1,4-Benzodioxane, an evergreen, versatile scaffold in medicinal chemistry: A review of its recent applications in drug design

Convenient Preparation, Thermal Properties and X-ray Structure Determination of 2,3-Dihydro-5,6,7,8-tetranitro-1,4-benzodioxine (TNBD): A Promising High-Energy-Density Material

2,3-dihydro-5,6,7,8-tetranitro-1,4-benzodioxine (TNBD), molecular formula = C8H4N4O10, is a completely nitrated aromatic ring 1,4-benzodioxane derivative. The convenient method of TNBD synthesis was developed (yield = 81%). The detailed structure of this compound was investigated by X-ray crystallography. The results of the thermal analysis (TG) obtained with twice re-crystallized material revealed the onset at 240 °C (partial sublimation started) and melting at 286 °C. The investigated material degraded completely at 290-329 °C. The experimental density of 1.85 g/cm3 of TNBD was determined by X-ray crystallography. The spectral properties of TNBD (NMR, FT-IR and Raman) were explored. The detonation properties of TNBD calculated by the EXPLO 5 code were slightly superior in comparison to standard high-energy material-tetryl (detonation velocity of TNBD-7727 m/s; detonation pressure-278 kbar; and tetryl-7570 m/s and 226.4 kbar at 1.614 g/cm3, or 260 kbar at higher density at 1.71 g/cm3. The obtained preliminary results might suggest TNBD can be a potential thermostable high-energy and -density material (HEDM).

Benzodioxane-benzamides as promising inhibitors of Escherichia coli FtsZ

The conserved process of cell division in bacteria has been a long-standing target for antimicrobials, although there are few examples of potent broad-spectrum compounds that inhibit this process. Most currently available compounds acting on division are directed towards the FtsZ protein, a self-assembling GTPase that is a central element of the division machinery in most bacteria. Benzodioxane-benzamides are promising candidates, but poorly explored in Gram-negatives. We have tested a number of these compounds on E. coli FtsZ and found that many of them significantly stabilized the polymers against disassembly and reduced the GTPase activity. Reconstitution in crowded cell-like conditions showed that FtsZ bundles were also susceptible to these compounds, including some compounds that were inactive on protofilaments in dilute conditions. They efficiently killed E. coli cells defective in the AcrAB efflux pump. The activity of the compounds on cell growth and division generally showed a good correlation with their effect in vitro, and our experiments are consistent with FtsZ being the target in vivo. Our results uncover the detrimental effects of benzodioxane-benzamides on permeable E. coli cells via its central division protein, implying that lead compounds may be found within this class for the development of antibiotics against Gram-negative bacteria.

Advances in small molecule selective ligands for heteromeric nicotinic acetylcholine receptors

The study of nicotinic acetylcholine receptors (nAChRs) has significantly progressed in the last decade, due to a) the improved techniques available for structural studies; b) the identification of ligands interacting at orthosteric and allosteric recognition sites on the nAChR proteins, able to tune channel conformational states; c) the better functional characterization of receptor subtypes/subunits and their therapeutic potential; d) the availability of novel pharmacological agents able to activate or block nicotinic-mediated cholinergic responses with subtype or stoichiometry selectivity. The copious literature on nAChRs is related to the pharmacological profile of new, promising subtype selective derivatives as well as the encouraging preclinical and early clinical evaluation of known ligands. However, recently approved therapeutic derivatives are still missing, and examples of ligands discontinued in advanced CNS clinical trials include drug candidates acting at both neuronal homomeric and heteromeric receptors. In this review, we have selected heteromeric nAChRs as the target and comment on literature reports of the past five years dealing with the discovery of new small molecule ligands or the advanced pharmacological/preclinical investigation of more promising compounds. The results obtained with bifunctional nicotinic ligands and a light-activated ligand as well as the applications of promising radiopharmaceuticals for heteromeric subtypes are also discussed.

Efficient enzymatic synthesis of chiral 2,3-dihydro-1,4-benzodioxane motif using engineered Candida antarctica lipase B

Chiral motifs of 2,3-dihydro-1,4 benzodioxane are extensively utilized in diverse medicinal substances and bioactive natural compounds, exhibiting significant biological activities. Notable examples of such therapeutic agents include prosympal, dibozane, piperoxan, and doxazosin. In this work, using 1,4-benzodioxane-2-carboxylic acid methyl ester as the substrate, after screening 38 CALB covariant residues, we found that mutants A225F and A225F/T103A can catalyze the kinetic resolution of the substrate. The effect of temperature, cosolvent, and cosolvent concentration on kinetic resolution was investigated, revealing that the best results were achieved at 30 °C with 20% n-butanol as a cosolvent, resulting in an optimal resolution (e.e._s 97%, E = 278) at 50 mM substrate concentration. Structure analysis showed that mutation sites 225 and 103 are not among the sites that interact directly with the substrate, which means that covariant amino acids that interact remotely with the substrate also regulate enzyme catalysis. This research may provide us with a new strategy for enzyme evolution.

