Minimaxity and nonminimaxity of a preliminary test estimator for the multivariate normal mean

Summary The problem is to estimate the mean of ap-dimensional normal distribution in the situation where there is vague information that the mean vector might be equal to zero vector. Minimax property of the preliminary test estimator obtained by the use of AIC (Akaike's Information Criterion) procedure is discussed under a loss function which is based on Kullback-Leibler information measure and evaluates both an error of model selection and that of estimation. Whenp is even, the minimaxity is shown to hold for small values ofp but not for large values.     

Semiconductor-metal phase diagram of Co-doped NiS2

The phase diagram of the semiconductor-metal and antiferromagnetic transitions in 5 at.% Co- and 7 at.% Co-doped NiS₂ is determined from the electrical resistance measurements below room temperature to 77 K at pressures up to 35 kbar. It is indicated that the antiferromagnetic transition occurs in both semiconducting and metallic phases.     

Synthesis of a nitrogen analogue of sphingomyelin as a sphingomyelinase inhibitor

[structure: see text] Sphingomyelin nitrogen analogue 1 was designed and synthesized as a sphingomyelinase inhibitor. The synthesis was established by continuous Hofmann rearrangement and Crutius rearrangement as key steps in constructing the 3-hydroxy-1,2-diamine structure in the backbone of 1. This analogue showed moderate inhibitory activity toward SMase isolated from B. cereus.     

γ Radiolysis of polyethylene grafted with styrene

γ Radiolysis of polyethylene grafted with styrene of 0–76 wt % was carried out at 30–100°C in vacuo with a dose rate of 6.35 × 10⁵ rad/hr. The formation of hydrogen and trans-vinylene unsaturation decreased as the content of styrene unit in polymer increased and the rate of formation was described by zero-order formation kinetics with respect to each concentration combined with first-order disappearance. The gel fraction changed with the content of styrene unit according to irradiation time and temperature. The gel data were evaluated by using the Charlesby–Pinner equation. Kinetic analysis showed that in γ radiolysis of polyethylene grafted with styrene the formation of hydrogen is somewhat retarded, the crosslinking and main chain scission are accelerated, and the disappearance of hydrogen and formation and disappearance of trans-vinylene unsaturation are almost entirely unaffected. On the basis of these results the reactions induced by γ rays in graft polymer were discussed in connection with the reaction mechanisms of the γ radiolyses of polyethylene and polystyrene.     

Design of chiral tin(IV) aryloxide as a mild Lewis acid catalyst for enantioselective Diels-Alder reaction

A novel Sn(IV) aryloxide Lewis acid has been designed and prepared from SnCl₄ and (S)-3,3′-bis(3,5-bis(trifluoromethyl)phenyl)-1,1′-bi-2-naphthol. The chiral Sn(IV) Lewis acid has been successfully applied to the enantioselective Diels-Alder reaction.     

Synthesis of platinum complexes of 2-aminomethylpyrrolidine derivatives for use as carrier ligands and their antitumor activities

In order to study a new antitumor platinum complex, various platinum complexes were prepared from 2-amino-methylpyrrolidine derivatives synthesized to serve as carrier ligands and tested for their antitumor activity against Colon 26 carcinoma (s.c.-i.p. system) and P388 leukemia (i.p.-i.p. system) in mice. 2-Aminomethylpyrrolidine proved to be the most effective carrier ligand in its amine derivatives. The structure-activity relationships of the carrier ligands in the platinum complexes with dichloro, oxalato, 1,1-cyclobutanedicarboxylato and dichlorodihydroxo as leaving group were clearly shown on the Colon 26 carcinoma screen and were as follows: the antitumor activity of the platinum complexes with any leaving groups was considerably decreased by the substitution of hydrogen by alkyl group (Me, Et) on nitrogen of aminomethyl and the effects of 1,1-cyclobutanedicarboxylato Pt(II) complexes completely disappeared with the same substitution on nitrogen of pyrrolidine. In all the tested platinum complexes 2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platin um(II) (15) exhibited the most potent antitumor activity. 15 was superior to 1,1-cyclobutanedicarboxylatodiammineplatinum(II) (CBDCA) and similar to cis-diamminedichloroplatinum(II) (CDDP) on the Colon 26 carcinoma screen but it was inferior to CBDCA and CDDP on the P388 leukemia screen. Furthermore, 15 showed more potent antitumor activity than CBDCA against Colon 38 carcinoma (s.c.-i.p. system).     

