Acid-labile Compounds Research Articles

Hydrolysis of Cellulose Acetate Phthalate and Hydroxypropyl Methylcellulose Phthalate in Amorphous Solid Dispersions

The preparation of amorphous solid dispersions (ASDs) represents a promising strategy for addressing the solubility limitations of poorly soluble drugs, facilitating enhanced absorption. Acidic polymers such as cellulose acetate phthalate (CAP) and hydroxypropyl methylcellulose phthalate (HPMCP) have emerged as effective carriers for ASDs. Although the hydrolytic degradation of these polymers has been documented, its impact on the stability of ASDs has not been systematically investigated. This research aimed to explore the potential hydrolysis of CAP and HPMCP and how it influences the stability of ASDs containing ketoconazole (KTZ), at drug loadings of 10 % and 50 %. Our study utilized thermal analysis, infrared spectroscopy, and evaluations of physical and chemical stability. The results revealed that although KTZ remained physically stable in all ASDs over a 60-day period under various stability conditions, the emergence of crystalline phthalic acid (PA), a byproduct of polymer hydrolysis, was observed at elevated temperatures and relative humidity levels. The acidic microenvironment fostered by the release of PA further catalyzed drug chemical degradation. This study underscores the susceptibility of CAP and HPMCP to hydrolytic degradation, highlighting the inherent risk of PA-induced drug degradation, particularly for acid-labile compounds. These insights into the understanding of polymer hydrolysis in ASDs pave the way for the development of targeted approaches to safeguard drug stability and optimize pharmaceutical formulations for enhanced bioavailability, efficacy, and safety.

Mass Spectrometric Determination of Polyfunctionalized Nucleoside Phosphoramidites Using LSI/FAB

Nucleoside phosphoramidites (PAs) are the most widely used building blocks in the contemporary solid-phase synthesis of oligonucleotides. Accurate molecular weight measurements of such acid-labile compounds may be easily determined in a matrix system comprising triethanolamine (TEOA)-NaCl by liquid secondary ionization mass spectrometry (LSIMS) or fast atom bombardment mass spectrometry (FABMS), using a double-focusing mass spectrometer. The present method rapidly and easily measures the accurate MWs of various PAs as adduct ions [M+Na]⁺, affording molecular formulas in place of elemental analysis. Further, the intensities by LSIMS of [M+Na]⁺ were found to be enhanced to the highest degree by adjustment of the mole ratio of PA and NaCl, fixing the amount of TEOA. In addition, the effects of the metal ion in the matrix were investigated. The present method is a powerful tool for the mass spectral identification of polyfunctionalized nucleoside PAs.

Acid detergent lignin, Klason, digestibility

The objective of this work was to study the effects of both Klason lignin (KL) and acid detergent lignin (ADL) on in vitro neutral detergent fibre (NDF) digestion (IVNDFd) i n an effort to assess if acid labile phenolic compounds affect the rate of degradation ( k d). Eighty five forages (lucerne, maize silages and grasses) were analyzed for NDF, ADL, KL and IVNDFd (6, 12, 24, 30, 36, 48, and 96 h fermentations were used for k d estimations). Correlations were estimated among li gnin types (KL vs . ADL), lignin and extent of IVNDFd, and lignin type and NDF kd and tested for significance. Within and among all forage types, the correlation between ADL and KL was in general positive when on NDF basis and high and positive when on DM basis (0.77 to 0.90). Within and among all forages, only ADL was consistently negatively correlated with IVNDFd at all time points (-0.54 to -0.94). Co rrelations among forages for NDF kd and lignin type were not consistent. Among all forages, KL was negativel y correlated with IVNDFd and NDF kd. The correlation between IVNDFd and ADL increased as fermentation length increased among all forages. However, the correlation of KL and IVNDFd was greatest up to 48 h of fermentation suggesting that the soluble pheno lics affected both the rate and extent of IVNDFd. Unlike ADL, KL disappeared during IVNDFd, and in most forages there was a high negative correlation assoc iated with the difference between KL and ADL ( �L) and IVNDFd, except for brown midrib hybrids maize and early cut grasses that had a different behaviour. Am ong

ChemInform Abstract: Improved Protocols for the Selective Deprotection of Trialkylsilyl Ethers Using Fluorosilicic Acid.

