Nitric Acid on Silica Gel: A Useful Nitrating Reagent for Activated Aromatic Compounds

Photoelectrocyclization Reactions of Amidonaphthoquinones

Readily available acrylamide naphthoquinones can be converted into the corresponding aza-anthraquinones using 6π-photoelectrocyclization reactions. Not only do these reactions not proceed thermally but, as demonstrated here, they can also be used to generate a range of aza-anthraquinone and aza-tetracycline derivatives including the natural products griffithazanone A and marcanine A. Several of the aza-anthraquinones generated in this work showed antibacterial activity.

One-pot Nitration of Phenols under Mild and Heterogeneous Conditions

Nitrophenols can be obtained via nitrosation–oxidation of phenols with Oxone®, NaNO2 and wet SiO2 at room temperature in moderate to high yields. In situ generation of HNO2 and the radical cation mechanism via the nitrous acid catalysed (NAC) pathway or hydrogen abstraction involving NO2 appear to be applicable to phenol nitration using these reagents.

Silica gel-mediated organic reactions under organic solvent-free conditions

Silica gel was found to be an excellent medium for some useful organic transformations under organic solvent-free conditions, such as (1) the Friedel-Crafts-type nitration of arenes using commercial aqueous 69% nitric acid alone at room temperature, (2) one-pot Wittig-type olefination of aldehydes with activated organic halides in the presence of tributyl- or triphenylphosphine and Hunig's base, and (3) the Morita-Baylis-Hillman reaction of aldehydes with methyl acrylate. After the reactions, the desired products were easily obtained in good to excellent yields through simple manipulation.

Transfer, amplification, and inversion of helical chirality mediated by concerted interactions of C3-supramolecular dendrimers

The synthesis, structural, and retrostructural analysis of two libraries containing 16 first and second generation C(3)-symmetric self-assembling dendrimers based on dendrons connected at their apex via trisesters and trisamides of 1,3,5-benzenetricarboxylic acid is reported. A combination of X-ray diffraction and CD/UV analysis methods demonstrated that their C(3)-symmetry modulates different degrees of packing on the periphery of supramolecular structures that are responsible for the formation of chiral helical supramolecular columns and spheres self-organizable in a diversity of three-dimensional (3D) columnar, tetragonal, and cubic lattices. Two of these periodic arrays, a 3D columnar hexagonal superlattice and a 3D columnar simple orthorhombic chiral lattice with P222(1) symmetry, are unprecedented for supramolecular dendrimers. A thermal-reversible inversion of chirality was discovered in helical supramolecular columns. This inversion is induced, on heating, by the change in symmetry from a 3D columnar simple orthorhombic chiral lattice to a 3D columnar hexagonal array and, on cooling, by the change in symmetry from a 2D hexagonal to a 2D centered rectangular lattice, both exhibiting intracolumnar order. A first-order transition from coupled columns with long helical pitch, to weakly or uncorrelated columns with short helical pitch that generates a molecular rotator, was also discovered. The torsion angles of the molecular rotator are proportional to the change in temperature, and this effect is amplified in the case of the C(3)-symmetric trisamide supramolecular dendrimers forming H-bonds along their column. The structural changes reported here can be used to design complex functions based on helical supramolecular dendrimers with different degree of packing on their periphery.

Silica Sulfuric Acid/ NaNO2 as a Novel Heterogeneous System for the Nitration of Phenols under Mild Conditions

Nitrophenols can be obtained in moderate to high yields via nitrosation-oxidation of phenols with silica sulfuric acid, NaNO₂ and wet SiO₂ at room temperature. In situ generation of HNO₂ and a radical cation mechanism via the nitrous acid catalyzed (NAC) pathway appear to be applicable to phenol nitration using these reagents.

Studies on quinones. Part 37. Synthesis and biological activity of o-aminoester functionalised benzo- and naphtho[2,3-b]thiophenequinones

The synthesis of 3-amino-2-methoxycarbonyl-4,7-dimethoxybenzo[b]thiophene (5) and benzothieno[3,2-d][1,3]oxazin 15 from 3,6-dimethoxy-2-nitrobenzaldehyde (1) is reported. Benzo[b]thiophene-4,7-quinones 9 and 10 were prepared in good yields by oxidative deprotection of the corresponding dimethoxybenzothiophenes 8 and 7. Cycloaddition reaction of quinone 8 with 1-(E)-trimethylsilyloxy-1,3-butadiene followed by acid-induced aromatization provides access to naphtho[2,3-b]thiophene-4,9-quinone 13 and 14. The in vitro activity of the new quinones against Leishmania amazonensis and human-T-cell leukemia virus type 1 (HTLV-1) is reported.

Nitration Of Phenols Under Mild And Heterogeneous Conditions

Nitrophenols can be obtained in moderate to high yields using a combination of Mg(HSO₄)₂ or NaHSO₄.H₂O, NaNO₃ and wet SiO₂ in dichloromethane at room temperature.

Improved P1/P1' substituents for cyclic urea based HIV-1 protease inhibitors: synthesis, structure-activity relationship, and X-ray crystal structure analysis

We present several novel P1/P1' substituents that can replace the characteristic benzyl P1/P1' moiety of the cyclic urea based HIV protease inhibitor series. These substituents typically provide 5-10-fold improvements in binding affinity compared to the unsubstituted benzyl analogs. The best substituent was the 3,4-(ethylenedioxy)benzyl group. Proper balancing of the molecule's lipophilicity facilitated the transfer of this improved binding affinity into a superior cellular antiviral activity profile. Several analogs were evaluated further for protein binding and resistance liabilities. Compound 18 (IC90 = 8.7 nM) was chosen for oral bioavailability studies based on its log P and solubility profile. A 10 mg/kg dose in dogs provided modest bioavailability with Cmax = 0.22 microg/mL. X-ray crystallographic analysis of two analogs revealed several interesting features responsible for the 3,4-(ethylenedioxy)benzyl-substituted analog's potency: (1) Comparing the two complexes revealed two distinct binding modes for each P1/P1' substituent; (2) The ethylenedioxy moieties are within 3.6 A of Pro 81 providing additional van der Waals contacts missing from the parent structure; (3) The enzyme's Arg 8 side chain moves away from the P1 substituent to accommodate the increased steric volume while maintaining a favorable hydrogen bond distance between the para oxygen substituent and the guanidine NH.