Ulrike Dr. Holzgrabe

University of Wuerzburg | JMU · Institute of Pharmacy and Food Chemistry

An alternative to the time-consuming and error-prone pharmacopoeial gas chromatography method for the analysis of fatty acids (FAs) is urgently needed. The objective was therefore to propose a robust liquid chromatography method with charged aerosol detection for the analysis of polysorbate 80 (PS80) and magnesium stearate. FAs with different numbe...

The ongoing threat of Antimicrobial Resistance (AMR) complicated by the rise of Multidrug-Resistant (MDR) pathogens calls for increased efforts in the search for novel treatment options. While deriving inspiration from antibacterial natural compounds, this study aimed at using synthetic approaches to generate a series of glucovanillin derivatives a...

In the last few years, fluorescence resonance energy transfer (FRET) receptor sensors have contributed to the understanding of GPCR ligand binding and functional activation. FRET sensors based on muscarinic acetylcholine receptors (mAChRs) have been employed to study dual-steric ligands, allowing for the detection of different kinetics and distingu...

The human African trypanosomiasis is a devastating parasitic infection, which is caused by the protozoan Trypanosoma brucei and transmitted by the bite of the tsetse fly. An untreated infection usually results in death and only few drugs with significant drawbacks are currently available for treatment. Previous investigations revealed the quinolone...

Reports of therapy failures related to the use of daptomycin (DAP) are steadily increasing. This is mainly due to emerging DAP resistance for which, however, the underlying mechanism is often unknown. To elucidate the mode of action of novel DAP resistance traits it is indispensable to reliably detect and quantify DAP in complex matrices such as ba...

Capillary electrophoresis was chosen as cost-effective and robust method to separate ketamine enantiomers. For the method development, first different native and modified cyclodextrins were tested. The most promising chiral selector was α-cyclodextrin. A design of experiments (DoE) was carried out, which started with the screening of relevant facto...

Introduction: Red fruit oil (RFO) is a natural product extracted from Pandanus conoideus Lam. fruit, a native plant from Papua, Indonesia. Recent studies indicate that RFO is popularly consumed as herbal medicine. Therefore, the quality of RFO must be assured. Objectives: This study aimed to develop a chemometric analysis applied to 1 H nuclear...

A series of piperidine‐3‐carbohydrazide‐hydrazones bearing phenylethyl, phenylpropyl, and phenylbutyl substituents on piperidine nitrogen were designed and synthesized as cholinesterase (ChE) inhibitors. The title compounds were screened for acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) inhibitory activities and antioxidant capacities,...

For a more comprehensive characterization of a drug substance and its impurities, multidetector approaches are a helpful tool in liquid chromatography. In particular, the relatively inexpensive hyphenation of the ultraviolet (UV) with the charged aerosol detector (CAD) extends the scope from UV-active to non- or weak chromophore analytes, respectiv...

Most drugs, especially those with acidic or neutral moieties, are bound to the plasma protein albumin, whereas basic drugs are preferentially bound to human alpha-1-acid glycoprotein (AGP). The protein binding of the long-established drugs ephedrine and pseudoephedrine, which are used in the treatment of hypotension and colds, has so far only been...

Increasing resistance against antimycotic drugs challenges anti‐infective therapies today and contributes to the mortality of infections by drug‐resistant Candida species and strains. Therefore, novel antifungal agents are needed. A promising approach in developing new drugs is using naturally occurring molecules as lead structures. In this work, 4...

Red fruit oil (RFO) can be extracted from fruits of Pandanus conoideus, Lam., an endogenous plant of Papua, Indonesia. It is a commonly used essential original traditional medicine. By applying a newly developed quantitative ¹ H NMR (qNMR) spectroscopy method for quality assessment, a simultaneous determination of the saponification value (SV), aci...

Even though the impurity analysis of the Ph. Eur. is considered well-studied, its methodology should be reviewed periodically to ensure that it is working properly, and all impurities are captured by the section „Related substances” of the monograph. Within this study, the biotechnological produced antidiabetic drug acarbose was chosen to demonstra...

H/D exchange reactions can be observed by NMR spectroscopy of acebutolol (ACE). The results obtained showed deuterium incorporation at α-posi t ion of the carbonyl group of acebutolol, when using deuterium oxide or deuterated methanol as deuterium source and solvent. The spontaneous deuteration is proceeded by the following pathway CH₃→CH₂D→CHD→CD₃...

