A General Method for Nucleophilic Aromatic Substitution of Aryl Fluorides and Chlorides with Dimethylamine using Hydroxide-Assisted Decomposition of N,N-Dimethylforamide

Radiosynthesis and In Vitro Evaluation of [11C]tozadenant as Adenosine A2A Receptor Radioligand

Tozadenant (4-hydroxy-N-(4-methoxy-7-morpholinobenzo[d]thiazol-2-yl)-4-methylpiperidine-1-carboxamide) is a highly selective adenosine A2A receptor (A2AR) antagonist and a promising lead structure for the development of A2AR-selective positron emission tomography (PET) probes. Although several 18F-labelled tozadenant derivatives showed favorable in vitro properties, recent in vivo PET studies observed poor brain penetration and lower specific binding than anticipated from the in vitro data. While these findings might be attributable to the structural modification associated with 18F-labelling, they could also reflect inherent properties of the parent compound. However, PET studies with radioisotopologues of tozadenant to evaluate its cerebral pharmacokinetics and brain distribution are still lacking. In the present work, we applied N-Boc-O-desmethyltozadenant as a suitable precursor for the preparation of [O-methyl-11C]tozadenant ([11C]tozadenant) by O-methylation with [11C]methyl iodide followed by acidic deprotection. This approach afforded [11C]tozadenant in radiochemical yields of 18 ± 2%, with molar activities of 50-60 GBq/µmol (1300-1600 mCi/µmol) and radiochemical purities of 95 ± 3%. In addition, in vitro autoradiography in pig and rat brain slices demonstrated the expected striatal accumulation pattern and confirmed the A2AR specificity of the radioligand, making it a promising tool for in vivo PET studies on the cerebral pharmacokinetics and brain distribution of tozadenant.

Synthesis of Fluoro-Bridged Ho3+ and Gd3+ 1,3,5-Tris(4-carboxyphenyl)benzene Metal-Organic Frameworks from Perfluoroalkyl Substances

A new fluoro-bridged rare-earth (RE) metal-organic framework consisting of 15-connected nonanuclear and 9-connected trinuclear clusters {[RE₉-(μ₃-F)₁₄(H₂O)₆][RE₃(μ₃-F)(H₂O)₃](HCO₂)₃-(BTB)₆}·(solvent)x 2 (RE = Ho³⁺ and Gd³⁺) was synthesized through the transformation of a dimeric complex formulated as bis(2,2'-bipyridine)tetrakis(μ-2-fluorobenzoato-O,O')-bis(2-fluorobenzoato)diRE(III) 1 with the bridging linker 1,3,5-tris(4-carboxyphenyl)benzene (H₃BTB). The rare-earth metal ions Ho³⁺ and Gd³⁺ were also found to remove fluorine from other organo-fluorine compounds such as perfluorohexanoic acid (PFHxA) and perfluorooctanoic acid (PFOA), resulting in the new fluoro-bridged RE-MOFs.

Room-Temperature Dialkylamination of Chloroheteroarenes Using a Cu(II)/PTABS Catalytic System

The dimethylamino functionality has significant importance in industrially relevant molecules and methodologies to install these efficiently are highly desirable. We report herein a highly efficient, room-temperature dimethylamination of chloroheteroarenes performed via the in-situ generation of dimethylamine using N,N-dimethylformamide (DMF) as precursor wiith a large substrate scope that includes various heteroarenes, purines as well as commercially relevant drugs such as altretamine, ampyzine and puromycin precursor.

Synthesis of Rhodamines and Rosamines Using 3,6-Difluoroxanthone as a Common Intermediate

Rhodamines and structurally similar rosamines are some of the most highly utilized tools for molecular imaging experiments. We report a general and high-yielding route to produce 18 examples of rhodamines and rosamines, including tetramethylrhodamine, rhodamine B, and Janelia Fluor 549, from a single xanthone intermediate, 3,6-difluoroxanthone. Spectroscopic studies revealed trends in fluorophore efficiency based on substitution patterns at the 3'-, 6'-, and 9'-positions, providing insights to aid future designs of rhodamines/rosamines.

Photoassisted Charge Transfer Between DMF and Substrate: Facile and Selective N,N-Dimethylamination of Fluoroarenes

A reversible Van der Waals complex formation between the electron-deficient fluorinated aromatic ring and N,N-dimethylformamide (DMF) molecules followed by light irradiation resulted in charge transfer (CT) process. The complex was stabilized by ammonium formate and further decomposed to form the C-N bond. Control experiments revealed that the simultaneous S_N Ar pathway also contributes to product formation. This methodology is mild, metal-free, and effective for the amination of a variety of substrates. The reproducibility of this methodology was also verified on gram-scale reactions. The CT states were supported by control UV/Vis spectroscopy and computational studies.

Rapid synthesis of pomalidomide-conjugates for the development of protein degrader libraries

Current methods for the preparation of heterobifunctional pomalidomide-conjugates rely on methods that are often low yielding and produce intractable byproducts. Herein we describe our strategy for the reliable and succinct preparation of pomalidomide-linkers which is essential to the formation of these conjugates. We present the preparation of 18 pomalidomide-linkers in high yield compared to current literature methods. Our findings show that secondary amines consistently afford greater yields than their primary counterparts, a trend that we were able to exploit in the synthesis of several new pomalidomide homo-dimers in enhanced yields compared to similar literature syntheses. This trend was further utilised to develop the first one-pot synthesis of JQ1-pomalidomide conjugates in yields up to 62%, providing a method that is suited to rapid preparation of conjugate libraries as is frequently required for the development of new protein degraders.

Current methods for the preparation of heterobifunctional pomalidomide-conjugates rely on methods that are often low yielding and produce intractable byproducts. Herein we describe our strategy for the succinct preparation of pomalidomide-linkers.

