Improvement of Dispersion and Release Properties of Nifedipine in Suppositories by Complexation with 2-Hydroxypropyl-β-cyclodextrin

Geometries, electronic properties and NMR-shielding of cucurbit[5]uril, decamethylcucurbit[5]uril, cucurbit[6]uril, cucurbit[7]uril, and cucurbit[8]uril are investigated with DFT calculations. All molecules are highly symmetrical with a distinct geometric flexibility. In addition with a characteristic partial charge distribution these findings account for their chemical complex building ability.     

Improvement of some pharmaceutical properties of nocloprost by β- and γ-Cyclodextrin Complexation

Inclusion complexation of nocloprost, a potent antiulcer prostaglandin derivative, with -, -, and -cyclodextrins (CyDs) in aqueous solutions has been studied by the solubility method and¹³C-NMR spectroscopy. The steric requirement of host-guest interaction was reflected in the magnitude of the stability constants and the thermodynamic parameters of the inclusion complexes. Solid complexes of nocloprost with - and -CyDs in a molar ratio of 1 : 2 were obtained on the basis of aBs-type phase solubility diagram. The X-ray diffraction data suggested that nocloprost is included in the cylindrical channel formed by coaxial alignment of -CyD molecules to give a channel type structure. Release and thermal behavior of the solid complexes was examined and compared with nocloprost itself. The results indicated that the -CyD complex may have great utility among the three CyDs, being a rapid dissolving form of nocloprost with improved thermal stability.     

Ru3(CO)12-catalyzed silylation of benzylic C-H bonds in arylpyridines and arylpyrazoles with hydrosilanes via C-H bond cleavage

Ruthenium-catalyzed silylation of sp3 C-H bonds at a benzylic position with hydrosilanes gave benzylsilanes. For this silylation reaction, Ru3(CO)12 complex showed high catalytic activity. This silylation proceeded at the methyl C-H bond selectively. For this silylation reaction, pyridyl and pyrazolyl groups, and the imino group in hydrazones, can function as a directing group. Several hydrosilanes involving triethyl-, dimethylphenyl-, tert-butyldimethyl-, and triphenylsilanes can be used as a silylating reagent. Coordination of an sp2 nitrogen atom to the ruthenium complex is important for achieving this silylation reaction.     

The influence of polytypic structures on the M011-->M101 solid-solid phase transition of n-C36H74: an application of the oblique infrared transmission method

The molecular displacements on the M011-->M101 phase transition of n-hexatriacontane (n-C36H74) have been investigated with an IR microscope designed for the oblique infrared transmission method. It has been clarified that two polytypic structures of the M011 modification, single-layered structure (Mon) and double-layered one (Orth II), both transform to the M101 modification of single-layered structure with their respective mechanisms. On the M011(Mon)-->M101 transition, the inclination direction of molecular axis is changed by 90 degrees through an intermediate state in which the molecular chain is set perpendicular to the basal plane of the single crystal. On the other hand, a polymorphic-polytypic composite structural change on the M011(Orth II)-->M101 transition is accomplished through two kinds of molecular displacements occurring alternately along the stacking direction of molecular layers.     

Study of thermodynamic stabilities of polytypes of n-C36H74 by solubility measurements and incoherent inelastic neutron scattering

The thermodynamic properties of the two polytypes of n-hexatriacontane (n-C36H74), single-layered structure Mon and double-layered structure Orth II have been investigated by means of solubility measurements and incoherent inelastic neutron scattering. The solubility measurements reveal that Orth II is more stable than Mon by 1.2 kJ/mol because of the advantage of larger entropy. The neutron scattering measurements show that the vibrational modes of Orth II shift to the lower frequencies compared with those of Mon in the frequency region below 120 cm(-1). The advantage of Orth II in vibrational entropy due to the low-frequency shifts is estimated to be 9.6 J K(-1)/mol at 288 K under the harmonic approximation, which nearly agrees with the entropy difference of 6.8 J K(-1)/mol between Mon and Orth II determined by solubility measurements. These results suggest that the difference in vibrational entropy due to low-frequency modes mainly contributes to the relative thermodynamic stabilities of polytypic structures of long-chain compounds. From the frequency of methyl torsional mode, it is suggested that the cohesive force at the lamellar interface is stronger in Mon than in Orth II.     

