Opening of tartrate acetals using dialkylboron bromide: evidence for stereoselectivity downstream from ring fission

Johnson-type acetals derived from dimethyl tartrate give, after opening with Me(2)BBr and cuprate displacement, secondary alcohols with high diastereoselectivity (>30:1). The mechanism proposed for the induction of diastereoselectivity is downstream from the ring fission. It implies a direct participation of the Lewis acid as a source of nucleophile and the stereospecific transformation of the resulting bromo acetal through an invertive and temperature-dependent process. The acetals are prepared by reaction of the desired aldehyde with dimethyl tartrate. Removal of the auxiliary is accomplished through SmI(2) reduction or by an addition-elimination protocol using methoxide.     

Nonaqueous oxidation of phosphites to phosphates in nucleotide synthesis

$\text{m}$-Chloroperbenzoic acid in methylene chloride represents a rapid non-aqueous method for the conversion of phosphites to phosphates during oligonucleotide synthesis both in solution and on a solid support.     

Analysis of Pure Rotational and Vibration‐rotational Spectra of NaCl X 1Σ+ and Quantum‐chemical Calculation of Related Molecular Properties

We fitted published frequency and wave number data for pure rotational and vibration‐rotational spectra, respectively, of ²³Na³⁵Cl and ²³Na³⁷Cl to derive parameters related to potential energy and to the rotational g factor. For comparison with these experimental data we undertook quantum‐chemical computation of adiabatic corrections, rotational and vibrational g factors, electric dipolar moment and its derivative as a function of internuclear distance in a range near R_e as a test of an algebraic approach to spectral analysis; experimental, 0.0287 ± 0.0014, and calculated, 0.02149, values of g_r at R_e are in moderate agreement. The combined results are discussed from a point of view of computational spectrometry.     

Mass spectrometry of trialkylsilyl and acyl derivatives of 2′-deoxynucleosides

The electron impact mass spectra of monosilyl and mixed acyl-silyl derivatives of 2′-deoxynucleosides are described in detail. (Silyl = tert-butyldimethylsilyl, cyclo-tetramethylene-isopropylsilyl, or cyclo-tetramethylene-tert-butylsilyl; acyl = acetyl or trifluoroacetyl.) The interpretation of the fragmentation pathways was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements. Mass spectrally, the acyl substituents are mostly ‘passive’ and have (with possibly one exception) little fragmentation directing capability. In contrast, the silyl groups have powerful fragmentation directing properties. Elimination of the bulky alkyl radical R^˙ (tert-butyl or isopropyl) from the molecular ion produces the siliconium ion, [M–R]⁺, which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion centre with the electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [M–R]⁺ ions formed from 3′- or 5′-O-silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.     

Evolved CYP102A1 (P450BM3) variants oxidise a range of non-natural substrates and offer new selectivity options

The evolution of CYP102A1 variants with enhanced activity and altered specificity characteristics.     

N-levulination of nucleosides

Procedures have been developed for the synthesis of the N-levulinyl derivatives of cytidine, adenosine and guanosine.     

Spin waves,vortices, fermions,and duality in the Ising and Baxter models

Field-theoretic methods are applied to a number of two-dimensional lattice models with Abelian symmetry groups. It is shown, using a vortex + spin-wave decomposition, that the Z_p^? Villain models are related to a class of continuum field theories with analogous duality properties. Fermion operators for these field theories are discussed. In the case of the Ising model, the vortices and spin-waves conspire to produce a free, massive Majorana field theory in the continuum limit. The continuum limit of the Baxter model is also studied, and the recent results of Kadanoff and Brown are rederived and extended.