Interactions and photoreactivity of 5-alkoxypsoralens with thymine. A model approach

Unique Crosslinking Properties of Psoralen-Conjugated Oligonucleotides Developed by Novel Psoralen N-Hydroxysuccinimide Esters

Psoralens and their derivatives, such as trioxsalen, have unique crosslinking features to DNA. However, psoralen monomers do not have sequence-specific crosslinking ability with the target DNA. With the development of psoralen-conjugated oligonucleotides (Ps-Oligos), sequence-specific crosslinking with target DNA has become achievable, thereby expanding the application of psoralen-conjugated molecules in gene transcription inhibition, gene knockout, and targeted recombination by genome editing. In this study, we developed two novel psoralen N-hydroxysuccinimide (NHS) esters that allow the introduction of psoralens into any amino-modified oligonucleotides. Quantitative evaluation of the photo-crosslinking efficiencies of the Ps-Oligos to target single-stranded DNAs revealed that the crosslinking selectivity to 5-mC is the unique feature of trioxsalen. We found that the introduction of an oligonucleotide via a linker at the C-5 position of psoralen can promote favorable crosslinking to target double-stranded DNA. We believe our findings are essential information for the development of Ps-Oligos as novel gene regulation tools.

Alpha-methylene-gamma-butyrolactones: versatile skin bioactive natural products

Natural products containing an alpha-methylene-gamma-butyrolactone moiety, mainly of the sesquiterpene type, are widely observed in plants, which upon coming into contact with skin, will induce major skin toxicological side effects or phytodermatitis. Indeed two main dermatological pathologies have been associated with a skin exposure to molecules containing an alpha-methylene-gamma-butyrolactone moiety: allergic contact dermatitis (ACD) and chronic actinic dermatitis (CAD). ACD is an immunologically based disease resulting from modifications of epidermal proteins by sensitizers or haptens. Indeed, alpha-methylene-gamma-butyrolactones are highly electrophilic structures that can act as Michael acceptors towards nucleophilic residues of proteins. Cysteine and lysine are the most modified residues leading, in the case of enantiomerically pure lactones, to the formation of diastereomeric adducts. This chemical enantioselectivity induces an enantiospecificity of the allergic reaction, i.e., an individual sensitized to one enantiomer will not develop clinical symptoms when exposed to the other enantiomer and vice versa. Sesquiterpene lactones have been also associated with another pathology that involves UV irradiation and DNA modifications. Interestingly, it was found that alpha-methylene-gamma-butyrolactones, in addition to their electrophilic properties, were highly photoreactive molecules able to react with thymine/thymidine to form [2 + 2] photoadducts in very high yields. In all cases a syn regioselectivity was observed, probably associated with the polarization of the exomethylenic bond. This high photoreactivity of alpha-methylene-gamma-butyrolactones towards thymidine could be an explanation of the progressive evolution of allergic contact dermatitis towards chronic actinic dermatitis.

Reversible photocycloaddition of a 4',5'-dihydropsoralen derivative with thymine

The photocycloaddition reaction between a 4',5'-dihydropsoralen derivative and thymine was studied in solution using a synthetic bichromophoric model 8 in which the two rings are associated by a tetramethylene chain. In water this model molecule exhibits intramolecular ring-ring stacking interactions as evidenced by UV and NMR spectroscopies. Irradiation at 365 nm at usual concentrations (greater than or equal to 5.10(-4) M) leads exclusively to a regio- and stereo-selective dimerization reaction involving the 3,4 double bonds of the psoralen moities. Extreme dilutions (ca less than or equal to 2.10(-5) M) were necessary to observe the intramolecular reaction which results in the exclusive formation of a 3,4 cis-anti adduct. This reaction is completely reversed by irradiation at 254 nm. These results are discussed with regard to the behavior of the homologous models in which the furan part of the psoralen ring is not hydrogenated. These latter compounds also lead exclusively to a 3,4 cis-anti adduct. It appears that saturation of the furan ring increases strongly the quantum yield of the photoaddition at 365 nm (0.01----0.18) and that the triplet excited state of the 4',5'-dihydropsoralen is involved in the photoaddition.

Photoreactions of furocoumarins with biomolecules

Recent aspects of the photoreactions of linear and angular furocoumarins with DNA and related compounds, including [2 + 2] cycloaddition to pyrimidine bases, covalent attachment to the osidic moiety of adenine nucleosides and photodynamic effects, are surveyed. Reactions of photoexcited furocoumarins with proteins and unsaturated lipids and the possible biological roles of the resulting adducts are also presented and discussed.