ABSTRACT
A new methodology for aromatic difluoromethylation is described. Aryl iodides reacted with α-silyldifluoroacetates upon treatment with copper catalyst in DMSO or DME to give the corresponding aryldifluoroacetates in moderate to good yields. The subsequent hydrolysis of aryldifluoroacetates and KF-promoted decarboxylation afforded a variety of difluoromethyl aromatics.
Subject(s)
Copper/chemistry , Hydrocarbons, Fluorinated/chemical synthesis , Hydrocarbons, Iodinated/chemistry , Catalysis , Decarboxylation , Hydrocarbons, Fluorinated/chemistry , Molecular StructureABSTRACT
The biosynthesis, structure and function of neuromelanin (NM), the dark brown melanin-like pigment present in the substantia nigra (SN), are not well characterized, in spite of the possible involvement of NM in the etiology and pathogenesis of Parkinson's disease. NM was isolated from the SN of five non-Parkinsonian human brains. NM and synthetic melanins, employed as models, were characterized by chemical analysis. Alkaline hydrogen peroxide (H2O2) oxidation of NM generated four degradation products, pyrrole-2,3-dicarboxylic acid (PDCA), pyrrole-2,3,5-tricarboxylic acid (PTCA), thiazole-4,5-dicarboxylic acid (TDCA) and thiazole-2,3,5-tricarboxylic acid (TTCA), whose ratios, especially the TTCA to PDCA ratio, indicate that NM is derived mostly from dopamine (DA) with 25% incorporation of cysteine (Cys) in the form of a benzothiazine structure. Hydriodic acid (HI) reductive hydrolysis of NM yielded 4-amino-3-hydroxyphenylethylamine (4-AHPEA) as a marker of cysteinyldopamine (CysDA)-derived units. The 4-AHPEA to PDCA ratio indicates a 21% incorporation of CysDA-derived units into NM. These degradative experiments also suggest that DOPA is not incorporated into NM to a significant extent (approximately 6% the level of DA). It is concluded that the TTCA to PDCA ratio is a useful indicator of CysDA-derived units in NM, and NM consists mainly of DA-melanin with some contribution from CysDA-melanin. The involvement of DA and CysDA as building blocks of NM demonstrates the detoxifying role of NM synthesis, since it prevents the intraneuronal accumulation of DA and CysDA, which would cause toxic effects.
Subject(s)
Melanins/chemistry , Substantia Nigra/chemistry , Tyramine/analogs & derivatives , Aged , Aged, 80 and over , Dicarboxylic Acids/chemistry , Female , Humans , Hydrogen Peroxide/chemistry , Hydrolysis , Molecular Structure , Oxidants/chemistry , Oxidation-Reduction , Pyrroles/chemistry , Thiazoles/chemistry , Tyramine/chemistryABSTRACT
The authors developed an HPLC assay for determining blood sirolimus concentration using a relatively simple solid-phase extraction and UV detection. The retention times of sirolimus and the internal standard, 32-desmethoxyrapamycin, are 8.7 and 9.3 minutes, respectively. The assay possesses linearity up to 200 ng/mL, sensitivity to 2.0 ng/mL, and day-to-day reproducibility of 8.8, 9.8, 6.1, and 6.4% at sirolimus concentrations of 6, 10, 20, and 30 ng/mL, respectively. A patient correlation study using this HPLC method and an established LC/MS/MS assay revealed a slope of 0.982 and intercept of -0.021 ng/mL and a correlation coefficient of 0.99 (n = 37). Of the 31 different drugs tested none interfered with the measurement of the drug of interest, and a recovery study gave an overall mean recovery of 101.8%. The authors conclude that the method described here is suited for the therapeutic monitoring of blood sirolimus concentration.