The search for new antibiotics against multidrug-resistant (MDR), Gram-negative bacteria is crucial with respect to filling the antibiotics development pipeline, which is subject to a critical shortage of novel molecules. Screening of natural products is a promising approach for identifying antimicrobial compounds hosting a higher degree of novelty...

Medicine quality and methods for its assessment play a major role in the effectiveness of therapies and the treatment of many infectious diseases. However, poor-quality and/or falsified products are circulating in huge amounts in many low- and middle-income countries and are one of the major reasons why more and more resistant bacteria emerge. The...

The ¹H NMR spectra obtained from 56 different paracetamol tablets were thoroughly investigated to analyse and quantify besides paracetamol, the excipients and eventual minor components present in the formulations. In the NMR spectra the amide-iminol tautomerism of paracetamol was observed, with the iminol form present at a quantity of only 0.80% of...

Background: The macrophage infectivity potentiator (Mip) protein, which belongs to the immunophilin superfamily, is a peptidyl-prolyl cis/trans isomerase (PPIase) enzyme. Mip has been shown to be important for virulence in a wide range of pathogenic microorganisms. It has previously been demonstrated that small-molecule compounds designed to targe...

It is often difficult to trace back drugs to the manufacturer, even though this can be important, especially when fake or low quality drugs are circulating. Drug formulations contain of the active pharmaceutical ingredient (API) and excipients and the finished products from different manufacture usually differ. Hence, the characterization of the co...

Several examples of the emergence of unexpected impurities in medicinal products in the past, e.g. the 2018 valsartan scandal, disclosed the need for sophisticated approaches in impurity profiling. Advanced techniques in mass spectrometry offer the possibility to detect impurities in untargeted approaches complementing the targeted search for poten...

To take advantage of the charged aerosol detector (CAD) for sensitive LC analysis of analytes with weak chromophore, the volatility of the entire mobile phase is a prerequisite. Therefore, it is not feasible to use common non-volatile ion-pairing reagents such as tetrabutylammonium hydroxide for the analysis of polar, acidic amino acids. This case...

Forced oxidative mechanochemical degradation of clopidogrel hydrogensulfate as a model compound leads to selective formation of degradants in less than 15 minutes.

The GABA B receptor agonist baclofen is a medication commonly used for the treatment of muscle spasticity. It is an amino acid and related to the neurotransmitter GABA. In this study, we developed a new, gradient high-performance liquid chromatography (HPLC) method for the impurity assessment of baclofen, which is appropriate for pharmacopoeial pur...

The charged aerosol detector (CAD) is frequently employed in liquid chromatography for the analysis of small polar and ionizable compounds such as amino acids and amino sugars, which provide a weak chromophore only. Separation of these compounds is achieved by means of ion pair chromatography (IPC), and, more recently, hydrophilic interaction chrom...

In 1998, the aminoglycoside antibiotic gentamicin sulfate caused several cases of deaths in the United States, after the switch from twice- to once-daily application. Endotoxins were discussed as the cause for the adverse effects and sisomicin was identified as the lead impurity; batches containing sisomicin were contaminated with more impurities a...

Background: Reproducibility of reported antibacterial activities of plant extracts has long remained questionable. Although plant-related factors should be well considered in serious pharmacognostic research, they are often not addressed in many research papers. Here we highlight the challenges in reproducing antibacterial activities of plant extr...

The charged aerosol detector (CAD) is the latest representative of aerosol-based detectors that generate a response independent of the analytes’ chemical structure. This study was aimed at accurately predicting the CAD response of homologous fatty acids under varying experimental conditions. Fatty acids from C12 to C18 were used as model substances...

Upon emergence of nitrosamines in various drugs, e.g in valsartan, metformin and ranitidine, 4-methyl-1-nitrosopiperazine (MeNP) was found in rifampicin in August 2020. Rifampicin is used, amongst others, for post-exposure prophylaxis of leprosy. The occurrence of MeNP can be explained by the synthesis, because 1-amino-4-methylpiperazine is concomi...

Recently, charged aerosol detection (CAD), a universal detection technique in liquid chromatography, has been introduced into monographs of the European Pharmacopoeia (Ph. Eur.), which now employs HPLC-UV-CAD for assessing the impurities of the drug vigabatrin. The separation of vigabatrin and its impurities is facilitated by ion pair chromatograph...

Most drugs are no longer produced in their own countries by the pharmaceutical companies, but by contract manufacturers or at manufacturing sites in countries that can produce more cheaply. This not only makes it difficult to trace them back but also leaves room for criminal organizations to fake them unnoticed. For these reasons, it is becoming in...

