Corrected solid-state 13 C nuclear magnetic resonance peak assignment and side-group quantification of hydroxypropyl methylcellulose acetyl succinate pharmaceutical excipients.

Hydroxypropyl methylcellulose acetyl succinate (HPMCAS) is widely used as a pharmaceutical excipient, making a detailed understanding of its tunable structure important for formulation design. Several recently reported peak assignments in the solid-state 13 C NMR spectrum of HPMCAS have been corrected here using peak integrals in quantitative spectra, spectral editing, empirical chemical-shift predictions based on solution NMR, and full spectrum simulation analogous to deconvolution. Unlike in cellulose, the strong peak at 84 ppm must be assigned to C2 and C3 methyl ethers, instead of regular C4 of cellulose. The proposed assignment of signals at <65 ppm to OCH sites, including C5 of cellulose, could not be confirmed. CH2 spectral editing showed two resolved OCH2 bands, a more intense one from O-CH2 ethers of C6 at >69 ppm and a smaller one from its esters and possibly residual CH2 -OH groups, near 63 ppm. The strong intensities of resolved signals of acetyl, succinoyl, and oxypropyl substituents indicated the substitution of >85% of the OH groups in HPMCAS. The side-group concentrations in three different grades of HPMCAS were quantified.

Ortho-Alkoxy-benzamide Directed Formation of a Single Crystalline Hydrogen-bonded Crosslinked Organic Framework and Its Boron Trifluoride Uptake and Catalysis.

Boron trifluoride (BF3 ) is a highly corrosive gas widely used in industry. Confining BF3 in porous materials ensures safe and convenient handling and prevents its degradation. Hence, it is highly desired to develop porous materials with high adsorption capacity, high stability, and resistance to BF3 corrosion. Herein, we designed and synthesized a Lewis basic single-crystalline hydrogen-bond crosslinked organic framework (HC OF-50) for BF3 storage and its application in catalysis. Specifically, we introduced self-complementary ortho-alkoxy-benzamide hydrogen-bonding moieties to direct the formation of highly organized hydrogen-bonded networks, which were subsequently photo-crosslinked to generate HC OFs. The HC OF-50 features Lewis basic thioether linkages and electron-rich pore surfaces for BF3 uptake. As a result, HC OF-50 shows a record-high 14.2 mmol/g BF3 uptake capacity. The BF3 uptake in HC OF-50 is reversible, leading to the slow release of BF3 . We leveraged this property to reduce the undesirable chain transfer and termination in the cationic polymerization of vinyl ethers. Polymers with higher molecular weights and lower polydispersity were generated compared to those synthesized using BF3 ⋅ Et2 O. The elucidation of the structure-property relationship, as provided by the single-crystal X-ray structures, combined with the high BF3 uptake capacity and controlled sorption, highlights the molecular understanding of framework-guest interactions in addressing contemporary challenges.

Perfect and Defective 13C-Furan-Derived Nanothreads from Modest-Pressure Synthesis Analyzed by 13C NMR.

The molecular structure of nanothreads produced by the slow compression of 13C4-furan was studied by advanced solid-state NMR. Spectral editing showed that >95% of carbon atoms were bonded to one hydrogen (C-H) and that there were 2-4% CH2, 0.6% C═O, and <0.3% CH3 groups. Alkenes accounted for 18% of the CH moieties, while trapped, unreacted furan made up 7%. Two-dimensional (2D) 13C-13C and 1H-13C NMR identified 12% of all carbon in asymmetric O-CH═CH-CH-CH- and 24% in symmetric O-CH-CH═CH-CH- rings. While the former represented defects or chain ends, some of the latter appeared to form repeating thread segments. Around 10% of carbon atoms were found in highly ordered, fully saturated nanothread segments. Unusually slow 13C spin-exchange with sites outside the perfect thread segments documented a length of at least 14 bonds; the small width of the perfect-thread signals also implied a fairly long, regular structure. Carbons in the perfect threads underwent relatively slow spin-lattice relaxation, indicating slow spin exchange with other threads and smaller amplitude motions. Through partial inversion recovery, the signals of the perfect threads were observed and analyzed selectively. Previously considered syn-threads with four different C-H bond orientations were ruled out by centerband-only detection of exchange NMR, which was, on the contrary, consistent with anti-threads. The observed 13C chemical shifts were matched well by quantum-chemical calculations for anti-threads but not for more complex structures like syn/anti-threads. These observations represent the first direct determination of the atomic-level structure of fully saturated nanothreads.