New and promising type of leukotriene B4 (LTB4) antagonists based on the 1,4-benzodioxine structure

New leukotriene B4 (LTB4) antagonists have been synthesized that can be considered as potential anti-inflammatory drugs. Structures containing the dioxygenated nucleus of 1,4-benzodioxine constitute a potential group of leukotriene B4 (LTB4) antagonists. The objective of this study was to access efficient and selective LTB4 antagonists as a way to elucidate the role of LTB4 in inflammatory processes and therefore allow the development of new types of structures based on 1,4-benzodioxine. Forty-one new 1,4-benzodioxine molecules substituted at different positions of the heterocyclic nucleus were synthesized to determine the minimum structural requirements by studying structure-activity relationships. Eighteen of them were tested in vitro and in vivo for their anti-inflammatory activity related to the antagonist character of LTB4. Pharmacological tests have shown satisfactory in vitro activity for compounds 24b, 24c and 24e with IC50's of 288, 439, 477 nM respectively. The results of the in vivo tests, carried out with the compound that presented greater activity in the in vitro tests 24b, have shown significant anti-inflammatory properties.

Tannins-Based Extracts: Effects on Gut Chicken Spontaneous Contractility

The impossibility of using drugs for the health of farm animals leads to the search for alternative strategies with two purposes: to maintain animal health and safeguard human health. In this perspective, tannins have shown great promises. These phytocomplexes obtained from natural matrices with multiple health properties may be used as a feed supplement in chicken farms. In this work, we studied two tannin-based extracts (from Castanea sativa Mill. wood and from Schinopsis balansae Engl. Quebracho Colorado hardwood) with different chemical compositions on the spontaneous contractility on the isolated intestinal tissues of healthy chicken. The results showed that the chemical composition of the two phytocomplexes influenced the spontaneous intestinal contractility in different ways by regulating the tone and consequent progression of the food bolus. The chemical analysis of the two extracts revealed that Castanea sativa Mill. wood mainly contains hydrolysable tannins, while Schinopsis balansae Engl. hardwood mainly contains condensed tannins. The two phytocomplexes showed different effects towards gastrointestinal smooth muscle contractility, with Castanea sativa Mill. wood providing a better activity profile than Schinopsis balansae Engl. hardwood.

Pyrrolidinyl benzofurans and benzodioxanes: Selective α4β2 nicotinic acetylcholine receptor ligands with different activity profiles at the two receptor stoichiometries

A series of racemic benzofurans bearing N-methyl-2-pyrrolidinyl residue at C(2) or C(3) has been synthesized and tested for affinity at the α4β2 and α3β4 nicotine acetylcholine receptors (nAChRs). As previously reported for the benzodioxane based analogues, hydroxylation at proper position of benzene ring results in high α4β2 nAChR affinity and α4β2 vs. α3β4 nAChR selectivity. 7-Hydroxy-N-methyl-2-pyrrolidinyl-1,4-benzodioxane (2) and its 7- and 5-amino benzodioxane analogues 3 and 4, which are all α4β2 nAChR partial agonists, and 2-(N-methyl-2-pyrrolidinyl)-6-hydroxybenzofuran (12) were selected for functional characterization at the two α4β2 stoichiometries, the high sensitivity (α4)₂(β2)₃ and the low sensitivity (α4)₃(β2)₂. The benzene pattern substitution, which had previously been found to control α4β2 partial agonist activity and α4β2 vs. α3β4 selectivity, proved to be also involved in stoichiometry-selectivity. The 7-hydroxybenzodioxane derivative 2 selectively activates (α4)₂(β2)₃ nAChR, which cannot be activated by its 5-amino analogue 4. A marginal structural modification, not altering the base pyrrolidinyl benzodioxane scaffold, resulted in opposite activity profiles at the two α4β2 nAChR isoforms providing an interesting novel case study.

Crystal structure of C10H10O4

C10H10O4, monoclinic, P21/c (no. 14), a = 9.464(6) Å, b = 10.302(7) Å, c = 10.589(7) Å, β = 114.174(11)°, V = 941.8(10) Å3, Z = 4, R gt (F) = 0.0453, wR ref(F 2) = 0.1394, T = 173 K.

Potential of the Compounds from Bixa orellana Purified Annatto Oil and Its Granules (Chronic®) against Dyslipidemia and Inflammatory Diseases: In Silico Studies with Geranylgeraniol and Tocotrienols

Some significant compounds present in annatto are geranylgeraniol and tocotrienols. These compounds have beneficial effects against hyperlipidemia and chronic diseases, where oxidative stress and inflammation are present, but the exact mechanism of action of such activities is still a subject of research. This study aimed to evaluate possible mechanisms of action that could be underlying the activities of these molecules. For this, in silico approaches such as ligand topology (PASS and SEA servers) and molecular docking with the software GOLD were used. Additionally, we screened some pharmacokinetic and toxicological parameters using the servers PreADMET, SwissADME, and ProTox-II. The results corroborate the antidyslipidemia and anti-inflammatory activities of geranylgeraniol and tocotrienols. Notably, some new mechanisms of action were predicted to be potentially underlying the activities of these compounds, including inhibition of squalene monooxygenase, lanosterol synthase, and phospholipase A₂. These results give new insight into new mechanisms of action involved in these molecules from annatto and Chronic^®.