The quantitative structure-retention relationship (QSRR) models are not only employed in retention behaviour prediction, but also in an in-depth understanding of complex chromatographic systems. The goal of the present research is to enable the comprehensive understanding of retention underlying the separation in β-cyclodextrin (CD) modified revers...

Strychnine is the prototypic antagonist of glycine receptors, a family of pentameric ligand-gated ion channels. Recent high-resolution structures of homomeric glycine receptors have confirmed the presence of five orthosteric binding sites located in the extracellular subunit interfaces of the receptor complex that are targeted by strychnine. Here,...

The quality control of active pharmaceutical ingredients (APIs) is a very important aspect for drug products entering the market. However, also for the well-established drugs, there ought to be a state-of-the-art impurity control. Some of the pharmacopoeial tests for related substances still make use of thin layer chromatography, even though select...

Binding between cyclodextrin (CD) cavity and guest molecule in Reversed Phase High-Performance Liquid Chromatography (RP-HPLC) is dynamic process. In general, increasing CD concentration is inducing inclusion complex formation, leading to reduction of analyte's retention time. Consequently, the shortness in retention time is a measure of complex st...

Besides the racemate, the S‐enantiomer of ibuprofen (Ibu) is used for the treatment of inflammation and pain. Since the configurational stability of S‐Ibu in solid state is of interest, it was studied by means of ball milling experiments. For the evaluation of the enantiomeric composition, a chiral CE method was developed and validated according to...

Background Even though the international combat against Neglected Tropical Diseases such as schistosomiasis or soil-transmitted helminthiases depends on reliable therapeutics, anthelminthic pharmacovigilance has been neglected on many national African drug markets. Therefore, quality and composition of Albendazole, Mebendazole and Praziquantel loca...

The muscarinic M1 acetylcholine receptor is an important drug target for the treatment of various neurological disorders. Designing M1 receptor-selective drugs has proven challenging, mainly due to the high conservation of the acetylcholine binding site among muscarinic receptor subtypes. Therefore, less conserved and topographically distinct allos...

Charged aerosol detection (CAD) is an universal technique in liquid chromatography that is increasingly used for the quality control of drugs. Consequently, it has found its way into compendial monographs promoted by its simple and robust application. However, the response of CAD is inherently nonlinear due to its principle of function. Thus, easy...

Controlling physicochemical properties of light-unresponsive drugs, by light, prima facie, a paradox approach. We expanded light control by ion pairing light-unresponsive salicylate or ibuprofen to photoswitchable azobenzene counterions, thereby reversibly controlling supramolecular structures, hence the drugs' physicochemical and kinetic propertie...

Ischemic stroke is one of the leading causes of death worldwide. It damages neurons and other supporting cellular elements in the brain. However, the impairment is not only confined to the region of assault but the surrounding area as well. Besides, it also brings about damage to the blood-brain barrier (BBB) which in turn leads to microvascular fa...

Delphinidin (DEL) is a plant-derived antioxidant with clinical potential to treat inflammatory pain but suffers from poor solubility and low bioavailability. Aims: To develop a well-tolerated CD-DEL complex with enhanced bioavailability and to investigate the mechanisms behind its an-tinociceptive effects in a preclinical model of inflammatory pa...

Background and Objectives Remdesivir and hydroxychloroquine are or were among the most promising therapeutic options to tackle the current SARS-CoV-2 pandemic. Besides the use of the prodrug remdesivir itself, the direct administration of GS-441 524, the resulting main metabolite of remdesivir, could be advantageous and even more effective. All sub...

Marine natural products have achieved great success as an important source of new lead compounds for drug discovery. The Red Sea provides enormous diversity on the biological scale in all domains of life including micro- and macro-organisms. In this review, which covers the literature to the end of 2019, we summarize the diversity of bioactive seco...

Marine natural products have achieved great success as an important source of new lead compounds for drug discovery. The Red Sea provides enormous diversity on the biological scale in all domains of life including micro- and macro-organisms. In this review, which covers the literature to the end of 2019, we summarize the diversity of bioactive seco...

Allosteric coupling describes a reciprocal process whereby G protein-coupled receptors (GPCRs) relay ligand-induced conformational changes from the extracellular binding pocket to the intracellular signaling surface. Therefore, GPCR activation is sensitive to both the type of extracellular ligand and intracellular signaling protein. We hypothesized...

