Biomedical subjects
Publications and source records attributed to G B Evans.
Means have been developed for the synthesis and addition of 9-deaza-9-lithiopurine derivatives to the carbohydrate-derived cyclic imine 6 in facile convergent syntheses of biologically active aza-C-nucleosides.
Alterations of the C-12 and C-13 aromatic ring substituents of totarol (1) afforded the series of derivatives 2-14, and introduction of substituents at C-12 gave exclusively 2a-14a. The majority of these analogues were tested in vitro against the following organisms: beta-lactamase-positive and high level gentamycin-resistant Enterococcus faecalis, penicillin-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus (MRSA), and multiresistant Klebsiella pneumoniae. The results were evaluated in terms of structure-activity relationship which reveals that: (a) the phenolic moiety at C-13, in general, is essential for antibacterial activity at < 32 microg/mL against gram-positive species, and (b) derivatization at C-12 has an undesirable effect on the antibacterial activity of this class of compounds, while (c) all compounds tested are ineffective against the gram-negative Klebsiella pneumoniae.
Ring-B derivatization of totarol (1) afforded the series of compounds 2-22 which were screened in vitro against: beta-lactamase-positive and high level gentamycin-resistant Enterococcus faecalis, penicillin-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus (MRSA), and multiresistant Klebsiella pneumoniae. Several of the derivatives retained much of the antibacterial activity of totatol against the first three of these organisms (all gram-positive), but none was more active. The gram-negative Klebsiella was resistant to all compounds examined. Totarol (1) was shown to uncouple oxidative phosphorylation in isolated mitochondria at 50 microM.
Nucleoside N-ribohydrolases from protozoan parasites are targets for inhibitor design in these purine-auxotrophic organisms. Purine-specific and purine/pyrimidine-nonspecific nucleoside hydrolases have been reported. Iminoribitols that are 1-substituted with meta- and para-derivatized phenyl groups [(1S)-substituted 1, 4-dideoxy-1,4-imino-D-ribitols] are powerful inhibitors for the nonspecific nucleoside N-ribohydrolases, but are weak inhibitiors for purine-specific isozymes [Parkin, D. W., Limberg, G., Tyler, P. C., Furneaux, R. H., Chen, X.-Y., and Schramm, V. L. (1997) Biochemisty 36, 3528-3534]. Binding of these inhibitors to nonspecific nucleoside hydrolase occurs primarily via interaction with the iminoribitol, a ribooxocarbenium ion analogue of the transition state. Weaker interactions arise from hydrophobic interactions between the phenyl group and the purine/pyrimidine site. In contrast, the purine-specific enzymes obtain equal catalytic potential from leaving group activation and ribooxocarbenium ion formation. Knowledge of the reaction mechanisms and transition states for these enzymes has guided the design of isozyme-specific transition state analogue inhibitors. New synthetic efforts have produced novel inhibitors that incorporate features of the leaving group hydrogen-bonding sites while retaining the iminoribitol group. These compounds provide the first transition state analogue inhibitors for purine-specific nucleoside hydrolase. The most inhibitory 1-substituted iminoribitol heterocycle is a sub-nanomolar inhibitor for the purine-specific nucleoside hydrolase from Trypanosoma brucei brucei. Novel nanomolar inhibitors are also described for the nonspecific nucleoside hydrolase from Crithidia fasciculata. The compounds reported here are the most powerful iminoribitol inhibitors yet described for the nucleoside hydrolases.
A series of analogues of, and potential pro-drugs derived from, the potent antibacterial diterpene totarol (1) were synthesized in order to elucidate the minimum structural requirements for antibacterial activity and to seek compounds with good bioavailability in vivo. These analogues varied in the structural features of their aromatic rings and the prodrugs were O-glycosylated derivatives. They were tested in vitro against three gram-positive bacteria: beta-lactamase-positive and high level gentamycin-resistant Enterococcus faecalis, penicillin-resistant Streptococcus pneumoniae, and methicillin-resistant Staphylococcus aureus (MRSA); and against the gram-negative multi-drug-resistant Klebsiella pneumoniae. None of the analogues was more potent than totarol itself, which is effective against these gram-positive bacteria at MIC values of 7 microM. The results were evaluated in terms of a structure-activity relationship and this showed that a phenolic moiety was essential for potent antibacterial activity. Amongst the pro-drugs, totaryl alpha-D-mannopyranoside (22) proved the most active in vitro (MIC 18 microM). The in vivo antibacterial activities of compounds 1, 22 and totarol beta-lactoside (23) were assessed in a mouse model of infection, but they were found to be ineffective. Compounds 1 and 22 were shown to be cytotoxic towards proliferating human cell cultures, CH 2983, HeLa, and MG 63, but only at concentrations of > 30 microM.
Enteric hyperoxaluria, a complication of jejuno-ileal bypass, is associated with renal failure owing to oxalate nephrosis or tubulo-interstitial nephritis. A 54 year old woman developed renal failure 17 months after jejuno-ileal bypass for morbid obesity. Renal biopsy showed widespread acute on chronic damage to the tubulo-interstitial compartment with extensive deposition of oxalate crystals. The extent of oxalate deposition was only evident on polarisation of the biopsy.
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Transport of critically sick neonates of any gestation on scheduled commercial passenger aircraft is practical, safe, and cost effective. There is no disruption to boarding or egress of passengers and no seats need be removed or rearranged. Civil Aviation and Federal Aviation Authority regulations are obeyed. Power supply modifications and strengthening of the transport incubator are necessary. Other standard neonatal intensive care equipment can be used in battery mode. Replacement of an endotracheal tube in-flight is not difficult.
Dopamine's effect on calcium influx into the bursting neuron, R15, of Aplysia californica was tested by tail current measurements and by measurement of absorbance of intracellular Arsenazo III, a calcium-sensitive indicator. Slow outward tail currents were elicited by subthreshold depolarization in voltage clamp and were demonstrated to be dependent upon transient increases in intracellular calcium activity, (Ca)i), using calcium-free seawater, calcium blockers (Mn2+ and La3+), and intracellular injection of EGTA. Dopamine reduces these tail currents as it reduces the slow inward current. Next, the transient elevations of (Ca)i accompanying subthreshold depolarization were measured directly in Arsenazo III-loaded neurons. Dopamine did not reduce the rise in (Ca)i measured in the soma during depolarization. However, when absorbance of the axodendritic region was monitored, dopamine did reduce calcium influx. Voltage monitoring in the axon indicated that the reduced calcium influx could not simply be ascribed to altered space clamp. In keeping with the apparent axodendritic location of dopamine action, isolation of the soma by ligation of the axon markedly reduced the dopamine response. Dopamine seems to reduce calcium influx into R15, but this effect is topographically limited to nonsomatic membrane, an area of the neuron not usually monitored in optical studies of (Ca)i.
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Explore the source record for details and available documents.