Regioisomers Salviprolin A and B, Unprecedented Rosmarinic Acid Conjugated Dinorditerpenoids from Salvia przewalskii Maxim

Salvia przewalskii Maxim is a perennial plant from the genus Salvia (family Lamiaceae). The roots of S. przewalskii were long used as a traditional herb to treat blood circulation related illnesses in China. As part of our continuing interest in polycyclic natural products from medicinal plants, two unprecedented adducts comprised of a dinor-diterpenoid and a 9'-nor-rosmarinic acid derivative, linked by a 1,4-benzodioxane motif (1 and 2), were isolated from the roots of S. przewalskii. Their structures were established by extensive spectroscopic approaches including 1D, 2D NMR, and HRFABMS. Their cytotoxic activities against five human tumor cell lines were evaluated.

Uniting Amide Synthesis and Activation by PIII/PV-Catalyzed Serial Condensation: Three-Component Assembly of 2-Amidopyridines

An organophosphorus (P^III/P^V redox) catalyzed method for the three-component condensation of amines, carboxylic acids, and pyridine N-oxides to generate 2-amidopyridines via serial dehydration is reported. Whereas amide synthesis and functionalization usually occur under divergent reaction conditions, here a phosphetane catalyst (together with a mild bromenium oxidant and terminal hydrosilane reductant) is shown to drive both steps chemoselectively in an auto-tandem catalytic cascade. The ability to both prepare and functionalize amides under the action of a single organocatalytic reactive intermediate enables new possibilities for the efficient and modular preparation of medicinal targets.

Determinants for α4β2 vs. α3β4 Subtype Selectivity of Pyrrolidine-Based nAChRs Ligands: A Computational Perspective with Focus on Recent cryo-EM Receptor Structures

The selectivity of α4β2 nAChR agonists over the α3β4 nicotinic receptor subtype, predominant in ganglia, primarily conditions their therapeutic range and it is still a complex and challenging issue for medicinal chemists and pharmacologists. Here, we investigate the determinants for such subtype selectivity in a series of more than forty α4β2 ligands we have previously reported, docking them into the structures of the two human subtypes, recently determined by cryo-electron microscopy. They are all pyrrolidine based analogues of the well-known α4β2 agonist N-methylprolinol pyridyl ether A-84543 and differ in the flexibility and pattern substitution of their aromatic portion. Indeed, the direct or water mediated interaction with hydrophilic residues of the relatively narrower β2 minus side through the elements decorating the aromatic ring and the stabilization of the latter by facing to the not conserved β2-Phe119 result as key distinctive features for the α4β2 affinity. Consistently, these compounds show, despite the structural similarity, very different α4β2 vs. α3β4 selectivities, from modest to very high, which relate to rigidity/extensibility degree of the portion containing the aromatic ring and to substitutions at the latter. Furthermore, the structural rationalization of the rat vs. human differences of α4β2 vs. α3β4 selectivity ratios is here proposed.

Efficient conversion of d-mannitol into 1,2:5,6-diacetonide with Aquivion-H as a recyclable catalyst

Heterogeneous solid catalysis by the commercially available perfluorosulfonic ionomer Aquivion-H allowed 1,2:5,6-diacetonide of d-mannitol (1), immediate precursor of important unichiral C3-synthons, to be efficiently obtained from d-mannitol and 2,2-dimethoxypropane in DMF at room temperature. The 1,2-monoacetonide, whose intermediate formation is the rate-limiting step, could be almost completely converted into 1 with limited concurrent transformation of 1 into triacetonides. In line with recent literature reports, these results indicate that heterogeneous catalysis by Aquivion-H surpasses the performances of homogeneous acidic catalysis assuring, presumably for its peculiar morphology, a higher product selectivity. Easy recovery at the end of the reaction and recyclability are additional advantages of this solid acid catalyst.

Modifications at C(5) of 2-(2-Pyrrolidinyl)-Substituted 1,4-Benzodioxane Elicit Potent α4β2 Nicotinic Acetylcholine Receptor Partial Agonism with High Selectivity over the α3β4 Subtype

A series of diastereomeric 2-(2-pyrrolidinyl)-1,4-benzodioxanes bearing a small, hydrogen-bonding substituent at the 7-, 6-, or 5-position of benzodioxane have been studied for α4β2 and α3β4 nicotinic acetylcholine receptor affinity and activity. Analogous to C(5)H replacement with N and to a much greater extent than decoration at C(7), substitution at benzodioxane C(5) confers very high α4β2/α3β4 selectivity to the α4β2 partial agonism. Docking into the two receptor structures recently determined by cryo-electron microscopy and site-directed mutagenesis at the minus β2 side converge in indicating that the limited accommodation capacity of the β2 pocket, compared to that of the β4 pocket, makes substitution at C(5) rather than at more projecting C(7) position determinant for this pursued subtype selectivity.