma samples at steady state after repeated doses when conducting metabolite analysis for the safety testing of drug metabolites. All 12 major nonconjugate metabolites of AZD7325 observed in human plasma at steady state were also observed in dog, rat, and mouse plasma samples collected from 3-month safety studies and at higher exposures in the animals than humans. This eliminated concern about human specific or disproportional metabolites.

Synthesis of C-14 labeled GABAA α2/α3 selective partial agonists and the investigation of late-occurring and long-circulating metabolites of GABAA receptor modulator AZD7325.

Anxiolytic activity has been associated with GABAA α2 and α3 subunits. Several target compounds were identified and required in C-14 labeled form to enable a better understanding of their drug metabolism and pharmacokinetic properties. AZD7325 is a selective GABAA α2 and α3 receptor modulator intended for the treatment of anxiety through oral administration. A great number of AZD7325 metabolites were observed across species in vivo, whose identification was aided by [14 C]AZD7325. An interesting metabolic cyclization and aromatization pathway leading to the tricyclic core of M9 and the oxidative pathways to M10 and M42 are presented.

New trends and applications in carboxylation for isotope chemistry.

Carboxylations are an important method for the incorporation of isotopically labeled 14 CO2 into molecules. This manuscript will review labeled carboxylations since 2010 and will present a perspective on the potential of recent unlabeled methodology for labeled carboxylations. The perspective portion of the manuscript is broken into 3 major sections based on product type, arylcarboxylic acids, benzylcarboxylic acids, and alkyl carboxylic acids, and each of those sections is further subdivided by substrate.

Cucurbit[7]uril as a Supramolecular Artificial Enzyme for Diels-Alder Reactions.

The ability to mimic the activity of natural enzymes using supramolecular constructs (artificial enzymes) is a vibrant scientific research field. Herein, we demonstrate that cucurbit[7]uril (CB[7]) can catalyse Diels-Alder reactions for a number of substituted and unreactive N-allyl-2-furfurylamines under biomimetic conditions, without the need for protecting groups, yielding powerful synthons in previously unreported mild conditions. CB[7] rearranges the substrate in a highly reactive conformation and shields it from the aqueous environment, thereby mimicking the mode of action of a natural Diels-Alderase. These findings can be directly applied to the phenomenon of product inhibition observed in natural Diels-Alderase enzymes, and pave the way toward the development of novel, supramolecular-based green catalysts.

Design, Synthesis, and Evaluation of Inhibitors of Hedgehog Acyltransferase.

Hedgehog signaling is involved in embryonic development and cancer growth. Functional activity of secreted Hedgehog signaling proteins is dependent on N-terminal palmitoylation, making the palmitoyl transferase Hedgehog acyltransferase (HHAT), a potential drug target and a series of 4,5,6,7-tetrahydrothieno[3,2-c]pyridines have been identified as HHAT inhibitors. Based on structural data, we designed and synthesized 37 new analogues which we profiled alongside 13 previously reported analogues in enzymatic and cellular assays. Our results show that a central amide linkage, a secondary amine, and (R)-configuration at the 4-position of the core are three key factors for inhibitory potency. Several potent analogues with low- or sub-µM IC50 against purified HHAT also inhibit Sonic Hedgehog (SHH) palmitoylation in cells and suppress the SHH signaling pathway. This work identifies IMP-1575 as the most potent cell-active chemical probe for HHAT function, alongside an inactive control enantiomer, providing tool compounds for validation of HHAT as a target in cellular assays.