Environmentally Benign, Base-Promoted Selective Amination of Polyhalogenated Pyridines

An environmentally benign, highly efficient, and base-promoted selective amination of various polyhalogenated pyridines including the challenging pyridine chlorides to 2-aminopyridine derivatives using water as solvent has been developed. Featuring the use of the new method, the reaction is extended to the transformation on a large scale. Mechanistic studies indicate that the pathway involving a base aidant dissociation of N,N-dimethylformamide to generate dimethylamine is likely.

Biocatalytic Carbon-Hydrogen and Carbon-Fluorine Bond Cleavage through Hydroxylation Promoted by a Histidyl-Ligated Heme Enzyme

LmbB2 is a peroxygenase-like enzyme that hydroxylates L-tyrosine to L-3,4-dihydroxyphenylalanine (DOPA) in the presence of hydrogen peroxide. However, its heme cofactor is ligated by a proximal histidine, not cysteine. We show that LmbB2 can oxidize L-tyrosine analogs with ring-deactivated substituents such as 3-nitro-, fluoro-, chloro-, iodo-L-tyrosine. We also found that the 4-hydroxyl group of the substrate is essential for reacting with the heme-based oxidant and activating the aromatic C-H bond. The most interesting observation of this study was obtained with 3-fluoro-L-tyrosine as a substrate and mechanistic probe. The LmbB2-mediated catalytic reaction yielded two hydroxylated products with comparable populations, i.e., oxidative C-H bond cleavage at C5 to generate 3-fluoro-5-hydroxyl-L-tyrosine and oxygenation at C3 concomitant with a carbon-fluorine bond cleavage to yield DOPA and fluoride. An iron protein-mediated hydroxylation on both C-H and C-F bonds with multiple turnovers is unprecedented. Thus, this finding reveals a significant potential of biocatalysis in C-H/C-X bond (X = halogen) cleavage. Further ¹⁸O-labeling results suggest that the source of oxygen for hydroxylation is a peroxide, and that a commonly expected oxidation by a high-valent iron intermediate followed by hydrolysis is not supported for the C-F bond cleavage. Instead, the C-F bond cleavage is proposed to be initiated by a nucleophilic aromatic substitution mediated by the iron-hydroperoxo species. Based on the experimental results, two mechanisms are proposed to explain how LmbB2 hydroxylates the substrate and cleaves C-H/C-F bond. This study broadens the understanding of heme enzyme catalysis and sheds light on enzymatic applications in medicinal and environmental fields.

Synthesis and cytotoxic evaluation of novel quinozalinone derivatives with substituted benzimidazole in position 3

Quinazolinone and benzimidazole are both fused heterocyclic compounds which have shown valuable biological properties including cytotoxic, antibacterial, and antifungal activities. In this study, a series of novel quinazolinone derivatives substituted with benzimidazole were synthesized in two parts. In the first part 2 - phenyl - 1H - benzimidazol - 6 - amine (4) was synthesized from the reaction of 4-nitro-o-phenylenediamine and benzoic acid. In the second part, new 3-(2-phenyl-1H benzoimidazol-5-yl)- 3H-quinazolin-4-one derivatives (8a-8f) were also prepared. Finally compound 4 was reacted with the different benzoxazinone derivatives (8a-8f) to give the target compounds. The structures of the synthesized compounds were confirmed by IR and ¹HNMR. Cytotoxic activities of the final compounds were assessed at 100, 200, 300, 400, and 500 μM against MCF-7 and HeLa cell lines using the MTT colorimetric assay. Almost all compounds exhibited good cytotoxic activity against both cell lines. Compound 9d demonstrated the highest cytotoxic activity against MCF7 and Hela cell lines with IC₅₀ 70 μM and 50 μM, respectively.

Transition-metal-free access to 2-aminopyridine derivatives from 2-fluoropyridine and acetamidine hydrochloride

Under catalyst-free conditions, an efficient method for the synthesis of 2-aminopyridine derivatives through the nucleophilic substitution and hydrolysis of 2-fluoropyridine and acetamidine hydrochloride has been developed. This amination uses inexpensive acetamidine hydrochloride as the ammonia source and has the advantages of a high yield, high chemoselectivity and wide substrate adaptability. The results suggest that other N-heterocycles containing fluorine substituents can also complete the reaction via these reaction conditions and yield the target products.

Stabilising fleeting intermediates of stilbene photocyclization with amino-borane functionalisation: the rare isolation of persistent dihydrophenanthrenes and their [1,5] H-shift isomers

Amino-borane functionalization is the key for isolating rare air-stable dihydrophenanthrene intermediates in stilbene photocyclization.

The key intermediate, 4a,4b-dihydrophenanthrene (DPH), involved in the photocyclization of stilbene and derivatives is known to be unstable, and is therefore poorly characterized/understood. We have found that functionalising stilbenes with NMe₂ and BMes₂ groups can greatly enhance the stability of 4a,4b-DPHs, allowing quantitative isolation and full characterization of these rare species. Furthermore, we discovered that the new amino-borane decorated 4a,4b-DPHs can undergo thermal [1,5] H sigmatropic shift, forming isomers 4a,10a-DPHs. Both 4a,4b-DHPs and 4a,10a-DHPs are stable towards air and moisture, while only the former were found to undergo oxidative dehydrogenation upon irradiation at 365 nm under air, yielding brightly blue/green fluorescent NMe₂ and BMes₂ functionalised phenanthrene analogues. Control studies established that the trans-Mes₂B–Ph–NMe₂ unit is responsible for the stability of these isolated 4a,4b-DHPs and their [1,5]-H shift isomers.