Epimerization and racemization of some chiral drugs in the presence of cyclodextrin and liposomes

The effects of alpha-, beta-, gamma- and dimethyl-beta-cyclodextrins (alpha-, beta-, gamma- and DM-beta-CyDs) and liposomes on epimerization or racemization of etoposide, ethiazide and carbenicillin were examined kinetically. alpha- and beta-CyDs accelerated both epimerization and hydrolysis of carbenicillin. They had no effect on epimerization of etoposide, and did not affect racemization and hydrolysis of ethiazide. DM-beta-CyD retarded epimerization of etoposide, hydrolysis of picroetoposide (which is an epimer of etoposide), and racemization and hydrolysis of ethiazide, but had no effect on epimerization and hydrolysis of carbenicillin. gamma-CyD retarded epimerization of etoposide and hydrolysis of picroetoposide. On the other hand, gamma-CyD accelerated epimerization of carbenicillin. It is suggested that the formation of inclusion complexes between CyDs and etoposide, picroetoposide and ethiazide inhibited the attack of bases such as OH- and buffer components, thereby retarding epimerization, racemization and hydrolysis. On the other hand, alpha-, beta- and gamma-CyDs increased the reactivity of carbenicillin through the OH group, accelerating its epimerization and hydrolysis. Liposomes retarded epimerization of etoposide, hydrolysis of picroetoposide and racemization of ethiazide. Liposomes did not affect epimerization and hydrolysis of carbenicillin. These differences in the effect of liposomes on reactivity may be interpreted in terms of the solubility of the drugs.     

Structure of the photocolored 2-(2',4'-dinitrobenzyl)pyridine crystal: two-photon induced solid-state proton transfer with minor structural perturbation

The X-ray structure of the blue phototautomer of 2-(2',4'-dinitrobenzyl)pyridine (DNBP) produced by two-photon excitation in a single crystal is the first direct evidence of a product in the DNBP photochromic family. A nitro-assisted proton transfer mechanism is attributed to the photocoloration of solid DNBP.     

Extended Hartree-Fock (EHF) theory in chemical reactions

The roles of orbital, spin and permutation symmetries in the extended Hartree-Fock (EHF) wavefunction are investigated in relation to the applications of group theory to chemical reactions. The utility of the magnetically ordered set for an extended HF calculation is pointed out. The relative stabilities among linear Hückel and Möbius three-center three-electron (3,3) systems are investigated by the generalized Hartree-Fock (GHF) and EHF methods in order to confirm the reliability of the valence-bond (VB) selection rule for free radical reactions.     

Theoretical studies on structures and reactivities of organocuprate(I) and organocopper(III) species

Systematic evaluation of method and basis set on the structure and energetics of organocuprate(I) and organocopper(III) species has been carried out. Various structures of organocuprate(I) and organocuprate(III) complexes were optimized with the HF, MP2, and B3LYP methods, and compared with the structures determined by X-ray crystallography (i.e., Me(2)Cu(I)(-), (CF(3))(4)Cu(III)(-)). Both the MP2 and B3LYP methods reasonably reproduce the X-ray structures while the HF method does not. Using larger basis set and incorporating the relativistic effects for Cu afford the best results. In the studies on the energetics of a Libond;Cu cluster model (Me(2)CuLi. LiCl) and Me(3)Cu model with the MP2, MP3, MP4DQ, MP4SDQ, CCSD(T), and B3LYP methods, the B3LYP method gives energetics similar to those obtained with the CCSD(T) method with much less cost, and hence, is judged to be the best practical method. The studies have shown that B3LYP method with the basis set incorporating the relativistic effective core potentials for Cu and the 6-31G* basis set for the rest is the theoretical method that is the most cost-effective for the studies of the structure and energetics of organocuprate(I) and organocopper(III) species.     

Chemoselective fluorination for primary alcohols

Primary alcohols and their silylated derivatives are selectively fluorinated by tetraalkylammonium fluoride and aryl (or alkyl )sulfonyl fluoride.     