Extraction is a key step in studying compounds from plants and other natural sources. The common use of high temperatures in pressurized microwave‐assisted extraction (PMAE) makes it unsuitable for the extraction of compounds with low or unknown thermal stability. This study aimed at determining the suitability of low‐temperature, short‐time PMAE i...

Infectious diseases are a major cause of morbidity and mortality worldwide, exacerbated by increasing antibiotic resistance in many bacterial species. The development of drugs with new modes of action is essential. A leading strategy is antivirulence, with the aim to target bacterial proteins which are important in disease causation and progression...

Microbial, mammalian, and plant cells produce and contain secondary metabolites, which typically are soluble in water to prevent cell damage by crystallization. The formation of ion pairs, for example, with carboxylic acids or mineral acids, is a natural blueprint to maintain basic metabolites in solution. Here, we aim at showing whether the mostly...

Fast and inexpensive analytical tools for identification of the origin of pharmaceutical formulations are important to ensure consumers safety. This study explores the potential of potentiometric multisensor systems (“electronic tongues”) in this type of application. 72 paracetamol samples purchased in different countries and produced by various co...

Vanadium, a transition series metal released during some industrial activities, induces oxidative stress and lipid peroxidation. Ameliorative effect of a pure compound from the methanolic extract of Moringa oleifera leaves, code-named MIMO2, in 14-day old mice administered with vanadium (as sodium metavanadate 3 mg/kg) for 2 weeks was assessed. Res...

We report on the antibacterial activity of five phenolic lipids derived from anacardic acid characterized by increasing alkyl chain lengths with C6, C8, C10, C12, or C14 carbon atoms. The compounds were profiled for their physicochemical properties, transport across epithelial monolayers, cytotoxicity and antibacterial activity as compared to commo...

Plant extracts from Cecropia genus have been used by Latin-American traditional medicine to treat metabolic disorders and diabetes. Previous reports have shown that roots of Cecropia telenitida that contains serjanic acid are one of the most prominent and representative pentacyclic triterpenes. The study aimed to isolate serjanic acid and evaluate...

Hydroperoxides are formed as the primary product during lipid oxidation, being analyzed as the peroxide value to detect the degradation level of oils and fats. As an alternative to the classical titration method according to Wheeler, a ¹H‐{³¹P} decoupled NMR method is developed using triphenylphosphine (TPP) as a tagging agent. TPP reacts with pero...

This paper introduces an 1H NMR method to identify individual divalent metal cations Be2+, Mg2+, Ca2+, Sr2+, Zn2+, Cd2+, Hg2+, Sn2+, and Pb2+ in aqueous salt solutions through their unique signal shift and coupling after complexation with the salt of ethylenediamine tetraacetic acid (EDTA). Furthermore, quantitative determination applied for the di...

For the compendial related substances test of l-aspartic acid (Asp) and glycine (Gly), two separate reversed-phase ion-pair high-performance liquid chromatography methods coupled with charged aerosol and ultraviolet detection were developed. Separation of all putative impurities, in particular of the related carboxylic and amino acids, was achieved...

We synthesized a set of new hybrid derivatives (7-C8, 7-C10, 7-C12 and 8-C8, 8-C10, 8-C12), in which a polymethylene spacer chain of variable length connected the pharmacophoric moiety of xanomeline, an M1/M4-preferring orthosteric muscarinic agonist, with that of tacrine, a well-known acetylcholinesterase (AChE) inhibitor able to allosterically mo...

High performance liquid chromatography (HPLC) methods with UV/vis detection are the most widespread analytical procedures in modern pharmaceutical applications, but reach their limitations when it comes to non-chromophore molecules. Hence, instead of using tiresome derivatization procedures, many liquid chromatography methods make use of the so-cal...

Sacha inchi oil is a premier raw material with highly nutritional and functional features for the foodstuff, pharmaceutical, beauty, and personal care industries. One of the most important facts about this oil is the huge chemical content of unsaturated and polyunsaturated fatty acids. However, the current available information on the characterizat...

Background: Quality issues in pharmaceuticals are identified as a huge global and public health problem, especially with reference to low- and middle-income countries like Pakistan. The 2011 “Fake Drug Crisis” acted as a driving force to reform the regulatory structures of the country and for establishing the autonomous “Drug Regulatory Authority o...

NSC‑631570 (Ukrain) is an aqueous extract of Chelidonium majus, a herbaceous perennial plant, one of two species in the genus Chelidonium, which has been demonstrated to selectively kill tumor cells without affecting non‑malignant cells. In the present study, the components of NSC‑631570 were examined by combined liquid chromatography/mass spectros...

