Synthesis, conformational studies, and biological properties of phosphonomethoxyethyl derivatives of nucleobases with a locked conformation via a pyrrolidine ring

The importance of selecting crystal form for triazole fungicide tebuconazole to enhance its botryticidal activity

The growing evidences of resistant fungi stimulate fully understanding tebuconazole regarding its crystal structure on fungicidal activity. In this study, the crystal structures of six technical tebuconazoles (BX, HH, JP, QZ, SJ, and YT) were characterized by using high-resolution X-ray powder diffraction and three-dimensional crystal structure modeling. A structure-activity relationship of the tebuconazoles on the susceptible (HLS and YJS) or resistant (XHR) Botrytis cinerea isolates was analyzed, the differential tricarboxylic acid (TCA) cycle metabolism was determined, and molecular docking with sterol 14α-demethylase (CYP51) was performed. The results showed that tebuconazole existed in three types of crystal forms: an overlapping-pair conformation, a side-by-side-pair conformation, and a parallel-pair conformation. QZ with the parallel-pair conformation and the minimum crystal cell volume exhibited a higher activity and a lower resistant level. XHR possessed a higher content of TCA cycle metabolites and phosphate than YJS, but the exposure to QZ significantly reduced the contents of citrate, isocitrate, α-ketoglutarate and oxaloacetate in XHR, as did the exposure to other technical tebuconazoles. Moreover, the point mutations F487L, G464S, and G443S altered the binding properties of chiral stereoscopic R-QZ with CYP51 protein. Especially the G443S mutation promoted a weak linking of R-QZ with LEU380 and TYR126, and greatly slashed the binding action at lower docking score. In conclusion, our results evidenced an efficient crystal conformation of tebuconazole to improve botryticidal activity and a potential adaptability of B. cinerea to tebuconazole inhibition in TCA cycle metabolism and CYP51 protein mutation.

Overview of Biologically Active Nucleoside Phosphonates

The use of the phosphonate motif featuring a carbon-phosphorous bond as bioisosteric replacement of the labile P–O bond is widely recognized as an attractive structural concept in different areas of medicinal chemistry, since it addresses the very fundamental principles of enzymatic stability and minimized metabolic activation. This review discusses the most influential successes in drug design with special emphasis on nucleoside phosphonates and their prodrugs as antiviral and cancer treatment agents. A description of structurally related analogs able to interfere with the transmission of other infectious diseases caused by pathogens like bacteria and parasites will then follow. Finally, molecules acting as agonists/antagonists of P2X and P2Y receptors along with nucleotidase inhibitors will also be covered. This review aims to guide readers through the fundamentals of nucleoside phosphonate therapeutics in order to inspire the future design of molecules to target infections that are refractory to currently available therapeutic options.

Structure controlled solvatochromism and halochromic fluorescence switching of 2,2′-bipyridine based donor–acceptor derivatives

Simple donor–acceptor derivatives were prepared by substituting alicyclic amines into the 2,2′-bipyridine (Bpy) core unit and they exhibited substituent and structure dependent  tunable and switchable fluorescence.

Pyrrolidine nucleoside bisphosphonates as antituberculosis agents targeting hypoxanthine-guanine phosphoribosyltransferase

Therapeutic treatment of tuberculosis (TB) is becoming increasingly problematic due to the emergence of drug resistant Mycobacterium tuberculosis (Mt). Thus, new targets for anti-TB drug discovery need to be identified to combat and eradicate this disease. One such target is hypoxanthine-guanine phosphoribosyltransferase (HGPRT) which synthesises the 6-oxopurine nucleoside monophosphates essential for DNA/RNA production. [3R,4R]-4-Hypoxanthin-9-yl-3-((S)-2-hydroxy-2-phosphonoethyl)oxy-1-N-(phosphonopropionyl)pyrrolidine and [3R,4R]-4-guanin-9-yl-3-((S)-2-hydroxy-2-phosphonoethyl)oxy-1-N-(phosphonopropionyl)pyrrolidine (compound 6) are the most potent inhibitors of MtHGPRT yet discovered having K_i values of 60 nM. The crystal structure of the MtHGPRT.6 complex was obtained and compared with that of human HGPRT in complex with the same inhibitor. These structures provide explanations for the 60-fold difference in the inhibition constants between these two enzymes and a foundation for the design of next generation inhibitors. In addition, crystal structures of MtHGPRT in complex with two pyrrolidine nucleoside phosphosphonate inhibitors plus pyrophosphate provide insights into the final stage of the catalytic reaction. As the first step in ascertaining if such compounds have the potential to be developed as anti-TB therapeutics, the tetra-(ethyl L-phenylalanine) tetraamide prodrug of 6 was tested in cell based assays. This compound arrested the growth of virulent Mt not only in its replicating phase (IC₅₀ of 14 μΜ) but also in its latent phase (IC₅₀ of 29 μΜ). Furthermore, it arrested the growth of Mt in infected macrophages (MIC₅₀ of 85 μΜ) and has a low cytotoxicity in mammalian cells (CC₅₀ of 132 ± 20 μM). These inhibitors are therefore viewed as forerunners of new anti-TB chemotherapeutics.

Molecular mutagenesis of ppGpp: turning a RelA activator into an inhibitor

The alarmone nucleotide (p)ppGpp is a key regulator of bacterial metabolism, growth, stress tolerance and virulence, making (p)ppGpp-mediated signaling a promising target for development of antibacterials. Although ppGpp itself is an activator of the ribosome-associated ppGpp synthetase RelA, several ppGpp mimics have been developed as RelA inhibitors. However promising, the currently available ppGpp mimics are relatively inefficient, with IC₅₀ in the sub-mM range. In an attempt to identify a potent and specific inhibitor of RelA capable of abrogating (p)ppGpp production in live bacterial cells, we have tested a targeted nucleotide library using a biochemical test system comprised of purified Escherichia coli components. While none of the compounds fulfilled this aim, the screen has yielded several potentially useful molecular tools for biochemical and structural work.

Regioselective Palmitoylation of 9-(2,3-Dihydroxy- propyl)adenine Catalyzed by a Glycopolymer-enzyme Conjugate

The enzymatic regioselective monopalmitoylation of racemic 9-(2,3-dihydroxypropyl)- adenine (DHPA), an approved antiviral agent, has been performed by an immobilized form of Candida antarctica B lipase (CAL-B) using a 4:1 DMF/hexane mixture as the reaction medium. To improve the chemical yield of the desired monopalmitoylation reaction, solid-phase chemical modifications of the lipase were evaluated. The reaction yield was successfully increased obtaining 100% product after a second treatment of the product solution with fresh immobilised chemically glycosylated-CAL-B.

Base catalysed intermolecular cyclisation of N-protected o-amino benzaldehyde/acetophenone with phosphorus/sulphur based allenes: facile synthesis of substituted quinolines

Base catalyzed reaction of N-Bz protected o-aminobenzaldehyde with allenylphosphonates affords O-phosphorylated quinolines via a route involving a thermal rearrangement.