5‐Butyl‐4‐(4,4,5,5‐tetra­methyl‐1,3,2‐dioxaborolan‐2‐yl)‐3‐(2,4,6‐tri­methyl­phenyl)­isoxazole

A novel [3+2]‐cyclo­addition reaction of alkynyl­boronates and nitrile oxides gave the title compound, C₂₂H₃₂BNO₃, as a single regioisomer. The X‐ray crystal structure analysis of this compound shows two independent mol­ecules in the asymmetric unit, each with approximately coplanar isoxazole and boronate rings.     

Nickel-manganese sulfido carbonyl cluster complexes. synthesis, structure, and properties of the unusual paramagnetic complexes Cp2Ni2Mn(CO)3(mu 3-E)2, E = S, Se

The reaction of Mn(2)(CO)(7)(mu-S(2)) with [CpNi(CO)](2) yielded the paramagnetic new compound Cp(2)Ni(2)Mn(CO)(3)(mu(3)-S)(2) (1) and a new hexanuclear metal product Cp(2)Ni(2)Mn(4)(CO)(14)(mu(6)-S(2))(mu(3)-S)(2) (2). Structurally, compound 1 contains two triply bridging sulfido ligands on opposite sides of an open Ni(2)Mn triangular cluster. EPR and temperature-dependent magnetic susceptibility measurements of 1 show that it contains one unpaired electron. The electronic structure of 1 was determined by Fenske-Hall molecular orbital calculations which show that the unpaired electron occupies a low lying antibonding orbital delocalized unequally across the three metal atoms. The selenium homologue Cp(2)Ni(2)Mn(CO)(3)(mu(3)-Se)(2) (3) was obtained from the reaction of a mixture of Mn(2)(CO)(10) and [CpNi(CO)](2) with elemental selenium and Me(3)NO.2H(2)O. It also has one unpaired electron. Compound 1 reacted with elemental sulfur to yield the dinickeldimanganese compound, Cp(2)Ni(2)Mn(2)(CO)(6)(mu(4)-S(2))(mu(4)-S(5)), 4, which can also be made from the reaction of Mn(2)(CO)(7)(mu-S(2)) with [CpNi(CO)](2) and sulfur. Compound 4 was converted back to 1 by sulfur abstraction using PPh(3). The reaction of Mn(2)(CO)(10) with [CpNi(CO)](2) in the presence of thiirane yielded the ethanedithiolato compound CpNiMn(CO)(3)(mu-SCH(2)CH(2)S) (5), which was also obtained from the reaction of Mn(4)(CO)(15)(mu(3)-S(2))(mu(4)-S(2)) with [CpNi(CO)](2) in the presence of thiirane. Compound 5 reacted with additional quantities of thiirane to yield the new compound CpNiMn(CO)(3)[mu-S(CH(2)CH(2)S)(2)], 6, which contains a 3-thiapentanedithiolato ligand that bridges the two metal atoms. Compound 6 was also obtained from the reaction of Mn(2)(CO)(10) with [CpNi(CO)](2) and thiirane. The molecular structures of the new compounds 1-6 were established by single-crystal X-ray diffraction analyses.     

Triphenylphosphonium-alloxan betaines

Alloxan and 1,3-dimethylalloxan react with triarylphosphines to generate zwitterionic adducts involving the phosphorus and the C-5 carbonyl oxygen atoms of alloxan. The adducts, unlike alloxan, did not induce permanent hyperglycemia but one analog did effect a transient rise in blood glucose.     

Synthesis and characterization of novel epoxy monomers and liquid crystal thermosets

Four new epoxy monomers have been synthesized and characterized as part of a program to prepare novel liquid crystal thermoset (LCT) materials. Three of the new epoxy monomers contained a biphenyl mesogen and were not liquid crystalline (LC). The remaining epoxy monomer, which contained a 1,4-dibenzoyloxybenzene mesogen, was synthesized in an overall yield of 30% and displayed a broad (83°C) nematic liquid crystalline phase. The new liquid crystalline epoxy monomer was cured at 120°C and postcured at 175°C with a stoichiometric amount of 1,4-phenylenediamine. The thermal transitions of the resulting LCT were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM), thermomechanical analysis (TMA), and wide angle x-ray diffraction (WAXD) as a function of cure time and temperature. A process characterization diagram was constructed which shows that LCTs based on this new LC monomer can be processed in the liquid crystalline phase over a broad range of times and temperatures. Qualitative agreement with previous epoxy LCT results was found, as LCT's with smectic phases and without clearing temperatures were observed at long cure times (high crosslink densities), whereas nematic phases with clearing temperatures predominated in networks at short cure times (low crosslink densities). © 1993 John Wiley & Sons, Inc.     

Assay of Kanamycin A by HPLC with Direct UV Detection

The development of a simple reversed phase ion pair liquid chromatographic method for the assay of kanamycin A has been described. Because of the lack of a UV chromophore in the structure of kanamycin A, borate complexation was used to allow direct UV detection at 205 nm. Three columns were evaluated in this study: Zorbax Extend C18 (4.6 mm × 250 mm; 5 μm), XBridge C18 (4.6 mm × 250 mm; 5 μm) and apHera C18 (4.6 mm × 250 mm; 5 μm). The mobile phase was a mixture of 0.1 M disodium tetraborate (pH 9.0) and water (20:80, v/v) supplemented with 0.5 g L^?1 sodium octanesulphonate. Final chromatographic conditions were achieved on the XBridge column at 50 °C. The method was validated according to ICH guidelines and applied to a commercially available sample. It is much faster and more specific than the current microbiological assay prescribed in the European Pharmacopoeia. No expensive equipment is necessary to perform this assay making it a viable replacement.