Preparation of 3-(10′-halo-9′-anthracenyl) isoxazolecarboxylic esters

Syntheses and crystal structures of a nitro–anthracene–isoxazole and its oxidation product

The title compounds arose as unexpected by-products of an iodination reaction: in each case the fused-ring and isoxazole planes are almost perpendicular to each other.

The syntheses and structures of an unexpected by-product from an iodination reaction, namely, ethyl 5-methyl-3-(10-nitro­anthracen-9-yl)isoxazole-4-carb­oxy­l­ate, C₂₁H₁₆N₂O₅, (I), and its oxidation product, ethyl 3-(9-hy­droxy-10-oxo-9,10-di­hydro­anthracen-9-yl)-5-methyl­isoxazole-4-carboxyl­ate, C₂₁H₁₇NO₅ (V) are described. Compound (I) crystallizes with two mol­ecules in the asymmetric unit in which the dihedral angles between the anthracene fused-ring systems and isoxazole ring mean planes are 88.67 (16) and 85.64 (16)°; both mol­ecules feature a disordered nitro group. In (V), which crystallizes with one mol­ecule in the asymmetric unit, the equivalent dihedral angle between the almost planar anthrone ring system (r.m.s. deviation = 0.029 Å) and the pendant isoxazole ring is 89.65 (5)°. In the crystal of (I), the mol­ecules are linked by weak C—H⋯O inter­actions into a three-dimensional network and in the extended structure of (V), inversion dimers linked by pairwise O—H⋯O hydrogen bonds generate R₂²(14) loops.

9-Anthraldehyde oxime: a synthetic tool for variable applications

Abstract

Oximes are one of the most important and prolific functional groups in organic chemistry; among them, 9-anthraldehyde oxime represents a valuable example both from the preparative side and the synthetic applications. There are many strategies to prepare 9-anthraldehyde oxime from different functional groups that were summarized in the present review, focusing on the most recent and innovative. The main synthetic applications of 9-anthraldehyde oxime are presented and thoroughly discussed, focusing on the most recent and innovative synthetic strategies.

Graphic abstract

AIMing towards improved antitumor efficacy

Using the structure-activity relationship emerging from previous Letter, and guided by pharmacokinetic properties, new AIMs have been prepared with both improved efficacy against human glioblastoma cells and cell permeability as determined by fluorescent confocal microscopy. We present our first unambiguous evidence for telomeric G4-forming oligonucleotide anisotropy by NMR resulting from direct interaction with AIMs, which is consistent with both our G4 melting studies by CD, and our working hypothesis. Finally, we show that AIMs induce apoptosis in SNB-19 cells.

Ethyl 3-(9-chloro-10-oxo-9,10-di-hydro-anthracen-9-yl)-5-methyl-isoxazole-4-carboxyl-ate

The asymmetric unit of the title compound, C21H16ClNO4, contains two independent mol-ecules (A and B), each adopting a conformation wherein the isoxazole ring is roughly orthogonal to the anthrone ring. The dihedral angle between the mean plane of the isoxazole (all atoms) and the mean plane of the anthrone (all atoms) is 88.48 (3)° in one mol-ecule and 89.92 (4)° in the other. The ester is almost coplanar with the isoxazole ring, with mean-plane dihedral angles of 2.48 (15) and 8.62 (5)°. In both mol-ecules, the distance between the ester carbonyl O atom and the anthrone ketone C atom is about 3.3 Å. The anthrone ring is virtually planar (r.m.s. deviations of 0.070 and 0.065 Å) and adopts a shallow boat conformation in each mol-ecule, as evidenced by the sum of the six intra-B-ring torsion angles [41.43 (15) and 34.38 (15)° for molecules A and B, respectively]. The closest separation between the benzene moieties of anthrones A and B is 5.1162 (7) Å, with an angle of 57.98 (5)°, consistent with an edge-to-face π-stacking inter-action. In the crystal, weak C-H⋯O and C-H⋯N inter-actions link the mol-ecules, forming a three-dimensional network.

Fluorescent probes of the isoxazole-dihydropyridine scaffold: MDR-1 binding and homology model

Isoxazole-1,4-dihydropyridines (IDHPs) were tethered to fluorescent moieties using double activation via a lanthanide assisted Weinreb amidation. IDHP-fluorophore conjugate 3c exhibits the highest binding to date for IDHPs at the multidrug-resistance transporter (MDR-1), and IDHP-fluorophore conjugates 3c and 7 distribute selectively in SH-SY5Y cells. A homology model for IDHP binding at MDR-1 is presented which represents our current working hypothesis.

Ethyl 3-(10-bromo-anthracen-9-yl)-5-methyl-1,2-oxazole-4-carboxyl-ate

In the title compound, C21H16BrNO3, the mean planes of the anthracene tricycle and isoxazole ring are inclined to each other at a dihedral angle of 72.12 (7)°. The carb-oxy group is slightly out of the isoxazole mean plane, with a maximum deviation of 0.070 (5) Å for the carbonyl O atom. In the crystal, pairs of weak C-H⋯O hydrogen bonds link the mol-ecules into dimers, and weak C-H⋯N inter-actions further link these dimers into corrugated layers parallel to the bc plane.

Improved synthesis of 3-aryl isoxazoles containing fused aromatic rings

A critical comparison of methods to prepare sterically hindered 3-aryl isoxazoles containing fused aromatic rings using the nitrile oxide cycloaddition (NOC) reveal that modification of the method of Bode, Hachisu, Matsuura, and Suzuki (BHMS), utilizing either triethylamine as base or sodium enolates of the diketone, ketoester, and ketoamide dipolarophiles, respectively, was the method of choice for this transformation.

Bis-anthracenyl isoxazolyl amides have enhanced anticancer activity

Dimeric analogs of Anthracenyl Isoxazole Amides (AIMs) (the designation AIM is in honor of the memory of Professor Albert I. Meyers) were prepared and dimer 6 exhibited the highest efficacy to date for this class of anti-tumor compounds against the human glioma Central Nervous System cell line SNB-19.

3-(10-Chloro-9-anthryl)-5-[3-(prop-2-ynyloxy)phenoxymethyl]isoxazole

In the title molecule, C27H18ClNO3, the anthracene mean plane forms dihedral angles of 67.43 (2) and 15.75 (3)° with the isoxazole and benzene rings, respectively. In the crystal structure, C—H...π interactions link molecules into centrosymmetric dimers, which are further linked by weak intermolecular C—H...N hydrogen bonds into ribbons propagating in the [110] direction.

Design, synthesis and biological evaluation of a novel class of anticancer agents: anthracenylisoxazole lexitropsin conjugates

The synthesis and in vitro anti-tumor 60 cell lines screen of a novel series of anthracenyl isoxazole amides (AIMs) (While not a strict acronym, the designation AIM is in honor of the memory of Professor Albert I. Meyers.) (22-33) are described. The molecules consist of an isoxazole that pre-organizes a planar aromatic moiety and a simple amide and/or lexitropsin-oligopeptide. The new conjugate molecules were prepared via doubly activated amidation modification of Weinreb's amide formation technique, using SmCl(3) as an activating agent which produces improved yields for sterically hindered 3-aryl-4-isoxazolecarboxylic esters. The results of the National Cancer Institute's (NCI) 60 cell line screening assay show a distinct structure activity relationship (SAR), wherein a trend of the highest activity for molecules with one N-methylpyrrole peptide. Evidence consistent with a mechanism of action via the interaction of these compounds with G-quadruplex (G4) DNA and a structural based rational for the observed selectivity of the AIMs for G4 over B-DNA is presented.