Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Stereoselective synthesis of tetrahydropyran-4-ones from dioxinones catalyzed by scandium(III) triflate

[reaction: see text] A scandium triflate catalyzed, diastereoselective cyclization between aldehydes and beta-hydroxy dioxinones has been discovered. This process capitalizes on the untapped nucleophilicity of the embedded enol ether within the dioxinone core. The bicyclic compounds from the resulting cyclization can be isolated, or alternatively, alkoxide nucleophiles can be directly added. This in situ addition fragments the dioxinone rings and delivers the 3-carboxy-substituted tetrahydropyran-4-ones in good yields with high levels of diastereoselectivity.     

Total synthesis and structural revision of the marine macrolide neopeltolide

The total synthesis and structural revision of the marine natural product neopeltolide is reported. The key bond-forming step involves a Lewis acid-catalyzed intramolecular cyclization to install the tetrahydropyran ring and the macrocycle simultaneously. This type of cyclization is the first of its kind and assembles the carbon backbone of the natural product efficiently. The synthesis of the reported structure revealed differences in the data between the natural and synthetic material. After significant investigation, the diastereomeric molecule with the C11 and C13 configurations inverted was synthesized using the initial route. This compound matches the data reported for neopeltolide (1H, 13C, HRMS, IR, NOESY, [alpha]), thereby establishing the correct overall structure for this potent macrolide natural product, including the relative and absolute stereochemistry.     

Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.