Improvements for the application of aqueous fluorosilicic acid to the selective cleavage of tert-butyldimethylsilyl ethers in the presence of triisopropylsilyl ethers are described. Deprotection conditions have been optimized for cleavage selectivity, tolerance by acid-labile compounds, and cleavage rate. Mechanistic features of the desilylation reaction are discussed

Urea, Glycolic Acid, and Glycerol in an Organic Residue Produced by Ultraviolet Irradiation of Interstellar/Pre-Cometary Ice Analogs

More than 50 stable organic molecules have been detected in the interstellar medium (ISM), from ground-based and onboard-satellite astronomical observations, in the gas and solid phases. Some of these organics may be prebiotic compounds that were delivered to early Earth by comets and meteorites and may have triggered the first chemical reactions involved in the origin of life. Ultraviolet irradiation of ices simulating photoprocesses of cold solid matter in astrophysical environments have shown that photochemistry can lead to the formation of amino acids and related compounds. In this work, we experimentally searched for other organic molecules of prebiotic interest, namely, oxidized acid labile compounds. In a setup that simulates conditions relevant to the ISM and Solar System icy bodies such as comets, a condensed CH(3)OH:NH(3) = 1:1 ice mixture was UV irradiated at approximately 80 K. The molecular constituents of the nonvolatile organic residue that remained at room temperature were separated by capillary gas chromatography and identified by mass spectrometry. Urea, glycolic acid, and glycerol were detected in this residue, as well as hydroxyacetamide, glycerolic acid, and glycerol amide. These organics are interesting target molecules to be searched for in space. Finally, tentative mechanisms of formation for these compounds under interstellar/pre-cometary conditions are proposed.

Assessment of the conventional molybdenum-blue and magnesium-induced coprecipitation procedures in phosphorus measurement in various aquatic environments

Phosphorus (P) is an essential nutrient utilized by all organisms for energy transport and growth. Both the conventional molybdenum-blue method and the magnesium-induced coprecipitation (MAGIC) procedures were applied for the measurement of dissolved inorganic phosphorus (DIP) and total dissolved phosphorus (TDP) in more than 840 water samples collected between 2003 and 2005, including seawater (the Huanghai Sea, the East China Sea, and the northern South China Sea), water from rivers and estuaries (the Changjiang, the Huanghe, and the major rivers emptying into the Jiaozhou Bay), groundwater (in the drainage basin surrounding the Jiaozhou Bay), rainwater, and aquaculture water samples. The MAGIC method allows the investigation of phosphorus distributions and cycling for systems in which DIP is below the detection limits of conventional methods. Comparison between the two methods demonstrated that the concentrations obtained with both methods were significantly correlated. The differences of DIP and TDP concentrations measured with the two methods were higher when the concentrations of DIP and TDP were lower, implying the lower reproducibility at low concentrations. The concentration differences increase with the increase in the proportion of DOP in TDP, which indicates that the discrepancy of DIP concentrations measured with the two methods increases when the DOP concentration is high. The discrepancies indicated that the composition of P compounds differs depending on sample sources and water type; it would be useful to infer the presence of different phosphorus compound pools from differences between the two methods. This study indicates the potential presence of a pool of alkaline-labile compounds for samples from rainwater and rivers and estuaries surrounding the Jiaozhou Bay; the potential presence of acid-labile compounds that were adsorbed by Mg(OH)2 for samples from the Changjiang Estuary, Huanghai Sea, East China Sea, and groundwater; the potential presence of a substantial pool of acid-labile compounds that were not adsorbed by Mg(OH)2 for samples from the Huanghe Estuary, aquaculture water, the East China Sea algal bloom water, and the northern South China Sea.

