Samy Abdel-Baky

Electrophore-labeling and alkylation of standards of nucleic acid pyrimidine bases for analysis by gas chromatography with electron-capture detection

The pyrimidine bases cytosine, uracil and thymine, along with some analogues, are electrophore-labeled either with pentafluorobenzoyl chloride (PFBC), pentafluorophenylsulfonyl chloride (PPSC), or heptafluorobutyric anhydride. Subsequent alkylation is most successful for PFB-cytosine, PPS-uracil, and PPS-thymine. These same alkylated compounds also have the highest aqueous stability and respond most strongly by gas chromatography-electron-capture detection. One of these derivatives, determined to be N4-PFB-1,3-dimethylcytosine by authentic synthesis, and its 5-methyl analogue, can be detected with good precision down to the 100-fg level. Poor reproducibility is encountered at the 10-fg level.

Release of 2-aminofluorene from N-(deoxyguanosin-8-yl)-2-aminofluorene by hydrazinolysis

Abstract High temperature (160°C) hydrazinolysis is demonstrated to be a useful chemical transformation reaction for releasing an aminopolyaromatic hydrocarbon, 2-aminofluorene, from a parent DNA adduct, N-(deoxyguanosin-8-yl)-2-aminofluorene.

MEASURING DNA ADDUCTS BY GAS CHROMATOGRAPHY-ELECTRON CAPTURE-MASS SPECTROMETRY : TRACE ORGANIC ANALYSIS

Publisher Summary This chapter discusses the practical experience in method development for the determination of trace amounts of DNA adducts, by gas chromatography-electron capture-mass spectrometry (GC-EC-MS). It has detected femtomole amounts of such analytes, by optimizing sample preparation (involving extraction, chemical reaction, and purification steps, starting with a biological sample) and low-attomole amounts of pure, derivatized standards, by GC-EC-MS. Although such methodology is already useful, the concepts and techniques described extend the sample preparation to the attomole level. In this chapter, the work on chemical transformation is emphasized as a part of sample preparation. This is a means to broaden the range of compounds that can be detected by GC-EC-MS. Also, the experience, in operating a GC-EC-MS to achieve attomole detection limits routinely (for standards), is discussed in the chapter. New ionization techniques for MS, such as electrospray and matrix-assisted laser desorption, are increasing the ability of MS to analyze “nonvolatile” substances present even in aqueous samples. Less new but of continuing importance, as a desorption/ionization technique, in this respect is fast atom bombardment, In contrast, this chapter discusses the procedures, in which significant chemical treatment of the sample precedes the “old technique” of GC, to deliver the analyte into the MS. The desorption approaches are attractive, because they can minimize sample preparation. They are also unique in their ability to achieve the direct detection of medium to high molecular weight biopolymers by MS.

Novel synthesis of 2-fluoroestradiol from 19-Cortestosterone: Biomimetic oxidative defluorination to 2-hydroxyestradiol

A new, short synthetic route to 2-fluoroestradiol from 19-nortestosterone is described which gives the target compound in an approximately 25% overall yield. Oxidative defluorination of 2-fluoroestradiol to 2-hydroxyestradiol via treatment with Frémys salt/iodide ion is reported. This process is regarded as biomimetic with respect to cytochrome P-450-dependent oxidative defluorination.

Superoxide chemical transformation of diolepoxide polyaromatic hydrocarbon DNA adducts: Determination of benzo[α]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol by gas chromatography

Benzo[a]pyrene-r-7,t-8,9,c-10-tetrahydrotetrol (100 pg, 342 fmol) was measured using the following sequence of steps: (1) chemical transformation with potassium superoxide to 2,3-pyrenedicarboxylic acid; (2) electrophore derivatization with pentafluorobenzyl bromide; (3) sample clean-up by high-performance liquid chromatography and (4) measurement by gas chromatography with electron-capture detection and by gas chromatography with electron-capture negative-ion mass spectrometry. The overall, absolute yields obtained by the two procedures were 69% and 60%, respectively. This work completes the first stage towards the establishment of a general method for detecting diolepoxide polyaromatic hydrocarbon DNA adducts by gas chromatography.

Reaction of trimethylsilylimidazole with 5,10β-epoxy-3-ketosteroids: Enolization and aromatization of the A-ring

The reaction of trimethylsilylimidazole (TSIM) and 3-keto-5,10-epoxy-nor-19-methylandrostanone 3 and its 17-acetate analog 4 was examined at two different temperatures. In both compounds, reaction at 90 degrees C gave predominantly a delta 3-silyl-enol ether plus a minor product as a result of the epoxide ring opening. Under reflux conditions, besides the aforementioned products, aromatization of the A-ring was observed as a major process. The results suggest the potential use of silylation reactions with epoxyketones towards the synthesis of aromatic compounds.

Superoxide oxidation of 1-nitropyrene-cis-dihydrodiols

KO2 oxidation of cis-4,5-dihydro-4,5-dihydroxy-3-nitropyrene, 1 gives the known lactone, 3-nitro-5H-phenanthro[4,5-bcd]pyran-5-one, 2. Similarly the analogous 4,5-dihydrodiol, 3, gives the known lactone, 1-nitro-5H-phenanthro[4,5-bcd]pyran-5-one, 4.While the yield of 2 is 80%, it is only 16% for 4. A study of the latter oxidation, relying especially on the use of HPLC, led to a change in the conditions that increased the yield of 4 from 16 to 88%. The change was to quench the reaction with H2O2 shortly after it began instead of letting it proceed, as usual, for several hours before quenching with water.

Glycol and olefin electrophoric release tags

Abstract An “electrophoric release tag” is a molecular labeling reagent which comprises three covalently-connected groups: electrophore/release/ reactivity. This reagent is first covalently attached via its reactivity group to a substance of interest. The subsequent release tag-substance conjugate is detected by chemically cleaving the release group within the release tag, liberating the electrophore for eventual detection by electron capture in the gas phase. Here electrophoric release tags are advanced by the preparation of three similar tags having a glycol release group. One of the glycol tags, N -(pentafluorobenzoyl)-4-piperidylidenyl-acetic acid glycol, is attached to glycine methyl ester as a model analyte. The resulting conjugate is cleaved within 5 minutes by aqueous periodate at room temperature, releasing the electrophore N -(pentafluorobenzoyl)-4-piperidone, for detection. Also a tag with an olefin release group is prepared: m -(pentafluorobenzyloxy)-E-3-methylcinnamoyl chloride. The latter reagent is attached to thymidine as a model analyte and a subsequent methylated conjugate is cleaved within 1 hr by aqueous permanganate/ periodate, releasing the electrophore m -(pentafluorobenzyloxy)-acetophenone for detection.

Improved Synthesis of 8-Hydroxy-2′-Deoxyadenosine-5′-monophosphate

Abstract Sequential reaction of 2′-deoxyadenosine-5′-monophosphate with bromine, sodium benzyloxide and hydrogen (Pd/C) conveniently gave 8-hydroxy-2′-deoxyadenosine-5′-monophosphate in a 58% overall yield.

Reduction of Nitroaromatics by Non-Metal Hydrazinolysis

Abstract High temperature (160°C) can substitute for a metal catalyst in achieving the complete reduction of nitroaromatic compounds to corresponding amines by hydrazine.