Pharmacophore-based design and discovery of (-)-meptazinol carbamates as dual modulators of cholinesterase and amyloidogenesis.

Multifunctional carbamate-type acetylcholinesterase (AChE) inhibitors with anti-amyloidogenic properties like phenserine are potential therapeutic agents for Alzheimer's disease (AD). We reported here the design of new carbamates using pharmacophore model strategy to modulate both cholinesterase and amyloidogenesis. A five-feature pharmacophore model was generated based on 25 carbamate-type training set compounds. (-)-Meptazinol carbamates that superimposed well upon the model were designed and synthesized, which exhibited nanomolar AChE inhibitory potency and good anti-amyloidogenic properties in in vitro test. The phenylcarbamate 43 was highly potent (IC50 31.6 nM) and slightly selective for AChE, and showed low acute toxicity. In enzyme kinetics assay, 43 exhibited uncompetitive inhibition and reacted by pseudo-irreversible mechanism. 43 also showed amyloid-ß (Aß) lowering effects (51.9% decrease of Aß42) superior to phenserine (31% decrease of total Aß) in SH-SY5Y-APP695 cells at 50 µM. The dual actions of 43 on cholinergic and amyloidogenic pathways indicated potential uses as symptomatic and disease-modifying agents.

Structural determinants for the interactions between muscarinic toxin 7 and muscarinic acetylcholine receptors.

Muscarinic acetylcholine receptors (mAChRs) have five subtypes and play crucial roles in various physiological functions and pathophysiological processes. Poor subtype specificity of mAChR modulators has been an obstacle to discover new therapeutic agents. Muscarinic toxin 7 (MT7) is a natural peptide toxin with high selectivity for the M1 receptor. With three to five residues substituted, M3, M4, and M5 receptor mutants could bind to MT7 at nanomolar concentration as the M1 receptor. However, the structural mechanisms explaining MT7-mAChRs binding are still largely unknown. In this study, we constructed 10 complex models of MT7 and each mAChR subtype or its mutant, performed molecular dynamics simulations, and calculated the binding energies to investigate the mechanisms. Our results suggested that the structural determinants for the interactions on mAChRs were composed of some critical residues located separately in the extracellular loops of mAChRs, such as Glu4.56, Leu4.60, Glu/Gln4.63, Tyr4.65, Glu/Asp6.67, and Trp7.35. The subtype specificity of MT7 was attributed to the non-conserved residues at positions 4.56 and 6.67. These structural mechanisms could facilitate the discovery of novel mAChR modulators with high subtype specificity and enhance the understanding of the interactions between ligands and G-protein-coupled receptors.

Determination of Meserine, a new candidate for Alzheimer's disease in mice brain by liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic and tissue distribution study.

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Meserine ((-)-meptazinol phenylcarbamate), a novel potent inhibitor of acetylcholinesterase (AChE), was developed, validated, and applied to a pharmacokinetic study in mice brain. The lower limit of quantification (LLOQ) was 1 ng mL(-1) and the linear range was 1-1,000 ng mL(-1). The analyte was eluted on a Zorbax SB-Aq column (2.1 × 100 mm, 3.5 µm) with the mobile phase composed of methanol and water (70:30, v/v, aqueous phase contained 10 mM ammonium formate and 0.3% formic acid) using isocratic elution, and monitored by positive electrospray ionization in multiple reaction monitoring (MRM) mode. The flow rate was 0.25 mL min(-1). The injection volume was 5 µL and total run time was 4 min. The relative standard deviation (RSD) of intraday and interday variation was 2.49-7.81 and 3.01-7.67%, respectively. All analytes were stable after 4 h at room temperature and 6 h in autosampler. The extraction recoveries of Meserine in brain homogenate were over 90%. The main brain pharmacokinetic parameters obtained after intranasal administration were T max = 0.05 h, C max = 462.0 ± 39.7 ng g(-1), T 1/2 = 0.4 h, and AUC(0-∞) = 283.1 ± 9.1 ng h g(-1). Moreover, Meserine was distributed rapidly and widely into brain, heart, liver, spleen, lung, and kidney tissue. The method is validated and could be applied to the pharmacokinetic and tissue distribution study of Meserine in mice.

Vinyl and methyl-ester groups in the insoluble polymer drug patiromer identified and quantified by solid-state NMR.