Ion chromatography for determination of nitrite and nitrate in seawater using monolithic ODS columns

A fast and highly sensitive ion chromatographic method using monolithic ODS columns was developed for the determination of nitrite (NO2-) and nitrate (NO3-) in seawater. Two monolithic ODS columns (50 mm x 4.6 mm i.d. + 100 mm x 4.6 mm i.d.) connected in series were coated and equilibrated with 5 mM cetyltrimethylammonium chloride (CTAC) aqueous solution. The column efficiency with 0.5 M NaCl as the mobile phase did not decrease in spite of the increase in flow rate of the mobile phase. Thus, good chromatograms were obtained within 3 minutes for NO2- and NO3 in artificial seawater without interferences by coexisting ions. The detection limit (S/N = 3) with UV detection at 225 nm was 0.8 and 1.6 microg/L for NO2- and NO3-, respectively. The characteristics of the monolithic CTA(+)-coated ODS columns were discussed. The present method was successfully applied to the fast and sensitive determination of NO2- and NO3- in real seawater samples.     

Regiocontrolled benzannulation of diaryl(gem-dichlorocyclopropyl)methanols for the synthesis of unsymmetrically substituted alpha-arylnaphthalenes: application to total synthesis of natural lignan lactones

[reaction: see text] An efficient synthesis of highly substituted alpha-arylnaphthalene analogues has been developed utilizing Lewis acid-promoted regiocontrolled benzannulation of aryl(aryl')-2,2-dichlorocyclopropylmethanols (aryl not equal aryl'; abbreviated as AACMs). Both AACM diastereomers were easily prepared via highly stereoselective addition (>95/5) of ArLi to gem-dichlorocyclopropropyl aryl' ketones. The choice of Lewis acids determined the cyclization regioselectivity of the present benzannulation. TiCl4 and SnCl4 used the chelation pathway, whereas silyl triflates used a nonchelation pathway to give unsymmetrically substituted regioisomeric alpha-arylnaphthalenes in 40-91% yields with moderate to excellent regioselectivity (TiCl4 or SnCl4; >99/1-3/1, TBDMSOTf; >1/99-1/4). Thus, the alpha-aryl or alpha-aryl' moiety (accessory aryl group) was alternatively introduced to alpha-arylnaphthalenes by choosing either the order of the reaction sequences or the appropriate catalyst. Application of the present method to the total synthesis for unsymmetrically substituted natural lignan lactones, justicidin B, retrojusticidin B, dehydrodesoxypodophyllotoxin, and a related analogue, 5'-methoxyretrochinensin, was demonstrated. Lignan retrolactones (retrojusticidin B and 5'-methoxyretrochinensin) were synthesized by the conventional lactonization of the diol precursor, whereas a novel Bu2SnO-mediated monoacylation method was applied to the synthesis of normal lignan lactones (justicidin B and dehydrodesoxypodophyllotoxin).     

Synthesis of sphingomyelin carbon analogues as sphingomyelinase inhibitors

The highly efficient and stereocontrolled syntheses of sphingomyelin carbon analogues 1 and 2 were achieved by effectively utilizing Hofmann rearrangement of enantiomerically pure beta-hydroxyamide 7, which was prepared by an asymmetric hydrogenation of alpha-acyl-gamma-butyrolactone 9 and ring opening with NH(3). Intermediary isocyanate 6 was selectively trapped with the vicinal hydroxy group in an intramolecular fashion to produce an oxazolidinone derivative, 5. In the synthesis of a quite polar compound such as 1, a convenient one-pot procedure of the introduction of a benzyloxycarbonyl group into the hydroxy group resulting from the oxazolidinone ring opening is another key point, because, in addition to the efficiency, this protecting group was easily removable by a simple procedure and workup at the final step. Both synthesized compounds 1 and 2 showed moderate inhibitory activity toward sphingomyelinase from B. cereus.     

Asymmetric carbon-carbon coupling of phenols or anilines with aryllead triacetates

The asymmetric coupling of various phenol or aniline derivatives with bulky aryllead triacetates was thoroughly investigated using optically active amines, including strychnine and brucine. We found that conformationally restricted tertiary amines, as well as lithium aryloxides and molecular sieves, are essential for accelerating the rate of phenol coupling. Consequently, the reaction can be carried out at a low temperature (-40 to -20 degrees C) and gives a high degree of diastereo- and enantioselectivity. In contrast to the effectiveness of lithiation in phenol coupling, magnesation of anilines was a critical technique for aniline coupling with aryllead triacetates. Using these coupling methods, a diverse set of di-, tri, and polyaryl compounds with axial chirality can be easily obtained, and these should be useful for the construction of a variety of aryl-aryl frameworks involved in metal ligands, natural products, and artificial helical polymers.