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Biomedical subjects

B W King

Publications and source records attributed to B W King.

18 recordsLinked to original sources
PubMed2001

Asymmetric aldol additions: use of titanium tetrachloride and (-)-sparteine for the soft enolization of N-acyl oxazolidinones, oxazolidinethiones, and thiazolidinethiones.

Asymmetric aldol additions using chlorotitanium enolates of N-acyloxazolidinone, oxazolidinethione, and thiazolidinethione propionates proceed with high diastereoselectivity for the Evans or non-Evans syn product depending on the nature and amount of the base used. With 1 equiv of titanium tetrachloride and 2 equiv of (-)-sparteine as the base or 1 equiv of (-)-sparteine and 1 equiv of N-methyl-2-pyrrolidinone, selectivities of 97:3 to > 99:1 were obtained for the Evans syn aldol products using N-propionyl oxazolidinones, oxazolidinethiones, and thiazolidinethiones. The non-Evans syn aldol adducts are available with the oxazolidinethione and thiazolidinethiones by altering the Lewis acid/amine base ratios. The change in facial selectivity in the aldol additions is proposed to be a result of switching of mechanistic pathways between chelated and nonchelated transition states. The auxiliaries can be reductively removed or cleaved by nucleophilic acyl substitution. Iterative aldol sequences with high diastereoselectivity can also be accomplished.

Magnetic Resonance Spectroscopy↗
PubMed2000

An efficient, general asymmetric synthesis of carbocyclic nucleosides: application of an asymmetric aldol/ring-closing metathesis strategy.

A general and efficient synthesis of carbocyclic and hexenopyranosyl nucleosides has been developed. The strategy combines three key transformations: an asymmetric aldol addition to establish the relative and absolute configuration of the pseudosugar, a ring-closing metathesis to construct the pseudosugar ring, and a Trost-type palladium(0)-mediated substitution to assemble the pseudosugar and the aromatic base. Carbovir, abacavir, and their 2'-methyl derivatives as well as hexenopyranosyl nucleoside analogues have been prepared by this sequence.

Antiviral Agents↗
PubMed2000

Synthesis of the C1-C13 fragment of leucascandrolide A.

[reaction: see text] The synthesis of the C1-C13 fragment 3 of leucascandrolide A has been completed utilizing a stereoselective and regioselective reductive cleavage of a highly functionalized spiroketal to incorporate the cis-2,6-disubstituted tetrahydropyan. The spiroketal was constructed by addition of a lithiated pyrone 5 to aldehyde 6.

Sesquiterpenes↗
PubMed1998

Comparison of the SimPlate total plate count method with Petrifilm, Redigel, conventional pour-plate methods for enumerating aerobic microorganisms in foods.

The SimPlate Total Plate Count (TPC) method, developed by IDEXX Laboratories, Inc., is designed to determine the most probable number of aerobic microorganisms in foods. The 24-h test was compared to the conventional plate count agar (PCA) method, the Petrifilm Aerobic Count plates, and the Redigel Total Count procedure for enumerating microflora in 751 food samples. Results using the SimPlate TPC method were highly correlated (r > or = 0.96) with results from other test methods. Slopes (0.96-0.97) were not significantly different from 1, and y intercepts (-0.03-0.08) were not different from O. The SimPlate has a high counting range (> 1600 most probable number per single dilution), thus requiring fewer dilutions of samples compared to other methods evaluated. Some foods, e.g., raw liver, wheat flour, and nuts, contain enzymes that gave false-positive reactions on SimPlates. Overall, however, the SimPlate TPC method is a suitable alternative to conventional PCA, Petrifilm, and Redigel methods for estimating populations of mesophilic aerobic microorganisms in a wide range of foods.

Aerobiosis↗
PubMed1993

Spinal anaesthesia for caesarean section after Harrington instrumentation.

A case is presented of a 33-yr-old parturient with Harrington fusion of her spine who received spinal anaesthesia with 15 mg hyperbaric bupivacaine for Caesarean delivery. Multiple attempts of needle insertion in both midline and paramedian at the L3-4 interspace were unsuccessful, whereas the procedure was performed uneventfully at the midline of the L5S1 interspace. The anatomical considerations and difficulties in achieving reliable epidural anaesthesia after Harrington fusion are reviewed. Spinal anaesthesia performed at the L5S1 interspace may provide less technical difficulty and a more reliable result in such patients.

Adult↗
PubMed1988

Control of interval-force relation in canine ventricular myocardium studied with ryanodine.

