A convenient efficient method for synthesis of a flexible cyclic polyamide (cβ, 1) was developed through cyclodimerization. Electrospray ionization mass spectrometry and nuclear magnetic resonance results showed that 1 selectively binds to the c-myb G- quadruplex with high affinity, and there was no binding with the ILPR, bcl-2, and c-kit G- quadruplexes. This is the first time that a flexible cyclic polyamide was found to have high ...