Patiromer (Veltassa®) is a crosslinked, insoluble co-polymer drug used as a nonabsorbent potassium binder, approved for treatment of hyperkalemia. Quantitative solid-state 13C nuclear magnetic resonance (NMR) analysis with comprehensive peak assignment, component quantification, and calculation of mole and weight fractions of monomer units was performed on three doses of patiromer. The workflow is documented in detail. Spectrally edited solid-state 13C NMR spectra of patiromer show =CHn peaks of matching intensity at 116 and 141 ppm, characteristic of -CH=CH2 vinyl groups. Similar spectral features can be observed in earlier studies but were previously ignored. In this study, the vinyl signals are well-resolved in a 2-s direct polarization (DP) spectrum without and with dipolar dephasing, which confirms that these sp2-hybridized carbons are bonded to hydrogen and partially mobile, consistent with vinyl side groups from incompletely reacted divinyl crosslinkers. The vinyl groups account for 1.6% of all carbon, 3% of the monomer units, and nearly 1/3 of the crosslinkers. Furthermore, an unexpected OCH3 moiety accounting for ∼1.2% of all carbons was identified by spectral editing; its chemical shift of 54 ppm is more consistent with a methyl ester than with a methyl ether. It can originate from incomplete hydrolysis of ∼6% of methyl-2-fluoroacrylate, the main monomer of patiromer. Characteristic cross peaks in two-dimensional 1H-13C heteronuclear correlation NMR confirm the presence of the vinyl and OCH3 groups. Trace amounts of xanthan gum are also detected. The quantitative 13C NMR spectrum of patiromer has been matched in a simulation using a model with five monomer units.

N-stearoyltyrosine dipotassium ameliorates high-fat diet-induced obesity in C57BL/6 mice.

N-stearoyltyrosine dipotassium (NST-2K) as a neuroprotective candidate is currently in preclinical studies in China. This study investigated the anti-obese effect of NST-2K in high-fat diet-induced obese (DIO) mice. The DIO mice were induced from male C57BL/6 mice by feeding high-fat diet for 11-weeks and treated orally with NST-2K for other 4 weeks. The treatments of DIO mice with NST-2K at 60 or 100 mg/kg/day suppressed the body weight gain, decreased both visceral fat weight and adipocyte size without influence on food intake. To evaluate the effect of NST-2K on lipid metabolism, lipid parameters and several key molecules in the plasma, liver, duodenum mucosa and adipose tissue were analyzed. NST-2K ameliorated the low-grade inflammation in liver, inhibited pancreatic lipase activity in duodenum mucosa, activated ß-oxidation system and reduced lipogenesis, thus suppressed lipid accumulation in the liver, reduced adipocyte size and improved lipid and carbohydrate metabolism. Overall, without influence on food intake, NST-2K ameliorated high-fat diet-induced obesity via suppressing liver inflammation, inhibiting dietary fat absorption, promoting lipolysis and reducing lipogenesis.

The expression of insulin-like growth factor-I mRNA and polypeptide in rat osteoblasts with exposure to parathyroid hormone.

OBJECTIVE: To investigate the insulin-like growth factor-I (IGF-I) gene and polypeptide expression in cultured rat osteoblast (ROB) and the role of IGF-I in mediating the cell-to-cell communication by mimicking the pharmacokinetics of parathyroid hormone (PTH). METHODS: The ROB was cultured with three kinds of treatment: (1) Control (Ctr), the cells were cultured without PTH during the first 6 hours and the subsequent 42 hours in a 48-hour cycle; (2) Intermittent exposure to PTH (Itm), the cells were cultured with PTH during the first 6 hours, but without PTH in the subsequent 42 hours; and (3) Continuous exposure to PTH (Ctu), the cells were cultured with PTH during the first 6 hours and the subsequent 42 hours. RESULTS: The bone-forming activities of ROB were increased in Itm and inhibited in Ctu. The IGF-I mRNA content in Itm cells was elevated only during the first 6 hours and that in Ctu cells was elevated at any time during an incubation cycle. The free IGF-I concentration in the medium of Itm cells was generally higher and that of the Ctu cells was generally lower compared with those of the Ctr cells. The IGF-I antibody significantly reduced the alkaline phosphatase activity within the cells of Ctr and Itm. CONCLUSIONS: PTH rapidly and constantly stimulates the IGF-I gene transcription of osteoblast. There was an obvious discrepancy between the IGF-I mRNA content within the osteoblast and the free IGF-I level around the osteoblast in either mode of PTH action. The IGF-I might be important for osteoblast-osteoblast communication and bone-forming activity, not only in intermittent PTH administration, but also in the physiological functioning of osteoblasts.