Asymmetric synthesis of anti-(2S,3S)- and syn-(2R,3S)-diaminobutanoic acid

Conjugate addition of homochiral lithium N-benzyl-N-alpha-methylbenzylamide to tert-butyl (E)-cinnamate or tert-butyl (E)-crotonate and in situ amination with trisyl azide results in the exclusive formation of the corresponding 2-diazo-3-amino esters in > 95% de. Amination of the lithium (E)-enolates of tert-butyl (3S,alphaR)-3-N-benzyl-N-alpha-methylbenzylamino-3-phenylpropanoate or tert-butyl (3S,alphaS)-3-N-benzyl-N-alpha-methylbenzylaminobutanoate with trisyl azide gives the (2R,3R,alphaR)- and (2S,3S,alphaS )-anti-2-azido-3-amino esters in good yields and in 85% de and > 95% de respectively. Alternatively, tert-butyl anti-(2S,3S,alphaS)-2-hydroxy-3-N-benzyl-N-alpha-methylbenzylaminobutanoate may be converted selectively to tert-butyl anti-(2S,3S,alphaS)-2-azido-3-N-benzyl-N-alpha-methylbenzylaminobutanoate by aziridinium ion formation and regioselective opening with azide. Deprotection of tert-butyl (2S,3S,alphaS)-2-azido-3-aminobutanoate via Staudinger reduction, hydrogenolysis and ester hydrolysis furnishes anti-(2S,3S)-diaminobutanoic acid in 98%, de and 98% ee. The asymmetric synthesis of the diastereomeric syn-(2R,3S)-diaminobutanoic acid (98% de and 98% ee) was accomplished via functional group manipulation of tert-butyl anti-(2S,3S,alphaS)-2-hydroxy-3-N-benzyl-N-alpha-methylbenzylaminobutanoate in a protocol involving azide inversion of tert-butyl (2S,3S)-2-mesyloxy-3-N-Boc-butanoate and subsequent deprotection.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Synthesis, structure, and physical properties of Ce2PdGa10

A new ternary compound, Ce₂PdGa₁₀, has been synthesized using Ga flux and characterized by single-crystal X-ray diffraction. Ce₂PdGa₁₀ adopts a tetragonal structure in the I₄/mmm space group and is isostructural to Ce₂NiGa₁₀. Lattice parameters are , , , and Z=2. The compound is metallic (dρ/dT>0), with the resistance decreasing roughly linearly with temperature from 300 to 175 K. The magnetic susceptibility of Ce₂PdGa₁₀ is consistent with local-moment paramagnetism and no long-range magnetic ordering occurs down to 2 K. A large positive magnetoresistance over 200% is observed at 2 K for fields of 9 T. In this paper, we present the structure and physical properties of Ce₂PdGa₁₀ and compared them to CePdGa₆.     

Databases, quality control and interpretation of DNA profiling in the Home office Forensic Science Service

The history of DNA profiling in the Home Office Forensic Science Service began with the introduction of multilocus probes into casework in 1986. The use of single-locus probes was introduced in 1990, supported by databases of three ethnic groups; interpretation is backed up using a Bayesian approach. Databases were compiled using an image analysis computing system. Quality control systems are described, detailing requirements before a sample can be included in the database.     

Asymmetric synthesis of vicinal amino alcohols: xestoaminol C, sphinganine and sphingosine

The highly diastereoselective anti-aminohydroxylation of alpha,beta-unsaturated esters, via conjugate addition of lithium (S)-N-benzyl-N-(alpha-methylbenzyl)amide and subsequent in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine, has been used as the key step in the asymmetric synthesis of N,O-diacetyl xestoaminol C (41% yield over 8 steps), N,O,O-triacetyl sphinganine (30% yield over 8 steps) and N,O,O-triacetyl sphingosine (30% yield over 7 steps).