The McKenna reaction - avoiding side reactions in phosphonate deprotection

One-Pot Synthesis of Bioinspired Peptide-Decorated Apatite Nanoparticles for Nanomedicine

Hybrid organic-inorganic bio-inspired apatite nanoparticles (NPs) are attractive for biomedical applications and especially in nanomedicine. Unfortunately, their applications in nanomedicine are limited by their broad particle size distributions and uncontrolled drug loading due to their multistep synthesis process.  Besides, very few attempts at exposing bioactive peptides on apatite NPs are made. In this work, an original one-pot synthesis of well-defined bioactive hybrid NPs composed of a mineral core of bioinspired apatite surrounded by an organic corona of bioactive peptides is reported. Dual stabilizing-bioactive agents, phosphonated polyethylene glycol-peptide conjugates, are prepared and directly used during apatite precipitation i) to form the organic corona during apatite precipitation, driving the size and shape of resulting hybrid NPs with colloidal stabilization and ii) to expose peptide moieties (RGD or YIGSR sequences) at the NPs periphery in view of conferring additional surface properties to enhance their interaction with cells. Here, the success of this approach is demonstrated, the functionalized NPs are fully characterized by Fourier-transform infrared, Raman, X-ray diffraction, solid and liquid state NMR, transmission electron microscopy, and dynamic light scattering, and their interaction with fibroblast cells is followed, unveiling a synergistic proliferative effect.

Design, Synthesis, and Biological Evaluation of Small-Molecule-Based Radioligands with Improved Pharmacokinetic Properties for Imaging of Programmed Death Ligand 1

Small molecules offer some advantages for developing positron emission tomography (PET) tracers and are therefore a promising approach for imaging and therapy monitoring of programmed death ligand 1 (PD-L1) positive tumors. Here, we report six biphenyl PD-L1 radioligands using the NODA-GA-chelator for efficient copper-64 complexation. These radioligands contain varying numbers of sulfonic and/or phosphonic acid groups, serving as hydrophilizing units to lower the log D7.4 value down to -4.28. The binding affinities of compounds were evaluated using saturation binding and a real-time binding assay, with a highest binding affinity of 21 nM. Small-animal PET imaging revealed vastly different pharmacokinetic profiles depending on the quantity and type of hydrophilizing units. Of the investigated radioligands, [64Cu]Cu-3 showed the most favorable kinetics in vitro. This was also found in vivo, with a predominantly renal clearance and a specific uptake in the PD-L1-overexpressing tumor. With further modifications, this compound could be a promising candidate for the imaging of PD-L1 in the clinical setting.

Exploring Hydrophilic PD-L1 Radiotracers Utilizing Phosphonic Acids: Insights into Unforeseen Pharmacokinetics

Immune checkpoint inhibitor therapy targeting the PD-1/PD-L1 axis in cancer patients, is a promising oncological treatment. However, the number of non-responders remains high, causing a burden for the patient and the healthcare system. Consequently, a diagnostic tool to predict treatment outcomes would help with patient stratification. Molecular imaging provides said diagnostic tool by offering a whole-body quantitative assessment of PD-L1 expression, hence supporting therapy decisions. Four PD-L1 radioligand candidates containing a linker-chelator system for radiometalation, along with three hydrophilizing units-one sulfonic and two phosphonic acids-were synthesized. After labeling with 64Cu, log D7.4 values of less than -3.03 were determined and proteolytic stability confirmed over 94% intact compound after 48 h. Binding affinity was determined using two different assays, revealing high affinities up to 13 nM. µPET/CT imaging was performed in tumor-bearing mice to investigate PD-L1-specific tumor uptake and the pharmacokinetic profile of radioligands. These results yielded an unexpected in vivo distribution, such as low tumor uptake in PD-L1 positive tumors, high liver uptake, and accumulation in bone/bone marrow and potentially synovial spaces. These effects are likely caused by Ca2+-affinity and/or binding to macrophages. Despite phosphonic acids providing high water solubility, their incorporation must be carefully considered to avoid compromising the pharmacokinetic behavior of radioligands.