Synthesis of Arenethiolate Complexes of Divalent and Trivalent Lanthanides from Metallic Lanthanides and Diaryl Disulfides: Crystal Structures of [{Yb(hmpa)(3)}(2)(&mgr;-SPh)(3)][SPh] and Ln(SPh)(3)(hmpa)(3) (Ln = Sm, Yb; hmpa = Hexamethylphosphoric Triamide)

A convenient and one-pot synthetic method of lanthanide thiolate compounds was developed. An excess of metallic samarium, europium, and ytterbium directly reacted with diaryl disulfides in THF to give selectively Ln(II) thiolate complexes, [Ln(SAr)(&mgr;-SAr)(thf)(3)](2) (1, Ln = Sm; 2, Ln = Eu; Ar = 2,4,6-triisopropylphenyl), Yb(SAr)(2)(py)(4) (3, py = pyridine), and [{Ln(hmpa)(3)}(2)(&mgr;-SPh)(3)][SPh] (6, Ln = Sm; 7, Ln = Eu; 8, Ln = Yb; hmpa = hexamethylphosphoric triamide). Reaction of metallic lanthanides with 3 equiv of disulfides afforded Ln(III) thiolate complexes, Ln(SAr)(3)(py)(n)()(thf)(3)(-)(n)() (9a, Ln = Sm, n = 3; 9b, Ln = Sm, n = 2; 10, Ln = Yb, n = 3) and Ln(SPh)(3)(hmpa)(3) (11, Ln = Sm; 12, Ln = Eu; 13, Ln = Yb). Thus, Ln(II) and Ln(III) thiolate complexes were prepared from the same source by controlling the stoichiometry of the reactants. X-ray analysis of 8 revealed that 8 has the first ionic structure composed of triply bridged dinuclear cation and benezenethiolate anion [8, orthorhombic, space group P2(1)2(1)2(1) with a = 21.057(9), b = 25.963(7), c = 16.442(8) ?, V = 8988(5) ?(3), Z = 4, R = 0.040, R(w) = 0.039 for 5848 reflections with I > 3sigma(I) and 865 parameters]. The monomeric structures of 11 and 13 were revealed by X-ray crystallographic studies [11, triclinic, space group P&onemacr; with a = 14.719(3), b = 17.989(2), c = 11.344(2) ?, alpha = 97.91(1), beta = 110.30(2), gamma = 78.40(1) degrees, V = 2751.9(9) ?(3), Z = 2, R = 0.045, R(w) = 0.041 for 7111 reflections with I > 3sigma(I) and 536 parameters; 13, triclinic, space group P&onemacr; with a = 14.565(2), b = 17.961(2), c = 11.302(1) ?, alpha = 97.72(1), beta = 110.49(1), gamma = 78.37(1) degrees, V = 2706.0(7) ?(3), Z = 2, R = 0.031, R(w) = 0.035 for 9837 reflections with I > 3sigma(I) and 536 parameters]. A comparison with the reported mononuclear and dinuclear lanthanide thiolate complexes has been made to indicate that the Ln-S bonds weakened by the coordination of HMPA to lanthanide metals have ionic character.     

A ruthenium-catalyzed reaction of aromatic ketones with arylboronates: a new method for the arylation of aromatic compounds via C-H bond cleavage

The ruthenium-catalyzed reaction of aromatic ketones with arylboronic acid esters (arylboronates) gave the ortho arylation product. For this coupling reaction, a RuH2(CO)(PPh3)3 complex exhibited the highest catalytic activity among the complexes screened. Several aromatic ketones, for example, acetophenones, acetonaphthone, alpha-tetralone, and benzosuberone, can be used in this coupling reaction. A variety of arylboronates containing electron-donating (OMe and NMe2) and -withdrawing (F and CF3) groups were found to react with aromatic ketones to give the corresponding aylation products. The corresponding arylboronic acids could be used in this coupling reaction, but the yields were slightly lower, as compared to those of the reaction using the corresponding arylboronates.     

Some Pharmaceutical Properties of a New Branched Cyclodextrin, 6-O-α-(4-O- α-D-Glucuronyl)-D-glucosylβ-cyclodextrin

Some physicochemical and biological properties of a new branched cyclodextrin, 6-O--(4-O--d-glucuronyl)-d-glucosyl--cyclodextrin GUG--CyD) were investigated. Further, theinteraction of GUG--CyD with several drugs was studied by the solubility and spectroscopic methods, and compared with those of parent -CyD and 6-O--maltosyl--CyD(₂--CyD).The hemolytic activity of GUG--CyD on rabbit erythrocytes was lower than those of -CyD and ₂--CyD. GUG--CyD and ₂--CyD showed negligible cytotoxicity on Caco-2 cells up to at least 0.1 M. The inclusion ability of GUG--CyD to neutral and acidic drugs was comparable to or slightly smaller than those of -CyD and ₂--CyD, probably because of a steric hindrance of the branched sugar. On the other hand, GUG--CyD showed greater affinity for the basic drugs, compared with -CyD and ₂--CyD, owing to the electrostatic interaction of its carboxylate anion with positive charge of basic drugs. Thus GUG--CyD may be useful as a safe solubilizing agent particularly for basic drugs.