1. The mechanism of post-extrasystolic, rest and frequency potentiation was studied in canine isolated ventricular muscle. 2. Ryanodine, which impairs Ca availability from the sarcoplasmic reticulum (SR), reduced the amplitude of the extrasystole less than that of the steady state contraction. Ryanodine also inhibited post-extrasystolic potentiation and converted rest-potentiation into rest depression. Rest-potentiation was blocked preferentially by ryanodine compared to post-extrasystolic potentiation. An increase in the contribution of extracellular Ca to the extrasystolic contraction could not entirely account for the post-extrasystolic potentiation. 3. Prolonged rest, by itself, also caused depression of the first post-rest contraction. During rest-potentiation, SR Ca seemed to play a greater role in contraction than transmembrane Ca influx. However, the ability of the 'release pool' of Ca in the SR to be reprimed after a contraction was reduced. This was seen as a decrease in post-extrasystolic potentiation elicited immediately after rest. 4. A decrease in stimulus interval was associated with a transient decrease in contraction amplitude followed by an increase. An abrupt increase in stimulus interval had the opposite effect. Ryanodine blocked the initial transient changes and accelerated the delayed changes. These results suggest that the transient changes in contraction after sudden changes in drive interval are dependent on the SR. 5. Transmembrane Ca entry and the rate of recovery of the Ca release process (repriming) in the SR after a contraction seem to be interval-dependent. The data also indicate that different mechanisms are involved in post-extrasystolic and rest-potentiation. 6. The results are consistent with a model which proposes 'recirculation' of activator Ca within the SR after a contraction or of the presence of an appreciable amount of inactivation of the SR Ca release process during normal stimulation. An increased pool of releasable Ca due to longer recirculation time or a time-dependent decay in the level of inactivation of Ca release from the SR may give rise to rest-potentiation.

Alkaloids↗
PubMed1983

Mechanism of biphasic contractions in strontium-treated ventricular muscle.

Biphasic contractions were produced in dog trabeculae by replacing 90-95% of the calcium in the bathing solution with strontium. These conditions produced prolonged action potentials accompanied by contractions with two distinct phasic components. The early component disappeared slowly when the remaining Ca++ was removed, whereas the late component was eliminated quickly when Sr++ was removed. Manganese ion (0.25 mM) preferentially decreased the late component without changing the action potential, whereas caffeine and ryanodine decreased or eliminated the early component. Ryanodine did not alter the action potential. Isoproterenol rapidly increased the early component and, more slowly and to a lesser degree, increased the late component. The results suggest that the early component is caused by intracellular release of activator cation, probably from the sarcoplasmic reticulum, whereas the late component is the result of Sr++ entry across the sarcolemma, possibly by way of the slow inward current.

Animals↗
PubMedDate not supplied

Electrophysiological effects of encainide (MJ9067) on canine subendocardial Purkinje fibers surviving infarction.

The electrophysiological effects of encainide (MJ9067) on canine subendocardial Purkinje fibers surviving infarction were examined 22-24 h after coronary artery ligation, using standard microelectrode techniques at pH 7.4. Encainide (5 and 10 microM) shortened APD50, decreased the action potential amplitude and overshoot, caused a 2-3 mV depolarization of the cell, and decreased the maximum rate of phase 0 depolarization. All these effects were dose dependent. APD90 was slightly, but not significantly, shortened. Encainide had a greater effect on APD50 and APD90 at longer (1,000 ms) stimulation cycle lengths than at shorter (400 ms) cycle lengths. There was a significant interaction between the effects of stimulation rate and encainide concentration on APD90, APD50, amplitude, and overshoot. The same parameters measured at a lower pH (7.1) gave similar results. There was a significant correlation (r = -0.540, p less than 0.001) between the control APD90 and the degree and direction of change of APD90 after 10 microM encainide. Automaticity of the infarcted preparations was eliminated or slowed in a dose-dependent fashion by 5 and 10 microM encainide. The curve relating membrane potential and the maximum rate of phase 0 depolarization was shifted down and toward higher potentials by 5 microM encainide. The results show that encainide produces similar changes in the action potentials of Purkinje fibers surviving infarction as in normal Purkinje fibers, and is effective in lowering the rate of spontaneous depolarization in infarcted tissue. Furthermore, encainide appears to be the only antiarrhythmic drug which has been shown to increase and decrease APD90, depending on the initial APD90 of the cell.

Action Potentials↗
PubMedDate not supplied

Motivation theory.

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Emergency Medical Services↗