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ABSTRACT:In the formation of new bonds through the Michel-type addition of thiolates to a ␣,␤-conjugate system, it is observed that the reaction takes place faster if the thio donor compound contains an electron-rich group or the enone acceptor is highly electron deficient. In contrast, the hard-soft acid-base (HSAB) principle predicts that this reaction is favored when a soft-soft interaction between the reactants takes place. Taking into account that softness is related to a barely electronegative atom of high polarizability, we consider it of interest to analyze the effect of charge transfer of a p-substituent on the softness of sulfur in thiophenols, as well as its impact in the conjugate addition to 2-cyclohexen-1-one. Experiments-in-competition, net charge of Xgroups at the p-position of the aromatic ring, the global and local softness at sulfur, and the electrophilicity, obtained by density functional theory (DFT), led to the observation that the reaction is faster for electron attractor thiophenols. The softness at sulfur increases by delocalization of charge through the aromatic ring.

Cationic porphyrins have been widely used as tumor localizers in cancer therapies. When cationic porphyrins are flat they intercalate with double-stranded DNA, duplexes of RNA or RNA-DNA. The antitumor activity of some cationic porphyrins depends on their interaction with human telomeric quadruplexes. Here, we report that noncationic meso-(4-aminophenyl)triphenylporphyrin (H 2 TPPNH 2 ) (3) and its cobalt, copper, nickel, and zinc metallo derivatives (4-7) have DNA replication inhibitory activity in B16 mouse melanoma line cells. By means of quantification of 3 HdTT radiolabeled DNA, we observed that the nonplanar porphyrin [CoTPPNH 2 ] has the highest activity against carcinogenic DNA replication.