Isolation and purification of acid‐labile carotenoid 5,6‐epoxides on modified silica gels

The acid-labile carotenoid 5,6-epoxides occur in all green plants and in most fruits, but their isolation or purification is complicated and expensive because they decompose on normal silica gels. Alkaline stationary phases in open column chromatography (OCC) have low capacities, which makes them unsuitable for preparative scale. To find a simple high-capacity stationary phase for OCC that does not induce transformations of acid-labile compounds. Commercially available silica gel was treated with aqueous sodium bicarbonate solution to neutralise its slightly acidic character, and was then washed and dried. The effect of the treated gel (named silica-9) on violaxanthin was studied. The modified gel was also applied to the OCC of different complex natural extracts (maple leaves and fruits of yellow paprika). Carotenoids were examined by HPLC-PAD both before and after chromatography on the modified gel. Violaxanthin decomposed rapidly on normal silica gels but not on the modified gel. Chromatography of plant extracts showed that the modified gel had a similar capacity to the untreated gel but did not effect epoxy-carotenoids, which could be separated or enriched readily on a large scale. The modified gel does not induce any transformation or decomposition of epoxy-carotenoids but still exhibits a high capacity, suggesting that it can be used in preparative organic chemistry as an additional and convenient tool in the OCC for the separation of other acid-labile compounds.

Mass Determination of Phosphoramidites

Nucleoside phosphoramidites are the most widely used building blocks in contemporary solid-phase synthesis of oligonucleotides. The accurate molecular weight measurements of such molecules, which are acid-labile compounds, may be easily determined by mass spectrometry using a matrix system, triethanolamine/NaCl, on a liquid secondary ion mass spectrometer (LSIMS) or fast-atom bombardment (FAB) MS equipped with a double-focusing mass spectrometer. The present method rapidly and easily measures the accurate molecular weights of various phosphoramidites as adduct ions [M+Na]+ with an average mass error smaller than 0.4 ppm, allowing determination of the formulas of the phosphoramidites in place of elemental analysis. Further, it was found that intensities of molecular-related ions could be enhanced to the highest degree by adjustment of the molar ratio of phosphoramidite and NaCl, fixing the amount of triethanolamine on LSIMS, making the present method a powerful tool for identification of phosphoramidites by mass spectrometry.

Biochemical and Structural Studies of N5-Carboxyaminoimidazole Ribonucleotide Mutase from the Acidophilic Bacterium Acetobacter aceti

N5-carboxyaminoimidazole ribonucleotide (N5-CAIR) mutase (PurE) catalyzes the reversible interconversion of acid-labile compounds N5-CAIR and 4-carboxy-5-aminoimidazole ribonucleotide (CAIR). We have examined PurE from the acidophilic bacterium Acetobacter aceti (AaPurE), focusing on its adaptation to acid pH and the roles of conserved residues His59 and His89. Both AaPurE and Escherichia coli PurE showed quasi-reversible acid-mediated inactivation, but wt AaPurE was much more stable at pH 3.5, with a > or = 20 degrees C higher thermal unfolding temperature at all pHs. His89 is not essential and does not function as part of a proton relay system. The kcat pH-rate profile was consistent with the assignment of pK1 to unproductive protonation of bound nucleotide and pK2 to deprotonation of His59. A 1.85 A resolution crystal structure of the inactive mutant H59N-AaPurE soaked in CAIR showed that protonation of CAIR C4 can occur in the absence of His59. The resulting species, modeled as isoCAIR [4(R)-carboxy-5-iminoimidazoline ribonucleotide], is strongly stabilized by extensive interactions with the enzyme and a water molecule. The carboxylate moiety is positioned in a small pocket proposed to facilitate nucleotide decarboxylation in the forward direction (N5-CAIR --> CAIR) [Meyer, E., Kappock, T. J., Osuji, C., and Stubbe, J. (1999) Biochemistry 38, 3012-3018]. Comparisons with model studies suggest that in the reverse (nonbiosynthetic) direction PurE favors protonation of CAIR C4. We suggest that the essential role of protonated His59 is to lower the barrier to decarboxylation by stabilizing a CO2-azaenolate intermediate.

Porous polymer monolith for surface-enhanced laser desorption/ionization time-of-flight mass spectrometry of small molecules.