Background: As a library of cannabinoid (CB) derivatives with (-)-trans-cannabidiol (CBD) or (-)-trans-cannabidivarin (CBDV) scaffold, we synthesized nine novel cannabinoids: 2-hydroxyethyl cannabidiolate (2-HEC), 2-hydroxypentyl cannabidiolate (2-HPC), 2,3-dihydroxypropyl cannabidiolate (GCBD), cyclohexyl cannabidiolate (CHC), n-hexyl-cannabidiola...

Oncogenic RAS provides crucial survival signaling for up to half of multiple myeloma cases, but has so far remained a clinically undruggable target. RAL is a member of the RAS superfamily of small GTPases and is considered to be a potential mediator of oncogenic RAS signaling. In primary multiple myeloma, we found RAL to be overexpressed in the vas...

(11S)-11-Aminostrychnine (1) and N-[(11S)-strychnine-11-yl]propionamide (2) were synthesized and characterized as antagonists of homomeric α1 and heteromeric α1β glycine receptors in a functional fluorescence-based assay and a patch-clamp assay and in radioligand binding studies. The absolute configuration at C-11 of 1 was determined based on vicin...

The recent incidences of contaminated valsartan drug products gave rise to review the suitability of current impurity profiling workflows implemented at authorities and pharmaceutical companies. The major drawback of targeted impurity profiling, where a considerable amount of prior knowledge about possible contaminants is necessary, is the fact tha...

Parenteral amino acid solutions containing tryptophan tend to develop a yellow colouration upon storage. Hence, the aim of the present study was to find out whether tryptophan degradation products are the reason for the yellowing. The degree of discolouration and tryptophan degradation was examined by visual examination and UV/Vis measurements with...

The quantification of a drug, its impurities, and e.g. components of a mixture has become routine in NMR laboratories and many applications have been described in the literature. However, besides simply using 1D 1H or 13C NMR, a number of more advanced methods has been developed and used in the past. Here, we want to describe the applicability of n...

Quinolone antibiotics present an attractive oral treatment option in patients with cystic fibrosis (CF). Prior studies have reported comparable clearances and volumes of distribution in patients with CF and healthy volunteers for primarily renally cleared quinolones. We aimed to provide the first pharmacokinetic comparison for pefloxacin as a predo...

Bengkuang (Pachyrhizus erosus) has been traditionally used as sun screening and skin whitening. The active compounds in bengkuang extract already published included their activities in antioxidant and skin whitening. However, standardization of bengkuang extract has not been studied. This research aims to find out the analysis procedure by High Per...

Background: Melatonin-tamoxifen drug conjugate linked with a 5-carbon chain (C5) exhibited uterus protection in female mice, which did not occur when the same doses of unlinked melatonin and tamoxifen were co-administered. Anti-cancer actions of C5 and 4 others, with varying carbon lengths (C2, C4, C9, C15), were further tested in phenotypically di...

Background: Melatonin-tamoxifen drug conjugate linked with a 5-carbon chain (C5) exhibited uterus protection in female mice, which did not occur when the same doses of unlinked melatonin and tamoxifen were co-administered. Anti-cancer actions of C5 and 4 others, with varying carbon lengths (C2, C4, C9, C15), were further tested in phenotypically di...

Tamoxifen is used to prevent and treat estrogen receptor positive (ER+) breast cancer (BC); however, its chronic use can increase uterine cancer risk and induce tamoxifen resistance. Novel melatonin-tamoxifen drug conjugates may be promising to treat BC and may help offset the adverse effects of tamoxifen usage alone due to the presence of melatoni...

The pharmacokinetics in patients with cystic fibrosis (CF) has long been thought to differ considerably from that in healthy volunteers. For highly protein bound β-lactams, profound pharmacokinetic differences were observed between comparatively morbid patients with CF and healthy volunteers. These differences could be explained by body weight and...

For enantioseparations of chiral drugs in capillary electrophoresis, chiral ionic liquids (CIL) can be employed instead of traditional running buffer containing a chiral selector. CILs can be applied solely or in addition to the often used cyclodextrin derivatives. Here the separation of phenethylamines, especially of ephedrine, is described using...

In July 2018 one of the bestselling antihypertensive agents valsartan manufactured in China was found to be contaminated by the “probably carcinogenic” nitrosamine N-nitrosodimethylamine (NDMA), followed by the detection of N-nitrosodiethylamine (NDEA) by us and others soon after. Our work also revealed that two additional non-nitrosamine contamina...