Nuciferols A and B: Novel sesquineolignans from Cocos nucifera

Two novel epimers, named nuciferols A (1) and B (2), possessing a unique 6.9′, 9.6′, 7′.8″-cyclosesquineolignan skeleton, were isolated from the ethyl acetate fraction of the endocarp of Cocos nucifera. Their planar structure was elucidated by 1D-, 2D-NMR, HRESIMS and their absolute configuration was determined by ECD. Nuciferols A and B showed radical scavenging activity using DPPH assay, and only nuciferol B showed neuroprotective effects against t-BHP induced cell death in N2a cells.     

Synthesis of a 4,5-epoxy-2-cyclohexen-1-one derivative via epoxide ring opening, 1,3-carbonyl transposition and epoxide ring regeneration: a synthetic study on a scyphostatin analogue

A 6-alkyl-4,5-epoxy-6-hydroxy-2-cyclohexen-1-one derivative, a model compound for the hydrophilic moiety of scyphostatin, was stereoselectively synthesized from the Diels-Alder adduct. The key steps were the reductive cleavage of the 4,5-epoxide ring of the epoxidated adduct, the 1,3-carbonyl transposition of the 3-carbonyl group to the C1 position by a Wharton reaction and stereoselective bromination to provide a trans bromohydrin derivative, a precursor to the desired compound. Desilylation of the bromohydrin derivative with TBAF directly gave the target compound.     

Effect of microdermabrasion on barrier capacity of stratum corneum

A new microdermabrasion system is used for peeling the stratum corneum in a controlled manner. The system uses inert corundum powders under various degrees of vacuum. The fine corundum powders ejected by suction power, being quickly in contact with the skin surface, abrade and remove a tiny fragment of stratum corneum. The fraction of the stratum corneum removed by microdermabrasion can be controlled by the operating conditions; the duration of application (L) and the degree of vacuum setting (V). The stratum corneum barrier function with respect to the rate of skin penetration is well correlated by the product of the square of the degree of the vacuum and the duration of the probe setting.     

Specific heat study of the complex phase transitions in magnetism and dielectricity on triangular lattice antiferromagnets

The complex phase transitions involving dielectricity and magnetism on distorted triangular lattice antiferromagnets, "KNiC_l3-family" crystals, which have the crystal structures derived from the prototype CsNiCl₃, were studied through the heat capacity measurements. These crystals are classified into characteristic three groups from the viewpoint of magnetic and structural properties clarified so far. The results of the dielectric constant measurement as a function of temperature are also presented in detail. The present calorimetric study reveaed that the structural successive phase transitions rather than the magnetic transitions in these crystals are recognized more distinctly as the presence of specific heat anomalies at the respective phase transition points. This revised version was published online in August 2006 with corrections to the Cover Date.     

Facile, stereoselective synthesis of (24R)-24,25-dihydroxyvitamin D3 using D-glyceric acid as a chiral synthon

A facile, stereoselective, and efficient synthesis of (24R)-24,25-dihydroxyvitamin D₃, using D-glyceric acid as a chiral synthon to construct the side chain and ergosterol as a precursor of the secosteroid skeleton, is described.     

Asymmetric intramolecular michael addition of alpha-sulfinyl vinylic carbanion to enoates

The first example of an asymmetric intramolecular Michael addition reaction with use of alpha-lithiated vinylic sulfoxide as a Michael donor is reported. Michael addition of the alpha-lithiated vinylic sulfoxide to (Z)-enoates proceeds with high diastereoselectivity to give the adducts with (R)-configuration at the beta-position of the ester in the five-membered-ring formation. The selectivity was reversed in the six-membered-ring formation. The resulting ester enolates were reacted with alkyl halides or benzaldehyde with high diastereoselectivity.     

Loop-contraction mutagenesis of a type 1 copper site

Loop-contraction mutagenesis has been applied to the cupredoxin pseudoazurin to introduce the active-site loop of amicyanin. The mutation has a limited effect on the spectroscopic properties, and therefore structure, of the cupric protein. The loop contraction results in the increase of the pKa for the detachable His ligand of pseudoazurin by two pH units, similar to the value as found in amicyanin.     

Base-induced photocyclization of 1,2-diaryl-1-tosylethenes. A mechanistically novel approach to phenanthrenes and phenanthrenoids

The irradiation with UV light of a number of 1,2-diaryl-1-tosylstilbenes, in the presence of base, leads to the corresponding phenanthrenes and heterocyclic analogues. These results are consistent with a mechanism involving the base-induced elimination of p-toluenesulfinic acid from an intermediate 9-tosyl-4a,4b-dihydrophenanthrene, formed by photochemical cyclization of the starting 1,2-diaryl-1-tosylstilbenes. [reaction: see text]     

Specific-heat anomaly caused by ferroelectric nanoregions in Pb(Mg(1/3)Nb(2/3))O3 and Pb(Mg(1/3)Ta(2/3))O3 relaxors

The specific heat of typical relaxors, Pb(Mg(1/3)Nb(2/3))O3 (PMN) and Pb(Mg(1/3)Ta(2/3))O3 (PMT), was measured by adiabatic and relaxation methods between 2 and 420 K. A broad anomaly was found in the specific heat curve over the wide temperature range between 150 and 500 K for PMN, and between 50 and 400 K for PMT, which provides evidence for the formation of ferroelectric nanoregions (FNR) in the paraelectric matrix. The entropy of the anomaly was estimated as 3.3 J K(-1) mol(-1) and 2.9 J K(-1) mol(-1) for PMN and PMT, respectively, which implies an order-disorder-type mechanism for the formation of FNR.     

Complementary nucleobase interaction enhances peptide-peptide recognition and self-replicating catalysis

The availability of the complementary interaction of nucleobases for influencing the formation of peptide architectures was explored. Nucleobases were incorporated as additional recognition elements in coiled-coil peptides by employing nucleobase amino acids (NBAs), which are artificial L-alpha-amino gamma-nucleobase-butyric acids. The effect of the base-pair interaction on intermolecular recognition between peptides was evaluated through a self-replication reaction. The self-replication reactions of the peptides with complementary base pairs such as thymine-adenine or guanine-cytosine at the g-g' heptad positions were accelerated in comparison with those of the peptides with mismatched base pairs or without nucleobases. However, thymine-adenine pairs at the e-e' positions did not enhance the self-replication. In the presence of a denaturant, the enhancement effects of complementary base pairs on the reaction disappeared. Thermal denaturation studies showed that the thymine-adenine pairs contributed to stabilization of the coiled-coil structure and that the pairs at the g-g' positions were more effective than those at the e-e' positions. The peptide-peptide interaction was reinforced by complementary nucleobase interactions appropriately arranged in the peptide structure; these led to acceleration of the self-replication reactions.