Identification and Preclinical Development of a 2,5,6-Trisubstituted Fluorinated Pyridine Derivative as a Radioligand for the Positron Emission Tomography Imaging of Cannabinoid Type 2 Receptors

Despite the broad implications of the cannabinoid type 2 receptor (CB2) in neuroinflammatory processes, a suitable CB2-targeted probe is currently lacking in clinical routine. In this work, we synthesized 15 fluorinated pyridine derivatives and tested their binding affinities toward CB2 and CB1. With a sub-nanomolar affinity (K_i for CB2) of 0.8 nM and a remarkable selectivity factor of >12,000 over CB1, RoSMA-18-d₆ exhibited outstanding in vitro performance characteristics and was radiofluorinated with an average radiochemical yield of 10.6 ± 3.8% (n = 16) and molar activities ranging from 52 to 65 GBq/μmol (radiochemical purity > 99%). [¹⁸F]RoSMA-18-d₆ showed exceptional CB2 attributes as demonstrated by in vitro autoradiography, ex vivo biodistribution, and positron emission tomography (PET). Further, [¹⁸F]RoSMA-18-d₆ was used to detect CB2 upregulation on postmortem human ALS spinal cord tissues. Overall, these results suggest that [¹⁸F]RoSMA-18-d₆ is a promising CB2 PET radioligand for clinical translation.

Structure-Activity Relationship Studies of Pyridine-Based Ligands and Identification of a Fluorinated Derivative for Positron Emission Tomography Imaging of Cannabinoid Type 2 Receptors

The cannabinoid type 2 (CB2) receptor has emerged as a valuable target for therapy and imaging of immune-mediated pathologies. With the aim to find a suitable radiofluorinated analogue of the previously reported CB2 positron emission tomography (PET) radioligand [¹¹C]RSR-056, 38 fluorinated derivatives were synthesized and tested by in vitro binding assays. With a K_i (hCB2) of 6 nM and a selectivity factor of nearly 700 over cannabinoid type 1 receptors, target compound 3 exhibited optimal in vitro properties and was selected for evaluation as a PET radioligand. [¹⁸F]3 was obtained in an average radiochemical yield of 11 ± 4% and molar activities between 33 and 114 GBq/μmol. Specific binding of [¹⁸F]3 to CB2 was demonstrated by in vitro autoradiography and in vivo PET experiments using the CB2 ligand GW-405 833. Metabolite analysis revealed only intact [¹⁸F]3 in the rat brain. [¹⁸F]3 detected CB2 upregulation in human amyotrophic lateral sclerosis spinal cord tissue and may thus become a candidate for diagnostic use in humans.

The Albicidin Resistance Factor AlbD Is a Serine Endopeptidase That Hydrolyzes Unusual Oligoaromatic-Type Peptides

The para-aminobenzoic acid-containing peptide albicidin is a pathogenicity factor synthesized by Xanthomonas albilineans in infections of sugar cane. Albicidin is a nanomolar inhibitor of the bacterial DNA gyrase with a strong activity against various Gram-negative bacteria. The bacterium Pantoea dispersa expresses the hydrolase AlbD, conferring natural resistance against albicidin. We show that AlbD is a novel type of endopeptidase that catalyzes the cleavage of albicidin at a peptide backbone amide bond, thus abolishing its antimicrobial activity. Additionally, we determined the minimal cleavage motif of AlbD with substrates derived by chemical synthesis. Our results clearly identify AlbD as a unique endopeptidase that is the first member of a new subfamily of peptidases. Our findings provide the molecular basis for a natural detoxification mechanism, potentially rendering a new tool in biological chemistry approaches.

The gyrase inhibitor albicidin consists of p-aminobenzoic acids and cyanoalanine

Albicidin is a potent DNA gyrase inhibitor produced by the sugarcane pathogenic bacterium Xanthomonas albilineans. Here we report the elucidation of the hitherto unknown structure of albicidin, revealing a unique polyaromatic oligopeptide mainly composed of p-aminobenzoic acids. In vitro studies provide further insights into the biosynthetic machinery of albicidin. These findings will enable structural investigations on the inhibition mechanism of albicidin and its assessment as a highly effective antibacterial drug.

Total synthesis of albicidin: a lead structure from Xanthomonas albilineans for potent antibacterial gyrase inhibitors

The peptide antibiotic albicidin, which is synthesized by the plant pathogenic bacterium Xanthomonas albilineans, displays remarkable antibacterial activity against various Gram-positive and Gram-negative microorganisms. The low amounts of albicidin obtainable from the producing organism or through heterologous expression are limiting factors in providing sufficient material for bioactivity profiling and structure-activity studies. Therefore, we developed a convergent total synthesis route toward albicidin. The unexpectedly difficult formation of amide bonds between the aromatic amino acids was achieved through a triphosgene-mediated coupling strategy. The herein presented synthesis of albicidin confirms the previously determined chemical structure and underlines the extraordinary antibacterial activity of this compound. The synthetic protocol will provide multigram amounts of albicidin for further profiling of its drug properties.

Heterologous expression and engineering studies of labyrinthopeptins, class III lantibiotics from Actinomadura namibiensis

Labyrinthopeptins are class III lantibiotics produced by the actinomycete Actinomadura namibiensis. The most characteristic structural feature is the posttranslationally installed triamino triacid labionin with a quaternary α-carbon. In addition to the unique structure, labyrinthopeptin A2 possess remarkable antiviral and antiallodynic biological activities. To harness the substrate tolerance of the biosynthetic machinery, we developed an efficient system for the generation of labyrinthopeptin analogs. Streptomyces lividans was used as a heterologous host since the natural producer Actinomadura namibiensis remained genetically intractable. Generation of a library of 39 mutants allowed identification of variable and invariable regions in the labyrinthopeptin structures. Additional data on the flexibility of the biosynthetic machinery were provided by in vitro experiments. This study is detailed investigation on the potential to generate analogs of class III lantibiotics by genetic engineering.

Sub-20 nm short channel carbon nanotube transistors

Carbon nanotube field-effect transistors with sub-20 nm long channels and on/off current ratios of >10(6) are demonstrated. Individual single-walled carbon nanotubes with diameters ranging from 0.7 to 1.1 nm grown from structured catalytic islands using chemical vapor deposition at 700 degrees C form the channels. Electron beam lithography and a combination of HSQ, calix[6]arene, and PMMA e-beam resists were used to structure the short channels and source and drain regions. The nanotube transistors display on-currents in excess of 15 microA for drain-source biases of only 0.4 V.

Lack of involvement of sarcoplasmic reticulum in myopathy of acute phosphorous depletion

Acute and chronic hypophosphatemia are known to cause metabolic myopathy. It has been proposed that impaired Ca transport in subcellular membranes is involved in its genesis. In the present study, calcium transport in the sarcoplasmic reticulum (SR), concentrations of ions or nucleotides and transmembrane potential were investigated in muscles of acutely hypophosphatemic rats, i.e. animals with chronic dietary phosphorous deprivation (PD) and superimposed acute hypophosphatemia resulting from the administration of insulin and glucose. Despite hypophosphatemia and low muscle phosphorous concentration, no significant change of the initial rate of Ca uptake or Ca concentrating ability was observed in the SR of PD rats. Storing capacity was decreased; this may result from altered vesicle geometry. Water content, Na concentration, the concentration of several nucleotides and transmembrane potential of muscle were unchanged in PD rats. The findings document that no intrinsic abnormality of vectorial Ca transport is present in the SR of acutely hypophosphatemic PD animals.