Solvolysis of 14,17-etheno-bridged 16α-nitroestratrienyl acetate and lactam formation pathways studied by LC-NMR and LC-MS. Structures of minor products.

The ethanol solvolysis of 3-methoxy-14,17-etheno-16α-nitroestra-1,3,5(10)-trien-17ß-yl acetate in the presence of NaHCO3 was studied by means of real-time NMR experiments, LC-SPE-NMR, and LC-MS. The pathway to form 3-methoxy-2'-oxopyrrolidino-[4',5':14ß,15ß]-estra-1,3,5(10)-trien-17-one was disclosed. The intermediacy of nitrile oxide and alkoxynitrone was postulated based on the analysis of the reaction products. The proposed mechanism of cleaving the bridge in the nitro compound is legal for the formation of N-acetoxylactams, nitriles, isoxazoles and isoxazolines.

Diels-Alder reaction of androsta-14,16-dien-17-yl acetates with nitroethylene: product distribution and selected adduct transformations.

The Diels-Alder cycloaddition of nitroethylene to some androsta-14,16-dien-17-yl acetates has been studied. The addition occurs stereoselectively, giving predominantly head-to-head-adduct. 14ß-Cyanomethyl steroids were obtained via the reductive cleavage reaction of bridged nitro compounds. The structures of the new compounds have been fully characterized by 2D NMR and tandem mass-spectrometry methods.

Practical synthesis of isomerically pure 5- and 6-carboxytetramethylrhodamines, useful dyes for DNA probes.

Simple and scalable synthesis of 5- and 6-carboxytetramethylrhodamines (TAMRAs) is reported. Acylation of 3-dimethylaminophenol with 1,2,4-benzenetricarboxylic anhydride afforded a mixture of 4-dimethylamino-2-hydroxy-2',4'(5')-dicarboxybenzophenones, which can be easily separated into individual compounds upon recrystallization from methanol and acetic acid. Individual benzophenones were reacted with 3-dimethylaminophenol to give 5- or 6-carboxytetramethylrhodamines. The dyes were converted into hydroxyprolinol-based phosphoramidite reagents suitable for oligonucleotide synthesis. 5- and 6-TAMRA isomers on oligonucleotides showed similar absorption and emission spectra. Fluorescence quantum yield of the dyes correlates with the presence of dG nucleosides in the adjacent region of oligonucleotide sequence. Several energy transfer primers containing on their 5'-termini (6-FAM)dT(n)(6-TAMRA) dye system (n = 0, 2, 4, 6, 8, 10, 12, 14) were prepared, and their spectral properties were studied.

Synthesis and molecular structure of 14,15-pyrrolidino-and 14,16-ethano derivatives of estrone.

Hydrolysis of 3-methoxy-16alpha-nitro-14,17-ethenoestra-1,3,5(10)-trien-17beta-yl acetate under weakly basic conditions leads to formation of 3-methoxy-2'-oxopyrrolidino-[4',5':14beta,15beta]-estra-1,3,5 (10)-trien-17-one, the structure of which has been confirmed by X-ray analysis and some chemical transformations. The reactivity of 3-methoxy-16alpha-nitro-14,17-ethanoestra-1,3,5(10)-trien-17beta-yl acetate under various conditions of basic hydrolysis has been investigated. The derived compounds have been identified by means of NMR spectroscopy and X-ray analysis.

Oxidative modification of quercetin by hemeproteins.

The ability of a number of hemeproteins to oxidize the flavonoid quercetin has been shown. It was found that quercetin undergoes chemical modification in the presence of cytochrome c, myoglobin, and hemoglobin but not cytochrome b(5). In the range of investigated proteins the most effective oxidant appears to be cytochrome c. Chromatographic analysis of the reaction mixture revealed a number of quercetin oxidation products. The main oxidation product was purified and characterized by means of LC-MS and NMR analyses. It has a dimeric structure similar to the product of quercetin oxidation by horseradish peroxidase and is formed during radical-driven reactions. Our results indicate that a number of hemeproteins can react and modify biologically active flavonoids. However, these reactions might also lead to the generation of active species with deleterious consequences for the cellular macromolecules.