EPR spectroscopy is a powerful method to elucidate the structure of molecules through the measurement of distances between conformationally well-defined spin labels. Here we report a sequence-flexible approach to the synthesis of double spin-labeled DNA duplexes, where 2′-alkynylnucleosides are incorporated at terminal and internal positions on complementary strands. Post-DNA synthesis copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions with a variety of spin labels enable the use of double electron-electron resonance experiments to measure a number of distances on the duplex, thus affording a high level of detailed structural information.

Isatin and its derivatives have been widely studied due to their biological activities. Recently there has been a renewed interest in the synthesis of new derivatives by use of organocatalysts. This review deals with this area.