Modular Synthesis of Methyl-Substituted Novel Psoralen N-Hydroxysuccinimide Esters and Evaluation of DNA Photo-Crosslinking Properties of the Corresponding Triplex-Forming Oligonucleotide Conjugates

Abstract

Psoralen-conjugated triplex-forming oligonucleotides (Ps-TFOs) have been used to induce DNA mutations or suppress gene expression via the formation of crosslinked products with DNA in a sequence-specific manner. Psoralen can crosslink with DNA at its furan ring and/or pyrone ring side, yielding either a monoadduct or diadduct (interstrand crosslinking) product. The differences in the crosslinked structures of Ps-TFOs with the target DNAs are closely related to the changes in the biological outcomes induced by the Ps-TFOs. However, only few reports have discussed the photo-crosslinking properties of Ps-TFOs. The photo-crosslinking properties of Ps-TFOs with structurally diverse psoralen derivatives remain elusive. Herein, we report the modular synthesis of methyl-substituted novel psoralen N-hydroxysuccinimide (NHS) esters. Using these esters, the effect of the methyl substituent of psoralen on the photo-crosslinking of the corresponding Ps-TFOs was examined. Results revealed that the amount of the diadduct product was significantly reduced in the presence of the methyl substituents at C-3 and C-4 position while maintaining the total amount of photo-crosslinking product. This work demonstrates the possibility to control the crosslinked product of Ps-TFOs by introducing methyl groups into psoralen—this ability to manipulate the product is an important factor in the biological applications of Ps-TFOs.