[5]Helicenes with a substituent exclusively oriented toward the interior curvature of the helix are synthesized by metal-catalyzed cycloisomerization. In addition, novel azulene-fused helicenes have been found through cycloisomerization studies. These [5]helicenes shows a high enough configurationally stability to allow resolution by HPLC on a chiral stationary phase.
A series of novel optically active [5]helicene-derived phosphine ligands (L1, with a 7,8-dihydro[5]helicene core structure- and L2, with a fully aromatic [5]helicene core structure) were synthesized. Despite their structural similarities, L1 and L2 exhibit particularly different characteristics in their use as chiral ligands. L1 was highly effective in the asymmetric allylation of indoles with 1,3-diphenylallyl acetate (up to 99% ee), and in the etherification of alcohols (up to 96% ee). In contrast, L2 was highly effective in the stereocontrol of helical chirality in Suzuki–Miyaura coupling (SMC) reaction (up to 99% ee). Density functional theory analysis was employed to propose a model that accounts for the origin of the enantioselectivity in these reactions.
[Structure: see text] We synthesized oligodeoxynucleotide (ODN, 3), which contains 4'-o-nitrobenzyloxythymidine (4) as a caged precursor of C4'-oxidized abasic site (1). Photoirradiation of 3 at 365 nm followed by amine treatment under neutral conditions afforded the lactam (2) efficiently. Duplexed ODN 3 was converted to 1 faster and more efficiently than single stranded 3, whereas amine treatment of 1 formed from single stranded 3 resulted in slightly faster lactam formation than with the duplex.
Bleomycin-induced oxidative DNA damage under limited oxygen conditions results in the formation of the C4'-oxidized abasic site (1). We synthesized the oligodeoxynucleotides (ODN) 5, which contains 4'-o-nitrobenzyloxythymidine (3), and 6, which contains 2-nitrobenzyloxy-4'-methoxy-2'-deoxy-d-ribofuranoside (4), as the caged precursors of 7, an ODN containing 1, to study its reactivity with amines. Photoirradiation of the single- and double-stranded 5 led to the formation of 7. Uncaging of the duplex was faster and the yield of 7 was higher with the double-stranded than with the single-stranded ODN. It was suggested that a low dielectric environment of the o-nitrobenzyloxy group in the minor groove of the duplex might accelerate the uncaging rate. Similarly, 6 and its duplex yielded 7 by photoirradiation. However, the yields of 7 were lower than those of 5, and duplex formation slowed the uncaging rate. Reaction of the obtained 7 with an amine resulted in the formation of the lactam 2b in good yield in both single- and double-stranded forms, showing that amine modification of biomolecules by an ODN containing 1 is possible under physiologic conditions.
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