Dyscusins A-C, three new steroids from the leaves of Dysoxylum cumingianum

Three new steroids dyscusins A-C (1-3), including a stigmastane-type sterol and two pregnanes, together with two known steroids were isolated from the leaves of Dysoxylum cumingianum (Meliaceae). Their structures were elucidated on the basis of extensive spectroscopic analyses. In a cytotoxicity assay, compound 1 showed ten-fold enhanced cytotoxicity against multi-drug resistant cancer cells (KB-C2) in the presence of 2.5 μM colchicine as compared with the absence of colchicine. This notable finding indicated that 1 possessed a multi-drug resistant reversal effect.     

Spicachlorantins G-J, new lindenane sesquiterpenoid dimers from the roots of Chloranthus spicatus

Four new lindenane sesquiterpenoid dimers, spicachlorantins G-J (1-4), were isolated from the roots of Chloranthus spicatus together with seven known compounds, including chloramultilide A, shizukaol B, shizukaol D, shizukaol F, shizukaol P, chlorahololide D, and cycloshizukaol A. The planar structures of the new compounds were established by 1D-, 2D-NMR, and MS analyses. The absolute configurations of these compounds were determined by analyzing rotating Overhauser enhancement and exchange spectroscopy (ROESY) and circular dichroism (CD) spectra.     

Two new phenylethanoid glycosides from the roots of Phlomis umbrosa

Two new phenylethanoid glycosides were isolated from the roots of Phlomis umbrosa. Their structures were elucidated by spectroscopic methods.     

Hydrostatic compression of the monoclinic form of polyethylene

Lattice constants of the monoclinic form of polyethylene under pressures up to 1.8 GPa at 298 K are investigated by x-ray diffraction. The thermal expansion from 100 K to 300 K at atmospheric pressure is also studied. The equation of state is calculated by Pastine's method, taking into account the zero-point vibration, and is compared with experimental results. The calculated results depend largely on the interatomic potential used and the limit of the interatomic distance for summation of the potentials. A change in the angle γ between the a and b axes results in an anisotropic change in the unit cell dimension with both pressure and temperature; the a and b axes change at nearly the same rate. The monoclinic form may have a higher density than the orthorhombic form at pressures above 1.0 GPa.     

Crystal structure of acetyl 29-methyl-29-methylidene-D:C-friedoolean-8-en-3beta-ol.

Acetyl 29-methyl-29-methylidene-D:C-friedoolean-8-en-3beta-o1 (2), derived from bryonolic acid (D:C-friedoolean-8-en-3beta-ol-29-oic acid) (1), was crystallographically analyzed. Rings A-E of 2 adopted chair, half-chair, half-chair, boat (with bow and stern at C-13 and C-16), boat (with bow and stem at C-19 and C-22) conformations, respectively. Good agreement was found between the structures from X-ray crystallography and that from MM2 calculations.     

Synthesis and reduction ability of borane complexes of 2-aminopyridine derivative having a chiral center at the amino nitrogen

A novel method for synthesis of a chiral amine borane is described and selective reductions of carbonyl compounds with the amine borane are investigated.     

Testing the PCAC prediction for the π0 lifetime

We compare the PCAC prediction based on the chiral anomaly for the π⁰ lifetime with a recent experiment. We find that the QED corrections are as large as 3%. After these corrections the experiment and the PCAC prediction disagree by 8.5 ± 2%. We estimate the corrections to the PCAC prediction. We find that reliably calculable corrections are not large enough to account for the discrepancy. However, contributions from the excited π⁰'s may be able to explain the difference.     

Hydrolysis of 4-cyano-1-ethoxypyrimido[1,6-a]benzimidazole: Formation of a ynaminonitrile and benzimidazolidines

The title compound 4 was hydrolyzed to a new type of ynaminonitrile 5 and benzimidazolidines 7 and 9 under acidic or basic conditions. Reaction mechanisms were proposed.     

An analysis of medium noise of Co-Cr double-layer films in perpendicular magnetic recording

The medium noise in perpendicular magnetic recording is discussed. The perpendicular recording mode was expected to prevent zig-zag walls around transitions, and the experimental result of low transition noise in Co-Cr media confirms this. Also, the main origin of the noise is concluded to be irregular clusters of grains in the film.