Porous poly(butyl methacrylate-co-ethylene dimethacrylate), poly(benzyl methacrylate-co-ethylene dimethacrylate), and poly(styrene-co-divinylbenzene) monoliths have been prepared on the top of standard sample plates used for matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and the modified plates were used for laser desorption/ionization mass spectrometry (LDI-MS). The hydrophobic porous surface of these monoliths enables the transfer of sufficient energy to the analyte to induce desorption and ionization prior to TOFMS analysis. Both UV and thermally initiated polymerization using a mask or circular openings in a thin gasket have been used to define spot locations matching those of the MALDI plates. The desorption/ionization ability of the monolithic materials depends on the applied laser power, the solvent used for sample preparation, and the pore size of the monoliths. The monolithic matrices are very stable and can be used even after long storage times in a typical laboratory environment without observing any deterioration of their properties. The performance of the monolithic material is demonstrated with the mass analysis of several small molecules including drugs, explosives, and acid labile compounds. The macroporous spots also enable the archiving of samples.

Persistent organic pollutants in plasma of delivering women from Arkhangelsk

The high levels of persistent organic pollutants have caused concern about human health, especially the health of the foetus and newborn child. This has especially been the case for Greenlandic and Canadian Inuits, where elevated levels of PCB and p,p′-DDE have been reported. In recent studies from arctic Russia the levels of β-HCH and the DDT-group have been reported to be high, whereas the levels of PCB are low. However, the information from Northern Russia is, so far, incomplete. In this study, 27 delivering women from the city of Arkhangelsk, Russia, participated. They completed a questionnaire before delivery and plasma samples were collected after delivery. The analytical method developed to support this study involved gel permeation chromatography and silica gel purification, in addition to a traditional GC-MS method, and thus include acid labile compounds. The arithmetic mean levels of p,p′-DDE, β-HCH and p,p′-DDT were 5.42, 3.59 and 1.17 μg/l, respectively. Toxaphene 26 and 50 were the only toxaphenes above the limit of detection, with arithmetic mean levels of 0.05 and 0.09 μg/l, respectively. Among the PCB congeners, PCB 138/163 was the most abundant with an arithmetic mean of 0.53 μg/l. The elevated levels of β-HCH and p,p′-DDT as well as a low DDE/DDT ratio is a strong indication of fresh and maybe local sources in this area.

Non-Acidic Matrix for the Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry of Acid-Labile Compounds

Non-Acidic Matrix for the Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry of Acid-Labile Compounds

Electrospray mass spectrometry of phosphoramidites, a group of acid-labile compounds† Paper presented at 17th Informal Meeting on Mass Spectrometry, Fiera di Primiero, Italy, May 1999.

Electrospray mass spectrometry of phosphoramidites, a group of acid-labile compounds† Paper presented at 17th Informal Meeting on Mass Spectrometry, Fiera di Primiero, Italy, May 1999.

Electrospray mass spectrometry of phosphoramidites, a group of acid-labile compounds

In contemporary solid-phase synthesis of oligonucleotides, phosphoramidites containing O-beta-cyanoethyl and N,N -diisopropyl groups are the most widespread monomer units. The N,N -diisopropyl phosphoramidite group can be activated by mild acidic treatment and then it easily reacts with nucleophiles (alcohols, water, etc.) to furnish the required phosphodiester linkage efficiently and cleanly. Owing to these properties, these compounds cannot be investigated using classical electrospray ionization. Their mass spectometric analysis is further hampered by the fact that they are often transiently protected with acid-sensitive groups (4, 4'-dimethoxytrityl, 4-monomethoxytrityl or trityl), which give intense signals in the spectra. Nanoelectrospray measurements from non-aqueous solvents (e.g. acetonitrile, methanol, tetrahydrofuran) were carried out in order to eliminate the nucleophilic water. Different types of alkali metal salts were used to form adduct ions. Among these salts, lithium chloride was found to be the most suitable for the analysis of amidites. Fairly abundant [M+Li](+) and [M+Cl](-) ions are formed in the positive and negative ion mode, respectively. These ions represent the base peaks in most cases whereas the intensities of the peaks corresponding to the protecting group are reduced by approximately 20%. This method is a powerful tool for the mass spectrometric identification of phosphoramidites. Copyright 1999 John Wiley & Sons, Ltd.

