Preparation and synthetic application of a novel ketene silyl acetal of methyl trifluoropyruvate

[reaction: see text] A novel trifluoromethyl ketene silyl acetal (4) of methyl trifluoropyruvate (1) was prepared in 82% yield by metal Mg reduction in a (TMS)Cl/THF system. Subsequent carbon-carbon bond formation such as Mukaiyama aldol, Michael addition, and other nucleophilic reactions of 4 at the trifluoromethylated carbon with various electrophiles gave various coupling products in high yields.     

Berberine/γ‐Cyclodextrin Inclusion Structure Studied by 1H‐NMR Spectroscopy and Molecular‐Dynamics Calculations

To understand the increased solubility and decreased bitter taste of berberine, a clinically important isoquinoline alkaloid, in the presence of cyclodextrins, the interaction with γ‐cyclodextrin (γ‐CD) in aqueous solution was studied by a combination of ¹H‐NMR analyses and molecular‐dynamics calculations. The proposed complexation mode of berberine by γ‐CD could explain the increased solubility in water. No difference in germicidal activity between berberine alone and its inclusion complex with γ‐ or β‐CD was observed, which is important to further develop the pharmacological application of berberine.     

Diastereoselective synthesis of S-tert-butyl-beta-(trifluoromethyl)isocysteine

Both diastereoisomers of S-tert-butyl-beta-(trifluoromethyl)isocysteine have been synthesized stereoselectively by the sequential reactions of trifluoroacetimidoyl chloride with the lithium enolate of tert-butyl alpha-tert-butylthioacetate, followed by the diastereoselective reduction of the imino group with sodium borohydride in the presence of zinc(II) or di(ethylene glycol) dimethyl ether, and finally by the deprotection of N-aryl and tert-butyl ester groups.     

Basis-Set dependence of exterior electron distributions of molecular orbitals

Interior electron densities are divided from exterior electron densities (EED ), when an effective boundary is introduced. The EED concept was used to study the quality of wavefunction tails; the basis-set dependence of ab initio MO for NH₃ was studied from EED . The EED for the nonbonding orbital (3a₁) increases dramatically with the size of basis sets, whereas that for the bonding orbital (1e) shows saturation even at the double zeta class. Although inclusion of polarization functions always gives the better total energy the EED (3a₁) may either increase or decrease or decrease depending on the choice of the smaller or the larger exponents. The conventional choice of the polarization functions for 6-311G* and 6-311G* was found to yield worse wavefunction tails than the case of 6-311G. Much better results were obtained with the more diffuse polarization functions. The (11s7p)/[5s4p] set designed for Rydberg states as well as the 6-311 + G set proposed for negative ions gave excellent results comparable to the case of the near Hartree-Fock calculation with 56 CGTO. Considerable improvements were also achieved for 4-31G and 6-311G sets, when the exponent for the outermost s-type function was modified. The largest EED (3a₁) gave the best agreement with the experimental ratio of EED 's derived from Penning ionization electron spectroscopy.     

X-Ray Crystallographic and MO Studies on the Conformation of Corynoline and the Related Compounds

The crystal structure of (±)-corynoline ( 1 ) has been determined by X-ray diffraction methods. The rings B and C form the half-chair and the twist-half-chair conformations, respectively. The B/C ring conjunction exists in an anti-cis conformation, with a N …? H? O intramolecular H-bond. Conformational energy calculation by the CNDO/2 method show that the conformations of 1 , (+)-chelidonine ( 2 ), and their acetates, observed in crystal structures, are all in the one of total energy minimum.     

Human liver dihydrodiol dehydrogenase 1-catalyzed reaction generating 9alpha,11beta-prostaglandin F2 from prostaglandin D2 followed by micellar electrokinetic chromatography

An enzyme reaction converting prostaglandin D2 (PGD2) into 9alpha,11beta-prostaglandin F2 (9alpha,11beta-PGF2) by a human liver-originated recombinant dihydrodiol dehydrogenase 1 (DD1) has been studied using CE. Four prostaglandins, viz. PGD2, 9alpha,11beta-PGF2, PGE2, and PGF2a (see Fig. 1, the latter two major PGs are possibly coexisting compounds in the assay mixtures), were completely separated by using SDS or PEG as buffer additives. Because analysis times in the SDS system were shorter than in the PEG system, SDS was employed in measurements of the enzyme activity of DD1. The pH dependence and the reaction temperature dependence of enzyme activity have been studied. The present method enabled us to detect all of the participants in the enzyme reaction: PGD2, 9alpha,11beta-PGF2, nicotinamide adenine dinucleotide phosphate (NADPH), and NADP+. Thus, direct, comprehensive, and reliable analysis of the enzyme reaction becomes possible. Enzyme activity has hitherto been estimated indirectly from the decrease of fluorescence derived from NADPH as an index of progress of the enzyme reactions in batch methods employed in conventional studies. In addition, the low sample consumption characteristic of CE should be a significant advantage of the present method in characterization of less commonly available enzymes such as the recombinant species used in this work.     

Reaction of grayanotoxin-II with thallium (III) nitrate

Reaction of grayanotoxin-II (1) with thallium nitrate gave 3(S), 20-epoxy-6 (S), 14 (R), 16 (R)-trihydroxy-5-oxo-5, 10-seco-ent-kaur-1 (10) -ene (2). The structure of 2 was elucidated by the X-ray diffraction analysis of its reduction product (3).     

On the removal of forbidden graphs by edge-deletion or by edge-contraction

If π is a property on graphs, the corresponding edge deletion (edge contraction, respectively) problem is: Given a graph G, determine the minimum number of edges of G whose deletion (contraction) results in a graph satisfying property π. We show that these problems are NP-hard if π is finitely characterizable by 3-connected graphs.     

Synthesis and physical properties of N-2-phenylethyl- and N-2-(3-indolyl)ethyl-5′-deoxy-5′-adenosineacetamides

The synthesis and physical properties of N-2-phenylethyl- and N-2-(3-indolyl)ethyl-5′-deoxy-5′-adenosineacetamides ( 2 and 3 ), which are stable compounds of phenylalanyl- and tryptophanyl-AMPs, are described.     

Crystal Structure of (−)-Corycavinium (+)-10-Camphorsulfonate,a biosynthetic intermediate to hexahydrobenzo[c]phenanthridine alkaloids

The crystal structure of (?)-corycavinium (+)-10-camphorsulfonate has been investigated by X-ray analysis. The structure of (?)-corycavinium ion ( ? (?)-(7S,13S,14R)-5,6,13,13a-tetrahydro-13a-hydroxy-7-methyl-2,3;9,10-bis(methylenedioxy)-8H-dibenzo[a,g]quinolizinium), has been determined. The conformation with B/C-cis-conjunction, a twisted half-chair of ring B , and a half-chair of ring C , as well as α-oriented substituted groups N…Me, C…Me, and C…OH is revealed. Feeding experiments with cell suspension cultures of Corydalis incisa (Papaveraceae) defined the intermediacy of (?)-corycavinium in the route from protoberberine-type to hexahydrobenzo[c]phenanthridine-type of alkaloids. On the basis of the present crystal conformation, the stereospecificity of the relating enzyme is biogenetically considered.