PubMed · 4683217
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N Lotan. 1973-01-18. Pseudopolyelectrolyte polyamino acids.. https://doi.org/10.1021/j100621a021
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Radiation myelopathy is a rare, but extremely serious side-effect of radiotherapy. Recovery from radiation-induced motor sequelae is rare, whereas, the regeneration of sensory losses is relatively frequent. Among the sensory radiogenic injuries of the spinal cord, Lhermitte's sign (LS) is most frequent. This review describes the clinical picture and diagnostic imaging signs of radiogenic LS. There have been only a few studies on large patient groups with radiogenic LS, demonstrating a rate of occurrence of 3.6-13%, relating mainly to mantle irradiation or the radiotherapy of head and neck tumors. These cases typically manifest themselves 3 months following radiotherapy and gradually disappear within 6 months. Only 3 LS cases have been described in the English literature with extraordinarily severe symptoms lasting for more than 1 year. MRI, a sensitive tool in the detection of demyelination, failed to reveal any pathological sign accompanying radiogenic LS. However, positron emission tomography demonstrated increased [18F]fluorodeoxyglucose accumulation and [15O]butanol perfusion, but a negligible [11C]methionine uptake in the irradiated spinal cord segments in patients with long-standing LS. These imaging data are suggestive of a close direct relationship between the regional perfusion and metabolism of the spinal cord, very much like the situation in the brain. We postulate that an altered, energy-demanding conduction along the demyelinated axons of patients with chronic radiogenic LS may explain the increased metabolism and perfusion.
A solvent engineering strategy was applied to the lipase-catalyzed synthesis of xylitol-oleic acid monoesters. The different esterification degrees for this polyhydroxylated molecule were examined in different organic solvent mixtures. In this context, conditions for high selectivity towards monooleoyl xylitol synthesis were enhanced from 6 mol% in pure n-hexane to 73 mol% in 2-methyl-2-propanol/dimethylsulfoxide (DMSO) 80:20 (v/v). On the contrary, the highest production of di- and trioleoyl xylitol, corresponding to 94 mol%, was achieved in n-hexane. Changes in polarity of the reaction medium and in the molecular interactions between solvents and reactants were correlated with the activity coefficients of products. Based on experimental results and calculated thermodynamic activities, the effect of different binary mixtures of solvents on the selective production of xylitol esters is reported. From this analysis, it is concluded that in the more polar conditions (100% dimethylsulfoxide (DMSO)), the synthesis of xylitol monoesters is favored. However, these conditions are unfavorable in terms of enzyme stability. As an alternative, binary mixtures of solvents were proposed. Each mixture of solvents was characterized in terms of the quantitative polarity parameter E(T)(30) and related with the activity coefficients of xylitol esters. To our knowledge, the characterization of solvent mixtures in terms of this polarity parameter and its relationship with the selectivity of the process has not been previously reported.
Fluoxetine hydrochloride has been prepared using two similar synthetic routes, both of which rely upon an ether formation reaction mediated by a base. The base used can affect the impurity profile of this reaction. It was proposed that the synthesis of fluoxetine carried out using potassium t-butoxide as base and 4-chlorobenzotrifluoride (or 4-fluorobenzotrifluoride) in the ether formation step may result in the formation of 4-benzotrifluoride t-butyl ether as a reaction by-product. To test this hypothesis, capillary gas chromatography-mass spectrometry (GC/MS) was utilized to evaluate samples of free base fluoxetine synthesized using sodium hydride (NaH) or potassium t-butoxide as the base. Assay conditions using selected ion monitoring (SIM) were developed, which allowed detection of trace levels (parts per million, ppm) of 4-benzotrifluoride t-butyl ether in fluoxetine free base sample matrix. Response linearity, precision, and standard spike recovery were examined during development, and were found to be suitable. Comparisons of fluoxetine samples generated from both NaH and potassium t-butoxide processes were performed using the GC/MS assay.