Surfactants with controlled half-lives

Surfactants with controlled half-lives normally contain a bond that is susceptible to either acid or alkaline hydrolysis. In recent years particular attention has been directed towards ester-containing quaternary ammonium surfactants, ‘ester-quats’, which readily break down under alkaline conditions. Surfactants containing acetal and ketal groups have been widely studied as acid-labile compounds. The main incentive behind the development in this area has been the synthesis of surfactants that will biodegrade rapidly.

Role of Coccoliths in the Utilization of Inorganic Carbon by a Marine Unicellular Coccolithophorid, Emiliania huxleyi: a Survey Using Intact Cells and Protoplasts

The utilization of inorganic carbon and role of the coccoliths were investigated in intact cells and protoplasts of a marine unicellular calcareous alga, Emiliania huxleyi. Protoplasts with high photosynthetic activity were obtained by artificial decalcification with 50 mM MES-NaOH (pH5.5). (1) The kinetics of the photosynthetic evolution of O2 at various concentrations of externally added NaHCO3 were the same for intact cells and protoplasts, indicating that the kinetic properties with respect to dissolved inorganic carbon (DIC) were not affected by the presence or absence of the coccoliths on the cell surface. Double-reciprocal plots and plots of the concentration of substrate divided by velocity (s/v) against the concentration of substrate (s) were biphasic in the case of both intact cells and protoplasts. The CO2-utilization reaction was, therefore, considered to involve two processes with different values of Km and Vmax. From the kinetic analyses, Km and Vmax [μmoles O2 (ml PCV)−1 h−1] were deduced to be 92 μM and 76.3 for a “low-Km” reaction and 4.1 mM and 252 for a “high-Km” reaction, respectively. (2) In short-term (40-min) experiments, time courses of the total uptake of 14C-DIC and the incorporation of 14C into acid-stable products of photosynthesis and the internal pool of DIC, determined as acid-labile compounds, under CO2-limiting conditions (80 μM) were very similar for intact cells and protoplasts. However, incorporation of 14C into CaCO3 apparently occurred more slowly in protoplasts than in intact cells. (3) In long term (24-h) experiments, patterns of incorporation of 14C were almost same for intact cells and protoplasts, with the exception that the amount of 14C incorporated into CaCO3 was much smaller in the former than the latter. The production of Ca14CO3 increased during the course of 10 h after a 4-h lag. However, after 10 h the level of Ca14CCO3 started to decrease. The decrease was accompanied by an increase in 14C in the products of photosynthesis, suggesting that CaCO3 was reutilized for the photosynthetic fixation of CO2 and, therefore, that the coccoliths function as sites of storage of DIC. However, the internal level of DIC remained at the same level even after the supply of external DIC has been almost completely depleted.

Improved protocols for the selective deprotection of trialkylsilyl ethers using fluorosilicic acid

Improvements for the application of aqueous fluorosilicic acid to the selective cleavage of tert-butyldimethylsilyl ethers in the presence of triisopropylsilyl ethers are described. Deprotection conditions have been optimized for cleavage selectivity, tolerance by acid-labile compounds, and cleavage rate. Mechanistic features of the desilylation reaction are discussed

Synthesis of deoxyglucose-1-phosphate, deoxyglucose-1,6-bisphosphate, and other metabolites of 2-deoxy-D-[14C]glucose in rat brain in vivo: influence of time and tissue glucose level.

