Synthetic studies on β-lactam antibiotics. VII. Mild removal of the benzyl ester protecting group with aluminum trichloride

The benzyl ester protecting group in β-lactam derivatives can be cleanly removed by treatment with aluminum trichloride under mild conditions, preferably in the presence of anisole, to give the corresponding free acids in high yields.     

Synthesis and dynamic mechanical properties of heterogeneous network polymers from poly(L-glutamic acid) and poly(oxyethylene glycol)

Heterogeneous network polymers composed of rigid polypeptide chains and flexible polyether chains were synthesized. That is, poly(L -glutamic acid) (PLGA) was crosslinked with poly(oxyethylene glycol) (PEG) at various carboxy/hydroxyl mole ratios K. The solubility tests and hydrolysis of heterogeneous network polymers suggest that the crosslinking reaction proceeds by esterification. The dynamic mechanical properties of these polymers(100 Hz, ?100–200°C) are greatly influenced by the presence of a trace of water and the weight per cent of PLGA. In addition, some of these polymers show only one maximum in the temperature dispersion of dynamic loss modulus E″ and tan δ, although their shape is rather broad. The x-ray photographs of these polymers show an amorphous halo or weak Debye-Sherrer rings. These findings suggest that these polymers are not simple adducts; neverthless PLGA and/or PEG domains exist.     

Constituents of Holothuroidea, 15. Isolation of ante-iso type regio-isomer on long chain base moiety of glucocerebroside from the sea cucumber Holothuria leucospilota

An ante-iso type regio-isomer on the long chain base moiety of a glucocerebroside, HLC-2-A, has been isolated from its parent glucocerebroside molecular species HLC-2 composed of iso and ante-iso isomers, from the less polar lipid fraction of a chloroform/methanol extract of the sea cucumber Holothuria leucospilota. Reverse-phase HPLC that included a recycling system was effective in separating the regio-isomer from its counterpart, revealing a very close resemblance in structure. Other typical glucocerebroside molecular species HLC-1 and HLC-3 were obtained together with HLC-2. The structures of these glucocerebrosides were determined on the basis of chemical and spectroscopic evidence.     

Preparation and electrical resistivities of tetrathiafulvalen (TTF) and tetraselenafulvalen salts with the [SnR2Cln]2-n anions (n = 3 or 4: R = Et or Ph) and X-ray crystal structure of [TTF]3[SnEt2Cl4]

Tetrathiafulvalen (TTF) and tetraselenafulvalen (TSF) salts with diorganochloro-stannate anions, [TTF][SnEt₂Cl₃] (1), [TTF]₂[SnPh₂Cl₄] (2), [TTF]₃[SnEt₂Cl₄] (3), [TTF]_3.3[SnPh₂Cl₄] (4), [TSF]₂[SnPh₂Cl₄] (5) and [TSF]_3.3[SnPh₂Cl₄] (6), were prepared by the reactions of [TTF or TSF]₃[BF₄]₂ with SnR₂Cl₂ (R = Et or Ph) in the presence of [Ph₃PCH₂Ph]Cl and by electrocrystallization of TTF or TSF in acetonitrile containing SnR₂Cl₂ and [Ph₃PCH₂Ph]Cl. All the salts behave as semiconductors with electrical resistivities of the order of 10–10⁸ Ω cm as compacted samples at 25°C. Electronic reflectance spectra of the simple salts 1, 2 and 5, show a band due to the dimeric(TTF⁺)₂ or (TSF⁺)₂ unit in the 12,200–12,800-cm^?1 region. The complex salt 3 exhibits a TTF⁺/TTF° charge-transfer (CT) band at 8700 cm^?1, and the remaining complex salts, 4 and 6, both display CT bands between the radical cations and between the radical cation and the neutral donor molecule. The crystal structure of 3 was determined by a single-crystal X-ray diffraction. The tetragonal crystal, space group I4cm, has cell dimensions a = 11.710(3) Å, c = 25.242(7) Å, and Z = 4. The structure was solved by the heavy-atom method and refined to a final R value of 0.082 for 479 independent reflections with >F_° > 3σ(F). TTF molecules exist as trimers, in which a slight lateral shift from the eclipsed TTF overlap occurs, although TTF molecules are arranged with equal spacing between them. The trimer units are located perpendicularly to each other, forming a two-dimensional layer. The [SnEt₂Cl₄]^2? anion is disordered with respect to the two SnEt and two SnCl bonds.     

Metric packing for K 3+K 3

In this paper, we consider the metric packing problem for the commodity graph of disjoint two triangles K ₃+K ₃, which is dual to the multiflow feasibility problem for the commodity graph K ₃+K ₃. We prove a strengthening of Karzanov’s conjecture concerning quarterintegral packings by certain bipartite metrics.     

Sorption of water vapor into polyelectrolyte complex of poly(styrenesulfonic acid)/poly(4-vinyl-N-ethylpyridinium bromide)

Successive differential and integral sorptions of water vapor into the polyelectrolyte complex of poly (sty renesulfonic acid) / poly(4-vinyl-N-ethylpyridinum bromide) have been measured; films of stoichiometric (1/1 molar ratio) and nonstoichiometric (2/1 molar ratio) complex were employed in the experiments. Sorption isotherms have been also determined by using the values obtained from integral sorption experiments. The sorption data have suggested the following. (i) The rearrangement of polymer chains plays a relatively unimportant role in sorption of water. (ii) The relaxation motion of network chains is suppressed. (iii) The change of morphological structure caused by vapor sorption is obscure. (iv) The ionic character of the 1/1 complex is higher than that of 2/1 complex. (v) A small amount of water can be dispersed on specific polymer sites, but the sorption of a large amount of water is accompanied by an expansion of network structure. Points (i)-(v) have been consistently interpreted on the basis of the network structure and ionic character of this complex.