Persistent Micelle Corona Chemistry Enables Constant Micelle Core Size with Independent Control of Functionality and Polyelectrolyte Response

Polymer micelles have found significant uses in areas such as drug/gene delivery, medical imaging, and as templates for nanomaterials. For many of these applications, the micelle performance depends on its size and chemical functionalization. To date, however, these parameters have often been fundamentally coupled since the equilibrium size of a micelle is a function of the chemical composition in addition to other parameters. Here, we demonstrate a novel processing pathway allowing for the chemical modification to the corona of kinetically trapped "persistent" polymer micelles, termed Persistent Micelle Corona Chemistry (PMCC). Judicious planning is crucial to this size-controlled functionalization where each step requires all reagents and polymer blocks to be compatible with (1) the desired chemistry, (2) micelle persistency, and (3) micelle dispersion. A desired functionalization can be implemented with PMCC by pairing the synthetic planning with polymer solubility databases. Specifically, poly(cyclohexyl methacrylate-b-(diethoxyphosphoryl)methyl methacrylate) (PCHMA-b-PDEPMMA) was prepared to combine a glassy-core block (PCHMA) for kinetic control with a block (PDEPMMA) that is able to be hydrolyzed to yield acid groups. The processing sequence determines the resulting micelle size distribution where the hydrolyzed-then-micellized sequence yields widely varying micelle dimensions due to equilibration. In contrast, the micellized-then-hydrolyzed sequence maintains kinetically trapped micelles throughout the PMCC process. Statistically significant transmission electron microscopy (TEM) measurements demonstrate that PMCC uniquely enables this functionalization with constant average micelle core dimensions. Furthermore, these kinetically trapped micelles also subsequently maintain constant micelle core size when modifying the Coulombic interactions of the micelle corona via pH changes.

MCR under Microwave Irradiation: Synthesis in Water of New 2-Amino-bis(2-phosphonoacetic) Acids

Novel 2-amino bis(2-phosphonoacetic) acids were prepared by microwave irradiation of a mixture of amine, glyoxylic acid and phosphorous acid. The reaction takes place with various amines including primary and secondary amines and polyamines, but this reaction is more sensitive to steric hindrance of amine than the similar Kabachnik–Fields reaction. Amino acids can be also transformed into the expected bis(2-phosphonoacetic) acids, with the exception of tryptophan, which gives a β-carboline product.

Synthesis of the 6-Substituted Imidazo[1,2-a]Pyridine-3-yl-2- Phosphonopropionic Acids as Potential Inhibitors of Rab Geranylgeranyl Transferase

Twelve phosphonopropionates derived from 2-hydroxy-3-imidazo[1,2-a]pyridin-3-yl-2-phosphonopropionic acid (3-IPEHPC) were synthesized and evaluated for their activity as inhibitors of protein geranylgeranylation. The nature of the substituent in the C6 position of imidazo[1,2-a]pyridine ring was responsible for the compound's activity against Rab geranylgeranyl transferase (RGGT). The most active inhibitors disrupted Rab11A prenylation in the human cervical carcinoma HeLa cell line. The esterification of carboxylic acid in the phosphonopropionate moiety turned the inhibitor into an inactive analog.

Sustainable Triazine-Based Dehydro-Condensation Agents for Amide Synthesis

Conventional methods employed today for the synthesis of amides often lack of economic and environmental sustainability. Triazine-derived quaternary ammonium salts, e.g., 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM(Cl)), emerged as promising dehydro-condensation agents for amide synthesis, although suffering of limited stability and high costs. In the present work, a simple protocol for the synthesis of amides mediated by 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and a tert-amine has been described and data are compared to DMTMM(Cl) and other CDMT-derived quaternary ammonium salts (DMT-Ams(X), X: Cl- or ClO4-). Different tert-amines (Ams) were tested for the synthesis of various DMT-Ams(Cl), but only DMTMM(Cl) could be isolated and employed for dehydro-condensation reactions, while all CDMT/tert-amine systems tested were efficient as dehydro-condensation agents. Interestingly, in best reaction conditions, CDMT and 1,4-dimethylpiperazine gave N-phenethyl benzamide in 93% yield in 15 min, with up to half the amount of tert-amine consumption. The efficiency of CDMT/tert-amine was further compared to more stable triazine quaternary ammonium salts having a perchlorate counter anion (DMT-Ams(ClO4)). Overall CDMT/tert-amine systems appear to be a viable and more economical alternative to most dehydro-condensation agents employed today.