Photocrosslinking of DNA using 4-methylpyranocarbazole nucleoside with thymine base selectivity

This report describes a novel photocrosslinker, 4-methylpyranocarbazole nucleoside (^MEPK), that can be induced to crosslink using visible light. Previously, we reported a visible light-responsive artificial nucleic acid, pyranocarbazole nucleoside (^PCX). ^MEPK can selectively photocrosslink to thymine bases in a complementary nucleic acid strand. It was synthesized by introducing a methyl group at the 4-position of ^PCX, and it can differentiate between thymine and cytosine. The previously reported visible light-responsive artificial nucleic acid ^PCX has a low synthetic yield. ^MEPK was synthesized by Pechmann condensation which suppressed by-product formation, making the synthesis more efficient, and resulting in a higher yield than that of ^PCX. ^MEPK is expected to have practical applications as a photocrosslinker that can be manipulated with visible light and that selectively targets thymine bases.