When the kinetics of interconversion of deoxy[14C]glucose ([14C]DG) and [14C]DG-6-phosphate ([14C]DG-6-P) in brain in vivo are estimated by direct chemical measurement of precursor and products in acid extracts of brain, the predicted rate of product formation exceeds the experimentally measured rate. This discrepancy is due, in part, to the fact that acid extraction regenerates [14C]DG from unidentified labeled metabolites in vitro. In the present study, we have attempted to identify the 14C-labeled compounds in ethanol extracts of brains of rats given [14C]DG. Six 14C-labeled metabolites, in addition to [14C]DG-6-P, were detected and separated. The major acid-labile derivatives, DG-1-phosphate (DG-1-P) and DG-1,6-bisphosphate (DG-1,6-P2), comprised approximately 5 and approximately 10-15%, respectively, of the total 14C in the brain 45 min after a pulse or square-wave infusion of [14C]DG, and their levels were influenced by tissue glucose concentration. Both of these acid-labile compounds could be synthesized from DG-6-P by phosphoglucomutase in vitro. DG-6-P, DG-1-P, DG-1,6-P2, and ethanol-insoluble compounds were rapidly labeled after a pulse of [14C]DG, whereas there was a 10-30-min lag before there was significant labeling of minor labeled derivatives. During the time when there was net loss of [14C]DG-6-P from the brain (i.e., between 60 and 180 min after the pulse), there was also further metabolism of [14C]DG-6-P into other ethanol-soluble and ethanol-insoluble 14C-labeled compounds. These results demonstrate that DG is more extensively metabolized in rat brain than commonly recognized and that hydrolysis of [14C]DG-1-P can explain the overestimation of the [14C]DG content and underestimation of the metabolite pools of acid extracts of brain. Further metabolism of DG does not interfere with the autoradiographic DG method.

Metabolites of 2-deoxy-[14C]glucose in plasma and brain: influence on rate of glucose utilization determined with deoxyglucose method in rat brain.

The [14C]deoxyglucose ([14C]DG) method depends upon quantitative trapping of metabolites in brain at the site of phosphorylation, and in the usual procedure it is assumed that all the label in plasma is in free DG. Our previous finding of labeled nonacidic derivatives of DG in plasma raised the possibility that some metabolites of DG might not be fully retained in body tissues and therefore cause overestimation of the integrated specific activity of the precursor pool determined from assay of label in plasma and/or underestimation of the true size of the metabolite fraction in brain. In the present study, metabolism of DG in rat tissues by secondary pathways was examined and found to be more extensive than previously recognized. When 14C-labeled compounds in ethanol extracts of either plasma or brain were separated by anion exchange HPLC, eight fractions were obtained. 14C-labeled metabolites in plasma were detected after a 35-min lag and gradually increased in amount with time after an intravenous pulse. In brain, deoxyglucose-6-phosphate was further metabolized, mainly to deoxyglucose-1-phosphate and deoxyglucose-1,6-phosphate. These are acid-labile compounds and accounted for approximately 20% of the 14C in the metabolite pool in brain. The rate constants for net loss of 14C from the metabolite pool between 45 and 180 min after a pulse were similar (0.4-0.5%/min) in vivo and in intact postmortem brain. The rate constant for loss of deoxyglucose-6-phosphate (DG-6-P) in vivo (approximately 0.7%/min) was, however, about twice that for postmortem brain, suggesting that a significant fraction of the DG-6-P lost in vivo is due to its further metabolism by energy-dependent reactions. 14C-labeled metabolites of [14C]DG in plasma and brain do not interfere with determination of local rates of glucose utilization in brain in normal, conscious rats by the autoradiographic method if the prescribed procedures and a 45-min experimental period are used.

Group-selective determination of total N-nitroso compounds in nitrate-containing human urine samples.

A group-selective method for the determination of total N-nitroso compounds (NOC) has been adapted for analysing human urine samples. Nitrate was first removed from urine by an anion-exchange procedure that prevented the significant loss of various added reference NOC and unidentified urinary NOC. The total NOC were then determined by injecting the urine sample (nitrate content less than 1 mmol l-1) or anion-exchange eluate into refluxing ethyl acetate containing either acetic acid for determining heat and acetic acid labile thermal energy analyser responsive compounds (TAC) or into hydrogen bromide for the determination of TAC and NOC. The nitrogen monoxide levels released were measured using thermal energy analysis with chemiluminescence detection, and the differnce between the two determinations represented the concentrations of NOC. The optimum conditions for preventing artefactual nitrosation in urine samples by the addition of sodium hydroxide or sulphamic acid without decomposition of NOC were determined. The influence of time and storage conditions on NOC stability was investigated. Fifteen urine samples collected from volunteers dosed with proline were analysed for total NOC and N-nitrosamino acids revealing a preponderance of unknown NOC. The determination of total NOC in human urine using this group-selective method offers a new approach to the estimation of human exposure to NOC and to isolate hitherto unknown NOC and their metabolites.