Design of chiral bis-phosphoric acid catalyst derived from (R)-3,3'-di(2-hydroxy-3-arylphenyl)binaphthol: catalytic enantioselective Diels-Alder reaction of α,β-unsaturated aldehydes with amidodienes

Chiral bis-phosphoric acid 1 was designed to identify a new class of structural features in chiral Br?nsted acid catalysts. X-ray diffraction analysis revealed the single atropisomer 1, bearing S axial chirality at 3,3'-biaryl substituents on (R)-binaphthyl and intramolecular hydrogen bonding between the two phosphoric acid moieties. The newly designed bis-phosphoric acid 1 was evaluated in the Diels-Alder reaction of α,β-unsaturated aldehydes 4 with 1-N-acylamino-1,3-butadienes 3. After systematic variation of the catalyst substituents, as well as the N-acyl substituents of 1,3-butadiene, the use of an N-Cbz amidodiene 3a in the presence of bis-phosphoric acid 1e with a 2,4,6-tri-isopropylphenyl group was found to be optimal to yield the 1S,6R enantiomeric product 5aa in a Diels-Alder reaction of acrolein (4a). Application of this method to substituted substrates was found to be an efficient approach to the enantioselective synthesis of 3- and 3,6-substituted cyclic formylcarbamates 5. The specific character as well as the utility of 1e was further established by comparing its enantioselectivity, absolute stereochemistry, and catalytic efficiency with those of mono-phosphoric acid 2.     

Influence of particle design on oral absorption of poorly water-soluble drug in a silica particle-supercritical fluid system

The physicochemical characteristics and oral absorption of a poorly water-soluble drug, K-832, adsorbed onto porous silica (Sylysia 350), were compared with those of K-832 adsorbed onto non-porous silica (Aerosil 200). K-832 and silica were treated with supercritical CO(2) (scCO(2)) to produce K-832-Sylysia 350 and K-832-Aerosil 200 formulations. Scanning electron microscopy, polarizing microscopy, powder X-ray diffraction, and differential scanning calorimetry results suggested that K-832 mainly existed in an amorphous state in both formulations. The specific surface area of both formulations was much larger than that of pure K-832 crystals. The dissolution rate of K-832 from both formulations was considerably greater than that from corresponding physical mixtures due to rapid wetting of the hydrophilic carrier surfaces and amorphous state, the dissolution from the K-832-Sylysia 350 formulation being the fastest. In vivo absorption tests on the two formulations indicated no significant differences in their peak concentration (C(max)) and the area under their plasma concentration-time curve (AUC), while the concentrations of K-832 in the K-832-Sylysia 350 formulation were significantly higher than those in the K-832-Aerosil 200 formulation 1 h and 1.5 h after administration of these formulations (p<0.05). This could be attributed to the different dispersion states of K-832 in the formulations due to their different three-dimensional structures (porous and non-porous). In physical stability tests, the amorphous drugs in both formulations were stable at room temperature for at least 14 months. Thus, the absorption of poorly water-soluble drugs could be greatly improved by adsorption onto porous silica using scCO(2).     

Preconcentration of palladium(II) from water with thionalide loaded on silica gel

2-Mercapto-N-2-naphthylacetamide (thionalide) on silica gel is used for rapid preconcentration of μg l^?1 levels of palladium(II) from aqueous solution, followed by atomic absorption spectrometric measurement. In batch experiments, palladium was quantitatively retained on the gel from solutions 5 M in acid to pH 8; equilibrium was achieved within 10 s. The chelating capacity of the gel was 7.5 μmol Pd g^?1 at pH < 4. The effect of flow rate on retention was studied. Palladium retained on the column was completely eluted with 20 ml of 0.2 M thiourea in 0.1 M hydrochloric acid. The palladium concentration in sea water is shown to be < 0.3 μg l^?1.