Cycloaddition of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) to bicycloalkenes via rearrangement of zwitterionic intermediates

The formation of tricyclic urazoles between PTAD and bicyclic olefins via rearrangement of the intermediary 1,4-dipoles appears to be general, including moderately strained, benzo-annulated, and functionalized substrates.     

Singlet oxygenation of cycloocta-1,3,5-triene: Formation of (4.2.2)- and (2.2.2)- cycloadducts.

Photosensitized singlet oxygenation of 1,3,5-cyclooctatriene affords the (4.2.2)- and (2.2.2)-type endoperoxides, which were reduced with diimide, thermally isomerized, and deoxygenated with triphenylphosphine.     

The Synthesis of Oxazaborolo-benzoxazaborinine Derivatives of Resorcinarene from (1S,2R)-ephedrine

The oxazaborolo-benzoxazaborinine derivatives (3) of resorcinarene have been synthesized from (1S,2R)-ephedrine. The reaction yields the crown and diamond conformers of the bora derivative of resorcinarene in high diastereomeric excess (de > 97%). The crystallographic structure of the crown conformer of (3) was determined.     

Stereocontrol within confined spaces: enantioselective photooxidation of enecarbamates inside zeolite supercages

Dye-exchanged Y zeolite is shown to be an effective medium to control the stereoselectivity in the photooxygenation of chiral oxazolidinone-functionalized Z/E-1 enecarbamates. An enantioselectivity (ee) as high as 80% was observed in the methyldesoxybenzoin (MDB) product, obtained in the methylene-blue-exchanged NaY zeolite at room temperature. The efficacy of the asymmetric induction in the MDB product depends on the Z/E geometry of the alkene, the Z-isomer being more effective than the corresponding E-isomer. The stereoselectivity is rationalized in terms of conformational effects through cationic interactions between the zeolite and the substrate.     

Parabolic subgroups of Vershik-Kerov's group

In this note we show that all parabolic subgroups of Vershik-Kerov's group (i.e. subgroups containing --the group of infinite dimensional upper triangular matrices) are net subgroups for a wide class of semilocal rings .

     

Structural studies of an oligodeoxynucleotide containing a trimethylene interstrand cross-link in a 5'-(CpG) motif: model of a malondialdehyde cross-link.

Malondialdehyde (MDA), a known mutagen and suspected carcinogen, is a product of lipid peroxidation and byproduct of eicosanoid biosynthesis. MDA can react with DNA to generate potentially mutagenic adducts on adenine, cytosine, and particularly guanine. In addition, repair-dependent frame shift mutations in a GCGCGC region of Salmonella typhimurium hisD3052 have been attributed to formation of interstrand cross-links (Mukai, F. H. and Goldstein, B. D. Science 1976, 191, 868--869). The cross-linked species is unstable and has never been characterized but has been postulated to be a bis-imino linkage between N(2) positions of guanines. An analogous linkage has now been investigated as a stable surrogate using the self-complementary oligodeoxynucleotide sequence 5'-d(AGGCG*CCT)(2,) in which G* represents guanines linked via a trimethylene chain between N(2) positions. The solution structure, obtained by NMR spectroscopy and molecular dynamics using a simulated annealing protocol, revealed the cross-link only minimally distorts duplex structure in the region of the cross-link. The tether is accommodated by partially unwinding the duplex at the lesion site to produce a bulge and tipping the guanine residues; the two guanines and the tether attain a nearly planar conformation. This distortion did not result in significant bending of the DNA, a result which was confirmed by gel electrophoresis studies of multimers of a 21-mer duplex containing the cross-link.