Pessia Gilinsky-Sharon

On the Oxidative Degradation of Nadic End-Capped Polyimides. 3; Synthesis and Characterization of Model Compounds for End-Cap Degradation Products

The oxidative degradation of PMR (for polymerization of monomeric reactants) polyimides at elevated temperatures was followed by cross-polarized magic angle spinning (CP-MAS) NMR. Labeling of selected sites in the polymers with 13C allowed for direct observation of the transformations arising from oxidation processes. The formation of several degradation products has been proposed to be occurring in the cross-links derived from the nadic end caps on oxidation. Model compounds have been synthesized and characterized by CPMAS NMR with both normal and delayed decoupling to distinguish between protonated and unprotonated carbons. Comparison of these spectra to predicted chemical shifts of proposed products for the aged polymer provides further insight to degradation occurring in the cross-linked moieties.

A facile two-step high yield approach to 2-oxasteroids

The base catalyzed autoxidation of 3-oxo-Δ4 steroids in aprotic media at circa -25°C occurs nearly exclusively at C2 of the A-ring, generating rapidly (< 4 hrs) and in high yield the corresponding enol (2-hydroxy-3-oxo-Δ1,4 analog) When the reaction is then allowed to continue at room temperature for several days, the enol is further autoxidized to the related lactol (1-hydroxy-2-oxa-3-oxo-Δ4 analog) in overall yields generally in the range of 85–95%. Sodium borohydride reduction of the lactol yields the pharmacologically important 2-oxasteroids.

The reaction of enols with superoxide anion radical [02???]1. Synthesis of 2,3-unsaturated-δ-valerolactones.

3- and 4-Hydroxycoumarin (1 and 3) as well as 2-hydroxy-2,5-cyclohexadien-1-ones 5a–f were reacted with KO2/18-crown-6 in benzene. Initial deprotonation of the enol hydrogen was followed by nucleophilic attack by O2/t- (for 1 and 3) and/or autoxidation of the resulting anion (for 1 and 5a–e). A convenient synthesis of 2,3-unsaturated-δ-valerolactones from the corresponding 2-cyclohexen-1-ones is also described.

1,1‐Diamino‐2,2‐dinitroethylenes are always zwitterions

The nitration of tetraiodoethylene (7) yields 1,1‐diiodo‐2,2‐dinitroethylene (8). The latter reacts with alkylamines 9 or alkyldiamines 11 to give the corresponding acyclic 1,1‐diamino‐2,2‐dinitroethylenes 10 or their cyclic analogs 12, respectively. On the basis of liquid and solid‐state 13C and 15N NMR data, x‐ray analysis and ab initio calculations, we suggest that the title compounds are always zwitterionic and that the CA–CN bond is not a true double bond. Copyright

The photosensitized oxidation of α-keto enols: A singlet oxygen approach to 2-oxasteroids

Abstract Fluoride ion catalyzed photosensitized singlet oxygenation of 2-hydroxycyclohexa-2,5-dien-1-ones 15a and b and the related steroidal α-keto enols 18a–g, generated the cyclohexenone lactols 16a–b and the corresponding steroidal analogs 19a–g generally in moderate to good yields (60–75%). Since the lactols can be conveniently reduced to the desired 2-oxasteroids in high yields, this 1O2 route presents itself as a synthetically acceptable alternative to the previously reported BCA approach for the preparation of 2-oxasteroids, especially in the case of base sensitive compounds.

THE REACTION OF SUPEROXIDE WITH CINNAMYL BROMIDE : THE SURPRISING FORMATION OF AN ETHER AND AN EPOXY ACETAL

Abstract The reaction of O2−• ( KO 2 18- crown -6 in toluene) with cinnamyl bromide yielded neither the expected cinnamyl peroxide nor its Kornblum-DeLaMare fragmentation products, cinnamaldehyde (4) and cinnamyl alcohol. Instead we observed the novel formation of dicinnamyl ether and 2,3-epoxycinnamylaldehyde dicinnamyl acetal (88% yield). Benzyl bromide reacted with O2−• in the presence of 4 yielding dibenzyl ether and epoxycinnamaldehyde dibenzyl acetal. When the reaction was repeated with CH3I, the corresponding epoxycinnamaldehyde dimethyl acetal was the major product.

NMR-based molecular ruler for determining the depth of intercalants within the lipid bilayer. Part IV: studies on ketophospholipids.

In our companion paper, we described the preparation and intercalation of two homologous series of dicarbonyl compounds, methyl n-oxooctadecanoates and the corresponding n-oxooctadecanoic acids (n=4-16), into DMPC liposomes. (13)C NMR chemical shift of the various carbonyls was analyzed using an E(T)(30) solvent polarity-chemical shift correlation table and the corresponding calculated penetration depth (in Å). An iterative best fit analysis of the data points revealed an exponential correlation between E(T)(30) micropolarity and the penetration depth (in Å) into the liposomal bilayer. However, this study is still incomplete, since the plot lacks data points in the important area of moderately polarity, i.e., in the E(T)(30) range of 51-45.5 kcal/mol. To correct this lacuna, a family of ketophospholipids was prepared in which the above n-oxooctadecanoic acids were attached to the sn-2 position of a phosphatidylcholine with a palmitic acid chain at sn-1. To assist in assignment and detection several derivatives were prepared (13)C-enriched in both carbonyls. The various homologs were intercalated into DMPC liposomes and give points specifically in the missing area of the previous polarity-penetration correlation graph. Interestingly, the calculated exponential relationship of the complete graph was essentially the same as that calculated in the companion paper based on the methyl n-oxooctadecanoates and the corresponding n-oxooctadecanoic acids alone. The polarity at the midplane of such DMPC systems is ca. 33 kcal/mol and is not expected to change very much if we extend the lipid chains. This paper concludes with a chemical ruler that maps the changing polarity experienced by an intercalant as it penetrates the liposomal bilayer.