Regioselective hydroborations of methylvinylchlorosilanes

The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl_nMe_3?nSiCHCH₂ (n= 0 ? 3), has been investigated using BH₃←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols forn= 0 and 1. Forn= 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol-0-d provides a more effective means of derivatization. Addition of the alkenes,n= 2 or 3, to excess BH₃←THF givesca. 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes giveca. 80% of the β-boron adducts.     

A convenient one-pot synthesis of 1,8-naphthyridones

In this paper, we disclose an efficient one-pot procedure for the preparation of substituted 1,8-naphthyridin-4-one analogues. Previous efforts to effect this type of transformation were complicated by the formation of benzene tricarboxylate. Via the use of excess base, the impurity formation was completely inhibited. This allowed for the clean preparation of the desired intermediate and subsequent formation of naphthyridone analogues in a single flask, which could then be crystallized directly from the reaction mixture in good yield and high purity.     

Functionalization of single-walled carbon nanotubes via the Bingel reaction

Single-walled carbon nanotubes have been cyclopropanated under Bingel reaction conditions, and the functionalized nanotubes have been characterized by atomic force microscopy using "chemical tagging" techniques.     

Preparation of ordered large pore SBA-15 silica functionalized with aminopropyl groups through one-pot synthesis

Highly ordered large pore SBA-15 silica functionalized with up to 16% aminopropyl groups, which gave high catalytic activity and selectivity toward flavanone synthesis through aldol condensation and subsequent intramolecular Michael addition of benzaldehyde and 2'-hydroxyacetophenone, was synthesized for the first time via co-condensation of tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) using an amphiphilic block copolymer as the structure-directing agent.     

Studies directed toward synthesis of quassinoids. VI—mass spectral fragmentation of D-ring seco esters and δ-lactone derivatives of cholic acid

Analogy and deuterium labeling demonstrate that considerable remote group interaction occurs between functional groups at positions 7 and 16 in 16, 17-secosteroids. It is proposed that ion-dipole interact?ions separations of distances of 10 to 2 Å will involve energies of 1–30 kcal mol^?1 and can play a significant role in fragmentation processes. Successive loss of one, two and three HOAc molecules from a milecular or daughter ion increase progressively in relative intensity; irregularity in this pattern indicates the operation of special factors or multiple genesis of daughter ions having the same m/e. Evidence is presented which suggests that facile ketene ejection from the acetate functional group only occurs from a radical ion and must be preceded by transfer of a hydrogen radical from the acetate group to the site of charge localization.     

Evaluation and validation of the ABI 3700, ABI 3100, and the MegaBACE 1000 capillary array electrophoresis instruments for use with short tandem repeat microsatellite typing in a forensic environment

The demand for high-throughput DNA profiling has increased with the introduction of national DNA databases and has led to the development of automated methods of short tandem repeat (STR) profile production; however, a potential bottleneck still exists at the gel electrophoresis stage. Capillary electrophoresis sequencers capable of processing 96 samples with considerably reduced manual intervention are now available. In this paper, we compare the ABI Prism 377 slab-gel sequencer currently used by the Forensic Science Service with three leading capillary array electrophoresis instruments: the ABI Prism 3700, the Amersham MegaBACE 1000 and the 16-capillary ABI Prism 3100. We describe the experiments used to evaluate and validate these platforms for forensic use with the STR multiplex Ampf/STR SGMplus [1, 2], along with comparative data from the ABI Prism 377 sequencer.     

Release of adenosine by C1300 neuroblastoma cells in tissue culture

Previous work in our laboratory led us to postulate that N2a cells release adenosine into growth medium, where it acts at the extracellular adenosine receptors to modulate the sensitivity of the cells to the cyclic AMP-elevating effect of adenosine [Green, RD, J Pharmacol Exp Ther 201:610, 1977]. We have now devised a high-performance liquid chromatographic (HPLC) procedure capable of quantitating the concentrations of adenosine in cells and tissue culture media. Growth media of N2a cells and a variant of N2a cells deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRT-) contain 10-20 nM adenosine, while that of a variant deficient in adenosine kinase (AK-) is elevated severalfold. It appears that the concentration of adenosine in growth media is determined by both the rate at which it is released by cells into the medium and the rate at which it is metabolized by adenosine deaminase present in the serum in the growth medium. Both N2a and AK- cells release considerable amounts of adenosine into serum-free medium (SFM) over a short period. Adenosine release is greater from AK- cells and is accelerated by erythro-9-(2-hydroxy-3-nonyl)-adenine (EHNA), a potent adenosine deaminase inhibitor. This accelerated release is retarded by dipyridamole and homocysteine. Surprisingly, dipyridamole and 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20 1724), a potent phosphodiesterase inhibitor, stimulate basal adenosine release from N2a but not from AK- cells. It remains to be determined if this is due to an effect of these compounds on adenosine kinase. These results give further support for the hypothesis that adenosine in growth medium modulates the sensitivity of the cells to the cyclic AMP-elevating affect of adenosine, and furthermore they suggest that adenosine in growth media may tonically stimulate adenylate cyclase and affect processes controlled by the cyclic AMP:cyclic AMP-dependent protein kinase system.     

Photoelectron spectra of substituted benzenes

Photoelectron spectra of several substituted dimethylanilines, nitrobenzenes, acetophenones and nitrosobenzenes have been studied with a view to examine the electronic effects of substituents on the various φ and n levels. The results are discussed in the light of molecular orbital calculations and electronic absorption spectra. Correlation of substituent effects on the IE's with π-electron densities and Hammett substituent constants has enabled rationalization of all available data on mono- and disubstituted benzenes. The IE's generally increase with the electron-withdrawing power of the substituents.