Regioselective and diastereoselective amination with use of chlorosulfonyl isocyanate: a short and efficient synthesis of (-)-cytoxazone

The total synthesis of (-)-cytoxazone 1 was achieved in six linear steps (34% overall yield) from p-anisaldehyde. The key steps in this route are the regioselective and stereoselective introduction of a N-protected amine group, using the CSI reaction of the anti-1,2-dimethyl ether 3, and the subsequent regioselective cyclization of the N-protected amino diol 13 to give the 2-oxazolidinone unit of (-)-cytoxazone 1. [reaction: see text]     

A reflected energy prediction model for long-range hydroacoustic reflection in the oceans

Acoustic energy from underwater earthquakes and explosions can propagate over long distances with very little attenuation in the deep ocean. When this sound encounters a seamount, island, or continental margin, it can scatter and again propagate over long distances. Hydrophones in the deep sound channel can detect these reflections tens of minutes or hours after arrivals from the direct source-to-receiver path. This paper presents the Reflected Energy Prediction (REP) model, a model for predicting these reflected arrivals. For a given source and receiver, the REP model uses a detailed knowledge of the underwater environment and components of the Hydroacoustic Coverage Assessment Model, HydroCAM, to predict the impulse response of the ocean. When this impulse response is convolved with a source function, a waveform envelope prediction is made that can be compared with recorded data. In this paper we present the model and a few applications of the model using data recorded from earthquakes and explosions in the Atlantic and Indian Oceans. These examples illustrate the use of the model and initial steps toward model calibration.     

Affinity determination of ricinus communis agglutinin ligands identified from combinatorial O- and S-,N-glycopeptide libraries

Two combinatorial glycopeptide libraries were synthesized on solid support via the "split-and-mix" method combined with the ladder synthesis strategy. The O-glycopeptide library contained Gal(beta1-O)Thr, whereas the S-,N-glycopeptide library contained both Gal(beta1-S)Cys and Gal(beta1-N)Asn. In this model study, the two libraries were screened against the fluorescently labeled lectin Ricinus communis agglutinin (RCA120). The screening results showed that both O- and S- or S-,N-glycopeptides were recognized by the lectin with similar amino acid recognition patterns. Surface plasmon resonance interaction studies demonstrated that both the selected S- or S-,N-glycopeptide hits and the O-glycopeptides bound to the lectin with a similar affinity. Structure 19, containing two glycosylated cysteine residues, bound to the receptor with the highest affinity (KA = 3.81 x 10(4) M(-1)), which is comparable to N-acetyllactosamine. Competition assays, in which some selected glycopeptides and methyl beta-d-galactopyranoside competed for the binding site of immobilized RCA120, showed that the glycopeptide-lectin interaction was carbohydrate-specific. Incubation of the O- and S-,N-glycopeptides with beta-galactosidase demonstrated the complete stability of S-,N-glycopeptides toward enzymatic degradation, whereas O-glycopeptides were not completely stable.     

Regioselective and diastereoselective allylic amination using chlorosulfonyl isocyanate. A novel asymmetric synthesis of unsaturated aromatic 1,2-amino alcohols

The diastereoselective synthesis of unsaturated aromatic 1,2-amino alcohols can be achieved on an epimeric mixture of optically active allylic ethers having a hydroxyl group attached to an allylic chiral center to the pi-system using chlorosulfonyl isocyanate. These reactions produced the unsaturated anti-1,2-amino alcohols either exclusively or predominantly only for aromatic derivatives. The anti-selectivity may be explained by the Cieplak electronic model during the conversion from ethers to carbamates.     

Synthesis of (±) Peperomins

The total synthesis of natural antitumor agent (±) peperomin A, B and C are reported. These syntheses were started from benzophenones and diethyl succinate by Stobbe condensation. Three successive steps were employed to give the (±)-peperomins.     

Simultaneous determination of cefamandole and cefamandole nafate in human plasma and urine by high-performance liquid chromatography with column switching

A high-performance liquid chromatographic method with column switching has been developed for the simultaneous determination of cefamandole and cefamandole nafate in plasma and urine. The plasma and urine samples were injected onto a precolumn packed with Corasil RP C18 (37-50 microns) after simple dilution with an internal standard solution in 0.05 M phosphoric acid. Polar plasma and urine components were washed out using 0.05 M phosphoric acid. After valve switching, the concentrated drugs were desorbed in back-flush mode and separated by a reversed-phase C8 column with methanol-5 mM tetrabutylammonium bromide (45:55, v/v) as the mobile phase. The method showed excellent precision with good sensitivity and speed, and a detection limit of 0.5 microgram/ml. The total analysis time per sample was less than 30 min, and the mean coefficients of variation for intra- and inter-assay were both less than 4.9%. The method has been successfully applied to plasma and urine samples for human volunteers after intravenous injection of cefamandole nafate.