Effect of tea catechins on the structure of lipid membrane and beta-ray induced lipid peroxidation

Inhibiting effect of four tea catechins, (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCG), on the lipid peroxidation induced by β-ray in tritiated water was examined using a spin probe method. 16-Doxylstearic acid (16NS) was incorporated into the liposome prepared from egg yolk phosphatidylcholine and the rate of the decrease of ESR intensity of 16NS was used as a measure of the inhibiting effect. In the low concentration region below 10⁻⁵M, catechins showed their inhibitions on the lipid peroxidation according to the order of ECG>EGCG>EC>EGC. This result was explained by a model that the initiator of the peroxidation is the hydroxyl radical (·OH) and the catechins adsorbed on the lipid membrane surface acting as scavengers of ·OH. In the high concentration range, however, the effect was diverse and it decreased with the increase of it in the case of EGCG. EGCG in this range was considered to enter into the interior of the membrane and break the structure, which causes the decrease of 16NS. Observation with transmission electron microscope (TEM) revealed that the size of the liposome became larger with the increasing concentration of EGCG and finally it was broken into fragments, showing that EGCG broadened the area of the liposome as expected from the result of ESR.     

Stereocontrolled,straightforward synthesis of 3-substituted methyl 7α-methoxy-1-oxacephems

Stereocontrolled and industrially feasible synthesis of a new antibiotic $\text{1a}$ and related derivatives, which is characterized by using all the carbon atoms of the penicillin skeleton, is described.     

Kinetic studies of AMP-dependent phosphorolysis of amylopectin catalyzed by phosphorylase b on a 27 MHz quartz-crystal microbalance

Catalytic cleavage reactions of phosphorylase b were monitored directly on an amylopectin-immobilized 27 MHz quartz-crystal microbalance (QCM). When the inactivated phosphorylase b was injected into a phosphate buffer solution of amylopectin-immobilized QCM (method A), the binding of the enzyme to amylopectin was observed as a frequency decrease (mass increase). Then, when AMP (adenosine monophosphate) was added to activate the enzyme, the frequency gradually increased (mass decreased) due to the phosphorolysis of amylopectin in the presence of phosphates as buffers. When the AMP-activated phosphorylase b was employed (method B), the continuous reaction was observed which includes both the mass increase due to the enzyme binding to amylopectin at first and then the following mass decrease due to the phosphorolysis by the AMP-activated enzyme. All kinetic parameters for the enzyme binding to the substrate (binding and dissociation rate constants, k(on) and k(off), and dissociation constant, K(d)), the AMP binding to the enzyme as activator (K(AMP)), the catalytic rate constant (k(cat)) were obtained from curve fittings of time-courses of frequency (mass) changes. The obtained kinetic parameters were compared with those from Michaelis-Menten kinetics.     

Ab initio MO calculation of force constants and dipole derivatives for the formamide dimer. An estimation of hydrogen-bond force constants

Ab initio SCF MO calculations (with the 4-31G basis set) have been carried out to determine the equilibrium geometry, vibrational frequencies, dipole-moment derivatives, and force constants for intermolecular modes of the formamide dimer and its d₄ and d₆ derivatives. The results are correlated with monomer calculations and experimental data for crystalline formamide.     

Conjugate addition of aromatic amines to ethenetricarboxylates

The conjugate addition of amines is considered to be a useful reaction in synthetic organic chemistry. The reaction of reactive electrophilic olefins, ethenetricarboxylates, and aromatic amines with and without catalytic Lewis acids such as ZnCl₂ and ZnBr₂ at room temperature gave amine adducts in high yields. The products were converted to α-amino acid, dl-aspartic acid derivatives. Using Lewis acids such as Sc(OTf)₃ and Zn(OTf)₂ at higher temperature (40-80 °C), the reaction of ethenetricarboxylates and N-methylaniline gave an aromatic substitution product. A catalytic enantioselective conjugate addition using a chiral Lewis acid was also investigated. For example, the reaction of 1,1-diethyl 2-tert-butyl ethenetricarboxylate with N-methylaniline in the presence of chiral bisoxazoline-Cu(II) complex in THF at −20 °C for 17 h gave an amine adduct in 91% yield and 78% ee. On the other hand, the reaction with aniline and primary aniline derivatives gave adducts with almost no ee%.