Simple entry to 3'-substituted analogues of anti-HIV agent stavudine based on an anionic O --> C stannyl migration

Reaction of 5'-O-protected derivatives of the anti-HIV agent stavudine (d4T) with LTMP was investigated with the aim to lithiate the vinylic hydrogens (H-3' and H-2'). When the lithiation of the 5'-O-tert-butyldiphenylsilyl derivative 5 was carried out in the presence of HMPA, an anionic silyl migration took place to give the 3'-C-silylated product 4a. The stannyl version of this reaction was found to be also possible, which has disclosed a highly simple entry to the d4T analogues variously substituted at the 3'-position by manipulating the 3'-C-stannyl d4T as a common intermediate.     

Synthesis of optically active homocysteine from methionine and its use in preparing four stereoisomers of cystathionine

In order to synthesize four stereoisomers of cystathionine (CYT), D- and L-homocysteines (D- and L-Hcy) were synthesized from methionine (Met) by a facile procedure. L-Met was reacted with dichloroacetic acid in concentrated hydrochloric acid under reflux to give (4S)-1,3-thiazane-2,4-dicarboxylic acid hydrochloride [(4S)-TDC.HCl]. L-Hcy was obtained by treatment of (4S)-TDC.HCl with hydroxylamine. D-Hcy was also synthesized from D-Met via (4R)-TDC.HCl intermediate. The obtained D- and L-Hcy were condensed with (R)- and (S)-2-amino-3-chloropropanoic acid hydrochlorides under alkaline conditions to give four stereoisomers of CYT.     

Relative Projectivity of Modules and Cohomology Theory of Finite Groups

In the modular representation theory of finite groups the theory of projectivity relative to subgroups is of fundamental importance. To generalize this notion the theory of projectivity relative to modules was introduced by the first author. Our aim is to show some aspects of cohomology theory of finite groups concerning projectivity of modules relative to both subgroups and modules. We shall give some applications to the cohomology theory; especially we shall calculate the mod 2 cohomology algebras of finite groups with wreathed Sylow 2-subgroups.     

First stable 7,7,8,8-tetraaryl-o-quinodimethane: isolation, X-ray structure, electrochromic response of 9,10-bis(dianisylmethylene)-9,10-dihydrophenanthrene

Oxidative cyclization of 2,2'-bis(dianisylethenyl)biphenyl yielded the dicationic salt of phenanthrene-9,10-diylbis(dianisylmethylium), which in turn afforded the severely congested title molecule as the first stable tetraaryl-o-quinodimethane derivative upon reduction.     

Synthesis of crystalline boron nanowires by laser ablation

Crystalline boron nanowires with tetragonal structure have been synthesized based on laser ablation of a B/NiCo target; the nanowires are sometimes single crystals and have a droplet at one end of the nanowire; the droplet contains B, Ni and Co elements, which indicates that the vapor-liquid-solid (VLS) mechanism may play a key role in the growth of the boron nanowires.     

2-(1,3-Dithiolan-2-ylidene)-5-(1,3-dithian-2-ylidene)-1,3,4,6- tetrathiapentalene(DHDA-TTP), a hybrid of BDH-TTP and BDA-TTP,and its metallic cation-radical salts

The synthesis and electrochemical properties of the DHDA-TTP donor, a hybrid of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) and 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP), has been investigated, and its ability to form metallic cation-radical salts is elucidated.     

Synthesis in the diazasteroid group XI. A convenient route to the 4,8-diazasteroid system

The reaction of 1,6-naphthyridine 3 with acetic anhydride results in the formation of the 1:1 adduct 4 . Upon catalytic hydrogenation followed by acid hydrolysis and esterification, 4 affords 7 as an A-B steroid ring system synthon in moderate yield. Upon condensation with cyclopentanone and cyclohexanone, 7 , gives the 4,8-diazasteroid system 8 and the D-homo compound 9 , respectively.     

Diastereomeric selective effects for growth inhibition of synthesized mini parallel double-stranded peptides on Escherichia coli and Staphylococcus aureus

The synthesis of a series of mini double-stranded peptides containing chiral-x-Phe-y-Phe-peptide residues and the diastereomeric selective effects of these compounds on Escherichia coli NIHJ JC-2 and Staphylococcus aureus FDA 209P growth are described. In the case of bis(y-Phe-x-Phe)-N,N-ethane-1,2-diamine, bis(y-Phe-x-Phe)-N,N-buthane-1,4-diamine, bis(y-Phe-x-Phe)-N,N-hexane-1,6-diamine, and bis(y-Phe-x-Phe)-N,N-dodecane-1,12-diamine, etc., the four configurations, (L-, L-), (D-, L-), (L-, D-) and (D-, D-), where the symbols x- and y- represent optical isomers with L- and D- forms, were used to investigate the relationship between chirality and antibacterial activity. The level of activity increased in the following order: (L-, L-)<(D-, D-)<(L-, D-)<(D-, L-). The data show that (D-, L-) chilarity is more potent than (L-, L-) chilarity. Then, these results suggest that the -y-Phe-x-Phe Phe-sequence in the double-stranded peptide has anti-bacterial activity and the chirality of -y-Phe-x-Phe affects the anti-bacterial activity. Our results show that the uptake by penetration through the membrane of bis(y-Phe-x-Phe)(2)-Spacers is a first step in the expression of anti-bacterial activity. This study provides new insights in the chirality-antibacterial activity relationships of a series of mini double-stranded peptides.     

Charge ordering and spin frustration in AlV2-x CrxO4

The relationship between charge and spin degrees of freedom in a geometrically frustrated system, AlV2-xCrxO4 spinel, is investigated. Upon Cr doping, the charge-ordered phase of AlV2O4 is rapidly suppressed and a charge-disordered phase grows up instead. It is found that the magnetic ground state is a spin-glass state dominated by geometrical frustration for both phases, but larger spin entropy remains down to low temperatures in the charge-ordered phase, possibly owing to its two-dimensional character.