Enhanced photodecarboxylation of an aryl ester in polyethylene films

[reaction: see text] Photodecarboxylation is the exclusive photoreaction of 2,4,6-trimethylphenyl (S)-2-methylbutanoate in unstretched high-density polyethylene films. The sole product, (S)-1-(2-methylpropyl)-2,4,6-trimethylbenzene, is formed with complete retention of stereochemistry. In other polyethylene films, organic solvents, and beta-cyclodextrin cavities, cage-escaped products derived from Fries-type bond scission are obtained as well. The results indicate the importance of the media in controlling the conformations of aryl esters and, thereby, their photoreactions.     

Further studies on the structure of polysaccharides from the lichen Flavoparmelia caperata (L.) Hale

A water-soluble polysaccharide called PC-2 was previously isolated from Flavoparmelia caperata (L.) Hale and assigned to alpha(1-3)(1-4)glucan. However, PC-2 separated into three components, PC-2A, PC-2B, and PC-2C (a single peak in HPLC, respectively) on further purification. Methylation analysis and (1)H- and (13)C-NMR spectroscopic studies suggested that PC-2A is composed of repeating units of [alpha-D-Glc1-3](3), : [alpha-D-Glc1-4](2), while PC-2B and PC-2C are partly branched galactoglucomannans consisting of (1-3)- and (1-4)-linked alpha-D-glucopyranosyl units as the main chain. In addition we confirmed that the polysaccharide fraction PB-2 from the lichen of the same genus, Flavoparmelia baltimorensis (Gyelink & Foriss) Hale, is identical to PC-2 based on the chemical and spectroscopic data.     

The fibril structure of type V collagen triple-helical domain

Although the triple-helical structure of fibrillar collagen is regarded in general as being quite similar, each type of collagen molecule has inherent characteristics in the triple-helical domain. Few studies have ever been performed in terms of the aggregate structure of the triple-helical domain of fibrillar collagen. Reconstituted aggregates from the purified triple-helical domain of each type of fibrillar collagen might amplify the subtle differences in the structural characteristics of each type of collagen molecule. In this study, the reconstituted aggregate structure of pepsin-treated type V collagen (type Vp collagen), that is, virtually its triple-helical domain was characterized by transmission electron microscopy. Pepsin-treated type I (type Ip) and type II (type IIp) collagen were compared with type Vp collagen. Unique features of the aggregate structure of the triple-helical domain of the type V collagen can be summarized as follows:These results suggested that the lateral packing of the triple-helical domain of type V collagen is determined by its molecular structure. The characteristics of type Vp collagen fibrils might be explained by their characteristic amino acid composition. A significant feature of the triple-helical domain of type V collagen is the high content of glycosylated hydroxylysine residues. Molecular model building of the collagenous structure suggests that a change in surface roughness is conspicuous by incorporating the glycosylated hydroxylysine residues. More than a ten-fold content of bulky glycosylated hydroxylysine residues in type V collagen compared to that of type I might have a significant influence on both the intermolecular and interfibrillar interactions of the triple-helical domain of type V collagen molecule.     

Flavonol glycosides from Elaeagnus bockii (Elaeagnaceae)

A new flavonol glycoside was isolated together with five known glycosides. Their structures were characterized by spectroscopic and chemical studies.     

A primal—dual infeasible-interior-point algorithm for linear programming

As in many primal—dual interior-point algorithms, a primal—dual infeasible-interior-point algorithm chooses a new point along the Newton direction towards a point on the central trajectory, but it does not confine the iterates within the feasible region. This paper proposes a step length rule with which the algorithm takes large distinct step lengths in the primal and dual spaces and enjoys the global convergence.Part of this research was done when M. Kojima and S. Mizuno visited at the IBM Almaden Research Center. Partial support from the Office of Naval Research under Contract N00014-91-C-0026 is acknowledged.Supported by Grant-in-Aids for Co-operative Research (03832017) of The Japan Ministry of Education, Science and Culture.Supported by Grant-in-Aids for Encouragement of Young Scientist (03740125) and Co-operative Research (03832017) of The Japan Ministry of Education, Science and Culture.     

Synthesis of macrocyclic terpenoids by intramolecular cyclization IX. Total synthesis of (±)-obscuronatin and (±)-biflora-4,10(19),15-triene.

Stereoselective total synthesis of (±)-obscuronatin, a marine diterpene with a 10-membered ring, has been achieved utilizing the anion-induced cyclization of an acyclic epoxy sulfide. The synthesis confirmed the stereostructure of the natural product.     

Synthesis of novel 2-chloro-1,4-dihydropyridines by chlorination of 2-hydroxy-1,4-dihydropyridines with phosphorus oxychloride

Novel 2-chloro-1,4-dihydropyridine derivatives were synthesized by chlorination of 2-hydroxy-1,4-dihydropyridines with POCl3. The dihydropyridines chlorinated at position 2 exhibited more potent vasodilative and hypotensive activities than the dihydropyridines (nicardipine and nitrendipine) with a methyl group at position 2.     

Noise characteristics in low-impedance NiFe/Al2O3/NiFe tunnel junctions

We have studied the low-frequency voltage noise in micron-scale magnetic tunnel junctions. Random telegraph noise (RTN) dominates over 1/f noise in the switching region of magnetic hysteresis loops, suggesting that RTN comes mostly from local magnetization fluctuations. The temperature dependence of the 1/f noise and the size of the magnetic fluctuators responsible for the RTN are discussed.