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.  MEPK can selectively photocrosslink to thymine bases in a complementary nucleic acid strand.  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.
MEPK
Previously, we reported a visible light-responsive artificial nucleic acid, pyranocarbazole nucleoside (PCX).  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. 
PCX
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. 
Pechmann condensation